The relationship between methyl bromide and chlorophyll α in high latitude ocean waters

Abstract

We present a set of measurements of methyl bromide concentrations along with chlorophyll a data made in the high latitude, biologically productive, waters of the Labrador Sea in July 1995. Methyl bromide concentrations are found not to show a positive linear correlation with chlorophyll a above a chlorophyll concentration of ca. 0.7 mg L⁻¹. Production rates of methyl bromide, calculated from a steady‐state balance with ocean‐atmosphere exchange, chemical degradation and downward mixing, are also found to have no positive linear correlation with chlorophyll a. If chlorophyll levels higher than ca. 0.7 mg L⁻¹ are selected, a negative linear correlation is found between methyl bromide production rates (calculated using climatological wind speeds) and chlorophyll a. Labrador Sea waters were found to be undersaturated with methyl bromide, an observation which, when taken with evidence for a negative correlation between calculated methyl bromide production rate and the higher chlorophyll values, points to the existence of a biological consumption process. We conclude that models depending on an assumed positive linear correlation between methyl bromide and chlorophyll cannot be used to infer the source strength of methyl bromide in high latitude, productive waters.