Are phytoplankton blooms occurring earlier up North?
Fruit trees and garden flowers aren’t the only things blooming earlier due to climate change. In the Arctic Ocean, tiny floating phytoplankton are also blooming earlier each year, according to a new analysis of satellite records. The question now is how this shift at the base of the food web will ripple out through Arctic ecosystems.
The one- to two-week-long spring bloom “provides a major source of food for zooplankton, fish and bottom-dwelling animals,” says Mati Kahru, an oceanographer at the Scripps Institution of Oceanography at the University of California, San Diego. Many of those creatures rely on the annual spring feed to fuel egg-laying and larval growth, so an earlier bloom could create a potentially problematic mismatch.
To plot the shifting bloom, Kahru and colleagues in Portugal and Mexico examined satellite data from 1997 to 2009 that charted changes in ocean color and phytoplankton production. They detected “significant” trends toward earlier blooms in about 11% of the surveyed area, they report in Global Change Biology. “These areas roughly coincide with areas where ice concentration has decreased in early summer (June),” the authors write. The melt makes “the earlier blooms possible.” Overall, the blooms in these areas now peak up to 50 days earlier than they did 13 years ago.
Although analyzing satellite data is fraught with complications, and the trend appears to be playing out differently in different parts of the Arctic, the researchers have little doubt that what they are seeing is real. And while the advancement trend probably won’t sustain its recent rapid pace in many areas due to limitations created by ice cover and cold temperatures, the trend could “expand into other areas of the Arctic Ocean and impact the whole food chain,” including commercially-exploited fish stocks.
The shift could also influence the global carbon cycle, since phytoplankton play a major role in sucking carbon dioxide out of the atmosphere. – David Malakoff | March 3, 2011
Source: KAHRU, M., BROTAS, V., MANZANO-SARABIA, M., & MITCHELL, B. (2011). Are phytoplankton blooms occurring earlier in the Arctic? Global Change Biology, 17 (4), 1733-1739 DOI: 10.1111/j.1365-2486.2010.02312.x
Image © Nancy Nehring