Physical processes mediating climate change impacts on regional sea ecosystems

Abstract

<p><strong>Abstract.</strong> Regional seas are exceptionally vulnerable to climate change, yet are the most directly societally important regions of the marine environment. The combination of widely varying conditions of mixing, forcing, geography (coastline and bathymetry) and exposure to the open-ocean makes these seas subject to a wide range of physical processes that mediates how large scale climate change impacts on these seas' ecosystems. In this paper we explore these physical processes and their biophysical interactions, and the effects of atmospheric, oceanic and terrestrial change on them. Our aim is to elucidate the controlling dynamical processes and how these vary between and within regional seas. We focus on primary production and consider the potential climatic impacts: on long term changes in elemental budgets, on seasonal and mesoscale processes that control phytoplankton's exposure to light and nutrients, and briefly on direct temperature response. We draw examples from the MEECE FP7 project and five regional models systems using ECOSMO, POLCOMS-ERSEM and BIMS_ECO. These cover the Barents Sea, Black Sea, Baltic Sea, North Sea, Celtic Seas, and a region of the Northeast Atlantic, using a common global ocean-atmosphere model as forcing. We consider a common analysis approach, and a more detailed analysis of the POLCOMS-ERSEM model. <br><br> Comparing projections for the end of the 21st century with mean present day conditions, these simulations generally show an increase in seasonal and permanent stratification (where present). However, the first order (low- and mid-latitude) effect in the open ocean projections of increased permanent stratification leading to reduced nutrient levels, and so to reduced primary production, is largely absent, except in the NE Atlantic. Instead, results show a highly heterogeneous picture of positive and negative change arising from the varying mixing and circulation conditions. Even in the two highly stratified, deep water seas (Black and Baltic Seas) the increase in stratification is not seen as a first order control on primary production. The approaches to downscaled experiment design and lessons learned from the MEECE project are also discussed.</p>

Projected Change—North Sea

“…Both ensembles using one regional model with different global models (e.g. Wakelin et al 2012a;Holt et al 2014Holt et al , 2016Pushpadas et al 2015) and ensemble downscaling from one GCM using different regional model systems are available for the North Sea (Bülow et al 2014). The ensemble simulations allow for a first estimation of uncertainty arising from different GCMs and RCMs (regional climate models).…”

“…Friocourt et al 2012;Wakelin et al 2012a;Bülow et al 2014;Holt et al 2014Holt et al , 2016Pushpadas et al 2015). Both ensembles using one regional model with different global models (e.g.…”

“…the SRES scenario A1B (see Annex 4). These experiments were performed either as time slice experiments of 20-30 years for present-day and future (end-of-the-century or middle-of-the-century) climates (Ådlandsvik 2008;Holt et al 2010Holt et al , 2012Holt et al , 2014Holt et al , 2016Friocourt et al 2012;Wakelin et al 2012a;Pushpadas et al 2015) or as continuous integrations (e.g. Gröger et al 2013;Bülow et al 2014;Mathis and Pohlmann 2014).…”

“…The resulting changes in SST from these experiments are typically very similar for different regional ocean models and differ only by around a tenth of a degree. On the other hand, ensemble studies performed with one regional ocean model and different forcing GCMs clearly show that the magnitude of the projected changes significantly depend on the forcing GCM (Wakelin et al 2012a;Holt et al 2010Holt et al , 2012Holt et al , 2014Holt et al , 2016Pushpadas et al 2015;Fig. 6.8).…”

“…These use the IPSL-CM4.0 ESM (Wakelin et al 2012a;Chust et al 2014;Holt et al 2014Holt et al , 2016 and MPIOM Gröger et al 2013) as global forcing. The resulting changes in SST from these experiments are typically very similar for different regional ocean models and differ only by around a tenth of a degree.…”