Short - term sediment trap fluxes from Chatham Rise , southwest Pacific Ocean

Sediment trap, nephelometer, and particulate matter (PM) data were collected in the vicinity of the Subtropical Convergence, north of Chatham Rise (42-43”S), southwest Pacific Ocean, in austral autumn 1992. Free-floating cylindrical sediment traps were deployed below the euphotic zone at 200-, 300-, and 500-m water depths. Increases in total mass flux and concomitant proportional decreases in other particulate fluxes (total carbon, nitrogen, and phosphorus) with depth reflected the collection of relatively refractory material, enriched in particulate carbon, as evinced by increases in C : N and C: P ratios below 300 m. Nephelometer and PM concentration profiles indicate that resuspension of sea-floor sediments from the nearby submarine high (Chatham Rise) probably contributed to the observed increase in total mass flux with depth. Published $0, estimates, biological productivity data, and moderate particulate fluxes, as indicated by the present study suggest that oceanic water types east of New Zealand may be a biologically mediated regional sink for atmospheric CO,. Over the last 20 years, insights into the transfer of biologically fixed carbon from oceanic surface waters to the deep ocean have been gained from the deployment of sediment traps below the euphotic zone (e.g. Bruland et al. 1989; U.S. GOFS Report No. 10, 1989). Numerous sediment trap studies have been conducted in the Northern Hemisphere from continental shelf to abyssal environments over equatorial to subarctic latitudes (e.g. Knauer et al. 1979; Deuser 1986; Martin et al. 1987, 1993; Lohrenz et al. 1992; Honjo et al. 1995; Karl et al. 1996). In contrast, little sediment trap research has been undertaken in the Southern Hemisphere, particularly in the open oceanic waters of the southwest Pacific Ocean. This anomalous situation has arisen despite indications that midlatitude (30-50”s) oceanic waters of the southwest Pacific Ocean act as a moderate sink for atmospheric CO, (ApCO, < -20 patm; Takahashi and Azevedo 1982). Murphy et al. (1991) related this observation to enhanced biological productivity in the vicinity of one of the world’s major circumglobal oceanic fronts, the Subtropical Convergence (STC) (Fig. 1). The STC represents the complex mixing zone between warm (summer >15”C, winter