Towards global-scale estimates of fresh submarine groundwater discharge

Abstract:

The flow of fresh groundwater to the ocean through the coast (fresh submarine groundwater discharge, or fresh SGD) plays an important role in global biogeochemical cycles and coastal water quality. Here we estimate groundwater discharge rates through the near-global coast (60 degrees North to 60 degrees South) at high-resolution using a water budget approach. We find that tropical coasts export more than 56% of all fresh SGD, while mid-latitude arid regions export only 10%. Fresh SGD rates from tectonically active margins (coastlines along tectonic plate boundaries) are also substantially greater than passive margins, where most field studies have been focused. Active margins combine rapid uplift and weathering with high rates of fresh SGD and may therefore host exceptionally large groundwater-borne solute fluxes to the coast. There is a clear need for additional global-scale estimates of fresh SGD using diverse modeling approaches. More field observations are also needed to constrain and validate model results, particularly along active margins.