Hydroclimatic changes in the British Isles through the Last-Glacial-Interglacial Transition:Multiproxy reconstructions from the Vale of Pickering, NE England

European paleoenvironmental records through the Last Glacial-Interglacial Transition (LGIT; ca 16-8 cal ka BP) record a series of climatic events occurring over decadal to multi-centennial timescales. Changes in components of the climatic system other than temperature (e.g. hydrology) through the LGIT are relatively poorly understood however, and further records of hydroclimatic changes are required in order to develop a more complete understanding on the phasing of environmental and anthropogenic responses in Europe to abrupt climate change. Here, we present a multiproxy palaeoenvironmental record (macroscale and microscale sedimentology, macrofossils, and carbonate stable isotopes) from a palaeolake sequence in the Vale of Pickering (VoP), NE England, which enables the reconstruction of hydroclimatic changes constrained by a radiocarbon-based chronology. Relative lake-level changes in the VoP occurred in close association (although not necessarily in phase) to threshold shifts across abrupt climate change transitions, most notably lowering during cooling intervals of the LGIT (∼GI-1d, ∼GI-1b, and ∼GS-1). This reflects more arid hydroclimates associated with these cooling episodes in the British Isles. Comparisons to hydrological records elsewhere in Europe show a latitudinal bifurcation, with Northern Europe (50–60°N) becoming more arid (humid), and Southern Europe (40–50°N) becoming more humid (arid) in response to these cooling (warming) intervals. We attribute these bifurcating signals to the relative positions of the Atlantic storm tracks, sea-ice margin, and North Atlantic Polar Front (NAPF) during the climatic events of the LGIT

High resolution Late-glacial and early-Holocene summer air temperature records from Scotland inferred from Chironomid assemblages

Lateglacial and early-Holocene mean July air temperatures have been reconstructed, using a chironomid-based inference model, from lake-sediment sequences from Abernethy Forest, in the eastern Highlands of Scotland, and Loch Ashik, on the Isle of Skye in north-west Scotland. Chronology for Abernethy Forest was derived from radiocarbon dates of terrestrial plant macrofossils deposited in the lake sediments. Chronology for Loch Ashik was derived from tephra layers of known ages, the first age-depth model of this kind. Chironomid-inferred temperatures peak early in the Lateglacial Interstadial and then gradually decline by about 1 °C to the beginning of the Younger Dryas (YD). At Abernethy Forest, the Lateglacial Interstadial is punctuated by three centennial-scale cold oscillations which appear to be synchronous with the Greenland Interstadial events GI-1d, when temperatures at Abernethy fell by 5.9 °C, GI-1c, when temperatures fell by 2.3 °C, and GI-1b, when temperatures fell by 2.8 °C. At Loch Ashik only the oscillation correlated with GI-1d is clearly defined, when temperatures fell by 3.8 °C. The start of the YD is clearly marked at both sites when temperatures fell by 5.5 °C at Abernethy Forest and 2.8 °C at Loch Ashik. A warming trend is apparent during the late-YD at Abernethy Forest but at Loch Ashik late-YD temperatures became very cold, possibly influenced by its close proximity to the Skye ice-field. The rapidly rising temperatures at the YD – Holocene transition occur about 300 years earlier at both sites than changes in sediment lithology and loss-on-ignition. The temperature trends at both sites are broadly similar, although between-site differences may result from the influence of local factors. Similar climate trends are found at other sites in the northern British Isles. However, the British summer temperature records differ in detail from trends in the oxygen-isotope records from the Greenland ice-cores and from other chironomid-inferred temperature records available from Scandinavia, north-west Europe and central Europe, which suggest important differences in the influence of climatic forcing at regional scales.publishedVersio

First evidence of cryptotephra in palaeoenvironmental records associated with Norse occupation sites in Greenland

The Norse/Viking occupation of Greenland is part of a dispersal of communities across the North Atlantic coincident with the supposed Medieval Warm Period of the late 1st millennium AD. The abandonment of the Greenland settlements has been linked to climatic deterioration in the Little Ice Age as well as other possible explanations. There are significant dating uncertainties over the time of European abandonment of Greenland and the potential influence of climatic deterioration. Dating issues largely revolve around radiocarbon chronologies for Norse settlements and associated mire sequences close to settlement sites. Here we show the potential for moving this situation forward by a combination of palynological, radiocarbon and cryptotephra analyses of environmental records close to three ‘iconic’ Norse sites in the former Eastern Settlement of Greenland – Herjolfsnes, Hvalsey and Garðar (the modern Igaliku). While much work remains to be undertaken, our results show that palynological evidence can provide a useful marker for both the onset and end of Norse occupation in the region, while the radiocarbon chronologies for these sequences remain difficult. Significantly, we here demonstrate the potential for cryptotephra to become a useful tool in resolving the chronology of Norse occupation, when coupled with palynology. For the first time, we show that cryptotephra are present within palaeoenvironmental sequences located within or close to Norse settlement ruin-groups, with tephra horizons detected at all three sites. While shard concentrations were small at Herjolfsnes, concentrations sufficient for geochemical analyses were detected at Igaliku and Hvalsey. WDS-EPMA analyses of these tephra indicate that, unlike the predominantly Icelandic tephra sources reported in the Greenland ice core records, the tephra associated with the Norse sites correlate more closely with volcanic centres in the Aleutians and Cascades. Recent investigations of cryptotephra dispersal from North American centres, along with our new findings, point to the potential for cryptotephra to facilitate hypothesis testing, providing a key chronological tool for refining the timing of Norse activities in Greenland (e.g. abandonment) and of environmental contexts and drivers (e.g. climate forcing)

Reply to comments by Bourgois et al. (2019) on: “Glacial lake evolution and Atlantic-Pacific drainage reversals during deglaciation of the Patagonia Ice Sheet”

We welcome the comments of Bourgois et al. (2019) and the opportunity to debate geomorphology, geochronology and palaeoclimate during the Late Glacial Interglacial Transition (LGIT, ~18.0-8.0 ka) in the region of the Río Baker, central Patagonia. Bourgois et al. (2019) conclude that we have propagated inconsistencies in our proposed reconstruction of palaeolake evolution due to geomorphic analytical bias. However, in our view the empirical geomorphological data we have compiled over many field seasons has resulted in a data-rich (though still incomplete) relative chronology that enables us to evaluate inconsistencies in landscape interpretations from previously published geochronological datasets. We would argue that a geochronological bias, over any geomorphological bias, has represented the main reason for multiple landscape interpretations in this region. Indeed, the conflicting palaeolake evolution models published for the Río Baker basin (Turner et al. 2005; Bell, 2008; Hein et al., 2010; Bourgois et al., 2016; Glasser et al., 2016; Martinod et al., 2016) was a major impetus for our paper. These contrasting models were in part a result of the coincident publication of two separate geochronological datasets in 2016, one focused on optically stimulated luminescence (OSL) dating of palaeolake landforms (Glasser et al., 2016), the other cosmogenic nuclide exposure ages (Bourgois et al., 2016). Both datasets provided updates on what we termed the Turner/Hein model in Thorndycraft et al. (2019), but as they did not have access to each other’s datasets they ended up with different landscape interpretations

Reply to comments by Bourgois et al. (2019) on: “Glacial lake evolution and Atlantic-Pacific drainage reversals during deglaciation of the Patagonia Ice Sheet”

No abstract available

Spherical probes at ion saturation in E × B fields

The ion saturation current to a spherical probe in the entire range of ion magnetization is computed with SCEPTIC3D, a newthree-dimensional version of the kinetic code SCEPTIC designed to study transverse plasma flows. Results are compared with prior two-dimensional calculations valid in the magneticfree regime (Hutchinson 2002 Plasma Phys. Control. Fusion 44 1953), and with recent semi-analytic solutions to the strongly magnetized transverse Mach probe problem (Patacchini and Hutchinson 2009 Phys. Rev. E 80 036403). At intermediate magnetization (ion Larmor radius close to the probe radius) the plasma density profiles show a complex three-dimensional structure that SCEPTIC3D can fully resolve, and, contrary to intuition, the ion current peaks provided the ion temperature is low enough. Our results are conveniently condensed in a single factor M[subscript c], function of ion temperature and magnetic field only, providing the theoretical calibration for a transverse Mach probe with four electrodes placed at 45◦ to the magnetic field in a plane of flow and magnetic field

The Samurai Project: verifying the consistency of black-hole-binary waveforms for gravitational-wave detection

We quantify the consistency of numerical-relativity black-hole-binary waveforms for use in gravitational-wave (GW) searches with current and planned ground-based detectors. We compare previously published results for the $(\ell=2,| m | =2)$ mode of the gravitational waves from an equal-mass nonspinning binary, calculated by five numerical codes. We focus on the 1000M (about six orbits, or 12 GW cycles) before the peak of the GW amplitude and the subsequent ringdown. We find that the phase and amplitude agree within each code's uncertainty estimates. The mismatch between the $(\ell=2,| m| =2)$ modes is better than $10^{-3}$ for binary masses above $60 M_{\odot}$ with respect to the Enhanced LIGO detector noise curve, and for masses above $180 M_{\odot}$ with respect to Advanced LIGO, Virgo and Advanced Virgo. Between the waveforms with the best agreement, the mismatch is below $2 \times 10^{-4}$. We find that the waveforms would be indistinguishable in all ground-based detectors (and for the masses we consider) if detected with a signal-to-noise ratio of less than $\approx14$, or less than $\approx25$ in the best cases.Comment: 17 pages, 9 figures. Version accepted by PR