Seasonal variation in alkenones, bulk suspended POM, plankton and temperature in Monterey Bay, California: implications for carbon cycling and climate assessment

The utility of alkenone abundance and U37K′ ratios as proxies for haptophyte productivity and temperature variations, respectively, was examined in an upwelling setting by comparison of alkenones with other environmental variables including carbon concentrations, plankton populations, productivity, and temperature. Suspended particulate organic material (SPOM) was collected from surface waters (1–5 m) in Monterey Bay, California during the 1992 El Niño. Haptophyte algae comprise a small but significant fraction of the plankton assemblage (0.5–30%). In this upwelling environment either the haptophytes contain low cellular abundances of alkenones (0.4–5% Corg) and/or alkenone producers are weakly represented among their populations. The U37K′-temperature relationship for SPOM exhibits a better correlation (r2=0.870; n=8) during periods of active upwelling and in the winter than throughout the entire annual cycle (r2=0.308; n=18). The alkenone-based temperatures also suggest, as observed elsewhere, that these compounds originated in colder waters at depth and were subsequently transferred to surface waters.