Late Holocene Climate Research Articles

Geomorphic response to Late Holocene climate variation and anthropogenic pressure, northeastern Prince Edward Island, Canada

Geomorphic response provides an index to climate change and variability. Differing time scales of both weather/climate events and landform response complicate interpretation. Anthropogenic modification, particularly in coastal and aeolian dune environments, represents a further geomorphic influence. Northeastern Prince Edward Island (PEI), Canada, is a marine-dominated environment subjected to rising sea level throughout the late Holocene. The combination of rising sea levels, increased anthropogenic utilization of the coast for residential, and tourism purposes, and limited offshore winter ice conditions have resulted in accelerated erosion and degradation of the dunes and coastline. The aeolian succession indicates that temporal and spatial transitions from isolated shield dunes to parabolic dunes to linked coastal transverse dune complexes are characteristic of the coastal dune fields. Sand supply is the most significant control on dune morphology, development, and extent. Superimposed dome dunes and shield dunes are prevalent in areas of anthropogenic disturbance. Dune migration along the coastal zone has varied considerably, with rates locally in excess of 10m/a over short times. Winters marked by relatively limited sea ice and scarce snow cover, resulting from more temperate winter conditions, allow increased erosion by strong storms. Deflation of dune crests and development of blowouts is notably accentuated along human trails. The climate variations recorded in Atlantic Canada over the past decade fall within the range of those recorded previously within the twentieth century, and thus do not indicate conclusive evidence of a pronounced trend of climate change in this region. However, analysis of northeastern PEI demonstrates that dune coastlines can evolve rapidly in response to short-term and intermediate-term climate variation, particularly when coupled with anthropogenic pressure. Similar geomorphic effects in combination with climate variation and storm activity should be anticipated along other dune coastlines that have been subjected to intense anthropogenic utilization during earlier periods of the Quaternary.

Reconstructing Late Holocene climate

Studying the past few millennia, the Late Holocene, can help us better understand modern‐day natural climate variability. With this in mind, a group of paleoclimate researchers and climate modelers recently convened at a workshop to discuss three distinct approaches to reconstructing Late Holocene climate history.

Late Holocene climate and cultural changes in the southwestern United States.

Columnar stalagmites in caves of the Guadalupe Mountains during the late Holocene record a 4000-year annually resolved climate history for the southwestern United States. Annual banding, hiatuses, and high-precision uranium-series dating show a present day-like climate from 4000 to 3000 years ago, following a drier middle Holocene. A distinctly wetter and cooler period from 3000 to 800 years ago was followed by a period of present day-like conditions, with the exception of a slightly wetter interval from 440 to 290 years before the present. The stalagmite record correlates well with the archaeological record of changes in cultural activities of indigenous people. Such climate change may help to explain evidence of dwelling abandonment and population redistribution.

Holocene Vegetation and Paleoclimatic and Paleomagnetic History from Lake Johnston, Tasmania

Lake Johnston cirque contains some of the best subalpine rainforest in Tasmania. Pollen from the sediments shows Lagarostrobos franklinii, which presently reaches 1040 m, may be a glacial relict. Nothofagus cunninghamii–Nothofagus gunnii subalpine rainforest developed between 9000 and 6000 14C yr B.P., with a maximum at 8700 14C yr B.P. After 6000 14C yr B.P. Nothofagus gunnii became more important, and from 3600 14C yr B.P. sclerophyll and heath components increased. Partial burning of the catchment occurred periodically. Early Holocene climate was warmer and wetter than late Holocene climate. The vegetation and climate changes are similar to those recorded from western South Island New Zealand and Chile. Radiocarbon dates give a sedimentation rate of 0.43 mm/yr. Cores are correlated by magnetic susceptibility. Magnetic ages are assigned by matching with the 14C-dated secular variation master curve for southeastern Australia. Magnetic ages are consistent with the 14C chronology when the former are adjusted by 350 years.

Late Holocene climate change for the eastern interior United States: evidence from high-resolution δ18O values of sagittal otoliths

Stable oxygen isotope values were determined for freshwater drum (Aplodinotus grunniens) sagittal otoliths recovered from the Eastman rockshelter archaeological site in northeast Tennessee to evaluate climate change for the eastern interior United States from 5500 calendar years ago to the present. Micromilled samples representing less than six days of otolith growth were extracted to acquire high-resolution intra-otolith variation in δ18O values. Freshwater drum sagittal otoliths form annual bands due to thermally induced growth cessation below 10°C. δ18O(H2O) values can be calculated once a high-resolution carbonate sample representing the beginning of the growing season is isolated. Maximum summer temperature can be calculated using the seasonal minimum δ18O(CaCO3) value and the δ18O(H2O) value.Maximum summer temperatures calculated from the freshwater drum sagittae suggest that summer temperatures generally decrease from 29°C at ∼5.5ka to 22°C at ∼0.3ka. However, warmer climates at 2.9, 1.7–1.6, and 1.2–1.0ka punctuate this trend. A more complete picture of the climate is reconstructed, because δ18O(H2O) values, which are a function of the ratio of summer to winter precipitation, are also calculated. A relatively low average δ18O(H2O) value of −8.1‰ VSMOW was calculated at 1.0ka, suggesting cold winters, dry summers, and/or wet winters may have prevailed during part of the Medieval Warm Period in Tennessee. Contrary to studies suggesting that the Holocene was extremely stable and the Hypsithermal was invariably warm and dry, additional evidence suggesting both significant climate variability and evidence for a wetter mid-Holocene is presented.

Late-Holocene changes in ocean circulation and climate: foraminiferal and isotopic evidence from Sulafjord, western Norway

A 278 cm long sediment core spanning the last 5500 years was collected from 440 m water depth in Sulafjorden, western Norway. Detailed analyses of benthonic foraminfera, stable isotopes and lithology have been performed on the core, and a chronology based on five AMS dates on benthonic foraminifera has been established. The foraminiferal assemblages consist of species that are common in the North Sea region today. The benthonic fauna seems to respond to changes in oxygenation of the bottom water in the fjord indicating relatively low dissolved oxygen contents prior to c. 2000 cal. bc followed by a gradual increase until c. 700 cal. bc. The oxygen levels in the water masses are assumed to reflect the ingress of oceanic water from the shelf. Downcore variations in the oxygen isotope ratios in the benthonic species Uvigerina mediterranea in Sulafjorden are interpreted to reflect temperature variations with a minimum amplitude of 2°C. The isotopic data indicate five cold periods at c. 2150–1800 cal. bc, c. 850–600 cal. bc, 150 cal. bc to cal. ad 150, c. cal. ad 500–650, and one in the top of the core corresponding to the ‘Little Ice Age’ ( c. cal. ad 1625). These periods are characterized by 1.5–2°C reduction in the bottom-water temperatures in Sulafjorden. Some of the cold periods in the fjord record are contemporaneous with the Holocene ice-rafting events in the North Atlantic and glacier fluctuations in western Norway and Northern Scandinavia. This implies that late-Holocene climate fluctuations in Scandinavia are caused by circulation changes in the North Atlantic region.

Influence of late Holocene hillslope processes and landforms on modern channel dynamics in upland watersheds of central Nevada

Stratigraphic, geomorphic, and paleoecological data were collected from upland watersheds in the Great Basin of central Nevada to assess the relationships between late Holocene climate change, hillslope processes and landforms, and modern channel dynamics. These data indicate that a shift to drier, warmer climatic conditions from approximately 2500 to 1300 YPB led to a complex set of geomorphic responses. The initial response was massive hillslope erosion and the simultaneous aggradation of both side-valley alluvial fans and the axial valley system. The final response was fan stabilization and axial channel incision as fine-grained sediments were winnowed from the hillslope sediment reservoirs, and sediment yield and runoff processes were altered. The primary geomorphic response to disturbance for approximately the past 1900 years has been channel entrenchment, suggesting that the evolutionary history of hillslopes has produced watersheds that are prone to incision. The magnitude of the most recent phase of channel entrenchment varies along the valley floor as a function of geomorphic position relative to side-valley alluvial fans. Radial fan profiles suggest that during fan building, fan deposits temporarily blocked the flow of sediment down the main stem of the valley, commonly creating a stepped longitudinal valley profile. Stream reaches located immediately upvalley of these fans are characterized by low gradients and alternating episodes of erosion and deposition. In contrast, reaches coincident with or immediately downstream of the fans exhibit higher gradients and limited valley floor deposition. Thus, modern channel dynamics and associated riparian ecosystems are strongly influenced by landforms created by depositional events that occurred approximately 2000 years ago.

A Late Pleistocene to Holocene Record of Precipitation Reflected in Margaritifera falcata Shell δ18O From Three Archaeological Sites in the Lower Salmon River Canyon, Idaho

Oxygen-18 (δ18O) concentrations in Margaritifera falcata shells preserved in three archaeological sites in the Lower Salmon River Canyon of Idaho are compared with modern mussel shells. Shell δ18O records show that Late Pleistocene and Early Holocene climates were drier with occasional periods of increased precipitation. After c.4000 years bp, precipitation is higher in the Salmon River basin than at present and trends toward modern conditions after c.1800 years bp. The climatic conditions reflected by fluctuations in shell δ18O are matched by regional palaeoenvironmental records, including pollen, glacial and palaeohydraulic proxy sources, and are compared with major changes in Plateau prehistoric cultural patterns. Studies of late Quaternary records of freshwater bivalve shell δ18O are useful for reconstructing climatic conditions and complement geoarchaeological studies in riparian contexts.

Late Holocene Climate of the James Bay Area, Quebec, Canada, Reconstructed Using Fossil Beetles

We used fossil beetles recovered from three peatlands of the James Bay area (Radisson, northern Quebec, Canada), and the mutual climatic range (MCR) method, to produce a quantitative reconstruction of summer temperatures during the last 5000 yr. Our main objective was to test the hypothesis that a significant climatic cooling episode occurred during the late Holocene epoch, leading to the opening up of the boreal forest, and to the progressive replacement of black spruce (Picea mariana) forests by jack pine (Pinus banksiana) stands. Beetle assemblages in the Radisson area were very stable during the late Holocene epoch. We used a total of 22 beetle species to conduct the MCR analyses. Reconstructed mean July temperatures ranged from 14.5 to 17.5°C, which is close to the present-day (A.D. 1977–1996) temperature range found in the Radisson area. The general stability of beetle assemblages, and the MCR analyses, suggest that there was no major change in July temperatures during the last 5000 yr in the Radisson area. This study provides no evidence that the progressive replacement of black spruce forests by jack pine stands in the Radisson area during the last 2700 yr can be explained by a longterm climatic cooling episode affecting the postfire regeneration potential of trees. Consequently, an alternative hypothesis (more frequent fires favoring jack pine) should be seriously considered to explain the late Holocene changes in the forest environment of the Radisson area.

Late Holocene Climate of the James Bay Area, Quebec, Canada, Reconstructed Using Fossil Beetles

We used fossil beetles recovered from three peatlands of the James Bay area (Radisson, northern Quebec, Canada), and the mutual climatic range (MCR) method, to produce a quantitative reconstruction of summer temperatures during the last 5000 yr. Our main objective was to test the hypothesis that a significant climatic cooling episode occurred during the late Holocene epoch, leading to the opening up of the boreal forest, and to the progressive replacement of black spruce (Picea mariana) forests by jack pine (Pinus banksiana) stands. Beetle assemblages in the Radisson area were very stable during the late Holocene epoch. We used a total of 22 beetle species to conduct the MCR analyses. Reconstructed mean July temperatures ranged from 14.5 to 17.5°C, which is close to the present-day (A.D. 1977–1996) temperature range found in the Radisson area. The general stability of beetle assemblages, and the MCR analyses, suggest that there was no major change in July temperatures during the last 5000 yr in the Radisson area. This study provides no evidence that the progressive replacement of black spruce forests by jack pine stands in the Radisson area during the last 2700 yr can be explained by a longterm climatic cooling episode affecting the postfire regeneration potential of trees. Consequently, an alternative hypothesis (more frequent fires favoring jack pine) should be seriously considered to explain the late Holocene changes in the forest environment of the Radisson area.

Late Pleistocene-Holocene paleolimnology of three north-western Russian lakes

The vegetation history and development of three different types of lakes, lakes Valday, Kubenskoye and Vishnevskoye (northwest of the East European Plain) were reconstructed using paleolimnological techniques. Watershed vegetation demonstrates a close connection with climate fluctuations: gradual expansion of the southern broad-leaved trees to the North during the Holocene with the maximum extent during the climate optimum (8000–5000 BP); and their subsequent retreat afterwards; followed by the extension of spruce during the cold and dry Subboreal time; and dominance of pine-spruce-birch forests in the Subatlantic time. The Late Pleistocene and Holocene climate changes resulted in lake-level fluctuations and other ecosystem changes. Valday Lake was formed ca. 12,500 BP as an oligotrophic, deep water basin. The lake level decreased during the dry Boreal, then increased again during the humid Atlantic period. The large shallow Kubenskoye Lake was formerly a part of an ice margin lake, which was then separated (ca. 13,000 BP) and developed into the Sukhona Basin with an outflow to the northwest. During the Atlantic, the outflow direction changed to the east. As a result, the ancient Sukhona Lake disappeared and Kubenskoye Lake formed in its modern size and shape. Vishnevskoye Lake, on the Karelian Isthmus, was formed at the beginning of the Preboreal after the disappearance of the Baltic Ice Lake. It was flooded by waters of the Boreal Ancylus transgression of the Baltic Basin and had become a small eutrophic lake by the time.

A proxy record of late Holocene climate change from May Moss, northeast England

Quantitative reconstruction of changes in mire surface wetness has been used to reconstruct proxy climate from an upland ombrotrophic blanket mire on the North York Moors in northeast England (May Moss). Testate amoebae, plant macrofossil and humification analyses were carried out for six peat profiles. Transfer functions are used to generate estimates of water table levels from the testate amoebae stratigraphy, which complement the semi-quantitative indications of changing surface wetness provided by plant macrofossil and humification analysis. 14C dates provide the chronology for the stratigraphy. Differences were encountered between AMS 14C dates on pure Sphagnum remains and radiometric dates on bulk peat from the same horizon, which perhaps arise from the heterogeneity of peat. Replicate palaeoecological analysis of adjacent cores identifies consistency within testate amoebae and plant macrofossil stratigraphies, and reveals a strong agreement between the water table level proxies. The record of hydrological changes at sites across May Moss are in synchrony, and so climate change is the most likely cause of the moisture fluctuations. Changes to a wetter or cooler climate were identified cal. ad 260–540, ca. ad 550–650, cal. ad 670–980, ca. ad 1350–1450, cal. ad 1400–1620 and ca. ad 1700–1800. Periods with a drier or warmer climate precede all of these wet shifts, with particularly dry periods between cal. ad 650–860 and 690–980 and between cal. ad 1290–1410 and 1400–1620. Copyright © 2001 John Wiley & Sons, Ltd.

Wetter and cooler late Holocene climate in the southwestern United States from mites preserved in stalagmites

The presence of at least 12 species of well-preserved mites in two late Holocene stalagmites from Hidden Cave, Guadalupe Mountains, New Mexico, depicts changing climate over the past 3200 yr. Growth of both stalagmites, determined by uranium-series dating, occurred from at least 3171 ± 48 yr ago and ceased by 819 ± 82 yr ago. Some of the 12 subfossil genera and species in the stalagmites are like those currently found in wetter and cooler climates, northern-like, and distinctly different from those known in the cave (n = 16) and on the surface immediately around the cave (n = 32). The mismatch of genera and species in the stalagmites, cave, and surface near the cave argues for a wetter and cooler late Holocene climate in the southwestern United States from ca. 3200 to 800 yr ago.

Postglacial climate and vegetation history, north‐central Kola Peninsula, Russia: pollen and diatom records from Lake Yarnyshnoe‐3

A sediment core from Lake Yarnyshnoe‐3 (69°04'N; 36°04'E), an emerged coastal lake from the tundra of the north‐central Kola Peninsula, has been analyzed for fossil pollen and diatoms. The pollen record shows the Younger Dryas event marked by increasing Artemisia coupled with decreases in Poaceae, Cyperaceae and Salix at c. 10 700 to 10 000 BP. This core provides the first well‐defined palynological record of the Younger Dryas event on the Kola Peninsula. Stomates from Pinus were recovered from the core interval between 8000 and 6000 BP. The stomates, coupled with elevated values of pine pollen, indicate that Pinus sylvestris grew near the arctic coastline of the central Kola Peninsula in the middle Holocene. However, the small number of stomates suggests that pines were not plentiful. The diatom record from the core reflects basin isolation from the sea and indicates additional limnological changes during the climate transition between c. 5000 and 4000 BP. The broadly similar climate and vegetation history on the north‐central Kola Peninsula and in Fennoscandia demonstrates the propagation of late glacial and Holocene climate events from the North Atlantic region into the Eurasian Arctic.

Climatic events during the Late Pleistocene and Holocene in the Upper Parana River: Correlation with NE Argentina and South-Central Brazil

Most Quaternary studies in Brazil are restricted to the Atlantic Coast and are mainly based on coastal morphology and sea level changes, whereas research on inland areas is largely unexplored. The study area lies along the Parana River, state of Parana, Brazil, at 22° 43′S latitude and 53° 10′W longitude, where the river is as yet undammed. Paleoclimatological data were obtained from 10 vibro cores and 15 motor auger holes. Sedimentological and pollen analyses plus TL and 14C dating were used to establish the following evolutionary history of Late Pleistocene and Holocene climates: First drier episode ?40,000–8000 BP First wetter episode 8000–3500 BP Second drier episode 3500–1500 BP Second (present) wet episode 1500 BP–Present Full-size table Table options View in workspace Download as CSV Climatic intervals are in agreement with prior studies made in southern Brazil and in northeastern Argentina.

Late Holocene sea-level change and climate

Although records of late Holocene relative sea-level (RSL) change have been reported from high-energy coastal environments, such as the raised beaches of Alaska (Jordon and Mason, 1999) and Antarctica (Zwartz et al., 1998), some of the most detailed records are preserved in the saltmarsh deposits which have accumulated on the passive margins of the Atlantic Ocean under a predominantly upward trend in RSL. This situation contrasts with that found in much of the Pacific Ocean or the Mediterranean, where tectonic processes control patterns of RSL and coastal evolution, often overprinting any sea level - climate link (e.g., Long and Shennan, 1998; Nelson et al., 1998; Pirazzoli, 1998; Benson et al., 1999; Goff and Chague-Goff, 1999; Hindson and Andrade, 1999; Hindson et al., 1999; Shennan et al., 1998; 1999; Stanley, 1999). Recently published research into late Holocene sea-level change and climate in North America and Canada, northwest Europe and the Pacific is now considered, before some general issues emerging from this work are explored.

Late Holocene sea-level change and climate

Late Holocene sea-level change and climate

Holocene environmental and climatic change in the Northern Great Plains as recorded in the geochemistry of sediments in Pickerel Lake, South Dakota

The sediments in Pickerel Lake, northeastern South Dakota, provide a continuous record of climatic and environmental change for the last 12000 yr. Sediments deposited between 12 and 6 ka (radiocarbon) show extreme variations in composition, oxygen and carbon isotopic composition of bulk carbonate, carbon isotopic composition of organic matter, and magnetic susceptibility. These variations reflect changes in sources of moisture, regional vegetation types, precipitation–evaporation balance, ground- and surface-water influx, water residence time, erosion, lake productivity, water level, and water temperature. The total carbonate content of late Pleistocene sediments steadily increased from <20% at the base of the core to as much as 80% in sediments deposited between 11 and 9 ka. By about 8 ka, the total carbonate content of the sediments had declined to about 40% where it remained with little variation for the past 8 kyr, suggesting relatively stable conditions. There are marked increases in values of δ13C and δ18O in bulk carbonate, and δ13C of organic matter, in sediments deposited between 10 and 6 ka as evaporation increased, and the vegetation in the watershed changed from forest to prairie. This shift toward more 18O-enriched carbonate may also reflect a change in source or seasonality of precipitation. During this early Holocene interval the organic carbon (OC) content of the sediments remained relatively low (2–3%), but then increased rapidly to 4.5% between 7 and 6 ka, reflecting the rapid transition to a prairie lake. The OC content fluctuates slightly between 4 and 6% in sediments deposited over the past 6 kyr. Like OC and total carbonate, most variables measured show little variation in the 13 m of sediment deposited over the past 6 kyr, particularly when compared with early Holocene variations. Although the magnetic susceptibility of this upper 13 m of sediment is generally low (<10 SI units), the upper six meters of the section is marked by striking 1 m cycles (ca. 400–500 yr periodicity) in susceptibility. These cycles are interpreted as being due to variations in the influx of eolian detrital-clastic material. Century-scale cyclic variations in different proxy variables for aridity and eolian activity from sediments deposited over the past 2000 yr in other lakes in the northern Great Plains, as well as in sand dune activity, suggest that aridity cycles were the dominant feature of late Holocene climate of the northern Great Plains.

Stable carbon isotope record of middle to late Holocene climate changes from land snail shells at Hinds Cave, Texas

Stable carbon isotope ratios of shell carbonate and shell organic matter from land snails ( Rabdotus alternatus ) from Hinds Cave, Texas, are used to reconstruct the climate history of the drier western part of the southern Great Plains (present mean annual rainfall of 400 mm) over the last ca. 5000 yr. AMS radiocarbon analyses of four individual shells from each of two strata indicate that there are no problems of reworking or age mixtures within strata. However, burning is evident in many shells. Amino acid composition and racemization were used to identify shells that had been significantly heated and these were rejected for isotopic analysis because of possible alteration of the isotopic signal. Fourteen samples of snails from Hinds Cave, each consisting of 2–6 individual shells from the same provenience, were radiocarbon dated by AMS and analyzed for stable carbon isotopes. In addition, a sample collected alive ca. AD 1890 from a nearby site, was analyzed to represent modern conditions. The shells show no decrease in organic content with age, indicating good preservation of shell organic matter. Both the organic and carbonate isotope values show similar temporal trends. The oldest samples (4100–4600 cal yr BP) are relatively depleted in 13 C . Maximum δ 13 C values are reached at ca. 3500 cal yr BP. Thereafter there is a regular depletion in 13 C , with the recent sample showing the lowest δ 13 C value. The change in the isotopic values over time is quite large (range of 4.5‰ for organic matter) and indicates substantial climatic changes. The variations in isotopic values are interpreted as resulting primarily from changes in moisture conditions, affecting the abundance of drought-adapted CAM (Crassulacean acid metabolism) plant species (enriched in 13 C ). Thus relatively moist mid-Holocene conditions are indicated, with increasingly dry conditions reaching a maximum at ca. 3500 cal yr BP, followed by progressively moister conditions through the late Holocene.

Tree-Ring Based Reconstructions of Paleo-Precipitation Regimes in the Eastern Yellowstone Region

There are few other regions where the influence of climate on basic ecosystem attributes has been as well documented as the Greater Yellowstone Ecosystem (GYE). Research has shown that elk, bison, and grizzly bear populations in the GYE are tightly linked to annual climate variation (Meagher 1976, Picton 1978). Authors have shown that the distribution of vegetation types in Grand Teton and Yellowstone National Parks is influenced by the seasonality of precipitation (Despain 1987, 1990). Natural disturbances, especially fires and insect outbreaks, are also known to coincide with specific climate scenarios in this region (Knight 1987, Balling et al. 1992). Therefore, understanding how climate can vary over time is essential for the proper management of these areas (Luckman 1996). Modem instrumental records have contributed greatly to our understanding of the current GYE climate system. In particular, work by Mock (1996) and Bartlein et al. (1997) has demonstrated how local manifestations of large-scale circulation patterns produce distinct climates within the GYE. In addition, studies using modem climate records and General Circulation Models by Balling et al. (1992) and Bartlein et al. (1997) have identified trends toward increasing aridity in the GYE and the potential for these trends to continue well into the future. Late Pleistocene and Holocene (18-1 kya) climate in the GYE is known mainly from lake­sediment cores. Work by Whitlock (1993), Whitlock and Bartlein (1993), and Thompson et al. (1993) indicates that after deglaciation, increased solar radiation during summer months led to a highly seasonal climate regime. As levels of solar radiation changed through the Holocene, GYE climate became increasingly more like today until the modem regime became established around 1500-1600 AD (Whitlock 1993, Elias 1997). While existing modem and paleoecological studies reveal important aspects of the GYE climate system, there is a distinct lack of high-resolution data for most of the last millennium. Lake sediments only record climate variation at a resolution of hundreds to thousands of years, and instrumental records do not exist before the 1890s. Dendroclimatology, the study of climate using patterns of tree-ring growth (Fritts 1976) is particularly well suited to fill this gap in our knowledge of GYE climate. Tree-rings have been used successfully for climate reconstructions worldwide, offer records spanning decades to millennia, and can provide annual resolution. Therefore, we are developing a network of tree-ring sites in the western Absaroka Mountains and eastern Bighorn Basin to fill important spatial (areas east of Yellowstone NP) and temporal (high resolution for the past 700-1,000+year) gaps in our knowledge of GYE climate.