Author: Elin Darelius

You might have heard on the news a few weeks ago that a large iceberg
broke off from the Brunt Ice Shelf, in the Weddell Sea. If you follow
the “Antarctic” news – and have a good memory – you might also remember
that a few years ago (2016), the UK research station Halley, that used
to be situated on what is now an iceberg, had to evacuate scientists and
personnel and  move the relatively newly built station as the crack
suddenly started propagating faster than anyone expected. Halley is the
only research station that I know about which is built on skis, so it
was “simply” pulled to a new, safe location on the other side of the
crack!

Anyway – the iceberg, which got the official name A74, finally broke
off, and it has now drifted a couple of nautical miles away from the
remaining iceshelf, leaving a “canyon” between the shelf and the iceberg
that is wide enough for Polarstern to enter. The scientists studying the
ocean floor – benthic ecosystems and sediments – where very eager to get
there to sample what was until recently a sub-iceshelf (and thus very
difficult to access) system.

We were all excited about circumnavigating A74, and to enter what we
quickly named the “Grand Canyon” – and most of us have followed the
motion of the iceberg on the satellite pictures that we receive every so
often. Is the “canyon” widening or shrinking? Are there smaller icebergs
blocking the passage? Can we get through? The sun, which we haven’t seen
much of during this expedition, obviously were just as excited as we
were, because it decided to join us for most of the day in the canyon
offering a spectacular view of the glittering bluish ice walls around
us!

We got to do three stations in the “canyon” – with intensive sampling of
both the water column and the bottom sediments. The AWI OFOBS team sent
down their camera system, and we could watch the ocean floor beneath us
live on their screens. To me, a non-biologist who are just about able to
distinguish a fish from a sponge it looked mostly like the open ocean
stations we’ve occupied earlier, but to the experts, things were
apparently different. Hopefully they get to repeat the station in the
years to come, to study how the community evolves now that it no-longer
has an ice shelf roof over its heads.

The CTD-profiles we made in the “canyon” all looked more or less the
same – a straight line from surface to bottom (i.e. close to constant
salinity and temperature). Supercooled Ice shelf water (a lighter
version than what we find in the Filchner Trough) was flowing out of the
Brunt ice shelf cavity, and the formation of buoyant  ice crystals at
depth  were clearly visible in the images from the OFOBS team! The ice
crystals had also clearly aggregated on the “geo-bio-chemical-lander*”
line, which were deployed for about 8 hours at one of the stations. When
the lander was recovered, there was a 1 cm thick layer of ice on the
line!

*a big thing full of instruments (for bio-geo-chemical process studies)
that looks like something that would land on the moon.

Breakfast on Polarstern is served between 07:30 and 08:30, and my usual
order to Maya behind the counter is “Zwei Pfannkuchen, bitte” – two
pancakes, please. But today there were pancakes not only on my plate in
the canteen –  the ship is surrounded by them! Rounded, small ice floes
with slightly elevated edges. My favorite type of ice!

It’s been quite cold the last couple of days and ice formation has
really kicked off. Autumn and winter is approaching rapidly! When I’ve
been up at the bridge to do sea ice observations in the mornings*, I’ve
started to use terms like “Nilas” and “fingerrafting” in addition to
“first and second year ridged floes” which is what we have had around us
before. When ice is formed on the ocean during calm (little wind)
conditions, the ice crystal initially makes a grey  ice “carpet”
(Nilas), that bends nicely over waves and that will break in “fingers”
that slide alternatively under and above fingers from the neighboring
“carpet” when the ice converges.

In windy conditions, the ice crystals will be forming not only at the
surface, but also in the upper (10-20m) of the water column and the
buoyant ice platelets rise to the surface and form what’s called grease
ice (it looks really greasy). Because of the motion in the water
initiated by the wind (Langmuir cells), the grease ice will typically
form streaks in the water surface, aligned with the wind. If freezing
continues, the grease ice will turn into small floes, that continuously
bump into the neighboring floes as they are moved around by wind and
waves, and the floes therefor end up having rounded shapes and elevated
edges – pancakes! With time, the pancakes grow, as small pancakes grow
together or raft on top of each other.

The pancakes we have around us now was formed further north – and the
biologists on board are super excited about these pancakes. Pancake ice
is generally white or grey – but our pancakes are turning more and more
yellow! Some form of biology is thriving on (or under?) the pancakes –
and since the bio-geo-chemists have not seen this before they are all
very keen to get out on the ice to sample!

Personally, I prefer white pancakes on the ocean and yellow pancakes
(with jam) on my plate!

*we do sea ice observations every hour when there is daylight, and seven
o’clock is my slot