The influence of atmospheric organic carbon and organic nitrogen on biogeochemistry of the (sub-) tropical North Atlantic Ocean

• Main Author: Mingkwan, Pornsri
• Format: Thesis
• Language: English
• Published: 2011
• Subjects: North Atlantic
• Online Access: https://eprints.soton.ac.uk/338872/; https://eprints.soton.ac.uk/338872/1/Mingkwan_PhD_2011.pdf; https://eprints.soton.ac.uk/338872/2/land_based_sampling.pdf; https://eprints.soton.ac.uk/338872/3/ship_based_sampling.pdf

The (sub-) tropical North Atlantic Ocean is a region which is influenced by oceanic upwelling along the West African coast, an extensive oxygen minimum zone and also by atmospheric dust deposition from the Sahara and Sahel regions and the industrial continental regions of Europe and North America. In this study, samples from water column profiles were collected to investigate the distributions of dissolved organic carbon (DOC) and dissolved organic itrogen (DON), including dissolved free amino acids (DFAA) and dissolved hydrolysable amino acids (DHAA). In addition, bulk aerosol samples were collected on the island of São Vicente (Cape Verde Islands) to quantify the deposition fluxes into the surface waters of the (sub-) tropical North Atlantic Ocean of atmospheric organic matter; namely leachable organic carbon (LOC), leachable organic nitrogen (LON), leachable free amino acids (LFAA) and leachable hydrolysable amino acids (LHAA). DOC, LOC, total dissolved nitrogen (TDN) and leachable total nitrogen (LTN) were determined using a high temperature combustion technique (HTC). DON values were defined as the difference between TDN and dissolved inorganic nitrogen (DIN). LON values were derived as the difference between LTN and leachable inorganic nitrogen (LIN). DFAA, LFAA, DHAA and LHAA were analysed using the method optimized in this study. The determination was performed using reversed-phase high performance liquid chromatography (RP-HPLC) combined with AQC pre-column derivatisation. Hydrolysis was conducted using vapour phase hydrolysis for 24 hours at a temperature of 110-115 ºC. In general, DOC concentrations were high in surface waters of the (sub-) tropical North Atlantic Ocean and declined toward the thermocline, whereas DON exhibited non-typical vertical profiles, with the concentrations increasing with depth, in the tropical North Atlantic Ocean. Mean surface water DOC and DON concentrations ranged from 67.2 ?M to 72.3 ?M and 4.6 ?M to 8.1 ?M, respectively. Enhanced DON values in sub-surface waters were ...