Assessing Marine Snow Dynamics During the Demise of the North Atlantic Spring Bloom Using In Situ Particle Imagery
David A. Siegel, Adrian Burd, Margaret Estapa, Erik Fields, Leah R. Johnson, Uta Passow, Elisa Romanelli, Mark A. Brzezinski, Ken O. Buesseler, Samantha J. Clevenger, Ivona Cetinić, Laetitia Drago, Colleen A. Durkin, Rainer Kiko, Sasha J. Kramer, Amy E. Maas, Melissa Omand, Deborah K. Steinberg
Abstract
Abstract The ocean's biological pump, a critical component of the Earth's carbon cycle, transports organic matter from the surface ocean to depth and is dominated by sinking particles, often in the form of marine snow‐sized (diameter ≥0.5 mm) aggregates. Controls of sinking particle carbon export are thought to be driven largely using ecological processes that create and transform sinking particles. We diagnose the importance of both biotic and abiotic processes in the dynamics of marine snow and other suspended particles using image‐based determination of their size distribution. These observations were made during the demise of the North Atlantic spring bloom in May 2021 as part of the Export Processes in the Ocean from RemoTe Sensing‐North Atlantic (EXPORTS‐NA) field campaign. We show that intense storm events generated high turbulent mixing rates in the upper ocean that impacted the abundance, size distribution, porosity and sinking of marine snow. Mixed‐layer turbulence levels both created and destroyed marine snow and the sequence of entrainment and detrainment of the mixed layer induced by repeated storm forcings enhanced the vertical transport of aggregates to depth. Evidence of biological transformations was also observed at mesopelagic depths, both for the consumption of particulate matter and in the creation of smaller particles from larger ones, likely due to interactions with zooplankton. Collectively, these results illustrate the complex interplay of physical and biological processes regulating the dynamics of marine snow and suggest their inclusion in predictive models of the ocean's biological pump.