Submarine Groundwater Discharge (SGD) and Biogeochemical Cycling

Submarine groundwater discharge (SGD) is a significant, yet often overlooked, pathway for the transfer of solutes and nutrients from land to the coastal ocean. It plays an important role in shaping coastal biogeochemical cycles and contributes to long-term changes in ocean chemistry. In this theme, we emphasize a novel approach that seeks to quantify the solute fluxes associated with the individual components of SGD—such as wave-driven, tidally-driven, and density-driven flow. By disentangling these mechanisms and their geochemical signatures, we aim to better constrain how SGD contributes to elemental budgets and oceanic biogeochemical cycling.

Quantifying Long-Term Submarine Groundwater Discharge and Solute Fluxes

Our research quantifies water and solute transport through long-term SGD using a major element budget in the ocean. We estimate that the global flux of long-term SGD is on the order of 1000 km³ per year, and the associated solute input or removal is of the same magnitude as riverine transport.

Disentangling SGD Mechanisms Using Geospatial Models

In a related project led by Yehuda Levy, we used geospatial databases and sensitivity tests on groundwater flow models to quantify individual SGD components, including density-driven flow, wave-driven exchange, tidal pumping, and nearshore circulation. This novel approach allows us to better resolve the distinct contributions of each SGD mechanism to coastal and global element cycles.

Glacial–Interglacial Changes in SGD and Ocean Chemistry

We are also conducting preliminary calculations to explore how small changes in solute fluxes associated with glacial-interglacial sea-level shifts may impact the ratios between major elements in the ocean. These changes could alter alkalinity and the marine carbon cycle, potentially influencing atmospheric CO₂ and moderating the rates of global cooling and warming.

Microbial Responses to Coastal Groundwater Inputs

Finally, we are initiating exciting new studies on microbiology and SGD. Our findings show that, beyond supplying nutrients, microbial interactions influence the balance between autotrophic and heterotrophic communities. As groundwater enters the ocean, it undergoes sharp changes in light, salinity, and redox conditions—affecting microbial community structure and potentially driving adaptive responses. We are also using chlorophyll a as a tracer to monitor short-term residence times (on the scale of hours to days), offering a new window into SGD-driven microbial processes.