This award funded a graduate student to complete analysis of data obtained during cruises made during the ONR funded TOPO ARI cruises (l989-l991) to Fieberling Guyot. The analysis specifically addressed a) using the dominant pigments to identify the phytoplankton groups contributing to productivity station by station, to examine if there were differences above, on the side and away from the seamount, and b) identifying the nutracline at each station using detailed nanomolar and micromolar measurements, and overlaying the fluorescence maxima data to compare relative nutracline/chlorophyll maxima relationships of Fieberling with those at shallower topographical features. N- 15 uptake showed that depth-integrated values of ammonium uptake were greater than for nitrate-the ecosystem is a recycling microbial loop system. The pigment data supported this with pigments characteristic of small-celled autotrophs (typically that use ammonium as a nitrogen source rather than nitrate), dominating after chlorophylls a and b, i.e. zeaxanthin (contained by phycobilin-containing cyanobacteria); 1 9-hexanoyfoxyfucoxanthin (characteristic of the prymnesiophytes) and l9-butanoyloxyfucoxanthin). As predicted fucoxanthin, the characteristic pigment of diatoms (the major new productivity engines of the ocean that are usually large cell-sized and take up nitrate) and peridinin, characteristic of dinoflagellates were uncommon. Fucoxanthin was found in flank station samples rather than over or away from Fieberling.