ausblenden:
Schlagwörter:
Deglaciation; Sedimentology; End-member modeling; MacRobertson Shelf; Prydz Bay
Zusammenfassung:
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.
