Some like it hot: marine algae in warm oceans of the past

Description

Ocean productivity is driven by marine phytoplankton that rely on the availability of nutrients, which are quickly exhausted in the sun-lit surface waters if not replenished by ocean mixing processes. Mixing is weaker in warm waters, which explains the apparent patchy distribution of cooler, high-productivity areas (upwelling and high-latitude regions) and warmer, lowproductivity regions (subtropical gyres) within the global oceans. Phytoplankton are sensitive recorders of environmental change, and their seasonal successions and pop-up, opportunistic blooming behavior may largely underpin algal resilience in the highly variable marine environment.
Coccolithophores (single-celled, calcifying haptophyte algae) are able to sustain photosynthesis and growth under low nutrient concentrations, and are expected to perform better than diatoms (opaline silica-producing algae) in future warm and more stratified oceans. Yet, the long-term impacts of (poleward) shifts in the biogeographic distribution of prominent primary producers, such as changes in global primary production and carbon sequestration in the deep ocean, remain largely unknown. Detailed studies of the MCO are important for constraining future warming scenarios, because it was a time interval of sustained global warmth and sea level rise, under moderately high atmospheric CO2 levels (400-600 ppm) and a much weaker latitudinal temperature gradient than today. We are especially interested in resolving latitudinal gradients in paleoproductivity and shifts in the biogeographical distribution of the dominant taxa. Our empirical results will be compared to model simulations of the MCO, using fully coupled, global biogeochemical and climate models run by colleagues at the University of Michigan.