Gas exchange rates for three closed‐basin lakes1

Long term monitoring of the 14 C: 12 C ratio in three closed‐basin lakes in the western United States has resulted in reliable estimates of the mean CO 2 invasion rates. When normalized to sea level pressure the results are 6 mol·m −2 ·yr −1 for Pyramid Lake, 17 for Walker Lake, and 38 for Mono Lake. Except for Mono Lake, these bomb 14 C‐derived invasion rates are consistent with those derived from the distribution of natural radiocarbon. The big difference in the invasion rates estimated for Mono Lake by the two methods is attributed to the influx of 14 C‐free spring waters to the lake. Possible causes for the difference in CO 2 invasion rates among the three lakes are wind velocity, salinity, and pH.