Modified Circumpolar Deep Water intrusions in Vincennes Bay, East
Antarctica.
Abstract
Antarctic Bottom Water (AABW) production supplies the deep limb of the
global overturning circulation and ventilates the deep ocean. While the
Weddell and Ross Seas are recognised as key sites for AABW production,
additional sources have been discovered in coastal polynya regions
around East Antarctica, Vincennes Bay being the latest. Vincennes Bay,
despite encompassing two distinct polynya regions, is considered the
weakest source, producing Dense Shelf Water (DSW) only just dense enough
to contribute to the lighter density classes of AABW found offshore.
Importantly, the network of local glaciers and upstream Totten Ice Shelf
system are all reportedly thinning and the freshwater input from such
melting is likely to influence water mass structure. Accordingly,
Vincennes Bay presents an interesting test case for DSW/AABW sensitivity
to climate-driven changes in Antarctic coastal oceanography. Here we
provide the first detailed observations of the Vincennes Bay shelf
region and surrounds, using CTD data from instrumented elephant seals in
late summer/early fall. We find that Vincennes Bay has East Antarctica’s
warmest recorded intrusions of modified Circumpolar Deep Water (mCDW),
intrusions that both hinder sea-ice production and contribute salt to
new DSW formation. Warm mCDW is also observed to be driving basal melt
in Vincennes Bay, as seal CTD data provide the first direct
observational evidence for inflow of basal melt to this region. As the
most marginal of AABW sources, Vincennes Bay is a particularly useful
region for assessment of the sensitivity of AABW production to changes
in climate.