Predicting Future Distributions of Picophytoplankton Lineages in Response to Climate Change Scenarios

FLOMBAUM, P; ADAM C MARTINY

Portland

Congreso; Ocean Sciences Meeting; 2018

AGU

Two approaches are being used to project phytoplankton abundance in future climate scenarios, mechanistic or niche models. The former models represent biological mechanisms that govern abundance, and rely on reduced scale experiments to set physiological response parameters. Evidence from these models suggests future declines of picophytoplankton abundance at low latitudes as well as expansions to high latitudes due to increased water column stratification. Yet, picophytoplankton thrive in oligotrophic warm waters as a diversity of physiological mechanisms allows them to assimilate nutrients at very low concentrations while exhibiting high growth rates. Alternatively, niche models are based on field observations and thus implicitly include the diversity of physiological responses to environmental conditions. We used niche models for Prochlorococcus, Synechococcus, and eukaryotic picophytoplankton to project cell abundance for future climate scenarios (IPCC-CMIP5: RCP 2.6; 4.5; 8.5) by six climate models (CanESM; GFDL-ESM; HadGEM; IPSL-CM5; MPI-ESM; NorESM), and explored the uncertainty ratio for scenarios:climate-models:niche-models. We found that the largest increase in abundance was observed at low latitude, and that Prochlorococcus global abundance was up to 1.8 times bigger than that of the historic scenario. No detectable effect was found for the eukaryotic picophytoplankton, and a maximum of 16% increase for Synechococcus. The source of uncertainty changed over time. By the end of XXI century, different scenarios accounted for a largest proportion of uncertainty followed by climate models and was negligible for niche models for Prochlorococcus (70:30:0) and Synechococcus (50:50:0). In contrast, uncertainty for scenarios was small for picoeukaryotic phytoplankton compared to climate and niche models (5:75:20). Overall, our niche model approach suggests previously unrecognized complex responses of marine phytoplankton lineages to climate change scenarios.