HR: 09:30h
AN: GP51B-07
TI: Geomagnetic Links to Climate Change and Orbital Cycles
AU: * Acton, G
EM: acton@geology.ucdavis.edu
AF: University of California, Davis, Department of Geology, Davis, CA 95616 United States
AB: Years of speculation, newly recognized mechanisms for interactions, and a sparse but expanding number of observations support some form of link between geomagnetic field variability and climate change and/or orbital cycles. Early paleomagnetic observations only hinted at the links and failed to withstand scrutiny for a number of reasons including poor data quality, poor age control, poor resolution of short-term geomagnetic directional variability over sufficiently long time periods, and a reliance on relative paleointensity records. Even though Milankovitch periodicities have been observed in the latter, proving that these are not influenced by climatically induced lithologic changes rather than by geomagnetic field variability is difficult. At this point, the speculation has been more interesting that the evidence has been convincing. New long continuous records of short-term paleomagnetic directional variability that span the past 1 m.y., however, show intriguing correlations of geomagnetic excursions with precession cycles and with deglacials. The changes in directions for these excursions are too large to be attributed to lithologic variations nor can they be attributed to local sedimentary or tectonic processes as the excursion are observed regionally or globally. Although such correlations might have been regarded as fortuitous in the past, age constraints have improved significantly by obtaining stable isotope records or other climate proxies directly from the same stratigraphic sections as the geomagnetic records. Furthermore, speculation about mechanisms for geomagnetic links to climate and orbital cycles have been succeeded by climate studies that have found that cloud formation is associated with the amount of cosmogenic radiation, which is largely controlled by the geomagnetic field. Similarly, precession had been disregarded as a driving force for the geodynamo, but recent modeling shows that such conclusions were premature. Thus, causal relationships between geomagnetic field variability, climate change, and orbital cycles are not unexpected nor are they unobserved.
DE: 1513 Geomagnetic excursions
DE: 1522 Paleomagnetic secular variation
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 3036 Ocean drilling
DE: 4901 Abrupt/rapid climate change (1605)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2006 Fall Meeting

HR: 14:55h
AN: GP13A-06
TI: Micromagnetic Coercivity Distributions and Interactions in Chondrules With Implications for Paleointensities of the Early Solar System
AU: Yin, Q
EM: qyin@ucdavis.edu
AF: University of California, Davis, Department of Geology, Davis, CA 95616 United States
AU: * Acton, G
EM: acton@geology.ucdavis.edu
AF: University of California, Davis, Department of Geology, Davis, CA 95616 United States
AU: Verosub, K L
EM: verosub@geology.ucdavis.edu
AF: University of California, Davis, Department of Geology, Davis, CA 95616 United States
AU: Jovane, L
EM: jovane@ingv.it
AF: University of California, Davis, Department of Geology, Davis, CA 95616 United States
AU: Jovane, L
EM: jovane@ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, 605, Rome, 00143 Italy
AU: Roth, A
EM: allouroth@gmail.com
AF: University of California, Davis, Department of Geology, Davis, CA 95616 United States
AU: Jacobsen, B
EM: jacobsen@geology.ucdavis.edu
AF: University of California, Davis, Department of Geology, Davis, CA 95616 United States
AU: Ebel, D S
EM: debel@amnh.org
AF: American Museum of Natural History, Department of Earth and Planetary Sciences, New York, NY 10024 United States
AB: Chondrules in chondritic meteorites record the earliest stages of formation of the Solar System, potentially providing information about the magnitude of early magnetic fields and early physical and chemical conditions. Using first-order reversal curves (FORCs), we map the coercivity distributions and interactions of 32 chondrules from the Allende, Karoonda, and Bjurbole meteorites. Distinctly different distributions and interactions exist for the three meteorites. The coercivity distributions are log-normal shaped, with Bjurbole distributions being bimodal or trimodal. Allende FORC distributions have coercivities that extend out to about 250-350 mT, with little or no interaction above 10 mT. Karoonda FORC distributions are triangular shaped with high interactions at low coercivity and progressively lower interactions out to the peak coercivity of about 130 mT. In Bjurbole chondrules, a high coercivity mode (400-700 mT) arising from tetrataenite interacts strongly with one or more lower coercivity modes in a manner unlike that seen in terrestrial rocks. Such strong interactions have the potential to bias paleointensity estimates. Moreover, because a significant portion of the coercivity distributions for most of the chondrules is <10 mT, low-coercivity magnetic overprints are common. Therefore, paleointensities based on the REM method, which rely on ratios of the natural remanent magnetization (NRM) to the saturation isothermal remanent magnetization (IRM) without magnetic cleaning, will probably be biased. The paleointensity bias is found to be about an order of magnitude for most chondrules with low-coercivity overprints. Paleointensity estimates based on a method we call REMc, which uses NRM/IRM ratios after magnetic cleaning, avoid this overprinting bias. Allende chondrules, which are the most pristine and possibly record the paleofield of the early Solar System, have a mean REMc paleointensity of 10.4 μT. Karoonda and Bjurbole chondrules, which have experienced some thermal alteration, have REMc paleointensities of 4.6 and 3.2 μT, respectively.
DE: 1519 Magnetic mineralogy and petrology
DE: 1521 Paleointensity
DE: 1595 Planetary magnetism: all frequencies and wavelengths
DE: 2134 Interplanetary magnetic fields
DE: 6030 Magnetic fields and magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2006 Fall Meeting

HR: 0800h
AN: C41C-0344
TI: Initial Magnetostratigraphic and Environmental Magnetic Results from Old Cores from the Ross Sea Sector (Antarctica)
AU: * Verosub, K L
EM: verosub@geology.ucdavis.edu
AF: University of California - Davis, Geology Dept. One Shields Ave., Davis, CA 95616 United States
AU: Jovane, L
EM: jovane@geology.ucdavis.edu
AF: University of California - Davis, Geology Dept. One Shields Ave., Davis, CA 95616 United States
AU: Jovane, L
EM: jovane@geology.ucdavis.edu
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, Rome, 00143 Italy
AU: Acton, G C
EM: acton@geology.ucdavis.edu
AF: University of California - Davis, Geology Dept. One Shields Ave., Davis, CA 95616 United States
AB: We are undertaking new paleomagnetic and rock magnetic studies of old cores from the Ross Sea sector of Antarctica. Our goals are 1) to gain new insights into the timing and nature of paleoclimate events in the Ross Sea sector; 2) to stimulate new research on a large collection of cores from the Ross Sea sector that were collected at great expense and that have been subjected to little or no scientific study; and 3) to provide a broader context for interpreting results from cores from the Ross Sea sector that will be obtained from the ANDRILL project. The first systematic piston coring of the Southern Ocean was conducted during the 1960s by the USNS Eltanin as part of Operation Deep Freeze. Of particular interest are Cruise 27 in 1968 and Cruise 32 in 1969, which collected several dozen cores from the Ross Sea sector. Subsequent piston coring in the Ross Sea sector was done by the USCGC Glacier (1970s), R/V Polar Duke (1980s), and the R/V Nathaniel B. Palmer (1990s to present). We have acquired preliminary data from eight sites that demonstrate that even after thirty years, there is valuable magnetic information that can be gathered from these cores. Following the removal of a low-coercivity overprint, which probably originates from drilling, handling or storage, most cores have a strong, stable remanent magnetization over a demagnetization interval of 25-50 mT. Given the frequent occurrence of normal polarity in these cores and the relative shallow depths of coring in most holes, the sediment in many of these cores is probably mostly of Brunhes age. Nevertheless,from the stable magnetic components, we have been able to construct magnetostratigraphies and, in some cases, relative paleointensity records, which provide new age constraints. In addition, we have obtained environmental magnetic data that provide new insights about geologic processes, such as weathering, erosion, transport, deposition and post-depositional alteration. When tied with the chronostratigraphic observations, our results provide new constraints about paleoclimate events in the Ross Sea sector, especially those that affect the availability of sediment and its transport into the basin.
DE: 1512 Environmental magnetism
DE: 1520 Magnetostratigraphy
DE: 1521 Paleointensity
DE: 4207 Arctic and Antarctic oceanography (9310, 9315)
DE: 9310 Antarctica (4207)
SC: Cryosphere [C]
MN: 2006 Fall Meeting

HR: 0800h
AN: GP11A-0053
TI: A New Apparent Polar Wander Path for Antarctica
AU: * Jovane, L
EM: jovane@geology.ucdavis.edu
AF: Department of Geology, University of California, Davis, 1 Shields Av., Davis, ca 95616 United States
AU: * Jovane, L
EM: jovane@geology.ucdavis.edu
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, Rome, 00143 Italy
AU: Acton, G
EM: acton@geology.ucdavis.edu
AF: Department of Geology, University of California, Davis, 1 Shields Av., Davis, ca 95616 United States
AU: Verosub, K L
EM: verosub@geology.ucdavis.edu
AF: Department of Geology, University of California, Davis, 1 Shields Av., Davis, ca 95616 United States
AU: Florindo, F
EM: florindo@ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, Rome, 00143 Italy
AU: Sagnotti, L
EM: sagnotti@ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, Rome, 00143 Italy
AU: Wilson, G
EM: gary.wilson@otago.ac.nz
AF: University of Otago, Department of Geology, Dunedin, PO Box 56 New Zealand
AB: The apparent polar wander path (APWP) for Antarctica contains very few paleomagnetic observations and is probably the most poorly constrained APWP for any of the major lithospheric plates. The poor coverage and temporal distribution of paleomagnetic studies can be attributed to the sparse occurrence of outcrops and to the small number of deep drill cores that have been collected on the continent and surrounding oceans, in part because of high costs and logistical difficulties. In addition, although studies of the Antarctic APWP have not received much attention, global plate reconstructions that link Pacific basin plates to the plates in the Indian and Atlantic Oceans must pass through Antarctica. Understanding the past position and motion of the Antarctic plate is therefore important for plate reconstructions and has implications for geodynamic, geomagnetic, and paleoclimatic studies. We are attempting to refine the Antarctic APWP along Cenozoic by using inclination data from DSDP Sites 270 and 274, ODP Sites 689, 690, 738, 744, 748, 1095, 1096, 1101, 1165, 1166, 1167, and the CIROS-1 and CRP-1, 2 and 3 drill cores. Several of these sites have high sedimentation rates and detailed magnetostratigraphy, which provide high-resolution observation and well- constrained ages. We first divided each of these datasets into several time subunits based on sedimentation rate, data availability and lithological discontinuities and have then combined coeval subunits from different cores. This procedure allows us to estimate paleocolatitudes and "relative" virtual geomagnetic poles (VGPs) along with their confidence limits. The paleocolatitudes from all cores of a given age or time period define multiple small circles of possible paleomagnetic pole positions, and their intersection defines the most probable position of the pole. Angular dispersion of the inclination averages has also been calculated in order to test for secular variation and the goodness of the sampling.
DE: 1522 Paleomagnetic secular variation
DE: 1525 Paleomagnetism applied to tectonics: regional, global
DE: 9310 Antarctica (4207)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2006 Fall Meeting

HR: 0800h
AN: GP51A-0941
TI: Testing for Links Between Geomagnetic Field Variability and Climate Change
AU: * Wetter, L
EM: wetter@geology.ucdavis.edu
AF: Department of Geology, University of California, Davis, One Shields Avenue, Davis, CA 95616
AU: Acton, G
EM: acton@geology.ucdavis.edu
AF: Department of Geology, University of California, Davis, One Shields Avenue, Davis, CA 95616
AU: Hill, T
EM: tmhill@ucdavis.edu
AF: Department of Geology, University of California, Davis, One Shields Avenue, Davis, CA 95616
AB: Although orbital forcing controls much of long-term climate change and increases in greenhouse gases are thought to be driving recent global warming, other factors may also play a significant role. Recent studies have hypothesized various forms of links between climate change and solar irradiance, solar activity, and cosmic ray flux. Because changes in geomagnetic field strength affect the cosmic ray flux, it is possible that changes in the geomagnetic field contribute to long- and short-term climate change. Alternatively, it has been hypothesized that geomagnetic field variability is influenced by climate change or solar activity. We test such claims through a paleomagnetic and stable isotope study of Ocean Drilling Program (ODP) sediment cores from the Blake Outer Ridge (BOR), western North Atlantic Ocean. The goal of the study is to create a continuous, high-resolution record of geomagnetic field variability with an accurate, astronomically tuned chronology. Sediment cored on the BOR in four holes at Site 1061 during ODP Leg 172 is being used for this investigation. The high sedimentation rate, averaging 22 cm/k.y. over the Brunhes, and the exceptional paleomagnetic properties of the area make Site 1061 an excellent candidate to test for links between short- term geomagnetic events and climate. The paleomagnetic record, originally constructed mainly from continuous split-core measurements, is being refined and rock magnetic analyses are being conducted on U- channel samples that span the Brunhes. We have also refined the between-hole correlation and constructed a more detailed composite stratigraphic section for Site 1061 in order to improve the continuity and relative chronology of the record and to confirm the existence of distinct geomagnetic excursions and other short-term events in multiple drill holes. Additionally, planktonic forams are being measured for δ¹⁸ O variations across, and extending to one meter beyond each observed excursion, allowing for direct tie-points between the geomagnetic and the marine oxygen isotopic record. Using these data, the timing of climatic events such as glaciations, stadials and interstadials will be compared with large scale variations in geomagnetic field strength or direction in hopes of finding conclusive results that will either confirm or refute the possible link between the two records.
DE: 1513 Geomagnetic excursions
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 3036 Ocean drilling
DE: 4901 Abrupt/rapid climate change (1605)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2006 Fall Meeting

HR: 0800h
AN: GC51A-0450
TI: Evidence for Highstand of Lake Tahoe During the Last Glacial Maximum
AU: * Delusina, I
EM: delusina@geology.ucdavis.edu
AF: University of California, Davis, Department of Geology, Davis, CA 95616 United States
AU: Verosub, K L
EM: verosub@geology.ucdavis.edu
AF: University of California, Davis, Department of Geology, Davis, CA 95616 United States
AU: Acton, G
EM: acton@geology.ucdavis.edu
AF: University of California, Davis, Department of Geology, Davis, CA 95616 United States
AU: Osleger, D
EM: osleger@geology.ucdavis.edu
AF: University of California, Davis, Department of Geology, Davis, CA 95616 United States
AU: Starratt, S W
EM: sstarrat@usgs.gov
AF: U. S. G. S., 345 Middlefield Road, Menlo Park, CA 94025 United States
AB: We have been studying a core of opportunity obtained as a result of geotechnical drilling in the Upper Truckee Marsh on South Lake Tahoe, California. The core is 51.8 meters long and provides new information about conditions in the Lake Tahoe basin toward the end of the last glacial. We have conducted sedimentological, environmental magnetic, palynological and paleontological studies of the core. Detailed particle size analysis shows that the upper 9 meters of the core consists primarily of coarse sand, which is underlain by 8 meters of silty sand. A silty clay layer spans the interval from 17 to 21 meters, and that is underlain by another 29 meters of silty sand. At the base of the core is a second silty clay interval. The magnetic intensity is generally higher in the fine-grained units than in the coarser-grained units although other magnetic properties do not vary significantly. The trends in magnetic grain-size mirror those in overall sediment particle size. The pollen spectrum is dominated by two types of pine and by fir, but there is little variation in either the concentration or relative abundances. Diatoms have not been found in the fine-grained portions of the core. Radiocarbon dating of the upper fine-grained interval gives an age of 14,000 BP for the top and 25, 000 BP for the bottom. The concentration of radiocarbon in the basal fine-grained interval is too low to provide an age. As indicated by the radiocarbon dates, this core provides information about conditions in the Lake Tahoe basin before, during and after the Last Glacial Maximum. Previous workers have suggested that the lower part of the Upper Truckee River, which drains into Lake Tahoe, was never glaciated. Our results support the idea that the valley was occupied by a glacial outwash plain that provided the coarse sediment that predominates in the core. We hypothesize that the fine-grained layer in the upper part of the core reflects a time when the canyon of the Lower Truckee River, into which Lake Tahoe drains, was blocked by one or more glaciers extending down from Squaw Valley or another drainage. This blockage raised the level of the lake above its natural sill and moved the depocenter of the outwash plain up the Upper Truckee Valley, resulting in deposition of finer- grained material at the coring site. Although a 10-15 meter rise in lake level dramatically changed the sediment being deposited at the coring site, it did not have a significant impact on the surrounding landscape, as evidenced by the lack of abrupt changes in the pollen and the magnetic properties. The presence of the basal silty clay indicates that the glacial blockage of the canyon of the Lower Truckee River was probably a recurring phenomenon.
DE: 0732 Icebergs
DE: 1105 Quaternary geochronology
DE: 1512 Environmental magnetism
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 4952 Palynology
SC: Global Climate Change [GC]
MN: 2006 Fall Meeting

HR: 15:10h
AN: GP13A-07
TI: Magnetic Stratigraphy and Relative Paleointensity from IODP Site U1313 from 2.4-6 Ma
AU: * Evans, H F
EM: geohelen@ufl.edu
AF: Department of Geological Sciences, University of Florida, 241 Williamson Hall, PO Box 112120,, Gainesville, FL 32611 United States
AU: Acton, G D
AF: Department of Geology University of California, Davis, One Shields Avenue, Davis, CA 95616 United States
AU: Guyodo, Y
AF: Laboratoire des Sciences du Climat et de l'Environnement (LSCE), Campus du CNRS 12 Ave de la Terrasse, Gif-sur-Yvette Cedex, 91198 France
AU: Channell, J E
AF: Department of Geological Sciences, University of Florida, 241 Williamson Hall, PO Box 112120,, Gainesville, FL 32611 United States
AU: Ohno, M
AF: Graduate School of Social and Cultural Studies Kyushu University, 4-2-1 Ropponmatsu Chuo-ku, Fukuoka, 810-8560 Japan
AU: Kanamatsu, T
AF: Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho Yokosuka, Kanagawa, 236-0061 Japan
AB: IODP Expedition 306 to the North Atlantic drilled three sites in the Spring of 2005 including Site U1313 which is a re-occupation of DSDP Site 607. A complete spliced composite section was obtained down to 300 mcd (meters composite depth) from 4 holes drilled at the site. U-channel samples were collected for the upper ~280 meters of the section. The 2.4-6 Ma interval has produced a magnetic reversal stratigraphy that defines all the subchrons of the Gauss and Gilbert chrons. The Gauss and Gilbert chrons are ~ 45 meters and ~100 meters thick respectively and have mean sedimentation rates of 4.5 cm/kyr. The sediments carry a weak low- coercivity magnetization most likely carried by magnetite. In the upper part of the section (0-130 mcd) the sediments show a cyclic alternation between nannofossil oozes and silty-clay nannofossil ooze. The light nannofossil oozes represent interglacials while the darker silty clay nannofossil oozes represent the glacials. The sediment in the lower part of the section (130-300 mcd) consists of white nannofossil oozes. The volume magnetic susceptibility, although very weak when measured on the u-channel samples, is reproducible as demonstrated by replicate measurements. Natural gamma data collected shipboard on the whole core and magnetic susceptibility from u-channel samples can be correlated to a benthic oxygen isotope stack. The resulting age model based on this correlation and the reversal chronology is applied to the normalized remanence record between 2.4 and 4 Ma. Three relative paleointensity proxies have been calculated: NRM/ARM, NRM/IRM and the slope of NRM/ARM-acquisition. Consistency among the three proxies and acceptable correlation to Pacific records of the same age implies that the site has yielded useful a paleointensity record for the Gauss and Gilbert chrons.
DE: 1520 Magnetostratigraphy
DE: 1521 Paleointensity
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2006 Fall Meeting

HR: 0800h
AN: B31B-1090
TI: Drilling a complete in situ section of upper oceanic crust formed at a superfast spreading rate: Hole 1256D
AU: * Teagle, D A
EM: dat@noc.soton.ac.uk
AF: National Oceanography Centre, University of Southampton, Southampton, SO14 3ZH United Kingdom
AU: Wilson, D S
EM: dwilson@geol.ucsb.edu
AF: University of California, Department of Earth Science, Santa Barbara, CA 93106 United States
AU: Alt, J C
EM: jalt@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109 United States
AU: Banerjee, N R
EM: neil.banerjee@uwo.ca
AF: University of Western Ontario, Department of Earth Sciences, London, ON N6A 5B7 Canada
AU: Umino, S
EM: sesumin@ipc.shizuoka.ac.jp
AF: Shizuoka University, Department of Biology and Geosciences, Shizuoka, 422-8529 Japan
AU: Miyashita, S
EM: miyashit@geo.sc.niigata-u.ac.jp
AF: Niigata University, Department of Geology, Niigata, 950-2181 Japan
AU: Acton, G D
EM: acton@geology.ucdavis.edu
AF: University of California, Geology Department, Davis, CA 95616 United States
AU: and Expedition 312 Scientific Parties, L
EM: neil.iodp@gmail.com
AF: Integrated Ocean Drilling Program, Texas A and M University, College Station, TX 77845 United States
AB: The Superfast Spreading Rate Crust mission is a multi-cruise program to drill a complete section of the upper oceanic crust into the underlying gabbros. Hole 1256D was initiated during Ocean Drilling Program Leg 206 in the eastern equatorial Pacific in 15 Ma crust that formed at the East Pacific Rise during a period of superfast spreading (~220 mm per year). This site was chosen to exploit the inverse relationship between spreading rate and the depth to axial low-velocity zones, thought to be magma chambers now frozen as gabbros, observed from seismic experiments. During Integrated Ocean Drilling Program (IODP) Expedition 309 in Jul- Aug 2005, Hole 1256D was deepened to a total depth of 1255 meters below seafloor (mbsf; 1005 m subbasement). Expedition 312 returned to Hole 1256D in Nov-Dec 2005 and deepened it to 1507 mbsf. The hole now extends through 810 m of extrusive normal mid-ocean-ridge basalt, 345 m of sheeted dikes, and 101 m into plutonic rocks, completing the first penetration of an intact section of the upper oceanic crust. Gabbros were encountered at 1407 mbsf, precisely within the depth range predicted from the extrapolation of multichannel seismic results at modern mid-ocean ridges to this superfast spreading rate. The uppermost crust at Site 1256 comprises a >74 m thick ponded lava overlying massive, sheet, and minor pillow flows. Dike contacts, and mineralized breccias indicate a lithologic transition from 1004 to 1061 mbsf. Below the transition zone, massive basalts with doleritic textures, commonly with brecciated and mineralized chilled margins, dominate the sheeted dikes. The transition zone marks a change from predominantly low temperature alteration minerals to greenschist hydrothermal assemblages. Actinolite, hornblende, and secondary plagioclase occur within 100-200 meters of the dike transition indicating a very steep thermal gradient in the dikes. The lowermost ~70 m of dikes are strongly recrystallized to granoblastic minerals resulting from intrusion of underlying gabbros. The plutonic complex comprises a ~60 m thick upper gabbroic body that intrudes the sheeted dikes, separated from a lower gabbroic body by a screen of granoblastic dikes. Gabbroic rocks are highly altered, fine to coarse grained and range from gabbro to oxide gabbro and gabbronorite with some differentiated rocks (quartz-rich oxide diorite and trondhjemite). The gabbro compositions are evolved compared to primary magmas in equilibrium with mantle olivine but similar to the overlying dikes and lavas, precluding the formation of the lower oceanic crust from the geophysically imaged melts lens.
UR: http://iodp.tamu.edu/scienceops/expeditions/exp312.html
DE: 3017 Hydrothermal systems (0450, 1034, 3616, 4832, 8135, 8424)
DE: 3035 Midocean ridge processes
DE: 3036 Ocean drilling
SC: Biogeochemistry [B]
MN: 2006 Fall Meeting

HR: 0800h
AN: GC51A-0458
TI: Evidence for the Climatic Impact of the 1600 Eruption of Huaynaputina Volcano, Peru
AU: * Lippman, J
EM: jdlippman@ucdavis.edu
AF: University of California - Davis, Geology Dept. One Shields Ave., Davis, CA 95616 United States
AU: Verosub, K L
EM: verosub@geology.ucdavis.edu
AF: University of California - Davis, Geology Dept. One Shields Ave., Davis, CA 95616 United States
AB: The global climatic impact of the 1815 eruption of Tambora volcano has been well-documented. However, any assessment of the risk from Tambora-type eruptions requires information about the frequency of such events. Briffa et al. (1998) have suggested on the basis of tree-ring data that the most severe short-term Northern Hemisphere cooling event of the past 600 years occurred in 1601, which is the year following the 1600 eruption of Huaynaputina volcano in Peru. The estimated Volcanic Explosivity Index for this eruption is 6, which is comparable to that of Tambora. We have been looking for other climate proxies that could provide information about the nature and extent of the cooling that might have been associated with the eruption of Huaynaputina in 1600, including records of speleothem thickness, first flowering of plants, beginning of wine harvests, coral growth, thickness of ice layers, dust veil indices, glacial positions, additional tree-ring records and historical documents. Although the signal is difficult to discern, there seems to be good evidence that the effects of the 1600 eruption of Huaynaputina volcano are comparable to those of the 1815 eruption of Tambora. This result is important because it documents that Tambora was not an isolated occurrence in the Holocene and supports the idea that such events might occur with a return frequency of as little as 200 years. Thus, any realistic discussion of the societal risk from natural perils needs to include the possibility of volcanically-induced global climate change.
DE: 1807 Climate impacts
DE: 1817 Extreme events
DE: 8408 Volcano/climate interactions (1605, 3309)
DE: 8488 Volcanic hazards and risks
SC: Global Climate Change [GC]
MN: 2006 Fall Meeting

HR: 0800h
AN: PP51A-1125
TI: Project REPEAT: Rates and Evolution of Peat Accretion through Time in the Sacramento- San Joaquin Delta, California, USA
AU: * Drexler, J Z
EM: jdrexler@usgs.gov
AF: U.S. Geological Survey, California Water Science Center, 6000 J Street, Placer Hall, Sacramento, CA 95819-6129 United States
AU: Verosub, K L
EM: verosub@geology.ucdavis.edu
AF: University of California, Davis, Geology Department, One Shields Avenue, Davis, CA 95616 United States
AU: Delusina, I
EM: delusina@geology.ucdavis.edu
AF: University of California, Davis, Geology Department, One Shields Avenue, Davis, CA 95616 United States
AU: de Fontaine, C S
EM: fontaine@usgs.gov
AF: U.S. Geological Survey, California Water Science Center, 6000 J Street, Placer Hall, Sacramento, CA 95819-6129 United States
AU: Lunning, N
EM: nglunning@ucdavis.edu
AF: University of California, Davis, Geology Department, One Shields Avenue, Davis, CA 95616 United States
AU: Wong, S
EM: stlwong@ucdavis.edu
AF: U.S. Geological Survey, California Water Science Center, 6000 J Street, Placer Hall, Sacramento, CA 95819-6129 United States
AB: There is great interest in restoring wetland habitat in the Sacramento-San Joaquin Delta of California in order to improve the status of sensitive species as well as to mitigate land-surface subsidence on historically farmed islands. Little is known about the rates of vertical peat accretion throughout the history of the Delta. This type of knowledge is critical for designing successful wetland restoration projects and identifying reasonable restoration timeframes. The objectives of the RE-PEAT project are (1) to quantify rates of vertical peat accretion for the history of the Delta, (2) to determine key environmental processes controlling peat development in the Delta through time, and (3) to compare characteristics of peat before and after gold-mining activities and the reclamation of the Delta for agriculture. During the summer of 2005, we collected 3 sets of cores from four pairs of sites throughout the Delta. Each pair consists of a reclaimed, farmed island and a relatively undisturbed marsh island situated in an adjacent channel. The thickness of the peat on the farmed and marsh islands averaged approximately 220 cm and 640 cm, respectively. Currently we are analyzing the cores in the laboratory to determine an array of physical and chemical properties including organic matter content, bulk density, % carbon content, magnetic mineralogy, concentration and grain-size distribution, and pollen spectra. Radiocarbon is being used to determine the basal ages of the cores and rates of vertical peat accretion through time. Our preliminary results indicate that most of the peat thicknesses on the farmed islands are thinner than values reported in the literature ten years ago and earlier, indicating that land-surface subsidence has continued to occur in the area. Bulk density measurements show that peat from the farmed islands is significantly denser than peat on the marsh channel islands (Student's t-test, p < 0.0001) because of compaction subsequent to reclamation and drainage. The pollen record from the base of the peat indicates a predominance of xerophytic elements in the pollen assemblages and a lower arboreal/non-arboreal pollen ratio than at present. This suggests that peat accretion was associated with a drier landscape and cooler conditions and demonstrates that there was landscape evolution. These conclusions are consistent with the magnetic properties, which show that the appearance of the peat was associated a hundredfold decrease in the concentration of magnetic material.
DE: 0429 Climate dynamics (1620)
DE: 0497 Wetlands (1890)
DE: 4952 Palynology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2006 Fall Meeting