A significant discrepancy of up to 0.6 Myr exists between radio-isotopically calibrated and astronomically tuned time scales of the late Eocene-Oligocene. We explore the possible causes of this discrepancy through the acquisition of “high-precision” 206Pb/238U dating of zircons from 11 volcanic ash beds from the Umbria-Marche sedimentary succession, which hosts the Global Stratotype Section and Point for the base of the Oligocene. Our results indicate that the four 40Ar/39Ar dates from the Umbria-Marche succession, which underpin the late Eocene-Oligocene portion of the Paleogene geomagnetic polarity time scale in the 2012 edition of the Geological Time Scale, are anomalously old by up to 0.5 Myr. Conversely, when integrated with the established magnetic polarity record of the Umbria-Marche succession, 206Pb/238U (zircon) data from this study result in Oligocene magnetic reversal ages that are generally equivalent to those obtained through the tuning of Ocean Drilling Program (ODP) Site 1218 (equatorial Pacific). Furthermore, our results indicate that the late Eocene tuning of ODP Site 1218, and International Ocean Discovery Program (IODP) Sites U1333–1334 (equatorial Pacific), to the 405 kyr eccentricity signal is accurate, at least back to 36 Ma. Propagating the full uncertainty of our radio-isotopic data set and, where appropriate, taking into account locally derived astronomical time scales, we arrive at an age of 34.09 ± 0.08 Ma for the Eocene-Oligocene boundary and 28.11 ± 0.17 Ma for the base of the Chattian.
{"title":"Reducing Disparity in Radio-Isotopic and Astrochronology-Based Time Scales of the Late Eocene and Oligocene","authors":"D. Sahy, D. Condon, F. Hilgen, K. Kuiper","doi":"10.1002/2017PA003197","DOIUrl":"https://doi.org/10.1002/2017PA003197","url":null,"abstract":"A significant discrepancy of up to 0.6 Myr exists between radio-isotopically calibrated and astronomically tuned time scales of the late Eocene-Oligocene. We explore the possible causes of this discrepancy through the acquisition of “high-precision” 206Pb/238U dating of zircons from 11 volcanic ash beds from the Umbria-Marche sedimentary succession, which hosts the Global Stratotype Section and Point for the base of the Oligocene. Our results indicate that the four 40Ar/39Ar dates from the Umbria-Marche succession, which underpin the late Eocene-Oligocene portion of the Paleogene geomagnetic polarity time scale in the 2012 edition of the Geological Time Scale, are anomalously old by up to 0.5 Myr. Conversely, when integrated with the established magnetic polarity record of the Umbria-Marche succession, 206Pb/238U (zircon) data from this study result in Oligocene magnetic reversal ages that are generally equivalent to those obtained through the tuning of Ocean Drilling Program (ODP) Site 1218 (equatorial Pacific). Furthermore, our results indicate that the late Eocene tuning of ODP Site 1218, and International Ocean Discovery Program (IODP) Sites U1333–1334 (equatorial Pacific), to the 405 kyr eccentricity signal is accurate, at least back to 36 Ma. Propagating the full uncertainty of our radio-isotopic data set and, where appropriate, taking into account locally derived astronomical time scales, we arrive at an age of 34.09 ± 0.08 Ma for the Eocene-Oligocene boundary and 28.11 ± 0.17 Ma for the base of the Chattian.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"1018-1035"},"PeriodicalIF":0.0,"publicationDate":"2017-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003197","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46142607","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}
Changes in both silicate weathering rates and organic carbon burial have been proposed as drivers of the transient “Mi-1” glaciation event at the Oligocene-Miocene transition (OMT; ~23 Ma). However detailed geochemical proxy data are required to test these hypotheses. Here we present records of Li/Ca, Mg/Ca, Cd/Ca, U/Ca, δ18O, δ13C, and shell weight in planktonic foraminifera from marine sediments spanning the OMT in the equatorial Atlantic Ocean. Li/Ca values increase by 1 μmol/mol across this interval. We interpret this to indicate a ~20% increase in silicate weathering rates, which would have lowered atmospheric CO2, potentially forcing the Antarctic glaciation circa 23 Ma. δ13C of thermocline dwelling planktonic foraminifera track the global increase in seawater δ13C across the OMT and during the Mi-1 event, hence supporting a hypothesized global increase in organic carbon burial rates. High δ13C previously measured in epipelagic planktonic foraminifera and high Cd/Ca ratios during Mi-1 are interpreted to represent locally enhanced primary productivity, stimulated by increased nutrients supply to surface waters. The fingerprint of high export production and associated organic carbon burial at this site is found in reduced bottom water oxygenation (inferred from high foraminiferal U/Ca), and enhanced respiratory dissolution of carbonates, characterised by reduced foraminiferal shell weight. Replication of our results elsewhere would strengthen the case that weathering-induced CO2 sequestration preconditioned climate for Antarctic ice sheet growth across the OMT and increased burial of organic carbon acted as a feedback that intensified cooling at this time.
{"title":"Silicate weathering and carbon cycle controls on the Oligocene-Miocene transition glaciation","authors":"J. Stewart, R. James, P. Anand, P. Wilson","doi":"10.1002/2017PA003115","DOIUrl":"https://doi.org/10.1002/2017PA003115","url":null,"abstract":"Changes in both silicate weathering rates and organic carbon burial have been proposed as drivers of the transient “Mi-1” glaciation event at the Oligocene-Miocene transition (OMT; ~23 Ma). However detailed geochemical proxy data are required to test these hypotheses. Here we present records of Li/Ca, Mg/Ca, Cd/Ca, U/Ca, δ18O, δ13C, and shell weight in planktonic foraminifera from marine sediments spanning the OMT in the equatorial Atlantic Ocean. Li/Ca values increase by 1 μmol/mol across this interval. We interpret this to indicate a ~20% increase in silicate weathering rates, which would have lowered atmospheric CO2, potentially forcing the Antarctic glaciation circa 23 Ma. δ13C of thermocline dwelling planktonic foraminifera track the global increase in seawater δ13C across the OMT and during the Mi-1 event, hence supporting a hypothesized global increase in organic carbon burial rates. High δ13C previously measured in epipelagic planktonic foraminifera and high Cd/Ca ratios during Mi-1 are interpreted to represent locally enhanced primary productivity, stimulated by increased nutrients supply to surface waters. The fingerprint of high export production and associated organic carbon burial at this site is found in reduced bottom water oxygenation (inferred from high foraminiferal U/Ca), and enhanced respiratory dissolution of carbonates, characterised by reduced foraminiferal shell weight. Replication of our results elsewhere would strengthen the case that weathering-induced CO2 sequestration preconditioned climate for Antarctic ice sheet growth across the OMT and increased burial of organic carbon acted as a feedback that intensified cooling at this time.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"1070-1085"},"PeriodicalIF":0.0,"publicationDate":"2017-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003115","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48481941","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}
Enhanced vertical gradients in benthic foraminiferal δ13C and δ18O in the Atlantic and Pacific during the last glaciation have revealed that ocean overturning circulation was characterized by shoaling of North-Atlantic sourced interior waters; nonetheless our understanding of the specific mechanisms driving these glacial isotope patterns remains incomplete. Here we compare high-resolution depth transects of Cibicidoides spp. δ13C and δ18O from the Southwest Pacific and the Southwest Atlantic to examine relative changes in northern and southern sourced deep waters during the Last Glacial Maximum (LGM) and deglaciation. During the LGM, our transects show that water mass properties and boundaries in the South Atlantic and Pacific were different from one another. The Atlantic between ~1.0 and 2.5 km was more than 1 ‰ enriched in δ13C relative to the Pacific and remained more enriched through the deglaciation. During the LGM, Atlantic δ18O was ~ 0.5 ‰ more enriched than the Pacific, particularly below 2.5 km. This compositional difference between the deep portions of the basins implies independent deep water sources during the glaciation. We attribute these changes to a ‘deep gateway’ effect whereby northern sourced waters shallower than the Drake Passage sill were unable to flow southward into the Southern Ocean because a net meridional geostrophic transport cannot be supported in the absence of a net east-west circumpolar pressure gradient above the sill depth. We surmise that through the LGM and early deglaciation, shoaled northern-sourced waters were unable to escape the Atlantic and contribute to deep water formation in the Southern Ocean.
{"title":"Enhanced δ13C and δ18O Differences Between the South Atlantic and South Pacific During the Last Glaciation: The Deep Gateway Hypothesis","authors":"E. Sikes, K. Allen, D. Lund","doi":"10.1002/2017PA003118","DOIUrl":"https://doi.org/10.1002/2017PA003118","url":null,"abstract":"Enhanced vertical gradients in benthic foraminiferal δ13C and δ18O in the Atlantic and Pacific during the last glaciation have revealed that ocean overturning circulation was characterized by shoaling of North-Atlantic sourced interior waters; nonetheless our understanding of the specific mechanisms driving these glacial isotope patterns remains incomplete. Here we compare high-resolution depth transects of Cibicidoides spp. δ13C and δ18O from the Southwest Pacific and the Southwest Atlantic to examine relative changes in northern and southern sourced deep waters during the Last Glacial Maximum (LGM) and deglaciation. During the LGM, our transects show that water mass properties and boundaries in the South Atlantic and Pacific were different from one another. The Atlantic between ~1.0 and 2.5 km was more than 1 ‰ enriched in δ13C relative to the Pacific and remained more enriched through the deglaciation. During the LGM, Atlantic δ18O was ~ 0.5 ‰ more enriched than the Pacific, particularly below 2.5 km. This compositional difference between the deep portions of the basins implies independent deep water sources during the glaciation. We attribute these changes to a ‘deep gateway’ effect whereby northern sourced waters shallower than the Drake Passage sill were unable to flow southward into the Southern Ocean because a net meridional geostrophic transport cannot be supported in the absence of a net east-west circumpolar pressure gradient above the sill depth. We surmise that through the LGM and early deglaciation, shoaled northern-sourced waters were unable to escape the Atlantic and contribute to deep water formation in the Southern Ocean.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"1000-1017"},"PeriodicalIF":0.0,"publicationDate":"2017-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003118","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41626087","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}
I. Niezgodzki, G. Knorr, G. Lohmann, J. Tyszka, P. Markwick
We investigate the impact of different CO2 levels and different subarctic gateway configurations on the surface temperatures during the latest Cretaceous using the Earth System Model COSMOS. The simulated temperatures are compared with the surface temperature reconstructions based on a recent compilation of the latest Cretaceous proxies. In our numerical experiments, the CO2 level ranges from 1 to 6 times the preindustrial (PI) CO2 level of 280 ppm. On a global scale, the most reasonable match between modeling and proxy data is obtained for the experiments with 3 to 5 × PI CO2 concentrations. However, the simulated low- (high-) latitude temperatures are too high (low) as compared to the proxy data. The moderate CO2 levels scenarios might be more realistic, if we take into account proxy data and the dead zone effect criterion. Furthermore, we test if the model-data discrepancies can be caused by too simplistic proxy-data interpretations. This is distinctly seen at high latitudes, where most proxies are biased toward summer temperatures. Additional sensitivity experiments with different ocean gateway configurations and constant CO2 level indicate only minor surface temperatures changes (<~1°C) on a global scale, with higher values (up to ~8°C) on a regional scale. These findings imply that modeled and reconstructed temperature gradients are to a large degree only qualitatively comparable, providing challenges for the interpretation of proxy data and/or model sensitivity. With respect to the latter, our results suggest that an assessment of greenhouse worlds is best constrained by temperatures in the midlatitudes.
{"title":"Late Cretaceous climate simulations with different CO2 levels and subarctic gateway configurations: A model-data comparison","authors":"I. Niezgodzki, G. Knorr, G. Lohmann, J. Tyszka, P. Markwick","doi":"10.1002/2016PA003055","DOIUrl":"https://doi.org/10.1002/2016PA003055","url":null,"abstract":"We investigate the impact of different CO2 levels and different subarctic gateway configurations on the surface temperatures during the latest Cretaceous using the Earth System Model COSMOS. The simulated temperatures are compared with the surface temperature reconstructions based on a recent compilation of the latest Cretaceous proxies. In our numerical experiments, the CO2 level ranges from 1 to 6 times the preindustrial (PI) CO2 level of 280 ppm. On a global scale, the most reasonable match between modeling and proxy data is obtained for the experiments with 3 to 5 × PI CO2 concentrations. However, the simulated low- (high-) latitude temperatures are too high (low) as compared to the proxy data. The moderate CO2 levels scenarios might be more realistic, if we take into account proxy data and the dead zone effect criterion. Furthermore, we test if the model-data discrepancies can be caused by too simplistic proxy-data interpretations. This is distinctly seen at high latitudes, where most proxies are biased toward summer temperatures. Additional sensitivity experiments with different ocean gateway configurations and constant CO2 level indicate only minor surface temperatures changes (<~1°C) on a global scale, with higher values (up to ~8°C) on a regional scale. These findings imply that modeled and reconstructed temperature gradients are to a large degree only qualitatively comparable, providing challenges for the interpretation of proxy data and/or model sensitivity. With respect to the latter, our results suggest that an assessment of greenhouse worlds is best constrained by temperatures in the midlatitudes.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"980-998"},"PeriodicalIF":0.0,"publicationDate":"2017-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003055","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43856971","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}
I. Voigt, A. P. Cruz, S. Mulitza, C. Chiessi, A. Mackensen, J. Lippold, Benny Antz, M. Zabel, Yancheng Zhang, C. Barbosa, A. Tisserand
Negative stable carbon isotopic excursions have been observed throughout most of the mid-depth (~1000–3000 m) Atlantic Ocean during Heinrich Stadial 1 (HS1) and the Younger Dryas (YD). Although there is an agreement that these mid-depth excursions were in some way associated with a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), there is still no consensus on the precise mechanism(s). Here we present benthic stable carbon and oxygen isotopic (δ13C and δ18O) records from five cores from the western equatorial Atlantic (WEA). Together with published benthic isotopic records from nearby cores, we produced a WEA depth transect (~800–2500 m). We compare HS1 and YD data from this transect with data from previously published North and South Atlantic cores and demonstrate that the largest negative δ13C excursions occurred in the WEA during these times. Moreover, our benthic δ18O records require the presence of two water masses flowing from the Southern Ocean, bisected by a Northern Component Water (NCW). Given that δ18O is a conservative water mass tracer, we suggest that δ13C was decoupled from water mass composition and does not correspond to simple alternations between northern and southern sourced waters. Instead, δ13C behaved non-conservatively during HS1 and the YD. Consistently with our new 231Pa/230Th record from the WEA transect, that allowed the reconstruction of AMOC strength, we hypothesize that the negative δ13C excursions reflect an increase in the residence time of NCW in response to a weakened AMOC, allowing for a marked accumulation of 13C-depleted respired carbon at the mid-depth WEA.
{"title":"Variability in mid‐depth ventilation of the western Atlantic Ocean during the last deglaciation","authors":"I. Voigt, A. P. Cruz, S. Mulitza, C. Chiessi, A. Mackensen, J. Lippold, Benny Antz, M. Zabel, Yancheng Zhang, C. Barbosa, A. Tisserand","doi":"10.1002/2017PA003095","DOIUrl":"https://doi.org/10.1002/2017PA003095","url":null,"abstract":"Negative stable carbon isotopic excursions have been observed throughout most of the mid-depth (~1000–3000 m) Atlantic Ocean during Heinrich Stadial 1 (HS1) and the Younger Dryas (YD). Although there is an agreement that these mid-depth excursions were in some way associated with a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), there is still no consensus on the precise mechanism(s). Here we present benthic stable carbon and oxygen isotopic (δ13C and δ18O) records from five cores from the western equatorial Atlantic (WEA). Together with published benthic isotopic records from nearby cores, we produced a WEA depth transect (~800–2500 m). We compare HS1 and YD data from this transect with data from previously published North and South Atlantic cores and demonstrate that the largest negative δ13C excursions occurred in the WEA during these times. Moreover, our benthic δ18O records require the presence of two water masses flowing from the Southern Ocean, bisected by a Northern Component Water (NCW). Given that δ18O is a conservative water mass tracer, we suggest that δ13C was decoupled from water mass composition and does not correspond to simple alternations between northern and southern sourced waters. Instead, δ13C behaved non-conservatively during HS1 and the YD. Consistently with our new 231Pa/230Th record from the WEA transect, that allowed the reconstruction of AMOC strength, we hypothesize that the negative δ13C excursions reflect an increase in the residence time of NCW in response to a weakened AMOC, allowing for a marked accumulation of 13C-depleted respired carbon at the mid-depth WEA.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"948-965"},"PeriodicalIF":0.0,"publicationDate":"2017-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003095","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48004293","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}
G. S. Marks, M. LaVigne, T. Hill, W. Sauthoff, T. Guilderson, E. Roark, R. Dunbar, T. Horner
Trace elemental ratios preserved in the calcitic skeleton of bamboo corals have been shown to serve as archives of past ocean conditions. The concentration of dissolved barium (BaSW), a bioactive nutrientlike element, is linked to biogeochemical processes such as the cycling and export of nutrients. Recent work has calibrated bamboo coral Ba/Ca, a new BaSW proxy, using corals spanning the oxygen minimum zone beneath the California Current System. However, it was previously unclear whether Ba/Cacoral records were internally reproducible. Here we investigate the accuracy of using laser ablation inductively coupled plasma mass spectrometry for Ba/Cacoral analyses and test the internal reproducibility of Ba/Ca among replicate radial transects in the calcite of nine bamboo corals collected from the Gulf of Alaska (643–720 m) and the California margin (870–2054 m). Data from replicate Ba/Ca transects were aligned using visible growth bands to account for nonconcentric growth; smoothed data were reproducible within ~4% for eight corals (n = 3 radii/coral). This intracoral reproducibility further validates using bamboo coral Ba/Ca for BaSW reconstructions. Sections of the Ba/Ca records that were potentially influenced by noncarbonate bound Ba phases occurred in regions where elevated Mg/Ca or Pb/Ca and coincided with anomalous regions on photomicrographs. After removing these regions of the records, increased Ba/Cacoral variability was evident in corals between ~800 and 1500 m. These findings support additional proxy validation to understand BaSW variability on interannual timescales, which could lead to new insights into deep sea biogeochemistry over the past several centuries.
{"title":"Reproducibility of Ba/Ca variations recorded by northeast Pacific bamboo corals","authors":"G. S. Marks, M. LaVigne, T. Hill, W. Sauthoff, T. Guilderson, E. Roark, R. Dunbar, T. Horner","doi":"10.1002/2017PA003178","DOIUrl":"https://doi.org/10.1002/2017PA003178","url":null,"abstract":"Trace elemental ratios preserved in the calcitic skeleton of bamboo corals have been shown to serve as archives of past ocean conditions. The concentration of dissolved barium (BaSW), a bioactive nutrientlike element, is linked to biogeochemical processes such as the cycling and export of nutrients. Recent work has calibrated bamboo coral Ba/Ca, a new BaSW proxy, using corals spanning the oxygen minimum zone beneath the California Current System. However, it was previously unclear whether Ba/Cacoral records were internally reproducible. Here we investigate the accuracy of using laser ablation inductively coupled plasma mass spectrometry for Ba/Cacoral analyses and test the internal reproducibility of Ba/Ca among replicate radial transects in the calcite of nine bamboo corals collected from the Gulf of Alaska (643–720 m) and the California margin (870–2054 m). Data from replicate Ba/Ca transects were aligned using visible growth bands to account for nonconcentric growth; smoothed data were reproducible within ~4% for eight corals (n = 3 radii/coral). This intracoral reproducibility further validates using bamboo coral Ba/Ca for BaSW reconstructions. Sections of the Ba/Ca records that were potentially influenced by noncarbonate bound Ba phases occurred in regions where elevated Mg/Ca or Pb/Ca and coincided with anomalous regions on photomicrographs. After removing these regions of the records, increased Ba/Cacoral variability was evident in corals between ~800 and 1500 m. These findings support additional proxy validation to understand BaSW variability on interannual timescales, which could lead to new insights into deep sea biogeochemistry over the past several centuries.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"966-979"},"PeriodicalIF":0.0,"publicationDate":"2017-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003178","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48731236","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}
M. Saavedra‐Pellitero, K. Baumann, F. Lamy, P. Köhler
Proxy-based reconstructions of past changes in the marine biological carbon pumps are limited, especially in the Southern Ocean. This work provides new insights into the productivity variations in the Pacific sector of the Southern Ocean. We present new data derived from three sediment cores that show glacial/interglacial coccolithophore variability across Marine Isotope Stage 11 (MIS 11). The cores were retrieved during R/V Polarstern cruise PS75 from the Subantarctic Zone and Polar Front Zone at the western flank of the East Pacific Rise and in the vicinity of the Antarctic-Pacific Ridge. Coccolithophore assemblages were overwhelmingly dominated by the species Gephyrocapsa caribbeanica and small Gephyrocapsa. Total numbers of coccoliths, coccolith accumulation rates, coccolith fraction (CF; <20 μm fraction) Sr/Ca data, and temperature-corrected CF Sr/Ca records consistently showed an increase in coccolithophore productivity during Termination V (MIS 12-11 boundary), highest productivity throughout MIS 11 (~424–374 kyr), and a decrease during late MIS 11 in all the cores. We end with a discussion of back-calculated coccolith calcification rate in the surface ocean and its potential contribution to changes in the concentration of atmospheric CO2.
基于代理的海洋生物碳泵过去变化的重建是有限的，特别是在南大洋。这项工作为南大洋太平洋部分的生产力变化提供了新的见解。我们提出了来自三个沉积物岩心的新数据，这些数据显示了海洋同位素阶段11 (MIS 11)的冰期/间冰期球石团变化。这些岩心是在R/V北极星巡航PS75期间从东太平洋隆起西侧和南极-太平洋脊附近的亚南极区和极锋区回收的。球石藻组合中以加勒比海Gephyrocapsa和小Gephyrocapsa占绝对优势。球粒总数、球粒积累速率、球粒分数(CF;<20 μm分数)Sr/Ca数据和温度校正的CF Sr/Ca记录一致表明，在终止V (MIS 12-11边界)，所有岩心的球石藻生产力均有所增加，在整个MIS 11期间(~ 424-374 kyr)生产力最高，而在MIS 11后期，所有岩心的球石藻生产力均有所下降。最后，我们讨论了海洋表面回溯计算的球粒钙化率及其对大气CO2浓度变化的潜在贡献。
{"title":"Coccolithophore variability across Marine Isotope Stage 11 in the Pacific sector of the Southern Ocean and its potential impact on the carbon cycle","authors":"M. Saavedra‐Pellitero, K. Baumann, F. Lamy, P. Köhler","doi":"10.1002/2017PA003156","DOIUrl":"https://doi.org/10.1002/2017PA003156","url":null,"abstract":"Proxy-based reconstructions of past changes in the marine biological carbon pumps are limited, especially in the Southern Ocean. This work provides new insights into the productivity variations in the Pacific sector of the Southern Ocean. We present new data derived from three sediment cores that show glacial/interglacial coccolithophore variability across Marine Isotope Stage 11 (MIS 11). The cores were retrieved during R/V Polarstern cruise PS75 from the Subantarctic Zone and Polar Front Zone at the western flank of the East Pacific Rise and in the vicinity of the Antarctic-Pacific Ridge. Coccolithophore assemblages were overwhelmingly dominated by the species Gephyrocapsa caribbeanica and small Gephyrocapsa. Total numbers of coccoliths, coccolith accumulation rates, coccolith fraction (CF; <20 μm fraction) Sr/Ca data, and temperature-corrected CF Sr/Ca records consistently showed an increase in coccolithophore productivity during Termination V (MIS 12-11 boundary), highest productivity throughout MIS 11 (~424–374 kyr), and a decrease during late MIS 11 in all the cores. We end with a discussion of back-calculated coccolith calcification rate in the surface ocean and its potential contribution to changes in the concentration of atmospheric CO2.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"864-880"},"PeriodicalIF":0.0,"publicationDate":"2017-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003156","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42093245","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. Prebble, H. Bostock, G. Cortese, A. Lorrey, B. Hayward, E. Calvo, L. Northcote, G. H. Scott, H. Neil
The early Holocene sea surface temperature (SST) gradient across the subtropical front (STF) to the east of New Zealand was ~2°C (measured between core sites MD97-2121 and MD97-2120): considerably less than the ~6°C modern gradient between the two core sites. We document the surface ocean temperatures east and south of New Zealand during the early and middle Holocene, to test and expand upon this reconstruction. This new study samples a latitudinal transect of seven sediment cores from 37°S to 60°S in the southwest Pacific from subtropical waters north of New Zealand to polar waters in the Southern Ocean. Our compilation of SST proxies consists of 525 SST estimates from five different methods and includes 243 new data points. We confirm that an early Holocene warm peak in this region was mostly restricted to the area immediately south of the STF, which resulted in a lower temperature gradient across the STF than in modern times. However, there is no change in Holocene SST south of the polar front. Faunal assemblages suggest an early Holocene meridional expansion of fauna characteristic of the modern subtropical front in the Bounty Gyre. We suggest that such an expansion could be achieved by a reduced inflow of Subantarctic Surface Water into the Bounty Gyre. Results from a modern-analog matching platform called the Past Interpretation of Climate Tool (PICT) suggest that the early Holocene SST is most consistent with reduced westerly winds in the New Zealand sector of the Southern Ocean.
{"title":"Evidence for a Holocene Climatic Optimum in the southwest Pacific: A multiproxy study","authors":"J. Prebble, H. Bostock, G. Cortese, A. Lorrey, B. Hayward, E. Calvo, L. Northcote, G. H. Scott, H. Neil","doi":"10.1002/2016PA003065","DOIUrl":"https://doi.org/10.1002/2016PA003065","url":null,"abstract":"The early Holocene sea surface temperature (SST) gradient across the subtropical front (STF) to the east of New Zealand was ~2°C (measured between core sites MD97-2121 and MD97-2120): considerably less than the ~6°C modern gradient between the two core sites. We document the surface ocean temperatures east and south of New Zealand during the early and middle Holocene, to test and expand upon this reconstruction. This new study samples a latitudinal transect of seven sediment cores from 37°S to 60°S in the southwest Pacific from subtropical waters north of New Zealand to polar waters in the Southern Ocean. Our compilation of SST proxies consists of 525 SST estimates from five different methods and includes 243 new data points. We confirm that an early Holocene warm peak in this region was mostly restricted to the area immediately south of the STF, which resulted in a lower temperature gradient across the STF than in modern times. However, there is no change in Holocene SST south of the polar front. Faunal assemblages suggest an early Holocene meridional expansion of fauna characteristic of the modern subtropical front in the Bounty Gyre. We suggest that such an expansion could be achieved by a reduced inflow of Subantarctic Surface Water into the Bounty Gyre. Results from a modern-analog matching platform called the Past Interpretation of Climate Tool (PICT) suggest that the early Holocene SST is most consistent with reduced westerly winds in the New Zealand sector of the Southern Ocean.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"763-779"},"PeriodicalIF":0.0,"publicationDate":"2017-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003065","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48304051","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}
Carbon isotope minima were a ubiquitous feature of the mid-depth Atlantic during Heinrich Stadial 1 (HS1, 14.5-17.5 kyr BP) and the Younger Dryas (YD, 11.5-12.9 kyr BP) yet their cause remains unclear. Recent evidence indicates that North Atlantic processes triggered the δ13C anomalies, with weakening of the Atlantic Meridional Overturning Circulation (AMOC) being the most likely driver. Model simulations suggest slowing of the AMOC increases the residence time of mid-depth waters in the Atlantic, resulting in the accumulation of respired carbon. Here we assess ΣCO2 storage in the South Atlantic using benthic foraminiferal B/Ca, a proxy for [CO32-]. Using replicated high resolution B/Ca records from ~ 2 km water depth on the Brazil Margin, we show that [CO32-] decreased during HS1 and the YD, synchronous with apparent weakening of the AMOC. The [CO32-] response is smaller than in the tropical North Atlantic during HS1, indicating there was a north-south gradient in the [CO32-] signal similar to that for δ13C. The implied variability in ΣCO2 is consistent with model results, suggesting that carbon is temporarily sequestered in the mid-depth Atlantic during millennial-scale stadial events. Using a carbon isotope mass balance, we estimate that approximately 75% of the HS1 δ13C signal at the Brazil Margin was driven by accumulation of remineralized carbon, highlighting the non-conservative behavior of δ13C during the last deglaciation.
{"title":"Carbon storage in the mid-depth Atlantic during millennial-scale climate events","authors":"M. Lacerra, D. Lund, Jimin Yu, A. Schmittner","doi":"10.1002/2016PA003081","DOIUrl":"https://doi.org/10.1002/2016PA003081","url":null,"abstract":"Carbon isotope minima were a ubiquitous feature of the mid-depth Atlantic during Heinrich Stadial 1 (HS1, 14.5-17.5 kyr BP) and the Younger Dryas (YD, 11.5-12.9 kyr BP) yet their cause remains unclear. Recent evidence indicates that North Atlantic processes triggered the δ13C anomalies, with weakening of the Atlantic Meridional Overturning Circulation (AMOC) being the most likely driver. Model simulations suggest slowing of the AMOC increases the residence time of mid-depth waters in the Atlantic, resulting in the accumulation of respired carbon. Here we assess ΣCO2 storage in the South Atlantic using benthic foraminiferal B/Ca, a proxy for [CO32-]. Using replicated high resolution B/Ca records from ~ 2 km water depth on the Brazil Margin, we show that [CO32-] decreased during HS1 and the YD, synchronous with apparent weakening of the AMOC. The [CO32-] response is smaller than in the tropical North Atlantic during HS1, indicating there was a north-south gradient in the [CO32-] signal similar to that for δ13C. The implied variability in ΣCO2 is consistent with model results, suggesting that carbon is temporarily sequestered in the mid-depth Atlantic during millennial-scale stadial events. Using a carbon isotope mass balance, we estimate that approximately 75% of the HS1 δ13C signal at the Brazil Margin was driven by accumulation of remineralized carbon, highlighting the non-conservative behavior of δ13C during the last deglaciation.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"780-795"},"PeriodicalIF":0.0,"publicationDate":"2017-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003081","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44222723","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}
I. Hernández‐Almeida, G. Cortese, P. Yu, Min‐Te Chen, M. Kučera
{"title":"Environmental determinants of radiolarian assemblages in the western Pacific since the last deglaciation: New Regional Radiolaria Ecological Model","authors":"I. Hernández‐Almeida, G. Cortese, P. Yu, Min‐Te Chen, M. Kučera","doi":"10.1002/2017pa003159","DOIUrl":"https://doi.org/10.1002/2017pa003159","url":null,"abstract":"","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"830-847"},"PeriodicalIF":0.0,"publicationDate":"2017-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017pa003159","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48551959","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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