• Energy Research

The management of the water resources of the Murray-Darling Basin (MDB) has long been contested, and the effects of the recent Millennium drought and subsequent flooding events have generated acute contests over the appropriate allocation of water supplies to agricultural, domestic and environmental uses. This water-availability crisis has driven demand for improved knowledge of climate change trends, cycles of variability, the range of historical climates experienced by natural systems and the ecological health of the system relative to a past benchmark. A considerable volume of research on the past climates of southeastern Australia has been produced over recent decades, but much of this work has focused on longer geological time-scales, and is of low temporal resolution. Less evidence has been generated of recent climate change at the level of resolution that accesses the cycles of change relevant to management. Intra-decadal and near-annual resolution (high-resolution) records do exist and provide evi...

Abstract. Stable isotope records from speleothems provide information on past climate changes, most particularly information that can be used to reconstruct past changes in precipitation and atmospheric circulation. These records are increasingly being used to provide “out-of-sample” evaluations of isotope-enabled climate models. SISAL (Speleothem Isotope Synthesis and Analysis) is an international working group of the Past Global Changes (PAGES) project. The working group aims to provide a comprehensive compilation of speleothem isotope records for climate reconstruction and model evaluation. The SISAL database contains data for individual speleothems, grouped by cave system. Stable isotopes of oxygen and carbon (δ18O, δ13C) measurements are referenced by distance from the top or youngest part of the speleothem. Additional tables provide information on dating, including information on the dates used to construct the original age model and sufficient information to assess the quality of each data set and to erect a standardized chronology across different speleothems. The metadata table provides location information, information about the full range of measurements carried out on each speleothem and information about the cave system that is relevant to the interpretation of the records, as well as citations for both publications and archived data. The compiled data are available at http://dx.doi.org/10.17864/1947.139.

Abstract. Paleoclimate information on multiple climate variables at different espaciotiotemporal scales is increasingly important to understand environmental and societal responses to climate change. A lack of high-quality reconstructions of past hydroclimate has recently been identified as a critical research gap. Speleothems, with their precise chronologies, widespread distribution, and ability to record changes in local to regional hydroclimate variability, are an ideal source of such information. Here we present a new version of the Speleothem Isotopes Synthesis and AnaLysis database (SISALv3), which has been expanded to include trace element ratios and Sr-isotopes as additional, hydroclimate-sensitive geochemical proxies. The oxygen and carbon isotope data included in previous versions of the database have been substantially expanded. SISALv3, contains speleothem data from 364 sites from across the globe, including 94 Mg/Ca, 83 Sr/Ca, 51 Ba/Ca, 25 U/Ca, 29 P/Ca and 14 Sr-isotope records. The database also has increased espaciotiotemporal coverage for stable oxygen (831) and carbon (588) isotope records compared to SISALv2. Additional meta information has been added to improve machine-readability and filtering of data. Standardized chronologies are included for all new entities together with the originally published chronologies. The SISALv3 database thus constitutes a unique resource of speleothem paleoclimate information that allows regional-to-global paleoclimate analyses based on multiple geochemical proxies, allowing more robust interpretations of past hydroclimate and comparisons with isotope-enabled climate models and other earth system and hydrological models. Abstract. Paleoclimate information on multiple climate variables at different spatiotemporal scales is increasingly important to understand environmental and societal responses to climate change. A lack of high-quality reconstructions of past hydroclimate has recently been identified as a critical research gap. Speleothems, with their precise chronologies, widespread distribution, and ability to record changes in local to regional hydroclimate variability, are an ideal source of such information. Here we present a new version of the Speleothem Isotopes Synthesis and AnaLysis database (SISALv3), which has been expanded to include trace element ratios and Sr-isotopes as additional, hydroclimate-sensitive geochemical proxies. The oxygen and carbon isotope data included in previous versions of the database have been substantially expanded. SISALv3, contains speleothem data from 364 sites from across the globe, including 94 Mg/Ca, 83 Sr/Ca, 51 Ba/Ca, 25 U/Ca, 29 P/Ca and 14 Sr-isotope records. The database also has increased spatiotemporal coverage for stable oxygen (831) and carbon (588) isotope records compared to SISALv2. Additional meta information has been added to improve machine-readability and filtering of data. Standardized chronologies are included for all new entities together with the originally published chronologies. The SISALv3 database thus constitutes a unique resource of speleothem paleoclimate information that allows regional-to-global paleoclimate analyses based on multiple geochemical proxies, allowing more robust interpretations of past hydroclimate and comparisons with isotope-enabled climate models and other earth system and hydrological models. Abstract. Paleoclimate information on multiple climate variables at different spatiotemporal scales is increasingly important to understand environmental and societal responses to climate change. A lack of high-quality reconstructions of past hydroclimate has recently been identified as a critical research gap. Speleothems, with their precise chronologies, widespread distribution, and ability to record changes in local to regional hydroclimate variability, are an ideal source of such information. Here we present a new version of the Speleothem Isotopes Synthesis and AnaLysis database (SISALv3), which has been expanded to include trace element ratios and Sr-isotopes as additional, hydroclimate-sensitive geochemical proxies. The oxygen and carbon isotope data included in previous versions of the database have been substantially expanded. SISALv3, contains speleothem data from 364 sites from across the globe, including 94 Mg/Ca, 83 Sr/Ca, 51 Ba/Ca, 25 U/Ca, 29 P/Ca and 14 Sr-isotope records. The database also has increased spatiotemporal coverage for stable oxygen (831) and carbon (588) isotope records compared to SISALv2. Additional meta information has been added to improve machine-readability and filtering of data. Standardized chronologies are included for all new entities together with the originally published chronologies. The SISALv3 database thus constitutes a unique resource of speleothem paleoclimate information that allows regional-to-global paleoclimate analyses based on multiple geochemical proxies, allowing more robust interpretations of past hydroclimate and comparisons with isotope-enabled climate models and other earth system and hydrological models. ملخص. تزداد أهمية معلومات المناخ القديم حول المتغيرات المناخية المتعددة على نطاقات مكانية وزمنية مختلفة لفهم الاستجابات البيئية والمجتمعية لتغير المناخ. تم تحديد الافتقار إلى عمليات إعادة البناء عالية الجودة للمناخ المائي السابق مؤخرًا على أنه فجوة بحثية حرجة. تعد الكلمات، مع تسلسلها الزمني الدقيق، وتوزيعها على نطاق واسع، والقدرة على تسجيل التغييرات في تقلب المناخ المائي المحلي إلى الإقليمي، مصدرًا مثاليًا لهذه المعلومات. نقدم هنا نسخة جديدة من قاعدة بيانات Spleothem Isotopes Synthesis and AnaLysis (SISALv3)، والتي تم توسيعها لتشمل نسب العناصر النزرة والنظائر المتسلسلة كوكلاء جيوكيميائيين إضافيين حساسين للمناخ المائي. تم توسيع بيانات نظائر الأكسجين والكربون المدرجة في الإصدارات السابقة من قاعدة البيانات بشكل كبير. SISALv3، يحتوي على بيانات speleothem من 364 موقعًا من جميع أنحاء العالم، بما في ذلك 94 ملغ/كالسيوم و 83 ريال سعودي/كالسيوم و 51 باسكال/كالسيوم و 25 وحدة دولية/كالسيوم و 29 P/Ca و 14 سجل نظائر سر. كما زادت قاعدة البيانات من التغطية المكانية والزمانية لسجلات النظائر المستقرة للأكسجين (831) والكربون (588) مقارنة بـ SISALv2. تمت إضافة معلومات تعريف إضافية لتحسين قابلية القراءة الآلية وتصفية البيانات. يتم تضمين التسلسل الزمني الموحد لجميع الكيانات الجديدة جنبًا إلى جنب مع التسلسل الزمني المنشور في الأصل. وبالتالي، تشكل قاعدة بيانات SISALv3 موردًا فريدًا لمعلومات المناخ القديم التي تسمح بتحليلات المناخ القديم الإقليمية إلى العالمية بناءً على وكلاء جيوكيميائيين متعددين، مما يسمح بتفسيرات أكثر قوة للمناخ المائي السابق ومقارنات مع نماذج المناخ التي تدعم النظائر والنماذج الأرضية والهيدرولوجية الأخرى.

Providing estimates of past climate changes on interannual–millenial timescales requires suitable regression models between climate and climate proxies. Many proxies appear to show relationships with climate that are timescale dependent. Any proxy‐climate model should be able to replicate the major patterns that are observed at multiple timescales. Here we develop a new climate‐isotope regression model for speleothems from a middle latitude site. In the low to middle latitudes, daily variation in precipitation isotopes (within individual months) is largely negatively correlated with daily rainfall amount. On interdecadal timescales, though, this relationship appears to be nonstationary. These two points provide a theoretical basis for a new climate‐isotope regression model in which the slope and the intercept of a δ18Oday–Pday line for a given month are modulated by organized patterns of climate variability, such as the extratropical zonal waves (including the annular modes). In constructing this new regression model, we show how daily precipitation–δ18O relationships can be estimated using only monthly δ18O data and daily rainfall amounts. The new regression model provides a consistent picture of 18O variability over a range of timescales, and this has not been the case with any previous climate‐isotope regression model.

We present a record of seasonal and inter-annual oxygen (δO) and carbon (δC) isotope ratios from an 81-year-old stalagmite from Moondyne Cave, southwest Australia. The growth history of stalagmite MND-S1 is known since it grew on a cave boardwalk that was installed in 1911 and removed in 1992. This stalagmite provides an excellent test of speleothem climate proxies because the regional climate is strongly seasonal (wet winter/dry summer) and has experienced a 200 mm (20%) reduction of mean rainfall since the mid-1960s, and a 0.8 °C temperature rise since ∼ 1953. Seasonal variations in calcite δO were measured in situ by high spatial resolution ion microprobe, whilst inter-annual variations of δO and δC were measured by conventional gas-source mass spectrometry. Comparison of the speleothem stable isotopes and instrumental temperature records reveals that δO variations are too large to be driven by temperature alone, and are in the opposite sense. However, daily rainfall δO measurements show that the mean seasonal range in δO of rainfall in southwest Australia is large (2‰) and inversely correlated with rainfall amount. A rainfall driver for the speleothem δO is confirmed by the detection of seasonal shifts of 0.7-1.5‰ in speleothem δ that track rainfall δO, smoothed by storage in the overlying limestone. The seasonal range in speleothem δO is larger than any inter-annual and decadal variation observed in the record. The prominent annual cycles in speleothem δO revealed by ion microprobe analysis indicate that subtle changes in the frequency of intense winter rainfall events, or possibly also moisture sources, could produce significant changes in mean speleothem δO. The ion microprobe results also raise the possibility that the masses of speleothem calcite deposited in winter and summer could vary as a function of the seasonal drip rate and carbonate saturation state of these waters. If this is the case, then small changes in the relative masses of calcite deposited in winter and summer could produce significant shifts in mean δO and δC that have a complex relation to climate. This finding should be generally applicable to the interpretation of long-term trends in speleothem geochemical records for shallow cave sites where seasonal variations in geochemical tracers are relatively large, including most of the sub-tropical monsoon belts and mid to high latitudes with distinct rainfall seasons.

Abstract. Although quantitative isotopic data from speleothems has been used to evaluate isotope-enabled model simulations, currently no consensus exists regarding the most appropriate methodology through which achieve this. A number of modelling groups will be running isotope-enabled palaeoclimate simulations in the framework of the Coupled Model Intercomparison Project Phase 6, so it is timely to evaluate different approaches to use the speleothem data for data-model comparisons. Here, we accomplish this using 456 globally-distributed speleothem δ18O records from an updated version of the Speleothem Isotopes Synthesis and Analysis (SISAL) database and palaeoclimate simulations generated using the ECHAM5-wiso isotope-enabled atmospheric circulation model. We show that the SISAL records reproduce the first-order spatial patterns of isotopic variability in the modern day, strongly supporting the application of this dataset for evaluating model-derived isotope variability into the past. However, the discontinuous nature of many speleothem records complicates procuring large numbers of records if data-model comparisons are made using the traditional approach of comparing anomalies between a control period and a given palaeoclimate experiment. To circumvent this issue, we illustrate techniques through which the absolute isotopic values during any time period could be used for model evaluation. Specifically, we show that speleothem isotope records allow an assessment of a model’s ability to simulate spatial isotopic trends and the degree to which the model reproduces the observed environmental controls of isotopic spatial variability. Our analyses provide a protocol for using speleothem isotopic data for model evaluation, including screening the observations, the optimum period for the modern observational baseline, and the selection of an appropriate time-window for creating means of the isotope data for palaeo time slices.