Rain triggers seasonal stratification in a temperate shelf sea

The North Atlantic Storm Track acts as a conveyor belt for extratropical cyclones that frequently deliver high winds and rainfall to northwest European shelf seas. Storms are primarily considered detrimental to shelf sea stratification due to wind-driven mixing countering thermal buoyancy, but their impact on shelf scale stratification cycles remains poorly understood. Here, we show that storms trigger stratification through enhanced surface buoyancy from rainfall. A multidecadal model confirms that rainfall contributed to triggering seasonal stratification 88% of the time from 1982 to 2015. Stratification could be further modulated by large-scale climate oscillations, such as the Atlantic Multidecadal Variability (AMV), with stratification onset dates being twice as variable during a positive AMV phase than a negative one. Further insights into how changing storm activity will impact shelf seas are discussed beyond the current view of increasing wind-driven mixing, with significant implications for marine productivity and ecosystem function. Seasonal stratification on the northwest European Shelf is found to be triggered by rainfall from passing storms. Further links are made between the onset of stratification to large-scale pressure changes in the North Atlantic.

Automated summary

The North Atlantic Storm Track brings frequent high winds and rainfall to northwest European shelf seas. It was found that storms trigger stratification through enhanced surface buoyancy from rainfall, and this accounts for 88% of the seasonal stratification from 1982 to 2015. The stratification onset is also influenced by large-scale climate oscillations, such as the Atlantic Multidecadal Variability (AMV). The impact of changing storm activity on shelf seas has significant implications for marine productivity and ecosystem function.