Repository logo

Browsing by Author "Braun, Kerstin"

Now showing 1 - 3 of 3
  • Evaluating model outputs using integrated global speleothem records of climate change since the last glacial
    Publication . Comas-Bru, Laia; Harrison, Sandy P.; Werner, Martin; Rehfeld, Kira; Scroxton, Nick; C. Veiga-Pires, C.; Ahmad, Syed Masood; Brahim, Yassine Ait; Mozhdehi, Sahar Amirnezhad; Arienzo, Monica; Atsawawaranunt, Kamolphat; Baker, Andy; Braun, Kerstin; Breitenbach, Sebastian; Burstyn, Yuval; Chawchai, Sakonvan; Columbu, Andrea; Deininger, Michael; Demeny, Attila; Dixon, Bronwyn; Hatvani, István Gábor; Hu, Jun; Kaushal, Nikita; Kern, Zoltan; Labuhn, Inga; Lachniet, Matthew S.; Lechleitner, Franziska A.; Lorrey, Andrew; Markowska, Monika; Nehme, Carole; Novello, Valdir F.; Oster, Jessica; Perez-Mejias, Carlos; Pickering, Robyn; Sekhon, Natasha; Wang, Xianfeng; Warken, Sophie; Atkinson, Tim; Ayalon, Avner; Baldini, James; Bar-Matthews, Miryam; Bernal, Juan Pablo; Boch, Ronny; Borsato, Andrea; Boyd, Meighan; Brierley, Chris; Cai, Yanjun; Carolin, Stacy; Cheng, Hai; Constantin, Silviu; Couchoud, Isabelle; Cruz, Francisco; Denniston, Rhawn; Dragusin, Virgil; Duan, Wuhui; Ersek, Vasile; Finne, Martin; Fleitmann, Dominik; Fohlmeister, Jens; Frappier, Amy; Genty, Dominique; Holzkamper, Steffen; Hopley, Philip; Johnston, Vanessa; Kathayat, Gayatri; Keenan-Jones, Duncan; Koltai, Gabriella; Li, Ting-Yong; Lone, Mahjoor Ahmad; Luetscher, Marc; Mattey, Dave; Moreno, Ana; Moseley, Gina; Psomiadis, David; Ruan, Jiaoyang; Scholz, Denis; Sha, Lijuan; Smith, Andrew Christopher; Strikis, Nicolas; Treble, Pauline; Unal-Imer, Ezgi; Vaks, Anton; Vansteenberge, Stef; Voarintsoa, Ny Riavo G.; Wong, Corinne; Wortham, Barbara; Wurtzel, Jennifer; Zhang, Haiwei
    Although quantitative isotope data from speleothems has been used to evaluate isotope-enabled model simulations, currently no consensus exists regarding the most appropriate methodology through which to 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 using the speleothem data for data-model comparisons. Here, we illustrate this using 456 globally distributed speleothem delta O-18 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 the process of 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 isotope 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. Our analyses provide a protocol for using speleothem isotope data for model evaluation, including screening the observations to take into account the impact of speleothem mineralogy on delta O-18 values, 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.
    2019-08Journal article Open access Show more
  • A new MIS 5 to MIS 2 speleothem record from Sandkraal Cave on the South African Cape south coast
    Publication . Braun, Kerstin; Bar-Matthews, Miryam; Ayalon, Avner; Matthews, Alan; Zilberman, Tami; Zolotova, Natalya; Cowling, Richard M.; Karkanas, Panagiotis; Cawthra, Hayley C.; Fisher, Erich; Edwards, R. Lawrence; Li, Xianglei; Marean, Curtis W.
    We present new stable oxygen and carbon isotope composite records (delta O-18, delta C-13) of speleothems from Sandkraal Cave 1 (SK1) on the South African south coast for the time interval between 104 and 18 ka (with a hiatus between 48 and 41 ka). Statistical comparisons using kernel-based correlation analyses and semblance analyses based on continuous wavelet transforms inform the relationships of the new speleothem records to other proxies and their changes through time. Between 105 and similar to 70 ka, changes of speleothem delta O-18 values at SK1 are likely related to rainfall seasonality. Variations of delta C-13 values are associated with changes of vegetation density, prior carbonate precipitation (PCP), CO2 degassing in the cave, and possibly variations of the abundance of C-3 and C-4 grasses in the vegetation. The relationships of delta O-18 with other proxies shift between similar to 70 and 48 ka (Marine Isotope Stages 4-3) so that both stable isotope records now reflect CO2 degassing, evaporation, and PCP. Similar relationships also continue after the hiatus for the deposition phase between 42 and 18 ka. Our findings support modeling results suggesting drier conditions in the study area when the Southern Hemisphere westerlies are shifted north and the paleo-Agulhas Plain is exposed.
    2024Journal article Open access Show more
  • The SISAL database: a global resource to document oxygen and carbon isotope records from speleothems
    Publication . Atsawawaranunt, Kamolphat; Comas-Bru, Laia; Amirnezhad Mozhdehi, Sahar; Deininger, Michael; Harrison, Sandy P.; Baker, Andy; Boyd, Meighan; Kaushal, Nikita; Ahmad, Syed Masood; Ait Brahim, Yassine; Arienzo, Monica; Bajo, Petra; Braun, Kerstin; Burstyn, Yuval; Chawchai, Sakonvan; Duan, Wuhui; Hatvani, István Gábor; Hu, Jun; Kern, Zoltán; Labuhn, Inga; Lachniet, Matthew; Lechleiter, Franziska A.; Lorrey, Andrew; Pérez-Mejías, Carlos; Pickering, Robyn; Scroxton, Nick; Veiga-Pires, C.
    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.
    2018Journal article Open access Show more