Multi-proxy paleoenvironmental reconstruction of Robertson Bay, East Antarctica, since the last glacial period
Résumé
Antarctic fjords and coastal bays are excellent traps for sediment and represent key areas for high-resolution
investigation of past environmental conditions. Robertson Bay is an understudied coastal area located at the
confluence of the Ross Sea and the Southern Ocean. Recently obtained seafloor morphology data indicate the
presence of a cross-shelf elongated valley, composed of three minor basins separated by sills and seabed ridges
with an arcuate shape. Several cores were collected within the basins, and investigated using a multiproxy
approach including sedimentological, chemical, geochemical, and micropaleontological characterization to
reconstruct the paleoenvironmental evolution from the last glacial period to present. The ages of two of these
cores are constrained using ramped pyrolysis oxidation radiocarbon dating. Four sedimentary facies were recognised
from which we developed a sedimentary model covering the last 21,000 years (21 ka BP). Our record
provide evidence for a covering ice shelf cover from 21 to 16.5 ka BP, which gradually receded between 16,5 and
11 ka BP due to the progressive intrusion of modified Circumpolar Deep Water, thereby promoting the formation
of Ice Shelf Water and High Salinity Shelf Water. From 11 to 5,8 ka BP, the ice shelf continued shrinking and
nutrient-rich of modified Circumpolar Deep Water penetration onto the continental shelf progressively favoured
diatom blooms and a general increase in primary productivity until 5.8 ka BP. The Late Holocene is characterised
by an alternation of prolonged sea ice cover with stratified water column and strong bottom current with prolonged
sea-ice free season with the intrusion of modified Circumpolar Deep Water and very slow energy bottom
current.