Graph of the Day: Arctic PhytoPlankton Blooming 50 Days Earlier
March 7, 2011
The Washington Post reports:
A new report finds that the disappearing ice has apparently triggered another dramatic event – one that could disrupt the entire ecosystem of fish, shellfish, birds and marine mammals that thrive in the harsh northern climate.
Each summer, an explosion of tiny ocean-dwelling plants and algae, called phytoplankton, anchors the Arctic food web.But these vital annual blooms of phytoplankton are now peaking up to 50 days earlier than they did 14 years ago, satellite data show.
“The ice is retreating earlier in the Arctic, and the phytoplankton blooms are also starting earlier,” said study leader Mati Kahru, an oceanographer at the Scripps Institution of Oceanography in San Diego.
The study was conducted by researchers from the Scripps Oceanographic Institute. A story at that website fleshed out details.
Scientists at Scripps Institution of Oceanography at UC San Diego, along with colleagues in Portugal and Mexico, plotted the yearly spring bloom of phytoplankton—tiny plants at the base of the ocean food chain—in the Arctic Ocean and found the peak timing of the event has been progressing earlier each year for more than a decade. The researchers analyzed satellite data depicting ocean color and phytoplankton production to determine that the spring bloom has come up to 50 days earlier in some areas in that time span.
The earlier Arctic blooms have roughly occurred in areas where ice concentrations have dwindled and created gaps that make early blooms possible, say the researchers, who publish their findings in the March 9 edition of the journal Global Change Biology.
During the one- to two-week spring bloom, which occurs in warm as well as cold regions, a major influx of new organic carbon enters the marine ecosystem through a massive peak in phytoplankton photosynthesis, which converts carbon dioxide into organic matter as part of the global carbon cycle. Phytoplankton blooms stimulate production of zooplankton, microscopic marine animals, which become a food source for fish.
Plankton populations that, in former decades, peaked in September, as of 2009, were peaking in July – with unknown consequences for the arctic food chain for which they are the foundation.
The Post story noted:
A 50-day shift is a big shift,” said plankton researcher Michael Behrenfeld of Oregon State University, who was not involved in the study. “As the planet warms, the threat is that these changes seen closer to land may spread across the entire Arctic.”
Ecologists worry that the early blooms could unravel the region’s ecosystem and “lead to crashes of the food web,” said William Sydeman, who studies ocean ecology as president of the nonprofit Farallon Institute in Petaluma, Calif.
When phytoplankton explode in population during the blooms, tiny animals called zooplankton – which include krill and other small crustaceans – likewise expand in number as they harvest the phytoplankton. Fish, shellfish and whales feed on the zooplankton, seabirds snatch the fish and shellfish, and polar bears and seals subsist on those species.
The timing of this sequential harvest is programmed into the reproductive cycles of many animals, Sydeman said. “It’s all about when food is available.” So the disrupted phytoplankton blooms could “have cascading effects up the food web all the way to marine mammals.”
But the Arctic food web is poorly studied, and so any resulting decline in fish, seabirds and mammals will bedifficult to spot.
The researchers underlined that the changes are almost certainly due to the declining extent of arctic sea ice. Last month, the National Snow and Ice Data center reported that February sea ice was tied for the lowest extent in the satellite era.