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• 71. [Article] Lahar hazard mapping of Mount Shasta, California : a GIS-based delineation of potential inundation zones in Mud and Whitney Creek basins

  Mount Shasta, the southernmost stratovolcano in the Cascade Range (41.4°N) has frequently produced lahars of various magnitudes during the last 10,000 yr. These include large flows of eruptive origin, ...

  Citation × Citation Citation Abstract Copy Title: Lahar hazard mapping of Mount Shasta, California : a GIS-based delineation of potential inundation zones in Mud and Whitney Creek basins Author: McClung, Steven C. Mount Shasta, the southernmost stratovolcano in the Cascade Range (41.4°N) has frequently produced lahars of various magnitudes during the last 10,000 yr. These include large flows of eruptive origin, reaching more than 40km from the summit, and studies have shown that at least 70 debris flows of noneruptive origin have occurred during the last 1,000 yr in various stream channels. The Mud and Whitney Creek drainages have historically produced more debris flows than any other glacier-headed channel on the volcano. Periods of accelerated glacial melt have produced lahars in Whitney Creek with a volume of 4 x 106 m3 and a runout distance of about 27 km from the summit. Mud Creek flows from 1924 – 1931 covered an area of more than 6 km2 near the community of McCloud with an estimated 23 x 106 m3 of mud. A much older lahar in Big Canyon Creek may have deposited a volume of 70 x 106 m3 over present day Mount Shasta City and beyond. A lahar inundation modeling tool developed by USGS analysts is used to objectively delineate lahar inundation zones on Mount Shasta by embedding predictive equations in a geographic information system (GIS) that uses a digital elevation model, hypothetical lahar volumes, and geometric relationships as input. Volumes derived from these lahar deposits are extrapolated to the selected drainages to generate probable lahar inundation hazard zones with a focus on mapping and hazards implications. Title: Lahar hazard mapping of Mount Shasta, California : a GIS-based delineation of potential inundation zones in Mud and Whitney Creek basins Author: McClung, Steven C. Mount Shasta, the southernmost stratovolcano in the Cascade Range (41.4°N) has frequently produced lahars of various magnitudes during the last 10,000 yr. These include large flows of eruptive origin, reaching more than 40km from the summit, and studies have shown that at least 70 debris flows of noneruptive origin have occurred during the last 1,000 yr in various stream channels. The Mud and Whitney Creek drainages have historically produced more debris flows than any other glacier-headed channel on the volcano. Periods of accelerated glacial melt have produced lahars in Whitney Creek with a volume of 4 x 106 m3 and a runout distance of about 27 km from the summit. Mud Creek flows from 1924 – 1931 covered an area of more than 6 km2 near the community of McCloud with an estimated 23 x 106 m3 of mud. A much older lahar in Big Canyon Creek may have deposited a volume of 70 x 106 m3 over present day Mount Shasta City and beyond. A lahar inundation modeling tool developed by USGS analysts is used to objectively delineate lahar inundation zones on Mount Shasta by embedding predictive equations in a geographic information system (GIS) that uses a digital elevation model, hypothetical lahar volumes, and geometric relationships as input. Volumes derived from these lahar deposits are extrapolated to the selected drainages to generate probable lahar inundation hazard zones with a focus on mapping and hazards implications. Close

• 72. [Article] Tidal range changes in the Delaware Bay : past conditions and future scenarios

  Throughout the Holocene, appreciable changes in bathymetry are hypothesized to have resulted in large changes to tidal datums in coastal and estuarine areas. An understanding of tidal change is an important ...

  Citation × Citation Citation Abstract Copy Title: Tidal range changes in the Delaware Bay : past conditions and future scenarios Author: Hall, George F. Throughout the Holocene, appreciable changes in bathymetry are hypothesized to have resulted in large changes to tidal datums in coastal and estuarine areas. An understanding of tidal change is an important contribution to the knowledge of relative historical sea-level change and future coastal planning. To test this hypothesis, the Advanced Circulation (ADCIRC) model was used, with representative bathymetric grids based on glacial isostatic adjustment models and semi-empirical sea level rise predictions, in order to model the time-varying tidal behavior of the Delaware Bay. Model runs were conducted at various time slices between 10,000 years before present and 300 years into the future on high resolution grids that allowed for inundation moving forward in time. Open boundary tidal forcing was held constant in time to highlight the effect of the changing regional bathymetry. With each change in sea level, the shape of the Delaware Bay was considerably altered, leading to changes in the tides. Resonance and shallow water dissipation appeared to be the primary mechanisms behind these changes. Results showed that tidal ranges have nearly doubled in the upper Delaware Bay over the past 3000 years, while decreasing in the lower bay by 8%. Tidal range change represents a possible correction to past sea level rise estimates from the geologic record. Scenarios incorporating future sea level predictions primarily showed a small decrease in tidal range, potentially impacting future water levels and tidal sediment transport. Trends modeled were consistent with field measurements of relative change over similar time periods. Title: Tidal range changes in the Delaware Bay : past conditions and future scenarios Author: Hall, George F. Throughout the Holocene, appreciable changes in bathymetry are hypothesized to have resulted in large changes to tidal datums in coastal and estuarine areas. An understanding of tidal change is an important contribution to the knowledge of relative historical sea-level change and future coastal planning. To test this hypothesis, the Advanced Circulation (ADCIRC) model was used, with representative bathymetric grids based on glacial isostatic adjustment models and semi-empirical sea level rise predictions, in order to model the time-varying tidal behavior of the Delaware Bay. Model runs were conducted at various time slices between 10,000 years before present and 300 years into the future on high resolution grids that allowed for inundation moving forward in time. Open boundary tidal forcing was held constant in time to highlight the effect of the changing regional bathymetry. With each change in sea level, the shape of the Delaware Bay was considerably altered, leading to changes in the tides. Resonance and shallow water dissipation appeared to be the primary mechanisms behind these changes. Results showed that tidal ranges have nearly doubled in the upper Delaware Bay over the past 3000 years, while decreasing in the lower bay by 8%. Tidal range change represents a possible correction to past sea level rise estimates from the geologic record. Scenarios incorporating future sea level predictions primarily showed a small decrease in tidal range, potentially impacting future water levels and tidal sediment transport. Trends modeled were consistent with field measurements of relative change over similar time periods. Close

• 73. [Article] A Reconstruction of Plant Species Composition at the Devil's Kitchen Site (Southern Oregon Coast) using Plant Opal Phytoliths and Charcoal Macro-remains

  Although plant remains, such as opal phytolith and charcoal analyses, have been used since the beginning of the 20th century to reconstruct past environments by ecologists and botanists, only recently ...

  Citation × Citation Citation Abstract Copy Title: A Reconstruction of Plant Species Composition at the Devil's Kitchen Site (Southern Oregon Coast) using Plant Opal Phytoliths and Charcoal Macro-remains Author: Bulder, Nicholas H. Although plant remains, such as opal phytolith and charcoal analyses, have been used since the beginning of the 20th century to reconstruct past environments by ecologists and botanists, only recently have these techniques been considered by archaeologists in understanding the past at the site level. This study employs opal phytolith analysis with charcoal analysis to determine both the plant community composition and the possible use of tree species by humans at the site of Devil’s Kitchen (Southern Oregon coast) across the time interval of ca. 11,600 to 1,900 Radiocarbon Years Before Present (RCYBP). A total of 44 phytolith sample slides and 73 charcoal samples were analyzed from 5 lithostratigraphic units representing different depositional environments reflecting the site's distance from the ocean and elevation above sea level. This is due to the dynamic nature of landforms on the Oregon Coast, which since the last glacial maximum, have been influenced by sea level rise, tectonic uplift, and coseismic subduction. This dynamic landscape is confirmed by the botanical evidence. Charcoal macro-remains from the oldest sediments (10,638 ± 35 to 11,698± 38 RCYBP) indicate a forest of Douglas-fir and western hemlock. Phytolith evidence from later sediments (4,274± 26 to 1,901± 28 RCYBP) shows first, a mixture of saltwater inundation tolerant saltgrass and non-inundatuion tolerant fescues, followed by a period of time when only saltgrass is present. The site then returns to a mixture of saltgrass and fescue (ca. 2101± 23 RCYBP), until the site is buried by sand dunes.This updated perspective on the plant species surrounding the site through time provides important information on habitat and resources, and will assist archaeologists in interpreting other aspects of the archaeological record by placing artifacts in the environmental contexts in which they were used. Title: A Reconstruction of Plant Species Composition at the Devil's Kitchen Site (Southern Oregon Coast) using Plant Opal Phytoliths and Charcoal Macro-remains Author: Bulder, Nicholas H. Although plant remains, such as opal phytolith and charcoal analyses, have been used since the beginning of the 20th century to reconstruct past environments by ecologists and botanists, only recently have these techniques been considered by archaeologists in understanding the past at the site level. This study employs opal phytolith analysis with charcoal analysis to determine both the plant community composition and the possible use of tree species by humans at the site of Devil’s Kitchen (Southern Oregon coast) across the time interval of ca. 11,600 to 1,900 Radiocarbon Years Before Present (RCYBP). A total of 44 phytolith sample slides and 73 charcoal samples were analyzed from 5 lithostratigraphic units representing different depositional environments reflecting the site's distance from the ocean and elevation above sea level. This is due to the dynamic nature of landforms on the Oregon Coast, which since the last glacial maximum, have been influenced by sea level rise, tectonic uplift, and coseismic subduction. This dynamic landscape is confirmed by the botanical evidence. Charcoal macro-remains from the oldest sediments (10,638 ± 35 to 11,698± 38 RCYBP) indicate a forest of Douglas-fir and western hemlock. Phytolith evidence from later sediments (4,274± 26 to 1,901± 28 RCYBP) shows first, a mixture of saltwater inundation tolerant saltgrass and non-inundatuion tolerant fescues, followed by a period of time when only saltgrass is present. The site then returns to a mixture of saltgrass and fescue (ca. 2101± 23 RCYBP), until the site is buried by sand dunes.This updated perspective on the plant species surrounding the site through time provides important information on habitat and resources, and will assist archaeologists in interpreting other aspects of the archaeological record by placing artifacts in the environmental contexts in which they were used. Close

• 74. [Article] Stratigraphy of the silurian and devonian rocks, Northwestern Pend Oreille County, Washington

  Silurian and Devonian rocks are exposed for approximately 8 square kilometers inthe KootenayArc structural province of northeastem Washington. These Middle Paleozoic rocks overlie the Upper Cambrian Metaline ...

  Citation × Citation Citation Abstract Copy Title: Stratigraphy of the silurian and devonian rocks, Northwestern Pend Oreille County, Washington Author: Greenman, Celia Silurian and Devonian rocks are exposed for approximately 8 square kilometers inthe KootenayArc structural province of northeastem Washington. These Middle Paleozoic rocks overlie the Upper Cambrian Metaline Limestone and the Ordovician Ledbetter Formation, which includes slates, siltstones, and limestones. Two Silurian units crop out in this area. Unit A is composed of Lower Silurian graptolitic argillites and siltstones and Upper Silurian siltstones and fossiliferous limestone. These lithologies represent a trend towards shallower water conditions than those operative during deposition of the Ledbetter Formation. Above Unit A lies the quartz granule conglomerate Unit. This unit consists of a silica rich granule conglomerate with associated beds of slate and is interpreted as an inner submarine fan deposit. Devonian rocks are found locally at Limestone Hill. The polymictic Givetian limestone conglomerate crops out at the base of the bill. This conglomerate contains limestone clasts of Lower and lower Middle Devonian rocks, thereby documenting a break in the sedimentary record. The Givetian limestone occurs as float fragments of dark-gray limestone, which preserve a diverse conodont fauna. On the crest of Limestone Hill lies the Frasnian massive and bedded lime stones, which are believed to represent a reef build-up. The post-Paleozoic sedimentary record consists of Quaternary glacial deposits. An olivine trachybasalt of probable Tertiary age crops out for a short distance in the central portion of the map area. The region has undergone several periods of deformation of probable Mesozoic age. The structure is dominated by northeast and northerly trending folds, and northeast and northerly trending steeply dipping normal faults. Title: Stratigraphy of the silurian and devonian rocks, Northwestern Pend Oreille County, Washington Author: Greenman, Celia Silurian and Devonian rocks are exposed for approximately 8 square kilometers inthe KootenayArc structural province of northeastem Washington. These Middle Paleozoic rocks overlie the Upper Cambrian Metaline Limestone and the Ordovician Ledbetter Formation, which includes slates, siltstones, and limestones. Two Silurian units crop out in this area. Unit A is composed of Lower Silurian graptolitic argillites and siltstones and Upper Silurian siltstones and fossiliferous limestone. These lithologies represent a trend towards shallower water conditions than those operative during deposition of the Ledbetter Formation. Above Unit A lies the quartz granule conglomerate Unit. This unit consists of a silica rich granule conglomerate with associated beds of slate and is interpreted as an inner submarine fan deposit. Devonian rocks are found locally at Limestone Hill. The polymictic Givetian limestone conglomerate crops out at the base of the bill. This conglomerate contains limestone clasts of Lower and lower Middle Devonian rocks, thereby documenting a break in the sedimentary record. The Givetian limestone occurs as float fragments of dark-gray limestone, which preserve a diverse conodont fauna. On the crest of Limestone Hill lies the Frasnian massive and bedded lime stones, which are believed to represent a reef build-up. The post-Paleozoic sedimentary record consists of Quaternary glacial deposits. An olivine trachybasalt of probable Tertiary age crops out for a short distance in the central portion of the map area. The region has undergone several periods of deformation of probable Mesozoic age. The structure is dominated by northeast and northerly trending folds, and northeast and northerly trending steeply dipping normal faults. Close

• 75. [Article] Large fluctuations of dissolved oxygen in the Indian and Pacific oceans during Dansgaard-Oeschger oscillations caused by variations of North Atlantic Deep Water Subduction: Paleoceanography

  Paleoclimate records from glacial Indian and Pacific oceans sediments document millennial-scale fluctuations of subsurface dissolved oxygen levels and denitrification coherent with North Atlantic temperature ...

  Citation × Citation Citation Abstract Copy Title: Large fluctuations of dissolved oxygen in the Indian and Pacific oceans during Dansgaard-Oeschger oscillations caused by variations of North Atlantic Deep Water Subduction: Paleoceanography Author: Schmittner, Andreas Paleoclimate records from glacial Indian and Pacific oceans sediments document millennial-scale fluctuations of subsurface dissolved oxygen levels and denitrification coherent with North Atlantic temperature oscillations. Yet the mechanism of this teleconnection between the remote ocean basins remains elusive. Here we present model simulations of the oxygen and nitrogen cycles that explain how changes in deepwater subduction in the North Atlantic can cause large and synchronous variations of oxygen minimum zones throughout the Northern Hemisphere of the Indian and Pacific oceans, consistent with the paleoclimate records. Cold periods in the North Atlantic are associated with reduced nutrient delivery to the upper Indo-Pacific oceans, thereby decreasing productivity. Reduced export production diminishes subsurface respiration of organic matter leading to higher oxygen concentrations and less denitrification. This effect of reduced oxygen consumption dominates at low latitudes. At high latitudes in the Southern Ocean and North Pacific, increased mixed layer depths and steepening of isopycnals improve ocean ventilation and oxygen supply to the subsurface. Atmospheric teleconnections through changes in wind-driven ocean circulation modify this basin-scale pattern regionally. These results suggest that changes in the Atlantic Ocean circulation, similar to those projected by climate models to possibly occur in the centuries to come because of anthropogenic climate warming, can have large effects on marine ecosystems and biogeochemical cycles even in remote areas. Title: Large fluctuations of dissolved oxygen in the Indian and Pacific oceans during Dansgaard-Oeschger oscillations caused by variations of North Atlantic Deep Water Subduction: Paleoceanography Author: Schmittner, Andreas Paleoclimate records from glacial Indian and Pacific oceans sediments document millennial-scale fluctuations of subsurface dissolved oxygen levels and denitrification coherent with North Atlantic temperature oscillations. Yet the mechanism of this teleconnection between the remote ocean basins remains elusive. Here we present model simulations of the oxygen and nitrogen cycles that explain how changes in deepwater subduction in the North Atlantic can cause large and synchronous variations of oxygen minimum zones throughout the Northern Hemisphere of the Indian and Pacific oceans, consistent with the paleoclimate records. Cold periods in the North Atlantic are associated with reduced nutrient delivery to the upper Indo-Pacific oceans, thereby decreasing productivity. Reduced export production diminishes subsurface respiration of organic matter leading to higher oxygen concentrations and less denitrification. This effect of reduced oxygen consumption dominates at low latitudes. At high latitudes in the Southern Ocean and North Pacific, increased mixed layer depths and steepening of isopycnals improve ocean ventilation and oxygen supply to the subsurface. Atmospheric teleconnections through changes in wind-driven ocean circulation modify this basin-scale pattern regionally. These results suggest that changes in the Atlantic Ocean circulation, similar to those projected by climate models to possibly occur in the centuries to come because of anthropogenic climate warming, can have large effects on marine ecosystems and biogeochemical cycles even in remote areas. Close

• 76. [Article] Stratigraphy and structure of the Greenstone Mountain area, Beaverhead County, Montana

  The Greenstone Mountain area, which includes the Utopia mining district, is located in the foothills of the Pioneer Range, Beaverhead County, Montana. Approximately 12, 600 feet of Paleozoic and Mesozoic ...

  Citation × Citation Citation Abstract Copy Title: Stratigraphy and structure of the Greenstone Mountain area, Beaverhead County, Montana Author: Sharp, George Carter, Jr The Greenstone Mountain area, which includes the Utopia mining district, is located in the foothills of the Pioneer Range, Beaverhead County, Montana. Approximately 12, 600 feet of Paleozoic and Mesozoic sedimentary rocks and an undetermined thickness of Precambrian sediments and Late Cretaceous igneous rocks are exposed within the area of investigation. Most of the sedimentary rocks were deposited along the margin of the Cordilleran miogeosyncline. Precambrian Beltian sediments are the oldest exposed rocks in the map area. Pre-Mississippian Paleozoic rocks have not been differentiated in this study but probably represent the Cambrian and Devonian Systems. Other Paleozoic rock units include the Lodgepole and Mission Canyon Formations of Mississippian age, the Amsden Formation of Mississippian to Pennsylvanian age, the Quadrant Formation of Pennsylvanian age, and the Phosphoria Formation of Permian age. Mesozoic sediments include the Dinwoody and Woodside Formations of Triassic age and the Kootenai Formation and Colorado Group of Cretaceous age. The Jurassic System is not represented. During the Late Cretaceous Laramide orogeny the sedimentary rocks of the area were folded and faulted. The dominant structures produced during this period of deformation are northeast- to north-trending anticlines and synclines that are locally overturned to the east. Steep faults of small to moderate displacement disrupt the folds. Quartz monzonite intrusive rocks were emplaced following the Laramide orogeny and are probably genetically related to the Boulder Batholith. The intrusion gave rise to mineralization and thermal metamorphism of the surrounding country rocks. Quaternary glacial and fluvial deposits mantle parts of the area. At least three valley glaciers advanced into the northwestern corner of the area in Late Pleistocene time and left lateral and terminal moraines. Pleistocene terrace gravels are situated along Birch Creek and on lowlands in the west, and Recent alluvium is being deposited along existing streams. Title: Stratigraphy and structure of the Greenstone Mountain area, Beaverhead County, Montana Author: Sharp, George Carter, Jr The Greenstone Mountain area, which includes the Utopia mining district, is located in the foothills of the Pioneer Range, Beaverhead County, Montana. Approximately 12, 600 feet of Paleozoic and Mesozoic sedimentary rocks and an undetermined thickness of Precambrian sediments and Late Cretaceous igneous rocks are exposed within the area of investigation. Most of the sedimentary rocks were deposited along the margin of the Cordilleran miogeosyncline. Precambrian Beltian sediments are the oldest exposed rocks in the map area. Pre-Mississippian Paleozoic rocks have not been differentiated in this study but probably represent the Cambrian and Devonian Systems. Other Paleozoic rock units include the Lodgepole and Mission Canyon Formations of Mississippian age, the Amsden Formation of Mississippian to Pennsylvanian age, the Quadrant Formation of Pennsylvanian age, and the Phosphoria Formation of Permian age. Mesozoic sediments include the Dinwoody and Woodside Formations of Triassic age and the Kootenai Formation and Colorado Group of Cretaceous age. The Jurassic System is not represented. During the Late Cretaceous Laramide orogeny the sedimentary rocks of the area were folded and faulted. The dominant structures produced during this period of deformation are northeast- to north-trending anticlines and synclines that are locally overturned to the east. Steep faults of small to moderate displacement disrupt the folds. Quartz monzonite intrusive rocks were emplaced following the Laramide orogeny and are probably genetically related to the Boulder Batholith. The intrusion gave rise to mineralization and thermal metamorphism of the surrounding country rocks. Quaternary glacial and fluvial deposits mantle parts of the area. At least three valley glaciers advanced into the northwestern corner of the area in Late Pleistocene time and left lateral and terminal moraines. Pleistocene terrace gravels are situated along Birch Creek and on lowlands in the west, and Recent alluvium is being deposited along existing streams. Close

• 77. [Article] Ocean Temperature Variability during the Late Pleistocene

  This dissertation explores one overarching question relevant to the paleoclimate of the latest Pleistocene glacial cycle (approximately the last 130,000 years): “How did spatial and temporal evolution ...

  Citation × Citation Citation Abstract Copy Title: Ocean Temperature Variability during the Late Pleistocene Author: Hoffman, Jeremy Scott This dissertation explores one overarching question relevant to the paleoclimate of the latest Pleistocene glacial cycle (approximately the last 130,000 years): “How did spatial and temporal evolution of ocean temperature, both at the surface and interior, relate to other parts of the climate system in the late Pleistocene?” Results from three studies are presented that seek to address longstanding questions in paleoceanography and paleoclimatology for the late Pleistocene using a combination of novel and accepted statistical and geochemical analysis techniques and leveraging comparisons with available global climate model data. The last interglaciation (LIG; ~129-116 ka) was the most recent period in Earth’s history with higher-than-present global sea level (≥6-9 m) under similar-to-preindustrial concentrations of atmospheric CO₂. This suggests that additional feedbacks related to albedo, insolation, and ocean overturning circulation may have resulted in the apparent warming required to cause the higher sea level. Our understanding of how much warmer the LIG was relative to the present interglaciation remains uncertain, however, with current estimates suggesting that sea-surface temperatures (SSTs) were 0-2°C warmer than late-20th century average global temperatures. We present a global compilation of proxy-based annual SST spanning the LIG. Using Monte Carlo and Bayesian techniques to propagate uncertainties in age-model and proxy-based SST reconstructions, our results quantify the spatial timing, amplitude, and uncertainty in global and regional SST change during the LIG. Our conclusions suggest that the LIG surface ocean was indistinguishable from the average surface ocean temperatures observed for the last two decades (1995-2014). This may ultimately imply that the Earth is currently committed to ≥6-9m of equilibrium sea-level rise. Although the LIG is not an analogue for present and future climate change due to the large differences in seasonal orbital insolation and absence of anthropogenic greenhouse gas radiative forcing, it provides an opportunity to test the ability of global climate models to simulate the mechanisms and climate feedbacks responsible for the warmer climate and higher global mean sea level during the LIG. However, when forced only by LIG greenhouse gas concentrations and insolation changes, climate models suggest that the annual mean temperature response was not significantly different from preindustrial control simulations. We present the first multi-model and multiscenario ensemble of transient and equilibrium global climate modeling results spanning the LIG. We show, using a novel model-data comparison framework, that these scenario-specific model results exhibit regionally independent agreement with ocean basin-specific proxy-based SST stacks. This result ultimately implies structural uncertainties and/or misrepresentations of climate feedbacks in the existing suite of climate model simulations, or underestimations of additional proxy-based SST uncertainties. Our conclusions suggest a new target LIG time period for future model-data comparisons and highlight the need for higher resolution transient climate modeling of the LIG and its dependence on meltwater input to the high latitude oceans during the preceding deglaciation. Few discoveries have stimulated the paleoclimate community more so than Heinrich events. Nevertheless, the cause of Heinrich events, characterized by a large flux of icebergs sourced from the Hudson Strait Ice Stream into the North Atlantic, remains debated. Commonly attributed to internal ice-sheet instability, the occurrence of Heinrich events during the coldest intervals of the last glacial cycle instead suggests an external climate control. We expand on recent studies that have shown that incursions of warm subsurface waters into the intermediate depth North Atlantic Ocean destabilized an ice shelf fronting the Hudson Strait Ice Stream, causing a Heinrich event. We present new surface- and bottom-water stable isotope, trace metal, and sedimentary records from two cores taken along the Labrador margin that further support subsurface warming as a trigger of Hudson Strait Heinrich events. We further relate these changes to other sediment core records from the North Atlantic and transient deglacial climate modeling results to show that subsurface warming was ubiquitous across the intermediate North Atlantic during the early part of the last deglaciation and was most likely caused by a preceding reduction in the Atlantic Meridional Overturning Circulation. Title: Ocean Temperature Variability during the Late Pleistocene Author: Hoffman, Jeremy Scott This dissertation explores one overarching question relevant to the paleoclimate of the latest Pleistocene glacial cycle (approximately the last 130,000 years): “How did spatial and temporal evolution of ocean temperature, both at the surface and interior, relate to other parts of the climate system in the late Pleistocene?” Results from three studies are presented that seek to address longstanding questions in paleoceanography and paleoclimatology for the late Pleistocene using a combination of novel and accepted statistical and geochemical analysis techniques and leveraging comparisons with available global climate model data. The last interglaciation (LIG; ~129-116 ka) was the most recent period in Earth’s history with higher-than-present global sea level (≥6-9 m) under similar-to-preindustrial concentrations of atmospheric CO₂. This suggests that additional feedbacks related to albedo, insolation, and ocean overturning circulation may have resulted in the apparent warming required to cause the higher sea level. Our understanding of how much warmer the LIG was relative to the present interglaciation remains uncertain, however, with current estimates suggesting that sea-surface temperatures (SSTs) were 0-2°C warmer than late-20th century average global temperatures. We present a global compilation of proxy-based annual SST spanning the LIG. Using Monte Carlo and Bayesian techniques to propagate uncertainties in age-model and proxy-based SST reconstructions, our results quantify the spatial timing, amplitude, and uncertainty in global and regional SST change during the LIG. Our conclusions suggest that the LIG surface ocean was indistinguishable from the average surface ocean temperatures observed for the last two decades (1995-2014). This may ultimately imply that the Earth is currently committed to ≥6-9m of equilibrium sea-level rise. Although the LIG is not an analogue for present and future climate change due to the large differences in seasonal orbital insolation and absence of anthropogenic greenhouse gas radiative forcing, it provides an opportunity to test the ability of global climate models to simulate the mechanisms and climate feedbacks responsible for the warmer climate and higher global mean sea level during the LIG. However, when forced only by LIG greenhouse gas concentrations and insolation changes, climate models suggest that the annual mean temperature response was not significantly different from preindustrial control simulations. We present the first multi-model and multiscenario ensemble of transient and equilibrium global climate modeling results spanning the LIG. We show, using a novel model-data comparison framework, that these scenario-specific model results exhibit regionally independent agreement with ocean basin-specific proxy-based SST stacks. This result ultimately implies structural uncertainties and/or misrepresentations of climate feedbacks in the existing suite of climate model simulations, or underestimations of additional proxy-based SST uncertainties. Our conclusions suggest a new target LIG time period for future model-data comparisons and highlight the need for higher resolution transient climate modeling of the LIG and its dependence on meltwater input to the high latitude oceans during the preceding deglaciation. Few discoveries have stimulated the paleoclimate community more so than Heinrich events. Nevertheless, the cause of Heinrich events, characterized by a large flux of icebergs sourced from the Hudson Strait Ice Stream into the North Atlantic, remains debated. Commonly attributed to internal ice-sheet instability, the occurrence of Heinrich events during the coldest intervals of the last glacial cycle instead suggests an external climate control. We expand on recent studies that have shown that incursions of warm subsurface waters into the intermediate depth North Atlantic Ocean destabilized an ice shelf fronting the Hudson Strait Ice Stream, causing a Heinrich event. We present new surface- and bottom-water stable isotope, trace metal, and sedimentary records from two cores taken along the Labrador margin that further support subsurface warming as a trigger of Hudson Strait Heinrich events. We further relate these changes to other sediment core records from the North Atlantic and transient deglacial climate modeling results to show that subsurface warming was ubiquitous across the intermediate North Atlantic during the early part of the last deglaciation and was most likely caused by a preceding reduction in the Atlantic Meridional Overturning Circulation. Close

• 78. [Article] Abundance, Life History, and Distribution of Bull Trout in the Hood River Basin: A Summary of Findings from 2006 to 2009 Information Reports number 2010-01

  Abstract -- Bull trout have been adversely affected by many land, water, and fisheries management activities throughout the range of the species. Degraded and fragmented habitat and negative interactions with ...

  Citation × Citation Citation Abstract Copy Title: Abundance, Life History, and Distribution of Bull Trout in the Hood River Basin: A Summary of Findings from 2006 to 2009 Information Reports number 2010-01 Abstract -- Bull trout have been adversely affected by many land, water, and fisheries management activities throughout the range of the species. Degraded and fragmented habitat and negative interactions with nonnative fishes have led to a decline in bull trout distribution and abundance, several local extirpations, and a federal listing in 1998 as a threatened species under the Endangered Species Act (USFWS 2002). Distribution and abundance of bull trout also have declined in Oregon, and most management units in the state are considered to be threatened by conservation risks (ODFW 2005). One of these at-risk management units exists in the Hood River basin (ODFW 2005). Bull trout in Hood River basin currently are thought to exist as two independent reproductive units (USFWS 2002), known as local populations (Rieman and McIntyre 1995). The Clear Branch local population was isolated from the rest of the basin by the construction of Clear Branch Dam in 1968. This dam provides limited downstream fish passage during periods of spill and no voluntary upstream passage. Bull trout in this population inhabit Laurance Lake reservoir and the tributaries Pinnacle Creek and upper Clear Branch, which flow into the reservoir. The Hood River local population is distributed in the mainstem Hood River, Middle Fork Hood River (Middle Fork), and a few Middle Fork tributaries. Fluvial migrants from Hood River basin also forage and winter in the Columbia River (Pribyl et al. 1996, Buchanan et al. 1997). Bull trout have been observed in the East and West Fork basins of the Hood River, but these sightings have been rare. Presently, there is little evidence to suggest local populations exist in these tributary basins (USFWS 2002, Reagan and Olsen 2008). The status of both local populations is extremely precarious. Threats that put the Clear Branch population at risk of extirpation include low abundance, negative interactions with illegally introduced smallmouth bass, isolation from upstream migration and immigration, and diminished spawning and rearing habitat (USFW 1998). The Hood River population also appears to be small and is affected by passage barriers, unscreened irrigation diversions, impaired water quality, and periodic debris flows during glacial outbursts (USFWS 1998). As mandated by their federally designated threatened status, recovery plans were drafted by the US Fish and Wildlife Service (USFWS) for each distinct population segment, including for Hood River bull trout in 2002. This draft plan listed four goals for recovery in this basin: 1) establish at least one more local population in addition to the two existing populations, 2) increase the estimated adult population in the basin to at least 500 individuals, 3) achieve a stable or increasing trend at the population recovery level for at least two generations (=10 years), and 4) improve habitat connectivity by addressing problems with passage and screening at diversions and seasonal water quality barriers (USFWS 2002). The recovery plan also sets out research and monitoring needs critical to the recovery of these populations. Needed are accurate adult abundance estimates; a standardized monitoring program; more life history information for each local population, including how Hood River bull trout use of the Columbia River and the effects of potential passage obstructions on movement; and more information on the threat posed to the Clear Branch population by the illegal introduction of smallmouth bass in Lake Laurance reservoir. The Oregon Department of Fish and Wildlife (ODFW), with the help of the USDA Forest Service (USFS), initiated a four-year study in 2006 seeking to address these needs by synthesizing available data and conducting further studies to improve our understanding of the abundance, life history, and potential limiting factors of bull trout in the Hood River recovery unit. This report describes our findings, summarizes previous studies in the context of new information, and recommends a standardized monitoring protocol and future research. Our specific study objectives were as follows: 1. Assess adult abundance of the Clear Branch local population and develop a monitoring protocol to track abundance trends that is statistically reliable, cost-effective, and that minimizes potential adverse effects on this small isolated population. 2. Describe the juvenile and adult life history patterns of the Clear Branch local population. 3. Assess the potential impact of smallmouth bass on bull trout in Laurance Lake reservoir. 4. Determine current distribution of bull trout reproduction and early rearing in potential bull trout streams in the Hood River basin. 5. Describe the migratory life history of Hood River bull trout and assess the potential impacts of Coe Diversion and two new falls on the Middle Fork Hood River (scoured by the November 2006 glacial outburst) on bull trout migrations. Title: Abundance, Life History, and Distribution of Bull Trout in the Hood River Basin: A Summary of Findings from 2006 to 2009 Information Reports number 2010-01 Abstract -- Bull trout have been adversely affected by many land, water, and fisheries management activities throughout the range of the species. Degraded and fragmented habitat and negative interactions with nonnative fishes have led to a decline in bull trout distribution and abundance, several local extirpations, and a federal listing in 1998 as a threatened species under the Endangered Species Act (USFWS 2002). Distribution and abundance of bull trout also have declined in Oregon, and most management units in the state are considered to be threatened by conservation risks (ODFW 2005). One of these at-risk management units exists in the Hood River basin (ODFW 2005). Bull trout in Hood River basin currently are thought to exist as two independent reproductive units (USFWS 2002), known as local populations (Rieman and McIntyre 1995). The Clear Branch local population was isolated from the rest of the basin by the construction of Clear Branch Dam in 1968. This dam provides limited downstream fish passage during periods of spill and no voluntary upstream passage. Bull trout in this population inhabit Laurance Lake reservoir and the tributaries Pinnacle Creek and upper Clear Branch, which flow into the reservoir. The Hood River local population is distributed in the mainstem Hood River, Middle Fork Hood River (Middle Fork), and a few Middle Fork tributaries. Fluvial migrants from Hood River basin also forage and winter in the Columbia River (Pribyl et al. 1996, Buchanan et al. 1997). Bull trout have been observed in the East and West Fork basins of the Hood River, but these sightings have been rare. Presently, there is little evidence to suggest local populations exist in these tributary basins (USFWS 2002, Reagan and Olsen 2008). The status of both local populations is extremely precarious. Threats that put the Clear Branch population at risk of extirpation include low abundance, negative interactions with illegally introduced smallmouth bass, isolation from upstream migration and immigration, and diminished spawning and rearing habitat (USFW 1998). The Hood River population also appears to be small and is affected by passage barriers, unscreened irrigation diversions, impaired water quality, and periodic debris flows during glacial outbursts (USFWS 1998). As mandated by their federally designated threatened status, recovery plans were drafted by the US Fish and Wildlife Service (USFWS) for each distinct population segment, including for Hood River bull trout in 2002. This draft plan listed four goals for recovery in this basin: 1) establish at least one more local population in addition to the two existing populations, 2) increase the estimated adult population in the basin to at least 500 individuals, 3) achieve a stable or increasing trend at the population recovery level for at least two generations (=10 years), and 4) improve habitat connectivity by addressing problems with passage and screening at diversions and seasonal water quality barriers (USFWS 2002). The recovery plan also sets out research and monitoring needs critical to the recovery of these populations. Needed are accurate adult abundance estimates; a standardized monitoring program; more life history information for each local population, including how Hood River bull trout use of the Columbia River and the effects of potential passage obstructions on movement; and more information on the threat posed to the Clear Branch population by the illegal introduction of smallmouth bass in Lake Laurance reservoir. The Oregon Department of Fish and Wildlife (ODFW), with the help of the USDA Forest Service (USFS), initiated a four-year study in 2006 seeking to address these needs by synthesizing available data and conducting further studies to improve our understanding of the abundance, life history, and potential limiting factors of bull trout in the Hood River recovery unit. This report describes our findings, summarizes previous studies in the context of new information, and recommends a standardized monitoring protocol and future research. Our specific study objectives were as follows: 1. Assess adult abundance of the Clear Branch local population and develop a monitoring protocol to track abundance trends that is statistically reliable, cost-effective, and that minimizes potential adverse effects on this small isolated population. 2. Describe the juvenile and adult life history patterns of the Clear Branch local population. 3. Assess the potential impact of smallmouth bass on bull trout in Laurance Lake reservoir. 4. Determine current distribution of bull trout reproduction and early rearing in potential bull trout streams in the Hood River basin. 5. Describe the migratory life history of Hood River bull trout and assess the potential impacts of Coe Diversion and two new falls on the Middle Fork Hood River (scoured by the November 2006 glacial outburst) on bull trout migrations. Close

• 79. [Article] Present-day and future contributions of glacier melt to the Upper Middle Fork Hood River : implications for water management

  Glaciers are effective reservoirs because they moderate variations in runoff and supply reliable flow during drought periods. Thus, there needs to be a clear understanding of the influence of glacier runoff ...

  Citation × Citation Citation Abstract Copy Title: Present-day and future contributions of glacier melt to the Upper Middle Fork Hood River : implications for water management Author: Phillippe, Jeff Glaciers are effective reservoirs because they moderate variations in runoff and supply reliable flow during drought periods. Thus, there needs to be a clear understanding of the influence of glacier runoff at both the basin and catchment scale. The objectives of this study were to quantify the late summer contributions of glacier melt to the Upper Middle Fork Hood River and to simulate potential impacts of climate change on late summer streamflow. The Upper Middle Fork Hood River catchment (50.6 km²) is located on the northeast flanks of Mount Hood Oregon. Discharge measurements and isotope samples were used to calculate glacier meltwater contributions to the entire catchment, which feeds into a major water diversion used for farmland irrigation. Data were collected over the period August 10 - September 7, 2007. This late summer period was selected because there is typically little rain and suspected high glacier melt contributions. Discharge measurements taken at glacier termini, show that just two of the mountains glaciers, Eliot and Coe, contributed 41% of the total surface water in the catchment. The Eliot Glacier contributed 87% of the total flow in the Eliot Creek, while the Coe Glacier supplied 31% of the runoff in Coe Creek. Isotopic analyses, which include the inputs of all other glacier surfaces in the catchment, show a total glacier contribution of 88% from the Eliot Glacier to the Eliot Creek, in excellent agreement with the streamflow measurements. Isotopes also showed an 88% contribution from the Coe Glacier to the Coe Creek, higher than the amount measured from streamflow. This latter discrepancy is likely due to undersampling of streamflow from the Coe Glacier. During the isotope measurement period, overall contributions of both Coe and Eliot Glaciers to the Upper Middle Fork Hood River were 62 - 74% of catchment discharge. A temperature index model was used to simulate projected impacts of glacier recession and warmer temperatures on streamflow. The Snowmelt Runoff Model (SRM) was chosen for this task because it has been shown to effectively model runoff in glacierized catchments where there are limited meteorological records. SRM was calibrated using the 2007 discharge records to quantify August – September glacier runoff in the Upper Middle Fork catchment under a variety of glacier and temperature scenarios. SRM simulations indicate that runoff from the catchment glaciers are highly sensitive to changes in glacial area, glacier debris-cover, and air temperature. Model simulations show that glacier recession has a greater effect on runoff than do projected temperature increases. Thus, even without warmer summer temperatures, glacier contributions to streamflow will decrease as long as the glacier continues to lose mass. Applying both current glacier recession rates and a 2°C temperature forcing, the model predicts a decrease of 31% of late summer glacier runoff by 2059, most of which is lost in August. This study suggests that glaciers currently play a significant hydrological role in the headwater catchments of the Hood River Basin at a time when water is needed most, and that these contributions are projected to diminish over time. Title: Present-day and future contributions of glacier melt to the Upper Middle Fork Hood River : implications for water management Author: Phillippe, Jeff Glaciers are effective reservoirs because they moderate variations in runoff and supply reliable flow during drought periods. Thus, there needs to be a clear understanding of the influence of glacier runoff at both the basin and catchment scale. The objectives of this study were to quantify the late summer contributions of glacier melt to the Upper Middle Fork Hood River and to simulate potential impacts of climate change on late summer streamflow. The Upper Middle Fork Hood River catchment (50.6 km²) is located on the northeast flanks of Mount Hood Oregon. Discharge measurements and isotope samples were used to calculate glacier meltwater contributions to the entire catchment, which feeds into a major water diversion used for farmland irrigation. Data were collected over the period August 10 - September 7, 2007. This late summer period was selected because there is typically little rain and suspected high glacier melt contributions. Discharge measurements taken at glacier termini, show that just two of the mountains glaciers, Eliot and Coe, contributed 41% of the total surface water in the catchment. The Eliot Glacier contributed 87% of the total flow in the Eliot Creek, while the Coe Glacier supplied 31% of the runoff in Coe Creek. Isotopic analyses, which include the inputs of all other glacier surfaces in the catchment, show a total glacier contribution of 88% from the Eliot Glacier to the Eliot Creek, in excellent agreement with the streamflow measurements. Isotopes also showed an 88% contribution from the Coe Glacier to the Coe Creek, higher than the amount measured from streamflow. This latter discrepancy is likely due to undersampling of streamflow from the Coe Glacier. During the isotope measurement period, overall contributions of both Coe and Eliot Glaciers to the Upper Middle Fork Hood River were 62 - 74% of catchment discharge. A temperature index model was used to simulate projected impacts of glacier recession and warmer temperatures on streamflow. The Snowmelt Runoff Model (SRM) was chosen for this task because it has been shown to effectively model runoff in glacierized catchments where there are limited meteorological records. SRM was calibrated using the 2007 discharge records to quantify August – September glacier runoff in the Upper Middle Fork catchment under a variety of glacier and temperature scenarios. SRM simulations indicate that runoff from the catchment glaciers are highly sensitive to changes in glacial area, glacier debris-cover, and air temperature. Model simulations show that glacier recession has a greater effect on runoff than do projected temperature increases. Thus, even without warmer summer temperatures, glacier contributions to streamflow will decrease as long as the glacier continues to lose mass. Applying both current glacier recession rates and a 2°C temperature forcing, the model predicts a decrease of 31% of late summer glacier runoff by 2059, most of which is lost in August. This study suggests that glaciers currently play a significant hydrological role in the headwater catchments of the Hood River Basin at a time when water is needed most, and that these contributions are projected to diminish over time. Close

• 80. [Article] Hood River Bull Trout Abundance, Life History, and Habitat Connectivity, 2007 Progress Reports 2007

  Abstract -- Hood River bull trout are thought to exist as two independent reproductive units (USFWS 2004), known as local populations (Rieman and McIntyre 1995). The Clear Branch local population is isolated ...

  Citation × Citation Citation Abstract Copy Title: Hood River Bull Trout Abundance, Life History, and Habitat Connectivity, 2007 Progress Reports 2007 Abstract -- Hood River bull trout are thought to exist as two independent reproductive units (USFWS 2004), known as local populations (Rieman and McIntyre 1995). The Clear Branch local population is isolated above Clear Branch Dam, which provides limited downstream fish passage during infrequent and sporadic periods of spill and no upstream passage. Bull trout in this population inhabit Laurance Lake Reservoir and tributaries upstream of Clear Branch Dam. The Hood River local population occurs in the mainstem Hood River and Middle Fork Hood River downstream of the Clear Branch Dam and a small number of adult bull trout migrate each year into the Hood River from the Columbia River (Figure 1). The status of both populations is extremely precarious. The Clear Branch population is at risk of a random extinction event due to low numbers, negative interactions with non-native smallmouth bass, isolation and limited spawning habitat (USFWS, 1998). The Hood River population also appears to be small and is threatened by passage barriers, unscreened irrigation systems, impaired water quality and periodic siltation of spawning substrate by glacial outbursts. Clear Branch bull trout spawn in Clear Branch and Pinnacle Creek. After rearing in these two natal streams for an unknown time period, most are believed to migrate downstream to Laurance Lake Reservoir. Clear Branch bull trout have been documented passing over the dam spillway during high water events (Pribyl et al. 1996) and may provide a recruitment source for the Hood River local population. Adult bull trout tagged at Powerdale Dam have been observed at Coe Branch irrigation diversion and in a trap at the base of Clear Branch dam. These fish may have been attempting to reach spawning areas located upstream of the dam. However, the success of bull trout migrating downstream via the spillway or the possibility of successfully navigating through the diversion network has never been determined. Depending on the water year, the Middle Fork Irrigation District (MFID) may not spill at all, or the timing of the spill may not coincide with the timing of downstream migration, which is currently unknown (East Fork Hood River and Middle Fork Hood River Watershed analysis). Smallmouth bass were discovered in Lake Laurance Reservoir in the 1990s. Creel surveys have shown that large adult bass are caught occasionally in the reservoir and schools of bass fry have been seen by district fish biologist (Rod French, ODFW, personal communication), suggesting that they are spawning successfully. This illegal introduction poses a potential threat to the Clear Branch bull trout population, but its magnitude is unknown because the bass population size and degree of interaction between the two species are unknown. Bull trout and smallmouth bass have significantly different temperature preferences and tolerances, with bull trout being one of the most sensitive coldwater species and bass being a warm water species. Lake Laurance, a relatively high-altitude reservoir at 890 m (2,920 feet), does not provide ideal bass habitat so these two species may have largely non-overlapping distributions or differing activity periods (Terry Shrader, ODFW warmwater fish biologist, personal communication). However, based on past reservoir temperature data (Berger et al. 2005), there are periods in the reservoir when there is potential for bull trout and bass interaction: periods when bull trout are susceptible to bass predation and when juvenile fish might compete for resources. Spawning activity of the Hood River local population has been observed in a few locations within the Middle Fork of Hood River (Figure 1). Although consistent and extensive spawning areas for this population are not known, some of the locations where juvenile rearing or potential bull trout redds have been observed include the Middle Fork Hood River and some of its tributaries: Bear Creek, Compass Creek and Coe Branch (USFWS 2004). However, Coe Branch, Compass Creek, and the Middle Fork are glacial streams with a high volume of sand and silt which may compromise spawning success. No bull trout spawning or rearing has been observed on the East and West Forks of Hood River. The Middle Fork and mainstem Hood River provide foraging, migration and overwintering habitat. Hood River bull trout are also known to migrate into the Columbia River. Two bull trout tagged at Powerdale Dam (RK 7.2 of mainstem Hood River) were recovered near Drano Lake in Washington State; and one was captured 11 kilometers downstream of the confluence of the Hood and Columbia Rivers (USFWS 2004). Every year (usually between May and July), adult bull trout, presumably migrating upstream from the Columbia River, are captured and anchor tagged at Powerdale Dam. Although some of these tagged fish have been observed upstream (one in Coe Branch and three below Clear Branch dam), the spawning destination of fluvial adults within the Hood River basin is largely unknown. Dispersing juvenile bull trout and migrating adults in this local population are threatened by flow diversions with inadequate screening and passage facilities. Several structures are suspected to impede upstream migration or entrain juvenile and adult bull trout into irrigation works (Pribyl et al. 1996, HRWG 1999). These structures include: the diversion at Clear Branch Dam (passage and screening), Coe Branch (passage and screening), and the Farmers Irrigation District diversion (screening) on the mainstem Hood River (HRWG 1999). However, little research has been conducted to assess the impacts of these structures on migrating bull trout. Beyond a general knowledge of the distribution of Hood River bull trout and the nature of anthropogenic factors that potentially restrict their life history and habitat connectivity, little is known about this recovery unit. Baseline information about adult abundance is lacking for both local populations, the potential of a source (Clear Branch) and sink (Hood River) relationship between the two local populations has not been explored, and the migratory life history of adult fish caught at Powerdale Dam is unknown. The degree to which irrigation and hydropower diversions hamper connectivity within the Hood River basin is also poorly understood. Migratory life histories have been viewed as key to species persistence (Rieman and McIntyre 1995; Dunham and Rieman 1999), and understanding movement patterns and associated habitat requirements are critical to maintaining those migratory forms (Muhlfeld and Morotz 2005; Hostettler 2005). Gaining this information is also critical to evaluating bull trout recovery in the Hood River Subbasin (Coccoli 2004). The Oregon Department of Fish and Wildlife (ODFW) initiated a study in 2006 to improve our understanding of the abundance, life history, and potential limiting factors of the bull trout in this recovery unit. This report describes findings for the first two years of the study (2006-2007). Specific study objectives for the first two years were: 1. Determine the migratory life history of Hood River bull trout and assess the potential impacts of flow diversions and two new falls on the Middle Fork Hood River (scoured by the November 2006 glacial outburst) on bull trout migrations. 2. Determine current distribution of bull trout reproduction and early rearing in historical and potential bull trout streams in the Hood River Subbasin. 3. Determine the juvenile and adult life history the Clear Branch local population and develop a statistically reliable and cost-effective protocol for monitoring the abundance of adult Clear Branch bull trout. 4. Assess the potential impact of smallmouth bass on bull trout in Laurance Lake Reservoir. Title: Hood River Bull Trout Abundance, Life History, and Habitat Connectivity, 2007 Progress Reports 2007 Abstract -- Hood River bull trout are thought to exist as two independent reproductive units (USFWS 2004), known as local populations (Rieman and McIntyre 1995). The Clear Branch local population is isolated above Clear Branch Dam, which provides limited downstream fish passage during infrequent and sporadic periods of spill and no upstream passage. Bull trout in this population inhabit Laurance Lake Reservoir and tributaries upstream of Clear Branch Dam. The Hood River local population occurs in the mainstem Hood River and Middle Fork Hood River downstream of the Clear Branch Dam and a small number of adult bull trout migrate each year into the Hood River from the Columbia River (Figure 1). The status of both populations is extremely precarious. The Clear Branch population is at risk of a random extinction event due to low numbers, negative interactions with non-native smallmouth bass, isolation and limited spawning habitat (USFWS, 1998). The Hood River population also appears to be small and is threatened by passage barriers, unscreened irrigation systems, impaired water quality and periodic siltation of spawning substrate by glacial outbursts. Clear Branch bull trout spawn in Clear Branch and Pinnacle Creek. After rearing in these two natal streams for an unknown time period, most are believed to migrate downstream to Laurance Lake Reservoir. Clear Branch bull trout have been documented passing over the dam spillway during high water events (Pribyl et al. 1996) and may provide a recruitment source for the Hood River local population. Adult bull trout tagged at Powerdale Dam have been observed at Coe Branch irrigation diversion and in a trap at the base of Clear Branch dam. These fish may have been attempting to reach spawning areas located upstream of the dam. However, the success of bull trout migrating downstream via the spillway or the possibility of successfully navigating through the diversion network has never been determined. Depending on the water year, the Middle Fork Irrigation District (MFID) may not spill at all, or the timing of the spill may not coincide with the timing of downstream migration, which is currently unknown (East Fork Hood River and Middle Fork Hood River Watershed analysis). Smallmouth bass were discovered in Lake Laurance Reservoir in the 1990s. Creel surveys have shown that large adult bass are caught occasionally in the reservoir and schools of bass fry have been seen by district fish biologist (Rod French, ODFW, personal communication), suggesting that they are spawning successfully. This illegal introduction poses a potential threat to the Clear Branch bull trout population, but its magnitude is unknown because the bass population size and degree of interaction between the two species are unknown. Bull trout and smallmouth bass have significantly different temperature preferences and tolerances, with bull trout being one of the most sensitive coldwater species and bass being a warm water species. Lake Laurance, a relatively high-altitude reservoir at 890 m (2,920 feet), does not provide ideal bass habitat so these two species may have largely non-overlapping distributions or differing activity periods (Terry Shrader, ODFW warmwater fish biologist, personal communication). However, based on past reservoir temperature data (Berger et al. 2005), there are periods in the reservoir when there is potential for bull trout and bass interaction: periods when bull trout are susceptible to bass predation and when juvenile fish might compete for resources. Spawning activity of the Hood River local population has been observed in a few locations within the Middle Fork of Hood River (Figure 1). Although consistent and extensive spawning areas for this population are not known, some of the locations where juvenile rearing or potential bull trout redds have been observed include the Middle Fork Hood River and some of its tributaries: Bear Creek, Compass Creek and Coe Branch (USFWS 2004). However, Coe Branch, Compass Creek, and the Middle Fork are glacial streams with a high volume of sand and silt which may compromise spawning success. No bull trout spawning or rearing has been observed on the East and West Forks of Hood River. The Middle Fork and mainstem Hood River provide foraging, migration and overwintering habitat. Hood River bull trout are also known to migrate into the Columbia River. Two bull trout tagged at Powerdale Dam (RK 7.2 of mainstem Hood River) were recovered near Drano Lake in Washington State; and one was captured 11 kilometers downstream of the confluence of the Hood and Columbia Rivers (USFWS 2004). Every year (usually between May and July), adult bull trout, presumably migrating upstream from the Columbia River, are captured and anchor tagged at Powerdale Dam. Although some of these tagged fish have been observed upstream (one in Coe Branch and three below Clear Branch dam), the spawning destination of fluvial adults within the Hood River basin is largely unknown. Dispersing juvenile bull trout and migrating adults in this local population are threatened by flow diversions with inadequate screening and passage facilities. Several structures are suspected to impede upstream migration or entrain juvenile and adult bull trout into irrigation works (Pribyl et al. 1996, HRWG 1999). These structures include: the diversion at Clear Branch Dam (passage and screening), Coe Branch (passage and screening), and the Farmers Irrigation District diversion (screening) on the mainstem Hood River (HRWG 1999). However, little research has been conducted to assess the impacts of these structures on migrating bull trout. Beyond a general knowledge of the distribution of Hood River bull trout and the nature of anthropogenic factors that potentially restrict their life history and habitat connectivity, little is known about this recovery unit. Baseline information about adult abundance is lacking for both local populations, the potential of a source (Clear Branch) and sink (Hood River) relationship between the two local populations has not been explored, and the migratory life history of adult fish caught at Powerdale Dam is unknown. The degree to which irrigation and hydropower diversions hamper connectivity within the Hood River basin is also poorly understood. Migratory life histories have been viewed as key to species persistence (Rieman and McIntyre 1995; Dunham and Rieman 1999), and understanding movement patterns and associated habitat requirements are critical to maintaining those migratory forms (Muhlfeld and Morotz 2005; Hostettler 2005). Gaining this information is also critical to evaluating bull trout recovery in the Hood River Subbasin (Coccoli 2004). The Oregon Department of Fish and Wildlife (ODFW) initiated a study in 2006 to improve our understanding of the abundance, life history, and potential limiting factors of the bull trout in this recovery unit. This report describes findings for the first two years of the study (2006-2007). Specific study objectives for the first two years were: 1. Determine the migratory life history of Hood River bull trout and assess the potential impacts of flow diversions and two new falls on the Middle Fork Hood River (scoured by the November 2006 glacial outburst) on bull trout migrations. 2. Determine current distribution of bull trout reproduction and early rearing in historical and potential bull trout streams in the Hood River Subbasin. 3. Determine the juvenile and adult life history the Clear Branch local population and develop a statistically reliable and cost-effective protocol for monitoring the abundance of adult Clear Branch bull trout. 4. Assess the potential impact of smallmouth bass on bull trout in Laurance Lake Reservoir. Close