Implications of climate change on phytoplankton - trace metal interactions

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Many trace metals are essential micronutrients for manne phytoplankton. However, some of these metals can also have toxic effects at higher concentrations. Trace metal bioavailability influences marine phytoplankton productivity, nitrogen fixation, and species composition in vast regions ofthe ocean and therefore plays an outstanding role in the global carbon cycle. The bioavailability of trace metals in the ocean is not only determined by their total concentration but rather by their inorganic speciation as well as by their binding to organic ligands. Ocean acidification and sea surface warming will affect the inorganic speciation as well as the organic ligand complexation of trace metals in seawater which will potentially significantly affect their bioavailability. Several trace metals compete with each other for biological uptake via membrane transporters. Therefore, even slight changes in the concentration of their bioavailable chemical forms can affect the sensitive equilibnum of fertilizing and toxic effects of these metals in natural systems. This could have a significant effect for the biological implications of trace metals from natural sources such as e.g. volcanic ash. So far we only know very little about how ocean acidification and sea surface warming will influence the bioavailability of trace metals in natural marine systems and how this will affect the productivity of these systems. To be able to understand and predict the implications of this process for marine phytoplankton primary production, nitrogen fixation, and species composition we urgently need detailed investigations of this topic. The focus of the here proposed Emmy Noether will thereby be threefold: 1) How will changing seawater pC02 and temperature influence antagonistic and/or synergistic effects of different trace metals for marine phytoplankton? 2) How will these climate change factors affect the biological production and binding strength of organic trace metal ligands with implications for trace metal bioavailability? 3) Will ocean acidification influence the toxicity of aluminium fluoride complexes from volcanic ash in seawater? My group will address these research questions in laboratory experiments as well as in mesocosm field studies. Thereby we will use specifically developed methods and incubation conditions that are as natural as possible.