Climate Change Impacts Differ for Little-Known Arctic and Antarctic Seafloor Life

15 May 2006 - Interviews, Logistics, Water & Oceans, Flora & Fauna

Dr Gutt's work in Antarctica includes using remotely operated vehicles to obtain underwater images from otherwise inaccessible locations

Sciencepoles talked to Dr. Julian Gutt, of Germany's Alfred Wegener Institute, just after his address, at the BEPOLES workshop, on "Climate-induced biodiversity shift in polar benthic communities?", which looked at how climate change might affect ecosystems on polar sea floors. Towards the end of 2006, Dr Gutt will lead a team of scientists from 14 nations aboard Polarstern, Germany's polar research ice vessel, as they conduct work in connection with the Census of Antarctic Marine Life and the Convention on the Conservation of Antarctic Marine Living Resources.

SciencePoles: Why is it important to know what's under the polar ice on the sea floor?

Dr Gutt: The polar sea-floor communities, especially below the large Antarctic floating ice shelves, are a substantial uncharted resource. We think there are around 20,000 species involved but it could be anywhere up to 50,000. At the moment we just don't have enough information. It makes it particularly hard to do any kind of cost/benefit analysis of the impending impacts of climate change when the reference points, namely the food supply and previous states of these communities, are still comparatively undocumented.

In my address to the workshop I pointed out the opportunity cost of not knowing enough about these communities. As with tropical rainforests, there might be extraordinarily interesting life-forms under the ice. Who knows - there might even be animals or microorganisms with the potential to yield chemical compounds with beneficial applications for humanity. The real point is we need to know more in order to assess what climate change might cost us.

Another important reason for studying these systems is being able to look at really pristine ecosystems. For example, the North Sea might seem inaccessible to many, but given the extent of fishing there over many centuries, it could be regarded as agriculture compared with the polar regions, particularly the Antarctic. The high Antarctic is the most isolated ecosystem on earth. It is the least affected by human contact. The whaling and seal hunting activities really took place further north in the sub-polar regions. In the high Antarctic it is possible to study completely undisturbed communities.

With respect to climate change, you've pointed out that there would be different impacts on marine life in the Arctic and Antarctic?

Broadly speaking, the most serious environmental impacts are certainly being experienced in the Arctic. Decreasing sea ice extent over the last 20 years, most significantly on the Pacific side but also on the Atlantic side, has been affecting all coastal systems. The ice is starting to melt and coastlines which were glaciated for long periods will not experience ice anymore. This is having a huge impact on the Arctic megafauna, such as polar bears, while the Antarctic, with the exception of the peninsular region, is much less affected, at least for the time being.

Turning to marine life, it's important to note that even though greater temperature shifts are being experienced in the Arctic the benthic life there has also previously been more exposed to a range of temperatures, making them more resilient to change. Antarctic benthic marine life will likely be more sensitive than their Arctic counterparts to temperature shifts if they start to be experienced more generally around the continent. The Antarctic continent is, however, currently less exposed to temperature increases in general, with the exception of the Peninsula, which extends further North and is the site of recent rapid glacial disintegration.

So what will happen to the sea-floor communities? The Arctic communities are more temperature tolerant, but there will be greater impacts there because of the magnitude of the shifts in temperature in the Arctic?

The temperature shifts in the Arctic are certainly greater but it is the indirect consequences for the benthos, rather than the direct exposure to warmer waters, that can be expected to be really significant. Sea ice, phytoplankton and the whole change in the pelagic system ... these have major flow-on impacts for the life on the sea-floor. The food chain effect will be much more serious than the direct response to a slight increase in temperature.

At the moment ice algae hangs in "curtain-like" formations from the underside of the sea-ice. As the ice melts at the end of winter then the "curtains" fall to the sea-floor. The benthos profits from that as there are then more nutrients on the sea floor. The changing sea ice margins are having a big impact on the distribution of nutrients over the sea floors.

The marginal ice zone is where you get the highest productivity. At the moment, in winter, the ice reaches the continent over much of Siberia and North America, so there are no ice margins above the ocean floor in many parts of the Arctic. Also, there is no phytoplankton, just ice algae. If there is less sea ice in general, as is increasingly the case, we move to a more phytoplankton-dominated system. These tiny single-celled organisms are consumed by small crustaceans and then there is a totally different flux of organic material going to the bottom - maybe less, maybe more ... . the situation becomes more and more complex to predict. It could mean that the nutrients will continue to sink rapidly down - or they could be recycled in the upper water column. It is very difficult to predict what the outcome will be.

If a situation arises where, over the whole winter, a new marginal ice zone exists offshore we will then also have year-round phytoplankton production going on in a new open water zone. The sea floor may or may not profit from that. In the end, both scenarios are possible - the benthos could profit or suffer from the retreat of the sea-ice.

Can you tell us a bit about the objectives of your mission later this year to do research connected with the Census of Antarctic Marine Life (CAML)?

The Census of Antarctic Marine Life (CAML) is a vast project aimed at improving our knowledge of Antarctica's marine biodiversity. Involving coordination and cooperation of many national research programs, it is part of the Scientific Committee on Antarctic Research (SCAR) Evolution and Biodiversity (EBA) program and has been approved as a project under the International Polar Year (IPY) 2007-08.

Our contribution to the CAML project work is part of a trip to Antarctica by the Polarstern, Germany's flagship polar research vessel, and will take place in the former Larsen A & B areas. It is difficult to reach these areas but it is also of high scientific relevance so international cooperation is important - 14 different countries are participating on this trip. As you know there is also an interesting proposal for the International Polar Foundation to be involved on this trip as observers to communicate some of the research developments "as they happen". The mission is also involved with working on research for the Convention on the Conservation of Marine Life Resources (CCAMLR), which will take place mainly at (or around) the Shetland Islands.

Once in Antarctica, we will study how the disintegration of the ice shelves has affected the local benthic communities, comparing what they look like now with their previous state. This may help us to forecast the future for these unique ecosystems if the kind of climate change impacts we've seen in the Peninsula become more widespread in the Antarctic.

Also we are engaging in some more fundamental research about the limits of life. Under such hostile cold conditions there still exists a rich biodiversity. Where are the limits? On the high Antarctic shelf, at 75 degrees South and minus 1.7 centigrade in the water, life is still plentiful. If we can find the limiting factors then we can perhaps, conversely, identify the enabling factors which support such a rich ecosystem under these extremely harsh conditions.

So if we look at both ends of the spectrum - where life is rich and where it is extremely poor - we can hopefully begin to find some answers to the puzzle of how life can thrive in one of the world's most challenging environments.

By: Gauthier Chapelle