Rates of Vertical Mixing, Gas Exchange, and New Production: Estimates from Seasonal Gas Cycles in the Upper Ocean Near Bermuda

摘要

Argon measurements, obtained from three years of monthly detailed vertical profiles near Bermuda (Station S, 32 deg N 64 deg W), show a maximum in argon supersaturation of about 4 percent in the seasonal thermocline in late summer. Since the argon supersaturation is 3-4 times smaller than that of oxygen, most of the oxygen supersaturation is not of physical origin and hence must result from biological production. In the winter mixed layer, air injection produces argon supersaturation despite high gas exchange rates. During spring and summer, radiative heating, air injection, and an upward argon flux create an even larger supersaturation in the mixed layer. In the seasonal thermocline, radiative heating creates argon supersaturations that persist in spite of vertical mixing. The observed seasonal cycles of temperature, argon, helium, and oxygen are simulated with an upper ocean model. The author linearizes the model's response to variations in vertical diffusivity, air injection, gas exchange rate, and new production and then uses an inverse technique (singular value decomposition) to determine the values of these parameters that best fit the data.