Proteorhodopsin enables marine bacteria to gain energy from light. Metagenome surveys have shown that proteorhodopsin is prevalent among bacterioplankton and found in up to 80 % of genomes. Pigment measurements in oligotrophic systems suggest significant energy uptake rates rivaling Chlorophyll based phototrophy. We hypothesize that explicitly accounting for the use of light as energy source for heterotrophic bacteria challenges our understanding of the marine carbon cycle. We developed a model linking the proteorhodopsin phototrophy to cell maintenance of heterotrophic bacteria and parameterized it using lab experiments. The model is implemented as a submodule in the full-scale ecosystem model ERSEM. Physical ocean models GOTM and NEMO simulate results for different regions and light regimes across the North Atlantic. In surface waters, results show relatively higher bacteria concentrations leading to an enhanced microbial carbon pump, producing more refractory organic carbon, and an enhanced bacteria-zooplankton carbon flux than previously predicted (and vice versa in deep layers). Bacteria maintenance energy saved from proteorhodopsin phototrophy is quantified to be one order of magnitude less than the energy gained from photosynthesis in coastal regions while this ratio increases towards the open ocean regions eventually reaching parity and exceeding 1. Our result will offer a possible explanation for high DAPI counts in surface waters of oligotrophic systems and could present a new approach to spatial and temporal patterns of dissolved organic carbon turnover.

Primary Presenter: Carsten Lackner, Technische Universität Berlin (carsten.vick@tu-berlin.de)

Authors:

Carsten Lackner, Technische Universität Berlin  (carsten.lackner@tu-berlin.de)

Ferdi Hellweger, Technische Universität Berlin  (ferdi.hellweger@tu-berlin.de)