Isotopic composition of particulate black carbon in the northern Indian Ocean

The dataset contains the concentration and stable isotopic composition of particulate black carbon (PBC) in the surface waters of the northern Indian Ocean. Samples were collected during multiple cruises to the Northern Indian Ocean (locations, date and time are provided in the datasheet) along with end member sampling of riverine particulate. Surface water samples were filtered onto 0.7 micron GF/F filters (precombusted at 400 degree Celsius) and oven-dried. Particulate black carbon was estimated following the chemothermal oxidation (CTO - 375) method. Briefly, samples were treated using HCl fumes to remove inorganic carbon fractions followed by heating at 400 degree celsius for 24 hours in active airflow to remove the organic carbon fraction. The residual carbon (BC in micromoles per litre) and its isotopic composition (represented by delta notation in permil) was measured using an elemental analyzer (EA: Flash 2000, Thermo Scientific) connected to an isotope ratio mass spectrometer (IRMS: Delta V, Thermo Scientific). The precision of measurement by repeated analysis of standards was better than 10 % for PBC concentration and 0.1 permil for its isotopic composition. The data is associated with the manuscript accepted in Geophysical Research Letters titled, 'Isotopic evidence for degradation of particulate black carbon in the ocean.

Methods
Samples were collected during multiple cruises to the Northern Indian Ocean (locations, date and time are provided in the data sheet) along with end member sampling of riverine particulate. Surface water samples were filtered onto 0.7 micron GF/F filters (precombusted at 400 degree celcius) and oven dried. Particulate black carbon was estimated following the chemothermal oxidation (CTO - 375) method. Briefly samples were treated using HCl fumes to remove inorganic carbon fractions foloowed by heating at 400 degree celcius for 24 hours in active airflow to remove the organic carbon fraction. The residual carbon (BC in micro moles per litre) and its isotopic composition (represented by delta notation in permil) was measured using an elemental analyzer (EA: Flash 2000, Thermo Scientific) connected to an isotope ratio mass spectrometer (IRMS: Delta V, Thermo Scientific). The precision of measurement by repeated analysis of standards was better than 10 % for PBC concentration and 0.1 permil for its isotopic composition.