Will less ice be good or bad for Arctic ecosystems? Scientists discuss.
- 18 Feb 2013, 10:15
- Roz Pidcock
US Geological Survey
A new study suggests thinning Arctic sea ice could be boosting
growth of algae underneath it by allowing more sunlight through -
which sounds like good news for Arctic ecosystems. But other
research suggests it's more complicated. We look at what scientists
are saying about the new findings.
The area covered by sea ice in the Arctic is declining by about
per cent per decade. The latest
satellite data suggest it's also getting significantly
A big question is what effect this will have on Arctic fish and
mammal populations. At the base of the marine food chain, changes
to algae will affect the whole Arctic ecosystem.
Scientists can't know for sure the ecological consequences of
thinning ice due to greenhouse gas warming. But looking at changes
in ice cover over shorter timescales can offer some clues.
The new study, just
published in the journal Science, measured biological activity
in the Central Arctic during 2012. Sea ice cover decreases in
summer as part of a natural cycle. But in 2012, the summer minimum
reached a record
Using camera-guided and remotely operated sampling devices, the
scientists found huge quantities of algae underneath the melting
ice. They attributed this to more sunlight being able to reach the
algae below. As Professor Kevin Arrigo from Stanford University in
California told Carbon Brief, this effect is not unheard of:
"The results are certainly consistent
with the massive under-ice bloom we discovered in the Chukchi Sea
in 2011 as part of ICESCAPE - which was also the result of thinning
sea ice and increasingly widespread melt ponds."
More surprisingly for the scientists, the seabed directly below
the thinning ice was also covered in patches of algae. As
microbiologist and lead author Professor Antje Boetius put it:
"The seabed at a depth of more than 400
metres was littered with clumps of ice algae".
It's thought this is because as the ice melts, algae are
released and fall to the seabed. There, algae become food for sea
floor-dwelling animals such as sea cucumbers and brittle stars.
What's not eaten is metabolised in the seabed by bacteria, a
process which uses up oxygen. Data from tiny sensors showed the
seabed under thinning ice was depleted of oxygen - an indication
that a lot of biological activity had taken place.
Long term benefits?
The fact that over a seasonal cycle, elements of the Arctic
ecosystem appeared to benefit from thinning ice led the scientists
to suggest the longer term decline in ice cover due to climate
change could also be a positive thing.
But other scientists are wary of drawing this conclusion. Partly
because there has been uncertainty over how much algae is produced
during the bloom at the surface and how much makes it down to the
seafloor. Past estimates of both haven't always matched up.
Professor Paul Wassman from the University of Tromso told us:
"Indeed, [the new research] comes as a
surprise … I think this is a challenge for the entire community of
biological oceanographers in the Arctic Ocean."
Wassman suggests a lot more research is needed to support the
new study, but he welcomes the findings, saying:
"There is no reason to doubt the results
of this paper … I more than willing to revise my ideas and [I'm]
actually thankful to this publication as it questions our generic
There's also more to consider than just the amount of sunlight
getting through - such as the
availability of nutrients. As Dr Ekaterina Popova from the
National Oceanography Centre told us:
"[W]e need to be careful and not try to
jump to a conclusion that Arctic Ocean is turning into an
ecological paradise as ice becomes thinner and retreats.
Productivity of this ocean basin is severely limited by
The Arctic Ocean exists in layers, which do not easily mix.
Warming could strengthen those layers, limiting mixing even
further. This could mean once algae use up all the nutrients at the
surface, not enough makes it up to the surface to sustain the
initial growth burst.
As the oceans absorb carbon dioxide from the atmosphere they
acidic. Scientists are concerned about even small shifts in
ocean acidity, as it can
affect how some marine algae grow their shells, which can be
crucial to their survival.
Research like this helps shed light on some of the uncertainties
over the effects of climate change on Arctic ecosystems - but the
debate continues. As with most aspects of climate science, the
reality is likely to be far more complicated than any single study