Abrupt climate changes of the past and diatom community response.

So far in this blog, many of the posts have been on studies done on microbes from the present day oceans. The focus of this post is the fossilized marine diatoms from the Late Quaternary, when there were abrupt changes in the climate. Geology’s underpinning principle is that the world preserved in the fossil record operated in the same way/ or at least it was fairly similar to the one today. I think that by using this principle and the fossil record, the future of oceans may become slightly clearer. I hope to promote geological records of marine microbes as a useful part of the study of how marine microbes could be affected by climate change.

Data that had been previously reported by a couple of separate studies was used. They focused on the ecological response of diatom communities by measuring the diatom communities at different Heinrich events (the end of glaciations). They used ¹⁴C and benthic delta ¹⁸O isotopes to date the samples.  To study the diatoms they used qualitive and quantitive analysis (they counted them) at x1000 magnification. Analysis was carried out using the Jaccard index which quantifies the similarity between communities, in terms of taxonomic composition and the BC similarity index which does the same but gives weighting to the abundance of the species measured. Cooling episodes match with periods of increased wind, upper-ocean mixing and diatom productivity.  Chaetoceros is a genus of diatoms which requires high levels of turbulence for growth; therefore these are used as indicators in the fossil record for intense wind conditions and mixing.

They found that higher nutrient availability increased the total diatom abundance and probably increased the relative contribution of diatoms to slow growing phytoplankton. Also that diatom abundance and species richness reduced by more than 50% during the change in climate. Data analysis showed that numbers and species richness rapidly recovered after hydrographic conditions were re-established. They found this pattern repeatedly during/after the Heinrich events.

No counts for Coccolithophores were available for these cores but the relative dominance can be suggested by the percentages of opal and calcium carbonated in the marine sediments. Enhanced wind intensity and upper-ocean mixing the percentage of opal in sediments increased in respect to calcium carbonate giving the competitive advantage to siliceous plankton, however the warmer climates weakened the global atmospheric gradients and the intensity of the wind decreased causing diatom abundance to decrease.

By using the BC similarity index they could weight the most dominant species found that, usually, there is a locally dominant fauna which would have large numbers, these would be susceptible to local extinction events, which is why there was large species richness in the rare species, as they would not be impacted as much by local effects. 

The authors conclude that the diatoms have shown the enormous potential for recovery and that diatoms have been stable and resilient in the past 10,000 years despite any abrupt changes in climate and hydrograqphic conditions. In reference to the coming changes in global warming, the authors suggest that the microbial community of the oceans will be affected by these changes. However they will retain the ability to bounce back if conditions are restored. 

Cermeño, Pedro, Emilio Marañón, and Oscar E. Romero. "Response of marine diatom communities to Late Quaternary abrupt climate changes." Journal of Plankton Research (2012): 35, 12-21.

http://plankt.oxfordjournals.org/content/early/2012/10/18/plankt.fbs073.short