Project SANTA CLAµS
in the Laboratory for Microbial Oceanography at the University of Hawai'i at Manoa

Accomplishments & Reports: Bio-optics and OCM Drifter Program


Ricardo Letelier and Mark Abbott
Oregon State University, College of Ocean and Atmospheric Sciences
Corvallis, OR 97331
(letelier@oce.orst.edu)

The objective of our participation in the PD94-12 cruise was (1) to characterize the passive fluorescence of chlorophyll at the sea surface (0.3 m) of Antarctic pelagic marine ecosystems and (2) to analyze this fluorescence signal in relation to other physiological and ambient parameters to understand its variability. Two main instruments were used during the cruise to measure the sub-surface upwelling spectral irradiance. A Tethered Spectral Radiometer Buoy (TSRB, Satlantic Inc., Halifax, NS, Canada) was routinely deployed between one and three times a day during 20 minutes to measure irradiance at 412, 443, 490, 510, 555, 670, 683 nm. The TSRB also measures sea surface temperature (SST) and surface radiance at 490 nm. Free drifting Ocean Colour Monitoring sensors (OCM, Satlantic Inc.) were deployed in the Gerlache Strait and Drake Passage to monitor temporal changes in the sub-surface ocean spectral irradiance during the austral summer. The OCM drifters measure the same parameters as the TSRB and relay the data through satellite linkage (ARGOS) to our shore-based facilities.

During this cruise we accomplished all of our main objectives. The TSRB was deployed in waters with chlorophyll a concentration ranging from < 0.7 µg/l to > 14 µg/l. Measurement of primary production experiments using radiocarbon uptake, in vivo induced fluorescence, nutrient concentrations, and algal pigments will provide a basis to analyze the variability in the chlorophyll natural fluorescence yield. Preliminary results indicate that, although natural fluorescence can be used as an estimator of chlorophyll concentration when looking at large changes, significant variations in fluorescence yield appear to correlate with salinity fluctuations in our Paradise Bay TSRB deployments. This correlation suggests that changes in the physiology and species composition of the algal assemblage may be taking place at small spatial scales round the Antarctic Peninsula.

The OCN drifter deployed in the Gerlache Strait has moved northeast into the Bransfield Strait where chlorophyll concentrations appear to be lower while fluorescence yield is higher. The OCM drifter deployed in the Drake Passage has moved north and was caught in an eddy field during January 1995 in which chlorophyll concentration increased. Both drifters were still transmitting data at the end of February 1995 and are providing a continuous Lagrangian record of the change in sub-surface spectral irradiance during the austral summer.