OFFshore freshened groundwater systems – Emergence and persistence analysis by geochemical modellING (OFFING)

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Offshore freshened groundwater (OFG) is a ubiquitous phenomenon in continental margins worldwide. The identification of OFG occurrences and the prediction of their volumes gained increasing attention over the past two decades due to implications for water resources, ecosystem function and global element budgets. However, in spite of recent scientific progress, our knowledge of emplacement mechanisms and the evolution of fresh groundwater in the offshore environment still remains sketchy. In many cases, it is not known if OFG bodies are actively recharged at present or are rather remnants of past environmental conditions. The proposed study will address this knowledge gap by applying innovative 1D and 2D numerical transport-reaction models to geochemical data from IODP drilling efforts at two continental margins, offshore New Zealand (Leg 317) and New Jersey (Leg 313). To date, our perception of OFG flow patterns in these areas and their development over time are essentially derived from large-scale hydrogeological models. These, however, do not sufficiently reproduce (due to insufficient spatial resolution) or are even in conflict with available geochemical data from IODP drilling. In this proposal, we suggest conducting an unprecedented, quantitative evaluation of pore water geochemical data from several drill cores in order to constrain and evaluate emplacement mechanisms and timing of OFG at Legs 313 and 317. Our findings may have important implications for sustainable exploitation of OFG as a source of potable water in coastal cities and its role in global element cycles.