The paleoclimate community uses a variety of different proxies to reconstruct past sea surface temperatures. Estimates from different paleothermometers are often used interchangeably despite a scarcity of studies exploring the validity of this practice. Here, we provide an orbital resolution case study from the Pliocene using Mg/Ca and alkenone paleothermometry that reinforces results from previous studies showing consistent estimates for some climate parameters and inconsistent results for others. We argue that the paleoclimate community should undertake an effort to more systematically evaluate if, when, and where climate estimates from different paleothermometers can be used interchangeably.
{"title":"Past sea surface temperatures as measured by different proxies—A cautionary tale from the late Pliocene","authors":"K. Lawrence, S. Woodard","doi":"10.1002/2017PA003101","DOIUrl":"https://doi.org/10.1002/2017PA003101","url":null,"abstract":"The paleoclimate community uses a variety of different proxies to reconstruct past sea surface temperatures. Estimates from different paleothermometers are often used interchangeably despite a scarcity of studies exploring the validity of this practice. Here, we provide an orbital resolution case study from the Pliocene using Mg/Ca and alkenone paleothermometry that reinforces results from previous studies showing consistent estimates for some climate parameters and inconsistent results for others. We argue that the paleoclimate community should undertake an effort to more systematically evaluate if, when, and where climate estimates from different paleothermometers can be used interchangeably.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"318-324"},"PeriodicalIF":0.0,"publicationDate":"2017-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003101","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43225736","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}
Xiaoxia Huang, Michael Stärz, K. Gohl, G. Knorr, G. Lohmann
The Weddell Sea is a main location of bottom water formation and, thus, an important component of global ocean circulation. In this study we examine the ocean and climatic responses to a shelf progradation induced by ice sheet advance and glacially transported sediments during the Miocene, using a general circulation model. Our investigations show that relative to a Miocene standard bathymetry, a farther southerly placed shelf break, as reconstructed in a state-of-the-art bathymetry for the Weddell Sea, enables enhanced Antarctic Bottom Water (AABW) formation and gyre transport during the middle Miocene for both relatively high and low atmospheric CO2 concentrations. Furthermore, CO2 sensitivity experiments show that an atmospheric CO2 decline for a setup with the southerly placed shelf break of a new bathymetry has only a minor impact on AABW formation, while the standard setup shows an increase. In combination, these impacts may explain the pronounced deep water formation in the southern high latitudes from the middle Miocene to the late Miocene.
{"title":"Impact of Weddell Sea shelf progradation on Antarctic bottom water formation during the Miocene","authors":"Xiaoxia Huang, Michael Stärz, K. Gohl, G. Knorr, G. Lohmann","doi":"10.1002/2016PA002987","DOIUrl":"https://doi.org/10.1002/2016PA002987","url":null,"abstract":"The Weddell Sea is a main location of bottom water formation and, thus, an important component of global ocean circulation. In this study we examine the ocean and climatic responses to a shelf progradation induced by ice sheet advance and glacially transported sediments during the Miocene, using a general circulation model. Our investigations show that relative to a Miocene standard bathymetry, a farther southerly placed shelf break, as reconstructed in a state-of-the-art bathymetry for the Weddell Sea, enables enhanced Antarctic Bottom Water (AABW) formation and gyre transport during the middle Miocene for both relatively high and low atmospheric CO2 concentrations. Furthermore, CO2 sensitivity experiments show that an atmospheric CO2 decline for a setup with the southerly placed shelf break of a new bathymetry has only a minor impact on AABW formation, while the standard setup shows an increase. In combination, these impacts may explain the pronounced deep water formation in the southern high latitudes from the middle Miocene to the late Miocene.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"304-317"},"PeriodicalIF":0.0,"publicationDate":"2017-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA002987","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42027868","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Hodell, J. Nicholl, T. Bontognali, Steffan Danino, J. Dorador, J. Dowdeswell, J. Einsle, H. Kuhlmann, B. Martrat, M. J. Mleneck-Vautravers, F. Rodríguez-Tovar, U. Röhl
This research used data acquired at the XRF Core Scanner Lab at the MARUM–Center for Marine Environmental Sciences, University of Bremen, Germany. This research used samples provided by the International Ocean Discovery Program (IODP). Funding for this research was provided by the UK Natural Environmental Research Council (NERC) to Hodell. The NERC Radiocarbon Facility supported two radiocarbon dates, and Wally Broecker generously supported the remainder with funding from the Comer Family Foundation. Research by Rodriguez-Tovar and Dorador was financed by Project CGL2015-66835-P. B.M. acknowledges support from the CSIC-Ramon y Cajal postdoctoral programme RYC-2013-14073. J.F.E. would like to acknowledge funding under ERC Advanced grant 320750- Nanopaleomagnetism.
这项研究使用了在德国不来梅大学海洋环境科学中心的XRF岩心扫描仪实验室获得的数据。这项研究使用了国际海洋探索计划（IODP）提供的样本。这项研究的资金由英国自然环境研究委员会（NERC）提供给霍德尔。NERC放射性碳基金会支持了两个放射性碳日期，Wally Broecker在科默家庭基金会的资助下慷慨支持了其余日期。Rodriguez Tovar和Dorador的研究由CGL2015-66835-P项目资助。B.M.感谢CSIC Ramon y Cajal博士后项目RYC-2013-14073的支持。J.F.E.感谢ERC高级拨款320750-纳米磁。
{"title":"Anatomy of Heinrich Layer 1 and its role in the last deglaciation","authors":"D. Hodell, J. Nicholl, T. Bontognali, Steffan Danino, J. Dorador, J. Dowdeswell, J. Einsle, H. Kuhlmann, B. Martrat, M. J. Mleneck-Vautravers, F. Rodríguez-Tovar, U. Röhl","doi":"10.1002/2016PA003028","DOIUrl":"https://doi.org/10.1002/2016PA003028","url":null,"abstract":"This research used data acquired at the XRF Core Scanner Lab at the MARUM–Center for Marine Environmental Sciences, University of Bremen, Germany. This research used samples provided by the International Ocean Discovery Program (IODP). Funding for this research was provided by the UK Natural Environmental Research Council (NERC) to Hodell. The NERC Radiocarbon Facility supported two radiocarbon dates, and Wally Broecker generously supported the remainder with funding from the Comer Family Foundation. Research by Rodriguez-Tovar and Dorador was financed by Project CGL2015-66835-P. B.M. acknowledges support from the CSIC-Ramon y Cajal postdoctoral programme RYC-2013-14073. J.F.E. would like to acknowledge funding under ERC Advanced grant 320750- Nanopaleomagnetism.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"284-303"},"PeriodicalIF":0.0,"publicationDate":"2017-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003028","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45276579","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}
Foraminifera are the backbone of paleoceanography. Planktic foraminifera are one of the leading tools for reconstructing water column structure. However, there are unconstrained variables when dealing with uncertainty in the reproducibility of oxygen isotope measurements. This study presents the first results from a simple model of foraminiferal calcification (Foraminiferal Isotope Reproducibility Model; FIRM), designed to estimate uncertainty in oxygen isotope measurements. FIRM uses parameters including location, depth habitat, season, number of individuals included in measurement, diagenesis, misidentification, size variation, and vital effects, to produce synthetic isotope data in a manner reflecting natural processes. Reproducibility is then tested using Monte Carlo simulations. Importantly, this is not an attempt to fully model the entire complicated process of foraminiferal calcification; instead we are trying to include only enough parameters to estimate the uncertainty in foraminiferal δ18O records. Two well-constrained empirical datasets are simulated successfully, demonstrating the validity of our model. The results from a series of experiments with the model show that reproducibility is largely controlled by the number of individuals in each measurement, but also strongly a function of local oceanography, if the number of individuals is held constant. Parameters like diagenesis or misidentification have an impact on both the precision and the accuracy of the data. FIRM is a tool to estimate isotopic uncertainty values and to explore the impact of myriad factors on the fidelity of paleoceanographic records, particularly for the Holocene.
{"title":"Defining uncertainty and error in planktic foraminiferal oxygen isotope measurements","authors":"A. Fraass, C. Lowery","doi":"10.1002/2016PA003035","DOIUrl":"https://doi.org/10.1002/2016PA003035","url":null,"abstract":"Foraminifera are the backbone of paleoceanography. Planktic foraminifera are one of the leading tools for reconstructing water column structure. However, there are unconstrained variables when dealing with uncertainty in the reproducibility of oxygen isotope measurements. This study presents the first results from a simple model of foraminiferal calcification (Foraminiferal Isotope Reproducibility Model; FIRM), designed to estimate uncertainty in oxygen isotope measurements. FIRM uses parameters including location, depth habitat, season, number of individuals included in measurement, diagenesis, misidentification, size variation, and vital effects, to produce synthetic isotope data in a manner reflecting natural processes. Reproducibility is then tested using Monte Carlo simulations. Importantly, this is not an attempt to fully model the entire complicated process of foraminiferal calcification; instead we are trying to include only enough parameters to estimate the uncertainty in foraminiferal δ18O records. Two well-constrained empirical datasets are simulated successfully, demonstrating the validity of our model. The results from a series of experiments with the model show that reproducibility is largely controlled by the number of individuals in each measurement, but also strongly a function of local oceanography, if the number of individuals is held constant. Parameters like diagenesis or misidentification have an impact on both the precision and the accuracy of the data. FIRM is a tool to estimate isotopic uncertainty values and to explore the impact of myriad factors on the fidelity of paleoceanographic records, particularly for the Holocene.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"104-122"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003035","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44078137","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. Ezat, T. L. Rasmussen, D. Thornalley, J. Olsen, L. Skinner, B. Hönisch, J. Groeneveld
Formation of deep water in the high-latitude North Atlantic is important for the global meridional ocean circulation, and its variability in the past may have played an important role in regional and global climate change. Here we study ocean circulation associated with the last (de)glacial period, using water-column radiocarbon age reconstructions in the Faroe-Shetland Channel, southeastern Norwegian Sea, and from the Iceland Basin, central North Atlantic. The presence of tephra layer Faroe Marine Ash Zone II, dated to ~26.7 ka, enables us to determine that the middepth (1179 m water depth) and shallow subsurface reservoir ages were ~1500 and 1100 14C years, respectively, older during the late glacial period compared to modern, suggesting substantial suppression of the overturning circulation in the Nordic Seas. During the late Last Glacial Maximum and the onset of deglaciation (~20–18 ka), Nordic Seas overflow was weak but active. During the early deglaciation (~17.5–14.5 ka), our data reveal large differences between 14C ventilation ages that are derived from dating different benthic foraminiferal species: Pyrgo and other miliolid species yield ventilation ages >6000 14C years, while all other species reveal ventilation ages <2000 14C years. These data either suggest subcentennial, regional, circulation changes or that miliolid-based 14C ages are biased due to taphonomic or vital processes. Implications of each interpretation are discussed. Regardless of this “enigma,” the onset of the Bolling-Allerod interstadial (14.5 ka) is clearly marked by an increase in middepth Nordic Seas ventilation and the renewal of a stronger overflow.
{"title":"Ventilation history of Nordic Seas overflows during the last (de)glacial period revealed by species‐specific benthic foraminiferal 14C dates","authors":"M. Ezat, T. L. Rasmussen, D. Thornalley, J. Olsen, L. Skinner, B. Hönisch, J. Groeneveld","doi":"10.1002/2016PA003053","DOIUrl":"https://doi.org/10.1002/2016PA003053","url":null,"abstract":"Formation of deep water in the high-latitude North Atlantic is important for the global meridional ocean circulation, and its variability in the past may have played an important role in regional and global climate change. Here we study ocean circulation associated with the last (de)glacial period, using water-column radiocarbon age reconstructions in the Faroe-Shetland Channel, southeastern Norwegian Sea, and from the Iceland Basin, central North Atlantic. The presence of tephra layer Faroe Marine Ash Zone II, dated to ~26.7 ka, enables us to determine that the middepth (1179 m water depth) and shallow subsurface reservoir ages were ~1500 and 1100 14C years, respectively, older during the late glacial period compared to modern, suggesting substantial suppression of the overturning circulation in the Nordic Seas. During the late Last Glacial Maximum and the onset of deglaciation (~20–18 ka), Nordic Seas overflow was weak but active. During the early deglaciation (~17.5–14.5 ka), our data reveal large differences between 14C ventilation ages that are derived from dating different benthic foraminiferal species: Pyrgo and other miliolid species yield ventilation ages >6000 14C years, while all other species reveal ventilation ages <2000 14C years. These data either suggest subcentennial, regional, circulation changes or that miliolid-based 14C ages are biased due to taphonomic or vital processes. Implications of each interpretation are discussed. Regardless of this “enigma,” the onset of the Bolling-Allerod interstadial (14.5 ka) is clearly marked by an increase in middepth Nordic Seas ventilation and the renewal of a stronger overflow.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"172-181"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003053","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49530423","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}
W. Deng, Xuefei Chen, G. Wei, T. Zeng, Jian-xin Zhao
Many factors influence the seasonal changes in δC levels in coral skeletons; consequently, the climatic and environmental significance of such changes is complicated and controversial. However, it is widely accepted that the secular declining trend of coral δC over the past 200 years reflects the changes in the additional flux of anthropogenic CO from the atmosphere into the surface oceans. Even so, the centennial-scale variations, and their significance, of coral δC before the Industrial Revolution remain unclear. Based on an annually resolved coral δC record from the northern South China Sea, the centennial-scale variations of coral δC over the past millennium were studied. The coral δC and total solar irradiance (TSI) have a significant positive Pearson correlation and coupled variation during the Medieval Warm Period and Little Ice Age, when natural forcing controlled the climate and environment. This covariation suggests that TSI controls coral δC by affecting the photosynthetic activity of the endosymbiotic zooxanthellae over centennial timescales. However, there was a decoupling of the coral skeletal δC and TSI during the Current Warm Period, the period in which the climate and environment became linked to anthropogenic factors. Instead, coral δC levels have a significant Pearson correlation with both the atmospheric CO concentration and δC levels in atmospheric CO. The correlation between coral δC and atmospheric CO suggests that the oceanic C Suess effect, caused by the addition of increasing amounts of anthropogenic CO to the surface ocean, has led to the decoupling of coral δC and TSI at the centennial scale.
{"title":"Decoupling of coral skeletal δ13C and solar irradiance over the past millennium caused by the oceanic Suess effect","authors":"W. Deng, Xuefei Chen, G. Wei, T. Zeng, Jian-xin Zhao","doi":"10.1002/2016PA003049","DOIUrl":"https://doi.org/10.1002/2016PA003049","url":null,"abstract":"Many factors influence the seasonal changes in δC levels in coral skeletons; consequently, the climatic and environmental significance of such changes is complicated and controversial. However, it is widely accepted that the secular declining trend of coral δC over the past 200 years reflects the changes in the additional flux of anthropogenic CO from the atmosphere into the surface oceans. Even so, the centennial-scale variations, and their significance, of coral δC before the Industrial Revolution remain unclear. Based on an annually resolved coral δC record from the northern South China Sea, the centennial-scale variations of coral δC over the past millennium were studied. The coral δC and total solar irradiance (TSI) have a significant positive Pearson correlation and coupled variation during the Medieval Warm Period and Little Ice Age, when natural forcing controlled the climate and environment. This covariation suggests that TSI controls coral δC by affecting the photosynthetic activity of the endosymbiotic zooxanthellae over centennial timescales. However, there was a decoupling of the coral skeletal δC and TSI during the Current Warm Period, the period in which the climate and environment became linked to anthropogenic factors. Instead, coral δC levels have a significant Pearson correlation with both the atmospheric CO concentration and δC levels in atmospheric CO. The correlation between coral δC and atmospheric CO suggests that the oceanic C Suess effect, caused by the addition of increasing amounts of anthropogenic CO to the surface ocean, has led to the decoupling of coral δC and TSI at the centennial scale.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"161-171"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003049","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42731286","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Alpert, A. Cohen, D. Oppo, T. DeCarlo, G. Gaetani, E. Hernández-Delgado, A. Winter, M. Gonneea
Coral skeletons are valuable archives of past ocean conditions. However, interpretation of coral paleotemperature records is confounded by uncertainties associated with single element-ratio thermometers, including Sr/Ca. A new approach, Sr-U, uses U/Ca to constrain the influence of Rayleigh fractionation on Sr/Ca [DeCarlo et al., 2016]. Here, we build on the initial Pacific Porites Sr-U calibration to include multiple Atlantic and Pacific coral genera from multiple coral reef locations spanning a temperature range of 23.15-30.12 °C. Accounting for the wintertime growth cessation of one Bermuda coral, we show that Sr-U is strongly correlated with the average water temperature at each location (r2 = 0.91, P < 0.001, n = 19). We applied the multi-species spatial calibration between Sr-U and temperature to reconstruct a 96-year long temperature record at Mona Island, Puerto Rico using a coral not included in the calibration. Average Sr-U derived temperature for the period 1900-1996 is within 0.12 °C of the average instrumental temperature at this site and captures the 20th century warming trend of 0.06 °C per decade. Sr-U also captures the timing of multi-year variability but with higher amplitude than implied by the instrumental data. Mean Sr-U temperatures and patterns of multi-year variability were replicated in a second coral in the same grid box. Conversely, Sr/Ca records from the same two corals were inconsistent with each other and failed to capture absolute sea temperatures, timing of multi-year variability or the 20th century warming trend. Our results suggest that coral Sr-U paleothermometry is a promising new tool for reconstruction of past ocean temperatures.
{"title":"Twentieth century warming of the tropical Atlantic captured by Sr‐U paleothermometry","authors":"A. Alpert, A. Cohen, D. Oppo, T. DeCarlo, G. Gaetani, E. Hernández-Delgado, A. Winter, M. Gonneea","doi":"10.1002/2016PA002976","DOIUrl":"https://doi.org/10.1002/2016PA002976","url":null,"abstract":"Coral skeletons are valuable archives of past ocean conditions. However, interpretation of coral paleotemperature records is confounded by uncertainties associated with single element-ratio thermometers, including Sr/Ca. A new approach, Sr-U, uses U/Ca to constrain the influence of Rayleigh fractionation on Sr/Ca [DeCarlo et al., 2016]. Here, we build on the initial Pacific Porites Sr-U calibration to include multiple Atlantic and Pacific coral genera from multiple coral reef locations spanning a temperature range of 23.15-30.12 °C. Accounting for the wintertime growth cessation of one Bermuda coral, we show that Sr-U is strongly correlated with the average water temperature at each location (r2 = 0.91, P < 0.001, n = 19). We applied the multi-species spatial calibration between Sr-U and temperature to reconstruct a 96-year long temperature record at Mona Island, Puerto Rico using a coral not included in the calibration. Average Sr-U derived temperature for the period 1900-1996 is within 0.12 °C of the average instrumental temperature at this site and captures the 20th century warming trend of 0.06 °C per decade. Sr-U also captures the timing of multi-year variability but with higher amplitude than implied by the instrumental data. Mean Sr-U temperatures and patterns of multi-year variability were replicated in a second coral in the same grid box. Conversely, Sr/Ca records from the same two corals were inconsistent with each other and failed to capture absolute sea temperatures, timing of multi-year variability or the 20th century warming trend. Our results suggest that coral Sr-U paleothermometry is a promising new tool for reconstruction of past ocean temperatures.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"146-160"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA002976","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47506971","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}
B. Lougheed, S. Obrochta, C. Lenz, A. Mellström, B. Metcalfe, R. Muscheler, Maja Reinholdsson, I. Snowball, L. Zillén
Abstract Due to a lack of marine macrofossils in many sediment cores from the estuarine Baltic Sea, researchers are often forced to carry out 14C determinations on bulk sediment samples. However, ambiguity surrounding the carbon source pathways that contribute to bulk sediment formation introduces a large uncertainty into 14C geochronologies based on such samples, and such uncertainty may not have been fully considered in previous Baltic Sea studies. We quantify this uncertainty by analyzing bulk sediment 14C determinations carried out on densely spaced intervals in independently dated late-Holocene sediment sequences from two central Baltic Sea cores. Our results show a difference of ~600?14C?yr in median bulk sediment reservoir age, or R(t)bulk, between the two core locations (~1200?14C?yr for one core, ~620?14C?yr for the other), indicating large spatial variation. Furthermore, we also find large downcore (i.e., temporal) R(t)bulk variation of at least ~200?14C?yr for both cores. We also find a difference of 585?14C?yr between two samples taken from the same core depth. We propose that studies using bulk sediment 14C dating in large brackish water bodies should take such spatiotemporal variation in R(t)bulk into account when assessing uncertainties, thus leading to a larger, but more accurate, calibrated age range. (Less)
{"title":"Bulk sediment 14C dating in an estuarine environment: How accurate can it be?","authors":"B. Lougheed, S. Obrochta, C. Lenz, A. Mellström, B. Metcalfe, R. Muscheler, Maja Reinholdsson, I. Snowball, L. Zillén","doi":"10.1002/2016PA002960","DOIUrl":"https://doi.org/10.1002/2016PA002960","url":null,"abstract":"Abstract Due to a lack of marine macrofossils in many sediment cores from the estuarine Baltic Sea, researchers are often forced to carry out 14C determinations on bulk sediment samples. However, ambiguity surrounding the carbon source pathways that contribute to bulk sediment formation introduces a large uncertainty into 14C geochronologies based on such samples, and such uncertainty may not have been fully considered in previous Baltic Sea studies. We quantify this uncertainty by analyzing bulk sediment 14C determinations carried out on densely spaced intervals in independently dated late-Holocene sediment sequences from two central Baltic Sea cores. Our results show a difference of ~600?14C?yr in median bulk sediment reservoir age, or R(t)bulk, between the two core locations (~1200?14C?yr for one core, ~620?14C?yr for the other), indicating large spatial variation. Furthermore, we also find large downcore (i.e., temporal) R(t)bulk variation of at least ~200?14C?yr for both cores. We also find a difference of 585?14C?yr between two samples taken from the same core depth. We propose that studies using bulk sediment 14C dating in large brackish water bodies should take such spatiotemporal variation in R(t)bulk into account when assessing uncertainties, thus leading to a larger, but more accurate, calibrated age range. (Less)","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"123-131"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA002960","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48653447","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}
Alkenone mass accumulation rates (MARs) provide a proxy for export productivity in the northwestern Pacific (Ocean Drilling Program Site 1208) spanning the late Pliocene through early Pleistocene (3.0-1.8 Ma). We investigate changes in productivity associated with global cooling during the onset and expansion of Northern Hemisphere glaciation (NHG). Alkenone MARs vary on obliquity time-scales throughout, but the amplitude increases at 2.75 Ma concurrent with the intensification of NHG and cooling of the sea surface by 3 °C. The obliquity-scale variations in alkenone MARs parallel shipboard measurements of sediment color reflectance (%) with higher MARs significantly correlated (>95%) with darker (opal-rich) intervals. Variations in both lead benthic foraminiferal δ18O values by 1.5-2 kyr, suggesting that export productivity may be a contributing factor, rather than a response, to the extent of continental glaciation. The biological pump is therefore a plausible mechanism for transferring atmospheric CO2 into the deep ocean during the onset of NHG and the ensuing obliquity dominated climate regime. Obliquity-scale correlation between productivity and magnetic susceptibility is consistent with a link via westerly winds delivering terrigenous sediments and mixing the upper water column. Alkenone MARs also contain a ~400 kyr modulation. Because this periodicity is a multiple of the residence time of carbon in the ocean, it may reflect inputs of new nutrients associated with eccentricity forced changes in the terrestrial biosphere and weathering. We ascribe these findings to interactions between the East Asian winter monsoon and productivity in the North Pacific Ocean, perhaps contributing to Plio-Pleistocene climate change.
在西北太平洋(Ocean Drilling Program Site 1208)，从上新世晚期到更新世早期(3.0-1.8 Ma)，烯烃质量积累率(MARs)是衡量出口产能的一个指标。我们研究了北半球冰川(NHG)开始和扩展期间与全球变冷相关的生产力变化。在整个过程中，烯酮火星在倾角时间尺度上有所变化，但在2.75 Ma振幅增加的同时，NHG的增强和海面冷却3°C。alkenone MARs平行船载测量沉积物颜色反射率(%)的倾角尺度变化与较高MARs的较深(富含蛋白石)层段显著相关(>95%)。这两种底栖有孔虫的δ18O值变化了1.5-2 kyr，表明出口生产力可能是大陆冰川作用程度的促成因素，而不是响应因素。因此，生物泵是在NHG开始和随后的倾角主导气候状态期间将大气中的二氧化碳转移到深海的一种合理机制。生产力与磁化率的倾角尺度相关性与西风携带陆源沉积物和混合上层水柱的联系相一致。烯酮MARs也含有~ 400kyr调制。由于这种周期性是碳在海洋中停留时间的倍数，它可能反映了与陆地生物圈的偏心强迫变化和风化有关的新营养物质的输入。我们将这些发现归因于东亚冬季季风与北太平洋生产力之间的相互作用，可能有助于上新世-更新世的气候变化。
{"title":"Paleoproductivity in the northwestern Pacific Ocean during the Pliocene‐Pleistocene climate transition (3.0–1.8 Ma)","authors":"N. Venti, K. Billups, T. Herbert","doi":"10.1002/2016PA002955","DOIUrl":"https://doi.org/10.1002/2016PA002955","url":null,"abstract":"Alkenone mass accumulation rates (MARs) provide a proxy for export productivity in the northwestern Pacific (Ocean Drilling Program Site 1208) spanning the late Pliocene through early Pleistocene (3.0-1.8 Ma). We investigate changes in productivity associated with global cooling during the onset and expansion of Northern Hemisphere glaciation (NHG). Alkenone MARs vary on obliquity time-scales throughout, but the amplitude increases at 2.75 Ma concurrent with the intensification of NHG and cooling of the sea surface by 3 °C. The obliquity-scale variations in alkenone MARs parallel shipboard measurements of sediment color reflectance (%) with higher MARs significantly correlated (>95%) with darker (opal-rich) intervals. Variations in both lead benthic foraminiferal δ18O values by 1.5-2 kyr, suggesting that export productivity may be a contributing factor, rather than a response, to the extent of continental glaciation. The biological pump is therefore a plausible mechanism for transferring atmospheric CO2 into the deep ocean during the onset of NHG and the ensuing obliquity dominated climate regime. Obliquity-scale correlation between productivity and magnetic susceptibility is consistent with a link via westerly winds delivering terrigenous sediments and mixing the upper water column. Alkenone MARs also contain a ~400 kyr modulation. Because this periodicity is a multiple of the residence time of carbon in the ocean, it may reflect inputs of new nutrients associated with eccentricity forced changes in the terrestrial biosphere and weathering. We ascribe these findings to interactions between the East Asian winter monsoon and productivity in the North Pacific Ocean, perhaps contributing to Plio-Pleistocene climate change.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"92-103"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA002955","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46729495","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}
E. Gill, B. Rajagopalan, P. Molnar, Y. Kushnir, T. Marchitto
Using a multiproxy reduced dimension methodology, we reconstruct fields of Arabian Sea summer wind stress curl and Indian monsoon rainfall anomalies since early Holocene using sea surface temperature (SST) proxies (Mg/Ca and alkenones) from 27 locations scattered across the equatorial Pacific. Reconstructions of summer wind stress curl reveal positive anomalies of ∼30% greater than present day off the coastlines of Oman and Yemen at 10 ka, suggesting enhanced ocean upwelling and an enhanced monsoon jet during this time. Positive wind stress curl anomalies in these regions continued but weakened to ∼12% greater than present day at 6 ka. Wind stress curl anomalies increased by about 8% from 6 to 4 ka but declined again until 2 ka. Positive anomalies in wind stress curl during the early to middle Holocene are consistent with greater early Holocene abundances of the upwelling indicator Globigerina bulloides in the western Arabian Sea, which accumulates most rapidly in present climates during periods of marked upwelling. Spatial rainfall reconstructions reveal the greatest difference in precipitation at 10 ka over the core monsoon region (∼20–60% greater than present day) and concurrently the greatest deficit in rainfall in North East India and on the eastern side of the Western Ghats (∼10–30% less than present day). Specifically, reconstructions for 10 ka reveal 40–60% greater rainfall than present day over northwest India. These findings advance the hypothesis that teleconnections from the equatorial Pacific contributed to, if not accounted for, greater early to middle Holocene wetness over India as recorded by various (e.g., cave, lacustrine, and discharge) paleoclimate proxies throughout the monsoon region.
{"title":"Reconstruction of Indian summer monsoon winds and precipitation over the past 10,000 years using equatorial pacific SST proxy records","authors":"E. Gill, B. Rajagopalan, P. Molnar, Y. Kushnir, T. Marchitto","doi":"10.1002/2016PA002971","DOIUrl":"https://doi.org/10.1002/2016PA002971","url":null,"abstract":"Using a multiproxy reduced dimension methodology, we reconstruct fields of Arabian Sea summer wind stress curl and Indian monsoon rainfall anomalies since early Holocene using sea surface temperature (SST) proxies (Mg/Ca and alkenones) from 27 locations scattered across the equatorial Pacific. Reconstructions of summer wind stress curl reveal positive anomalies of ∼30% greater than present day off the coastlines of Oman and Yemen at 10 ka, suggesting enhanced ocean upwelling and an enhanced monsoon jet during this time. Positive wind stress curl anomalies in these regions continued but weakened to ∼12% greater than present day at 6 ka. Wind stress curl anomalies increased by about 8% from 6 to 4 ka but declined again until 2 ka. Positive anomalies in wind stress curl during the early to middle Holocene are consistent with greater early Holocene abundances of the upwelling indicator Globigerina bulloides in the western Arabian Sea, which accumulates most rapidly in present climates during periods of marked upwelling. Spatial rainfall reconstructions reveal the greatest difference in precipitation at 10 ka over the core monsoon region (∼20–60% greater than present day) and concurrently the greatest deficit in rainfall in North East India and on the eastern side of the Western Ghats (∼10–30% less than present day). Specifically, reconstructions for 10 ka reveal 40–60% greater rainfall than present day over northwest India. These findings advance the hypothesis that teleconnections from the equatorial Pacific contributed to, if not accounted for, greater early to middle Holocene wetness over India as recorded by various (e.g., cave, lacustrine, and discharge) paleoclimate proxies throughout the monsoon region.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"195-216"},"PeriodicalIF":0.0,"publicationDate":"2017-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA002971","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43233190","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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