Scales of spatial variability for surface ocean pCO(2) in the Gulf of Alaska and Bering Sea: toward a sampling strategy

Twenty-four near-exact repeat tracks lover a 48-month period) of ocean surf ace pCO(2) data from the North Pacific offer an unprecedented opportunity t o examine the space scales of pCO(2) in this region. Because previous basin scale studies of air-sea carbon flux have shown that the field of Delta pC O(2) lair-sea disequilibrium) largely controls the field of flux land atmos pheric pCO(2) is relatively constant), knowing how to sample pCO(2) in seaw ater is a crucial element of the design of a basin scale carbon flux observ ing system. Unbiased (within 3 mu atm) along-track means for Delta pCO(2) c an be obtained from measurements made every 40 km (similar to hourly for a ship traveling 20 knots). We find distinctly different characteristics of s patial variability in two open ocean regions, the Bering Sea and the Gulf o f Alaska. The first zero crossing of the mean spatial autocorrelation funct ion is 1.5 degrees longitude in the Bering Sea and 3.5 degrees in the Gulf of Alaska, when the cruise data are linearly detrended to remove the larger scale field. There is a strong seasonal variation in the zero crossing, wi th shorter scales in the summer. In near-shore waters there is extreme vari ability, often with very small space scales and very large cruise-to-cruise differences. Neither the mean nor variability statistics from a single shi p cruise data set appear likely to produce reliable information for designi ng an observing system.