Multimillion-year proxy records across the Paleocene and Eocene show prominent variations on orbital time scales. The cycles, which have been identified at various sites across the globe, preferentially concentrate spectral power at eccentricity and precessional frequencies. It is evident that these cycles are an expression of changes in global climate and carbon cycling paced by astronomical forcing. However, little is currently known about the link between orbital forcing and the carbon cycle-climate system and the amplitude of associated atmospheric CO2 variations. Here we use simple and complex carbon cycle models to explore the basic effect of different orbital forcing schemes and noise on the carbon cycle. Our primary modeling target is the high-resolution, ∼7.7 Myr long, benthic isotope record at Ocean Drilling Program Site 1262 in the South Atlantic. For direct insolation forcing (as opposed to artificial eccentricity-tilt-precession), one major challenge is understanding how the system transfers spectral power from high to low frequencies. We discuss feasible solutions, including insolation transformations analogous to electronic AC-DC conversion (DC'ing). Regarding mechanisms, we focus on tropical insolation and a long-term carbon imbalance in terrestrial organic burial/oxidation but do not rule out other scenarios. Our analysis shows that high-latitude mechanisms are unlikely drivers of orbitally paced changes in the late Paleocene-early Eocene (LPEE) Earth system. Furthermore, we provide constraints on the origin and isotopic composition of a possible LPEE cyclic carbon imbalance/source responding to astronomical forcing. Our simulations also reveal a mechanism for the large δ13C-eccentricity lag at the 400 kyr period observed in Paleocene, Oligocene, and Miocene sections. We present the first estimates of orbital-scale variations in atmospheric CO2 during the late Paleocene and early Eocene.
{"title":"Orbital forcing of the Paleocene and Eocene carbon cycle","authors":"R. Zeebe, T. Westerhold, K. Littler, J. Zachos","doi":"10.1002/2016PA003054","DOIUrl":"https://doi.org/10.1002/2016PA003054","url":null,"abstract":"Multimillion-year proxy records across the Paleocene and Eocene show prominent variations on orbital time scales. The cycles, which have been identified at various sites across the globe, preferentially concentrate spectral power at eccentricity and precessional frequencies. It is evident that these cycles are an expression of changes in global climate and carbon cycling paced by astronomical forcing. However, little is currently known about the link between orbital forcing and the carbon cycle-climate system and the amplitude of associated atmospheric CO2 variations. Here we use simple and complex carbon cycle models to explore the basic effect of different orbital forcing schemes and noise on the carbon cycle. Our primary modeling target is the high-resolution, ∼7.7 Myr long, benthic isotope record at Ocean Drilling Program Site 1262 in the South Atlantic. For direct insolation forcing (as opposed to artificial eccentricity-tilt-precession), one major challenge is understanding how the system transfers spectral power from high to low frequencies. We discuss feasible solutions, including insolation transformations analogous to electronic AC-DC conversion (DC'ing). Regarding mechanisms, we focus on tropical insolation and a long-term carbon imbalance in terrestrial organic burial/oxidation but do not rule out other scenarios. Our analysis shows that high-latitude mechanisms are unlikely drivers of orbitally paced changes in the late Paleocene-early Eocene (LPEE) Earth system. Furthermore, we provide constraints on the origin and isotopic composition of a possible LPEE cyclic carbon imbalance/source responding to astronomical forcing. Our simulations also reveal a mechanism for the large δ13C-eccentricity lag at the 400 kyr period observed in Paleocene, Oligocene, and Miocene sections. We present the first estimates of orbital-scale variations in atmospheric CO2 during the late Paleocene and early Eocene.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"440-465"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003054","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43921102","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lineke Woelders, J. Vellekoop, D. Kroon, J. Smit, S. Casadío, M. Prámparo, J. Dinarès‐Turell, F. Peterse, A. Sluijs, J. Lenaerts, R. Speijer
Latest Maastrichtian climate change caused by Deccan volcanism has been invoked as a cause of mass extinction at the Cretaceous-Paleogene (K-Pg) boundary (~66.0 Ma). Yet late Maastrichtian climate and ecological changes are poorly documented, in particular on the Southern Hemisphere. Here we present upper Maastrichtian-lower Danian climate and biotic records from the Bajada del Jaguel (BJ) shelf site (Neuquen Basin, Argentina), employing the TEX86 paleothermometer, marine palynology (dinoflagellate cysts), and micropaleontology (foraminifera). These records are correlated to the astronomically tuned Ocean Drilling Program Site 1262 (Walvis Ridge). Collectively, we use these records to assess climatic and ecological effects of Deccan volcanism in the Southern Atlantic region. Both the TEX86-based sea surface temperature (SST) record at BJ and the bulk carbonate δ18O-based SST record of Site 1262 show a latest Maastrichtian warming of ~2.5–4°C, at 450 to 150 kyr before the K-Pg boundary, coinciding with the a large Deccan outpouring phase. Benthic foraminiferal and dinocyst assemblage changes indicate that this warming resulted in enhanced runoff and stratification of the water column, likely resulting from more humid climate conditions in the Neuquen Basin. These climate conditions could have been caused by an expanding and strengthening thermal low over the South American continent. Biotic changes in response to late Maastrichtian environmental changes are rather limited, when compared to the major turnovers observed at many K-Pg boundary sites worldwide. This suggests that environmental perturbations during the latest Maastrichtian warming event were less severe than those following the K-Pg boundary impact.
德干火山活动引起的马斯特里赫特阶最新气候变化被认为是白垩纪-古近系（K-Pg）边界（约66.0 Ma）大规模灭绝的原因。然而，马斯特里赫特纪晚期的气候和生态变化记录很少，尤其是在南半球。在这里，我们使用TEX86古温度计、海洋孢粉学（甲藻囊肿）和微古生物学（有孔虫），介绍了上马斯特里赫特阶-下达尼亚阶Bajada del Jaguel（BJ）陆架遗址（阿根廷Neuquen盆地）的气候和生物记录。这些记录与经过天文调整的海洋钻探计划地点1262（沃尔维斯山脊）有关。总之，我们使用这些记录来评估南大西洋地区德干火山活动的气候和生态影响。BJ的基于TEX86的海面温度（SST）记录和1262号站点的基于大块碳酸盐δ18O的SST记录都显示，在K-Pg边界之前的450至150 kyr，马斯特里赫特阶最新变暖约为2.5–4°C，和大型德干喷溢相吻合。底栖有孔虫和恐龙囊肿组合的变化表明，这种变暖导致了水柱的径流和分层增加，这可能是由于Neuquen盆地更潮湿的气候条件造成的。这些气候条件可能是由南美洲大陆上空不断扩大和增强的热低压造成的。与世界各地许多K-Pg边界点观测到的主要失误相比，响应马斯特里赫特晚期环境变化的生物变化相当有限。这表明，最近马斯特里赫特变暖事件期间的环境扰动不如K-Pg边界影响之后的环境扰动严重。
{"title":"Latest Cretaceous climatic and environmental change in the South Atlantic region","authors":"Lineke Woelders, J. Vellekoop, D. Kroon, J. Smit, S. Casadío, M. Prámparo, J. Dinarès‐Turell, F. Peterse, A. Sluijs, J. Lenaerts, R. Speijer","doi":"10.1002/2016PA003007","DOIUrl":"https://doi.org/10.1002/2016PA003007","url":null,"abstract":"Latest Maastrichtian climate change caused by Deccan volcanism has been invoked as a cause of mass extinction at the Cretaceous-Paleogene (K-Pg) boundary (~66.0 Ma). Yet late Maastrichtian climate and ecological changes are poorly documented, in particular on the Southern Hemisphere. Here we present upper Maastrichtian-lower Danian climate and biotic records from the Bajada del Jaguel (BJ) shelf site (Neuquen Basin, Argentina), employing the TEX86 paleothermometer, marine palynology (dinoflagellate cysts), and micropaleontology (foraminifera). These records are correlated to the astronomically tuned Ocean Drilling Program Site 1262 (Walvis Ridge). Collectively, we use these records to assess climatic and ecological effects of Deccan volcanism in the Southern Atlantic region. Both the TEX86-based sea surface temperature (SST) record at BJ and the bulk carbonate δ18O-based SST record of Site 1262 show a latest Maastrichtian warming of ~2.5–4°C, at 450 to 150 kyr before the K-Pg boundary, coinciding with the a large Deccan outpouring phase. Benthic foraminiferal and dinocyst assemblage changes indicate that this warming resulted in enhanced runoff and stratification of the water column, likely resulting from more humid climate conditions in the Neuquen Basin. These climate conditions could have been caused by an expanding and strengthening thermal low over the South American continent. Biotic changes in response to late Maastrichtian environmental changes are rather limited, when compared to the major turnovers observed at many K-Pg boundary sites worldwide. This suggests that environmental perturbations during the latest Maastrichtian warming event were less severe than those following the K-Pg boundary impact.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"466-483"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003007","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49463483","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Ordovician-Silurian transition (approximate to 455-430Ma) is characterized by repeated climatic perturbations, concomitant with major changes in the global oceanic redox state best exemplified by the periodic deposition of black shales. The relationship between the climatic evolution and the oceanic redox cycles, however, remains largely debated. Here using an ocean-atmosphere general circulation model accounting for ocean biogeochemistry (MITgcm), we investigate the mechanisms responsible for the burial of organic carbon immediately before, during, and right after the latest Ordovician Hirnantian (445-444Ma) glacial peak. Our results are compared with recent sedimentological and geochemical data. We show that the late Katian time slice (approximate to 445Ma), typified by the deposition of black shales at tropical latitudes, represents an unperturbed oceanic state, with regional organic carbon burial driven by the surface primary productivity. During the Hirnantian, our experiments predict a global oxygenation event, in agreement with the disappearance of the black shales in the sedimentary record. This suggests that deep-water burial of organic matter may not be a tenable triggering factor for the positive carbon excursion reported at that time. Our simulations indicate that the perturbation of the ocean circulation induced by the release of freshwater, in the context of the post-Hirnantian deglaciation, does not sustain over sufficiently long geological periods to cause the Rhuddanian (approximate to 444Ma) oceanic anoxic event. Input of nutrients to the ocean, through increased continental weathering and the leaching of newly exposed glaciogenic sediments, may instead constitute the dominant control on the spread of anoxia in the early Silurian.
{"title":"THE CLIMATIC SIGNIFICANCE OF LATE ORDOVICIAN–EARLY SILURIAN BLACK SHALES","authors":"A. Pohl, Y. Donnadieu, G. Hir, D. Ferreira","doi":"10.1002/2016PA003064","DOIUrl":"https://doi.org/10.1002/2016PA003064","url":null,"abstract":"The Ordovician-Silurian transition (approximate to 455-430Ma) is characterized by repeated climatic perturbations, concomitant with major changes in the global oceanic redox state best exemplified by the periodic deposition of black shales. The relationship between the climatic evolution and the oceanic redox cycles, however, remains largely debated. Here using an ocean-atmosphere general circulation model accounting for ocean biogeochemistry (MITgcm), we investigate the mechanisms responsible for the burial of organic carbon immediately before, during, and right after the latest Ordovician Hirnantian (445-444Ma) glacial peak. Our results are compared with recent sedimentological and geochemical data. We show that the late Katian time slice (approximate to 445Ma), typified by the deposition of black shales at tropical latitudes, represents an unperturbed oceanic state, with regional organic carbon burial driven by the surface primary productivity. During the Hirnantian, our experiments predict a global oxygenation event, in agreement with the disappearance of the black shales in the sedimentary record. This suggests that deep-water burial of organic matter may not be a tenable triggering factor for the positive carbon excursion reported at that time. Our simulations indicate that the perturbation of the ocean circulation induced by the release of freshwater, in the context of the post-Hirnantian deglaciation, does not sustain over sufficiently long geological periods to cause the Rhuddanian (approximate to 444Ma) oceanic anoxic event. Input of nutrients to the ocean, through increased continental weathering and the leaching of newly exposed glaciogenic sediments, may instead constitute the dominant control on the spread of anoxia in the early Silurian.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"397-423"},"PeriodicalIF":0.0,"publicationDate":"2017-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003064","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42286255","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Indo-Pacific coral Diploastrea heliopora reveals regional multidecadalto centennialscale climate variability using coral carbonate δO (δOc) as a combined proxy for sea surface temperature (SST) and sea surface salinity (SSS). However, to assess the coral’s full potential in resolving climatic events, an independent SST proxy would be more advantageous. We examined both Sr/Ca and δO of Diploastrea against an adjacent Porites lobata core collected from northeast Luzon, Philippines. Winter Sr/Ca data from Diploastrea show a significant correlation to SST (r = 0.41, p < 0.05, (root-mean-square of the residual) RMSR = 0.81°C) and provide a proxy with similar sensitivity as Porites (r = 0.57, p< 0.05, RMSR = 0.62°C). An interspecies SST record is shown to be robust and used for a reconstruction of the Pacific Decadal Oscillation during boreal winter (r = 0.70, p = 0.02). While we were unable to generate a robust Diploastrea δO-SSS calibration at interannual timescale, the freshening trend toward the present, commonly observed in the region, is qualitatively captured in Diploastrea δO. Comparison with Porites δO and instrumental SSS records shows that the magnitude of freshening is consistent between coral species. Wet and dry season Porites δO provide support for the relative influence of El Niño–Southern Oscillation events and local precipitation to SSS variability at our site. The multiproxy, multispecies approach of this study further strengthens the evidence for Diploastrea as an alternate climate archive in the Indo-Pacific region and seals its potential in helping resolve less understood global-scale climate phenomena.
{"title":"Diploastrea heliopora Sr/Ca and δ18O records from northeast Luzon, Philippines : an assessment of interspecies coral proxy calibrations and climate controls of sea surface temperature and salinity","authors":"R. Ramos, N. Goodkin, F. Siringan, K. Hughen","doi":"10.1002/2017PA003098","DOIUrl":"https://doi.org/10.1002/2017PA003098","url":null,"abstract":"The Indo-Pacific coral Diploastrea heliopora reveals regional multidecadalto centennialscale climate variability using coral carbonate δO (δOc) as a combined proxy for sea surface temperature (SST) and sea surface salinity (SSS). However, to assess the coral’s full potential in resolving climatic events, an independent SST proxy would be more advantageous. We examined both Sr/Ca and δO of Diploastrea against an adjacent Porites lobata core collected from northeast Luzon, Philippines. Winter Sr/Ca data from Diploastrea show a significant correlation to SST (r = 0.41, p < 0.05, (root-mean-square of the residual) RMSR = 0.81°C) and provide a proxy with similar sensitivity as Porites (r = 0.57, p< 0.05, RMSR = 0.62°C). An interspecies SST record is shown to be robust and used for a reconstruction of the Pacific Decadal Oscillation during boreal winter (r = 0.70, p = 0.02). While we were unable to generate a robust Diploastrea δO-SSS calibration at interannual timescale, the freshening trend toward the present, commonly observed in the region, is qualitatively captured in Diploastrea δO. Comparison with Porites δO and instrumental SSS records shows that the magnitude of freshening is consistent between coral species. Wet and dry season Porites δO provide support for the relative influence of El Niño–Southern Oscillation events and local precipitation to SSS variability at our site. The multiproxy, multispecies approach of this study further strengthens the evidence for Diploastrea as an alternate climate archive in the Indo-Pacific region and seals its potential in helping resolve less understood global-scale climate phenomena.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"424-438"},"PeriodicalIF":0.0,"publicationDate":"2017-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003098","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43741682","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Bingbin Qin, Tiegang Li, Z. Xiong, T. Algeo, F. Chang
We present new “size-normalized weight” (SNW)-Δ[CO32−] core-top calibrations for three planktonic foraminiferal species and assess their reliability as a paleo-alkalinity proxy. SNWs of Globigerina sacculifer and Neogloboquadrina dutertrei can be used to reconstruct past deep Pacific [CO32−], whereas SNWs of Pulleniatina obliquiloculata are controlled by additional environmental factors. Based on this methodological advance, we reconstruct SNW-based deepwater [CO32−] for core WP7 from the western tropical Pacific since 250 ka. Secular variation in the SNW proxy documents little change in deep Pacific [CO32−] between the Last Glacial Maximum and the Holocene. Further back in time, deepwater [CO32−] shows long-term increases from marine isotope stage (MIS) 5e to MIS 3 and from early MIS 7 to late MIS 6, consistent with the “coral reef hypothesis” that the deep Pacific Ocean carbonate system responded to declining shelf carbonate production during these two intervals. During deglaciations, we have evidence of [CO32−] peaks coincident with Terminations 2 and 3, which suggests that a breakdown of oceanic vertical stratification drove a net transfer of CO2 from the ocean to the atmosphere, causing spikes in carbonate preservation (i.e., the “deglacial ventilation hypothesis”). During MIS 4, a transient decline in SNW-based [CO32−], along with other reported [CO32−] and/or dissolution records, implies that increased deep-ocean carbon storage resulted in a global carbonate dissolution event. These findings provide new insights into the role of the deep Pacific in the global carbon cycle during the late Quaternary.
{"title":"Deepwater carbonate ion concentrations in the western tropical Pacific since 250 ka: Evidence for oceanic carbon storage and global climate influence","authors":"Bingbin Qin, Tiegang Li, Z. Xiong, T. Algeo, F. Chang","doi":"10.1002/2016PA003039","DOIUrl":"https://doi.org/10.1002/2016PA003039","url":null,"abstract":"We present new “size-normalized weight” (SNW)-Δ[CO32−] core-top calibrations for three planktonic foraminiferal species and assess their reliability as a paleo-alkalinity proxy. SNWs of Globigerina sacculifer and Neogloboquadrina dutertrei can be used to reconstruct past deep Pacific [CO32−], whereas SNWs of Pulleniatina obliquiloculata are controlled by additional environmental factors. Based on this methodological advance, we reconstruct SNW-based deepwater [CO32−] for core WP7 from the western tropical Pacific since 250 ka. Secular variation in the SNW proxy documents little change in deep Pacific [CO32−] between the Last Glacial Maximum and the Holocene. Further back in time, deepwater [CO32−] shows long-term increases from marine isotope stage (MIS) 5e to MIS 3 and from early MIS 7 to late MIS 6, consistent with the “coral reef hypothesis” that the deep Pacific Ocean carbonate system responded to declining shelf carbonate production during these two intervals. During deglaciations, we have evidence of [CO32−] peaks coincident with Terminations 2 and 3, which suggests that a breakdown of oceanic vertical stratification drove a net transfer of CO2 from the ocean to the atmosphere, causing spikes in carbonate preservation (i.e., the “deglacial ventilation hypothesis”). During MIS 4, a transient decline in SNW-based [CO32−], along with other reported [CO32−] and/or dissolution records, implies that increased deep-ocean carbon storage resulted in a global carbonate dissolution event. These findings provide new insights into the role of the deep Pacific in the global carbon cycle during the late Quaternary.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"351-370"},"PeriodicalIF":0.0,"publicationDate":"2017-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003039","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45103584","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
High δ18O values (>3.0 ‰) from a 9-kyr resolution benthic foraminiferal stable isotope record from the Ocean Drilling Program (ODP) Site 690B located on the Maud Rise, Antarctica indicate a heavily glaciated Antarctic continent during Late Oligocene (27.8-24.5 Ma). Values ranging 2.5-3.0 ‰ during interglacial periods and 3.0-3.6 ‰ during glacial intervals are consistent with an ice sheet near or larger than modern size. In addition, this record does not exhibit the long-term Late Oligocene warming trend seen in records from low-latitude drill sites. Oxygen isotope values from 26.0-24.5 Ma are comparable (ranging between 2.5 and 3.3 ‰) to values that preceded the δ18O event Oi2b at 26.7 Ma, indicating no significant glacial collapse occurred during the Late Oligocene. A gradient between ocean basins during the Oligocene has already been linked to the development of a modern, multi-layered ocean, and worked to bathe the low to mid-latitude, deep-sea records with a warmer water mass. We suggest this masked the significant Antarctic glaciation in low-latitude paleoceanographic records. Additionally, we propose a resolution for conflicting lines of evidence from some Antarctic proximal records suggesting significant glaciation and others suggesting reduced glaciation during the Late Oligocene by allowing a modern-sized ice sheet to grow on an Antarctic continent as more land surface area existed above sea-level during this time. This could allow at least some portions of the Antarctic coastline to remain ice-free during glacial minima while still maintaining modern or near-modern ice volume.
{"title":"Evidence for a heavily glaciated Antarctica during the late Oligocene “warming” (27.8–24.5 Ma): Stable isotope records from ODP Site 690","authors":"D. Hauptvogel, S. Pekar, V. Pincay","doi":"10.1002/2016PA002972","DOIUrl":"https://doi.org/10.1002/2016PA002972","url":null,"abstract":"High δ18O values (>3.0 ‰) from a 9-kyr resolution benthic foraminiferal stable isotope record from the Ocean Drilling Program (ODP) Site 690B located on the Maud Rise, Antarctica indicate a heavily glaciated Antarctic continent during Late Oligocene (27.8-24.5 Ma). Values ranging 2.5-3.0 ‰ during interglacial periods and 3.0-3.6 ‰ during glacial intervals are consistent with an ice sheet near or larger than modern size. In addition, this record does not exhibit the long-term Late Oligocene warming trend seen in records from low-latitude drill sites. Oxygen isotope values from 26.0-24.5 Ma are comparable (ranging between 2.5 and 3.3 ‰) to values that preceded the δ18O event Oi2b at 26.7 Ma, indicating no significant glacial collapse occurred during the Late Oligocene. A gradient between ocean basins during the Oligocene has already been linked to the development of a modern, multi-layered ocean, and worked to bathe the low to mid-latitude, deep-sea records with a warmer water mass. We suggest this masked the significant Antarctic glaciation in low-latitude paleoceanographic records. Additionally, we propose a resolution for conflicting lines of evidence from some Antarctic proximal records suggesting significant glaciation and others suggesting reduced glaciation during the Late Oligocene by allowing a modern-sized ice sheet to grow on an Antarctic continent as more land surface area existed above sea-level during this time. This could allow at least some portions of the Antarctic coastline to remain ice-free during glacial minima while still maintaining modern or near-modern ice volume.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"384-396"},"PeriodicalIF":0.0,"publicationDate":"2017-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA002972","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45351050","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The global ocean state for the modern age and for the Last Glacial Maximum (LGM) was dynamically reconstructed with a sophisticated data assimilation technique. A substantial amount of data including global seawater temperature, salinity (only for the modern estimate), and the isotopic composition of oxygen and carbon (only in the Atlantic for the LGM) were integrated into an ocean general circulation model with the help of the adjoint method, thereby the model was optimized to reconstruct plausible continuous fields of tracers, overturning circulation and water mass distribution. The adjoint-based LGM state estimation of this study represents the state of the art in terms of the length of forward model runs, the number of observations assimilated, and the model domain. Compared to the modern state, the reconstructed continuous sea-surface temperature field for the LGM shows a global-mean cooling of 2.2 K, and the reconstructed LGM ocean has a more vigorous Atlantic meridional overturning circulation, shallower North Atlantic Deep Water (NADW) equivalent, stronger stratification, and more saline deep water.
{"title":"Dynamical reconstruction of the global ocean state during the Last Glacial Maximum","authors":"T. Kurahashi‐Nakamura, A. Paul, M. Losch","doi":"10.1002/2016PA003001","DOIUrl":"https://doi.org/10.1002/2016PA003001","url":null,"abstract":"The global ocean state for the modern age and for the Last Glacial Maximum (LGM) was dynamically reconstructed with a sophisticated data assimilation technique. A substantial amount of data including global seawater temperature, salinity (only for the modern estimate), and the isotopic composition of oxygen and carbon (only in the Atlantic for the LGM) were integrated into an ocean general circulation model with the help of the adjoint method, thereby the model was optimized to reconstruct plausible continuous fields of tracers, overturning circulation and water mass distribution. The adjoint-based LGM state estimation of this study represents the state of the art in terms of the length of forward model runs, the number of observations assimilated, and the model domain. Compared to the modern state, the reconstructed continuous sea-surface temperature field for the LGM shows a global-mean cooling of 2.2 K, and the reconstructed LGM ocean has a more vigorous Atlantic meridional overturning circulation, shallower North Atlantic Deep Water (NADW) equivalent, stronger stratification, and more saline deep water.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"326-350"},"PeriodicalIF":0.0,"publicationDate":"2017-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003001","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49307314","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A new radiolarian data set for transfer function estimates of past sea surface temperature (SST) and intermediate water temperature was developed in this study for the northwestern Pacific Ocean covering a region from 1° to 50°N and 120° to 167°E. We analyzed 87 sediments surface samples, selected 30 species and/or species group found in shallow water for estimating past summer SST and 17 species and/or species group found in the intermediate water for estimating past intermediate water temperature. Since the intermediate water temperature changes greatly between 200 and 500 m, our estimates provide values at 500 m because temperatures are relatively stable between 500 and 1000 m. In this context, we estimated past summer SST and intermediate water (at ~500 m) temperature within an error margin of 0.9 and 1.2°C, respectively. A test of the accuracy of our transfer functions, conducted on core samples provided by IODP Expedition 346 Site U1429 in the northern East China Sea, showed that the reconstructed summer SSTs fluctuated between 17.2 and 26.5°C in selected late Pleistocene sequences. These temperatures corresponded to modern winter and summer SST, respectively, which highlights the ability of our new database to accurately reconstruct summer SST. The reconstructed intermediate water temperature fluctuates between 3 and 8°C, which corresponds to the observed temperature range at depths of ~500 m at high and midlatitudes, respectively.
{"title":"New northwest Pacific radiolarian data as a tool to estimate past sea surface and intermediate water temperatures","authors":"K. Matsuzaki, T. Itaki","doi":"10.1002/2017PA003087","DOIUrl":"https://doi.org/10.1002/2017PA003087","url":null,"abstract":"A new radiolarian data set for transfer function estimates of past sea surface temperature (SST) and intermediate water temperature was developed in this study for the northwestern Pacific Ocean covering a region from 1° to 50°N and 120° to 167°E. We analyzed 87 sediments surface samples, selected 30 species and/or species group found in shallow water for estimating past summer SST and 17 species and/or species group found in the intermediate water for estimating past intermediate water temperature. Since the intermediate water temperature changes greatly between 200 and 500 m, our estimates provide values at 500 m because temperatures are relatively stable between 500 and 1000 m. In this context, we estimated past summer SST and intermediate water (at ~500 m) temperature within an error margin of 0.9 and 1.2°C, respectively. A test of the accuracy of our transfer functions, conducted on core samples provided by IODP Expedition 346 Site U1429 in the northern East China Sea, showed that the reconstructed summer SSTs fluctuated between 17.2 and 26.5°C in selected late Pleistocene sequences. These temperatures corresponded to modern winter and summer SST, respectively, which highlights the ability of our new database to accurately reconstruct summer SST. The reconstructed intermediate water temperature fluctuates between 3 and 8°C, which corresponds to the observed temperature range at depths of ~500 m at high and midlatitudes, respectively.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"218-245"},"PeriodicalIF":0.0,"publicationDate":"2017-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003087","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43106182","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The intensity of the Oxygen minimum zone (OMZ) of the eastern North Paci fi c (ENP) experienced strong variations during the last glacial, mirroring changes in the balance between export production (O 2 consumption) and water mass ventilation (O 2 renewal). In this paper we present a new benthic foraminiferal assemblages record from Core MD02-2508, recovered from the Paci fi c slope off Baja California, Mexico. The record re fl ects oxygen conditions at the northern limit of the OMZ during the last 80kyr. We statistically identi fi ed three assemblages, characteristic of dysoxic, suboxic, and oxic conditions, which we used to produce the fi rst semiquantitative reconstruction of [O 2 ] for the northeastern Paci fi c Ocean. Our results show that the estimated [O 2 ] covaries with δ 18 O records from the North Greenland Ice Core Project. Oxygen concentrations overall exhibit moderate values (~1mL.L (cid:1) 1 ) during stadials, reaching ~2 mL.L (cid:1) 1 during stadials corresponding to Heinrich events in the Atlantic Ocean. Conversely, bottom waters at the core location were strongly depleted in oxygen ( < 0.5 mL.L (cid:1) 1 ) during interstadials. Benthic foraminiferal abundance increased with higher export production as recorded by geochemical tracers (Cd/Al ratio). This export production signal increases (decreases) with a fall (rise) in [O 2 ] during interstadials (stadials), suggesting a relationship between both parameters during these intervals. The in fl uence of ventilation on oxygenation is also a key player. O 2 pulses suggested by the downcore records of serial/spiral test ratio and abundance of oxic species may be explained by enhanced ventilation during Heinrich stadials, in agreement with latest modeling-based oceanic circulation reconstructions.
{"title":"Oxygen history off Baja California over the last 80 kyr: A new foraminiferal-based record: Oxygen History in the California Margin","authors":"M. Tetard, L. Licari, L. Beaufort","doi":"10.1002/2016pa003034","DOIUrl":"https://doi.org/10.1002/2016pa003034","url":null,"abstract":"The intensity of the Oxygen minimum zone (OMZ) of the eastern North Paci fi c (ENP) experienced strong variations during the last glacial, mirroring changes in the balance between export production (O 2 consumption) and water mass ventilation (O 2 renewal). In this paper we present a new benthic foraminiferal assemblages record from Core MD02-2508, recovered from the Paci fi c slope off Baja California, Mexico. The record re fl ects oxygen conditions at the northern limit of the OMZ during the last 80kyr. We statistically identi fi ed three assemblages, characteristic of dysoxic, suboxic, and oxic conditions, which we used to produce the fi rst semiquantitative reconstruction of [O 2 ] for the northeastern Paci fi c Ocean. Our results show that the estimated [O 2 ] covaries with δ 18 O records from the North Greenland Ice Core Project. Oxygen concentrations overall exhibit moderate values (~1mL.L (cid:1) 1 ) during stadials, reaching ~2 mL.L (cid:1) 1 during stadials corresponding to Heinrich events in the Atlantic Ocean. Conversely, bottom waters at the core location were strongly depleted in oxygen ( < 0.5 mL.L (cid:1) 1 ) during interstadials. Benthic foraminiferal abundance increased with higher export production as recorded by geochemical tracers (Cd/Al ratio). This export production signal increases (decreases) with a fall (rise) in [O 2 ] during interstadials (stadials), suggesting a relationship between both parameters during these intervals. The in fl uence of ventilation on oxygenation is also a key player. O 2 pulses suggested by the downcore records of serial/spiral test ratio and abundance of oxic species may be explained by enhanced ventilation during Heinrich stadials, in agreement with latest modeling-based oceanic circulation reconstructions.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"246-264"},"PeriodicalIF":0.0,"publicationDate":"2017-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016pa003034","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49402908","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Combined seawater radiogenic hafnium (Hf) and neodymium (Nd) isotope compositions were extracted from bulk sediment leachates and foraminifera of Site 1088, ODP Leg 177, 2082 m water depth on the Agulhas Ridge. The new data provide a continuous reconstruction of long and short-term changes in ocean circulation and continental weathering inputs since the Mid-Miocene. Due to its intermediate water depth the sediments of this core sensitively recorded changes in admixture of North Atlantic Deep Water (NADW) to the Antarctic Circumpolar Current (ACC) as a function of the strength of the Atlantic Meridional Overturning Circulation (AMOC). Nd isotope compositions (eNd) range from -7 to -11 with glacial values generally 1 to 3 units more radiogenic than during the interglacials of the Quaternary. The data reveal episodes of significantly increased AMOC strength during late Miocene and Pliocene warm periods whereas peak radiogenic eNd values mark a strongly diminished AMOC during the major intensification of Northern Hemisphere Glaciation near 2.8 Ma and in the Pleistocene after 1.5 Ma. In contrast, the Hf isotope compositions (eHf) show an essentially continuous evolution from highly radiogenic values of up to +11 during the Miocene to less radiogenic present day values (+2 to +4) during the late Quaternary. The data document a long-term transition in dominant weathering inputs, where inputs from the South America are replaced by those from Southern Africa. Moreover, radiogenic peaks provide evidence for the supply of radiogenic Hf originating from Patagonian rocks to the Atlantic sector of the Southern Ocean via dust inputs.
从Agulhas山脊ODP Leg 1772082m水深的1088号场地的大量沉积物浸出物和有孔虫中提取了海水放射性铪（Hf）和钕（Nd）同位素组合。新数据提供了自中新世中期以来海洋环流和大陆风化输入的长期和短期变化的连续重建。由于其中等水深，该岩芯的沉积物敏感地记录了北大西洋深水（NADW）与南极环极流（ACC）的混合变化，作为大西洋经向翻转环流（AMOC）强度的函数。Nd同位素组成（eNd）范围从-7到-11，冰川值通常比第四纪间冰期高1到3个单位。数据显示，在中新世晚期和上新世温暖期，AMOC强度显著增加，而辐射成因eNd峰值标志着在2.8 Ma附近北半球冰川作用的主要强化期间和1.5 Ma后的更新世AMOC显著减少。相反，Hf同位素组成（eHf）显示出从中新世期间高达+11的高辐射成因值到第四纪晚期的低辐射成因现今值（+2至+4）的基本上连续的演化。数据记录了主要风化输入的长期转变，其中来自南美洲的输入被来自南部非洲的输入所取代。此外，放射成因峰值为源自巴塔哥尼亚岩石的放射成因Hf通过尘埃输入提供了证据。
{"title":"Glacial reduction of AMOC strength and long term transition in weathering inputs into the Southern Ocean since the Mid Miocene: Evidence from radiogenic Nd and Hf isotopes","authors":"V. Dausmann, M. Frank, M. Gutjahr, J. Rickli","doi":"10.1002/2016PA003056","DOIUrl":"https://doi.org/10.1002/2016PA003056","url":null,"abstract":"Combined seawater radiogenic hafnium (Hf) and neodymium (Nd) isotope compositions were extracted from bulk sediment leachates and foraminifera of Site 1088, ODP Leg 177, 2082 m water depth on the Agulhas Ridge. The new data provide a continuous reconstruction of long and short-term changes in ocean circulation and continental weathering inputs since the Mid-Miocene. Due to its intermediate water depth the sediments of this core sensitively recorded changes in admixture of North Atlantic Deep Water (NADW) to the Antarctic Circumpolar Current (ACC) as a function of the strength of the Atlantic Meridional Overturning Circulation (AMOC). \u0000 \u0000Nd isotope compositions (eNd) range from -7 to -11 with glacial values generally 1 to 3 units more radiogenic than during the interglacials of the Quaternary. The data reveal episodes of significantly increased AMOC strength during late Miocene and Pliocene warm periods whereas peak radiogenic eNd values mark a strongly diminished AMOC during the major intensification of Northern Hemisphere Glaciation near 2.8 Ma and in the Pleistocene after 1.5 Ma. \u0000 \u0000In contrast, the Hf isotope compositions (eHf) show an essentially continuous evolution from highly radiogenic values of up to +11 during the Miocene to less radiogenic present day values (+2 to +4) during the late Quaternary. The data document a long-term transition in dominant weathering inputs, where inputs from the South America are replaced by those from Southern Africa. Moreover, radiogenic peaks provide evidence for the supply of radiogenic Hf originating from Patagonian rocks to the Atlantic sector of the Southern Ocean via dust inputs.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"265-283"},"PeriodicalIF":0.0,"publicationDate":"2017-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003056","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48608185","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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