Field observations of the temporal evolution of meltwater and
false bottoms for underformed level ice during MOSAiC expedition
There is a limited number of
studies covering the temporal evolution and spatial distribution of the
under-ice meltwater and false bottoms. At the same time, they both have
a significant effect on the desalinization of sea ice and the ice bottom
melt rates. Additionally, these observations are an important part of
the total mass balance of the melt water.
The MOSAiC drifting expedition was aimed to collect field data of
coupled processes between ice, ocean, and atmosphere. During the melt
season ice cores were collected every week from the unponded first-
(FYI) and second-year level ice (SYI) of the investigated ice floe. In
addition, ice mass balance buoys were installed in the vicinity of two
coring sites, but in the ponded areas. This allowed to compare snow,
ice, melt pond, bottom meltwater, and false bottom thickness evolution,
as well as ice and water physical parameters.
Despite the 130 m between unponded and ponded FYI sites, the thickness
of both under-ice meltwater and false bottom was almost identical. For
the SYI, the thicker unponded area had a draft below the meltwater layer
and experienced only a warming at the ice bottom up to -1.2°C, while for
thinner ponded SYI under-ice meltwater was observed. The depth of the
seawater and under-ice meltwater interface was similar for FYI and SYI.
The temperature of under-ice meltwater was close to 0, above its
freezing point with pronounced diurnal cycles. The under-ice meltwater
formed under SYI three weeks earlier than under FYI. Due to presence of
under-ice meltwater, the FYI bulk salinity decreased from both direction
until values below typical for multiyear ice due to top surface
flushing. The thickness of under-ice meltwater layer was stable, around
47 cm for FYI and 26 cm for SYI, in contrast to gradually increasing
water equivalent of melted snow and ice. This imbalance indicates a
significant horizontal transfer of meltwater.
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