Thursday, April 2, 2009
What a tangled web we weave..... everything really is connected to everything. Over the past several decades, the climate of the western shelf of the Antarctic Peninsula (WAP) has been changing from a cold, dry polar climate to a warmer, more humid climate marked by retreating glaciers. As a result, populations of species that depend on sea ice -- such as krill and Adelie penguins -- are being displaced poleward and replaced by other species that are typically averse to ice. According to Montes-Hugo et al. in the 13 Mar 2009 Science, climate-related shifts at the base of the marine food web may be contributing to these displacements. Using three decades of satellite and field data, the team documented that ocean biological productivity has been significantly reduced along parts of the WAP and increased elsewhere due to shifting patterns of ice cover, cloud formation, and windiness affecting water-column mixing. In the northern region of the WAP, the skies have become cloudier, reducing the amount of light reaching phytoplankton. Less light and less freshwater inhibit water column stratification, resulting in lower plankton productivity. By contrast, in the southern region, the skies are staying cloudless for longer and the Antarctic current has increased its flow rate, pulling up more micronutrients and thus contributing to greater primary productivity. These regional changes in phytoplankton coincide with observed shifts in krill, fish, and penguin populations in the western Antarctic.