In coastal areas, the ocean can respond to the atmosphere rapidly and is highly variable over short spatial scales. In these cases, significant feedbacks between the ocean and atmosphere occur regularly. This project explores the contribution of optically active water constituents (OACs) to energy fluxes in the upper ocean using a coupled bio-optical-ocean-atmosphere model. Our aim is to understand how heterogeneity in OACs in shelf seas affects the characteristics of sub-mesoscale vertical mixing and advective fluxes, through feedbacks with upper ocean heating rates and water density. Our approach involves quantifying the contribution of optically active water constituents to heating rates in a shelf sea region, the Western Baltic Sea, where different freshwater and nutrient regimes, and complex bio-optical and hydrodynamic processes take place.

Using a coupled bio-optical-ocean-atmosphere circulation model, we spectrally resolve the underwater light field in a dynamic ocean and model the inherent optical properties (IOPs) of the different water constituents under varying environmental conditions. The explicit calculation of in-water spectrally-resolved absorption, scattering and backscattering coefficients, as well as the attenuation coefficient, and upward, downward and scalar irradiance fields, means that the optically active water constituents' contribution to the divergence of the heat flux can be calculated and accounted for within the full hydrodynamic solution. Knowing the relative
contributions of water constituents to the divergence of the heat flux and heating rates will provide insight
into the relationship between ocean state, variability in IOPs, phytoplankton community structure and air-sea energy fluxes. The impact these heating rates have on the ocean SST is fed back to the atmospheric component of the modelling system, so that we can evaluate the importance of considering a coupled ocean-atmosphere system for our purpose.

An dem Projekt beteiligt sind:

• Freie Universität Berlin (FUB,WEW)
• Leibniz Institut für Ostseeforschung Warnemünde (IOW)
• Rutgers University
• Woods Hole Coastal and Marine Research Center (USGS-WHCMSC)