The downward flux of marine snow particles is critical for the ocean's carbon sequestration, although a significant fraction of the organic carbon carried in marine snow is remineralized in the mesopelagic zone. Canonically, a positive correlation between aggregate size and sinking velocities is assumed; however, recent studies concluded that aggregate composition is crucial to constrain sinking velocity-size relationships. In May 2022, we collected intact marine snow-sized aggregates (ESD > 0.5 mm) in the Northwest Atlantic by deploying Marine Snow Catchers (MSC) below the mixed layer (between 80 and 160 m) at eight stations dominated by different phytoplankton communities. Here we show the concentrations of particulate organic carbon and nitrogen (POC/N), amino acids, and exopolymeric particles associated with suspended, slow- and fast-sinking particles and assessed aggregate size and shape. We found that more than 80% of the POC pool was suspended at all the stations and depths. POC concentrations of fast-sinking particles were 60% to 90% higher than those of slow-sinking particles, increasing with depth, except at stations characterized by a Phaeocystis bloom. The POC concentration at those stations was twice that at non-bloom stations, and the contribution of suspended and slow-sinking particles increased with depth. Fast-sinking particles contributed 17% of the POC concentration at 80 m but only 2% at 500 m. This data set allows us to explore compositional differences between suspended and sinking marine snow.  

Primary Presenter: Carolina Cisternas-Novoa, Memorial University of Newfoundland (acisternasno@mun.ca)

Authors:

Elisa Romanelli, University of California, Santa Barbara, USA  (elisa_romanelli@ucsb.edu)

Uta Passow, Ocean Science Centre, Memorial University of Newfoundland, St. John’s, NL, Canada  (uta.passow@mun.ca)