TY  - JOUR
A1  - Goswami, Bedartha
A1  - Boers, Niklas
A1  - Rheinwalt, Aljoscha
A1  - Marwan, Norbert
A1  - Heitzig, Jobst
A1  - Breitenbach, Sebastian Franz Martin
A1  - Kurths, Jürgen
T1  - Abrupt transitions in time series with uncertainties
JF  - Nature Communications
N2  - Identifying abrupt transitions is a key question in various disciplines. Existing transition detection methods, however, do not rigorously account for time series uncertainties, often neglecting them altogether or assuming them to be independent and qualitatively similar. Here, we introduce a novel approach suited to handle uncertainties by representing the time series as a time-ordered sequence of probability density functions. We show how to detect abrupt transitions in such a sequence using the community structure of networks representing probabilities of recurrence. Using our approach, we detect transitions in global stock indices related to well-known periods of politico-economic volatility. We further uncover transitions in the El Niño-Southern Oscillation which coincide with periods of phase locking with the Pacific Decadal Oscillation. Finally, we provide for the first time an ‘uncertainty-aware’ framework which validates the hypothesis that ice-rafting events in the North Atlantic during the Holocene were synchronous with a weakened Asian summer monsoon.
Y1  - 2018
U6  - https://doi.org/10.1038/s41467-017-02456-6
SN  - 2041-1723
VL  - 9
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Lechleitner, Franziska A.
A1  - Breitenbach, Sebastian Franz Martin
A1  - Cheng, Hai
A1  - Plessen, Birgit
A1  - Rehfeld, Kira
A1  - Goswami, Bedartha
A1  - Marwan, Norbert
A1  - Eroglu, Deniz
A1  - Adkins, Jess F.
A1  - Haug, Gerald
T1  - Climatic and in-cave influences on delta O-18 and delta C-13 in a stalagmite from northeastern India through the last deglaciation
JF  - Quaternary research : an interdisciplinary journal
N2  - Northeastern (NE) India experiences extraordinarily pronounced seasonal climate, governed by the Indian summer monsoon (ISM). The vulnerability of this region to floods and droughts calls for detailed and highly resolved paleoclimate reconstructions to assess the recurrence rate and driving factors of ISM changes. We use stable oxygen and carbon isotope ratios (delta O-18 and delta C-13) from stalagmite MAW-6 from Mawmluh Cave to infer climate and environmental conditions in NE India over the last deglaciation (16-6ka). We interpret stalagmite delta O-18 as reflecting ISM strength, whereas delta C-13 appears to be driven by local hydroclimate conditions. Pronounced shifts in ISM strength over the deglaciation are apparent from the delta O-18 record, similarly to other records from monsoonal Asia. The ISM is weaker during the late glacial (LG) period and the Younger Dryas, and stronger during the BOlling-Allerod and Holocene. Local conditions inferred from the delta C-13 record appear to have changed less substantially over time, possibly related to the masking effect of changing precipitation seasonality. Time series analysis of the delta O-18 record reveals more chaotic conditions during the late glacial and higher predictability during the Holocene, likely related to the strengthening of the seasonal recurrence of the ISM with the onset of the Holocene.
KW  - Indian Summer Monsoon
KW  - stalagmite
KW  - oxygen isotopes
KW  - carbon isotopes
KW  - deglaciation
Y1  - 2017
U6  - https://doi.org/10.1017/qua.2017.72
SN  - 0033-5894
SN  - 1096-0287
VL  - 88
SP  - 458
EP  - 471
PB  - Cambridge Univ. Press
CY  - New York
ER  - 
TY  - JOUR
A1  - Breitenbach, Sebastian Franz Martin
A1  - Rehfeld, Kira
A1  - Goswami, Bedartha
A1  - Baldini, James U. L.
A1  - Ridley, H. E.
A1  - Kennett, D. J.
A1  - Prufer, K. M.
A1  - Aquino, Valorie V.
A1  - Asmerom, Yemane
A1  - Polyak, V. J.
A1  - Cheng, Hai
A1  - Kurths, Jürgen
A1  - Marwan, Norbert
T1  - Constructing Proxy Records from Age models (COPRA)
JF  - Climate of the past : an interactive open access journal of the European Geosciences Union
N2  - Reliable age models are fundamental for any palaeoclimate reconstruction. Available interpolation procedures between age control points are often inadequately reported, and very few translate age uncertainties to proxy uncertainties. Most available modeling algorithms do not allow incorporation of layer counted intervals to improve the confidence limits of the age model in question.
 We present a framework that allows detection and interactive handling of age reversals and hiatuses, depth-age modeling, and proxy-record reconstruction. Monte Carlo simulation and a translation procedure are used to assign a precise time scale to climate proxies and to translate dating uncertainties to uncertainties in the proxy values. The presented framework allows integration of incremental relative dating information to improve the final age model. The free software package COPRA1.0 facilitates easy interactive usage.
Y1  - 2012
U6  - https://doi.org/10.5194/cp-8-1765-2012
SN  - 1814-9324
VL  - 8
IS  - 5
SP  - 1765
EP  - 1779
PB  - Copernicus
CY  - Göttingen
ER  - 
TY  - JOUR
A1  - Comas-Bru, Laia
A1  - Harrison, Sandy P.
A1  - Werner, Martin
A1  - Rehfeld, Kira
A1  - Scroxton, Nick
A1  - Veiga-Pires, Cristina
A1  - Ahmad, Syed Masood
A1  - Brahim, Yassine Ait
A1  - Mozhdehi, Sahar Amirnezhad
A1  - Arienzo, Monica
A1  - Atsawawaranunt, Kamolphat
A1  - Baker, Andy
A1  - Braun, Kerstin
A1  - Breitenbach, Sebastian Franz Martin
A1  - Burstyn, Yuval
A1  - Chawchai, Sakonvan
A1  - Columbu, Andrea
A1  - Deininger, Michael
A1  - Demeny, Attila
A1  - Dixon, Bronwyn
A1  - Hatvani, Istvan Gabor
A1  - Hu, Jun
A1  - Kaushal, Nikita
A1  - Kern, Zoltan
A1  - Labuhn, Inga
A1  - Lachniet, Matthew S.
A1  - Lechleitner, Franziska A.
A1  - Lorrey, Andrew
A1  - Markowska, Monika
A1  - Nehme, Carole
A1  - Novello, Valdir F.
A1  - Oster, Jessica
A1  - Perez-Mejias, Carlos
A1  - Pickering, Robyn
A1  - Sekhon, Natasha
A1  - Wang, Xianfeng
A1  - Warken, Sophie
A1  - Atkinson, Tim
A1  - Ayalon, Avner
A1  - Baldini, James
A1  - Bar-Matthews, Miryam
A1  - Bernal, Juan Pablo
A1  - Boch, Ronny
A1  - Borsato, Andrea
A1  - Boyd, Meighan
A1  - Brierley, Chris
A1  - Cai, Yanjun
A1  - Carolin, Stacy
A1  - Cheng, Hai
A1  - Constantin, Silviu
A1  - Couchoud, Isabelle
A1  - Cruz, Francisco
A1  - Denniston, Rhawn
A1  - Dragusin, Virgil
A1  - Duan, Wuhui
A1  - Ersek, Vasile
A1  - Finne, Martin
A1  - Fleitmann, Dominik
A1  - Fohlmeister, Jens Bernd
A1  - Frappier, Amy
A1  - Genty, Dominique
A1  - Holzkamper, Steffen
A1  - Hopley, Philip
A1  - Johnston, Vanessa
A1  - Kathayat, Gayatri
A1  - Keenan-Jones, Duncan
A1  - Koltai, Gabriella
A1  - Li, Ting-Yong
A1  - Lone, Mahjoor Ahmad
A1  - Luetscher, Marc
A1  - Mattey, Dave
A1  - Moreno, Ana
A1  - Moseley, Gina
A1  - Psomiadis, David
A1  - Ruan, Jiaoyang
A1  - Scholz, Denis
A1  - Sha, Lijuan
A1  - Smith, Andrew Christopher
A1  - Strikis, Nicolas
A1  - Treble, Pauline
A1  - Unal-Imer, Ezgi
A1  - Vaks, Anton
A1  - Vansteenberge, Stef
A1  - Voarintsoa, Ny Riavo G.
A1  - Wong, Corinne
A1  - Wortham, Barbara
A1  - Wurtzel, Jennifer
A1  - Zhang, Haiwei
T1  - Evaluating model outputs using integrated global speleothem records of climate change since the last glacial
JF  - Climate of the past : an interactive open access journal of the European Geosciences Union
N2  - 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 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 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 δ18O 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.
Y1  - 2019
U6  - https://doi.org/10.5194/cp-15-1557-2019
SN  - 1814-9324
SN  - 1814-9332
VL  - 15
IS  - 4
SP  - 1557
EP  - 1579
PB  - Copernicus
CY  - Göttingen
ER  - 
TY  - JOUR
A1  - Lechleitner, Franziska A.
A1  - Baldini, James U. L.
A1  - Breitenbach, Sebastian Franz Martin
A1  - Fohlmeister, Jens Bernd
A1  - McIntyre, Cameron
A1  - Goswami, Bedartha
A1  - Jamieson, Robert A.
A1  - van der Voort, Tessa S.
A1  - Prufer, Keith
A1  - Marwan, Norbert
A1  - Culleton, Brendan J.
A1  - Kennett, Douglas J.
A1  - Asmerom, Yemane
A1  - Polyak, Victor
A1  - Eglinton, Timothy I.
T1  - Hydrological and climatological controls on radiocarbon concentrations in a tropical stalagmite
JF  - Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society
N2  - Precisely-dated stalagmites are increasingly important archives for the reconstruction of terrestrial paleoclimate at very high temporal resolution. In-depth understanding of local conditions at the cave site and of the processes driving stalagmite deposition is of paramount importance for interpreting proxy signals incorporated in stalagmite carbonate. Here we present a sub-decadally resolved dead carbon fraction (DCF) record for a stalagmite from Yok Balum Cave (southern Belize). The record is coupled to parallel stable carbon isotope (delta C-13) and U/Ca measurements, as well as radiocarbon (C-14) measurements from soils overlying the cave system. Using a karst carbon cycle model we disentangle the importance of soil and karst processes on stalagmite DCF incorporation, revealing a dominant host rock dissolution control on total DCF. Covariation between DCF, delta C-13, and U/Ca indicates that karst processes are a common driver of all three parameters, suggesting possible use of delta C-13 and trace element ratios to independently quantify DCF variability. A statistically significant multi-decadal lag of variable length exists between DCF and reconstructed solar activity, suggesting that solar activity influenced regional precipitation in Mesoamerica over the past 1500 years, but that the relationship was non-static. Although the precise nature of the observed lag is unclear, solar-induced changes in North Atlantic oceanic and atmospheric dynamics may play a role. (C) 2016 Elsevier Ltd. All rights reserved.
KW  - Stalagmite
KW  - Tropics
KW  - Radiocarbon
KW  - Trace elements
KW  - Hydroclimate
Y1  - 2016
U6  - https://doi.org/10.1016/j.gca.2016.08.039
SN  - 0016-7037
SN  - 1872-9533
VL  - 194
SP  - 233
EP  - 252
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Breitenbach, Sebastian Franz Martin
A1  - Adkins, Jess F.
A1  - Meyer, Hanno
A1  - Marwan, Norbert
A1  - Kumar, Kanikicharla Krishna
A1  - Haug, Gerald H.
T1  - Strong influence of water vapor source dynamics on stable isotopes in precipitation observed in Southern Meghalaya, NE India
N2  - To calibrate delta O-18 time-series from speleothems in the eastern Indian summer monsoon (ISM) region of India, and to understand the moisture regime over the northern Bay of Bengal (BoB) we analyze the delta O-18 and delta D of rainwater, collected in 2007 and 2008 near Cherrapunji, India. delta D values range from + 18.5 parts per thousand to 144.4 parts per thousand, while delta O-18 varies between +0.8 parts per thousand and 18.8 parts per thousand. The Local Meteoric Water Line (LMWL) is found to be indistinguishable from the Global Meteoric Water Line (GMWL). Late ISM (September-October) rainfall exhibits lowest delta O-18 and delta D values, with little relationship to the local precipitation amount. There is a trend to lighter isotope values over the course of the ISM, but it does not correlate with the patterns of temperature and rainfall amount delta O-18 and delta D time-series have to be interpreted with caution in terms of the 'amount effect' in this subtropical region. We find that the temporal trend in delta O-18 reflects increasing transport distance during the ISM, isotopic changes in the northern BoB surface waters during late ISM, and vapor re-equilibration with rain droplets. Using an isotope box model for surface ocean waters, we quantify the potential influence of river runoff on the isotopic composition of the seasonal freshwater plume in the northern BoB. Temporal variations in this source can contribute up to 25% of the observed changes in stable isotopes of precipitation in NE India. To delineate other moisture sources, we use backward trajectory computations and find a strong correlation between source region and isotopic composition. Palaeoclimatic stable isotope time-series from northeast Indian speleothems likely reflect changes in moisture source and transport pathway, as well as the isotopic composition of the BoB surface water, all of which in turn reflect ISM strength. Stalagmite records from the region can therefore be interpreted as integrated measures of the ISM strength.
Y1  - 2010
UR  - http://www.sciencedirect.com/science/journal/0012821X
U6  - https://doi.org/10.1016/j.epsl.2010.01.038
SN  - 0012-821X
ER  - 
TY  - JOUR
A1  - Atsawawaranunt, Kamolphat
A1  - Comas-Bru, Laia
A1  - Mozhdehi, Sahar Amirnezhad
A1  - Deininger, Michael
A1  - Harrison, Sandy P.
A1  - Baker, Andy
A1  - Boyd, Meighan
A1  - Kaushal, Nikita
A1  - Ahmad, Syed Masood
A1  - Brahim, Yassine Ait
A1  - Arienzo, Monica
A1  - Bajo, Petra
A1  - Braun, Kerstin
A1  - Burstyn, Yuval
A1  - Chawchai, Sakonvan
A1  - Duan, Wuhui
A1  - Hatvani, Istvan Gabor
A1  - Hu, Jun
A1  - Kern, Zoltan
A1  - Labuhn, Inga
A1  - Lachniet, Matthew
A1  - Lechleitner, Franziska A.
A1  - Lorrey, Andrew
A1  - Perez-Mejias, Carlos
A1  - Pickering, Robyn
A1  - Scroxton, Nick
A1  - Atkinson, Tim
A1  - Ayalon, Avner
A1  - Baldini, James
A1  - Bar-Matthews, Miriam
A1  - Pablo Bernal, Juan
A1  - Breitenbach, Sebastian Franz Martin
A1  - Boch, Ronny
A1  - Borsato, Andrea
A1  - Cai, Yanjun
A1  - Carolin, Stacy
A1  - Cheng, Hai
A1  - Columbu, Andrea
A1  - Couchoud, Isabelle
A1  - Cruz, Francisco
A1  - Demeny, Attila
A1  - Dominguez-Villar, David
A1  - Dragusin, Virgil
A1  - Drysdale, Russell
A1  - Ersek, Vasile
A1  - Finne, Martin
A1  - Fleitmann, Dominik
A1  - Fohlmeister, Jens Bernd
A1  - Frappier, Amy
A1  - Genty, Dominique
A1  - Holzkamper, Steffen
A1  - Hopley, Philip
A1  - Kathayat, Gayatri
A1  - Keenan-Jones, Duncan
A1  - Koltai, Gabriella
A1  - Luetscher, Marc
A1  - Li, Ting-Yong
A1  - Lone, Mahjoor Ahmad
A1  - Markowska, Monika
A1  - Mattey, Dave
A1  - McDermott, Frank
A1  - Moreno, Ana
A1  - Moseley, Gina
A1  - Nehme, Carole
A1  - Novello, Valdir F.
A1  - Psomiadis, David
A1  - Rehfeld, Kira
A1  - Ruan, Jiaoyang
A1  - Sekhon, Natasha
A1  - Sha, Lijuan
A1  - Sholz, Denis
A1  - Shopov, Yavor
A1  - Smith, Andrew
A1  - Strikis, Nicolas
A1  - Treble, Pauline
A1  - Unal-Imer, Ezgi
A1  - Vaks, Anton
A1  - Vansteenberge, Stef
A1  - Veiga-Pires, Cristina
A1  - Voarintsoa, Ny Riavo
A1  - Wang, Xianfeng
A1  - Wong, Corinne
A1  - Wortham, Barbara
A1  - Wurtzel, Jennifer
A1  - Zong, Baoyun
T1  - The SISAL database
BT  - a global resource to document oxygen and carbon isotope records from speleothems
JF  - Earth System Science Data
N2  - 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 (delta O-18, delta C-13) measurements are referenced by distance from the top or bottom 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 on the full range of measurements carried out on each speleothem and information on the cave system that is relevant to the interpretation of the records, as well as citations for both publications and archived data.
Y1  - 2018
U6  - https://doi.org/10.5194/essd-10-1687-2018
SN  - 1866-3508
SN  - 1866-3516
VL  - 10
IS  - 3
SP  - 1687
EP  - 1713
PB  - Copernicus
CY  - Göttingen
ER  - 
TY  - JOUR
A1  - Lechleitner, Franziska A.
A1  - Breitenbach, Sebastian Franz Martin
A1  - Rehfeld, Kira
A1  - Ridley, Harriet E.
A1  - Asmerom, Yemane
A1  - Prufer, Keith M.
A1  - Marwan, Norbert
A1  - Goswami, Bedartha
A1  - Kennett, Douglas J.
A1  - Aquino, Valorie V.
A1  - Polyak, Victor
A1  - Haug, Gerald H.
A1  - Eglinton, Timothy I.
A1  - Baldini, James U. L.
T1  - Tropical rainfall over the last two millennia: evidence for a low-latitude hydrologic seesaw
JF  - Scientific reports
N2  - The presence of a low-to mid-latitude interhemispheric hydrologic seesaw is apparent over orbital and glacial-interglacial timescales, but its existence over the most recent past remains unclear. Here we investigate, based on climate proxy reconstructions from both hemispheres, the inter-hemispherical phasing of the Intertropical Convergence Zone (ITCZ) and the low-to mid-latitude teleconnections in the Northern Hemisphere over the past 2000 years. A clear feature is a persistent southward shift of the ITCZ during the Little Ice Age until the beginning of the 19th Century. Strong covariation between our new composite ITCZ-stack and North Atlantic Oscillation (NAO) records reveals a tight coupling between these two synoptic weather and climate phenomena over decadal-to-centennial timescales. This relationship becomes most apparent when comparing two precisely dated, high-resolution paleorainfall records from Belize and Scotland, indicating that the low-to mid-latitude teleconnection was also active over annual-decadal timescales. It is likely a combination of external forcing, i.e., solar and volcanic, and internal feedbacks, that drives the synchronous ITCZ and NAO shifts via energy flux perturbations in the tropics.
Y1  - 2017
U6  - https://doi.org/10.1038/srep45809
SN  - 2045-2322
VL  - 7
PB  - Nature Publ. Group
CY  - London
ER  -