Delivery of halogenated very short-lived substances from the West Indian Ocean to the stratosphere during Asian summer monsoon.

Fiehn, Alina, Quack, Birgit, Hepach, Helmke , Fuhlbrügge, Steffen, Tegtmeier, Susann, Toohey, Matthew , Atlas, Elliot and Krüger, Kirstin (2017) Delivery of halogenated very short-lived substances from the West Indian Ocean to the stratosphere during Asian summer monsoon. Open Access Atmospheric Chemistry and Physics, 17 . pp. 6723-6741. DOI 10.5194/acp-17-6723-2017.

[img]
Preview
Text
acp-17-6723-2017.pdf - Published Version
Available under License Creative Commons: Attribution 3.0.

Download (3104Kb) | Preview
[img]
Preview
Text
acp-17-6723-2017-supplement.pdf - Supplemental Material
Available under License Creative Commons: Attribution 3.0.

Download (1515Kb) | Preview

Supplementary data:

Abstract

Halogenated very short-lived substances (VSLSs) are naturally produced in the ocean and emitted to the atmosphere. When transported to the stratosphere, these compounds can have a significant influence on the ozone layer and climate. During a research cruise on RV Sonne in the subtropical and tropical west Indian Ocean in July and August 2014, we measured the VSLSs, methyl iodide (CH3I) and for the first time bromoform (CHBr3) and dibromomethane (CH2Br2), in surface seawater and the marine atmosphere to derive their emission strengths. Using the Lagrangian particle dispersion model FLEXPART with ERA-Interim meteorological fields, we calculated the direct contribution of observed VSLS emissions to the stratospheric halogen burden during the Asian summer monsoon. Furthermore, we compare the in situ calculations with the interannual variability of transport from a larger area of the west Indian Ocean surface to the stratosphere for July 2000–2015. We found that the west Indian Ocean is a strong source for CHBr3 (910 pmol m−2 h−1), very strong source for CH2Br2 (930 pmol m−2 h−1), and an average source for CH3I (460 pmol m−2 h−1). The atmospheric transport from the tropical west Indian Ocean surface to the stratosphere experiences two main pathways. On very short timescales, especially relevant for the shortest-lived compound CH3I (3.5 days lifetime), convection above the Indian Ocean lifts oceanic air masses and VSLSs towards the tropopause. On a longer timescale, the Asian summer monsoon circulation transports oceanic VSLSs towards India and the Bay of Bengal, where they are lifted with the monsoon convection and reach stratospheric levels in the southeastern part of the Asian monsoon anticyclone. This transport pathway is more important for the longer-lived brominated compounds (17 and 150 days lifetime for CHBr3 and CH2Br2). The entrainment of CHBr3 and CH3I from the west Indian Ocean to the stratosphere during the Asian summer monsoon is lower than from previous cruises in the tropical west Pacific Ocean during boreal autumn and early winter but higher than from the tropical Atlantic during boreal summer. In contrast, the projected CH2Br2 entrainment was very high because of the high emissions during the west Indian Ocean cruise. The 16-year July time series shows highest interannual variability for the shortest-lived CH3I and lowest for the longest-lived CH2Br2. During this time period, a small increase in VSLS entrainment from the west Indian Ocean through the Asian monsoon to the stratosphere is found. Overall, this study confirms that the subtropical and tropical west Indian Ocean is an important source region of halogenated VSLSs, especially CH2Br2, to the troposphere and stratosphere during the Asian summer monsoon.

Document Type: Article
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-ME Maritime Meteorology
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.5194/acp-17-6723-2017
ISSN: 1680-7316
Projects: BMBF SONNE, SPACES
Expeditions/Models/Experiments:
Date Deposited: 13 Jan 2017 12:19
Last Modified: 23 May 2019 10:23
URI: http://oceanrep.geomar.de/id/eprint/35653

Actions (login required)

View Item View Item

Document Downloads

More statistics for this item...