The surface energy balance during foehn events at Joyce Glacier, McMurdo Dry Valleys, Antarctica

The McMurdo Dry Valleys (MDV) are a polar desert, where glacial melt is the main source of water to streams and the ecosystem. Summer air temperatures are typically close to zero, and therefore foehn events can have a large impact on the meltwater production. A 14-month record of automatic weather station (AWS) data on Joyce Glacier is used to force a 1D surface energy balance model to study the impact of foehn events on the energy balance. AWS data and output of the Antarctic Mesoscale Prediction System (AMPS) on a 1.7 km grid are used to detect foehn events at the AWS site. Foehn events at Joyce Glacier occur under the presence of cyclones over the Ross Sea. The location of Joyce Glacier on the leeward side of the Royal Society Range during these synoptic events causes foehn warming through isentropic drawdown. This mechanism differs from the foehn warming through gap flow that was earlier found for other regions in the MDV and highlights the complex interaction of synoptic flow with local topography of the MDV. Shortwave radiation is the primary control on melt at Joyce Glacier, and melt often occurs with subzero air temperatures. During foehn events, melt rates are enhanced, contributing to 23 % of the total annual melt. Foehn winds cause a switch from a diurnal stability regime in the atmospheric surface layer to a continuous energy input from sensible heat flux throughout the day. The sensible heating during foehn, through an increase in turbulent mixing resulting from gustier and warmer wind conditions, is largely compensated for by extra heat losses through sublimation. Melt rates are enhanced through an additional energy surplus from a reduced albedo during foehn.</p

A revised chronology of key Vatnajökull (Iceland) outlet glaciers during the Little Ice Age

Glacier fluctuations from key Vatnajökull outlets have been redated using tephrochronology coupled with two lichenometric techniques to ascertain the timing of the Little Ice Age (LIA) maximum in southeast Iceland. An updated tephrochronology for southeast Iceland (both the number of tephra layers present and their geochemical signatures) indicates a LIA maximum for both glaciers between AD 1755 and 1873. Based on a population gradient approach, lichenometrically dated moraines along the margins of Skálafellsjökull and Heinabergsjökull narrow this window to the early to mid-19th century respectively. These revised chronologies, in addition to emerging evidence from elsewhere in Iceland, support a late 18th- to early 19th-century LIA glacier maximum. In contrast, the Norwegian LIA glacial maximum is strongly centred around AD 1750. This implies differing glaciological responses to secular shifts in the North Atlantic Oscillation. Such revisions to the Vatnajökull record are crucial, as accurately identifying the timing and delimiting the spatial extent of the Icelandic LIA glacier maximum will allow further light to be shed on glacier–climate interactions in the North Atlantic

Spatial and Temporal Shifts in Historic and Future Temperature and Precipitation Patterns Related to Snow Accumulation and Melt Regimes in Alberta, Canada

Shifts in winter temperature and precipitation patterns can profoundly affect snow accumulation and melt regimes. These shifts have varying impacts on local to large-scale hydro-ecological systems and freshwater distribution, especially in cold regions with high hydroclimatic heterogeneity. We evaluate winter climate changes in the six ecozones (Mountains, Foothills, Prairie, Parkland, Boreal, and Taiga) in Alberta, Canada, and identify regions of elevated susceptibility to change. Evaluation of historic trends and future changes in winter climate use high-resolution (~10 km) gridded data for 1950–2017 and projections for the 2050s (2041–2070) and 2080s (2071–2100) under medium (RCP 4.5) and high (RCP 8.5) emissions scenarios. Results indicate continued declines in winter duration and earlier onset of spring above-freezing temperatures from historic through future periods, with greater changes in Prairie and Mountain ecozones, and extremely short or nonexistent winter durations in future climatologies. Decreases in November–April precipitation and a shift from snow to rain dominate the historic period. Future scenarios suggest winter precipitation increases are expected to predominantly fall as rain. Additionally, shifts in precipitation distributions are likely to lead to historically-rare, high-precipitation extreme events becoming more common. This study increases our understanding of historic trends and projected future change effects on winter snowpack-related climate and can be used inform adaptive water resource management strategies

A framework for characterizing fluvial sediment fluxes from source to sink in cold environments

Fluvial processes dominate sediment flux from most cold environments and as such are particularly sensitive to environmental change. However, these systems demonstrate high variability in flow and sediment transfer rates in both the short and long-term which presents specific problems for establishing integrated sediment flux studies. The objective of this paper is to briefly review the nature of fluvial and floodplain sediment sources in cold environments and to make recommendations on the measurement of fluvial sediment fluxes from these sources to sinks. The paper outlines a framework for examining fluvial sediment fluxes in cold environments including: sources of sediment in glacial and periglacial environments; techniques for measuring fluvial sediment transfers; and methods for measuring contemporary deposition in lacustrine sediment sinks. Within this framework, we stress that it is particularly important to provide consistency in methods for monitoring sediment flux and to adopt appropriate sampling frequencies. We recommend that the most appropriate methods for establishing integrated sediment flux studies in these cold environments are: repeat surveys and terrestrial laser scanning of valley and slope sediment stores on a monthly – daily frequency; weekly-daily sediment budgeting of bedload transfer using rapid resurvey methods; hourly or better time series of suspended and solute transport using data logger acquisition systems; and monitoring of lacustrine sedimentation using sediment accumulation sensors and/or weekly-daily estimates from passive sediment traps. Application of the proposed integrated framework will improve our understanding of sediment flux in cold environments and allow us to better assess the sensitivity of cold environments to environmental change within the context of contemporary and past sediment flux

Organic nutrient uptake by mycorrhizal fungi enhances ecosystem carbon storage:a model-based assessment

Understanding the factors that drive soil carbon (C) accumulation is of fundamental importance given their potential to mitigate climate change. Much research has focused on the relationship between plant traits and C sequestration, but no studies to date have quantitatively considered traits of their mycorrhizal symbionts. Here, we use a modelling approach to assess the contribution of an important mycorrhizal fungal trait, organic nutrient uptake, to soil C accumulation. We show that organic nutrient uptake can significantly increase soil C storage, and that it has a greater effect under nutrient-limited conditions. The main mechanism behind this was an increase in plant C fixation and subsequent increased C inputs to soil through mycorrhizal fungi. Reduced decomposition due to increased nutrient limitation of saprotrophs also played a role. Our results indicate that direct uptake of nutrients from organic pools by mycorrhizal fungi could have a significant effect on ecosystem C cycling and storage

Shoulder MR arthrography of the posterior labrocapsular complex in overhead throwers with pathologic internal impingement and internal rotation deficit

To determine if overhead-throwing athletes with internal impingement pain and internal rotation deficit have thickening of the posterior inferior labrocapsular complex on MR arthrogram images. This study was approved and a waiver of consent granted by our institutional review board. Twenty-six overhead-throwing athletes with internal impingement pain and internal rotation deficit, and 26 controls who had undergone MR arthrograms, were retrospectively examined. The MR studies were combined and read in a blind fashion. On an axial image through the posteroinferior glenoid rim, the readers measured the labral length, capsule-labrum length, and the posterior recess angle. A t-test was used to determine statistical significance. The mean labral length was 4.9 mm [standard deviation (SD) 1.4 mm] for the controls, and 6.4 mm (SD 1.6 mm) for the athletes (P = 0.001). The mean capsule-labrum length was 5.4 mm (SD 2.1 mm) for the controls, and 8.8 mm (SD 2.9 mm) for the athletes (P < 0.001). The mean posterior recess angle measured 65 degrees (SD 27 degrees) for the controls and 94 degrees (SD 38 degrees) for the athletes (P = 0.002). Overhead-throwing athletes with internal impingement pain and internal rotation deficit tend to have a thicker labrum and a shallower capsular recess in the posterior inferior shoulder joint than do non-overhead-throwing athletes. In many, the posteroinferior capsule is also thickened. These MR findings should alert the radiologist to closely inspect the posterior cuff and posterosuperior labrum for the tears associated with internal impingement