Modeling marine dissolved organic carbon response to climate change

Abstract

At 662 Pg C, the marine reservoir of dissolved organic carbon (DOC) represents the ocean’s largest pool of reduced carbon, holding over 200 times the carbon contained in marine biomass and rivaling the atmospheric carbon inventory. Recent work has suggested that the size of the DOC reservoir may respond to future changes in sea temperatures and global overturning circulation strength. Moreover, mobilization of marine DOC has been implicated in several paleoclimate change events. Despite these suggestions, however, the temporal dynamics of the marine DOC reservoir are poorly understood, and previous carbon cycle modeling work has generally assumed this reservoir to be static. In this study, we utilized an Earth system model of intermediate complexity calibrated with respect to DOC observations to assess the response of the marine DOC reservoir to climate changes representative of the last glacial maximum climate state, reduced ocean overturning circulation strength, and future warming scenarios. Our results indicate that the marine DOC reservoir is mobile in response to climate forcings and may shrink or expand depending on changes in its production rate. Moreover, variability in the ocean’s DOC reservoir was directly linked to changes in atmospheric CO2 concentrations, explaining a significant portion of CO2 drawdown or ventilation by the ocean across three sets of climate change experiments. These findings point to an integral role of marine DOC in the global carbon cycle and indicate that consideration of this reservoir is critical in improving our understanding of the connection between ocean processes and global climate of the past, present, and future.