SHALLOW-WATER HYDROTHERMAL SYSTEMS: NATURAL LABORATORIES TO STUDY GEOCHEMICAL AND BIOGEOCHEMICAL PROCESSES

Previous research on seafloor hydrothermal activity has focused primarily on deep-sea locations found along volcanically active portions of the mid-ocean ridges or in deep back-arc basins. Submarine hydrothermal activity, however, is not confined to deep-water environments. Much shallower hydrothermal activity has been documented on the flanks of volcanic islands, on the tops of seamounts and in other near-shore environments, characterized by high heat flow. The study of these systems has brought new and exciting information about mineral precipitation and water-rock interaction. Until recently, however, the driving force behind this work was of a more qualitative nature, rather than testing fundamental principles.

Shallow-water hydrothermal systems provide us with excellent natural laboratories to study a wide range of geochemical and biogeochemical processes. While the necessary SCUBA diving can impede the study of shallow vents, it also has profound advantages. 3-D work, for example, is greatly facilitated and divers can get much closer to the point of discharge than around on-land hot springs.

Three studies are currently underway that utilize shallow-water hydrothermal settings as natural laboratories:

(1) Determination of isotope fractionation factor for dolomite at temperatures below 100°C. The basic idea is to utilize a seafloor hydrothermal setting where dolomite is actively precipitating to systematically measure dolomite-water oxygen isotope fractionation as a function of variable water temperatures.

(2) Ecosystem response to elevated concentration of arsenic. The project will be one of the first to systematically integrate detailed aqueous geochemistry, mineralogy, the diversity of micro- and macrofauna, bioenergetic computations, and mathematical models of benthic biota in an environment where arsenic is essentially the only stressor. The purpose is to answer a set of first order question that relate to the organic and inorganic cycling of arsenic.

(3) Coral response to environmental stress. Shallow-water hydrothermal settings provide us with an opportunity to study how corals react to elevated temperatures and chemical stress. A combination of, calcification, growth rate and trace element studies in response to hydrothermal activity should provide new information about the causes of coral bleaching.