A BIOMARKER PERSPECTIVE ON PRYMNESIOPHYTE PRODUCTIVITY IN THE NORTHEAST PACIFIC-OCEAN

Long-chain alkenones derived from prymnesiophyte algae were analysed i n 1-year sediment trap time series (September 1987-1988) from three si tes along a 630 km offshore transect at similar to 42 degrees N in the northeast Pacific Ocean. Biomarker flux monitored at 1000 m water dep th was evident throughout the year at all sites and showed a consisten t seasonal maximum in late spring which increased in amplitude with di stance offshore. The integrated annual biomarker flux was constant alo ng the transect, despite differences in seasonality between sites. Alk enone unsaturation patterns were remarkably uniform throughout the tim e series, reflecting an algal growth temperature of 10.6 +/- 1.1 degre es C. This value corresponds to regional water temperature at the sea- surface in winter. It recurs in seasonal upwelling near the coast and at the depth of the subsurface chlorophyll maximum offshore during sea sons of stratification. These biomarker observations, interpreted in v iew of trap data for total organic (TOC) and inorganic carbon and anci llary hydrographic information, help to clarify seasonal productivity patterns for alkenone-producing prymnesiophytes in the northeast Pacif ic Ocean. Sediments accumulating with distance offshore along the samp ling transect change from suboxic and Mn-reducing at the water-sedimen t interface to aerobic throughout the depths penetrated by box coring. Comparison of alkenone and TOC accumulation rates in surface (0-1 cm) sediments with corresponding annual fluxes integrated by the trap tim e series, shows that the fraction of both properties accounted at the seafloor is highest and similar under sub-oxic conditions (similar to 25%), and declines steeply and disproportionately as aerobic condition s are encountered farther offshore. Only 0.25 and 3.1% of the annual i nventory for alkenones and TOC in traps are accountable in surface sed iments from the slowest accumulating, most oxidizing site farthest off shore. Despite major loss of biomarker to early diagenesis, surface se diments and trap particles display consistent alkenone unsaturation pa tterns. Results from this study provide a necessary background for pal aeoceanographic reconstruction of the northeast Pacific Ocean from str atigraphic analysis of alkenone abundances, unsaturation patterns and isotopic compositions in sediment cores.