Black carbon (BC) has emerged as an integral part of the global carbon (C) cycle with a potential to generate negative climate feedbacks and sequester C at long timescales. There is a limited understanding of the pathways of transformation of BC in aquatic systems. Photodegradation of BC along the land-ocean continuum provides a fresh perspective of their role in aquatic C biogeochemistry and to the uncertainty in the global C budget. However, to reach to certain conclusions, extensive research is warranted in the field of BC cycling. Although research on dissolved black carbon has accelerated in recent years, their particulate counterpart remains largely unexplored. In this study, we investigated the particulate black carbon (PBC) dynamics in the estuarine and marine settings of the Northern Indian Ocean by measuring its concentrations and isotopic compositions (δ¹³C_PBC). after removing inorganic and organic C fractions from the collected particulate samples (on 0.7 µm Whatman GF/F) using HCl fumigation and CTO-375 method, respectively. Significantly higher δ¹³C_PBC in the open ocean (Arabian Sea: –16.2 ± 1.3‰ and Bay of Bengal: –20.0 ± 0.7‰) compared to estuarine (Andaman: –24.5 ± 1.1‰; Mahanadi: –25.0 ± 1.3‰), riverine (Ambika: –26.9‰) and atmospheric (–25.5 and –27.8‰) environments was observed. This unequivocal increase in δ¹³C_PBC indicated potential aging of PBC in the seawater through processes like photodegradation or leaching. This finding adds new dimension to the PBC cycling in our environment which might have implications on BC burial at longer timescale.

Primary Presenter: Siddhartha Sarkar, Physical Research Laboratory (siddhartha.academia@gmail.com)

Authors:

Siddhartha Sarkar, Physical Research Laboratory  (siddhartha@prl.res.in)

Abdur Rahman, Physical Research Laboratory  (abdur@prl.res.in)

Mohammad Atif Khan, Physical Research Laboratory  (atif@prl.res.in)

Km Ajayeta Rathi, Physical Research Laboratory  (ayajeta@prl.res.in)

P Ragavan, Physical Research Laboratory  (van.ragavan@gmail.com)

Arvind Singh, Physical Research Laboratory  (arvinds@prl.res.in)

Sanjeev Kumar, Physical Research Laboratory  (sanjeev@prl.res.in)