- Email: [email protected]
Millennial-scale climate oscillations over the past 735,000 years as recorded in high-resolution marine sediment records from Santa Barbara Basin, California
Abstracts / Quaternary International 310 (2013) 227–246
Palmyra Atoll, a remote uninhabited series of islets in the central Pacific, represents one of these rare viable sites. Using multiple proxies to reconstruct past sea surface conditions, we seek to understand the relationship between ENSO variability and known late Holocene climate events (i.e. the Medieval Climate Anomaly and Little Ice Age). We report preliminary data from a 3.2 m sediment core retrieved from the west lagoon on Palmyra Atoll (5 530 05.2500 N; 162 050 21.6300 W; water depth 51 m). Radiocarbon determinations on pteropods from the basal sediment of the core indicate the record extends to w640 cal yr BP (AD 1310). Evidence for construction on the atoll during WWII includes a discreet horizon of coarse-grained carbonate, providing a chronologic marker at 8 cal yr BP (AD 1942). Oxygen isotopic composition of authigenic carbonates, high-resolution scanning XRF, 14C, and 210Pb data are currently being collected, and together will be used to construct a model of changing sea surface conditions for the region.
245
occurred at this magnitude. Reconstructing high-resolution disturbance regimes (fire and MPB) from sedimentary records for the Holocene (the last 10,000 years) will provide insight on disturbance ecology in subalpine forests. The records presented here use charcoal to identify past fire disturbance and a new pollen method to identify past MPB outbreaks. The new pollen method was developed from recent studies in spruce-fir forests where changes in pollen composition were used to identify past spruce beetle outbreaks. Initially, it was unclear if this would work in pinedominated systems where there is not the same trade-off between dominant tree taxa. Two late Holocene records from Fishstick Lake, Idaho and Lake of the Woods, Montana demonstrate that pollen ratios can be used to identify past bark beetle outbreaks in pine-dominated forests. FROM ATMOSPHERIC CIRCULATION TO GRAPE TEMPERATURES: MACRO-, MESO-, TOPO-, AND MICROCLIMATE IN VINEYARDS (AND YOUR GLASS)
ELKHORN SLOUGH TIDAL WETLANDS: PAST, PRESENT AND FUTURE Elizabeth Burke Watson a, b, Eric Van Dyke b, Kerstin Wasson b, c. a Department of Land, Air and Water Resources, University of California, Davis, CA 95616, USA; b Elkhorn Slough National Estuarine Research Reserve, Watsonville, CA 95076, USA; c Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95064, USA E-mail address: [email protected].
Tectonic uplift, a narrow continental shelf, and heavy surf place strong natural limits on the areal extent of tidal wetland habitat along the California coast. Concurrently, human activities and associated landscape changes have led to the large-scale destruction of much of the region's tidal wetlands. Tidal wetlands at Elkhorn Slough, central Monterey Bay, are thus a regionally important resource: this area supports among the largest remaining extents of tidal wetlands in California. Unfortunately, these wetlands are in deteriorated condition: a large portion were diked off from tidal exchange (these areas exist today as shallow eutrophic ponds), and in fully tidal locations, hydrologic modifications to the estuary have resulted in plant mortality and marsh loss. At Elkhorn Slough National Estuarine Research Reserve, we are conducting a study utilizing stratigraphic assessments and habitat modeling in order to address key questions about the historical extent, current trajectory, and future distribution of estuarine wetlands at Elkhorn Slough, with an emphasis on understanding the impacts of climate variability and climate change on this coastal resource. For the purposes of habitat reconstruction, sediment stratigraphies with chronologic control established using radiocarbon dating, have revealed dramatic variability in marsh extent at Elkhorn Slough, revealing clear episodes of past marsh deterioration. Studies of contemporary sediment accumulation undertaken using sediment-erosion tables, sediment tiles, marker beds, and recent radiometric dating (e.g. 137Cs/210Pb) reflect a submerging marsh plain and escalating accumulation rates in both vegetated and deteriorated tidal marsh. Implementation of a habitat model (sea level affecting marshes – SLAMM) has identified low suspended sediment concentrations as an obstacle to marsh sustainability under even the most moderate sea level rise/climate scenarios, but has identified potential future marsh migration pathways. These data will be used to help set well-informed targets for marsh acreage in the estuary and to understand what geographical areas are likely sites for marsh migration.
Stuart B. Weiss. Viticision/Creekside Center for Earth Observation, 27 Bishop Lane, Menlo Park, CA 94025, USA E-mail address: [email protected]
Few agricultural crops are as sensitive to weather and climate as wine grapes. Small fluctuations in temperature and phenology can make the difference between high quality and poor quality crops. Climate change will challenge continued production of quality wine grapes in the Pacific States. In order to effectively consider climate change in vineyard design and management, a multi-scale approach to climate is required, descending scales from macroclimate through mesoclimate, topoclimate, and microclimate. In this presentation, I describe applications of this hierarchy to vineyards. Station data, and interpolated surfaces such as PRISM account for macroclimatic and mesoclimatic gradients down to a scale of 800 m. Ripening dates, both past and projected, of grape varieties can be estimated from monthly data at these scales. Topoclimatic gradients are derived from digital elevation models (DEMs) using solar radiation models, topographic position, and slope, and have profound effects on minimum and maximum temperatures. At the finest scale, microclimate encompasses the effects of vegetation canopies on solar radiation, humidity, and temperature, such as the effects of trellis design on berry temperature on either side of the trellis. Hemispherical photography quantifies trellises from a “grapes' eye view,” allowing estimation of solar radiation on grape clusters at half hourly intervals for each month. By combining all of these methods with inexpensive temperature sensors, the temperatures of grape clusters can be tracked through growing seasons using local weather station data, with numerous key insights into vineyard design and management in a variable and changing climate. MILLENNIAL-SCALE CLIMATE OSCILLATIONS OVER THE PAST 735,000 YEARS AS RECORDED IN HIGH-RESOLUTION MARINE SEDIMENT RECORDS FROM SANTA BARBARA BASIN, CALIFORNIA Sarah M. White a, Tessa M. Hill a, James P. Kennett b, Richard Behl c. a Department of Geology, University of California, Davis, CA 95616, USA; b Department of Earth Science, University of California, Santa Barbara, CA 93106, USA; c Department of Geological Sciences, California State University, Long Beach, CA 90840, USA E-mail address: [email protected].
A LATE HOLOCENE RECORD OF DISTURBANCE FROM THE NORTHERN ROCKY MOUNTAINS, USA Jennifer H. Watt a, Andrea Brunelle a, Kurt Kipfmueller b. a Department of Geography, RED Lab, University of Utah, Salt Lake City, UT 84112, USA; b Department of Geography, Center for Dendrochronology, University of Minnesota, Minneapolis, MN 55455, USA E-mail address: [email protected].
Mountain pine beetle (MPB) outbreaks have impacted or are currently affecting many pine communities in the western US. It is not clear if these large-scale outbreaks are unprecedented or if they have previously
A lack of high-resolution climate records beyond the last glacial period has limited understanding of causes, effects, and temporal development of Quaternary abrupt climate shifts. Santa Barbara Basin (SBB), with a sedimentation rate of 100 cm/1000 yr, provides uniquely well-preserved sediments spanning the past w700,000. Five piston cores from SBB, each spanning w5000, were dated to w735,000, 460,000, and 290,000 years ago. These cores allow us to see whether millennial-scale climate shifts have changed in amplitude, shape, and/or timing since the Mid-Pleistocene Transition, and how they are expressed in the Pacific in terms of ocean circulation, productivity, and oxygenation. We use stable isotopes of planktonic (Globigerina bulloides, Neogloboquadrina pachyderma), and
246
Abstracts / Quaternary International 310 (2013) 227–246
benthic foraminifera (Uvigerina peregrina) and planktonic foraminiferal assemblage analyses including % N. pachyderma (d), and sediment lamination data. d18O data of G. bulloides and N. pachyderma show shifts of up to 1.4& in as briefly as w80 years and 2.5& over w1000 years during warming. Water column stratification (shown by the difference between G. bulloides and N. pachyderma d18O) increases during interstadials. The % N. pachyderma (d) often varies in tandem with planktonic d18O, but exhibits threshold behavior instead of smooth change, and is generally higher during interstadials and/or moderate water column stratification. d13C values broadly correlate with shifts in d18O, and reflect changing ocean circulation, carbon cycling, and/or methane release. Preserved sediment laminations coincide with intervals of warm, stratified upper waters. A comparison of our data to SBB records from the past 60,000 years (Behl and Kennett, 1996; Hendy and Kennett, 1999, 2000; Hill et al., 2006) shows that typical stadial-interstadial shifts in planktonic d18O (w1.5&) are similar to those recorded during the past 60,000 years, although changes in % N. pachyderma (d) are smaller, and planktonic assemblages are slightly different, with fewer G. bulloides, Globigerina quinqueloba, Globorotalia scitula, and more N. pachyderma (s). Behl, R.J., Kennett, J.P., 1996. Brief interstadial events in the Santa Barbara Basin, NE Pacific, during the last 60 kyr: Nature 376, 243-246. Hendy, I.L., Kennett, J.P., 1999. Latest Quaternary North Pacific surface water responses imply atmospherically-driven climate instability: Geology 27 (4), 291-294. Hendy, I.L., Kennett, J.P., 2000. Stable isotope stratigraphy and paleoceanography of the last 170 ka: ODP Site 1014, Tanner Basin, California: Ocean Drilling Program Scientific Reports 167, 129-140. Hill, T.M., Kennett, J.P., Pak, D.K., Behl, R.J., Robert, C., Beaufort, L., 2006. PreBølling warming in Santa Barbara Basin, California: Surface and intermediate water records of early deglacial warmth: Quaternary Science Reviews 25 (21-22), 2835-2845. CLIMATE DRIVERS OF STREAMFLOW SYNCHRONICITY IN WESTERN US RIVERS OVER MULTIPLE CENTURIES Erika K. Wise. Department of Geography, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA E-mail address: [email protected]
Twentieth century high- and low-streamflow events in the western US have been linked to Pacific and Atlantic Ocean influences, including those described by the El Niño–Southern Oscillation (ENSO), the Pacific Decadal Oscillation, and the Atlantic Multidecadal Oscillation. Extended streamflow records, reconstructed using tree rings, have identified drought and pluvial periods in the past that were more extreme than those recorded during in the instrumental record. This study compares a new tree-ring based reconstruction of Snake River streamflow with streamflow reconstructions of the Colorado, Sacramento, and Verde rivers. Results suggest that changes in the predominance of zonal versus meridional atmospheric flow may have influenced patterns of synchronous and asynchronous streamflow in the four rivers. Spatial drought patterns indicate a zonal flow pattern during two of the most severe droughts in the Snake River record (the 1630s and the 1930s), which were much less severe in the Verde River record. The Snake River's low-flow period in the early 1700s, which was less severe in magnitude, is replicated in the flow of all four rivers and may be indicative of persistent meridional flow. These drought patterns appear to correspond to shifts in Pacific Ocean conditions; however, direct comparisons between these periods and reconstructed indices such as ENSO are hindered by inconsistencies between existing reconstructions of paleo-teleconnections. VARIATION IN FORAMINIFERAL DISTRIBUTIONS ACROSS THE PLEISTOCENE-HOLOCENE TRANSITION OFF THE KAYAK SLOPE, NORTHERN GULF OF ALASKA Sarah D. Zellers, Kathryn Mueller, Diana D. Hill. Department of Biology and Earth Science, University of Central Missouri, Warrensburg, MO 64093, USA E-mail address: [email protected].
The Integrated Ocean Drilling Program is considering drilling in the Gulf of Alaska (GOA), where the interplay among climate, tectonics, and deposition can be examined. A slope site off Kayak Island, sampled by jumbo piston core (EW040885JC), is providing insight into paleoceanographic, depositional, geochemical, and climatic changes across the PleistoceneHolocene transition, including the Bølling–Alleröd (Bø–Al) warm interval and the Younger Dryas (YD) cold interval. These intervals were determined by geochemical analyses, siliceous microfossil distributions, and isotopic analyses by various researchers. Foraminiferal biofacies also track the Bø– Al and YD intervals. Core EW040885JC contains four intervals with distinct faunal assemblages. From 1124 to 680 cm core depth, samples consist of a sandy diamicton with a mixture of outer shelf taxa (Epistominella pacifica, Uvigerina, Cassidulina, Islandiella, and Cibicides), and common Elphidium clavatum, indicating transport into deep water by ice rafting and/or turbidity currents. Planktonic foraminifera are abundant and consist mainly of Neogloboquadrina pachyderma (sinistral and some dextral) and Globigerina bulloides. Two samples from a short interval (680 to 640 cm), corresponding to the Bø–Al, consist of brown, laminated calcareous ooze dominated by benthic taxa (Bolivina and Bulimina) indicative of low oxygen and a few planktonic foraminifera. Above this zone (640 to 410 cm) are bioturbated, silty muds with low abundances of Gyroidina, Bolivina, and the shelf taxa listed above, along with abundant planktic foraminifera (N. pachyderma and G. bulloides), corresponding, in part, to the YD. From 410 cm to the top of the core (0 cm), foraminifera are not common, with muds dominated by abundant radiolarians, diatoms, and sponge spicules. Assemblages show a change from glacially-influenced deposition, to low oxygen bottom waters, to climatic conditions favoring silica production at the top. DEVELOPING ROBUST AGE MODELS FOR LAKE RECORDS: CASE STUDIES FROM CALIFORNIA Susan R.H. Zimmerman, Tom Guilderson, Tom Brown. Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA E-mail address: [email protected].
In recent years, it has become apparent that Earth's climate system is variable on many scales of time and space, and includes abrupt changes that have global effects. When attempting to understand the relationships of decadal- to centennial-scale variability between sites and depositional environments, a “coarse” age model with a handful of ages does not suffice. To better describe patterns of past drought in California, we are establishing robust, high-resolution 14C chronologies for regional lakes ranging from 34 to 42 latitude, 540 to 2100 m elevation, and in a variety of vegetational, hydrological, geochemical, and biological settings. Almost 300 radiocarbon dates have been measured on terrestrial and aquatic macrofossils, as well as bulk sediment – macrofossil pairs. The latter have yielded no single answer to the meaning of bulk-sediment dates; in a few instances, a constant off-set is implied, but in most cases there is no pattern, reinforcing the unreliability of bulk sediment dates. As a complement to the radiocarbon measurements, some sediment sequences have also had 210Pb, 137Cs, and paleomagnetic secular variation (PSV) measurements, providing independent information to refine the age model. Construction of a robust age model from any set of measured ages requires honest recognition of uncertainties due to the reliability of individual ages and methods, differences in calendar-year calibration datasets, interpolation between discretely-dated horizons, and sources of geological variability. Calibration of radiocarbon dates to calendar years requires an internationally-accepted calibration data-set (e.g, INTCAL-09), and is relatively simple to do with programs like Calib and OxCal, but requires a rigorous propagation of errors which in reality should yield an age envelope and probability distribution. Several calibration programs contain the ability to include Bayesian statistics (priors) of the calibration curve and construct an age-model with simulated calendar uncertainties. We present examples of various methods for construction of robust, highprecision age models, and a picture of past droughts in California emerging from our lacustrine records.
Palmyra Atoll, a remote uninhabited series of islets in the central Pacific, represents one of these rare viable sites. Using multiple proxies to reconstruct past sea surface conditions, we seek to understand the relationship between ENSO variability and known late Holocene climate events (i.e. the Medieval Climate Anomaly and Little Ice Age). We report preliminary data from a 3.2 m sediment core retrieved from the west lagoon on Palmyra Atoll (5 530 05.2500 N; 162 050 21.6300 W; water depth 51 m). Radiocarbon determinations on pteropods from the basal sediment of the core indicate the record extends to w640 cal yr BP (AD 1310). Evidence for construction on the atoll during WWII includes a discreet horizon of coarse-grained carbonate, providing a chronologic marker at 8 cal yr BP (AD 1942). Oxygen isotopic composition of authigenic carbonates, high-resolution scanning XRF, 14C, and 210Pb data are currently being collected, and together will be used to construct a model of changing sea surface conditions for the region.
245
occurred at this magnitude. Reconstructing high-resolution disturbance regimes (fire and MPB) from sedimentary records for the Holocene (the last 10,000 years) will provide insight on disturbance ecology in subalpine forests. The records presented here use charcoal to identify past fire disturbance and a new pollen method to identify past MPB outbreaks. The new pollen method was developed from recent studies in spruce-fir forests where changes in pollen composition were used to identify past spruce beetle outbreaks. Initially, it was unclear if this would work in pinedominated systems where there is not the same trade-off between dominant tree taxa. Two late Holocene records from Fishstick Lake, Idaho and Lake of the Woods, Montana demonstrate that pollen ratios can be used to identify past bark beetle outbreaks in pine-dominated forests. FROM ATMOSPHERIC CIRCULATION TO GRAPE TEMPERATURES: MACRO-, MESO-, TOPO-, AND MICROCLIMATE IN VINEYARDS (AND YOUR GLASS)
ELKHORN SLOUGH TIDAL WETLANDS: PAST, PRESENT AND FUTURE Elizabeth Burke Watson a, b, Eric Van Dyke b, Kerstin Wasson b, c. a Department of Land, Air and Water Resources, University of California, Davis, CA 95616, USA; b Elkhorn Slough National Estuarine Research Reserve, Watsonville, CA 95076, USA; c Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95064, USA E-mail address: [email protected].
Tectonic uplift, a narrow continental shelf, and heavy surf place strong natural limits on the areal extent of tidal wetland habitat along the California coast. Concurrently, human activities and associated landscape changes have led to the large-scale destruction of much of the region's tidal wetlands. Tidal wetlands at Elkhorn Slough, central Monterey Bay, are thus a regionally important resource: this area supports among the largest remaining extents of tidal wetlands in California. Unfortunately, these wetlands are in deteriorated condition: a large portion were diked off from tidal exchange (these areas exist today as shallow eutrophic ponds), and in fully tidal locations, hydrologic modifications to the estuary have resulted in plant mortality and marsh loss. At Elkhorn Slough National Estuarine Research Reserve, we are conducting a study utilizing stratigraphic assessments and habitat modeling in order to address key questions about the historical extent, current trajectory, and future distribution of estuarine wetlands at Elkhorn Slough, with an emphasis on understanding the impacts of climate variability and climate change on this coastal resource. For the purposes of habitat reconstruction, sediment stratigraphies with chronologic control established using radiocarbon dating, have revealed dramatic variability in marsh extent at Elkhorn Slough, revealing clear episodes of past marsh deterioration. Studies of contemporary sediment accumulation undertaken using sediment-erosion tables, sediment tiles, marker beds, and recent radiometric dating (e.g. 137Cs/210Pb) reflect a submerging marsh plain and escalating accumulation rates in both vegetated and deteriorated tidal marsh. Implementation of a habitat model (sea level affecting marshes – SLAMM) has identified low suspended sediment concentrations as an obstacle to marsh sustainability under even the most moderate sea level rise/climate scenarios, but has identified potential future marsh migration pathways. These data will be used to help set well-informed targets for marsh acreage in the estuary and to understand what geographical areas are likely sites for marsh migration.
Stuart B. Weiss. Viticision/Creekside Center for Earth Observation, 27 Bishop Lane, Menlo Park, CA 94025, USA E-mail address: [email protected]
Few agricultural crops are as sensitive to weather and climate as wine grapes. Small fluctuations in temperature and phenology can make the difference between high quality and poor quality crops. Climate change will challenge continued production of quality wine grapes in the Pacific States. In order to effectively consider climate change in vineyard design and management, a multi-scale approach to climate is required, descending scales from macroclimate through mesoclimate, topoclimate, and microclimate. In this presentation, I describe applications of this hierarchy to vineyards. Station data, and interpolated surfaces such as PRISM account for macroclimatic and mesoclimatic gradients down to a scale of 800 m. Ripening dates, both past and projected, of grape varieties can be estimated from monthly data at these scales. Topoclimatic gradients are derived from digital elevation models (DEMs) using solar radiation models, topographic position, and slope, and have profound effects on minimum and maximum temperatures. At the finest scale, microclimate encompasses the effects of vegetation canopies on solar radiation, humidity, and temperature, such as the effects of trellis design on berry temperature on either side of the trellis. Hemispherical photography quantifies trellises from a “grapes' eye view,” allowing estimation of solar radiation on grape clusters at half hourly intervals for each month. By combining all of these methods with inexpensive temperature sensors, the temperatures of grape clusters can be tracked through growing seasons using local weather station data, with numerous key insights into vineyard design and management in a variable and changing climate. MILLENNIAL-SCALE CLIMATE OSCILLATIONS OVER THE PAST 735,000 YEARS AS RECORDED IN HIGH-RESOLUTION MARINE SEDIMENT RECORDS FROM SANTA BARBARA BASIN, CALIFORNIA Sarah M. White a, Tessa M. Hill a, James P. Kennett b, Richard Behl c. a Department of Geology, University of California, Davis, CA 95616, USA; b Department of Earth Science, University of California, Santa Barbara, CA 93106, USA; c Department of Geological Sciences, California State University, Long Beach, CA 90840, USA E-mail address: [email protected].
A LATE HOLOCENE RECORD OF DISTURBANCE FROM THE NORTHERN ROCKY MOUNTAINS, USA Jennifer H. Watt a, Andrea Brunelle a, Kurt Kipfmueller b. a Department of Geography, RED Lab, University of Utah, Salt Lake City, UT 84112, USA; b Department of Geography, Center for Dendrochronology, University of Minnesota, Minneapolis, MN 55455, USA E-mail address: [email protected].
Mountain pine beetle (MPB) outbreaks have impacted or are currently affecting many pine communities in the western US. It is not clear if these large-scale outbreaks are unprecedented or if they have previously
A lack of high-resolution climate records beyond the last glacial period has limited understanding of causes, effects, and temporal development of Quaternary abrupt climate shifts. Santa Barbara Basin (SBB), with a sedimentation rate of 100 cm/1000 yr, provides uniquely well-preserved sediments spanning the past w700,000. Five piston cores from SBB, each spanning w5000, were dated to w735,000, 460,000, and 290,000 years ago. These cores allow us to see whether millennial-scale climate shifts have changed in amplitude, shape, and/or timing since the Mid-Pleistocene Transition, and how they are expressed in the Pacific in terms of ocean circulation, productivity, and oxygenation. We use stable isotopes of planktonic (Globigerina bulloides, Neogloboquadrina pachyderma), and
246
Abstracts / Quaternary International 310 (2013) 227–246
benthic foraminifera (Uvigerina peregrina) and planktonic foraminiferal assemblage analyses including % N. pachyderma (d), and sediment lamination data. d18O data of G. bulloides and N. pachyderma show shifts of up to 1.4& in as briefly as w80 years and 2.5& over w1000 years during warming. Water column stratification (shown by the difference between G. bulloides and N. pachyderma d18O) increases during interstadials. The % N. pachyderma (d) often varies in tandem with planktonic d18O, but exhibits threshold behavior instead of smooth change, and is generally higher during interstadials and/or moderate water column stratification. d13C values broadly correlate with shifts in d18O, and reflect changing ocean circulation, carbon cycling, and/or methane release. Preserved sediment laminations coincide with intervals of warm, stratified upper waters. A comparison of our data to SBB records from the past 60,000 years (Behl and Kennett, 1996; Hendy and Kennett, 1999, 2000; Hill et al., 2006) shows that typical stadial-interstadial shifts in planktonic d18O (w1.5&) are similar to those recorded during the past 60,000 years, although changes in % N. pachyderma (d) are smaller, and planktonic assemblages are slightly different, with fewer G. bulloides, Globigerina quinqueloba, Globorotalia scitula, and more N. pachyderma (s). Behl, R.J., Kennett, J.P., 1996. Brief interstadial events in the Santa Barbara Basin, NE Pacific, during the last 60 kyr: Nature 376, 243-246. Hendy, I.L., Kennett, J.P., 1999. Latest Quaternary North Pacific surface water responses imply atmospherically-driven climate instability: Geology 27 (4), 291-294. Hendy, I.L., Kennett, J.P., 2000. Stable isotope stratigraphy and paleoceanography of the last 170 ka: ODP Site 1014, Tanner Basin, California: Ocean Drilling Program Scientific Reports 167, 129-140. Hill, T.M., Kennett, J.P., Pak, D.K., Behl, R.J., Robert, C., Beaufort, L., 2006. PreBølling warming in Santa Barbara Basin, California: Surface and intermediate water records of early deglacial warmth: Quaternary Science Reviews 25 (21-22), 2835-2845. CLIMATE DRIVERS OF STREAMFLOW SYNCHRONICITY IN WESTERN US RIVERS OVER MULTIPLE CENTURIES Erika K. Wise. Department of Geography, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA E-mail address: [email protected]
Twentieth century high- and low-streamflow events in the western US have been linked to Pacific and Atlantic Ocean influences, including those described by the El Niño–Southern Oscillation (ENSO), the Pacific Decadal Oscillation, and the Atlantic Multidecadal Oscillation. Extended streamflow records, reconstructed using tree rings, have identified drought and pluvial periods in the past that were more extreme than those recorded during in the instrumental record. This study compares a new tree-ring based reconstruction of Snake River streamflow with streamflow reconstructions of the Colorado, Sacramento, and Verde rivers. Results suggest that changes in the predominance of zonal versus meridional atmospheric flow may have influenced patterns of synchronous and asynchronous streamflow in the four rivers. Spatial drought patterns indicate a zonal flow pattern during two of the most severe droughts in the Snake River record (the 1630s and the 1930s), which were much less severe in the Verde River record. The Snake River's low-flow period in the early 1700s, which was less severe in magnitude, is replicated in the flow of all four rivers and may be indicative of persistent meridional flow. These drought patterns appear to correspond to shifts in Pacific Ocean conditions; however, direct comparisons between these periods and reconstructed indices such as ENSO are hindered by inconsistencies between existing reconstructions of paleo-teleconnections. VARIATION IN FORAMINIFERAL DISTRIBUTIONS ACROSS THE PLEISTOCENE-HOLOCENE TRANSITION OFF THE KAYAK SLOPE, NORTHERN GULF OF ALASKA Sarah D. Zellers, Kathryn Mueller, Diana D. Hill. Department of Biology and Earth Science, University of Central Missouri, Warrensburg, MO 64093, USA E-mail address: [email protected].
The Integrated Ocean Drilling Program is considering drilling in the Gulf of Alaska (GOA), where the interplay among climate, tectonics, and deposition can be examined. A slope site off Kayak Island, sampled by jumbo piston core (EW040885JC), is providing insight into paleoceanographic, depositional, geochemical, and climatic changes across the PleistoceneHolocene transition, including the Bølling–Alleröd (Bø–Al) warm interval and the Younger Dryas (YD) cold interval. These intervals were determined by geochemical analyses, siliceous microfossil distributions, and isotopic analyses by various researchers. Foraminiferal biofacies also track the Bø– Al and YD intervals. Core EW040885JC contains four intervals with distinct faunal assemblages. From 1124 to 680 cm core depth, samples consist of a sandy diamicton with a mixture of outer shelf taxa (Epistominella pacifica, Uvigerina, Cassidulina, Islandiella, and Cibicides), and common Elphidium clavatum, indicating transport into deep water by ice rafting and/or turbidity currents. Planktonic foraminifera are abundant and consist mainly of Neogloboquadrina pachyderma (sinistral and some dextral) and Globigerina bulloides. Two samples from a short interval (680 to 640 cm), corresponding to the Bø–Al, consist of brown, laminated calcareous ooze dominated by benthic taxa (Bolivina and Bulimina) indicative of low oxygen and a few planktonic foraminifera. Above this zone (640 to 410 cm) are bioturbated, silty muds with low abundances of Gyroidina, Bolivina, and the shelf taxa listed above, along with abundant planktic foraminifera (N. pachyderma and G. bulloides), corresponding, in part, to the YD. From 410 cm to the top of the core (0 cm), foraminifera are not common, with muds dominated by abundant radiolarians, diatoms, and sponge spicules. Assemblages show a change from glacially-influenced deposition, to low oxygen bottom waters, to climatic conditions favoring silica production at the top. DEVELOPING ROBUST AGE MODELS FOR LAKE RECORDS: CASE STUDIES FROM CALIFORNIA Susan R.H. Zimmerman, Tom Guilderson, Tom Brown. Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA E-mail address: [email protected].
In recent years, it has become apparent that Earth's climate system is variable on many scales of time and space, and includes abrupt changes that have global effects. When attempting to understand the relationships of decadal- to centennial-scale variability between sites and depositional environments, a “coarse” age model with a handful of ages does not suffice. To better describe patterns of past drought in California, we are establishing robust, high-resolution 14C chronologies for regional lakes ranging from 34 to 42 latitude, 540 to 2100 m elevation, and in a variety of vegetational, hydrological, geochemical, and biological settings. Almost 300 radiocarbon dates have been measured on terrestrial and aquatic macrofossils, as well as bulk sediment – macrofossil pairs. The latter have yielded no single answer to the meaning of bulk-sediment dates; in a few instances, a constant off-set is implied, but in most cases there is no pattern, reinforcing the unreliability of bulk sediment dates. As a complement to the radiocarbon measurements, some sediment sequences have also had 210Pb, 137Cs, and paleomagnetic secular variation (PSV) measurements, providing independent information to refine the age model. Construction of a robust age model from any set of measured ages requires honest recognition of uncertainties due to the reliability of individual ages and methods, differences in calendar-year calibration datasets, interpolation between discretely-dated horizons, and sources of geological variability. Calibration of radiocarbon dates to calendar years requires an internationally-accepted calibration data-set (e.g, INTCAL-09), and is relatively simple to do with programs like Calib and OxCal, but requires a rigorous propagation of errors which in reality should yield an age envelope and probability distribution. Several calibration programs contain the ability to include Bayesian statistics (priors) of the calibration curve and construct an age-model with simulated calendar uncertainties. We present examples of various methods for construction of robust, highprecision age models, and a picture of past droughts in California emerging from our lacustrine records.