Minor Contribution by Biomineralizing Phytoplankton to Surface Ocean Biomineral Pools in the Late Stratified Period

Vertical distributions of biogenic silica (bSi), particulate inorganic carbon (PIC) and key biomineral-forming phytoplankton indicate vertical zoning, or partitioning, during the late summer stratified period in northeast Atlantic. Coccolithophores were generally more numerous surface mixed layer, whilst PIC concentrations homogenous with depth throughout euphotic zone. Diatoms notably abundant diverse lower zone beneath layer association subsurface maxima chlorophyll-a, bSi oxygen concentrations. The four dominant coccolithophore species (Emiliania huxleyi, Gephyrocapsa muellerae, Syracosphera spp., Rhabdosphaera clavigera) represented 78 ± 20% (range 31–100%) observed community across all sampled depths yet simultaneously contributed an average only 13% to measured pools. diatom community, which was dominated by Pseudo-nitzschia spp. a tentatively identified as Nanoneis longta, ~1% pool on average, contributions increasing within chlorophyll maximum. Despite slow gradual deepening prior observation, adequate nutrient availability biomineral pools at this time consisted largely detrital rather than cellular material.