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Rüdiger Henrich - One of the best experts on this subject based on the ideXlab platform.
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Carbonate dissolution revealed by silt grain-size distribution: comparison of Holocene and Last Glacial Maximum sediments from the pelagic South Atlantic
Sedimentology, 2007Co-Authors: Michael Frenz, Rüdiger HenrichAbstract:The current issue of global warming and the role of the ocean in global exchange of CO2 increases the interest in solid budgets of marine carbonate production and dissolution. The present study utilizes grain-size composition of pelagic sediments in order to trace spatial and temporal variability of carbonate sedimentation in the South Atlantic for the Holocene and Last Glacial Maximum (LGM, 19–23 cal kyr BP). A decrease in grain size (e.g. sand content, mean grain size of coarse carbonate silt) indicates increased carbonate dissolution as a result of increased fragmentation of calcareous microfossils. The spatial grain-size pattern suggests a threshold water depth below which a gradual grain-size decrease becomes increasingly rapid. This water depth is considered as the sedimentary Lysocline. For the Holocene time slice, a constant, gradual decrease of foraminifer carbonate of about 5–10% per 1000 m water depth above the Lysocline gives evidence for supra-lysoclinal dissolution. The water depth of the Lysocline for the Holocene is tied to the interface of North Atlantic Deep Water and Antarctic Bottom Water (AABW) (ca 4100 m). Submarine ridges which restrict intrusion of AABW into the Angola Basin cause an asymmetry in carbonate preservation across the Mid-Atlantic Ridge. The Lysocline was reconstructed at ca 3100 m for the LGM. These data suggest that the ca 1000 m rise of the Lysocline eradicated the Holocene east–west asymmetry.
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Calcium carbonate corrosiveness in the South Atlantic during the Last Glacial Maximum as inferred from changes in the preservation of Globigerina bulloides: A proxy to determine deep-water circulation patterns?
Marine Geology, 2004Co-Authors: Andrea N A Volbers, Rüdiger HenrichAbstract:Abstract The modern Atlantic Ocean, dominated by the interactions of North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW), plays a key role in redistributing heat from the Southern to the Northern Hemisphere. In order to reconstruct the evolution of the relative importance of these two water masses, the NADW/AABW transition, reflected by the calcite Lysocline, was investigated by the Globigerina bulloides dissolution index (BDX′). The depth level of the Late Glacial Maximum (LGM) calcite Lysocline was elevated by several hundred metres, indicating a more corrosive water mass present at modern NADW level. Overall, the small range of BDX′ data and the gradual decrease in preservation below the calcite Lysocline point to a less stratified Atlantic Ocean during the LGM. Similar preservation patterns in the West and East Atlantic demonstrate that the modern west–east asymmetry did not exist due to an expansion of southern deep waters compensating for the decrease in NADW formation.
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Carbonate Preservation in Deep and Intermediate Water Masses in the South Atlantic: Evaluation and Geological Record (a Review)
The South Atlantic in the Late Quaternary, 2003Co-Authors: Rüdiger Henrich, Karl-heinz Baumann, Sabine Gerhardt, Matthias Gröger, Andrea N A VolbersAbstract:Evaluation of conventional dissolution proxies in South Atlantic surface sediments revealed broad applicability only in far offshore, rather oligotrophic regimes in the western basins. In contrast, they fail or produce misleading and incorrect results in the more productive eastern South Atlantic basins, due to the combined effects of variable dilution by non-carbonate material and fluctuating ecological conditions. Much more promising are the results from new dissolution proxies on the planktic foraminifer Globigerina bulloides (BDX’) and the pteropod Limacina inflate (LDX) which were calibrated with carbonate saturation as indicated by GEOSECS data. In the western South Atlantic, the sedimentary calcite Lysocline is encountered by the BDX’ at the transition between AABW and LNADW. However, it rises up into the LNADW close to the equator due to additional supralysoclinal dissolution. In the eastern South Atlantic basins, supralysoclinal dissolution results in an elevation of the sedimentary calcite Lysocline of several hundred metres to a maximum of 1600 m as compared to the position of the hydrographic Lysocline, with aragonite preservation in the eastern South Atlantic being even poorer. At most sites investigated, the surface sediments are void of pteropods and thus LDX failure is indicated. However, in the western South Atlantic the LDX displays a double Lysocline for aragonite, the upper Lysocline at a water depth of 750 m and the lower at 2500 m. Aragonite and calcite preservation profiles indicate much weaker stratification of the water during the LGM. With 3200 m, the position of the calcite Lysocline is encountered at the same level in the southern parts of the eastern and western basins dropping to 4000 m near the equator. Along the western continental margin no indication for aragonite-corrosive glacial AAIW was found, providing clear evidence for a strengthened GNAIW flow along the Brazil margin. The long-term history of carbonate dissolution in the equatorial Atlantic was reconstructed by a multiproxy approach combining benthic foraminifer stable isotopes and new proxies from silt analysis. For the first time, this allows a reconstruction of the chemical (nutrient content, carbonate corrosiveness) and physical (bottom current strength) properties of deep and intermediate water masses. The terrigenous silt records of ODP Site 927 at the Ceara Rise show rapid shifts from low to very high bottom-currents speeds for nearly all the isotopic transitions in the Brunhes epoch, indicating subsequent phases of shutdown and rapid reinstatement of LNADW circulation. A drastic reduction of glacial bottom-current strength at Site 927 is inferred after 2.75 Ma, synchronous with the first occurrence of larger continental ice shields and with a drastic decrease in deep convection in the Norwegian-Greenland Sea. After the mid-Pleistocene climate transition, progressively weaker bottom currents and poorer carbonate preservation during glacials indicate a progressive reduction of LNADW from the Late Pliocene to Pleistocene. On the contrary, an opposite trend with progressive improvement of preservation during glacials from Late Pliocene to the Pleistocene is observed in the Caribbean at Site 999. This indicates a contemporaneous progressive increase in the contribution of UNADW to the Atlantic in glacial periods. Altogether, a progressive weakening of the circulation in the LNADW loop and a contemporaneous strengthening of the UNADW loop are evident since the mid Pleistocene transition.
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Present water mass calcium carbonate corrosiveness in the eastern South Atlantic inferred from ultrastructural breakdown of Globigerina bulloides in surface sediments
Marine Geology, 2002Co-Authors: Andrea N A Volbers, Rüdiger HenrichAbstract:Abstract The Atlantic is regarded as a huge carbonate depocenter due to an on average deep calcite Lysocline. However, calculations and models that attribute the calcite Lysocline to the critical undersaturation depth (hydrographic or chemical Lysocline) and not to the depth at which significant calcium carbonate dissolution is observed (sedimentary calcite Lysocline) strongly overestimate the preservation potential of calcareous deep-sea sediments. Significant calcium carbonate dissolution is expected to begin firstly below 5000 m in the deep Guinea and Angola Basin and below 4400 m in the Cape Basin. Our study that is based on different calcium carbonate dissolution stages of the planktic foraminifera Globigerina bulloides clearly shows that it starts between 400 and 1600 m shallower depending on the different hydrographic settings of the South Atlantic Ocean. In particular, coastal areas are severely affected by increased supply of organic matter and the resultant production of metabolic CO2 which seems to create microenvironments favorable for dissolution of calcite well above the hydrographic Lysocline.
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Carbonate dissolution in the South Atlantic Ocean: evidence from ultrastructure breakdown in Globigerina bulloides
Deep Sea Research Part I: Oceanographic Research Papers, 2000Co-Authors: Nicolas Dittert, Rüdiger HenrichAbstract:Abstract Ultrastructure dissolution susceptibility of the planktic foraminifer Globigerina bulloides , carbonate ion content of the water column, calcium carbonate content of the sediment surface, and carbonate/carbon weight percentage ratio derived from sediment surface samples were investigated in order to reconstruct the position of the calcite saturation horizon, the sedimentary calcite Lysocline, and the calcium carbonate compensation depth (CCD) in the modern South Atlantic Ocean. Carbonate ion data from the water column refer to the GEOSECS locations 48, 103, and 109 and calcium carbonate data come from 19 GeoB sediment surface samples of 4 transects into the Brazil, the Guinea, and the Cape Basins. We present a new (paleo-) oceanographic tool, namely the Globigerina bulloides dissolution index (BDX). Further, we give evidence (a) for progressive G. bulloides ultrastructural breakdown with increasing carbonate dissolution even above the Lysocline; (b) for a sharp BDX increase at the sedimentary Lysocline; and (c) for the total absence of this species at the CCD. BDX puts us in the position to distinguish the upper open ocean and the upwelling influenced continental margin above from the deep ocean below the sedimentary Lysocline. Carbonate ion data from water column samples, calcite weight percentage data from surface sediment samples, and carbonate/carbon weight percentage ratio appear to be good proxies to confirm BDX. As shown by BDX both the calcite saturation horizon (in the water column) and the sedimentary Lysocline (at the sediment–water interface) mark the boundary between the carbonate ion undersaturated and highly corrosive Antarctic Bottom Water and the carbonate ion saturated North Atlantic Deep Water (NADW) of the modern South Atlantic.
David Archer - One of the best experts on this subject based on the ideXlab platform.
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A data-driven model of the global calcite Lysocline
Global Biogeochemical Cycles, 1996Co-Authors: David ArcherAbstract:Gridded maps of sediment calcium carbonate (calcite) concentration and overlying water saturation state [Archer, 1996] are combined with maps of benthic oxygen fluxes and sediment accumulation rates from Jahnke [1996] and Cweink [1986] to drive a diagenetic model of calcium carbonate preservation in deep-sea sediments. The only model input for which we cannot draw a detailed map is the rain rate of calcite to the seafloor, so I use the model to calculate the calcite rain rate required to simulate the observed distribution of calcite concentration on the seafloor. The predictive power of the model can be checked by searching for input parameters to which the model is sensitive and comparing the model requirements with independent data. The model is sensitive to the ratio of organic carbon to calcite rain rates (the rain ratio) and, within the constraint of pelagic sediment trap rain ratio data, is unable to reproduce the calcite field without respiratory dissolution, the promotion of calcium carbonate dissolution by the oxic degradation of organic carbon. However, relative to variability in sediment trap data, the required model rain ratio is insensitive to the extent of anoxic respiration, the stoichiometric ratio of O:C during respiration, the bioturbation rate, the dissolution rate constant, the effect of borate chemistry, and small offsets in the saturation state for CaCO3. The model is sensitive to the accumulation rate of non-CaCO3 material and predicts an Atlantic/Pacific difference in non-CaCO3 rain rate which is consistent with observations. The model predicts that the dissolution flux of CaCO3 from sediments is 25–40 × 1012 mol yr−1, roughly half of the total deep sea CaCO3 dissolution rate estimated from the water column alkalinity distribution [Broecker and Peng, 1987; Archer and Maier-Reimer, 1994; Wollast, 1994]. The model also predicts that only 20–30% of the flux of CaCO3 to the seafloor globally escapes dissolution.
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An atlas of the distribution of calcium carbonate in sediments of the deep sea
Global Biogeochemical Cycles, 1996Co-Authors: David ArcherAbstract:Historical observations of the concentration of calcium carbonate in global deep sea sediments are compiled and compared with a new gridded field of seawater CO3= concentration to reveal regional variations in the calcite Lysocline. The most obvious mode of variability of the calcite Lysocline is the thickness of the Lysocline (defined here as the difference in overlying water carbonate saturation, ΔCO3=, between high and low calcite sediments) with a thicker Lysocline in the Atlantic than in the Pacific. I attribute this variation to differences in the delivery rate of terriginous material. A recent model for the lower glacial atmospheric pCO2 proposed to change the relationship between the depth of the Lysocline and the ΔCO3= of the water column by changing the rain rate ratio of organic carbon to calcite production (the “rain ratio model”: Archer and Maier-Reimer, 1994). I search the data set for analogs to the proposed glacial world, by looking for a link between the regional climate at the sea surface and the depth of the Lysocline below. The ΔCO3= at the carbonate compensation depth (CCD) in the tropics appears to be 10–20 μmol kg−1 ΔCO3= more undersaturated than in high latitudes, but this is smaller than the ∼40 μmol kg−1 shift required by the model. In addition, the general resemblance of the glacial Lysocline to the present day requires that the proposed shift in ΔCO3= at the CCD be globally uniform rather than locally variable, as climate forcing would probably generate. I conclude that the rain ratio model would probably require some globally uniform perturbation during glacial time, such as a change in ocean Si content, if it is to explain the entire pCO2 decrease observed in the glacial atmosphere. Finally, I grid the sedimentary data to estimate that the inventory CaCO3 which is available to neutralize fossil fuel CO2 is approximately 1600 Gt carbon, a quantity which may be exceeded by fossil fuel release in the next several centuries.
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Modeling the calcite Lysocline
Journal of Geophysical Research, 1991Co-Authors: David ArcherAbstract:A numerical model of calcite dissolution in contact with sediment pore water is used to predict the depth and shape of the calcite Lysocline in the deep sea. Model results are compared with Lysocline data from 13 regions in the Atlantic, Pacific, and Indian Oceans. The model Lysocline shape is sensitive to the calcite dissolution rate constant, the calcite, organic carbon, and refractory material rain rates, and the rates of oxic versus anoxic organic carbon degradation in the sediment. The model is able to reproduce the observed Lysocline, within the constraints of the sediment trap and calcite accumulation data, using a calcite dissolution rate constant of 30–100%d−1, a molar ratio of organic carbon to calcite rain rates of 0.5–1.0, and an initial CaCO3 fraction of 90% (excluding organic carbon). This rate constant is consistent with microelectrode results presented by Archer et al. [1989]. The model predicts that 30–50% of the calcite rain to the sea floor at the saturation horizon dissolves in response to organic carbon respiration, consistent with previous modeling studies. The range in the best fit value of the organic-inorganic carbon rain rates arises from model sensitivity to uncertainty in the rate of anoxic carbon degradation in the sediment and in the rain rate of refractory material, rather than from scatter in the data. Lysocline data from the western equatorial Atlantic are anomalous to the rest of the data; this anomaly may be explained by high rates of refractory material sedimentation from the Amazon River.
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Equatorial Pacific Calcite Preservation Cycles: Production or Dissolution?
Paleoceanography, 1991Co-Authors: David ArcherAbstract:In the Equatorial Pacific Ocean, the depth and shape of the calcite Lysocline appears to have changed significantly in response to climate forcing (Farrell and Prell, 1989). Taking the Farrell and Prell record at face value, the Lysocline apparently became steeper during each of the last eight glacial stages. Also, the accumulation rate of calcite during the last glacial maximum was 2–4 times higher than it was during the previous interglacial (Arrhenius; 1952,1988; Broecker, 1971; Farrell, 1991). A numerical model for calcite dissolution in sediment is used to interpret these observations. The model was validated by comparison with observations from the present-day ocean; these results are presented elsewhere. If the Lysocline fluctuations in the equatorial Pacific are primarily a dissolution record, then changes in the glacial Pacific [CO3] of 20–40 µM can be inferred. Here I offer the alternative explanation that cycles in equatorial production are responsible for the observations. Higher rates of calcite and organic carbon rain to the sediment in the equatorial region would have depressed the calcite Lysocline and increased the calcite accumulation rate, as observed. A twofold increase in glacial production appears to be adequate to explain the observations, but a precise determination is prevented by uncertainties in some of the model parameters.
R. G. Rothwell - One of the best experts on this subject based on the ideXlab platform.
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Underlying causes for long-term global ocean δ13C fluctuations over the last 1.20 Myr
Earth and Planetary Science Letters, 2006Co-Authors: Babette A A Hoogakker, Eelco J. Rohling, Martin R. Palmer, Toby Tyrrell, R. G. RothwellAbstract:Pleistocene stable carbon isotope (δ13C) records from surface and deep dwelling foraminifera in all major ocean basins show two distinct long-term carbon isotope fluctuations since 1.00 Ma. The first started around 1.00 Ma and was characterised by a 0.35‰ decrease in δ13C values until 0.90 Ma, followed by an increase of 0.60‰ lasting until 0.50 Ma. The subsequent fluctuation started with a 0.40‰ decrease between 0.50 and 0.25 Ma, followed by an increase of 0.30‰ between 0.25 and 0.10 Ma. Here, we evaluate existing evidence and various hypotheses for these global Pleistocene δ13C fluctuations and present an interpretation, where the fluctuations most likely resulted from concomitant changes in the burial fluxes of organic and inorganic carbon due to ventilation changes and/or changes in the production and export ratio. Our model indicates that to satisfy the long-term ‘stability’ of the Pleistocene Lysocline, the ratio between the amounts of change in the organic and inorganic carbon burial fluxes would have to be close to a 1:1 ratio, as deviations from this ratio would lead to sizable variations in the depth of the Lysocline. It is then apparent that the mid-Pleistocene climate transition, which, apart from the glacial cycles, represents the most fundamental change in the Pleistocene climate, was likely not associated with a fundamental change in atmospheric pCO2. While recognising that high frequency glacial/interglacial cycles are associated with relatively large (100 ppmv) changes in pCO2, our model scenario (with burial changes close to a 1:1 ratio) produces a maximum long-term variability of only 20 ppmv over the fluctuation between 1.00 and 0.50 Ma.
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Underlying causes for long-term global ocean δ13C fluctuations over the last 1.20 Myr
Earth and Planetary Science Letters, 2006Co-Authors: Babette A A Hoogakker, Eelco J. Rohling, Martin R. Palmer, Toby Tyrrell, R. G. RothwellAbstract:Pleistocene stable carbon isotope (δ13C) records from surface and deep dwelling foraminifera in all major ocean basins show two distinct long-term carbon isotope fluctuations since 1.00 Ma. The first started around 1.00 Ma and was characterised by a 0.35‰ decrease in δ13C values until 0.90 Ma, followed by an increase of 0.60‰ lasting until 0.50 Ma. The subsequent fluctuation started with a 0.40‰ decrease between 0.50 and 0.25 Ma, followed by an increase of 0.30‰ between 0.25 and 0.10 Ma. Here, we evaluate existing evidence and various hypotheses for these global Pleistocene δ13C fluctuations and present an interpretation, where the fluctuations most likely resulted from concomitant changes in the burial fluxes of organic and inorganic carbon due to ventilation changes and/or changes in the production and export ratio. Our model indicates that to satisfy the long-term ‘stability’ of the Pleistocene Lysocline, the ratio between the amounts of change in the organic and inorganic carbon burial fluxes would have to be close to a 1:1 ratio, as deviations from this ratio would lead to sizable variations in the depth of the Lysocline. It is then apparent that the mid-Pleistocene climate transition, which, apart from the glacial cycles, represents the most fundamental change in the Pleistocene climate, was likely not associated with a fundamental change in atmospheric pCO2. While recognising that high frequency glacial/interglacial cycles are associated with relatively large (100 ppmv) changes in pCO2, our model scenario (with burial changes close to a 1:1 ratio) produces a maximum long-term variability of only 20 ppmv over the fluctuation between 1.00 and 0.50 Ma
Babette A A Hoogakker - One of the best experts on this subject based on the ideXlab platform.
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Underlying causes for long-term global ocean δ13C fluctuations over the last 1.20 Myr
Earth and Planetary Science Letters, 2006Co-Authors: Babette A A Hoogakker, Eelco J. Rohling, Martin R. Palmer, Toby Tyrrell, R. G. RothwellAbstract:Pleistocene stable carbon isotope (δ13C) records from surface and deep dwelling foraminifera in all major ocean basins show two distinct long-term carbon isotope fluctuations since 1.00 Ma. The first started around 1.00 Ma and was characterised by a 0.35‰ decrease in δ13C values until 0.90 Ma, followed by an increase of 0.60‰ lasting until 0.50 Ma. The subsequent fluctuation started with a 0.40‰ decrease between 0.50 and 0.25 Ma, followed by an increase of 0.30‰ between 0.25 and 0.10 Ma. Here, we evaluate existing evidence and various hypotheses for these global Pleistocene δ13C fluctuations and present an interpretation, where the fluctuations most likely resulted from concomitant changes in the burial fluxes of organic and inorganic carbon due to ventilation changes and/or changes in the production and export ratio. Our model indicates that to satisfy the long-term ‘stability’ of the Pleistocene Lysocline, the ratio between the amounts of change in the organic and inorganic carbon burial fluxes would have to be close to a 1:1 ratio, as deviations from this ratio would lead to sizable variations in the depth of the Lysocline. It is then apparent that the mid-Pleistocene climate transition, which, apart from the glacial cycles, represents the most fundamental change in the Pleistocene climate, was likely not associated with a fundamental change in atmospheric pCO2. While recognising that high frequency glacial/interglacial cycles are associated with relatively large (100 ppmv) changes in pCO2, our model scenario (with burial changes close to a 1:1 ratio) produces a maximum long-term variability of only 20 ppmv over the fluctuation between 1.00 and 0.50 Ma.
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Underlying causes for long-term global ocean δ13C fluctuations over the last 1.20 Myr
Earth and Planetary Science Letters, 2006Co-Authors: Babette A A Hoogakker, Eelco J. Rohling, Martin R. Palmer, Toby Tyrrell, R. G. RothwellAbstract:Pleistocene stable carbon isotope (δ13C) records from surface and deep dwelling foraminifera in all major ocean basins show two distinct long-term carbon isotope fluctuations since 1.00 Ma. The first started around 1.00 Ma and was characterised by a 0.35‰ decrease in δ13C values until 0.90 Ma, followed by an increase of 0.60‰ lasting until 0.50 Ma. The subsequent fluctuation started with a 0.40‰ decrease between 0.50 and 0.25 Ma, followed by an increase of 0.30‰ between 0.25 and 0.10 Ma. Here, we evaluate existing evidence and various hypotheses for these global Pleistocene δ13C fluctuations and present an interpretation, where the fluctuations most likely resulted from concomitant changes in the burial fluxes of organic and inorganic carbon due to ventilation changes and/or changes in the production and export ratio. Our model indicates that to satisfy the long-term ‘stability’ of the Pleistocene Lysocline, the ratio between the amounts of change in the organic and inorganic carbon burial fluxes would have to be close to a 1:1 ratio, as deviations from this ratio would lead to sizable variations in the depth of the Lysocline. It is then apparent that the mid-Pleistocene climate transition, which, apart from the glacial cycles, represents the most fundamental change in the Pleistocene climate, was likely not associated with a fundamental change in atmospheric pCO2. While recognising that high frequency glacial/interglacial cycles are associated with relatively large (100 ppmv) changes in pCO2, our model scenario (with burial changes close to a 1:1 ratio) produces a maximum long-term variability of only 20 ppmv over the fluctuation between 1.00 and 0.50 Ma
Lucas Joost Lourens - One of the best experts on this subject based on the ideXlab platform.
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Patterns and magnitude of deep sea carbonate dissolution during Eocene Thermal Maximum 2 and H2, Walvis Ridge, southeastern Atlantic Ocean
Paleoceanography, 2009Co-Authors: Lucy Stap, Appy Sluijs, Ellen Thomas, Lucas Joost LourensAbstract:[1] Eocene Thermal Maximum 2 (ETM2 or H1; ∼53.7 Ma) represents a short-lived warming episode, associated with the injection of a large mass of 13C-depleted carbon into the ocean-atmosphere system. The mass of injected carbon, the extent of deep sea dissolution, and the amount of warming during ETM2 appear to be approximately half of those documented for the Paleocene-Eocene thermal maximum (PETM, ∼55.5 Ma), but the pattern of Lysocline migration during ETM2 has not yet been documented sufficiently to decipher potential differences in carbon sources and sequestration mechanisms. We present high-resolution carbonate dissolution and bulk stable isotope records across ETM2 and the successive H2 event (∼53.6 Ma) on a common age model for four sites along the Walvis Ridge depth transect (1500 to 3600 m paleowater depth) to assess Lysocline evolution. The onset of ETM2 is characterized by multiple, depth-dependent transitions of carbonate dissolution (up to ∼96% of the total flux), associated with rapid depletions in bulk carbonate carbon (up to ∼1–1.5‰) and oxygen (up to ∼0.7–1.5‰) isotope values. H2 shows a ∼0.7‰ negative carbon isotope excursion, with a coeval decrease in δ18O of ∼0.5‰ and ∼80% of carbonate dissolution. During ETM2, the Lysocline recovered within ∼30 ka. We attribute this rapid recovery to terrestrial CaCO3 neutralization through enhanced chemical weathering of carbonates in soils and rocks. According to theory, carbonate dissolution was lower after recovery than prior to ETM2, indicating carbonate ion oversaturation and a deeper position of the Lysocline. Spectral analysis indicates that the changes in carbonate dissolution and δ13C values were precession paced, implying that weathering feedbacks and short-term perturbations in the carbon cycle were important in determining early Eocene background and hyperthermal ocean [CO32−] conditions.
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Patterns and magnitude of deep sea carbonate dissolution during Eocene Thermal Maximum 2 and H2, Walvis Ridge, southeastern
2009Co-Authors: Atlantic Ocean, Lucy Stap, Appy Sluijs, Ellen Thomas, Lucas Joost LourensAbstract:associated with the injection of a large mass of 13 C-depleted carbon into the ocean-atmosphere system. The mass of injected carbon, the extent of deep sea dissolution, and the amount of warming during ETM2 appear to be approximately half of those documented for the Paleocene-Eocene thermal maximum (PETM, � 55.5 Ma), but the pattern of Lysocline migration during ETM2 has not yet been documented sufficiently to decipher potential differences in carbon sources and sequestration mechanisms. We present high-resolution carbonate dissolution and bulk stable isotope records across ETM2 and the successive H2 event (� 53.6 Ma) on a common age model for four sites along the Walvis Ridge depth transect (1500 to 3600 m paleowater depth) to assess Lysocline evolution. The onset of ETM2 is characterized by multiple, depth-dependent transitions of carbonate dissolution (up to � 96% of the total flux), associated with rapid depletions in bulk carbonate carbon (up to � 1–1.5%) and oxygen (up to � 0.7–1.5%) isotope values. H2 shows a � 0.7% negative carbon isotope excursion, with a coeval decrease in d 18 Oo f� 0.5% and � 80% of carbonate dissolution. During ETM2, the Lysocline recovered within � 30 ka. We attribute this rapid recovery to terrestrial CaCO3 neutralization through enhanced chemical weathering of carbonates in soils and rocks. According to theory, carbonate dissolution was lower after recovery than prior to ETM2, indicating carbonate ion oversaturation and a deeper position of the Lysocline. Spectral analysis indicates that the changes in carbonate dissolution and d 13 C values were precession paced, implying that weathering feedbacks and short-term perturbations in the carbon cycle were important in determining early Eocene background and hyperthermal ocean [CO3� ] conditions.
