Deployment of autosamplers
Michael Bender’s lab measures the O2/N2 ration of air. This measurement provides a tool for tracking global CO2 uptake by the land biosphere as well as by the ocean, and reflects the fertility of ecosystems on the scale of ocean basins. This year Bender’s group has installed three automatic samplers that collect air at Samoa, Barrow, and Sable Island (in the Northwest Atlantic) for measurement of oxygen-nitrogen ratios. The autosamplers are expected to improve the reproducibility of O2/N2 measurements, thus giving more precise information about carbon cycle variability The Samoa and Barrow stations are operational and sending samples back to the lab and the sampler at Sable Island should be up and running soon.
During the coming year, Bender’s group plans to install another autosampler on MacQuarie Island, about halfway between Tasmania and Antarctica. The samples collected from MacQuarie will be compared with data from 3 other stations in the region – Cape Grim, Syowa, and Amsterdam Island – to see if the samples reflect regional or hemispheric variations in productivity.
Measurement of Oxygen, Argon and Nitrogen
Also this year, Jan Kaiser has developed a new device to measure oxygen and argon supersaturation in ocean surface waters to monitor biological productivity in ocean surface waters. The supersaturation of oxygen in seawater is a function of both biological activity and bubble entrainment due to waves breaking at the ocean’s surface. Subtracting argon supersaturation, which is only affected by bubbles, from oxygen supersaturation thus allows calculation of the net organic matter production in the region of the ocean sampled.
The new mass spectrometer allows rapid and continuous sampling of surface seawater intake on board a ship, rather than requiring that individual samples be brought back to a laboratory on land for analysis. The efficiency of the new device is allowing Kaiser to make high resolution measurements of the variability of marine biological activity in space and time. The team is now analyzing data from two equatorial cruises, and plans to sample the Southern Ocean in the coming year.
In a related project, Nicolas Cassar is working on updating the global database of argon/nitrogen ratios. A previous modeling study had indicated a significant discrepancy in timing of observed and model gas fluxes between the atmosphere and ocean, indicating a problem with mixed layer physics in the GFDL ocean model. The model has now been improved, and the team hopes that incorporating new data to almost double the number of measurements will provide a more accurate diagnostic to compare with model simulations.
O2/N2 measurements and Ocean CO2 uptake
The Bender team is also examining interannual variability in CO2 uptake by the ocean and land biosphere. Most independent evidence suggests that ocean uptake is roughly constant, with the land biosphere accounting for most of the interannual variability in the global CO2 sink. However, observations of oxygen concentration in the atmosphere over the last several years suggest that there have been large interannual variations in ocean CO2 uptake.
However, it is possible that the oxygen variations actually reflect yearly air-sea transfers in O2 that are not linked to variations in carbon dioxide uptake. It is also possible that some of the variability is an artifact of experimental uncertainties. Bender’s group is undertaking a detailed comparison of O2/N2 records with those of Ralph Keeling (Scripps Instition of Oceanography) to identify analytical errors in the records. The will then analyze variations in terms of oceanic processes that both link and separate O2 and CO2 fluxes.