Ice thickness and volume changes across the Southern Alps, New Zealand, from the little ice age to present

Rapid changes observed today in mountain glaciers need to be put into a longer-term context to understand global sea-level contributions, regional climate-glacier systems and local landscape evolution. In this study we determined volume changes for 400 mountain glaciers across the Southern Alps, New Zealand for three time periods; pre-industrial “Little Ice Age (LIA)” to 1978, 1978 to 2009 and 2009 to 2019. At least 60 km3 ± 12 km3 or between 41 and 62% of the LIA total ice volume has been lost. The rate of mass loss has nearly doubled from − 0.4 m w.e year−1 during 1,600 to 1978 to − 0.7 m w.e year−1 at present. In comparison Patagonia has lost just 11% of it’s LIA volume. Glacier ice in the Southern Alps has become restricted to higher elevations and to large debris-covered ablation tongues terminating in lakes. The accelerating rate of ice loss reflects regional-specific climate conditions and suggests that peak glacial meltwater production is imminent if not already passed, which has profound implications for water resources and riverine habitats

Proglacial Lakes Control Glacier Geometry and Behavior During Recession

Ice‐contact proglacial lakes are generally absent from numerical model simulations of glacier evolution, and their effects on ice dynamics and on rates of deglaciation remain poorly quantified. Using the BISICLES ice flow model, we analyzed the effects of an ice‐contact lake on the Pukaki Glacier, New Zealand, during recession from the Last Glacial Maximum. The ice‐contact lake produced a maximum effect on grounding line recession >4 times further and on ice velocities up to 8 times faster, compared to simulations of a land‐terminating glacier forced by the same climate. The lake contributed up to 82% of cumulative grounding line recession and 87% of ice velocity during the first 300 years of the simulations, but those values decreased to just 6% and 37%, respectively, after 5,000 years. Numerical models that ignore lake interactions will, therefore, misrepresent the rate of recession especially during the transition of a land‐terminating to a lake‐terminating environment

The Tamar Trough revisited: correlations berween sedimentary beds, basalts, their ages and valley evolution, North Tasmania

The Tamar Trough, an Early Palaeogene fault structure, contains sedimentaty beds and interleaved basaltic flows that infill the structure along its 70 km length. These infills represent a complex interplay between sedimentation, channel erosion, eruptive dislocations, and even 'out of trough' diyersions of the ancestral Tamar drainage. Several areas of resistant basalt flows remain in the south, upper, middle and lower Tamar reaches. Although some palynological control was known, radiometric dating of previously untested basalts now allows close integration and age-pegging for observed palynological biozones. The K-Ar and Ar-Ar ages of the basalt bodies indicate eruptive events at 47, 33-37 and 25 Ma, correlating with Proteacidites asperopolus-Malvacipollis diversus, Nothofagites asperus and Proteacidites tuberculatus biozone age sedimentary beds respectively. Basanite, alkali basalt and hawaiite flows dominate basalt lithology with lesser olivine nephelinite, transitional olivine basalt, olivine tholeiite and quartz tholeiite. Basalt geochemistry suggests derivation from different degrees of partial mande melting (from 7 to 35%), with alkaline and tholeiitic basalts being derived from separate source regions. Most alkaline basalts have high-jl (HIMU) related trace element signatures, which are absent in the tholeiitic rocks. A basalt plug on the trough margin at Loira gave a Jurassic age and has Jurassic dolerite-like geochemistry. The Tamar sequence suggests that the initial fluvio-Iacustrine and later channel-fill sedimentation from 65(?) to 24(?) Ma was then punctuated in places by periods of alkaline volcanism between 47 to 33(?) Ma, and alkaline and tholeiitic volcanism between 33 to 24(?) Ma. No Neogene fossils are known, so this later period was probably one of net erosion. These contrasting quiet sedimentary and more volcanic intervals are related here to a tectonic model that involves northerly drift of Victorian and Tasmanian lithosphere over several former Tasman metasomatised mantle plume sources

Cooling glaciers in a warming climate since the Little Ice Age at Qaanaaq, northwest Kalaallit Nunaat (Greenland)

The centennial response of land-terminating glaciers in Greenland to climate change is largely unknown. Yet, such information is important to understand ongoing changes and for projecting the future evolution of Arctic subpolar glaciers, meltwater runoff, and sediment fluxes. This paper analyses the topography, geomorphology, and sedimentology of prominent moraine ridges and the proglacial areas of ice cap outlet glaciers on the Qaanaaq peninsula (Piulip Nunaa). We determine geometric changes of glaciers since the neoglacial maximum; the Little Ice Age (LIA), and we compare glacier behaviour during the LIA with that of the present day. There has been very little change in the rate of volume loss of each outlet glacier since the LIA compared with the rate between 2000 and 2019. However, the percentage of each glacier that is likely composed of cold-based ice has increased since the LIA, typically by 20%. The LIA moraines comprise subrounded, striated, and faceted clasts that evidence subglacial transport, and outwash plains, flutes, kames, and eskers that evidence subglacial motion and meltwater within temperate ice. Contrastingly, contemporary ice margins and their convex ice surfaces comprise pronounced primary foliation, ephemeral supraglacial drainage, sediment drapes from thrust plane fractures, and an absence of open crevasses and moulins. These calculations and observations together lead us to interpret that these outlet glaciers have transitioned towards an increasingly cold-based thermal regime despite a warming regional climate. Thermal regime transitions control glacier dynamics and therefore should be incorporated into glacier evolution models, especially where polythermal glaciers prevail and where climate is changing rapidly

Toward Numerical Modeling of Interactions Between Ice-Marginal Proglacial Lakes and Glaciers

Global climate change is evidently manifest in disappearing mountain glaciers and receding and thinning ice sheet margins. Concern about contemporaneous proglacial lake development has spurred an emerging area of research seeking to quantitatively understand lake - glacier interactions. This perspectives article identifies spatio-temporal disparity between the coverage of field data, remote sensing observations and numerical modelling efforts. Throughout, an overview of the physical effects of ice-marginal lakes on glaciers and on ice sheet margins is provided, drawing evidence together from very recent and high-impact studies of both modern glaciology and of the Quaternary record. We identify and discuss six challenges for numerical modelling of lake - glacier interactions, namely that there are meltwater exchanges between glaciers and ice-marginal lakes, lake bathymetry and glacier bed topography are often unknown, lake - glacier interactions affect the longitudinal stress regime of glaciers, lake water temperature affects glacier melting but is very poorly constrained, the interactions persist with considerable spatio-temporal variability and with boundary migration, and data for model parameterisation and validation is extremely scarce. Overall, we contend that numerical modelling is a key frontier in the cryospheric sciences to deliver process understanding of lake - glacier interactions

A litho-tectonic event stratigraphy from dynamic Late Devensian ice flow of the North Sea Lobe, Tunstall, east Yorkshire, UK

The central sector of the British-Irish Ice Sheet during the last glaciation was characterised by complex ice-flow reflecting interacting ice streams and changing dominance of different ice dispersal centres. At Tunstall, east Yorkshire, two subglacial till units have been traditionally identified as the Late Devensian Skipsea and Withernsea tills, and thought to record two separate ice advances onto the Holderness coast, from divergent ice flow directions. Our study presents the first quantitative lithological, sedimentological and structural evaluation of glacial sediments at the site. The lithological composition of both till units suggests that ice extended southwards from southern Scotland, incorporating material from north-east England and the western margin of the North Sea Basin. Notably, the bulk lithological properties of both the Skipsea and Withernsea tills are very similar. Subtle variations in colour, texture and lithology that do occur simply appear to reflect spatial and temporal variability in subglacial entrainment along the flow path of the North Sea Lobe. The relative arrangements of the units plus the fracture sets also indicates phases of intra-till thrust-stacking and unloading (F2), consolidation and shrinkage (F1, F3) suggestive of cycles of ice re-advance (thrusting) and ice-marginal retreat (unloading and shrinkage) possibly relating to active recession. The findings from this study reveal a sedimentary and structural complexity that is not recognised by the current Late Devensian till stratigraphy of east Yorkshire

A Cretaceous phonolite dyke from the Tomahawk River, northeast Tasmania

Field mapping and indicate that a phonolite which intrudes Devonian granite in the upper Tomahawk River area, Tasmania, is 3.2 km long and with a true thickness of 10-15 m. The rock contains of anorthoclase, sparse fayalitic olivine and low-Ti and rare biotite in a alkali feldspar laths, with interstitial clinopyroxene to amphibole or analcime and accessory apatite. It is peralkaline and evolved, even for phonolites, with very and CaO, and high and incompatible elements. However, relatively high Sr and Ba and the absence of a negative Eu anomaly suggest little feldspar fractionation in its petrogenesis. Its Late Cretaceous age 80.4 ± 1.6 Ma, 4oAr/39Ar plateau 75.8 ± 0.3 Ma, 4oAr/39Ar total fusion 76 ± 3.1 Ma) and geochemistry are unique for Tasmania and it represents a recognised, although very minor, igneous episode. It may be related to a change in dynamic regime following continental rifting, the opening of the Tasman Sea and the subsidence of Bass Basin

Ice-contact proglacial lakes associated with the Last Glacial Maximum across the Southern Alps, New Zealand

Proglacial lakes can affect the stability of mountain glaciers and can partly disengage glacier behaviour from climatic perturbations. However, their role in controlling the onset and progression of deglaciation from the Last Glacial Maximum (LGM) remains poorly understood. This lack of understanding is partly because the evidence required to consistently and robustly identify the location and evolution of ice-contact lakes is not standardised. In this paper we therefore firstly present a new set of criteria for identifying the landform and sedimentary evidence that defines and characterises ice-marginal lakes. Secondly, we then apply these key criteria with the aid of high-resolution topographic mapping to produce the first holistic definition and assessment of major proglacial lake landforms and sediments pertaining to the end of the LGM across South Island, New Zealand. The major findings of this assessment can be grouped to include that: (i) The localised constraints to proglacial lake extent were topography, glacier size and meltwater/sediment fluxes, (ii) Lake damming was initiated by outwash fan-heads that interrupted water and sediment flows down-valley, and (iii) New Zealand LGM lakes were unequivocally in contact with a calving ice margin. These findings will be useful for reconstructing ice dynamics and landscape evolution in this region

Wide variation in susceptibility of transmitted/founder HIV-1 subtype C Isolates to protease inhibitors and association with in vitro replication efficiency

© 2016 The Author(s).The gag gene is highly polymorphic across HIV-1 subtypes and contributes to susceptibility to protease inhibitors (PI), a critical class of antiretrovirals that will be used in up to 2 million individuals as second-line therapy in sub Saharan Africa by 2020. Given subtype C represents around half of all HIV-1 infections globally, we examined PI susceptibility in subtype C viruses from treatment-naïve individuals. PI susceptibility was measured in a single round infection assay of full-length, replication competent MJ4/gag chimeric viruses, encoding the gag gene and 142 nucleotides of pro derived from viruses in 20 patients in the Zambia-Emory HIV Research Project acute infection cohort. Ten-fold variation in susceptibility to PIs atazanavir and lopinavir was observed across 20 viruses, with EC50 s ranging 0.71-6.95 nM for atazanvir and 0.64-8.54 nM for lopinavir. Ten amino acid residues in Gag correlated with lopinavir EC50 (p < 0.01), of which 380 K and 389I showed modest impacts on in vitro drug susceptibility. Finally a significant relationship between drug susceptibility and replication capacity was observed for atazanavir and lopinavir but not darunavir. Our findings demonstrate large variation in susceptibility of PI-naïve subtype C viruses that appears to correlate with replication efficiency and could impact clinical outcomes