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\begin{document}

\title{Field observations of the temporal evolution of meltwater and false
bottoms for level ice during MOSAiC expedition}



\author[1]{Evgenii Salganik}%
\author[2]{Benjamin Allen Lange}%
\author[3]{Ruibo Lei}%
\author[4]{Steven Fons}%
\author[1]{Sönke Maus}%
\author[5]{Marc Oggier}%
\author[6]{Ilkka Matero}%
\author[7]{Christian Katlein}%
\author[1]{Knut Høyland}%
\author[2]{Mats Granskog}%
\affil[1]{Norwegian University of Science and Technology}%
\affil[2]{Norwegian Polar Institute}%
\affil[3]{Polar Research Institute of China}%
\affil[4]{University of Maryland College Park}%
\affil[5]{University of Alaska Fairbanks}%
\affil[6]{Svalbard Integrated Arctic Earth Observing System - SIOS}%
\affil[7]{Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung}%


\vspace{-1em}



  
  \date{May 26, 2024}


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\selectlanguage{english}
\begin{abstract}
There are a limited number of studies covering the temporal evolution
and spatial distribution of under-ice meltwater and false bottoms for
Arctic sea ice. 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 meltwater
budget. 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 ponded areas. This allowed for the comparison of
snow, ice, melt pond, under-ice meltwater layer, and false bottom
thickness evolution, as well as ice and water physical parameters.
Despite the 130 m distance between unponded and ponded FYI sites, the
thickness of both under-ice meltwater layer and false bottoms was almost
identical. For the SYI, the thicker unponded area had a draft below the
meltwater layer and experienced only an ice bottom temperature rise to
-1.2\selectlanguage{ngerman}°C, while for thinner ponded SYI under-ice meltwater layer was
observed. The depth of the seawater and under-ice meltwater layer
interface was similar for FYI and SYI. The temperature of under-ice
meltwater was close to 0°C, above its freezing point with pronounced
diurnal cycles. The under-ice meltwater layer formed three weeks earlier
below SYI than below FYI. Due to presence of under-ice meltwater, the
FYI bulk salinity decreased from both top and bottom to bulk values
below typical for multiyear ice due to only 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.%
\end{abstract}\selectlanguage{ngerman}%



\sloppy


\textbf{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\selectlanguage{ngerman}°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.

3 minutes = 450 words

\textbf{AGU eLightning 3-minutes poster talk}

{[}intro{]}

Hi everyone. This poster presents a study about the temporal evolution
of under-ice meltwater and false bottoms. It is based on the field
investigations during May-July 2020 during the MOSAiC expedition. This
analysis use data from the ice coring and ROV multibeam sonar.

{[}left figure{]}

During the summer season, the meltwater is accumulating above, inside,
and underneath sea ice. The under-ice meltwater may form an additional
layer of ice at the interface with colder seawater, and this ice layer
is called a false bottom. Weekly coring program allowed us to collect
physical parameters of first-year ice, meltwater, and false bottoms. On
the left image you can see the temporal evolution of salinity and
thickness of those three layers. During the melt season the first-year
ice salinity decreased from 5 to 1, and the presence of under-ice
meltwater doubled loss of ice salt.

While sea ice was melting gradually, this under-ice meltwater appeared
instantly reaching its mean thickness of 50~cm. This indicates a
significant horizontal transfer of meltwater. The salinity of that
meltwater was changing between 4 and 10 with a strong input from the
brine flushing.

{[}central figure{]}

It is important to know how the presence of this meltwater affects the
ice melt. As you can see in the central figure, we had 3\% lower ice
draft decrease for the ice with false bottoms. Additional 5 \%
difference can be added from the final thickness of false bottom.

From the sonar measurements of the ice draft, we can see the strong
draft increase in the areas with false bottoms, shown here as a black
dashed line.

{[}right figure{]}

This pronounced draft change allowed us to estimate the areal coverage
of false bottoms, which you can see in the right figure as blue-shaded
areas. The estimated areal coverage of false bottoms was 21\%, which is
larger than in most previous observations. We also confirmed an
importance of small ridges for keeping this meltwater under the ice.
Areas not surrounded with ridges, like the unponded ice in the left
bottom corner of the map, didn't have any false bottoms.

{[}summary{]}

As a summary, we presented an overview of the temporal evolution of
under-ice meltwater and false bottoms. This meltwater appeared instantly
and had a stable thickness, defined by the draft of the surrounding
ridges. It also doubled rates of the ice desalinization and slightly
decreased ice melt. The areal fraction of false bottoms was defined as
21\%.

Thank you.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/essoar/essoar}

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\end{figure}

\selectlanguage{english}
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