Shipboard Scientific Party. 1999. Leg 179 Summary. In Pettigrew,
T. L., Casey, J. F., and Miller, D. J. (eds.), Proceeding of ODP,
Initial Reports. College Station: Ocean Drilling Program,
Vol. 179, pp. 1–26.
Singh, S. C., Kent, G. M., Collier, J. S., Harding, A. J., and Orcutt,
J. A., 1998. Melt to mush variations in crustal magma properties
along the ridge crest at the southern East Pacific Rise. Nature,
394, 874–878.
Singh, S. C., Collier, J. S., Kent, G. M., Harding, A. J., and Orcutt,
J. A., 1999. Seismic evidence for a hydrothermal layer above the
solid roof of axial magma chamber at the southern East Pacific
Rise. Geology, 27, 219–222.
Singh, S. C., Harding, A., Kent, G., Sinha, M. C., Combier, V.,
Hobbs, R., Barton, P., White, R., Tong, V., Pye, J., and Orcutt,
J. A., 2006a. Seismic reflection images of Moho underlying melt
sills at the East Pacific Rise. Nature, 442, 287–290.
Singh, S. C., Crawford, W., Carton, H., Seher, T., Combier, V.,
Cannat, M., Canales, J., Dusunur, D., Escartin, J., and Miranda,
M., 2006b. Discovery of a magma chamber and faults beneath a
hydrothermal field at the Mid-Atlantic Ridge. Nature, 442,
1029–1033.
Sinha, M. C., Navin, D., MacGregor, L., et al., 1997. Evidence for
accumulated melt beneath the slow spreading Mid-Atlantic
Ridge. Philosophical Transactions of the Royal Society A, 355,
233–253.
Sleep, N. H., and Rosendhal, B. R., 1979. Topography and tectonics
of Mid-Oceanic Ridge axes. Journal of Geophysical Research,
84(B12), 6831–6839.
Taylor, B., Zellmer, K., Martinnez, F., and Goodliffe, A., 1996. Seafloor spreading in the Lau backarc basin. Earth and Planetary
Science Letters, 144, 35–40.
Tolstoy, M., et al., 2008. Seismic identification of along-axis
hydrothermal flow on the East Pacific Rise. Nature, 451,
181–185.
Toomey, D. R., Jousselin, D., Dunn, R., Wilcock, W., and Detrick,
R., 2007. Skew of mantle upwelling beneath the East Pacific
Rise governs segmentation. Nature, 446, 409–414.
Toomey, D. R., Wilcock, W., Solomon, S and Orcutt, J.A., 1998.
Mantle seismic structure beneath the MELT region of the East
Pacific Rise from P and S wave tomography. Science, 280,
1224–1227.
Tucholke, B. E., Lin, J., and Kleinrock, M. C., 1998. Megamullions
and mullions structure defining oceanic metamorphic core complexes on the Mid-Atlantic Ridge. Journal of Geophysical
Research, 103, 9857–9866.
Tucholke, B. E., Behn, M. D., Buck, W. R., and Lin, J., 2008. Role
of melt supply in oceanic detachment faulting and formation of
megamullions. Geology, 36, 455–458.
Turner, I. M., Peirce, C., and Sinha, M. C., 1999. Seismic imaging
of the axial region of the Valu Fa Ridge, Lau Basin – the accretionary process of an intermediate back-arc spreading ridge.
Geophysical Journal International, 138, 495–519.
Wanless, V. D., Behn, M. D., Shaw, A. M., and Plank, T., 2014. Variations in melting dynamics and mantle compositions along the
Eastern Volcanic Zone of the Gakkel Ridge: insights from
olivine-hosted melt inclusions. Contributions to Mineralogy
and Petrology, 167, 1005.
Cross-references
Crustal Accretion
Layering of Oceanic Crust
Marginal Seas
Oceanic Rifts
Ophiolites
Plate Tectonics
OIL SPILL
Erich Gundlach
E-Tech International Inc., Boulder, CO, USA
Definition
An oil spill is the accidental release of liquid hydrocarbons
to the environment as crude oil or a petroleum product.
Introduction
Experts in coastal geosciences play a key role in understanding the processes affecting a spill, measures appropriate to remove spilled oil, and, importantly, when to
end cleanup activities and let nature continue the cleansing
process. The major processes affecting oil on sedimentary
shorelines are illustrated in Figure 1.
Oil composition and weathering
The spilled oil’s composition and subsequent changes
over time (weathering) greatly influence the interaction
of oil in coastal environments. Oil is composed of a complex mixture of straight-chained and ringed/cyclic hydrocarbon compounds, with small amounts of N, S, O, and
trace metals, depending on the source reservoir and petroleum processing (cracking). Spilled oil is commonly categorized into broad categories. Light oils have a low
specific gravity (SG < 0.8) and low viscosity
(0.5–2.0 cSt) and include gasoline/petrol, naphtha, and
kerosene. Medium-grade oils are mostly crude oils and
medium fuel oils (SG 0.80–0.95, 8–275 cSt), while heavy
fuel oils comprise the heavy oil category (SG > 0.95 and
viscosity >1,500 cSt).
Weathering refers to the biochemical processes affecting oil when released to the open environment and
includes spreading, advection, evaporation, emulsification, dissolution, dispersion, photooxidation, sedimentation, and biodegradation (Reed et al., 1999). Of these,
evaporation and emulsification are the primary affecting
processes. Evaporation potentially reduces the quantity
of remaining oil up to 40 % for light oils, whereas the generation of emulsified oil (a water-in-oil mixture commonly
called “mousse”) potentially doubles the amount of oily
material. As oil weathers, viscosity, density, and adhesion
(stickiness) to sediments and rock surfaces all increase.
Biodegradation is a long-term process slowly reducing
the amount of remaining oil. These major processes have
been summarized for the Amoco Cadiz (Gundlach et al.,
1983), Exxon Valdez (Wolfe et al., 1994), and Deepwater
Horizon (FISG, 2010) oil spills.
Applying geosciences to oil spills
The impetus to understand the dynamic processes of
spilled oil in coastal environments began in the 1970s as
a result of an increasingly strong environmental movement, several major oil spills (e.g., Torrey Canyon,
1967; Santa Barbara, 1969), and offshore oil and gas
OIL SPILL
587
T. L., Casey, J. F., and Miller, D. J. (eds.), Proceeding of ODP,
Initial Reports. College Station: Ocean Drilling Program,
Vol. 179, pp. 1–26.
Singh, S. C., Kent, G. M., Collier, J. S., Harding, A. J., and Orcutt,
J. A., 1998. Melt to mush variations in crustal magma properties
along the ridge crest at the southern East Pacific Rise. Nature,
394, 874–878.
Singh, S. C., Collier, J. S., Kent, G. M., Harding, A. J., and Orcutt,
J. A., 1999. Seismic evidence for a hydrothermal layer above the
solid roof of axial magma chamber at the southern East Pacific
Rise. Geology, 27, 219–222.
Singh, S. C., Harding, A., Kent, G., Sinha, M. C., Combier, V.,
Hobbs, R., Barton, P., White, R., Tong, V., Pye, J., and Orcutt,
J. A., 2006a. Seismic reflection images of Moho underlying melt
sills at the East Pacific Rise. Nature, 442, 287–290.
Singh, S. C., Crawford, W., Carton, H., Seher, T., Combier, V.,
Cannat, M., Canales, J., Dusunur, D., Escartin, J., and Miranda,
M., 2006b. Discovery of a magma chamber and faults beneath a
hydrothermal field at the Mid-Atlantic Ridge. Nature, 442,
1029–1033.
Sinha, M. C., Navin, D., MacGregor, L., et al., 1997. Evidence for
accumulated melt beneath the slow spreading Mid-Atlantic
Ridge. Philosophical Transactions of the Royal Society A, 355,
233–253.
Sleep, N. H., and Rosendhal, B. R., 1979. Topography and tectonics
of Mid-Oceanic Ridge axes. Journal of Geophysical Research,
84(B12), 6831–6839.
Taylor, B., Zellmer, K., Martinnez, F., and Goodliffe, A., 1996. Seafloor spreading in the Lau backarc basin. Earth and Planetary
Science Letters, 144, 35–40.
Tolstoy, M., et al., 2008. Seismic identification of along-axis
hydrothermal flow on the East Pacific Rise. Nature, 451,
181–185.
Toomey, D. R., Jousselin, D., Dunn, R., Wilcock, W., and Detrick,
R., 2007. Skew of mantle upwelling beneath the East Pacific
Rise governs segmentation. Nature, 446, 409–414.
Toomey, D. R., Wilcock, W., Solomon, S and Orcutt, J.A., 1998.
Mantle seismic structure beneath the MELT region of the East
Pacific Rise from P and S wave tomography. Science, 280,
1224–1227.
Tucholke, B. E., Lin, J., and Kleinrock, M. C., 1998. Megamullions
and mullions structure defining oceanic metamorphic core complexes on the Mid-Atlantic Ridge. Journal of Geophysical
Research, 103, 9857–9866.
Tucholke, B. E., Behn, M. D., Buck, W. R., and Lin, J., 2008. Role
of melt supply in oceanic detachment faulting and formation of
megamullions. Geology, 36, 455–458.
Turner, I. M., Peirce, C., and Sinha, M. C., 1999. Seismic imaging
of the axial region of the Valu Fa Ridge, Lau Basin – the accretionary process of an intermediate back-arc spreading ridge.
Geophysical Journal International, 138, 495–519.
Wanless, V. D., Behn, M. D., Shaw, A. M., and Plank, T., 2014. Variations in melting dynamics and mantle compositions along the
Eastern Volcanic Zone of the Gakkel Ridge: insights from
olivine-hosted melt inclusions. Contributions to Mineralogy
and Petrology, 167, 1005.
Cross-references
Crustal Accretion
Layering of Oceanic Crust
Marginal Seas
Oceanic Rifts
Ophiolites
Plate Tectonics
OIL SPILL
Erich Gundlach
E-Tech International Inc., Boulder, CO, USA
Definition
An oil spill is the accidental release of liquid hydrocarbons
to the environment as crude oil or a petroleum product.
Introduction
Experts in coastal geosciences play a key role in understanding the processes affecting a spill, measures appropriate to remove spilled oil, and, importantly, when to
end cleanup activities and let nature continue the cleansing
process. The major processes affecting oil on sedimentary
shorelines are illustrated in Figure 1.
Oil composition and weathering
The spilled oil’s composition and subsequent changes
over time (weathering) greatly influence the interaction
of oil in coastal environments. Oil is composed of a complex mixture of straight-chained and ringed/cyclic hydrocarbon compounds, with small amounts of N, S, O, and
trace metals, depending on the source reservoir and petroleum processing (cracking). Spilled oil is commonly categorized into broad categories. Light oils have a low
specific gravity (SG < 0.8) and low viscosity
(0.5–2.0 cSt) and include gasoline/petrol, naphtha, and
kerosene. Medium-grade oils are mostly crude oils and
medium fuel oils (SG 0.80–0.95, 8–275 cSt), while heavy
fuel oils comprise the heavy oil category (SG > 0.95 and
viscosity >1,500 cSt).
Weathering refers to the biochemical processes affecting oil when released to the open environment and
includes spreading, advection, evaporation, emulsification, dissolution, dispersion, photooxidation, sedimentation, and biodegradation (Reed et al., 1999). Of these,
evaporation and emulsification are the primary affecting
processes. Evaporation potentially reduces the quantity
of remaining oil up to 40 % for light oils, whereas the generation of emulsified oil (a water-in-oil mixture commonly
called “mousse”) potentially doubles the amount of oily
material. As oil weathers, viscosity, density, and adhesion
(stickiness) to sediments and rock surfaces all increase.
Biodegradation is a long-term process slowly reducing
the amount of remaining oil. These major processes have
been summarized for the Amoco Cadiz (Gundlach et al.,
1983), Exxon Valdez (Wolfe et al., 1994), and Deepwater
Horizon (FISG, 2010) oil spills.
Applying geosciences to oil spills
The impetus to understand the dynamic processes of
spilled oil in coastal environments began in the 1970s as
a result of an increasingly strong environmental movement, several major oil spills (e.g., Torrey Canyon,
1967; Santa Barbara, 1969), and offshore oil and gas
OIL SPILL
587