Global average of air‐sea CO2 transfer velocity from QuikSCAT scatterometer wind speeds

[1] The absolute calibration of the relationship between air-sea CO 2 transfer velocity, , k, and wind speed, U, has been a topic of debate for some time, because k global average, (k), as deduced from Geochemical Ocean Sections Study oceanic 14 C inventory has differed from that deduced from experimental k-U relationships. Recently, new oceanic 14 C inventories and inversions have lead to a lower (k). In addition, new measurements performed at sea in high―wind speed conditions have led to new k-U relationship. Meanwhile, quality and sampling of satellite wind speeds has greatly improved. The QuikSCAT scatterometer has provided high-quality wind speeds for more than 7 years. This allows us to estimate the global distributions of k computed using k-U relationships and temperature-dependent Schmidt numbers from 1999 to 2006. Given the difficulty of measuring in situ wind speed very accurately, we performed a sensitivity study of the (k) uncertainty which results from QuikSCAT U uncertainties. New QuikSCAT-buoy U comparisons in the northern Atlantic Ocean and in the Southern Ocean confirm the excellent precision of QuikSCAT U (RMS difference of about 1 m s ―1 ), but it is possible that QuikSCAT overestimates wind speeds by 5%, leading to a possible overestimation of k derived with quadratic relationships by 10%. The (k) values obtained with two recent experimental k-U relationships are very close, between 15.9 and 17.9 cm h ―1 , and within the error bar of k average deduced from the new oceanic 14 C inventory.

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