N. R. Mollica, A. L. Cohen, F. Horton, Delia W. Oppo, Andrew S. Solow, David McGee
Abstract Sr‐U, a coral‐based paleothermometer, corrects for the effects of Rayleigh Fractionation on Sr/Ca by regressing multiple, paired U/Ca and Sr/Ca values. Prior applications of Sr‐U captured mean annual sea surface temperatures (SSTs), inter‐annual variability, and long‐term trends. However, because many Sr/Ca‐U/Ca pairs are needed for a single Sr‐U value as originally formulated, the temporal resolution of the proxy is typically limited to 1 year. Here, we address this limitation by applying laser ablation inductively coupled plasma mass spectrometry (LA‐ICPMS) to three Porites colonies from Jarvis and Nikumaroro Islands in the central equatorial Pacific (CEP), generating ∼25 Sr/Ca‐U/Ca pairs per month of skeletal growth. Both Sr/Ca and U/Ca vary significantly over small (sub‐mm) length scales and support the calculation of Sr‐U values using the original regression method. Over the represented temperature range of 24–31°C, the Sr/Ca‐U/Ca‐SST relationships are nonlinear, a finding consistent with predictions of the Rayleigh model. To reflect this non‐linearity, we developed a calibration using multivariate nonlinear regression. The multivariate, three‐coral calibration was applied to 20 years of monthly resolved Sr/Ca and U/Ca of a coral interval not included in the calibration, yielding RMSE = 0.73°C and r 2 = 0.85 ( p < 0.05; df = 256). The multivariate calibration performed significantly better than Sr/Ca alone ( r 2 = 0.28). Applying the new calibration to a subfossil Porites from Kiritimati Atoll, CEP (2200 Before Present) yields equivalent phase and amplitude of interannual variability, but water temperatures ∼1.6°C cooler than they are in this region today.
{"title":"Capturing Equatorial Pacific Variability with Multivariate Sr‐U Coral Thermometry","authors":"N. R. Mollica, A. L. Cohen, F. Horton, Delia W. Oppo, Andrew S. Solow, David McGee","doi":"10.1029/2022pa004508","DOIUrl":"https://doi.org/10.1029/2022pa004508","url":null,"abstract":"Abstract Sr‐U, a coral‐based paleothermometer, corrects for the effects of Rayleigh Fractionation on Sr/Ca by regressing multiple, paired U/Ca and Sr/Ca values. Prior applications of Sr‐U captured mean annual sea surface temperatures (SSTs), inter‐annual variability, and long‐term trends. However, because many Sr/Ca‐U/Ca pairs are needed for a single Sr‐U value as originally formulated, the temporal resolution of the proxy is typically limited to 1 year. Here, we address this limitation by applying laser ablation inductively coupled plasma mass spectrometry (LA‐ICPMS) to three Porites colonies from Jarvis and Nikumaroro Islands in the central equatorial Pacific (CEP), generating ∼25 Sr/Ca‐U/Ca pairs per month of skeletal growth. Both Sr/Ca and U/Ca vary significantly over small (sub‐mm) length scales and support the calculation of Sr‐U values using the original regression method. Over the represented temperature range of 24–31°C, the Sr/Ca‐U/Ca‐SST relationships are nonlinear, a finding consistent with predictions of the Rayleigh model. To reflect this non‐linearity, we developed a calibration using multivariate nonlinear regression. The multivariate, three‐coral calibration was applied to 20 years of monthly resolved Sr/Ca and U/Ca of a coral interval not included in the calibration, yielding RMSE = 0.73°C and r 2 = 0.85 ( p < 0.05; df = 256). The multivariate calibration performed significantly better than Sr/Ca alone ( r 2 = 0.28). Applying the new calibration to a subfossil Porites from Kiritimati Atoll, CEP (2200 Before Present) yields equivalent phase and amplitude of interannual variability, but water temperatures ∼1.6°C cooler than they are in this region today.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135324812","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Planktic foraminiferal‐based trace element‐calcium ratios (TE/Ca) are a cornerstone in paleoceanographic reconstructions. While TE‐environment calibrations are often established through culturing experiments, shell growth in culture is not always consistent with growth in a natural setting. For example, many species of planktic foraminifera thicken their shell at the end of their life cycle, producing a distinct “gametogenic” crust. Crust is common in fossil foraminifers, however, shells grown in culture do not often develop a thick crust. Here, we investigate potential vital effects associated with the crusting process by comparing the trace element (Mg/Ca, Na/Ca, Ba/Ca, Sr/Ca, Mn/Ca, Zn/Ca) and stable isotope (δ13C, δ18O) composition of alive, fully mature, uncrusted shells to recently deceased, crusted shells of Neogloboquadrina pachyderma collected from the same plankton tows off the Oregon (USA) coast. We find that uncrusted (N = 55) shells yield significantly higher Ba/Ca, Na/Ca, Mn/Ca, and Sr/Ca than crusted (N = 66) shells, and crust calcite records significantly lower TE/Ca values for all elements examined. Isotopic mixing models suggest that the crust calcite accounts for ∼40%–70% of crusted shell volume. Comparison of foraminiferal and seawater isotopes indicate that N. pachyderma lives in the upper 90 m of the water column, and that crust formation occurs slightly deeper than their average living depth habitat. Results highlight the necessity to establish calibrations from crusted shells, as application of calibrations from TE‐enriched uncrusted shells may yield attenuated or misleading paleoceanographic reconstructions.
{"title":"Geochemical differences between alive, uncrusted and dead, crusted shells of <i>Neogloboquadrina pachyderma</i>: Implications for paleoreconstruction","authors":"Brittany N. Hupp, Jennifer S. Fehrenbacher","doi":"10.1029/2023pa004638","DOIUrl":"https://doi.org/10.1029/2023pa004638","url":null,"abstract":"Planktic foraminiferal‐based trace element‐calcium ratios (TE/Ca) are a cornerstone in paleoceanographic reconstructions. While TE‐environment calibrations are often established through culturing experiments, shell growth in culture is not always consistent with growth in a natural setting. For example, many species of planktic foraminifera thicken their shell at the end of their life cycle, producing a distinct “gametogenic” crust. Crust is common in fossil foraminifers, however, shells grown in culture do not often develop a thick crust. Here, we investigate potential vital effects associated with the crusting process by comparing the trace element (Mg/Ca, Na/Ca, Ba/Ca, Sr/Ca, Mn/Ca, Zn/Ca) and stable isotope (δ13C, δ18O) composition of alive, fully mature, uncrusted shells to recently deceased, crusted shells of Neogloboquadrina pachyderma collected from the same plankton tows off the Oregon (USA) coast. We find that uncrusted (N = 55) shells yield significantly higher Ba/Ca, Na/Ca, Mn/Ca, and Sr/Ca than crusted (N = 66) shells, and crust calcite records significantly lower TE/Ca values for all elements examined. Isotopic mixing models suggest that the crust calcite accounts for ∼40%–70% of crusted shell volume. Comparison of foraminiferal and seawater isotopes indicate that N. pachyderma lives in the upper 90 m of the water column, and that crust formation occurs slightly deeper than their average living depth habitat. Results highlight the necessity to establish calibrations from crusted shells, as application of calibrations from TE‐enriched uncrusted shells may yield attenuated or misleading paleoceanographic reconstructions.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135369371","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ashly B. Padgett, Ethan G. Hyland, Christopher K. West, Landon K. Burgener, David R. Greenwood, James F. Basinger
Abstract Ancient greenhouse periods are useful analogs for predicting effects of anthropogenic climate change on regional and global temperature and precipitation patterns. A paucity of terrestrial data from polar regions during warm episodes challenges our understanding of polar climate responses to natural/anthropogenic change and therefore our ability to predict future changes in precipitation. Ellesmere and Axel Heiberg Islands in the Canadian Arctic preserve terrestrial deposits spanning the late Paleocene to middle Eocene (59–45 Ma). Here we expand on existing regional sedimentology and paleontology through the addition of stable (δ 13 C, δ 18 O) and clumped (Δ 47 ) isotope analyses on palustrine carbonates. δ 13 C isotope values range from −4.6 to +12.3‰ (VPDB), and δ 18 O isotope values range from −23.1 to −15.2‰ (VPDB). Both carbon and oxygen isotope averages decrease with increasing diagenetic alteration. Unusually enriched carbon isotope (δ 13 C) values suggest that analyzed carbonates experienced repeated dissolution‐precipitation enrichment cycles, potentially caused by seasonal fluctuations in water availability resulting in summer carbonate dissolution followed by winter carbonate re‐precipitation. Stable isotopes suggest some degree of precipitation seasonality or reduction in winter water availability in the Canadian Arctic during the Paleogene. Clumped (Δ 47 ) temperature estimates range from 52 to 121°C and indicate low temperature solid‐state reordering of micritic samples and diagenetic recrystallization in sparry samples. Average temperatures agree with vitrinite reflectance data for Eureka Sound Group and underlying sediments, highlighting structural complexity across the region. Broadly, combined stable and clumped isotope data from carbonates in complex systems are effective for describing both paleoclimatic and post‐burial conditions.
{"title":"Paleogene Paleohydrology of Ellesmere and Axel Heiberg Islands (Arctic Canada) From Palustrine Carbonates","authors":"Ashly B. Padgett, Ethan G. Hyland, Christopher K. West, Landon K. Burgener, David R. Greenwood, James F. Basinger","doi":"10.1029/2023pa004609","DOIUrl":"https://doi.org/10.1029/2023pa004609","url":null,"abstract":"Abstract Ancient greenhouse periods are useful analogs for predicting effects of anthropogenic climate change on regional and global temperature and precipitation patterns. A paucity of terrestrial data from polar regions during warm episodes challenges our understanding of polar climate responses to natural/anthropogenic change and therefore our ability to predict future changes in precipitation. Ellesmere and Axel Heiberg Islands in the Canadian Arctic preserve terrestrial deposits spanning the late Paleocene to middle Eocene (59–45 Ma). Here we expand on existing regional sedimentology and paleontology through the addition of stable (δ 13 C, δ 18 O) and clumped (Δ 47 ) isotope analyses on palustrine carbonates. δ 13 C isotope values range from −4.6 to +12.3‰ (VPDB), and δ 18 O isotope values range from −23.1 to −15.2‰ (VPDB). Both carbon and oxygen isotope averages decrease with increasing diagenetic alteration. Unusually enriched carbon isotope (δ 13 C) values suggest that analyzed carbonates experienced repeated dissolution‐precipitation enrichment cycles, potentially caused by seasonal fluctuations in water availability resulting in summer carbonate dissolution followed by winter carbonate re‐precipitation. Stable isotopes suggest some degree of precipitation seasonality or reduction in winter water availability in the Canadian Arctic during the Paleogene. Clumped (Δ 47 ) temperature estimates range from 52 to 121°C and indicate low temperature solid‐state reordering of micritic samples and diagenetic recrystallization in sparry samples. Average temperatures agree with vitrinite reflectance data for Eureka Sound Group and underlying sediments, highlighting structural complexity across the region. Broadly, combined stable and clumped isotope data from carbonates in complex systems are effective for describing both paleoclimatic and post‐burial conditions.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135762946","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Laura L. Haynes, Bärbel Hönisch, Kate Holland, Stephen Eggins, Yair Rosenthal
Abstract Foraminiferal Mg/Ca has proven to be a powerful paleothermometer for reconstructing past sea‐surface temperature, which, among other applications, is a critical parameter for boron isotope reconstructions of past surface ocean pH and PCO 2 . However, recent laboratory culture studies indicate seawater pH and the total dissolved inorganic carbon content (DIC) may both exert a significant additional control on foraminiferal Mg/Ca, likely influencing paleotemperature records as a result of seawater chemistry evolution on geologic timescales. In addition, the seawater Mg/Ca composition (Mg/Ca sw ) has been shown to reduce the sensitivity of foraminiferal Mg/Ca to temperature and possibly its sensitivity to the carbonate system as well. Here we present new Mg/Ca data from laboratory culture experiments with living planktic foraminifera— Globigerinoides ruber (p), Trilobatus sacculifer , and Orbulina universa — grown under a range of different pH and/or seawater DIC conditions and in low Mg/Ca sw to mimic the chemical composition of the Paleocene ocean. We also conducted targeted [Ca] experiments to help define Mg/Ca calcite –Mg/Ca sw relationships for each species and conducted new pH experiments with G . bulloides . We find that pH effects on foraminiferal Mg/Ca are reduced or absent at Mg/Ca sw = 1.5 mol/mol in all three species, and that T . sacculifer is generally insensitive to variable DIC and pH, making it the ideal species for Mg/Ca SST reconstructions back to 20 Ma. We apply our new T . sacculifer calibration to a Middle Miocene Mg/Ca record and provide recommendations for interpreting Mg/Ca records from extinct species.
{"title":"Calibrating Non‐Thermal Effects on Planktic Foraminiferal Mg/Ca for Application Across the Cenozoic","authors":"Laura L. Haynes, Bärbel Hönisch, Kate Holland, Stephen Eggins, Yair Rosenthal","doi":"10.1029/2023pa004613","DOIUrl":"https://doi.org/10.1029/2023pa004613","url":null,"abstract":"Abstract Foraminiferal Mg/Ca has proven to be a powerful paleothermometer for reconstructing past sea‐surface temperature, which, among other applications, is a critical parameter for boron isotope reconstructions of past surface ocean pH and PCO 2 . However, recent laboratory culture studies indicate seawater pH and the total dissolved inorganic carbon content (DIC) may both exert a significant additional control on foraminiferal Mg/Ca, likely influencing paleotemperature records as a result of seawater chemistry evolution on geologic timescales. In addition, the seawater Mg/Ca composition (Mg/Ca sw ) has been shown to reduce the sensitivity of foraminiferal Mg/Ca to temperature and possibly its sensitivity to the carbonate system as well. Here we present new Mg/Ca data from laboratory culture experiments with living planktic foraminifera— Globigerinoides ruber (p), Trilobatus sacculifer , and Orbulina universa — grown under a range of different pH and/or seawater DIC conditions and in low Mg/Ca sw to mimic the chemical composition of the Paleocene ocean. We also conducted targeted [Ca] experiments to help define Mg/Ca calcite –Mg/Ca sw relationships for each species and conducted new pH experiments with G . bulloides . We find that pH effects on foraminiferal Mg/Ca are reduced or absent at Mg/Ca sw = 1.5 mol/mol in all three species, and that T . sacculifer is generally insensitive to variable DIC and pH, making it the ideal species for Mg/Ca SST reconstructions back to 20 Ma. We apply our new T . sacculifer calibration to a Middle Miocene Mg/Ca record and provide recommendations for interpreting Mg/Ca records from extinct species.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135274781","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Y. Zhang, T. Andrade, A. C. Ravelo, L. Gong, A. Holbourn, G. Connock, XL. Liu, I.W. Aiello
Abstract Studying tropical hydroclimate and productivity change in the past is critical for understanding global climate dynamics. Northwest Australia is an ideal location for investigating Australian monsoon dynamics, the variability of the Indonesian Throughflow (ITF), and their impact on past productivity and Pacific warm pool evolution, which remain poorly understood during the 40 kyr world in the mid‐early Pleistocene. In this study, we present multi‐proxy records from International Ocean Discovery Program (IODP) Site U1483 in the Timor Sea spanning the last 2,000 ka, including orbitally‐resolved records from the 40 kyr world between 2,000 and 1,300 ka. Our results suggest that northwest Australia underwent a step of increased aridification and that productivity in the Timor Sea declined during the transition from ∼1,700 to ∼1,400 ka. We attribute this aridification to the reduced moisture supply to this region caused by the ITF restriction and warm pool contraction. We ascribe the declined productivity to a decrease in the nutrient supply of the Pacific source water associated with global nutrient redistribution. At orbital timescale, multiple mechanisms, including sea level changes, monsoon, and the Intertropical Convergence Zone (ITCZ) dynamics, and variations in the ITF and Walker circulation could have controlled variations of productivity and terrigenous input in the Timor Sea during the 40 kyr world. Our bulk nitrogen and benthic carbon isotope records suggest a strong coupling to biogeochemical changes in the Pacific during this period. This research contributes to a better understanding of tropical hydroclimate and productivity changes during the 40 kyr world.
{"title":"Aridification of northwest Australia and nutrient decline in the Timor Sea during the 40 kyr world","authors":"Y. Zhang, T. Andrade, A. C. Ravelo, L. Gong, A. Holbourn, G. Connock, XL. Liu, I.W. Aiello","doi":"10.1029/2023pa004683","DOIUrl":"https://doi.org/10.1029/2023pa004683","url":null,"abstract":"Abstract Studying tropical hydroclimate and productivity change in the past is critical for understanding global climate dynamics. Northwest Australia is an ideal location for investigating Australian monsoon dynamics, the variability of the Indonesian Throughflow (ITF), and their impact on past productivity and Pacific warm pool evolution, which remain poorly understood during the 40 kyr world in the mid‐early Pleistocene. In this study, we present multi‐proxy records from International Ocean Discovery Program (IODP) Site U1483 in the Timor Sea spanning the last 2,000 ka, including orbitally‐resolved records from the 40 kyr world between 2,000 and 1,300 ka. Our results suggest that northwest Australia underwent a step of increased aridification and that productivity in the Timor Sea declined during the transition from ∼1,700 to ∼1,400 ka. We attribute this aridification to the reduced moisture supply to this region caused by the ITF restriction and warm pool contraction. We ascribe the declined productivity to a decrease in the nutrient supply of the Pacific source water associated with global nutrient redistribution. At orbital timescale, multiple mechanisms, including sea level changes, monsoon, and the Intertropical Convergence Zone (ITCZ) dynamics, and variations in the ITF and Walker circulation could have controlled variations of productivity and terrigenous input in the Timor Sea during the 40 kyr world. Our bulk nitrogen and benthic carbon isotope records suggest a strong coupling to biogeochemical changes in the Pacific during this period. This research contributes to a better understanding of tropical hydroclimate and productivity changes during the 40 kyr world.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135132014","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xuan Ding, Franck Bassinot, Xiaolei Pang, Yingxin Kou, Liping Zhou
As the only low‐latitude connection along the return branch of the Great Conveyor Belt, the Indonesian Throughflow (ITF) plays an important role in the large‐scale ocean–atmosphere interaction in the tropical region. However, the heat transport processes of the ITF along the outflow pathway in the eastern Indian Ocean over the recent geologic period is still debated. In this study, by using Mg/Ca ratios of the surface‐dwelling and thermocline‐dwelling planktonic foraminifera Globigerinoides ruber and Pulleniatina obliquiloculata, we reconstruct surface and thermocline water temperatures and thermocline structure at two sites in the main outflow path of the ITF in the eastern Indian Ocean for the last 160 kyr, and compare these new data with those from two cores in the central Indo‐Pacific Warm Pool. Our results show that, on the orbital time scale, the thermocline structure changes above the equatorial 90°E Ridge mimic those of the eastern Timor Sea, indicating that the ITF vertical structure remained unchanged during its penetration into the Indian Ocean. The thermocline water temperature in the equatorial western Pacific and eastern Indian Ocean presents similar change trend, suggesting that ITF is likely to be an important route for thermocline water transport into the Indian Ocean. However, the vertical structure of the ITF varied through time, reflecting the effects of sea level and orbitally‐driven monsoonal activity. This impacted heat transport processes, resulting in changes in the surface water temperature along the outflow pathway in the eastern Indian Ocean.This article is protected by copyright. All rights reserved.
{"title":"Heat transport processes of the Indonesian Throughflow along the outflow pathway in the eastern Indian Ocean during the last 160 kyr","authors":"Xuan Ding, Franck Bassinot, Xiaolei Pang, Yingxin Kou, Liping Zhou","doi":"10.1029/2023pa004620","DOIUrl":"https://doi.org/10.1029/2023pa004620","url":null,"abstract":"As the only low‐latitude connection along the return branch of the Great Conveyor Belt, the Indonesian Throughflow (ITF) plays an important role in the large‐scale ocean–atmosphere interaction in the tropical region. However, the heat transport processes of the ITF along the outflow pathway in the eastern Indian Ocean over the recent geologic period is still debated. In this study, by using Mg/Ca ratios of the surface‐dwelling and thermocline‐dwelling planktonic foraminifera Globigerinoides ruber and Pulleniatina obliquiloculata, we reconstruct surface and thermocline water temperatures and thermocline structure at two sites in the main outflow path of the ITF in the eastern Indian Ocean for the last 160 kyr, and compare these new data with those from two cores in the central Indo‐Pacific Warm Pool. Our results show that, on the orbital time scale, the thermocline structure changes above the equatorial 90°E Ridge mimic those of the eastern Timor Sea, indicating that the ITF vertical structure remained unchanged during its penetration into the Indian Ocean. The thermocline water temperature in the equatorial western Pacific and eastern Indian Ocean presents similar change trend, suggesting that ITF is likely to be an important route for thermocline water transport into the Indian Ocean. However, the vertical structure of the ITF varied through time, reflecting the effects of sea level and orbitally‐driven monsoonal activity. This impacted heat transport processes, resulting in changes in the surface water temperature along the outflow pathway in the eastern Indian Ocean.This article is protected by copyright. All rights reserved.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47946948","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
H. Kolling, Ralph Schneider, Felix Gross, C. Hamann, Markus Kienast, S. Kienast, K. Doering, K. Fahl, R. Stein
The ultimate demise of the Laurentide Ice Sheet (LIS) and the preceding and succeeding oceanographic changes along the western Labrador Sea offer insights critically important to improve climate predictions of expected future climate warming and further melting of the Greenland ice cap. However, while the final disappearance of the LIS during the Holocene is rather well constrained, the response of sea ice during the resulting meltwater events is not fully understood. Here, we present reconstructions of paleoceanographic changes over the past 9.3 Kyr BP on the northwestern Labrador Shelf, with a special focus on the interaction between the final meltwater event around 8.2 Kyr BP and sea ice and phytoplankton productivity (e.g., IP25, HBI III (Z), brassicasterol, dinosterol, biogenic opal, total organic carbon). Our records indicate low sea‐ice cover and high phytoplankton productivity on the Labrador Shelf prior to 8.9 Kyr BP, sea‐ice formation was favored by decreased surface salinities due to the meltwater events from Lake Agassiz‐Ojibway and the Hudson Bay Ice Saddle from 8.55 Kyr BP onwards. For the past ca. 7.5 Kyr BP sea ice is mainly transported to the study area by local ocean currents such as the inner Labrador and Baffin Current. Our findings provide new insights into the response of sea ice to increased meltwater discharge as well as shifts in atmospheric and oceanic circulation.
{"title":"Biomarker Records of Environmental Shifts on the Labrador Shelf During the Holocene","authors":"H. Kolling, Ralph Schneider, Felix Gross, C. Hamann, Markus Kienast, S. Kienast, K. Doering, K. Fahl, R. Stein","doi":"10.1029/2022PA004578","DOIUrl":"https://doi.org/10.1029/2022PA004578","url":null,"abstract":"The ultimate demise of the Laurentide Ice Sheet (LIS) and the preceding and succeeding oceanographic changes along the western Labrador Sea offer insights critically important to improve climate predictions of expected future climate warming and further melting of the Greenland ice cap. However, while the final disappearance of the LIS during the Holocene is rather well constrained, the response of sea ice during the resulting meltwater events is not fully understood. Here, we present reconstructions of paleoceanographic changes over the past 9.3 Kyr BP on the northwestern Labrador Shelf, with a special focus on the interaction between the final meltwater event around 8.2 Kyr BP and sea ice and phytoplankton productivity (e.g., IP25, HBI III (Z), brassicasterol, dinosterol, biogenic opal, total organic carbon). Our records indicate low sea‐ice cover and high phytoplankton productivity on the Labrador Shelf prior to 8.9 Kyr BP, sea‐ice formation was favored by decreased surface salinities due to the meltwater events from Lake Agassiz‐Ojibway and the Hudson Bay Ice Saddle from 8.55 Kyr BP onwards. For the past ca. 7.5 Kyr BP sea ice is mainly transported to the study area by local ocean currents such as the inner Labrador and Baffin Current. Our findings provide new insights into the response of sea ice to increased meltwater discharge as well as shifts in atmospheric and oceanic circulation.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41659858","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The δ13C composition of Cibicidoides wuellerstorfi and other Cibicidoides spp is an important tool to reconstruct past changes in the deep ocean carbon cycle. The species are expected to match the δ13C of ambient dissolved inorganic carbon (DIC), although it has been recognized that substantial offsets can occur. Here, I present a compilation of modern δ13C and δ18O data for named Cibicidoides species in combination with fully resolved carbonate chemistry at each core location. The data show for C. wuellerstorfi that the offset from the expected value in both carbon (∆13C) and oxygen (∆18O) is correlated with seawater carbonate chemistry. The result is comparable to, but not identical with, published culture experiments in which marine organisms were grown under variable pH‐conditions. Overall, ∆13C in C. wuellerstorfi correlates positively with carbonate saturation, [DIC], and temperature. The three variables together explain 47.1% of the variation in ∆13C. The trend for ∆18O is similar, except that the effect of temperature has been removed through correction with a published δ18O‐temperature equation. Up to 35% of the remaining variation in ∆18O can be explained by ambient carbonate chemistry. Data for other named Cibicidoides species are broadly similar, but are too sparse for a detailed analysis. The results indicate that strongly negative ∆13C occurs predominantly in the deep Atlantic in response to a combination of low [DIC], low temperature, and undersaturation within the lysocline. Implications for paleoceanographic reconstructions are discussed.
{"title":"The Effect of Seawater Carbonate Chemistry on the Stable Isotope Composition of Cibicidoides wuellerstorfi and Other Cibicidoides Species","authors":"Alexandra J. Nederbragt","doi":"10.1029/2023PA004667","DOIUrl":"https://doi.org/10.1029/2023PA004667","url":null,"abstract":"The δ13C composition of Cibicidoides wuellerstorfi and other Cibicidoides spp is an important tool to reconstruct past changes in the deep ocean carbon cycle. The species are expected to match the δ13C of ambient dissolved inorganic carbon (DIC), although it has been recognized that substantial offsets can occur. Here, I present a compilation of modern δ13C and δ18O data for named Cibicidoides species in combination with fully resolved carbonate chemistry at each core location. The data show for C. wuellerstorfi that the offset from the expected value in both carbon (∆13C) and oxygen (∆18O) is correlated with seawater carbonate chemistry. The result is comparable to, but not identical with, published culture experiments in which marine organisms were grown under variable pH‐conditions. Overall, ∆13C in C. wuellerstorfi correlates positively with carbonate saturation, [DIC], and temperature. The three variables together explain 47.1% of the variation in ∆13C. The trend for ∆18O is similar, except that the effect of temperature has been removed through correction with a published δ18O‐temperature equation. Up to 35% of the remaining variation in ∆18O can be explained by ambient carbonate chemistry. Data for other named Cibicidoides species are broadly similar, but are too sparse for a detailed analysis. The results indicate that strongly negative ∆13C occurs predominantly in the deep Atlantic in response to a combination of low [DIC], low temperature, and undersaturation within the lysocline. Implications for paleoceanographic reconstructions are discussed.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49485610","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We integrate 10 new with five published 40Ar/39Ar age determinations, both on primary volcanic deposits and on detrital sanidine, which provide precise geochronologic control on the Marine Isotope Stage (MIS) 5.5 and MIS 5.3 sea‐level indicators that occur at three coastal caves in a tectonically stable region of the central Tyrrhenian Sea of Italy. The age of a Strombus‐bearing bioclastic conglomerate, associated with a tidal notch occurring at 9.5 m a.s.l. at Cape Circeo, is constrained to between 121.5 ± 5.8 and 116.2 ± 1.2 ka. Moreover, backbeach deposits intercalated in the sedimentary filling of Guattari and Capre coastal caves are directly correlated with a tidal notch at ∼2.5 m associated with another bioclastic conglomerate at Cape Circeo and dated to 110.4 ± 1.4–104.9 ± 0.9 ka. The latter deposit is also correlated with the adjacent marine terrace, occurring at 3–5 m on the coast between Capes Circeo and Anzio, for which a maximum age of 100.7 ± 6.6 ka was previously reported. These data provide evidence for a maximum sea level around 9.5 m above the present sea level and a duration of MIS 5.5 highstand until 116 ka, in agreement with estimates from other regions in the world. In contrast, they suggest a maximum sea level during MIS 5.3 highstand that is similar to the present level, and only ∼7 m lower than the MIS 5.5 highstand, challenging the reconstructions of the MIS 5 ice‐sheet volumes and derived global sea levels that are based on benthic oxygen isotope records.
{"title":"40Ar/39Ar Age Constraints on MIS 5.5 and MIS 5.3 Paleo‐Sea Levels: Implications for Global Sea Levels and Ice‐Volume Estimates","authors":"F. Marra, F. Florindo, M. Gaeta, B. Jicha","doi":"10.1029/2023PA004679","DOIUrl":"https://doi.org/10.1029/2023PA004679","url":null,"abstract":"We integrate 10 new with five published 40Ar/39Ar age determinations, both on primary volcanic deposits and on detrital sanidine, which provide precise geochronologic control on the Marine Isotope Stage (MIS) 5.5 and MIS 5.3 sea‐level indicators that occur at three coastal caves in a tectonically stable region of the central Tyrrhenian Sea of Italy. The age of a Strombus‐bearing bioclastic conglomerate, associated with a tidal notch occurring at 9.5 m a.s.l. at Cape Circeo, is constrained to between 121.5 ± 5.8 and 116.2 ± 1.2 ka. Moreover, backbeach deposits intercalated in the sedimentary filling of Guattari and Capre coastal caves are directly correlated with a tidal notch at ∼2.5 m associated with another bioclastic conglomerate at Cape Circeo and dated to 110.4 ± 1.4–104.9 ± 0.9 ka. The latter deposit is also correlated with the adjacent marine terrace, occurring at 3–5 m on the coast between Capes Circeo and Anzio, for which a maximum age of 100.7 ± 6.6 ka was previously reported. These data provide evidence for a maximum sea level around 9.5 m above the present sea level and a duration of MIS 5.5 highstand until 116 ka, in agreement with estimates from other regions in the world. In contrast, they suggest a maximum sea level during MIS 5.3 highstand that is similar to the present level, and only ∼7 m lower than the MIS 5.5 highstand, challenging the reconstructions of the MIS 5 ice‐sheet volumes and derived global sea levels that are based on benthic oxygen isotope records.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44170606","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Oppo, Lu, K.‐F. Huang, N. Umling, W. Guo, J. Yu, W. Curry, T. Marchitto, S. Wang, W. Lu
Variations in the Atlantic Meridional Overturning Circulation (AMOC) redistribute heat and nutrients, causing pronounced anomalies of temperature and nutrient concentrations in the subsurface ocean. However, exactly how millennial‐scale deglacial AMOC variability influenced the subsurface is debated, and the role of other deglacial forcings of subsurface temperature change is unclear. Here, we present a new deglacial temperature reconstruction, which, with published records, helps assess competing hypotheses for deglacial warming in the upper tropical North Atlantic. Our record provides new evidence of regional subsurface warming in the western tropical North Atlantic within the core of modern Antarctic Intermediate Water (AAIW) during Heinrich Stadial 1 (HS1), an early deglacial interval of iceberg discharge into the North Atlantic. Our results are consistent with model simulations that suggest subsurface heat accumulates in the northern high‐latitude convection regions and along the upper AMOC return path when the AMOC weakens, and with warming due to rising greenhouse gases. Warming of AAIW may have also contributed to warming in the tropics at modern AAIW depths during late HS1. Nutrient and ΔCO32− ${Delta }left[{mathrm{C}mathrm{O}}_{3}^{2-}right]$ reconstructions from the same site suggest a link between AMOC intensity and the northward extent of AAIW in the northern tropics across the deglaciation and on millennial time scales. However, the timing of the initial deglacial increase in AAIW to the northern tropics is ambiguous. Deglacial trends and variability of ΔCO32− ${Delta }left[{mathrm{C}mathrm{O}}_{3}^{2-}right]$ in the upper North Atlantic have likely biased temperature reconstructions based on the elemental composition of calcitic benthic foraminifera.
{"title":"Deglacial Temperature and Carbonate Saturation State Variability in the Tropical Atlantic at Antarctic Intermediate Water Depths","authors":"D. Oppo, Lu, K.‐F. Huang, N. Umling, W. Guo, J. Yu, W. Curry, T. Marchitto, S. Wang, W. Lu","doi":"10.1029/2023PA004674","DOIUrl":"https://doi.org/10.1029/2023PA004674","url":null,"abstract":"Variations in the Atlantic Meridional Overturning Circulation (AMOC) redistribute heat and nutrients, causing pronounced anomalies of temperature and nutrient concentrations in the subsurface ocean. However, exactly how millennial‐scale deglacial AMOC variability influenced the subsurface is debated, and the role of other deglacial forcings of subsurface temperature change is unclear. Here, we present a new deglacial temperature reconstruction, which, with published records, helps assess competing hypotheses for deglacial warming in the upper tropical North Atlantic. Our record provides new evidence of regional subsurface warming in the western tropical North Atlantic within the core of modern Antarctic Intermediate Water (AAIW) during Heinrich Stadial 1 (HS1), an early deglacial interval of iceberg discharge into the North Atlantic. Our results are consistent with model simulations that suggest subsurface heat accumulates in the northern high‐latitude convection regions and along the upper AMOC return path when the AMOC weakens, and with warming due to rising greenhouse gases. Warming of AAIW may have also contributed to warming in the tropics at modern AAIW depths during late HS1. Nutrient and ΔCO32− ${Delta }left[{mathrm{C}mathrm{O}}_{3}^{2-}right]$ reconstructions from the same site suggest a link between AMOC intensity and the northward extent of AAIW in the northern tropics across the deglaciation and on millennial time scales. However, the timing of the initial deglacial increase in AAIW to the northern tropics is ambiguous. Deglacial trends and variability of ΔCO32− ${Delta }left[{mathrm{C}mathrm{O}}_{3}^{2-}right]$ in the upper North Atlantic have likely biased temperature reconstructions based on the elemental composition of calcitic benthic foraminifera.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2023-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49361916","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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