16 | New Scientist | 27 February 2021
Field notes Iceberg A-On the trail of icy ocean invaders We travelled to the
Southern Ocean to investigate one of the world’s largest
icebergs, says expedition leader Povl AbrahamsenIT IS a relief when we finally see
the iceberg, first as a line on the
ship’s radar and then as a wall
of ice emerging from a foggy
horizon, stretching further than
we can see.
This is part of the remains of
iceberg A-68, the third largest
iceberg ever recorded, which broke
away from Antarctica’s Larsen C
ice shelf in 2017. After drifting
northwards, A-68 was on a
collision course with the island of
South Georgia in December 2020
before being swept back into
deeper water south of the island.
It has begun to disintegrate and
is no longer a continuous island
of ice. There are now 12 named
iceberg fragments from A-
and countless smaller icebergs.
The largest of these, dubbed
A-68A, is 50 kilometres long
and 200 metres thick in places,
and covers an area of around
900 square kilometres, similar to
that of the Isle of Mull in the UK.
Ships have to be very cautious
around icebergs due to the
damage that can be caused by
the hard, freshwater ice, so we
keep a distance of 1 nautical mile
from the largest icebergs, and
the crew navigate carefully
around the smaller pieces. But
we can still hear when larger parts
break off, even above the sounds
of the ship’s whirring engines
and machinery.
Whether in one piece or dozens,News
Researchers on the RRS
James Cook launching an
underwater gliderAL
ICEMARZ
OCCH
I,^ NOCSatellite
imagery from
12 February
shows the
position of
some of the
iceberg piecesA-68 could have a large impact on
the ocean and ecosystems around
South Georgia, which sustain large
colonies of penguins and seals, as
well as whales.
The cooling and freshening
that takes place as the giant
iceberg breaks up and melts might
affect the life forms at the very
bottom of the food chain: tiny
algae called phytoplankton. At the
same time, large icebergs can also
stir up nutrients from the deep,
increasing biological productivity
in their wake.
To find out, I am near the
island of South Georgia in theSouthern Ocean, which surrounds
Antarctica, on the research ship
RRS James Cook. We will monitor
the temperatures, salinities and
plankton concentrations in
the water, and compare the
findings with long-term data
from oceanographic studies
in the region.
Leading an oceanographic
expedition to the Southern
Ocean is always exciting and
unpredictable. It is even more
so when the target of your
observations is spinning around
in meandering currents while
gradually breaking up.
Due to the pandemic, we have a
reduced team of just 11 scientists,
engineers and technicians
from the National Oceanography
Centre in Southampton, UK, and
the British Antarctic Survey in
Cambridge in addition to
the ship’s crew and a doctor.
After two weeks of quarantine,we are trying to fit our research
into the iceberg into a short time
window between our other work
carrying out annual monitoring of
the ecosystems and climate of the
Southern Ocean. Luckily the A68-A
iceberg has ended up in a location
that doesn’t require a large detour.
We are spending three days near
this iceberg as part of five intensive
weeks of research at sea. The
weather is typical for the Southern
Ocean at this time of year: cloudy,
windy and chilly, with daytime
temperatures just above freezing.
After admiring the iceberg
briefly, we carry on with our
measurements. On our second
day, we deploy an underwater
robotic glider. This 1.5-metre-long
submersible will continue
monitoring the ocean around the
iceberg for months after we leave.
We can barely see the iceberg
through the fog, and hope that our
third day affords us better views.
The ship circles around the
iceberg overnight, and this time
we approach it from the north as
the weather clears, only to find
that the many fragments of ice,
large and small, that have broken
off the iceberg impede our passage.
In the end, we deploy our
second glider near A-68P, the
newest named iceberg, which is
“only” 100 square kilometres big.
It will make its way to A-68A,
through iceberg-infested waters
unsafe for the ship to navigate.
As we start heading north to our
next study area, I look back on the
vast field of icebergs in the sunset.
One small iceberg has a few
penguins on it, and albatrosses
and smaller seabirds are flying
around the ship.
The oceans around Antarctica
are a remarkable place to work,
constantly changing. Although
icebergs are a fact of life in these
parts, who knows what we will
find when we return. ❚South
Georgia
IslandA-68lA-68EA-68H A-68PA-68JA-68A
A-68MA-68G
50 km
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