A long-term, high-latitude record of Eocene hydrological change in the Greenland region

Abstract

A range of proxy approaches have been used to reconstruct short-term changes to Earth's hydrological cycle during the early Eocene hyperthermals. However, little is known about the response of Earth's hydrological and biogeochemical systems to long-term Cenozoic cooling, which began following the Early Eocene Climatic Optimum (53.3-49.4 million years ago; Ma). Here, we use the molecular distribution and isotopic composition of terrestrial biomarkers preserved in marine sediments of ODP Site 913, East Greenland, to develop a long-term record of high-latitude hydrological change between 50 and 34 Ma. There is a marked decline in the concentration of conifer-derived diterpenoids and angiosperm-derived triterpenoids during the Eocene. As the input of wind-blown conifer pollen remains stable during this interval, this implies that decreasing di-and triterpenoid concentrations reflect declining influence of fluvial inputsand perhaps terrestrial runoffthroughout the Eocene. Branched GDGTs and bacterial-derived hopanes indicate an increased input of soil-and kerogen-derived organic matter, respectively, after 38 Ma. This coincides with evidence for ice rafted debris and suggests input of organic matter via glacial processes. This also implies some continental glaciation occurred in the middle-tolate Eocene. Leaf wax hydrogen isotopes extending throughout this sectionthe first such long-term record from the Paleogene-indicate that precipitation δ 2 H was persistently higher than that of modern coastal Greenland, consistent with warmer ocean source waters and enhanced poleward moisture transport. Non-intuitively, however, this effect appears to have been smallest during the warmest part of the record, and higher δ 2 H values occur in the middle Eocene. Although interpretation of these hydrogen isotope trends is unclear, they clearly indicatealongside the changes in biomarker abundancesa perturbed hydrological cycle through the This is a non-peer reviewed pre-print uploaded to EarthArXix Eocene in coastal Greenland. More long-term records are required to ascertain if this represents regional or global hydrological reorganisation.

Late Eocene Record of Hydrology and Temperature From Prydz Bay, East Antarctica

“…Within the alkane fraction, we detected hopanes, bacterial membrane lipids that are used as thermal maturity markers (Inglis et al, 2020). We found hopanes in the alkane fractions of all Prydz Bay sediments, including the most mature samples (high abundance of short-chain n-alkanes with low CPI, UCM and no alkanes > C 25 ) from the coal-rich layer.…”

Northward Shifts in the Polar Front Preceded Bølling and Holocene Warming in Southwestern Scandinavia

“…Terrestrial (C 28 ) and aquatic (C 22 ) n ‐alkanoic acid δ 2 H reflect the δ 2 H value of source water (Thomas et al, 2020), with a biosynthetic offset that is generally constant for a given plant community (Daniels et al, 2017; Sachse et al, 2012). Changes in the relative abundance of plant growth forms (i.e., grasses vs. shrubs) within a catchment can cause changes to δ 2 H wax due to differences in biosynthetic fractionation; however, the timing of δ 2 H wax changes at Kringlemyr is asynchronous with plant community changes as recorded by pollen in nearby Liastemmen (Paus, 1989), and we do not attempt a pollen‐based correction of our δ 2 H wax data (Text S3) (Feakins, 2013; Inglis et al, 2020; McFarlin et al, 2019). The δ 2 H of water in lakes with residence times less than 6 months is similar to the δ 2 H of precipitation during any given season (Cluett & Thomas, 2020; Thomas et al, 2020).…”

Climate system asymmetries drive eccentricity pacing of hydroclimate during the early Eocene greenhouse

“…Climate simulations of the early Eocene broadly suggest an intensification of the hydrologic cycle; however, intermodel differences in the distribution of precipitation within the continents are large due to the high sensitivity of model results to paleoclimate boundary conditions and model parameterizations (12). This is compounded by a general lack of paleohydrologic proxy data for the Eocene after the Paleocene Eocene Thermal Maximum (PETM), because only a few studies have developed geochemical proxy records for hydrological change in the low and mid-latitudes (13)(14)(15)(16). Furthermore, studies published to date typically lack sufficient sampling resolution and temporal control to investigate potential astronomical influences on continental hydrologic variability, despite evidence for the presence of orbital cycles in a diverse range of paleoclimate records from the early Eocene (17)(18)(19)(20).…”