REACTIVE SILICATE IN SHELF WATERS NEAR OTAGO PENINSULA, NEW-ZEALAND

Reactive Si data from 19 monthly occupations of two transects near Ota go Peninsula in 1986-87 showed low surface values (less than or equal to 1 mu M) during spring and summer, and high values (>4 mu M) in wint er. Concentrations were greatest after flooding in the Clutha River, 1 00 km south of the study area. In spring and early summer, concentrati ons were lowest inshore at the surface. At other times of the year, co ncentrations were highest in inshore surface waters, and usually coinc ided with the salinity minimum. Vertical gradients across the Southlan d Front, a near-horizontal thermal front outcropping near the shelf br eak, were calculated and compared with phosphorus gradients from the s ame samples. Nine of 21 Si gradients were negative (i.e. concentration s decreased with depth), whereas only 1 of 24 phosphorus gradients was negative. This implies that riverine Si flux is important in establis hing Si gradients across the Southland Front. The results are a furthe r indication of the importance of the Clutha River to the Otago shelf system.