Rubidium-strontium date of possibly 3 billion years for a granitic rock from antarctica

A single total rock sample of biotite granite from Jule Peaks, Antarctica, has been dated by the rubidium-strontium method at about 3 billion years. The juxtaposition of this sector of Antarctica with Africa in the Dietz and Sproll continental drift reconstruction results in a possible geochronologic fit of the Princess Martha Coast of Antarctica with a covered possible notheastern extension of the African Swaziland Shield, which contains granitic rocks that are also 3 billion years old.     

Extensive 200-million-year-Old continental flood basalts of the central atlantic magmatic province

The Central Atlantic Magmatic Province (CAMP) is defined by tholeiitic basalts that crop out in once-contiguous parts of North America, Europe, Africa, and South America and is associated with the breakup of Pangea. 40Ar/39Ar and paleomagnetic data indicate that CAMP magmatism extended over an area of 2.5 million square kilometers in north and central Brazil, and the total aerial extent of the magmatism exceeded 7 million square kilometers in a few million years, with peak activity at 200 million years ago. The magmatism coincided closely in time with a major mass extinction at the Triassic-Jurassic boundary.     

Aeromagnetic and radio echo ice-sounding measurements show much greater area of the dufek intrusion, antarctica

A combined aeromagnetic and radio echo ice-sounding survey made in 1978 in Antarctica over the Dufek layered mafic intrusion suggests a minimum area of the intrusion of about 50,000 square kilometers, making it comparable in size with the Bushveld Complex of Africa. Comparisons of the magnetic and subglacial topographic profiles illustrate the usefulness of this combination of methods in studying bedrock geology beneath ice-covered areas. Magnetic anomalies range in peak-to-through amplitude from about 50 nanoteslas over the lowermost exposed portion of the section in the Dufek Massif to about 3600 nanoteslas over the uppermost part of the section in the Forrestal Range. Theoretical magnetic anomalies, computed from a model based on the subice topography fitted to the highest amplitude observed magnetic anomalies, required normal and reversed magnetizations ranging from 10(-3) to 10(-2) electromagnetic units per cubic centimeter. This result is interpreted as indicating that the Dufek intrusion cooled through the Curie isotherm during one or more reversals of the earth's magnetic field.     

Antarctic pack ice: boundaries established from nimbus I pictures

Television and photofacsimile constructed infrared pictures taken by the Nimbus I meteorological satellite between 28 August and 22 September 1964 were analyzed for indications of the pack-ice boundary around Antarctica. Mean ice boundaries were established around the entire continent from both TV and infrared pictures, from which were estimated pack-ice areas of 19.81 by 10(6) and16.78 by 10(6) square kilometers, respectively; the difference is attributed to difference in subjective discernment of a boundary.     

Expansion of industrial logging in Central Africa

Industrial logging has become the most extensive land use in Central Africa, with more than 600,000 square kilometers (30%) of forest currently under concession. With use of a time series of satellite imagery for the period from 1976 to 2003, we measured 51,916 kilometers of new logging roads. The density of roads across the forested region was 0.03 kilometer per square kilometer, but areas of Gabon and Equatorial Guinea had values over 0.09 kilometer per square kilometer. A new frontier of logging expansion was identified within the Democratic Republic of Congo, which contains 63% of the remaining forest of the region. Tree felling and skid trails increased disturbance in selectively logged areas.     

Airborne geophysical study in the pensacola mountains of antarctica

A seismic reflection, gravity, and aeromagnetic reconnaissance was made in the Pensacola Mountains, Antarctica, during the 1965-66 austral summer. Prominent ice streams located between the Neptune and Patuxent Ranges and east of the Forrestal Range overlie channels in the rock surface 2000 meters below sea level which are probably of glacial origin. Seismic reflections show that the Filchner Ice Shelf is 1270 meters thick near its southern margin. Along the boundary between West and East Antarctica, Bouguer anomalies decrease from +60 milligals in West Antarctica to -80 milligals in East Antarctica. An abrupt change in crustal structure across this boundary is required to explainl the 2 milligals per kilometer gradient. This may indicate a fault extending through the crust into the mantle. Aeromagnetic profiles delineate anomalies up to 1800 gamma associated with the basic stratiform intrusion which comprises the Dufek and Forrestal ranges. A probable minimum area of 9500 square kilometers is calculated for the intrusive body on the basis of the magnetic anomalies, making it one of the largest bodies of its type. The extension of this magnetic anominaly across a fault forming the north border of the Pensacola Mountains probably precludes transcurrent movement.     

Singing icebergs

Sustained harmonic tremor signals were recorded by the seismographs of the German Neumayer Base seismological network in western Dronning Maud Land, Antarctica. These tremor episodes, lasting up to 16 hours, were recorded up to 820 kilometers from the source. Their spectra show narrow peaks with fundamental frequencies ranging from 0.5 to 6 hertz, more than 30 integer harmonic overtones, and frequency gliding, resembling volcanic tremor. Frequency-wave number analysis suggested a moving source, which was recognized as iceberg B-09A traveling along the coast of eastern Antarctica. The most probable tremor sources are fluid-flow-induced vibrations inside the iceberg's tunnel/crevasse systems.     

Sharp sides to the African superplume

Beneath southern Africa is a large structure about 1200 kilometers across and extending obliquely 1500 kilometers upward from the core-mantle boundary with a shear velocity reduction of about 3%. Using a fortuitous set of SKS phases that travel along its eastern side, we show that the boundary of the anomaly appears to be sharp, with a width less than 50 kilometers, and is tilted outward from its center. Dynamic models that fit the seismic constraints have a dense chemical layer within an upwardly flowing thermal structure. The tilt suggests that the layer is dynamically unstable on geological time scales.     

Ice flow of the Antarctic ice sheet

We present a reference, comprehensive, high-resolution, digital mosaic of ice motion in Antarctica assembled from multiple satellite interferometric synthetic-aperture radar data acquired during the International Polar Year 2007 to 2009. The data reveal widespread, patterned, enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent. This view of ice sheet motion emphasizes the importance of basal-slip-dominated tributary flow over deformation-dominated ice sheet flow, redefines our understanding of ice sheet dynamics, and has far-reaching implications for the reconstruction and prediction of ice sheet evolution.     

Lateral isotopic discontinuity in the lower crust: an example from antarctica

The lower continental crust is one of the least known variables in the crust-mantle evolutionary equation. In order to study the nature and compositional heterogeneity of the lower crust, more than 20 inclusions of lower crustal granulites in volcanic rocks from the McMurdo Sound region of Antarctica were analyzed for strontium and oxygen isotopes. These inclusions were erupted from volcanic centers covering an area of 12,000 square kilometers. Along with results from analyses of major and trace elements, the isotopic data reveal a profound discontinuity in the composition and probably the age of the lower crust that coincides with the boundary between the Transantarctic Mountains and the Ross Embayment. Although this topographic boundary between East and West Antarctica is largely a Cenozoic development, which apparently reflects a simple subvertical faulting relationship due to crustal rifting, the isotopic differences in the lower crust across the boundary suggest that the current faulting and rifting may coincide with an older crustal suture, the age of which is uncertain.     

Free-drifting icebergs: hot spots of chemical and biological enrichment in the Weddell Sea

The proliferation of icebergs from Antarctica over the past decade has raised questions about their potential impact on the surrounding pelagic ecosystem. Two free-drifting icebergs, 0.1 and 30.8 square kilometers in aerial surface area, and the surrounding waters were sampled in the northwest Weddell Sea during austral spring 2005. There was substantial enrichment of terrigenous material, and there were high concentrations of chlorophyll, krill, and seabirds surrounding each iceberg, extending out to a radial distance of approximately 3.7 kilometers. Extrapolating these results to all icebergs in the same size range, with the use of iceberg population estimates from satellite surveys, indicates that they similarly affect 39% of the surface ocean in this region. These results suggest that free-drifting icebergs can substantially affect the pelagic ecosystem of the Southern Ocean and can serve as areas of enhanced production and sequestration of organic carbon to the deep sea.     

Expansion and contraction of the sahara desert from 1980 to 1990

Data from polar-orbiting meteorological satellites have been used to determine the extent of the Sahara Desert and to document its interannual variation from 1980 to 1990. The Sahara Desert ranged from 8,633,000 square kilometers in 1980 to 9,982,000 square kilometers in 1984. The greatest annual north-south latitudinal movement of the southern Saharan boundary was 110 kilometers from 1984 to 1985 and resulted in a decrease in desert area of 724,000 square kilometers.     

The 1990 to 1991 Sudan earthquake sequence and the extent of the East african rift system

One of the largest earthquakes ever recorded in Africa (surface wave magnitude M(s) = 7.2) occurred about 50 kilometers east of the Upper River Nile on 20 May 1990. Four days later, two more large earthquakes (M(s) = 6.4 and 7.0) occurred about 50 kilometers to the northwest in the Nile Valley. In the following months, a further 60 events were recorded by seismic stations worldwide. The earthquakes are associated with two fault systems: one east of the Nile with azimuth southeast and one along the Nile Valley with azimuth north-northeast. The activity alternated between the two fault systems and indicates that the northern extremity of the western branch of the East African Rift System extends at least 350 kilometers north of Lake Albert.     

The South pole region of the moon as seen by clementine

The Clementine mission has provided the first comprehensive set of high-resolution images of the south pole region of the moon. Within 5 degrees of latitude of the pole, an area of an estimated 30,000 square kilometers remained in shadow during a full lunar rotation and is a promising target for future exploration for ice deposits. The Schr?dinger Basin (320 kilometers in diameter), centered at 75 degrees S, is one of the two youngest, least modified, great multiring impact basins on the moon. A large maar-type volcano localized along a graben within the Schr?dinger Basin probably erupted between 1 and 2 billion years ago.     

Ice Movement of Valley Glaciers Flowing into the Ross Ice Shelf, Antarctica

Seven glaciers from 9 to 26 kilometers in width move 0.3 to 2.3 meters per day. Byrd Glacier is the fastest moving of the known valley glaciers in Antarctica.     

Tropical deforestation and habitat fragmentation in the Amazon: satellite data from 1978 to 1988

Landsat satellite imagery covering the entire forested portion of the Brazilian Amazon Basin was used to measure, for 1978 and 1988, deforestation, fragmented forest, defined as areas less than 100 square kilometers surrounded by deforestation, and edge effects of 1 kilometer into forest from adjacent areas of deforestation. Tropical deforestation increased from 78,000 square kilometers in 1978 to 230,000 square kilometers in 1988 while tropical forest habitat, severely affected with respect to biological diversity, increased from 208,000 to 588,000 square kilometers. Although this rate of deforestation is lower than previous estimates, the effect on biological diversity is greater.     

Fish, crustaceans, and the sea floor under the ross ice shelf

Baited traps and a camera lowered through the Ross Ice Shelf, Antarctica, at a point 475 kilometers from the open Ross Sea and to 597 meters below sea level revealed the presence of fish, many amphipods, and one isopod. Biological or current markings were not evident on a soft bottom littered with subangular lumps. A fish was caught through a crevasse 80 kilometers from the shelf edge.     

Coeval large-scale magmatism in the Kalahari and Laurentian cratons during Rodinia assembly

We show that intraplate magmatism occurred 1106 to 1112 million years ago over an area of two million square kilometers within the Kalahari craton of southern Africa, during the same magnetic polarity chron as voluminous magmatism within the cratonic core of North America. These contemporaneous magmatic events occurred while the Rodinia supercontinent was being assembled and are inferred to be parts of a single large igneous province emplaced across the two cratons. Widespread intraplate magmatism during Rodinia assembly shows that mantle upwellings required to generate such provinces may occur independently of the supercontinent cycle.     

Ice flow direction change in interior West Antarctica

Upstream of Byrd Station (West Antarctica), ice-penetrating radar data reveal a distinctive fold structure within the ice, in which isochronous layers are unusually deep. The fold has an axis more than 50 kilometers long, which is aligned up to 45 degrees to the ice flow direction. Although explanations for the fold's formation under the present flow are problematic, it can be explained if flow was parallel to the fold axis approximately 1500 years ago. This flow change may be associated with ice stream alterations nearer the margin. If this is true, central West Antarctica may respond to future alterations more than previously thought.     

Viscosity of oceanic asthenosphere inferred from remote triggering of earthquakes

A sequence of large interplate earthquakes from 1952 to 1965 along the Aleutian arc and Kurile-Kamchatka trench released accumulated stresses along nearly the entire northern portion of the Pacific Plate boundary. The postseismic stress evolution across the northern Pacific and Arctic basins, calculated from a viscoelastic coupling model with an asthenospheric viscosity of 5 x 10(17) pascal seconds, is consistent with triggering of oceanic intraplate earthquakes, temporal patterns in seismicity at remote plate boundaries, and space-based geodetic measurements of anomalous velocity over an area 7000 by 7000 kilometers square during the 30-year period after the sequence.