Regurgitation of Black Carbon Aerosols from the Ocean During a Cyclone

ASHISH SONI, Pawan S. Soyam, Shivdas Bankar, Thara Prabhakaran, Harindra J Fernando, Devmi Gamage, Griffin Modjeski, Selina Bolella, Joaquim Goes, Charles Kovach, Sudarsan Bera, A. Aravindhavel, Maria Laura Zaffoli, Amit Tandon, Mahen Konwar, P. Murugavel, Pramod Safai, Stefano Decesari, Maria Cristina Facchini, Craig M. Lee, Nandakumar Kalarikkal, Indian Institute of Tropical Meteorology

     Abstract Number: 312
     Working Group: Carbonaceous Aerosols

Abstract
In-situ observations of atmospheric Black Carbon (BC) aerosols over the northern Indian Ocean are sparse, especially during the Indian Summer Monsoon season due to harsh and challenging oceanic conditions associated with strong south-westerly winds and rough sea states. In the present study, we measured atmospheric BC over the Arabian Sea (AS) during June on board a research expedition. While BC is expected to decrease as we move away from continental landmass, surprisingly, despite negligible land-based combustion activities at this time of the year, a zone of high BC was observed offshore within a narrow band impacted by the Biparjoy cyclone. The median BC concentration was two-fold higher within the cyclone-impacted zone than in the region east of this zone. Airmass back-trajectory and satellite fire map analysis revealed that savanna burning in Africa could significantly affects elevated BC signals over the AS. However, the absence of correlation of BC with biomass-burning tracers inside the high-BC zone clearly suggested some other active source(s). Correlation analysis of BC with oceanic deep-water vertical mixing indicators as well as atmospheric processes provides vital pointers that a significant amount of this BC can be regurgitated from waters, which are brought to the surface from depth, as the deep ocean is one of largest reservoirs of BC aerosols. These findings demand a nascent scope for controlled simulation experiments to estimate regurgitated BC from the ocean to reduce its uncertainty.