Noble Gases in Ocean Waters and Sediments

Abstract

Noble gases are widely used in studies of the basic properties and dynamics of natural systems including the ocean. This chapter describes some of the more extensive applications of noble gases (mainly helium isotopes) to studies of oceanographic problems. They include the modern oceanic circulation, paleo-oceanography, hydrothermal and cold brine systems in the deep ocean, and ocean/atmosphere gas exchange. Originally, oceanic noble gas studies were focused on geochemical problems such as the question of the existence of excess helium in seawater derived from radioactive decay of the elements of the uranium and thorium series in ocean sediments (Suess and Wanke 1965; Bieri et al. 1966). After the discovery of mantle (primordial) helium during the 1960s (Clarke et al. 1969; Craig and Weiss 1971; Craig et al. 1975) and 3He derived from decay of tritium in the near-surface waters of the ocean (Jenkins and Clarke 1976), large programs were developed to exploit helium isotopes, frequently in combination with tritium, for studies of water mass formation, circulation and variability (e.g., Jenkins 1987; Schlosser et al. 1991). More recent studies started to explore the use of helium isotopes to paleoceanographic objectives. These studies build upon the discovery of extraterrestrial helium in deep-sea sediments in the early 1960s (Merrihue 1964). This signal is now being systematically examined for its potential as a tool for investigations of sediment accumulation rates on very long time scales (millions of years) and their correlation with changes in paleoceanography (e.g., Farley 1995; Farley and Patterson 1995; Marcantonio et al. 1995, 1996, 2001). Soon after the discovery of mantle helium in seawater, noble gases were applied to studies of hydrothermal systems. Originally, these studies were focused on the source of the fluids emanating from hydrothermal vents as well as …