Source and Scope of the Data

Oceans take up about 40% of the fossil fuel CO₂ introduced into the atmosphere by man. Presently, more information is needed on the physical and chemical processes involved in this uptake, such as gas exchange, winter water mass formation, and water mass circulation, before predictions can be made about the sensitivity of these processes to future climate change caused by the type of information needed to better understand the physical and chemical processes involved in the uptake of CO₂ by oceans.

The TTO North Atlantic experiment cruise consisted of seven legs during which a total of 250 hydrographic stations were occupied in 200 days. About 9,000 water samples were taken with most of the samples being analyzed for salinity, oxygen, and nutrients. Over 3,000 samples for tritium analysis were collected and over 1,000 samples for radiocarbon were taken.

Leg 1 of the cruise (stations 1-14) was designed to allow two crossings of the western boundary undercurrent (WBUC) and the Gulf Stream and to allow remeasurment of the tracer field in the current off the Blake-Bahamas outer ridge at 30°N where tritium penetration had been previously observed. Leg 2 (stations 15-41) studied the southern extremity of the WBUC and reoccupied several 1972 GEOSECS stations (TTO stations 32-38). Leg 3 (stations 42-109) of the cruise track crossed the mid-Atlantic ridge and studied eddy and mean-flow yields south of Azores. Leg 4 (stations 110-140) made observations in the eastern basin of the Atlantic where the Mediterranean outflow occurs ant in the Gibbs Fracture Zone. Leg 5 (stations 110-167) explored the Norwegian and Greenland Seas. Leg 6 (stations 168-210) examined the Denmark Strait outflow and Labrador Sea stations, connecting with work done on Leg 4. Leg 7 (stations 211-250) crossed the Grand Banks and followed the 1972 line of GEOSECS stations to 28°N, then to Nova Scotia for completion of the field work.

The total co₂ concentration data obtained during the program should be revised based on the results of a review of the data by Brewer et al. (1986) and from the results of other studies. This revised data package includes measured quantities of pCO₂ for seawater at 20°C and the total CO ₂concentration values, which were computed using measured alkalinity and pCO₂ values. These new CO₂ concentration values are smaller by about 20µm/kg and the discrepancy is greatest for seawater samples collected at depths less than several hundred meters. These computed CO₂ values are more reliable and should be used for interpretive studies instead of the previously reported ones (Takahashi and Brewer 1986).