John. C. H. Chiang, P. Maffre, N. Swanson‐Hysell, Francis A. Macdonald
The geography of the Southeast Asian Islands (SEAI) has changed over the last 15 million years, as a result of tectonic processes contributing to both increased land area and high topography. The presence of the additional land area has been postulated to enhance convective rainfall, facilitating both increased silicate weathering and the development of the modern‐day Walker circulation. Using an Earth System Model in conjunction with a climate‐silicate weathering model, we argue instead for a significant role of SEAI topography for both effects. SEAI topography increases orographic rainfall over land, through intercepting moist Asian‐Australian monsoon winds and enhancing land‐sea breezes. Large‐scale atmospheric uplift over the SEAI region increases by ∼14% as a consequence of increased rainfall over the SEAI and enhancement through dynamical ocean‐atmosphere feedback. The atmospheric zonal overturning circulation over the Indo‐Pacific increases modestly arising from dynamical ocean‐atmosphere feedback, more strongly over the tropical Indian Ocean. On the other hand, the effect of the SEAI topography on global silicate weathering is substantial, resulting in a ∼109 ppm reduction in equilibrium pCO2 and decrease in global mean temperature by ∼1.7ºC. The chemical weathering increase comes from both enhanced physical erosion rates and increased rainfall due to the presence of SEAI topography. The lowering of pCO2 by SEAI topography also enhances the Indo‐Pacific atmospheric zonal overturning circulation. Our results support a significant role for the progressive emergence of SEAI topography in global cooling over the last several million years.
{"title":"The Role of Southeast Asian Island Topography on Indo‐Pacific Climate and Silicate Weathering","authors":"John. C. H. Chiang, P. Maffre, N. Swanson‐Hysell, Francis A. Macdonald","doi":"10.1029/2023pa004672","DOIUrl":"https://doi.org/10.1029/2023pa004672","url":null,"abstract":"The geography of the Southeast Asian Islands (SEAI) has changed over the last 15 million years, as a result of tectonic processes contributing to both increased land area and high topography. The presence of the additional land area has been postulated to enhance convective rainfall, facilitating both increased silicate weathering and the development of the modern‐day Walker circulation. Using an Earth System Model in conjunction with a climate‐silicate weathering model, we argue instead for a significant role of SEAI topography for both effects. SEAI topography increases orographic rainfall over land, through intercepting moist Asian‐Australian monsoon winds and enhancing land‐sea breezes. Large‐scale atmospheric uplift over the SEAI region increases by ∼14% as a consequence of increased rainfall over the SEAI and enhancement through dynamical ocean‐atmosphere feedback. The atmospheric zonal overturning circulation over the Indo‐Pacific increases modestly arising from dynamical ocean‐atmosphere feedback, more strongly over the tropical Indian Ocean. On the other hand, the effect of the SEAI topography on global silicate weathering is substantial, resulting in a ∼109 ppm reduction in equilibrium pCO2 and decrease in global mean temperature by ∼1.7ºC. The chemical weathering increase comes from both enhanced physical erosion rates and increased rainfall due to the presence of SEAI topography. The lowering of pCO2 by SEAI topography also enhances the Indo‐Pacific atmospheric zonal overturning circulation. Our results support a significant role for the progressive emergence of SEAI topography in global cooling over the last several million years.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140273472","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}
Glacial‐interglacial oscillations exhibit a periodicity of approximately 100 Kyr during the late Pleistocene. Insolation variations are understood to play a vital role in these ice ages, yet their exact effect is still unknown; the 100 Kyr ice ages may be explained in two different ways. They could be purely insolation‐driven, such that ice ages are a consequence of insolation variations and would not have existed without these variations. Or, ice ages may be self‐sustained oscillations, where they would have existed even without insolation variations. We develop several observable measures that are used to differentiate between the two scenarios and can help to determine which one is more likely based on the observed proxy record. We demonstrate these analyses using two representative models. First, we find that the self‐sustained model best fits the ice volume proxy record for the full 800‐Kyr time period. Next, the same model also shows a 100 Kyr peak consistent with observations, yet the insolation‐driven model exhibits a dominant 400 Kyr spectral peak inconsistent with observations. Our third measure indicates that midpoints in ice volume during terminations do not always occur during the same phase of insolation in both observations and the self‐sustained scenario, whereas they do in the insolation‐driven scenario. While some of these results suggest that the self‐sustained ice ages are more consistent with the observed record, they rely on simple representations of the two scenarios. To draw robust conclusions, a broader class of models should be tested using this method of producing observable differences.
在更新世晚期，冰川-间冰期振荡呈现出约 100 K 年的周期性。据了解，日照变化在这些冰期中起着至关重要的作用，但其确切影响尚不清楚。它们可能纯粹是日照驱动的，即冰期是日照变化的结果，没有日照变化就不会有冰期。或者，冰期可能是自我维持的振荡，即使没有日照变化，冰期也会存在。我们开发了几种可观测的测量方法，用于区分这两种情况，并有助于根据观测到的代用记录确定哪种情况更有可能发生。我们使用两个具有代表性的模型来演示这些分析。首先，我们发现自持模型最符合整个 800Kyr 时间段的冰量代用记录。其次，同一模型也显示出与观测结果一致的 100Kyr 峰值，而日照驱动模型则显示出与观测结果不一致的 400Kyr 主光谱峰值。我们的第三个测量结果表明，在观测结果和自持情景中，冰量终止时的中点并不总是出现在同一日照阶段，而在日照驱动情景中，冰量终止时的中点却总是出现在同一日照阶段。虽然其中一些结果表明，自我维持的冰期与观测记录更加一致，但它们依赖于对两种情景的简单描述。为了得出可靠的结论，应该用这种产生可观测差异的方法对更多的模型进行检验。
{"title":"Distinguishing Between Insolation‐Driven and Phase‐Locked 100‐Kyr Ice Age Scenarios Using Example Models","authors":"Kirstin Koepnick, Eli Tziperman","doi":"10.1029/2023pa004739","DOIUrl":"https://doi.org/10.1029/2023pa004739","url":null,"abstract":"Glacial‐interglacial oscillations exhibit a periodicity of approximately 100 Kyr during the late Pleistocene. Insolation variations are understood to play a vital role in these ice ages, yet their exact effect is still unknown; the 100 Kyr ice ages may be explained in two different ways. They could be purely insolation‐driven, such that ice ages are a consequence of insolation variations and would not have existed without these variations. Or, ice ages may be self‐sustained oscillations, where they would have existed even without insolation variations. We develop several observable measures that are used to differentiate between the two scenarios and can help to determine which one is more likely based on the observed proxy record. We demonstrate these analyses using two representative models. First, we find that the self‐sustained model best fits the ice volume proxy record for the full 800‐Kyr time period. Next, the same model also shows a 100 Kyr peak consistent with observations, yet the insolation‐driven model exhibits a dominant 400 Kyr spectral peak inconsistent with observations. Our third measure indicates that midpoints in ice volume during terminations do not always occur during the same phase of insolation in both observations and the self‐sustained scenario, whereas they do in the insolation‐driven scenario. While some of these results suggest that the self‐sustained ice ages are more consistent with the observed record, they rely on simple representations of the two scenarios. To draw robust conclusions, a broader class of models should be tested using this method of producing observable differences.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140275963","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. J. Anderson, Z. Chase, H. C. Bostock, T. L. Noble, R. Shuttleworth, B. Taiapa, W. H. Chen, H. Ren, G. E. Jacobsen
Antarctic ice cores reveal a glacial climate state during Marine Isotope Stage 3 (MIS‐3; 57–29 ka) punctuated by millennial‐scale warming events and pulses of CO2. This study further explores how changes in Southern Ocean carbon cycling contributed to these millennial‐scale fluctuations in climate. Evidence from South Atlantic sediment cores suggests that warming events were associated with decreased dust‐borne iron flux, reduced export production, and increased upwelling from the deep Southern Ocean (SO). These processes are considered to have contributed to rising atmospheric CO2 during periods of rapid warming. Here we investigate whether the same processes occurred in the southwest Pacific sector of the SO at TAN1106‐28. We show that reduced New Zealand glaciation and localized iron limitation in the southwest Pacific led to reduced export production during millennial‐scale warming events. Decreases in foraminifera‐bound δ15N during all MIS‐3 warming events may reflect increased nutrient supply by upwelling. Increased calcium carbonate flux during MIS‐3 warming events likely reflects coccolithophore production in response to sea surface temperatures, which, would increase carbonate counter pump strength and reduce CO2 sequestration. Concomitant decreases in bottom water oxygen, inferred from redox‐sensitive U and Mn sediment concentrations, and increases in the 14C age of deep waters, suggest that old, nutrient‐rich waters influenced southwest Pacific middepth waters during warming events. This signature may reflect an expansion of Pacific Deep Water into the SO during warming. Taken together, our multi‐proxy data set reveals that the southwest subantarctic Pacific acted as a source of CO2 during millennial‐scale warming events of MIS‐3.
{"title":"Millennial‐Scale Carbon Flux Variability in the Subantarctic Pacific During Marine Isotope Stage 3 (57–29 ka)","authors":"H. J. Anderson, Z. Chase, H. C. Bostock, T. L. Noble, R. Shuttleworth, B. Taiapa, W. H. Chen, H. Ren, G. E. Jacobsen","doi":"10.1029/2023pa004776","DOIUrl":"https://doi.org/10.1029/2023pa004776","url":null,"abstract":"Antarctic ice cores reveal a glacial climate state during Marine Isotope Stage 3 (MIS‐3; 57–29 ka) punctuated by millennial‐scale warming events and pulses of CO2. This study further explores how changes in Southern Ocean carbon cycling contributed to these millennial‐scale fluctuations in climate. Evidence from South Atlantic sediment cores suggests that warming events were associated with decreased dust‐borne iron flux, reduced export production, and increased upwelling from the deep Southern Ocean (SO). These processes are considered to have contributed to rising atmospheric CO2 during periods of rapid warming. Here we investigate whether the same processes occurred in the southwest Pacific sector of the SO at TAN1106‐28. We show that reduced New Zealand glaciation and localized iron limitation in the southwest Pacific led to reduced export production during millennial‐scale warming events. Decreases in foraminifera‐bound δ15N during all MIS‐3 warming events may reflect increased nutrient supply by upwelling. Increased calcium carbonate flux during MIS‐3 warming events likely reflects coccolithophore production in response to sea surface temperatures, which, would increase carbonate counter pump strength and reduce CO2 sequestration. Concomitant decreases in bottom water oxygen, inferred from redox‐sensitive U and Mn sediment concentrations, and increases in the 14C age of deep waters, suggest that old, nutrient‐rich waters influenced southwest Pacific middepth waters during warming events. This signature may reflect an expansion of Pacific Deep Water into the SO during warming. Taken together, our multi‐proxy data set reveals that the southwest subantarctic Pacific acted as a source of CO2 during millennial‐scale warming events of MIS‐3.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140282476","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}
I. Kocken, P. Nooteboom, Kasper van der Veen, H. Coxall, I. A. Müller, A. N. Meckler, Martin Ziegler
The Eocene‐Oligocene transition (EOT) (∼34 Ma) is marked by the rapid development of a semi‐permanent Antarctic ice‐sheet, as indicated by ice‐rafted debris and a 1–1.5‰ increase in deep sea δ18O. Proxy reconstructions indicate a drop in atmospheric CO2 and global cooling. How these changes affected surface ocean temperatures in the North Atlantic and ocean water stratification remains poorly constrained. In this study, we apply clumped‐isotope thermometry to well‐preserved planktonic foraminifera, that are associated with lower mixed‐layer to subthermocline dwelling depths from the drift sediments at international ocean discovery program Site 1411, Newfoundland, across four intervals bracketing the EOT. The thermocline/lower mixed‐layer dwelling foraminifera record a cooling of 1.9 ± 3.5 K (mean ± 95% CI) across the EOT. While the cooling amplitude is similar to previous sea surface temperature (SST) reconstructions, absolute temperatures (Eocene 20.0 ± 2.9°C, Oligocene 18.0 ± 2.2°C) appear colder than previous organic proxy reconstructions for the northernmost Atlantic extrapolated to this location. We discuss seasonal bias, recording depth, and appropriate consideration of paleolatitudes, all of which complicate the comparison between SST reconstructions and model output. Our subthermocline dwelling foraminifera record a larger cooling across the EOT (Eocene 19.0 ± 3.5°C, Oligocene 13.0 ± 3.2°C, cooling of 5.5 ± 4.6 K) than foraminifera from the thermocline/lower mixed‐layer, consistent with global cooling and an increase in ocean stratification which may be related to the onset or intensification of the Atlantic meridional overturning circulation.
{"title":"North Atlantic Temperature Change Across the Eocene‐Oligocene Transition From Clumped Isotopes","authors":"I. Kocken, P. Nooteboom, Kasper van der Veen, H. Coxall, I. A. Müller, A. N. Meckler, Martin Ziegler","doi":"10.1029/2023pa004809","DOIUrl":"https://doi.org/10.1029/2023pa004809","url":null,"abstract":"The Eocene‐Oligocene transition (EOT) (∼34 Ma) is marked by the rapid development of a semi‐permanent Antarctic ice‐sheet, as indicated by ice‐rafted debris and a 1–1.5‰ increase in deep sea δ18O. Proxy reconstructions indicate a drop in atmospheric CO2 and global cooling. How these changes affected surface ocean temperatures in the North Atlantic and ocean water stratification remains poorly constrained. In this study, we apply clumped‐isotope thermometry to well‐preserved planktonic foraminifera, that are associated with lower mixed‐layer to subthermocline dwelling depths from the drift sediments at international ocean discovery program Site 1411, Newfoundland, across four intervals bracketing the EOT. The thermocline/lower mixed‐layer dwelling foraminifera record a cooling of 1.9 ± 3.5 K (mean ± 95% CI) across the EOT. While the cooling amplitude is similar to previous sea surface temperature (SST) reconstructions, absolute temperatures (Eocene 20.0 ± 2.9°C, Oligocene 18.0 ± 2.2°C) appear colder than previous organic proxy reconstructions for the northernmost Atlantic extrapolated to this location. We discuss seasonal bias, recording depth, and appropriate consideration of paleolatitudes, all of which complicate the comparison between SST reconstructions and model output. Our subthermocline dwelling foraminifera record a larger cooling across the EOT (Eocene 19.0 ± 3.5°C, Oligocene 13.0 ± 3.2°C, cooling of 5.5 ± 4.6 K) than foraminifera from the thermocline/lower mixed‐layer, consistent with global cooling and an increase in ocean stratification which may be related to the onset or intensification of the Atlantic meridional overturning circulation.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140403867","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}
M. Oksman, A. B. Kvorning, C. Pearce, N. Korsgaard, J. M. Lea, M. Seidenkrantz, S. Ribeiro
Greenlandic fjords, located between the ice sheet and the ocean, are dynamic systems that can sustain highly variable levels of primary productivity and are sensitive to climate change. In our current climate trajectory, meltwater discharge is expected to significantly increase but its long‐term effects on fjord productivity are still poorly constrained. Paleo‐archives can offer valuable insights into long‐term effects. Here, we present two marine sediment core records from Nuup Kangerlua, Southwest Greenland. Our goal is to better understand to what extent, and on what time‐scales, climate fluctuations and associated glacier dynamic changes have impacted fjord productivity over the past ca. 3300 years. Our multiproxy records include diatom fluxes and assemblage composition, sediment biogeochemistry, and grain‐size distribution. Our study reveals that fjord productivity is tightly linked to regional climate variability; relatively higher productivity levels coincided with mild climate periods whereas the climate cooling of the last millennium led to a decrease in productivity. The diatom records suggest that lower productivity is associated with shorter or less intense summer blooms, increased sea‐ice cover and/or a stratified water column. Diatom assemblages demonstrate cold sea‐surface conditions around 1600 CE that might be linked to local advance of glaciers. Cold conditions and decreasing productivity culminated at 1850 CE, when glaciers in the fjord retreated and high glacial meltwater discharge would have altered the fjord hydrography, likely leading to limited nutrient availability. Our long‐term records support the idea that changing climate and cryosphere conditions have a non‐linear impact on the productivity of Greenlandic fjords.
{"title":"Climate Variability and Glacier Dynamics Linked to Fjord Productivity Changes Over the Last ca. 3300 Years in Nuup Kangerlua, Southwest Greenland","authors":"M. Oksman, A. B. Kvorning, C. Pearce, N. Korsgaard, J. M. Lea, M. Seidenkrantz, S. Ribeiro","doi":"10.1029/2023pa004710","DOIUrl":"https://doi.org/10.1029/2023pa004710","url":null,"abstract":"Greenlandic fjords, located between the ice sheet and the ocean, are dynamic systems that can sustain highly variable levels of primary productivity and are sensitive to climate change. In our current climate trajectory, meltwater discharge is expected to significantly increase but its long‐term effects on fjord productivity are still poorly constrained. Paleo‐archives can offer valuable insights into long‐term effects. Here, we present two marine sediment core records from Nuup Kangerlua, Southwest Greenland. Our goal is to better understand to what extent, and on what time‐scales, climate fluctuations and associated glacier dynamic changes have impacted fjord productivity over the past ca. 3300 years. Our multiproxy records include diatom fluxes and assemblage composition, sediment biogeochemistry, and grain‐size distribution. Our study reveals that fjord productivity is tightly linked to regional climate variability; relatively higher productivity levels coincided with mild climate periods whereas the climate cooling of the last millennium led to a decrease in productivity. The diatom records suggest that lower productivity is associated with shorter or less intense summer blooms, increased sea‐ice cover and/or a stratified water column. Diatom assemblages demonstrate cold sea‐surface conditions around 1600 CE that might be linked to local advance of glaciers. Cold conditions and decreasing productivity culminated at 1850 CE, when glaciers in the fjord retreated and high glacial meltwater discharge would have altered the fjord hydrography, likely leading to limited nutrient availability. Our long‐term records support the idea that changing climate and cryosphere conditions have a non‐linear impact on the productivity of Greenlandic fjords.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-02-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140409291","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}
Antarctic ice core records suggest that atmospheric CO2 increased by 15–20 ppm during Heinrich stadials (HS). These periods of abrupt CO2 increase are associated with a significant weakening of the Atlantic meridional overturning circulation (AMOC), and a warming at high southern latitudes. As such, modeling studies have explored the link between changes in AMOC, high southern latitude climate and atmospheric CO2. While proxy records suggest that the aeolian iron input to the Southern Ocean decreased significantly during HS, the potential impact on CO2 of reduced iron input combined with oceanic circulation changes has not been studied in detail. Here, we quantify the respective and combined impacts of reduced iron fertilization and AMOC weakening on CO2 by performing numerical experiments with an Earth system model under boundary conditions representing 40,000 years before present (ka). Our study indicates that reduced iron input can contribute up to 6 ppm increase in CO2 during an idealized Heinrich stadial. This is caused by a 5% reduction in nutrient utilization in the Southern Ocean, leading to reduced export production and increased carbon outgassing from the Southern Ocean. An AMOC weakening under 40ka conditions and without changes in surface winds leads to a ∼0.5 ppm CO2 increase. The combined impact of AMOC shutdown and weakened iron fertilization is almost linear, leading to a total CO2 increase of 7 ppm. Therefore, this study highlights the need of including changes in aeolian iron input when studying the processes leading to changes in atmospheric CO2 concentration during HS.
{"title":"Transient Response of Southern Ocean Ecosystems During Heinrich Stadials","authors":"Himadri Saini, K. Meissner, L. Menviel, K. Kvale","doi":"10.1029/2023pa004754","DOIUrl":"https://doi.org/10.1029/2023pa004754","url":null,"abstract":"Antarctic ice core records suggest that atmospheric CO2 increased by 15–20 ppm during Heinrich stadials (HS). These periods of abrupt CO2 increase are associated with a significant weakening of the Atlantic meridional overturning circulation (AMOC), and a warming at high southern latitudes. As such, modeling studies have explored the link between changes in AMOC, high southern latitude climate and atmospheric CO2. While proxy records suggest that the aeolian iron input to the Southern Ocean decreased significantly during HS, the potential impact on CO2 of reduced iron input combined with oceanic circulation changes has not been studied in detail. Here, we quantify the respective and combined impacts of reduced iron fertilization and AMOC weakening on CO2 by performing numerical experiments with an Earth system model under boundary conditions representing 40,000 years before present (ka). Our study indicates that reduced iron input can contribute up to 6 ppm increase in CO2 during an idealized Heinrich stadial. This is caused by a 5% reduction in nutrient utilization in the Southern Ocean, leading to reduced export production and increased carbon outgassing from the Southern Ocean. An AMOC weakening under 40ka conditions and without changes in surface winds leads to a ∼0.5 ppm CO2 increase. The combined impact of AMOC shutdown and weakened iron fertilization is almost linear, leading to a total CO2 increase of 7 ppm. Therefore, this study highlights the need of including changes in aeolian iron input when studying the processes leading to changes in atmospheric CO2 concentration during HS.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140463489","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}
O. Knebel, T. Felis, R. Asami, Pierre Deschamps, M. Kölling, Denis Scholz
On glacial‐interglacial time scales, changes in the Earth's orbital configuration control climate seasonality and mean conditions. Tropical coral skeletons can be sampled at a sufficient resolution to reconstruct past seasonality. Here, last deglacial Porites skeletons from Integrated Ocean Drilling Program Expedition 310 to Tahiti are investigated and, supported by a modern calibration, monthly resolved time series in geochemical proxies (Sr/Ca, δ18O, δ13C) are constructed. For most of the deglaciation, Sr/Ca seasonality was similar to modern (0.139 ± 0.010 mmol mol−1; 2.8 ± 0.2°C) reflecting the small change in insolation seasonality. However, during the Younger Dryas, high values in Sr/Ca seasonality (0.171 ± 0.017 mmol mol−1; 3.4 ± 0.3°C) suggest a reduced mixed layer depth and enhanced influence of the South Pacific Subtropical Gyre due to South Pacific Convergence Zone (SPCZ) inactivity. Furthermore, high amplitudes in Younger Dryas skeletal δ18O (0.40 ± 0.22 ‰) and δ13C (0.86 ± 0.22 ‰) seasonality compared to modern (δ18O = 0.29 ± 0.08 ‰; δ13C = 0.27 ± 0.08 ‰) point to elevated winter‐summer discrepancies in rainfall and runoff. Mean coral Sr/Ca variability suggests an influence of Northern Hemisphere climate events, such as the Younger Dryas cooling (+0.134 ± 0.012 mmol mol−1;−2.6 ± 0.2°C), or the Bølling–Allerød warming (+0.032 ± 0.040 mmol mol−1; −0.6 ± 0.4°C). Deglacial mean coral Δδ18O (δ18Oseawater contribution to skeletal δ18O), corrected for the ice volume effect, was elevated pointing to more saline, thus dryer conditions, likely due to a northward migration of the SPCZ. Seasonal cycles in coral δ13C were likely caused by variations in linear extension rates that were reduced during the last deglaciation (1.00 ± 0.6 cm year−1) compared to today (1.6 ± 0.3 cm year−1).
{"title":"Last Deglacial Environmental Change in the Tropical South Pacific From Tahiti Corals","authors":"O. Knebel, T. Felis, R. Asami, Pierre Deschamps, M. Kölling, Denis Scholz","doi":"10.1029/2022pa004585","DOIUrl":"https://doi.org/10.1029/2022pa004585","url":null,"abstract":"On glacial‐interglacial time scales, changes in the Earth's orbital configuration control climate seasonality and mean conditions. Tropical coral skeletons can be sampled at a sufficient resolution to reconstruct past seasonality. Here, last deglacial Porites skeletons from Integrated Ocean Drilling Program Expedition 310 to Tahiti are investigated and, supported by a modern calibration, monthly resolved time series in geochemical proxies (Sr/Ca, δ18O, δ13C) are constructed. For most of the deglaciation, Sr/Ca seasonality was similar to modern (0.139 ± 0.010 mmol mol−1; 2.8 ± 0.2°C) reflecting the small change in insolation seasonality. However, during the Younger Dryas, high values in Sr/Ca seasonality (0.171 ± 0.017 mmol mol−1; 3.4 ± 0.3°C) suggest a reduced mixed layer depth and enhanced influence of the South Pacific Subtropical Gyre due to South Pacific Convergence Zone (SPCZ) inactivity. Furthermore, high amplitudes in Younger Dryas skeletal δ18O (0.40 ± 0.22 ‰) and δ13C (0.86 ± 0.22 ‰) seasonality compared to modern (δ18O = 0.29 ± 0.08 ‰; δ13C = 0.27 ± 0.08 ‰) point to elevated winter‐summer discrepancies in rainfall and runoff. Mean coral Sr/Ca variability suggests an influence of Northern Hemisphere climate events, such as the Younger Dryas cooling (+0.134 ± 0.012 mmol mol−1;−2.6 ± 0.2°C), or the Bølling–Allerød warming (+0.032 ± 0.040 mmol mol−1; −0.6 ± 0.4°C). Deglacial mean coral Δδ18O (δ18Oseawater contribution to skeletal δ18O), corrected for the ice volume effect, was elevated pointing to more saline, thus dryer conditions, likely due to a northward migration of the SPCZ. Seasonal cycles in coral δ13C were likely caused by variations in linear extension rates that were reduced during the last deglaciation (1.00 ± 0.6 cm year−1) compared to today (1.6 ± 0.3 cm year−1).","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140467797","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}
Long‐lived Atlantic coral species like Orbicella faveolata are important archives of oceanographic change in shallow, marine environments like the Florida Keys. Not only can coral‐based records extend for multiple centuries beyond the limits of the instrumental record, but they can also provide a more accurate representation of in situ conditions than gridded interpolated sea‐surface temperature (SST) products for nearshore reef environments. We use the coral Sr/Ca paleothermometer to produce a 150‐year (1830–1980 C.E.) monthly SST reconstruction from an O. faveolata colony collected in the Marquesas Keys, FL, USA. An important feature of our record is a significant 20th‐century warming trend in winter SSTs. We hypothesize that the winter warming trend was driven partially by a decrease in upwelling associated cyclonic eddies spinning off the Florida Current. A long‐term weakening of winter Florida Current transport over the 20th century could be responsible for decreased cyclonic eddy formation in the Florida Straits. Another feature of the record is pronounced multidecadal fluctuations of mean annual warming and cooling in the record, which correspond to Atlantic Multidecadal Variability (AMV), with the AMV lagging behind western Florida Keys temperatures by 5–11 years. Strong coherence between coral‐based SST reconstructions in the western Florida Keys with broader scale Atlantic oceanographic trends over the past century suggests a common driver of regional SST variability.
{"title":"20th Century Warming in the Western Florida Keys Was Dominated by Increasing Winter Temperatures","authors":"J. A. Flannery, J. Richey, L. Toth, M. Mette","doi":"10.1029/2023pa004748","DOIUrl":"https://doi.org/10.1029/2023pa004748","url":null,"abstract":"Long‐lived Atlantic coral species like Orbicella faveolata are important archives of oceanographic change in shallow, marine environments like the Florida Keys. Not only can coral‐based records extend for multiple centuries beyond the limits of the instrumental record, but they can also provide a more accurate representation of in situ conditions than gridded interpolated sea‐surface temperature (SST) products for nearshore reef environments. We use the coral Sr/Ca paleothermometer to produce a 150‐year (1830–1980 C.E.) monthly SST reconstruction from an O. faveolata colony collected in the Marquesas Keys, FL, USA. An important feature of our record is a significant 20th‐century warming trend in winter SSTs. We hypothesize that the winter warming trend was driven partially by a decrease in upwelling associated cyclonic eddies spinning off the Florida Current. A long‐term weakening of winter Florida Current transport over the 20th century could be responsible for decreased cyclonic eddy formation in the Florida Straits. Another feature of the record is pronounced multidecadal fluctuations of mean annual warming and cooling in the record, which correspond to Atlantic Multidecadal Variability (AMV), with the AMV lagging behind western Florida Keys temperatures by 5–11 years. Strong coherence between coral‐based SST reconstructions in the western Florida Keys with broader scale Atlantic oceanographic trends over the past century suggests a common driver of regional SST variability.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140468046","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}
A. Viganò, E. Dallanave, L. Alegret, T. Westerhold, R. Sutherland, G. Dickens, C. Newsam, C. Agnini
The Eocene‐Oligocene transition (EOT; ∼34 Ma) was one of the most prominent global cooling events of the Cenozoic, coincident with the emergence of continental‐scale ice‐sheets on Antarctica. Calcareous nannoplankton experienced significant assemblage turnover at a time of long‐term surface ocean cooling and trophic conditions, suggesting cause‐effect relationships between Antarctic glaciation, broader climate changes, and the response of phytoplankton communities. To better evaluate the timing and nature of these relationships, we generated calcareous nannofossil and geochemical data sets (δ18O, δ13C and %CaCO3) over a ∼5 Myr stratigraphic interval recovered across the EOT from IODP Site U1509 in the Tasman Sea, South Pacific Ocean. Based on trends observed in the calcareous nannofossil assemblages, there was an overall decline of warm‐oligotrophic communities, with a shift toward taxa better adapted to cooler more eutrophic conditions. Assemblage changes indicate four distinct phases caused by temperature decrease and variations in paleocurrents: late Eocene warm‐oligotrophic phase, precursor diversity‐decrease phase, early Oligocene cold‐eutrophic phase, and a steady‐state cosmopolitan phase. The most prominent shift in the assemblages occurred during the ∼550 kyr‐long precursor diversity‐decrease phase, which has relatively high bulk δ18O and %CaCO3 values, and predates the phase of maximum glacial expansion (Earliest Oligocene Glacial Maximum–EOGM).
{"title":"Calcareous Nannofossils and Paleoclimatic Evolution Across the Eocene‐Oligocene Transition at IODP Site U1509, Tasman Sea, Southwest Pacific Ocean","authors":"A. Viganò, E. Dallanave, L. Alegret, T. Westerhold, R. Sutherland, G. Dickens, C. Newsam, C. Agnini","doi":"10.1029/2023pa004738","DOIUrl":"https://doi.org/10.1029/2023pa004738","url":null,"abstract":"The Eocene‐Oligocene transition (EOT; ∼34 Ma) was one of the most prominent global cooling events of the Cenozoic, coincident with the emergence of continental‐scale ice‐sheets on Antarctica. Calcareous nannoplankton experienced significant assemblage turnover at a time of long‐term surface ocean cooling and trophic conditions, suggesting cause‐effect relationships between Antarctic glaciation, broader climate changes, and the response of phytoplankton communities. To better evaluate the timing and nature of these relationships, we generated calcareous nannofossil and geochemical data sets (δ18O, δ13C and %CaCO3) over a ∼5 Myr stratigraphic interval recovered across the EOT from IODP Site U1509 in the Tasman Sea, South Pacific Ocean. Based on trends observed in the calcareous nannofossil assemblages, there was an overall decline of warm‐oligotrophic communities, with a shift toward taxa better adapted to cooler more eutrophic conditions. Assemblage changes indicate four distinct phases caused by temperature decrease and variations in paleocurrents: late Eocene warm‐oligotrophic phase, precursor diversity‐decrease phase, early Oligocene cold‐eutrophic phase, and a steady‐state cosmopolitan phase. The most prominent shift in the assemblages occurred during the ∼550 kyr‐long precursor diversity‐decrease phase, which has relatively high bulk δ18O and %CaCO3 values, and predates the phase of maximum glacial expansion (Earliest Oligocene Glacial Maximum–EOGM).","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139966304","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}
C. A. Sandoval, A. Yabe, H. Nishida, L. F. Hinojosa
The changing climate during the Cenozoic affected the diversity of plants in Patagonia, as species richness tends to increase during warm periods and decrease during cold periods. Precipitation is a significant factor shaping diversity, as shown in the case of central Chile during the Miocene. This study presents a reconstruction of the climate and vegetation in Tierra del Fuego Island, located approximately 52°S, using fossil flora recovered from the Filaret Formation to understand the Miocene epoch, characterized by contrasting global climatic changes. Filaret flora comprises twenty‐seven morpho‐taxa, including nine Nothofagus species and other Gondwanan and Neotropical families, such as Atherospermataceae and Anacardiaceae, in agreement with a forest habitat. Leaf physiognomy climate reconstruction suggests microthermal conditions, with a mean annual temperature of 9.4–11°C and annual precipitation ranging from 985 to 1,130 mm. These conditions are warmer and wetter than the modern record of the area, with a MAT of 6°C and mean annual precipitation of 300 mm. As the Filaret fossil record suggests, the forest habitat under a microthermal climate is consistent with the global climatic reconstruction of the Early Miocene. This Miocene landscape on Tierra del Fuego was possible because the Andes could not rain‐shadow humid westerly winds by this timeframe.
{"title":"Climate and Vegetation of the Miocene of Tierra del Fuego: Filaret Formation","authors":"C. A. Sandoval, A. Yabe, H. Nishida, L. F. Hinojosa","doi":"10.1029/2023pa004770","DOIUrl":"https://doi.org/10.1029/2023pa004770","url":null,"abstract":"The changing climate during the Cenozoic affected the diversity of plants in Patagonia, as species richness tends to increase during warm periods and decrease during cold periods. Precipitation is a significant factor shaping diversity, as shown in the case of central Chile during the Miocene. This study presents a reconstruction of the climate and vegetation in Tierra del Fuego Island, located approximately 52°S, using fossil flora recovered from the Filaret Formation to understand the Miocene epoch, characterized by contrasting global climatic changes. Filaret flora comprises twenty‐seven morpho‐taxa, including nine Nothofagus species and other Gondwanan and Neotropical families, such as Atherospermataceae and Anacardiaceae, in agreement with a forest habitat. Leaf physiognomy climate reconstruction suggests microthermal conditions, with a mean annual temperature of 9.4–11°C and annual precipitation ranging from 985 to 1,130 mm. These conditions are warmer and wetter than the modern record of the area, with a MAT of 6°C and mean annual precipitation of 300 mm. As the Filaret fossil record suggests, the forest habitat under a microthermal climate is consistent with the global climatic reconstruction of the Early Miocene. This Miocene landscape on Tierra del Fuego was possible because the Andes could not rain‐shadow humid westerly winds by this timeframe.","PeriodicalId":54239,"journal":{"name":"Paleoceanography and Paleoclimatology","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140469142","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：