Influence of microbial and molecular diversity on the storage of marine dissolved organic matter: Insights from a modelling perspective

Sinikka Lennartz1, Andrea Mentges2, Bernd Blasius2, Curtis A. Deutsch3, David P Keller4, Andreas Oschlies4, Christoph Feenders2 and Thorsten Dittmar5, (1)University of Oldenburg, Institute for Chemistry and Biology of the Marine Environment (ICBM), Oldenburg, Germany, (2)Carl von Ossietzky University Oldenburg, Institute for Chemistry and Biology of the Marine Environment (ICBM), Oldenburg, Germany, (3)University of Washington Seattle Campus, School of Oceanography, Seattle, United States, (4)GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany, (5)University of Oldenburg, ICBM, Oldenburg, Germany
Heterotrophic microorganisms play a central role in the global carbon cycle by oxidizing dissolved organic carbon (DOC) to CO2. Marine DOC is one of the largest active organic carbon pools on Earth, thus, small changes in its size can affect the global carbon cycle and the climate system. A major fraction of DOC in the ocean is stable for time scales around 4000-6000 years, but the reasons for this long-term stability are still uncertain. A better knowledge about main factors determining the dynamic of this large carbon reservoir is vital for understanding biological feedbacks in the ocean and climate system. Here we present a novel model framework addressing the hypothesis of molecular diversity as a reason for its recalcitrance. In a box model approach, we show that the formation of a recalcitrant DOC pool is not necessarily a function of its structural lability, but rather a function of the diversity of the network between molecules and microbes. We scale this simple network-model up to the global ocean using an Earth System Model of Intermediate complexity and discuss emerging spatial patterns in relation to present-day observations. Our results highlight the importance of accounting for the ecology of heterotrophic picoplankton to understand the dynamics of this major carbon reservoir.