Open AccessShipboard measurements and modeling of the distribution of CH 4 and 13 CH 4 in the western Pacific
Author(s) -
Bromley T.,
Allan W.,
Martin R.,
Mikaloff Fletcher S. E.,
Lowe D. C.,
Struthers H.,
Moss R.
Publication year - 2012
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2011jd016494
Subject(s) - transect , intertropical convergence zone , latitude , pacific decadal oscillation , convergence zone , pacific ocean , climatology , oceanography , mixing ratio , geology , environmental science , atmospheric sciences , meteorology , physics , geodesy , precipitation
We present observations of methane (CH 4 ) mixing ratio and 13 C/ 12 C isotopic ratios in CH 4 ( δ 13 C) data from a collaborative shipboard project using bulk carrier ships sailing between Nelson, New Zealand, and Osaka, Japan, in the western Pacific Ocean. Measurements of the CH 4 mixing ratio and δ 13 C in CH 4 were obtained from large clean‐air samples collected in each 2.5° to 5° of latitude between 30°S and 30°N on eight voyages from 2004 to 2007. The data show large variations in CH 4 mixing ratio in the tropical western Pacific, and data analysis suggests that these large variations are related to the positions and strengths of the South Pacific Convergence Zone and the Intertropical Convergence Zone, with variability in the sources playing a much smaller role. These measurements are compared with results from a modified version of the Unified Model (UMeth) general circulation model along two transects, one similar to the ship transects and another 18.75° to the east. Although UMeth was run to a steady state with the same sources and sinks each year, the gradient structures varied considerably from year to year, supporting our conclusion that variability in transport is a major driver for the observed variations in CH 4 . Simulations forced with an idealized representation of the El Niño‐Southern Oscillation (ENSO) suggest that a large component of the observed variability in latitudinal gradients of CH 4 and its δ 13 C arises from intrinsic variability in the climate system that does not occur on ENSO time scales.