ABSTRACT: New phytoplankton production (P_new; nitrate uptake) and production of large phytoplankton (>5 um, P_L; carbon fixation) were monitored on the Scotian Shelf (Northwest Atlantic) every month for 1 yr. On a daily basis, P_new and P_L were seldom the same. When nitrate uptake accounted for less than 20% of total primary production (f-ratio < 0.2), P_L was generally higher than P_new. Above this threshold, P_new was higher than P_L. This was true independently of actual production, i.e. the difference between P_new and P_L depended on the f-ratio and not on the level of primary production (high or low). When averaged over periods of 6 mo or more, P_L and P_new were roughly balanced. Over the year, P_new and P_L were equivalent, i.e. 121.8 and 115.2 mg C m^-2 d^-1, respectively. Assuming that the system was in steady state, which implies a balance between new and exported production, these results lead to the conclusion that at time scales of 6 mo or more, exportable production (P_L) was equivalent to new production.

KEY WORDS: New production . Nitrate uptake . Carbon uptake . Phytoplankton . Size fractionation

Published in MEPS Vol. 135 (1996) on May 17
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996