What Happens to Ecosystems When Antarctica's Ice Melts?
By Marty Downs
A special section in the October issue of BioScience examines the effects of a single season of intense melting on two Antarctic ecosystems, tracking impacts all the way from microbial food webs to shifting penguin populations.
In the spring of 2001-2002, two climatic cycles (Southern Annular Mode and the El Niño Southern Oscillation) intersected to produce a particularly warm and windy spring season across Antarctica, with melting glaciers, thinning of lake ice, and changes in sea ice area. For the far-flung researchers who were prepared to capture it, this natural experiment offered a glimpse into the ecological future of this most remote continent.
Two Long-Term Ecological Research (LTER) sites operate in Antarctica. Palmer LTER, established on the West Antarctic Peninsula (WAP) with National Science Foundation funding in 1990, focuses on the ways that changing sea ice extent influences marine ecology and the multilayered food webs of the coastal, nearshore, and continental slope ecosystems. McMurdo LTER, established in 1992, explores the ecology of the terrestrial and freshwater ecosystems of the Antarctic dry valleys—a polar desert where glacial meltwater exerts a profound influence on connectivity, nutrient inputs, and the availability of sunlight.
“These two vastly different polar ecosystems offer insights into how diverse ecosystems around the world will respond to climate change,” said Hugh Ducklow, who leads the Palmer LTER and is an ecologist at Columbia University’s Lamont-Doherty Earth Observatory. “With long-term studies already in place, we were able to observe the effects on so many different levels.”
Sea Ice Changes Ricochet up the Food Web
In the West Antarctic Peninsula, 2001-2002 atmospheric conditions resulted in thicker sea ice compacted against the edge of the peninsula, with increased melting at the edge releasing large quantities of fresh water and ice algae directly into the upper mixed layer of the ocean. These nutrient inputs supported a large spring algal bloom and a population boom of Antarctic krill, a major food source for penguins, whales, seals, fish and flighted seabirds.
The same atmospheric patterns delivered greater snowfall and earlier spring snowmelt to the coastal region along the peninsula, flooding the nests of early-hatching Adélie penguins and lending an advantage to later-nesting Gentoo and Chinstrap species.
Wetting the Dry Valleys
Inland, in the dry valleys, the warm, windy spring accelerated melting of mountain glaciers, feeding a pulse of water across the parched landscape, scouring streambeds, raising lake levels, and revealing windblown dust deposits hidden in the glaciers. The characteristic thick layer of lake ice (typically 4-6 meters) also thinned rapidly, allowing more sunlight than usual to reach the upper layers of the plankton community that thrives in lake water under the ice.
At the same time, inputs of dissolved organic carbon from newly-active streams fed increased bacterial productivity deeper in the lakes. Hints from genomic data suggest that the competition for these two different carbon sources could drive long term changes in the structure of the lakes’ microbial communities.
Today’s Anomaly; Tomorrow’s Normal?
At Palmer LTER, the physical impacts of the 2001-2002 climate anomaly were transient. At McMurdo, that single season of warming marked the start of nearly a decade of rising lake levels and increased turbidity.
In so many ways, ice mediates the response of these two systems to environmental change. The relationships are rarely simple, but long term ecological research is allowing scientists to capture the insights from today’s brief climate excursions to understand how ecosystems may respond when the unusual becomes the typical.
The papers appearing in the BioScience special section leverage more than two decades of observations at Palmer and McMurdo. In one, Lamont post-doctoral research scientist Jeff Bowman, working with Ducklow and other colleagues, explores microbial ecosystem dynamics in the two polar extremes and how those ecosystems respond to changes in climate. Another paper, co-authored by Ducklow, looks at the sensitivity of Antarctic sea ice and lake ice to climate variations and the impact on ecosystems.
Marty Downs is the communications lead for the Long Term Ecological Research Network. The Long Term Ecological Research Network was created by the National Science Foundation to conduct research on ecological issues that can last decades and span huge geographical areas. It provides scientific expertise, research platforms, and long-term datasets necessary to document and analyze environmental change.