The MOOS Upper-Water-Column Science Experiment (MUSE)
MUSE Field Experiment, August 2000, Monterey Bay, CA 

Biogeochemical Response to Coastal Upwelling
Francisco Chavez

Introduction

This investigation focuses on the process of coastal upwelling and its biological and chemical consequences. The goal of this investigation is to track the evolution of biological communities across iron-rich upwelling fronts. Recent investigations have demonstrated that the upwelling process entrains not only macronutrients from deeper waters but also iron from the sediments. Other entrainment processes that recruit waters not in contact with the sediments will not have the same nutritional effect on the primary producers. Sediment-laden waters have been observed at a site of active shallow upwelling in northern Monterey Bay. This site is a natural analog to the initial stages of the iron fertilization experiments carried out in the equatorial Pacific upwelling system. These experiments have greatly furthered the understanding of the influence of nutrient fertilization on phytoplankton physiology and community structure. In collaboration with several other groups in this experiment, this group will also follow the patch of upwelled water and observe the chemical and ecological transformations that occur as the patch is advected away from the upwelling site. Questions to investigate include:

• When do phytoplankton communities take up the different nutrients and when and where are these nutrients lost from the system?
• What are the successional changes in the bacterial, phytoplankton, and zooplankton communities as upwelled water ages?
• What are the consequences of the temporal and spatial variability of the upwelling process on the mid-water and benthic communities?

Another observable product of the upwelling process is the formation of strong physical and biological fronts between the recently upwelled water and the warmer surface water displaced by upwelling. Interest in these frontal regions is two-fold. First, a significant proportion of the upwelled water and nutrients is likely mixed laterally along these edges rather than being advected downstream and offshore. Second, the nutrient fertilization, together with physical phenomena like convergence, down-welling, and increased stratification, make these frontal regions areas of increased biological activity. The biological consequences may make these regions more important to the coastal upwelling ecosystem than one might presume from their areal extent. This investigation seeks to gain a better understanding of the biological and physical coupling that occurs along frontal boundaries.

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      Last Updated: 07 June, 2002