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  • 1
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    PANGAEA
    In:  Supplement to: Griffiths, James D; Barker, Stephen; Hendry, Katharine R; Thornalley, David JR; van de Flierdt, Tina; Hall, Ian R; Anderson, Robert F (2013): Evidence of silicic acid leakage to the tropical Atlantic via Antarctic Intermediate Water during Marine Isotope Stage 4. Paleoceanography, 28(2), 307-318, https://doi.org/10.1002/palo.20030
    Publication Date: 2020-01-17
    Description: Antarctic Intermediate Water (AAIW) and Subantarctic Mode Water (SAMW) are the main conduits for the supply of dissolved silicon (silicic acid) from the deep Southern Ocean (SO) to the low-latitude surface ocean and therefore have an important control on low-latitude diatom productivity. Enhanced supply of silicic acid by AAIW (and SAMW) during glacial periods may have enabled tropical diatoms to outcompete carbonate-producing phytoplankton, decreasing the relative export of inorganic to organic carbon to the deep ocean and lowering atmospheric pCO2. This mechanism is known as the "silicic acid leakage hypothesis" (SALH). Here we present records of neodymium and silicon isotopes from the western tropical Atlantic that provide the first direct evidence of increased silicic acid leakage from the Southern Ocean to the tropical Atlantic within AAIW during glacial Marine Isotope Stage 4 (~60-70 ka). This leakage was approximately coeval with enhanced diatom export in the NW Atlantic and across the eastern equatorial Atlantic and provides support for the SALH as a contributor to CO2 drawdown during full glacial development.
    Type: Dataset
    Format: application/zip, 3 datasets
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  • 2
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    PANGAEA
    In:  Supplement to: Barker, Stephen; Kiefer, Thorsten; Elderfield, Henry (2004): Temporal changes in North Atlantic circulation constrained by planktonic foraminiferal shell weights. Paleoceanography, 19(3), PA3008, https://doi.org/10.1029/2004PA001004
    Publication Date: 2020-01-17
    Description: Records of planktonic foraminiferal shell weights for Globigerina bulloides, covering Termination I from four proximal sites at waters depths from 1150 to 4045 m in the northeast Atlantic, demonstrate the influence of dissolution superimposed upon initial shell weight variability. Records of shell weight, unaffected by dissolution, may be used as a reference for interpreting deeper records in terms of preservation history. Combining records of planktonic shell weight (and benthic d13C) from shallow and deep sites suggests that maximum oceanic stratification and incursion of southern sourced deep waters in the North Atlantic occurred at about 18-20 ka, defining the glacial mode of Atlantic circulation. Reduced stratification and enhanced preservation in deeper waters reflect conditions during Heinrich event 1. A state similar to the modern mode of Atlantic circulation was attained by about 10 ka.
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 3
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    PANGAEA
    In:  Supplement to: Jonkers, Lukas; Barker, Stephen; Hall, Ian R; Prins, Maarten A (2015): Correcting for the influence of ice-rafted detritus on grain size-based paleocurrent speed estimates. Paleoceanography, 30(10), 1347-1357, https://doi.org/10.1002/2015PA002830
    Publication Date: 2020-01-17
    Description: The grain size of deep-sea sediments provides an apparently simple proxy for current speed. However, grain size-based proxies may be ambiguous when the size distribution reflects a combination of processes, with current sorting only one of them. In particular, such sediment mixing hinders reconstruction of deep circulation changes associated with ice-rafting events in the glacial North Atlantic because variable ice-rafted detritus (IRD) input may falsely suggest current speed changes. Inverse modeling has been suggested as a way to overcome this problem. However, this approach requires high-precision size measurements that register small changes in the size distribution. Here we show that such data can be obtained using electrosensing and laser diffraction techniques, despite issues previously raised on the low precision of electrosensing methods and potential grain shape effects on laser diffraction. Down-core size patterns obtained from a sediment core from the North Atlantic are similar for both techniques, reinforcing the conclusion that both techniques yield comparable results. However, IRD input leads to a coarsening that spuriously suggests faster current speed. We show that this IRD influence can be accounted for using inverse modeling as long as wide size spectra are taken into account. This yields current speed variations that are in agreement with other proxies. Our experiments thus show that for current speed reconstruction, the choice of instrument is subordinate to a proper recognition of the various processes that determine the size distribution and that by using inverse modeling meaningful current speed reconstructions can be obtained from mixed sediments.
    Type: Dataset
    Format: application/zip, 7 datasets
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  • 4
    Publication Date: 2020-01-17
    Type: Dataset
    Format: text/tab-separated-values, 26 data points
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  • 5
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    PANGAEA
    In:  Supplement to: Broecker, Wallace S; Clark, Elizabeth; Barker, Stephen; Hajdas, Irena; Bonani, Georges; Moreno, Eva (2007): Radiocarbon age of late glacial deep water from the equatorial Pacific. Paleoceanography, 22(2), PA2206, https://doi.org/10.1029/2006PA001359
    Publication Date: 2020-01-17
    Description: Radiocarbon age differences for pairs of coexisting late glacial age benthic and planktic foraminifera shells handpicked from 10 sediment samples from a core from a depth of 2.8 km in the western equatorial Pacific are not significantly different from that of 1600 years calculated from measurements on prenuclear seawater. This places a lower limit on the depth of the interface for the hypothetical radiocarbon-depleted glacial age seawater reservoir required to explain the 190 per mil drop in the 14C/C for atmospheric CO2, which occurred during the mystery interval (17.5 to 14.5 calendar years ago). These measurements restrict the volume of this reservoir to be no more than 35% that of the ocean. Further, 14C measurements on a single Last Glacial Maximum age sample from a central equatorial Pacific core from a depth of 4.4 km water fail to reveal evidence for the required 5- to 7-kyr age difference between benthic and planktic foraminifera shells if the isolated reservoir occupied only one third of the ocean. Nor does the 13C record for benthic forams from this abyssal core yield any evidence for the excess respiration CO2 expected to be produced during thousands of years of isolation. Nor, as indicated by the presence of benthic foraminifera, was the dissolved oxygen used up in this abyssal water.
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 6
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    PANGAEA
    In:  Supplement to: Broecker, Wallace S; Barker, Stephen; Clark, Elizabeth; Hajdas, Irka; Bonani, Georges (2006): Anomalous radiocarbon ages for foraminifera shells. Paleoceanography, 21(2), PA2008, https://doi.org/10.1029/2005PA001212
    Publication Date: 2020-01-17
    Description: The causes for discordant radiocarbon results on multiple species of planktonic foraminifera from high-sedimentation-rate marine sediments are investigated. We have documented two causes for these anomalous results. One is the addition of secondary radiocarbon for which we have, to date, only one firm example. It involves an opal-rich sediment. The other is the incorporation of reworked material. Again, we have, to date, only one firm example. It involves a rapidly deposited ocean margin sediment. However, we have three other examples where reworking is the most likely explanation. On the basis of this study it is our conclusion that, where precise radiocarbon dating of high-deposition-rate marine sediment is required, a prerequisite is to demonstrate that concordant ages can be obtained on pairs of fragile and robust planktic shells. For sediment rich in opal, it is advisable to check for secondary calcite by comparing ages obtained on acid-leached samples with those on unleached samples.
    Type: Dataset
    Format: application/zip, 4 datasets
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  • 7
    Publication Date: 2020-01-17
    Type: Dataset
    Format: text/tab-separated-values, 60 data points
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  • 8
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    PANGAEA
    In:  Supplement to: Anderson, Robert F; Barker, Stephen; Fleisher, Martin Q; Gersonde, Rainer; Goldstein, Steven L; Kuhn, Gerhard; Mortyn, P Graham; Pahnke, Katharina; Sachs, Julian P (2014): Biological response to millennial variability of dust and nutrient supply in the Subantarctic South Atlantic Ocean. Philosophical Transactions of the Royal Society A-Mathematical Physical and Engineering Sciences, 372(2019), 20130054, https://doi.org/10.1098/rsta.2013.0054
    Publication Date: 2020-01-17
    Description: Fluxes of lithogenicmaterial and fluxes of three palaeo productivity proxies (organic carbon, biogenic opal and alkenones) over the past 100,000 years were determined using the 230Th-normalization method in three sediment cores from the Subantarctic South Atlantic Ocean. Features in the lithogenic flux record of each core correspond to similar features in the record of dust deposition in the EPICA Dome C ice core. Biogenic fluxes correlate with lithogenic fluxes in each sediment core. Our preferred interpretation is that South American dust, most probably from Patagonia, constitutes a major source of lithogenic material in Subantarctic South Atlantic sediments, and that past biological productivity in this region responded to variability in the supply of dust, probably due to biologically available iron carried by the dust. Greater nutrient supply as well as greater nutrient utilization (stimulated by dust) contributed to Subantarctic productivity during cold periods, in contrast to the region south of the Antarctic Polar Front (APF), where reduced nutrient supply during cold periods was the principal factor limiting productivity. The anti-phased patterns of productivity on opposite sides of the APF point to shifts in the physical supply of nutrients and to dust as cofactors regulating productivity in the Southern Ocean.
    Type: Dataset
    Format: application/zip, 3 datasets
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  • 9
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    PANGAEA
    In:  Supplement to: Barker, Stephen; Broecker, Wallace S; Clark, Elizabeth; Hajdas, Irka (2007): Radiocarbon age offsets of foraminifera resulting from differential dissolution and fragmentation within the sedimentary bioturbated zone. Paleoceanography, 22(2), PA2205, https://doi.org/10.1029/2006PA001354
    Publication Date: 2020-01-17
    Description: Shells of coexisting species of planktonic foraminifera from the Ontong Java Plateau reveal radiocarbon age offsets of up to 2200 years. Similar offsets are found between fragments and whole shells of single species. Steady state modelling of dissolution and bioturbation within the sedimentary mixed layer predicts age differences of up to several kiloyears due to the interplay between differential dissolution and fragmentation of foraminifer shells and bioturbation. The observation that fragile foraminiferal shells are systematically older than those of more robust species is more difficult to explain. Mechanisms of chemical erosion, interface dissolution, and sediment redistribution are all apparently unable to explain this phenomenon. A possible solution is presented in which a particular species may be represented by two distinct classes of shells which are more or less robust. In this case, differential dissolution and fragmentation causes an increase in the mean age as the fragile class contributes less to the remaining intact shells. This study highlights the vulnerability of low sedimentation rate cores to the effects of dissolution and bioturbation.
    Type: Dataset
    Format: text/tab-separated-values, 78 data points
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  • 10
    Publication Date: 2020-01-17
    Type: Dataset
    Format: text/tab-separated-values, 32 data points
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