PIs: Michael Bender and Mary-Lynn Dickson
Graduate School of Oceanography
University of Rhode Island
South Ferry Road
Narragansett, RI 02882-1197

Point of contact: Mary-Lynn Dickson

Gross and net oxygen production and respiration rates

Project/cruise: Process Cruise 2, Ross Sea, NBP97-1 Ship: Nathaniel B. Palmer
Methodology: Gross oxygen production rates were measured by spiking seawater samples with 18O-labelled water and measuring the amount of 18O-labelled oxygen produced photosynthetically. This method measures gross primary production and has been described by Bender et al., 1987 (Limnology and Oceanography 32:1085-1098) and Grande et al., 1989 (Deep-Sea Research 36: 1621-1634). Net oxygen production was measured from changes in the oxygen concentration in incubated bottles. This represents net community production and is equivalent to gross oxygen production minus the oxygen consumed by autotrophic and heterotrophic respiration. Dark oxygen respiration rates were measured by incubating samples in the dark for 24 hours in shipboard incubators, cooled with running surface seawater.

Seawater samples for the productivity experiments were collected using either 30 litre Go-Flo bottles attached to a trace metal clean rosette or from 10 litre Niskin bottles attached to the frame of a CTD rosette. Care was taken to minimize contamination of the seawater during sampling by using trace metal free powderless PVC gloves and silicon tubing that was cleaned prior to sampling by rinsing several times with 10% HCl, followed by rinses with distilled/deionized water. Once the rosette was retrieved, a member of the hydrographic team took a seawater sample for determination of the oxygen concentration from each Go-Flo or Niskin bottle first, followed by the oxygen production group. Quartz incubation bottles having a nominal volume of 100 ml were filled and allowed to overflow three to five volumes of seawater before being closed with a glass stopper. Oxygen production measurements were made by incubating samples in situ. The primary production array was launched prior to sunrise and retrieved within an hour after sunset. Samples were placed in shipboard incubators overnight and processed the following morning when 24 hours of incubation time had elapsed.