Contribution of sources and sinks to the photochemistry of the present and past atmosphere of West Antarctica based on air, snow and ice-core records

• Main Author: Masclin, Sylvain
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: eScholarship, University of California 2014
• Subjects: Environmental science; Antarctica; Atmosphere; Ice core; Photochemistry; Snow; Antarctic; West Antarctica; Antarc*; ice core
• Online Access: http://www.escholarship.org/uc/item/3cp6q8q4; http://n2t.net/ark:/13030/m5qn7mz3

A framework is presented for defining the present atmospheric chemistry of West Antarctica and the photochemistry of the atmosphere during the early- to mid-Holocene transition (9,000-6,000 yr BP). Little is known on the contributions of local and regional sources to the photochemical composition of the current atmosphere of West Antarctica and the early- to mid-Holocene atmosphere. Measurements over the West Antarctic continent were scarce in regards of exploring its present photochemical composition, while the contribution of the atmospheric oxidative capacity, namely OH radicals, to the methane decline over the early- to mid-Holocene has been assumed negligible. In this study, investigation of the present atmospheric chemistry was run during Antarctic summer at the WAIS Divide site, through multi-week continuous measurements of photochemical active species: atmospheric NO, O 3 , H 2 O 2 , MHP, and snow NO 3 - , NO 2 - and H 2 O 2 . Then, estimation of the mixing ratios of past atmospheric oxidants from ice-core records was made possible from the latest findings on air-ice partition equilibrium of reversibly deposited species, HCHO and H 2 O 2 . Results from the West Antarctic campaign show that the levels of short-lived species above this region, such as NO X , are driven by local sources, mainly snowpack emissions, whereas regional air mass transport controls the atmospheric concentrations of species with longer lifetime, such as O 3 . Atmospheric estimates from the early- to mid-Holocene reveal that both methane sources and sink (low-latitude emissions and oxidation with OH) contributed to the CH 4 budget between 12,000-9,000 yr BP, whereas only the sources drove the decline of CH 4 between 9,000-6,000 yr BP.