The impact of water constituents on radiative heat transfer in the open ocean and shelf seas

• Applicant: Dr. Bronwyn Cahill, Ph.D.
• Subject Area: Oceanography
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 326263211

Radiant energy fluxes impact biological production in the ocean and are themselves modulated as a result of biological production. This has fundamental consequences for upper ocean physics, surface nutrient supply, net primary and export production and the exchange of soluble gases across the air-sea interface into the marine atmospheric boundary layer. The contribution of optically active water constituents to heating rates in the upper ocean is intrinsically linked to net primary productivity and export production, through the direct effect of temperature on metabolic rates of marine plankton. As compared to the open ocean, the heterogeneity of water constituents in shelf seas and coastal waters is increased by the highly variable presence of inorganic suspended particulate matter and coloured dissolved organic matter (CDOM). Sources of CDOM and changes to its composition through non-conservative processes are tightly coupled to the underwater light field. These will vary with environmental conditions and phytoplankton community structure. Moreover, heterogeneity in phytoplankton pigments and other water constituents will have implications for sub-mesoscale vertical mixing and advective fluxes, and thus water temperature, density and the supply of nutrients to the surface. Understanding what the consequences are for energy fluxes in the upper ocean and across the air-sea interface, and the accumulative effect on the upper ocean heat budget in shelf seas and coastal waters is of particular importance for our capacity to adequately model regional ocean climate.In this project, we will quantitatively examine the contribution of optically active water constituents (including phytoplankton, CDOM and inorganic suspended sediments) to energy fluxes in the upper ocean and across the air-sea interface. We will investigate how heterogeneity in water constituents impacts the characteristics of sub-mesoscale vertical turbulent mixing and advective fluxes and examine how variability in CDOM attenuation is reflected by environmental conditions and in phytoplankton community structure. This shall be achieved by using a coupled ocean-atmosphere circulation model incorporating a bio-optical module with multiple phytoplankton groups in tandem with an atmosphere-ocean radiative transfer model such that heating rates due to the highly variable concentrations of optically active water constituents can be rigorously estimated and their impact on ocean biophysical processes evaluated.

• DFG Programme: Research Grants
• International Connection: USA
• Cooperation Partners: Professor Dr. Hans Burchard; Dr. Ulf Graewe; Dr. John Warner; Professor Dr. John Wilkin