Climate Intervals Research Articles

Pre-contact adaptations to the Little Ice Age in Southwest Alaska: New evidence from the Nunalleq site

The reconstruction of diet, subsistence strategies and human-animal relationships are integral to understanding past human societies, adaptations and resilience - especially in the circumpolar Arctic. Even in relatively recent periods, climatic excursions may have posed specific challenges for hunter-gatherer groups living at latitudinal and climatic extremes, and archaeological research in Arctic North America is increasingly looking to better understand the impact of past climate change on human groups. Here, through a unique multi-proxy approach (zooarchaeology, bone technology and stable isotope analysis), we explore human subsistence strategies, adaptation and resilience at Nunalleq, a recently excavated pre-contact Yup'ik coastal site in southwest Alaska. The main phase of occupation of the site (16th-17th centuries AD) corresponds with one of the coolest periods of the Little Ice Age – a climatic interval from the early 14th century through the mid-19th associated with global and more localised cooling events. The analyses reveal a subsistence strategy centred around the exploitation of three major resources, including salmon, marine mammals and caribou, supplemented by secondary resources such as birds and medium-sized mammals. This tripartite resource base (salmon, marine mammals, caribou) is similar to that seen at other Thule-era sites in Alaska and likely permitted a flexibility in resource use in the face of changes in resource availability (and competition over resources) during the Little Ice Age. Comparison of the different datasets, however, reveals variability and nuance in the use of animals for both dietary and broader subsistence needs. While caribou represent a vital and heavily-exploited resource at Nunalleq (evident from both the zooarchaeology and the bone technology), they did not represent a key dietary resource (indicated by stable isotope data). Instead, caribou played an integral and key part as a major source of raw material, especially antler, in order to manufacture the necessary acquisition technology to exploit primary coastal resources.

10Be-derived sub-Milankovitch chronology of Late Pleistocene alluvial terraces along the piedmont of SW Tian Shan

Using topographic maps and terrestrial cosmogenic nuclide (TCN) 10Be exposure dating methods, we reconstructed a chronology with robust age constraints based on four alluvial terrace abandonment features in two study sites along the SW piedmont of Kepingtage Mountain in SW Tian Shan. Agreement between alluvial terrace abandonment ages and Guliya ice-core δ18O, LR04 stack of benthic δ18O, EPICA Dome C CH4, and solar insolation records suggests that alluvial terraces with 10Be age sequences at 63.7 ± 5.9 ka, 40.9 ± 3.84 ka, 36.2 ± 3.4 ka, and 22.1+5.1–4.7 ka correspond to three wetter climate intervals, possibly triggered by intensified South Asian summer monsoons since the Late Pleistocene. Given that the active thrust Kepingtage Fault experienced sustained uplift during this period, we suggest that the abandonment of alluvial terraces that formed since 22.1+5.1–4.7 ka may be related to sudden tectonic uplift. The occurrence of these four younger well-preserved alluvial terraces may also be related to the fact that the transient climatic incision has been no higher than the temporary tectonic uplift since 22.1+5.1–4.7 ka.

Tracking the Paleocene‐Eocene Thermal Maximum in the North Atlantic: A Shelf‐to‐Basin Analysis With a Regional Ocean Model

AbstractThe Paleocene‐Eocene Thermal Maximum (PETM), a transient greenhouse climate interval spurred by a large release of carbon to the ocean‐atmosphere approximately 56 million years ago, provides a geological point of comparison for potential effects of anthropogenic carbon emission. Geochemical proxies and fossil assemblages offer insight into the continental shelf response to the PETM, but global ocean‐atmosphere models cannot resolve shelf processes at sufficient resolution for model‐data comparisons. We present high‐resolution simulations of the pre‐PETM and PETM North Atlantic basin using the Regional Ocean Modeling System (ROMS), including a resolved continental shelf along the eastern margin of North America in the Salisbury Embayment. ROMS' high‐resolution, terrain‐following coordinate system permits greater vertical resolution and eddy resolution along continental margins while also capturing open‐ocean processes. We find that during the PETM, benthic oxygen concentration ([O2]) in the Salisbury Embayment decreases 18% to an average state of year‐round mild hypoxia, while average benthic calcite saturation (Ω) declines from 4.4 to 2.3. These benthic decreases are driven largely by enhanced benthic oxic respiration, which occurs despite no increase in shelf productivity. Instead, increased respiration stems from less vigorous off‐shelf transport of organic matter due to (a) weakened along‐shelf water currents and (b) weakened coastal upwelling that forces productivity closer to the shelf seafloor. Model results do not include riverine inputs, which would have further lowered benthic [O2] and Ω. Our data suggest lowered benthic calcite saturation and mild hypoxia as an upper bound on the oxygenation state of the Salisbury Embayment seafloor during the PETM.

A high-resolution paleolimnological study of climate and human impacts on Lac Noir, Québec, over the past 1000 yr

AbstractDiatom assemblages in lake sediments of Lac Noir, southwestern Québec, were studied at a resolution of 10 yr to determine principal drivers of primary producers for the past ~1000 yr. Generalized additive modeling revealed strong links between broadscale climate intervals of the late Holocene, forest composition, and diatom flora. During the Medieval Warm Period (~AD 1200) and onset of the Little Ice Age (~AD 1450), increases in Tabellaria flocculosa str. IIIp at the expense of Discostella stelligera reflected low lake productivity. At AD 1630, an abrupt shift to cooler temperatures and dry conditions triggered a decline in hemlock (Tsuga), replaced by disturbance and cool-adapted taxa. Greater nutrient availability and soil erosion in the catchment led to a corresponding and rapid increase in diatoms with higher optima for nitrogen, such as Asterionella formosa and Fragilaria crotonensis. After AD 1870, an increase in pollen of taxa associated with disturbances signaled the arrival of Euro-Canadians, and associated nutrient inputs to the lake triggered increases in Stephanodiscus minutulus and Achnanthidium minutissimum. Overall results of the study indicate that climate played an important underlying role in lake-ecosystem dynamics; however, disturbances affecting forest composition had more direct influences on the diatom communities of Lac Noir.

An 11,000‐yr record of diatom assemblage responses to climate and terrestrial vegetation changes, southwestern Québec

AbstractA high‐resolution diatom sequence was developed from continuously laminated lake sediments in southwestern Québec, which spanned the Holocene (~11,000 yr). General and species‐specific changes in the diatom record were synchronous with patterns of vegetation succession inferred from regional palynological studies, demonstrating significant influences of terrestrial ecosystems on lake water chemistry and aquatic biota. Principal components analysis was used to identify three major diatom biostratigraphic zones corresponding broadly to early, mid‐, and late Holocene climate intervals. Benthic alkaliphilus diatom taxa were abundant when the landscape was a Picea‐dominated woodland in the early Holocene (11.1–8.0 ka), and when climate conditions were inferred as relatively cool and dry. In the mid‐Holocene (8.0–3.6 ka), warmer temperatures resulted in a stabilization of soils and forests in the catchment area. Shade‐tolerant tree species (Tsuga, Fagus, and Betula) increased during this time, and planktonic diatom taxa (Discostella stelligera and Fragilaria tenera) were abundant in the lake. The well‐known decline in Tsuga across eastern North America between 6.0 and 5.0 ka corresponded to a shift toward more nutrient‐rich lake conditions for several centuries, indicated by an increase in benthic diatom taxa and a lower ratio of chrysophytes relative to diatoms. Neoglacial cooling in the late Holocene (3.6 ka to present) triggered an initial decline in D. stelligera, which later recovered as a result of nutrient inputs that were associated with increased abundances of hardwood, deciduous species (Betula and Alnus) in the catchment. In addition to providing a high‐resolution record of lake ontogeny for the region, the full Holocene record from this lake adds a new perspective on the spatial extent of regional aridity during the Medieval Warm Period (1.2–0.8 ka).

Climate history of the southwestern United States based on Estancia Basin hydrologic variability from 69 to 10 ka

Newly acquired UTh dates on gypsum sands contained within Pleistocene lake sediments allow us to extend the record of climatic change in the Estancia Basin of central New Mexico back to ∼69 ka from a previous limit of ∼29 ka. Using a hydrologic balance index (HBI) that reflects variations in sediment mineralogy and bedding characteristics, we find strong similarities to speleothem oxygen isotopic records for the southwestern United States as well as to isotopic variations in Greenland ice cores. Intervals of wetter climate in the Estancia Basin generally appear to correlate to colder conditions in the North Atlantic and conversely. The existence of a pronounced dry period from 18.1 to 17 ka matches in timing the Extrapolar Climate Reversal of Asmerom et al. (2017) at Fort Stanton cave in southern New Mexico and confirms a different origin for this stadial-like event. Furthermore, the new UTh dates support the existing Estancia Basin interpretation of a dry Bølling/Allerød followed by a wet Younger Dryas, a result consistent with speleothem and wet meadow evidence from New Mexico and Arizona (Asmerom et al., 2010, 2017; Polyak et al., 2004; Hall et al., 2012; Wagner et al., 2010) but in conflict with an interpretation of speleothem evidence from central Texas (Feng et al., 2014).

Investigations into the Holocene geology of the Dead Sea basin

This paper discusses the geological history and paleoclimate of the Dead Sea region based on drill hole data. A composite stratigraphic column for the Holocene period, of multiple lime carbonate and halite sedimentation, has been constructed for the southern Dead Sea basin. Integration of stratigraphic data with geochronology has shed new light on our understanding of Holocene sedimentation rates, tectonics, diapirism, the formation of sinkholes, lake levels, and paleoclimate. During this period, the southern basin has subsided at a rate of 8.5–11 m/ka, while the subsidence of the northern basin may have reached 25–30 m/ka. The Holocene has been divided into 13 major climatic intervals, starting with a very arid climate from ~ 11,700 to ~ 8800 BP, where halite precipitated in both basins, with the Dead Sea possibly reaching a level of ~ − 419 m msl. After ~ 8800 BP, there was a very intense pluviatile period, with the formation of alluvial fans opposite wadi channels reaching up to 45 m in thickness. An attempt has been made to construct a new Dead Sea-level curve, based on the mineralogical data and corrected for diapirism under the Lynch Straits and tectonic subsidence. The previous lake-level curves were based on elevations of shore-line facies in a tectonically active basin with differential subsidence. A new hypothesis is presented for sinkhole formation in both the northern and southern basins, which is considered to be initiated and controlled by active faulting, with the dissolution of the halite by artesian, undersaturated waters, more than the receding Dead Sea level. The brine level is rising in the southern basin. The findings from this research can act as a model for understanding the development of ancient and modern evaporites worldwide.

Climatic change and human-marine interactions in the uttermost tip of South America in Late Holocene

Palaeoclimatic records from southern tip of South America during the Last Holocene, indicate important climate intervals, such as the Medieval Climate Anomaly and Little Ice Age, which offered new scenarios to hunter-gatherer groups who inhabited the region. The aim of this paper is to explore the social practices carried out by hunter-fisher-gatherer societies of the southern part of the Atlantic Coast of Tierra del Fuego island (53–55°S, 66–74°W) in order to deal with these environmental changes. From our perspective, foragers have played an active role in designing strategies to cope with environmental fluctuations. Consequently, we argue that in a context of ecological uncertainty, these societies would have developed flexible strategies in terms of subsistence, technology and settlement patterns. In order to test this proposal, zooarchaeological and technological analysis of different archaeological assemblages dated between the 1300 to 220 BP were undertaken.The results show that these hunter-fisher-gatherer societies exploited a broad range of faunal resources using a versatile technology which encompassed tools with low production values and high use values. Likewise, the analysis of landscape organization revealed a settlement strategy centered on the most productive habitats, which were preferentially reoccupied.We suggest that these strategies, supported by cumulative knowledge and material conditions, could have enhanced social resilience and sustainability.

Perspective on warm climate intervals and their history: How might coastal Canada adapt to an ocean-related and potentially negative impact of predicted warmer conditions?

Past warm intervals lasting from decades to centuries can be observed throughout the late Holocene geologic record using various proxy physical, chemical and fossil indices, in conjunction with seasonal information such as the timing of the first flowers of the spring season, or by the dates of first freezing and thaws of fresh water bodies, that have been recorded in various journals. Three important warm intervals that have been identified over the past 3500 years include the Late Bronze Age Optimum (BAO)(~1350 to ~1200 BC), the Iron/Roman Age Optimum (I/RAO)(~250 BC to ~400 AD) and the Medieval Warm Period (MWP)(~950 to ~1250 AD). The early phase of the BAO featured maximum development of the Hittite Empire and the evolution of the palace economy. The timing and duration of the later I/RAO show considerable variation from place to place in the Northern Hemisphere. MWP proxy records from several regions indicate that, like the I/RAO pattern, peak warmth occurred at different times in different places included in the Period’s overall footprint. Paleo-temperatures, both slightly cooler and warmer than present, have been reported. The WMP occurred during the Middle Ages at a time of the expansion of major commercial routes along the Mediterranean Sea coast and during an interval when Vikings explored and settled in some areas of the North Atlantic region.Sea level rise is among the suite of important ocean-related negative impacts that are often associated with contemporary global warming scenarios. Both early and modern societies have developed effective adaptation strategies and mitigation techniques to resist rising sea levels and flooding. Many of these have utility for Canada in both inland and especially in coastal areas of the Maritime Provinces. Early sea level rise and tidal flow mitigation measures include the construction of dykes around low-lying areas, sand dune stabilization and shoreline armoring using large boulders in concert with breakwaters and groynes. Today, there is also opportunity for the application of beach nourishment and artificial dune construction to resist erosion by storm waves and alongshore currents but these typically require annual maintenance to remain effective. Last resort mechanisms range from stilt home construction to abandonment (managed retreat) of previously impacted coastal areas. It is very likely that, when needed, Canadians will be able to apply a broad range of modern and ancient effective technologies and to engage engineering expertise to develop new (e.g., hybrid) approaches for combating specific negative coastal impacts than were available to BAO, I/RAO and MWP societies.

Microbial community composition along a 50 000-year lacustrine sediment sequence

For decades, microbial community composition in subseafloor sediments has been the focus of extensive studies. In deep lacustrine sediments, however, the taxonomic composition of microbial communities remains undercharacterized. Greater knowledge on microbial diversity in lacustrine sediments would improve our understanding of how environmental factors, and resulting selective pressures, shape subsurface biospheres in marine and freshwater sediments. Using high-throughput sequencing of 16S rRNA genes across high-resolution climate intervals covering the last 50 000 years in Laguna Potrok Aike, Argentina, we identified changes in microbial populations in response to both past environmental conditions and geochemical changes of the sediment during burial. Microbial communities in Holocene sediments were most diverse, reflecting a layering of taxa linked to electron acceptors availability. In deeper intervals, the data show that salinity, organic matter and the depositional conditions over the Last Glacial-interglacial cycle were all selective pressures in the deep lacustrine assemblage resulting in a genetically distinct biosphere from the surface dominated primarily by Bathyarchaeota and Atribacteria groups. However, similar to marine sediments, some dominant taxa in the shallow subsurface persisted into the subsurface as minor fraction of the community. The subsequent establishment of a deep subsurface community likely results from a combination of paleoenvironmental factors that have shaped the pool of available substrates, together with substrate depletion and/or reworking of organic matter with depth.

Integrating the Holocene tephrostratigraphy for East Asia using a high-resolution cryptotephra study from Lake Suigetsu (SG14 core), central Japan

Tephra (volcanic ash) layers have the potential to synchronise disparate palaeoenvironmental archives on regional to hemispheric scales. Highly productive arc regions, like those in East Asia, offer a considerable number of widespread isochrons, but before records can be confidently correlated using these layers, a refined and integrated framework of these eruptive events is required. Here we present the first high-resolution Holocene cryptotephra study in East Asia, using the Lake Suigetsu sedimentary archive in central Japan. The Holocene tephrostratigraphy has been extended from four to twenty ash layers using cryptotephra extraction techniques, which integrates the deposits from explosive eruptions from North Korea/China, South Korea and along the Japanese arc. This Lake Suigetsu tephrostratigraphy is now the most comprehensive record of East Asian volcanism, and the linchpin site for correlating sequences across this region. Major element glass geochemical compositions are presented for the tephra layers in the sequence, which have been compared to proximal datasets to correlate them to their volcanic source and specific eruptions. This study has significantly extended the ash dispersal of many key Holocene marker layers, and has identified the first distal occurrence of isochrons from Ulleungdo and Changbaishan volcanoes. Utilising the high-precision Lake Suigetsu chronology, we are able to provide constrained eruption ages for the tephra layers, which can be transferred into other site-specific age models containing these markers. This new framework indicates that several isochrons stratigraphically bracket abrupt climate intervals in Japan, and could be used to precisely assess the regional and hemispheric synchronicity of these events.

Human response to habitat suitability during the Last Glacial Maximum in Western Europe

ABSTRACTThis research takes a multi‐dimensional approach to the study of the archaeological record of Western Europe during the Last Glacial Maximum (LGM), combining two distinct components of the human adaptive system (technological organization and mobility) to test the impact of environmental variability on the mobility of Upper Palaeolithic groups. To this end we make use of two models. The first predicts landscape suitability as a function of a suite of environmental variables including topography, climate and inter‐annual climate variability. The second model explores the link between patterns of mobility and technological organization, using lithic retouch frequencies as a proxy for mobility strategies. Combining detailed environmental and lithic data allows us to derive a clearer picture of human adaptation to environmental conditions during a particularly rigorous climatic interval in Western Europe. Our results show that while foragers generally favoured more suitable habitats, logistical mobility strategies were deployed across a wide spectrum of habitat suitability. Residential mobility strategies, on the other hand, tend to occur in relatively less suitable and thus inherently more variable habitats. We conclude that foragers made use of a predominantly logistic strategy during the LGM while adopting more residential strategies in response to local and relatively short‐term fluctuations in the environment. The approach adopted here offers several promising avenues for future research on the ecology of human groups during the LGM.

Reconstruction of Holocene hydroclimatic variability in subarctic treeline lakes using lake sediment grain-size end-members

Current climate trends are expected to result in the northward expansion of the subarctic treeline leading to changes in vegetation cover and permafrost distribution, as they did during the Holocene Climate Optimum when the treeline was 150 km north of its current position. The impacts of these changes on the region’s hydrology are still poorly understood. The grain-size distributions of treeline lake sediments provide an important proxy related to spring melt conditions that can be used to reconstruct hydroclimatic variability. End-member mixing analysis was used to model depositional end-members in 55 modern lake sediment samples and two sediment cores spanning the mid- to late Holocene collected from above and below the treeline in the central Northwest Territories, Canada. Cold climatic intervals (e.g. ‘Dark Ages Cold Period’, ‘Little Ice Age’) were characterised by an increase in the very coarse silt and the fine sand end-members. This was interpreted to be a response to degradation of vegetation cover and/or permafrost development. We observed increases in fine and coarse silt end-members during warmer climatic intervals (e.g. Medieval Climate Anomaly) and over the past c. 300 yr BP. This pattern is probably the result of extended melt seasons, with greater losses to evaporation and increased infiltration. The most pronounced palaeo-hydroclimatological change over the past c. 8000 yr BP was the abrupt increase in a very coarse silt end-member (mode = 50–200 µm) at c. 6300 yr BP. We interpreted the sedimentological change as an increase in winter precipitation and more energetic spring melt conditions, leading to the spring melt becoming the dominant lacustrine sediment delivery mechanism. These results place modern hydrological changes in a millennial context and show that analysis of temporal changes in the hydroclimatological system can provide insight into the future states of these sensitive subarctic ecosystems.

Oceanographic and Climatic Change in the Bering Sea, Last Glacial Maximum to Holocene

AbstractPost‐glacial sea level rise led to a direct connection between the Arctic and Pacific Oceans via the Bering Strait. Consequently, the Bering Sea experienced changes in connectivity, size, and sediment sources that were among the most drastic of any ocean basin in the past 30,000 years. However, the sedimentary response to the interplay between climate change and sea level rise in high‐latitude settings such as Beringia remains poorly resolved. To ascertain changes in sediment delivery, productivity, and regional oceanography from the Last Glacial Maximum (LGM) to the Holocene, we analyzed sedimentological, geochemical, and isotopic characteristics of three sediment cores from the Bering Sea. Interpretations of productivity, terrestrial input, nutrient utilization, and circulation are based on organic carbon isotopes (δ13Corg), total organic carbon (TOC), bulk nitrogen isotopes, total organic nitrogen, carbon/nitrogen ratios, elemental X‐ray fluorescence data, grain size, and presence of laminated or dysoxic, green intervals. Principal component analysis of these data captures key climatic intervals. The LGM was characterized by low productivity across the region. In the Bering Sea, deglaciation began around 18–17 ka, with increasing terrestrial sediment and TOC input. Marine productivity increased during the Bølling‐Allerød when laminated sediments revealed dysoxic bottom waters where denitrification was extreme. The Younger Dryas manifested increased terrestrial input and decreased productivity, in contrast with the Pre‐Boreal, when productivity markedly rebounded. The Pre‐Boreal and Bølling‐Allerød were similarly productive, but changes in the source of TOC and a δ13Corg depletion suggest the influence of a gradually flooding Bering Shelf during the Pre‐Boreal and Holocene.

Impact of an icehouse climate interval on tropical vegetation and plant evolution

Impact of an icehouse climate interval on tropical vegetation and plant evolution

Was the drought really responsible? Assessing statistical relationships between climate extremes and cultural transitions

It is commonplace to assert causal relationships between episodes of extreme climate with dramatic cultural shifts. We explore the problem of statistically assessing the correspondence between episodes of extreme climate (such as droughts) and cultural events (such as depopulation) they are purported to explain. In order to do this: 1) We describe a method that permits the objective identification of climate extremes in a way that is independent of their supposed causal outcomes; 2) We discuss how we identify and date cultural transitions of interest; 3) We explore a variety of decision rules for determining whether or not there is a match between a given extreme climate interval and the interval during which a transition began; and 4) We propose an intuitive Monte Carlo approach to statistically assess the observed correspondence between the climate extremes and the cultural transitions. Our application does not indicate statistical support for a linkage between intervals of extreme climate and major transitions in any of the seven cultural traditions in the Southwest US that we examined.

The Nature and Pace of Change in American Indian Cultures: Pennsylvania, 4000 to 3000 BP

The Nature and Pace of Change in American Indian Cultures: Pennsylvania, 4000 to 3000 BP

Late Pleistocene to Holocene paleoenvironmental evolution of Lake Hazar, Eastern Anatolia, Turkey

High-resolution seismic reflection profiles and core analyses in Lake Hazar provide a detailed record of the lake level fluctuations and the robust chronology of paleoclimatic events of the Eastern Anatolia during the late Pleistocene to Holocene. The earlier period of Marine Isotope Stage 3 (MIS-3) prior to 48 cal ka BP was accompanied by considerable lake level drop below −95 m, whereas the lake level increase during the later period (ca. 48-29 cal ka BP) gave rise to deposition of a transgressive unit with typical of aggradational architecture in the seismic reflection profiles. High climate variability with the Greenland interstadials and stadials (Dansgard-Oeschger and Heinrich events) in Lake Hazar are sensitively recorded in the core sediments by using multi-proxy analyses. Adjustment of seismic units correlating with the radiocarbon-dated chronostratigraphic units in the studied cores implies that the early Marine Isotope Stage 2 (MIS-2) is marked by an another lowstand lake level existed at ca. −90 m during 29–23 cal ka BP. In comparision to MIS-3 stage, the multi-proxy analyses reveal a general dry evaporative condition during most of the Last Glacial Maximum. In Lake Hazar, the maximum humidity in the late glacial period existed during 14.9–13.5 cal ka BP. The existence of a hiatus in the sedimentary record is documented in the seismic data that coincides with the cold and dry Younger Dryas period, implying a remarkable lake level drop. The multi-proxy records of the Holocene sediments reveal that a maximum precipitation in the early Holocene period prevailed during 10.1–9.3 cal ka BP, leading water level rise in the lake. In Lake Hazar, the middle Holocene until 4.9 cal ka BP is represented by highly climate variations, indicating a series of shorter wet and longer dry climate periods. The late Holocene is accompanied by lake level rises under a general wet climate condition that was interrupted by short dry climate intervals during 3.7–3.3 cal ka BP, 2.8–2.6 cal ka BP and 2.1–1.8 cal ka BP.

Paleoenvironmental and geomorphic significance of bluff-top dunes along the Au Sable River in Northeastern Lower Michigan, USA

We report on the age and evolution of five well-developed parabolic dunes that are perched on high (~40m) bluffs along the southern lip of the Au Sable River valley in northeastern Lower Michigan, U.S.A. These dunes are located on west/northwest-facing exposures and mantle the Jackpines Delta, which formed when the glacial Au Sable River system deposited sands and gravels into glacial Lake Warren in the Huron basin sometime between ~15.1 and 14.7ka. Lake level subsequently fell >35m as the ice margin retreated northward during the Twocreekan Interstadial. This regression resulted in abandonment of the Jackpines Delta and incision of the associated surface by the ancestral Au Sable River. Lake level subsequently rose ~50m during the Algonquin transgression, which likely promoted valley widening through channel migration. Eight samples were collected for OSL age determination of the dunes and yielded ages that suggest dune formation occurred mostly between ~13.5ka and 13ka. This result, coupled with the landscape position of the dunes (i.e., south side of river; west/northwest-facing bluffs) suggests that the dunes largely formed: 1) during the Algonquin transgression when bluffs were eroded by stream-channel migration, and 2) by west-northwesterly winds that transported eolian sands from exposed bluff faces to the adjacent valley edge. This study contributes to the understanding of perched-dune formation in the Great Lakes region and further supports models indicating that westerly winds prevailed within 150km of the ice margin during the late Pleistocene. It also demonstrates that interior dunes in this region formed in similar environmental settings to interior dunes in northern Europe and suggests that local factors, rather than specific climate intervals, should also be considered as they relate to dune evolution.

Atmospheric gas records from Taylor Glacier, Antarctica, reveal ancient ice with ages spanning the entire last glacial cycle

Abstract. Old ice for paleo-environmental studies, traditionally accessed through deep core drilling on domes and ridges on the large ice sheets, can also be retrieved at the surface from ice sheet margins and blue ice areas. The practically unlimited amount of ice available at these sites satisfies a need in the community for studies of trace components requiring large sample volumes. For margin sites to be useful as ancient ice archives, the ice stratigraphy needs to be understood and age models need to be established. We present measurements of trapped gases in ice from Taylor Glacier, Antarctica, to date the ice and assess the completeness of the stratigraphic section. Using δ18O of O2 and methane concentrations, we unambiguously identify ice from the last glacial cycle, covering every climate interval from the early Holocene to the penultimate interglacial. A high-resolution transect reveals the last deglaciation and the Last Glacial Maximum (LGM) in detail. We observe large-scale deformation in the form of folding, but individual stratigraphic layers do not appear to have undergone irregular thinning. Rather, it appears that the entire LGM–deglaciation sequence has been transported from the interior of the ice sheet to the surface of Taylor Glacier relatively undisturbed. We present an age model that builds the foundation for gas studies on Taylor Glacier. A comparison with the Taylor Dome ice core confirms that the section we studied on Taylor Glacier is better suited for paleo-climate reconstructions of the LGM due to higher accumulation rates.