Projected Expansion Oftrichodesmium'S Geographical Distribution And Increase In Growth Potential In Response To Climate Change

Estimates of marine N(2)fixation range from 52 to 73 Tg N/year, of which we calculate up to 84% is fromTrichodesmiumbased on previous measurements ofnifHgene abundance and our new model ofTrichodesmiumgrowth. Here, we assess the likely effects of four major climate change-related abiotic factors on the spatiotemporal distribution and growth potential ofTrichodesmiumfor the last glacial maximum (LGM), the present (2006-2015) and the end of this century (2100) by mapping our model ofTrichodesmiumgrowth onto inferred global surface ocean fields ofpCO(2), temperature, light and Fe. We conclude that growth rate was severely limited by lowpCO(2)at the LGM, that currentpCO(2)levels do not significantly limitTrichodesmiumgrowth and thus, the potential for enhanced growth from future increases in CO(2)is small. We also found that the area of the ocean where sea surface temperatures (SST) are withinTrichodesmium's thermal niche increased by 32% from the LGM to present, but further increases in SST due to continued global warming will reduce this area by 9%. However, the range reduction at the equator is likely to be offset by enhanced growth associated with expansion of regions with optimal or near optimal Fe and light availability. Between now and 2100, the ocean area of optimal SST and irradiance is projected to increase by 7%, and the ocean area of optimal SST, irradiance and iron is projected to increase by 173%. Given the major contribution of this keystone species to annual N(2)fixation and thus pelagic ecology, biogeochemistry and CO(2)sequestration, the projected increase in the geographical range for optimal growth could provide a negative feedback to increasing atmospheric CO(2)concentrations.