DOCSLIB.ORG

Paleoclimatic Context of Geomagnetic Dipole Lows and Excursions in the Brunhes, Clue for an Orbital Influence on the Geodynamo?

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Paleoclimatic Context of Geomagnetic Dipole Lows and Excursions in the Brunhes, Clue for an Orbital Influence on the Geodynamo? Earth and Planetary Science Letters 275 (2008) 269–284 Contents lists available at ScienceDirect Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl Paleoclimatic context of geomagnetic dipole lows and excursions in the Brunhes, clue for an orbital influence on the geodynamo? Nicolas Thouveny a,⁎, Didier L. Bourlès a, Ginette Saracco a, Julien T. Carcaillet a,b, F. Bassinot c a CEREGE, Aix-Marseille Université et CNRS, Europôle Méditerranéen de l'Arbois, BP 80, 13545, Aix en Provence, cedex 4, France b Laboratoire de Géodynamique des Chaînes Alpines (LGCA), Université Joseph Fourier et CNRS, BP53, 38041 Grenoble cedex 09, France c Laboratoire des Sciences du Climat et de l'Environnement, CNRS-CEA, Avenue de la Terrasse, 91198, Gif/Yvette, France article info abstract Article history: The hypothesis of an influence of the astronomical precession on the geodynamo energy budget was recently Received 8 July 2008 reappraised by theoreticians. Paleomagnetic indications of such an influence remain controversial because Accepted 15 August 2008 reconstructions of paleointensity variations from sediments are suspected to be contaminated by lithological, Available online 2 October 2008 paleoclimatically induced influences. Three sets of complementary indicators are however available: Editor: R.D. van der Hilst 1) records of the direction of magnetization in sediments, 2) records of magnetic anomalies of the deep sea floor basalts and 3) records of production variations of cosmogenic isotopes from sediment and ice cores. Keywords: These records confirm the genuine geomagnetic origin of paleointensity lows and their narrow link with geomagnetic dipole lows excursions or short reversals recorded in various materials and often dated by radiometric methods. The excursions analysis of these time series and their comparison with δ18O records of the paleoclimate suggest that such cosmogenic isotope overproduction globally recorded geomagnetic dipole lows have preferentially occurred in the context of interglacial or dating transitional paleoclimates at the time of low or decreasing obliquity. The dominant periods, extracted with correlation the complex continuous wavelet transform technique, range from 40 to 125 ka, further suggesting a link with paleoclimates orbital parameters. These results encourage future efforts of research to improve the precision, the resolution astronomical precession obliquity and the dating of the time series of geomagnetic dipole low, in order to better decipher orbital signatures and geodynamo understand their origin. An important implication of this topic is that the next geomagnetic dipole low should be related with the present interglacial. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Geodynamo generation mechanisms became better understood with numerical modeling and experimental systems involving highly The Earth's magnetic field generation is attributed to a self-excited conducting liquids, usually liquid sodium, in rotating containers. Vanyo dynamo process, maintained by the active convection of electrically (1991) showed that former calculation by Rochester et al. (1975) and conducting fluids in the outer core modified by the Earth's rotation (e.g. Loper (1975) had largely underestimated the energy of the precession. Glatzmaier and Roberts,1995), and by a tidally-driven periodic forcing of New numerical experiments have re-evaluated this energy (Vanyo and the core boundary and by a shearing stresses due to the Earth's axis Dunn, 2001; Roberts and Wu, 2005). The power required to drive the precession, conditions known to produce rotational parametric instabil- geodynamo also appears to be smaller than previously estimated ities (e.g. Aldridge et al., 1997; Aldridge and Baker, 2003). (Christensen and Tilgner, 2004). Experiments contributed in showing After Poincaré's (1910) and Bullard's (1949) suggestions, Malkus that the flow geometry generated in a rotating and precessing (1963, 1968) proposed that the internal Earth's magnetic field could be spheroidal envelope filled with water, is similar to the flow in the maintained by the luni-solar precession, i.e. by a motion of the core outer core inferred from geomagnetic secular variation (Vanyo, 2004). relative to the mantle, able to generate frictions transferring mechan- Finally, numerical reconstructions of the dynamo effect of a precession- ical, or magnetic, energy into the conducting fluids of the outer core. driven flow in a spherical container (Tilgner, 2005) showed that i) Calculations then suggested that precession could produce only 10% of laminar and unstable flows maintain the dynamo; ii) for low ratios of the energy supposed to be required to maintain the geodynamo viscosity/geostrophic forces (i.e. low Ekman numbers), the dynamo (Rochester et al., 1975; Loper, 1975). predominantly relies on the flow components excited by instabilities; iii) the periods of motion are equal to the rotation period of the boundaries; iv) a magnetic dipole moment undergoes slow variations interrupted by reversals. Roberts and Wu (2005) gave the most synthetic and positive “ ⁎ Corresponding author. opinion on this issue: all that has been unequivocally established in E-mail address: [email protected] (N. Thouveny). the intervening 55 yr is that precession can in principle supply the 0012-821X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2008.08.020 270 N. Thouveny et al. / Earth and Planetary Science Letters 275 (2008) 269–284 geodynamo with abundant power. The question of whether the observation for an “evidence for orbital forcing of the geomagnetic geodynamo draw on this power is still unanswered, though it seems field”. probable from the work of Tilgner (2005)”. A dominant 100 ka period was found in RPI records from the Pacific Attempts to extract information from paleomagnetic records started Ocean (Yokoyama and Yamazaki, 2000). The absence of this period in in the late 70s: using the protocol of Levi and Banerjee (1976), Kent and the normalizing parameter (IRM) record supported the “possibility of Opdyke (1977) constructed a relative paleointensity (RPI) record for the an external energy supply of the geodynamo variation through orbital last 700 ka by dividing the natural remanent magnetization (NRM) forcing or climate change”. This observation, initially limited to the last intensities by the anhysteretic remanent magnetization (ARM) inten- 700 ka, was extended to the last 2 Ma for inclination (Yamazaki and sities measured along a core. They interpreted an emerging 43 ka period Oda, 2002)andRPIvariations(Yokoyama et al., 2007). NRM as the sign of a modulation of a precession-driven dynamo by changes of inclination variation in the Equatorial band record reversals, excur- the Earth's axis tilt (obliquity) and noted that a future confirmation of sions, and paleosecular variation and have no reason to be biased by such observation (i.e. correlation between geomagnetic paleointensity lithological changes. The latter are moreover paced by the 41 ka, and and obliquity) should evidence the contribution of forces arising from not by the 100 ka, period in this time interval. the Earth's precession to the geodynamo. Considering the “good Fuller (2006) compared paleointensity records, excursions and evidence that long term climatic variations have been controlled at reversals with obliquity variations, over various time ranges and least in part by Earth's orbital parameters”, they added that “a reached radically different clues: 1) the strongest RPI minima of the correspondence between some component of climatic change and last 800 ka correlate with obliquity minima, 2) polarity intervals variations of the Earth's magnetic field could be expected”. The shorter than 100 ka occur at 30–40 ka periods, “marginally shorter suggestion that geomagnetic excursions could be related to global ice than the obliquity period”, 3) reversals preferentially occurred when volume and Earth's eccentricity (Doake,1977 and Rampino,1979) laid on the average amplitude of the obliquity is low, 4) the most recent non-normalized magnetic intensity records, which imposed a first bias. reversals occurred near the inflection point of the descent slope from Kent (1982) denounced the “apparent correlation of paleomagnetic obliquity maxima (verified for most of the reversals of the last 4 Ma intensity and climatic records in deep sea sediments resulting from a except the boundaries of the Olduvai event), 5) the last nine reversals pronounced dependence of NRM intensity on sediment composition” have a non-random phase relation to the obliquity signal, 6) the dating and concluded that “a weak positive correlation between the NRM/IRM of older reversals is not accurate enough: an error of 0.33% is sufficient ratio and CaCO3” can be “optimistically related to some geomagnetic– to destroy the relationship. Testing the relationship between the climatic dependence or more likely to an inadequacy in the normal- obliquity and eccentricity phases and the ages of reversals or ization by IRM to take into account fully the strong lithological effect on excursions, Xuan and Channell (2006) have confirmed that reversals the NRM”. Various strategies were then employed to attempt improving of the last 5 Ma preferentially occurred during decrease of the the reliability of RPI records. Selective criteria for the reliability of the maximum obliquity envelope. normalization by susceptibility, IRM and ARM were proposed (King et al., Other studies found no orbital
Load more

Recommended publications
  • Geologic Map of the Long Valley Caldera, Mono-Inyo Craters
    DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP 1-1933 US. GEOLOGICAL SURVEY GEOLOGIC MAP OF LONG VALLEY CALDERA, MONO-INYO CRATERS VOLCANIC CHAIN, AND VICINITY, EASTERN CALIFORNIA By Roy A. Bailey GEOLOGIC SETTING VOLCANISM Long Valley caldera and the Mono-Inyo Craters Long Valley caldera volcanic chain compose a late Tertiary to Quaternary Volcanism in the Long Valley area (Bailey and others, volcanic complex on the west edge of the Basin and 1976; Bailey, 1982b) began about 3.6 Ma with Range Province at the base of the Sierra Nevada frontal widespread eruption of trachybasaltic-trachyandesitic fault escarpment. The caldera, an east-west-elongate, lavas on a moderately well dissected upland surface oval depression 17 by 32 km, is located just northwest (Huber, 1981).Erosional remnants of these mafic lavas of the northern end of the Owens Valley rift and forms are scattered over a 4,000-km2 area extending from the a reentrant or offset in the Sierran escarpment, Adobe Hills (5-10 km notheast of the map area), commonly referred to as the "Mammoth embayment.'? around the periphery of Long Valley caldera, and The Mono-Inyo Craters volcanic chain forms a north- southwestward into the High Sierra. Although these trending zone of volcanic vents extending 45 km from lavas never formed a continuous cover over this region, the west moat of the caldera to Mono Lake. The their wide distribution suggests an extensive mantle prevolcanic basement in the area is mainly Mesozoic source for these initial mafic eruptions. Between 3.0 granitic rock of the Sierra Nevada batholith and and 2.5 Ma quartz-latite domes and flows erupted near Paleozoic metasedimentary and Mesozoic metavolcanic the north and northwest rims of the present caldera, at rocks of the Mount Morrisen, Gull Lake, and Ritter and near Bald Mountain and on San Joaquin Ridge Range roof pendants (map A).
    [Show full text]
  • Is Earth's Magnetic Field Reversing? ⁎ Catherine Constable A, , Monika Korte B
    Earth and Planetary Science Letters 246 (2006) 1–16 www.elsevier.com/locate/epsl Frontiers Is Earth's magnetic field reversing? ⁎ Catherine Constable a, , Monika Korte b a Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093-0225, USA b GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany Received 7 October 2005; received in revised form 21 March 2006; accepted 23 March 2006 Editor: A.N. Halliday Abstract Earth's dipole field has been diminishing in strength since the first systematic observations of field intensity were made in the mid nineteenth century. This has led to speculation that the geomagnetic field might now be in the early stages of a reversal. In the longer term context of paleomagnetic observations it is found that for the current reversal rate and expected statistical variability in polarity interval length an interval as long as the ongoing 0.78 Myr Brunhes polarity interval is to be expected with a probability of less than 0.15, and the preferred probability estimates range from 0.06 to 0.08. These rather low odds might be used to infer that the next reversal is overdue, but the assessment is limited by the statistical treatment of reversals as point processes. Recent paleofield observations combined with insights derived from field modeling and numerical geodynamo simulations suggest that a reversal is not imminent. The current value of the dipole moment remains high compared with the average throughout the ongoing 0.78 Myr Brunhes polarity interval; the present rate of change in Earth's dipole strength is not anomalous compared with rates of change for the past 7 kyr; furthermore there is evidence that the field has been stronger on average during the Brunhes than for the past 160 Ma, and that high average field values are associated with longer polarity chrons.
    [Show full text]
  • Yosemite, Lake Tahoe & the Eastern Sierra
    Emerald Bay, Lake Tahoe PCC EXTENSION YOSEMITE, LAKE TAHOE & THE EASTERN SIERRA FEATURING THE ALABAMA HILLS - MAMMOTH LAKES - MONO LAKE - TIOGA PASS - TUOLUMNE MEADOWS - YOSEMITE VALLEY AUGUST 8-12, 2021 ~ 5 DAY TOUR TOUR HIGHLIGHTS w Travel the length of geologic-rich Highway 395 in the shadow of the Sierra Nevada with sightseeing to include the Alabama Hills, the June Lake Loop, and the Museum of Lone Pine Film History w Visit the Mono Lake Visitors Center and Alabama Hills Mono Lake enjoy an included picnic and time to admire the tufa towers on the shores of Mono Lake w Stay two nights in South Lake Tahoe in an upscale, all- suites hotel within walking distance of the casino hotels, with sightseeing to include a driving tour around the north side of Lake Tahoe and a narrated lunch cruise on Lake Tahoe to the spectacular Emerald Bay w Travel over Tioga Pass and into Yosemite Yosemite Valley Tuolumne Meadows National Park with sightseeing to include Tuolumne Meadows, Tenaya Lake, Olmstead ITINERARY Point and sights in the Yosemite Valley including El Capitan, Half Dome and Embark on a unique adventure to discover the majesty of the Sierra Nevada. Born of fire and ice, the Yosemite Village granite peaks, valleys and lakes of the High Sierra have been sculpted by glaciers, wind and weather into some of nature’s most glorious works. From the eroded rocks of the Alabama Hills, to the glacier-formed w Enjoy an overnight stay at a Yosemite-area June Lake Loop, to the incredible beauty of Lake Tahoe and Yosemite National Park, this tour features lodge with a private balcony overlooking the Mother Nature at her best.
    [Show full text]
  • Consequences of Drying Lake Systems Around the World
    Consequences of Drying Lake Systems around the World Prepared for: State of Utah Great Salt Lake Advisory Council Prepared by: AECOM February 15, 2019 Consequences of Drying Lake Systems around the World Table of Contents EXECUTIVE SUMMARY ..................................................................... 5 I. INTRODUCTION ...................................................................... 13 II. CONTEXT ................................................................................. 13 III. APPROACH ............................................................................. 16 IV. CASE STUDIES OF DRYING LAKE SYSTEMS ...................... 17 1. LAKE URMIA ..................................................................................................... 17 a) Overview of Lake Characteristics .................................................................... 18 b) Economic Consequences ............................................................................... 19 c) Social Consequences ..................................................................................... 20 d) Environmental Consequences ........................................................................ 21 e) Relevance to Great Salt Lake ......................................................................... 21 2. ARAL SEA ........................................................................................................ 22 a) Overview of Lake Characteristics .................................................................... 22 b) Economic
    [Show full text]
  • Introducing Terminal Lakes Joe Eilers and Ron Larson
    Terminal Lakes Introducing Terminal Lakes Joe Eilers and Ron Larson Study Lakes akes tend to be among the more ephemeral features of the landscape Land generally are formed and disappear rapidly on a geological time frame. However, to see groups of lakes disappear within a lifetime is typically not a natural phenomenon. Here in Oregon, we’ve witnessed the desiccation of what was formerly a 16-mile-long lake in a little over a decade. Endorehic lakes, commonly referred to as terminal lakes because they lack an outlet, are among the most vulnerable of lakes to human intervention. Because terminal lakes are usually located in arid environments where water is extremely valuable, they are the first to lose among the competing forces for water. But that doesn’t have to be the case. In some respects, terminal lakes are far easier to restore than eutrophic/hypereutrophic systems. No expensive alum treatments, no dredging, no chemicals . just add water and life returns: but as those in West know, “Whiskey is for drinking; water is for fighting over.” And fight we must. In this issue of LakeLine, we describe a series of terminal lakes in the western United States starting with the least saline lake among the group, Walker Lake, and ending with Lake Winnemucca, which was desiccated in the 20th century (Figure 1). Like all lakes, each of these has a unique story to relate with different Figure 1. Terminal lakes in the western United States described in this issue. chemistry and biota. The loss of Lake Winnemucca is an informative tale, but it a wider audience and reach a solution migration when the birds replenish fat is not necessarily the inevitable outcome that ensures adequate water to save the reserves.
    [Show full text]
  • Open-File/Color For
    Questions about Lake Manly’s age, extent, and source Michael N. Machette, Ralph E. Klinger, and Jeffrey R. Knott ABSTRACT extent to form more than a shallow n this paper, we grapple with the timing of Lake Manly, an inconstant lake. A search for traces of any ancient lake that inundated Death Valley in the Pleistocene upper lines [shorelines] around the slopes Iepoch. The pluvial lake(s) of Death Valley are known col- leading into Death Valley has failed to lectively as Lake Manly (Hooke, 1999), just as the term Lake reveal evidence that any considerable lake Bonneville is used for the recurring deep-water Pleistocene lake has ever existed there.” (Gale, 1914, p. in northern Utah. As with other closed basins in the western 401, as cited in Hunt and Mabey, 1966, U.S., Death Valley may have been occupied by a shallow to p. A69.) deep lake during marine oxygen-isotope stages II (Tioga glacia- So, almost 20 years after Russell’s inference of tion), IV (Tenaya glaciation), and/or VI (Tahoe glaciation), as a lake in Death Valley, the pot was just start- well as other times earlier in the Quaternary. Geomorphic ing to simmer. C arguments and uranium-series disequilibrium dating of lacus- trine tufas suggest that most prominent high-level features of RECOGNITION AND NAMING OF Lake Manly, such as shorelines, strandlines, spits, bars, and tufa LAKE MANLY H deposits, are related to marine oxygen-isotope stage VI (OIS6, In 1924, Levi Noble—who would go on to 128-180 ka), whereas other geomorphic arguments and limited have a long and distinguished career in Death radiocarbon and luminescence age determinations suggest a Valley—discovered the first evidence for a younger lake phase (OIS 2 or 4).
    [Show full text]
  • 2021 Falling for the Migration
    Falling for the Migration: Bridgeport, Crowley, Mono American Avocets in flight, photo by Bob Steele August 20–22, 2021 ● Dave Shuford $182 per person / $167 for Mono Lake Committee members enrollment limited to 10 participants Welcome to our field seminar on the fall migration of birds in the Bridgeport Valley and the adjacent Sierra, the Mono Basin, Crowley Lake, Long Valley, and the outskirts of Mammoth Lakes. Beginners as well as experts will enjoy this introduction to the area’s birdlife found in a wide variety of habitats, from the shimmering shores of Mono Lake to lofty Sierra peaks. We will identify about 100 species by plumage and calls, and probe the secrets of their natural history. This seminar will include informal discussions on migration strategies, behavior, and ecology that complement our field observations. This seminar will involve easy hiking at elevations ranging from 6,400 to 9,600 feet above sea level. We will hike 1–2 miles a day, mostly on level terrain. The first stop Friday morning is at Bridgeport Reservoir, a mecca for migrant and late‐breeding waterbirds. For those who prefer to meet the seminar at this location (arriving Friday morning from points north), please contact Nora Livingston at [email protected] or (760) 647‐6595 to obtain directions. Dave Shuford is an expert birder, avid naturalist and teacher, and a retired professional ornithologist. Dave’s bird research in the region includes a long‐term study on the ecology of Mono Lake’s California Gull colony, an atlas of breeding birds in the Glass Mountain area, and surveys of Snowy Plovers at Mono and Owens lakes.
    [Show full text]
  • Most Recent Eruption of the Mono Craters, Eastern Central California
    JOURNALOF GEOPHYSICALRESEARCH, VOL. 91, NO. B12, PAGES12,539-12,571, NOVEMBER10, 1986 MOST RECENT ERUPTION OF THE MONO CRATERS, EASTERN CENTRAL CALIFORNIA Kerry Sieh and Marcus Bursik Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena Abstract. The most recent eruption at the gradually diminishing explosiveness of the North Mono Craters occurred in the fourteenth century Mono eruption probably resulted from a decrease A.D. Evidence for this event includes 0.2 km3 of of water content downward in the dike. The pyroclastic fall, flow, and surge deposits and pulsating nature of the early, explosive phase of 0.4 km3 of lava domesand flows. These rhyolitic the eruption may represent the repeated rapid deposits emanated from aligned vents at the drawdown of slowly rising vesiculated magma to northern end of the volcanic chain. Hence we about the saturation depth of the water within have named this volcanic episode the North Mono it. eruption. Initial explosions were Plinian to sub-Plinian events whose products form Introduction overlapping blankets of air fall tephra. Pyroclastic flow and surge deposits lie upon Several dozen silicic eruptions have occurred these undisturbed fall beds within several along the tectonically active eastern flank of kilometers of the source vents. Extrusion of the central Sierra Nevada within the past 35,000 five domes and coulees, including Northern Coulee years; many of these eruptions have, in fact, and Panurn Dome, completed the North Mono occurred within the past 2000 years. This eruption. Radiocarbon dates and violent, exciting, and youthful past suggests an dendrochronological considerations constrain the interesting future and encouraged us to undertake eruption to a period between A.D.
    [Show full text]
  • Decline of the World's Saline Lakes
    PERSPECTIVE PUBLISHED ONLINE: 23 OCTOBER 2017 | DOI: 10.1038/NGEO3052 Decline of the world’s saline lakes Wayne A. Wurtsbaugh1*, Craig Miller2, Sarah E. Null1, R. Justin DeRose3, Peter Wilcock1, Maura Hahnenberger4, Frank Howe5 and Johnnie Moore6 Many of the world’s saline lakes are shrinking at alarming rates, reducing waterbird habitat and economic benefits while threatening human health. Saline lakes are long-term basin-wide integrators of climatic conditions that shrink and grow with natural climatic variation. In contrast, water withdrawals for human use exert a sustained reduction in lake inflows and levels. Quantifying the relative contributions of natural variability and human impacts to lake inflows is needed to preserve these lakes. With a credible water balance, causes of lake decline from water diversions or climate variability can be identified and the inflow needed to maintain lake health can be defined. Without a water balance, natural variability can be an excuse for inaction. Here we describe the decline of several of the world’s large saline lakes and use a water balance for Great Salt Lake (USA) to demonstrate that consumptive water use rather than long-term climate change has greatly reduced its size. The inflow needed to maintain bird habitat, support lake-related industries and prevent dust storms that threaten human health and agriculture can be identified and provides the information to evaluate the difficult tradeoffs between direct benefits of consumptive water use and ecosystem services provided by saline lakes. arge saline lakes represent 44% of the volume and 23% of the of migratory shorebirds and waterfowl utilize saline lakes for nest- area of all lakes on Earth1.
    [Show full text]
  • Methods and Spatial Extent of Geophysical Investigations, Mono Lake, California, 2009 to 2011
    Methods and Spatial Extent of Geophysical Investigations, Mono Lake, California, 2009 to 2011 Open-File Report 2013–1113 U.S. Department of the Interior U.S. Geological Survey FRONT COVER: Map showing location of seismic tracklines in Mono Lake: 2009 (solid lines), 68 tracklines, total 318 km; 2011 (dashed lines), 60 tracklines, total 199 km. Map prepared by Florence Wong, USGS Coastal and Marine Geology. Methods and Spatial Extent of Geophysical Investigations, Mono Lake, California, 2009 to 2011 By A.S. Jayko, P.E. Hart, J.R. Childs, M.H. Cormier, D.A.Ponce, N.D. Athens, and J.S. McClain Open-File Report 2013–1113 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior SALLY JEWELL, Secretary U.S. Geological Survey Suzette M. Kimball, Acting Director U.S. Geological Survey, Reston, Virginia: 2013 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod To order this and other USGS information products, visit http://store.usgs.gov Suggested citation: Jayko, A.S., Hart, P.E., Childs, J.R., Cormier, M.H., Ponce, D.A., Athens, N.A., and McClain, J.S., 2013, Methods and spatial extent of geophysical Investigations, Mono Lake, California, 2009 to 2011; U.S. Geological Survey Open-File Report 2013–1113, 18 p., http://pubs.usgs.gov/of/2013/1113/.
    [Show full text]
  • Eastern Sierra Fall Color
    Quick Fall Facts When and How to Get Here WHY OUR FALL COLOR SEASON FIND OUT WHEN TO “GO NOW!” GOES ON AND ON AND ON See detailed fall color reporting at The Eastern Sierra’s varied elevations — from www.CaliforniaFallColor.com approximately 5,000 to 10,000 feet (1,512 to 3,048 m) Follow the Eastern Sierra on Facebook: — means the trees peak in color at different times. Mono County (VisitEasternSierra) Bishop Creek, Rock Creek, Virginia Lakes and Green Mammoth Lakes (VisitMammoth) Creek typically turn color first (mid-to late September), Bishop Chamber of Commerce (VisitBishop) with Mammoth Lakes, McGee Creek, Bridgeport, Conway Summit, Sonora and Monitor passes peaking next (late September), and finally June Lake Loop, Lundy Canyon, Lee Vining Canyon, Convict Lake and the West Walker River offering a grand finale from FLY INTO AUTUMN! the first to third week of October. The City of Bishop From any direction, the drive to the shows color into early November. Eastern Sierra is worth it…but the flight connecting through LAX to Mammoth Yosemite Airport is TREE SPECIES possibly more spectacular and gets you here faster: Trees that change color in the Eastern Sierra www.AlaskaAir.com include aspen, cottonwood and willow. LIKE CLOCKWORK NEED HELP PLANNING YOUR TRIP? Ever wonder how Eastern Sierra leaves know CONTACT US: to go from bright green to gold, orange and russet Bishop Chamber of Commerce & Visitor Center as soon as the calendar hits mid-September? Their 760-873-8405 www.BishopVisitor.com cue is actually from the change in air temperature 690 N.
    [Show full text]
  • Revised Chronology for Late Pleistocene Mono Lake Sediments Based on Paleointensity Correlation to the Global Reference Curve ⁎ Susan H
    Earth and Planetary Science Letters 252 (2006) 94–106 www.elsevier.com/locate/epsl Revised chronology for late Pleistocene Mono Lake sediments based on paleointensity correlation to the global reference curve ⁎ Susan H. Zimmerman a, , Sidney R. Hemming a,b, Dennis V. Kent b,c, Stephanie Y. Searle a a Department of Earth and Environmental Sciences, Columbia University, New York, NY 10027, USA b Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA c Department of Geological Sciences, Rutgers University, Piscataway, NJ 08854, USA Received 2 May 2006; received in revised form 12 September 2006; accepted 13 September 2006 Available online 25 October 2006 Editor: M.L. Delaney Abstract Lakes are highly sensitive recorders of climate processes, but are extremely difficult to correlate precisely to ice-core and marine records, especially in the absence of reliable radiocarbon dates. Relative paleointensity (RPI) of Earth's magnetic field is an independent method of correlating high-resolution climate records, and can be applied to both marine and terrestrial sediments, as well as (inversely) correlated to the cosmogenic nuclide records preserved in ice cores. Here we present the correlation of an RPI record from Mono Lake, California to GLOPIS, the Global PaleoIntensity Stack, which increases the age estimation of the basal Mono Lake sediments by N20000 yr (20 kyr), from ∼40 ka (kyr before present) to 67 ka. The Mono Lake sediments thus preserve paleoclimatic records of most of the last glacial period, from 67 to 14 ka. In addition, the paleointensity-based age of 40 ka for the geomagnetic excursion preserved at Mono Lake indicates that this is a record of the global Laschamp excursion.
    [Show full text]