Insufficient in-situ observations from the Antarctic marginal ice zone
limit our understanding and description of relevant mechanical and
thermodynamic processes that regulate the seasonal sea ice cycle. Here
we present high-resolution thermal images of the ocean surface and
complementary measurements of atmospheric variables that were acquired
underway during one austral winter and one austral spring expedition in
the Atlantic and Indian sectors of the Southern Ocean. Skin temperature
data and ice cover images were used to estimate the partitioning of the
heterogeneous surface and calculate the heat fluxes to compare with ERA5
reanalyses. The winter marginal ice zone was composed of different but
relatively regularly distributed sea ice types with sharp thermal
gradients. The surface-weighted skin temperature compared well with the
reanalyses due to a compensation of errors between the sea ice fraction
and the ice floe temperature. These uncertainties determine the dominant
source of inaccuracy for heat fluxes as computed from observed
variables. In spring, the sea ice type distribution was more irregular,
with alternation of sea ice cover and large open water fractions even
400 km from the ice edge. The skin temperature distribution was more
homogeneous and did not produce substantial uncertainties in heat
fluxes. The discrepancies relative to reanalysis data are however larger
than in winter and are attributed to biases in the atmospheric
variables, with the downward solar radiation being the most critical.