dataesr/scientific-paragraphs-categorization huggingface dataset:
Here we use an expanded paleoclimate database of Antarctic ice core isotope records and new reconstruction methodologies to reconstruct the climate of the past 2000 years, on a decadal scale and regional basis. Seven distinct climatic regions have been selected: the Antarctic Peninsula, the West Antarctic Ice Sheet (WAIS), the East Antarctic Plateau and four coastal domains of East Antarctica. This regional selection, which is supported by regional atmospheric RACMO2. 3p2 model results  (Thomas et al. , 2017; Van Wessem et al. , 2014) , is applied to both Antarctic ice-core-derived isotopic (temperature proxy) and snow accumulation rate reconstructions (see companion paper in the same issue by  Thomas et al. ). Section 2 describes the ice core and the temperature data sets used in this study, as well as the modelling framework used to support the analysis.
Ice core records Here we present and use a new expanded database that has been compiled in the framework of the PAGES Antarc-tica2k working group. The initial selection criteria are those requested by the PAGES 2k network (http://www. pages-igbp. org/ini/wg/2k-network/data) for the building of the community-sourced database of temperature-sensitive proxy records  (PAGES 2k Consortium, 2017). Briefly, (i) the records must be publicly available and published, (ii) a relation between the climate proxies and variables should be stated, (iii) the record duration should be between 300 and 2000 years, (iv) the chronology, certified by the data owner, should contain at least one chronological control point near the end (most recent) part of the record and another near the oldest part of the record and (v) the resolution should be at least one analysis every 50 years.
In building the Antarctica2k database we also allow shorter records to be included, although we request a strati-graphic control using volcanic markers  (Sigl et al. , 2014)  and, whenever possible, a dating by annual layer counted chronology. This last requirement is only possible in the high-accumulation regions of West Antarctica, the Antarctic Peninsula and coastal areas of East Antarctica. The inclusion of shorter records is designed to improve data coverage for assessments of climatic trends in Antarctica during the past century. The 11 records included in the previous continentscale reconstruction (PAGES 2k Consortium, 2013) relied on a highly precise chronological framework consisting of a common chronology, which used 42 volcanic events to synchronize the records. Here, we use both high-and lowresolution records.
Most of the records have a data resolution ranging from 0. 025 to 5 years (only three records have a resolution of > 10 years). Previous studies  (Frezzotti et al. , 2007; Ekaykin et al. , 2014)  have shown that post-depositional and wind scouring effects, acting more effectively when the accumulation rate is very low, limit our ability to obtain temperature reconstructions at annual resolution in most of the interior of Antarctica. Because of this, in our regional reconstructions we use 5-year-averaged data for reconstructing the last 200 years, and 10-year averages for reconstructing the last 2000 years. Using 5-or 10-year averages also decreases our dependence on an annually precise chronological constraint between the ice core records, allowing us to more confidently use the expanded database.
The data have been also screened for glaciological problems, with those records that are very likely to be affected by ice flow dynamics excluded. This enlarged database consists of 112 isotopic records. A list of the records used are reported in Table  S1  (in the Supplement) and their spatial distribution is shown in Fig. 1. Figure  S1  shows the location of the ice core sites along with a visualization of the record lengths. Most of the records of this new database cover the last 200 years and this is particularly true for the more coastal areas. Within the database, 36 records cover just the last 50 years or less, while 50 records cover the whole length of the past 200 years. There are 15 records that cover the last 1000 years, while only nine records reach as far back as 0 CE.
Temperature product The instrumental record is very short in Antarctica, and most ice core sites do not have weather station measurements associated with the cores. In addition, the retrieval of the first metre of firn can be difficult, due to poor cohesion of the snow. As a result, for many sites, there is no overlap between instrumental and proxy data, which complicates the proxy calibration exercise. To enlarge the calibration data set, we use the climate field reconstruction from Nicolas and Bromwich (2014) (hereafter NB2014; http://polarmet. osu. edu/datasets/ Antarctic_recon/). This surface temperature data set provides homogeneous data at 60 km resolution, extends from 1957 to 2013 and includes the revised Byrd temperature record  (Bromwich et al. , 2013)  that improves the skill of the tem- perature product over West Antarctica.
It covers a longer time span than reliable atmospheric reanalysis products for Antarctica (which begin only in 1979 CE) and has a higher spatial resolution than available isotope-enabled general circulation model (GCM) outputs. This data set is used to estimate the spatial representativeness of individual core sites (Sect. 3. 3. 2), to scale the normalized isotopic anomaly data to temperature (Sect. 3. 4. 2) and to calculate the surface temperature reconstructions with the CPS method (Sect. 3. 4. 4).
Modelling framework In order to use model information on isotope-temperature relationships in Antarctic precipitation, we use a reference simulation performed using the general atmospheric circulation model ECHAM5-wiso. The initial ECHAM5 model  (Roeckner et al. , 2003)  has been equipped with water stable isotopes  (Werner et al. , 2011) , following earlier work on ECHAM3  (Hoffmann et al. , 1998)  and ECHAM4  (Werner et al. , 2001) , and accounting for fractionation processes during phase changes. This model is used here because recent studies, based on model-data comparisons using observations of precipitation and surface vapour isotopic composition on a global scale and in the Arctic (e. g. Werner et al. , 2011; Steen-Larsen et al. , 2017)  have shown strong model skill of ECHAM5-wiso when it is run in high resolution as in this study (T106, with a mean horizontal grid resolution of approximately 1.
Broadscale East Antarctic (incorporating the climatic regions of the East Antarctic Plateau, as well as the Weddell Sea, Dronning Maud Land, Wilkes Land and Victoria Land coasts) and West Antarctic (incorporating the climatic regions of the West Antarctic Ice Sheet and Antarctic Peninsula) reconstructions are also presented. These additional reconstructions facilitate comparisons of our new results, using additional methods and an expanded database, with earlier findings of the Antarctica2k working group and subsequent research using the 2013 continent-scale reconstruction for Antarctic temperature.
Data preprocessing All ice core records in the Antarctica2k database were assigned to one of the climatic regions described in Sect. 3. 1 (as well as to East vs. West Antarctica and to the Antarcticwide classifications). The majority (94 out of 112) of ice core water isotope records in the database are based on oxygen isotope ratios (δ 18 O). In cases in which only deuterium isotope (δD) data are available, the ice core time series were converted to an δ 18 O equivalent by dividing by 8, a value Clim. Past, 13, 1609-1634, 2017 www. clim-past. net/13/1609/2017/ that represents the slope of the global mean meteoric relationship of oxygen and deuterium isotopes in precipitation and is close to the ratio of 7. 75 observed in surface Antarctic snow  (Masson-Delmotte et al. , 2008). The ice core δ 18 O (and δ 18 O equivalent) records were compiled on a common annual average age scale.
g. wind erosion, diffusion) processes  (Frezzotti et al. , 2007; Ekaykin et al. , 2014). The 5-year resolution records were converted to anomalies relative to their mean over the 1960-1990 CE interval, and records that do not include a minimum of six bins (30 years) of coverage since 1800 CE are excluded based on length. Overall, 79 records in the new Antarctica2k water isotope database meet the minimum requirement of having at least 30 years of data coverage since 1800 CE. In some cases, records meet this minimum length requirement but do not include data for the full 1960-1990 CE reference interval. We adjust the mean value of each of these records by matching the mean δ 18 O of their most recent six bins (30 years) of data to the mean of all anomaly records from the same climatic region and over the same six-bin interval.
We also produce normalized records by adjusting the variance in the records using the same reference period and method as for the anomaly records. The 10-year resolution anomaly and normalized records were generated using the same method but using a reference period of 1900-1990 CE and a minimum data coverage of nine bins (90 years) since 0 CE. Similarly, records that do not include the full 1900-1990 CE reference period have the mean of their most recent nine-bin (90 years) interval adjusted to match the mean of all other anomaly records from the same region and over the same nine-bin interval. Overall, 67 records in the new Antarctica2k water isotope database meet the minimum requirement of having at least 90 years of data coverage since 0 CE. Some regions of Antarctica, such as coastal and plateau sites in Dronning Maud Land, include dense networks of ice core data (Fig.
Replication of the 2013 Antarctica2k reconstruction method To facilitate comparison with the preceding Antarctica2k temperature reconstruction published by the PAGES 2k Consortium (2013), we apply their reconstruction method to the updated ice core isotope data collection. The method is a simple CPS approach  (Jones et al. , 2009) , updated from Schneider et al. (  2006 ) and implemented similarly to  Neukom et al. (2014). We apply this method to all subregions defined above, the broad East and West Antarctic divisions and to the Antarctic-wide database, replicating the Antarctic reconstructions presented in the PAGES 2k Consortium (2013) study. First, the annual-average records are allocated to the climatic regions as defined above. The following steps are then repeated for each region separately.
Second, only the records with no missing values in the 1961-1991 CE calibration period are selected. These records are then scaled to mean zero and unit SD over their common interval of data availability. Next, the normalized records are correlated with the NB2014 regional mean temperatures over 1961-1991 CE. Between 0 and 33 % of the ice core records within each region have negative correlations (physically implausible) with the target and are removed from the proxy matrix. A composite of the remaining records is then calculated by creating a weighted average, where the weighting of each ice core record is based on its temperature correlation from the previous step. The composite is then scaled to the mean and SD of the NB2014 regional temperatures over the 1961-1991 CE period. The compositing and scaling steps are carried out with a nested approach, i.
e. repeated for all periods with different proxy data availability. In the reconstruction of the PAGES 2k Consortium (2013), three records were infilled with neighbouring sites to have no missing data in the calibration window: WDC06A was infilled with data from WDC05A, and Siple Station and Plateau Remote records were infilled by a least median of squares multiple linear regression using nearby records (PAGES 2k Consortium, 2013). To allow comparison, we also used the infilled data for these records. Thus, the only difference from the reconstruction of PAGES 2k Consortium (  2013 ) is that we use an extended proxy database with more records and an updated temperature target (NB2014 instead of  Steig et al. , 2009). While this CPS approach allows a quantitative calibration to the NB2014 temperature data, it has some limitations compared to the methods above.
Results and discussion We use the varying reconstruction methods to identify robust trends in the Antarctic ice core database. We present results based on isotopic trends, as well as temperature reconstructions, and examine these for the seven climatic regions and for the larger-scale Antarctic regions (Sect. 4. 1), compare our results to the previous Antarctic temperature reconstruction (Sect. 4. 2), and investigate the link between temperature and volcanic activity (Sect. 4. 3). 4. 1 Regional-scale δ 18 O and temperature reconstructions For each of the seven climatic regions in Fig. S2  (unweighted isotope anomalies) and Fig. 2  (weighted and unweighted data), 5-year-binned δ 18 O composite records since 1800 CE are reported. The unweighted composites are shown with respect to the distributions of data within each bin and expressed relative to the 1960-1990 CE interval.
These trend analyses are based on 10-yearbinned isotopic anomalies for trends prior to 1900 CE and 5-year-binned data for trends over the last 100 years of the composites (although equivalent results are found if 10-yearbinned data are used to assess trends in the last 100 years). Results of unweighted composite trend analysis are summarized in Table  2. This analysis shows that for the unweighted composites the long-term cooling trend from 0 to 1900 CE is only significant for the East Antarctic Plateau. Visual examination of the unweighted composites (Fig. 3 ) suggests that many of the other climate regions appear to also have a negative unweighted isotopic trend over part of the last 2000 years (e. g. Wilkes Land and West Antarctic Ice Sheet regions), but these trends are not significant in the unweighted composites when calculated across the full interval from 0 to 1900 CE.
The Victoria Land Coast trend prior to 1900 CE is not significant in the mean or median unweighted composites, but over the interval in which two or more ice cores contribute to the composites the Monte Carlo assessments indicate that negative isotopic trends are produced in all 10 000 ensemble members and are significant (p < 0. 05) more often than can be explained by chance alone. The significant trend that is produced in the unweighted composite for the East Antarctic Plateau climate region is also evident in the broader East Antarctic compilation and for the Antarctic continent-scale composite. The continentscale cooling trend produced in unweighted composites using the expanded Antarctica2k database is in agreement with the PAGES 2k Consortium (  2013 ) results for which a longterm cooling trend over the Antarctic continent was identified.
It is also consistent with robust pre-industrial cooling www. clim-past. net/13/1609/2017/ Clim. Past, 13, 1609-1634, 2017 trends that have been identified in other continental reconstructions  (PAGES 2k Consortium, 2013)  and in the global oceans  (McGregor et al. , 2015). Isotopic trends in the last 100 years of the unweighted composites show significant positive trends across a number of regions. In particular, significant isotopic trends, indicative of climate warming, are evident in the unweighted composites for the Antarctic Peninsula and the Wilkes Land and Dronning Maud Land coasts. The West Antarctic Ice Sheet region does not display a significant (p < 0. 05) positive trend in the mean or median of the unweighted composites, but the Monte Carlo analysis across the distribution of isotopic data within each 10-year bin suggests that positive trends are produced in 99.
Continent-scale temperature reconstructions Figure  7  shows the results obtained by applying the CPS method published in 2013  (PAGES 2k Consortium, 2013)  to the expanded Antarctica2k database to reconstruct temperature across the whole Antarctic continent. A good agreement is observed between the new reconstruction and the previously published one (Fig. 7 ), on both annual and decadal scales (r = 0. 89 and 0. 91, respectively). There is a slightly stronger negative temperature trend, which is related mainly to a slightly cooler temperature estimate for the 1600-1900 CE interval using the expanded database, in the new Antarctic continent-scale reconstruction. Figures in the Supplement similarly repeat this CPS comparison for the West Antarctica and East Antarctica regions and find similar agreement between the 2013 results and those using the expanded ice core database  (Figs S11, S12 and S13).
By comparison, cooling trends of -0. 25 and -0. 56 • C 1000 yr -1 are calculated from the 10year-binned data obtained with the same CPS methods but applied to this new database. East Antarctica is one of the last places on the globe where the long-term cooling trend of the last millennium has not been inverted  (PAGES 2k Consortium, 2013; Abram et al. , 2016). This feature of delayed onset of industrial warming is clear in our reconstruction, but is not captured by climate models  (PAGES 2k-PMIP3 group, 2015). Climate models are known to overestimate inter-hemispheric synchronicity  (Neukom et al. , 2014). The model-data mismatch may come from an overestimation of the response to external forcing in climate models, an underestimation of the role of internal ocean-atmosphere dynamics in models or incorrect inference from proxy data.
Further studies will require a focus on ice core records with a solid chronological control and sufficient regional records to assess the common climatic signal from the deposition noise. Second-order isotopic parameters such as deuterium excess, which preserves a signal associated with moisture source characteristics, may also provide insights into the response of the Southern Ocean surface state to volcanic forcing. This analysis represents only a preliminary attempt to assess the possible short-term climatic response of Antarctic climate to volcanic forcing, and we suggest that this is a good avenue for further detailed study using the expanded Antarc-tica2k isotope database assembled here.
Conclusions and implications We have presented a new enlarged database of high-and low-resolution ice core water stable isotope records from Antarctica, which has been compiled in the framework of the PAGES Antarctica2k working group. To further develop our scientific understanding based on continent-scale reconstructions of Antarctic temperature, we define seven climatic regions based on our knowledge of the regional Antarctic climate and further supported by spatial correlation of temperature using the NB2014 reanalysis data. In our reconstructions of both regional-and continent-scale climate, we use 5-and 10-year-averaged data in order to limit our depen-Clim. Past, 13, 1609 Past, 13, -1634 Past, 13, , 2017  www. clim-past. net/13/1609/2017/ dence on annually precise dating, which faces real problems, especially in interior Antarctica, due to the very low snow accumulation there.
Similar conclusions are reached using different approaches (ECHAM, NB2014 and borehole methods), giving support to our temperature reconstructions. Furthermore, replication of the CPS approach used in a previous continent-scale reconstruction but adapted to the new database also produces consistent results. The range of the values obtained from these four methods provides information on the uncertainties related to the temperature reconstructions on regional and continental scales. Our new continent-scale reconstructions, based on the extended database, corroborate previously published findings for Antarctica from the PAGES 2k Consortium (  2013 ): (1) temperatures over the Antarctic continent show an overall cooling trend during the period from 0 to 1900 CE, which appears strongest in West Antarctica, and (2) no continentscale warming of Antarctic temperature is evident in the last century.
, 2016). As noted in other studies (e. g. Abram et al. , 2016; Jones et al. , 2016)  the absence of continent-scale warming over Antarctica is not in agreement with climate model simulations, which consistently produce a 20th century warming trend over Antarctica in response to greenhouse gas forcing. The high interannual climate variability with respect to the magnitude of climate trends over Antarctica, and the small number of ice core records that have contributed to previous continent-scale reconstructions of Antarctic temperature, have been suggested as possible sources for the lack of detection of continentscale warming trends in palaeoclimate records from Antarctica. However, we replicate this finding of a continent-scale absence of 20th century warming using our greatly expanded ice core database and with composites and reconstructions based on a range of methods.
A companion paper  (Thomas et al. , 2017) , which examines the snow accumulation rate variability over Antarctica during the last millennium, reaches the same conclusion, showing that in the Antarctic Peninsula region the late 20th century snowfall increase is unusual in the context of the past 300 years. The regional-to local-scale patterns of climate changes, and the processes that these illustrate, are another target for future research that could be explored using the new Antarc-tica2k database. Future work will also consider the comparison of the results obtained in this study with those by  Thomas et al. (2017) , assessing the snow accumulation rate variability in the same regions, with the aim of exploring a longstanding question about the relationship between temperature and precipitation in Antarctica.
Our new regional-and continent-scale reconstructions of Antarctic temperatures again highlight the urgent need to increase the spatial coverage of the sparse data for this continent with new temperature records, particularly focusing in the coastal areas. These regions are typically seen to be data-poor areas in our extended database. However, the coastal areas are also the places where high-resolution ice cores can be retrieved, where strong climatic differences can occur over relatively short distances, where there is some evidence for non-significant but emerging development of warming trends, where even small amounts of warming can rapidly move the local climate beyond the threshold and where surface melting of snow occurs, potentially leading to widespread impacts of any future Antarctic warming.
Data availability. The target data set of NB2014 is archived at http://polarmet. osu. edu/datasets/Antarctic_recon/. Table  S1  (in the Supplement) contains the data citations, as well as the primary bibliographic reference, for each record used in this study. We used the URL links for existing published data from public repositories. The regional-and continent-scale isotopic composites, including the statistical information for the 5-and 10-year unweighted composites, and temperature reconstructions generated during the current study and Table  S1  are available in the NOAA World Data Center for Paleoclimatology (WDC Paleo) at the following link: https://www. ncdc. noaa. gov/paleo/study/22589. The Supplement related to this article is available online at https://doi. org/10. 5194/cp-13-1609-2017-supplement.
2. At the bottom of the cell (20 µm height), a peak due to graphitic carbon at 1. 39 Å (marked by (g)) is detectable only, and attributed to the NwC current collector. Higher in the cell (220 µm), the characteristic pattern of orthorhombic α-sulfur (labeled with *) can be seen. Above, the sulfur peaks vanish while the peaks from the components of the electrolyte layer (500 µm height), both Viledon ® (#) and Celgard ® (&) appear and persist until one observes the lithium layer marked by the peak (Li) at 2. 54 Å. By comparing the 3-D tomographic reconstruction and XRD patterns in the initial state, it is thus possible to associate all of observed morphological objects with the corresponding chemical species. The cell was then cycled, and X-ray diffraction patterns and absorption data were measured operando as described above.