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1
Molinari, John, and David Vollaro. "A Subtropical Cyclonic Gyre Associated with Interactions of the MJO and the Midlatitude Jet." Monthly Weather Review 140, no. 2 (February 2012): 343–57. http://dx.doi.org/10.1175/mwr-d-11-00049.1.
Анотація:
This paper describes a large cyclonic gyre that lasted several days in the northwest Pacific during July 1988. Cyclonic winds at 850 hPa extended beyond the 2000-km radius with a radius of maximum winds of 700–800 km. The gyre exhibited clear skies within and north of its center. Active convection extended 4000 km in longitude to its south. The Madden–Julian oscillation (MJO) was in its active phase in the Indian Ocean prior to gyre formation. Consistent with earlier studies, diabatic heating in the MJO was associated with an anomalous upper-tropospheric westerly jet over the northeast Asian coast and a jet exit region over the northwest Pacific. Repeated equatorward wave-breaking events developed downwind of the jet exit region. One such event left behind a region of lower-tropospheric cyclonic vorticity and convection in the subtropics that played a key role in the gyre formation. A second wave-breaking event produced strong subsidence north of the mature gyre that contributed to its convective asymmetry. Gyres from 1985 and 1989 were compared to the 1988 case. All three gyres developed during an active MJO in the Indian Ocean. Each gyre displayed the same strong convective asymmetry. Each developed in July or August during the climatological peak in breaking Rossby waves in the northwest Pacific. Finally, all of the gyres developed during La Niña at nearly the same location. This location and the convective structure of the gyres closely matched composite La Niña anomalies during boreal summer.
2
BEHERA, S. K., and P. S. SALVEKAR. "A numerical modelling study of the interannual variability in the Indian Ocean." MAUSAM 46, no. 4 (January 2, 2022): 409–22. http://dx.doi.org/10.54302/mausam.v46i4.3325.
Анотація:
A simple reductA1 gravity wind-driven ocean circulation model is used to study the interannual variability in the upper layer of the Indian Ocean (24°S-23°N and 3S°E-IIS0E). The monthly mean wind stress for the period 1977-1986 are used as a forcing in the model. The model reproduces most of the observed features of the annual cycle of the upper layer circulation in the Indian Ocean when was forced with the ten-year average monthly mean wind. The circulation features and the model upper layer thickness show considerable interannual variability in most part of the basin; in particular, the Somali Current, the basin wide southern hemisphere gyre, the Equatorial Currents and the gyres in the Bay of Bengal. Six consecutive years starting from 1978 to 1983 which include two bad monsoon years of 1979 and 1982 are chosen to study the interannual variability. February circulation field shows stronger Equatorial Counter Currents in bad monsoon years, whereas. the cunents north of Madagascar flowing up to the African coast are found to be stronger in good monsoon years. The southward return flow from the Southern Gyre in August is strong and more to southern latitudes in the bad monsoon years. The flow circulated eastward to form another eddy east of Southern Gyre. The basin wide gyre of the southern hemisphere (SH) shows less variability in two consecutive normal years than in contrasting years.
3
Davis, Russ E. "Intermediate-Depth Circulation of the Indian and South Pacific Oceans Measured by Autonomous Floats." Journal of Physical Oceanography 35, no. 5 (May 1, 2005): 683–707. http://dx.doi.org/10.1175/jpo2702.1.
Анотація:
Abstract As part of the World Ocean Circulation Experiment, 306 autonomous floats were deployed in the tropical and South Pacific Ocean and 228 were deployed in the Indian Ocean to observe the basinwide circulation near 900-m depth. Mean velocities, seasonal variability, and lateral eddy diffusivity from the resultant 2583 float-years of data are presented. Area averages, local function fits, and a novel application of objective mapping are used to estimate the mean circulation. Patterns of mean circulation resemble those at the surface in both basins. Well-developed subtropical gyres, twice as strong in the Indian Ocean as in the Pacific, feed western boundary currents. Tropical gyres are separated by eastward flow along the equator in both hemispheres of both basins, although the Indian subcontinent splits the north Indian tropical gyre. The Antarctic Circumpolar Current (ACC) and west wind drifts are prominent in both basins, generally tending slightly southward but deviating to the north behind the Del Cano, Kerguelen, and Campbell Plateaus and, of course, South America. Remarkably, the eastern boundaries of the southern subtropical gyres in all three basins apparently occur in the ocean interior, away from land. The Indian Ocean’s subtropical gyre, and perhaps part of the South Atlantic’s, reaches east to a retroflection just upstream of the Campbell Plateau south of New Zealand. Seasonal variability at 900 m is focused around the equator with weaker variability found near certain bathymetric features. There is a remarkable agreement between the observed seasonable variability and that predicted by the Jet Propulsion Laboratory (JPL)–Estimating the Circulation and Climate of the Ocean (ECCO) data-assimilating numerical model. Aside from seasonal effects, eddy variability is greatest along the equator, in tropical and subtropical western basins, and along the ACC. Integrals of velocity across regional passages (Tasman Sea, Mozambique Channel) provide useful reference for hydrographic analyses of transport. Across whole ocean basins, however, the uncertainty associated with the appropriate continuity relation for horizontal flow (e.g., geostrophy vs nondivergence) is comparable to the mean flow.
4
Karstensen, Johannes, and Detlef Quadfasel. "Water subducted into the Indian Ocean subtropical gyre." Deep Sea Research Part II: Topical Studies in Oceanography 49, no. 7-8 (January 2002): 1441–57. http://dx.doi.org/10.1016/s0967-0645(01)00160-6.
5
Palastanga, V., H. A. Dijkstra, and W. P. M. de Ruijter. "Inertially Induced Connections between Subgyres in the South Indian Ocean." Journal of Physical Oceanography 39, no. 2 (February 1, 2009): 465–71. http://dx.doi.org/10.1175/2008jpo3872.1.
Анотація:
Abstract A barotropic shallow-water model and continuation techniques are used to investigate steady solutions in an idealized South Indian Ocean basin containing Madagascar. The aim is to study the role of inertia in a possible connection between two subgyres in the South Indian Ocean. By increasing inertial effects in the model, two different circulation regimes are found. In the weakly nonlinear regime, the subtropical gyre presents a recirculation cell in the southwestern basin, with two boundary currents flowing westward from the southern and northern tips of Madagascar toward Africa. In the highly nonlinear regime, the inertial recirculation of the subtropical gyre is found to the east of Madagascar, while the East Madagascar Current overshoots the island’s southern boundary and connects through a southwestward jet with the current off South Africa.
6
Vozchikov, Lev M., and Lab Selena. "Experimental Drift Mapping of Indian Ocean Gyre Aircraft Debris." Open Journal of Applied Sciences 06, no. 02 (2016): 95–99. http://dx.doi.org/10.4236/ojapps.2016.62010.
7
Pattiaratchi, Charitha, Mirjam van der Mheen, Cathleen Schlundt, Bhavani E. Narayanaswamy, Appalanaidu Sura, Sara Hajbane, Rachel White, Nimit Kumar, Michelle Fernandes, and Sarath Wijeratne. "Plastics in the Indian Ocean – sources, transport, distribution, and impacts." Ocean Science 18, no. 1 (January 4, 2022): 1–28. http://dx.doi.org/10.5194/os-18-1-2022.
Анотація:
Abstract. Plastic debris is the most common and exponentially increasing human pollutant in the world's ocean. The distribution and impact of plastic in the Pacific and Atlantic oceans have been the subject of many publications but not so the Indian Ocean (IO). Some of the IO rim countries have the highest population densities globally and mismanagement of plastic waste is of concern in many of these rim states. Some of the most plastic-polluted rivers empty into the IO, with all this suggesting that the IO receives a tremendous amount of plastic debris each year. However, the concentration, distribution, and impacts of plastics in the IO are poorly understood as the region is under-sampled compared to other oceans. In this review, we discuss sources and sinks, which are specific to the IO. We also discuss unique atmospheric, oceanographic, and topographic features of the IO that control plastic distribution, such as reversing wind directions due to the monsoon, fronts, and upwelling regions. We identify hotspots of possible plastic accumulation in the IO, which differ between the two hemispheres. In the southern IO, plastics accumulate in a garbage patch in the subtropical gyre. However, this garbage patch is not well defined, and plastics may leak into the southern Atlantic or the Pacific Ocean. There is no subtropical gyre and associated garbage in the northern IO due to the presence of landmasses. Instead, the majority of buoyant plastics most likely end up on coastlines. Finally, we identify the vast knowledge gaps concerning plastics in the IO and point to the most pressing topics for future investigation.
8
Scussolini, P., and E. van Sebille. "Paleo Agulhas rings enter the subtropical gyre during the penultimate deglaciation." Climate of the Past Discussions 9, no. 2 (April 11, 2013): 2095–114. http://dx.doi.org/10.5194/cpd-9-2095-2013.
Анотація:
Abstract. A maximum in the strength of Agulhas Leakage has been registered at the interface between Indian and South Atlantic oceans during glacial Termination II (T II), presumably transporting the salt and heat necessary to maintain the Atlantic Meridional Overturning Circulation (AMOC) at rates similar to the present day. However, it was never shown whether these were effectively incorporated in the South Atlantic gyre, or whether they retroflected into the Indian and/or Southern Oceans. To solve this question, we investigate the presence of paleo Agulhas rings from a sediment core on the central Walvis Ridge, almost 1800 km farther into the Atlantic basin than previously studied. Analysis of a 20 yr dataset from a global ocean circulation model allows us to relate density perturbations, at the depth of the thermocline, to the passage of individual rings over the core site. Using this relation from the numerical model as the basis for a proxy, we generate a time series of δ18O variability of Globorotalia truncatulinoides single specimens, revealing high levels of pycnocline depth variability at the site, suggesting enhanced numbers of Agulhas rings moving into the South Atlantic gyre around and before T II. Our record closely follows the published quantifications of Agulhas Leakage from the east of the Cape Basin, and thus shows that Indian Ocean waters entered the South Atlantic circulation. This provides crucial support to the view of a prominent role of the Agulhas Leakage in the shift from a glacial to an interglacial mode of AMOC.
9
Lambert, Erwin, Dewi Le Bars, and Wilhelmus P. M. de Ruijter. "The connection of the Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current." Ocean Science 12, no. 3 (June 2, 2016): 771–80. http://dx.doi.org/10.5194/os-12-771-2016.
Анотація:
Abstract. East of Madagascar, the shallow “South Indian Ocean Counter Current (SICC)” flows from west to east across the Indian Ocean against the direction of the wind-driven circulation. The SICC impinges on west Australia and enhances the sea level slope, strengthening the alongshore coastal jet: the Leeuwin Current (LC), which flows poleward along Australia. An observed transport maximum of the LC around 22° S can likely be attributed to this impingement of the SICC. The LC is often described as a regional coastal current that is forced by an offshore meridional density gradient or sea surface slope. However, little is known about the controls of these open-ocean gradients. The regional circulation system is embedded in the subtropical “super gyre” that connects the Indo-Pacific via the Tasman Gateway and the Indonesian passages. The Indonesian Throughflow (ITF) circulates through the Indian Ocean back into the Pacific south of Australia. This return pathway appears to be partly trapped in the upper layer north of an outcrop line. It is redirected along this outcrop line and joins the eastward flow of the SICC. To study the connection of the basin-scale and the inter-ocean-scale dynamics, we apply both an ocean general circulation model and a conceptual two-layer model. Shutdown of the ITF in the models leads to a large decrease in Leeuwin Current transport. Most of the SICC was found to then reconnect to the internal gyre circulation in the Indian Ocean. ITF, SICC and LC thus appear to be dynamically connected.
10
Wang, Jinbo, Matthew R. Mazloff, and Sarah T. Gille. "The Effect of the Kerguelen Plateau on the Ocean Circulation." Journal of Physical Oceanography 46, no. 11 (November 2016): 3385–96. http://dx.doi.org/10.1175/jpo-d-15-0216.1.
Анотація:
AbstractThe Kerguelen Plateau is a major topographic feature in the Southern Ocean. Located in the Indian sector and spanning nearly 2000 km in the meridional direction from the polar to the subantarctic region, it deflects the eastward-flowing Antarctic Circumpolar Current and influences the physical circulation and biogeochemistry of the Southern Ocean. The Kerguelen Plateau is known to govern the local dynamics, but its impact on the large-scale ocean circulation has not been explored. By comparing global ocean numerical simulations with and without the Kerguelen Plateau, this study identifies two major Kerguelen Plateau effects: 1) The plateau supports a local pressure field that pushes the Antarctic Circumpolar Current northward. This process reduces the warm-water transport from the Indian to the Atlantic Ocean. 2) The plateau-generated pressure field shields the Weddell Gyre from the influence of the warmer subantarctic and subtropical waters. The first effect influences the strength of the Antarctic Circumpolar Current and the Agulhas leakage, both of which are important elements in the global thermohaline circulation. The second effect results in a zonally asymmetric response of the subpolar gyres to Southern Hemisphere wind forcing.
11
Pinault, Jean-Louis. "Weakening of the Geostrophic Component of the Gulf Stream: A Positive Feedback Loop on the Melting of the Arctic Ice Sheet." Journal of Marine Science and Engineering 11, no. 9 (August 27, 2023): 1689. http://dx.doi.org/10.3390/jmse11091689.
Анотація:
The North Atlantic gyre experiences both a significant temperature rise at high latitudes and a considerable weakening of the geostrophic component of the Gulf Stream, which is reflected by the 64-year fundamental gyral Rossby wave (GRW). This singular behavior compared to the South Atlantic and South Indian Ocean gyres highlights a feedback loop of Arctic ice sheet melting on mid-latitude Atlantic Ocean temperature. The warming of the northern oceanic gyre at high latitudes due to the retreat of Arctic ice sheet via the Labrador Current decreases the thermal gradient between the high and low latitudes of the north Atlantic gyre. This results in a weakening of the geostrophic forces at the basin scale and a reduction in the amplitude of the GRWs. Reducing the amplitude of the variation of the upward and downward movement of the pycnocline modifies air–sea interactions, weakening vertical mixing as well as the evaporation processes and the departure of latent heat when the pycnocline rises. The resulting thermal anomaly stretching along the Gulf Stream from where it leaves the American continent is partly transferred to the Arctic sea ice via the drift current and thermohaline circulation, which contributes to the retreat of the ice sheet, and the closing of the feedback loop. The 64-year-period GRW should disappear around 2050 if its damping continues linearly, favoring an increasingly rapid warming of the ocean at mid-latitudes. These interactions are less acute in the southern hemisphere due to the circumpolar current.
12
Bard, Edouard, Maurice Arnold, J. R. Toggweiler, Pierre Maurice, and Jean-Claude Duplessy. "Bomb 14C in the Indian Ocean Measured by Accelerator Mass Spectrometry: Oceanographic Implications." Radiocarbon 31, no. 03 (1989): 510–22. http://dx.doi.org/10.1017/s0033822200012108.
Анотація:
AMS 14C measurements on samples collected in the tropical-equatorial Indian Ocean during the INDIGO program (leg II, 1986) are presented and compared with β-counting results obtained under both INDIGO program and GEOSECS expedition in the Indian Ocean (1978). The most significant observation is a doubling of the bomb-14C inventory and mean penetration depth in the equatorial zone. Based on hydrologic considerations, two hypotheses can be proposed: 1) direct influx of Pacific mid-latitude waters through the Indonesian archipelago and 2) advection and/or mixing with Mode Water from the southern gyre of the Indian Ocean. Results obtained with a general circulation model of the ocean suggest that the influx from the Pacific is important in the upper 300m and that below 500m the bomb-14C budget is dominated by Mode Water advection.
13
Tsubouchi, T., T. Suga, and K. Hanawa. "Indian Ocean subtropical mode water: its water characteristics and spatial distribution." Ocean Science Discussions 6, no. 1 (April 21, 2009): 723–39. http://dx.doi.org/10.5194/osd-6-723-2009.
Анотація:
Abstract. We examined Indian Ocean Subtropical Mode Water (IOSTMW) and described its characteristics using an isopycnally averaged three-dimensional hydrographic dataset. Through careful examination of the spatial distribution and water characteristics of the core in the layer of minimum vertical temperature gradient, we concluded that the IOSTMW exists as a robust structure in the western part of the Indian Ocean subtropical gyre in summer. The averaged IOSTMW properties during approximately 1960–2004 were 16.54±0.49°C, 35.51±0.04 psu, and 26.0±0.1 σθ. The IOSTMW distribution area was 27–38° S, 25–50° E.
14
Harms, Natalie C., Niko Lahajnar, Birgit Gaye, Tim Rixen, Kirstin Dähnke, Markus Ankele, Ulrich Schwarz-Schampera, and Kay-Christian Emeis. "Nutrient distribution and nitrogen and oxygen isotopic composition of nitrate in water masses of the subtropical southern Indian Ocean." Biogeosciences 16, no. 13 (July 12, 2019): 2715–32. http://dx.doi.org/10.5194/bg-16-2715-2019.
Анотація:
Abstract. The Indian Ocean subtropical gyre (IOSG) is one of five extensive subtropical gyres in the world's ocean. In contrast to those of the Atlantic and Pacific oceans, the IOSG has been sparsely studied. We investigate the water mass distributions based on temperature, salinity and oxygen data, and the concentrations of water column nutrients and the stable isotope composition of nitrate, using water samples collected between ∼30∘ S and the Equator during two expeditions: MSM 59/2 in 2016 and SO 259 in 2017. Our results are the first from this oceanic region and provide new information on nitrogen sources and transformation processes. We identify the thick layer of nutrient-depleted surface waters of the oligotrophic IOSG with nitrate (NO3-) and phosphate (PO43-) concentrations of < 3 and < 0.3 µmol kg−1, respectively (< 300 m; σ < 26.4 kg−1 m−3). Increased nutrient concentrations towards the Equator represent the northern limb of the gyre, which is characterized by typical strong horizontal gradients of the outcropping nutriclines. The influx of the Subantarctic Mode Water (SAMW) from the Southern Ocean injects oxygen-saturated waters with preformed nutrients, indicated by the increased N and O isotope composition of nitrate (δ15N > 7 ‰; δ18O > 4 ‰) at 400–500 m (26.6–26.7 kg−1 m−3), into the subtropical thermocline. These values reflect partial N assimilation in the Southern Ocean. Moreover, in the northern study area, a residue of nitrate affected by denitrification in the Arabian Sea is imported into intermediate and deep water masses (> 27.0 kg−1 m−3) of the gyre, indicated by an N deficit (N* ∼-1 to −4 µmol kg−1) and by elevated isotopic ratios of nitrate (δ15N > 7 ‰; δ18O > 3 ‰). Remineralization of partially assimilated organic matter, produced in the subantarctic, leads to a decoupling of N and O isotopes in nitrate and results in a relatively low Δ(15–18) value of < 3 ‰ within the SAMW. In contrast, remineralization of 15N-enriched organic matter from the Arabian Sea indicates higher Δ(15–18) values of > 4 ‰ within the Red Sea–Persian Gulf Intermediate Water (RSPGIW). Thus, the subtropical southern Indian Ocean is supplied by preformed nitrate from the lateral influx of water masses from regions exhibiting distinctly different N-cycle processes documented in the dual isotope composition of nitrate. Additionally, a significant contribution of N2 fixation between 20.36 and 23.91∘ S is inferred from reduced δ15N–NO3- values towards surface waters (upward decrease of δ15N ∼2.4 ‰), N* values of > 2 µmol kg−1 and a relatively low Δ(15–18) value of < 3 ‰. A mass and isotope budget implies that at least 32 %–34 % of the nitrate in the upper ocean between 20.36 and 23.91∘ S is provided from newly fixed nitrogen, whereas N2 fixation appears to be limited by iron or temperature south of 26∘ S.
15
Scussolini, P., E. van Sebille, and J. V. Durgadoo. "Paleo Agulhas rings enter the subtropical gyre during the penultimate deglaciation." Climate of the Past 9, no. 6 (November 25, 2013): 2631–39. http://dx.doi.org/10.5194/cp-9-2631-2013.
Анотація:
Abstract. A maximum in the strength of Agulhas leakage has been registered at the interface between the Indian and South Atlantic oceans during glacial Termination II (T-II). This presumably transported the salt and heat necessary for maintaining the Atlantic circulation at rates similar to the present day. However, it was never shown whether these waters were effectively incorporated into the South Atlantic gyre, or whether they retroflected into the Indian and/or Southern oceans. To resolve this question, we investigate the presence of paleo Agulhas rings from a sediment core on the central Walvis Ridge, almost 1800 km farther into the Atlantic Basin than previously studied. Analysis of a 60 yr data set from the global-nested INALT01 model allows us to relate density perturbations at the depth of the thermocline to the passage of individual rings over the core site. Using this relation from the numerical model as the basis for a proxy, we generate a time series of variability of individual Globorotalia truncatulinoides δ18O. We reveal high levels of pycnocline depth variability at the site, suggesting enhanced numbers of Agulhas rings moving into the South Atlantic Gyre around T-II. Our record closely follows the published quantifications of Agulhas leakage from the east of the Cape Basin, and thus shows that Indian Ocean waters entered the South Atlantic circulation. This provides crucial support for the view of a prominent role of the Agulhas leakage in the shift from a glacial to an interglacial mode of the Atlantic circulation.
16
Hörstmann, Cora, Eric J. Raes, Pier Luigi Buttigieg, Claire Lo Monaco, Uwe John, and Anya M. Waite. "Hydrographic fronts shape productivity, nitrogen fixation, and microbial community composition in the southern Indian Ocean and the Southern Ocean." Biogeosciences 18, no. 12 (June 22, 2021): 3733–49. http://dx.doi.org/10.5194/bg-18-3733-2021.
Анотація:
Abstract. Biogeochemical cycling of carbon (C) and nitrogen (N) in the ocean depends on both the composition and activity of underlying biological communities and on abiotic factors. The Southern Ocean is encircled by a series of strong currents and fronts, providing a barrier to microbial dispersion into adjacent oligotrophic gyres. Our study region straddles the boundary between the nutrient-rich Southern Ocean and the adjacent oligotrophic gyre of the southern Indian Ocean, providing an ideal region to study changes in microbial productivity. Here, we measured the impact of C and N uptake on microbial community diversity, contextualized by hydrographic factors and local physico-chemical conditions across the Southern Ocean and southern Indian Ocean. We observed that contrasting physico-chemical characteristics led to unique microbial diversity patterns, with significant correlations between microbial alpha diversity and primary productivity (PP). However, we detected no link between specific PP (PP normalized by chlorophyll-a concentration) and microbial alpha and beta diversity. Prokaryotic alpha and beta diversity were correlated with biological N2 fixation, which is itself a prokaryotic process, and we detected measurable N2 fixation to 60∘ S. While regional water masses have distinct microbial genetic fingerprints in both the eukaryotic and prokaryotic fractions, PP and N2 fixation vary more gradually and regionally. This suggests that microbial phylogenetic diversity is more strongly bounded by physical oceanographic features, while microbial activity responds more to chemical factors. We conclude that concomitant assessments of microbial diversity and activity are central to understanding the dynamics and complex responses of microorganisms to a changing ocean environment.
17
Stramma, L., and J. R. E. Lutjeharms. "The flow field of the subtropical gyre of the South Indian Ocean." Journal of Geophysical Research: Oceans 102, no. C3 (March 15, 1997): 5513–30. http://dx.doi.org/10.1029/96jc03455.
18
Miller, Michael J., Sam Wouthuyzen, Eric Feunteun, Jun Aoyama, Shun Watanabe, Augy Syahailatua, Mari Kuroki, et al. "Contrasting biodiversity of eel larvae across the central Indian Ocean subtropical gyre." Deep Sea Research Part II: Topical Studies in Oceanography 161 (March 2019): 120–31. http://dx.doi.org/10.1016/j.dsr2.2018.02.012.
19
Ditkovsky, Sam, Laure Resplandy, and Julius Busecke. "Unique ocean circulation pathways reshape the Indian Ocean oxygen minimum zone with warming." Biogeosciences 20, no. 23 (November 29, 2023): 4711–36. http://dx.doi.org/10.5194/bg-20-4711-2023.
Анотація:
Abstract. The global ocean is losing oxygen with warming. Observations and Earth system model projections, however, suggest that this global ocean deoxygenation does not equate to a simple and systematic expansion of tropical oxygen minimum zones (OMZs). Previous studies have focused on the Pacific Ocean; they showed that the outer OMZ deoxygenates and expands as oxygen supply by advective transport weakens, the OMZ core oxygenates and contracts due to a shift in the composition of the source waters supplied by slow mixing, and in between these two regimes oxygen is redistributed with little effect on OMZ volume. Here, we examine the OMZ response to warming in the Indian Ocean using an ensemble of Earth system model high-emissions scenario experiments from the Coupled Model Intercomparison Project Phase 6. We find a similar expansion–redistribution–contraction response but show that the unique ocean circulation pathways of the Indian Ocean lead to far more prominent OMZ contraction and redistribution regimes than in the Pacific Ocean. As a result, only the outermost volumes (oxygen>180 µmol kg−1) expand. The Indian Ocean experiences a broad oxygenation in the southwest driven by a reduction in waters supplied by the Indonesian Throughflow in favor of high-oxygen waters supplied from the southern Indian Ocean gyre. Models also project a strong localized deoxygenation in the northern Arabian Sea due to the rapid warming and shoaling of marginal sea outflows (Red Sea and Persian Gulf) and increases in local stratification with warming. We extend the existing conceptual framework used to explain the Pacific OMZ response to interpret the response in the Indian Ocean.
20
Utama, Andria Ansri, and Wudianto Wudianto. "DINAMIKA SPASIAL IKAN MESOPELAGIS (ceratoscopelus warmingii LÜTKEN, 1892) DI SAMUDERA HINDIA." Jurnal Penelitian Perikanan Indonesia 22, no. 4 (January 27, 2017): 263. http://dx.doi.org/10.15578/jppi.22.4.2016.263-270.
Анотація:
Kajian mengenai ikan mesopelagis di perairan Samudera Hindia masih sangat terbatas, sehingga informasi terkait kelimpahan jenis ikan mesopelagis di Samudera Hindia sangat penting. Survei trawl lapisan pertengahan dilakukan pada tanggal 26 Juni-16 Juli 2015 di perairan laut lepas (high seas) Samudera Hindia untuk memperoleh data dan informasi tersebut dengan menggunakan kapal penelitian R.V. Dr. Fridtjof Nansen. Hasil penelitian menunjukkan distribusi kedalaman vertikal di malam hari jenis yang dominan C.warmingii sesuai dengan kedalaman operasi trawl yaitu 86,9 ± 38,6 m. Namun pada siang hari tidak ditemukan spesies C. warmingii saat operasi trawl pada kedalaman rata-rata 444,3 ± 45,96 m. Diperkirakan ketika siang hari distribusi C. warmingii terkonsentrasi pada lapisan perairan lebih dalam sehingga tidak terjangkau oleh jaring trawl tersebut. Distribusi spasial secara horizontal pada malam hari menunjukkan pola konsentrasi tertinggi berada pada area gyre yang diindikasikan dengan pola geostrophic circulation. Sementara, prosentase C. warmingii yang merupakan hasil tangkapan seluruh stasiun trawl selama penelitian terdiri dari 2,58% fase larva, 27,21% juvenile, dan 60,21% dalam keadaan dewasa.Studies on mesopelagic fishes in the Indian Ocean are relatively limited, therefore data and information regarding spatial dynamic of the most abundant mesopelagic fish species Ceratoscopelus warmingii in the Indian Ocean would contribute a significant information on deepsea marine biodiversity. Pelagic-trawl stations were used to collect and identify the spatial dynamic of C. warmingii in the main scattering layers of the water column. Survey were carried out by RV Dr. Fridtjof Nansen in the high seas of Indian Ocean. Observation were made during day and night on 26th June to 16th July 2015 as part of the second International Indian Ocean Expedition (IIOE 2). The result shows that vertical distributions of C. warmingii were concentrated at the average depth 86.9 ± 38.6 m during nighttime. There were no individuals found during the daytime at the average depth 444.3 ± 45.96 m, diurnal migrations of C. warmingii to more than the depth of trawl operation might explain the absent of this species. Horizontal spatial distribution of trawl catches (number per hour) during nighttime show high concentration of C. warmingii close to gyre indicated by geostrophic circulation. Moreover, the total catches of C. warmingii across the Indian Ocean are dominated by 60.21% adult, 27.21% juvenile, and 2.58% larvae, respectively.
21
Friocourt, Yann, Sybren Drijfhout, Bruno Blanke, and Sabrina Speich. "Water Mass Export from Drake Passage to the Atlantic, Indian, and Pacific Oceans: A Lagrangian Model Analysis." Journal of Physical Oceanography 35, no. 7 (July 1, 2005): 1206–22. http://dx.doi.org/10.1175/jpo2748.1.
Анотація:
Abstract The northward export of intermediate water from Drake Passage is investigated in two global ocean general circulation models (GCMs) by means of quantitative particle tracing diagnostics. This study shows that a total of about 23 Sv (Sv ≡ 106 m3 s−1) is exported from Drake Passage to the equator. The Atlantic and Pacific Oceans are the main catchment basins with 7 and 15 Sv, respectively. Only 1–2 Sv of the water exported to the Atlantic equator follow the direct cold route from Drake Passage without entering the Indian Ocean. The remainder loops first into the Indian Ocean subtropical gyre and flows eventually into the Atlantic Ocean by Agulhas leakage. The authors assess the robustness of a theory that relates the export from Drake Passage to the equator to the wind stress over the Southern Ocean. Our GCM results are in reasonable agreement with the theory that predicts the total export. However, the theory cannot be applied to individual basins because of interocean exchanges through the “supergyre” mechanism and other nonlinear processes such as the Agulhas rings. The export of water from Drake Passage starts mainly as an Ekman flow just northward of the latitude band of the Antarctic Circumpolar Current south of South America. Waters quickly subduct and are transferred to the ocean interior as they travel equatorward. They flow along the eastern boundaries in the Sverdrup interior and cross the southern basins northwestward to reach the equator within the western boundary current systems.
22
Du, Yan, and Yuhong Zhang. "Satellite and Argo Observed Surface Salinity Variations in the Tropical Indian Ocean and Their Association with the Indian Ocean Dipole Mode." Journal of Climate 28, no. 2 (January 15, 2015): 695–713. http://dx.doi.org/10.1175/jcli-d-14-00435.1.
Анотація:
Abstract This study investigates sea surface salinity (SSS) variations in the tropical Indian Ocean (IO) using the Aquarius/Satelite de Aplicaciones Cientificas-D (SAC-D) and the Soil Moisture and Ocean Salinity (SMOS) satellite data and the Argo observations during July 2010–July 2014. Compared to the Argo observations, the satellite datasets generally provide SSS maps with higher space–time resolution, particularly in the regions where Argo floats are sparse. Both Aquarius and SMOS well captured the SSS variations associated with the Indian Ocean dipole (IOD) mode. Significant SSS changes occurred in the central equatorial IO, along the Java–Sumatra coast, and south of the equatorial IO, due to ocean circulation variations. During the negative IOD events in 2010, 2013, and 2014, westerly wind anomalies strengthened along the equator, weakening coastal upwelling off Java and Sumatra and decreasing SSS. South of the equatorial IO, an anomalous cyclonic gyre changed the tropical circulation, which favored the eastward high-salinity tongue along the equator and the westward low-saline tongue in the south. An upwelling Rossby wave favored the increase of SSS farther to the south. During the positive IOD events in 2011 and 2012, the above-mentioned processes reversed, although the decrease of SSS was weaker in magnitude.
23
Romanov, Evgeny V., Natacha Nikolic, Zahirah Dhurmeea, Nathalie Bodin, Alexis Puech, Stewart Norman, Stéphanie Hollanda, Jérôme Bourjea, Wendy West, and Michel Potier. "Trophic ecology of albacore tuna (Thunnus alalunga) in the western tropical Indian Ocean and adjacent waters." Marine and Freshwater Research 71, no. 11 (2020): 1517. http://dx.doi.org/10.1071/mf19332.
Анотація:
In this study we investigated the trophic ecology of albacore tuna in the western Indian Ocean and adjacent Atlantic waters based on stomach content analysis using a reconstituted length and weight of prey approach. From 686 non-empty stomachs collected between 2001 and 2015 across three biogeographic provinces, we describe the diet composition of albacore tuna, analyse its feeding habits and investigate the structure and diversity of mid-trophic-level communities. Epipelagic fish were found to be the principal prey by number and reconstituted weight; cephalopods were the second important prey group. Small organisms prevailed in the diet of albacore tuna, with predation on juvenile fish commonplace. Albacore tuna exhibits a flexible, opportunistic feeding strategy, from ram filter feeding on abundant schooling prey to visual predation on large individuals. Prey species richness varied highly across the region. Oligotrophic conditions within the subtropical gyre of the Indian Ocean generated the most diverse mid-trophic-level communities, with less diverse communities occurring in productive areas. Albacore tuna occupies a similar trophic niche throughout the global ocean, foraging on the same prey families and even species. This study indicates overall temporal stability of the Indian Ocean and south-east Atlantic ecosystems where principal prey species remain unchanged over decades.
24
Hydén, Lars. "The Influence on Summer Rainfall in the Lesotho Lowlands from Indian Ocean SSTs." Hydrology Research 33, no. 4 (August 1, 2002): 305–18. http://dx.doi.org/10.2166/nh.2002.0010.
Анотація:
Lesotho is located approximately at latitude 30 degrees south in the interior of Southern Africa. The mesoscale climate is complicated and governed by various weather systems. The inter-annual rainfall variability is great, resulting in low food security, since the growing of crops in the Lesotho Lowlands is almost exclusively rain-fed. Reliable forecasts of austral summer rainfall are thus valuable. Earlier research has shown that the sea surface temperatures (SST) in the Indian Ocean to some extent govern rainfall in Southern Africa. The research presented is part of an on-going project to find suitable oceanographic and meteorological predictors, which can be used in a forecast model for summer rainfall, to be developed later. The first part of this paper investigates the correlation between the average SSTs in the Equatorial Indian Ocean, the Central Indian Ocean, and the Agulhas Gyre, respectively, and rainfall two months later in the Lesotho Lowlands during early austral summer, October until December for the period 1949-1995. No significant correlations have been found, probably because the three ocean areas are too large. In the second part of this paper the monthly SST in 132 grid squares in the Indian Ocean were investigated and found to be correlated with rainfall in the Lesotho Lowlands two months later, October until March. Significant correlations have been found between the SSTs and certain ocean areas and December, January, and February rainfall, respectively. There is significant negative correlation between December rainfall and October SST in an ocean area between Kenya and Somalia across the Indian Ocean to Sumatra. In the area where the Somali Current flows there is also significant correlation between December SST and December rainfall. January rainfall is significantly negatively correlated with November SST in an ocean area, northeast of Madagascar. February rainfall is significantly, but weakly, negatively correlated with SST in a narrow north-south corridor in the Eastern Indian Ocean from the equator down to latitude 40 degrees south.
25
Morel, A., H. Claustre, and B. Gentili. "The most oligotrophic subtropical zones of the global ocean: similarities and differences in terms of chlorophyll and yellow substance." Biogeosciences Discussions 7, no. 4 (July 1, 2010): 5047–79. http://dx.doi.org/10.5194/bgd-7-5047-2010.
Анотація:
Abstract. The cores of the subtropical anticyclonic gyres are characterized by their oligotrophic status and minimal chlorophyll concentration, compared to that of the whole ocean. These zones are unambiguously detected by space borne ocean color sensors thanks to their typical spectral reflectance, which is that of extremely clear and deep blue waters. Not only the low chlorophyll (denoted [Chl]) level, but also a reduced amount of colored dissolved organic matter (CDOM or "yellow substance") account for this clarity. The oligotrophic waters of the North and South Pacific gyres, the North and South Atlantic gyres, and the South Indian gyre have been comparatively studied with respect to both [Chl] and CDOM contents, by using 10-year data (1998–2007) of the Sea-viewing Wide field-of-view Sensor (SeaWiFS, NASA). Albeit similar these oligotrophic zones are not identical regarding their [Chl] and CDOM contents, as well as their seasonal cycles. According to the zone, the averaged [Chl] value varies from 0.026 to 0.059 mg m−3, whereas the ay(443) average (the absorption coefficient due to CDOM at 443 nm) is comprised between 0.0033 and 0.0072 m−1. The CDOM-to-[Chl] relative proportions also differ between the zones. The clearest waters, corresponding to the lowest [Chl] and CDOM concentrations, are found near Easter Island and near Mariana Islands in the western part of the North Pacific Ocean. In spite of its low [Chl], the Sargasso Sea presents the highest CDOM content amongst the six zones studied. Except in the North Pacific gyre (near Mariana and south of Hawaii islands), a conspicuous seasonality appears to be the rule in the other 4 gyres and affects both [Chl] and CDOM; both quantities vary in a ratio of about 2 (maximum-to-minimum). Coinciding [Chl] and CDOM peaks occur just after the local winter solstice, which is also the period of the maximal mixed layer depth in these latitudes. It is hypothesized that the vertical transport of unbleached CDOM from the subthermocline layers is the main process enhancing the CDOM concentration within the upper layer in winter. In summer, the CDOM experiences its minimum which is delayed with respect to the [Chl] minimum; apparently, the solar photo-bleaching of CDOM is a slower process than the post-bloom algal Chl decay. Where they exist, the seasonal cycles are repeated without notable change from year to year; long term (10 years) trends have not been detected in these zones. These oligotrophic gyres can conveniently be used for in-flight calibration and comparison of ocean color sensors, provided that their marked seasonal variations are accounted for.
26
Morel, A., H. Claustre, and B. Gentili. "The most oligotrophic subtropical zones of the global ocean: similarities and differences in terms of chlorophyll and yellow substance." Biogeosciences 7, no. 10 (October 14, 2010): 3139–51. http://dx.doi.org/10.5194/bg-7-3139-2010.
Анотація:
Abstract. The cores of the subtropical anticyclonic gyres are characterized by their oligotrophic status and minimal chlorophyll concentration, compared to that of the whole ocean. These zones are unambiguously detected by space borne ocean color sensors thanks to their typical spectral reflectance, which is that of extremely clear and deep blue waters. Not only the low chlorophyll (denoted [Chl]) level, but also a reduced amount of colored dissolved organic matter (CDOM or "yellow substance") account for this clarity. The oligotrophic waters of the North and South Pacific gyres, the North and South Atlantic gyres, and the South Indian gyre have been comparatively studied with respect to both [Chl] and CDOM contents, by using 10-year data (1998–2007) of the Sea-viewing Wide field-of-view Sensor (SeaWiFS, NASA). Albeit similar these oligotrophic zones are not identical regarding their [Chl] and CDOM contents, as well as their seasonal cycles. According to the zone, the averaged [Chl] value varies from 0.026 to 0.059 mg m−3, whereas the ay(443) average (the absorption coefficient due to CDOM at 443 nm) is between 0.0033 and 0.0072 m−1. The CDOM-to-[Chl] relative proportions also differ between the zones. The clearest waters, corresponding to the lowest [Chl] and CDOM concentrations, are found near Easter Island and near Mariana Islands in the western part of the North Pacific Ocean. In spite of its low [Chl], the Sargasso Sea presents the highest CDOM content amongst the six zones studied. Except in the North Pacific gyre (near Mariana and south of Hawaii islands), a conspicuous seasonality appears to be the rule in the other 4 gyres and affects both [Chl] and CDOM; both quantities vary in a ratio of about 2 (maximum-to-minimum). Coinciding [Chl] and CDOM peaks occur just after the local winter solstice, which is also the period of the maximal mixed layer depth in these latitudes. It is hypothesized that the vertical transport of unbleached CDOM from the subthermocline layers is the main process enhancing the CDOM concentration within the upper layer in winter. In summer, the CDOM experiences its minimum which is delayed with respect to the [Chl] minimum; apparently, the solar photo-bleaching of CDOM is a slower process than the post-bloom algal Chl decay. Where they exist, the seasonal cycles are repeated without notable change from year to year. Long term (10 y) trends have not been detected in these zones. These oligotrophic gyres can conveniently be used for in-flight calibration and comparison of ocean color sensors, provided that their marked seasonal variations are accounted for.
27
Nagura, Motoki, and Shinya Kouketsu. "Spiciness Anomalies in the Upper South Indian Ocean." Journal of Physical Oceanography 48, no. 9 (September 2018): 2081–101. http://dx.doi.org/10.1175/jpo-d-18-0050.1.
Анотація:
AbstractThis study investigates an isopycnal temperature/salinity T/S, or spiciness, anomaly in the upper south Indian Ocean for the period from 2004 to 2015 using observations and reanalyses. Spiciness anomalies at about 15°S on 24–26σθ are focused on, whose standard deviation is about 0.1 psu in salinity and 0.25°C in temperature, and they have a contribution to isobaric temperature variability comparable to thermocline heave. A plausible generation region of these anomalies is the southeastern Indian Ocean, where the 25σθ surface outcrops in southern winter, and the anticyclonic subtropical gyre advects subducted water equatorward. Unlike the Pacific and Atlantic, spiciness anomalies in the upper south Indian Ocean are not T/S changes in mode water, and meridional variations in SST and sea surface salinity in their generation region are not density compensating. It is possible that this peculiarity is owing to freshwater originating from the Indonesian Seas. The production of spiciness anomalies is estimated from surface heat and freshwater fluxes and the surface T/S relationship in the outcrop region, based on several assumptions including the dominance of surface fluxes in the surface T/S budget and effective mixed layer depth proposed by Deser et al. The result agrees well with isopycnal salinity anomalies at the outcrop line, which indicates that spiciness anomalies are generated by local surface fluxes. It is suggested that the Ningaloo Niño and El Niño–Southern Oscillation lead to interannual variability in surface heat flux in the southeastern Indian Ocean and contribute to the generation of spiciness anomalies.
28
Lambert, E., D. Le Bars, and W. P. M. de Ruijter. "The dynamic connection of the Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current." Ocean Science Discussions 12, no. 5 (September 25, 2015): 2231–56. http://dx.doi.org/10.5194/osd-12-2231-2015.
Анотація:
Abstract. East of Madagascar, wind and surface buoyancy fluxes reinforce each other, leading to frontogenesis, outcrop and an eastward along-front flow: the South Indian Ocean Countercurrent (SICC). In the east the Leeuwin Current (LC) is a unique eastern boundary current which flows poleward along Australia. It is often described as a regional coastal current forced by an off-shore meridional density gradient or a sea surface slope, yet little is known of the forcing and dynamics that control these open ocean meridional gadients. To complete this understanding, we make use of both an ocean general circulation model and a conceptual two-layer model. The SICC impinges on west Australia and adds to a sea level slope and a southward geostrophic coastal jet: the Leeuwin Current. The SICC and the LC are thus dynamically connected. An observed transport maximum of the LC around 22° S is directly related to this impingement of the SICC. The circulation of the Indonesian Throughflow (ITF) through the Indian Ocean appears to be partly trapped in the upper layer north of the outcrop line and is redirected along this outcrop line to join the eastward flow of the SICC. Shutdown of the ITF in both models strongly decreases the Leeuwin Current transport and breaks the connection between the LC and SICC. In this case, most of the SICC was found to reconnect to the internal gyre circulation in the Indian Ocean. The Indonesian Throughflow, South Indian Ocean Countercurrent and the Leeuwin Current are thus dynamically coupled.
29
Liu, Rongjie, Jie Zhang, Tingwei Cui, and Haocheng Yu. "Impact of Monsoon-Transported Anthropogenic Aerosols and Sun-Glint on the Satellite-Derived Spectral Remote Sensing Reflectance in the Indian Ocean." Remote Sensing 13, no. 2 (January 7, 2021): 184. http://dx.doi.org/10.3390/rs13020184.
Анотація:
Spectral remote sensing reflectance (Rrs(λ), sr−1) is one of the most important products of ocean color satellite missions, where accuracy is essential for retrieval of in-water, bio-optical, and biogeochemical properties. For the Indian Ocean (IO), where Rrs(λ) accuracy has not been well documented, the quality of Rrs(λ) products from Moderate Resolution Imaging Spectroradiometer onboard both Terra (MODIS-Terra) and Aqua (MODIS-Aqua), and Visible Infrared Imaging Radiometer Suite onboard the Suomi National Polar-Orbiting Partnership spacecraft (VIIRS-NPP), is evaluated and inter-compared based on a quality assurance (QA) system, which can objectively grade each individual Rrs(λ) spectrum, with 1 for a perfect spectrum and 0 for an unusable spectrum. Taking the whole year of 2016 as an example, spatiotemporal pattern of Rrs(λ) quality in the Indian Ocean is characterized for the first time, and the underlying factors are elucidated. Specifically, QA analysis of the monthly Rrs(λ) over the IO indicates good quality with the average scores of 0.93 ± 0.02, 0.92 ± 0.02 and 0.92 ± 0.02 for VIIRS-NPP, MODIS-Aqua, and MODIS-Terra, respectively. Low-quality (~0.7) data are mainly found in the Bengal Bay (BB) from January to March, which can be attributed to the imperfect atmospheric correction due to anthropogenic absorptive aerosols transported by the northeasterly winter monsoon. Moreover, low-quality (~0.74) data are also found in the clear oligotrophic gyre zone (OZ) of the south IO in the second half of the year, possibly due to residual sun-glint contributions. These findings highlight the effects of monsoon-transported anthropogenic aerosols, and imperfect sun-glint removal on the Rrs(λ) quality. Further studies are advocated to improve the sun-glint correction in the oligotrophic gyre zone and aerosol correction in the complex ocean–atmosphere environment.
30
Liu, Rongjie, Jie Zhang, Tingwei Cui, and Haocheng Yu. "Impact of Monsoon-Transported Anthropogenic Aerosols and Sun-Glint on the Satellite-Derived Spectral Remote Sensing Reflectance in the Indian Ocean." Remote Sensing 13, no. 2 (January 7, 2021): 184. http://dx.doi.org/10.3390/rs13020184.
Анотація:
Spectral remote sensing reflectance (Rrs(λ), sr−1) is one of the most important products of ocean color satellite missions, where accuracy is essential for retrieval of in-water, bio-optical, and biogeochemical properties. For the Indian Ocean (IO), where Rrs(λ) accuracy has not been well documented, the quality of Rrs(λ) products from Moderate Resolution Imaging Spectroradiometer onboard both Terra (MODIS-Terra) and Aqua (MODIS-Aqua), and Visible Infrared Imaging Radiometer Suite onboard the Suomi National Polar-Orbiting Partnership spacecraft (VIIRS-NPP), is evaluated and inter-compared based on a quality assurance (QA) system, which can objectively grade each individual Rrs(λ) spectrum, with 1 for a perfect spectrum and 0 for an unusable spectrum. Taking the whole year of 2016 as an example, spatiotemporal pattern of Rrs(λ) quality in the Indian Ocean is characterized for the first time, and the underlying factors are elucidated. Specifically, QA analysis of the monthly Rrs(λ) over the IO indicates good quality with the average scores of 0.93 ± 0.02, 0.92 ± 0.02 and 0.92 ± 0.02 for VIIRS-NPP, MODIS-Aqua, and MODIS-Terra, respectively. Low-quality (~0.7) data are mainly found in the Bengal Bay (BB) from January to March, which can be attributed to the imperfect atmospheric correction due to anthropogenic absorptive aerosols transported by the northeasterly winter monsoon. Moreover, low-quality (~0.74) data are also found in the clear oligotrophic gyre zone (OZ) of the south IO in the second half of the year, possibly due to residual sun-glint contributions. These findings highlight the effects of monsoon-transported anthropogenic aerosols, and imperfect sun-glint removal on the Rrs(λ) quality. Further studies are advocated to improve the sun-glint correction in the oligotrophic gyre zone and aerosol correction in the complex ocean–atmosphere environment.
31
Nagura, Motoki, and Michael J. McPhaden. "The Shallow Overturning Circulation in the Indian Ocean." Journal of Physical Oceanography 48, no. 2 (February 2018): 413–34. http://dx.doi.org/10.1175/jpo-d-17-0127.1.
Анотація:
AbstractThe number of in situ observations in the Indian Ocean has dramatically increased over the past 15 years thanks to the implementation of the Argo profiling float program. This study estimates the mean circulation in the Indian Ocean using hydrographic observations obtained from both Argo and conductivity–temperature–depth (CTD) observations. Absolute velocity at the Argo float parking depth is used so there is no need to assume a level of no motion. Results reveal previously unknown features in addition to well-known currents and water masses. Some newly identified features include the lack of an interior pathway to the equator from the southern Indian Ocean in the pycnocline, indicating that water parcels must transit through the western boundary to reach the equator. High potential vorticity (PV) intrudes from the western coast of Australia in the depth range of the Subantarctic Mode Water, which leads to a structure similar to a PV barrier. The subtropical anticyclonic gyre retreats poleward with depth, as happens in the subtropical Atlantic and Pacific. An eastward flow was found in the eastern basin along 15°S at the depth of the Antarctic Intermediate Water—a feature expected from property distributions but never before detected in velocity estimates. Meridional mass transport indicates about 10 Sv (1 Sv ≡ 106 m3 s−1) southward flow at 6°S and 18 Sv northward flow at 20°S, which results in meridional convergence of currents and thermocline depression at about 16°–20°S. These estimated absolute velocities agree well with those of an ocean reanalysis, which lends credibility to the strictly databased analysis.
32
Duan, Jing, Yuanlong Li, Lei Zhang, and Fan Wang. "Impacts of the Indian Ocean Dipole on Sea Level and Gyre Circulation of the Western Tropical Pacific Ocean." Journal of Climate 33, no. 10 (May 15, 2020): 4207–28. http://dx.doi.org/10.1175/jcli-d-19-0782.1.
Анотація:
AbstractInterannual variabilities of sea level and upper-ocean gyre circulation of the western tropical Pacific Ocean (WTPO) have been predominantly attributed to El Niño–Southern Oscillation (ENSO). The results of the present study put forward important modulation effects by the Indian Ocean dipole (IOD) mode. The observed sea level in the WTPO shows significant instantaneous and lagged correlations (around −0.60 and 0.40, respectively) with the IOD mode index (DMI). A composite of 14 “independent” IOD events for 1958–2017 shows negative sea level anomalies (SLAs) of 4–7 cm in the WTPO during positive IOD events and positive SLAs of 6–8 cm in the following year that are opposite in sign to the El Niño effect. The IOD impacts are reproduced by large-ensemble simulations of a climate model that generate respectively 430 and 519 positive and negative independent IOD events. A positive IOD induces westerly winds over the western and central tropical Pacific and causes negative SLAs through Ekman upwelling, and it facilitates the establishment of a La Niña condition in the following year that involves enhanced Pacific trade winds and causes positive SLAs in the WTPO. Ocean model experiments confirm that the IOD affects the WTPO sea level mainly through modulating the tropical Pacific winds. Variability of the Indonesian Throughflow (ITF) induced by IOD winds has a relatively weak effect on the WTPO. The IOD’s impacts on the major upper-ocean currents are also considerable, causing anomalies of 1–4 Sv (1 Sv ≡ 106 m3 s−1) in the South Equatorial Current (SEC) and North Equatorial Countercurrent (NECC) volume transports.
33
van der Mheen, Mirjam, Erik van Sebille, and Charitha Pattiaratchi. "Beaching patterns of plastic debris along the Indian Ocean rim." Ocean Science 16, no. 5 (October 30, 2020): 1317–36. http://dx.doi.org/10.5194/os-16-1317-2020.
Анотація:
Abstract. A large percentage of global ocean plastic waste enters the Northern Hemisphere Indian Ocean (NIO). Despite this, it is unclear what happens to buoyant plastics in the NIO. Because the subtropics in the NIO are blocked by landmass, there is no subtropical gyre and no associated subtropical garbage patch in this region. We therefore hypothesize that plastics “beach” and end up on coastlines along the Indian Ocean rim. In this paper, we determine the influence of beaching plastics by applying different beaching conditions to Lagrangian particle-tracking simulation results. Our results show that a large amount of plastic likely ends up on coastlines in the NIO, while some crosses the Equator into the Southern Hemisphere Indian Ocean (SIO). In the NIO, the transport of plastics is dominated by seasonally reversing monsoonal currents, which transport plastics back and forth between the Arabian Sea and the Bay of Bengal. All buoyant plastic material in this region beaches within a few years in our simulations. Countries bordering the Bay of Bengal are particularly heavily affected by plastics beaching on coastlines. This is a result of both the large sources of plastic waste in the region and the ocean dynamics that concentrate plastics in the Bay of Bengal. During the intermonsoon period following the southwest monsoon season (September, October, November), plastics can cross the Equator on the eastern side of the NIO basin into the SIO. Plastics that escape from the NIO into the SIO beach on eastern African coastlines and islands in the SIO or enter the subtropical SIO garbage patch.
34
Tsubouchi, T., T. Suga, and K. Hanawa. "Indian Ocean Subtropical Mode Water: its water characteristics and spatial distribution." Ocean Science 6, no. 1 (January 22, 2010): 41–50. http://dx.doi.org/10.5194/os-6-41-2010.
Анотація:
Abstract. We have improved a basic description (water characteristics and spatial distribution) of the Indian Ocean Subtropical Mode Water (IOSTMW) using an isopycnally averaged three-dimensional hydrographic dataset. Two mode waters and corresponding wintertime mixed layer depth maxima were observed north of the subtropical front (STF) in the South Indian Ocean: IOSTMW (within 25.8–26.2 σθ) in the region of 28–45° E and another subtropical mode water in the subtropical gyre (within 26.4–26.7 σθ) in the 60–80° E longitudinal band. Through careful examination of the spatial distribution and water characteristics of a core in the layer of minimum vertical temperature gradient (LMVTG), we identified that a mass of LMVTG corresponds to IOSTMW. The average water characteristics of the IOSTMW during approximately 1960–2004 were 16.54 ± 0.49 °C, 35.51 ± 0.04 psu and 26.0 ± 0.1 σθ. The IOSTMW distribution area was estimated to be 25–50° E, 27–38° S. The formation region and approximate water characteristics of the second subtropical mode water were also estimated. Its probable formation region was 37–42° S, 60–80° E and north of the STF, with approximate water characteristics of 12.84 ± 0.57 °C, 35.17 ± 0.11 psu and 26.57 ± 0.04 σθ.
35
Thomalla, S. J., H. N. Waldron, M. I. Lucas, J. F. Read, I. J. Ansorge, and E. Pakhomov. "Phytoplankton distribution and nitrogen dynamics in the southwest indian subtropical gyre and Southern Ocean waters." Ocean Science 7, no. 1 (February 8, 2011): 113–27. http://dx.doi.org/10.5194/os-7-113-2011.
Анотація:
Abstract. During the 1999 Marion Island Oceanographic Survey (MIOS 4) in late austral summer, a northbound and reciprocal southbound transect were taken along the Southwest Indian and Madagascar Ridge, between the Prince Edward Islands and 31° S. The sections crossed a number of major fronts and smaller mesoscale features and covered a wide productivity spectrum from subtropical to subantarctic waters. Associated with the physical survey were measurements of size fractionated chlorophyll, nutrients and nitrogen (NO3, NH4 and urea) uptake rates. Subtropical waters were characterised by low chlorophyll concentrations (max = 0.27.3 mg m−3 dominated by pico-phytoplankton cells (> 81%) and very low f-ratios (< 0.1), indicative of productivity based almost entirely on recycled ammonium and urea. Micro-phytoplankton growth was limited by the availability of NO3 (< 0.5 mmol m−3 and Si(OH)4 (< 1.5 mmol m−3 through strong vertical stratification preventing the upward flux of nutrients into the euphotic zone. Biomass accumulation of small cells was likely controlled by micro-zooplankton grazing. In subantarctic waters, total chlorophyll concentrations increased (max = 0.74 mg m−3 relative to the subtropical waters and larger cells became more prevalent, however smaller phytoplankton cells and low f-ratios (< 0.14) still dominated, despite sufficient NO3 availability. The results from this study favour Si(OH)4 limitation, light-limited deep mixing and likely Fe deficiency as the dominant mechanisms controlling significant new production by micro-phytoplankton. The percentage of micro-phytoplankton cells and rates of new production did however increase at oceanic frontal regions (58.6% and 11.22%, respectively), and in the region of the Prince Edward archipelago (61.4% and 14.16%, respectively). Here, water column stabilization and local Fe-enrichment are thought to stimulate phytoplankton growth rates. Open ocean regions such as these provide important areas for local but significant particulate organic carbon export and biological CO2 draw-down in an overall high nutrient low chlorophyll Southern Ocean.
36
Thomalla, S. J., H. N. Waldron, M. I. Lucas, J. F. Read, I. J. Ansorge, and E. Pakhomov. "Phytoplankton distribution and nitrogen dynamics in the Southwest Indian subtropical gyre and Southern Ocean Waters." Ocean Science Discussions 7, no. 4 (July 23, 2010): 1347–403. http://dx.doi.org/10.5194/osd-7-1347-2010.
Анотація:
Abstract. During the 1999 Marion Island Oceanographic Survey (MIOS 4) in late austral summer, a northbound and reciprocal southbound transect were taken along the Southwest Indian and Madagascar Ridge, between the Prince Edward Islands and 31° S. The sections crossed a number of major fronts and smaller mesoscale features and covered a wide productivity spectrum from subtropical to subantarctic waters. Associated with the physical survey were measurements of size fractionated chlorophyll, nutrients and nitrogen (NO3, NH4 and urea) uptake rates. Subtropical waters were characterised by low concentrations (<0.27 mg m−3) of pico-phytoplankton cells (>81%) and very low f-ratios (<0.1), indicative of productivity based almost entirely on recycled ammonium and urea. Diatom growth was limited by the availability of NO3 (<1 mmol m-3) and SiO4 (<1.5 mmol m−3) through vertical stratification that prevents the upward flux of nutrients into the euphotic zone. Biomass accumulation of small cells was likely controlled by microzooplankton grazing. In subantarctic waters, total chlorophyll concentrations increased (<0.74 mg m−3) and larger cells became more prevalent, however smaller phytoplankton cells and low f-ratios (>0.15) still dominated, despite sufficient NO3 availability. The results from this study favour Si limitation, light-limited deep mixing and likely Fe deficiency as the dominant mechanisms controlling significant new production by micro-phytoplankton. Increased concentrations of micro-phytoplankton cells and and rates of new production did however occur at oceanic frontal regions (58.6% and 11.22%, respectively), and in the region of the Prince Edward archipelago (61.4% and 14.16%, respectively). Here water column stabilization and local Fe-enrichment are thought to stimulate phytoplankton growth rates, especially of diatoms. Open ocean regions such as these provide important areas for local but significant POC export and biological CO2 draw-down in an overall HNLC Southern Ocean.
37
Jena, Babula, Shanghamitra Sahu, Kumar Avinash, and Debadatta Swain. "Observation of oligotrophic gyre variability in the south Indian Ocean: Environmental forcing and biological response." Deep Sea Research Part I: Oceanographic Research Papers 80 (October 2013): 1–10. http://dx.doi.org/10.1016/j.dsr.2013.06.002.
38
Singh, Naman Deep, Venkatesh Chinni, and Sunil Kumar Singh. "Dissolved aluminium cycling in the northern, equatorial and subtropical gyre region of the Indian Ocean." Geochimica et Cosmochimica Acta 268 (January 2020): 160–85. http://dx.doi.org/10.1016/j.gca.2019.09.028.
39
Maes, C., N. Grima, B. Blanke, E. Martinez, T. Paviet-Salomon, and T. Huck. "A Surface “Superconvergence” Pathway Connecting the South Indian Ocean to the Subtropical South Pacific Gyre." Geophysical Research Letters 45, no. 4 (February 20, 2018): 1915–22. http://dx.doi.org/10.1002/2017gl076366.
40
Qu, Tangdong, and Gary Meyers. "Seasonal Characteristics of Circulation in the Southeastern Tropical Indian Ocean*." Journal of Physical Oceanography 35, no. 2 (February 1, 2005): 255–67. http://dx.doi.org/10.1175/jpo-2682.1.
Анотація:
Abstract The circulation in the southeastern tropical Indian Ocean is studied using historical temperature and salinity data. A southward shift of the subtropical gyre at increasing depth dominates the structure of the annual mean circulation. Near the southern Indonesian coast the westward South Equatorial Current (SEC) is at the sea surface and strongest near 10°–11°S, reflecting strong influence of the Indonesian Throughflow (ITF). In latitudes 13°–25°S the SEC is a subsurface flow and its velocity core deepens toward the south, falling below 500 m at 25°S. The eastern gyral current (EGC) is a surface flow overlying the SEC, associated with the meridional gradients of near-surface temperature and salinity. The ITF supplies water to the SEC mainly in the upper 400 m, and below that depth the flow is reversed along the coast of Sumatra and Java. Monsoon winds strongly force the annual variation in circulation. Dynamic height at the sea surface has a maximum amplitude at 10°–13°S, and the maximum at deeper levels is located farther south. Annual variation is also strong in the coastal waveguides, but is mainly confined to the near-surface layer. Although the South Java Current at the sea surface is not well resolved in the present dataset, semiannual variation is markedly evident at depth and tends to extend much deeper than the annual variation along the coast of Sumatra and Java.
41
Caínzos, Verónica, M. Dolores Pérez-Hernández, Daniel Santana-Toscano, Cristina Arumí-Planas, and Alonso Hernández-Guerra. "Consistent picture of the horizontal circulation of the Atlantic Ocean over 3 decades." Ocean Science 19, no. 4 (July 6, 2023): 1009–45. http://dx.doi.org/10.5194/os-19-1009-2023.
Анотація:
Abstract. The circulation in the Atlantic Ocean is marked by the complex system of pathways of the Atlantic Meridional Overturning Circulation (AMOC). These currents change meridionally due to the interaction with nearby water masses. Hydrographic data provide the opportunity to characterize these currents for the whole water column with high-resolution data over the last 30 years. Moreover, inverse methods enable the quantification of absolute zonal transports across these sections, determining the strength of each current at a certain latitude in terms of mass, heat, and freshwater, as well as their transport-weighted temperature and salinity. Generally, no changes can be found among decades for each of the currents in terms of transport or their properties. In the South Atlantic, the circulation describes the subtropical gyre affected by several recirculations. There are nearly 61 Sv entering from the Southern and Indian oceans at 45∘ S. The South Atlantic subtropical gyre exports 17.0 ± 1.2 Sv and around 1 PW northward via the North Brazil Current, as well as −55 Sv southward at 45∘ S into the Antarctic Circumpolar Current. In the North Atlantic, most of the transport is advected northward via the western boundary currents, which reduce their strength as they take part in convection processes in the subpolar North Atlantic, also reflected in the northward progress of mass and heat transport. Deep layers carry waters southward along the western boundary, maintaining similar values of mass and heat transport until the separation into an eastern branch crossing the mid-Atlantic Ridge in the South Atlantic. Abyssal waters originating in the Southern Ocean are distributed along the South Atlantic mainly through its western subbasin, flowing northward up to 24.5∘ N, subjected to an increasing trend in their temperature with time.
42
Kim, Yong Sun, and Alejandro H. Orsi. "On the Variability of Antarctic Circumpolar Current Fronts Inferred from 1992–2011 Altimetry*." Journal of Physical Oceanography 44, no. 12 (November 26, 2014): 3054–71. http://dx.doi.org/10.1175/jpo-d-13-0217.1.
Анотація:
Abstract Antarctic Circumpolar Current (ACC) fronts, defined as water mass boundaries, have been known to respond to large-scale atmospheric variabilities, especially the Southern Hemisphere annular mode (SAM) and El Niño–Southern Oscillation (ENSO). Distinct patterns of localized variability in meridional front displacements during 1992–2011 are derived from the analysis of satellite sea surface height data. Major basin-scale differences are found between the southeast Pacific (150°–90°W) and the southeast Indian (75°–150°E) sectors of the ACC. Frontal positions in the southeast Pacific show large year-to-year meridional fluctuations, attributed mostly to ENSO and in part SAM, and no apparent seasonal cycles or long-term trends. In contrast, summer (winter) frontal locations in the southeast Indian extend farther to the south (north) of their long-term mean distribution. A southward drift of ACC fronts is indicated over the Indian sector during the past two decades. This long-term shift is not directly related to the atmospheric variabilities, but this is most likely in response to changes in large-scale ocean circulation, in particular to the poleward expansion of the Indian subtropical gyre. The existence of these localized, contrasting variability patterns suggests that a circumpolar-averaging analysis could possibly smooth out a local climate signal, with an emphasis on a basin-scale investigation for climate studies in the Southern Ocean.
43
Harms, Natalie C., Niko Lahajnar, Birgit Gaye, Tim Rixen, Ulrich Schwarz-Schampera, and Kay-Christian Emeis. "Sediment trap-derived particulate matter fluxes in the oligotrophic subtropical gyre of the South Indian Ocean." Deep Sea Research Part II: Topical Studies in Oceanography 183 (January 2021): 104924. http://dx.doi.org/10.1016/j.dsr2.2020.104924.
44
Chinni, Venkatesh, and Sunil Kumar Singh. "Dissolved iron cycling in the Arabian Sea and sub-tropical gyre region of the Indian Ocean." Geochimica et Cosmochimica Acta 317 (January 2022): 325–48. http://dx.doi.org/10.1016/j.gca.2021.10.026.
45
Carton, James A., Semyon A. Grodsky, and Hailong Liu. "Variability of the Oceanic Mixed Layer, 1960–2004." Journal of Climate 21, no. 5 (March 1, 2008): 1029–47. http://dx.doi.org/10.1175/2007jcli1798.1.
Анотація:
Abstract A new monthly uniformly gridded analysis of mixed layer properties based on the World Ocean Atlas 2005 global ocean dataset is used to examine interannual and longer changes in mixed layer properties during the 45-yr period 1960–2004. The analysis reveals substantial variability in the winter–spring depth of the mixed layer in the subtropics and midlatitudes. In the North Pacific an empirical orthogonal function analysis shows a pattern of mixed layer depth variability peaking in the central subtropics. This pattern occurs coincident with intensification of local surface winds and may be responsible for the SST changes associated with the Pacific decadal oscillation. Years with deep winter–spring mixed layers coincide with years in which winter–spring SST is low. In the North Atlantic a pattern of winter–spring mixed layer depth variability occurs that is not so obviously connected to local changes in winds or SST, suggesting that other processes such as advection are more important. Interestingly, at decadal periods the winter–spring mixed layers of both basins show trends, deepening by 10–40 m over the 45-yr period of this analysis. The long-term mixed layer deepening is even stronger (50–100 m) in the North Atlantic subpolar gyre. At tropical latitudes the boreal winter mixed layer varies in phase with the Southern Oscillation index, deepening in the eastern Pacific and shallowing in the western Pacific and eastern Indian Oceans during El Niños. In boreal summer the mixed layer in the Arabian Sea region of the western Indian Ocean varies in response to changes in the strength of the southwest monsoon.
46
Nagura, Motoki. "Spiciness Anomalies of Subantarctic Mode Water in the South Indian Ocean." Journal of Climate 34, no. 10 (May 2021): 3927–53. http://dx.doi.org/10.1175/jcli-d-20-0482.1.
Анотація:
AbstractThis study investigates spreading and generation of spiciness anomalies of the Subantarctic Mode Water (SAMW) located on 26.6 to 26.8 σθ in the south Indian Ocean, using in situ hydrographic observations, satellite measurements, reanalysis datasets, and numerical model output. The amplitude of spiciness anomalies is about 0.03 psu or 0.13°C and tends to be large along the streamline of the subtropical gyre, whose upstream end is the outcrop region south of Australia. The speed of spreading is comparable to that of the mean current, and it takes about a decade for a spiciness anomaly in the outcrop region to spread into the interior up to Madagascar. In the outcrop region, interannual variability in mixed layer temperature and salinity tends to be density compensating, which indicates that Eulerian temperature or salinity changes account for the generation of isopycnal spiciness anomalies. It is known that wintertime temperature and salinity in the surface mixed layer determine the temperature and salinity relationship of a subducted water mass. Considering this, the mixed layer heat budget in the outcrop region is estimated based on the concept of effective mixed layer depth, the result of which shows the primary contribution from horizontal advection. The contributions from Ekman and geostrophic currents are comparable. Ekman flow advection is caused by zonal wind stress anomalies and the resulting meridional Ekman current anomalies, as is pointed out by a previous study. Geostrophic velocity is decomposed into large-scale and mesoscale variability, both of which significantly contribute to horizontal advection.
47
Dunne, John P., Jasmin G. John, Alistair J. Adcroft, Stephen M. Griffies, Robert W. Hallberg, Elena Shevliakova, Ronald J. Stouffer, et al. "GFDL’s ESM2 Global Coupled Climate–Carbon Earth System Models. Part I: Physical Formulation and Baseline Simulation Characteristics." Journal of Climate 25, no. 19 (April 5, 2012): 6646–65. http://dx.doi.org/10.1175/jcli-d-11-00560.1.
Анотація:
Abstract The physical climate formulation and simulation characteristics of two new global coupled carbon–climate Earth System Models, ESM2M and ESM2G, are described. These models demonstrate similar climate fidelity as the Geophysical Fluid Dynamics Laboratory’s previous Climate Model version 2.1 (CM2.1) while incorporating explicit and consistent carbon dynamics. The two models differ exclusively in the physical ocean component; ESM2M uses Modular Ocean Model version 4p1 with vertical pressure layers while ESM2G uses Generalized Ocean Layer Dynamics with a bulk mixed layer and interior isopycnal layers. Differences in the ocean mean state include the thermocline depth being relatively deep in ESM2M and relatively shallow in ESM2G compared to observations. The crucial role of ocean dynamics on climate variability is highlighted in El Niño–Southern Oscillation being overly strong in ESM2M and overly weak in ESM2G relative to observations. Thus, while ESM2G might better represent climate changes relating to total heat content variability given its lack of long-term drift, gyre circulation, and ventilation in the North Pacific, tropical Atlantic, and Indian Oceans, and depth structure in the overturning and abyssal flows, ESM2M might better represent climate changes relating to surface circulation given its superior surface temperature, salinity, and height patterns, tropical Pacific circulation and variability, and Southern Ocean dynamics. The overall assessment is that neither model is fundamentally superior to the other, and that both models achieve sufficient fidelity to allow meaningful climate and earth system modeling applications. This affords the ability to assess the role of ocean configuration on earth system interactions in the context of two state-of-the-art coupled carbon–climate models.
48
Meijers, A. J., N. L. Bindoff, and J. L. Roberts. "On the Total, Mean, and Eddy Heat and Freshwater Transports in the Southern Hemisphere of a ⅛° × ⅛° Global Ocean Model." Journal of Physical Oceanography 37, no. 2 (February 1, 2007): 277–95. http://dx.doi.org/10.1175/jpo3012.1.
Анотація:
Abstract The large-scale volume, heat, and freshwater ocean transports in the Southern Hemisphere are investigated using time-averaged output from a seasonless, high-resolution general circulation model. The ocean circulation is realistic, and property transports are comparable to observations. The Antarctic Circumpolar Current (ACC) carries 144 Sv (Sv ≡ 106 m3 s−1) of water eastward across Drake Passage, increasing to 155 Sv south of Australia because of the Indonesian Throughflow (ITF). There is a clear Indo-Pacific gyre around Australia exchanging −10 Sv, 0.9 PW of heat, and 0.2 Sv of freshwater through the ITF, and there is a 9-Sv leakage from the Tasman Sea to the Indian Ocean. The transport of heat and freshwater by eddies is localized to the upper 1000 m of the water column and specific regions, such as western boundary currents, confluences, and the subantarctic front (SAF). Eddy transport of heat and freshwater is negligible in gyre interiors and south of the SAF but is vital across the northern edge of the ACC, in particular at the Agulhas Retroflection where eddies accomplish almost 100% of the net ocean heat and 60% of the southward freshwater transport. The eddy transport is almost zero across the latitude of Drake Passage while in a quasi-Lagrangian frame eddy transports are significant across the ACC but surprisingly are still smaller than the mean transport of heat. Mean and eddy property transport divergences are found to be strongly compensating in areas of high eddy activity. This is caused by increased baroclinic instability in strong mean flows, which induces an opposing eddy transport. This relationship is observed to be stronger in the case of horizontal heat transport than in corresponding horizontal freshwater transports.
49
Li, Tim, Chongbo Zhao, Pang-chi Hsu, and Tomoe Nasuno. "MJO Initiation Processes over the Tropical Indian Ocean during DYNAMO/CINDY2011*." Journal of Climate 28, no. 6 (March 13, 2015): 2121–35. http://dx.doi.org/10.1175/jcli-d-14-00328.1.
Анотація:
Abstract A multination joint field campaign called the Dynamics of MJO/Cooperative Indian Ocean Experiment on Intraseasonal Variability in Year 2011 (DYNAMO/CINDY2011) took place in the equatorial Indian Ocean (IO) in late 2011. During the campaign period, two strong MJO events occurred from the middle of October to the middle of December (referred to as MJO I and MJO II, respectively). Both the events were initiated over the western equatorial Indian Ocean (WIO) around 50°–60°E. Using multiple observational data products (ERA-Interim, the ECMWF final analysis, and NASA MERRA), the authors unveil specific processes that triggered the MJO convection in the WIO. It is found that, 10 days prior to MJO I initiation, a marked large-scale ascending motion anomaly appeared in the lower troposphere over the WIO. The cause of this intraseasonal vertical motion anomaly was attributed to anomalous warm advection by a cyclonic gyre anomaly over the northern IO. The MJO II initiation was preceded by a low-level specific humidity anomaly. This lower-tropospheric moistening was attributed to the advection of mean moisture by anomalous easterlies over the equatorial IO. The contrast of anomalous precursor winds at the equator (westerly versus easterly) implies different triggering mechanisms for the MJO I and II events. It was found that upper-tropospheric circumnavigating signals did not contribute the initiation of both the MJO events. The EOF-based real-time multivariate MJO (RMM) indices should not be used to determine MJO initiation time and location because they are primarily used to capture large zonal scale and eastward-propagating signals, not localized features.
50
O’HARA, TIMOTHY D., and BEN THUY. "Biogeography and taxonomy of Ophiuroidea (Echinodermata) from the Îles Saint-Paul and Amsterdam in the southern Indian Ocean." Zootaxa 5124, no. 1 (March 31, 2022): 1–49. http://dx.doi.org/10.11646/zootaxa.5124.1.1.
Анотація:
The ophiuroid fauna of the Île Amsterdam and Île Saint-Paul territories (SPA) is reviewed. Four new species are described: Ophiolebes felli, Ophiolebes paulensis, Ophiocomina arnaudi and Amphiura remota. Recent phylogenetic results required a partial reorganisation of Ophiacanthidae and Amphiuridae genera, including the transfer of some Ophiacantha and Ophiomitrella species to a new genus Ophiosabine (O. rosea, O. anomala, O. aristata, O. cuspidata, O. densispina, O. nodosa, O. notata, O. parcita, O. pentactis, O. vivipara, O. wolfarntzi) and existing genera Ophiosemnotes (O. conferta, O. ingrata, O. corynephora, O. clavigera, O. hamata) and Ophiolebes (O. yaldwyni), Ophiacantha spectabilis to Ophiotreta in the Ophiotomidae, and some Amphioplus species to Amphiura (A, acutus, A. ctenacantha, A. cipus). The combination Ophiophycis nixastrum is restored. The SPA endemic species Ophiocten lymani and Amphiura brevispina, and the southern Australian/New Zealand species Ophiactis cuspidata and Ophiocten australis, are recognised as valid species. The North Atlantic species Ophiura ljungmani, Ophiacantha veterna, Ophiosabine cuspidata, Ophiolimna bairdi and Ophiactis nidarosiensis are recorded from the southern Indian Ocean. Shallow water specimens of Ophiura ljungmani from the Western Atlantic are re-identified as O. fallax and O. acervata. The monotypic Ophiothauma heptactis from northern Australia is synonymised with Ophiocomella sexradia and thus the genus Ophiothauma with Ophiocomella. The biogeography of the ophiuroid fauna reflects the position of the islands near the eastward-flowing currents of the South Indian Ocean gyre. The closest affinities are with faunas in the SW Indian Ocean and SE Atlantic Ocean. Despite its proximity, no species are shared with the Kerguelen Plateau to the south. The large temperature gradient across the subtropical front between Île Saint-Paul and Kerguelen appears to be a distribution limit for littoral and upper bathyal invertebrates.