Drivers of Marine Snow Morphology along an Atlantic Meridional Transect

The ocean’s biological pump (BCP) exerts a major control on global carbon cycling, maintaining atmospheric CO2 100-200 ppm lower than it would otherwise be. The BCP’s primary vehicle that transfers organic carbon to depth is a diverse assemblage of sinking of organic particles collectively called ‘marine snow’. It is thought that the morphological characteristics of marine snow (e.g. size, compactness, and shape) govern the efficiency with which sinking carbon is transferred to the deep ocean. With the rapid advance of in situ camera systems, we are now in the position to collect images of marine snow at high temporospatial scales. As in-situ imaging approaches become more widespread in the study of the BCP, classifying marine snow and relating marine snow morphology to biogeochemical functioning will form a crucial lens through which to view the BCP. With the large amount of images, the challenge is to categorise marine snow particles into a practical number of ecologically meaningful groups, reducing complexity whilst maintaining nuance.

Here we explore the vertical and spatial patterns in marine snow composition across an Atlantic meridional transect. We classified non-organism particles into 8 groups and used manual expert classification for the zooplankton. We found that primary production appears to drive particle composition in the upper 100 m, while temperature strongly constrains Rhizaria distribution and diversity both with depth and along the transect. Our approach provides an elegant way to explore marine snow characteristics across the Atlantic. However, though they show that marine snow types vary - as expected -  considerably across the Atlantic, the drivers of this variability appear unexpectedly complex. Determining the key drivers and their interactions that govern BCP efficiency on basin scales will be crucial for mechanistically explaining and predicting how climate changes may impact BCP function.