Melt layer statistic of two firn cores recently drilled at Dye3 and South Dome in the dry snow zone of Southern Greenland

In the last couple of years remote sensing data have shown large areas of wet snow in the Southern part of the Greenland ice sheet. These melt features are attributed to the overall warming trend. Persistent warming implies changes in the firn layer as well. Even in areas of the dry snow zone one can observe sporadically a few ice lenses within the firn column indicating refrozen meltwater from warm events in the past. In our contribution we want to close the gap between investigations of firn cores drilled in the 70's and the observational record of remote sensing data over the last decade in South Greenland. The focus lies on firn of the dry snow zone which is sensitive against changes in a warming atmosphere and cold enough to prevent a longway percolation path of meltwater to several firn layers. To this end we had drilled two 45m-long firn cores at the former drilling sites of DYE3 (65°11'N, 43°49'W) and South Dome (SD) (63°32'N, 44°34'W) during a aircraft-supported field campaign 2012. The retrieved 3inch-firn core segments of 1m length are measured by a X-ray-scanning routine with the means of the core-scale AWI-ICE-CT. The 2d-density fields are calculated and allow to distinguish between refreezing meltwater and compacted firn. The depth-scales are converted to time-scales by using DEP (dielectric profiling) and (in case of DYE3) discrete sampled d18O measurements. Number density of melt layers and relative amount of melt show an synchronized behavior with an general increase over the last 30 years. Local maxima are observed in both sites at around 6-9m and 25m at DYE3 and 5-8m, 22m and 40m at SD

Meltwater retention in polar firn - A new method to estimate refrozen meltwater by the means of radioscopic imaging and its application to firn cores drilled in 2012 in southern Greenland

The reported warming trend of global mean temperatures during the last three decades has a high influence on polar ice caps and associated sea level changes. In Greenland wide spread melt events associated with these temperature changes have been inferred from satellite data. As melt layers in deep ice cores have previously been used as a temperature proxy for past summer climate a melt layer analysis of firn cores should provide climatic information of the last decades. In this work a method is developed to determine the amount of refrozen meltwater in firn cores by analysing radioscopic images of the firn and using the density contrast between regular firn and refrozen meltwater for the separation. 3D computer tomography on selected firn samples is used to verify the developed automatic melt percentage determination procedure which allows for a quantification of refrozen meltwater content of firn cores in an unprecedented accuracy, resolution and speed. By applying the developed method to two southern Greenland firn cores drilled in 2012 at Dye3 and South Dome a melt history for both cores is developed using d18O measurements performed on the Dye3 core and grain size stratigraphy as dating tools. A significant increase in melting during the last decade can be inferred from the resulting annual melt percentage profiles of both cores. This increase however is not exceptional if compared to melt records extending more than 2000 years back in time. While a comparison with the d18O signal often used as a proxy parameter for paleo-temperatures hardly shows any correlation, a good correlation is found between the melt record and mean summer (especially mean July) air temperatures at the South Dome site. Significant differences are found between the annual melt record found in the firn cores and the surface melt events inferred from passive microwave data gathered by satellites

Early Holocene Antarctic climate variability - Drivers and consequences as captured by major ions in the Roosevelt Island Climate Evolution (RICE) ice core

In a warming world, rapid disintegration of the West Antarctic Ice Sheet (WAIS) remains a primary uncertainty in the Intergovernmental Panel on Climate Change (IPCC) sea level rise projections. A deep ice core was drilled at the northeastern edge of the Ross Ice Shelf as part of the Roosevelt Island Climate Evolution (RICE) project. The site is located in a major drainage pathway of the marine based WAIS and the primary focus of the RICE project is to provide new insights into our understanding of the stability of the Ross Ice Shelf (RIS) in a warming climate and associated sea-level rise contributions of the WAIS. Due to its coastal location Roosevelt Island is sensitive to ice-ocean-atmosphere interactions and is characterised by high snow accumulation of 20 cm per year affording a high resolution ice core record. This PhD project focuses on the Early Holocene major ion record, comprising measurements of the anions Cl– , NO – 3 , SO 2 – 4 and MSA– and the cations Na+, K+, Mg2+ and Ca2+ as they can provide insight into changing atmospheric circulation patterns, sea ice conditions and primary productivity. This time period is particularly interesting as recent results from marine studies, integrated with the latest generation of ice sheet models, suggest that the majority of deglacial retreat of Ross Sea grounded ice occurred during the Early Holocene. Using chemical signatures in a seasonally resolved section of the core the RICE sea salt (ss) aerosol (e.g. ssNa+) is shown to be sensitive to sea ice extent in the Ross Sea. The biogenic sulphur species methanesulphonic acid (MSA– ) is used to investigate sea ice extent and primary productivity in the Ross Sea region. Primary productivity responds to availability of light and nutrients and this makes MSA– a sensitive recorder of sea ice conditions and perhaps upwelling of nutrient rich deep waters. The common centennial scale variability in the RICE MSA– and sea salt proxy during the early Holocene optimum is interpreted as a reflection of the thermohaline circulation’s internal variability driving seasonal sea ice and open water conditions as well as primary productivity in the Ross Sea. The comparison of the Mid-Early Holocene (12-6 thousand years before present, ka BP) RICE record to available regional ice core records highlights the sensitivity of RICE to changing oceanic conditions in the proximity to Roosevelt Island and provides new insights into our understanding of Holocene RIS grounding line retreat: The most significant increase in both sea salt aerosol (ssNa+) and primary productivity (MSA– ) occurs from 11.3 to 9 ka BP. During this time regional non-sea salt Ca2+ records from existing ice cores in the Ross Sea region (WAIS Divide, Siple Dome and TALDICE) suggest a period of reduced westerly wind intensity. Supported by evidence from marine records and modelling studies this Early Holocene baseline shift is linked to the retreat of grounded ice in the Ross Sea embayment. As the grounding line retreats, new space is created for the establishment of a seasonal sea ice cycle with seasonally open water conditions in the central/eastern Ross Sea facilitating enhanced sea salt aerosol formation (ssNa+), from both sea ice surfaces and the open ocean and increased phytoplankton activity in summer.</p

Efficacy of an executive function intervention programme in MS: a placebo-controlled and pseudo-randomized trial

Contains fulltext : 90285.pdf (publisher's version ) (Closed access)We evaluated a rehabilitation programme for executive deficits in multiple sclerosis patients by comparing outcome scores of a cognitive intervention group (CIG; n = 11) with those of a placebo group (n = 14) and an untreated group (n = 15). Executive functioning and verbal learning improved significantly more in the CIG. The treatment effect on verbal learning was still present at 1-year follow-up. Baseline brain atrophy, quantified by the brain parenchymal fraction, was associated with treatment effects for one aspect of executive functioning. Consequently, cognitive intervention may be beneficial and baseline brain atrophy has some predictive value in determining treatment outcome for executive functioning

Roosevelt Island Climate Evolution (RICE) ice core isotope record

High-resolution, well-dated climate archives provide an opportunity to investigate the dynamic interactions of climate patterns relevant for future projections. Here, we present data from a new, annually-dated ice core record from the eastern Ross Sea. Comparison of the Roosevelt Island Climate Evolution (RICE) ice core records with climate reanalysis data for the 1979-2012 calibration period shows that RICE records reliably capture temperature and snow precipitation variability of the region. RICE is compared with data from West Antarctica (West Antarctic Ice Sheet Divide Ice Core) and the western (Talos Dome) and eastern (Siple Dome) Ross Sea. For most of the past 2,700 years, the eastern Ross Sea was warming with perhaps increased snow accumulation and decreased sea ice extent. However, West Antarctica cooled whereas the western Ross Sea showed no significant temperature trend. From the 17th Century onwards, this relationship changes. All three regions now show signs of warming, with snow accumulation declining in West Antarctica and the eastern Ross Sea, but increasing in the western Ross Sea. Analysis of decadal to centennial-scale climate variability superimposed on the longer term trend reveal that periods characterised by opposing temperature trends between the Eastern and Western Ross Sea have occurred since the 3rd Century but are masked by longer-term trends. This pattern here is referred to as the Ross Sea Dipole, caused by a sensitive response of the region to dynamic interactions of the Southern Annual Mode and tropical forcings

The Ross Sea Dipole - temperature, snow accumulation and sea ice variability in the Ross Sea region, Antarctica, over the past 2700 years

Abstract. High-resolution, well-dated climate archives provide an opportunity to investigate the dynamic interactions of climate patterns relevant for future projections. Here, we present data from a new, annually dated ice core record from the eastern Ross Sea, named the Roosevelt Island Climate Evolution (RICE) ice core. Comparison of this record with climate reanalysis data for the 1979–2012 interval shows that RICE reliably captures temperature and snow precipitation variability in the region. Trends over the past 2700 years in RICE are shown to be distinct from those in West Antarctica and the western Ross Sea captured by other ice cores. For most of this interval, the eastern Ross Sea was warming (or showing isotopic enrichment for other reasons), with increased snow accumulation and perhaps decreased sea ice concentration. However, West Antarctica cooled and the western Ross Sea showed no significant isotope temperature trend. This pattern here is referred to as the Ross Sea Dipole. Notably, during the Little Ice Age, West Antarctica and the western Ross Sea experienced colder than average temperatures, while the eastern Ross Sea underwent a period of warming or increased isotopic enrichment. From the 17th century onwards, this dipole relationship changed. All three regions show current warming, with snow accumulation declining in West Antarctica and the eastern Ross Sea but increasing in the western Ross Sea. We interpret this pattern as reflecting an increase in sea ice in the eastern Ross Sea with perhaps the establishment of a modern Roosevelt Island polynya as a local moisture source for RICE

The Ross Sea Dipole – Temperature, Snow Accumulation and Sea Ice Variability in the Ross Sea Region, Antarctica, over the Past 2,700 Years

Abstract. High-resolution, well-dated climate archives provide an opportunity to investigate the dynamic interactions of climate patterns relevant for future projections. Here, we present data from a new, annually-dated ice core record from the eastern Ross Sea. Comparison of the Roosevelt Island Climate Evolution (RICE) ice core records with climate reanalysis data for the 1979–2012 calibration period shows that RICE records reliably capture temperature and snow precipitation variability of the region. RICE is compared with data from West Antarctica (West Antarctic Ice Sheet Divide Ice Core) and the western (Talos Dome) and eastern (Siple Dome) Ross Sea. For most of the past 2,700 years, the eastern Ross Sea was warming with perhaps increased snow accumulation and decreased sea ice extent. However, West Antarctica cooled whereas the western Ross Sea showed no significant temperature trend. From the 17th Century onwards, this relationship changes. All three regions now show signs of warming, with snow accumulation declining in West Antarctica and the eastern Ross Sea, but increasing in the western Ross Sea. Analysis of decadal to centennial-scale climate variability superimposed on the longer term trend reveal that periods characterised by opposing temperature trends between the Eastern and Western Ross Sea have occurred since the 3rd Century but are masked by longer-term trends. This pattern here is referred to as the Ross Sea Dipole, caused by a sensitive response of the region to dynamic interactions of the Southern Annual Mode and tropical forcings