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For assessment of the potential of the Beppu Bay sediments as a Global boundary Stratotype Section and Point (GSSP) candidate for the Anthropocene, we have integrated datasets of 99 proxies. The datasets for the sequences date back 100 years for most proxy records and 1300 years for several records. The cumulative number of occurrences of the anthropogenic fingerprint reveal unprecedented increases above the base of the 1953 flood layer at 64.6 cm (1953 CE), which coincides with an initial increase in global fallout of 239Pu+240Pu. The onset of the proliferation of anthropogenic fingerprints was followed by diverse human-associated events, including a rapid increase in percent modern 14C in anchovy scales, changes in nitrogen and carbon cycling as recorded by anchovy δ15N and δ13C, elevated pollution of heavy metals, increased deposition of novel materials (spheroidal carbonaceous particles, microplastics, polychlorinated biphenyls), the occurrence of hypoxia (Re/Mo ratio) and eutrophication (biogenic opal, TOC, TN, diatoms, chlorophyll a), unprecedented microplankton community changes (compositions of carotenoids, diatoms, dinoflagellates), abnormally high spring air temperatures as inferred from diatom fossils, and lithological changes. These lines of evidence indicate that the base of the 1953 layer is the best GSSP level candidate in the stratigraphy at this site.

Little is known about the dynamics of marine food chains spanning primary to higher trophic levels on centennial and longer timescales, especially where the supply of dissolved iron limits primary productivity. To elucidate the long-term dynamics of biological productivity in the Coastal Oyashio (CO), which is a major pathway for transporting dissolved iron into the western North Pacific from winter to spring, we reconstructed the lower trophic level productivity over the last 3000 years in the CO. Our results demonstrate that the concentrations and mass accumulation rates of both Chl-a (chlorophyll a and its derivatives) and biogenic opal used as proxies of primary productivity, and steryl chlorin esters (SCEs) used as that of zooplankton productivity, show a millennial-scale increasing trend and centennial-scale variability beginning ca. AD 400. SCEs were positively correlated with Chl-a, indicating that changes in zooplankton productivity were induced by bottom-up control of primary productivity. The Chl-a and SCEs showed synchronous centennial-scale patterns with a relative abundance of sea-ice-associated diatom species transported by CO, and with a ventilation index in the Okhotsk Sea Intermediate Water. This synchronous pattern indicates that lower trophic-level productivity during the spring bloom responded to the intensity of iron-replete CO.

The stock‐specific distribution of maturing salmon in the North Pacific has been a persistent information gap that has prevented us from determining the ocean conditions experienced by individual stocks. This continues to impede understanding of the role of ocean conditions in stock‐specific population dynamics. We assessed scale archives for 17 sockeye salmon (Oncorhynchus nerka) stocks covering the entire North Pacific, from the Columbia River (Washington State and British Columbia) to Kamchatka Peninsula (Russia), to infer salmon locations during their last growing season before returning to their spawning grounds. The approach used, first pioneered in salmon stocks in the Atlantic, relies on the relationship between temporal changes in δ13C in salmon scales and sea surface temperature to estimate salmon distribution based on correlation strength. An advantage of this approach is that it does not require fish sampling at sea, but relies on existing fishery agency collections of salmon scales. Significant correlations were found for 7 of the stocks allowing us to propose plausible feeding grounds. Complementary information from δ15N, historical tagging studies, and connectivity analysis were used to further refine distribution estimates. This study is a first step toward estimating stock‐specific distributions of salmon in the North Pacific and provides a basis for the application of the approach to other salmon scale archives. This information has the potential to improve our ability to relate stock dynamics to ocean conditions, ultimately enabling improved stock management. For example, our estimated distributions of Bristol Bay and NE Pacific stocks demonstrated that they occupy different areas with a number of the former being distributed in the high productivity shelf waters of the Aleutian Islands and Bering Sea. This may explain why these stocks seem to have responded differently to changes in ocean conditions, and the long‐term trend of increased productivity of Bristol Bay sockeye., Stock‐specific salmon high seas distribution is largely unknown. We used the correlation between sea temperature and stable isotope ratio in scales of 17 salmon stocks to estimate their distributions during their last year at sea. This has resulted in a better comprehension of salmon migration routes, differences in stock productivity trends over large areas (e.g., Bristol Bay vs Northeast Pacific) and differences in productivity of stocks with geographically close spawning grounds.

Peri-urban lakes offer many valued ecosystem services, but their vulnerability to climate change and anthropogenic disturbances increases with increasing human populations the effects and interactions of multiple stressors on lakes can lead to unexpected outcomes, affecting societal and ecological values, it is necessary to evaluate ecosystem trajectories and respective drivers in peri-urban lakes. Better management practices could thus be applied to preserve ecosystem services of peri-urban lakes. We conducted a multi-proxy paleolimnological study on Cultus Lake, British Columbia, a Canadian peri-urban lake experiencing cultural eutrophication, to reconstruct a comprehensive ecological trajectory of the lake over the past ~ 200 years. We also integrated historical data as well as historical archival information to identify the potential drivers of the changes. We identified ca. 1800–1900 CE as a reference period, reflected in muted variations across most paleo-indicators. Minor increases in sedimentary δ15N ca. 1880–1940 CE coincided with the onset of anthropogenic modifications to the Cultus Lake watershed. Signs of early eutrophication were evident by ca. 1940 CE, as indicated by increases in all sedimentary pigments. By ca. 1970–1990 CE, elevated concentrations of sedimentary cyanobacterial pigments and changes in diatom species assemblages highlighted the potential interactive effects of multiple stressors, including cultural eutrophication, climate warming and declines in the endangered Cultus Lake sockeye salmon population. Recent (ca. 1990–2008 CE) declines in sedimentary pigments and increases in cladoceran fluxes suggested an increase in top-down control of the lake food web. From the collection of changes observed in the past ~ 200 years in our study, it is clear that Cultus Lake and its associated ecosystem services would benefit from abatement of nutrient loadings from terrestrial and atmospheric sources. Our study emphasizes the complexity and interactivity of drivers in peri-urban lake ecosystems and the necessity of long-term perspectives to contextualize modern ecological conditions to inform lake and watershed management.

A high-resolution, multiproxy analysis of a core from Tokotan Lake, Urup Island, illustrates the complex paleoenvironmental signals that can be preserved in sedimentary deposits from geologically active areas, such as the Kuril Archipelago. Diatom and geochemical analyses of the Tokotan core suggest a shallowing and lessening of the lake area over the last ∼3450 cal BP. Without other proxies, the record could be interpreted as showing a general decrease in precipitation over the Late Holocene. However, palynological data indicate no change in vegetation, thereby implying no significant climatic variation. Neither of these paleoclimatic interpretations agrees with Late Holocene reconstructions from the Kuril Archipelago or the Russian mainland. Paleomagnetic data imply variable sediment sources during the lake's history, indicating alterations within the Tokotan catchment (e.g., shifts in gradients or sediment loads in the inflowing streams). Such changes would be particularly important in the Shabalina River, which today has formed a partial dam across the lake's outlet. The results of the Tokotan study indicate that other factors (e.g., volcanism, seismic activity, sea-level changes) rather than climate were more probable determinants of the Late Holocene lake record. Given the geologic dynamism of the region, it is perhaps not surprising that paleo-records from the Kuril Islands display an inconsistency in the numbers and/or duration of proposed Holocene climatic oscillations, underscoring the importance of multiproxy investigations in areas that are or have been geologically dynamic.

Failure-prone Cenozoic volcanic rocks distributed across central Idaho, USA, promote large landslides, consequent drainage impoundment, and the formation of regionally asynchronous landslide-dammed lakes. Examination of sedimentary records shows that extant lakes formed in this way exhibit high primary productivity relative to other lakes in the region, apparently sustained through relatively elevated watershed phosphorous loading and the contribution of nitrogen-fixing cyanobacteria. The resulting high rates of sediment and carbon accumulation exceed those found in regional lakes formed by other processes and underlain by other bedrock lithologies lower in phosphorous. These unusually high biogenic sediment accumulation rates produce highly resolved, often annually laminated sedimentary sequences. The result is a high-resolution temporal matrix for the runoff-intensity signal of episodically delivered, watershed-derived clastic sediment. Elemental analysis by core-scanning X-ray fluorescence (XRF) effectively highlights these clastic pulses, and spectral analysis of lithogenic elemental intensities indicates they carry spectral power (including significant harmonic signals) concentrated in the 3–5 yr period. Patterns shown by episodic sediment delivery events support winter snowpack as a modulator of late Holocene sediment export from these watersheds.

Floodplain development, land-use, and flooding on the lower Ohio River are investigated with a 3100-year-long sediment archive from Avery Lake, a swale lake on the Black Bottom floodplain in southern Illinois, US. In all, 12 radiocarbon dates show that Avery Lake formed at 1130 BCE (3100 cal. yr BP), almost 3000 years later than previously thought, indicating that the Black Bottom floodplain is younger and more dynamic than previously estimated. Three subsequent periods of extensive land clearance were identified by changes in pollen composition, corresponding to Native American occupations before 1500 CE and the current Euro-American occupation beginning in the 18th century. Sedimentation rates prior to 1820 CE changed independently of land clearance events, suggesting natural as opposed to land-use controls. Comparison with high-resolution paleoclimate data from Martin Lake, IN, indicates that lower Ohio River flooding was frequent when cold-season precipitation originating from the Pacific/Arctic predominated when atmospheric circulation resembled positive Pacific North American (PNA) conditions and the Pacific Decadal Oscillation (PDO) was in a positive mean state (1130 BCE to 350 CE and 1150–1820 CE). Conversely, Ohio River flooding was less frequent when warm-season precipitation from the Gulf of Mexico prevailed during negative PDO- and PNA-like mean states (350 and 1150 CE). This flood dynamic appears to have been fundamentally altered after 1820 CE. We suggest that extensive land clearance in the Ohio River watershed increased runoff and landscape erosion by reducing interception, infiltration, and evapotranspiration, thereby increasing flooding despite a shift to negative PDO- and PNA-like mean states. Predicted increases in average precipitation and extreme rainfall events across the mid-continental US are likely to perpetuate current trends toward more frequent flood events, because anthropogenic modifications have made the landscape less resilient to changing hydroclimatic conditions.

Stable isotope analyses show that Ancient Beringian diets were seasonally structured and included substantial summer salmon., The earliest Native Americans have often been portrayed as either megafaunal specialists or generalist foragers, but this debate cannot be resolved by studying the faunal record alone. Stable isotope analysis directly reveals the foods consumed by individuals. We present multi-tissue isotope analyses of two Ancient Beringian infants from the Upward Sun River site (USR), Alaska (~11,500 years ago). Models of fetal bone turnover combined with seasonally-sensitive taxa show that the carbon and nitrogen isotope composition of USR infant bone collagen reflects maternal diets over the summer. Using comparative faunal isotope data, we demonstrate that although terrestrial sources dominated maternal diets, salmon was also important, supported by carbon isotope analysis of essential amino acids and bone bioapatite. Tooth enamel samples indicate increased salmon use between spring and summer. Our results do not support either strictly megafaunal specialists or generalized foragers but indicate that Ancient Beringian diets were complex and seasonally structured.

Multi-proxy sediment records from Castor Lake and Scanlon Lake, north-central Washington, provide a late Quaternary perspective on lake/catchment hydrologic and ecosystem responses to climate change and the Mazama volcanic ashfall event. Analyses of authigenic carbonate mineral oxygen and carbon isotope values, organic carbon and nitrogen content, and sedimentological facies were conducted on sediment from Castor Lake in order to reconstruct lake/catchment hydrologic balance, the source and abundance of organic matter, and variations in lake level. Sedimentary facies characterization was conducted on the Scanlon Lake sediment in order to provide supporting evidence for the lake-level shifts inferred from the Castor Lake data. Marked changes in Castor Lake proxy values occur from 12,860 to 11,440 calendar years before present (yr BP), suggesting lake/catchment responses to the Younger Dryas cold reversal including higher lake levels, substantial variability in productivity, and increased catchment erosion. High δ18O values at 9630 yr BP indicate that lake levels were lower than at present and that the early Holocene was dry. Sedimentological analyses and δ18O data demonstrate that subsequent to the Mazama climactic eruption (∼7600 yr BP), a transition to the lowest lake levels of the Holocene occurred over several centuries, with maximum δ18O values at 7290 (90% uncertainty range: 7020–7500) yr BP and low lake levels persisting until 6190 (5960–6410) yr BP. Lithological changes in the Scanlon Lake record support these inferences. The lowest δ18O values of the Holocene occur in sediment from ∼5000 yr BP, indicating high lake levels at this time, after which a secular trend toward higher δ18O values and lower lake levels occurred. The prolonged lowstand in the centuries following the Mazama eruption suggests that catchment hydrologic characteristics were strongly impacted by the ashfall through effects on soil water retention capacity, that similar responses may have occurred in comparable settings within the Mazama ashfall zone, and that such volcanic events have the potential confound the climate signal in lake sediment records. Were a similar event to happen in the future, catchment hydrology, stream/river discharge, and lake/catchment ecosystem dynamics could be affected for centuries.

The ability to distinguish between different migratory behaviours (e.g., anadromy and potamodromy) in fish can provide important insights into the ecology, evolution, and conservation of many aquatic species. We present a simple stable carbon isotope (δ13C) approach for distinguishing between sockeye (anadromous ocean migrants) and kokanee (potamodromous freshwater residents), two migratory ecotypes of Oncorhynchus nerka (Salmonidae) that is applicable throughout most of their range across coastal regions of the North Pacific Ocean. Analyses of kokanee (n = 239) and sockeye (n = 417) from 87 sites spanning the North Pacific (Russia to California) show that anadromous and potamodromous ecotypes are broadly distinguishable on the basis of the δ13C values of their scale and bone collagen. We present three case studies demonstrating how this approach can address questions in archaeology, archival, and conservation research. Relative to conventional methods for determining migratory status, which typically apply chemical analyses to otoliths or involve genetic analyses of tissues, the δ13C approach outlined here has the benefit of being non-lethal (when applied to scales), cost-effective, widely available commercially, and should be much more broadly accessible for addressing archaeological questions since the recovery of otoliths at archaeological sites is rare.

Holocene records of lacustrine primary production are commonly used to reconstruct past changes in environmental and climatic conditions. While several methods exist to infer paleoproductivity trends, few studies to date have applied multiple geochemical indices in the same core sequence from Arctic lakes to evaluate their fidelity and sensitivity to specific climate variables over long (Holocene length) timescales. In this study, we evaluate sub-century to millennial-scale fluctuations in paleoproductivity over the Holocene using geochemical (biogenic opal and sedimentary chlorin) analyses of sediments from Burial Lake in the western Brooks Range, Alaska. Large fluctuations in opal and related proxies occur at millennial timescales over the last 10,000 years. We interpret the changes in opal to result from variability in diatom productivity, which is indirectly mediated by climate primarily through changes in the duration of the ice-free growing season and the availability of limiting nutrients at this oligotrophic, tundra lake. Comparison of the opal and sedimentary chlorin record, which is correlated with TOC, shows contrasting patterns on both short (century to multi-century) and relatively long (millennial) time scales. The concentration of opal far exceeds that of TOC and variations in sediment dry bulk density, driven by changes in the accumulation of opal, are likely responsible in part for the variations in sedimentary chlorin. Further, C/N ratio values indicate a mixed algal-terrestrial source of sedimentary organic matter. This result highlights the complexity in the climatic interpretation of sedimentary chlorin as an index of whole lake production, because the signal is prone to dilution/concentration from opal and also reflects a combination of aquatic and terrestrial production. Time series analysis of the productivity records indicates the presence of a significant ∼1500-yr oscillation in opal concentration, which has been found in North Atlantic Ocean proxy records and numerous other marine and terrestrial paleorecords. Comparison of diatom productivity against a sea-ice inferred reconstruction of the Arctic Oscillation (AO) from the Beaufort Sea (Darby et al., 2012) shows that periods of reduced productivity at Burial Lake coincide with inferred positive phases of the AO (AO+). Combined with modern observations of sea ice extent and meteorological data, we hypothesize that AO + conditions and a strengthened polar jet correspond with a shortened ice-free growing season, a decrease in the availability of limiting nutrients, and lower levels of diatom production at Burial Lake. Comparison of the spectral properties between opal and the AO reconstruction reveal similar millennial scale variations with ∼1500-yr variability during the middle Holocene that transition to ∼1000-yr variability during the late Holocene. In light of these findings, we suggest the possibility that millennial variations in diatom productivity observed in the Burial Lake record are related to millennial variability in high-latitude atmospheric circulation similar to the AO. These results shed light on the sensitivity of aquatic ecosystems in northern Alaska to changes in the duration of the ice-free growing season, the availability of limiting nutrients for phytoplankton growth, and Arctic-wide atmospheric circulation dynamics over the Holocene on millennial timescales.

The Holocene upwelling history of the northern California continental slope is examined using the high-resolution record of TN062-O550 (40.9°N, 124.6°W, 550 m water depth). This 7-m-long marine sediment core spans the last ∼7500 years, and we use it to test the hypothesis that marine productivity in the California Current System (CCS) driven by coastal upwelling has co-varied with Holocene millennial-scale warm intervals. A combination of biogenic sediment concentrations (opal, total organic C, and total N), stable isotopes (organic matter δ13C and bulk sedimentary δ15N), and key microfossil indicators of upwelling were used to test this hypothesis. The record of biogenic accumulation in TN062-O550 shows considerable Holocene variability despite being located within 50 km of the mouth of the Eel River, which is one of the largest sources of terrigenous sediment to the Northeast Pacific Ocean margin. A key time interval beginning at ∼2900 calibrated years before present (cal yr BP) indicates the onset of modern upwelling in the CCS, and this period also corresponds to the most intense period of upwelling in the last 7500 years. When these results are placed into a regional CCS context during the Holocene, it was found that the timing of upwelling intensification at TN062-O550 corresponds closely to that seen at nearby ODP Site 1019, as well as in the Santa Barbara Basin of southern California. Other CCS records with less refined age control show similar results, which suggest late Holocene upwelling intensification may be synchronous throughout the CCS. Based on the strong correspondence between the alkenone sea surface temperature record at ODP Site 1019 and the onset of late Holocene upwelling in northern California, we suggest that CCS warming may be conducive to upwelling intensification, though future changes are unclear as the mechanisms forcing SST variability may differ.

The population size of anadromous salmon in the Pacific Northwest is strongly influenced by decadal variation in watershed and oceanographic conditions and therefore should also be influenced by larger magnitude millennial-scale variations in these conditions. We studied δ15N of bulk organic matter in lake sediment from Woahink Lake, Oregon, as a proxy of marine-derived nutrients (MDN) from spawning coho salmon. We compared this site to a control lake with a natural barrier to salmon migration. From 7.5 to 5.4 ka, a dune was emplaced, breached, and emplaced again, forming Woahink Lake in a former estuary. δ15N decreased steadily since 5.4 ka at Woahink but not at the control lake. δ15N reached a minimum just prior to anthropogenic nutrient loading, which caused an increase in δ15N, thus precluding a comparison with the historical decline in salmon abundance. A mixing model of lake-water nitrate, developed to explore alternate scenarios for the observed range of δ15N, could not explain these results without invoking MDN input from at least several hundred salmon annually. Our results show a previously unreported pattern of a millennial-scale decline in salmon that has plausible linkages to parallel changes in ocean circulation and productivity.

RATIONALE Reconstructing stable isotope (SI) ratios at the base of paleo-food webs is often challenging. For coastal systems, the SI ratios of organic matter in archeological shell represent a possible solution, providing a direct record of primary consumer SI ratios in the littoral zone. However, shell is often porous, with organic compounds being susceptible to diagenetic alteration or contamination. If molecular isotopic information is well preserved, compound-specific amino acid isotope analysis (CSI-AA) has the potential to provide direct proxies for baseline SI ratios, bypass many contamination issues, and allow assessment of the diagenetic state. METHODS We collected shell from both archeological middens and nearby littoral zones in coastal Alaska, and used a simple organic extraction approach based on decalcification with sequential weak HCL additions to liberate organic material. We measured CSI-AA patterns, molar AA distributions, and the CSI-AA degradation parameter (ΣV), in the context of bulk SI ratios in fossil shell, modern shell, and soft tissue from five common taxa (urchin, limpet, mussel, periwinkle, chiton). RESULTS CSI-AA patterns in both soft tissue and shell were consistent with primary consumers, and were indistinguishable in most modern and fossil shell pairs, showing that amino acid δ15N values can be well preserved in archeological shell. AA molar distributions were also similar, although most fossil shell was enriched in Asx and Gly. Comparison between CSI-AA results from modern specimens confirmed that source AA groups (tracking isotopic baselines) are transferred without substantial modification into the shell record. In contrast, the trophic AA group had elevated δ15N values in shell versus soft tissue for all taxa examined, suggesting that a correction will be required for any CSI-AA proxies using these AAs. CONCLUSIONS Overall, this new data indicates that the CSI-AA analysis of fossil shell represents a promising new approach to determining isotopic baselines in coastal paleo-ecosystems.

Two lake records document Holocene changes in sea level, vegetation, and climate on the Okhotsk and Pacific sides of central Iturup Island, southern Kuril Islands. The sediment cores originated within tidal flats that subsequently developed into a marine strait which crosscut the island as sea levels rose during the early Holocene. Brackish lagoons and eventually freshwater lakes formed by ~7100 cal yr BP associated with warmer than present conditions. Past vegetation changes indicate a clear Holocene thermal maximum recorded on the Pacific coast but a less distinct optimum on the western shores (~7200–6100 cal yr BP). A gradual cooling toward modern levels occurred ~6100–3500 cal yr BP. Four prominent layers of coarse sediment found in mid- to late Holocene lake deposits may correspond to intervals of climate cooling/dune formation previously documented in coastal sections. Although chronological limitations question the synchronicity of these events across the south Russian Far East, it seems probable that they have a regional signature. However, the mechanisms responsible for Holocene climatic changes are likely the result of complex interactions of hemispheric-scale atmospheric patterns, marine characteristics, and regional feedbacks rather than simply fluctuations in sea levels as suggested in the current interpretative model.

Objectives: Stable isotope ratio analysis of bulk bone collagen dominates research into past diet; however, bone carbonate and compound specific isotope analyses (CSIA) of amino acids provide alternative, yet complementary, lines of evidence toward that same research goal. Together they inform on different aspects of diet, allowing greater certainty in reconstructions. Here we present new data on carbonate isotopes for Rapa Nui and reevaluate prehistoric diet in the context of these new and previously published bulk collagen and CSIA data. Materials and methods: We analyzed carbon isotopes in bone carbonate from 28 prehistoric human teeth from Rapa Nui. These represent a subset of material examined previously for carbon and nitrogen isotope ratios in bulk collagen. We then reevaluate prehistoric diet in light of these and other published data. In addition, we analyzed carbon and nitrogen isotope ratios in 28 modern plant specimens from Rapa Nui to better approximate the isotopic value of the terrestrial endmember. Results: Bulk data suggest a predominantly terrestrial diet, with the amount of marine sources incorporated varying though time. While previously argued to reveal greater amounts of marine consumption, reanalysis of recently published CSIA data suggests this result may relate to the proportion of carbon assimilated rather than consumed. Utilizing models incorporating concentration dependence for estimating dietary proportions results in much lower estimates of marine consumption, in line with findings of the bulk data. Discussion: While these data indicate a larger focus on terrestrial resources, limitations in all forms of analysis make it difficult to determine exact dietary contributions in this mixed system. Better understanding of the complex physiological processes governing isotopic routing and fractionation, and knowledge of appropriate isotopic endmember values are needed to advance this research.

The current state of permafrost in Alaska and meaningful expectations for its future evolution are informed by long-term perspectives on previous permafrost degradation. Thermokarst processes in permafrost landscapes often lead to widespread lake formation and the spatial and temporal evolution of thermokarst lake landscapes reflects the combined effects of climate, ground conditions, vegetation, and fire. This study provides detailed analyses of thermokarst lake sediments of Holocene age from the southern loess uplands of the Yukon Flats, including bathymetry and sediment core analyses across a water depth transect. The sediment core results, dated by radiocarbon and 210Pb, indicate the permanent onset of finely laminated lacustrine sedimentation by ∼8,000 cal yr BP, which followed basin development through inferred thermokarst processes. Thermokarst expansion to modern shoreline configurations continued until ∼5000 cal yr BP and may have been influenced by increased fire. Between ∼5000 and 2000 cal yr BP, the preservation of fine laminations at intermediate and deep-water depths indicate higher lake levels than present. At that time, the lake likely overflowed into an over-deepened gully system that is no longer occupied by perennial streams. By ∼2000 cal yr BP, a shift to massive sedimentation at intermediate water depths indicates that lake levels lowered, which is interpreted to reflect a response to drier conditions based on correspondence with Yukon Flats regional fire and local paleoclimate reconstructions. Consideration of additional contributing mechanisms include the possible influence of catastrophic lake drainages on down-gradient base-flow levels that may have enhanced subsurface water loss, although this mechanism is untested. The overall consistency between the millennial lake-level trends documented here with regional paleoclimate trends indicates that after thermokarst lakes formed, their size and depth has been affected by North Pacific atmospheric circulation in addition to the evolution of permafrost, ground ice, and subsurface hydrology. As the first detailed study of a Holocene thermokarst basin that links expansion, stabilization and subsequent climate-driven lake level variations in a loess upland, these results provide a framework for future investigations of paleoclimatic signals from similar lake systems that characterize large regions of Alaska and Siberia.

The oligotrophic condition of salmon-bearing catchments in the Columbia River Basin is a potential limiting factor for the recovery of Pacific salmon (Oncorhynchus spp.). To address this issue, nutrient supplementation programs attempt to mitigate for reduced marine-derived nutrients (MDN). We examined the assimilation of MDN in the biota of tributaries of the Salmon River Basin, Idaho, USA, following the addition of salmon carcass analogs (SCA). We measured carbon (C) and nitrogen (N) stable isotopes from biofilm, macroinvertebrate, salmonid fish, and riparian vegetation samples and found significant 15N enrichment and substantial assimilation of SCA material in all aquatic trophic levels and in riparian vegetation. Our results suggest that SCA are incorporated primarily through indirect pathways and provide a source of MDN to multiple trophic levels in freshwater and linked riparian ecosystems.

Sedimentological and geochemical results from Nir’pa Co, an alpine lake on the southeastern Tibetan Plateau, detail late-Holocene Indian summer monsoon (ISM) hydroclimate during the last 3300 years. Constrained by modern calibration, elevated silt and lithics and low sand and clay between 3.3 and 2.4 ka and 1.3 ka and the present indicate two pluvial phases with lake levels near their current overflow elevation. Between 2.4 and 1.3 ka, a sharp increase in sand and corresponding decrease in lithics and silt suggest drier conditions and lower lake levels at Nir’pa Co. Hydroclimate expressions in the sedimentological proxies during the Medieval Climate Anomaly (MCA) and ‘Little Ice Age’ (LIA) are not statistically significant, suggesting that these events were minor compared to the millennial scale variability on which they were superimposed. However, decreasing sand and increasing lithics and silt during the MCA between 950 and 800 cal. yr BP may suggest briefly wetter conditions, while increasing sand and reduced lithics and silt from 500 to 200 cal. yr BP suggest potentially drier conditions during the LIA. Similarities with regional records from lake sediment and ice cores and speleothem records from the central and eastern Tibetan Plateau, India, and the Arabian Sea, suggest generally coherent late-Holocene ISM variability in these regions. Increased late-Holocene ISM intensity occurred during times when Tibetan Plateau surface air temperatures were warmer, Indo-Pacific sea surface temperatures were elevated, and the tropical Pacific was in a La Niña–like mean state. Conversely, aridity between 2.4 and 1.3 ka occurred in concert with cooling on the Tibetan Plateau and in the Indo-Pacific with more El Niño–like conditions in the tropical Pacific. Differences with western Tibetan records may reflect a weakened ISM and stronger westerlies in this region during the late-Holocene.

Psychoactive pharmaceuticals have been found as teratogens at clinical dosage during pregnancy. These pharmaceuticals have also been detected in minute (ppb) concentrations in drinking water in the US, and are environmental contaminants that may be complicit in triggering neurological disorders in genetically susceptible individuals. Previous studies have determined that psychoactive pharmaceuticals (fluoxetine, venlafaxine and carbamazepine) at environmentally relevant concentrations enriched sets of genes regulating development and function of the nervous system in fathead minnows. Altered gene sets were also associated with potential neurological disorders, including autism spectrum disorders (ASD). Subsequent invitro studies indicated that psychoactive pharmaceuticals altered ASD-associated synaptic protein expression and gene expression in human neuronal cells. However, it is unknown if environmentally relevant concentrations of these pharmaceuticals are able to cross biological barriers from mother to fetus, thus potentially posing risks to nervous system development. The main objective of this study was to test whether psychoactive pharmaceuticals (fluoxetine, venlafaxine, and carbamazepine) administered through the drinking water at environmental concentrations to pregnant mice could reach the brain of the developing embryo by crossing intestinal and placental barriers. We addressed this question by adding (2)H-isotope labeled pharmaceuticals to the drinking water of female mice for 20 days (10 pre-and 10 post-conception days), and quantifying (2)H-isotope enrichment signals in the dam liver and brain of developing embryos using isotope ratio mass spectrometry. Significant levels of (2)H enrichment was detected in the brain of embryos and livers of carbamazepine-treated mice but not in those of control dams, or for fluoxetine or venlafaxine application. These results provide the first evidence that carbamazepine in drinking water and at typical environmental concentrations is transmitted from mother to embryo. Our results, combined with previous evidence that carbamazepine may be associated with ASD in infants, warrant the closer examination of psychoactive pharmaceuticals in drinking water and their potential association with neurodevelopmental disorders.

Previous research on the small mammal population recovered from archeological excavations at the Wasden Site in southeastern Idaho suggests that changing frequency distributions through time represent a shift in climate during the early Holocene from a cooler, wetter regime to a warmer, drier one. This conclusion was re-evaluated using stable carbon and nitrogen isotope analyses of bone collagen from the three species of small mammals examined in the earlier studies: pocket gophers (Thomomys talpoides), pygmy rabbits (Brachylagus idahoensis), and ground squirrels (Spermophilus townsendii). Resulting carbon and nitrogen isotopic values are consistent with known differences in feeding ecology, suggesting high fidelity as proxies for past vegetation (and thus climate) regimes. Patterns of 15N enrichment and increased representation of C4-CAM vegetation observed in the pocket gophers, and to a lesser extent ground squirrels, suggests increasing warmth and/or aridity from the early Holocene until ∼7000 cal yr BP, thus supporting previous hypotheses of climate change on the eastern Snake River Plain. The results highlight the potential contribution of such studies for archeological research by providing additional proxies for environmental conditions that bear on paleoecological adaptations to climatic change, including past human use and occupation of the region.

Stand-replacing wildfires are a keystone disturbance in the boreal forest, and they are becoming more common as the climate warms. Paleo-fire archives from the wildland–urban interface can quantify the prehistoric fire regime and assess how both human land-use and climate change impact ecosystem dynamics. Here, we use a combination of a sedimentary charcoal record preserved in varved lake sediments (annually layered) and fire scars in living trees to document changes in local fire return intervals (FRIs) and regional fire activity over the last 500 years. Ace Lake is within the boreal forest, located near the town of Fairbanks in interior Alaska, which was settled by gold miners in AD 1902. In the 400 years before settlement, fires occurred near the lake on average every 58 years. After settlement, fires became much more frequent (average every 18 years), and background charcoal flux rates rose to four times their preindustrial levels, indicating a region-wide increase in burning. Despite this surge in burning, the preindustrial boreal forest ecosystem and permafrost in the watershed have remained intact. Although fire suppression has reduced charcoal influx since the 1950s, an aging fuel load experiencing increasingly warm summers may pose management problems for this and other boreal sites that have similar land-use and fire histories. The large human-caused fire events that we identify can be used to test how increasingly common megafires may alter ecosystem dynamics in the future.

Lake sediment oxygen isotope records (calcium carbonate-δ 18 O) in the western North American Cordillera developed during the past decade provide substantial evidence of Pacific ocean–atmosphere forcing of hydroclimatic variability during the Holocene. Here we present an overview of 18 lake sediment δ 18 O records along with a new compilation of lake water δ 18 O and δ 2 H that are used to characterize lake sediment sensitivity to precipitation-δ 18 O in contrast to fractionation by evaporation. Of the 18 records, 14 have substantial sensitivity to evaporation. Two records reflect precipitation-δ 18 O since the middle Holocene, Jellybean and Bison Lakes, and are geographically positioned in the northern and southern regions of the study area. Their comparative analysis indicates a sequence of time-varying north–south precipitation-δ 18 O patterns that is evidence for a highly non-stationary influence by Pacific ocean–atmosphere processes on the hydroclimate of western North America. These observations are discussed within the context of previous research on North Pacific precipitation-δ 18 O based on empirical and modeling methods. The Jellybean and Bison Lake records indicate that a prominent precipitation-δ 18 O dipole (enriched-north and depleted-south) was sustained between ~ 3.5 and 1.5 ka, which contrasts with earlier Holocene patterns, and appears to indicate the onset of a dominant tropical control on North Pacific ocean–atmosphere dynamics. This remains the state of the system today. Higher frequency reversals of the north–south precipitation-δ 18 O dipole between ~ 2.5 and 1.5 ka, and during the Medieval Climate Anomaly and the Little Ice Age, also suggest more varieties of Pacific ocean–atmosphere modes than a single Pacific Decadal Oscillation (PDO) type analogue. Results indicate that further investigation of precipitation-δ 18 O patterns on short (observational) and long (Holocene) time scales is needed to improve our understanding of the processes that drive regional precipitation-δ 18 O responses to Pacific ocean–atmosphere variability, which in turn, will lead to a better understanding of internal Pacific ocean–atmosphere variability and its response to external climate forcing mechanisms.

Diatom, rock magnetic, geochemical, and lithological studies of a sediment core from Paramushir Island (northern Kuril Archipelago) trace environmental shifts from bog to salt-water lagoon to freshwater lake over the past 10,000 14C BP. Organic-rich mesic landscapes dominated the southern island until ~8200 14C BP. Transgression of the Sea of Okhotsk onto the island began sometime after 8200 14C BP, resulting in the formation first of a salty (~8200–5700 14C BP) then a brackish (~5700–5200 14C BP) lagoon. With lowering of sea level after 5200 14C BP, a freshwater lake formed, which has remained to the present day. This history parallels regional trends in the Russian Far East, where maximum sea levels occurred between ~8000 and 4600 14C BP, peaking at ~6400 14C BP. Sandy levels within the lake core suggest four intervals of aeolian activity (~4900–4800 14C BP; 4300–3800 14C BP; 3200–3000 14C BP; 1900–900 14C BP), perhaps related to drier than present climates. Palynological data indicate a dominance of Pinus pumila–Duschekia kamtschatica shrub tundra in the lowlands ~8200–5800 14C BP, marking the Holocene thermal maximum. This vegetation contrasts to modern, which established ~5800 14C BP and is a mix of coastal meadow, Betula–Salix low shrub tundra, and scattered Pinus and Duschekia thickets. The palynological record shows little response to mid-to-late Holocene climatic fluctuations except for a decrease in Pinus shrubs perhaps caused by changes in snow cover and/or summer temperature during the Little Ice Age.

Sediment cores from Burial Lake located in the western Brooks Range in Arctic Alaska record paleoenvironmental changes that span the last 37,000 calendar years before present (cal yr BP). We identified four distinct lithologic subunits based on physical properties (dry bulk density, magnetic susceptibility), sediment composition, and geochemical proxies (organic matter, biogenic silica, C/N, organic matter δ13C and δ15N, and elemental data from scanning X-ray fluorescence). The multi-proxy approach and relatively high temporal resolution (at multi-decadal to centennial time scales) of our proxy analysis, compared with previous studies of intermediate water depth cores from Burial Lake, provide new insights into the paleoenvironmental history of the region spanning the period prior to the Last Glacial Maximum. Relatively high lake-levels and gradually decreasing in-lake and terrestrial productivity occur during the mid-Wisconsin interstadial from 37,200 to 29,600 cal yr BP. The subsequent period is defined by falling and lower lake-levels with decreasing effective-moisture, windier conditions, and sustained low aquatic productivity throughout the LGM between 29,600 and 19,600 cal yr BP. The last deglaciation that commenced by 19,600 cal yr BP is characterized by gradual changes in several sediment physical and geochemical proxies, including increasing C/N ratios and terrestrial productivity, decreasing magnetic susceptibility and clastic sediment flux, along with rising and relatively higher lake-levels. A decrease in aeolian activity after 16,500 cal yr BP is inferred from the appearance of fine (very fine sandy silt) sediment, compared to coarse sediments through the LGM and last deglaciation. The highest levels of terrestrial inputs along with increasing and variable aquatic productivity occur during the Lateglacial to early Holocene interval between 16,500 and 8800 cal yr BP. The absence of multi-proxy evidence for a strong climatic reversal during the Younger Dryas from Burial Lake sediments contrasts with some paleorecords showing cooler temperatures and/or dry conditions in northern Alaska at this time. Peak levels of sediment organic content and terrestrial productivity at Burial Lake between 10,500 and 9900 cal yr BP coincide with the early Holocene summer insolation maxima, which likely represents summertime warming and an enhanced flux of watershed derived organic matter from permafrost degradation. The remainder of the Holocene (since 8800 cal yr BP) at Burial Lake is characterized by relatively high and stable lake levels, landscape stabilization, and relatively high and variable levels of aquatic productivity.

Significance Fish bones from the 11,500-y-old Upward Sun River site in interior Alaska represent the oldest evidence for salmon fishing in North America. We used ancient DNA analysis to identify the fish specimens as chum salmon ( Oncorhynchus keta ), and stable isotope analysis to confirm that the salmon were anadromous (sea-run). The exploitation of salmon at this early date is noteworthy because Paleoindians are traditionally portrayed as big-game hunting specialists. Furthermore, the presence of salmon at Upward Sun River over 1,400 km upriver from the coast shows that spawning runs had been established by the end of the last Ice Age. The early availability and use of anadromous salmon has important implications for understanding Paleoindian economies and expansion into North America.

During recent decades, lake levels in the Yukon Flats region of interior Alaska have fluctuated dramatically. However, prior to recorded observations, no data are available to indicate if similar or more extreme variations occurred during past centuries and millennia. This study explores the history of Yukon Flats lake origins and lake levels for the past approximately 5,500 years from sediment analyses guided by previous work on permafrost extent, thermokarst, and modern isotope hydrology. Sediments dated by 210Pb and AMS radiocarbon indicate stable chronologies following initial lake initiation. Subsequent lithology is autochthonous, and oxygen isotope ratios of endogenic carbonate reflect lake level change at multiple time scales. Sediment results indicate high lake levels between approximately 4000 and 1850 cal yr BP, which is interpreted to reflect wetter-than-modern conditions. Lower lake levels with short-lived high stands during the past approximately 800 years reflect generally arid conditions with brief wet intervals similar to the region’s moisture regime today. The millennial trend is one of increasing aridity and corresponds closely with fire reconstructions and regional paleoclimatic trends. We conclude that high-magnitude lake-level fluctuations and decadal scale trends occurred before the observational period and are persistent hydroclimatic features of the Yukon Flats region.

Deposition of distal tephra-fall deposits in lake systems with low watershed sediment fluxes can represent large geochemical anomalies in sediment elemental composition. We examine the persistence of compositional effects of fallout from the 7.63 kyr BP Mt. Mazama caldera-forming event and other tephra deposits in the micro-laminated abyssal sediments of Pettit Lake, central Idaho, which received ~50 kg m−2 of Mazama tephra-fall material. Persistent post-depositional dominance of the Mazama material is reflected in elemental composition and grain size distribution and is related to lake hypsometry and the presence of a large in-lake sediment reservoir subject to remobilization. Decoupling of recycled clastic mineral material with Mazama compositional affinity from both biogenic matter and from clastic material derived from within the watershed is shown by coherence between dated primary tephras and a radiocarbon chronology.

Food chain length provides insights into how ecosystems function and respond to global change. A recent synthesis has shown that food chain length is significantly related to both ecosystem productivity and ecosystem size. Relaxation of energetic constraints on top predators has been advanced as the primary mechanism explaining the importance of ecosystem productivity whereas the significance of ecosystem size may be related to the fact that larger ecosystems provide more refuge that stabilizes intermediate predators. Given that submerged macrophytes in lakes are known to enhance both ecosystem productivity and the amount of available refuge, we hypothesized that food chain lengths, measured as the trophic positions of top predators, would be significantly related to macrophyte biomass. We tested our hypothesis by conducting a field survey of shallow lakes across a strong macrophyte but limited morphometric gradient using a hierarchical mixed effect modeling approach. We determined that macrophyte biomass was positively related to the trophic position of numerous piscivores and to food chain length across lakes. Both lake volume and macrophyte biomass were retained as fixed predictors in our model with lowest AICc, and this model explained 85% of the variation in piscivorous fish trophic positions considering both fixed and random effects (i.e., lake and species-specific responses to lake volume). Macrophyte biomass explained 29% of the residual variation in food chain length when the effect of lake volume was removed. These results are the first to directly relate macrophyte biomass to piscivore trophic positions and food chain length. We conclude that shallow lakes with higher macrophyte biomass support longer food chains independent of ecosystem size and nutrient concentration. We suggest that loss of macrophytes largely driven by human activities reduces food chain length, with potential consequences for ecosystem function.

Article history: Sedimentological data and hydrogen isotopic measurements of leaf wax long-chain n-alkanes (δDwax) from an alpine lake sediment archive on the southeastern Tibetan Plateau (Paru Co) provide a Holocene perspective of Indian summer monsoon (ISM) activity. The sedimentological data reflect variations in lake level and erosion related to local ISM rainfall over the Paru Co catchment, whereas δDwax reflects integrated, synoptic-scale ISM dynamics. Our results indicate that maximum ISM rainfall occurred between 10.1 and ∼5.2 ka, during which time there were five century-scale high and low lake stands. After 5.2 ka, the ISM trended toward drier conditions to the present, with the exception of a pluvial event centered at 0.9 ka. The Paru Co results share similarities with paleoclimate records from across the Tibetan Plateau, suggesting millennial-scale ISM dynamics were expressed coherently. These millennial variations largely track gradual decreases in orbital insolation, the southward migration of the Intertropical Convergence Zone (ITCZ), decreasing zonal Pacific sea surface temperature (SST) gradients and cooling surface air temperatures on the Tibetan Plateau. Centennial ISM and lake-level variability at Paru Co closely track reconstructed surface air temperatures on the Tibetan Plateau, but may also reflect Indian Ocean Dipole events, particularly during the early Holocene when ENSO variability was attenuated. Variations in the latitude of the ITCZ during the early and late Holocene also appear to have exerted an influence on centennial ISM rainfall. © 2014 Elsevier B.V. All rights reserved.

Accurate prediction of future climate requires an understanding of the mechanisms of the Holocene climate; however, the driving forces, mechanisms, and processes of climate change in the Holocene associated with different time scales remain unclear. We investigated the drivers of Holocene sea surface temperature (SST) and sea ice extent in the North Pacific Ocean, and the Okhotsk and Bering Seas, as inferred from sediment core records, by using the alkenone unsaturation index as a biomarker of SST and abundances of sea ice-related diatoms (F. cylindrus and F. oceanica) as an indicator of sea ice extent to explore controlling mechanisms in the high-latitude Pacific. Temporal changes in alkenone content suggest that alkenone production was relatively high during the middle Holocene in the Okhotsk Sea and the western North Pacific, but highest in the late Holocene in the eastern Bering Sea and the eastern North Pacific. The Holocene variations of alkenone-SSTs at sites near Kamchatka in the Northwest Pacific, as well as in the western and eastern regions of the Bering Sea, and in the eastern North Pacific track the changes of Holocene summer insolation at 50°N, but at other sites in the western North Pacific, in the southern Okhotsk Sea, and the eastern Bering Sea they do not. In addition to insolation, other atmosphere and ocean climate drivers, such as sea ice distribution and changes in the position and activity of the Aleutian Low, may have systematically influenced the timing and magnitude of warming and cooling during the Holocene within the subarctic North Pacific. Periods of high sea ice extent in both the Okhotsk and Bering Seas may correspond to some periods of frequent or strong winter–spring dust storms in the Mongolian Gobi Desert, particularly one centered at ∼4–3 thousand years before present (kyr BP). Variation in storm activity in the Mongolian Gobi Desert region may reflect changes in the strength and positions of the Aleutian Low and Siberian High. We suggest that periods of eastward displacement or increased intensity of the Aleutian Low correspond with times of increased extent of sea ice in the western Okhotsk Sea and eastern Bering Sea.

Reconstructing centennial timescale hydroclimate variability during the late Holocene is critically important for understanding large-scale patterns of drought and their relationship with climate dynamics. We present sediment oxygen isotope records spanning the last two millennia from 10 lakes, as well as climate model simulations, indicating that the Little Ice Age was dry relative to the Medieval Climate Anomaly in much of the Pacific Northwest of North America. This pattern is consistent with observed associations between the El Nino–Southern Oscillation (ENSO), the Northern Annular Mode, and drought as well as with proxy-based reconstructions of Pacific and Atlantic ocean-atmosphere variations over the past 1000 years. The large amplitude of centennial variability indicated by the lake data suggests that regional hydroclimate is characterized by longer-term shifts in ENSO-like dynamics and that an improved understanding of the centennial timescale relationship between external forcing and drought is necessary for projecting future hydroclimatic conditions in western North America.

Physical and geochemical proxy analyses of sediment cores from Harding Lake in central Alaska are used to reconstruct paleoenvironmental change and millennial scale fluctuations in lake level for the last ∼31,000 years. We analyzed a composite 422 cm core from the lake depocenter (42.1 m water depth) and identified 4 distinct lithologic units based on variability in dry bulk density, organic matter, biogenic silica, carbon to nitrogen mass ratios (C/N), organic matter carbon isotopes (δ13C), pollen, and elemental abundances via scanning X-ray fluorescence, with age control provided by 16 Accelerator Mass Spectrometry radiocarbon dates and 210Pb dating. In addition, we analyzed a transect of cores from 7.1 m, 10.75 m, 15.91 m, and 38.05 m water depths to identify lake level fluctuations and to characterize sediment compositional changes as a function of water depth. Organic matter content and magnetic susceptibility values in surface sediments from all transect cores show a strong correlation with water depth. Interpretation of four lithologic units with well-dated contacts produced a record of water-depth variations that is consistent with independent climate records from eastern Beringia. Basal coarse-grained sediments (quartz pebble diamicton) were deposited prior to 30,700 calendar years before present (yr BP), possibly from fluvial reworking or deflation during a period of severe aridity. Unit 1 sediments were deposited between 30,700 and 15,700 yr BP and are characterized by a low organic matter content, a high magnetic susceptibility, and low biogenic silica concentrations resulting from very low lake levels, low terrestrial and in-lake productivity and a high flux of clastic sediment. An abrupt increase in organic matter and biogenic silica concentration marks the transition into Unit 2 sediments, which were deposited between 15,700 and 9,400 yr BP when lake levels were higher and variable (relative to Unit 1). The transition to full interglacial conditions at 9,400 yr BP marks the beginning of Unit 3. Here an abrupt increase in the sedimentation rate, organic matter and biogenic silica concentration occurs (along with a corresponding decrease to low magnetic susceptibility). These high values persist until 8,700 yr BP, signifying a rapid rise to higher lake levels (in comparison to Units 1 and 2). Unit 4 sediments were deposited between 8,700 yr BP to 2010 AD and generally contain high concentrations of organic matter and biogenic silica with low magnetic susceptibility, suggesting that lake levels were relatively high and stable during the middle to late Holocene.

Diatoms and silicoflagellate assemblages were examined in two year-increments of varved samples spanning the interval from 1748 through 2007 in Santa Barbara Basin (SBB) box core SBBC0806 to determine the timing and impact of possible 20th century warming on several different components of the plankton. Diatoms ( Thalassionema nitzschioides = TN) and silicoflagellates ( Distephanus speculum s.l. = DS) indicative of cooler waters and a shallow thermocline begin to decline in the 1920s and persistently compose a lower percentage of the assemblage in the SBB by about 1940. Prior to 1940, TN constituted on average ∼30% of the Chaetoceros -free diatom sediment assemblage and DS on average ∼36% of the silicoflagellate assemblage. Between 1940 and 1996, these relative abundances were ∼20% (TN) and ∼8% (DS). These results are consistent with results from planktonic foraminifera and radiolarians that indicate an influence of 20th century warming on marine ecosystems before most scientific observations began. Cooling of surface waters coincident with the one of the strongest La Nina events of the 20th century (and a return to negative PDO conditions) in late 1998 brought about a return to pre-1940 values of these cool water taxa (TN ∼31%, DS ∼25%). However, this recent regional cooling appears to have been accompanied by profound changes in the diatom assemblage. Pseudo-nitzschia australis , and Pseudo-nitzschia multiseries , diatom species associated with domoic acid, a neurotoxin that causes shellfish poisoning and marine mammal deaths, rapidly became dominant in the SBB sediment record at the time of the regional cooling (1999) and increased substantially in numbers as a bloom-forming taxon (relative to Chaetoceros spores) in 2003. Prior to 2003, diatom blooms recorded in the SBB sediment record consisted predominantly of Chaetoceros spores and less commonly of Rhizosolenia -related species ( Neocalyptrella robusta and Rhizosolenia setigera ). Fecal pellets dominated by valves of P. australis , however, were particularly abundant in both the 2003 and 2006 samples, coincident with recorded incidents of domoic acid increase and widespread shellfish poisoning in the SBB.

Simulations conducted using a coupled lake-catchment isotope mass balance model forced with continuous precipitation, temperature, and relative humidity data successfully reproduce (within uncertainty limits) long-term (i.e., multidecadal) trends in reconstructed lake surface elevations and sediment core oxygen isotope ( δ 18 O) values at Castor Lake and Scanlon Lake, north-central Washington. Error inherent in sediment core dating methods and uncertainty in climate data contribute to differences in model reconstructed and measured short-term (i.e., sub-decadal) sediment (i.e., endogenic and/or biogenic carbonate) δ 18 O values, suggesting that model isotopic performance over sub-decadal time periods cannot be successfully investigated without better constrained climate data and sediment core chronologies. Model reconstructions of past lake surface elevations are consistent with estimates obtained from aerial photography. Simulation results suggest that precipitation is the strongest control on lake isotopic and hydrologic dynamics, with secondary influence by temperature and relative humidity. This model validation exercise demonstrates that lake-catchment oxygen isotope mass balance models forced with instrumental climate data can reproduce lake hydrologic and isotopic variability over multidecadal (or longer) timescales, and therefore, that such models could potentially be used for quantitative investigations of paleo-lake responses to hydroclimatic change.