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Standard proxies for reconstructing surface mass balance (SMB) in Antarctic ice cores are often inaccurate or coarsely resolved when applied to more complicated environments away from dome summits. Here, we propose an alternative SMB proxy based on photolytic fractionation of nitrogen isotopes in nitrate observed at 114 sites throughout East Antarctica. Applying this proxy approach to nitrate in a shallow core drilled at a moderate SMB site (Aurora Basin North), we reconstruct 700 years of SMB changes that agree well with changes estimated from ice core density and upstream surface topography. For the under-sampled transition zones between dome summits and the coast, we show that this proxy can provide past and present SMB values that reflect the immediate local environment and are derived independently from existing techniques. Snow accumulation rates in Antarctica can now be reconstructed from nitrate isotopes in snow and ice. This independent technique offers scientists a new tool for studying how Antarctic climate changed in the past and how it may change in the future. [ABSTRACT FROM AUTHOR]

Climate trends in the Antarctic region remain poorly characterized, owing to the brevity and scarcity of direct climate observations and the large magnitude of interannual to decadal-scale climate variability. Here, within the framework of the PAGES Antarctica2k working group, we build an enlarged database of ice core water stable isotope records from Antarctica, consisting of 112 records. We produce both unweighted and weighted isotopic (°18O) composites and temperature reconstructions since 0 CE, binned at 5- and 10-year resolution, for seven climatically distinct regions covering the Antarctic continent. Following earlier work of the Antarctica2k working group, we also produce composites and reconstructions for the broader regions of East Antarctica, West Antarctica and the whole continent. We use three methods for our temperature reconstructions: (i) a temperature scaling based on the δ18O-temperature relationship output from an ECHAM5-wiso model simulation nudged to ERA-Interim atmospheric reanalyses from 1979 to 2013, and adjusted for the West Antarctic Ice Sheet region to borehole temperature data, (ii) a temperature scaling of the isotopic normalized anomalies to the variance of the regional reanalysis temperature and (iii) a composite-plusscaling approach used in a previous continent-scale reconstruction of Antarctic temperature since 1 CE but applied to the new Antarctic ice core database. Our new reconstructions confirm a significant cooling trend from 0 to 1900 CE across all Antarctic regions where records extend back into the 1st millennium, with the exception of the Wilkes Land coast and Weddell Sea coast regions. Within this long-term cooling trend from 0 to 1900 CE, we find that the warmest period occurs between 300 and 1000 CE, and the coldest interval occurs from 1200 to 1900 CE. Since 1900 CE, significant warming trends are identified for the West Antarctic Ice Sheet, the Dronning Maud Land coast and the Antarctic Peninsula regions, and these trends are robust across the distribution of records that contribute to the unweighted isotopic composites and also significant in the weighted temperature reconstructions. Only for the Antarctic Peninsula is this most recent century-scale trend unusual in the context of natural variability over the last 2000 years. However, projected warming of the Antarctic continent during the 21st century may soon see significant and unusual warming develop across other parts of the Antarctic continent. The extended Antarctica2k ice core isotope database developed by this working group opens up many avenues for developing a deeper understanding of the response of Antarctic climate to natural and anthropogenic climate forcings. The first long-term quantification of regional climate in Antarctica presented herein is a basis for data-model comparison and assessments of past, present and future driving factors of Antarctic climate. [ABSTRACT FROM AUTHOR]

The Princess Elizabeth Land sector of the East Antarctic Ice Sheet is a significant reservoir of grounded ice and is adjacent to regions that experienced great change during Quaternary glacial cycles and Pliocene warm episodes. The existence of an extensive subglacial water system in Princess Elizabeth Land (to date only inferred from satellite imagery) bears the potential to significantly impact the thermal and kinematic conditions of the overlying ice sheet. We confirm the existence of a major subglacial lake, herein referred to as Lake Snow Eagle (LSE), for the first time using recently acquired aerogeophysical data. We systematically investigated LSE's geological characteristics and bathymetry from two-dimensional geophysical inversion models. The inversion results suggest that LSE is located along a compressional geologic boundary, which provides reference for future characterization of the geologic and tectonic context of this region. We estimate LSE to be ~42 km in length and 370 km² in area, making it one of the largest subglacial lakes in Antarctica. Additionally, the airborne ice-penetrating radar observations and geophysical inversions reveal a layer of unconsolidated water-saturated sediment around and at the bottom of LSE, which--given the ultralow rates of sedimentation expected in such environments--may archive valuable records of paleoenvironmental changes and the early history of East Antarctic Ice Sheet evolution in Princess Elizabeth Land. [ABSTRACT FROM AUTHOR]

The search is on for a site in Antarctica where an ice core older than 800 ka can be retrieved. A key issue will be to date the core correctly and synchronise it to other records. We still have hopes of accessing the old ice rapidly with new drilling tools that would allow profiles of water isotopes, dust and methane to be retrieved. However, the main ice core will be a challenge to date. A host of methods will be used, involving parameters with orbital signals, cosmogenic isotopes, and radiometric methods. However another option will be to match the new records with existing data from dated marine or terrestrial data.To do this, we need to look at existing marine and terrestrial datasets that have shown similarities with the ice core record over the 800 ka that already exists, using various approaches to consider whether the similarity should be expected to continue in the deeper ice. While the primary purpose is to assess what a well-preserved record should look like, we can also consider how diffusion and ice deformation might affect the records we retrieve. For the water isotopes, we consider the marine sediment record. It has been argued that the deep-sea temperature (Mg/Ca) record at a southern Pacific site has the same pattern as Antarctic δD. With newer data is this still supported? Similarly, dust proxies in southern hemisphere marine records show similar patterns to dust in Antarctic ice, and there is a good theoretical reason to expect this if they have the same source. We will consider both the similarities and differences in the two datasets. It is hard to predict the overall pattern of methane, but recent data showing the millennial scale variability in well-resolved marine cores off Portugal raise the possibility of matching the millennial event pattern between methane in ice and oxygen isotopes in these cores. Our aim in this paper is to predict what some of the ice core measures may look like so they can be used as "self-tuning targets". [ABSTRACT FROM AUTHOR]

Atmospheric circulation variability in the Indo-Pacific mid- to high-latitudes prior to 1979 is poorly understood due to this region having few station climate data from before the satellite era. A small number of stations were established around the International Geophysical Year of 1958 on sub-Antarctic islands and coastal East Antarctica, which enables comparison with high resolution proxy records over the last 60 years. This study details initial trace chemistry, water isotope, and derived annual accumulation rates over 1958-2017 from the observation era section (upper 30 metres) of a new 295 metre ice core drilled south of Mount Brown in Wilhelm II land, East Antarctica. The site was chosen to fulfil a range of criteria, including to produce highly resolved (sub-annual) chemical and isotopic records spanning 1000+ years. A detailed site selection study prior to drilling showed this site should be strongly teleconnected to the mid-latitude circulation of the southern Indian Ocean, adding a new proxy source to the small existing East Antarctic ice core array covering the last 2000 years. Initial findings of the Mount Brown South ice core record will be presented. [ABSTRACT FROM AUTHOR]