Dependence of salinity and oxygen concentrations in the Baltic Sea on large-scale atmospheric circulation

Climate Research

Eduardo Zorita¹  Ari Laine¹ 

关键词: Baltic Sea;    Salinity;    Oxygen;    Downscaling;    Climate change scenarios;   

DOI  :  10.3354/cr014025

来源: Inter-Research Science Publishing

【 摘 要 】

ABSTRACT: The relationship between the low-frequency (annually averaged) salinity and oxygen concentrations in the last 30 yr in the Baltic Sea and the large-scale atmospheric circulation was statistically analyzed. It was found that at these time scalesthe evolution of salinity and oxygen is quite homogeneous in depth, i.e. deviations from the long-term mean tend to be of the same sign in the upper and deeper layers simultaneously. Moreover, the evolution of the salinity and oxygen concentrations arenegatively correlated within each layer: lower than normal salinities tend to be observed simultaneously with higher than normal oxygen concentrations, and vice versa. The statistical analysis seems to indicate that the forcing by the atmosphericcirculation may be responsible for this anticorrelation between salinity and oxygen. A stronger meridional sea-level-pressure (SLP) gradient over the North Atlantic, and therefore stronger westerly winds, causes positive rainfall anomalies in the BalticSea catchment area and increase run-off giving rise to decreased salinities at all depths. The mechanisms by which a stronger zonal atmospheric circulation enhances the oxygen concentrations may be related either to a weakened stratification through thereduced salinity (at long time scales), or by stronger or more frequent inflows of North Sea waters (at short time scales). The influence of the atmospheric circulation can explain at these time scales of the order of 60 and 40% of the variability ofthese hydrographic variables, respectively. The question of how salinity and oxygen in the Baltic Sea may respond to changes of the atmospheric circulation in a global climate change scenario is also addressed. For this purpose the intensities of therelevant atmospheric circulation patterns in a transient experiment with a coupled atmosphere-ocean general circulation model forced with increasing anthropogenic greenhouse gas concentrations between the years 1860 and 2099 were estimated. In thisintegration the change of the atmospheric circulation most relevant for salinity and oxygen in the Baltic Sea seems to be an enhancement of the meridional SLP gradient in the North Atlantic. Thus, under the assumption that the statistical relationshipbetween SLP and the hydrographic variables also holds in the future, this trend in the atmospheric circulation would lead to decreased salinity and improved oxygen conditions in the Baltic Sea.

【 授权许可】

Unknown