Preliminary site report for the 2005 ICDP-USGS deep corehole in the Chesapeake Bay impact crater

First report for the ICDP-USGS 1.7-km-deep corehole drilled into the central part of the Chesapeake Bay impact crater during 2005

Descent toward the icehouse: Eocene sea surface cooling inferred from GDGT distributions

The TEX86 proxy, based on the distribution of marine isoprenoidal glycerol dialkyl glycerol tetraether lipids (GDGTs), is increasingly used to reconstruct sea surface temperature (SST) during the Eocene epoch (56.0–33.9 Ma). Here we compile published TEX86 records, critically reevaluate them in light of new understandings in TEX86 palaeothermometry, and supplement them with new data in order to evaluate long-term temperature trends in the Eocene. We investigate the effect of archaea other than marine Thaumarchaeota upon TEX86 values using the branched-to-isoprenoid tetraether index (BIT), the abundance of GDGT-0 relative to crenarchaeol (%GDGT-0), and the Methane Index (MI). We also introduce a new ratio, % GDGTRS, which may help identify Red Sea-type GDGT distributions in the geological record. Using the offset between TEX86H and TEX86L(ΔH-L) and the ratio between GDGT-2 and GDGT-3 ([2]/[3]), we evaluate different TEX86 calibrations and present the first integrated SST compilation for the Eocene (55 to 34 Ma). Although the available data are still sparse some geographic trends can now be resolved. In the high latitudes (>55°), there was substantial cooling during the Eocene (~6°C). Our compiled record also indicates tropical cooling of ~2.5°C during the same interval. Using an ensemble of climate model simulations that span the Eocene, our results indicate that only a small percentage (~10%) of the reconstructed temperature change can be ascribed to ocean gateway reorganization or paleogeographic change. Collectively, this indicates that atmospheric carbon dioxide (pCO2) was the likely driver of surface water cooling during the descent toward the icehouse

Abundance of Discoasters during the PETM at Bass River, Wilson Lake and South Dover Bridge

The Paleocene-Eocene Thermal Maximum (PETM) is characterized by a transient group of nannoplankton, belonging to the genus Discoaster. Our investigation of expanded shelf sections provides unprecedented detail of the morphology and phylogeny of the transient Discoaster during the PETM and their relationship with environmental change. We observe a much larger range of morphological variation than previously documented suggesting that the taxa belonged to a plexus of highly gradational morphotypes rather than individual species. We propose that the plexus represents malformed ecophenotypes of a single species that migrated to a deep photic zone refuge during the height of PETM warming and eutrophication. Anomalously, high rates of organic matter remineralization characterized these depths during the event and led to lower saturation levels, which caused malformation. The proposed mechanism explains the co-occurrence of malformed Discoaster with pristine species that grew in the upper photic zone; moreover, it illuminates why malformation is a rare phenomenon in the paleontological record

Nannoplankton community across a shelf transect during the onset of the Paleocene-Eocene Thermal Maximum

Warming and other environmental changes during the Paleocene‐Eocene Thermal Maximum (PETM) led to profound shifts in the composition and structure of nannoplankton assemblages. Here we analyze the nature of these changes in expanded records from the Cambridge‐Dorchesterand Mattawoman Creek‐Billingsley Road cores in Maryland. These cores comprise part of a transect of five paleoshelf cores from Maryland and New Jersey. We integrate multivariate analysis of assemblage data with proxy data to revise understanding of the paleoecological affinities of key species. In particular, Discoaster and Fasciculithus are interpreted as thermophiles without adaptation to particular nutrient levels, while Hornibrookina is considered an opportunist adapted to highly variable nearshore environments. Together the cores show consistent margin‐wide changes across the onset of the PETM, including a pulse of pre‐event warming, possibly combined withlower salinity, high seasonality, or increased turbidity. The event itself was characterized by continued warming and eutrophication across the paleoshelf. The Maryland sites experienced higher environmental variability as a result of their proximity to large river systems

Biometric data for the Paleogene calcareous nannofossil genus Hornibrookina from light and scanning electron microscopy

Biometric measurements from specimens from the calcareous nannofossil Hornibrookina were collected to help determine taxonomic and evolutionary relationships within the genus. Two sets of data are included. The first (Supplementary Data 1) are measurements taken from SEM microphotographs (published and previously unpublished) to determine the number and arrangement of the bars or bar-like structures found in the nannofossil central areas of different Hornibrookina species. The second (Supplementary Data 2) contains measurements from light microphotographs for all Hornibrookina species include coccolith length and width measured along the cardinal axes of the elliptical nannofossils. Additional measurements of the length and width of the central areas of specimens from the Hornibrookina teuriensis-H. edwardsi lineage were taken to compare this feature for its taxonomic significance. The specimens measure range in age from early Paleocene to early Eocene. Specimens are from various locations globally including the Coastal Plain of eastern United States (Maryland, Virginia, New Jersey), Tunisia, North Sea, New Zealand, South Atlantic (São Paulo Plateau), and the Southern Ocean (Maud Rise)