Modelling primary production in the North Sea: Applying a light-dependent model on MERIS images between 2002-2012

Abstract

Primary production in coastal waters is important to monitor due to its implications on water quality, fish stocks and the carbon cycle, amongst others. Due to the economic and political importance of the North Sea, long-term monitoring primary production in this region is essential to fully assess the role of climate change on this process. To apply this to the North Sea, a simple light-dependent primary production model by Cole & Cloern was applied onto in-situ data of water quality parameters and regressed against gross primary production values from OS9, a station off the coast of the Eastern Scheldt. Following calibration at this station and validation of water quality parameters at Rijkswaterstaat stations for the Dutch North Sea, primary production was then successfully modelled for the entire North Sea between 2002-2011 using satellite-derived estimates of water quality parameters (Kd and chlorophyll-a) from Envisat MERIS and surface irradiance (Eo) from a NOAA atmospheric model. Results showed that the various hydrodynamic regions had different primary production values and also experienced variable fluctuations in primary production over the years. It was also found that small changes in the largest hydrodynamic regions had the greatest influence on the North Sea primary production budget. No significant trend was found in the annual primary production budget of the North Sea over the period 2003-2011 (p-value =0.595). The results also showed that modelled primary production values were able to detect shifts in trends as a result of climatic variability, although the period of analysis was quite short to properly assess significant long-terms shifts in primary production trends. Finally, the non-linear response of each region to climatic changes was evident in the annual primary production budget, especially in the case of 2010. A proposed method of conducting future analyses on primary production trends is assessing periods in the North Sea separated by regime shifts to understand the effects of environmental change on phytoplankton population shifts and the effects on primary production.