Figure 1: The marine foodweb of the west Antarctic Peninsula is characterized by large predators such as penguins, seals and whales sustained by upwelling that supports high productivity and large krill populations. Credit I. Heifetz, Rutgers University.
The PAL study region along the western Antarctic Peninsula is one of the most rapidly warming places on the planet (see below), and the ecosystem is responding to the rapid climate warming. Observations of the Antarctic marine food web since the 1970s indicate the development of a more complicated food web with new types of grazers and increased microbial activity (Figure 1). Krill populations - small shrimp-like animals eaten by penguins, seals and whales - are in decline. Recently, gelatinous salps have been found in nearly every net tow and if krill are replaced by salps it would have important repercussions for the diet of larger predators.
A technique called inverse modeling has helped scientists incorporate their observations into food web models that yield estimates of key ecosystem process like photosynthesis, feeding, respirations and growth rates of krill, salps, penguins and bacteria. Changes they are seeing in the Antarctic presage equally larger changes closer to home.
Figure 2: Yearly changes in duration of sea ice cover. Credit: Sharon Stammerjohn University of Colorado, Boulder.
Figure 3: Map of Antarctic sea ice duration trends. Credit: Sharon Stammerjohn University of Colorado, Boulder.
Increasing greenhouse-gas concentrations impact atmospheric circulation, sea surface temperature and sea ice. The atmospheric warming extends from the Antarctic Peninsula over the entire West Antarctic Ice Sheet. The Antarctic Peninsula region is showing the fastest atmospheric winter warming on Earth and 87% of the Peninsula’s glaciers are in retreat.
Since the 1970s satellites have allowed Palmer LTER scientists to track sea ice changes from space in great detail. The sea ice season has shortened by almost three months (Figures 2,3). It is likely that this melting will continue regardless of the rate of global warming and Palmer LTER scientists are studying the mechanisms delivering heat to the region to evaluate its present state and predict its future course.
Figure 4: Top, left to right: Adélie, Chinstrap and Gentoo penguins. Graph: changes in penguin populations in the Palmer study region, 1974 - 2010. The ice-dependent Adélie penguins have declined by 85% while Chinstrap and Gentoo penguin populations, two ice intolerant species, appeared for the first time and have greatly increased over the same period. Credits: Graph: Bill Fraser, Polar Oceans Research Group, Sheridan, MT. Photographs Donna Fraser & Beth Simmons, Palmer LTER.
PAL scientists have documented an 85 percent reduction in Adélie penguin populations along the western Antarctic Peninsula since 1974 (Figure 4). These records provide some of the earliest evidence that regional climate warming is negatively impacting the marine ecosystem. A true polar species, the Adélie penguin is dependent on the availability of sea ice which acts as a critical platform from which they forage for food. Without sea ice, their access to prey decreases and winter survival becomes more challenging. The gradual disappearance of sea ice is causing more evaporation to the atmosphere, increased cloud cover and snow. Snow is deeper and persists longer. Increased spring snow melt at the height of the Adélie breeding season floods nesting sites and can have devastating effects on egg and chick mortality. A new maritime, subpolar regime is displacing the existing polar climate along the WAP, allowing new species to immigrate, and shifting our penguin research to the Gentoo species as the Adélies decline.
Figure 5: Autonomous gliders, instrumented penguins and satellites survey the canyons near Palmer Station. Inset: a glider mission from Palmer Station to the British Antarctic Survey base at Rothera. Arrows in the inset show current direction and speed along the glider track. Credit: Oscar Schofield, Rutgers University.
Remotely-operated underwater vehicles and animal-mounted sensors generate new information and create new visualizations of the Antarctic seas. Sleek Slocum gliders are now being used to overcome the under-sampling of the Antarctic peninsula region. These 2-meter long torpedo- shaped, winged gliders maneuver through the ocean at a forward speed of 25 kilometers per day in a sawtooth trajectory through buoyancy changes and steering with a tail rudder. They are outfitted with a variety of sensors measuring ocean physics, chemistry, optics and acoustics. This gives scientists the ability to study ecosystem processes spanning from the tiniest plankton to penguin foraging ecology. Since 2007, Palmer gliders have flown 20 missions mapping over 2000 kilometers underwater over 100s of days. In 2009, a glider successfully flew from an American research vessel to the British Antarctic Base Rothera, the first joint international glider effort (Figure 5). Coupled with satellite-telemetry data collected by penguins, highly resolved maps can be generated at the specific locations and depths where penguins are foraging and eventually may even resolve ecological dynamics in natural populations.