[PAOCQ – New Date] Emily Zakem (Carnegie)

“Slow copiotrophs in the deep ocean”

Microorganisms drive global biogeochemical cycles, regulating the fluxes of nutrients and greenhouse gases. Microbial growth combines with the ocean circulation to control the losses of bioavailable nitrogen in anoxic zones, for example, as well as the amount of organic carbon stored in the ocean. However, our understanding of these controls remains incomplete, preventing accurate projections of how ocean nitrogen loss and carbon storage are changing with a warming ocean. I will share new insights into these controls gained from the use of ocean biogeochemical models that include a diverse array of microbial functional types. First, our work provides a mechanistic explanation for the surprisingly high abundances and respiration rates of slow-growing, chemoautotrophic, aerobic (oxygen-consuming) nitrite-oxidizing bacteria in anoxic zones, which retain bioavailable nitrogen, and may buffer perturbations in oxygen supply to anoxic waters. Second, we link coarse-grained, global-scale biogeographies of the immensely diverse communities of heterotrophic bacteria and archaea to the cycling of the organic carbon substrates they consume. Results propose grazing as an ecological mechanism for the accumulation of dissolved organic carbon in the upper ocean via the suppression of slow-growing microbial heterotrophs from fast-paced surface waters. In both cases, for different reasons, we find that slow-growing microbes living below the sunlit layer may be more copiotrophic than many surface types, optimized for relatively fast growth despite low absolute growth rates, which alters our view of deep ocean microbial communities.

PAOC Colloquium —

Interdisciplinary seminar series that brings together the whole PAOC (Program in Atmospheres, Oceans, and Climate) community. Seminar topics include all research concerning the physics, chemistry, and biology of the atmospheres, oceans and climate, as well as talks about societal impacts of climatic processes.

Contact: paoc-colloquium-comm@mit.edu