Coastal ocean metals

Frank Millero is a Professor of Marine and Physical Chemistry and Associate Dean at the Rosenstiel School of Marine and Atmospheric Science at the University of Miami. Dr. Millero s research interests include the application of physical chemical principles to natural waters to understand how ionic interactions affect the thermodynamics and kinetics of processes occurring in the oceans. He has extensive experience with many aspects of marine chemistry and chemical analysis including the analysis of trace metals and gases in seawater. Dr. Millero is a former member of the NRC s Ocean Studies Board and was a member of the Study Committee on Effects of Human Activities on the Coastal Ocean. 

Most cation exchange occurs in estuaries and the coastal ocean due to the large difference in cation concentrations between river and seawater. As riverborne clay minerals enter seawater, exchangeable potassium and calcium are displaced by sodium and magnesium because the Na /K and Mg /Ca ratios are higher in seawater than in river water. Trace metals are similarly displaced. 

Various workers have assembled relatively complete assessments of the annual input of the major biological nutrients (C, N, P), certain heavy metals (Mn, Cd, Pb, Cu), and petroleum hydrocarbons to Narragansett Bay. Other studies have developed inventories of the amounts of these materials in the sediments of the Bay. We have brought these data together with information on sediment accumulation rates in the Bay to determine the degree to which this one estuary serves as a sink for different types of materials in their passage between land and the coastal ocean. 

A global mean for the rate of net chemical denudation of the continental surface is about 14 mm 1000 yr-1 or 14 pm yr k In comparison to the corrosion rates of metals exposed to a range of environmental conditions, the global continental surface is less resistant to corrosion than zinc and copper, but it is considerably more resistant than iron exposed to coastal oceanic and industrial-area atmospheric conditions. 

The influence of river water inputs on trace metal distributions is illustrated in Figure 11.17c, which shows that the surface-water concentration of dissolved Mn in the Pacific Ocean decreases with increasing distance from the California coast. The vertical profile measured in the coastal zone (Figme 11.17b) exhibits a strong surface enrichment characteristic of scavenged trace elements. A similar vertical gradient is seen in the... 

Mid-depth maxima are produced by mid-depth sources of metals. Some of these maxima are created by remineralization of detrital biogenic particles, such as seen in Figure 11.4f for cadmium. Others are caused by lateral transport of metals mobilized from coastal sediments as illustrated in Figure 11.17(a) for manganese. Mid-depth maxima can also result from hydrothermal emissions as shown in Figure 11.19 for Mn (aq) and He(g) at a site in the Eastern North Pacific Ocean. Hydrothermal fluids are emitted into the ocean from chimneys located atop the East Pacific Rise at water depths of about 2500 m. After entering the ocean, the Mn and He are entrained in subsurfece currents and... 

The mixture of organic constituents in the marine environment is extremely complex. Their origin is partly terrigenuous many compounds are produced in the marine environment itself. The different sources and their relative importance for the complexation of trace metals in estuaries, coastal seas and open ocean are riverine input, runoff from the coastal zone, resuspension, import of water mases, atmospheric input and in situ biological production. 

Fitzwater SE, Johnson KS, Gordon RM, Coale KH, Smith WO (2000) Trace metal concentrations in the Ross Sea and their relationship with nutrients and growth. Deep-Sea Res Part II 47 3159-3179 Gerringa LJA, de Baar HJW, Timmermans KR (2000) A comparison of iron limitation of phytoplankton in natural oceanic waters and laboratory media conditioned with EDTA. Mar Chem 68 335-346 Gibson JAE, Garrick RC, Burton HR, McTaggart AR (1990) Dimethylsulfide and the alga Phaeocystis pouchetii in Antarctic coastal waters. Mar Biol 104 339-346... 

The alkenone-producing species are typically reduced in abundance or excluded in oceanic provinces that favor diatom growth (Brand, 1994). Thus, they do not occur in the truly polar Arctic waters, and in the much broader siliceous province in the Southern Ocean, where they taper to zero abundance poleward of —60° S (Nishida, 1986 Sikes and Volkman, 1993). The abundance of E. huxleyi and G. oceanica is also reduced in regions of high sihcate availability, such as in many coastal zones and upwelling regions. Where nutrients such as nitrate and phosphate, or trace metals, such as iron, are low, the competitive advantage reverses to favor coccolithophores over the siliceous phytoplankton (Brand, 1991). 

---