Gas exchange system for extended in situ benthic chamber flux measurements under controlled oxygen conditions: First application—Sea bed methane emission measurements at Captain Arutyunov mud volcano

Abstract

Mass transfer rates of many gases, nutrients, and trace metals across the sediment water interface are dependent on environmental oxygen conditions. In this article, a novel gas exchange system for extended in situ flux and respiration measurements in benthic chambers under defined oxygen conditions is described. Integrated within a GEOMAR modular lander, the gas exchange system was used to perform in situ measurements of the total oxygen uptake and sea bed methane emission rates under constant oxygen conditions at Captain Arutyunov mud volcano (Gulf of Cadiz) in a water depth of 1320 m. During two separate lander deployments, the oxygen concentration within the benthic chambers was kept constant for 37 and 47 h, respectively. Under these conditions total oxygen uptake rate remained constant at 4.4 and 13.2 mmol m -2 d -1 . Seabed methane emission was low, in the range 0 to 0.2 mmol m -2 d -1. The system is suited for prolonged (days) in situ flux determinations under natural background oxygen conditions and offers a wide range of experimental applications.

Precise continuous measurements of pelagic respiration in coastal waters with Oxygen Optodes

“…comm.). In other systems with Optodes, such as bottomlanders, neither Drazen et al (2005) nor Sommer et al (2008) reported any significant Optode drift over more than 9 h. Signs of system drift of other sensors during the first 10 h can, however, be seen in control samples, although drift rates were not estimated or discussed by the authors (Griffith 1988;Briand et al 2004). …”

“…The same system was used to estimate copepod respiration in small glass vessels (Koster et al 2008). Drazen et al (2005) presented a novel technique with an Optode to measure respiration rates of deep sea fish, and Sommer et al (2008) described an automatic system to regulate oxygen levels and measure sedimentwater fluxes during in situ sediment incubation at vent sites. Additionally, Pakhomova et al (2007), Almroth et al (2009), and Almroth-Rosell et al (2012) used the same type of Optodes with autonomous landers to perform sediment-water incubation studies.…”

Seabed methane emissions and the habitat of frenulate tubeworms on the Captain Arutyunov mud volcano (Gulf of Cadiz)

“…In situ flux measurements were conducted using the Biogeochemical Observatory (BIGO) and the Fluid Flux Observatory (FLUFO) as described in detail by Sommer et al (2006) and Sommer et al (2008). Each observatory contained 2 circular chambers (internal ∅ 28.8 cm; area 651.4 cm 2 ), herein referred to as EX and CO in BIGO, and FLUX and BU in FLUFO.…”

“…The EX chamber was equipped with a gas exchange system to keep the oxygen concentration constant. The technical design of this gas exchange device and results of second and third deployments of EX (BIGO 2EX and BIGO 3EX) have been described by Sommer et al (2008). The CO chamber was flushed with ambient seawater at the beginning of the incubation and subsequently at different time intervals (cf.…”

“…All methane emission measurements were conducted under oxic conditions. The oxygen concentration in all chambers did not fall below 102 µM (the value from the first CO deployment, BIGO 1CO), the bottom water oxygen concentration varied between 222 to 231 µM (Sommer et al 2008). After the in situ measurements, the incubated sediments were retrieved for onboard pore water analyses.…”