Methane oxidation in the eastern tropical North Pacific Ocean water column

Pack, Mary A.; Heintz, Monica B.; Reeburgh, William S.; Trumbore, Susan E.; Valentine, David L.; Xu, Xiaomei; Druffel, Ellen R. M.

doi:10.1002/2014JG002900

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Methane oxidation in the eastern tropical North Pacific Ocean water column

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http://dx.doi.org/10.1002/2014JG002900
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Citation

Pack, M. A., Heintz, M. B., Reeburgh, W. S., Trumbore, S. E., Valentine, D. L., Xu, X., et al. (2015). Methane oxidation in the eastern tropical North Pacific Ocean water column. Journal of Geophysical Research: Biogeosciences, 120(6), 1078-1092. doi:10.1002/2014JG002900.

Cite as: https://hdl.handle.net/11858/00-001M-0000-0028-336E-E

Abstract

We report methane (CH4) concentration and methane oxidation (MOx) rate measurements from
the eastern tropical north Pacific (ETNP) water column. This region comprises low-CH4 waters and a depth
interval (~200–760 m) of CH4 supersaturation that is located within a regional oxygen minimum zone (OMZ).
MOx rate measurements were made in parallel using tracer-based methods with low-level 14C-CH4 (LL 14C)
and 3H-CH4 (3H). The two tracers showed similar trends in MOx rate with water depth, but consistent with
previous work, the LL 14C rates (range: 0.034–15 × 103 nmol CH4 L1 d1) were systematically slower than the
parallel 3H rates (range: 0.098–4000 × 103 nmol CH4 L1 d1). Priming and background effects associated
with the 3H-CH4 tracer and LL 14C filtering effects are implicated as the cause of the systematic difference. The
MOx rates reported here include some of the slowest rates measured in the ocean to date, are the first rates for
the ETNP region, and show zones of slow CH4 turnover within the OMZ that may permit CH4 derived from
coastal sediments to travel great lateral distances. The MOx rate constants correlate with both CH4 and
oxygen concentrations, suggesting that their combined availability regulates MOx rates in the region.
Depth-integrated MOx rates provide an upper limit on the magnitude of regional CH4 sources and
demonstrate the importance of water column MOx, even at slow rates, as a sink for CH4 that limits the ocean-atmosphere CH4 flux in the ETNP region.