The Role of New Technology in Advancing Ocean

Introduction The rapid increase in atmospheric carbon dioxide (CO2) levels has stimulated a growing interest in understanding biogeochemical processes in the ocean and their interactions with the atmosphere. Interestingly, surface CO2 is also reported to be rising at the Joint Global Ocean Flux Study (JGOFS) ocean time series sites off Hawaii and Bermuda. Potential effects of rising CO~ levels include increases in global atmospheric and oceanic temperatures, melting of ice caps, sea-level rise and shifts in regional weather patterns, that lead to droughts and floods. One important question concerns our ability to discern natural versus anthropogenic contributions to this rise. Another question concerns the role the ocean plays in the cycling and variability of CO2. These and other unanswered questions stimulated the development and execution of JGOFS, a multidisciplinary and international program carried out between 1987 and 2001 by more than 20 nations. JGOFS was designed to study oceanic biogeochemical cycles and their interaction with a changing climate. On millennial time scales, the ocean dictates the atmospheric concentration of CO2. There is an inverse gradient in Dissolved Inorganic Carbon (DIC) in the ocean, such that higher concentrations of DIC are found at greater depths. In contrast, the upper portion of the water column is in overall equilibrium with the atmosphere to first order. This gradient is maintained by two carbon "pumps." The "solubility pump" depends on the fact that cold water holds more CO2 than warm water; for example, the solubility of cold, deep water is about twice as great as that of near-surface equatorial water. As a consequence, the net effect of sinking surface waters through thermohaline circulation is to enrich deeper waters in carbon. The second carbon pump is known as the "biological pump", and is the primary focus of this review of new technologies and observations (see Ducklow et al., this issue). The biological pump's process begins with phytoplankton living in the upper or euphotic layer of the ocean. Phytoplankton take up CO2 and nutrients to form organic matter. Although much of this organic matter is metabolized and recycled in the surface waters, a significant portion (roughly 10% to 20% but varying greatly over space and time) sinks into the deep ocean before it is remineralized into an inorganic form via the metabolism of microorganisms. Currents and upwelling return CO2 to the surface of the ocean, but the overall effect of the biological pump is to transport carbon into the deep ocean. The solubility and biological pumps have significant effects on atmospheric CO2 levels. The biological pump includes pathways of carbon export to the deeper layers through Dissolved Organic Carbon (DOC) molecules (see Hansell and Carlson, this issue) and Particulate Organic Carbon (POC) matter (see Berelson, this issue). The determination of primary production in the upper ocean is a vital step in quantifying the formation of POC, which is then available for transport via the biological pump. The following paragraphs introduce some of the key concepts regarding primary production in relation to the biological pump, with a focus on its quantification using autonomous measurements from moorings and other platforms. The biological pump is of interest to researchers studying bio-optics and upper-ocean physics as well as biogeochemistry. Primary productivity and phytoplankton biomass depend on photosynthetic processes, which implicitly involve the availability of light (measured as Photosynthetically Available Radiation or [PAR]) and nutrients such as nitrate, silicate, phosphate, and iron. The spectral quality and intensity of light varies with depth and is important for specific phytoplankton species with special pigmentation or photoadaptive characteristics. Light exposure for individual organisms is affected by variation in physical conditions including mixed layer depth, turbulence and currents, as well as the incident solar radiation, all of which vary in time and space. An important feedback concerns the modulation of the spectral light field