Articles de revues : « Oceanic Suess effect »

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Liu, Bo, Katharina D. Six et Tatiana Ilyina. « Incorporating the stable carbon isotope 13C in the ocean biogeochemical component of the Max Planck Institute Earth System Model ». Biogeosciences 18, n^o 14 (28 juillet 2021) : 4389–429. http://dx.doi.org/10.5194/bg-18-4389-2021.

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Abstract. The stable carbon isotopic composition (δ13C) is an important variable to study the ocean carbon cycle across different timescales. We include a new representation of the stable carbon isotope 13C into the HAMburg Ocean Carbon Cycle model (HAMOCC), the ocean biogeochemical component of the Max Planck Institute Earth System Model (MPI-ESM). 13C is explicitly resolved for all oceanic carbon pools considered. We account for fractionation during air–sea gas exchange and for biological fractionation ϵp associated with photosynthetic carbon fixation during phytoplankton growth. We examine two ϵp parameterisations of different complexity: ϵpPopp varies with surface dissolved CO2 concentration (Popp et al., 1989), while ϵpLaws additionally depends on local phytoplankton growth rates (Laws et al., 1995). When compared to observations of δ13C of dissolved inorganic carbon (DIC), both parameterisations yield similar performance. However, with regard to δ13C in particulate organic carbon (POC) ϵpPopp shows a considerably improved performance compared to ϵpLaws. This is because ϵpLaws produces too strong a preference for 12C, resulting in δ13CPOC that is too low in our model. The model also well reproduces the global oceanic anthropogenic CO2 sink and the oceanic 13C Suess effect, i.e. the intrusion and distribution of the isotopically light anthropogenic CO2 in the ocean. The satisfactory model performance of the present-day oceanic δ13C distribution using ϵpPopp and of the anthropogenic CO2 uptake allows us to further investigate the potential sources of uncertainty of the Eide et al. (2017a) approach for estimating the oceanic 13C Suess effect. Eide et al. (2017a) derived the first global oceanic 13C Suess effect estimate based on observations. They have noted a potential underestimation, but their approach does not provide any insight about the cause. By applying the Eide et al. (2017a) approach to the model data we are able to investigate in detail potential sources of underestimation of the 13C Suess effect. Based on our model we find underestimations of the 13C Suess effect at 200 m by 0.24 ‰ in the Indian Ocean, 0.21 ‰ in the North Pacific, 0.26 ‰ in the South Pacific, 0.1 ‰ in the North Atlantic and 0.14 ‰ in the South Atlantic. We attribute the major sources of underestimation to two assumptions in the Eide et al. (2017a) approach: the spatially uniform preformed component of δ13CDIC in year 1940 and the neglect of processes that are not directly linked to the oceanic uptake and transport of chlorofluorocarbon-12 (CFC-12) such as the decrease in δ13CPOC over the industrial period. The new 13C module in the ocean biogeochemical component of MPI-ESM shows satisfying performance. It is a useful tool to study the ocean carbon sink under the anthropogenic influences, and it will be applied to investigating variations of ocean carbon cycle in the past.

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Eide, Marie, Are Olsen, Ulysses S. Ninnemann et Tor Eldevik. « A global estimate of the full oceanic 13 C Suess effect since the preindustrial ». Global Biogeochemical Cycles 31, n^o 3 (mars 2017) : 492–514. http://dx.doi.org/10.1002/2016gb005472.

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Gruber, Nicolas, Charles D. Keeling, Robert B. Bacastow, Peter R. Guenther, Timothy J. Lueker, Martin Wahlen, Harro A. J. Meijer, Willem G. Mook et Thomas F. Stocker. « Spatiotemporal patterns of carbon-13 in the global surface oceans and the oceanic suess effect ». Global Biogeochemical Cycles 13, n^o 2 (juin 1999) : 307–35. http://dx.doi.org/10.1029/1999gb900019.

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King, Alexandra L., et William R. Howard. « Planktonic foraminiferal δ13C records from Southern Ocean sediment traps : New estimates of the oceanic Suess effect ». Global Biogeochemical Cycles 18, n^o 2 (20 mai 2004) : n/a. http://dx.doi.org/10.1029/2003gb002162.

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Holden, P. B., N. R. Edwards, S. A. Müller, K. I. C. Oliver, R. M. Death et A. Ridgwell. « Controls on the spatial distribution of oceanic δ13CDIC ; ». Biogeosciences Discussions 9, n^o 8 (31 août 2012) : 11843–83. http://dx.doi.org/10.5194/bgd-9-11843-2012.

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Abstract. We describe the design and evaluation of a large ensemble of coupled climate-carbon cycle simulations with the Earth-system model of intermediate complexity GENIE. This ensemble has been designed for application to a range of carbon cycle questions including utilizing carbon isotope (δ13C) proxy records to help constrain the state at the last glacial. Here we evaluate the ensemble by applying it to a transient experiment over the recent industrial era (1858 to 2008 AD). We employ singular vector decomposition and principal component emulation to investigate the spatial modes of ensemble-variability of oceanic dissolved inorganic carbon (DIC) δ13C, considering both the spun-up pre-industrial state and the transient change due to the 13C Suess Effect. These analyses allow us to separate the natural and anthropogenic controls on the δ13CDIC distribution. We apply the same dimensionally reduced emulation techniques to consider the drivers of the spatial uncertainty in anthropogenic DIC. We show that the sources of uncertainty governing the uptake of anthropogenic δ13CDIC and DIC are quite distinct. Uncertainty in anthropogenic δ13C uptake is dominated by uncertainties in air-sea gas exchange, which explains 63% of modelled variance. This mode of variability is absent from the ensemble variability in CO2 uptake, which is rather driven by uncertainties in ocean parameters that control mixing of intermediate and surface waters. Although the need to account for air-sea gas exchange is well known, these results suggest that, to leading order, uncertainties in the 13C Suess effect and anthropogenic CO2 ocean-uptake are governed by different processes. This illustrates the difficulties in reconstructing one from the other and furthermore highlights the need for improved spatial coverage of both δ13CDIC and DIC observations to better constrain the ocean sink of anthropogenic CO2.

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Deng, Wenfeng, Xuefei Chen, Gangjian Wei, Ti Zeng et Jian-xin Zhao. « Decoupling of coral skeletal δ13C and solar irradiance over the past millennium caused by the oceanic Suess effect ». Paleoceanography 32, n^o 2 (février 2017) : 161–71. http://dx.doi.org/10.1002/2016pa003049.

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Bacastow, Robert B., Charles D. Keeling, Timothy J. Lueker, Martin Wahlen et Willem G. Mook. « The13C Suess Effect in the world surface oceans and its implications for oceanic uptake of CO2 : Analysis of observations at Bermuda ». Global Biogeochemical Cycles 10, n^o 2 (juin 1996) : 335–46. http://dx.doi.org/10.1029/96gb00192.

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Jahn, A., K. Lindsay, X. Giraud, N. Gruber, B. L. Otto-Bliesner, Z. Liu et E. C. Brady. « Carbon isotopes in the ocean model of the Community Earth System Model (CESM1) ». Geoscientific Model Development 8, n^o 8 (5 août 2015) : 2419–34. http://dx.doi.org/10.5194/gmd-8-2419-2015.

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Abstract. Carbon isotopes in the ocean are frequently used as paleoclimate proxies and as present-day geochemical ocean tracers. In order to allow a more direct comparison of climate model results with this large and currently underutilized data set, we added a carbon isotope module to the ocean model of the Community Earth System Model (CESM), containing the cycling of the stable isotope 13C and the radioactive isotope 14C. We implemented the 14C tracer in two ways: in the "abiotic" case, the 14C tracer is only subject to air–sea gas exchange, physical transport, and radioactive decay, while in the "biotic" version, the 14C additionally follows the 13C tracer through all biogeochemical and ecological processes. Thus, the abiotic 14C tracer can be run without the ecosystem module, requiring significantly fewer computational resources. The carbon isotope module calculates the carbon isotopic fractionation during gas exchange, photosynthesis, and calcium carbonate formation, while any subsequent biological process such as remineralization as well as any external inputs are assumed to occur without fractionation. Given the uncertainty associated with the biological fractionation during photosynthesis, we implemented and tested three parameterizations of different complexity. Compared to present-day observations, the model is able to simulate the oceanic 14C bomb uptake and the 13C Suess effect reasonably well compared to observations and other model studies. At the same time, the carbon isotopes reveal biases in the physical model, for example, too sluggish ventilation of the deep Pacific Ocean.

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Jahn, A., K. Lindsay, X. Giraud, N. Gruber, B. L. Otto-Bliesner, Z. Liu et E. C. Brady. « Carbon isotopes in the ocean model of the Community Earth System Model (CESM1) ». Geoscientific Model Development Discussions 7, n^o 6 (6 novembre 2014) : 7461–503. http://dx.doi.org/10.5194/gmdd-7-7461-2014.

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Abstract. Carbon isotopes in the ocean are frequently used as paleo climate proxies and as present-day geochemical ocean tracers. In order to allow a more direct comparison of climate model results with this large and currently underutilized dataset, we added a carbon isotope module to the ocean model of the Community Earth System Model (CESM), containing the cycling of the stable isotope 13C and the radioactive isotope 14C. We implemented the 14C tracer in two ways: in the "abiotic" case, the 14C tracer is only subject to air–sea gas exchange, physical transport, and radioactive decay, while in the "biotic" version, the 14C additionally follows the 13C tracer through all biogeochemical and ecological processes. Thus, the abiotic 14C tracer can be run without the ecosystem module, requiring significantly less computational resources. The carbon isotope module calculates the carbon isotopic fractionation during gas exchange, photosynthesis, and calcium carbonate formation, while any subsequent biological process such as remineralization as well as any external inputs are assumed to occur without fractionation. Given the uncertainty associated with the biological fractionation during photosynthesis, we implemented and tested three parameterizations of different complexity. Compared to present-day observations, the model is able to simulate the oceanic 14C bomb uptake and the 13C Suess effect reasonably well compared to observations and other model studies. At the same time, the carbon isotopes reveal biases in the physical model, for example a too sluggish ventilation of the deep Pacific Ocean.

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Smoliński, Szymon, Côme Denechaud, Gotje von Leesen, Audrey J. Geffen, Peter Grønkjær, Jane A. Godiksen et Steven E. Campana. « Differences in metabolic rate between two Atlantic cod (Gadus morhua) populations estimated with carbon isotopic composition in otoliths ». PLOS ONE 16, n^o 4 (1 avril 2021) : e0248711. http://dx.doi.org/10.1371/journal.pone.0248711.

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The isotopic composition of inorganic carbon in otoliths (δ13Coto) can be a useful tracer of metabolic rates and a method to study ecophysiology in wild fish. We evaluated environmental and physiological sources of δ13Coto variation in Icelandic and Northeast Arctic (NEA) cod (Gadus morhua) over the years 1914–2013. Individual annual growth increments of otoliths formed at age 3 and 8 were micromilled and measured by isotope-ratio mass spectrometry. Simultaneously, all annual increment widths of the otoliths were measured providing a proxy of fish somatic growth. We hypothesized that changes in the physiological state of the organism, reflected by the isotopic composition of otoliths, can affect the growth rate. Using univariate and multivariate mixed-effects models we estimated conditional correlations between carbon isotopic composition and growth of fish at different levels (within individuals, between individuals, and between years), controlling for intrinsic and extrinsic effects on both otolith measurements. δ13Coto was correlated with growth within individuals and between years, which was attributed to the intrinsic effects (fish age or total length). There was no significant correlation between δ13Coto and growth between individuals, which suggests that caution is needed when interpreting δ13Coto signals. We found a significant decrease in δ13Coto through the century which was explained by the oceanic Suess effect-admixture of isotopically light carbon from fossil fuel. We calculated the proportion of the respired carbon in otolith carbonate (Cresp) using carbon isotopic composition in diet and dissolved inorganic carbon of the seawater. This approach allowed us to correct the values for each stock in relation to these two environmental baselines. Cresp was on average 0.275 and 0.295 in Icelandic and NEA stock, respectively. Our results provide an insight into the physiological basis for differences in growth characteristics between these two cod stocks, and how that may vary over time.

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Sonnerup, Rolf E., Paul D. Quay et Ann P. McNichol. « The Indian Ocean13C Suess Effect ». Global Biogeochemical Cycles 14, n^o 3 (septembre 2000) : 903–16. http://dx.doi.org/10.1029/1999gb001244.

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Binczewska, Anna, Bjørg Risebrobakken, Irina Polovodova Asteman, Matthias Moros, Amandine Tisserand, Eystein Jansen et Andrzej Witkowski. « Coastal primary productivity changes over the last millennium : a case study from the Skagerrak (North Sea) ». Biogeosciences 15, n^o 19 (8 octobre 2018) : 5909–28. http://dx.doi.org/10.5194/bg-15-5909-2018.

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Abstract. A comprehensive multi-proxy study on two sediment cores from the western and central Skagerrak was performed in order to detect the variability and causes of marine primary productivity changes in the investigated region over the last 1100 years. The cores were dated by Hg pollution records and AMS 14C dating and analysed for palaeoproductivity proxies such as total organic carbon, δ13C, total planktonic foraminifera, benthic foraminifera (total assemblages as well as abundance of Brizalina skagerrakensis and other palaeoproductivity taxa) and palaeothermometers such as Mg∕Ca and δ18O. Our results reveal two periods with changes in productivity in the Skagerrak region: (i) a moderate productivity at ∼ CE 900–1700 and (ii) a high productivity at ∼ CE 1700–present. During ∼ CE 900–1700, moderate productivity was likely driven by the nutrients transported with the warm Atlantic water inflow associated with a tendency for a persistent positive NAO phase during the warm climate of the Medieval Climate Anomaly, which continues into the LIA until ∼ CE 1450. The following lower and more variable temperature period at ∼ CE 1450–1700 was likely caused by a reduced contribution of warm Atlantic water, but stronger deep-water renewal, due to a generally more negative NAO phase and a shift to the more variable and generally cooler climate conditions of the Little Ice Age. The productivity and fluxes of organic matter to the seafloor did not correspond to the temperature and salinity changes recorded in the benthic Melonis barleeanus shells. For the period from ∼ CE 1700 to the present day, our data point to an increased nutrient content in the Skagerrak waters. This increased nutrient content was likely caused by enhanced inflow of warm Atlantic water, increased Baltic outflow, intensified river runoff, and enhanced human impact through agricultural expansion and industrial development. Intensified human impact likely increased nutrient transport to the Skagerrak and caused changes in the oceanic carbon isotope budget, known as the Suess effect, which is clearly visible in our records as a negative shift in δ13C values from ∼ CE 1800. In addition, a high appearance of S. fusiformis during the last 70 years at both studied locations suggests increased decaying organic matter at the sea floor after episodes of enhanced primary production.

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Tanaka, Takayuki, Yutaka W. Watanabe, Shuichi Watanabe, Shinichiro Noriki, Nobuo Tsurushima et Yukihiro Nojiri. « Oceanic Suess effect of δ13C in subpolar region : The North Pacific ». Geophysical Research Letters 30, n^o 22 (novembre 2003). http://dx.doi.org/10.1029/2003gl018503.

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Matthews, Cory JD, et Steven H. Ferguson. « Validation of dentine deposition rates in beluga whales by interspecies cross dating of temporal δ13C trends in teeth ». NAMMCO Scientific Publications 8 (26 novembre 2014). http://dx.doi.org/10.7557/3.3196.

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Isotopic time series from sequentially sampled growth layer groups (GLGs) in marine mammal teeth can be combined to build chronologies allowing assessment of isotopic variation in marine ecosystems. Synchronous recording of baseline isotopic variation across dentinal GLGs of species with temporal and spatial overlap in foraging offers a unique opportunity for validation of marine mammal age estimation procedures through calibration of GLG deposition rates in one species against another whose GLG deposition has been independently determined. In this study, we compare trends in stable carbon isotope ratios (d13C) across dentinal GLGs of three eastern Canadian Arctic (ECA) beluga (Delphinapterus leucas) populations through the 1960s-2000s with a d13C time series measured across dentinal GLGs of ECA/Northwest Atlantic killer whales (Orcinus orca) from 1944-1999. We use confirmed annual GLG deposition in killer whales as a means to assess beluga GLG deposition, and show linear d13C declines across chronologies of both species were statistically indistinguishable when based on annual GLG deposition in beluga whales, but differed when based on biannual deposition. We suggest d13C declines reflect the oceanic 13C Suess effect, and provide additional support for annual GLG deposition in beluga whales by comparing rates of d13C declines across beluga GLGs with published annual d13C declines attributed to the oceanic 13C Suess effect in the North Atlantic.

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Williams, Thomas J., Amy J. Wagner, Elisabeth L. Sikes et Ellen E. Martin. « Evolution of the Oceanic 13 C Suess Effect in the Southeastern Indian Ocean Between 1994 and 2018 ». Geochemistry, Geophysics, Geosystems 22, n^o 4 (avril 2021). http://dx.doi.org/10.1029/2020gc009402.

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Oakes, Rosie L., Catherine V. Davis et Jocelyn A. Sessa. « Using the Stable Isotopic Composition of Heliconoides inflatus Pteropod Shells to Determine Calcification Depth in the Cariaco Basin ». Frontiers in Marine Science 7 (14 janvier 2021). http://dx.doi.org/10.3389/fmars.2020.553104.

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Pteropods have been hailed as the “canary in the coal mine” for ocean acidification, however, questions remain about their life history, habitat, and the environmental parameters that the isotopic composition of their shells reflect. In order to use pteropods as recorders of ocean chemistry, it is first necessary to understand where they calcify and how this may change through the year, whether this signal is affected by dissolution, and if shells are retained in the subfossil, and eventually fossil, record. Here we create the first annual record of the stable isotopic composition of shells of the pteropod Heliconoides inflatus in the Cariaco Basin, Venezuela utilizing samples and data from the CARIACO time series. Sixty-four H. inflatus specimens from 17 sediment trap samples between November 1996 and April 1998, and 22 specimens from the late Holocene-aged CAR2000-MC-2 core were analyzed for shell condition (an assessment of the amount of dissolution that a shell has experienced), size, and carbon and oxygen isotopic composition. Carbon isotopic measurements of juveniles (< 1mm) were more variable than those in adults (>1 mm), suggesting juvenile pteropods likely have a higher growth rate, and therefore different metabolic vital effects, and a more varied diet than adult pteropods. H. inflatus was found to have an apparent calcification depth of 51.2 ± 34.0 m, suggesting they calcify at the shallowest part of their diurnal migration in the mixed layer (10–35 m in the Cariaco Basin). H. inflatus shell calcification will therefore only be impacted by changes in water chemistry at mixed layer depths. The shell condition did not impact the stable isotopic composition of the shells in either the sediment trap or core sample, suggesting the potential for using the isotopic composition of pteropod shells as oceanographic proxies when they are preserved. Comparisons between sediment trap and core sample show a 0.5°C warming that is marginally significant and a significant 0.45‰ decrease in δ13C between the late Holocene and the late 1990's. These measurements reflect changes in oceanic conditions linked to anthropogenic fossil fuel emissions known as the Suess effect, and lay the groundwork for establishing pteropods as paleoceanographic proxies in the future.

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Zinke, Jens, Neal E. Cantin, Kristine L. DeLong, Kylie Palmer, Arnoud Boom, Irka Hajdas, Nicolas Duprey et al. « North Flinders Reef (Coral Sea, Australia) Porites sp. corals as a candidate Global Boundary Stratotype Section and Point for the Anthropocene Series ». Anthropocene Review, 19 février 2023, 205301962211429. http://dx.doi.org/10.1177/20530196221142963.

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Corals are unique in the suite of proposed Anthropocene Global Boundary Stratotype Section and Point (GSSP) archives, as living organisms that produce aragonite exoskeletons preserved in the geological record that contain highly accurate and precise (<±1 year) internal chronologies. The GSSP candidate site North Flinders Reef in the Coral Sea (Australia) is an offshore oceanic reef, and therefore less vulnerable to local human influences than those closer to the coast. Here, we present geochemical records from two Porites sp. corals sampled at an annual to pluri-annual (i.e. 3–5 years) resolution that shows clear global and regional human impacts. Atmospheric nuclear bomb testing by-products (14C,239+240Pu) show a clear increase in the Flinders Reef corals coincident with well-dated nuclear testing operations. By contrast, the radionuclides 241Am and 137Cs are present at low or undetectable levels, as are spheroidal carbonaceous fly-ash particles. Coral δ13C shows centennial variability likely influenced by growth effects in the 18th century and with a progression to lower values starting in 1880 and accelerating post-1970. The latter may be related to the Suess Effect resulting from 13C-depleted fossil fuel burning. Coral δ15N decreased between 1710 and 1954 with a reversal post-1954. Coral temperature proxies indicate prominent centennial variability with equally warm conditions in the 18th and end of 20th century. However, the exact mechanisms responsible for the mid-20th century changes in these parameters need to be scrutinised in further detail. Plain Language summary: This work proposes a candidate natural archive for the official marker of the Anthropocene that geologists will use to mark this important interval in time. Our candidate is a live coral from North Flinders Reef in the Coral Sea (Australia), located 150 km east of the Great Barrier Reef, a location that is remote from direct local human influences. Corals are a unique archive of tropical ocean change because they incorporate the geochemical signature from seawater into their limestone skeleton during their long life-spans. Here we investigated a number of geochemical markers in yearly growth layers of the corals to define several markers for the Anthropocene based on changes in temperature, water chemistry, chemicals from pollution and fertilisers, radioactive products from nuclear bomb testing, and by-products from burning fossil fuels. We have detected clear human influences in several of these markers.

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Campana, Steven E., Sigríður Vala Finnsdóttir et Guðjón Már Sigurðsson. « Bomb radiocarbon determines absolute age of adult fin whales, and validates use of earplug growth bands for age determination ». Frontiers in Marine Science 11 (23 janvier 2024). http://dx.doi.org/10.3389/fmars.2024.1327752.

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Baleen whales are one of the few vertebrate taxa for which there are no confirmed estimates of longevity or methods of age determination. Lamina counts in the waxy earplug are assumed to represent age, but ageing accuracy is completely unknown. In this study, bomb radiocarbon assays of the earplug growth sequence in three adult fin whales (Balaenoptera physalus) were used to prepare the most complete within-individual bomb radiocarbon chronologies yet reported for any vertebrate. The whale radiocarbon chronologies matched those of known-age carbonate reference chronologies very well, indicating that the earplug laminae were both metabolically stable and formed throughout the life of the whale. Earplug lamina counts accurately represented absolute ages of 65-85 yr to within 6% of the correct age. Detection of a significant declining trend in δ13C with year of lamina formation within individual whales was consistent with that of the Suess effect, again underlining the metabolic stability of the earplug laminae. Given our results, recent applications of earplug laminae for reconstructing diet and life history events appear to be firmly based, with the potential for further elemental and isotopic applications analogous to those of the otolith.

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Ge, Tiantian, Chunle Luo, Peng Ren, Hongmei Zhang, Di Fan, Hongtao Chen, Zhaohui Chen, Jing Zhang et Xuchen Wang. « Stable carbon isotopes of dissolved inorganic carbon in the Western North Pacific Ocean : Proxy for water mixing and dynamics ». Frontiers in Marine Science 9 (23 septembre 2022). http://dx.doi.org/10.3389/fmars.2022.998437.

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The uptake of atmospheric CO2 and the cycle of dissolved inorganic carbon (DIC) in the ocean are the major mechanisms and pathways controlling global climate change and carbon cycling. The stable carbon isotope (δ13C) of DIC, therefore, provides an important tracer for processes such as air-sea exchange, photosynthesis, and water dynamics in the ocean. Here, we present new δ13C-DIC data on water samples collected from a north-south transect (13°N–40°N, 150°E) in the western North Pacific (NP) Ocean in November 2019 and compare the results with those previously reported for similar transects (149.3°E) during WOCE and CLIVAR projects over the past three decades. The values of δ13C-DIC, ranging from -0.83‰ to 0.86‰, were higher in the surface waters and decreased with depth. The high δ13C-DIC values in the surface waters were influenced primarily by isotopic fractionation during air-sea exchange and photosynthesis. With depth, the movement of different water masses and mixing, as well as bathypelagic respiration in the dark water of the ocean, all play important roles in influencing the distribution and isotopic signatures of δ13C-DIC in the western NP Ocean. The δ13C-DIC values of the 0–200 m water layer varied from -0.17‰ to 0.86‰, with lower values at high latitudes, affected by the low δ13C-DIC values carried by the Oyashio Current to the Kuroshio Extension (KE) region. A downward trend was present in the δ13C-DIC signature from north to south in the North Pacific Intermediate Water (NPIW) and Pacific Deep Water (PDW) in the western NP, which reflected the remineralization of organic matter with a horizontal transport of NPIW and PDW. We found a strong 13C Suess Effect in the upper 2,000 m in the western NP Ocean, and δ13C-DIC at the surface (<50 m) has decreased by 0.60‰-0.85‰ since 1993. The mean δ13C-DIC change in the surface ocean was estimated at 0.28‰ per decade between 1993 and 2019. The air-sea exchange and water mixing in the study area may have accelerated the absorption of anthropogenic CO2 in recent years, which likely caused a slightly faster rate of decrease in the δ13C-DIC from 2005–2019 than that observed from 1993–2005.

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