April 19, 2013
Emergence Of Antarctic Ecosystem Triggered Rapid Biological Evolution
redOrbit Staff & Wire Reports - Your Universe Online
The development of the sea-ice ecosystem in the circum-Antarctic Southern Ocean may have triggered further adaptation and evolution of larger organisms such as baleen whales and penguins, according to a new study published Thursday in the journal Science.The area´s ecosystem can be traced back to the emergence of the Antarctic ice sheets some 33.6 million years ago and plays an important role in global marine food webs and carbon cycling.
The team of international researchers based their conclusions on an analysis of sediment samples from drill cores on the seafloor, which were obtained in 2010 off the coast of Antarctica as part of the Integrated Ocean Drilling Program (IODP). The cores reach nearly 1,000 meters beneath the seafloor and provide new insights into a long gone past.
A 2012 study demonstrated that subtropical plants covered Antarctica about 53 million years ago, but the global climate cooled continuously during the 20 million years that followed.
The current study focuses on the interval 33.6 million years ago, when within a relatively short period of time an enormous ice sheet spread across Antarctica, dramatically altering the life conditions and the ecosystems on the continent and surrounding ocean.
The plankton during that time mainly consisted of algae, most of which were not preserved in sediment samples from drill cores. In contrast, single-celled dinoflagellates, a group of algae containing organic fossilizable substance, do preserve in sedimentary sequences over millions of years, making them a valuable tool to reconstruct environmental conditions.
The researchers found that when Antarctica was sub-tropical and ice-free, the surrounding seas were inhabited by a diverse array of single-celled organisms known as dinoflagellates, which are generally characteristic of relatively warm climates.
However, from the moment the ice cap formed, diversity suddenly collapsed. From that moment on, the only species that occurred were adapted to temporary sea-ice cover characteristic of modern sea-ice environments around Antarctica.
These species are present in high numbers only when the sea ice melts in spring and summer, and therefore are available as a food source for higher organisms only during a short period of the year.
The seas around Antarctica play a vital role in the ocean´s food web. Algal blooms, which only occur in summer when the sea ice melts, are a key food source for both small single-cell organisms like dinoflagellates as well as larger organisms.
"The sudden turnover in the dinoflagellate assemblages indicates clearly that the entire plankton ecosystem of the Antarctic waters had changed", said Professor JÃ¶rg Pross, co-author of the study and paleoclimatologist at the Goethe University and the Biodiversity and Climate Research Centre (BiK-F) in Frankfurt, Germany.
"The explosion of dinoflagellates adapted to a temporary sea-ice cover testifies to an in-depth reorganization of the food web in the Southern Ocean."
Larger animals higher up in the ocean's food chain likely adapted their diet because the algal growth season became shorter and more intense,” Pross said.
“Our data suggest that this change may have promoted the evolution of modern baleen whales and penguins.”
These results stress that major climate change is often accompanied by particularly rapid biological evolution, he concluded.