GFI/BCCR Seminar: Using the foraminifer fossil record to reveal the links between ocean circulation, plankton population dynamics and the extinction process

Phil Sexton (The Open University, UK):

Using the foraminifer fossil record to reveal the links between ocean circulation, plankton population dynamics and the extinction process

Abstract
Plankton form the base of oceanic food chains and thus limit the growth of all other marine creatures. Yet we have little idea of the rates, nature and causes of nearly all species disappearances (i.e. those occurring from ‘background’ extinctions, as opposed to mass extinctions). The controls on plankton species’ biogeographic distributions are similarly poorly understood, with two competing classes of explanations having arisen – those that invoke ‘barriers to dispersal’ versus those that instead invoke ‘high dispersal’.

Here I tackle these gaps in our understanding using the marine fossil record of foraminifera, which is unparalleled in its temporal resolution, continuity, chronological precision and spatial coverage. I show that species extinction can be abrupt, and species may disappear from different regions sequentially, with these regional disappearances paced by Earth's orbital cycles. I also show that a change in population dynamics towards globally synchronized biogeographic behaviour may provide an early warning signal of extinction risk. Finally, I show that the equator-to-Pole partitioning of surface ocean macro-nutrient distributions exerts a major (indirect) control on ocean-wide disappearances of zooplankton species via their dependency (for food) on phytoplankton.