Shipboard studies of the influence of inorganic seawater chemistry on calcareous microplankton and the biological carbon pump

Improved understanding of the ocean's biological carbon pump and the possible influence of ocean acidification on the effectiveness of this pump are key issues in climate change research. This proposed SOFI project will investigate relationships between ocean productivity, functional phytoplankton groups, carbonate system parameters and carbon export. This study will provide an important contribution to O2025, in particular Theme 2, and the proposed research will strengthen our international position in climate change research. The aim of the proposed SOFI PhD project is to study CaCO3 mineral dissolution processes and the role of CaCO3 particles in the transfer of POC from the surface to the deep ocean. The work will be undertaken by sampling depth profiles (and wherever possible sediment traps) along a latitudinal gradient. We propose to work in ocean regions of the Atlantic and Artic with contrasting CaCO3 saturation states (Arctic (?CaCO3 low) versus low latitudes (?CaCO3 high)), and contrasting abundances of calcifiers (low-mid latitudes (high cell numbers)) and diatom (mid-high latitudes (high cell numbers)) in order to assess the influence of carbonate chemistry on CaCO3 and opal mineral dissolution and POC export. We will use in situ stand alone pumps for sampling of sinking particles (and sediment traps whenever possible). We will undertake state-of the-art analytical analyses for the determination of dissolved carbonate system parameters and particulate matter analysis (including calcite/aragonite characterisation). A synthesis of the observational data on phytoplankton functional group abundance, carbonate chemistry, mineral phase dissolution, zooplankton abundance and POC export will be conducted to obtain a reconciliation of the controls on POC export and the potential influence of ocean acidification on POC export. The PhD student will receive an excellent training in carbonate chemistry and analysis of components of the biological pump. The student will become involved in research at SAMS, PML and NOCS and participate in multi-disciplinary research cruises in contrasting ocean regions.