Warming Hits Food Chain at the Bottom of the World

  • by Enrique Gili (san diego, california)
  • Monday, February 28, 2011
  • Inter Press Service

Much of the action takes place on the margins of the continent, where the effects of rising temperatures on the advance and retreat of sea ice are becoming more pronounced and coming at a rate faster than previously anticipated - in a region of the world once considered far too immense for humans to change. The Antarctic Peninsula is thawing out.

Dr. Maria Varnet, a research biologist at the Scripps Institution of Oceanography, has built a career in Antarctica, returning to the Palmer Research Station since 1988. As part of the Long-Term Ecological Research programme, she and a multidisciplinary team of scientists is unlocking the mysteries of the polar ecosystems.

Her focus as of late has been krill-algae interactions. Tiny shrimp-like crustaceans, krill reach maturity in a temporary zone at various times part water, part ice and part slush, which demarcates the watery realm between the permanent ice shelf and the open ocean. It is thought to be the cradle of Antarctica's food chain.

Krill are a key food source for predators. Their abundance or lack of it trickles up and down the food chain. 'Everyone eats the krill - the fish, the whales, the penguins,' Venert told IPS.

Young krill require sea ice in order to thrive. The larvae gather in the sea ice to eat algae accumulating in the crevices and to evade predators. 'If you don't have any ice, you don't have any growth,' she said.

The Antarctic Peninsula is thought to have had better sea ice years with greater consistency in the prior decades. Since 1950, sea ice cover has dropped by 40 percent, and the average annual period of ice cover has shrunk by 90 days. 'Good' ice years are occurring with less frequency.

'Timing is everything,' said Vernet, although factors such as prevailing winds, sunlight and ocean currents also have an important role to play in the formation of sea ice. Winter temperatures on the Antarctic Peninsula have increased five degrees C. over the past 70 years, much higher than other regions on the continent where temperatures have remained stable.

The loss of sea ice along the western edge of the peninsula can be correlated to a decline in krill and algae, which is the basis of the food chain. Whether the loss of sea ice can be attributed to natural seasonal variations or blamed on human-induced climate change is unclear. However, a warming trend is underway, said Vernet.

Different regions are responding differently to warming temperatures. Studies suggest that the declining sea ice is resulting in greater ocean mixing - a complex set of interactions ranging from prevailing winds and the tides down to the molecular level that affects salinity and the regulation of water temperature. One hypothesis is that without sea ice, algae drifts further the down the water column into darker water, reducing the ability to photosynthesise.

Another factor in the equation - the increased intensity of polar winds - is changing the seasonal cycle of sea ice. The sea ice is arriving late in the winter season and retreating earlier.

'The observation is that with global warming those winds have increased. The wind has changed the seasonality of the sea ice,' said Dr. Sharon Stammerjohn, a sea ice specialist at the University of California at Santa Cruz.

Data shows that huge green-hued algae blooms are no longer appearing on satellite images off the western peninsula. Images from the last 30 years reveal an 89 percent decline in phytoplankton in the northern part of the peninsula, but a 66 percent increase in the south. There was a 12 percent decline in phytoplankton, a trend that concerns scientists.

The shortfalls have impacts up and down the food system from penguins that feast on krill to whales that subsist on plankton. Activists also contend that the increasing commercial exploitation of krill is impacting the ecosystem. Krill are harvested to produce feedstock for aquaculture and marketed as Omega 3s in popular diet supplements.

This, along with declining sea ice, threatens Antarctic regions where commercial fishing overlaps with the feeding grounds of seal, penguins, and whales.

'We don't live in the Antarctic, but it's a harbinger of climate change everywhere,' Stammerjohn told IPS.

© Inter Press Service (2011) — All Rights ReservedOriginal source: Inter Press Service

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