Before the Oligocene epoch some 33.6 million years ago, the Earth was a warm place with a tropical climate. In this region, plankton diversity was high until glaciation - the Antarctic continental ice cap - reduced the populations leaving only those capable of surviving in the new climate.
Since that time, we have had seasonal primary productivity of plankton communities. This ice-cap is associated with the ice-pack, the frozen part that disappears and reappears as a function of seasonal climate changes. This phenomenon, still active today, influences global food webs, according to a paper in Science which used information contained in ice sediments from different depths.
Pre-glaciation sediment contained highly varied dinoflagellate communities, with star-shaped morphologies. When the ice appeared 33.6 million years ago, this diversity was limited and their activity subjected to the new seasonal climate.
The Integrated Ocean Drilling Program international expedition has obtained this information from the paleoclimatic history preserved in sediment strata in the Antarctic depths. Andalusian Institute of Earth Sciences researcher Carlota Escutia, who led the expedition, explains that “the fossil record of dinoflagellate cyst communities reflects the substantial reduction and specialization of these species that took place when the ice cap became established and, with it, marked seasonal ice-pack formation and melting began.”
A typical, simple dinoflagellate associated with the early Oligocene epoch and found in 33 million year-old sediments. Credit: University of Granada
The article reports that when the ice-pack melts as the Antarctic summer approaches, this marks the increase in primary productivity of endemic plankton communities. When it melts, the ice frees the nutrients it has accumulated and these are used by the plankton. Dr Escutia says “this phenomenon influences the dynamics of global primary productivity”.
Since ice first expanded across Antarctica and caused the dinoflagellate communities to specialize, these species have been undergoing constant change and evolution. However, the IACT researcher thinks “the great change came when the species simplified their form and found they were forced to adapt to the new climatic conditions”.
Reference: Alexander J. P. Houben, Peter K. Bijl, Jörg Pross, Steven M. Bohaty, Sandra Passchier, Catherine E. Stickley, Ursula Röhl, Saiko Sugisaki, Lisa Tauxe, Tina van de Flierdt, Matthew Olney, Francesca Sangiorgi, Appy Sluijs, Carlota Escutia Henk Brinkhuis and the Expedition 318 Scientists. Reorganization of Southern Ocean Plankton Ecosystem at the Onset of Antarctic Glaciation. Science. DOI: 10.1126/science.1223646
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