Glycerolipids track sinking particle sources and remineralization in two ocean basins

Henry C Holm , Helen F. Fredricks, Benjamin A. S. Van Mooy

The biological carbon pump is a major control on ocean carbon storage. On long time scales, changes in the biological carbon pump modulate atmospheric CO2 concentrations and climate. Attenuation in sinking carbon fluxes is derived from a combination of remineralization by bacteria, zooplankton, and fragmentation. However, the importance of these attenuation processes varies spatially and temporally. Constraining future changes to the biological carbon pump will therefore require improved knowledge of sinking particle dynamics. In this study we used high resolution mass spectrometry to measure glycerolipid compositions of sinking material from both the Pacific and Atlantic Oceans. These compositions revealed both sources and remineralization processes influencing the lipid fluxes. Most of the lipid carbon from sinking particles appears to be lost non-selectively; these results differ from previous reports of selective degradation in sinking lipids. In both ocean basins, we find that triacylglycerols are transferred better to depth than other glycerolipids. Utilizing a lipid class found almost entirely in phytoplankton, we show that there is a selection for saturated lipids at the onset of particle formation. Lastly, we use the compositions of isolated single particles to train a linear discriminant function that predicts the relative amounts of sinking material derived from fecal pellets versus aggregates. This new source metric implies that zooplankton reworking is a major control on lipid degradation. We discuss these results in the context of other flux observations and their future applications to study of the biological carbon pump.