of Brüning et al. (2010) documented that the asphalt is
subject to sequential alteration. While fresh asphalt was
gooey, older asphalt appeared fragmented and brittle.
Highly altered asphalt was often colonized by further chemosynthetic fauna like mytilid clams and others. The
change in the consistency of the asphalts goes along with
a change in the geochemical composition and microbial
signatures (Schubotz et al., 2011). Besides the unusual
asphalt formation, the putative “volcanic structure” is
representing a very interesting seepage area which
extended our knowledge about the broad spectrum of seafloor venting phenomena.
Beside the Gulf of Mexico, asphalt volcanoes are
known from the Santa Barbara Basin, California, in much
shallower water depths close to the coast. Seven of those
morphological structures were described as extinct asphalt
volcanoes by Valentine et al. (2010). Radiocarbon dating
of carbonate layers intercalated with the asphalt deposits
indicated formation of two of the volcanoes between
44 and 31 kyr ago. Based on quantitative assumptions
and the geochemistry of samples taken from the volcanoes, the authors estimated the amount of oil and accompanied methane gas, which are emitted at the sites where
the residues of the hydrocarbon seepage (i.e., the asphalt)
currently are deposited. Since the amount of greenhouse
gas (in this case methane) emissions is not known during
former times, the study is of great value to reveal estimates
of former seepage rates.
Bibliography
Brüning, M., Sahling, H., MacDonald, I. R., Ding, F., and
Bohrmann, G., 2010. Origin, distribution, and alteration of
asphalts at the Chapopote Knoll, Southern Gulf of Mexico.
Marine and Petroleum Geology, 27(5), 1093–1106,
doi:10.1016/j.marpetgeo.2009.09.005.
Hovland, M., MacDonald, I. R., Rueslatten, H., Johnsen, H. K.,
Naehr, T., and Bohrmann, G., 2005. Chapopote asphalt volcano
may have been generated by supercritical water. EOS, Transactions, 86(42), 397–402, doi:10.1029/2005EO420002.
MacDonald, I. R., Bohrmann, G., Escobar, E., Abegg, F., Blanchon, P.,
Blinova, V. N., Brueckmann, W., Drews, M., Eisenhauer, A., Han,
X., Heeschen, K. U., Meier, F., Mortera, C., Naehr, T., Orcutt, B.,
Bernard, B., Brooks, J., and de Farágo, M., 2004. Asphalt volcanism and chemosynthetic life, Campeche Knolls, Gulf of Mexico.
Science, 304(5673), 999–1002, doi:10.1126/science.1097154.
Schubotz, F., Lipp, J. S., Elvert, M., Kasten, S., Mollar, X. P., Zabel,
M., Bohrmann, G., and Hinrichs, K. U., 2011. Geochimica et
Cosmochimica Acta, 75(16), 4377–4398, doi:10.1016/j.
gca.2011.05.025.
Valentine, D. L., Reddy, C. M., Farwell, C., Hill, T. M., Pizzarro, O.,
Yoerger, D. R., Camilli, R., Nelson, R. K., Peacock, E. E.,
Bagby, S. C., Clarke, B. A., Roman, C. N., and Soloway, M.,
2010. Asphalt volcanoes as a potential source of methane to late
Pleistocene coastal waters. Nature Geosciences, 3, 345–348,
doi:10.1038/NGEO848.
Cross-references
Cold Seeps
Marine Gas Hydrates
Mud Volcano
ASTRONOMICAL FREQUENCIES IN
PALEOCLIMATES
André Berger
Georges Lemaître Center for Earth and Climate Research,
Catholic University of Louvain, Louvain-la-Neuve,
Belgium
Definition
The long-term variations of climate display periods characteristic of three astronomical parameters which are the
eccentricity (which fixes the shape of the Earth’s orbit),
obliquity (the tilt of the equatorial plane on the plane of
the Earth’s orbit around the Sun), and climatic precession
(a measure of the distance from the Earth to the Sun at the
summer solstice). Their main periods of variations are
400 and 100 kyr for eccentricity, 41 kyr for obliquity,
and 23 and 19 kyr for precession.
Introduction
As in the astronomical theory of paleoclimates the glacialinterglacial cycles are of primary interest, this entry
focuses on the long-term variations of the astronomical
parameters which are involved in the calculation of the
energy received by the Earth from the Sun (here called
incoming solar radiation or insolation) at time scales of
tens to hundreds of thousands of years.
These are the eccentricity, e, obliquity, e, and
climatic precession, e sin e
o , e
o being the longitude of
the perihelion.
The full spectral characteristics of these astronomical
elements and the resulting insolation changes date back
only to the 1970s. Although the precessional period of
21,000 years was well known since Adhémar (1842) at
least, Milankovitch and his contemporaries did not seem
to be much interested in these astronomical periods
(Berger, 2012). Milankovitch (1920), like Emiliani
(1955) 35 years later, estimated only their mean values
by counting the number of peaks from the curves that
Milankovitch calculated numerically, leading to about
92,000, 40,000, and 21,000 years for e, e, and e sin e
o ,
respectively. These periods were confirmed 20 years later
when Berger (1973) completed his calculation of the longterm variations of precession, obliquity, and eccentricity.
Besides its high accuracy over the Quaternary, the Berger
calculation provided, for the first time, a full list as well as
the origin of the periods characterizing the theoretical
expansion of e (with periods of 413,000, 95,000,
123,000, 99,000, 131,000, and 2,305,000 years in
decreasing order of the term’s amplitudes), of e (with
periods of 41,000, 53,600, and 29,700 years), and of
e sin e
o (with periods of 23,700, 22,400, 18,900, and
19,200 years) (see Berger, 1978, and for a slightly
improved solution Berger and Loutre, 1991). Among
these periods, those around 400,000, 2,300,000, and
54,000 and mainly of around 23,000 and 19,000 years
ASTRONOMICAL FREQUENCIES IN PALEOCLIMATES
25
subject to sequential alteration. While fresh asphalt was
gooey, older asphalt appeared fragmented and brittle.
Highly altered asphalt was often colonized by further chemosynthetic fauna like mytilid clams and others. The
change in the consistency of the asphalts goes along with
a change in the geochemical composition and microbial
signatures (Schubotz et al., 2011). Besides the unusual
asphalt formation, the putative “volcanic structure” is
representing a very interesting seepage area which
extended our knowledge about the broad spectrum of seafloor venting phenomena.
Beside the Gulf of Mexico, asphalt volcanoes are
known from the Santa Barbara Basin, California, in much
shallower water depths close to the coast. Seven of those
morphological structures were described as extinct asphalt
volcanoes by Valentine et al. (2010). Radiocarbon dating
of carbonate layers intercalated with the asphalt deposits
indicated formation of two of the volcanoes between
44 and 31 kyr ago. Based on quantitative assumptions
and the geochemistry of samples taken from the volcanoes, the authors estimated the amount of oil and accompanied methane gas, which are emitted at the sites where
the residues of the hydrocarbon seepage (i.e., the asphalt)
currently are deposited. Since the amount of greenhouse
gas (in this case methane) emissions is not known during
former times, the study is of great value to reveal estimates
of former seepage rates.
Bibliography
Brüning, M., Sahling, H., MacDonald, I. R., Ding, F., and
Bohrmann, G., 2010. Origin, distribution, and alteration of
asphalts at the Chapopote Knoll, Southern Gulf of Mexico.
Marine and Petroleum Geology, 27(5), 1093–1106,
doi:10.1016/j.marpetgeo.2009.09.005.
Hovland, M., MacDonald, I. R., Rueslatten, H., Johnsen, H. K.,
Naehr, T., and Bohrmann, G., 2005. Chapopote asphalt volcano
may have been generated by supercritical water. EOS, Transactions, 86(42), 397–402, doi:10.1029/2005EO420002.
MacDonald, I. R., Bohrmann, G., Escobar, E., Abegg, F., Blanchon, P.,
Blinova, V. N., Brueckmann, W., Drews, M., Eisenhauer, A., Han,
X., Heeschen, K. U., Meier, F., Mortera, C., Naehr, T., Orcutt, B.,
Bernard, B., Brooks, J., and de Farágo, M., 2004. Asphalt volcanism and chemosynthetic life, Campeche Knolls, Gulf of Mexico.
Science, 304(5673), 999–1002, doi:10.1126/science.1097154.
Schubotz, F., Lipp, J. S., Elvert, M., Kasten, S., Mollar, X. P., Zabel,
M., Bohrmann, G., and Hinrichs, K. U., 2011. Geochimica et
Cosmochimica Acta, 75(16), 4377–4398, doi:10.1016/j.
gca.2011.05.025.
Valentine, D. L., Reddy, C. M., Farwell, C., Hill, T. M., Pizzarro, O.,
Yoerger, D. R., Camilli, R., Nelson, R. K., Peacock, E. E.,
Bagby, S. C., Clarke, B. A., Roman, C. N., and Soloway, M.,
2010. Asphalt volcanoes as a potential source of methane to late
Pleistocene coastal waters. Nature Geosciences, 3, 345–348,
doi:10.1038/NGEO848.
Cross-references
Cold Seeps
Marine Gas Hydrates
Mud Volcano
ASTRONOMICAL FREQUENCIES IN
PALEOCLIMATES
André Berger
Georges Lemaître Center for Earth and Climate Research,
Catholic University of Louvain, Louvain-la-Neuve,
Belgium
Definition
The long-term variations of climate display periods characteristic of three astronomical parameters which are the
eccentricity (which fixes the shape of the Earth’s orbit),
obliquity (the tilt of the equatorial plane on the plane of
the Earth’s orbit around the Sun), and climatic precession
(a measure of the distance from the Earth to the Sun at the
summer solstice). Their main periods of variations are
400 and 100 kyr for eccentricity, 41 kyr for obliquity,
and 23 and 19 kyr for precession.
Introduction
As in the astronomical theory of paleoclimates the glacialinterglacial cycles are of primary interest, this entry
focuses on the long-term variations of the astronomical
parameters which are involved in the calculation of the
energy received by the Earth from the Sun (here called
incoming solar radiation or insolation) at time scales of
tens to hundreds of thousands of years.
These are the eccentricity, e, obliquity, e, and
climatic precession, e sin e
o , e
o being the longitude of
the perihelion.
The full spectral characteristics of these astronomical
elements and the resulting insolation changes date back
only to the 1970s. Although the precessional period of
21,000 years was well known since Adhémar (1842) at
least, Milankovitch and his contemporaries did not seem
to be much interested in these astronomical periods
(Berger, 2012). Milankovitch (1920), like Emiliani
(1955) 35 years later, estimated only their mean values
by counting the number of peaks from the curves that
Milankovitch calculated numerically, leading to about
92,000, 40,000, and 21,000 years for e, e, and e sin e
o ,
respectively. These periods were confirmed 20 years later
when Berger (1973) completed his calculation of the longterm variations of precession, obliquity, and eccentricity.
Besides its high accuracy over the Quaternary, the Berger
calculation provided, for the first time, a full list as well as
the origin of the periods characterizing the theoretical
expansion of e (with periods of 413,000, 95,000,
123,000, 99,000, 131,000, and 2,305,000 years in
decreasing order of the term’s amplitudes), of e (with
periods of 41,000, 53,600, and 29,700 years), and of
e sin e
o (with periods of 23,700, 22,400, 18,900, and
19,200 years) (see Berger, 1978, and for a slightly
improved solution Berger and Loutre, 1991). Among
these periods, those around 400,000, 2,300,000, and
54,000 and mainly of around 23,000 and 19,000 years
ASTRONOMICAL FREQUENCIES IN PALEOCLIMATES
25