the supply of many trace elements to the entire North Atlantic and North Pacific Oceans through atmospheric pollution. On that scale of ocean basins, the effect of our nitrogen and phosphorus inputs is almost inconsequential. As a result, we can conceive of fertilizing whole regions of the oceans with iron, whereas fertilizing them with nitrogen and phosphorus would be unfeasible. Thus, the subject of bioremediation using metals has a regional (if not quite global) dimension as well as a local one. I focus here exclusively on the use of metals in bioremediation and do not discuss the issue of remediation of metal pollution. Although it is true that metal pollution may be a problem in some marine systems (perhaps even on an ocean-basin scale), the natural biogeochemical processes that cycle trace metals in the marine environment are sufficiently rapid that stopping the pollution is generally all that is required for remediation. In some cases, of course, dredging of metal-laden sediments may be beneficial or necessary.

Here I examine the question of the use of trace metals in marine bioremediation using examples that span the whole range of spatial and temporal scales. My concern is with the establishment of a knowledge base that would make such bioremediation technically feasible as well as socially and environmentally responsible. I particularly focus on the need for fundamental understanding of marine processes, from the molecular to the ecological scale, and the development of molecular and synoptic tools appropriate to oceanographic research.

Perhaps the most obvious application of bioremediation technology in the marine realm is for the cleanup of oil spills. Stimulating the growth and metabolism of microorganisms that degrade hydrocarbons is certainly feasible on the scale of an oil spill and also one of the few practical options available to us—once prevention and containment have failed. In some instances, additions of nitrogen and phosphorus have been shown to be effective in accelerating the biodegradation of the oil, at least on shore. The relative proportions of these major nutrients to the available organic food source are well known, and it is a relatively simple matter to estimate how much should be added.

Not so for trace elements. Many trace elements are necessary for the growth of oil-degrading bacteria, and some, such as iron or copper, are essential cofactors in the very enzymes that catalyze hydrocarbon degradation. Thus, trace metal additions may well be useful, but we have little quantitative knowledge of how much of any particular trace metal is required. In fact it is possible that the metal content of the oil sometimes results in a concentration of some metal in seawater that is too high. For any trace metal, there is only a relatively narrow range of concentrations that is optimal for the growth of marine microorganisms. Below this range, a trace metal is limiting; above it is toxic.

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