Copper River Research Articles

Late Pleistocene marine resources from the Bering Glacier Foreland and human coastal migration in the northern Gulf of Alaska region

AbstractRecent research on the Bering Glacier forelands in the northern Gulf of Alaska provides new insights into late Pleistocene/early Holocene shorelines, providing a favorable route for human migration as early as ~16,000 cal yr BP. This route included an irregular coastline with embayments and islands offering protection from the open ocean; edible marine invertebrates dating from 15,000 to 5,500 cal yr BP; and marine vertebrates dating as early as 16,000 cal yr BP. The latter included walrus (Odobenus rosmarus), bearded seal (Erignathus barbatus), and ringed seal (Phoca cf. hispida), all associated with pack ice conditions unlike those present today. While this ecosystem could have supported humans migrating along the coastline, and coastal refugia may have existed elsewhere in the region, coastal archaeological sites in the northern Gulf of Alaska and southwest Alaska are no older than ~9,500 cal yr BP. This suggests that the earliest sites have been eroded or destroyed, that the earliest migrants ignored available marine resources, and/or that these migrants did not use a coastal route. In contrast, the earliest archaeological sites in southeast Alaska date to ~12,500 cal yr BP, suggesting migration from interior Alaska to the coast somewhere east of the Copper River delta.

Colony Connectivity and the Rapid Growth of a Caspian Tern (Hydroprogne caspia) Colony on Alaska's Copper River Delta, USA

North America's northernmost, sizable colony of Caspian Terns (Hydroprogne caspia) is located on the Copper River Delta of south-central Alaska, USA. The colony was monitored in June during 2008-2016 and in July during 2009-2013. This 9-year period coincided with reduction of Caspian Tern nesting habitat at East Sand Island in the Columbia River estuary, Oregon, USA, one of the world's largest Caspian Tern breeding colonies. The number of active nests on the Copper River Delta more than doubled during the early study period from 209 in 2008 to 423 in 2013. However, there was a steady decline in the number of nests during 2014 (281) to 2015 (115) and the colony failed in 2016. These declines were likely due to warm sea surface temperature anomalies across the northeastern Pacific Ocean in those years. Based on resightings of banded individuals, colony connectivity was documented between the Copper River Delta and other colonies, ranging from southeast Alaska (215 km) to central California, USA (> 3,000 km). The East Sand Island colony was the most important source of immigrants to the Copper River Delta. While the Copper River Delta now serves as important natural breeding habitat for Caspian Terns, increased flooding and severe storms associated with climate change will likely limit colony size and productivity in the long-term.

Contrasting Winter Moose Nutritional Carrying Capacity Models on a Dynamic Landscape

AbstractMany models used to estimate nutritional carrying capacity (NCC) for ungulates differ structurally, but the implications of those differences are frequently unclear. We present a comparative analysis of NCC estimates for a large herbivore in a dynamic landscape, using models that differ in structure and scope. We compared three model structures across three estimates of winter ranges under three winter-severity scenarios for an isolated, introduced moose Alces alces population on the Copper River Delta of south-central Alaska. Model estimates of NCC ranged from 205 to 4,592 moose, demonstrating the critical influences of model structure and assumptions when applying NCC. Furthermore, population estimates during recent severe winters suggest that past models underestimated NCC on the Copper River Delta. We conducted a sensitivity analysis of a preferred model and determined that model components with the highest and lowest sensitivity were snow depth and lignin- and tannin-caused reductions in forage nutritional quality, respectively. Our low sensitivity values for lignin and tannin influences on NCC contrast with results in other NCC estimates. Overall, our results reinforce the need for, and will hopefully assist, adaptive management in response to landscape, population, behavioral, and climatic changes on the Copper River Delta, and demonstrate the importance of understanding model assumptions and structure in application of NCC estimates in the management of large herbivores in variable ecosystems.

Assessment of the high-resolution paleoseismicity record from sediment gravity flows in Prince William Sound, Alaska

Located along the Aleutian Megathrust Boundary, South-Central Alaska is one of the most seismically active areas in the world. Central to this region, Prince William Sound is a glacially carved basin that receives abundant sediment from multiple sources. Primary inputs include the Columbia Glacier and the Copper River, which have diagnostic signatures of Sr/Pb, Cu/Pb, K/Ca, Rb/Sr, and Rb/Ca. As a result, earthquake induced sediment gravity flows originating from different locations deposit event layers that have distinct provenance signatures. A previous study (Kuehl et al., 2017) identified five such event layers preserved in two cores from the southern part of the deep central channel of Prince William Sound that were attributed to large historical earthquakes. To better understand the spatial continuity of these event layers along the entire length of the central channel, seven new gravity cores were collected in a north-south transect. Sedimentation rates were determined by 210Pb, 137Cs, and 239,240Pu geochronology, and cores were assessed for variations in elemental content, grain size patterns, bulk organic and stable isotopic signatures (C/N, δ13C, δ15N). Based on a spatial analysis of these cores, local earthquakes of Mw < 7.0 deposit event layers in the central channel with signatures reflecting the epicenter location, and those of Mw > 7.0 (including an event layer from the 1964 great Alaskan earthquake) have mixed signatures resulting from the widespread generation of numerous flows throughout Prince William Sound. Complete gravity flow records are captured within deep ponded sediment basins and the area spanning the southern end of the central channel. Considering the thick (>100 m) late-Holocene sequence, the approach utilized in this study has the potential to provide a rich record of earthquake recurrence intervals to 4 ka.

Seasonal variability of 7Be in suspended sediments from the Copper River, Alaska: implications for quantifying recent flood deposits in coastal environments

Over the past three decades, particle-reactive cosmogenic 7Be (t1/2 = 53.3 d) has frequently been used to quantify recent fluvial sediment inputs to estuaries and coastal marine environments, providing an important tool to understand the timing and pathways of sediment dispersal. This study utilizes a 2-year high-resolution time series collected from the Copper River, Alaska, to examine the seasonal fluctuation in 7Be activity of suspended sediments near the river mouth. We show that there is considerable variability (particulate 7Be = ≤ 3.3–47 Bq kg−1) throughout the hydrograph, with a significant negative correlation to discharge and suspended sediment concentration. This variability is interpreted to be driven by a combination of fluctuations in atmospheric deposition, water aging, and dilution by 7Be-depleted sediments, reflecting erosion within the streambed/watershed and/or differing freshwater/sediment source. Particularly within this high-latitude setting, seasonal differences in provenance (snowpack/glacial melting vs. rainfall) likely influence 7Be activities. Importantly, 7Be was below detectable limits in river suspended sediments during peak discharge periods in both years, indicating that the flood signal in adjacent coastal environments will be negligible at this time. These results suggest that 7Be will not be an effective tracer of fluvial sediment deposition in some coastal environments.

A Physically Based Daily Simulation of the Glacier‐Dominated Hydrology of the Copper River Basin, Alaska

AbstractThe large, highly glacierized Copper River basin is an important water resource for the south‐central region of Alaska. Thus, information is needed on the reaction of its hydrologic timing and streamflow volumes to historical changes in climate, in order to assess the possible impact of future changes. However, the basin is remote, and therefore, it has proved difficult to collect field data in a frequent temporal and spatial manner. An extension of the distributed‐parameter, physical‐process code Precipitation Runoff Modeling System, PRMSglacier, has been specifically developed to simulate daily hydrology without requiring extensive input data. In this study, PRMSglacier was used to characterize the hydrology of the Copper River basin from 1959 to 2015. The basin was split into subbasins for specific regional climatic calibrations and finer resolution characterization. The model was calibrated and performed well against data of glacier mass balance, glacier area change, snow cover, gaged streamflow, evapotranspiration, and solar radiation. Ice melt contributed 26% of the total basin streamflow, with differences temporally from climate oscillations. Furthermore, differences were seen geographically in subbasins depending on the state of the glaciers in each subbasin. Decreasing trends in ice melt volume were mostly seen on smaller steeper glaciers responding to a critical level of glacier recession, while increasing trends in ice melt volume were mostly seen on larger valley glaciers responding to increasing temperature. The areas with substantially decreasing ice melt had decreasing streamflow, possibly indicating health concerns for the ecosystems therein.

Correction: Evaluating signals of oil spill impacts, climate, and species interactions in Pacific herring and Pacific salmon populations in Prince William Sound and Copper River, Alaska.

[This corrects the article DOI: 10.1371/journal.pone.0172898.].

Enhancement of a Parsimonious Water Balance Model to Simulate Surface Hydrology in a Glacierized Watershed

AbstractThe U.S. Geological Survey monthly water balance model (MWBM) was enhanced with the capability to simulate glaciers in order to make it more suitable for simulating cold region hydrology. The new model, MWBMglacier, is demonstrated in the heavily glacierized and ecologically important Copper River watershed in Southcentral Alaska. Simulated water budget components compared well to satellite‐based observations and ground measurements of streamflow, evapotranspiration, snow extent, and total water storage, with differences ranging from 0.2% to 7% of the precipitation flux. Nash Sutcliffe efficiency for simulated and observed streamflow was greater than 0.8 for six of eight stream gages. Snow extent matched satellite‐based observations with Nash Sutcliffe efficiency values of greater than 0.89 in the four Copper River ecoregions represented. During the simulation period 1949 to 2009, glacier ice melt contributed 25% of total runoff, ranging from 12% to 45% in different tributaries, and glacierized area was reduced by 6%. Statistically significant (p &lt; 0.05) decreasing and increasing trends in annual glacier mass balance occurred during the multidecade cool and warm phases of the Pacific Decadal Oscillation, respectively, reinforcing the link between climate perturbations and glacier mass balance change. The simulations of glaciers and total runoff for a large, remote region of Alaska provide useful data to evaluate hydrologic, cryospheric, ecologic, and climatic trends. MWBM glacier is a valuable tool to understand when, and to what extent, streamflow may increase or decrease as glaciers respond to a changing climate.

Hydrologic Regime Changes in a High-Latitude Glacierized Watershed under Future Climate Conditions

A calibrated conceptual glacio-hydrological monthly water balance model (MWBMglacier) was used to evaluate future changes in water partitioning in a high-latitude glacierized watershed in Southcentral Alaska under future climate conditions. The MWBMglacier was previously calibrated and evaluated against streamflow measurements, literature values of glacier mass balance change, and satellite-based observations of snow covered area, evapotranspiration, and total water storage. Output from five global climate models representing two future climate scenarios (RCP 4.5 and RCP 8.5) was used with the previously calibrated parameters to drive the MWBMglacier at 2 km spatial resolution. Relative to the historical period 1949–2009, precipitation will increase and air temperature in the mountains will be above freezing for an additional two months per year by mid-century which significantly impacts snow/rain partitioning and the generation of meltwater from snow and glaciers. Analysis of the period 1949–2099 reveals that numerous hydrologic regime shifts already occurred or are projected to occur in the study area including glacier accumulation area, snow covered area, and forest vulnerability. By the end of the century, Copper River discharge is projected to increase by 48%, driven by 21% more precipitation and 53% more glacial melt water (RCP 8.5) relative to the historical period (1949–2009).

Phenology of hatching, emergence, and end-of-season body size in young-of-year coho salmon in thermally contrasting streams draining the Copper River Delta, Alaska

Phenology can be linked to individual fitness, particularly in strongly seasonal environments where the timing of events has important consequences for growth, condition, and survival. We studied the phenology of coho salmon (Oncorhynchus kisutch) hatching and emergence in streams with contrasting thermal variability but in close geographic proximity. Following emergence, we tracked body sizes of cohorts of young-of-year fish until the end of the growing season. Hatch and emergence occurred at the same time among streams with marked variability in thermal regimes. We demonstrate that this can be explained in part by the thermal units accumulated during embryo development. At the end of the first growing season, there were some differences in body size, but overall fish size was similar among streams despite strong differences in thermal regimes. Collectively, these results provide novel insights into the interactions between environmental variability and the early life-history stages of coho salmon, furthering our understanding of the consequences of phenology on growth and survival for individuals within the critical first summer of life.

Seasonal and spatial variabilities in northern Gulf of Alaska surface water iron concentrations driven by shelf sediment resuspension, glacial meltwater, a Yakutat eddy, and dust

AbstractPhytoplankton growth in the Gulf of Alaska (GoA) is limited by iron (Fe), yet Fe sources are poorly constrained. We examine the temporal and spatial distributions of Fe, and its sources in the GoA, based on data from three cruises carried out in 2010 from the Copper River (AK) mouth to beyond the shelf break. April data are the first to describe late winter Fe behavior before surface water nitrate depletion began. Sediment resuspension during winter and spring storms generated high “total dissolvable Fe” (TDFe) concentrations of ~1000 nmol kg−1 along the entire continental shelf, which decreased beyond the shelf break. In July, high TDFe concentrations were similar on the shelf, but more spatially variable, and driven by low‐salinity glacial meltwater. Conversely, dissolved Fe (DFe) concentrations in surface waters were far lower and more seasonally consistent, ranging from ~4 nmol kg−1 in nearshore waters to ~0.6–1.5 nmol kg−1 seaward of the shelf break during April and July, despite dramatic depletion of nitrate over that period. The reasonably constant DFe concentrations are likely maintained during the year across the shelf by complexation by strong organic ligands, coupled with ample supply of labile particulate Fe. The April DFe data can be simulated using a simple numerical model that assumes a DFe flux from shelf sediments, horizontal transport by eddy diffusion, and removal by scavenging. Given how global change is altering many processes impacting the Fe cycle, additional studies are needed to examine controls on DFe in the Gulf of Alaska.

Recent paleoseismicity record in Prince William Sound, Alaska, USA

Sedimentological and geochemical investigation of sediment cores collected in the deep (>400 m) central basin of Prince William Sound, along with geochemical fingerprinting of sediment source areas, are used to identify earthquake-generated sediment gravity flows. Prince William Sound receives sediment from two distinct sources: from offshore (primarily Copper River) through Hinchinbrook Inlet, and from sources within the Sound (primarily Columbia Glacier). These sources are found to have diagnostic elemental ratios indicative of provenance; Copper River Basin sediments were significantly higher in Sr/Pb and Cu/Pb, whereas Prince William Sound sediments were significantly higher in K/Ca and Rb/Sr. Within the past century, sediment gravity flows deposited within the deep central channel of Prince William Sound have robust geochemical (provenance) signatures that can be correlated with known moderate to large earthquakes in the region. Given the thick Holocene sequence in the Sound (~200 m) and correspondingly high sedimentation rates (>1 cm year−1), this relationship suggests that sediments within the central basin of Prince William Sound may contain an extraordinary high-resolution record of paleoseismicity in the region.

Evaluating signals of oil spill impacts, climate, and species interactions in Pacific herring and Pacific salmon populations in Prince William Sound and Copper River, Alaska.

The Exxon Valdez oil spill occurred in March 1989 in Prince William Sound, Alaska, and was one of the worst environmental disasters on record in the United States. Despite long-term data collection over the nearly three decades since the spill, tremendous uncertainty remains as to how significantly the spill affected fishery resources. Pacific herring (Clupea pallasii) and some wild Pacific salmon populations (Oncorhynchus spp.) in Prince William Sound declined in the early 1990s, and have not returned to the population sizes observed in the 1980s. Discerning if, or how much of, this decline resulted from the oil spill has been difficult because a number of other physical and ecological drivers are confounded temporally with the spill; some of these drivers include environmental variability or changing climate regimes, increased production of hatchery salmon in the region, and increases in populations of potential predators. Using data pre- and post-spill, we applied time-series methods to evaluate support for whether and how herring and salmon productivity has been affected by each of five drivers: (1) density dependence, (2) the EVOS event, (3) changing environmental conditions, (4) interspecific competition on juvenile fish, and (5) predation and competition from adult fish or, in the case of herring, humpback whales. Our results showed support for intraspecific density-dependent effects in herring, sockeye, and Chinook salmon, with little overall support for an oil spill effect. Of the salmon species, the largest driver was the negative impact of adult pink salmon returns on sockeye salmon productivity. Herring productivity was most strongly affected by changing environmental conditions; specifically, freshwater discharge into the Gulf of Alaska was linked to a series of recruitment failures—before, during, and after EVOS. These results highlight the need to better understand long terms impacts of pink salmon on food webs, as well as the interactions between nearshore species and freshwater inputs, particularly as they relate to climate change and increasing water temperatures.

Spring stopover sites used by the Red Knot Calidris canutus roselaari in Alaska, USA: connectivity between the Copper River Delta and the Yukon-Kuskokwim River Delta

Spring stopover sites used by the Red Knot Calidris canutus roselaari in Alaska, USA: connectivity between the Copper River Delta and the Yukon-Kuskokwim River Delta

Alaska’s Skyboys: Cowboy Pilots and the Myth of the Last Frontier . By Katherine Johnson Ringsmuth.

Alaska’s Skyboys: Cowboy Pilots and the Myth of the Last Frontier . By Katherine Johnson Ringsmuth. (Seattle: University of Washington Press, 2015. xiii + 267 pp. Illustrations, maps, notes, bibliography, index. $34.95.) As the title implies, Katherine Johnson Ringsmuth’s Alaska’s Skyboys grapples with entrenched stereotypes that equate bush pilots with cowboys and other heroes of frontier mythology. Focusing on the history of aviation in eastern Alaska—primarily the Copper River Basin/Wrangell Mountains—she challenges the notion that the history of bush pilots follows the well-worn grooves of Frederick Jackson Turner’s frontier. Instead, she argues that bush pilots were at the leading edge of modern aviation and essential to the incorporation of Alaska into global pathways. Ringsmuth provides a detailed history of flying in eastern Alaska. … dldistefano{at}alaska.edu

Fishermen, markets, and population diversity

Fishing impacts biodiversity on multiple levels, potentially resulting in unintended feedbacks to the economic performance of the fishery over time. For example, targeting observable traits within a population can impact genetic diversity and targeting valuable species can impact biodiversity at the ecosystem level. The bioeconomic literature, however, has given little attention to the effect of fishing on population diversity, even though population diversity contributes to ecosystem services and estimates of population extinction rates are three orders of magnitude higher than species extinction rates. Here we develop a stochastic bioeconomic model that links the harvest of multiple salmon populations in a single commercial fishery to the trajectory of population diversity in a salmon stock complex. We parameterize our model with biological and economic data from the Copper River Chinook salmon fishery. We show that markets can incentivize the degradation of population diversity, reducing infra-marginal fishery rents, and increasing variability in economic returns. We also show that second-best management can conserve population diversity and improve welfare. Furthermore, depending on fishermen׳s time preferences, this management strategy is potentially self-financing.

Cultural Consensus on Salmon Fisheries and Ecology in the Copper River, Alaska

This study assessed levels of agreement in knowledge and opinions about salmon fisheries and ecology of the Copper River, Alaska, in three user groups: the Ahtna, an Alaska Native people indigenous to the upper river; commercial fishers who fish at the mouth of the river; and fishery managers and biologists with jurisdiction over the entire watershed. We anticipated that cultural background, academic training, long-term experience on the water, and spatial focus would be reflected in each group’s knowledge and opinions. Cultural consensus analysis showed agreement within each group, similar opinions between commercial fishers and managers and biologists, and distinct Ahtna opinions. Managers and biologists were the most cohesive group; they related to the entire watershed and relied on quantitative information as the basis for fisheries management. Ahtna focused on the upper river and incorporated observed long-term sociocultural, economic, and environmental changes into their opinions about the fisheries. Commercial fishers focused on the lower river and had strong familiarity with scientific principles of fisheries management. The similar views of commercial fishers and managers and biologists may result from the fact that commercial fishers’ economic success also depends on their understanding of fisheries management. To respond to socioeconomic and ecological sustainability issues, fisheries management would benefit from recognizing these perspectives and promoting participation of all stakeholder groups and effective communication among them.

Directionals, episodic structure, and geographic information systems: Area/punctual distinctions in Ahtna travel narration

Abstract Interest in the past decades in the way spatial cognition manifests in language has led to a growing body of literature on the topic. The concurrent development of user-friendly geographic information systems (GIS) software can give linguists new perspectives on spatial language, especially narratives describing geographic landscapes, by allowing the researcher access to those landscapes in a way that was previously only available by visiting the region in person. In this paper, I discuss how the use of GIS reveals that Ahtna speakers use subtle distinctions in the directional system to structure discourse about overland travel into narrative episodes. Ahtna is an Athabascan language spoken in the Copper River area of southcentral Alaska by about 35 native speakers.

A tribute to George Plafker

In a long and distinguished career, George Plafker made fundamental advances in understanding of megathrust tectonics, tsunami generation, paleoseismology, crustal neotectonics, and Alaskan geology, chiefly by means of geological field observations. George discovered that giant earthquakes result from tens of meters of seismic slip on subduction megathrusts, and he did this before the theory of plate tectonics had become a paradigm. The discovery was founded on George's comprehensive mapping of land-level changes in the aftermath of the 1964 earthquake in Alaska, and on his follow-up mapping, in 1968, in the region of the 1960 earthquakes in Chile. The mapping showed paired, parallel belts of coseismic uplift largely offshore and coseismic subsidence mostly onshore – a pattern now familiar as the initial condition assumed in simulations of subduction-zone tsunamis. George recognized, moreover, that splay faulting can play a major role in tsunami generation, and he also distinguished carefully between tectonic and landslide sources for the multiple tsunamis that accounted for nearly all the fatalities associated with the 1964 Alaska earthquake. George's classic monographs on the 1964 earthquake include findings on subduction-zone paleoseismology that he soon extended to include stratigraphic evidence for cyclic vertical deformation at the Copper River Delta, as well as recurrent uplift evidenced by flights of marine terraces at Middleton Island. As a geologist of earthquakes, George also clarified the tectonics and hazards of crustal faulting in Alaska, California, and other areas worldwide. All the while, George was mapping bedrock geology in Alaska, where he contributed importantly to today's understanding of how terranes were accreted and modified. Especially important was his documentation of the origin, movement, subduction, and collision of the Yakutat terrane in southern Alaska.

Constraints on regional drivers of relative sea-level change around Cordova, Alaska

New records of paleoenvironmental change from two lakes near Cordova, south central Alaska, combined with analysis of previously reported sediment sequences from the adjacent Copper River Delta, provide quantitative constraints on a range of Earth system processes through their expression in relative sea-level change. Basal sediment ages from Upper Whitshed Lake indicate ice-free conditions by at least 14,140–15,040 cal yr BP. While Upper and Lower Whitshed Lakes provide only upper limits to relative sea-level change, interbedded layers of freshwater peat and intertidal silt extending more than 11 m below present sea level in Copper River Delta indicate net submergence over the last 6000 years and multiple earthquake deformation cycles. In contrast, Lower Whitshed Lake, situated just above present high tide level, records only one episode of marine sedimentation, commencing AD 1120–1500, that we interpret as the result of isostatic subsidence due to Little Ice Age mass accumulation of the Chugach Mountain glaciers. Lower Whitshed Lake also records isostatic uplift at the end of the Little Ice Age before the end of marine sedimentation caused by ∼1.5 m coseismic uplift in the great Alaska earthquake of AD 1964. We successfully explain the records of relative sea-level change from both Copper River Delta and the Whitshed Lakes by integrating the effects of eustatic sea-level rise, glacial isostasy, earthquake deformation cycles, sediment loading, sediment compaction and Late Holocene changes in glacier mass into a single model. This approach provides initial quantitative constraints on the individual contributions of these processes. Taking reasonable estimates of eustasy, post-Last Glacial Maximum and Neoglacial glacial isostatic adjustment and a simple earthquake deformation cycle, we demonstrate that sediment loading and sediment compaction are both contributors to relative sea-level rise at Copper River Delta, together producing subsidence averaging approximately 1.2 mm yr−1 over the mid to Late Holocene. Further isolation basin studies have the potential to greatly improve our understanding of the individual contributions of these processes in this highly dynamic region.