CANNES, France?? Billionaire philanthropist Bill Gates told G20 leaders Thursday to protect aid budgets, saying cuts would not only hurt the poor but also undermine innovations in areas such as health and farming.
The Microsoft Corp co-founder, who has committed to give the majority of his wealth to charity, is the first businessman to be invited to address G20 leaders, who are gathered at the French resort to discuss pressing global issues.
French President Nicholas Sarkozy asked Gates to report to the G20 on new ways to finance development given deep budget cuts in advanced economies struggling with high public debt.
Gates urged the G20 to show leadership by coming up with a more comprehensive approach to improve the lives of the poor. He said innovations such as new seeds and vaccines had saved billions of lives and proved that if used properly, aid was effective in reducing poverty.
"Leadership from the G20 is critically important, especially in these tough economic times," Gates told G20 leaders.
"The world will not balance its books by cutting back on aid, but it will do irreparable damage to global stability, to the growth of the global economy and to livelihoods of millions of poor people," he added.
U.S. lawmakers are looking to cut more from Washington's aid budgets. Congress has already cut some $8 billion off President Barack Obama's request for the State Department and U.S. foreign aid for last year, and are proposing to slice another $8.6 billion in fiscal 2012.
Gates has proposed taxes on financial transactions, aviation and shipping fuels, and tobacco as ways to raise new development resources and help countries meet aid promises.
Even a small tax of 10 basis points on equities and two basis points on bonds would yield about $48 billion from G20 countries, or $9 billion if only larger European countries adopted the idea, he said.
While none of Gates' tax proposals are likely to be adopted at the Cannes summit, they have generated huge debate especially the thorny issue of taxing financial transactions.
The United States and Britain are opposed to a financial tax, dubbed a "Tobin Tax," because of the burden it places on their banks.
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In new developments in Cannes, EU and development officials said Washington had indicated it would not stand in the way of other countries who wanted to implement such a tax.
Gates also proposed that state-owned wealth funds invest in infrastructure in poor countries. If one percent of sovereign wealth fund assets were invested in an infrastructure fund it could reach $100 billion or more over a decade, he said.
Gates urged the G20 to show leadership on development at a time when developing countries have become major sources of global growth.
He said rising emerging powers such as Brazil, China and India were increasingly working with poorer countries and sharing practical knowledge on ways to reduce poverty.
Gates said advanced economies could help poorer nations raise more revenue by ensuring that oil and mining companies listed on stock exchanges were more transparent about their dealings in developing countries.
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"60 Minutes" commentator Andy Rooney, who passed on Friday, won Emmy Awards for his commentaries?targeting everything from politics to pennies in curmudgeonly three-minute essays.
Andy?Rooney?so dreaded the day he had to end his signature "60 Minutes" commentaries about life's large and small absurdities that he kept going until he was 92 years old.
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Even then, he said he wasn't retiring. Writers never retire. But his life after the end of "A Few Minutes With Andy?Rooney" was short: He died Friday night, according to CBS, only a month after delivering his 1,097th and final televised commentary.
Rooney?talked on "60 Minutes" about what was in the news, and his opinions occasionally got him in trouble. But he was just as likely to discuss the old clothes in his closet, why air travel had become unpleasant and why banks needed to have important sounding names.
He won one of his three Emmy Awards for a piece on whether there was a real Mrs. Smith who made Mrs. Smith's Pies. As it turned out, there was no Mrs. Smith.
"I obviously have a knack for getting on paper what a lot of people have thought and didn't realize they thought,"?Rooney?once said. "And they say, 'Hey, yeah!' And they like that."
Looking for something new to punctuate its weekly broadcast, "60 Minutes" aired its first?Rooney?commentary on July 2, 1987. He complained about people who keep track of how many people die in car accidents on holiday weekends. In fact, he said, the Fourth of July is "one of the safest weekends of the year to be going someplace."
More than three decades later, he was railing about how unpleasant air travel had become. "Let's make a statement to the airlines just to get their attention," he said. "We'll pick a week next year and we'll all agree not to go anywhere for seven days."
In early 2009, as he was about to turn 90,?Rooney?looked ahead to President Barack Obama's upcoming inauguration with a look at past inaugurations. He told viewers that Calvin Coolidge's 1925 swearing-in was the first to be broadcast on radio, adding, "That may have been the most interesting thing Coolidge ever did."
For his final essay,?Rooney?said that he'd live a life luckier than most.
"I wish I could do this forever. I can't, though," he said.
He said he probably hadn't said anything on "60 Minutes" that most of his viewers didn't already know or hadn't thought. "That's what a writer does," he said. "A writer's job is to tell the truth."
True to his occasional crotchety nature, though, he complained about being famous or bothered by fans. His last wish from fans: If you see him in a restaurant, just let him eat his dinner.
Rooney?wrote for CBS stars such as Arthur Godfrey and Garry Moore during the 1950s and early 1960s, before settling into a partnership with newsman Harry Reasoner. With?Rooney?as the writer, they collaborated on several news specials, including an Emmy-winning report on misrepresentations of black people in movies and history books. He wrote "An Essay on Doors" in 1964, and continued with contemplations on bridges, chairs and women.
"The best work I ever did,"?Rooney?said. "But nobody knows I can do it or ever did it. Nobody knows that I'm a writer and producer. They think I'm this guy on television."
SAN FRANCISCO ? LinkedIn suffered its first quarterly loss since its initial public offering roused Wall Street a few months ago.
The setback, announced Thursday, wasn't as severe as analysts anticipated. The online professional networking service invested in an expansion aimed at changing the way people find jobs and advance their careers.
LinkedIn Corp. absorbed a loss of $1.6 million, or 2 cents per share, in the July-September as it invested more money to expand. That contrasted with earnings of $4 million, or 2 cents per share, at the same time last year.
If not for items unrelated to its ongoing business, LinkedIn said it would have earned 6 cents per share. On that basis, analysts polled by FactSet had expected LinkedIn to break even.
Revenue more than doubled from last year to $139 million ? about $11 million higher than analysts forecast.
It wasn't enough to lift a stock that has been flying high since LinkedIn's stock market debut nearly six months ago. The company's shares shed $5, or 5.7 percent, to $82.50 in Thursday's extended trading.
After LinkedIn shares were priced at $45 in the initial public offering, they quickly doubled. Investors' rabid response sparked a debate about whether another investment bubble is forming around rapidly growing Internet companies, similar to what happened in the late 1990s when a dot-com boom set the stage for a costly meltdown.
Unlike the Internet startups of the 1990s, LinkedIn had been consistently generating profits.
The increasing spending that triggered the third-quarter loss appeared to yield dividends.
Besides producing impressive revenue growth, LinkedIn added 15.4 million more accounts in the quarter to end September with 131.2 million members. That may have been a slight letdown for investors, though, because LinkedIn Jeff Weiner had indicated the company was on a pace that would result in 132 million members at the end of the quarter.
LinkedIn doesn't charge people to post their resumes, but attracting more members is important because a bigger audience makes the service more compelling to employment recruiters and advertisers.
The company, based in Mountain View, Calif., gets more than two-thirds of its revenue from fees it charges companies, recruiting services and other people who want broader access to the profiles and other data on the company's website. The rest comes from advertising.
TALLAHASSEE-- Religious leaders from around the state met in Tallahassee Monday to being laying out their strategy to defeat a controversial gaming bill that would dramatically expand gambling in the state by bringing three Las Vegas-style casinos to the South Florida market.
The Florida Catholic Conference, the Florida Family Policy Council, the Florida Baptist Convention and Florida Casino Watch all firmly declared their opposition at a press conference, warning of social costs that a gaming expansion could bring to the state.
"We believe that the casino bills are amazingly short sighted," said John Stemberger, who heads the Florida Family Policy Council. "We do not solve short term economic pressures by creating permanent institutions that are regressive, counterproductive and not in the best interest of the common good."
The opposition of the religious community is no surprise. They've rejected attempts to expand gambling in the past, but the group said the scope of the bill being floated by Rep. Erik Fresen, R-Miami, and Sen. Ellyn Bogdanoff, R-Fort Lauderdale, is so broad that they wanted to attack the issue as a group.
Stemberger said his group, which typically endorses Republican candidates for family friendly views, will be publishing the voting records of all members in committees and on the floor for the bill. It will also be putting out information on which lawmakers are taking gaming industry money.
Bill Bunkley, a lobbyist for Florida Baptist Witness, said additionally, he plans to reach out to leaders of churches or synagogues of individual lawmakers to see if they can help persuade them of problems they see with the bill.
The percentage of Americans morally opposed to gambling has remained flat, according to surveys conducted by the American Gaming Association, an industry information clearinghouse based in Washington, D.C. Since 1999, about 16 percent of respondents have said gambling is ?not acceptable for anyone,? while about 81 percent have said it is either ?perfectly acceptable for anyone? or ?acceptable for others but not you personally.? Another 3 percent did not respond.
Meanwhile, 60 percent of respondents in the 2011 survey ?view casinos as an integral part of their tourism mix,? and say casinos are ?very? or ?somewhat? important to the overall U.S. travel and tourism industry.
Supporters have said the presence of new casinos could be a major economic boost to South Florida, which has struggled under the foreclosure crisis and high unemployment.
Rep. Dennis Baxley, R-Ocala, who appeared at the press conference, said potential social costs outweighed any economic benefit.
"Some things you don't do no matter how broke you are," he said. "You don't do it."
FILE - Lindsay Lohan poses at the Amfar charity event, part of the Fashion Week in Milan, Italy, in this Sept. 23, 2011 file photo. Lohan returns to a Los Angeles court on Wednesday Nov. 2, 2011 for a probation violation hearing that could end with the starlet returning for jail (AP Photo/Giuseppe Aresu, File)
FILE - Lindsay Lohan poses at the Amfar charity event, part of the Fashion Week in Milan, Italy, in this Sept. 23, 2011 file photo. Lohan returns to a Los Angeles court on Wednesday Nov. 2, 2011 for a probation violation hearing that could end with the starlet returning for jail (AP Photo/Giuseppe Aresu, File)
LOS ANGELES (AP) ? Lindsay Lohan returns to court Wednesday to learn whether a judge will agree with a prosecutor advocating that the actress be returned to jail for failing to complete a community service assignment at a women's shelter.
Superior Court Judge Stephanie Sautner revoked Lohan's probation at a hearing nearly two weeks ago, but now must formally determine whether Lohan violated the terms of her sentence. The judge has asked prosecutors to calculate how long of a jail term the actress would have to serve if she is formally found in violation of her probation for misdemeanor drunken driving and theft cases.
Sautner, who is the fifth judge that Lohan has faced since her first arrest in 2007, has expressed exasperation with the actress and California's budget-strapped jail system.
"If jail meant something in the state of California now, maybe I'd put her in jail," Sautner said at Lohan's last court appearance.
The Los Angeles City Attorney's Office is advocating jail time for the actress, however spokesman Frank Mateljan declined to say Tuesday what sentence a prosecutor would seek.
Lohan's spokesman, Steve Honig, declined comment before the hearing.
The "Mean Girls" star has been reporting to the Los Angeles morgue regularly, which Sautner ordered her to do at the last court appearance. The judge had sentenced Lohan to serve 120 hours doing janitorial work at coroner's office in April, but expressed hope that the actress would benefit from working three times that amount of hours at a women's shelter.
Lohan, 25, was terminated from the shelter program after failing to show up nine times at the center. She told her probation officer the assignment was not fulfilling, according to the actress' probation report.
The actress' morgue service has not been without drama ? she was turned away the first day after showing up 40 minutes late. She has shown up early several times since then. Assistant Chief Coroner Ed Winter declined to characterize how Lohan's service was progressing Tuesday.
There are few, if any, untried punishment options if Sautner determines Lohan violated her orders. The former Disney star has been sent to jail, rehab, counseling and community service numerous times since being arrested twice for drunken driving in 2007. Her probation on that case is nearly over, but her release remains supervised after Lohan in May pleaded no contest to misdemeanor theft for taking a $2,500 necklace without permission in January.
Once a headlining actress, Lohan's court and personal troubles have overshadowed her career for years.
___
McCartney can be reached at http://twitter.com/mccartneyAP
SAGA COMMUNICATIONS has reported third-quarter financial results.
Net income for Q3 increased 3.9% to $3.7 million ($0.87 per fully diluted share compared to $0.84 per fully diluted share for the same period last year). Free cash flow was flat with the same period last year at $6.0 million.?
For the three month period ended SEPTEMBER 30th, 2011, net operating revenue decreased 1.0% from the comparable period in 2010 to $32.5 million with operating income of $7.0 million compared to $7.4 million for the same period last year. For the same period, station operating expense was also even with last year at $23.6 million (station operating expense includes depreciation and amortization attributable to the stations).
GSA Bulletin Highlights: New research posted ahead of printPublic release date: 2-Nov-2011 [ | E-mail | Share ]
Contact: Christa Stratton cstratton@geosociety.org Geological Society of America
Boulder, CO, USA - Highlights for GSA Bulletin articles published ahead of print between 30 Sept. and 21 Oct. 2011 are provided below. Studies include U-Pb geochronology and major and trace element geochemistry in the Andes; wide-angle reflections generated by five controlled blasts and over 110 timed quarry blasts in the Appalachians; cosmogenic isotope burial dating in Wonderwerk Cave, South Africa; and SHRIMP analysis of zircons in Redoubt Volcano, Alaska.
GSA BULLETIN articles published ahead of print can be accessed online at http://gsabulletin.gsapubs.org/content/early/recent. When articles are assigned to a print issue they will be removed from the pre-issue publication folder, but doi numbers will remain constant.
Keywords: Ligurian accretionary complex, Italy, Eastern Cordillera-Llanos basin boundary, Colombia, ice stream flow, Barents Sea, Fonte dei Pulcini A (FPA) section, Messinian salinity crisis, Mediterranean, Central Appalachians, Asheville Basin. Pliocene, Colorado River, Grand Canyon, Central Anatolian plateau, Turkey, Wonderwerk Cave, South Africa, Kalahari Dunes, SHRIMP, Redoubt volcano, Alaska, Gediz graben, Central Menderes Massif, Alasehir supradetachment, Wallowa arc terrane, Blue Mountains Province, Oregon, Idaho, Canadian Arctic, Geological Survey of Canada, Panamint and Spring Mountains.
Representatives of the media may obtain complimentary copies of GSA BULLETIN articles by contacting Christa Stratton at the address above. Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GSA BULLETIN in articles published. Abstracts for issues of GSA BULLETIN are available at http://gsabulletin.gsapubs.org/. Contact Christa Stratton for additional information or assistance.
Non-media requests for articles may be directed to GSA Sales and Service, gsaservice@geosociety.org.
On the tectonic evolution of the Ligurian accretionary complex in southern Italy
S. Ciarcia et al., Dipartimento Scienze della Terra, Universita di Napoli Federico II, Largo San Marcellino 10, 80138 Naples, Italy; doi: 10.1130/B30437.1. Posted online ahead of print 21 Oct. 2011.
The combined role of internal wedge dynamics and continental margin architecture in controlling the tectonic evolution of an accretionary complex during its final emplacement onto the foreland continent is discussed in this study. S. Ciarcia of the University of Naples Federico II and colleagues conduct integrated structural, stratigraphic and low-T thermochronometric analyses on the Ligurian accretionary complex units exposed in the southern Italy and on continental margin successions located in their footwall, as well as on related foredeep and wedge-top basin deposits. Their results point out a series of late early Miocene shortening events, also involving buttressing of the accretionary wedge against the crustal ramp of the foreland continental margin. Emplacement of the over-thickened accretionary complex onto the distal part of the continental margin was followed by horizontal extension and wedge thinning, aiding the development of wedge-top depocenters. Early Miocene NW-SE shortening recorded by Ligurian accretionary complex units is completely unrelated with later NE-directed thrusting in the Apennines, which was coeval with back-arc extension in the Tyrrhenian Sea. These results emphasize the occurrence of a major discontinuity in the Neogene geodynamic evolution of the southern Apennines, whose tectonic history may be clearly subdivided, from a kinematic point of view, into pre- and syn-Tyrrhenian back-arc extension stages.
Clastic deposition, provenance, and sequence of Andean thrusting in the frontal Eastern Cordillera and Llanos foreland basin of Colombia
Alejandro Bande et al., Dept. of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78712, USA; doi: 10.1130/B30412.1. Posted online ahead of print 21 Oct. 2011.
Sedimentary deposits at the leading edge of the northern Andes (6 degrees N latitude) provide a long-term record of foreland-basin sedimentation along the Eastern Cordillera-Llanos basin boundary in Colombia. Sedimentological, provenance, and detrital thermochronological (U-Pb and (U-Th)/He) results for an upward-coarsening, ~5-km-thick succession (Nunchia syncline) reveal a systematic shift from (1) craton-derived, shallow-marine distal foreland (backbulge) accumulation, to (2) orogen-sourced, deltaic and coastal-influenced sedimentation of the distal to medial foreland (foredeep), to (3) anastomosing fluvial and distributive braided fluvial megafan systems of the proximal foreland (foredeep to wedge-top) basin. These changes record exhumation of evolving, compartmentalized sediment source areas in the Eastern Cordillera. Alejandro Bande of the Jackson School of Geosciences and colleagues interpret these data in terms of a progressive eastward advance in fold-thrust deformation, with late Eocene-Oligocene deformation in the axial zone of the Eastern Cordillera, early Miocene reactivation (inversion) of the eastern margin of the Mesozoic rift system, and middle-late Miocene propagation of a footwall shortcut fault along the transition from the Eastern Cordillera to Llanos foreland basin. They find that, collectively, the data for the frontal Eastern Cordillera define a general in-sequence pattern of eastward advancing fold-thrust deformation during Cenozoic east-west shortening in the Colombian Andes.
Late Miocene surface uplift of the southern margin of the Central Anatolian Plateau, Central Taurides, Turkey
Domenico Cosentino et al., Dipartimento de Scienze Geologiche, Universita degli Studi Roma Tre, Largo San Leonardo Murialdo 1, 00146 Rome, Italy; doi: 10.1130/B30466.1. Posted online ahead of print 21 Oct. 2011.
The timing and pattern of surface uplift of marine sediments capping the southern margin of the Central Anatolian plateau in southern Turkey provide a first-order constraint on possible mechanisms of regional uplift. Using biostratigraphy and paleomagnetic stratigraphy, Domenico Cosentino and colleagues determine an age of 8.35-8.108 Ma for the uppermost marine sediments now at ca. 2-km elevation, yielding a long-term average uplift rate of 0.24-0.25 mm/yr. The minimal deformation of these marine sediments over spatial distances of tens of kilometers implies that uplift mechanisms have originated deep within the crust or mantle. Recently published tomography data and Plio-Quaternary volcanism show evidence for asthenospheric upwelling in a pattern that matches very well the pattern of uplift we observe along the southern margin of the Central Anatolian plateau. This correspondence is consistent with slab break-off beneath the southern plateau margin triggering surface uplift.
U-Pb geochronology and geochemistry of intrusive rocks from the Cougar Creek Complex, Wallowa arc terrane, Blue Mountains Province, Oregon-Idaho
Gene A. Kurz et al., Dept. of Geosciences, Boise State University, 1910 University Drive, Boise, Idaho 83725, USA; doi: 10.1130/B30452.1. Posted online ahead of print 21 Oct. 2011.
This study utilizes high-precision U-Pb geochronology and major and trace element geochemistry to characterize magmatism in the Wallowa arc terrane of the Blue Mountains Province of northeastern Oregon and west-central Idaho. New data presented in this study provide valuable age and compositional context for magmatic rocks for a poorly understood, yet critical section of the North American Cordilleran orogen. U-Pb ages indicate two distinct cycles of magmatism recorded in the Cougar Creek Complex. Geochemical data indicate a switch from older Permian silicic arc-related magmatism to younger Late Triassic igneous activity that appears to have been derived from a depleted mantle source similar to mid-ocean ridge basalt. The apparent switch from normal arc-related magmatism to a depleted MORB-like magma source is inferred to be related to the upwelling of buoyant asthenosphere through an opening slab window beneath the Wallowa arc. In this paper, Gene Kurz of Boise State University and colleagues propose that Late Triassic mafic igneous rocks from the Wallowa terrane and Wrangellia of Alaska and western Canada resulted from the subduction of a spreading ridge and slab window magmatism beneath a late Paleozoic arc, thus linking the Late Triassic geologic evolution of two fundamental components of the Cordilleran orogen.
Orbitally forced paleoenvironmental and paleoclimate changes in the late postevaporitic Messinian of the central Mediterranean Basin
Domenico Cosentino et al., Dipartimento di Scienze Geologiche, Universita degli Studi Roma Tre, Largo San Leonardo Murialdo, 1-00146 Rome, Italy; doi: 10.1130/B30462.1. Posted online ahead of print 14 Oct. 2011.
Palaeoenvironmental and palaeoclimate changes that occurred between 5.394 and 5.336 Ma (late stage of the Messinian salinity crisis) in the Mediterranean Basin offer a new perspective on the relationship between orbital forcing and climate response. The magnetic susceptibility record of the Fonte dei Pulcini A (FPA) section (Maiella Mountains, Italy) allows Domenico Cosentino and colleagues to orbitally tune and to temporally constrain the palaeoenvironmental and palaeoclimate changes evidenced by quantitative palaeontological, stable isotope, and mineralogical analyses. The base of the FPA section is characterized by Paratethyan ostracods and dinocysts, which point to the late Messinian Lago-Mare biofacies (Loxocorniculina djafarovi Zone) of the Mediterranean Messinian stratigraphy. The major changes in terms of palaeodepth, palaeosalinity, evaporation vs. precipitation, aridity vs. humidity, and reworking processes occurred in the upper part of the FPA section during the last Messinian insolation cycle (i-cycle 511/512), which is characterized by high amplitude oscillations. In contrast, the lower part of the FPA section, which was deposited during relatively low amplitude insolation cycles, is characterized by more stable environmental conditions. Comparing summer insolation with the palaeoenvironmental changes at the FPA section, Cosentino and colleagues identify delays of several thousands of years between orbital forcing and climate response.
Isostatic compensation for a portion of the Southern Appalachians: Evidence from a reconnaissance study using wide-angle, three-component seismic soundings
Robert B. Hawman et al., Dept. of Geology, University of Georgia, Athens, Georgia 30602, USA; doi: 10.1130/B30464.1. Posted online ahead of print 14 Oct. 2011.
Robert B. Hawman of the University of Georgia and colleagues use wide-angle reflections generated by five controlled blasts and over 110 timed quarry blasts to test models for isostatic compensation of topography in the southern Appalachians. The profiles cross the Appalachian gravity gradient and gravity low and sample the highest elevations within the orogen. Migration of P and S reflections suggests an increase in crustal thickness from 35-39 km within the Coastal Plain to 50-52 km along the southeastern flank of the Blue Ridge Mountains. Crustal thickness within the Blue Ridge Mountains ranges from 47-56 km, with a local minimum beneath the Asheville Basin. Analysis of earthquake data for two broadband stations shows a similar pattern in crustal thickness. The greatest Moho depths are associated not with the tallest peaks, but rather with the broadest portions of the mountain chain. This observation combined with the persistence of thick crust beyond the southeastern flank of the mountains suggests that topography is supported by elastic bending of the lithosphere rather than Airy compensation. Estimates for the density contrast between the lowermost crust and uppermost mantle are consistent with models that propose an increase in lower crustal density with age to explain the preservation of roots for old mountain belts.
Dating of Pliocene Colorado River sediments: Implications for cosmogenic burial dating and the evolution of the lower Colorado River
A. Matmon et al., Dept. of Geology, Miami University, Shideler Hall, Oxford, Ohio 45056, USA; doi: 10.1130/B30453.1. Posted online ahead of print 14 Oct. 2011.
A. Matmon of Miami University and colleagues date sediments deposited by the ancestral Colorado using concentrations and ratios of cosmogenic nuclides. At one site, comparison of burial ages to the overlying 4.4 Ma basalt yielded good agreement and suggests that under the most favorable conditions, cosmogenic burial dating can extend back about 5 million years. Results from other sites highlight the complexities inherent in burial dating such as complicated burial histories, insufficient shielding, post burial production of cosmogenic isotopes, and unknown initial 26Al/10Be ratios. In spite of the large range of burial ages, Matmon et al. identify sediment deposition and burial periods at ca. 5.3, 4.7, and 3.6 Ma.
Reconstructing the history of sediment deposition in caves: A case study from Wonderwerk Cave, South Africa
A. Matmon et al., Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel; doi: 10.1130/B30410.1. Posted online ahead of print 14 Oct. 2011.
A. Matmon of Hebrew University and colleagues apply cosmogenic isotope burial dating, magnetostratigraphy, and grain size distribution analysis to elucidate the history of the sedimentary sequence in Wonderwerk Cave, South Africa. The source for the sand is the Kalahari dunes, located ~100 km to the north of the cave. Field observations and grain size analysis suggest aeolian transport of Kalahari sand, temporary storage on hill slopes, and later deposition in the cave. Results presented by Matmon et al. suggest burial ages for sediments that range between 2.63 plus or minus 0.17 Ma and 1.56 plus or minus 0.10 Ma. However, they note that 26Al/10Be ratios measured in sand collected from the surface outside the cave imply an initial burial signal equivalent to 0.78 plus or minus 0.15 Ma, thus reducing the possible age range of the buried samples to between 1.85 plus or minus 0.23 and 0.78 plus or minus 0.18 Ma. Paleomagnetic results for the front of the cave can be correlated with the cosmogenic burial age range. In contrast, such a correlation is not possible at the back of the cave, since the paleomagnetic polarity can be correlated to any Reverse-Normal transition that occurred during the Quaternary. Sedimentological and isotopic similarities between the sediment in the cave and that presently exposed outside the cave suggest that the environmental conditions and rates of geomorphic processes during the late Pliocene and early Pleistocene may have been similar to those currently experienced in the southern Kalahari.
Peninsular terrane basement ages recorded by Paleozoic and Paleoproterozoic zircon in gabbro xenoliths and andesite from Redoubt volcano, Alaska
Charles R. Bacon et al., U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA; doi: 10.1130/B30439.1. Posted online ahead of print 30 Sept. 2011.
Redoubt volcano is a historically active cone located 100 miles (160 km) southwest of Anchorage, Alaska. Plutonic rock fragments (xenoliths) ejected by Redoubt have been thought to be either geologically young or Mesozoic rocks that of the Peninsular terrane, a part of Earth's crust formed elsewhere and transported to its present location by plate tectonic motion. However, new sensitive high-resolution ion microprobe (SHRIMP) ages for zircon from xenoliths, presented here by Charles Bacon of the USGS and colleagues, are dominated by much older ca. 310 million-year-old Pennsylvanian and ca. 1865 million-year-old Paleoproterozoic grains. Textural evidence and ca. 1865 million-year-old zircon in Redoubt lava show that ancient rocks have been digested by Redoubt magma, most likely in the magma accumulation and storage region ~4-10 km below sea level. The zircon ages demonstrate that Pennsylvanian, and probably Paleoproterozoic, igneous rocks exist in or beneath Peninsular terrane basement. Discovery of Pennsylvanian xenoliths similar in age to Skolai arc rocks 310 miles (500 km) northeast of Redoubt indicates that the Peninsular terrane, along with the Wrangellia and Alexander terranes, has been part of the Wrangellia composite terrane since at least Pennsylvanian time. Moreover, the zircon data suggest that a hitherto unknown Paleoproterozoic continental fragment may be present in southern Alaska.
Detrital zircon geochronology and provenance of the Neoproterozoic to Late Devonian Franklinian Basin, Canadian Arctic Islands
Owen A. Anfinson et al., Dept. of Geoscience, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada; doi: 10.1130/B30503.1. Posted online ahead of print 30 Sept. 2011.
The Canadian Arctic Islands remain one of the last relatively unexplored frontiers with respect to geochronologic research. Research presented here by Owen Anfinson of the University of Calgary and colleagues utilizes detrital zircon U/Pb geochronology to help determine the sources of sediment for the northern margin of North America for a period of approximately 200 million years (560-360 Ma). The study utilizes the collection efforts of more than 40 years of expeditions to the Canadian Arctic Islands by Geological Survey of Canada geologists. The samples these geologists collected provide a geographic and stratigraphic distribution of samples that would take millions of dollars and numerous summers of field research to personally collect. In studying these samples, Anfinson and colleagues provide insights into the origins of terranes that collided with the northern margin of North America and provide information on the tectonic evolution of the Canadian Arctic Islands. The study also provides a "fingerprint" of the landmass Crockerland, which likely now lies somewhere in the arctic realm, but may be covered by the sea ice of the Arctic Ocean. By providing detailed geochronologic information on the first sedimentary basin of the Canadian Arctic Islands this paper will help provide a baseline for many future detrital zircon studies in the Canadian Arctic.
The influence of snow sublimation on the isotopic composition of spring and surface waters in the southwestern United States: Implications for stable isotope-based paleoaltimetry and hydrologic studies
Alex R. Lechler and Nathan A. Niemi, Dept. of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA; doi: 10.1130/B30467.1. Posted online ahead of print 30 Sept. 2011.
Stable isotope-based determinations of paleoclimate, paleoelevation and location and timing of groundwater recharge often rely on the fundamental assumption that terrestrial waters (e.g., lakes, streams, springs) are reliable recorders of the isotopic composition (delta-18O and delta-D) of the original precipitation from which they were derived. In cases where substantial post-depositional isotopic modification has taken place, these stable isotope-based reconstructions are prone to considerable errors. Alex Lechler and Nathan Niemi of the University of Michigan show that sublimation of the winter snowpack likely acts as a dominant post-depositional mechanism that influences spring and surface waters and partially erases the original isotopic signatures of precipitation in the Panamint and Spring Mountains located in the arid, continental interior western U.S. These sublimation effects can potentially lead to significant paleoelevation underestimates on the order of 2 km or more. Accounting for sublimation effects will greatly improve future stable isotope-based reconstructions, particularly in light of current climate warming trends in the water-stressed, western U.S. where earlier onset of spring season snowmelt and a greater proportion of annual precipitation falling as rain instead of snow threatens an already scarce seasonal water recharge supply.
Ice-stream flow switching during deglaciation of the southwestern Barents Sea
Monica C.M. Winsborrow et al., Dept. of Geology, University of Tromso, N-9037 Tromso, Norway; doi: 10.1130/B30416.1. Posted online ahead of print 30 Sept. 2011.
The dynamics of ice sheets are strongly influenced by fast-flowing ice streams which discharge the majority of ice, sediment and meltwater. Recent observations from contemporary ice sheets have revealed large variations in the location and velocity of ice streams over relatively short timescales. These "flow-switches" may have significant consequences for the dynamics of the ice sheet as a whole, but the underlying causes of this behavior and the extent to which it is predictable, are poorly known. In this paper, Monica Winsborrow of the University of Tromso, Norway, and colleagues document a major episode of ice stream flow-switching which took place during the final deglaciation of the southwestern Barents Sea. Based on differences in the landforms created by two neighboring ice streams, we reconstruct contrasting retreat histories; with one ice stream switching from fast to slow flow and stabilizing during retreat, whilst the adjacent ice stream rapidly retreated without stabilizing. Winsborrow and colleagues propose that variations in topography over which these ice streams flowed determined how they responded to variations in sea level and that this was the primary factor controlling their retreat behavior. This mechanism is likely an important factor on Greenlandic and Antarctic marine-based ice streams and outlet glaciers.
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GSA Bulletin Highlights: New research posted ahead of printPublic release date: 2-Nov-2011 [ | E-mail | Share ]
Contact: Christa Stratton cstratton@geosociety.org Geological Society of America
Boulder, CO, USA - Highlights for GSA Bulletin articles published ahead of print between 30 Sept. and 21 Oct. 2011 are provided below. Studies include U-Pb geochronology and major and trace element geochemistry in the Andes; wide-angle reflections generated by five controlled blasts and over 110 timed quarry blasts in the Appalachians; cosmogenic isotope burial dating in Wonderwerk Cave, South Africa; and SHRIMP analysis of zircons in Redoubt Volcano, Alaska.
GSA BULLETIN articles published ahead of print can be accessed online at http://gsabulletin.gsapubs.org/content/early/recent. When articles are assigned to a print issue they will be removed from the pre-issue publication folder, but doi numbers will remain constant.
Keywords: Ligurian accretionary complex, Italy, Eastern Cordillera-Llanos basin boundary, Colombia, ice stream flow, Barents Sea, Fonte dei Pulcini A (FPA) section, Messinian salinity crisis, Mediterranean, Central Appalachians, Asheville Basin. Pliocene, Colorado River, Grand Canyon, Central Anatolian plateau, Turkey, Wonderwerk Cave, South Africa, Kalahari Dunes, SHRIMP, Redoubt volcano, Alaska, Gediz graben, Central Menderes Massif, Alasehir supradetachment, Wallowa arc terrane, Blue Mountains Province, Oregon, Idaho, Canadian Arctic, Geological Survey of Canada, Panamint and Spring Mountains.
Representatives of the media may obtain complimentary copies of GSA BULLETIN articles by contacting Christa Stratton at the address above. Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GSA BULLETIN in articles published. Abstracts for issues of GSA BULLETIN are available at http://gsabulletin.gsapubs.org/. Contact Christa Stratton for additional information or assistance.
Non-media requests for articles may be directed to GSA Sales and Service, gsaservice@geosociety.org.
On the tectonic evolution of the Ligurian accretionary complex in southern Italy
S. Ciarcia et al., Dipartimento Scienze della Terra, Universita di Napoli Federico II, Largo San Marcellino 10, 80138 Naples, Italy; doi: 10.1130/B30437.1. Posted online ahead of print 21 Oct. 2011.
The combined role of internal wedge dynamics and continental margin architecture in controlling the tectonic evolution of an accretionary complex during its final emplacement onto the foreland continent is discussed in this study. S. Ciarcia of the University of Naples Federico II and colleagues conduct integrated structural, stratigraphic and low-T thermochronometric analyses on the Ligurian accretionary complex units exposed in the southern Italy and on continental margin successions located in their footwall, as well as on related foredeep and wedge-top basin deposits. Their results point out a series of late early Miocene shortening events, also involving buttressing of the accretionary wedge against the crustal ramp of the foreland continental margin. Emplacement of the over-thickened accretionary complex onto the distal part of the continental margin was followed by horizontal extension and wedge thinning, aiding the development of wedge-top depocenters. Early Miocene NW-SE shortening recorded by Ligurian accretionary complex units is completely unrelated with later NE-directed thrusting in the Apennines, which was coeval with back-arc extension in the Tyrrhenian Sea. These results emphasize the occurrence of a major discontinuity in the Neogene geodynamic evolution of the southern Apennines, whose tectonic history may be clearly subdivided, from a kinematic point of view, into pre- and syn-Tyrrhenian back-arc extension stages.
Clastic deposition, provenance, and sequence of Andean thrusting in the frontal Eastern Cordillera and Llanos foreland basin of Colombia
Alejandro Bande et al., Dept. of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78712, USA; doi: 10.1130/B30412.1. Posted online ahead of print 21 Oct. 2011.
Sedimentary deposits at the leading edge of the northern Andes (6 degrees N latitude) provide a long-term record of foreland-basin sedimentation along the Eastern Cordillera-Llanos basin boundary in Colombia. Sedimentological, provenance, and detrital thermochronological (U-Pb and (U-Th)/He) results for an upward-coarsening, ~5-km-thick succession (Nunchia syncline) reveal a systematic shift from (1) craton-derived, shallow-marine distal foreland (backbulge) accumulation, to (2) orogen-sourced, deltaic and coastal-influenced sedimentation of the distal to medial foreland (foredeep), to (3) anastomosing fluvial and distributive braided fluvial megafan systems of the proximal foreland (foredeep to wedge-top) basin. These changes record exhumation of evolving, compartmentalized sediment source areas in the Eastern Cordillera. Alejandro Bande of the Jackson School of Geosciences and colleagues interpret these data in terms of a progressive eastward advance in fold-thrust deformation, with late Eocene-Oligocene deformation in the axial zone of the Eastern Cordillera, early Miocene reactivation (inversion) of the eastern margin of the Mesozoic rift system, and middle-late Miocene propagation of a footwall shortcut fault along the transition from the Eastern Cordillera to Llanos foreland basin. They find that, collectively, the data for the frontal Eastern Cordillera define a general in-sequence pattern of eastward advancing fold-thrust deformation during Cenozoic east-west shortening in the Colombian Andes.
Late Miocene surface uplift of the southern margin of the Central Anatolian Plateau, Central Taurides, Turkey
Domenico Cosentino et al., Dipartimento de Scienze Geologiche, Universita degli Studi Roma Tre, Largo San Leonardo Murialdo 1, 00146 Rome, Italy; doi: 10.1130/B30466.1. Posted online ahead of print 21 Oct. 2011.
The timing and pattern of surface uplift of marine sediments capping the southern margin of the Central Anatolian plateau in southern Turkey provide a first-order constraint on possible mechanisms of regional uplift. Using biostratigraphy and paleomagnetic stratigraphy, Domenico Cosentino and colleagues determine an age of 8.35-8.108 Ma for the uppermost marine sediments now at ca. 2-km elevation, yielding a long-term average uplift rate of 0.24-0.25 mm/yr. The minimal deformation of these marine sediments over spatial distances of tens of kilometers implies that uplift mechanisms have originated deep within the crust or mantle. Recently published tomography data and Plio-Quaternary volcanism show evidence for asthenospheric upwelling in a pattern that matches very well the pattern of uplift we observe along the southern margin of the Central Anatolian plateau. This correspondence is consistent with slab break-off beneath the southern plateau margin triggering surface uplift.
U-Pb geochronology and geochemistry of intrusive rocks from the Cougar Creek Complex, Wallowa arc terrane, Blue Mountains Province, Oregon-Idaho
Gene A. Kurz et al., Dept. of Geosciences, Boise State University, 1910 University Drive, Boise, Idaho 83725, USA; doi: 10.1130/B30452.1. Posted online ahead of print 21 Oct. 2011.
This study utilizes high-precision U-Pb geochronology and major and trace element geochemistry to characterize magmatism in the Wallowa arc terrane of the Blue Mountains Province of northeastern Oregon and west-central Idaho. New data presented in this study provide valuable age and compositional context for magmatic rocks for a poorly understood, yet critical section of the North American Cordilleran orogen. U-Pb ages indicate two distinct cycles of magmatism recorded in the Cougar Creek Complex. Geochemical data indicate a switch from older Permian silicic arc-related magmatism to younger Late Triassic igneous activity that appears to have been derived from a depleted mantle source similar to mid-ocean ridge basalt. The apparent switch from normal arc-related magmatism to a depleted MORB-like magma source is inferred to be related to the upwelling of buoyant asthenosphere through an opening slab window beneath the Wallowa arc. In this paper, Gene Kurz of Boise State University and colleagues propose that Late Triassic mafic igneous rocks from the Wallowa terrane and Wrangellia of Alaska and western Canada resulted from the subduction of a spreading ridge and slab window magmatism beneath a late Paleozoic arc, thus linking the Late Triassic geologic evolution of two fundamental components of the Cordilleran orogen.
Orbitally forced paleoenvironmental and paleoclimate changes in the late postevaporitic Messinian of the central Mediterranean Basin
Domenico Cosentino et al., Dipartimento di Scienze Geologiche, Universita degli Studi Roma Tre, Largo San Leonardo Murialdo, 1-00146 Rome, Italy; doi: 10.1130/B30462.1. Posted online ahead of print 14 Oct. 2011.
Palaeoenvironmental and palaeoclimate changes that occurred between 5.394 and 5.336 Ma (late stage of the Messinian salinity crisis) in the Mediterranean Basin offer a new perspective on the relationship between orbital forcing and climate response. The magnetic susceptibility record of the Fonte dei Pulcini A (FPA) section (Maiella Mountains, Italy) allows Domenico Cosentino and colleagues to orbitally tune and to temporally constrain the palaeoenvironmental and palaeoclimate changes evidenced by quantitative palaeontological, stable isotope, and mineralogical analyses. The base of the FPA section is characterized by Paratethyan ostracods and dinocysts, which point to the late Messinian Lago-Mare biofacies (Loxocorniculina djafarovi Zone) of the Mediterranean Messinian stratigraphy. The major changes in terms of palaeodepth, palaeosalinity, evaporation vs. precipitation, aridity vs. humidity, and reworking processes occurred in the upper part of the FPA section during the last Messinian insolation cycle (i-cycle 511/512), which is characterized by high amplitude oscillations. In contrast, the lower part of the FPA section, which was deposited during relatively low amplitude insolation cycles, is characterized by more stable environmental conditions. Comparing summer insolation with the palaeoenvironmental changes at the FPA section, Cosentino and colleagues identify delays of several thousands of years between orbital forcing and climate response.
Isostatic compensation for a portion of the Southern Appalachians: Evidence from a reconnaissance study using wide-angle, three-component seismic soundings
Robert B. Hawman et al., Dept. of Geology, University of Georgia, Athens, Georgia 30602, USA; doi: 10.1130/B30464.1. Posted online ahead of print 14 Oct. 2011.
Robert B. Hawman of the University of Georgia and colleagues use wide-angle reflections generated by five controlled blasts and over 110 timed quarry blasts to test models for isostatic compensation of topography in the southern Appalachians. The profiles cross the Appalachian gravity gradient and gravity low and sample the highest elevations within the orogen. Migration of P and S reflections suggests an increase in crustal thickness from 35-39 km within the Coastal Plain to 50-52 km along the southeastern flank of the Blue Ridge Mountains. Crustal thickness within the Blue Ridge Mountains ranges from 47-56 km, with a local minimum beneath the Asheville Basin. Analysis of earthquake data for two broadband stations shows a similar pattern in crustal thickness. The greatest Moho depths are associated not with the tallest peaks, but rather with the broadest portions of the mountain chain. This observation combined with the persistence of thick crust beyond the southeastern flank of the mountains suggests that topography is supported by elastic bending of the lithosphere rather than Airy compensation. Estimates for the density contrast between the lowermost crust and uppermost mantle are consistent with models that propose an increase in lower crustal density with age to explain the preservation of roots for old mountain belts.
Dating of Pliocene Colorado River sediments: Implications for cosmogenic burial dating and the evolution of the lower Colorado River
A. Matmon et al., Dept. of Geology, Miami University, Shideler Hall, Oxford, Ohio 45056, USA; doi: 10.1130/B30453.1. Posted online ahead of print 14 Oct. 2011.
A. Matmon of Miami University and colleagues date sediments deposited by the ancestral Colorado using concentrations and ratios of cosmogenic nuclides. At one site, comparison of burial ages to the overlying 4.4 Ma basalt yielded good agreement and suggests that under the most favorable conditions, cosmogenic burial dating can extend back about 5 million years. Results from other sites highlight the complexities inherent in burial dating such as complicated burial histories, insufficient shielding, post burial production of cosmogenic isotopes, and unknown initial 26Al/10Be ratios. In spite of the large range of burial ages, Matmon et al. identify sediment deposition and burial periods at ca. 5.3, 4.7, and 3.6 Ma.
Reconstructing the history of sediment deposition in caves: A case study from Wonderwerk Cave, South Africa
A. Matmon et al., Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel; doi: 10.1130/B30410.1. Posted online ahead of print 14 Oct. 2011.
A. Matmon of Hebrew University and colleagues apply cosmogenic isotope burial dating, magnetostratigraphy, and grain size distribution analysis to elucidate the history of the sedimentary sequence in Wonderwerk Cave, South Africa. The source for the sand is the Kalahari dunes, located ~100 km to the north of the cave. Field observations and grain size analysis suggest aeolian transport of Kalahari sand, temporary storage on hill slopes, and later deposition in the cave. Results presented by Matmon et al. suggest burial ages for sediments that range between 2.63 plus or minus 0.17 Ma and 1.56 plus or minus 0.10 Ma. However, they note that 26Al/10Be ratios measured in sand collected from the surface outside the cave imply an initial burial signal equivalent to 0.78 plus or minus 0.15 Ma, thus reducing the possible age range of the buried samples to between 1.85 plus or minus 0.23 and 0.78 plus or minus 0.18 Ma. Paleomagnetic results for the front of the cave can be correlated with the cosmogenic burial age range. In contrast, such a correlation is not possible at the back of the cave, since the paleomagnetic polarity can be correlated to any Reverse-Normal transition that occurred during the Quaternary. Sedimentological and isotopic similarities between the sediment in the cave and that presently exposed outside the cave suggest that the environmental conditions and rates of geomorphic processes during the late Pliocene and early Pleistocene may have been similar to those currently experienced in the southern Kalahari.
Peninsular terrane basement ages recorded by Paleozoic and Paleoproterozoic zircon in gabbro xenoliths and andesite from Redoubt volcano, Alaska
Charles R. Bacon et al., U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA; doi: 10.1130/B30439.1. Posted online ahead of print 30 Sept. 2011.
Redoubt volcano is a historically active cone located 100 miles (160 km) southwest of Anchorage, Alaska. Plutonic rock fragments (xenoliths) ejected by Redoubt have been thought to be either geologically young or Mesozoic rocks that of the Peninsular terrane, a part of Earth's crust formed elsewhere and transported to its present location by plate tectonic motion. However, new sensitive high-resolution ion microprobe (SHRIMP) ages for zircon from xenoliths, presented here by Charles Bacon of the USGS and colleagues, are dominated by much older ca. 310 million-year-old Pennsylvanian and ca. 1865 million-year-old Paleoproterozoic grains. Textural evidence and ca. 1865 million-year-old zircon in Redoubt lava show that ancient rocks have been digested by Redoubt magma, most likely in the magma accumulation and storage region ~4-10 km below sea level. The zircon ages demonstrate that Pennsylvanian, and probably Paleoproterozoic, igneous rocks exist in or beneath Peninsular terrane basement. Discovery of Pennsylvanian xenoliths similar in age to Skolai arc rocks 310 miles (500 km) northeast of Redoubt indicates that the Peninsular terrane, along with the Wrangellia and Alexander terranes, has been part of the Wrangellia composite terrane since at least Pennsylvanian time. Moreover, the zircon data suggest that a hitherto unknown Paleoproterozoic continental fragment may be present in southern Alaska.
Detrital zircon geochronology and provenance of the Neoproterozoic to Late Devonian Franklinian Basin, Canadian Arctic Islands
Owen A. Anfinson et al., Dept. of Geoscience, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada; doi: 10.1130/B30503.1. Posted online ahead of print 30 Sept. 2011.
The Canadian Arctic Islands remain one of the last relatively unexplored frontiers with respect to geochronologic research. Research presented here by Owen Anfinson of the University of Calgary and colleagues utilizes detrital zircon U/Pb geochronology to help determine the sources of sediment for the northern margin of North America for a period of approximately 200 million years (560-360 Ma). The study utilizes the collection efforts of more than 40 years of expeditions to the Canadian Arctic Islands by Geological Survey of Canada geologists. The samples these geologists collected provide a geographic and stratigraphic distribution of samples that would take millions of dollars and numerous summers of field research to personally collect. In studying these samples, Anfinson and colleagues provide insights into the origins of terranes that collided with the northern margin of North America and provide information on the tectonic evolution of the Canadian Arctic Islands. The study also provides a "fingerprint" of the landmass Crockerland, which likely now lies somewhere in the arctic realm, but may be covered by the sea ice of the Arctic Ocean. By providing detailed geochronologic information on the first sedimentary basin of the Canadian Arctic Islands this paper will help provide a baseline for many future detrital zircon studies in the Canadian Arctic.
The influence of snow sublimation on the isotopic composition of spring and surface waters in the southwestern United States: Implications for stable isotope-based paleoaltimetry and hydrologic studies
Alex R. Lechler and Nathan A. Niemi, Dept. of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA; doi: 10.1130/B30467.1. Posted online ahead of print 30 Sept. 2011.
Stable isotope-based determinations of paleoclimate, paleoelevation and location and timing of groundwater recharge often rely on the fundamental assumption that terrestrial waters (e.g., lakes, streams, springs) are reliable recorders of the isotopic composition (delta-18O and delta-D) of the original precipitation from which they were derived. In cases where substantial post-depositional isotopic modification has taken place, these stable isotope-based reconstructions are prone to considerable errors. Alex Lechler and Nathan Niemi of the University of Michigan show that sublimation of the winter snowpack likely acts as a dominant post-depositional mechanism that influences spring and surface waters and partially erases the original isotopic signatures of precipitation in the Panamint and Spring Mountains located in the arid, continental interior western U.S. These sublimation effects can potentially lead to significant paleoelevation underestimates on the order of 2 km or more. Accounting for sublimation effects will greatly improve future stable isotope-based reconstructions, particularly in light of current climate warming trends in the water-stressed, western U.S. where earlier onset of spring season snowmelt and a greater proportion of annual precipitation falling as rain instead of snow threatens an already scarce seasonal water recharge supply.
Ice-stream flow switching during deglaciation of the southwestern Barents Sea
Monica C.M. Winsborrow et al., Dept. of Geology, University of Tromso, N-9037 Tromso, Norway; doi: 10.1130/B30416.1. Posted online ahead of print 30 Sept. 2011.
The dynamics of ice sheets are strongly influenced by fast-flowing ice streams which discharge the majority of ice, sediment and meltwater. Recent observations from contemporary ice sheets have revealed large variations in the location and velocity of ice streams over relatively short timescales. These "flow-switches" may have significant consequences for the dynamics of the ice sheet as a whole, but the underlying causes of this behavior and the extent to which it is predictable, are poorly known. In this paper, Monica Winsborrow of the University of Tromso, Norway, and colleagues document a major episode of ice stream flow-switching which took place during the final deglaciation of the southwestern Barents Sea. Based on differences in the landforms created by two neighboring ice streams, we reconstruct contrasting retreat histories; with one ice stream switching from fast to slow flow and stabilizing during retreat, whilst the adjacent ice stream rapidly retreated without stabilizing. Winsborrow and colleagues propose that variations in topography over which these ice streams flowed determined how they responded to variations in sea level and that this was the primary factor controlling their retreat behavior. This mechanism is likely an important factor on Greenlandic and Antarctic marine-based ice streams and outlet glaciers.
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Public release date: 2-Nov-2011
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