Research
Glenn Spinelli, Assistant Professor of Geophysics

Marine Hydrogeology
     In ocean crust, fluid flow between the basaltic basement aquifer and the ocean is an important control on heat transport, solute transport, and alteration of the crust. As sediments gradually accumulate on oceanic crust, they change the nature of fluid circulation within the basement aquifer. My interests in marine hydrogeology include fluid and heat circulation patterns in ocean crust, permeability evolution of ocean crust, and fluid and heat flow through seafloor sediments. I have modeled fluid and heat flow in the Nankai Trough subduction zone (southern Japan), the subduction zone offshore Costa Rica, and on the flank of the Juan de Fuca Ridge (offshore British Columbia and Washington).

     As ocean crust subducts, fluid circulation within it is an important control on subduction zone temperature. One of my former M.S. students (Troy Kummer, graduated 2008) studied the evolution of hydrothermal circulation in subducting crust. In this study, we examined some general aspects of fluid and heat circulation in subducting crust -- including, how far into a subduction zone that circulation in the ocean crust aquifer can persist, and the thermal consequences of that circulation. Following on this work, I have been examining fluid and heat circulation in the Nankai Trough subduction zone and I will be examining the potential for fluid circulation in the ocean crust aquifer to affect temperatures in the Cascadia subduction zone.

In fall 2009, I will be offshore Japan on the Chikyu (above) as part of an Integrated Ocean Drilling Program expedition. I will be determining the thermal state of the Nankai Trough subduction zone and examining sediment cementation & deformation.

Sedimentology/sediment physical properties
     Variations in sediment type and porosity can lead to large differences in sediment permeability. My previous sediment oriented studies range from determining sedimentation patterns on the northern California margin from reflection seismic data to laboratory consolidation and permeability testing of sediments from San Francisco Bay, the Juan de Fuca Ridge flank, and the Congo Fan.

     My most recent work in this area examines the thermal, diagenetic, and consolidation history of sediment approaching the Nankai Trough subduction zone off Japan. I am currently working with M.S. student Russell White, examining opal cementation of hemipelagic sediment on the Nankai margin. In the fall of 2009, I plan to sail on an IODP expedition to examine the thermal state of the Nankai Trough subduction zone and cementation/deformation of sediment approaching and entering the subduction zone.

Groundwater-surface water interactions/fluid flow through sediments
     Interactions between groundwater and surface water can affect fluid chemistry and chemical alteration of aquifer material. The groundwater seepage can be a source of fresh water to estuaries, lakes, rivers, and coastal environments; it can also transport nutrients and contaminants from aquifers or bottom sediments to surface waters. In San Francisco Bay, I have examined the potential importance of groundwater seepage transporting dissolved metals from sediments to overlying surface waters.

Above: Collecting and sampling a sediment core from San Francisco Bay to determine groundwater seepage rates. In both pictures, I'm on the left, Geoff Wheat (the geochemist working with us on the project) is on the right.