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Begoña Vendrell Simón

Begoña Vendrell Simón

Biologist specialized in marine ecology

Antarctic surprises

APRIL 27TH 2011


Taking advantage of the Antarctic expedition of my colleagues at the Institute of Marine Sciences aboard the German research vessel Polarstern, I’d like to focus on a current topic of polar science. For over 15 years, one of the major ice shelves in the western Weddell Sea (the Larsen shelf, discovered by Carl Anton Larsen, captain of a Norwegian whaling ship), on the east coast of the Antarctic Peninsula, has been collapsing into the sea. That means that in the last 15 years approximately 10,000 km2 of ice have melted. First, in 1995, the northernmost part (Larsen A) collapsed, and later, in February 2002, the Larsen B shelf of over 3,000 km2 of compact ice disintegrated in about three weeks.

Scientific Alarm

This dramatic incident caused great alarm among the scientific community. Why? Because ice shelves usually melt at a leisurely pace, through the continuous breaking off of icebergs. This “massive” collapse is linked to the gradual warming recorded in the Antarctic Peninsula, about half a degree Celsius per decade for the past 60 years. This is one of the consequences of global warming, a phenomenon in which human activity has played a significant role. Among the factors that help explain the sudden collapse of Larsen B, which are related to global warming, is the effect of the numerous pools and ponds of meltwater that form on the ice shelves during the summer months. This liquid water flows between the cracks in the ice, creating a “leverage” effect and making blocks of ice fall off. In addition, some warm ocean currents have been introduced below the ice zone, helping to make the shelves more susceptible to collapse. Now, scientists are asking whether environmental changes will also affect the Larsen C shelf, located farther south.

The release of icebergs and large ice blocks devastates the seabed

But let’s look at the effects of the collapse of the ice shelf: the large-scale collapse was estimated to have a devastating impact on benthic communities (i.e., on the communities of living organisms inhabiting the seabed), and scientists were concerned if they would ever recover. In general, the effect of the breaking off of icebergs and large ice blocks severely damages benthic communities, mostly composed of sessile organisms (non-moving creatures like sponges that cling to the rocks and floor). The time it takes for these benthic communities to recover depends on the intensity and frequency of these natural disturbances and their proximity to neighboring communities of organisms that contribute to providing elements for their re-colonization. We could compare these events in a way to catastrophic wildfires in forested areas, which happen from time to time and roll back these ecosystems to early stages, creating a mosaic of communities at different stages of ecological succession.

Resilient seabeds

It must be said that the collapse of the ice shelf has facilitated the study of the seabed by enabling scientists to gain access to areas that had spent more than a thousand years under the ice. Already in 2006, in an earlier campaign on board the same oceanographic research vessel, our colleagues at the Institute of Marine Sciences (CSIC) were surprised to find higher levels of richness and diversity than expected in the deep sea benthic communities where the Larsen shelves had collapsed. That means that the recovery of benthos after such dramatic events like the collapse of a major ice shelf is much faster than previously thought. This rapid recovery may be enhanced by the colonization of these devastated areas by neighboring benthic communities and due to the release of nutrients and particulate matter from the melted ice. However, if global climate change increases the frequency of the collapse of the ice sheet, greater and greater areas of the seabed will be affected, making their re-colonization by communities from adjacent areas impossible. We will have to follow the scientists’ expedition very closely to see how they find the Larsen seabed five years after the previous study.
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