Effect of the ocean acidification and warming in the biogeochemical cycle of Fe in the North Atlantic

The EACFe Project focuses on the effects of pH, T, O2 and organic matter in the behaviour of the Fe(II)-Fe(III) system in the Subarctic region, in the CLIVAR A1E (59.5ºN) hydrographic section, in order to compare these studies with experiments undertaken in the lab and to develop a global kinetic model for iron in the context of ocean acidification and global warming. Iron has a high impact in the carbon cycle through its effects on planktonic communities and their productivity. Reduced iron, Fe(II), is the bioavailable species for eukaryotic phytoplankton, rather than oxidized iron, Fe(III). Fe(III) presents a low solubility and is mostly complexed by organic ligands. Fe(II) is thermodynamically unstable due to pH and O2 conditions in the medium and tends to become oxidised. The acidification and the reduction of O2 favours the presence of Fe(II) in the medium. Moreover, organic matter plays an essential role in the Fe cycle in the ocean. The presence of organic compounds may reduce Fe(III) to Fe(II) and also stabilise Fe(II) by complexation. It has been observed that in the presence of organic compounds like polyphenols or saccharides, the growth of eukaryotic organisms is favoured.

The main goals of the EACFe project is to investigate which compounds and mechanisms determine the presence of Fe(II) in the marine environment and how ocean acidification and global warming affect them.

To achieve these goals we will combine the studies in the Atlantic Subarctic region, one of the most sensitive to ocean acidification, with studies in the lab using individual organic compounds and the exudates from cultures of phytoplankton. In the lab studies we will consider the different variables independently in order to define the contribution of each one to the process.