Variability of the apparent quantum efficiency of CO photoproduction in the Gulf of Maine and Northwest Atlantic

The photochemical oxidation of colored, dissolved organic matter (CDOM) is important for carbon cycling in the ocean. This oxidation process produces a number of products, including carbon monoxide (CO). While the photochemical production efficiency of CO (apparent quantum yield, AQY, defined in terms of CDOM absorbance) has been reported to be similar for many water types, a full evaluation of the observed natural variability in CO AQY requires additional study. Here we use a polychromatic irradiation system to determine twenty AQY spectra at sea on fresh samples ranging from the near coastal waters of the Gulf of Maine to the offshore waters of the Northwest Atlantic. Despite the geographic variability of these marine samples the AQY of CO production in the Gulf of Maine and Northwest Atlantic exhibited only a small degree of variability, none of which was not correlated with measured environmental parameters. Consequently, a single aggregate AQY spectrum ϕλ = e(−(9.134+0.0425(λ−290)))+e(−(11.316+0.0142(λ−290))) was found to adequately represent the entire data set. Significantly, the accuracy of an AQY spectrum determined using this multispectral/statistical technique was confirmed with data obtained from a monochromatic irradiation technique on a single open ocean sample. Taken together, the AQY spectra determined in this study were similar in magnitude and shape to those previously published for marine samples and, overall, were somewhat lower than those previously reported for freshwater studies.