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The late Paleocene and early Eocene (LPEE) are characterized by long-term (million years, Myr) global warming and by transient, abrupt (kiloyears, kyr) warming events, termed hyperthermals. Although both have been attributed to greenhouse (CO2) forcing, the longer-term trend in climate was likely influenced by additional forcing factors (i.e., tectonics) and the extent to which warming was driven by atmospheric CO2remains unclear. Here, we use a suite of new and existing observations from planktic foraminifera collected at Pacific Ocean Drilling Program Sites 1209 and 1210 and inversion of a multiproxy Bayesian hierarchical model to quantify sea surface temperature (SST) and atmospheric CO2over a 6-Myr interval. Our reconstructions span the initiation of long-term LPEE warming (~58 Ma), and the two largest Paleogene hyperthermals, the Paleocene–Eocene Thermal Maximum (PETM, ~56 Ma) and Eocene Thermal Maximum 2 (ETM-2, ~54 Ma). Our results show strong coupling between CO2and temperature over the long- (LPEE) and short-term (PETM and ETM-2) but differing Pacific climate sensitivities over the two timescales. Combined CO2and carbon isotope trends imply the carbon source driving CO2increase was likely methanogenic, organic, or mixed for the PETM and organic for ETM-2, whereas a source with higher δ13C values (e.g., volcanic degassing) is associated with the long-term LPEE. Reconstructed emissions for the PETM (5,800 Gt C) and ETM-2 (3,800 Gt C) are comparable in mass to future emission scenarios, reinforcing the value of these events as analogs of anthropogenic change.
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Staying Grounded: Establishing Baseline Critical Zone Conditions in Mississippi Prior to the Onset of Paleocene-Eocene Hyperthermals
Paleocene-Eocene hyperthermals are viewed as some of the best ancient analogs for projected future anthropogenic climate change. In order to fully evaluate the magnitude of these climactic perturbations, however, a more complete understanding of prevailing background conditions is necessary. The Mississippi Embayment, a major southwest-dipping sedimentary basin in the Gulf of Mexico coastal region of North America, contains an extensive record of Paleocene strata deposited prior to the onset of the Paleocene Carbon Isotope Maximum (PCIM), a gradual warming trend upon which the Paleocene-Eocene Thermal Maximum (PETM) was superimposed. In order to evaluate pre-PCIM paleoclimate, we focus on paleosols in the Upper Paleocene Naheola Formation. A continuous section of the Naheola is available in archival core collected by Mississippi Minerals Resources Institute from Tippah County, Mississippi, USA. We performed a suite of initial core description methods, including logging of visual observations (e.g., grain size and Munsell colors), gamma density, magnetic susceptibility, smear slide analysis, and scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDS). Results indicate a > 8-m-thick interval of 5 stacked paleosols associated with 4 lignite seams. The paleosols range in thickness from 0.6 m to 1.9 m, while the lignite seams range in thickness from 0.3 m to 1.3 m. Paleosols are characterized by low chroma matrix colors, mottling, and abundant carbonized roots. The thickest paleosols each exhibit an interval that coarsens and then fines upward; these are likely composite paleosols. Applying SEM-EDS results from all paleosols to the chemical index of alteration minus potash (CIA-K) yields preliminary mean annual precipitation estimates between 1200 and 1300 mm. The oldest paleosol contains abundant kaolinite and future stable isotope analysis will be used to reconstruct paleotemperature. Ongoing work will evaluate the relative influence of each of the five soil-forming factors on Naheola paleosol development and reexamine Paleocene- Eocene hyperthermals within the context of our results. Future work will include pollen analysis to improve chronostratigraphic control and evaluate paleoecological response to the Paleocene- Eocene climate change.
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- Award ID(s):
- 1929145
- PAR ID:
- 10315447
- Date Published:
- Journal Name:
- AGU Fall Meeting
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract. Eocene transient global warming events (hyperthermals) can provide insight into a future warmer world. While much research has focused on the Paleocene–Eocene Thermal Maximum (PETM), hyperthermals of a smaller magnitude can be used to characterize climatic responses over different magnitudes of forcing. This study identifies two events, namely the Eocene Thermal Maximum 2 (ETM2 and H2), in shallow marine sediments of the Eocene-aged Salisbury Embayment of Maryland, based on magnetostratigraphy, calcareous nannofossil, and dinocyst biostratigraphy, as well as the recognition of negative stable carbon isotope excursions (CIEs) in biogenic calcite. We assess local environmental change in the Salisbury Embayment, utilizing clay mineralogy, marine palynology, δ18O of biogenic calcite, and biomarker paleothermometry (TEX86). Paleotemperature proxies show broad agreement between surface water and bottom water temperature changes. However, the timing of the warming does not correspond to the CIE of the ETM2 as expected from other records, and the highest values are observed during H2, suggesting factors in addition to pCO2 forcing have influenced temperature changes in the region. The ETM2 interval exhibits a shift in clay mineralogy from smectite-dominated facies to illite-rich facies, suggesting hydroclimatic changes but with a rather dampened weathering response relative to that of the PETM in the same region. Organic walled dinoflagellate cyst assemblages show large fluctuations throughout the studied section, none of which seem systematically related to CIE warming. These observations are contrary to the typical tight correspondence between climate change and assemblages across the PETM, regionally and globally, and ETM2 in the Arctic Ocean. The data do indicate very warm and (seasonally) stratified conditions, likely salinity-driven, across H2. The absence of evidence for strong perturbations in local hydrology and nutrient supply during ETM2 and H2, compared to the PETM, is consistent with the less extreme forcing and the warmer pre-event baseline, as well as the non-linear response in hydroclimates to greenhouse forcing.more » « less
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Abstract The Paleocene‐Eocene Thermal Maximum (PETM) is the most pronounced global warming event of the early Paleogene related to atmospheric CO2increases. It is characterized by negative δ18O and δ13C excursions recorded in sedimentary archives and a transient disruption of the marine biosphere. Sites from the U.S. Atlantic Coastal Plain show an additional small, but distinct δ13C excursion below the onset of the PETM, coined the “pre‐onset excursion” (POE), mimicking the PETM‐forced environmental perturbations. This study focuses on the South Dover Bridge core in Maryland, where the Paleocene‐Eocene transition is stratigraphically constrained by calcareous nannoplankton and stable isotope data, and in which the POE is well‐expressed. The site was situated in a middle neritic marine shelf setting near a major outflow of the paleo‐Potomac River system. We generated high‐resolution benthic foraminiferal assemblage, stable isotope, trace‐metal, grain‐size and clay mineralogy data. The resulting stratigraphic subdivision of this Paleocene‐Eocene transition is placed within a depth transect across the paleoshelf, highlighting that the PETM sequence is relatively expanded. The geochemical records provide detailed insights into the paleoenvironment, developing from a well‐oxygenated water column in latest Paleocene to a PETM‐ecosystem under severe biotic stress‐conditions, with shifts in food supply and temperature, and under dysoxic bottom waters in a more river‐dominated setting. Environmental changes started in the latest Paleocene and culminated atthe onset of the PETM, hinting to an intensifying trigger rather than to an instantaneous event at the Paleocene‐Eocene boundary toppling the global system.more » « less
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