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Research Interests:

- Fluid mechanics applied to environmental and geological flows
- Multi-phase and variable-density flow and transport in porous media
- Computational fluid dynamics (CFD) and numerical modeling
- Software engineering for scientific computing and applied mathematics
- Deep oceanic and permafrost-associated methane hydrates
- Cold regions hydrology/flows involving water/ice phase change (permafrost)
- Submarine groundwater discharge and geohydrology
- Renewable energy; enhanced geothermal systems; reservoir management

Current Research Projects:

On submarine groundwater discharge as a control on gas hydrate evolution on the circum-Arctic continental margin.
J. M. Frederick (DRI) & B. A. Buffett (UCB)

Numerical modeling of the turbulent transport of heat and salt at the ice-ocean interface at the McMurdo Ice Shelf, Antarctica, to improve our understanding of local basal melt rates and turbulent transport properties.
J. M. Frederick (DRI), Scott Kobs (UNR), and Scott Tyler (UNR)

The effect of submarine groundwater discharge on relict Arctic submarine permafrost and permafrost-associated methane hydrate deposits.
J. M. Frederick (DRI) & B. A. Buffett (UCB)

Past Research Projects:

Taliks in relict Arctic submarine permafrost: Pathways for fluid and gas escape?
J. M. Frederick (UCB) & B. A. Buffett (UCB)

Permafrost-associated methane hydrate deposits exist at shallow depths within the sediments of the Arctic continental shelves. This icy carbon reservoir is thought to be a relict of cold glacial periods, when sea levels are much lower, and shelf sediments are exposed to freezing air temperatures. During interglacials, rising sea levels flood the shelf, bringing dramatic warming to the permafrost and gas hydrate bearing sediments. Degradation of this shallow-water reservoir has the potential to release large quantities of methane gas directly to the atmosphere.
Although relict permafrost-associated gas hydrate deposits likely make up only a small fraction of the global hydrate inventory, they have received a disproportionate amount of attention recently because of their susceptibility to climate change. This study is motivated by several recent field studies which report elevated methane levels in Arctic coastal waters. While these observations may be consistent with methane release as a result of decomposing submarine permafrost and gas hydrates, the source of gas cannot easily be distinguished from other possibilities, including the escape of deep thermogenic gas through permeable pathways such as faults, or microbial activity on thawing organic matter within the shelf sediments.
In this study, we investigate the response of relict Arctic submarine permafrost and permafrost-associated gas hydrate deposits to warming with a two-dimensional, finite-volume model for two-phase flow of pore fluid and methane gas within Arctic shelf sediments. We track the evolution of temperature, salinity, and pressure fields with prescribed boundary conditions, and account for latent heat of water ice and methane hydrate formation during growth/decay of permafrost or methane hydrate. The permeability structure of the sediments is coupled to changes in permafrost. We assess the role of taliks (unfrozen portions of continuous permafrost) as a pathway for methane gas escape and make predictions of gas flux to the water column as a result of relict permafrost-associated gas hydrate dissociation due to natural climate variations.
Model results suggest that taliks could have formed on the (now submerged) Arctic coastal plain beneath rivers 1 km in width or larger. Warming from ocean transgression is accelerated beneath submerged taliks relative to regions with an intact permafrost layer. Warming can destabilize methane hydrate deposits located in close proximity to taliks, causing dissociation and the release of methane gas which can reach the sediment surface by the present-day. However, the dissociation of ubiquitous, high-saturation hydrate deposits are required to match the observed dissolved methane levels. While gas venting through taliks formed by paleoriver channels can reproduce the spatial pattern in the observed methane observations, the size and distributions of the hydrate deposits required suggests an alternative source of methane gas, or an additional driver for gas hydrate destabilization.

Fluid focusing in compacting marine sediments: Implications on the age and spatial extent of the methane source for gas hydrates.
J. M. Frederick (UCB) & B. A. Buffett (UCB)

Pore fluid age is measured using the isotopic ratio of iodine, 129I/127I. The source of iodine in the pore fluids is likely derived from the same organic matter as the methane source for gas hydrates. Therefore, understanding the transport of iodine in marine sediments can help us understand methane hydrate formation mechanisms at large gas hydrate provinces.
Pore fluids in marine sediments are often much older than the host sediments, even when vertical flow due to sediment compaction is taken into account. The age separation between pore fluids and host sediment is not well understood, but implies extensive pore fluid transport and/or a complex transport history. Old pore fluid has been used in previous studies to argue for pervasive upward fluid flow and a deep methane source for hydrate deposits. More complex flows, however, are likely to exist in natural settings. I have developed a two-dimensional numerical model which describes fluid flow and solute transport in marine sediments with anisotropic permeability due to bedding planes or fractured zones. Results from the numerical model show that fluid focusing due to seafloor topography and high-angle, stress-induced fractures can substantially alter pore fluid pathlines relative to a 1D compaction model. Fluid flow and transport beneath topographic features and in close proximity to fractured zones has a significant lateral component to the flow pattern, and the model predicts regions where downward flow reverses direction and returns toward the seafloor. Long pathlines can produce pore fluid that is at least two times older than that expected with a 1D compaction model, and may explain the large age separations that are commonly observed between pore fluid and host sediments at gas hydrate provinces.
We have modeled fluid ages for geometry representative of Blake Ridge (USA), a well-studied gas hydrate province. Our model shows that pore fluid ages beneath regions of topography and within fractured zones can be up to 70 million years old. Results suggest that the source of methane in hydrate deposits such as Blake Ridge may be a mix of new and old sources. However, old sources need not originate at great depths or from isolated formations. Methane within pore fluids can be laterally taped from several kilometers, implying an extensive source region surrounding the deposit. This type of focusing may aid hydrate formation beneath topographic highs.

Topography- and fracture-driven fluid focusing as a control on methane hydrate formation.
J. M. Frederick (UCB) & B. A. Buffett (UCB)

Methane hydrate, a frozen mixture of water ice and methane gas, has been found within ocean sediments along continental margins. Its formation is controlled by many factors, such as local thermodynamic conditions and the availability of methane gas.
Because methane solubility increases with depth in marine sediments, upward flowing, methane-bearing pore fluids are often invoked to explain the occurrence of methane hydrate in marine sediments, because the fluid becomes increasingly saturated with methane during its upward migration. However, one-dimensional compaction models predict downward pore fluid flow relative to the seafloor, which implies the fluid becomes increasingly undersaturated in methane during its downward migration without an additional sources of gas. Pore fluid focusing by sloped bedding planes or fractures has been used to explain the presence of upward fluid flow in several previous conceptual models. Through the development of a two-dimensional numerical model for compaction-driven flow in marine sediments, we quantitatively investigated the feasibility of pore fluid focusing in marine sediments beneath regions of seafloor topography. Model results suggest that upward fluid flow relative to the seafloor can be explained with a sediment compaction model when anisotropic sediment permeability permits preferential flow along sloped bedding layers beneath regions of seafloor topography. Moreover, localized enhanced vertical sediment permeability, due to the presence of high-angle, stress-induced fractures, is a more efficient way of focusing pore fluids and can produce strong upward fluid advection. Model results suggest that pore fluid focusing may explain the preferential accumulation of methane hydrate beneath seafloor topographic highs.

Jennifer M. Frederick, PhD
Division of Hydrologic Sciences
Desert Research Institute, Reno, NV