Blake Ridge

Natural hydrate obtained from the deep sea core at Blake Ridge, off the eastern coast of USA, was irradiated by y-rays at 77K.131 A signal at g =2.0014 was observed in addition to those due to H° and CHj-. Preliminary work indicates the interaction of CH3 with nearby H20 in the clathrate and/or paired... 

Pauli et al. Proc. Ocean Drilling Program, Science Results for Leg 164 (Blake Ridge)... 

Pauli, C.K., Lorenson, T.D., Borowski, W.S., Ussier III, W., Olsen, K., and Rodriguez, N.M., Isotopic composition of CH4, CO2 species, and sedimentary organic matter within samples from the Blake Ridge gas source implications, in Proc. ODP, Sci. Results (Pauli, C.K., Matsumoto, R., Wallace, P.J., and Dillon, W.P. eds.), College Station, TX (Ocean Drilling Program), 164, 67-78 (2000). 

Pauli, C.K., Matsumoto, R., Wallace, P.J., et al., in Proc. Ocean Drilling Program Initial Reports, 164 (1997) Leg 164 (Blake Ridge). 

Table 7.7 contrasts FHF and DLF hydrates. It should be emphasized that both hydrates are end-member types with the frequent occurrence of mixed types. For example, while Table 7.7 typifies Blake Ridge as DLF hydrates and Barkley Canyon as FHF hydrates, there is often a mixture of both types as shown in the Leg 204 study in the Cascadia Margin. As a second example, while the Gulf of Mexico is normally known for FHF hydrate deposits, Hutchinson et al. (2004) provide evidence for some elements that have DLF characteristics. 

Found by BSR and GHOZ zones Usually structure I, biogenic gas hydrates Usually associated with shales, not fauna Represented by Blake Ridge hydrates... 

Dickens G. R. (2001b) Sulfate profiles and barium fronts in sediment on the Blake Ridge present and past methane fluxes through a large gas hydrate reservoir. Geochim. Cosmochim Acta 65, 529-543. 

In a novel approach, Dickens (2001) used sedimentary Ba records to assess temporal changes during the Late Pleistocene in the upward flux of methane within sediments of the Blake Ridge that are rich in sub-surface gas hydrates. Due to a lack of Ba enrichment above the present... 

Fig. 14.6 Seismic record from Blake Ridge (Shipley et al. 1979), showing a distinct reflection, known as bottom simulating reflection (BSR), which indicates the presence of methane hydrate within sediments (right). Below the BSR there are strong reflections caused by free gas in the pores. A seismic velocity model (left) shows the strong contrast of velocity across the BSR.

Blake Ridge was surprisingly heterogeneous and could not be explained in detail, except for the observation of two weakly defined zones where higher hydrate concentrations may indeed be caused by small differences in lithology. 

Egeberg, P.K., and Dickens, G.R., 1999. Thermodynamic and pore water halogen constraints on gas hydrate distribution at ODP Site 997 (Blake Ridge). Chemical Geology, 153 53-79. 

Flemings, R, Liu, C.-S., and Winters, W.J., 2003. Critical pressure and multiphase flow in Blake Ridge gas hydrates. Geology, 31 1057-1060. 

Fig. 3. Interpretive plot of molecular ratios of hydrocarbons vs. of methane in gas hydrate from the Nankai Trough and the Blake Ridge (Matsumoto et al, 2000). Genetic classification is modified from Bernard (1978).

Fig. 5. Gas isotope compositions, gas hydrate saturation and TOC in Site 977, ODP Leg 164, Blake Ridge, (a) Depth-trends of of CH4 and CO2. Data are from Paull et al (2000a,b). (b) Depth-trend of gas hydrate saturation estimated from CP anomalies. Modified from Shipboard Scientific Party (1996). (c) Depth-trend of TOC. Data are from Shipboard Scientific Party (1996).

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