Academic literature on the topic 'Antarctic Intermediate Water (AAIW)'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the lists of relevant articles, books, theses, conference reports, and other scholarly sources on the topic 'Antarctic Intermediate Water (AAIW).'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Journal articles on the topic "Antarctic Intermediate Water (AAIW)"
1
Schmidtko, Sunke, and Gregory C. Johnson. "Multidecadal Warming and Shoaling of Antarctic Intermediate Water*." Journal of Climate 25, no. 1 (January 1, 2012): 207–21. http://dx.doi.org/10.1175/jcli-d-11-00021.1.
Full textAbstract:
Abstract Antarctic Intermediate Water (AAIW) is a dominant Southern Hemisphere water mass that spreads from its formation regions just north of the Antarctic Circumpolar Current (ACC) to at least 20°S in all oceans. This study uses an isopycnal climatology constructed from Argo conductivity–temperature–depth (CTD) profile data to define the current state of the AAIW salinity minimum (its core) and thence compute anomalies of AAIW core pressure, potential temperature, salinity, and potential density since the mid-1970s from ship-based CTD profiles. The results are used to calculate maps of temporal property trends at the AAIW core, where statistically significant strong circumpolar shoaling (30–50 dbar decade−1), warming (0.05°–0.15°C decade−1), and density reductions [up to −0.03 (kg m−3) decade−1] are found. These trends are strongest just north of the ACC in the southeast Pacific and Atlantic Oceans and decrease equatorward. Salinity trends are generally small, with their sign varying regionally. Bottle data are used to extend the AAIW core potential temperature anomaly analysis back to 1925 in the Atlantic and to ~1960 elsewhere. The modern warm AAIW core conditions appear largely unprecedented in the historical record: biennially and zonally binned median AAIW core potential temperatures within each ocean basin are, with the notable exception of the subtropical South Atlantic in the 1950s–70s, 0.2–1°C colder than modern values. Zonally averaged sea surface temperature anomalies around the AAIW formation latitudes in each ocean and sectoral southern annular mode indices are used to put the AAIW core property trends and variations into context.
2
Urakawa, L. Shogo, and Hiroyasu Hasumi. "Eddy-Resolving Model Estimate of the Cabbeling Effect on the Water Mass Transformation in the Southern Ocean." Journal of Physical Oceanography 42, no. 8 (August 1, 2012): 1288–302. http://dx.doi.org/10.1175/jpo-d-11-0173.1.
Full textAbstract:
Abstract Cabbeling effect on the water mass transformation in the Southern Ocean is investigated with the use of an eddy-resolving Southern Ocean model. A significant amount of water is densified by cabbeling: water mass transformation rates are about 4 Sv (1 Sv ≡ 106 m3 s−1) for transformation from surface/thermocline water to Subantarctic Mode Water (SAMW), about 7 Sv for transformation from SAMW to Antarctic Intermediate Water (AAIW), and about 5 Sv for transformation from AAIW to Upper Circumpolar Deep Water. These diapycnal volume transports occur around the Antarctic Circumpolar Current (ACC), where mesoscale eddies are active. The water mass transformation by cabbeling in this study is also characterized by a large amount of densification of Lower Circumpolar Deep Water (LCDW) into Antarctic Bottom Water (AABW) (about 9 Sv). Large diapycnal velocity is found not only along the ACC but also along the coast of Antarctica at the boundary between LCDW and AABW. It is found that about 3 Sv of LCDW is densified into AABW by cabbeling on the continental slopes of Antarctica in this study. This densification is not small compared with observational and numerical estimates on the AABW formation rate, which ranges from 10 to 20 Sv.
3
Romahn, S., A. Mackensen, J. Groeneveld, and J. Pätzold. "Deglacial intermediate water reorganization: new evidence from the Indian Ocean." Climate of the Past Discussions 9, no. 4 (July 17, 2013): 4035–63. http://dx.doi.org/10.5194/cpd-9-4035-2013.
Full textAbstract:
Abstract. The importance of intermediate water masses in climate change and ocean circulation has been emphasized recently. In particular, Antarctic Intermediate Water (AAIW) is thought to have acted as an active interhemispheric transmitter of climate anomalies. Here we reconstruct changes in AAIW signature and spatial and temporal evolution based on a 40 kyr time series of oxygen and carbon isotopes as well as planktic Mg/Ca based thermometry from a site in the western Indian Ocean. Our data suggest that AAIW transmitted Antarctic temperature trends to the equatorial Indian Ocean via the "oceanic tunnel" mechanism. Moreover, our results reveal that deglacial AAIW carried a signature of aged Southern Ocean deep water. We find no evidence of increased formation of intermediate waters during the deglaciation.
4
Machín, F., and J. L. Pelegrí. "Northward Penetration of Antarctic Intermediate Water off Northwest Africa." Journal of Physical Oceanography 39, no. 3 (March 1, 2009): 512–35. http://dx.doi.org/10.1175/2008jpo3825.1.
Full textAbstract:
Abstract In this article, historical and climatological datasets are used to investigate the seasonal northward propagation of Antarctic Intermediate Waters (AAIW) along the eastern margin of the North Atlantic subtropical gyre. A cluster analysis for data north of 26°N shows the presence of a substantial number of hydrographic stations with AAIW characteristics that stretch northeast along the African slope. This water mass extends north during fall, as shown both through the comparison of actual and climatological data, and by applying a mixing analysis to normal-to-shore seasonal sections at both 28.5° and 32°N. The mixing analysis is further used with several fall cruises between 32° and 36°N, and shows that at these latitudes the core of AAIW propagates along the 27.5 isoneutral with contributions that reach as much as 50% at 32.5°N. An idealized Sverdrup-type model is used in combination with climatological hydrographic and wind data to examine what forces this eastern boundary propagation. It is found that column stretching, initiated in the tropical North Atlantic, is the dominant term in the vorticity balance of the AAIW stratum, capable of sustaining a winter–spring–summer northward transport of about 3–4 Sv (1 Sv ≡ 106 m3 s−1) that reaches as far north as the Canary Archipelago (28°N). In fall, this transport may continue beyond 28°N, sustained by a near-slope meridional stretching of this water stratum. AAIW probably fades away in the northeastern region as the result of several processes, specially enhanced double diffusion with surrounding waters and interaction with Mediterranean water lenses.
5
Graham, Jennifer A., David P. Stevens, and Karen J. Heywood. "Nonlinear Climate Responses to Changes in Antarctic Intermediate Water." Journal of Climate 26, no. 22 (October 29, 2013): 9175–93. http://dx.doi.org/10.1175/jcli-d-12-00767.1.
Full textAbstract:
Abstract The global impact of changes in Antarctic Intermediate Water (AAIW) properties is demonstrated using idealized perturbation experiments in a coupled climate model. Properties of AAIW were altered between 10° and 20°S in the Atlantic, Pacific, and Indian Oceans separately. Potential temperature was changed by ±1°C, along with density-compensating changes in salinity. For each of the experiments, sea surface temperature responds to changes in AAIW when anomalies surface at higher latitudes (>30°). Anomalous sea-to-air heat fluxes leave density anomalies in the ocean, resulting in nonlinear responses to opposite-sign perturbations. In the Southern Ocean, these affect the meridional density gradient, leading to changes in Antarctic Circumpolar Current transport. The response to cooler, fresher AAIW is both greater in magnitude and significant over a larger area than that for warmer, saltier AAIW. The North Atlantic is particularly sensitive to cool, fresh perturbations, with density anomalies causing reductions in the meridional overturning circulation of up to 1 Sv (1 Sv ≡ 106 m3 s−1). Resultant changes in meridional ocean heat transport, along with surfacing anomalies, cause basinwide changes in the surface ocean and overlying atmosphere on multidecadal time scales.
6
Close, Sally E., Alberto C. Naveira Garabato, Elaine L. McDonagh, Brian A. King, Martin Biuw, and Lars Boehme. "Control of Mode and Intermediate Water Mass Properties in Drake Passage by the Amundsen Sea Low." Journal of Climate 26, no. 14 (July 12, 2013): 5102–23. http://dx.doi.org/10.1175/jcli-d-12-00346.1.
Full textAbstract:
Abstract The evolution of the physical properties of Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) in the Drake Passage region is examined on time scales down to intraseasonal, within the 1969–2009 period. Both SAMW and AAIW experience substantial interannual to interdecadal variability, significantly linked to the action of the Amundsen Sea low (ASL) in their formation areas. Observations suggest that the interdecadal freshening tendency evident in SAMW over the past three decades has recently abated, while AAIW has warmed significantly since the early 2000s. The two water masses have also experienced a substantial lightening since the start of the record. Examination of the mechanisms underpinning water mass property variability shows that SAMW characteristics are controlled predominantly by a combination of air–sea turbulent heat fluxes, cross-frontal Ekman transport of Antarctic surface waters, and the evaporation–precipitation balance in the Subantarctic zone of the southeast Pacific and Drake Passage, while AAIW properties reflect air–sea turbulent heat fluxes and sea ice formation in the Bellingshausen Sea. The recent interdecadal evolution of the ASL is consistent with both the dominance of the processes described here and the response of SAMW and AAIW on that time scale.
7
Sloyan, Bernadette M., and Igor V. Kamenkovich. "Simulation of Subantarctic Mode and Antarctic Intermediate Waters in Climate Models." Journal of Climate 20, no. 20 (October 15, 2007): 5061–80. http://dx.doi.org/10.1175/jcli4295.1.
Full textAbstract:
Abstract The Southern Ocean’s Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) are two globally significant upper-ocean water masses that circulate in all Southern Hemisphere subtropical gyres and cross the equator to enter the North Pacific and North Atlantic Oceans. Simulations of SAMW and AAIW for the twentieth century in eight climate models [GFDL-CM2.1, CCSM3, CNRM-CM3, MIROC3.2(medres), MIROC3.2(hires), MRI-CGCM2.3.2, CSIRO-Mk3.0, and UKMO-HadCM3] that provided their output in support of the Intergovernmental Panel on Climate Change’s Fourth Assessment Report (IPCC AR4) have been compared to the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Atlas of Regional Seas. The climate models, except for UKMO-HadCM3, CSIRO-Mk3.0, and MRI-CGCM2.3.2, provide a reasonable simulation of SAMW and AAIW isopycnal temperature and salinity in the Southern Ocean. Many models simulate the potential vorticity minimum layer and salinity minimum layer of SAMW and AAIW, respectively. However, the simulated SAMW layer is generally thinner and at lighter densities than observed. All climate models display a limited equatorward extension of SAMW and AAIW north of the Antarctic Circumpolar Current. Errors in the simulation of SAMW and AAIW property characteristics are likely to be due to a combination of many errors in the climate models, including simulation of wind and buoyancy forcing, inadequate representation of subgrid-scale mixing processes in the Southern Ocean, and midlatitude diapycnal mixing parameterizations.
8
Naveira Garabato, Alberto C., Loïc Jullion, David P. Stevens, Karen J. Heywood, and Brian A. King. "Variability of Subantarctic Mode Water and Antarctic Intermediate Water in the Drake Passage during the Late-Twentieth and Early-Twenty-First Centuries." Journal of Climate 22, no. 13 (July 1, 2009): 3661–88. http://dx.doi.org/10.1175/2009jcli2621.1.
Full textAbstract:
Abstract A time series of the physical and biogeochemical properties of Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) in the Drake Passage between 1969 and 2005 is constructed using 24 transects of measurements across the passage. Both water masses have experienced substantial variability on interannual to interdecadal time scales. SAMW is formed by winter overturning on the equatorward flank of the Antarctic Circumpolar Current (ACC) in and to the west of the Drake Passage. Its interannual variability is primarily driven by variations in wintertime air–sea turbulent heat fluxes and net evaporation modulated by the El Niño–Southern Oscillation (ENSO). Despite their spatial proximity, the AAIW in the Drake Passage has a very different source than that of the SAMW because it is ventilated by the northward subduction of Winter Water originating in the Bellingshausen Sea. Changes in AAIW are mainly forced by variability in Winter Water properties resulting from fluctuations in wintertime air–sea turbulent heat fluxes and spring sea ice melting, both of which are linked to predominantly ENSO-driven variations in the intensity of meridional winds to the west of the Antarctic Peninsula. A prominent exception to the prevalent modes of SAMW and AAIW formation occurred in 1998, when strong wind forcing associated with constructive interference between ENSO and the southern annular mode (SAM) triggered a transitory shift to an Ekman-dominated mode of SAMW ventilation and a 1–2-yr shutdown of AAIW production. The interdecadal evolutions of SAMW and AAIW in the Drake Passage are distinct and driven by different processes. SAMW warmed (by ∼0.3°C) and salinified (by ∼0.04) during the 1970s and experienced the reverse trends between 1990 and 2005, when the coldest and freshest SAMW on record was observed. In contrast, AAIW underwent a net freshening (by ∼0.05) between the 1970s and the twenty-first century. Although the reversing changes in SAMW were chiefly forced by a ∼30-yr oscillation in regional air–sea turbulent heat fluxes and precipitation associated with the interdecadal Pacific oscillation, with a SAM-driven intensification of the Ekman supply of Antarctic surface waters from the south contributing significantly too, the freshening of AAIW was linked to the extreme climate change that occurred to the west of the Antarctic Peninsula in recent decades. There, a freshening of the Winter Water ventilating AAIW was brought about by increased precipitation and a retreat of the winter sea ice edge, which were seemingly forced by an interdecadal trend in the SAM and regional positive feedbacks in the air–sea ice coupled climate system. All in all, these findings highlight the role of the major modes of Southern Hemisphere climate variability in driving the evolution of SAMW and AAIW in the Drake Passage region and the wider South Atlantic and suggest that these modes may have contributed significantly to the hemispheric-scale changes undergone by those waters in recent decades.
9
Roque, David, Ivan Parras-Berrocal, Miguel Bruno, Ricardo Sánchez-Leal, and Francisco Javier Hernández-Molina. "Seasonal variability of intermediate water masses in the Gulf of Cádiz: implications of the Antarctic and subarctic seesaw." Ocean Science 15, no. 5 (October 22, 2019): 1381–97. http://dx.doi.org/10.5194/os-15-1381-2019.
Full textAbstract:
Abstract. Global circulation of intermediate water masses has been extensively studied; however, its regional and local circulation along continental margins and variability and implications on sea floor morphologies are still not well known. In this study the intermediate water mass variability in the Gulf of Cádiz (GoC) and adjacent areas has been analysed and its implications discussed. Remarkable seasonal variations of the Antarctic Intermediate Water (AAIW) and the Subarctic Intermediate Water (SAIW) are determined. During autumn a greater presence of the AAIW seems to be related to a reduction in the presence of SAIW and Eastern North Atlantic Central Water (ENACW). This interaction also affects the Mediterranean Water (MW), which is pushed by the AAIW toward the upper continental slope. In the rest of the seasons, the SAIW is the predominant water mass reducing the presence of the AAIW. This seasonal variability for the predominance of these intermediate water masses is explained in terms of the concatenation of several wind-driven processes acting during the different seasons. Our finding is important for a better understanding of regional intermediate water mass variability with implications in the Atlantic Meridional Overturning Circulation (AMOC), but further research is needed in order to decode their changes during the geological past and their role, especially related to the AAIW, in controlling both the morphology and the sedimentation along the continental slopes.
10
Downes, Stephanie M., Anand Gnanadesikan, Stephen M. Griffies, and Jorge L. Sarmiento. "Water Mass Exchange in the Southern Ocean in Coupled Climate Models." Journal of Physical Oceanography 41, no. 9 (September 1, 2011): 1756–71. http://dx.doi.org/10.1175/2011jpo4586.1.
Full textAbstract:
Abstract The authors estimate water mass transformation rates resulting from surface buoyancy fluxes and interior diapycnal fluxes in the region south of 30°S in the Estimating the Circulation and Climate of the Ocean (ECCO) model-based state estimation and three free-running coupled climate models. The meridional transport of deep and intermediate waters across 30°S agrees well between models and observationally based estimates in the Atlantic Ocean but not in the Indian and Pacific, where the model-based estimates are much smaller. Associated with this, in the models about half the southward-flowing deep water is converted into lighter waters and half is converted to denser bottom waters, whereas the observationally based estimates convert most of the inflowing deep water to bottom waters. In the models, both Antarctic Intermediate Water (AAIW) and Antarctic Bottom Water (AABW) are formed primarily via an interior diapycnal transformation rather than being transformed at the surface via heat or freshwater fluxes. Given the small vertical diffusivity specified in the models in this region, the authors conclude that other processes such as cabbeling and thermobaricity must be playing an important role in water mass transformation. Finally, in the models, the largest contribution of the surface buoyancy fluxes in the Southern Ocean is to convert Upper Circumpolar Deep Water (UCDW) and AAIW into lighter Subantarctic Mode Water (SAMW).
Dissertations / Theses on the topic "Antarctic Intermediate Water (AAIW)"
1
Bostock, Helen C., and Helen Bostock@anu edu au. "Geochemically tracing the intermediate and surface waters in the Tasman Sea, southwest Pacific." The Australian National University. Faculty of Science, 2005. http://thesis.anu.edu.au./public/adt-ANU20061106.123254.
Full textAbstract:
The relatively understudied intermediate waters of the world have been implicated as an important part of the global ocean circulation. This thesis discusses the intermediate waters of the Pacific over space and time. Initially, by using geochemical tracers to look at the present distribution, sources and mixing of the water masses. Secondly, by using oxygen and carbon isotopes from sediment cores to study changes in Antarctic Intermediate Waters (AAIW) over the late Quaternary in the north Tasman Sea. The sediment cores also provide sedimentological data on the hemipelagic sedimentation in the Capricorn Channel in the southern Great Barrier Reef as well information on changes in the East Australian surface current (EAC) over the last glacial-interglacial transition. [A more extended Abstract can be found in the files]
2
Marwood, Tim. "Antarctic intermediate water and the Antarctic circumpolar current in the Southwest Atlantic." Thesis, University of East Anglia, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365060.
Full text
3
Graham, Jennifer A. "Global climate impacts from changes in Antarctic Intermediate Water." Thesis, University of East Anglia, 2011. http://eprints.uea.ac.uk/36351/.
Full textAbstract:
Observations suggest that properties of Antarctic Intermediate Water (AAIW) are changing. The impact of these variations is explored using a series of idealised perturbation experiments. Two sets of ensembles have been used. The first varied initial atmospheric states; the second varied initial states in the ocean and atmosphere. The ensemble simulations were integrated over 120 and 100 years, respectively, altering AAIW from 10-200S in the Atlantic, Pacific and Indian oceans separately in a coupled climate model, HadCM3. Potential temperature was changed by ±1 DC, along with corresponding changes in salinity, maintaining constant potential density. There is a surface response to changes in AAIW in each of the three major ocean basins. When the water mass surfaces in the equatorial regions, there is no significant change in sea surface temperature (SST). However, there is a SST response when the anomalies surface at higher latitudes (>300). Anomalous sea-to-air heat fluxes leave density anomalies in the ocean. Resulting changes in ocean circulation cause responses to opposite perturbations to be nonlinear. In the Southern Ocean, changes in the meridional density gradient lead to changes in Antarctic Circumpolar Current transport. The North Atlantic is particularly sensitive, with density anomalies causing changes in the meridional overturning circulation of up to 1 Sv. Surfacing anomalies and changes in meridional ocean heat transport cause basin-wide changes in the surface ocean and overlying atmosphere on multi-decadal timescales. Cooling in the North Atlantic Current may be self-sustaining as it leads to high pressure anomalies in the overlying atmosphere, and increased wind stress over the sub-polar gyre. The spatial pattern of SST anomalies in the North Pacific resembles the Pacific Decadal Oscillation. Heat and salt distribution in the Indian Ocean is influenced by the Indonesian Through-Flow (ITF). Long-term trends in the ITF are caused by bottom pressure anomalies in the Pacific.
4
Cook, M. R. "Antarctic Intermediate Water – Pacific sector variations over the past 150ka." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597916.
Full textAbstract:
A variety of ice core and marine records have demonstrated regular climatic shifts in atmospheric and ocean temperature and nutrient content between glacial and interglacial periods. Reconstructions of Antarctic Intermediate Water (AAIW) have primarily focused upon the changes in the Atlantic, yet AAIW flows northward throughout the world’s oceans after forming in subantarctic waters in the Southern Ocean. The trace metal content of benthic foraminifera is commonly used to reconstruct changes in the nutrient content and temperature of waters. Trace metal incorporation into foraminiferal tests is usually controlled by environmental parameters. This proves not to be the case in the aragonitic foraminifera Hoeglundina elegans. Multi-element analysis demonstrates the covariance of unrelated proxies, suggesting there is an internal control upon trace metal incorporation. Calculating changes in the nutrient content and temperature of AAIW was accomplished by measuring calcitic foraminifera from core MD97-2120 located on Chatham Rise, East of New Zealand. AAIW is warmer and more nutrient rich during interglacial periods. Combining the nutrient data with previously published stable isotopic data from the same core allows estimation of changes in salinity and the average windspeed in the region of AAIW formation. During glacial times temperature decreased and salinity increased as a result of the incorporation of freshwater into continental ice caps. Nutrient levels decreased, as did the average wind speed. These changes were a result of the motion of the Westerlies away from the subantarctic and an increase in levels of export production in the region of AAIW formation. This reduced the preformed nutrient content of AAIW. AAIW also displays Heinrich Event signatures, which are resolvable as shifts related to the motion of the glacial Westerlies causing a change in the measured carbon isotopic signature.
5
Núñez-Riboni, Ismael. "Lagrangian circulation and transports of the Antarctic intermediate water in the south and tropical Atlantic." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=980259916.
Full text
6
Roberts, Jenny. "Insights into glacial terminations from a South Atlantic perspective." Thesis, University of Cambridge, 2016. https://www.repository.cam.ac.uk/handle/1810/267478.
Full textAbstract:
The last two glacial terminations represent the most recent, and best documented, periods of Earth warming in the geological record. During these terminations atmospheric CO\textsubscript{2 }rose by approximately 100 ppm and global mean temperatures increased by 4-6\textsuperscript{o}C. Whilst the driver for these deglaciations ultimately derives from changes in the insolation forcing at the edge of the atmosphere, feedbacks within the Earth\textquoteright s climate system act to amplify these small external forcings tipping the Earth from a cold glacial climate state to a warm interglacial climate state. A key question in Quaternary climate science is understanding which feedbacks are important in regulating global climate on glacial-interglacial timescales. On this topic, the Southern Ocean has long been considered to be an important player in regulating atmospheric CO\textsubscript{2 } on glacial-interglacial timescales. This thesis investigates some of the hypothesised drivers of changes in atmospheric CO\textsubscript{2 } on glacial-interglacial timescales by generating high-resolution multi-proxy records from the Southern Ocean spanning the last two glacial terminations. In particular, I focus on changes in the structure, circulation and biological productivity within the sub-Antarctic zone. A change in the deep ocean density structure has been hypothesised to have resulted in the release of CO\textsubscript{2 } from the deep ocean. Centennial records from the sub-Antarctic are used to reconstruct deep and intermediate water density for the first time. I demonstrate that timing of the major breakdown in the density gradient of the ocean significantly lagged the breakdown in the chemical gradient, suggesting that changes in the deep ocean density structure were not the major driver of the deglacial rise in atmospheric CO\textsubscript{2 }. Changes in the density structure of the Southern Ocean likely had significant implications for global circulation. In particular, the flow of low salinity water through the Drake Passage is thought to be important in setting the strength and geometry of Atlantic Overturning Circulation. Drake Passage through-flow speed was reconstructed from two sites in the central and northern margins of the Antarctic Circumpolar Current downstream of Drake Passage. These records suggest a very different structure of Antarctic Circumpolar flow through Drake Passage during glacial periods, and evidence significant changes in ocean temperature as a result of pronounced reductions in Drake Passage through-flow. The strength of the biological pump has long been identified as an important player in regulating atmospheric CO\textsubscript{2 }. In particular, a strong glacial increase in sub-Antarctic productivity has been observed at open ocean sites in the South Atlantic and Indian Ocean. However, the glacial-interglacial changes in productivity in sub-Antarctic shelf settings are less well-documented. The new high-resolution records presented here from the sub-Antarctic southwest Atlantic suggest a significant change in the CaCO\textsubscript{3}:C\textsubscript{org} ratio which likely has implications for the surface ocean\textquoteright s ability to uptake CO\textsubscript{2 }.
7
Signorelli, Natália Tasso. "Indirect investigations of the Atlantic Meridional Overturning changes in the South Atlantic Ocean in numerical models for the 20th century." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/21/21135/tde-27032014-111133/.
Full textAbstract:
The South Atlantic has a relevant role on the AMOC variability as it includes two main conduits of its upper-ocean return flow: the NBUC and the IWBC that carry, mainly, the SACW and the AAIW and are originated from the bifurcation of the SEC. One of the hypotheses of this work is that analyzing the bifurcation variability it is possible to get an index of the AMOC changes. Another hypothesis is that in a global warming scenario, changes in the hydrological cycle would drive modifications in the water masses that are part of the AMOC, and thus, contribute to its variability. Four global model results were used, with different forcing and spatial resolution. Results show that changes in the bifurcation are linked to modications in the currents both caused by variations in the wind stress curl. Good correlations were found between the SEC bifurcation at the surface and the AMOC. The NBUC seems to be the link between them. Shallowing of the SACW core is related to an increase of the salinity on neutral surfaces. The AAIW is occupying less space in the water column due to an increasing of the salinity in the neutral surfaces at 11°S, while the opposite happens at 27°SThe South Atlantic has a relevant role on the AMOC variability as it includes two main conduits of its upper-ocean return flow: the NBUC and the IWBC that carry, mainly, the SACW and the AAIW and are originated from the bifurcation of the SEC. One of the hypotheses of this work is that analyzing the bifurcation variability it is possible to get an index of the AMOC changes. Another hypothesis is that in a global warming scenario, changes in the hydrological cycle would drive modifications in the water masses that are part of the AMOC, and thus, contribute to its variability. Four global model results were used, with different forcing and spatial resolution. Results show that changes in the bifurcation are linked to modications in the currents both caused by variations in the wind stress curl. Good correlations were found between the SEC bifurcation at the surface and the AMOC. The NBUC seems to be the link between them. Shallowing of the SACW core is related to an increase of the salinity on neutral surfaces. The AAIW is occupying less space in the water column due to an increasing of the salinity in the neutral surfaces at 11°S, while the opposite happens at 27°S
8
Brookshire, Brian. "A Multidisciplinary Investigation of the Intermediate Depths of the Atlantic Ocean: AAIW delta^13C Variability During the Younger Dryas and Lithoherms in the Straits of Florida." Thesis, 2010. http://hdl.handle.net/1969.1/ETD-TAMU-2010-12-8675.
Full textAbstract:
A transect of cores ranging from 798 m to 1585 m water depth in the South Atlantic
Ocean document the relative intermediate water mass nutrient geometry and stable
isotopic variability of AAIW during the Younger Dryas cooling event. The data reveal
concurrent delta^13 C and delta^18 O excursions of 0.59 ppt and 0.37 ppt within the core of
Antarctic Intermediate Water (AAIW) centered at 11,381 calendar years before present
based on radiometric age control. A portion of the delta^1 3C variability (0.22 ppt) can be
explained by a shift in thermodynamic equilibrium concurrent with a drop in
temperature of 1.8°C at the locus of AAIW formation. The remaining 0.37 ppt increase
in delta^13 C most likely resulted from increased wind velocities, and a greater coupling
between the ocean and the atmosphere at the locus of AAIW formation (increased
efficiency of the thermodynamic process).
Deepwater coral mounds are aggregates of corals, other organisms, their skeletal
remains, and sediments that occur on the seafloor of the world’s oceans. In the Straits of
Florida, these features have been referred to as lithoherms. We use digital, side-scan sonar data collected from the submarine NR-1 from an 10.9 km^2 area at ~650 m water
depth to characterize quantitatively aspects of the morphology of 216. Their lengths,
widths, heights, areas, orientations and concentration on the seafloor have been
determined. Analysis indicates that the outlines of relatively small to medium sized
lithoherms can be effectively described with a piriform function. This shape is less
applicable to the largest lithoherms because they are aggregates of smaller lithoherms.
Nearly all of the lithoherms studied have axes parallel to the northward flowing Florida
Current, and the heads of 80 percent of these features face into the current. The shape and
orientation of the lithoherms, and evidence of megaripples and scouring in the sonar data
suggest that these features are formed by a unidirectional current.
Following an extensive investigation of over 200 lithoherms via side-scan sonar
imagery and direct observation, we have developed a qualitative model for the formation
of the lithoherm type of deep-water coral mounds in the Straits of Florida. Lithoherm
formation can be characterized by four main stages of development: nucleating, juvenile,
mature singular, and fused. Fused lithoherms can form via transverse and/or
longitudinal accretion, however, transverse accretion at the head of the mound is likely
the most efficient mechanism. A comparison of lithoherm spatial relationship to local
bathymetry agrees with previous observations of deep-water coral mound formations
along the levied margins of density flow scour channels.
9
Núñez-Riboni, Ismael [Verfasser]. "[Lagrangian circulation and transports of the Antarctic intermediate water in the south and tropical Atlantic] / Ismael Núñez-Riboni." 2005. http://d-nb.info/980259916/34.
Full text
10
Xie, Ruifang. "Tracing Paleoclimate over the Past 25,000 Years Using Evidence from Radiogenic Isotopes." Thesis, 2013. http://hdl.handle.net/1969.1/149618.
Full textAbstract:
The objective of this dissertation is to apply radiogenic isotopes extracted from marine sediments to investigate aspects of global climate change over the past 25 kyr, especially ocean and atmospheric circulation, continental aridity, and hydrology. By focusing on the geochemical records from marine sediments and authigenic precipitates preserved in these sediments, I aim to better understand climate forcing and feedback mechanisms, which are critical to models of climate change. Firstly, I have investigated the dynamics of the Intertropical Convergence Zone (ITCZ) over the past 25 kyr in the eastern equatorial Pacific by fingerprinting dust provenance using radiogenic isotopes (Nd, Sr, Pb) and trace elements (Fe, Si, Ba) in the detrital fraction of marine sediments along a transect across the equator at 110ºW. Results from this study suggest no glacial-Holocene difference in the mean position of the ITCZ, but a more northerly, possibly stronger, deglacial ITCZ. Secondly, I have applied Nd isotope ratios from authigenic precipitates extracted from marine sediments and those from fish debris to trace past intermediate water circulation changes on glacial-interglacial and millennial timescales. The authigenic Nd isotope record from the Florida Straits suggests a reduced circulation of Antarctic Intermediate Water (AAIW) into the tropical North Atlantic during the Younger Dryas (YD) and Heinrich 1 (H1) events, associated with a significant reduction in AMOC. However, in the Southern Caribbean, apparent deviations in the Nd isotopic compositions between the acid-reductive leachate and the fish debris suggest that the leachate method is not reliable at this location and that it needs to be tested in more detail in various oceanic settings. In the Southern Caribbean, the fish debris Nd isotope results suggest a two-step recovery of the upper North Atlantic Deep Water during the last deglaciation. Comparing our new fish debris Nd isotope data to authigenic Nd isotope data for sediments from the Florida Straits and the Demarara Rise, we propose that glacial and deglacial AAIW does not penetrate beyond the lower depth limit of modern AAIW in the tropical North Atlantic. Both studies suggest a tight connection between Atlantic intermediate water circulation variability and high-latitude North Atlantic climate change.
Book chapters on the topic "Antarctic Intermediate Water (AAIW)"
1
Talley, L. D. "Antarctic Intermediate Water in the South Atlantic." In The South Atlantic, 219–38. Berlin, Heidelberg: Springer Berlin Heidelberg, 1996. http://dx.doi.org/10.1007/978-3-642-80353-6_11.
Full text
2
Haddad, G. A., A. W. Droxler, D. Kroon, and D. W. Müller. "Quaternary CaCO3 Input and Preservation within Antarctic Intermediate Water Mineralogic and Isotopic Results from Holes 818B and 817A, Townsville Trough (Northeast Australian Margin)." In Proceedings of the Ocean Drilling Program. Ocean Drilling Program, 1993. http://dx.doi.org/10.2973/odp.proc.sr.133.229.1993.
Full text
3
Hope, Geoffrey. "The Quaternary in Southeast Asia." In The Physical Geography of Southeast Asia. Oxford University Press, 2005. http://dx.doi.org/10.1093/oso/9780199248025.003.0012.
Full textAbstract:
We live in the Quaternary period and are a product of its wide fluctuations in climate and rapid environmental change. From at least the Mid-Miocene, about 25 million years ago, the expansion of the Southern Ocean has supported a powerful westerly wind system. These winds prevent tropical heat from reaching the Antarctic region, which in turn has allowed the gradual refrigeration of the world’s oceans as ice built up on Antarctica (and eventually formed an ice shelf over the sea; Nunn 1999). Earlier in the Tertiary, when the ocean column was warm from top to bottom, seasonal cooling was offset by rising warm water, and the ocean currents effectively transported heat to the poles. For the last 2 million years the main mass of the oceans has remained at maximum density, around 4°C, with warmer surface waters of the tropical and temperate regions floating only in the upper few hundred metres above the thermocline. The Quaternary is the period of refrigerated ocean which marks an ice age, with the Earth in such a delicate thermal equilibrium that relatively minor changes in the amount of solar radiation received by a given hemisphere in a given season cause major fluctuations of ice volume in terrestrial ice caps. The marked asymmetry of land and sea in the two hemispheres means that the effects of changes in the season of closest approach to the sun, of the degree of tilt of the planet and the eccentricity of the orbit, cause instability in the long-term climate. The Quaternary is defined by successive expansions and retreats of ice caps, with the maximum episodes of ice and of warmth (the interstadials) each lasting around 10 000 years. Intermediate times are cooler than present, and these persist for around 100 000 years. The lock-up of ice is reflected by global changes in sea level, ocean levels falling about 125 m during glacial maxima and rising up to 6 m above present during some interglacials. The Antarctic ice cap retains about 75 m of the ocean’s water even during the interglacial phases.