Organic matter processing in continental shelf sediments—the subtidal pump revisited

Pressure variations along an uneven permeable bottom, generated by the passage of gravity waves and by bottom currents, force water into the sediment below regions of high pressure, such as ripple troughs, and draw it out at regions of low pressure, such as ripple crests. The resulting pore water circulation brings organic matter and oxygen to the interior of the sediment, creates horizontal concentration gradients that can be as strong as the vertical gradients, and increases the flux of pore water constituents across the sediment-water interface. Here we review the present knowledge of pore water circulation and organic carbon mineralization in sandy continental shelf sediments. We argue that the circulation of water through the pores of the sediment enhances the mineralization rate of dissolved and particulate organic matter and that continental shelf sediments play a more important role in the oceanic carbon cycle than is generally thought.