The relationship between new production and vertical flux on the Ross Sea continental shelf

Abstract

The relationship between new production, as assessed by short-term isotopic incubations, and vertical flux, quantified by both short- and long-term deployments of sediment traps, was investigated on the Ross Sea continental shelf in austral summer, 1990 and 1992. Three sites were analyzed, the first in the western Ross Sea where surface waters were dominated by pennate diatoms, the second in the south–central Ross Sea where the prymnesiophyte Phaeocystis antarctica dominated, and the third in the northern region which was dominated by diatoms. We found that the flux at the western site varied by a factor of 3.6 over a 1-month period (from 18.4 to 65.4 mg C m −2 day −1), whereas new production varied over nearly two orders of magnitude. At the Phaeocystis site, flux was much more variable. Although the temporally weighted flux averaged 7.34 mg C m −2 day −1, the flux at 570 m ranged from 0.5 to 74.8 mg C m −2 day −1, and the flux at 50 m in a floating trap reached 92.7 mg C m −2 day −1. New production ranged from 0.30 to 1.23 g C m −2 day −1. Primary production, new production and f-ratios at both sites decreased through time (mean February values of each were 42, 37 and 12% of January averages), but the seasonal decrease in vertical flux exhibited a significant time lag behind the productivity decrease. A carbon budget is constructed which suggests that heterotrophic mineralization within the water column is a significant removal term, and that substantial spatial variability in this term exists. The relationship between new production in the euphotic zone to that of export production is ambiguous in the Ross Sea, in part because isotopic methods quantify the material available for export on time scales that do not necessarily apply to processes which dominate export production. Integration of seasonal time scales, remineralization rates, and vertical flux rates is required to understand the quantitative relationships involved in export from the surface layer.