Download or read book Paleoclimate Paleoventilation and Paleomagnetism as Recorded in a 17kyr Marine Sediment Record from the SE Alaska Margin written by Maureen Helen Davies and published by . This book was released on 2011 with total page 164 pages. Available in PDF, EPUB and Kindle. Book excerpt: The deglacial behavior of the sub-Arctic North Pacific is poorly constrained, with many published records suffering from limited age control due to extensive post- depositional biogenic carbonate dissolution. Potential alternative dating methods could include the correlation of stable-isotopic and/or paleomagnetic secular variation records to an independently-dated regional template, however no such template currently exists. Cores EW0408-85JC (59°33.32'N, 144°9.21'W, 682 m water depth) and EW0408-79JC (59°33.32'N, 144°9.21'W, 682 m water depth) are located above the carbonate compensation depth on the Gulf of Alaska margin, affording an opportunity to inter- compare stable-isotopic and paleomagnetic variability from a single location, as well as to place observations of Northeast Pacific paleoclimate and paleomagnetic secular variation in a global context via an independent radiocarbon-based chronology. We evaluate three possible age models for core EW0408-85JC and their implications for North Pacific stable isotopic and paleoventilation behavior. These include calibrated planktonic and benthic foraminiferal radiocarbon dates, assuming constant reservoir ages, as well as a correlation of planktonic [delta]18O in foraminifera to [delta]18O in a layer-counted Greenland ice core (NGRIP). We conclude that the calibrated planktonic dates provide the most accurate chronology. Benthic foraminiferal radiocarbon dates evaluated on this age model indicate that intermediate-depth ventilation ages at the site increased to>2,670 ± 180 during Termination 1, implying reduced ventilation relative to the Holocene average of 1,740 ± 210 yr. The shift to lower ventilation ages occurs at ~10,500 cal ybp, coeval with the flooding of Beringia and the opening of the Bering Strait, suggesting that flooded shelves and net export of low- salinity surface waters enhanced ventilation of the North Pacific. Oxygen isotope data from planktonic and benthic foraminifera, interpreted on this age model, document surface freshening by 16,650 ± 170 cal ybp, likely due to freshwater input from retreating regional glaciers. A sharp transition to laminated hemipelagic sedimentation at 14,790 ± 380 cal ybp is coincident with abrupt warming and/or freshening of the surface ocean (i.e. additional [delta]18O reduction of 0.9 [per mil]), essentially coincident with the Bolling Interstade of Northern Europe and Greenland. Cooling and/or higher salinities returned during the Allerod interval, coeval with the Antarctic Cold Reversal and continuing until 11,740 ± 200 cal ybp, when the onset of warming coincides with the end of the Younger Dryas. This may indicate convolved Northern and Southern drivers of climate variability in the North Pacific. Two laminated opal-rich intervals record episodes of high productivity are observed from 14,790 ± 380 to 12,990 ± 190 cal ybp, and from 11,160 ± 130 to 10,750 ± 220 cal ybp. These events likely correlate to similar observations elsewhere on the margins of the North Pacific, and may be driven my remobilization of iron from newly inundated continental shelves during episodes of rapid sea-level rise. High-resolution paleomagnetic secular variation (PSV) records from the Gulf of Alaska constrain regional field behavior and provide information on larger scale geomagnetic dynamics. Both cores studied (EW0408-79JC and 85JC) preserve a generally strong and relatively stable (MAD
Download or read book A 37 000 year Record of Paleomagnetic and Environmental Magnetic Variability from Burial Lake Arctic Alaska written by Jason Michael Dorfman and published by . This book was released on 2013 with total page 126 pages. Available in PDF, EPUB and Kindle. Book excerpt: Burial Lake sediments from the Noatak Basin in the northwest Brooks Range of Arctic Alaska (68.43°N, 159.17°W, 21.5 m water depth) provide the oldest continuous lacustrine record of paleo-environmental change and paleomagnetic secular variation (PSV) in eastern Beringia. A precise radiocarbon chronology, determined through accelerator mass spectrometry (AMS) allows us to independently constrain the region's climatic and geomagnetic evolution over the last ~37,000 years. Progressive alternating field (AF) demagnetization of u-channel samples and additionally acquired physical, geochemical, and rock-magnetic datasets, reveal three distinct lithologic subunits associated with the last glacial period (37.2 - 19.4 ka), the deglacial transition (19.4 - 9.8 ka), and the Holocene (9.8 ka - present). Rock magnetic variability suggests changes in sediment provenance associated with the transition from glacial to interglacial conditions. This is interpreted to result from a variable flux of aeolian derived sediment, and is supported by complimentary internal proxy data from Burial Lake. Other regional paleoclimate data, various glacial chronologies for the Brooks Range, and a relative sea level reconstruction facilitate a discussion of possible local, widespread, and far-field sources of dust, and the time-dependency of potential forcing mechanisms governing its production, availability, transport, and deposition. Results indicate an overall reduction in dust input from the glacial period to the Holocene that is largely attributed to increases in terrestrial and aquatic productivity, warming, and moisture availability, which limited widespread landscape deflation and production of dust. Subaerial continental shelves may have provided significant far-field sources of dust to interior Alaska during the glacial period, that were shut off by sea level inundation following the Last Glacial Maximum (LGM; 19 - 26.5 ka), further contributing to diminishing dust emissions. While glacial activity in the Brooks Range may provide local revenue of dust, activation of those deposits and timing of deposition in Burial Lake often appears to be more directly linked with general aridity, lack of vegetative cover, and increased windiness, rather than glacial advances or retreats. Despite this lithologic complexity, we isolate a stable, single-component characteristic remanent magnetization, carried predominately by low-coercivity (titano)magnetite in the pseudo single-domain (PSD) to multi-domain (MD) magnetic grain size range. We reconstruct directional paleomagnetic secular variation (PSV) over the full length of the record, and relative paleointensity (RPI) for the last ~14,700 years, which are consistent with available regional PSV records and continuous spherical harmonic model outputs. We observe only small deviations from geocentric axial dipole (GAD) predictions during the Holocene, while larger amplitude directional features are prevalent before 10 ka, and inclinations lay significantly shallower than GAD. While this may be related to lithology and the sediment magnetic acquisition process, regional records (including those derived from lava flows) indicate similar Holocene-Pleistocene discrepancies. Following on the "eccentric dipole" hypothesis, subdued secular variation and GAD-like behavior in the Pacific appears confined to the Holocene high-intensity state, showing greater variability as Pleistocene field strength diminishes, and/or the dipole axis is shifted away from the Pacific hemisphere. Long period trends in PSV from in the Alaskan Arctic are also similar in character to far-field sites (e.g., Hawaii and Siberia), suggesting large-scale coherent core-fluid flow regimes, expressed over surface geographical extents>5,000 km, and spanning Holocene-Pleistocene time intervals. The well-dated Burial Lake record fills a significant data gap in the growing Holocene paleomagnetic database, while allowing us to extend our understanding of PSV beyond the Holocene and into the Pleistocene, and continue the development of regional stratigraphic dating curves.
Download or read book Paleomagnetic Rotations and Continental Deformation written by Catherine Kissel and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 516 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the most interesting results obtained in the last two decades in the study of crustal deformation has been the recognition that large regions of continental crust undergo rotations about vertical axis during deformation. Proof of such rotations has come through the paleomagnetic studies, which reveal rotations when paleomagnetic declinations within the deforming region arc compared with those found in coeval rocks in the stable regions outside the deforming zone. Such rotations were first described in Oregon then in the North American Cordilleras and in Southern California and were a surprise to everyone. Even in California which, as a result of oil exploration, was among the best geologically explored regions in the world, no one could claim to have predicted that these rotations would be found. Rotations have subsequently been found in other areas of recent continental tectonic activity, notably in the Basin and Range province, New Zealand, the Andes, Greece and Western Turkey, so that they appear as an important feature of continental deformation.
Download or read book Paleoclimate Paleomagnetism and Continental Drift written by J. K. A. Habicht and published by . This book was released on 1979 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: Library has 2 copies.
Download or read book A Dendroclimatic Record of Paleoclimate of the Last 10 000 Years Glacier Bay National Park and Preserve written by Daniel E. Lawson and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Paleomagnetism of Eocene Plutonic Rocks Matanuska Valley Alaska written by John A. Stamatakos and published by . This book was released on 1988 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Paleomagnetism and Environmental Magnetism of Sediment Cores from ODP Leg 169S Saanich Inlet British Columbia written by Adam Hershel Harris and published by . This book was released on 2002 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Separation of Geomagnetic Paleointensity and Paleoclimate Signals in Sediments written by Stefanie Ann Brachfeld and published by . This book was released on 1999 with total page 528 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Paleomagnetism of the Crater Creek Basalts Umnak Island Alaska written by Biswa Nath Chatterjee and published by . This book was released on 1970 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Paleomagnetism and Petrology of St Matthew Island Bering Sea Alaska written by Paul Raymond Wittbrodt and published by . This book was released on 1985 with total page 420 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Multi proxy Record of Holocene Paleoenvironmental and Paleoclimate Change at Lake Tokun South central Alaska written by Jonathan Gilbert Griffith and published by . This book was released on 2014 with total page 105 pages. Available in PDF, EPUB and Kindle. Book excerpt: Sediment cores from Lake Tokun were used to reconstruct paleoenvironmental and paleoclimate changes in the Copper River delta area, Alaska. A 4.2-m-long sediment sequence was analyzed for organic matter, chlorophyll-a, magnetic susceptibility, and bulk density. The chronology was based on radiocarbon ages and short-lived isotopes. Distinct changes in the sedimentary succession record major paleoenvironmental changes during the Holocene. Prior to 8.8 ka, Lake Tokun received meltwater from the Martin River Glacier at a time when sea level had transgressed at least 6 km inland of the present shoreline likely due to isostatic depression upon deglaciation. From 8.8 to 0.7 ka, Lake Tokun was a shallow lake receiving sporadic pulses of rock flour when Martin River overtopped its channels. At 735-1215 AD, rock flour deposited in Lake Tokun represents an aggrading outwash plain as the Martin River Glacier expanded and then deposited its terminal moraine. The proximal end of the associated outwash plain dammed Lake Tokun, deepening the lake and enhancing sediment deposition. The lake attained its present depth about 1215 AD and rock flour has not reentered the lake since then. The uppermost sedimentary unit (150 cm thick) was analyzed at 0.5 cm resolution (average of 3 year per sample) using VNIR reflectance spectroscopy to infer the concentration of chlorophyll-a (chl-a). Instrumental weather data from Cordova (1917 to 2009) show a strong inverse correlation (r2 = 0.49; p = 0.03) between August precipitation and sedimentary chl-a content in Lake Tokun. Storms beginning in the late summer and persisting through the fall are important in controlling peak discharges and the subsequent transport of allochthonous material into Lake Tokun. Winter (DJF) temperature is also inversely correlated with chl-a content (r2 = 0.33; p = 0.04), indicating that warm winters, which tend to be wet, also lead to enhanced runoff, which carries mineral matter that dilutes the chl-a content of the lake sediment. Decreased chl-a values suggest increased runoff during the early to middle Little Ice Age (LIA; 1215-1650 AD). Increased chl-a values during the late LIA (1650-1850 AD) are suggestive of decreased runoff. This study demonstrates that multi-proxy analysis of lake sediments is an effective method for inferring past paleoenvironmental and paleoclimate change.
Download or read book Paleomagnetism of Two Lake Sediment Cores from Seward Peninsula Alaska written by Robert John Marino and published by . This book was released on 1977 with total page 366 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Comparison of the Paleomagnetic Records in Sediments from Two Late Pleistocene Lake Basins in Colorado written by Joseph G. Rosenbaum and published by . This book was released on 1980 with total page 296 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Paleomagnetism of the Atlantic Tethys and Iapetus Oceans written by Rob van der Voo and published by Cambridge University Press. This book was released on 1993 with total page 424 pages. Available in PDF, EPUB and Kindle. Book excerpt: Continents move around continuously with respect to each other; this book describes what went where.
Download or read book High resolution paleomagnetic records from Holocene sediments from the Palmer Deep western Antarctic Peninsula written by S. BRACHFELD and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book An Investigation of the Magnetic Fabrics and the Paleomagnetism of the Ghost Rocks Formation Kodiak Islands Alaska written by Sean F. Gallen and published by . This book was released on 2008 with total page 238 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Paleomagnetism written by Robert F. Butler and published by Wiley-Blackwell. This book was released on 1992 with total page 319 pages. Available in PDF, EPUB and Kindle. Book excerpt:
