Sedimentological, mineralogical, biogeochemical and micropaleontological parameters on sediment core PS69/849-2, Burton Basin, MacRobertson Shelf, East Antarctica

A multi-proxy study including sedimentological, mineralogical, biogeochemical and micropaleontological methods was conducted on sediment core PS69/849-2 retrieved from Burton Basin, MacRobertson Shelf, East Antarctica. The goal of this study was to depict the deglacial and Holocene environmental history of the MacRobertson Land-Prydz Bay region. A special focus was put on the timing of ice-sheet retreat and the variability of bottom-water formation due to sea ice formation through the Holocene. Results from site PS69/849-2 provide the first paleo-environmental record of Holocene variations in bottom-water production probably associated to the Cape Darnley polynya, which is the second largest polynya in the Antarctic. Methods included end-member modeling of laser-derived high-resolution grain size data to reconstruct the depositional regimes and bottom-water activity. The provenance of current-derived and ice-transported material was reconstructed using clay-mineral and heavy-mineral analysis. Conclusions on biogenic production were drawn by determination of biogenic opal and total organic carbon. It was found that the ice shelf front started to retreat from the site around 12.8 ka BP. This coincides with results from other records in Prydz Bay and suggests warming during the early Holocene optimum next to global sea level rise as the main trigger. Ice-rafted debris was then supplied to the site until 5.5 cal. ka BP, when Holocene global sea level rise stabilized and glacial isostatic rebound on MacRobertson Land commenced. Throughout the Holocene, three episodes of enhanced bottom-water activity probably due to elevated brine rejection in Cape Darnley polynya occured between 11.5 and 9 cal. ka BP, 5.6 and 4.5 cal. ka BP and since 1.5 cal. ka BP. These periods are related to shifts from warmer to cooler conditions at the end of Holocene warm periods, in particular the early Holocene optimum, the mid-Holocene warm period and at the beginning of the neoglacial. In contrast, between 7.7 and 6.7 cal. ka BP, brine rejection shut down, maybe owed to warm conditions and pronounced open-water intervals.

Pacific Neogene carbonate accumulation rates

I have compiled CaCO3 mass accumulation rates (MARs) for the period 0-25 Ma for 144 Deep Sea Drilling Project and Ocean Drilling Program drill sites in the Pacific in order to investigate the history of CaCO3 burial in the world's largest ocean basin. This is the first synthesis of data since the beginning of the Ocean Drilling Program. Sedimentation rates, CaCO3 contents, and bulk density were estimated for 0.5 Myr time intervals from 0 to 14 Ma and for 1 Myr time intervals from 14 to 25 Ma using mostly data from Initial Reports volumes. There is surprisingly little coherence between CaCO3 MAR time series from different Pacific regions, although regional patterns exist. A transition from high to low CaCO3 MAR from 23-20 Ma is the only event common to the entire Pacific Ocean. This event is found worldwide. The most likely cause of lowered pelagic carbonate burial is a rising sea-level trend in the early Miocene. The central and eastern equatorial Pacific is the only region with adequate drill site coverage to study carbonate compensation depth (CCD) changes in detail for the entire Neogene. The latitude-dependent decrease in CaCO3 production away from the equator is an important defining factor of the regional CCD, which shallows away from the equatorial region. Examination of latitudinal transects across the equatorial region is a useful way to separate the effects of changes in carbonate production ('productivity') from changes in bottom water chemistry ('dissolution') upon carbonate burial.