title: Atmospheric deposition of N, P and Fe to the Northern Indian Ocean: implications to C- and N-fixation.
abstract: This study presents the first data set on atmospheric input of N, P and Fe to the Northern Indian Ocean. Based on the chemical analysis of ambient aerosols, collected from the marine atmospheric boundary layer (MABL) during the continental outflow (January-April), we document that dry-deposition fluxes (μmolm(-2) d(-1)) of N (2-167), P (0.5-4.8) and Fe (0.02-1.2) to the Bay of Bengal are significantly higher compared to those over the Arabian Sea [N: 0.2-18.6; P: 0.3-0.9; Fe: 0.001-0.015]. Using atmospherically derived P and Fe, C-fixation (1.1 Pg yr(-1)) in the Bay of Bengal is dominated by anthropogenic sources. In contrast, C-fixation (0.03 Pg yr(-1)) in the Arabian Sea is limited by P and Fe. This is attributed to the poor fractional solubility of atmospheric mineral dust transported to the Arabian Sea. However, N-fixation by diazotrophs in the two oceanic regions is somewhat similar (0.5 Tg yr(-1)). Our estimate of N-deposition (0.2 Tg yr(-1)) to the Northern Indian Ocean is significantly lower compared to model results (~800-1200 mg-Nm(-2)yr(-1)≈5.7-8.6 Tg yr(-1) by Duce et al. (2008); ~4.1 Tg yr(-1) by Okin et al. (2011); ~0.8 Tg yr(-1) by Kanakidou et al. (2012)). An overestimate of N-deposition by models could arise due to inappropriate parameterization of temporal variability associated with the continental outflow spread over only four months.
authors.affiliation: Physical Research Laboratory, Ahmedabad-380 009, India.
authors.forename: Bikkina
authors.initials: B
authors.lastname: Srinivas
authors.forename: M M
authors.initials: MM
authors.lastname: Sarin
mesh_terms: D000336:Aerosols; D000393:Air Pollutants / Q000032:analysis*; D057486:Carbon Cycle; D004784:Environmental Monitoring; D019156:Indian Ocean; D007501:Iron / Q000032:analysis*; D009584:Nitrogen / Q000032:analysis*; D009586:Nitrogen Fixation; D010758:Phosphorus / Q000032:analysis*; D012623:Seawater / Q000737:chemistry*
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D010758:Phosphorus; D007501:Iron; D009584:Nitrogen