Episodic particulate fluxes at southern temperate mid-latitudes (42-45 degrees S) in the Subtropical Front region, east of New Zealand

Sediment traps were deployed for almost 1 yr at two sites near 178 degrees 40'E in 1996-1997 on Chatham Rise (New Zealand). These sites were either si de of the Subtropical Front (STF), which is a biologically productive zone, characterised by moderate atmospheric CO2 uptake. At each site, PARFLUX se diment traps (Mk 7G-21) were deployed at 300 and 1000 m in 1500 m water dep th. At 42 degrees 42'S, north of the STF, approximately 80% of the integrat ed total mass, POC and biogenic silica flux at 300 m occurred in a 7-day pu lse in austral mid-spring(1064, 141 and 6 mg m(-2) d(-1), respectively, in early October). This pulse was recorded a week later in the 1000 m trap, in dicating a particle sinking rate of 100m d(-1). In contrast, at 44 degrees 37'S, south of the STF, the main flux of total mass and biogenic silica occ urred 3 weeks later in late spring (289 and 3 mg m(-2) d(-1), respectively, in early November). Organic carbon, nitrogen and phosphorus fluxes were pe rsistently high over spring at the southern site, although total POC flux i ntegrated over 3 months was only 60 mg m(-2) d(-1) Thus, up to 2-3 times mo re material was exported north of the STF, compared with fluxes measured < 200 km away to the south. As an integrated proportion of the annual total m ass flux, however, more organic carbon was exported south of the STF (17% c f. 5-14%). Furthermore, organic material exported in spring from southern w aters was labile and protein-rich (C:N - 8-16, C:P - 200-450, N:P - 13-36), compared to the more refractory, diatom-dominated material sinking out nor th of the STF in spring (C:N 9-22, C:P 50-230, N:P 5-19). These observation s are consistent with anomalously high benthic biomass and diversity observ ed on south Chatham Rise. Resuspension and differential particle settling a re probable causes for depth increases in particulate flux. Estimated parti cle source areas may be up to 120 km away due to high levels of mesoscale a ctivity and mean flow in the STF region. (C) 2000 Elsevier Science Ltd. All rights reserved.