Development and deployment of a novel deep-sea in situ bubble sampling instrument for understanding the fate of methane in the water column
Citable URI
https://hdl.handle.net/1912/24607DOI
10.1575/1912/24607Abstract
Methane (CH4) is a potent greenhouse gas that is often found in a solid, hydrate clathrate form in marine sediments along continental margins and will often escape from the seafloor and rise through the water column as bubbles. The estimated marine methane hydrate inventory is over 600 times greater than the current atmospheric concentration so the fate of this ebullitive methane flux is of great interest. Traditional methods of measuring this flux such as acoustic imaging, optical sensors, and modeling suffer from limited information regarding the bubbles’ composition. Studies that attempt to constrain CH4 bubble composition suffer from low spatiotemporal resolution and adaptability. The current study presents the design, development and deployment of a novel, in situ bubble sampling system, the Bubble Delivery System (BDS), to quantify gas chemical composition in the water column. The BDS was deployed at the Cascadia Margin – a region well known for its active CH4 bubble seeps – where 95 samples were collected from McArthur Ridge, Hydrate Ridge, Heceta Deep and Heceta Shallow over the course of seven remotely operated vehicle dives. By combining this approach with the use of an underwater mass spectrometer, in situ analysis of these samples indicated that the bubbles contained between 84.6 to 100% CH4 and exhibited a high level of variability both spatially and temporally. Bubbles emitted from Heceta Deep exhibited anomalously elevated levels of carbon dioxide compared to the other sites.
Description
Submitted in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2019.
Collections
Suggested Citation
Thesis: Johnson, Andrew S., "Development and deployment of a novel deep-sea in situ bubble sampling instrument for understanding the fate of methane in the water column", 2019-09, DOI:10.1575/1912/24607, https://hdl.handle.net/1912/24607Related items
Showing items related by title, author, creator and subject.
-
Seasonal oscillations in a mid-latitude ocean with barriers to deep flow
Firing, Eric (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1978-08)A two-layer linear analytic model is used to study the response of the mid-latitude ocean to the seasonal variation of the windstress. The most important component of the response is a barotropic quasi-steady Sverdrup ... -
Geoacoustic inversion by mode amplitude perturbation
Poole, Travis L. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2007-02)This thesis introduces an algorithm for inverting for the geoacoustic properties of the seafloor in shallow water. The input data required by the algorithm are estimates of the amplitudes of the normal modes excited by ... -
Emulating the fast-start swimming performance of the chain pickerel (Esox niger) using a mechanical fish design
Watts, Matthew Nicholas (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2006-09)Mean maximum start-up accelerations and velocities achieved by the fast-start specialist, northern pike, are reported at 120 ms-2 and 4 ms-1, respectively (Harper and Blake, 1990). In this thesis, a simple mechanical system ...