Pore Water Pumping

Introduction

Evaluating fluid flow rates through permeable sediments, and the impact of this flow on ocean chemistry, has been a challenging problem. In various settings, flow may be driven by groundwater recharged above sea level, or by circulation of seawater through the seabed in response to pressure gradients created as currents flow over irregular bottom topography or waves travel across the sea surface. In addition, water may be transported by bio-irrigation, although it is likely that physical irrigation may be more important in highly permeable sediments.

In our current project, we have been evaluating fluid circulation rates within sediments offshore from Huntington Beach, CA.?? Fluid flow rates have been computed from reaction-diffusion modeling of naturally-occurring radioisotope distributions in permeable sediments: 222Rn, 223Ra, 224Ra, and 228Ra. Previous work has established regional budgets for these isotopes that constrains their overall input from these shallow water sediments, and the proposed work will define how input varies with water depth and wave and current characteristics.?? This field work will provide an important in situ calibration point for models describing flow through permeable sediment.?? In addition to the radioisotopes, we also measured oxygen and nutrient profiles.?? This data set can be used to establish fluxes of these constituents, based on the model transport parameters developed with radioisotopes.?? These fluxes will help to constrain the role shelf sediments in regional biogeochemical budgets.??