- Email: [email protected]
A 7700 year record of paleoenvironmental change from Favre Lake, Ruby Mountains, Nevada
148
Abstracts / Quaternary International 387 (2015) 131e150
Greenland ice core at the same time based on high concentration of cosmogenic isotopes. At the same time, oxygen isotopes in the GRIP core suggest extremely cold temperatures in the North Atlantic region between Interstade #7 and #6 of the Dansgaard/Oeschger millennial-scale climate oscillations. To test the influence of these extremely cold North Atlantic temperatures on lake conditions in western North America, we counted the concentration of ostracode species in the BB3-I core within and outside of the interval of low paleointensity during the Mono Lake excursion. Ostracodes can be very sensitive to changes in both temperature and salinity and are effective indicators of paleoclimate in closed basins such as Summer Lake. Notably, Cytherissa lacustris, an ostracode with affinities for Arctic conditions, was observed in the BB3-I core in the low paleointensity interval of the Mono Lake excursion suggesting strongly that the Great Basin experienced very low temperatures at the same time as did the North Atlantic. Furthermore, alternating presence and absence of this ostracode down core reveals the same warm/cold climate oscillations as the GRIP core down to an unconformity in the BB3-I associated with a drought during the extremely cold, dry climate interval throughout the Great Basin that was probably due to the Heinrich 4 interval of extremely cold climate. This conclusion will be tested using other indicators of paleolake conditions including grain size, total organic and inorganic carbon, and carbon/nitrogen ratios.
A 10,500 YEAR RECORD OF VEGETATION AND FIRE HISTORY FROM LOWER WHITSHED LAKE NEAR CORDOVA, ALASKA Martina T. Tingley a, R. Scott Anderson a, b, Darrell Kaufman b, Megan Arnold b. a Bilby Research Center, Northern Arizona University, Flagstaff, AZ 86011, USA; b School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, AZ 86011, USA. E-mail address: [email protected], nau.edu, [email protected].
[email protected],
Darrell.Kaufman@
Lower Whitshed Lake is a small, coastal lake on the tectonically active eastern margin of Prince William Sound, near Cordova, Alaska. Coastal spruce-hemlock forest, with Picea sitchensis, Tsuga mertensiana, and T. heterophylla, currently dominates the site in a region where summers are cool and cloudy, winters are mild and precipitation is high. Few sites in this forest type have been investigated for their long-term histories, and the Lower Whitshed record is important in determining (1) the biogeography of coastal conifers and (2) the long-term history of fire for this vegetation type. It provides a continuum between sites in southeastern Alaska and those to the west on the Kenai Peninsula. We use a multi-proxy approach, including stratigraphies of pollen, charcoal particles, total organic-matter (TOC), and biogenic silica (BSi) to determine a centennial-scale view of long-term environmental change for the site for the last ca. 10,500 calendar years. Holocene sediments consist primarily of gyttja. Subsequent to deglaciation pollen evidence suggests a dwarf shrub-tundra (dwarf Betula, Salix, and Ericaceae, with Artemisia and Poaceae) existed around the lake until ca. 10,100 cal yr BP. Sediments were low in TOC but with relatively high BSi. A woodland of Alnus became established by 10,100 cal yr BP and dominated with little change until ca. 3500 cal yr BP. Sediment TOC increased during this period and modest values of BSi indicate a moderately productive lake. Finally, conifer forest dominated the site with rapid and successive immigrations of Picea sitchensis (ca. 3500 cal yr BP), P. mariana, and T. mertensiana (ca. 3000 cal yr BP). The arrival of T. heterophylla at ca. 2000 cal yr BP signifies development of the modern forest. Sedimentary charcoal is not abundant in this record. However, charcoal abundance increases at the transition from the shrub-tundra to dominance by Alnus woodland. Additional charcoal analyses are ongoing.
A HOLOCENE RECORD OF LARGE-SCALE DISTURBANCE EVENTS IN THE UINTA MOUNTAINS, UTAH, USA
evidence of large magnitude fire and flood events during the Holocene. The frequency of fire increased during the middle to late Holocene transition (~3000 cal yr BP), but then decreased in the last millennia. As fire frequency decreased the magnitude of fire and flood events have increased. The importance of large magnitude flood events is also explored in terms of frequency and magnitude. The recent (20th century) catastrophic draining of this montane lake that was dammed by a recessional moraine provides a recent example of an extreme disturbance event. The study site today, currently being colonized by lodgepole pine, affords a unique opportunity with excellent preservation of fossil pollen and paleobotanical remains to explore the magnitude and frequency of disturbance in this setting. Results from the fossil charcoal, pollen and lithologic analyses are compared with centennial-scale late Holocene climate records to evaluate the influence of climate ion disturbance, including the Medieval Climate Anomaly and Little Ice Age. These findings provide context for understanding recent large magnitude disturbance events in the Uinta Mountains.
DON'T WORRY ABOUT CLIMATE CHANGE; CALIFORNIA'S NATURAL CLIMATE VARIABILITY WILL PROBABLY “GET US” FIRST Kenneth L. Verosub. Department of Geology, University of California, Davis, CA, 95616, USA. E-mail address: [email protected].
California moves more water than any other political entity in the world, and it uses a lot of energy to do it. A growing population and growing demand for water, coupled with geotechnical and environmental threats to the Sacramento-San Joaquin Delta, the lynchpin of California's water delivery system, are causing Californians to make difficult decisions with regard to maintaining current supplies and developing new ones. Overlaid on these issues is the threat of reduced water flows resulting from climate change, particularly for the Colorado River basin and the Owens Valley/ Mono Lake system. What is often missing from the discussion about various alternatives is consideration of the natural climate variability in California over the past 10,000 years and particularly the past 1000 years. For example, river flow and lake level measurements from the twentieth century document the occurrence of several multi-year droughts in the past 100 years while tree ring records show that 20-year and 70-year droughts occurred during the last 300 years. On an even longer time scale, at least once and probably several times in the last few thousand years, there have been droughts severe enough to drop the level of Lake Tahoe by several tens of meters, which allowed Douglas fir trees to grow to maturity on exposed lake beds. Conversely, new information about the 1861e1862 water year, during which there was extensive flooding in the Sacramento Valley, suggests that the entire weather system of the West Coast “flipped” into a different mode that brought heavy rains and flooding all the way from northern Oregon to southern California. Thus, the paleoclimate history of California suggests that even in the absence of climate change due to anthropogenic greenhouse gases, decadal, multi-decadal or even century-long droughts are a real possibility in the future for California as is flooding on a greater scale than was seen in the twentieth century. A decade-long drought would wreck havoc with California’s delicately balanced water delivery system, and a repeat of the 1861e1862 precipitation regime could bring enough water into the Delta to overwhelm the levee system and destroy California’s ability to transfer water from north to south.
A 7700 YEAR RECORD OF PALEOENVIRONMENTAL CHANGE FROM FAVRE LAKE, RUBY MOUNTAINS, NEVADA
Lovina A. Turney, Mitchell J. Power. Department of Geography, University of Utah, Salt Lake City, UT 84112, USA.
David Wahl, Scott Starratt, Lysanna Anderson, Jennifer Kusler, Christopher Fuller, Elmira Wan, Holly Olson. US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94720, USA.
E-mail address: [email protected].
E-mail address: [email protected].
Holocene climate variability has resulted in a dynamic disturbance history in the Uinta Mountains. A 12,000-year-long lake sediment record provides
Few records of Holocene climate variability have been generated from high elevations in the Great Basin. By combining a broad suite of proxy data
Abstracts / Quaternary International 387 (2015) 131e150
(pollen, diatom, charcoal, biogenic silica, magnetic susceptibility, loss-onignition, density, and grain-size), this study evaluates changes in watershed vegetation, lake levels, and limnological conditions in order to understand millennial and centennial-scale changes in regional climate. Here we report data from a 4.2-meter-long sediment core collected from Favre Lake (2899 masl; 12 m deep; 7.7 hectares) in the northern Ruby Mountains. Age control is provided by the Mazama ash, six 14C AMS determinations, and 210Pb dating; an age-depth model was created using the CLAM program, which indicates an average sedimentation rate of 0.524 mm/year that extends to ~7700 cal yr BP. Pinus and Artemisia dominate the pollen record, followed by subordinate levels of Poaceae, Asteraceae, Amaranthaceae, and Sarcobatus. Biogenic silica results suggest fluctuating productivity from 7300e5750, followed by decreased variability. Between about 7700 and 6000 cal yr BP, the diatom flora is dominated by a diverse assemblage of benthic species. The remainder of the core is dominated by Fragilaria which suggests a rising lake level after 6000 cal yr BP, possibly a result of flooding a shallow shelf that surrounds the depocenter of the lake. This interpretation is supported by coeval increases in percentages of several aquatic plant taxa (Isoetes, Typha, and Pediastrum) around 5750 cal yr BP. Macroscopic charcoal influx increases at this time as well, suggesting an increase in fuel availability or ignition sources. Planktonic diatom taxa (Cyclotella, Asterionella, and Tabellaria) increase in abundance during the last 500 years of the record. This change in the assemblage may indicate modern conditions in which the lake drains into Kleckner Creek to the west.
PRELIMINARY POLLEN RECORD FROM ECHO LAKE, RUBY MOUNTAINS, NEVADA James A. Wanket a, David B. Wahl b, Jennifer E. Kusler b. a Department of Geography, Sacramento State University, Sacramento, CA 95819, USA; b US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, USA. E-mail address: [email protected].
A 60-cm-long sediment core from Echo Lake, a 45 m deep cirque lake in the Ruby Mountains of Nevada, provided a record of pollen and spanning the last several hundred years. Age control was provided by a combination of annual layering, 210Pb, and radiocarbon. The results of these analyses indicate that although limber pine, whitebark pine, and Great Basin sagebrush (the dominant plant species in the alpine areas of the Ruby Mountains today) have been important throughout the last several hundred years, some alpine species have been reduced in range or extirpated from the mountains during this time frame. Pollen of mountain hemlock and white fir are present in sediments deposited early in the period but not in more recent sediments. Today, white fir is found in only one isolated stand in the Ruby Mountains, while mountain hemlock is not found in the mountains of the Great Basin outside of the eastern Sierra Nevada. It is likely that other alpine species not well-represented in the pollen record were also reduced in range or extirpated along with white fir and mountain hemlock. It is likely that changes in temperature, snowpack, and/or fire frequency over the time frame represented by the sediment record drove changes in alpine species composition in the Ruby Mountains.
149
permeability, and human use. A basic water balance diagram provides a monthly view of hydrology for multi-year averages and individual years. Frequency and intensity of droughts in historical and projected climate time-series are calculated, and metrics based on multi-year running averages are developed. Projected droughts are compared with historical droughts (1976e1977, 1987e1992, and 2007e2009), providing analogs and benchmarks within recent experience. Bedrock permeability affects runoff to recharge ratios, and soil moisture capacity produces fine-scale variability in storage and CWD. Rising temperatures drive higher potential evapotranspiration, which increases CWD even with greater average annual precipitation, leading to greater stress on terrestrial and aquatic ecosystems. Quantifying probabilities of drought stress by using time series and quantile analysis of CWD, runoff, and recharge defines risks at fine spatial scales relevant to water and land managers, and can be incorporated into existing water supply and flood management frameworks.
ATMOSPHERIC PRESSURE VARIABILITY OVER WESTERN NORTH AMERICA AND THE NORTH PACIFIC RECONSTRUCTED USING TREE-RING RECORDS Erika K. Wise, Matthew P. Dannenberg. Department of Geography, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. E-mail address: [email protected].
Changes in moisture delivery to the West are largely controlled by interrelated, synoptic-scale atmospheric features, such as the strength and position of the Pacific sub-tropical high and the Aleutian low. Longterm records of these pressure patterns and associated atmospheric circulation are needed to understand the drivers of persistent droughts recorded in the paleoclimate record and to evaluate how climate changes may impact hydroclimatic systems in the future. In this study, we utilized 500hPa geopotential height (GPH) data from the 20th century Reanalysis (V2) project and existing tree-ring chronologies from the International Tree-Ring Data Bank to reconstruct a multi-century record of year-to-year variation in atmospheric pressure patterns. We tested four Climate Field Reconstruction methods that have been commonly utilized in paleoclimate studies: Canonical Correlation Analysis (CCA), Regularized Expectation Maximization with ridge regression (RegEM-ridge), Regularized Expectation Maximization with Truncated Total Least Squares regression (RegEM-TTLS), and Point-by-Point Regression (PPR). We found that each method produced similar spatial patterns of error, but that the RegEM-ridge method produced the most robust reconstruction of GPH based on calibration and validation statistics. The RegEM-ridge method was used to produce a 2 2 degree gridded reconstruction of 500 hPa GPH over western North America and the northeastern Pacific Ocean. This reconstruction of GPH rivals the robustness of tree-ring based temperature and precipitation reconstructions, although there is uneven performance over the spatial grid. The reconstructed atmospheric pressure record allows characterization of the frequency of certain circulation patterns, their variability through time, and their impact on hydroclimatic conditions.
INFLUENCE OF NORTHERN HEMISPHERE TELECONNECTIONS ON ENSORELATED PRECIPITATION PATTERNS IN THE UNITED STATES STOCHASTIC ANALYSIS OF MULTI-YEAR RUNOFF, RECHARGE, AND CLIMATIC WATER DEFICIT IN GEOLOGICALLY VARYING WATERSHEDS Stuart B. Weiss. Creekside Center for Earth Observation, 27 Bishop Lane, Menlo Park, CA 94025, USA.
Melissa Wrzesien a, Erika K. Wise b. a Curriculum for the Environment and Ecology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; b Department of Geography, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
E-mail address: [email protected].
E-mail address: [email protected], [email protected].
Numerous climate futures are now available from downscaled global climate models. The translation of monthly precipitation and temperatures into hydrologically and ecologically meaningful outputs for managers and planners is the next frontier. The Basin Characterization Model (BCM) is used to generate time series of annual runoff, recharge, and climatic water deficit (CWD) at the scale of small planning watersheds in the San Francisco Bay area. These watersheds differ in climate, soils, bedrock
~ oeSouthern Oscillation Oceaneatmosphere oscillations like the El Nin (ENSO) system have far-reaching effects on regional climate in teleconnected regions. Climate forecasts often consider ENSO when predicting regional climate for the United States. However, there are numerous other climate systems influencing temperature and precipitation patterns at any time, and incorporating the effects of other teleconnections (North American Oscillation, East Atlantic, Pacific-North
Abstracts / Quaternary International 387 (2015) 131e150
Greenland ice core at the same time based on high concentration of cosmogenic isotopes. At the same time, oxygen isotopes in the GRIP core suggest extremely cold temperatures in the North Atlantic region between Interstade #7 and #6 of the Dansgaard/Oeschger millennial-scale climate oscillations. To test the influence of these extremely cold North Atlantic temperatures on lake conditions in western North America, we counted the concentration of ostracode species in the BB3-I core within and outside of the interval of low paleointensity during the Mono Lake excursion. Ostracodes can be very sensitive to changes in both temperature and salinity and are effective indicators of paleoclimate in closed basins such as Summer Lake. Notably, Cytherissa lacustris, an ostracode with affinities for Arctic conditions, was observed in the BB3-I core in the low paleointensity interval of the Mono Lake excursion suggesting strongly that the Great Basin experienced very low temperatures at the same time as did the North Atlantic. Furthermore, alternating presence and absence of this ostracode down core reveals the same warm/cold climate oscillations as the GRIP core down to an unconformity in the BB3-I associated with a drought during the extremely cold, dry climate interval throughout the Great Basin that was probably due to the Heinrich 4 interval of extremely cold climate. This conclusion will be tested using other indicators of paleolake conditions including grain size, total organic and inorganic carbon, and carbon/nitrogen ratios.
A 10,500 YEAR RECORD OF VEGETATION AND FIRE HISTORY FROM LOWER WHITSHED LAKE NEAR CORDOVA, ALASKA Martina T. Tingley a, R. Scott Anderson a, b, Darrell Kaufman b, Megan Arnold b. a Bilby Research Center, Northern Arizona University, Flagstaff, AZ 86011, USA; b School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, AZ 86011, USA. E-mail address: [email protected], nau.edu, [email protected].
[email protected],
Darrell.Kaufman@
Lower Whitshed Lake is a small, coastal lake on the tectonically active eastern margin of Prince William Sound, near Cordova, Alaska. Coastal spruce-hemlock forest, with Picea sitchensis, Tsuga mertensiana, and T. heterophylla, currently dominates the site in a region where summers are cool and cloudy, winters are mild and precipitation is high. Few sites in this forest type have been investigated for their long-term histories, and the Lower Whitshed record is important in determining (1) the biogeography of coastal conifers and (2) the long-term history of fire for this vegetation type. It provides a continuum between sites in southeastern Alaska and those to the west on the Kenai Peninsula. We use a multi-proxy approach, including stratigraphies of pollen, charcoal particles, total organic-matter (TOC), and biogenic silica (BSi) to determine a centennial-scale view of long-term environmental change for the site for the last ca. 10,500 calendar years. Holocene sediments consist primarily of gyttja. Subsequent to deglaciation pollen evidence suggests a dwarf shrub-tundra (dwarf Betula, Salix, and Ericaceae, with Artemisia and Poaceae) existed around the lake until ca. 10,100 cal yr BP. Sediments were low in TOC but with relatively high BSi. A woodland of Alnus became established by 10,100 cal yr BP and dominated with little change until ca. 3500 cal yr BP. Sediment TOC increased during this period and modest values of BSi indicate a moderately productive lake. Finally, conifer forest dominated the site with rapid and successive immigrations of Picea sitchensis (ca. 3500 cal yr BP), P. mariana, and T. mertensiana (ca. 3000 cal yr BP). The arrival of T. heterophylla at ca. 2000 cal yr BP signifies development of the modern forest. Sedimentary charcoal is not abundant in this record. However, charcoal abundance increases at the transition from the shrub-tundra to dominance by Alnus woodland. Additional charcoal analyses are ongoing.
A HOLOCENE RECORD OF LARGE-SCALE DISTURBANCE EVENTS IN THE UINTA MOUNTAINS, UTAH, USA
evidence of large magnitude fire and flood events during the Holocene. The frequency of fire increased during the middle to late Holocene transition (~3000 cal yr BP), but then decreased in the last millennia. As fire frequency decreased the magnitude of fire and flood events have increased. The importance of large magnitude flood events is also explored in terms of frequency and magnitude. The recent (20th century) catastrophic draining of this montane lake that was dammed by a recessional moraine provides a recent example of an extreme disturbance event. The study site today, currently being colonized by lodgepole pine, affords a unique opportunity with excellent preservation of fossil pollen and paleobotanical remains to explore the magnitude and frequency of disturbance in this setting. Results from the fossil charcoal, pollen and lithologic analyses are compared with centennial-scale late Holocene climate records to evaluate the influence of climate ion disturbance, including the Medieval Climate Anomaly and Little Ice Age. These findings provide context for understanding recent large magnitude disturbance events in the Uinta Mountains.
DON'T WORRY ABOUT CLIMATE CHANGE; CALIFORNIA'S NATURAL CLIMATE VARIABILITY WILL PROBABLY “GET US” FIRST Kenneth L. Verosub. Department of Geology, University of California, Davis, CA, 95616, USA. E-mail address: [email protected].
California moves more water than any other political entity in the world, and it uses a lot of energy to do it. A growing population and growing demand for water, coupled with geotechnical and environmental threats to the Sacramento-San Joaquin Delta, the lynchpin of California's water delivery system, are causing Californians to make difficult decisions with regard to maintaining current supplies and developing new ones. Overlaid on these issues is the threat of reduced water flows resulting from climate change, particularly for the Colorado River basin and the Owens Valley/ Mono Lake system. What is often missing from the discussion about various alternatives is consideration of the natural climate variability in California over the past 10,000 years and particularly the past 1000 years. For example, river flow and lake level measurements from the twentieth century document the occurrence of several multi-year droughts in the past 100 years while tree ring records show that 20-year and 70-year droughts occurred during the last 300 years. On an even longer time scale, at least once and probably several times in the last few thousand years, there have been droughts severe enough to drop the level of Lake Tahoe by several tens of meters, which allowed Douglas fir trees to grow to maturity on exposed lake beds. Conversely, new information about the 1861e1862 water year, during which there was extensive flooding in the Sacramento Valley, suggests that the entire weather system of the West Coast “flipped” into a different mode that brought heavy rains and flooding all the way from northern Oregon to southern California. Thus, the paleoclimate history of California suggests that even in the absence of climate change due to anthropogenic greenhouse gases, decadal, multi-decadal or even century-long droughts are a real possibility in the future for California as is flooding on a greater scale than was seen in the twentieth century. A decade-long drought would wreck havoc with California’s delicately balanced water delivery system, and a repeat of the 1861e1862 precipitation regime could bring enough water into the Delta to overwhelm the levee system and destroy California’s ability to transfer water from north to south.
A 7700 YEAR RECORD OF PALEOENVIRONMENTAL CHANGE FROM FAVRE LAKE, RUBY MOUNTAINS, NEVADA
Lovina A. Turney, Mitchell J. Power. Department of Geography, University of Utah, Salt Lake City, UT 84112, USA.
David Wahl, Scott Starratt, Lysanna Anderson, Jennifer Kusler, Christopher Fuller, Elmira Wan, Holly Olson. US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94720, USA.
E-mail address: [email protected].
E-mail address: [email protected].
Holocene climate variability has resulted in a dynamic disturbance history in the Uinta Mountains. A 12,000-year-long lake sediment record provides
Few records of Holocene climate variability have been generated from high elevations in the Great Basin. By combining a broad suite of proxy data
Abstracts / Quaternary International 387 (2015) 131e150
(pollen, diatom, charcoal, biogenic silica, magnetic susceptibility, loss-onignition, density, and grain-size), this study evaluates changes in watershed vegetation, lake levels, and limnological conditions in order to understand millennial and centennial-scale changes in regional climate. Here we report data from a 4.2-meter-long sediment core collected from Favre Lake (2899 masl; 12 m deep; 7.7 hectares) in the northern Ruby Mountains. Age control is provided by the Mazama ash, six 14C AMS determinations, and 210Pb dating; an age-depth model was created using the CLAM program, which indicates an average sedimentation rate of 0.524 mm/year that extends to ~7700 cal yr BP. Pinus and Artemisia dominate the pollen record, followed by subordinate levels of Poaceae, Asteraceae, Amaranthaceae, and Sarcobatus. Biogenic silica results suggest fluctuating productivity from 7300e5750, followed by decreased variability. Between about 7700 and 6000 cal yr BP, the diatom flora is dominated by a diverse assemblage of benthic species. The remainder of the core is dominated by Fragilaria which suggests a rising lake level after 6000 cal yr BP, possibly a result of flooding a shallow shelf that surrounds the depocenter of the lake. This interpretation is supported by coeval increases in percentages of several aquatic plant taxa (Isoetes, Typha, and Pediastrum) around 5750 cal yr BP. Macroscopic charcoal influx increases at this time as well, suggesting an increase in fuel availability or ignition sources. Planktonic diatom taxa (Cyclotella, Asterionella, and Tabellaria) increase in abundance during the last 500 years of the record. This change in the assemblage may indicate modern conditions in which the lake drains into Kleckner Creek to the west.
PRELIMINARY POLLEN RECORD FROM ECHO LAKE, RUBY MOUNTAINS, NEVADA James A. Wanket a, David B. Wahl b, Jennifer E. Kusler b. a Department of Geography, Sacramento State University, Sacramento, CA 95819, USA; b US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, USA. E-mail address: [email protected].
A 60-cm-long sediment core from Echo Lake, a 45 m deep cirque lake in the Ruby Mountains of Nevada, provided a record of pollen and spanning the last several hundred years. Age control was provided by a combination of annual layering, 210Pb, and radiocarbon. The results of these analyses indicate that although limber pine, whitebark pine, and Great Basin sagebrush (the dominant plant species in the alpine areas of the Ruby Mountains today) have been important throughout the last several hundred years, some alpine species have been reduced in range or extirpated from the mountains during this time frame. Pollen of mountain hemlock and white fir are present in sediments deposited early in the period but not in more recent sediments. Today, white fir is found in only one isolated stand in the Ruby Mountains, while mountain hemlock is not found in the mountains of the Great Basin outside of the eastern Sierra Nevada. It is likely that other alpine species not well-represented in the pollen record were also reduced in range or extirpated along with white fir and mountain hemlock. It is likely that changes in temperature, snowpack, and/or fire frequency over the time frame represented by the sediment record drove changes in alpine species composition in the Ruby Mountains.
149
permeability, and human use. A basic water balance diagram provides a monthly view of hydrology for multi-year averages and individual years. Frequency and intensity of droughts in historical and projected climate time-series are calculated, and metrics based on multi-year running averages are developed. Projected droughts are compared with historical droughts (1976e1977, 1987e1992, and 2007e2009), providing analogs and benchmarks within recent experience. Bedrock permeability affects runoff to recharge ratios, and soil moisture capacity produces fine-scale variability in storage and CWD. Rising temperatures drive higher potential evapotranspiration, which increases CWD even with greater average annual precipitation, leading to greater stress on terrestrial and aquatic ecosystems. Quantifying probabilities of drought stress by using time series and quantile analysis of CWD, runoff, and recharge defines risks at fine spatial scales relevant to water and land managers, and can be incorporated into existing water supply and flood management frameworks.
ATMOSPHERIC PRESSURE VARIABILITY OVER WESTERN NORTH AMERICA AND THE NORTH PACIFIC RECONSTRUCTED USING TREE-RING RECORDS Erika K. Wise, Matthew P. Dannenberg. Department of Geography, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. E-mail address: [email protected].
Changes in moisture delivery to the West are largely controlled by interrelated, synoptic-scale atmospheric features, such as the strength and position of the Pacific sub-tropical high and the Aleutian low. Longterm records of these pressure patterns and associated atmospheric circulation are needed to understand the drivers of persistent droughts recorded in the paleoclimate record and to evaluate how climate changes may impact hydroclimatic systems in the future. In this study, we utilized 500hPa geopotential height (GPH) data from the 20th century Reanalysis (V2) project and existing tree-ring chronologies from the International Tree-Ring Data Bank to reconstruct a multi-century record of year-to-year variation in atmospheric pressure patterns. We tested four Climate Field Reconstruction methods that have been commonly utilized in paleoclimate studies: Canonical Correlation Analysis (CCA), Regularized Expectation Maximization with ridge regression (RegEM-ridge), Regularized Expectation Maximization with Truncated Total Least Squares regression (RegEM-TTLS), and Point-by-Point Regression (PPR). We found that each method produced similar spatial patterns of error, but that the RegEM-ridge method produced the most robust reconstruction of GPH based on calibration and validation statistics. The RegEM-ridge method was used to produce a 2 2 degree gridded reconstruction of 500 hPa GPH over western North America and the northeastern Pacific Ocean. This reconstruction of GPH rivals the robustness of tree-ring based temperature and precipitation reconstructions, although there is uneven performance over the spatial grid. The reconstructed atmospheric pressure record allows characterization of the frequency of certain circulation patterns, their variability through time, and their impact on hydroclimatic conditions.
INFLUENCE OF NORTHERN HEMISPHERE TELECONNECTIONS ON ENSORELATED PRECIPITATION PATTERNS IN THE UNITED STATES STOCHASTIC ANALYSIS OF MULTI-YEAR RUNOFF, RECHARGE, AND CLIMATIC WATER DEFICIT IN GEOLOGICALLY VARYING WATERSHEDS Stuart B. Weiss. Creekside Center for Earth Observation, 27 Bishop Lane, Menlo Park, CA 94025, USA.
Melissa Wrzesien a, Erika K. Wise b. a Curriculum for the Environment and Ecology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; b Department of Geography, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
E-mail address: [email protected].
E-mail address: [email protected], [email protected].
Numerous climate futures are now available from downscaled global climate models. The translation of monthly precipitation and temperatures into hydrologically and ecologically meaningful outputs for managers and planners is the next frontier. The Basin Characterization Model (BCM) is used to generate time series of annual runoff, recharge, and climatic water deficit (CWD) at the scale of small planning watersheds in the San Francisco Bay area. These watersheds differ in climate, soils, bedrock
~ oeSouthern Oscillation Oceaneatmosphere oscillations like the El Nin (ENSO) system have far-reaching effects on regional climate in teleconnected regions. Climate forecasts often consider ENSO when predicting regional climate for the United States. However, there are numerous other climate systems influencing temperature and precipitation patterns at any time, and incorporating the effects of other teleconnections (North American Oscillation, East Atlantic, Pacific-North