Equatorial Pacific TAO Moorings

Introduction

     The importance of time series in oceanographic research is clear. Time series measurements of physical and meteorological properties, currently taken throughout the globe, have allowed investigators to resolve the important scales of oceanic and atmospheric variability. With a few exceptions the time series are primarily physical in nature (i.e., temperature). Biological and chemical oceanographers are now looking to continuous observations so they can also determine the spectrum of variability and, when taken concurrently with the physical and meteorological observations, determine the relation to climate and ocean variability. The paucity of biological and chemical time series has been due, in part, to the lack of adequate instrumentation; however, increased effort has recently been placed on the development of chemical and bio-optical instrumentation for the collection of these time series. Spatial coverage will ultimately come from observations made from space, but high-frequency temporal and added vertical coverage will need to come from moorings and drifters with arrays of in situ sensors. Realizing that advances in ocean sciences are limited by the lack of instrumentation and systems capable of collecting these time series, the Monterey Bay Aquarium Research Institute (MBARI) has established a vigorous developmental program geared at making these observations possible. After initial testing of this instrumentation in Monterey Bay we have begun to move this developmental effort to other sites around the globe. Because of logistical and scientific reasons we chose the Equatorial Pacific and the platforms of the TAO mooring array.

Why the Equatorial Pacific?

     Recent calculations suggest that the equatorial Pacific is an important contributor to the global carbon and nitrogen cycles as a result of the upwelling of large quantities of inorganic carbon and nitrogen to the surface (Feely et al., 1987; Chavez and Barber, 1987). It is the atmosphere's largest natural source of carbon dioxide (CO2), supplying approximately 1-2 gigatons of carbon per year (Tans et al., 1990; Feely et al., 1987). Chavez and Barber (1987) suggested that, as a result of its large area and large proportion of new production, the equatorial Pacific could account for up to 50% of global new production. It is clear that global budgets need improved estimates of the exchange of carbon dioxide between ocean and atmosphere, nutrient supply and primary productivity in these areas, but equally important the regulation of variability needs to be understood to provide a mechanistic explanation of the climate/ocean circulation/marine chemistry/primary productivity feedback loop. Over a decade of shipboard observations suggest that phytoplankton biomass in this region is relatively constant in space and time and is lower than might be expected from the nutrient levels (Barber and Chavez, 1991; Chavez et al., 1991). This is surprising since the physics and chemistry of the equatorial region are highly variable, with different forms of waves propagating through the system on scales ranging from days (Halpern et al., 1988) to years (Philander, 1990). While phytoplankton biomass is relatively constant, the variability in nitrate (N(j) and partial pressure of carbon dioxide (pCO2) is clearly linked to the physical environment (Chavez et al., 1990; Feely et al., in press). Time series measurements of physical and meteorological properties, which resolve the important scales of variability, are currently being taken in the equatorial Pacific (TOGA, 1989), but there are no parallel time series of biological or chemical properties. This has been due to the fact that long-term, continuous instrumentation has been mostly limited to physical detectors. However, recent developments in chemical and optical instrumentation now allow for the collection of time series of biological and chemical properties. These questions can now be addressed with this instrumentation: What is the spectrum of biological and chemical variability in this productive, but highly variable region? Is the spectrum of variability coherent zonally? How, and to what extent, do propagating disturbances, advective fluctuations in water properties, or variations in the local and western Pacific meteorology, affect the biology and chemistry?
     This proposal describes a program for studying the spectrum of biological and chemical variability in the equatorial Pacific. The long-term goal of the study is to obtain continuous time series of biological and chemical properties on a time scale that is equivalent to measurements of currents, winds and temperature structure. The program is linked to an existing physical oceanographic study (Figure 1) headed by Dr. Michael McPhaden of the Pacific Marine Environmental Laboratory (PMEL) of NOAA. We propose to deploy biological instrumentation on moorings of the TAO array with support from MBARI and NASA. We have tested the initial suite of instruments and developed data storage and transmission protocols which are compatible with the ATLAS and PROTEUS mooring program on a mooring in central California. We propose to maintain this developmental mooring to allow for easy export of new technology. This platform would also provide bio-optical measurements in the coastal upwelling system off Monterey.

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