Tropical climate and vegetation simulations during the Heinrich event 1 using an Earth System Model of Intermediate Complexity (EMIC) - the University of Victoria Earth System-Climate Model (UVic ESCM)

Abrupt climate changes from 18 to 15 thousand years before present (kyr BP) associated with Heinrich Event 1 (HE1) had a strong impact on vegetation patterns not only at high latitudes of the Northern Hemisphere, but also in the tropical regions around the Atlantic Ocean. To gain a better understanding of the linkage between high and low latitudes, we used the University of Victoria (UVic) Earth System-Climate Model (ESCM) with dynamical vegetation and land surface components to simulate four scenarios of climate-vegetation interaction: the pre-industrial era, the Last Glacial Maximum (LGM), and a Heinrich-like event with two different climate backgrounds (interglacial and glacial). We calculated mega-biomes from the plant-functional types (PFTs) generated by the model to allow for a direct comparison between model results and palynological vegetation reconstructions. Our calculated mega-biomes for the pre-industrial period and the LGM corresponded well with biome reconstructions of the modern and LGM time slices, respectively, except that our pre-industrial simulation predicted the dominance of grassland in southern Europe and our LGM simulation resulted in more forest cover in tropical and sub-tropical South America. The HE1-like simulation with a glacial climate background produced sea-surface temperature patterns and enhanced inter-hemispheric thermal gradients in accordance with the "bipolar seesaw" hypothesis. We found that the cooling of the Northern Hemisphere caused a southward shift of those PFTs that are indicative of an increased desertification and a retreat of broadleaf forests in West Africa and northern South America. The mega-biomes from our HE1 simulation agreed well with paleovegetation data from tropical Africa and northern South America. Thus, according to our model-data comparison, the reconstructed vegetation changes for the tropical regions around the Atlantic Ocean were physically consistent with the remote effects of a Heinrich event under a glacial climate background.

Sea ice and wind variability during the Holocene in East Antarctica

A high-resolution continuous record of diatom census counts and diatom specific biomarkers in sediment core NBP0101-JPC24 allows assessment of oceanographic and environmental conditions in eastern Prydz Bay during the deglaciation (11 100-9000 cal yr BP) at decadal timescale. Our study improves previous snapshots investigations based on resin-embedded thin sections and presents a new proxy that compliments the diatom census counts. Our results suggest that the ice sheet retreat over the core site is dated at ~11 100 cal yr BP, setting the onset of local deglaciation and subsequent open marine conditions. The glacial retreat in Prydz Bay is due to global warming initiated at 18 cal ka BP and the regional development of the Prydz Bay cyclonic gyre. Our results further demonstrate that the deglaciation in eastern Prydz Bay can be separated in four phases: the first between 11 100 and 10 900 cal yr BP when the ice shelf was proximal and sea ice was almost perennial; the second and the third phases between 10 900-10 400 cal yr BP and 10 400-9900 cal yr BP, respectively, when the ice shelf retreated and seasonal sea ice cycle consequently developed promoting warmer water to pump into the bay within the gyre, which in turn forced the ice shelf recession and the yearly sea ice cycle establishment; and the fourth between 9900 and 9000 cal yr BP when Holocene condition were set with a recurrent seasonal sea ice cycle and a well established Prydz Bay gyre.