Studies biophysics of photosynthesis in marine organisms have remained a major concern in oceanography for half a century. Recent work has been centered on the effects of anthropogenically altered global conditions, such as increased atmospheric carbon dioxide, increased surface temperatures, and increased surface ultraviolet radiation in high latitudes. Remineralization of biomass is an example of a major chemical process that must be approached as a problem in microbial ecology and physiology as well as oceanography since energy that flows through most marine ecosystems is carried predominantly by very small unicellular organisms, both at the first trophic level and at the decomposer level. The in situ rates of cycling of carbon, nutrients, and oxygen can be obtained by using sensitive techniques for measuring the rate limiting enzymes in crucial metabolic pathways. For example, a tetrazolium dye assay for the electron transport system that mediates oxidative phosphorylation in virtually all organisms can be used to estimate oxygen consumption rates in the water column after direct or indirect calibration. Bioenergetic rates may also be evaluated by the turnover of the nucleotide phosphate pool (ATP). Polynucleotide (DNA, RNA) synthesis rates can be assayed as a measure of the growth of microbial communities that correlates with cell division and protein synthesis. Nitrogen cycling rates can be estimated from enzymatic assays such as glutamine synthetase (nitrogen assimilation) and nitrogenase (nitrogen fixation). The responses of organisms to pollution includes the induction of lysozyme, metal binding protein (metallothionein), and many other adaptative reactions. Adaptations to hyperbaric conditions and deep cold have also been investigated.