PAST PLANKTONIC DIVERSITY

Abstract:

Planktonic organisms have been extensively used in paleoceanographic studies as proxies for most marine environmental variables (temperature, salinity, currents, frontal zones, upwelling, etc.), both directly by species occurrences and indirectly through particular chemical components produced (e.g. Mg/Ca, stable isotopes, alkanones).

In 1965 Stehli pioneered by suggesting the use of planktonic organisms diversity to decipher ancient oceanic circulation, instead of the traditional approaches based on particular indicator species or assemblages composition (transfer functions). The use of species diversity has two main advantages. First, it is not restricted to a temporal epoch where the species existed and second, it does not assume that the species ecology is the same as in the present.

In the current work, we compare planktonic organisms diversity on the Atlantic Ocean, obtained from surface samples, with the main satellite measured oceanographic variables, i.e. SST (Sea Surface Temperature), CHL (as an indicator of primary productivity) and the main currents in the area. Three indices were used to quantify diversity: Shannon-Weaver diversity (H), specific richness (S) and Hulbert’s probability of interspecific encounter index of species evenness (PIE). Diversity was then modelled spatially using geostatistical tools at two scales: Atlantic Ocean oceanographic scale and the Iberian margin regional scale.

The main conclusions will then be used to interpret measured down core diversity, on a paleo perspective. This work will understand how did diversity reacted to major climatic events, and how long it took to recover – system resilience.