Physical control on methanotrophic potential in waters of the Santa Monica Basin, Southern California

Abstract

Methane concentrations and turnover rates were measured throughout the water column at nine stations in the Santa Monica Basin (SMB), at one station in the San Pedro Basin (SPB), and at one station in the Santa Catalina Basin (SCtB) in July 2007 and September 2009. Methane concentrations were elevated throughout the water column, with subsurface (4-15 nmol L 21 ), midwater (7.5-100 nmol L 21 ), and bottom-water (5-242 nmol L 21 ) maxima. The SMB water column was divided into four depth-dependent regimes, based on temperature-salinity relationships and patterns in methane concentration and fractional turnover rate. We propose that distinct physical controls on methane dynamics distinguish these regimes. In the upper water column, methanotrophic activity appears to be controlled by borderland-scale, seasonal fluctuations in circulation. The midwaters represent a transition regime between northern-sourced shallow waters and southern-sourced deep waters, wherein methanotrophic activity decreases with depth to its minimum at 500 m, coinciding with the midwater methane maxima. Below 500 m, methanotrophic activity increases to the sill depth of 737 m, coincident with increasingly restricted circulation of water. Bottom waters are restricted from through-basin circulation. These waters were oxygen depleted, but methane input sustained an active psychrotolerant methanotrophic community and had some of the fastest aerobic methane oxidation rates yet reported in the marine environment.

Vertical distribution of methane oxidation and methanotrophic response to elevated methane concentrations in stratified waters of the Arctic fjord Storfjorden (Svalbard, Norway)

“…However, our rates are 3 orders of magnitude lower compared to the measurements conducted after the Deep Water Horizon accident in the Gulf of Mexico, during which catastrophic amounts of hydrocarbons were released into the water column, triggering a rapid response in MO x activity (Valentine et al, 2010;Kessler et al, 2011). Other MO x rate measurements were conducted in Bristol Bay and the southeast Bering Sea (Griffith et al, 1982), the Cariaco Basin (Ward et al, 1987), Saanich Inlet (Ward, 1989 andWard andKilpatrick, 1990), in Southern California Bight (Ward, 1992;Pack et al, 2011;Heintz et al, 2012;Ward and Kilpatrick, 1993), in the Eel River basin (Valentine et al, 2001), the Gulf of Mexico (Kelley, 2003), and at hydrothermal vents at Juan de Fuca Ridge (de Angelis et al, 1991(de Angelis et al, , 1993). It appears that most of these MO x rates fall into the range between 0.001 and 10 nM day −1 and that MO x activity is elevated in ocean environments with high CH 4 concentrations.…”

“…Range of methane oxidation rates measured at different locations in the ocean water column derived from tracer incubations using 3 H-CH 4 (Reeburgh et al, 1991;Valentine et al, 2001Valentine et al, , 2010Heintz et al, 2012 …”

Environmental factors affecting methane distribution and bacterial methane oxidation in the German Bight (North Sea)

“…It was calculated as the inverse of the ratio (r), corrected for the incubation time (t). Thus, this parameter is independent of the ambient methane concentration, and gives a good measure of the methanotrophic potential (Heintz et al, 2012).…”

Climate relevant trace gases (N2O and CH4) in the Eurasian Basin (Arctic Ocean)

“…In contrast, the low levels of CH 4 found in the Amundsen Basin may be related to CH 4 oxidation through methanotrophic activity. In fact, Heintz et al (2012) showed that methane oxidation rates below 700 m in the Santa Monica Basin were between 0.12 and 1.35 nmol L −1 d −1 . Aerobic CH 4 oxidation is known to be performed by methanotrophic bacteria (MOB), typically belonging to the Gamma-(type I) or Alphaproteobacteria (type II) (Hanson and Hanson, 1996;Murrell, 2010).…”