Impact of monsoon circulations on oceanic emissions of light alkenes over Bay of Bengal

Abstract

Surface level measurements of ethene (C2H4) and propene (C3H6) were made in the marine boundary layer (MBL) of Bay of Bengal (BOB) during the summer and winter monsoon campaigns. The time series trends in the mixing ratios of alkenes were similar to that of wind speed, while no clear relations were observed with other meteorological parameters. The diurnal variations of ethene and propene show correlations with the intensity of solar flux as their daytime mixing ratios were ∼45% higher than the nighttime measurements in summer. While winter measurements of alkenes do not show any local time dependencies. The mixing ratios of alkenes were particularly elevated during the episodes of cyclones and convective activities in the summer season over BOB. The uptake rate of nutrients shows a similar trend to those of mixing ratios of alkenes in summer, and the measurements of phytoplankton indicate high primary production during the episodes of elevated alkenes over central BOB. The mixing ratios of alkenes showing minima in winter and maxima in summer are similar to the seasonal patterns reported for global oceans; however, their variability over BOB was less pronounced compared to the extratropical oceans. The ratios of ethene/propene were comparable to a mean ratio of 2.3 pptv/pptv derived from the database for global oceans confirming the fresh oceanic emissions of alkenes over BOB. The emissions of alkenes were mainly controlled by the distribution of dissolved organic carbon (DOC) in seawaters and actions of wind speed in the presence of sunlight. This study is an important step to understand the processes controlling the emissions of alkenes from equatorial oceans and also to improve their global budget estimates. © 2010 by the American Geophysical Union.