CARBON EXPORT AND REGENERATION IN THE COASTAL UPWELLING SYSTEM OF MONTEREY BAY, CENTRAL CALIFORNIA

In order to quantify the role of coastal upwelling regions as source o r sink areas for carbon, the relationships between particulate organic carbon (POC) production, export, remineralization, and accumulation w ere examined in Monterey Bay from 1989 through 1992. During a normal u pwelling year (1989-90), a high positive correlation (r=0.91) is obser ved between biweekly primary production and POC export at 450 m. Prima ry production values range from 500 mgC m(-2) d(-1) during the winter, to 2600 mgC m(-2) d(-1) in the spring and summer upwelling months. Co rresponding deep-water (450 m) POC fluxes vary from a minimum of 10 mg C m(-2) d(-1) in December, to 120 mgC m(-2) d(-1) in May. In contrast, the mid-1991 through 1992 data sets obtained during the '91-92 El Nin o period, show a relatively poor correlation (r=0.23) between producti vity and carbon export. Calculated ratios of POC export to POC product ion (defined as e-ratios) display a trend for the three-year data sets in which the e-ratio values are greatest during periods of low produc tivity and decrease to minimal values when surface production is high. Upwelling-induced, offshore Ekman transport of organic matter and pro bable seasonal changes in the planktonic community structure are the m echanisms likely to be responsible for the e-ratio trends. Based on th e data sets reported from this work, a simple box model of the annual export and regeneration of particulate organic carbon is presented for the Monterey Bay region. An appreciable advective and/or recycling '' loss'' from the euphotic zone of 362.8 gC m(-2) y(-1) is estimated, re presenting primarily algal material transported offshore and/or recycl ed within the upper 100 m of the water column. Annual mid-water (simil ar to 100-450 m) and deep-water (>450 m) POC remineralization rates of 71.8 gC m(-2) y(-1) of 7.2 gC m(-2) y(-1) respectively, are reported for Monterey Bay. The average POC rain rate to the underlying slope se diments is sufficient to satisfy reported benthic utilization requirem ents without invoking an additional input source of POC via deep later al advection and/or the downslope movement of particulate material.