W. Kuhnt, A. Holbourn, S. Beil, M. Aquit, T. Krawczyk, S. Flögel, E. H. Chellai, H. Jabour
We investigated the onset and development of Cretaceous Oceanic Anoxic Event 2 (OAE2) in a newly drilled core (SN degrees 4) from the Tarfaya Basin (southern Morocco), where this interval is unusually expanded. High-resolution (centimeter-scale equivalent to centennial) analysis of bulk organic and carbonate stable isotopes and of carbonate and organic carbon content in combination with XRF scanner derived elemental distribution reveal that the ocean-climate system behaved in a highly dynamic manner prior to and during the onset of OAE2. Correlation with the latest orbital solution indicates that the main carbon isotope shift occurred during an extended minimum in orbital eccentricity (similar to 400 kyr cycle). Shorter-term fluctuations in carbonate and organic carbon accumulation and in sea level related terrigenous discharge were predominantly driven by variations in orbital obliquity. Negative excursions in organic and carbonate delta C-13 preceded the global positive delta C-13 shift marking the onset of OAE2, suggesting injection of isotopically depleted carbon into the atmosphere. The main delta C-13 increase during the early phase of OAE2 in the late Cenomanian was punctuated by a transient plateau. Maximum organic carbon accumulation occurred during the later part of the main delta C-13 increase and was associated with climate cooling events, expressed as three consecutive maxima in bulk carbonate delta O-18. The extinctions of the thermocline dwelling keeled planktonic foraminifers Rotalipora greenhornensis and Rotalipora cushmani occurred during the first and last of these cooling events and were likely associated with obliquity paced, ocean-wide expansions, and intensifications of the oxygen minimum zone, affecting their habitat space on a global scale.
{"title":"Unraveling the onset of Cretaceous Oceanic Anoxic Event 2 in an extended sediment archive from the Tarfaya-Laayoune Basin, Morocco","authors":"W. Kuhnt, A. Holbourn, S. Beil, M. Aquit, T. Krawczyk, S. Flögel, E. H. Chellai, H. Jabour","doi":"10.1002/2017PA003146","DOIUrl":"https://doi.org/10.1002/2017PA003146","url":null,"abstract":"We investigated the onset and development of Cretaceous Oceanic Anoxic Event 2 (OAE2) in a newly drilled core (SN degrees 4) from the Tarfaya Basin (southern Morocco), where this interval is unusually expanded. High-resolution (centimeter-scale equivalent to centennial) analysis of bulk organic and carbonate stable isotopes and of carbonate and organic carbon content in combination with XRF scanner derived elemental distribution reveal that the ocean-climate system behaved in a highly dynamic manner prior to and during the onset of OAE2. Correlation with the latest orbital solution indicates that the main carbon isotope shift occurred during an extended minimum in orbital eccentricity (similar to 400 kyr cycle). Shorter-term fluctuations in carbonate and organic carbon accumulation and in sea level related terrigenous discharge were predominantly driven by variations in orbital obliquity. Negative excursions in organic and carbonate delta C-13 preceded the global positive delta C-13 shift marking the onset of OAE2, suggesting injection of isotopically depleted carbon into the atmosphere. The main delta C-13 increase during the early phase of OAE2 in the late Cenomanian was punctuated by a transient plateau. Maximum organic carbon accumulation occurred during the later part of the main delta C-13 increase and was associated with climate cooling events, expressed as three consecutive maxima in bulk carbonate delta O-18. The extinctions of the thermocline dwelling keeled planktonic foraminifers Rotalipora greenhornensis and Rotalipora cushmani occurred during the first and last of these cooling events and were likely associated with obliquity paced, ocean-wide expansions, and intensifications of the oxygen minimum zone, affecting their habitat space on a global scale.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"923-946"},"PeriodicalIF":0.0,"publicationDate":"2017-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003146","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47286275","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. Dickson, Benjamin C Gill, M. Ruhl, H. Jenkyns, D. Porcelli, E. Idiz, T. Lyons, S. V. D. Boorn
Molybdenum (Mo)-isotope chemostratigraphy of organic-rich mudrocks has been a valuable tool for testing the hypothesis that the Toarcian Oceanic Anoxic Event (T-OAE, Early Jurassic, ~183 Ma) was characterized by the spread of marine euxinia (and organic-matter burial) at a global scale. However, the interpretation of existing Mo-isotope data for the T-OAE (from Yorkshire, Cleveland Basin, U.K.) is equivocal. In this study, three new Mo-isotope profiles are presented: from Dotternhausen Quarry (South German Basin, Germany), the Rijswijk core (West Netherlands Basin, Netherlands) and the Dogna core (Belluno Basin, northern Italy). Precise bio- and chemo-stratigraphic correlation between the three sites allows a direct comparison of the data, enabling some key conclusions to be reached: (i) The Mo-isotope composition of seawater during the peak of the T-OAE was probably close to ~1.45 ‰, implicating a greater removal flux of sulphides from seawater, and a larger extent of global seafloor euxinia compared to the present day; (ii) Mo-isotope cycles previously identified in the Yorkshire sedimentary succession are attributed to changes in the degree of local Mo drawdown from overlying Cleveland Basin seawater; (iii) The consistency of the new multi-site Mo-isotope dataset indicates a secular reduction in the burial of sulphides globally in the late stages of the T-OAE, implying a contraction in the extent of global marine euxinia; (iv) Subtle differences in the Mo-isotope composition of deposits formed in different euxinic sub-basins of the European epicontinental shelf were probably governed by local variations in basin hydrography and rates of water renewal.
{"title":"Molybdenum‐isotope chemostratigraphy and paleoceanography of the Toarcian Oceanic Anoxic Event (Early Jurassic)","authors":"A. Dickson, Benjamin C Gill, M. Ruhl, H. Jenkyns, D. Porcelli, E. Idiz, T. Lyons, S. V. D. Boorn","doi":"10.1002/2016PA003048","DOIUrl":"https://doi.org/10.1002/2016PA003048","url":null,"abstract":"Molybdenum (Mo)-isotope chemostratigraphy of organic-rich mudrocks has been a valuable tool for testing the hypothesis that the Toarcian Oceanic Anoxic Event (T-OAE, Early Jurassic, ~183 Ma) was characterized by the spread of marine euxinia (and organic-matter burial) at a global scale. However, the interpretation of existing Mo-isotope data for the T-OAE (from Yorkshire, Cleveland Basin, U.K.) is equivocal. In this study, three new Mo-isotope profiles are presented: from Dotternhausen Quarry (South German Basin, Germany), the Rijswijk core (West Netherlands Basin, Netherlands) and the Dogna core (Belluno Basin, northern Italy). Precise bio- and chemo-stratigraphic correlation between the three sites allows a direct comparison of the data, enabling some key conclusions to be reached: (i) The Mo-isotope composition of seawater during the peak of the T-OAE was probably close to ~1.45 ‰, implicating a greater removal flux of sulphides from seawater, and a larger extent of global seafloor euxinia compared to the present day; (ii) Mo-isotope cycles previously identified in the Yorkshire sedimentary succession are attributed to changes in the degree of local Mo drawdown from overlying Cleveland Basin seawater; (iii) The consistency of the new multi-site Mo-isotope dataset indicates a secular reduction in the burial of sulphides globally in the late stages of the T-OAE, implying a contraction in the extent of global marine euxinia; (iv) Subtle differences in the Mo-isotope composition of deposits formed in different euxinic sub-basins of the European epicontinental shelf were probably governed by local variations in basin hydrography and rates of water renewal.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"813-829"},"PeriodicalIF":0.0,"publicationDate":"2017-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003048","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44338544","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}
D. Thompson, J. Conroy, Aaron F. Collins, Stephan R. Hlohowskyj, J. Overpeck, Melanie A. Riedinger-Whitmore, J. Cole, M. Bush, H. Whitney, T. Corley, M. Kannan
National Science Foundation (NSF) RAPID, Program [AGS-1256970, AGS-1561121]; NOAA Climate Program Office; University of Arizona Department of Geosciences; Philanthropic Education Organization; National Science Foundation (NSF) P2C2, Program [AGS-1256970, AGS-1561121]; National Science Foundation (NSF) Geospace Sciences Paleoclimate Program [AGS-1256970, AGS-1561121]
{"title":"Tropical Pacific climate variability over the last 6000 years as recorded in Bainbridge Crater Lake, Galápagos","authors":"D. Thompson, J. Conroy, Aaron F. Collins, Stephan R. Hlohowskyj, J. Overpeck, Melanie A. Riedinger-Whitmore, J. Cole, M. Bush, H. Whitney, T. Corley, M. Kannan","doi":"10.1002/2017PA003089","DOIUrl":"https://doi.org/10.1002/2017PA003089","url":null,"abstract":"National Science Foundation (NSF) RAPID, Program [AGS-1256970, AGS-1561121]; NOAA Climate Program Office; University of Arizona Department of Geosciences; Philanthropic Education Organization; National Science Foundation (NSF) P2C2, Program [AGS-1256970, AGS-1561121]; National Science Foundation (NSF) Geospace Sciences Paleoclimate Program [AGS-1256970, AGS-1561121]","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"903-922"},"PeriodicalIF":0.0,"publicationDate":"2017-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003089","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47084653","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}
Paleo-redox proxies are crucial for reconstructing past bottom water oxygen concentration changes brought about by ocean circulation and marine productivity shifts in response to climate forcing. Carbonate I/Ca ratios of multiple benthic foraminifera species from ODP Hole 1017E – a core drilled within the Californian oxygen minimum zone (OMZ), on the continental slope – are employed to re-examine the transition from the well oxygenated last glacial into poorly oxygenated modern conditions. The redox and export productivity history of this site is constrained by numerous proxies, used to assess sensitivity of I/Ca ratios of benthic foraminifera to changes in bottom- and pore water O2 concentrations. Reconstructed iodate (IO3-) availability from the I/Ca ratio of epifaunal (Cibicidoides sp.), shallow infaunal (Uvigerina peregrina), and deep infaunal (Bolivina spissa) foraminifera. The reconstructed IO3- availability profile is used to determine the contribution of bottom water O2 relative to oxidant demand on pore water O2 concentrations. These results suggest that high export productivity on the California Margin drove pore low water O2 concentrations during the Bolling. In contrast low bottom water O2 concentrations at 950 m water depth only contributed to reduced sediments during the Allerod. Increased contribution of modified North Pacific Intermediate Water to the California Current System ventilated the California OMZ during the late glacial and the Younger Dryas such that water overlying the site was oxygenated. These results highlight the promising potential of this new proxy for understanding the relative influence of bottom water O2 concentration and pore water oxidant demand on OMZs.
{"title":"Assessing oxygen depletion in the Northeastern Pacific Ocean during the last deglaciation using I/Ca ratios from multiple benthic foraminiferal species","authors":"M. Taylor, I. Hendy, A. Chappaz","doi":"10.1002/2016PA003062","DOIUrl":"https://doi.org/10.1002/2016PA003062","url":null,"abstract":"Paleo-redox proxies are crucial for reconstructing past bottom water oxygen concentration changes brought about by ocean circulation and marine productivity shifts in response to climate forcing. Carbonate I/Ca ratios of multiple benthic foraminifera species from ODP Hole 1017E – a core drilled within the Californian oxygen minimum zone (OMZ), on the continental slope – are employed to re-examine the transition from the well oxygenated last glacial into poorly oxygenated modern conditions. The redox and export productivity history of this site is constrained by numerous proxies, used to assess sensitivity of I/Ca ratios of benthic foraminifera to changes in bottom- and pore water O2 concentrations. Reconstructed iodate (IO3-) availability from the I/Ca ratio of epifaunal (Cibicidoides sp.), shallow infaunal (Uvigerina peregrina), and deep infaunal (Bolivina spissa) foraminifera. The reconstructed IO3- availability profile is used to determine the contribution of bottom water O2 relative to oxidant demand on pore water O2 concentrations. These results suggest that high export productivity on the California Margin drove pore low water O2 concentrations during the Bolling. In contrast low bottom water O2 concentrations at 950 m water depth only contributed to reduced sediments during the Allerod. Increased contribution of modified North Pacific Intermediate Water to the California Current System ventilated the California OMZ during the late glacial and the Younger Dryas such that water overlying the site was oxygenated. These results highlight the promising potential of this new proxy for understanding the relative influence of bottom water O2 concentration and pore water oxidant demand on OMZs.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"746-762"},"PeriodicalIF":0.0,"publicationDate":"2017-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003062","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43698740","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}
Guillaume Fontorbe, P. Frings, C. Rocha, K. Hendry, J. Carstensen, D. Conley
Silicon isotope ratios (expressed as δ30Si) in marine microfossils can provide insights into silica cycling over geologic time. Here we used δ30Si of sponge spicules and radiolarian tests from the Paleogene Equatorial Transect (Ocean Drilling Program Leg 199) spanning the Eocene and Oligocene (~50–23 Ma) to reconstruct dissolved silica (DSi) concentrations in deep waters and to examine upper ocean δ30Si. The δ30Si values range from −3.16 to +0.18‰ and from −0.07 to +1.42‰ for the sponge and radiolarian records, respectively. Both records show a transition toward lower δ30Si values around 37 Ma. The shift in radiolarian δ30Si is interpreted as a consequence of changes in the δ30Si of source DSi to the region. The decrease in sponge δ30Si is interpreted as a transition from low DSi concentrations to higher DSi concentrations, most likely related to the shift toward a solely Southern Ocean source of deep water in the Pacific during the Paleogene that has been suggested by results from paleoceanographic tracers such as neodymium and carbon isotopes. Sponge δ30Si provides relatively direct information about the nutrient content of deep water and is a useful complement to other tracers of deep water circulation in the oceans of the past.
{"title":"Enrichment of dissolved silica in the deep equatorial Pacific during the Eocene-Oligocene","authors":"Guillaume Fontorbe, P. Frings, C. Rocha, K. Hendry, J. Carstensen, D. Conley","doi":"10.1002/2017PA003090","DOIUrl":"https://doi.org/10.1002/2017PA003090","url":null,"abstract":"Silicon isotope ratios (expressed as δ30Si) in marine microfossils can provide insights into silica cycling over geologic time. Here we used δ30Si of sponge spicules and radiolarian tests from the Paleogene Equatorial Transect (Ocean Drilling Program Leg 199) spanning the Eocene and Oligocene (~50–23 Ma) to reconstruct dissolved silica (DSi) concentrations in deep waters and to examine upper ocean δ30Si. The δ30Si values range from −3.16 to +0.18‰ and from −0.07 to +1.42‰ for the sponge and radiolarian records, respectively. Both records show a transition toward lower δ30Si values around 37 Ma. The shift in radiolarian δ30Si is interpreted as a consequence of changes in the δ30Si of source DSi to the region. The decrease in sponge δ30Si is interpreted as a transition from low DSi concentrations to higher DSi concentrations, most likely related to the shift toward a solely Southern Ocean source of deep water in the Pacific during the Paleogene that has been suggested by results from paleoceanographic tracers such as neodymium and carbon isotopes. Sponge δ30Si provides relatively direct information about the nutrient content of deep water and is a useful complement to other tracers of deep water circulation in the oceans of the past.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"848-863"},"PeriodicalIF":0.0,"publicationDate":"2017-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003090","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49350533","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}
Grit Warratz, Ruediger Henrich, I. Voigt, C. Chiessi, G. Kuhn, H. Lantzsch
The deep southern component water (SCW), comprising Lower Circumpolar Deep Water (LCDW) and Antarctic Bottom Water (AABW), is a major component of the global oceanic circulation. It has been suggested that the deep Atlantic water mass structure changed significantly during the last glacial/interglacial cycle. However, deep SCW source-proximal records remain sparse. Here we present three coherent deep SCW paleocurrent records from the deep Argentine continental margin shedding light on deep water circulation and deep SCW flow strength in the Southwest Atlantic since the Last Glacial Maximum (LGM). Based on increased sortable silt values, we propose enhanced deep SCW flow strength from 14 to 10 cal ka B.P. relative to the early deglacial/LGM and the Holocene. We propose a direct influence of deep northern component water (NCW) on deep SCW flow strength due to vertical narrowing of deep SCW spreading, concurrent with a migration of the high-energetic LCDW/AABW interface occupying our core sites. We suggest a shoaled NCW until 13 cal ka B.P., thereby providing space for deep SCW spreading that resulted in reduced carbonate preservation at our core sites. Increased carbonate content from 13 cal ka B.P. indicates that the NCW expanded changing deep water properties at our core sites in the deep Southwest Atlantic. However, southern sourced terrigenous sediments continued to be deposited at our core sites, suggesting that deep SCW flow was uninterrupted along the Argentine continental margin since the LGM.
深南分量水(SCW)是全球海洋环流的主要组成部分，包括环极深水(LCDW)和南极底水(AABW)。在末次冰期/间冰期旋回期间，深大西洋水团结构发生了显著变化。然而，深海海水源-近端记录仍然稀少。本文介绍了阿根廷大陆边缘深层的三个相干深海流记录，揭示了末次盛冰期以来西南大西洋深水环流和深海流强度。基于可分选粉砂值的增加，我们提出相对于早冰期/LGM和全新世，深层SCW流动强度在14 ~ 10 calka B.P.之间增强。我们提出深层北方分量水(NCW)对深层水流动强度的直接影响是由于深层水扩散的垂直变窄，同时高能LCDW/AABW界面的迁移占据了我们的核心位置。我们认为在13 calka b.p.之前，NCW是浅滩状的，从而为深部SCW扩张提供了空间，导致我们的核心位置碳酸盐保存减少。从13 cal ka B.P.开始，碳酸盐含量的增加表明，在西南大西洋深处的核心位置，NCW扩大了不断变化的深水性质。然而，南方陆源沉积物继续沉积在我们的核心位置，这表明自LGM以来，阿根廷大陆边缘的深SCW流动不间断。
{"title":"Deglacial changes in the strength of deep southern component water and sediment supply at the Argentine continental margin","authors":"Grit Warratz, Ruediger Henrich, I. Voigt, C. Chiessi, G. Kuhn, H. Lantzsch","doi":"10.1002/2016PA003079","DOIUrl":"https://doi.org/10.1002/2016PA003079","url":null,"abstract":"The deep southern component water (SCW), comprising Lower Circumpolar Deep Water (LCDW) and Antarctic Bottom Water (AABW), is a major component of the global oceanic circulation. It has been suggested that the deep Atlantic water mass structure changed significantly during the last glacial/interglacial cycle. However, deep SCW source-proximal records remain sparse. Here we present three coherent deep SCW paleocurrent records from the deep Argentine continental margin shedding light on deep water circulation and deep SCW flow strength in the Southwest Atlantic since the Last Glacial Maximum (LGM). Based on increased sortable silt values, we propose enhanced deep SCW flow strength from 14 to 10 cal ka B.P. relative to the early deglacial/LGM and the Holocene. We propose a direct influence of deep northern component water (NCW) on deep SCW flow strength due to vertical narrowing of deep SCW spreading, concurrent with a migration of the high-energetic LCDW/AABW interface occupying our core sites. We suggest a shoaled NCW until 13 cal ka B.P., thereby providing space for deep SCW spreading that resulted in reduced carbonate preservation at our core sites. Increased carbonate content from 13 cal ka B.P. indicates that the NCW expanded changing deep water properties at our core sites in the deep Southwest Atlantic. However, southern sourced terrigenous sediments continued to be deposited at our core sites, suggesting that deep SCW flow was uninterrupted along the Argentine continental margin since the LGM.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"796-812"},"PeriodicalIF":0.0,"publicationDate":"2017-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003079","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46478272","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}
D. Tangunan, K. Baumann, J. Pätzold, R. Henrich, M. Kučera, R. Pol-Holz, J. Groeneveld
We present a new coccolithophore productivity reconstruction spanning the last 300 ka in core GeoB12613-1 retrieved from the western tropical Indian Ocean (IO), an area that mainly derives its warm and oligotrophic surface waters from the eastern IO. Application of a calibrated assemblage-based productivity index indicates a reduction in estimated primary productivity (EPP) from 300 ka to the present, with reconstructed EPP values ranging from 91 to 246 g C/m2/yr. Coccolithophore assemblages and coccolith fraction Sr/Ca indicate three main phases of productivity change, with major changes at 160 and 46 ka. The productivity and water-column stratification records show both dominant precession and obliquity periodicities, which appear to control the paleoproductivity in the study area over the last two glacial-interglacial cycles. Shallowing of the thermocline due to strengthening of the trade winds in response to insolation maxima resulted to peaks in EPP. Comparison with the eastern IO productivity and stratification coccolithophore data reveals good correspondence with our records, indicating a strong tropical Pacific influence in our study area. Both of these records show high productivity from 300 ka to 160 ka, interpreted to be due to stronger Walker Circulation while the declining productivity from 160 ka to the present day is a consequence of its weakening intensity.
我们提出了一种新的球藻生产力重建，该重建跨越了从热带印度洋西部（IO）取回的GeoB12613-1岩芯中的最后300 ka，该地区主要来自热带印度洋东部的温暖和贫营养地表水。基于校准组合的生产力指数的应用表明，估计的初级生产力（EPP）从300 ka降低到现在，重建的EPP值在91至246 g C/m2/yr之间。球团粒组合和球团粒分数Sr/Ca表明生产力变化的三个主要阶段，主要变化在160和46ka。生产力和水柱分层记录显示了主要的岁差和倾角周期性，这似乎控制了研究区在最后两个冰川-间冰期循环中的古生产力。温跃层的减弱是由于信风对日照最大值的响应而增强，导致EPP达到峰值。与东部IO生产力和分层尾石体数据的比较表明，与我们的记录吻合良好，表明热带太平洋对我们的研究区域有强烈的影响。这两项记录都显示，从300卡到160卡的生产力很高，这被解释为是由于沃克环流更强，而从160卡到今天的生产力下降是其强度减弱的结果。
{"title":"Insolation forcing of coccolithophore productivity in the western tropical Indian Ocean over the last two glacial-interglacial cycles","authors":"D. Tangunan, K. Baumann, J. Pätzold, R. Henrich, M. Kučera, R. Pol-Holz, J. Groeneveld","doi":"10.1002/2017PA003102","DOIUrl":"https://doi.org/10.1002/2017PA003102","url":null,"abstract":"We present a new coccolithophore productivity reconstruction spanning the last 300 ka in core GeoB12613-1 retrieved from the western tropical Indian Ocean (IO), an area that mainly derives its warm and oligotrophic surface waters from the eastern IO. Application of a calibrated assemblage-based productivity index indicates a reduction in estimated primary productivity (EPP) from 300 ka to the present, with reconstructed EPP values ranging from 91 to 246 g C/m2/yr. Coccolithophore assemblages and coccolith fraction Sr/Ca indicate three main phases of productivity change, with major changes at 160 and 46 ka. The productivity and water-column stratification records show both dominant precession and obliquity periodicities, which appear to control the paleoproductivity in the study area over the last two glacial-interglacial cycles. Shallowing of the thermocline due to strengthening of the trade winds in response to insolation maxima resulted to peaks in EPP. Comparison with the eastern IO productivity and stratification coccolithophore data reveals good correspondence with our records, indicating a strong tropical Pacific influence in our study area. Both of these records show high productivity from 300 ka to 160 ka, interpreted to be due to stronger Walker Circulation while the declining productivity from 160 ka to the present day is a consequence of its weakening intensity.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"692-709"},"PeriodicalIF":0.0,"publicationDate":"2017-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003102","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49515004","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}
We assess early-to-middle Eocene seawater neodymium (Nd) isotope records from seven Southern Ocean deep-sea drill sites to evaluate the role of Southern Ocean circulation in long-term Cenozoic climate change. Our study sites are strategically located on either side of the Tasman Gateway and are positioned at a range of shallow (<500 m) to intermediate/deep (~1000–2500 m) paleowater depths. Unradiogenic seawater Nd isotopic compositions, reconstructed from fish teeth at intermediate/deep Indian Ocean pelagic sites (Ocean Drilling Program (ODP) Sites 738 and 757 and Deep Sea Drilling Project (DSDP) Site 264), indicate a dominant Southern Ocean-sourced contribution to regional deep waters (eNd(t) = −9.3 ± 1.5). IODP Site U1356 off the coast of Adelie Land, a locus of modern-day Antarctic Bottom Water production, is identified as a site of persistent deep water formation from the early Eocene to the Oligocene. East of the Tasman Gateway an additional local source of intermediate/deep water formation is inferred at ODP Site 277 in the SW Pacific Ocean (eNd(t) = −8.7 ± 1.5). Antarctic-proximal shelf sites (ODP Site 1171 and Site U1356) reveal a pronounced erosional event between 49 and 48 Ma, manifested by ~2 eNd unit negative excursions in seawater chemistry toward the composition of bulk sediments at these sites. This erosional event coincides with the termination of peak global warmth following the Early Eocene Climatic Optimum and is associated with documented cooling across the study region and increased export of Antarctic deep waters, highlighting the complexity and importance of Southern Ocean circulation in the greenhouse climate of the Eocene.
{"title":"Antarctic climate, Southern Ocean circulation patterns, and deep-water formation during the Eocene","authors":"Claire E Huck, T. Flierdt, S. Bohaty, S. Hammond","doi":"10.1002/2017PA003135","DOIUrl":"https://doi.org/10.1002/2017PA003135","url":null,"abstract":"We assess early-to-middle Eocene seawater neodymium (Nd) isotope records from seven Southern Ocean deep-sea drill sites to evaluate the role of Southern Ocean circulation in long-term Cenozoic climate change. Our study sites are strategically located on either side of the Tasman Gateway and are positioned at a range of shallow (<500 m) to intermediate/deep (~1000–2500 m) paleowater depths. Unradiogenic seawater Nd isotopic compositions, reconstructed from fish teeth at intermediate/deep Indian Ocean pelagic sites (Ocean Drilling Program (ODP) Sites 738 and 757 and Deep Sea Drilling Project (DSDP) Site 264), indicate a dominant Southern Ocean-sourced contribution to regional deep waters (eNd(t) = −9.3 ± 1.5). IODP Site U1356 off the coast of Adelie Land, a locus of modern-day Antarctic Bottom Water production, is identified as a site of persistent deep water formation from the early Eocene to the Oligocene. East of the Tasman Gateway an additional local source of intermediate/deep water formation is inferred at ODP Site 277 in the SW Pacific Ocean (eNd(t) = −8.7 ± 1.5). Antarctic-proximal shelf sites (ODP Site 1171 and Site U1356) reveal a pronounced erosional event between 49 and 48 Ma, manifested by ~2 eNd unit negative excursions in seawater chemistry toward the composition of bulk sediments at these sites. This erosional event coincides with the termination of peak global warmth following the Early Eocene Climatic Optimum and is associated with documented cooling across the study region and increased export of Antarctic deep waters, highlighting the complexity and importance of Southern Ocean circulation in the greenhouse climate of the Eocene.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"674-691"},"PeriodicalIF":0.0,"publicationDate":"2017-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003135","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46804328","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}
J. Self‐Trail, M. Robinson, T. Bralower, J. Sessa, E. Hajek, L. Kump, S. Trampush, D. Willard, L. Edwards, D. Powars, G. A. Wandless
The Paleocene-Eocene Thermal Maximum (PETM) was an interval of extreme warmth that caused disruption of marine and terrestrial ecosystems on a global scale. Here we examine the sediments, flora and fauna from an expanded section at Mattawoman Creek-Billingsley Road (MCBR) in Maryland and explore the impact of warming at a nearshore shallow marine (30-100 m water depth) site in the Salisbury Embayment. Observations indicate that, at the onset of the PETM, the site abruptly shifted from an open-marine to prodelta setting with increased terrestrial and fresh water input. Changes in microfossil biota suggest stratification of the water column and low oxygen bottom water conditions in the earliest Eocene. Formation of authigenic carbonate through microbial diagenesis produced an unusually large bulk carbon isotope shift, while the magnitude of the corresponding signal from benthic foraminifera is similar to that at other marine sites. This proves that the landward increase in the magnitude of the carbon isotope excursion measured in bulk sediment is not due to a near instantaneous release of 12C-enriched CO2. We conclude that the MCBR site records nearshore marine response to global climate change that can be used as an analog for modern coastal response to global warming.
古新世-始新世热盛期（PETM）是一个极端温暖的时期，导致全球范围内海洋和陆地生态系统的破坏。在这里，我们检查了马里兰州Mattawoman Creek Billingsley路（MCBR）扩建路段的沉积物、动植物，并探讨了索尔兹伯里湾近岸浅海（30-100米水深）场地变暖的影响。观测表明，在PETM开始时，随着陆地和淡水输入的增加，该地点突然从开阔的海洋环境转变为前三角洲环境。微体化石生物群的变化表明，最早始新世的水柱分层和低氧底层水条件。通过微生物成岩作用形成的自生碳酸盐产生了异常大的体积碳同位素位移，而海底有孔虫的相应信号大小与其他海洋地点相似。这证明，在散装沉积物中测得的碳同位素漂移幅度向陆地增加并不是由于富含12C的二氧化碳几乎瞬间释放。我们得出的结论是，MCBR站点记录了近海海洋对全球气候变化的反应，可以作为现代海岸对全球变暖反应的模拟。
{"title":"Shallow marine response to global climate change during the Paleocene‐Eocene Thermal Maximum, Salisbury Embayment, USA","authors":"J. Self‐Trail, M. Robinson, T. Bralower, J. Sessa, E. Hajek, L. Kump, S. Trampush, D. Willard, L. Edwards, D. Powars, G. A. Wandless","doi":"10.1002/2017PA003096","DOIUrl":"https://doi.org/10.1002/2017PA003096","url":null,"abstract":"The Paleocene-Eocene Thermal Maximum (PETM) was an interval of extreme warmth that caused disruption of marine and terrestrial ecosystems on a global scale. Here we examine the sediments, flora and fauna from an expanded section at Mattawoman Creek-Billingsley Road (MCBR) in Maryland and explore the impact of warming at a nearshore shallow marine (30-100 m water depth) site in the Salisbury Embayment. Observations indicate that, at the onset of the PETM, the site abruptly shifted from an open-marine to prodelta setting with increased terrestrial and fresh water input. Changes in microfossil biota suggest stratification of the water column and low oxygen bottom water conditions in the earliest Eocene. Formation of authigenic carbonate through microbial diagenesis produced an unusually large bulk carbon isotope shift, while the magnitude of the corresponding signal from benthic foraminifera is similar to that at other marine sites. This proves that the landward increase in the magnitude of the carbon isotope excursion measured in bulk sediment is not due to a near instantaneous release of 12C-enriched CO2. We conclude that the MCBR site records nearshore marine response to global climate change that can be used as an analog for modern coastal response to global warming.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"710-728"},"PeriodicalIF":0.0,"publicationDate":"2017-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003096","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48124107","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}
H. Matsui, H. Nishi, A. Kuroyanagi, H. Hayashi, M. Ikehara, R. Takashima
Knowledge of the equatorial thermocline is essential for understanding climate changes in the tropical Pacific. Multispecies planktic foraminiferal analyses provide a way to examine temperature distributions and thus the structure of the thermocline. Although the secular thermocline development has been documented back to the late Miocene, the early to middle Miocene interval has rarely been examined. In addition, relationships with the dynamic Antarctic ice sheets remain unclear. Here we investigate the vertical thermal gradient in the upper water column at Integrated Ocean Drilling Program Site U1337 in the eastern equatorial Pacific (EEP) throughout the early to middle Miocene (23.1 to 11.7 Ma). The gradient increased over the Miocene Climatic Optimum, whereas it decreased during the East Antarctic Ice Sheet Expansion (EAIE). Comparison of the EEP record with its western equatorial Pacific (WEP) counterpart suggests that sea surface temperature was more stable in the WEP than in the EEP. We further estimated equatorial thermocline from two diagonal gradients between the EEP and the WEP: thermocline shoaled from 16.7 to 15.7 Ma and tilt weakened between 16.5 and 13.8 Ma. The onset of the “Monterey Excursion” and the reduced Antarctic ice sheet volume would have affected thermocline depth and tilt, respectively. Thermocline depth was likely much deeper compared to Pliocene-to-modern conditions. Furthermore, a 4-point-based distribution of isotherms (4DI index) was used as a metric of the evenness or unevenness of the isotherm distributions. The 4DI index considerably reduced at around the EAIE and other Mi-events, reflecting the evenly distributed isotherms under a more glaciated Antarctica.
{"title":"Vertical thermal gradient history in the eastern equatorial Pacific during the early to middle Miocene: Implications for the equatorial thermocline development","authors":"H. Matsui, H. Nishi, A. Kuroyanagi, H. Hayashi, M. Ikehara, R. Takashima","doi":"10.1002/2016PA003058","DOIUrl":"https://doi.org/10.1002/2016PA003058","url":null,"abstract":"Knowledge of the equatorial thermocline is essential for understanding climate changes in the tropical Pacific. Multispecies planktic foraminiferal analyses provide a way to examine temperature distributions and thus the structure of the thermocline. Although the secular thermocline development has been documented back to the late Miocene, the early to middle Miocene interval has rarely been examined. In addition, relationships with the dynamic Antarctic ice sheets remain unclear. Here we investigate the vertical thermal gradient in the upper water column at Integrated Ocean Drilling Program Site U1337 in the eastern equatorial Pacific (EEP) throughout the early to middle Miocene (23.1 to 11.7 Ma). The gradient increased over the Miocene Climatic Optimum, whereas it decreased during the East Antarctic Ice Sheet Expansion (EAIE). Comparison of the EEP record with its western equatorial Pacific (WEP) counterpart suggests that sea surface temperature was more stable in the WEP than in the EEP. We further estimated equatorial thermocline from two diagonal gradients between the EEP and the WEP: thermocline shoaled from 16.7 to 15.7 Ma and tilt weakened between 16.5 and 13.8 Ma. The onset of the “Monterey Excursion” and the reduced Antarctic ice sheet volume would have affected thermocline depth and tilt, respectively. Thermocline depth was likely much deeper compared to Pliocene-to-modern conditions. Furthermore, a 4-point-based distribution of isotherms (4DI index) was used as a metric of the evenness or unevenness of the isotherm distributions. The 4DI index considerably reduced at around the EAIE and other Mi-events, reflecting the evenly distributed isotherms under a more glaciated Antarctica.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"729-743"},"PeriodicalIF":0.0,"publicationDate":"2017-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003058","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45405241","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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