Accomplishments & Reports: Measurement of Dissolved Oxygen

Dale Hebel
University of Hawaii, SOEST, Department of Oceanography
Honolulu, HI 96822
dhebel@soest.hawaii.edu)

and

Albert Colman
Harvard University, Department of Earth Sciences

Dissolved oxygen was measured on approximately 600 samples with a high precision computer assisted potentiometric titration procedure developed at the University of Hawaii. Dissolved oxygen was measured on a broad range of samples from general hydrographic support of CTD profiling (i.e., oxygen sensor calibration and performance verification) to support of specific investigator experiments.

As on previous cruises dissolved oxygen was measured as one component of water mass identification. Dissolved oxygen levels were characterized on profiles from various water masses including outer shelf LTER 600 Line, offshore Gerlache Strait, Crystal Sound and Lemaire Channel, as well as inshore waters of Paradise Harbor and Andvord Bay. Experiments to assess specific biological properties were conducted which included dissolved oxygen primary production measurements, light-dark dissolved oxygen relationships from temporal in vitro incubations, photorespiration determinations as well as shipboard assessment of dissolved oxygen related sampling procedures and experimental treatments.

Initial results indicate that the CTD dissolved oxygen sensor performed properly although a relative offset was recognized. Diver collected samples of "brown" ice algae interface-water revealed only slightly elevated levels of dissolved oxygen relative to surrounding surface seawater, however, hand collection of whole ice "brown" algae communities exhibited extremely high levels of dissolved oxygen approaching 200% supersaturation. Dissolved oxygen based primary production experiments (light vs. dark bottle incubations) were performed in Paradise Harbor for comparison to the ¹⁴C experiments. An areal transect of potential bloom sites also revealed relatively low levels of oxygen supersaturation suggesting either early or perhaps late stages of the Austral bloom cycle. Areal dissolved oxygen measured across the Drake Passage decreased in step-like function reflecting the passage of different water masses with elevated temperature signatures along the south to north transect route.