In situ measurements of thermal diffusivity in sediments of the methane-rich zone of Cascadia Margin, NE Pacific Ocean

• Published in: Elementa (Washington, D.C.) Vol. 3
• Main Authors: Homola, Kira, Paul Johnson, H., Hearn, Casey
• Format: Journal Article
• Language: English
• Published: Oakland University of California Press, Journals & Digital Publishing Division 11.02.2015; BioOne
• Subjects: Bottom water; Cascadia Margin; Conduction model; Continental margins; Diffusivity; In situ measurement; Marine sediments; Mathematical models; Methane; Methane hydrates; Numerical models; Remotely operated vehicles; Sediments; Thermal diffusivity; Thermistors; Water depth; Water temperature; Cascadia; Pacific Ocean; INE, Pacific, Cascadia Margin; I, Pacific
• ISSN: 2325-1026; 2325-1026
• DOI: 10.12952/journal.elementa.000039

Abstract Thermal diffusivity (TD) is a measure of the temperature response of a material to external thermal forcing. In this study, TD values for marine sediments were determined in situ at two locations on the Cascadia Margin using an instrumented sediment probe deployed by a remotely operated vehicle. TD measurements in this area of the NE Pacific Ocean are important for characterizing the upslope edge of the methane hydrate stability zone, which is the climate-sensitive boundary of a global-scale carbon reservoir. The probe was deployed on the Cascadia Margin at water depths of 552 and 1049 m for a total of 6 days at each site. The instrumented probe consisted of four thermistors aligned vertically, one sensor exposed to the bottom water and one each at 5, 10, and 15 cm within the sediment. Results from each deployment were analyzed using a thermal conduction model applying a range of TD values to obtain the best fit with the experimental data. TD values corresponding to the lowest standard deviations from the numerical model runs were selected as the best approximations. Overall TDs of Cascadia Margin sediments of 4.33 and 1.15 × 10–7 m2 s–1 were calculated for the two deployments. These values, the first of their kind to be determined from in situ measurements on a methane hydrate-rich continental margin, are expected to be useful in the development of models of bottom-water temperature increases and their implications on a global scale.