NOAA/WDS Paleoclimatology - Simulations of ocean physical and biogeochemical fields under different biological functioning in CSIRO Mk3L 1.2 v1.0

The biogeochemistry of the ocean exerts a strong influence on the climate by modulating atmospheric greenhouse gases. In turn, ocean biogeochemistry depends on numerous physical and biological processes that change over space and time. Accurately simulating these processes is fundamental for accurately simulating the ocean's role within the climate. However, our simulation of these processes is often simplistic, despite a growing understanding of underlying biological dynamics. Here we explore how new parameterisations of biological processes affect simulated biogeochemical properties in a global ocean model. We combine 6 different physical realisations with 6 different biogeochemical parameterisations (36 unique ocean states). The biogeochemical parameterisations, all previously published, aim to more accurately represent the response of ocean biology to changing physical conditions. We make three major findings. First, oxygen, carbon, alkalinity and phosphate fields are more sensitive to changes in the ocean's physical state. Only nitrate is more sensitive to changes in biological processes, and we suggest that assessment protocols for ocean biogeochemical models formally include the marine nitrogen cycle to constrain biological processes. Second, we show that dynamic variations in the production, remineralisation and stoichiometry of organic matter in response to changing environmental conditions benefits the simulation of ocean biogeochemistry. Third, dynamic biological functioning reduces the sensitivity of biogeochemical properties to physical change. Carbon and nitrogen inventories were 50 % and 20 % less sensitive to physical changes, respectively, in simulations that incorporated dynamic biological functioning. These results highlight the importance of a dynamic biology for ocean properties and climate.