FLUID FLOW THROUGH SEAMOUNTS: IMPLICATIONS FOR GLOBAL HEAT AND MASS FLUX

Hydrothermal circulation through the oceanic crust plays an integral role in governing the physical, chemical, and biological state of both the crust and ocean. Estimates of seafloor heat transfer indicates that fluid flow is responsible for 34% of the global oceanic heat flux, and is thermally significant, on average, to 65 Ma (Stein and Stein, JGR, 1994). Processes responsible for limiting advective heat flux between the oceanic crust and the ocean include increasing accumulations of low permeability sediments that cap relatively high permeability basement, decreasing thermal energy to drive flow, and decreasing crustal permeability with increasing crustal age.

Several factors make seamounts ideally suited to overcome these flow limiting processes. First, bathymetric relief associated with seamounts generates thermal buoyancy forces in excess of those present in flat seafloor. Second, seamount edifices are constructed mainly of extrusive basalt that likely have relatively high permeability. Third, seamounts tend to remain relatively sediment free much longer than the surrounding seafloor, thereby providing areas of exposed basement where fluid can exchange with the ocean unencumbered by low-permeability sediments.

Several marine geophysical studies demonstrate that seamounts can efficiently recharge and discharge hydrothermal fluids and cool the oceanic crust. However, flow through these features is poorly understood. Numerical models of coupled heat and fluid flow illustrate how basement relief coupled with a constant bottom water temperature condition generates horizontal temperature gradients within the oceanic crust sufficient to drive flow at modest permeability. Using the global database of seamounts we show that seamounts can contribute to globally significant hydrothermal fluxes. We estimate that the mass flux associated with global database of ~15,000 seamounts is ~10¹⁴ kg/yr, a number comparable to mass flux through mid-ocean ridges and flanks. Seamount generated advective heat flux may be locally significant well beyond the 65 Ma average age at which advective lithospheric heat loss on ridge flanks ceases. These flows may be important for facilitating heat loss, geochemical exchange between the crust and ocean and may affect subseafloor microbial ecosystems.