Circulation and resource limitation control global pattern of phytoplankton diversity: Insights from a trait-based model

Diversity has been observed to decrease with latitude in many oceanic taxa, a pattern  often explained by the positive kinetic effect of high temperature on metabolic rates, but whether this pattern also apply to phytoplankton remains debated. In order to disentangle the drivers of phytoplankton diversity, we developed a global 3D phytoplankton ecological dynamics model, coupled to the MIT general circulation model at a resolution of 1°, where ecotypes differing by their cell size, temperature niche, and solar irradiance niche, compete for the same nutrients and are transported by oceanic currents. The phytoplankton diversity pattern we simulate, validated by PhytoBase observations, is neither monotonic in latitude nor governed by temperature. Instead, we find that diversity is increased by vertical stratification and horizontal mixing, and depressed by nutrient and light limitations. Warm waters host local diversity maxima in upwelling regions, where permanent  stratification allows each depth level to select a different community uniquely adapted to its environmental conditions, and minima in the nutrient-depleted centers of the subtropical gyres, where only the smallest cells have positive net growth rates. We also find maxima in the mid-latitudes, characterized by seasonality and meridional dispersal across strong temperature gradients, and minima in the well-mixed Southern Ocean south of 50°S. We conclude by some hypotheses on phytoplankton response to future changes in the physical environment, such as warming, mixed-layer shallowing or Gulf Stream weakening.

Presentation Preference: Oral

Primary Presenter: Guillaume Le Gland, Aix-Marseille Université (guillaume.le-gland@univ-amu.fr)

Authors:

Guillaume Le Gland, Mediterranean Institute of Oceanography  (guillaume.le-gland@univ-amu.fr)

Boris Sauterey, Laboratoire de Météorologie Dynamique, Sorbonne Université  (boris.sauterey@lmd.ipsl.fr)

Bingzhang Chen, Department of Mathematics and Statistics, University of Strathclyde  (bingzhang.chen@strath.ac.uk)

Stephanie Dutkiewicz, Department of Earth, Atmospheric and Planetary Sciences, Massachussetts Institute of Technology  (stephdut@mit.edu)

Oliver Jahn, Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology  (jahn@mit.edu)

Pedro Cermeño, Department of Marine Biology and Oceanography, Institute of Marine Sciences (CSIC)  (pedrocermeno@icm.csic.es)

Sergio Vallina, Instituto Español de Oceanografı́a (CSIC)  (sergio.vallina@csic.es)