Climatic controls on biophysical interactions in the Black Sea under present day conditions and a potential future (A1B) climate scenario

Abstract

A dynamical downscaling approach has been applied to investigate climatic controls on biophysical interactions and lower trophic level dynamics in the Black Sea. Simulations were performed under present day conditions (1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999) and a potential future (2080-2099) climate scenario, based on the Intergovernmental Panel for Climate Change A1B greenhouse gas emission scenario. Simulations project a 3.7°C increase in SST, a 25% increase in the stability of the seasonal thermocline and a 37 day increase in the duration of seasonal stratification. Increased winter temperatures inhibited the formation of Cold Intermediate Layer (CIL) waters resulting in near complete erosion of the CIL, with implications for the ventilation of intermediate water masses and the subduction of riverine nutrients. A 4% increase in nitrate availability within the upper 30 m of the water column reflected an increase in the retention time of river water within the surface mixed-layer. Changes in thermohaline structure, combined with a 27% reduction in positive wind stress curl, forced a distinct change in the structure of the basin-scale circulation. The predominantly cyclonic circulation characteristic of contemporary conditions was reversed within the southern and eastern regions of the basin, where under A1B climatic conditions, anticyclonic circulation prevailed. The change in circulation structure significantly altered the horizontal advection and dispersion of high nutrient river waters originating on the NW self. Net primary production increased by 5% on average, with much spatial variability in the response, linked to advective processes. Phytoplankton biomass also increased by 5% and the higher nutrient environment of the future scenario caused a shift in species composition in favour of larger phytoplankton. No significant change in zooplankton biomass was projected. These results constitute one of many possible future scenarios for the Black Sea, being dependent on the modelling systems employed in addition to the choice of emission scenario. Our results emphasise in particular the sensitivity of dynamical downscaling studies to the regional wind forcing fields extracted from global models (these being typically model dependent). As atmospheric warming is projected with a high degree of confidence warming of the Black Sea upper layer, increased water column stability, and erosion of the CIL are believed to be robust results of this study.

Understanding the Impact of Environmental Variability on Anchovy Overwintering Migration in the Black Sea and its Implications for the Fishing Industry

“…A limitation of this approach is that model results could not be validated against detailed, longterm anchovy survey data for lack of availability. Efforts to develop coupled hydrodynamic-ecosystem models of the Black Sea environment are underway (e.g., Cannaby et al, 2015) as are models that include food-web interactions to derive fisheries management advice (Akoglu et al, 2015;Salihoglu et al, in review). Application of the fish movement model presented here with a fully coupled hydrodynamic-ecosystem model, may be better able to address not only overwintering but also spawning migration behavior exhibited by anchovy in the Black Sea.…”

Controls of Multiple Stressors on the Black Sea Fishery

“…How the Black Sea ecosystem might respond to future changes in climate in combination with other drivers appears to depend on characteristics of other stressors (Niiranen et al, 2013). Preliminary studies have been conducted by Cannaby et al (2015) but a deeper analysis under different scenarios of stressor combinations (different combinations of fishing and nutrient load management scenarios) are worthwhile to perform.…”

Evolution of Future Black Sea Fish Stocks under Changing Environmental and Climatic Conditions

“…It uses Mellor-Yamada 2.5 turbulence parameterization (Blumberg and Mellor, 1987), incorporates parameterizations for the water fluxes at the Bosphorus and includes nine of the largest rivers that flow into the Black Sea. The physical model was initialized using World Ocean Atlas fields (WOA; Locarnini et al, 2013;Zweng et al, 2013) The biogeochemical model BIMS, is based on a 1D model by and an earlier 3-D version of the model (Cannaby et al, 2015). The vertical grid was designed to provide sufficient resolution at the surface and sub-surface layer where most of the biogeochemical dynamics take place.…”