Publication Abstract

Long-term variability in the primary production of the North Sea

 It is generally accepted that a regime shift occurred in the North Sea ecosystem in the late 1980s observed at different trophic levels (Alheit et al. 2005; Beaugrand 2004; Edwards et al. 2001 and 2002; McQuatters-Gollop et al. 2007; Pitois et al. 2012; Reid and Edwards 2001; Reid et al. 2001). In this study we aim to investigate long term changes in pelagic primary production of the North by examining whether chlorophyll concentration, sediment loads and the underwater light climate have changed. Light availability limits photosynthesis therefore primary production with consequences on higher trophic levels. In particular, we tested the hypothesis that the light penetration depth has decreased significantly in some areas of the North Sea over the last 100 years, with possible effects on primary production.

As a first step a total of 51,483 estimates of light attenuation coefficient (K_d), from Secchi depth and from CTD profiles, from different sources and spanning from 1903 to 2012, were collated together with 75,393 in situ estimates of chlorophyll concentration (from 1970s until 2012), and 40,400 estimates of suspended solids (SPM) concentration (from 1989 to 2012). Observations were aggregated by season and in 5 hydrodynamic regions (permanently mixed, East Anglian plume, fresh water influence, seasonally stratified and intermediate regions), based on the length of vertical stratification of the water column, using the GETM model (Burchard and Bolding 2002). Smoothing functions were applied to the time series of K_d and chlorophyll for each hydrodynamic region, and used to determine estimates of annual primary production, applying simple models from Cole and Cloern (1984), and Joint and Pomroy (1981).

The paper will discuss if there have been significant changes in the annual primary production of the North Sea in the last 3 decades, and how variations in primary production compare to variations in climate variables such as wind stress, cloud cover, precipitations and river run off. 

E. Capuzzo*, R. Forster*, T. Silva*, D. Stephens*, J. Barry*

45th International Liege Colloquium - Primary production in the ocean: from the synoptic to the global scale - 13-17 May 2013 Liege, Belgium