Tracers
When waters descend below the ocean surface, they carry with them dissolved atmospheric gases. These time-dependent tracers act as a record of the ventilation and mixing history of the water mass, and provide information on the ocean circulation and its variability.
Information regarding the timescale of when a water mass was last in contact with the atmosphere is critical in understanding and assessing the role of the ocean in climate, and its capacity to absorb anthropogenic (human-derived) constituents, such as CO2, from the atmosphere. Knowledge of the atmospheric time history of the tracer (see graphic) can help to age the water mass and when it was last at the surface. This can then be used as an to estimate the loading of anthropogenic carbon, and act as independent test for time integration of models and biogeochemical processes.
A number of ocean tracers with different oceanic input histories can be measured, thus estimating ventilation on a wide range of time scales, from the ‘steady state’ (3He, and PO4*, a linear combination of phosphate and oxygen) to the last 2-6 decades (CFCs, SF6 and the ratios of various combinations of tritium, CFC-11, CFC-12, CFC-113 and SF6).
In ANDREX, we will be looking in to how the tracer fields compare with those obtained in 1990 during the German WOCE S1 cruise, thus providing information on the uptake of anthropogenic gases and ocean circulation and mixing in the time in between the surveys. Measurements of CFC-11, CFC-12, CFC-113, CCl4 and SF6 will be made.
John Bullister, CDIAC website
