The resounding crack of yet another huge chunk of the Marr Glacier falling into neighboring Arthur Harbor is a sound that Chuck, Maggie, Ruth, Kate and I are growing far too accustomed to here at Palmer Station. The glacier is rapidly retreating. Take for example the lovely Marr Glacier ice arch that perched on Amsler Island next to the station. Three years ago, Maggie and Chuck sat on their zodiac for a great photo portrait with the arch framed behind them (see photo). A year later the ice arch collapsed (see photos), and this year, remarkably, there is no ice arch left whatsoever! (see photo).
The Antarctic Peninsula, stretching some 1000 km in length, is now the most rapidly warming region of our planet. Mid-winter air temperatures gathered over the past sixty years, just thirty miles down the coast at the Ukrainian Vernadsky Station, show a consistent trend of an increase of one degree centigrade per decade. A six degree centigrade, or ten degree Fahrenheit, increase over sixty years is unprecedented. The temperature of the sea is also rising, at a much slower rate, but small incremental increases have large consequences.
The ice, in its myriad forms, is reacting to the warming air and sea temperatures. Glaciers, such as the Marr Glacier, are receding very rapidly. Moreover, the large ice sheets surrounding the Antarctic Peninsula are beginning to disintegrate. The most famous break out to date was the Larsen B ice shelf on the eastern side of the Antarctic Peninsula that disintegrated over six weeks in 2002. Essentially, a chunk of ice the size of Rhode Island floated out to sea. More recently, in 2009, the Wilkins Ice Shelf, a Connecticut- sized piece of ice located on the lower western Antarctic Peninsula collapsed. All told, there have been nine major ice sheet break-outs in the past 30 years on the Antarctic Peninsula. Fortunately, these ice sheet break-outs do not contribute to sea level rise as the ice rests on seawater (just like ice in a glass of water does not raise the level of water in the glass after melting). However, in an insidious twist, the disintegration of the ice sheets releases land-locked glacial ice that had been previously barricaded by the ice sheets. Last week, a glaciologist visiting us here at Palmer Station told us at his evening science lecture that when released by disintegrating ice sheets, glaciers along the Antarctic Peninsula flow up to five times more rapidly into the sea. Unfortunately, glacial ice that was land-bound that enters the sea contributes directly to global sea level rise as it melts. Our glaciologist colleague told us that if the glaciers of Antarctica and Greenland continue to flow into the sea at the rates they are currently measuring, that by the end of the century global sea level may be as much as one meter higher than had been predicted. This is food for thought, and especially not good news for undeveloped, low-lying, countries.
The ecological consequences of these changes in the ice on the Antarctic Peninsula are profound, especially when considering the annual sea ice. A wide variety of organisms have complex ecologies that are intimately tied to the patterns of the annual sea ice. Diatoms, little plant cells called phytoplankton, use the sea ice as a residence during the winter months, and then bloom in the sea in the spring. Krill, the little shrimp-like animals that comprise the backbone of the food chains of Antarctica, depend on the diatoms for food, and also as juveniles graze on microalgae that grows on the undersurface of the annual sea ice. With a 40% reduction in the annual sea ice both in its extent and duration, work conducted by the National Science Foundation’s Long Term Ecological Research program currently directed by Dr. Hugh Ducklow, indicates that diatom and krill populations have now declined significantly on the western coast of the northern half of the peninsula.
Adelie penguins have become the poster child of climate warming on the Antarctic Peninsula. Bill Fraser, a world authority on penguins, has followed Adelies near Palmer Station for 35 years. When he started counting them, there were 14,000 breeding pairs near Palmer, now the numbers have plummeted to just three or four thousand pairs left, a 70% decline over just 35 years. Why are they disappearing? It seems that there are two reasons. First, as the air temperatures are rising, the air is becoming more humid, and as such it is snowing more, and later, each year. The Adelie are genetically hard wired to lay their eggs at a certain time in the spring, and now, tragically, later snow events are burying their eggs in slushy snow, suffocating them outright. Secondly, Adelie depend on rich offshore krill grounds for their foraging, and as such, have traditionally used the annual sea ice as a platform to better reach these regions. Now, they must swim much further to their food, wasting critical energy stores. As the Adelie penguins depart or die off in this region, they are being replaced by smaller numbers of warmer-climate sub-antarctic species of penguins, including the chinstrap and the gentoo. Paleontological evidence indicates that these species have never lived in this region of the Antarctic Peninsula before. Warmer temperatures are transforming a formerly true Antarctic ecosystem into a more temperate, sub-antarctic, environment.
The Antarctic Peninsula is the “canary in the coal mine” or the “bellwether” of the dramatic ecological regime shifts we are likely to see down the road in temperate and tropical regions of our planet. Similar to the Arctic, the Antarctic and its wildlife are highly sensitive to even small increases in air and sea temperatures. They are responding accordingly. We, humankind, need to heed the warning signs that are evident everywhere one looks along the northern half of the Antarctic Peninsula.