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, meaning 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.
Export fluxes from the surface ocean to deep-sea sediments and subsequent burial are both ‘relatively’ well characterised in terms of global magnitude and regional trends. The scale of biological formation of calcium carbonate in the upper ocean, however, is poorly constrained, in terms of both its magnitude and biogeography, due to knowledge gaps in our ecological and physiological understanding of the organisms involved. Despite recent advances in our understanding of the biomass distribution of coccolithophores (e.g. Daniels et al., 2018; Schiebel, 2002), foraminifera and pteropods, and how these may relate to ocean chemistry, we still have very little idea of the relative magnitude (or biogeography) of their respective rates in terms of production or export. Hence, we have a relatively poor understanding of how upper ocean production translates into export or burial; how much surface production is lost through dissolution in the upper ocean, and how may this differ between the organisms involved?
Hence, there are still large global uncertainties in who is doing the majority of surface calcium carbonate production and export (coccolithophores, foraminifera or pteropods), what the seasonal and annual magnitudes of these fluxes from different calcifiers are, and where in the world’s oceans the fluxes by each of them are high or low.
The goal of this studentship is to tackle this global problem through synthesis of existing data on growth and calcification rates, upper ocean biomass, 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.