Temperature and salinity changes in coastal waters of Western Europe: variability, trends and extreme events

Coastal marine ecosystems worldwide are not only highly affected by the effects of human activities, but also by the influence of natural climate variability and global climate change. However, it is still a challenge to assess the spatial and temporal scales at which forcings operate and their persistence over time, to determine the vulnerability of coastal ecosystems to climate changes and climate extreme events, and therefore to anticipate the ecological and biological responses of these areas. By investigating these knowledge gaps, our recent studies have shown that the combination of large- and local-scale hydroclimatic influences have induced obvious changes in the physical and chemical characteristics of coastal waters in Western Europe. Because of the complex and non-linear climate-coastal ecosystem relationships, a thorough understanding of the underlying processes is still needed, while extending the spatial and temporal scales of inference. Here, using both high- and low-frequency observations collected from 1998 onwards at the outlet of the Bay of Brest and off Roscoff, we described and documented monthly changes in (1) sea surface temperature, (2) sea surface salinity, (3) river discharges and (4) precipitation patterns. By focusing on the winter period (from December to February), our study revealed that coastal waters of Western Europe are not only significantly connected to large-scale atmospheric conditions and patterns, but also to local-scale drivers such as river discharges. Current strong impacts of regional climate extreme events worldwide led us to devote more attention on understanding the possible impacts of such episodes on the long-term variability and trends of these ecosystems in coastal waters of Western Europe. The signature of extreme events in the Bay of Brest is described and the numerical simulations allowed us to highlight the link between local rivers and changes in salinity.