Description: Publication date: 15 August 2018 Source: Quaternary Science Reviews, Volume 194 Author(s): Hannah L. Bailey, Darrell S. Kaufman, Hilary J. Sloane, Alun L. Hubbard, Andrew C.G. Henderson, Melanie J. Leng, Hanno Meyer, Jeffrey M. Welker The North Pacific is a zone of cyclogenesis that modulates synoptic-scale atmospheric circulation, yet there is a paucity of instrumental and paleoclimate data to fully constrain its long-term state and variability. We present the first Holocene oxygen isotope record (δ 18 O diatom ) from the Aleutian Islands, using siliceous diatoms preserved in Heart Lake on Adak Island (51.85° N, 176.69° W). This study builds on previous work demonstrating that Heart Lake sedimentary δ 18 O diatom values record the δ 18 O signal of precipitation, and correlate significantly with atmospheric circulation indices over the past century. We apply this empirical relationship to interpret a new 9.6 ka δ 18 O diatom record from the same lake, supported by diatom assemblage analysis. Our results demonstrate distinct shifts in the prevailing trajectory of storm systems that drove spatially heterogeneous patterns of moisture delivery and climate across the region. During the early-mid Holocene, a warmer/wetter climate prevailed due to a predominantly westerly Aleutian Low that enhanced advection of warm 18 O-enriched Pacific moisture to Adak, and culminated in a δ 18 O diatom maxima (33.3‰) at 7.6 ka during the Holocene Thermal Maximum. After 4.5 ka, relatively lower δ 18 O diatom indicates cooler/drier conditions associated with enhanced northerly circulation that persisted into the 21st century. Our analysis is consistent with surface climate conditions inferred from a suite of terrestrial and marine climate-proxy records. This new Holocene dataset bridges the gap in an expanding regional network of paleoisotope studies, and provides a fresh assessment of the complex spatial patterns of Holocene climate across Beringia and the atmospheric forces driving them.

Description: Publication date: 15 August 2018 Source: Quaternary Science Reviews, Volume 194 Author(s): Haixian Xiong, Yongqiang Zong, Peng Qian, Guangqing Huang, Shuqing Fu This study has collected and analyzed seven sediment cores from the Pearl River delta, from which 16 new and high-quality sea-level index points are generated using a new approach. This study has also re-checked and re-calibrated the previously published sea-level data from China's southeast coast with corrections made for tectonic subsidence and sediment compaction factors. These sea-level data indicate a rise of relative sea level from −49.3 ± 0.8 m to the present height between 10,500 and 7000 cal. a BP. This sea-level history is similar to those recorded from other far-field locations and ice-volume equivalent sea-level models. The early to early-middle Holocene sea-level history in the study area shows a phase of accelerated rise at a rate increasing rapidly from 16.4 ± 6.1 mm/a at 10,500 cal. a BP to 33.0 ± 7.1 mm/a at 9500 cal. a BP. This phase was followed by a period of rapid decrease in the rate of sea-level rise to 8.8 ± 1.9 mm/a at 8500 cal. a BP and 1.7 ± 1.3 mm/a at 7500 cal. a BP. During the past 7000 years, the relative sea level in the study area changed very little. This new and complete history of Holocene sea-level change supports the following findings: (1) no obvious higher-than-present sea-level highstand in the Holocene is found from the northern South China Sea; (2) certain proportion of the effects of the predicted glacial isostatic adjustment were cancelled out by the effects of the weak upper mantle viscosity in the study area; (3) meltwater pulse 1b likely exists spanning into the early Holocene; (4) there are significant misfit between sea-level data and glacial isostatic adjustment models, and a revision to the existing ice melting history for the early Holocene is possibly needed.

Description: Publication date: 1 August 2018 Source: Quaternary Science Reviews, Volume 193 Author(s): Emrys Phillips, Matteo Spagnolo, Alasdair C.J. Pilmer, Brice R. Rea, Jan A. Piotrowski, Jeremy C. Ely, Simon Carr This paper presents the results of a detailed microstructural study of a thick till formed beneath the Weichselian (Devensian) Odra palaeo-ice stream, west of Środa Wielkopolska, Poland. This SE-flowing ice stream was one of a number of corridors of faster flowing ice which drained the Scandinavian Ice Sheet in the Baltic region. Macroscopically, the massive, laterally extensive till which formed the bed of this ice stream lacks any obvious evidence of glaciotectonism (thrusting, folding). However, microscale analysis reveals that bed deformation was dominated by foliation development, recording progressive ductile shearing within a subhorizontal subglacial shear zone. Five successive generations of clast microfabric (S1 to S5) have been identified defining a set of up-ice and down-ice dipping Riedel shears, as well as a subhorizontal shear foliation coplanar to the ice-bed interface. Cross-cutting relationships between the shear fabrics record temporal changes in the style of deformation during this progressive shear event. Kinematic indicators (S-C and ECC-type fabrics) within the till indicate a consistent SE-directed shear sense, in agreement with the regional ice flow pattern. A model of bed deformation involving incremental progressive simple shear during till accretion is proposed. The relative age of this deformation was diachronous becoming progressively younger upwards, compatible with subglacial shearing having accompanied till accretion at the top of the deforming bed. Variation in the relative intensity of the microfabrics records changes in the magnitude of the cumulative strain imposed on the till and the degree of coupling between the ice and underlying bed during fast ice flow.

Description: Publication date: 1 August 2018 Source: Quaternary Science Reviews, Volume 193 Author(s): Maryam Yousefi, Glenn A. Milne, Ryan Love, Lev Tarasov We infer the GIA signal and its uncertainty along the central Pacific coast of North America using 680 sea-level index points and over 20,000 model runs sampling >700 (1-D) Earth viscosity models and 29 ice sheet reconstructions. Due to the large spatial extent and different tectonic settings of the study area, we divided it into three sub-regions (northern, central and southern) for which model parameters were inferred separately. Also, given that this region is tectonically active, the influence of this process (as well as sediment isostatic adjustment) was accounted for where possible by removing it from the data using published estimates. Our results indicate that it is not possible to produce an acceptable to for all of the RSL data with a single set of model parameters, suggesting significant lateral variability in viscous structure. Specifically, low viscosities (10 19 –10 20  Pas) are inferred in the upper mantle within the northern region (southwestern British Columbia and northwest Washington) compared to those inferred (2–5 × 10 20  Pas) for the central and southern regions (extending from southern Washington to southern California). High quality model fits were obtained for all data except those from the northern region where no single parameter set was able to capture both the rapid and large RSL fall during the late glacial and the monotonic rise during the mid-to-late Holocene at all localities. This suggests the need for an Earth model that incorporates departures from a linear Maxwell rheology (as applied here) and/or lateral variations in viscosity structure. Using our optimal model parameter sets, we show that GIA is a significant contributor to both contemporary vertical land motion and relative sea level change in our study region and so should be considered when interpreting observations of these signals and for making future relative sea level projections. Model output of present-day vertical land motion at 483 GPS stations and sea-level change at 56 tide gauge stations is provided (with estimated uncertainty) so that these data can be used to study non-GIA processes more accurately.

Description: Publication date: 1 August 2018 Source: Quaternary Science Reviews, Volume 193 Author(s): Cécile C. Remy, Cécile Fouquemberg, Hugo Asselin, Benjamin Andrieux, Gabriel Magnan, Benoît Brossier, Pierre Grondin, Yves Bergeron, Brigitte Talon, Martin P. Girardin, Olivier Blarquez, Lisa Bajolle, Adam A. Ali We present a comparative analysis of fire reconstructions from tree rings and from wood charcoal preserved in forest soils, peat and lake sediments. Our objective is to highlight the benefits and limits of different archives and proxies to reconstruct fire histories. We propose guidelines to optimize proxy and archive choice in terms of spatial and temporal scales of interest. Comparisons were performed for two sites in the boreal forest of northeastern North America. Compared to others archives, tree-ring analysis remains the best choice to reconstruct recent fires (〈1000 years). For longer periods (from several centuries to millennia), lake charcoal can be used to reconstruct regional or local fire histories depending on the method used, but the focus should be on historical trends rather than on the identification of individual fire events. Charcoal preserved in peat and soils can be used to identify individual fire, but sometimes cover shorter time periods than lake archives.

Description: Publication date: 1 August 2018 Source: Quaternary Science Reviews, Volume 193 Author(s): Michael N. Styllas, Irene Schimmelpfennig, Lucilla Benedetti, Mathieu Ghilardi In this study, we present a new glacial chronology based on 20 in situ -produced 36 Cl-based cosmic ray exposure datings from moraine boulders and bedrock from the Throne of Zeus (TZ) and Megala Kazania (MK) cirques on Mount Olympus. The 36 Cl derived ages of glacial landforms range from 15.6 ± 2.0 to 0.64 ± 0.08 ka, spanning the Late-glacial and the Holocene. The Late-glacial, recorded in both cirques, is partitioned in three distinct phases (LG1-3): an initial phase of moraine stabilization at 15.5 ± 2.0 ka with subsequent deglaciation starting at ∼14 ka (LG1), followed by a shift to marginal conditions for glaciation at 13.5 ± 2.0 ka (LG2), sustained by large amounts of wind-blown snow, despite regional warming. Glacial conditions returned at 12.5 ± 1.5 ka (LG3) and were characterized by low air temperatures and glacier shrinking. The Holocene glacial phases (HOL1-3) are recorded only in the MK cirque, likely due to its topographic attributes. An early Holocene glacier stillstand (HOL1) at 9.6 ± 1.1 ka follows the regional temperatures recovery. No glacier activity is observed during the mid-Holocene. The Late Holocene glacier expansions, include a moraine stabilization phase (HOL2) at 2.5 ± 0.3 ka, during wet conditions and solar insolation minima, while (HOL3) corresponds to the early part of the Little Ice Age (0.64 ± 0.08ka). Our glacial chronology is coherent with glacial chronologies from several cirques along the northeast Mediterranean mountains and in pace with numerous proxies from terrestrial and marine systems from the north Aegean Sea.

Description: Publication date: 1 August 2018 Source: Quaternary Science Reviews, Volume 193 Author(s): Wenhuo Liu, Xiaohua Gou, Jinbao Li, Yuxia Huo, Meixue Yang, Wei Lin Tree-ring width chronologies from the upper timberline are an important material to reconstruct past temperature variability on the northeastern Tibetan Plateau (NTP). However, precipitation signals are often encoded in the upper timberline chronologies, which complicate the temperature reconstructions and should be removed properly. Here, we propose to use the chronologies from the middle to lower forest zones to remove the precipitation signals encoded in the upper timberline chronologies on the NTP, as tree growth at the two elevation zones records similar precipitation signals but has different temperature responses. We compiled a dataset of 13 Qilian juniper ( Sabina przewalskii Kom.) tree-ring width chronologies, and employed two independent methods to develop millennial (AD 1000–2000) temperature reconstructions on the NTP. The two reconstructions are very consistent with each other over the past millennium, with a correlation of 0.97, and account for more than 50% of the observed temperature variance during 1958–2000. Both reconstructions contain little precipitation signals, suggesting that we have extracted purer temperature information than before. Our reconstructions show similar warm-cold patterns to the temperature records from the surrounding areas, indicating that they are capable of representing large-scale temperature variability during the past millennium. Comparison of our reconstructions with five millennial Northern Hemisphere (NH) temperature series indicates that temperature changes on the NTP are generally distinct from the NH temperature patterns except for the long-term trend during the past millennium, suggesting specific characteristics of regional temperature variability. The distinct variations may be related to the influence of local precipitation, which generally has inverse variations with the temperature on multi-decadal timescales. Our results also show that temperature variability on the NTP has a strong linkage with the strength of the Indian summer monsoon (ISM), with the warm and cool phases of NTP temperature associated with strong and weak ISM, respectively.

Description: Publication date: 1 August 2018 Source: Quaternary Science Reviews, Volume 193 Author(s): Jo McDonald, Wendy Reynen, Kane Ditchfield, Joe Dortch, Matthias Leopold, Birgitta Stephenson, Tom Whitley, Ingrid Ward, Peter Veth The Dampier Archipelago (including the Burrup Peninsula), now generally known as Murujuga, is a significant rock art province in north-western Australia which documents the transition of an arid-maritime cultural landscape through time. This archipelago of 42 islands has only existed since the mid-Holocene, when the sea level rose to its current height. Previous excavations across Murujuga have demonstrated Holocene occupation sequences, but the highly weathered rock art depicting extinct fauna and early styles suggests a far greater age for occupation and rock art production. The archaeological record from the Pilbara and Carnarvon bioregions demonstrates human occupation through 50,000 years of environmental change. While the regional prehistory and engraved art suggests that people were producing art here since they first occupied these arid rocky slopes, no clear evidence of Pleistocene occupation has been found across Murujuga, until now. Murujuga Rockshelter (MR1) reveals that occupation of this shelter began late in the Last Glacial Maximum, when the Murujuga Ranges would likely have served as one of a network of Pilbara refugia. In the terminal Pleistocene/Early Holocene, and likely in tandem with the last stages of sea level rise, the proportion of artefacts manufactured on exotic lithologies declines sharply, revealing a changed foraging range and increasing territorial focus in this period of increased demographic packing as the coastline advanced. Abandonment of the site as early as 7000 years ago is indicated, suggesting a changing resource focus to the increasingly proximal coastline. This paper provides the first evidence of how Aboriginal people adapted their Pleistocene procurement strategies in response to significant environmental and landscape changes in Murujuga. This changing logistical strategy provides an explanation for the increased rock art production in the terminal Pleistocene/Early Holocene.

Description: Publication date: 15 August 2018 Source: Quaternary Science Reviews, Volume 194 Author(s): T. Elliott Arnold, Aaron F. Diefendorf, Mark Brenner, Katherine H. Freeman, Allison A. Baczynski Hydrogen and carbon isotope values (δD & δ 13 C) were measured on lipid biomarkers from a sediment core collected in Lake Tulane, Florida, USA, to infer shifts in climate and hydrologic variables during the Last Glacial. Isotopic trends from 24 samples correlate with plant community shifts evaluated in a previous pollen study by Grimm et al. (2006). We observe maxima in Δ leaf values and minima in δD values concurrent with peaks in Pinus pollen abundances and Heinrich Events 4-2. Increased Δ leaf values during North Atlantic cold spells indicate lower water-use-efficiency among angiosperms around Lake Tulane. Combined δD values from terrestrial and aquatic lipids, confirm that aridity decreased during cold, stadial periods (Heinrich Events), and increased during warm, interstadials. Furthermore, lower δD values in aquatic lipids during stadials are attributed to warming, as well as changing moisture sources. The anti-phase relationship between temperatures and aridity derived from our subtropical lacustrine record and those at high latitude in the North Atlantic is likely the result of complex ocean-atmosphere teleconnections that resulted from the collapse of Atlantic Meridional Overturning Circulation during Heinrich Events in the North Atlantic.

Description: Publication date: 1 August 2018 Source: Quaternary Science Reviews, Volume 193 Author(s): Magali Delmas, Marc Calvet, Yanni Gunnell, Pierre Voinchet, Camille Manel, Régis Braucher, Hélène Tissoux, Jean-Jacques Bahain, Christian Perrenoud, Thibaud Saos The 120 km -longTêt River flows out of the Pyrenees to the Mediterranean. By displaying a mappable sequence of Quaternary alluvial units between the Pleistocene frontal moraines of the high range and the offshore sedimentary depocentres, its 1400 km 2 watershed is well suited to quantifying gradients of topographic uplift. Five main generations of terrace treads had previously been inferred from constrasts in regolith weathering features, but here we present the first radiometric age constraints based on 15 ESR sediment burial ages covering the full sequence, and 3 vertical TCN age profiles restricted to three mid-sequence terraces. Analytically robust results were obtained for the oldest and uppermost terrace T5 (ESR age: 1099 ± 179 ka), for T3b (ESR age: 374 ± 47 ka, ∼MIS 10), and for T2 (ESR age: 174 ± 44 ka, ∼MIS 6). These results are consistent with the contrasts in weathering grade of the deposits. The TCN profiles only yielded minimum exposure ages but provided precise post-depositional denudation rates for the fluvial terrace treads. The land-to-sea geometry of the chronosequence also provided clues about valley incision rates in response to topographic uplift during the last ∼1 Ma. Based on a critical review of similar data obtained for other Mediterranean and Atlantic watersheds in the Pyrenees, the full regional correlation reveals that post-orogenic topographic uplift was substantial and relatively uniform throughout the entire mountain range. Patterns and magnitudes suggest a shared, probably subcrustal driving mechanism of Neogene and Quaternary mountain growth, with only subsidiary influence from isostasy, and climatic forcing.