Mix and match: how climate selects phytoplankton

Unlike prokaryotes, which do not leave a fossil trail, the patterns of change over evolutionary time of eukaryotic phytoplankton can be derived from microfossils. Here, Paul Falkowski and Matthew Oliver use the fossil record, resource competition theory and the physical principles of ocean dynamics to propose how climate might have affected phytoplankton populations in the past, and make predictions for the future. Climate strongly influences the distribution and diversity of animals and plants, but its affect on microbial communities is poorly understood. By using resource competition theory, fundamental physical principles and the fossil record we review how climate selects marine eukaryotic phytoplankton taxa. We suggest that climate determines the equator-to-pole and continent-to-land thermal gradients that provide energy for the wind-driven turbulent mixing in the upper ocean. This mixing, in turn, controls the nutrient fluxes that determine cell size and taxa-level distributions. Understanding this chain of linked processes will allow informed predictions to be made about how phytoplankton communities will change in the future.