The formation, surface fluxes to depth and deep-sea burial of calcium carbonate are all key processes in the global marine carbon cycle, with the combination of the first two providing an important feedback to atmospheric CO2. Around half of global calcium carbonate production occurs in shallow coastal environments (e.g. by corals), with the remainder occurring in the open-ocean by a diverse range of organisms; from small single-celled plants and animals to large free-swimming multicellular snails and slugs (Fig. 1), and even fish. Such diversity in size and ecology, with differing roles in marine ecosystems (from primary producers to grazers), underpins the global calcium carbonate budget, however, this diversity is not recognised in our understanding. Few studies have attempted to partition calcium carbonate production, fluxes or deep-sea burial between the organisms involved (see examples: Broecker and Clark, 2009; Manno et al., 2018). Importantly, the impact and sensitivity to future climate change (ocean warming, acidification and de-oxygenation) also varies between calcifying organisms. This means that we urgently need a better understanding of their relative roles in upper ocean production, export from the upper ocean to the deep-sea, and burial into sediments if we are to understand how they will influence future atmospheric CO2.
Despite recent advances in our understanding of the biomass distribution of coccolithophores, foraminifera and pteropods (e.g. Daniels et al., 2018; Schiebel, 2002; Bednaršek et al., 2012), and how these may relate to ocean chemistry, the relative scale of biological formation of calcium carbonate in the upper ocean is poorly constrained, in terms of both its magnitude and biogeography. Hence, we have a relatively poor understanding of how much carbonate production in the upper ocean translates into export or burial; how much is lost through dissolution/remineralization in the surface ocean, and how this may differ between the organisms involved.
The goal of this studentship is to tackle this global problem through synthesis and a thorough analysis of existing data on growth and calcification rates, upper ocean biomass distribution, particulate matter fluxes to depth, and deep-sea sedimentation patterns for the different plankton groups. The student will also collect new comparative data through various methods; for example, examination of satellite data, biogeographical studies, analysis of water and net samples, sediment trap material, and allometric estimates. The outcomes of this studentship will have important implications for how we understand and model the current and future global ocean C-cycle.
Click on an image to expand
Fig. 1. Examples of different calcifying organisms in the ocean: (a) tiny (~0.02 mm) single-celled coccolithophores with their green chloroplasts and reflective outer calcium carbonate scales; (b) a large (~0.2 mm) single-celled foraminifera with feeding pseudopods and central multi-chambered calcium carbonate teste; and (c) a large (~500-1000 mm) multi-celled pteropod with two wings surrounding its mouth and its spiral shell of calcium carbonate. Image sources: (a) courtesy of Sam Gibbs, University of Southampton; (b) courtesy of Jennifer Fehrenbacher, Oregon State University; (c) NOAA Photo Library via NOAA News April 30, 2014 (cc-by-2.0).