Export and lateral advection of organic matter within the biological carbon pump

Abstract

The biological carbon pump (BCP) exports organic carbon from the surface to the deep ocean through which it drives the oceanic carbon storage of atmospheric CO2. The majority of this exported carbon is mediated by sinking marine particles, which are mostly formed by primary producers i.e. phytoplankton, and detrital material including dead zoo- and phytoplankton as well as fecal pellets. The efficiency at which these marine particles are exported is largely dependent on the interplay between their degradation and the duration the particles settle through the water column. Particle and aggregate degradation is largely driven by attached microbes and zooplankton grazing, which is most prominent in the upper few hundred meters of the water column. Settling velocities of particles or aggregates are largely determined by their density and thus composition. Therefore, fast settling aggregates or particles sink more rapidly through the upper water column, which increases the carbon export efficiency. The incorporation of ballasting components, such as sediments or minerals, during particle aggregation may increase the size-specific settling velocities of the aggregates and are thus an important process for carbon export via the biological pump. The manuscripts within this dissertation focus on the impact of aggregate morphology and ballasting on settling velocities and how carbon export is mediated by slow versus fast settling aggregates. We investigated (1) the horizontal relocation of slow vs. fast settling aggregates in form of subsurface particle clouds, (2) aggregate ballasting through the incorporation of minerals which are released by melting sea-ice and (3) the role of the aggregate microstructure on settling.