Showing papers in "Journal of Quaternary Science in 2017"

Holocene variability in sea ice cover, primary production, and Pacific‐Water inflow and climate change in the Chukchi and East Siberian Seas (Arctic Ocean)

Abstract: In this study, we present new detailed biomarker-based sea ice records from two sediment cores recovered in the Chukchi Sea and the East Siberian Sea. These new biomarker data may provide new insights on processes controlling recent and past sea ice changes. The biomarker proxy records show (i) minimum sea ice extent during the Early Holocene, (ii) a prominent Mid-Holocene short-term high-amplitude variability in sea ice,primary production and Pacific-Water inflow, and (iii) significantly increased sea ice extent during the last ca.4.5k cal a BP. This Late Holocene trend in sea ice change in the Chukchi and East Siberian Seas seems to be contemporaneous with similar changes in sea ice extent recorded from other Arctic marginal seas. The main factors controlling the millennial variability in sea ice (and surface-water productivity) are probably changes in surface water and heat flow from the Pacific into the Arctic Ocean as well as the long-term decrease in summer insolation. The short-term centennial variability observed in the high-resolution Middle Holocene record is probably related to solar forcing. Our new data on Holocene sea ice variability may contribute to synoptic reconstructions of regional to global Holocene climate change based on terrestrial and marine archives.

New age constraints for the limit of the British-Irish Ice Sheet on the Isles of Scilly

Abstract: The southernmost terrestrial extent of the Irish Sea Ice Stream (ISIS), which drained a large proportion of the last British–Irish Ice Sheet, impinged on to the Isles of Scilly during Marine Isotope Stage 2. However, the age of this ice limit has been contested and the interpretation that this occurred during the Last Glacial Maximum (LGM) remains controversial. This study reports new ages using optically stimulated luminescence (OSL) dating of outwash sediments at Battery, Tresco (25.5 ± 1.5 ka), and terrestrial cosmogenic nuclide exposure dating of boulders overlying till on Scilly Rock (25.9 ± 1.6 ka), which confirm that the ISIS reached the Isles of Scilly during the LGM. The ages demonstrate this ice advance on to the northern Isles of Scilly occurred at ∼26 ka around the time of increased ice-rafted debris in the adjacent marine record from the continental margin, which coincided with Heinrich Event 2 at ∼24 ka. OSL dating (19.6 ± 1.5 ka) of the post-glacial Hell Bay Gravel at Battery suggests there was then an ∼5-ka delay between primary deposition and aeolian reworking of the glacigenic sediment, during a time when the ISIS ice front was oscillating on and around the Llŷn Peninsula, ∼390 km to the north.

Late Quaternary environmental dynamics in the Atacama Desert reconstructed from rodent midden pollen records

Abstract: In the past two decades, much has been learned about the late Quaternary climate history of the Atacama Desert with some details still unclear about the seasonality, timing and extent of wet and dry phases. Modern climate studies reveal that, far from exhibiting a unique pattern, seasonal precipitation originates from many sources and mechanisms. For the last 16 ka, we attempt to sort out these complexities in pollen records from four fossil rodent midden series spanning 22°–25°S in northern Chile. Widespread wet conditions prevailed during the late Pleistocene and early Holocene, particularly between 13 and 9 ka, evidenced by <400 m lowering of pollen zones (plant communities) compared to today. Regional differences in the timing and magnitude of this displacement may be related to the prevailing source (tropical/extra-tropical) or mode (NNW/SE) of tropical precipitation through time. Wet conditions persisted well into the early Holocene, lasting ∼1–1.5 ka longer than previously suggested. The pollen record suggests extreme drying ∼8 ka, possibly associated with a northward shift of the Inter Tropical Convergence Zone, tracking minimum insolation values at subtropical latitudes during the austral summer. The establishment of conditions similar to today happened ∼4 ka. Copyright © 2017 John Wiley & Sons, Ltd.

Semi‐quantitative reconstruction of early to late Holocene spring and summer sea ice conditions in the northern Barents Sea

Abstract: Semi-quantitative estimates of early to late Holocene spring sea ice concentration (SpSIC) and occurrence of summer sea ice for the northern Barents Sea have been obtained by analysing the biomarkers IP25, brassicasterol and a tri-unsaturated highly branched isoprenoid lipid in a Holocene marine sediment core. Sub-surface water mass variations were derived from planktic foraminiferal assemblages and stable isotopes (δ18O, δ13C). The record indicates paleoceanographic changes over three intervals. During Period I (ca. 9500–5900 cal a BP), the study location experienced the lowest recorded SpSIC (ca. 25%) with short spring seasons and long productive summers, resulting partly from increased Atlantic Water inflow that caused a stronger ocean–atmosphere heat exchange. Throughout Period II (ca. 5900–2700 cal a BP), the winter sea ice margin migrated southwards and an overall cooling trend resulted in higher SpSIC (ca. 60%) and increased delivery of cold Arctic Water. During Period III (ca. 2700 cal a BP to present), SpSIC increased further (ca. 75%) and some sea ice remained during summer months. A sub-surface warming probably indicates a decoupling of heat exchange between the ocean and the atmosphere. Longer springs and shorter summers were accompanied by the most southerly location of the winter sea ice margin.

Dynamics of former ice lobes of the southernmost Patagonian Ice Sheet based on a glacial landsystems approach

Abstract: Reconstructions of former ice masses from glacial geomorphology help to constrain the nature and timing of glaciation in relation to climatic forcing. This paper presents a new reconstruction of the glacial history of five ice lobes in southernmost South America: the Bahia Inutil − San Sebastian, Magellan, Otway, Skyring and Rio Gallegos ice lobes. We use previous geomorphological mapping of glacial landforms to reconstruct former glacial limits and proglacial lakes, demarcate flow-sets from the distribution of glacial lineations, and evaluate glacial landsystem signatures and their palaeoglaciological implications. Evidence suggests that the ice lobes predominantly reflect active temperate glacial landsystems, which may have switched to polythermal systems when periods of cold-based ice developed ephemerally. This complex landsystem signature implies that the ice lobes were sensitive to regional climate variability, with active re-advances during overall retreat of the ice margins. There is also evidence for periods of fast ice flow and possible surge-like activity in the region, followed by the rapid retreat or even collapse of some of the ice lobes in association with proglacial lakes. Constraining our new reconstruction with published chronological information suggests that at least some of the ice lobes advanced before the global Last Glacial Maximum (gLGM: ca. 26.5–19 ka) during the last glacial cycle. Our new reconstruction demonstrates a more complex picture of ice dynamics than has previously been portrayed, and one in which the advance and retreat of the ice lobes was likely to have been primarily driven by changes in climate. As such, ice advances before the gLGM in the southernmost part of the Patagonian Ice Sheet are likely to indicate a wider climatic forcing at this time.

Glacial Lake Pickering: stratigraphy and chronology of a proglacial lake dammed by the North Sea Lobe of the British–Irish Ice Sheet

Abstract: We report the first chronology, using four new optically stimulated luminescence dates, on the sedimentary record of Glacial Lake Pickering, dammed by the North Sea Lobe of the British–Irish Ice Sheet during the Dimlington Stadial (24–11 ka cal BP). Dates range from 17.6 ± 1.0 to 15.8 ± 0.9 ka for the sedimentation of the Sherburn Sands at East Heslerton, which were formed by multiple coalescing alluvial fans prograding into the falling water levels of the lake and fed by progressively larger volumes of debris from the Wolds. Fan formation ceased ∼15.8 ka, at a time when permafrost was degrading and nival-fed streams were no longer capable of supplying sediment to the fans. A further age of 10.1 ± 0.7 ka dates the reworking of coversand into the early part of the Holocene, immediately post-dating Younger Dryas periglacial structures. A 45-m lake level dates to ∼17.6 ka, when the North Sea Lobe was already in retreat, having moved eastward of the Wykeham Moraine; it stood further east at the Flamborough Moraine by ∼17.3 ka. The highest (70 m) lake level and the occupation of the Wykeham Moraine date to an earlier phase of the North Sea Lobe occupation of the Vale of Pickering.

Short-term fluctuations in regional radiocarbon reservoir age recorded in coral skeletons from the Ryukyu Islands in the north-western Pacific

Abstract: Radiocarbon (14C) dating is a widely used and powerful tool for determining the ages of samples in studies of palaeoclimatology, palaeoseismology and archaeology. 14C ages of marine samples often require correction for local reservoir age (ΔR). Although ΔR in the mid- to low latitudes has varied through time, few spatiotemporal reconstructions of ΔR have been published for those regions. Here we report on new and previously published ΔR data for the early 1900s to 1950 obtained from coral skeletons from the Kuroshio region off southern Japan. The data presented here show a marked positive-to-negative shift of ΔR from the early 1900s to the 1940s, which has important implications for calibration of radiocarbon ages in the region and for understanding the relationship of ΔR in the western Pacific with both the El Nino–Southern Oscillation and the Pacific Decadal Oscillation.

The Middle Pleistocene glacial evolution of northern East Anglia, UK: a dynamic tectonostratigraphic–parasequence approach

Abstract: The Middle Pleistocene glacial history of northern East Anglia is a controversial topic with differing opinions surrounding chronology, provenance and the relative stratigraphic framework. Reconciling the stratigraphic framework of the region is an essential first step to developing onshore–offshore geological models and a robust event-driven chronological framework. Within this study a dynamic tectonostratigraphic–parasequence methodology is applied to deposits traditionally attributed to the Anglian Glaciation (Marine Isotope Stage 12). This approach offers an insight into ice-bed coupling during glaciation and how evolving boundary conditions influenced glacier dynamics. Six major tectonostratigraphic–parasequence assemblages (A1–A6) are recognized in northern East Anglia and correlate with successive advances into the region of North Sea or Pennine lobes of the British Ice Sheet. Individual tectonostratigraphic–parasequence assemblages are bound at their base by a sedimentary contact or, more commonly, a glacitectonic zone. The geometry and structural characteristics of these glacitectonic zones reflect temporal and spatial variations in ice-bed coupling (traction), a function of substrate rheology and, in turn, variations in lithology, porewater availability and thermo-mechanical properties. The role of permafrost may also be significant, promoting proglacial/ice-marginal thrust stacking in front of advancing ice and enhanced ice-bed decoupling during subsequent overriding and subglacial till accretion. © 2016 British Geological Survey, NERC Journal of Quaternary Science © 2016 John Wiley & Sons Ltd

Identifying remains of extinct kangaroos in Late Pleistocene deposits using collagen fingerprinting

Abstract: Our knowledge of past animal populations, including the geographical ranges of extinct species, has largely been derived from morphological analyses of skeletal fossil remains. However, a major barrier to the identification of the remains of extinct megafaunal species in archaeological and palaeontological sites is the highly fragmented nature of the material, which often precludes confident taxonomic identifications based on morphology. Biomolecular techniques are able to go beyond these limitations and are increasingly being used to make such identifications. Protein analysis offers a promising alternative to DNA techniques because they can be much cheaper, more amenable to high-throughput processing and work on much older specimens. Here we demonstrate the potential of collagen fingerprinting in an Australian context by extracting collagen from 50-ka kangaroo fossils from two caves in Tasmania, and identify several species including the extinct short-faced kangaroo Simosthenurus occidentalis. Importantly, of the five fossil bones sampled that had hitherto been ascribed morphology-based identifications below the family level, three had been incorrectly identified during an initial assessment of photographs taken in the field. Our results highlight the utility of using protein-based methods for making genus-level identification of marsupial bone, especially those that may form a basis for broader arguments such as that of late-surviving megafaunal species.

Evidence for late Middle Pleistocene glaciation of the British margin of the southern North Sea

Abstract: The timing and extent of late Middle Pleistocene glaciations in England and the southern North Sea are controversial topics. The recent Trent Valley Palaeolithic Project uncovered evidence for a post-Anglian, pre-Devensian glaciation that affected much of central and eastern England; the Wragby Till of Lincolnshire is associated with this glacial event, attributed here to Marine Oxygen Isotope Stage (MIS) 8. Coeval glacigenic deposits in the Middle Trent suggest that both western and eastern lobes of MIS 8 ice reached the Derby area. These various deposits have been assigned previously to MIS 12, 10 or 6, although the last can be excluded for the Wragby Till, which is overlain by Trent terrace deposits assigned to MIS 7 (from biostratigraphy and amino acid dating). The disposition of these glacigenic deposits within the landscape, particularly in relation to terrace deposits of the ancestral River Trent, and the absence of MIS 11 and 9 deposits within the footprint of the glaciation also provide compelling evidence. At its maximum extent in eastern England the MIS 8 ice reached the Peterborough area; identifying its extension (or otherwise) into areas such as north-west Norfolk and the West Midlands requires further work.

Interpreting exposure ages from ice-cored moraines: a Neoglacial case study on Baffin Island, Arctic Canada

Abstract: 10Be dating of moraines has greatly improved our ability to constrain the timing of past glaciations and thus past cold events. However, the spread in ages from a single moraine is often greater than would be expected from measurement uncertainty, making paleoclimatic interpretations equivocal. Here we present 28 new 10Be ages from ice-cored Neoglacial moraines on Baffin Island, Arctic Canada, and explore the processes at play in moraine formation and evolution through field observations and a numerical debris-covered glacier model. The insulating effect of debris cover modifies glacier lengths and results in the development of ice-cored moraines over multiple advances and thousands of years. Although ice cores can persist for several millennia, spatially variable ice core melt-out contributes to moraine degradation and boulder destabilization, making it likely that the 10Be clock is reset on moraine boulders in these settings. Thus, exposure ages from ice-cored moraines must be interpreted with caution. The oldest ages, after excluding samples with inheritance, provide the best estimates of initial moraine formation. Three Baffin Island moraines yield 10Be ages suggesting formation at 5.2, 4.6 and 3.5 ka, respectively, adding to a growing body of evidence for significant summer cooling millennia before the Little Ice Age.

Glacial landforms and their implications for glacier dynamics in Rijpfjorden and Duvefjorden, northern Nordaustlandet, Svalbard

Abstract: Observations of subglacial landforms yielding the configuration and dynamics of former ice-flows have for the first time been made in Rijpfjorden and Duvefjorden, Nordaustlandet, Svalbard, using sub-bottom acoustic, swath-bathymetric data and sediment cores. Five acoustic-stratigraphic units were distinguished suggesting the presence of a complete glacial–postglacial succession in the central fjord basins. 14C ages from the sediments indicate that the inner Rijpfjorden and central Duvefjorden were deglaciated before ca. 10.6 cal ka BP and 11.0 cal ka BP, respectively. Maximum sediment thickness in Rijpfjorden and Duvefjorden is 26 m, resulting in sediment accumulation rates of ca. 66 cm ka−1. The landform record suggests that the ice streaming in both fjords was topographically controlled. The considerably deeper basin and higher elongation ratios of the crag-and-tails in Duvefjorden are linked to the faulted bedrock and possibly to somewhat larger ice stream and/or more focused ice-flow compared to that in Rijpfjorden. De Geer moraines suggest slower retreat of a grounded ice margin from shallow areas of Rijpfjorden. In deeper areas of the fjords, the glaciers were probably floating, resulting in the lack of ice-marginal transverse landforms. The ice margin retreat from these areas was probably relatively rapid and dominated by calving.

New ages for the Upper Palaeolithic site of Xibaimaying in the Nihewan Basin, northern China: implications for small-tool and microblade industries in north-east Asia during Marine Isotope Stages 2 and 3

Abstract: It has been suggested that the ‘small-tool’ and microblade Upper Palaeolithic industries coexisted in the Nihewan Basin of northern China for about 8–14 000 years during Marine Isotope Stage (MIS) 2. This inference was based on uranium-series ages of around 15 and 18 ka for bovid teeth recovered from the ‘latest’ small-tool site of Xibaimaying – the youngest occurrence of such tools in the region – and optically stimulated luminescence (OSL) dating of the earliest typical microblade site (Youfang: ∼26–29 ka). In this study, we re-dated the Xibaimaying site using single-grain OSL methods and the resulting ages indicate that the cultural layer was deposited 46 ± 3 ka ago, during MIS 3 – more than 20 millennia earlier than previously thought and older also than the so-called earliest ‘primitive’ and typical microblade tools found at Zhiyu (∼31–39 ka cal BP) and Youfang. These new ages for human occupation of Xibaimaying remove support for the parallel development of the small-tool and microblade industries in the Nihewan Basin during the Upper Palaeolithic, but reliable age estimates from additional sites are needed to confidently infer the nature of the chronological relationship between these two Upper Palaeolithic industries and the associated toolmakers.

3D microstructural architecture of deformed glacigenic sediments associated with large‐scale glacitectonism, Jasmund Peninsula (NE Rügen), Germany

Abstract: The Wissower Bach Syncline on the Jasmund Peninsula (NE Germany) has been examined to understand the complicated glacitectonic environment in the southern Baltic Sea region, comprising folds and thrust faults from the Weichselian–Pleniglacial. Soft-sediment thin sections from a SW-dipping thrust fault at the south-western limb of the syncline between Cretaceous chalk (hangingwall) and Pleistocene deposits (footwall) were analysed using micromorphology and microstructural mapping. Within the diamicton bounding the fault, three different clast microfabrics were distinguished: an older, but dominant S1 fabric; a second S2 foliation orientated perpendicular to S1; and a younger subvertical S3 fabric. These fabrics developed during large-scale folding and thrusting, subsequent fabric rotation adjacent to the thrust fault accompanied by dewatering of the diamicton and extension; the extension implies late-stage reactivation and gravitational relaxation at the south-western limb of the syncline as the ice retreated. The combination of a 3D microstructural model and the macroscale information has led to the development of a detailed model for the evolution of the Wissower Bach Syncline during glacitectonism and the localized reactivation of the associated thrusts in response to ice retreat. Moreover, this methodology provides a robust dataset on which to interpret the structural evolution of glacitectonic complexes.

Mid‐Pleistocene thin‐skinned glaciotectonic thrusting of the Aberdeen Ground Formation, Central Graben region, central North Sea

Abstract: This paper presents the results of a high-resolution 2D seismic survey of mid-Pleistocene glaciogenic sediments in the Central Graben region of the central North Sea. Sediments have undergone major glaciotectonic thrusting and folding associated with the repeated southerly advance of a mid-Pleistocene ice sheet. The total observed length of the thrust-stacked section is approximately 5–6 km, comprising a series of discrete thrust slices, which range in length from 700 m. The basal detachment of the thrust complex occurs at a depth of ca. 220 m below the sea bed within the upper Aberdeen Ground Formation. A thin-skinned glaciotectonic model involving proglacial to ice-marginal glaciotectonic thrusting followed by post-tectonic deposition is proposed. Initial ice advance led to the over-pressurizing of groundwater within a laterally extensive sand sheet in the upper Aberdeen Ground Formation, promoting the formation of a major decollement surface at the base of the developing thrust-stack. Over-pressurization of the groundwater system is thought to have occurred in response to rapid ice advance, suggesting that the development of large-scale thrust complexes may be associated with surge-type behaviour. The proposed model evidences complex dynamics of mid-Pleistocene ice sheets within the central North Sea.

Younger Dryas glaciers and climate in the Mourne Mountains, Northern Ireland

Abstract: Here, we present evidence to suggest that the Mourne Mountains, Northern Ireland, were last occupied by glaciers during the Younger Dryas Stadial. The margins of these glaciers are marked by moraines, chronologically constrained to the Younger Dryas by Schmidt hammer exposure dating. Reconstructions indicate that these glaciers had equilibrium-line altitudes (ELAs) ranging from 356 ± 33 m (a.s.l.) to 570 ± 9 m (a.s.l.), with a mean of 475 ± 36 m (a.s.l.). ELAs rise from west to east, probably reflecting the contribution of windblown snow and ice to the accumulation of Younger Dryas glaciers in the western Mournes. Taking this into consideration, a mean ‘climatic’ ELA of 529 ± 4 m (a.s.l.) is calculated for the mountains as a whole. Assuming a mean annual sea level air temperature of −8 °C, and an annual temperature range of 34 °C, degree-day modelling suggests that during the Younger Dryas, accumulation at the ‘climatic’ ELA of glaciers in the Mournes was 846–990 mm a−1. This suggests increased aridity, relative to present, and is consistent with other parts of NW Europe, where reduced precipitation alongside notable cooling is thought to reflect increased North Atlantic sea ice extent during the Younger Dryas.

Late Holocene glacier reconstruction reveals retreat behind present limits and two‐stage Little Ice Age on subantarctic South Georgia

Abstract: Observational data show that climate in the Southern Ocean region is rapidly changing. However, past the instrumental period, our understanding of climate variability in the region is limited by a scarcity of highresolution palaeoclimate records. Alpine glaciers, present on many Southern Ocean islands, may provide such data because changes in their mass balance, extent and erosion rates often mark a response to climate shifts. Rock flour, the fine-grained fraction of the glacial erosion process, is suspended in meltwater streams and transferred into the sediments of downstream lakes, continuously recording glacier variations. Here, we utilize this relationship to present a reconstruction of the Late Holocene glacier history of subantarctic South Georgia, using sediments from the glacier-fed Middle Hamberg Lake. To fingerprint a glacial erosion/size signal, we used titanium counts, validated against changes in sediment density and grain size, allowing a continuous reconstruction of glacier variations over the past similar to 1250 years. Together with local moraine evidence and supporting evidence from other Southern Hemisphere glaciers on New Zealand and in Patagonia, our findings reveal a series of consecutively diminishing Late Holocene advances. In addition to a glacier maximum before 1250 cal a BP, these include a twostage Litle Ice Age with advances around 300 and 120 cal a BP, in line with evidence from southern Patagonia. In addition, we present evidence for an unreported retreat behind present limits around 500 cal BP.

Cosmogenic 10Be surface exposure dating and glacier reconstruction for the Last Glacial Maximum in the Quemuqu Valley, western Nyainqentanglha Mountains, south Tibet

Abstract: The nature and timing of glaciations enable inferences to be made about glacial climates. However, the paucity of reliable glacial chronologies impedes a full understanding of the Last Glacial Maximum (LGM) climate in the western Nyainqentanglha Mountains, south Tibet. In this study, we investigated the LGM glacial history in the Quemuqu Valley, western Nyainqentanglha, using 10Be surface exposure dating. We used a physically based glacier model to reconstruct the LGM glacial surfaces, and estimated the LGM equilibrium-line-altitude (ELA) using integrated methods. Combined with previously published 10Be exposure ages from the western Nyainqentanglha, ten 10Be exposure ages imply a relatively restricted glacial extent in the LGM but extensive growth in the early last glacial. The modeled LGM glaciers had ice areas of ∼36.3 km2, 3.21 km3 in volume and 89 m m in average thickness in the Quemuqu Valley. The reconstructed LGM ELAs have values of 5463–5583 m asl, with a depression of ∼244–364 m. By combining the reconstructed ELAs with an equation deduced from glacier mass balance, we concluded that the temperature dropped by ∼2.6–4.6 °C in the LGM relative to the present, with 30–70% lower precipitation than the present. Global cooling induced the LGM glacial advance in the western Nyainqentanglha despite decreased precipitation.

Contrasting evidence of Holocene ice margin retreat, south‐western Greenland

Abstract: Constraining the Greenland Ice Sheet's (GrIS) response to Holocene climate change provides calibrations for ice sheet models that hindcast past ice margin fluctuations. Ice sheet models predict enhanced ice retreat in south-western Greenland during the middle Holocene; however, few geological observations corroborating the extensive retreat are available. We present new data from lake sediment cores from the Isua region, south-western Greenland, which provide constraints on Holocene fluctuations of the GrIS margins. Our data indicate that the main GrIS margin was 30 km west of its present-day extent by ∼5.7k cal a BP and had retreated to within 3 km of its present-day margin by ∼4.6k cal a BP; with subsequent re-advances by ∼1.8 and at ∼1.7, ∼1.3 and ∼0.5k cal a BP. Times of ice retreat are coeval with increasing temperatures in western Greenland, suggesting that temperature was a dominant factor in ice retreat. The late retreat at Isua is in contrast to the early retreat observed in the Godthabsfjord area and is probably related to the lack of fjords extending to the present Isua ice margin. Our data are not consistent with current ice sheet models that overestimate the middle Holocene ice retreat in the Isua region of south-western Greenland.

Reconstructing late Holocene relative sea‐level changes at the Magdalen Islands (Gulf of St. Lawrence, Canada) using multi‐proxy analyses

Abstract: Proxy records of late Holocene relative sea-level changes are important for our understanding of mechanisms that drive contemporary sea-level trends. In the Gulf of Saint Lawrence (eastern Canada), the Magdalen Islands currently experience higher than global average rates of relative sea-level rise. This article presents original reconstruction data of sea-level changes from the Magdalen Islands over the past few millennia collected from a variety of coastal deposits and proxy records including salt-marsh foraminifera, testate amoebae and plant macrofossils. Reconstructed late Holocene relative sea-level trends are between 1.3 and 2.0mm a 1 for the past 2000 years. When combined with contemporaneous trends in tide-gauge data from Cap-aux-Meules (Magdalen Islands), multi-proxy data show acceleration in the rate of relative sea-level rise to over 4mm a 1 during the 20th century. This signal corresponds to similar inflexions also registered in salt marshes and tide-gauge data along the east coast of North America. Copyright # 2017 John Wiley & Sons, Ltd.

Comprehensive analysis of nanodiamond evidence relating to the Younger Dryas Impact Hypothesis

Abstract: During the end of the last glacial period in the Northern Hemisphere near 12.9k cal a BP, deglacial warming of the Bolling–Allerod interstadial ceased abruptly and the climate returned to glacial conditions for an interval of about 1300 years known as the Younger Dryas stadial. The Younger Dryas Impact Hypothesis proposes that the onset of the Younger Dryas climate reversal, Pleistocene megafaunal extinctions and disappearance of the Clovis paleoindian lithic technology were coeval and caused by continent-wide catastrophic effects of impact/bolide events in North America. While there are no known impact structures dated to the Younger Dryas onset, physical evidence of the impact/bolide events is argued to be present in sediments spanning several continents at stratigraphic levels inferred to date to the Bolling-Allerod/Younger Dryas boundary (YDB). Reports of nanometer to submicron-sized diamonds in YDB sediments, in particular the rare 2H hexagonal polytype of diamond, lonsdaleite, have been presented as strong evidence for shock processing of crustal materials. We review the available data on diamonds in sediments and provide new data. We find no evidence for lonsdaleite in YDB sediments and find no evidence of a spike in nanodiamond concentration at the YDB layer to support the impact hypothesis.

Glacial fluctuations around the Karola Pass, eastern Lhagoi Kangri Range, since the Last Glacial Maximum

Abstract: Mountain glaciers are sensitive to climate change, especially in climatic transition zones. We investigated Late Quaternary glacial history in two valleys around the Karola Pass of the eastern Lhagoi Kangri Range, central Himalaya, using cosmogenic 10Be surface exposure dating. Four glacial events were dated to 0.36 ± 0.09 to 0.13 ± 0.02 ka (LIA = Little Ice Age), 2.5 ± 0.2 ka (Neoglacial), 9.7 ± 0.4 to 8.2 ± 0.4 ka (Early Holocene) and 23.1 ± 0.9 to 16.3 ± 0.7 ka (LGM-LG, LGM = Last Glacial Maximum; LG = Lateglacial). The extent of glacier coverage has reduced successively since the LGM-LG, when ice coverage was about 2.69 times larger than at present (∼2010 CE). Equilibrium line altitude (ELA) values dropped 360, 265, 195 and 120 m during the LGM-LG, Early Holocene, Neoglacial and LIA, respectively, compared to the present value. These glacial events were broadly synchronous with other areas in the central Himalaya. It is likely that climate cooling was the major driver of glacial fluctuations during the LGM-LG. Abrupt and short-lived cooling phases, as well as increased Indian monsoonal precipitation, resulted in glacial expansions or standstills during the Early Holocene. In addition, cold and wet climatic conditions were attributed to the Neoglacial and LIA glacial events in this area.

Persistence of wetlands on North Stradbroke Island (south‐east Queensland, Australia) during the last glacial cycle: implications for Quaternary science and biogeography

Abstract: Few Australian wetlands have persisted since the Last Glacial Maximum, with fewer still in existence through the entire last glacial cycle. The absence of wetlands, which itself indicates periods of moisture deficit, means there are few continuous climate and environmental change records covering this critical period. The lack of wetland persistence also raises the question of how plant and animal species that require permanent wetlands survived the last glacial cycle. Sixteen wetlands have been cored and dated on North Stradbroke Island (Minjerribah) – a large east Australian sand island – with basal dates reported from 10 sites for the first time. These wetlands range in age to over 200 000 years old, with six dating to the Last Glacial Maximum or earlier. There is no evidence of a stratigraphic discontinuity in the radiocarbon-based age–depth profiles, suggesting continuous deposition of highly organic sediment through the period covered by these ages (c. 40 ka). The persistence of these wetlands suggests that for much of the last 40 000 years, and for perhaps much longer, the regional moisture balance has been positive. Over the last glacial cycle, persistently wet conditions may have provided a refuge from regional drying, and thus contributed to the high genetic diversity of rainforest plants in the region. Vegetation and climate records from these sites will allow hypothesis testing about the drivers of both local and regional climate variability. Copyright © 2017 John Wiley & Sons, Ltd.

The sedimentary history of the inner‐alpine Inn Valley, Austria: extending the Baumkirchen type section further back in time with new drilling

Abstract: The Baumkirchen clay pit near Innsbruck, western Austria, is a well-known site in Alpine Quaternary stratigraphy. Lacustrine sediments from the last glacial cycle from within the Alps provide a unique opportunity to investigate the regional palaeoclimate. Recent drilling has extended the known sequence to a total length of at least 250 m consisting of almost entirely well-laminated clayey silt. Luminescence dating identified two lake sequences, separated by a hiatus of ca. 7000–15 000 years. Lake phase 1 spans the period ca. 77–55 ka, i.e. from about Marine Isotope Stage (MIS) 5/4 to the MIS 4/3 transition. Lake phase 2 extends from mid- to late MIS 3 between ca. 45 and 33 ka. Down-core X-ray fluorescence core scanning confirmed the presence of the lake phases in the sediment composition, suggesting different sediment sources and/or transport mechanisms during these two intervals. A unique section of exotic, angular, silt matrix-supported gravel at the top of lake phase 1 is interpreted as ice-rafted debris. Luminescence dating constrains this layer to ca. 55 ka, thus providing the first evidence of a late MIS 4 or early MIS 3 ice advance confined to the interior of the Eastern Alps. A conceptual model of the sedimentary history of the valley is presented.

Quaternary evolution of the northern North Sea margin through glacigenic debris‐flow and contourite deposition

Abstract: The Norwegian Channel Ice Stream of the Scandinavian Ice Sheet extended across the northern North Sea margin during the mid- to late Quaternary, eroding older sediment from the continental shelf. Consequently, little is known about early Quaternary sedimentation on this margin. We use two- and threedimensional seismic-reflection data to investigate changing sediment volumes and sources in the northern North Sea through the Quaternary. The northern North Sea Basin was infilled during the early Quaternary by intercalated glacigenic debris-flows and contourites, which provide a record of the delivery of glacigenic sediment to the slope and the intensity of North Atlantic thermohaline circulation during early Quaternary glacial ± interglacial cycles. The infilling of the basin reduced accommodation and led to the deflection of mid- to late Quaternary sediments into the Norwegian Sea, forming the North Sea Fan. Close to the onset of the mid-Quaternary, the south-western Scandinavian Ice Sheet margin was drained by an ice stream located beneath Maluy Plateau, 60 km east of the Last Glacial Maximum Norwegian Channel Ice Stream. The southward-flowing Norwegian Sea Bottom Water current was directed into the partially filled northern North Sea Basin during the early Quaternary, and deflected progressively northwards as the basin became infilled.

Last Glacial pollen–climate reconstructions from Northland, New Zealand

Abstract: Despite wide-ranging interest in the vegetation and climate of Northland, New Zealand, during the last glacial cycle, the region and timeframe lack quantitative climate reconstructions while land-based pollen records have tended to be poorly dated and fragmentary. The region is also important for geochronology due to the co-occurrence of the Rotoehu tephra, a widely dispersed isochron near the current limits of radiocarbon dating, and extensive subfossil wood remains of Agathis australis, with strong dendrochronological and dendroclimatological potential. We present new pollen records and temperature reconstructions from three sites set in coastal dune belts from western mid-Northland (∼35°S), all containing Rotoehu tephra, that collectively span the last 70 ka. The phases and amplitude of temperature changes broadly align with those reported from elsewhere in New Zealand and with marine isotope climate–stratigraphic records, including maximum temperature depression of 6–8 °C during the last glacial maximum. We argue that these climatic patterns are intimately linked to shifts in the southern westerly wind belt, the northern margins of which extend to the region today. Correspondence between the Northland temperature shifts and atmospheric CO2 supports the model of ocean–atmosphere CO2 flux modulated by latitudinal migration of the southern westerlies. Copyright © 2017 John Wiley & Sons, Ltd.

Middle to Late Devensian glaciation of north‐east Scotland: implications for the north‐eastern quadrant of the last British–Irish ice sheet

Abstract: We present a review of over 175 years of research into the Middle to Late Devensian (Weichselian) glaciation of north-east Scotland based crucially on both its lithostratigraphic and geomorphic records. The location of the region, and surrounding seabed, makes this unusually detailed record significant for deciphering the former interactions and dynamics of Scottish and Scandinavian ice within the North Sea Basin (NSB), which continue to be controversial. A twelve-stage event stratigraphy is proposed based on a parsimonious interpretation of stratigraphic relationships, till lithology and regional clast fabrics, striae, subglacial bedforms, ice-marginal features and published geochronometry at critical sites. The record of regional glaciation supports converging evidence that the north-eastern quadrant of the last British and Irish Ice Sheet (BIIS) reached its maximum spatial extent in the late Middle- to early Late Devensian and later re-expanded following widespread internal glacial reorganisations, marine transgression and partial retreat from the central NSB. Retreat was interrupted by several glacial readvances of limited extent. Field-captured data helps identify important events that are not clearly resolved from remote sensing alone, particularly regarding growth phases of the last glaciation.