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  • 1
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    Controls over δ 44/40 Ca and Sr/Ca variations in coccoliths: New perspectives from laboratory cultures and cellular models (2018)
    Elsevier
    In:  Earth and Planetary Science Letters, 481 . pp. 48-60.
    Details
    Publication Date: 2021-02-08
    Description: Coccoliths comprise a major fraction of the global carbonate sink. Therefore, changes in coccolithophores' Ca isotopic fractionation could affect seawater Ca isotopic composition, affecting interpretations of the global Ca cycle and related changes in seawater chemistry and climate. Despite this, a quantitative interpretation of coccolith Ca isotopic fractionation and a clear understanding of the mechanisms driving it are not yet available. Here, we address this gap in knowledge by developing a simple model (CaSri–Co) to track coccolith Ca isotopic fractionation during cellular Ca uptake and allocation to calcification. We then apply it to published and new δ44/40Ca and Sr/Ca data of cultured coccolithophores of the species Emiliania huxleyi and Gephyrocapsa oceanica. We identify changes in calcification rates, Ca retention efficiency and solvation–desolvation rates as major drivers of the Ca isotopic fractionation and Sr/Ca variations observed in cultures. Higher calcification rates, higher Ca retention efficiencies and lower solvation–desolvation rates increase both coccolith Ca isotopic fractionation and Sr/Ca. Coccolith Ca isotopic fractionation is most sensitive to changes in solvation–desolvation rates. Changes in Ca retention efficiency may be a major driver of coccolith Sr/Ca variations in cultures. We suggest that substantial changes in the water structure strength caused by past changes in temperature could have induced significant changes in coccolithophores' Ca isotopic fractionation, potentially having some influence on seawater Ca isotopic composition. We also suggest a potential effect on Ca isotopic fractionation via modification of the solvation environment through cellular exudates, a hypothesis that remains to be tested.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.epsl.2017.10.013
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    The transition on North America from the warm humid Pliocene to the glaciated Quaternary traced by eolian dust deposition at a benchmark North Atlantic Ocean drill site (2014)
    Elsevier
    In:  Quaternary Science Reviews, 93 . pp. 125-141.
    Details
    Publication Date: 2016-09-15
    Description: We present Plio-Pleistocene records of sediment color, %CaCO3, foraminifer fragmentation, benthic carbon isotopes (δ13C) and radiogenic isotopes (Sr, Nd, Pb) of the terrigenous component from IODP Site U1313, a reoccupation of benchmark subtropical North Atlantic Ocean DSDP Site 607. We show that (inter)glacial cycles in sediment color and %CaCO3 pre-date major northern hemisphere glaciation and are unambiguously and consistently correlated to benthic oxygen isotopes back to 3.3 million years ago (Ma) and intermittently so probably back to the Miocene/Pliocene boundary. We show these lithological cycles to be driven by enhanced glacial fluxes of terrigenous material (eolian dust), not carbonate dissolution (the classic interpretation). Our radiogenic isotope data indicate a North American source for this dust (∼3.3–2.4 Ma) in keeping with the interpreted source of terrestrial plant wax-derived biomarkers deposited at Site U1313. Yet our data indicate a mid latitude provenance regardless of (inter)glacial state, a finding that is inconsistent with the biomarker-inferred importance of glaciogenic mechanisms of dust production and transport. Moreover, we find that the relation between the biomarker and lithogenic components of dust accumulation is distinctly non-linear. Both records show a jump in glacial rates of accumulation from Marine Isotope Stage, MIS, G6 (2.72 Ma) onwards but the amplitude of this signal is about 3–8 times greater for biomarkers than for dust and particularly extreme during MIS 100 (2.52 Ma). We conclude that North America shifted abruptly to a distinctly more arid glacial regime from MIS G6, but major shifts in glacial North American vegetation biomes and regional wind fields (exacerbated by the growth of a large Laurentide Ice Sheet during MIS 100) likely explain amplification of this signal in the biomarker records. Our findings are consistent with wetter-than-modern reconstructions of North American continental climate under the warm high CO2 conditions of the Early Pliocene but contrast with most model predictions for the response of the hydrological cycle to anthropogenic warming over the coming 50 years (poleward expansion of the subtropical dry zones).
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.quascirev.2014.04.005
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Response to “Comment on ‘The transition on North America from the warm humid Pliocene to the glaciated Quaternary traced by eolian dust deposition at a benchmark North Atlantic Ocean drill site’, by David Lang et al.” (2014)
    Elsevier
    In:  Quaternary Science Reviews, 103 . pp. 179-183.
    Details
    Publication Date: 2016-09-16
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.quascirev.2014.08.015
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Escape of methane gas from the seabed along the West Spitsbergen continental margin (2009)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 36 . L15608.
    Details
    Publication Date: 2017-10-13
    Description: More than 250 plumes of gas bubbles have been discovered emanating from the seabed of the West Spitsbergen continental margin, in a depth range of 150– 400 m, at and above the present upper limit of the gas hydrate stability zone (GHSZ). Some of the plumes extend upward to within 50 m of the sea surface. The gas is predominantly methane. Warming of the northward-flowing West Spitsbergen current by 1° C over the last thirty years is likely to have increased the release of methane from the seabed by reducing the extent of the GHSZ, causing the liberation of methane from decomposing hydrate. If this process becomes widespread along Arctic contine ntal margins, tens of Teragrams of methane per year could be released into the ocean.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2009GL039191
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Enhanced late Miocene chemical weathering and altered precipitation patterns in the watersheds of the Bay of Bengal recorded by detrital clay radiogenic isotopes (2021)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-07
    Description: The late Miocene was a period of declining CO2 levels and extensive environmental changes, which likely had a large impact on monsoon strength as well as on the weathering and erosion intensity in the South Asian Monsoon domain. To improve our understanding of these feedback systems, detrital clays from the southern Bay of Bengal (International Ocean Discovery Program Site U1443) were analysed for the radiogenic isotope compositions of Sr, Nd, and Pb to reconstruct changes in sediment provenance and weathering regime related to South Asian Monsoon rainfall from 9 to 5 Ma. The 100 kyr resolution late Miocene to earliest Pliocene record suggests overall low variability in the provenance of clays deposited on the Ninetyeast Ridge. However, at 7.3 Ma, Nd and Pb isotope compositions indicate a switch to an increased relative contribution from the Irrawaddy River (by ∼10 %). This shift occurred during the global benthic δ13C decline and we suggest that global cooling and increasing aridity resulted in an eastward shift of precipitation patterns leading to a more focussed erosion of the Indo-Burman Ranges. Sr isotope compositions were decoupled from Nd and Pb isotope signatures and became more radiogenic between 6 and 5 Ma. Grassland expansion generating thick, easily weatherable soils may have led to an environment supporting intense chemical weathering which is likely responsible for the elevated detrital clay 87Sr/86Sr ratios during this time. This change in Sr isotope signatures may also have contributed to the late Miocene increase of the global seawater Sr isotope composition.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: other
    Format: other
    Format: other
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Toward a Cenozoic history of atmospheric CO 2 (2023)
    AAAS (American Association for the Advancement of Science)
    Details
    Publication Date: 2024-02-23
    Description: The geological record encodes the relationship between climate and atmospheric carbon dioxide (CO 2 ) over long and short timescales, as well as potential drivers of evolutionary transitions. However, reconstructing CO 2 beyond direct measurements requires the use of paleoproxies and herein lies the challenge, as proxies differ in their assumptions, degree of understanding, and even reconstructed values. In this study, we critically evaluated, categorized, and integrated available proxies to create a high-fidelity and transparently constructed atmospheric CO 2 record spanning the past 66 million years. This newly constructed record provides clearer evidence for higher Earth system sensitivity in the past and for the role of CO 2 thresholds in biological and cryosphere evolution. Editor’s summary The concentration of atmospheric carbon dioxide is a fundamental driver of climate, but its value is difficult to determine for times older than the roughly 800,000 years for which ice core records are available. The Cenozoic Carbon dioxide Proxy Integration Project (CenCO2PIP) Consortium assessed a comprehensive collection of proxy determinations to define the atmospheric carbon dioxide record for the past 66 million years. This synthesis provides the most complete record yet available and will help to better establish the role of carbon dioxide in climate, biological, and cryosphere evolution. — H. Jesse Smith
    Type: Article , PeerReviewed
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    The middle to late Miocene "Carbonate Crash" in the equatorial Indian Ocean (2019)
    PANGAEA
    In:  Supplement to: Lübbers, Julia; Kuhnt, Wolfgang; Holbourn, Ann E; Bolton, Clara T; Gray, Emmeline; Usui, Yoichi; Kochhann, Karlos Guilherme Diemer; Beil, Sebastian; Andersen, Nils (2019): The Middle to Late Miocene "Carbonate Crash" in the Equatorial Indian Ocean. Paleoceanography and Paleoclimatology, 34(5), 813-832, https://doi.org/10.1029/2018PA003482
    Details
    Publication Date: 2023-02-24
    Description: We integrate benthic foraminiferal stable isotopes, X-ray fluorescence elemental ratios, and carbonate accumulation estimates in a continuous sedimentary archive recovered at International Ocean Discovery Program Site U1443 (Ninetyeast Ridge, Indian Ocean) to reconstruct changes in carbonate deposition and climate evolution over the interval 13.5 to 8.2 million years ago. Declining carbonate percentages together with a marked decrease in carbonate accumulation rates after ~13.2 Ma signal the onset of a prolonged episode of reduced carbonate deposition. This extended phase, which lasted until ~8.7 Ma, coincides with the middle to late Miocene Carbonate Crash, originally identified in the eastern equatorial Pacific Ocean and the Caribbean Sea. Inter-ocean comparison reveals that intense carbonate impoverishment at Site U1443 (~11.5 to ~10 Ma) coincides with prolonged episodes of reduced carbonate deposition in all major tropical ocean basins. This implies that global changes in the intensity of chemical weathering and riverine input of calcium and carbonate ions into the ocean reservoir were instrumental in driving the Carbonate Crash. An increase in U1443 Log(Ba/Ti) together with a change in sediment color from red to green indicate a rise in organic export flux to the sea floor after ~11.2 Ma, which predates the global onset of the Biogenic Bloom. This early rise in export flux from biological production may have been linked to increased advection of nutrients and intensification of upper ocean mixing, associated with changes in the seasonality and intensity of the Indian Monsoon.
    Keywords: Carbonate Crash; Indian Ocean; Integrated Ocean Drilling Program / International Ocean Discovery Program; IODP; stable carbon isotopes; stable oxygen isotopes; XRF
    Type: Dataset
    Format: application/zip, 6 datasets
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    DATA PANGAEA
  • 8
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    Mg, Al, Mn, Zn, Sr and Ba/Ca ratios of Globigerinoides ruber chamber f-1 from sediment core MD97-2121 (2013)
    PANGAEA
    Details
    Publication Date: 2023-06-27
    Keywords: AGE; CALYPSO; Calypso Corer; Depth, bottom/max; DEPTH, sediment/rock; Depth, top/min; Globigerinoides ruber; Globigerinoides ruber, Aluminium/Calcium ratio; Globigerinoides ruber, Aluminium/Calcium ratio, error; Globigerinoides ruber, Barium/Calcium ratio; Globigerinoides ruber, Barium/Calcium ratio, error; Globigerinoides ruber, Magnesium/Calcium ratio, error; Globigerinoides ruber, Manganese/Calcium ratio; Globigerinoides ruber, Manganese/Calcium ratio, error; Globigerinoides ruber, Strontium/Calcium ratio; Globigerinoides ruber, Strontium/Calcium ratio, error; Globigerinoides ruber, Zinc/Calcium ratio; Globigerinoides ruber, Zinc/Calcium ratio, error; IMAGES III - IPHIS; Marion Dufresne (1995); MD106; MD972121; MD97-2121
    Type: Dataset
    Format: text/tab-separated-values, 523 data points
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    DATA PANGAEA
  • 9
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    Geochemistry of planktonic foraminifera of sediment core MD97-2121 (2013)
    PANGAEA
    In:  Supplement to: Marr, Julene P; Carter, Lionel; Bostock, Helen C; Bolton, Clara T; Smith, Euan (2013): Southwest Pacific Ocean response to a warming world: Using Mg/Ca, Zn/Ca, and Mn/Ca in foraminifera to track surface ocean water masses during the last deglaciation. Paleoceanography, 28(2), 347-362, https://doi.org/10.1002/palo.20032
    Details
    Publication Date: 2023-06-27
    Description: In situ measurements of Mg/Ca, Zn/Ca, Mn/Ca, and Ba/Ca in Globigerinoides bulloides and Globigerina ruber from southwest Pacific core top sites and plankton tow are reported and their potential as paleoproxies is explored. The modern samples cover 20° of latitude from 34°S to 54°S, 7-19°C water temperature, and variable influence of subantarctic (SAW) and subtropical (STW) surface waters. Trace element signatures recorded in core top and plankton tow planktic foraminifera are examined in the context of the chemistry and nutrient profiles of their modern water masses. Our observations suggest that Zn/Ca and Mn/Ca may have the potential to trace SAW and STW. Intraspecies and interspecies offsets identified by in situ measurements of Mg/Ca and Zn/Ca indicate that these ratios may also record changes in thermal and nutrient stratification in the upper ocean. We apply these potential proxies to fossilized foraminifera from the high-resolution core MD97 2121. At the Last Glacial Maximum, surface water Mg/Ca temperature estimates indicate that temperatures were approximately 6-7°C lower than those of the present, accompanied by low levels of Mn/Ca and Zn/Ca and minimal thermal and nutrient stratification. This is consistent with regional dominance of SAW and reduced STW inflow associated with a reduced South Pacific Gyre (SPG). Upper ocean thermal and nutrient stratification collapsed during the Antarctic Cold Reversal, before poleward migration of the zonal winds and ocean fronts invigorated the SPG and increased STW inflow in the early Holocene. Together with reduced winds, this favored a stratified upper ocean from circa 10 ka to the present.
    Keywords: CALYPSO; Calypso Corer; IMAGES III - IPHIS; Marion Dufresne (1995); MD106; MD972121; MD97-2121
    Type: Dataset
    Format: application/zip, 3 datasets
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    DATA PANGAEA
  • 10
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    Late Miocene radiogenic Sr, Nd, and Pb isotope data of the detrital clay fraction from IODP Site 353-U1443 (2021)
    PANGAEA
    Details
    Publication Date: 2023-07-10
    Description: Data from Enhanced late Miocene chemical weathering and altered precipitation patterns in the watersheds of the Bay of Bengal recorded by detrital clay radiogenic isotopes in Paleoceanography and Paleoclimatology. Marine sediment samples from the late Miocene (approximately 9 to 5 million years ago) were taken from International Ocean Discovery Program (IODP) Site U1443 located on the top of the Ninety East ridge in the southern Bay of Bengal. Samples were taken along the composite sediment section or splice and the age model based on shipboard calcareous nannofossil biostratigraphy and magnetostratigraphy was refined using the stable carbon isotopes of benthic foraminifera. The detrital silicates of the clay size fraction were isolated and measured for their radiogenic Sr, Nd, and Pb isotope composition by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) to investigate the provenance of clays produced by weathering in the surrounding watersheds.
    Keywords: 353-U1443A; 353-U1443B; 353-U1443C; AGE; Bay of Bengal; calculated, 2 sigma; Core; Cruise/expedition; Depth, composite; detrital clays; DRILL; Drilling/drill rig; DSDP/ODP/IODP sample designation; Event label; Exp353; Hole; Interval number; Joides Resolution; Late Miocene; Lead-206/Lead-204 ratio; Lead-206/Lead-204 ratio, standard deviation; Lead-207/Lead-204 ratio; Lead-207/Lead-204 ratio, standard deviation; Lead-208/Lead-204 ratio; Lead-208/Lead-204 ratio, standard deviation; MC-ICP-MS; Neodymium-143/Neodymium-144 ratio; Radiogenic isotopes; Sample code/label; Sample comment; Section; Site; Strontium-87/Strontium-86 ratio; Strontium-87/Strontium-86 ratio, standard deviation; Type; Weathering; ε-Neodymium; ε-Neodymium, standard deviation
    Type: Dataset
    Format: text/tab-separated-values, 968 data points
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    DATA PANGAEA
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