Classic Maya populations living in peri-urban states were highly dependent on seasonally distributed rainfall for reliable surplus crop yields. Despite intense study of the potential impact of decadal to centennial-scale climatic changes on the demise of Classic Maya sociopolitical institutions (750-950 CE), its direct importance remains debated. We provide a detailed analysis of a precisely dated speleothem record from Yok Balum cave, Belize, that reflects local hydroclimatic changes at seasonal scale over the past 1600 years. We find that the initial disintegration of Maya sociopolitical institutions and population decline occurred in the context of a pronounced decrease in the predictability of seasonal rainfall and severe drought between 700 and 800 CE. The failure of Classic Maya societies to successfully adapt to volatile seasonal rainfall dynamics likely contributed to gradual but widespread processes of sociopolitical disintegration. We propose that the complex abandonment of Classic Maya population centres was not solely driven by protracted drought but also aggravated by year-to-year decreases in rainfall predictability, potentially caused by a regional reduction in coherent Intertropical Convergence Zone-driven rainfall.
<p>Speleothems (cave carbonates) are widely distributed in terrestrial regions, and provide highly resolved records of past changes in climate and ecosystem conditions, encoded in the oxygen and carbon isotope proxies. The SISALv2 database, created by the PAGES-SISAL&#160; Phase 1 Working Group, provided 700 speleothem records from 293 cave sites, 500 of which have standardized chronologies. The database provided access to records that were hitherto unavailable in the original publications and/or repositories, and enabled regional-to-global scale analysis of climatic patterns using a variety of approaches such as data-model comparisons.&#160;</p> <p>During the three&#160; year run of SISAL Phase 2,&#160; the working group members have:&#160;</p> <p>(i) explored ways to synthesize modern cave monitoring data to provide robust modern baselines and improve proxy interpretations</p> <p>(ii) added trace element proxies of Mg, Sr, Ba, and U concentrations, and Sr isotopes to a new SISAL database version to increase our understanding of regional climatic variability.</p> <p>(iii) updated the SISAL database to incorporate an additional ~100 speleothem stable isotope datasets&#160;</p> <p>(iv) and created an online interface web app (The SISAL App) with a user-friendly GUI to increase SISAL data accessibility.</p> <p>Here, we present ongoing work synthesizing cave monitoring data, a summary of speleothem proxy records available in the SISALv3 database update and of ongoing Working Group research projects and a simple use case of The SISAL App. We briefly present a synopsis of the SISAL-community level discussions on best practices for reporting trace element data, and reducing data measured with high resolution laser ablation methods.&#160;</p> <p>We conclude with a short discussion on research projects based on the latest SISAL database update and discuss ideas for potential future SISAL phases and projects. For this, we encourage participation and collaboration from researchers in different stages of their academic career and working in different geographical regions and allied disciplines interested in exploiting the new SISAL database version.&#160;</p> <p><br /><br /></p>
<p>Speleothems have been developed to be valuable climate archives. Albeit much progress has been made to understand speleothem proxies, it remains difficult to differentiate between a direct climate signal and variations, which occurred due to in-cave processes like prior calcite precipitation, CO<sub>2</sub> degassing or C exchange between dissolved inorganic C-species and cave air CO<sub>2</sub>. Here, we analyse palaeoclimate proxies of contemporaneously growing speleothems, which were extracted from the SISALv2 database (Comas-Bru et al., 2020). We argue that differences in their stable O and C isotopic composition as well as in their growth rate can only arise by differences of drip site specific conditions as climate conditions for pairs of contemporaneously growing speleothems are similar. To better understand differences in the isotopic composition and growth rate of contemporaneously growing speleothems, we investigate the in-cave processes by applying a speleothem isotope and growth model. The model is based on a Rayleigh process, which includes CO<sub>2</sub> degassing and CaCO<sub>3</sub> precipitation, HCO<sub>3</sub><sup>-</sup> <&#8212;> H<sub>2</sub>O buffering as well as CO<sub>2</sub> exchange and is able to calculate growth rates. The model accounts for CaCO<sub>3</sub> deposition as prior calcite precipitation as well as CaCO<sub>3</sub> deposition at the speleothem. We find that C-exchange processes are necessary to explain the linked isotopic and growth rate differences in speleothems.</p><p>&#160;</p><p><strong>References</strong></p><p>Comas-Bru, L., Atsawawaranunt, K., Harrison, S., SISAL working group members (2020): SISAL (Speleothem Isotopes Synthesis and AnaLysis Working Group) database version 2.0. University Of Reading.</p>
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