The ice ages made massive changes to the Earth'slandscape. But what was happening below the icein the oceans?
Research by marine scientists reveals that it wasa time of mass destruction as whole communitiesof animals were wiped out by ice sheets scouringthe sea floor.
In the past it has been thought that theseecosystems somehow dodged extinction byrecolonising from nearby habitats that escapedobliteration. But researchers at the NationalOceanography Centre, Southampton (NOC) and theBritish Antarctic Survey (BAS) reveal a bleakerscenario.
Dr Sven Thatje, an ecologist at NOC has beenworking with geoscientists, Dr Claus-DieterHillenbrand and Dr Rob Larter at BAS examiningone of the harshest environments on Earth - theAntarctic seafloor.
Writing in the October issue of Trends in Ecology& Evolution the scientists provide new evidencethat suggests that seafloor organisms were eithererased by the advance of ice sheets across theAntarctic continental shelf or starved to deathas links in the food chain were broken by thepermanent ice cover. There would have been norefuge for shallower living animals further downthe continental slope, as huge sediment slideswould have buried them. Typically theseecosystems would have been made up of sponges,urchins, sea fan corals, and starfish.
Dr Thatje said: 'We show that during ice agesseafloor organisms emigrated to the deep sea -below the effects of the sediment slides and ice.From there, organisms may have invaded openmarine shelters of the Antarctic shelf, whichwere not affected by the advance of ice masses.Or these animals may have recolonised theAntarctic shelf from the deep-sea during the warmperiod following each ice age.
'Either way it is an impressive feat against theodds as the extreme cold means that these animalsrespond much more slowly to the destruction oftheir habitat than elsewhere in the oceans. Theyhave lower metabolic rates that lower theirgrowth and reproductive rates. Elsewhere in theoceans, a brisingid starfish would reproduceannually and live for ten years. In the Antarcticthese starfish can reach 100-years-old butreproduce only once every ten years. This meansthat full community recuperation takes up tohundreds of years.'
Dr Claus-Dieter Hillenbrand explained: 'Until nowit was commonly thought that the destructiveaction of the ice sheets was not significantenough to eradicate all the fauna and thatdesolate patches were recolonised fromsurrounding areas. But our research confirms thatthe destruction was wholesale with very littlesurviving. Even today calving icebergs ploughingacross the seafloor destroy everything in theirpath. Imagine the impact of ice sheets during theice ages that covered a much wider area in a timeof lower sea levels.'
The team's research will lead to a radicalrethink of the evolutionary history of Antarcticaas the work challenges all the accepted theories.The scientists argue that shallow water animalswere retreating to the deep ocean and thenreturning to recolonise Antartica's shelf seas.Clues to how these two very different communitiescould have achieved this may lie in the animals'DNA.
Sven Thatje continued: 'Our work means that thetext books will need to be rewritten. Our nexttask is to reconstruct what happened inAntarctica during these periods of climate changeand study the genetic and biological linksbetween deep sea and shallow water communities.'
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