[SLS] Katy Abott (MIT-WHOI)

“Microbial respiration controls the fate of subducted organic carbon in the mesopelagic ocean”

Microbial community respiration (MCR), which transforms organic carbon into dissolved inorganic carbon, plays a critical role in regulating the flow of oxygen and carbon from the surface to interior ocean. It determines the fate of organic matter that is exported from the photosynthetically active surface layer by eddy subduction, a process that transports water enriched with non-sinking, microbial carbon and oxygen into the mesopelagic ocean. Here, we leverage a suite of physicochemical measurements made in a region of active eddy subduction in the northwestern Mediterranean Sea to unravel some of the key physical and biological processes controlling the rate of MCR. We selectively sampled intrusions of surface water that were subducted below the euphotic layer to depths of 50-250~m. By relating MCR to a range of observed variables, we show that respiration within these intrusions is shaped by the available living and detrital organic matter and the non-photosynthetic bacterioplankton community. Our analyses indicate that the freshness of organic matter influences MCR, motivating a parametrization for MCR using the chlorophyll-to-carbon ratio as a proxy for freshness of subducted water. Consistent with our observations, the parametrization predicts a slowdown of MCR within intrusions over time, which supports the persistence of subducted oxygen. Relating MCR to the prokaryotic community and bioavailable organic matter is a first step in creating a process-based model for MCR, which is often prescribed as a function of depth or temperature in Earth System Models.

Sack Lunch Seminar Series —
Informal seminar series within PAOC (Program in Atmospheres, Oceans, and Climate) that focuses on more specialized topics than the PAOC Colloquium. The presentations are either given by an invited speaker or by a member of PAOC and can focus on new research or discussion of a paper of particular interest.

Contact: sacklunch-committee@mit.edu