Large latitudinal gradients and temporal heterogeneity in aerosol black carbon and its mass mixing ratio over southern and northern oceans observed during a trans-continental cruise experiment

Abstract

Extensive, and collocated measurements of the mass concentrations (M_B) of aerosol black carbon (BC) and (M_T) of composite aerosols were made over the Arabian Sea, tropical Indian Ocean and the Southern Ocean during a trans-continental cruise experiment. Our investigations show that M_B remains extremely low (<50 ng m^-3) and remarkably steady (in space and time) in the Southern Ocean (20°S to 56°S). In contrast, large latitudinal gradients exist north of ~20°S; M_B increasing exponentially to reach as high as 2000 ng m^-3 in the Arabian Sea (~8°N). Interestingly, the share of BC showed a distinctly different latitudinal variation, with a peak close to the equator and decreasing on either side. Large fluctuations were seen in M_T over Southern Ocean associated with enhanced production of sea-salt aerosols in response to sea-surface wind speed. These spatio-temporal changes in M_B and its mixing ratio have important implications to regional and global climate.