Storm events alter marine snow fluxes in stratified marine environments

Marine snow is an important part of the biological pump and marine food web, and although previous research has provided a thorough understanding of the underlying mechanisms of marine snow dynamics in general, there is still a knowledge gap concerning extreme conditions, such as storm events. Storms are predicted to increase in magnitude and frequency in the future, and could potentially have a large impact on marine snow dynamics. For these reasons, we assessed the effects of storm events on marine snow dynamics in the Baltic Sea, an area chosen due to its well-studied and stable stratified conditions outside of meteorologically extreme events. The combination of in-situ imaging and biogeochemical environmental data from three different years facilitates an assessment of storm event impacts, while simultaneously excluding the possibility that patterns in particle distribution and abundances were due to other environmental influences. The results show that extreme meteorological events such as storms can increase the abundance of marine snow in stratified marine environments by a factor of 10 or more. The particles are distributed more widely and are larger, brighter, rounder and less complexly shaped. In non-extreme conditions, particles have been observed to deposit along the density gradients in thin-layer aggregations. This study indicates that storms can episodically disrupt these formations, thereby altering vertical flux and export potentials across stratification boundaries. In addition, we observed that marine snow abundances are drastically higher in the aftermath of storm events than under calm conditions, potentially due to the disaggregation of larger particles and lateral import of resuspended matter from shallower areas. In light of the increased frequency and magnitude of storms in the future due to climate change, our findings indicate that marine snow dynamics in stratified environments might be altered permanently.