SODIOM - Surface Ocean Density Influence On Mineralisers

While the processes of current and future ocean warming are well-established, the impact of ocean dilution (i.e. the combined effect of persistent temperature rise and freshening due to ice melts) on marine life and ecosystems are hardly considered. Planktonic calcifiers play essential roles in different marine ecosystems including being basal contributors to the marine food web and the marine carbonate pump. Besides the first order control on a large number of their physiological processes including calcification, temperature also affects their swimming behaviour. The thermal expansion of the ocean reduces its density, while seawater expands further by freshening. Under warmer climates the ocean becomes even more diluted by the glacial meltwater input due to shrinking continental ice sheets and this added dilution aggravates its acidification. The combined effects of lower ocean density and alkalinity may particularly influence non-motile calcifying plankton that solely depends on the physical properties of the water column for positioning, by affecting their flotation needs. The influence of future dilution on calcifying organisms may have a major impact on the modern carbon cycle and hence, rather than warming or acidification alone, it is oceanic dilution that might actually be a bigger challenge to the ecosystem and the society.

Although the effects of ocean chemistry on plankton are being extensively studied there is a lack in the literature about the effects of physical oceanic properties such as buoyancy or pressure, which very likely affect plankton physiology and morphology. Different calcifying species have different optimum living depth habitats, to which they adapt according to the oceanic inhomogeneity. These planktonic organisms are able to biosynthesize out of equilibrium with their ambient environment by maintaining chemical gradients however, as non-motile they must always retain equilibrium with the seawater to remain afloat. To inhabit certain depths, non-motile planktonic organisms should regulate their (cell) density to match that of the surrounding liquid in which they are immersed. Should this not be the case then the organisms must relocate until they reach a particular density horizon to equilibrate. It can thus be argued that plankton physiology is more sensitive to the physical rather than the chemical characteristics of seawater. To this extent the proposed research will help to elucidate the physical processes that control pelagic calcification, by investigating the control on planktonic foraminifera (PF) and coccolith shell mass changes of key environmental parameters such as ambient seawater density.