Diatoms and Climate Change.

Diatoms living between crystals of annual sea ice in McMurdo Sound, Antarctica. From Wikimedia Commons.

Diatoms living between crystals of annual sea ice in McMurdo Sound, Antarctica. From Wikimedia Commons.

Diatoms are unicellular algae with golden-brown photosynthetic pigments with a fossil record that extends back to Early Jurassic. The most distinctive feature of diatoms is their siliceous skeleton known as frustule that comprise two valves. The formation of this opaline frustule is linked  in modern oceans with the biogeochemical cycles of silicon and carbon.

Because their abundance and sensitivity to different parameters,  diatoms play a key role in Paleoceanography , particularly for evidence of climatic cooling and changing sedimentation rates in the Arctic and Antarctic oceans and to estimate sea surface temperature. Also, diatom diversity can be used as a proxy for the influence of diatoms on marine export productivity and the carbon cycle.

Diatoms are thought to have diversified over the Cenozoic. Early Cenozoic oceans were relatively warm, but in the early to mid Eocene, ocean surface temperatures began to cool, and polar regions and tropical regions began to be more strongly differentiated. It was suggested that Late Eocene diatom proliferation likely occurred in response to subsidence of Southern Ocean land bridges and the concurrent development of circum-Antarctic upwelling.

Actinocyclus ingens Rattray and Thalassiosira convexa (SEM, Neogene diatoms from the Southern Ocean, ODP)

Actinocyclus ingens Rattray and Thalassiosira convexa (SEM, Neogene diatoms from the Southern Ocean, ODP)

Peak species diversity in marine planktonic diatoms occurred at the Eocene–Oligocene boundary followed by a pronounced decline, from which they have not recovered (Rabosky 2009).  During the early late Miocene, when temperatures and pCO2 were only moderately higher than today, diatoms lost about 20% of its diversity. Warmer oceans are linked with lower diatom diversity, suggesting that future warmer oceans due to anthropogenic warming may result in lower diatom diversity (Lazarus, 2014).

During the last 15 million years, diatom diversity is correlated with global carbon isotope record and with the past atmospheric pCO2, suggesting that diatoms have played a very important role in the evolution of mid-Miocene to Recent climate for their prominent role in the carbon pump.

References:

Armstrong, H. A., Brasier, M. D., 2005. Microfossils (2nd Ed). Blackwell, Oxford.

Lazarus D, Barron J, Renaudie J, Diver P, Türke A (2014) Cenozoic Planktonic Marine Diatom Diversity and Correlation to Climate Change. PLoS ONE 9(1):e84857. doi:10.1371/journal.pone.0084857

Egan KE, Rickaby REM, Hendry KR, Halliday AN (2013) Opening the gateways for diatoms primes Earth for Antarctic glaciation. Earth and Planetary Science Letters 375: 34–43. doi: 10.1016/j.epsl.2013.04.030

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