Increased Surface Ocean Heating by Colored Detrital Matter (CDM) Linked to Greater Northern Hemisphere Ice Formation in the GFDL CM2Mc ESM

Abstract

ecent observations of Arctic Ocean optical properties have found that colored dissolved organic matter (CDOM) is of primary importance in determining the nonwater absorption coefficient of light in this region. Although CDOM is an important optical constituent in the Arctic Ocean, it is not included in most of the current generation of Earth system models (ESMs). In this study, model runs were conducted with and without light attenuation by colored detrital matter (CDM), the combined optical contribution of CDOM and nonalgal particles. The fully coupled GFDL CM2 with Modular Ocean Model version 4p1 (MOM4p1) at coarse resolution (CM2Mc) ESM was used to examine the differences in heating and ice formation in the high northern latitudes. The annual cycle of sea surface temperature (SST) is amplified in the model run where the optical attenuation by CDM is included. Annually averaged integrated ice mass is 5% greater and total ice extent is 6% greater owing to colder wintertime SSTs. Differences in ocean heating (i.e., temperature tendency) between the two model runs are well represented by the combined changes in heating by penetrating shortwave radiation, mixing, and surface heat fluxes in the upper 100 m. Shortwave radiation is attenuated closer to the surface, which reduces heating below 10 m during summer months. Mixing entrains colder waters into the mixed layer during the autumn and winter months. Increased cloudiness and ice thickness in the model run with CDM reduces incoming shortwave radiation.