Showing papers by "Ellen Thomas published in 2010"

High-resolution deep-sea carbon and oxygen isotope records of Eocene Thermal Maximum 2 and H2

Abstract: Eocene Thermal Maximum 2 (ETM2) and H2 were two short-lived global warming events that occurred ~2 m.y. after the Paleocene-Eocene thermal maximum (PETM, ca. 56 Ma). We have generated benthic foraminiferal stable carbon and oxygen isotope records of four sites along a depth transect on Walvis Ridge (~3.5-1.5 km paleodepth, southeast Atlantic Ocean) and one site on Maud Rise (Weddell Sea) to constrain the pattern and magnitude of their carbon isotope excursions (CIEs) and deep-sea warming. At all sites, ETM2 is characterized by ~3 °C warming and a -1.4‰ CIE. The H2 event that occurred ~100 k.y. later is associated with ~2 °C warming and a -0.8‰ CIE. The magnitudes of the δ 13 C and δ 18 O excursions of both events are signifi cantly smaller than those during the PETM, but their coherent relation indicates that the δ 13 C change of the exogenic carbon pool was similarly related to warming during these events, despite the much more gradual and transitioned onset of ETM2 and H2.

Coherent pattern and timing of the carbon isotope excursion and warming during Eocene Thermal Maximum 2 as recorded in planktic and benthic foraminifera

Abstract: [1] Eocene Thermal Maximum 2 (ETM2; ∼53.7 Ma) occurred approximately 2 Myr after the Paleocene‐ Eocene Thermal Maximum (∼55.5 Ma) and was characterized by a deep‐sea warming of >3°C, associated with massive release of carbon into the ocean‐atmosphere system. We performed single‐specimen stable isotope analyses of the planktic foraminiferal genera Acarinina (surface dweller) and Subbotina (thermocline dweller) from Ocean Drilling Program Sites 1265, 1267, and 1263 (Walvis Ridge, SE Atlantic Ocean) and compared high‐resolution planktic and benthic stable isotope records to constrain the surface warming and the bathymetric pathway of the carbon isotope excursion during ETM2. Tests of the thermocline dweller Subbotina are absent from sediment deposited during the peak of ETM2. The Acarinina carbon and oxygen isotope records of Sites 1263, 1265, and 1267 are strikingly similar, despite some test recrystallization and large differences in burial depths. Sea surface temperature (SST) estimates based on d 18 O isotope values of Acarinina indicate a SST increase of ∼2°C, significantly less than the >3°C estimated for bottom water warming. The maximum negative carbon isotope excursion for Acarinina was ∼1.7‰, slightly more than in the deep sea (∼1.4‰). The planktic and benthic isotope records do not show time lags, indicating that during ETM2 the isotopically depleted carbon injected into the ocean‐atmosphere system was rapidly mixed within all oceanic carbon reservoirs.

Export productivity and carbonate accumulation in the Pacific Basin at the transition from a greenhouse to icehouse climate (late Eocene to early Oligocene)

Abstract: [1] The late Eocene through earliest Oligocene (40–32 Ma) spans a major transition from greenhouse to icehouse climate, with net cooling and expansion of Antarctic glaciation shortly after the Eocene/Oligocene (E/O) boundary. We investigated the response of the oceanic biosphere to these changes by reconstructing barite and CaCO3 accumulation rates in sediments from the equatorial and North Pacific Ocean. These data allow us to evaluate temporal and geographical variability in export production and CaCO3 preservation. Barite accumulation rates were on average higher in the warmer late Eocene than in the colder early Oligocene, but cool periods within the Eocene were characterized by peaks in both barite and CaCO3 accumulation in the equatorial region. We infer that climatic changes not only affected deep ocean ventilation and chemistry, but also had profound effects on surface water characteristics influencing export productivity. The ratio of CaCO3 to barite accumulation rates, representing the ratio of particulate inorganic C accumulation to Corg export, increased dramatically at the E/O boundary. This suggests that long-term drawdown of atmospheric CO2 due to organic carbon deposition to the seafloor decreased, potentially offsetting decreasing pCO2 levels and associated cooling. The relatively larger increase in CaCO3 accumulation compared to export production at the E/O suggests that the permanent deepening of the calcite compensation depth (CCD) at that time stems primarily from changes in deep water chemistry and not from increased carbonate production.

Cenozoic record of elongate, cylindrical, deep-sea benthic foraminifera in the indian ocean (odp sites 722, 738, 744, 758, and 763)

Abstract: A group of ,100 species of elongate, cylindrical deep-sea benthic foraminifera (families Stilostomellidae, Pleurostomellidae, Nodosariidae) with complex, often constricted apertural structures, became extinct during increasingly cold glacial periods in the late Pliocene to mid-Pleistocene Climate Transition (MPT, ,2.6–0.6 Ma). We document the evolutionary history and architecture of this Extinction Group (Ext. Gp) through the Cenozoic at four lower bathyalupper abyssal Indian Ocean sites (ODP 722, 744/738, 758, 763), seeking clues to the cause of this morphologicallytargeted extinction episode late in the Cenozoic. Eighty percent of the 116 Ext Gp. species present in the Cenozoic of the Indian Ocean originated globally in the Eocene or earlier, compared with 23–37% of other Quaternary deep-sea foraminifera. The Ext. Gp had its peak species richness and relative and absolute abundances in the late Eocene. The rapid warming of the Paleocene-Eocene Thermal Maximum, that resulted in a loss of 30–50% of deep-sea foraminiferal species, had no impact on the Ext. Gp in the one Indian Ocean section (ODP 744/738) studied. Major Cenozoic changes in the Ext. Gp, including increased species turnover, changes in dominant species, a decline in abundance, loss in diversity, and finally extinction, mostly occurred during the middle Eocene to early Oligocene, middle to late Miocene, and late Pliocene to middle Pleistocene. These were times of stepped increase in the volume of polar ice, global oceanic cooling, surface-water eutrophication, seasonality of phytoplankton production, deep-water ventilation, and southern deep-water carbonate corrosiveness. The final decline and disappearance of the Ext. Gp began in the late Miocene at high latitudes (744/738), but not until the late Pliocene (758, 763) or MPT (722) at lower latitudes. We hypothesize that the loss of the Ext. Gp of deep-sea foraminifera may have been caused by the decline or demise of their specific food source (detrital phytoplankton or bottom-dwelling microbes) that was abundant in the Greenhouse World and was decimated by the stepwise cooling, ventilation, or eutrophication of the oceans that began in the middle and late Eocene.

Evolución paleoambiental del tránsito Eoceno-Oligoceno en el Atlántico sur (Sondeo 1263) basada en foraminíferos bentónicos Paleoenvironmental evolution of the Eocene-Oligocene transition in the South Atlantic (Site 1263) based on benthic foraminifera

Abstract: Quantitative analisis of benthic foraminiferal assemblages at South Atlantic Site 1263 provided information about paleobathymetry and changes in benthic foraminiferal faunas across the Eocene-Oligocene boundary. Benthic foraminifera indicate an upper abyssal depth (~ 2000 m). Changes in relative abundances of Epistominella exigua, Epistominella vitrea, Globocassidulina subglobosa and Nuttallides umbonifera, probably indicate variability in seasonality of export productivity, bottom current intensity and carbonate corrosivity. The transition into glaciation event Oi-1 is characterized by highly seasonal productivity, Oi-1 itself by less variability, probably at fairly active bottom currents.

Evolución paleoambiental del tránsito Eoceno-Oligoceno en el Atlántico sur (Sondeo 1263) basada en foraminíferos bentónicos

Abstract: Quantitative analisis of benthic foraminiferal assemblages at South Atlantic Site 1263 provided information about paleobathymetry and changes in benthic foraminiferal faunas across the Eocene-Oligocene boundary. Benthic foraminifera indicate an upper abyssal depth (~ 2000 m). Changes in relative abundances of Epistominella exigua, Epistominella vitrea, Globocassidulina subglobosa and Nuttallides umbonifera, probably indicate variability in seasonality of export productivity, bottom current intensity and carbonate corrosivity. The transition into glaciation event Oi-1 is characterized by highly seasonal productivity, Oi-1 itself by less variability, probably at fairly active bottom currents.

Cenozoic record of elongate, cylindrical, deep-sea benthic foraminifera in the Indian Ocean

Abstract: A group of ~100 species of elongate, cylindrical deep-sea benthic foraminifera (families Stilostomellidae, Pleurosto-mellidae, Nodosariidae) with complex, often constricted apertural structures, became extinct during increasingly cold glacial periods in the late Pliocene to mid-Pleistocene Climate Transition (MPT, ~26-06 Ma) We document the evolutionary history and architecture of this Extinction Group (Ext Gp) through the Cenozoic at four lower bathyal-upper abyssal Indian Ocean sites (ODP 722, 744/738, 758, 763), seeking clues to the cause of this morphologically-targeted extinction episode late in the Cenozoic Eighty percent of the 116 Ext Gp species present in the Cenozoic of the Indian Ocean originated globally in the Eocene or earlier, compared with 23-37% of other Quaternary deep-sea foraminifera The Ext Gp had its peak species richness and relative and absolute abundances in the late Eocene The rapid warming of the Paleocene-Eocene Thermal Maximum, that resulted in a loss of 30-50% of deep-sea foraminiferal species, had no impact on the Ext Gp in the one Indian Ocean section (ODP 744/738) studied Major Cenozoic changes in the Ext Gp, including increased species turnover, changes in dominant species, a decline in abundance, loss in diversity, and finally extinction, mostly occurred during the middle Eocene to early Oligocene, middle to late Miocene, and late Pliocene to middle Pleistocene These were times of stepped increase in the volume of polar ice, global oceanic cooling, surface-water eutrophication, seasonality of phytoplankton production, deep-water ventilation, and southern deep-water carbonate corrosiveness The final decline and disappearance of the Ext Gp began in the late Miocene at high latitudes (744/738), but not until the late Pliocene (758, 763) or MPT (722) at lower latitudes We hypothesize that the loss of the Ext Gp of deep-sea foraminifera may have been caused by the decline or demise of their specific food source (detrital phytoplankton or bottom-dwelling microbes) that was abundant in the Greenhouse World and was decimated by the stepwise cooling, ventilation, or eutrophication of the oceans that began in the middle and late Eocene

Marine carbon cycling following end Cretaceous extinction

Abstract: (1) University of Bristol, School of Geographical Sciences, Bristol, United Kingdom (andy@seao2.org), (2) Department of Geology & Geophysics, Yale University, New Haven, CT, (3) Department of Earth and Environmental Sciences, Wesleyan University, Middletown, CT, (4) Dept. Ciencias de la Tierra, Universidad de Zaragoza, Zaragoza (Spain) , (5) Instituto Universitario de Investigacion de Ciencias Ambientales de Aragon, Universidad de Zaragoza, Zaragoza (Spain), (6) Department of Earth Sciences, University of Bristol, Bristol (UK)

Paleocene Eocene Thermal Maximum and Eocene Thermal Maximum 2: hyperthermals of one kind?

Abstract: (1) Faculty of Geosciences, Utrecht University, Utrecht, Netherlands (stap@geo.uu.nl), (2) Department of Geology and Geophysics, Yale University, New Haven, USA, (3) Department of Earth and Environmental Sciences, Wesleyan University, Middletown, USA, (4) Biomarine Sciences, Institute of Environmental Biology, Utrecht University, The Netherlands, (5) School of Ocean and Earth Science, National Oceanography Centre, Southampton, UK, (6) Earth and Planetary Sciences, University of California, Santa Cruz, USA