Geochemistry

Sediment

Tectonics

Mantle (geology)

Lithosphere

Geotechnical engineering

Geomorphology

Subduction

Seafloor spreading

Basalt

Geology

Oceanography

Paleontology

Groundwater

Hydrothermal circulation

Crust

Geophysics

Seawater

Oceanic crust

Aquifer

Mid-ocean ridge

Annual Review of Earth and Planetary Sciences

Over 50% of Earth is covered by oceanic crust, the uppermost portion of which is a high-permeability layer of basaltic lavas through which seawater continuously circulates. Fluid flow is driven by heat lost from the oceanic lithosphere; the global fluid flux is dependent on plate creation rates and the thickness and distribution of overlying sediment, which acts as a low-permeability layer impeding seawater access to the crust. Fluid-rock reactions in the crust, and global chemical fluxes, depend on the average temperature in the aquifer, the fluid flux, and the composition of seawater. The average temperature in the aquifer depends largely on bottom water temperature and, to a lesser extent, on the average seafloor sediment thickness. Feedbacks between off-axis chemical fluxes and their controls may play an important role in modulating ocean chemistry and planetary climate on long timescales, but more work is needed to quantify these feedbacks.

Low-Temperature Alteration of the Seafloor: Impacts on Ocean Chemistry