The Mercury
Source: SHNS
Vanishing Arctic sea ice brought on by climate change is causing the crucially important microscopic marine plants called phytoplankton to bloom explosively and die away as never before, a phenomenon that is likely to create havoc among migratory creatures that rely on the ocean for food, Stanford scientists have found.
A few organisms may benefit from this disruption of the Arctic's fragile ecology, but a variety of animals, from grey whales to seabirds, will suffer, said Stanford biological oceanographer Kevin Arrigo.
"It's all a question of timing,'' Professor Arrigo said. "If migratory animals reach the Arctic and find the phytoplanktons gone, they'll have missed the boat.''
Phytoplankton throughout the world's oceans is the crucial nutrient at the base of the food web on which all marine life depends.
Prof Arrigo and his colleagues gathered 10 years of observations from six NASA satellites to study changes in the evidence of chlorophyll -- a key to measuring the annual abundance and disappearance of phytoplankton blooms -- at the surface of the oceans. The satellite network has also recorded the yearly appearance and disappearance of vast expanses of sea ice and the increasing areas of open ocean all around the Arctic, showing how climate change is taking hold in the northern reaches of the globe.
A report of their findings is to appear in the current issue of the journal Geophysical Research Letters.
The annual deep freeze was once a regular event, but what has been normal for millennia in the High Arctic is no longer the case. As global climate change has warmed the world's oceans, warmer water has moved into the frigid Arctic, causing changes in the once-regular appearance and disappearance of sea ice over vast areas.
The result is a shift in when explosive blooms of phytoplankton appear and disappear, Prof Arrigo's team has found.
"It's a complex system,'' Prof Arrigo said. "But as the changes in ice cover throw the timing of phytoplankton abundance off, then the birds and animals whose brains have long been programmed to migrate north at specific times of the year will have missed the boat if there's no nourishment for them when they get there.''
Every spring and summer, phytoplankton blooms richly in explosive pulses, nourished by nitrogen and phosphorous in the seawater, and when those chemicals are consumed, the blooms end, he said. The summer of 2007 experienced "by far the lowest sea ice cover ever recorded,'' the study found.
As a result of all that open water, "primary production'' of phytoplankton in the open ocean of the Arctic peaked at more than 10 million tonnes last year, compared with only 700,000 tonnes in 2006.
Most of the explosive increase in plant production was due to the longer growing season made possible by the increasing extent of ice-free open ocean.
But plankton is short-lived, and when its chemical nutrients run out and the plants disappear, the marine life that depends on it is threatened.