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E3SM Session: E2 - Land/Energy

Abstract

The ocean absorbs approximately 25% of present day anthropogenic CO₂ emissions [Doney et al., 2014]. The ocean CO₂ storage capacity is controlled by ocean circulation, deep water formation, temperature and stratification, and marine biogeochemical processes, all of which respond to the climate impacts of increased atmospheric CO₂.  Phase I of E3SM, with enabled biogeochemistry in the land and marine system, is designed to investigate earth system climate-carbon feedbacks and their sensitivities to nutrient process representation in the land system. Climate impacts due to ocean and sea ice biogeochemistry are not considered at this stage. Rather, ocean CO₂ uptake is diagnosed from the behavior of the marine primary production system.  Here we assess the fidelity of ocean and sea ice biogeochemical properties in the last 50 years of the 100 year E3SM-bgc spin-up under pre-industrial conditions.   We focus our analysis on the polar regions, where the influence of sea ice-ocean biogeochemical interactions is poorly studied. Evaluation of the mean state indicates notable biases in Arctic surface pCO₂ and upper ocean nutrient concentrations.  Of concern is low nitrate surface concentrations throughout the Arctic particularly in the Bering Sea, low surface dissolved iron concentrations in parts of the Southern Ocean, and depleted surface silicate in the sea ice zone bordering the Antarctic continent.  Simulations of ocean and sea ice chlorophyll and carbon production, in general, reflect these biases with underestimations throughout much of the polar zone. However, inter-annual variability of the marine biogeochemical state is large, and years of high polar production do fall within observational estimates. Contrasting the polar climate state in years of high and low production offers insights into key mechanisms that control polar carbon cycling.

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