Effects of Ocean Acidification on the Ballast of Surface Aggregates Sinking through the Twilight Zone

Abstract

The dissolution of CaCO3 is one of the ways ocean acidification can, potentially, greatly affect the ballast of aggregates. A diminution of the ballast could reduce the settling speed of aggregates, resulting in a change in the carbon flux to the deep sea. This would mean lower amounts of more refractory organic matter reaching the ocean floor. This work aimed to determine the effect of ocean acidification on the ballast of sinking surface aggregates. Our hypothesis was that the decrease of pH will increase the dissolution of particulate inorganic carbon ballasting the aggregates, consequently reducing their settling velocity and increasing their residence time in the upper twilight zone. Using a new methodology for simulation of aggregate settling, our results suggest that future pCO2 conditions can significantly change the ballast composition of sinking aggregates. The change in aggregate composition had an effect on the size distribution of the aggregates, with a shift to smaller aggregates. A change also occurred in the settling velocity of the particles, which would lead to a higher residence time in the water column, where they could be continuously degraded. In the environment, such an effect would result in a reduction of the carbon flux to the deep-sea. This reduction would impact those benthic communities, which rely on the vertical flow of carbon as primary source of energy.

Oceanic nitrogen cycling and N2O flux perturbations in the Anthropocene

“…Similarly, phytoplankton community restructuring toward the fast‐sinking calcifiers may remove nutrients more efficiently from the surface ocean to depth [ Kvale et al , ]. On the other hand, calcium carbonate production may be attenuated due to ongoing acidification [ de Jesus Mendes and Thomsen , ]. The combined net effects of these processes on the partitioning of nutrients between the surface and deep ocean requires further study.…”

Microbial Surface Colonization and Biofilm Development in Marine Environments

“…For example, the remineralization depth of sinking POC becomes shallower in warmer waters, indicating that the vertical POC flux and, thus, the carbon sequestration efficiency of the biological pump will be attenuated with future increases in ocean temperature (45,293). Ocean acidification can significantly change the ballast composition, reduce the settling velocity of sinking particles, and thus force the sinking particles to remain in the epipelagic and mesopelagic zones of the water column, with longer residence times and greater microbial decomposition (294). This may make the POC remineralization depth shallower as well.…”

Patterns of deoxygenation: sensitivity to natural and anthropogenic drivers

“…If calcium carbonate production is attenuated under ongoing acidification, there may be less ballast available to efficiently sink organic particles to great depth [52]. One consequence could be that remineralization and hence oxygen consumption occurs at shallower depths, possibly leading to a further expansion of low oxygen regions [54].…”