Climate change in Antarctica has caused a shift in phytoplankton, an important food source for larger animals.
Scientists have long established that the Antarctic Peninsula is one of the most rapidly warming spots on Earth. Now, new research using detailed satellite data indicates that changing climate is affecting not just the penguins at the apex of the food chain, but simultaneously the microscopic life at the lowest rung of the ecosystem. The changes appear to account for the observed relocations of some northern peninsula species.
Over the past 50 years, winter temperatures on the peninsula have risen five times faster than the global average, and the duration of sea-ice coverage has decreased. A warmer, moist maritime climate has moved into the northern peninsula region, pushing the cooler conditions southward toward the pole.
Satellite data on ocean color—which indicates the amount of chlorophyll—temperature, sea ice and winds, indicate that single-celled phytoplankton that carry out photosynthesis at the base of the food chain are also responding to changes in sea-ice cover and winds driven by climate change. And data gathered for 20 years from offshore sites and from an ecological research site near Antarctica’s Palmer Station show contrasting changes in northern and southern regions.
Hugh Ducklow, of the Marie Biological Laboratory at Woods Hole, the principal investigator for the Palmer Long-Term Ecological Research project, said the new findings are scientifically significant and are consistent with the climate trends on the peninsula and other observed changes.
"With the weight of all the other observations that we had on changes happening to organisms higher up in the food chain, we thought that phytoplankton weren't going to escape this level of climate change," Ducklow said.
In the north, where ice-dependent species are disappearing, sea-ice cover has declined and wind stress has increased. The wind intensity and reduced sea ice causes greater mixing of the surface ocean waters. The result: a deepening of the surface mixed layer that exposes phytoplankton cells to less light and, therefore, reduces its numbers and availability as a food source.
Consequently, the prevalence of species that depend on ice-edge diatom blooms, such as krill, Antarctic silverfish and Adelie penguins, has shifted southward from the peninsula's northern region. New species that typically avoid ice, such as Gentoo and Chinstrap penguins, and lanternfish are moving into the habitat.
Meanwhile, in the southern peninsula waters, where ice-dependent species continue to thrive, the situation is reversed. Now, ice is less prevalent, exposing more water to sunlight and stimulating phytoplankton growth. Ice loss in the south, combined with less wind stress, promotes the formation of a shallower mixed layer, with increased light and the development of large phytoplankton cells, such as diatoms.
The scientists say chlorophyll levels for the past 20 years have decreased an average of 89 percent in the northern regions and increased 66 percent in the southern regions.
The research was published in the March 13 edition of Science magazine by researchers with the National Science Foundation's Long Term Ecological Research program.
—By Peter West/NSF.
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