EPOW - Ecology Picture of the Week

"Dirty Ice:" Algae That Fuels the Arctic

Ice Floes With Algae Growth
Chukchi Sea, Alaska

Explanation:  In June 2009, I joined U.S. Geological Survey scientist Dr. Chad Jay on an expedition to the Arctic in a survey of Pacific walruses over the Chukchi Sea, north of Alaska.  We flew in a small 2-engine plane as far as 42 miles from north Alaskan coast out over the sea ... where we encountered these amazing seascape views of ... what?

At first, I thought we were viewing "dirty ice" ... with either seafloor sediments adhering to the ice surface as landfast ice blocks may have turned over from currents and winds ... or perhaps dark soil blown on to the ice from the North Slope such as suggested by this NASA space image of glacial dust being blown out to sea from the Copper River of southeast Alaska.  But neither idea was correct.

We were actually witnessing the base of the Arctic food web.  This was not dirt, but massive blooms of sea ice algae, such as the aptly named ice diatom Nitzschia frigida.   

One question is, when ice turns this dark, does it
significantly decrease the reflectivity (albedo) of the surface?
If so, this means that it would absorb more sunlight energy
and warm faster than would pure white ice cover.
And if that happens, then it might add to the already 
accelerating melting and loss of Arctic ice.
 

It is such microalgae that often forms especially on the undersurface of ice floes when the ice is just thin enough for sunlight to penetrate.  And -- in one food chain -- it is algae that then feeds the invertebrates such as euphasid shrimp, that feed the Arctic cod and other fish, that feed the seals, that feed the polar bears. 

The darkest (black) margins in this photo are mostly open-water areas ("leads"). 
The blue-green splotches (click for larger view) are likely standing-water
pools on the ice.  Much of the ice here is thin first-year ice rather than
thick multi-year ice, an increasing trend in the warming Arctic.
And it is thin ice and lots of open water that promotes algal growth
and allows the algae to work its way to the ice surface when
the ice floes collide.

So what will happen here under climate change and regional warming?  There may be a misleading paradox that will occur in the short run.  As the region warms, the ice cover may thin, letting more sunlight penetrate ... so there may first be a period of increased growth of the sea ice algae, which might temporarily enhance the food chain.  But then as the sea ice melts back more and more, especially vanishing from over the continental shelf of the Arctic Ocean, that food chain will collapse, bringing fish, seals, polar bears, and other dependent species with it.   

As colleague Steve Amstrup suggested, some of these rather amazing patterns
may have arisen where ice floes with algal growth were deformed by floe
collisions and flooding on top of the floes ... resulting in some ice overturning,
and some of the algae breaking loose and reattaching to other top surfaces.
The white ice has not been as subject to as much recent collision and
deformation.  Also, the darker ice may be floes that overturned by 
currents and wave action.

Information:

Bluhm, B. A., and R. Gradinger. 2008. Regional variability in food availability for Arctic marine mammals. Ecological Applications 18(Supplement):S77-S96.

Burek, K. A., F. M. D. Gulland, and T. M. O'Hara. 2008. Effects of climate change on Arctic marine mammal health. Ecological Applications 18(Supplement):S126-S134.

Freitas, C., K. M. Kovacs, R. A. Ims, and C. Lydersen. 2008. Predicting habitat use by ringed seals (Phoca hispida) in a warming Arctic. Ecological Modelling 217(1-2):19-32.

Juhl, A. R., and C. Krembs. 2010. Effects of snow removal and algal photoacclimation on growth and export of ice algae. Polar Biology 33(8):1057-1065.

 

Acknowledgments:

My thanks to Steve Amstrup, Dennis Darby, David Douglas, George Durner, Chad Jay, and Ignatius Rigor for discussions of these images and possible mechanisms, and further information on ice-algae relationships.  It was Steve, George, and Dennis who set me straight that algae growth is indeed the culprit in these photos.