Regional controls on the sea ice-mixed layer depth relationship in the
West Antarctic Peninsula (WAP)
Abstract
In the West Antarctic Peninsula (WAP), complex interactions between the
cryosphere, ocean and atmosphere produce an environment with large
geographical, seasonal and interannual variability which is highly
vulnerable to climate change. The seasonal sea ice cycle and its
interactions with upper-ocean mixing play an important role in
structuring this environment. Here we show that the relationship between
sea ice and mixed layer depth (MLD) varies regionally between the WAP
shelf and off-shelf regions. Using an MITgcm regional model of the WAP
and Bellingshausen Sea for 1989-2018, we find that on the WAP shelf,
high winter sea ice coverage is related to shallow spring mixed layers,
whereas in a region offshore of the shelf, high winter sea ice coverage
is related to deep spring mixed layers. The exact boundary between
positive and negative correlations between winter sea ice concentration
(SIC) and spring MLD varies decadally. Our results can be explained by a
nonlinear relationship between SIC and momentum flux into the ocean,
with a minor additional role for the timing of seasonal processes.
Transport of sea ice across the model domain dampens this mechanism
except in regions of very large sea ice export such as polynyas. With
sea ice conditions projected to undergo large changes over the course of
the century, understanding the relationship between sea ice and
upper-ocean mixing in this unique and vulnerable location is crucial for
understanding the wider impacts of climate change on biological
productivity in the polar oceans.