50provide spatiotemporally complete precipitation-minus-evaporation (P−E) products that are 51 nearly equivalent to SA over the dry, grounded AIS, and are most trustworthy over the satellite 52 4 era (1979-present). Notable biases in reanalysis P−E exist 15, 16 , however, they reproduce a 53 significant portion of the interannual variability 17 . Here, we modify the methodology in ref. 11 to 54 reconstruct 19 th and 20 th century SA over the entire grounded AIS and surrounding islands using 55 a combination of ice core records and atmospheric reanalysis P−E. A long-term, observationally 56 based reconstruction of SA is necessary to (i) ensure that any significant trends are observable 57 over the noise, (ii) quantify the role of AIS SA on observed sea-level change, (iii) better quantify 58 the relative importance of thermodynamical versus dynamical precipitation change, and (iv) 59 provide an AIS-wide observation-based SA record, along with uncertainties, for robust 60 evaluation of global and regional atmospheric AIS net precipitation estimates. 61Combining 53 ice core records with the spatial patterns of P−E from three reanalyses, we 62 reconstruct the 1801-2000 annual SA over the grounded AIS and surrounding islands ( Fig. 1a;63 Supplementary Table S1 and Supplementary Figs. S1-S2). We only show results from 64 reconstruction based on MERRA-2 P−E fields: R MERRA2 . The R MERRA2 performed better than the 65 ERA-Interim-and CFSR-based reconstructions (R ERAI and R CFSR ) because: (i) the reanalysis 66 showed the least bias in total magnitude (Supplementary Fig. S3) and (ii) exhibited the highest 67 skill in reproducing the observations (see Supplementary Methods; Supplementary Fig. S4 and 68 Supplementary Table S2). Here, we refer to the performance of the reconstruction and not the 69 reanalysis product itself. In addition, we find that the reconstructions replicate a significant 70 portion of the reanalysis P−E variability between 1980 and 2000 even though a few of the ice 71 cores used do not ( Supplementary Fig. S5). 72Trends in SA over the 20 th century (1901−2000) and late 20 th century (1957−2000) indicate that 73 inhomogeneous patterns of change dominate any AIS-wide signal (Fig. 1a-c), and that mass is 74 being significantly redistributed regionally over the AIS since the 1957-58 International 75 5Geophysical Year (IGY) and likely since the onset of the 20 th century. Integrated over the entire 76 ice sheet, however, we observe a clear and significant positive trend in SA ( Fig. 2a). A steady 77 increase is found over the EAIS, although it has reversed in the late 20 th century ( Fig. 2b) even 78 though local trends strengthened in the latter half ( Fig. 1b). We also observe a strong see-saw 79 pattern of increased SA over the AP and eastern WAIS contrasted with decreased accumulation 80 over the western WAIS. After nearly a century of decreasing SA over the AP, we find a rapid 81 and potentially accelerating increase over the 20 th century (Fig. 2d), whereas the gains and losses 82 from western ...

Abstract. 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 (δ18O) 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-plus-scaling 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.

Antarctic snowfall consists of frequent clear‐sky precipitation and heavier falls from intrusions of maritime airmasses associated with amplified planetary waves. We investigate the importance of different precipitation events using the output of the RACMO2 model. Extreme precipitation events consisting of the largest 10% of daily totals are shown to contribute more than 40% of the total annual precipitation across much of the continent, with some areas receiving in excess of 60% of the total from these events. The greatest contribution of extreme precipitation events to the annual total is in the coastal areas and especially on the ice shelves, with the Amery Ice Shelf receiving 50% of its annual precipitation in less than the 10 days of heaviest precipitation. For the continent as a whole, 70% of the variance of the annual precipitation is explained by variability in precipitation from extreme precipitation events, with this figure rising to over 90% in some areas.

The Northern Hemisphere experienced dramatic changes during the last glacial, featuring vast ice sheets and abrupt climate events, while high northern latitudes during the last interglacial (Eemian) were warmer than today. Here we use high-resolution aerosol records from the Greenland NEEM ice core to reconstruct the environmental alterations in aerosol source regions accompanying these changes. Separating source and transport effects, we find strongly reduced terrestrial biogenic emissions during glacial times reflecting net loss of vegetated area in North America. Rapid climate changes during the glacial have little effect on terrestrial biogenic aerosol emissions. A strong increase in terrestrial dust emissions during the coldest intervals indicates higher aridity and dust storm activity in East Asian deserts. Glacial sea salt aerosol emissions in the North Atlantic region increase only moderately (50%), likely due to sea ice expansion. Lower aerosol concentrations in Eemian ice compared to the Holocene are mainly due to shortened atmospheric residence time, while emissions changed little.

[1] This study uses ice core methanesulphonic acid (MSA) records from the Antarctic Peninsula, where temperatures have been warming faster than anywhere else in the Southern Hemisphere, to reconstruct the 20th century history of sea ice change in the adjacent Bellingshausen Sea. Using satellite-derived sea ice and meteorological data, we show that ice core MSA records from this region are a reliable proxy for regional sea ice change, with years of increased winter sea ice extent recorded by increased ice core MSA concentrations. Our reconstruction suggests that the satellite-observed sea ice decline in the Bellingshausen Sea during recent decades is part of a long-term regional trend that has occurred throughout the 20th century. The long-term perspective on sea ice in the Bellingshausen Sea is consistent with evidence of 20th century warming on the Antarctic Peninsula and may reflect a progressive deepening of the Amundsen Sea Low due to increasing greenhouse gas concentrations and, more recently, stratospheric ozone depletion. As a first-order estimate, our MSA-based reconstruction suggests that sea ice in the Bellingshausen Sea has retreated southward by ∼0.7°during the 20th century. Comparison with other 20th century sea ice observations, reconstructions, and model simulations provides a coherent picture of Antarctic sea ice decline during the 20th century, although with regional-scale differences evident in the timing and magnitude of this sea ice decline. This longer-term perspective contrasts with the small overall increase in Antarctic sea ice that is observed in post-1979 satellite data.

Interior Antarctica is among the most remote places on Earth and was thought to be beyond the reach of human impacts when Amundsen and Scott raced to the South Pole in 1911. Here we show detailed measurements from an extensive array of 16 ice cores quantifying substantial toxic heavy metal lead pollution at South Pole and throughout Antarctica by 1889 – beating polar explorers by more than 22 years. Unlike the Arctic where lead pollution peaked in the 1970s, lead pollution in Antarctica was as high in the early 20th century as at any time since industrialization. The similar timing and magnitude of changes in lead deposition across Antarctica, as well as the characteristic isotopic signature of Broken Hill lead found throughout the continent, suggest that this single emission source in southern Australia was responsible for the introduction of lead pollution into Antarctica at the end of the 19th century and remains a significant source today. An estimated 660 t of industrial lead have been deposited over Antarctica during the past 130 years as a result of mid-latitude industrial emissions, with regional-to-global scale circulation likely modulating aerosol concentrations. Despite abatement efforts, significant lead pollution in Antarctica persists into the 21st century.

Climate reanalyses provide key information to calibrate proxy records in regions with scarce direct observations. The climate reanalysis used to perform a proxy calibration should accurately reproduce the local climate variability. Here we present a regional scale evaluation of meteorological parameters using ERA-Interim and ERA5 reanalyses compared to in-situ observations from 13 automatic weather stations (AWS), located in the southern Antarctic Peninsula and Ellsworth Land, Antarctica. Both reanalyses seem to perform better in the escarpment area (>1000 m a.s.l) than on the coast. A significant improvement is observed in the performance of ERA5 over ERA-Interim. ERA5 is highly accurate, representing the magnitude and variability of near-surface air temperature and wind regimes. The higher spatial and temporal resolution provided by ERA5 reduces significantly the cold coastal biases identified in ERA-Interim and increases the accuracy representing the wind direction and wind speed in the escarpment. The slight underestimation in the wind speed obtained from the reanalyses could be attributed to an interplay of topographic factors and the effect of local wind regimes. Three sites in this region are highlighted for their potential for ice core studies. These sites are likely to provide accurate proxy calibrations for future palaeoclimatic reconstructions.

Studies of genomic copy number variants (CNVs) have identified genes associated with autism spectrum disorder (ASD) and intellectual disability (ID) such as NRXN1, SHANK2, SHANK3 and PTCHD1. Deletions have been reported in PTCHD1 however there has been little information available regarding the clinical presentation of these individuals. Herein we present 23 individuals with PTCHD1 deletions or truncating mutations with detailed phenotypic descriptions. The results suggest that individuals with disruption of the PTCHD1 coding region may have subtle dysmorphic features including a long face, prominent forehead, puffy eyelids and a thin upper lip. They do not have a consistent pattern of associated congenital anomalies or growth abnormalities. They have mild to moderate global developmental delay, variable degrees of ID, and many have prominent behavioral issues. Over 40% of subjects have ASD or ASD-like behaviors. The only consistent neurological findings in our cohort are orofacial hypotonia and mild motor incoordination. Our findings suggest that hemizygous PTCHD1 loss of function causes an X-linked neurodevelopmental disorder with a strong propensity to autistic behaviors. Detailed neuropsychological studies are required to better define the cognitive and behavioral phenotype.