Improving the estimation of North Sea primary production: Meris CHL and KD in VGPM

Remote sensing has several applications in the study of the carbon cycle, amongst which the estimation of marine primary production. This paper shows how to adapt the Vertically Generalised Production Model (VGPM) -originally developed for the open ocean by Behrenfeld and Falkowski -for application to the North Sea, a shallow marginal coastal sea containing Case 1 waters in the north and Case 2 waters in the south. VGPM describes a relationship between depth integrated primary production (PPeu) and maximum chlorophyll-a normalized carbon fixation rate (PoptB), sea surface daily PAR (E0), surface chlorophyll concentration derived by satellite (Csat), euphotic depth (Zeu) and photoperiod (D irr). Input for these variables can be derived with remote sensing. PPeu from VGPM is a MODIS Primary Productivity Level 4 product that has been brokered as the standard product. Results from regressions of chlorophyll derived from remote sensing (Csat) and chlorophyll derived from in situ measurements (Qis) show the HYDROPT MERIS CHL product to perform better than the MODIS standard CHL product. In this paper we are using the VGPM model with optimal parameterisation for the North Sea: C sat and Z6u estimation from MERIS HYDROPT. We are currently assessing the impact on the PPeu result, which might have important consequences on the perceived role of the North Sea in the carbon cycle.