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

The biological pump is a key regulator for the export and burial of atmospheric CO₂ in the ocean and serves as nutrient supply for ecosystems at depth through the export of organic matter. This organic matter is commonly referred to as marine snow or marine aggregates and the efficiency at which these are exported and ultimately sequestered, can be summarized by the interplay between its initial quantity, settling velocity and attenuation. Each of these factors in terms are affected by mechanisms of (trans)formation, translocation and degradation. This includes (1) biologically mediated factors such as community dependent aggregate formation of marine snow and microbial degradation or zooplankton grazing and “repackaging” into fast settling fecal pellets and (2) physicochemical factors such as salinity gradients, aggregate ballasting, diffusion processes or horizontal transport by currents.

Within my PhD, I focus on aspects which determine the formation and settling of marine snow using a combination of field- and laboratory-based observations. I develop a novel small-scale imaging method to visualize marine snow three-dimensional. These observations will help us understand the mechanisms of particle formation and the resulting microstructure which is crucial for particle settling velocities as well as diffusion and microbial degradation processes.

This will be set into a large-scale perspective by identifying the forcing factors that drive the biological pump in two key areas: The highly productive eastern boundary upwelling ecosystem (EBUS) off Cape Blanc, Mauretania and the main area of water exchange between the Arctic- and Atlantic Ocean at the FRAM strait. At the EBUS of Cape Blanc, we investigate the role of lateral transported shelf production on open ocean carbon export and to which extent shelf production contributes to deep ocean carbon sequestration. First results indicate that shelf production may cover up to half of the observed deep ocean carbon sequestration in the area.

At Fram strait, we aim to identify the role of sea ice and phytoplankton community composition on the export efficiency of the biological pump in the context of progressing atlantification. This will be achieved by comparing a predominantly polar vs. atlantic influenced mooring site from 2004 – 2013.