129 results on '"Breitenbach, Sebastian F. M."'
Search Results
2. Warming drives dissolved organic carbon export from pristine alpine soils
- Author
-
Pearson, Andrew R., Fox, Bethany R. S., Hellstrom, John C., Vandergoes, Marcus J., Breitenbach, Sebastian F. M., Drysdale, Russell N, Höpker, Sebastian N., Wood, Christopher T., Schiller, Martin, and Hartland, Adam
- Published
- 2024
- Full Text
- View/download PDF
3. Sampling rate-corrected analysis of irregularly sampled time series
- Author
-
Braun, Tobias, Fernandez, Cinthya N., Eroglu, Deniz, Hartland, Adam, Breitenbach, Sebastian F. M., and Marwan, Norbert
- Subjects
Statistics - Methodology ,Nonlinear Sciences - Chaotic Dynamics - Abstract
The analysis of irregularly sampled time series remains a challenging task requiring methods that account for continuous and abrupt changes of sampling resolution without introducing additional biases. The edit-distance is an effective metric to quantitatively compare time series segments of unequal length by computing the cost of transforming one segment into the other. We show that transformation costs generally exhibit a non-trivial relationship with local sampling rate. If the sampling resolution undergoes strong variations, this effect impedes unbiased comparison between different time episodes. We study the impact of this effect on recurrence quantification analysis, a framework that is well-suited for identifying regime shifts in nonlinear time series. A constrained randomization approach is put forward to correct for the biased recurrence quantification measures. This strategy involves the generation of a novel type of time series and time axis surrogates which we call sampling rate constrained (SRC) surrogates. We demonstrate the effectiveness of the proposed approach with a synthetic example and an irregularly sampled speleothem proxy record from Niue island in the central tropical Pacific. Application of the proposed correction scheme identifies a spurious transition that is solely imposed by an abrupt shift in sampling rate and uncovers periods of reduced seasonal rainfall predictability associated with enhanced ENSO and tropical cyclone activity.
- Published
- 2021
- Full Text
- View/download PDF
4. Deciphering local and regional hydroclimate resolves contradicting evidence on the Asian monsoon evolution
- Author
-
Wolf, Annabel, Ersek, Vasile, Braun, Tobias, French, Amanda D., McGee, David, Bernasconi, Stefano M., Skiba, Vanessa, Griffiths, Michael L., Johnson, Kathleen R., Fohlmeister, Jens, Breitenbach, Sebastian F. M., Pausata, Francesco S. R., Tabor, Clay R., Longman, Jack, Roberts, William H. G., Chandan, Deepak, Peltier, W. Richard, Salzmann, Ulrich, Limbert, Deborah, Trinh, Hong Quan, and Trinh, Anh Duc
- Published
- 2023
- Full Text
- View/download PDF
5. Decline in seasonal predictability potentially destabilized Classic Maya societies
- Author
-
Braun, Tobias, Breitenbach, Sebastian F. M., Skiba, Vanessa, Lechleitner, Franziska A., Ray, Erin E., Baldini, Lisa M., Polyak, Victor J., Baldini, James U. L., Kennett, Douglas J., Prufer, Keith M., and Marwan, Norbert
- Published
- 2023
- Full Text
- View/download PDF
6. Recurring summer and winter droughts from 4.2-3.97 thousand years ago in north India
- Author
-
Giesche, Alena, Hodell, David A., Petrie, Cameron A., Haug, Gerald H., Adkins, Jess F., Plessen, Birgit, Marwan, Norbert, Bradbury, Harold J., Hartland, Adam, French, Amanda D., and Breitenbach, Sebastian F. M.
- Published
- 2023
- Full Text
- View/download PDF
7. Detecting and quantifying palaeoseasonality in stalagmites using geochemical and modelling approaches
- Author
-
Baldini, James U. L., Lechleitner, Franziska A., Breitenbach, Sebastian F. M., van Hunen, Jeroen, Baldini, Lisa M., Wynn, Peter M., Jamieson, Robert A., Ridley, Harriet E., Baker, Alex J., Walczak, Izabela W., and Fohlmeister, Jens
- Subjects
Physics - Geophysics - Abstract
Stalagmites are an extraordinarily powerful resource for the reconstruction of climatological palaeoseasonality. Here, we provide a comprehensive review of different types of seasonality preserved by stalagmites and methods for extracting this information. A new drip classification scheme is introduced, which facilitates the identification of stalagmites fed by seasonally responsive drips and which highlights the wide variability in drip types feeding stalagmites. This hydrological variability, combined with seasonality in Earth atmospheric processes, meteoric precipitation, biological processes within the soil, and cave atmosphere composition means that every stalagmite retains a different and distinct (but correct) record of environmental conditions. Replication of a record is extremely useful but should not be expected unless comparing stalagmites affected by the same processes in the same proportion. A short overview of common microanalytical techniques is presented, and suggested best practice discussed. In addition to geochemical methods, a new modelling technique for extracting meteoric precipitation and temperature palaeoseasonality from stalagmite d18O data is discussed and tested with both synthetic and real-world datasets. Finally, world maps of temperature, meteoric precipitation amount, and meteoric precipitation oxygen isotope ratio seasonality are presented and discussed, with an aim of helping to identify regions most sensitive to shifts in seasonality.
- Published
- 2021
- Full Text
- View/download PDF
8. Linked fire activity and climate whiplash in California during the early Holocene
- Author
-
Homann, Julia, Oster, Jessica L., de Wet, Cameron B., Breitenbach, Sebastian F. M., and Hoffmann, Thorsten
- Published
- 2022
- Full Text
- View/download PDF
9. Drought-Induced Civil Conflict Among the Ancient Maya
- Author
-
Kennett, Douglas J., Masson, Marilyn, Lope, Carlos Peraza, Serafin, Stanley, George, Richard J., Spencer, Tom C., Hoggarth, Julie A., Culleton, Brendan J., Harper, Thomas K., Prufer, Keith M., Milbrath, Susan, Russell, Bradley W., González, Eunice Uc, McCool, Weston C., Aquino, Valorie V., Paris, Elizabeth H., Curtis, Jason H., Marwan, Norbert, Zhang, Mingua, Asmerom, Yemane, Polyak, Victor J., Carolin, Stacy A., James, Daniel H., Mason, Andrew J., Henderson, Gideon M., Brenner, Mark, Baldini, James U. L., Breitenbach, Sebastian F. M., and Hodell, David A.
- Published
- 2022
- Full Text
- View/download PDF
10. Spatio-temporal dynamics of speleothem growth and glaciation in the British Isles.
- Author
-
Panitz, Sina, Rogerson, Michael, Longman, Jack, Scroxton, Nick, Lawson, Tim J., Atkinson, Tim C., Ersek, Vasile, Baldini, James, Baldini, Lisa, Umbo, Stuart, Lone, Mahjoor A., Henderson, Gideon M., and Breitenbach, Sebastian F. M.
- Abstract
Reconstructing the spatio-temporal dynamics of glaciations and permafrost largely relies on surface deposits, and is therefore a challenge for every glacial older than the last due to erosion. Consequently, glaciations and permafrost remain poorly constrained worldwide before c. 30 ka. Since speleothems (carbonate cave deposits) form from drip water and generally indicate the absence of an ice sheet and permafrost, we evaluate how speleothem growth phases defined by U-series dates align with past glacial-interglacial cycles. Further, we make the first systematic comparison of the spatial distribution of speleothem dates with independent reconstructions of the history of the British-Irish Ice Sheet (BIIS) to test how well geomorphologic ice reconstructions are replicated in the cave record. The frequency distribution of 1,020 U-series dates based on three different dating methods between 300 and 5 ka shows statistically significant periods of speleothem growth during the last interglacial and several interstadials during the last glacial. A pronounced decline in speleothem growth coincides with the Last Glacial Maximum, before broad reactivation during deglaciation and into the Holocene. Spatio-temporal patterns in speleothem growth between 31 and 15 ka agree well with the surface-deposit-based reconstruction of the last BIIS. In data-rich regions, such as northern England, ice dynamics are well-replicated in the cave record, which provide additional evidence about the spatio-temporal distribution of permafrost dynamics. Beyond the Last Glacial Maximum, the distribution of speleothem dates across the British Isles offers the opportunity to improve chronological constraints on past ice sheet variability, with evidence for a highly dynamic Scottish ice sheet during the last glacial. The results provide independent evidence of ice distribution complementary to studies of surface geomorphology and geology, and the potential to extend reconstructions into permafrost and earlier glacial cycles. Whilst undersampling is currently the main limitation for speleothem-based ice and permafrost reconstruction even in relatively well-sampled parts of the British Isles, we show that speleothem dates obtained using modern mass spectrometry techniques reveal a higher spatio-temporal resolution of glacial-interglacial cycles and glacial extent than previously possible. Further study of leads and lags in speleothem growth compared to surface deposition may provide new insights into landscape-scale dynamics during ice sheet growth and retreat. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
11. Mid‐Holocene rainfall seasonality and ENSO dynamics over the south‐western Pacific
- Author
-
Nava‐Fernandez, Cinthya, primary, Braun, Tobias, additional, Pederson, Chelsea L., additional, Fox, Bethany, additional, Hartland, Adam, additional, Kwiecien, Ola, additional, Höpker, Sebastian N., additional, Bernasconi, Stefano, additional, Jaggi, Madalina, additional, Hellstrom, John, additional, Gázquez, Fernando, additional, French, Amanda, additional, Marwan, Norbert, additional, Immenhauser, Adrian, additional, and Breitenbach, Sebastian F. M., additional
- Published
- 2024
- Full Text
- View/download PDF
12. Rainfall variations in central Indo-Pacific over the past 2,700 y
- Author
-
Tan, Liangcheng, Shen, Chuan-Chou, Löwemark, Ludvig, Chawchai, Sakonvan, Edwards, R. Lawrence, Cai, Yanjun, Breitenbach, Sebastian F. M., Cheng, Hai, Chou, Yu-Chen, Duerrast, Helmut, Partin, Judson W., Cai, Wenju, Chabangborn, Akkaneewut, Gao, Yongli, Kwiecien, Ola, Wu, Chung-Che, Shi, Zhengguo, Hsu, Huang-Hsiung, and Wohlfarth, Barbara
- Published
- 2019
13. Author Correction: Climate variations of Central Asia on orbital to millennial timescales
- Author
-
Cheng, Hai, Spötl, Christoph, Breitenbach, Sebastian F. M., Sinha, Ashish, Wassenburg, Jasper A., Jochum, Klaus Peter, Scholz, Denis, Li, Xianglei, Yi, Liang, Peng, Youbing, Lv, Yanbin, Zhang, Pingzhong, Votintseva, Antonina, Loginov, Vadim, Ning, Youfeng, Kathayat, Gayatri, and Lawrence Edwards, R.
- Published
- 2021
- Full Text
- View/download PDF
14. Controls on Speleothem Initial 234U/238U Ratios in a Monsoon Climate
- Author
-
Oster, Jessica L., primary, Ronay, Elli R., additional, Sharp, Warren D., additional, Breitenbach, Sebastian F. M., additional, and Furbish, David J., additional
- Published
- 2023
- Full Text
- View/download PDF
15. Defining paleoclimatic routes and opportunities for hominin dispersals across Iran
- Author
-
Shoaee, Mohammad Javad, primary, Breeze, Paul S., additional, Drake, Nick A., additional, Hashemi, Seyyed Milad, additional, Vahdati Nasab, Hamed, additional, Breitenbach, Sebastian F. M., additional, Stevens, Thomas, additional, Boivin, Nicole, additional, and Petraglia, Michael D., additional
- Published
- 2023
- Full Text
- View/download PDF
16. Sensitivity of speleothem records in the Indian Summer Monsoon region to dry season infiltration
- Author
-
Ronay, Elli R., Breitenbach, Sebastian F. M., and Oster, Jessica L.
- Published
- 2019
- Full Text
- View/download PDF
17. Past fire dynamics inferred from polycyclic aromatic hydrocarbons and monosaccharide anhydrides in a stalagmite from the archaeological site of Mayapan, Mexico.
- Author
-
Homann, Julia, Karbach, Niklas, Carolin, Stacy A., James, Daniel H., Hodell, David, Breitenbach, Sebastian F. M., Kwiecien, Ola, Brenner, Mark, Peraza Lope, Carlos, and Hoffmann, Thorsten
- Subjects
STALACTITES & stalagmites ,SPELEOTHEMS ,POLYCYCLIC aromatic hydrocarbons ,ARCHAEOLOGICAL excavations ,MONOSACCHARIDES ,ANHYDRIDES ,FIRE management ,DETECTION limit - Abstract
Speleothems (cave stalagmites) contain inorganic and organic substances that can be used to infer past changes in local and regional paleoenvironmental conditions. Specific biomarkers can be employed to elucidate the history of past fires, caused by interactions among climate, regional hydrology, vegetation, humans, and fire activity. We conducted a simple solid–liquid extraction on pulverised carbonate samples to prepare them for analysis of 16 polycyclic aromatic hydrocarbons (PAHs) and three monosaccharide anhydrides (MAs). The preparation method requires only small samples (0.5–1.0 g); PAHs and MAs were measured by GC–MS and LC–HILIC–MS, respectively. Detection limits range from 0.05–2.1 ng for PAHs and 0.01–0.1 ng for MAs. We applied the method to 10 samples from a ∼ 400-year-old stalagmite from Cenote Ch'en Mul, at Mayapan (Mexico), the largest Postclassic Maya capital of the Yucatán Peninsula. We found a strong correlation (r = 0.75, p < 0.05) between the major MA (levoglucosan) and non-alkylated PAHs (Σ 15). We investigated multiple diagnostic PAH and MA ratios and found that although not all were applicable as paleo-fire proxies, ratios that combine PAHs with MAs are promising tools for identifying different fire regimes and inferring the type of fuel burned. In the 1950s and 1960s, levoglucosan and Σ 15 concentrations roughly doubled compared to other times in the last 400 years, suggesting greater fire activity at Mayapan during these two decades. The higher concentrations of fire markers may have been a consequence of land clearance at the site and exploration of the cave by Carnegie Institution archaeologists. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
18. Paleolithic occupation of arid Central Asia in the Middle Pleistocene
- Author
-
Finestone, Emma M., primary, Breeze, Paul S., additional, Breitenbach, Sebastian F. M., additional, Drake, Nick, additional, Bergmann, Laura, additional, Maksudov, Farhod, additional, Muhammadiyev, Akmal, additional, Scott, Pete, additional, Cai, Yanjun, additional, Khatsenovich, Arina M., additional, Rybin, Evgeny P., additional, Nehrke, Gernot, additional, Boivin, Nicole, additional, and Petraglia, Michael, additional
- Published
- 2022
- Full Text
- View/download PDF
19. Paleolithic occupation of arid Central Asia in the Middle Pleistocene
- Author
-
Peresani, Marco, Finestone, Emma M., Breeze, Paul S., Breitenbach, Sebastian F. M., Drake, Nick, Bergmann, Laura, Maksudov, Farhod, Muhammadiyev, Akmal, Scott, Pete, Cai, Yanjun, Khatsenovich, Arina M., Rybin, Evgeny P., Nehrke, Gernot, Boivin, Nicole, and Petraglia, Michael
- Subjects
Multidisciplinary ,Asia ,Archaeology ,Fossils ,Animals ,Water ,Hominidae ,Occupations - Abstract
Central Asia is positioned at a crossroads linking several zones important to hominin dispersal during the Middle Pleistocene. However, the scarcity of stratified and dated archaeological material and paleoclimate records makes it difficult to understand dispersal and occupation dynamics during this time period, especially in arid zones. Here we compile and analyze paleoclimatic and archaeological data from Pleistocene Central Asia, including examination of a new layer-counted speleothem-based multiproxy record of hydrological changes in southern Uzbekistan at the end of MIS 11. Our findings indicate that Lower Palaeolithic sites in the steppe, semi-arid, and desert zones of Central Asia may have served as key areas for the dispersal of hominins into Eurasia during the Middle Pleistocene. In agreement with previous studies, we find that bifaces occur across these zones at higher latitudes and in lower altitudes relative to the other Paleolithic assemblages. We argue that arid Central Asia would have been intermittently habitable during the Middle Pleistocene when long warm interglacial phases coincided with periods when the Caspian Sea was experiencing consistently high water levels, resulting in greater moisture availability and more temperate conditions in otherwise arid regions. During periodic intervals in the Middle Pleistocene, the local environment of arid Central Asia was likely a favorable habitat for paleolithic hominins and was frequented by Lower Paleolithic toolmakers producing bifaces. Introduction Climate of arid Central Asia The timing of the earliest occupation of Central Asia Features of the lower paleolithic of Central Asia Taxonomy of early paleolithic toolmakers Materials and methods - Geographic distribution and elevation of Paleolithic assemblages - A speleothem-based proxy record of hydrological changes Results - Geographic distribution of assemblages - Speleothem age model–combining U/Th dating and layer counting - Speleothem greyscale values - Stable isotopes - Laser ablation Mg/Ca element data Discussion - Climatic factors - Hominin habitat preference - Archaeological site preservation in arid Central Asia Conclusion
- Published
- 2022
20. Protracted Indian monsoon droughts of the past millennium and their societal impacts
- Author
-
Kathayat, Gayatri, primary, Sinha, Ashish, additional, Breitenbach, Sebastian F. M., additional, Tan, Liangcheng, additional, Spötl, Christoph, additional, Li, Hanying, additional, Dong, Xiyu, additional, Zhang, Haiwei, additional, Ning, Youfeng, additional, Allan, Robert J., additional, Damodaran, Vinita, additional, Edwards, R. Lawrence, additional, and Cheng, Hai, additional
- Published
- 2022
- Full Text
- View/download PDF
21. Controls on Speleothem Initial 234U/238U Ratios in a Monsoon Climate.
- Author
-
Oster, Jessica L., Ronay, Elli R., Sharp, Warren D., Breitenbach, Sebastian F. M., and Furbish, David J.
- Subjects
STALACTITES & stalagmites ,URANIUM isotopes ,WATER seepage ,RAINFALL ,MONSOONS ,SEEPAGE ,SPELEOTHEMS - Abstract
Speleothem initial uranium isotope ratios ((234U/238U)i) can be influenced by processes along the seepage water flow‐path including alpha‐recoil into porewater during 238U decay and hostrock weathering, the balance of which can reflect the infiltration rate. Thus, speleothem (234U/238U)i may provide information about past changes in rainfall amounts. However, the utility of (234U/238U)i as a paleo‐infiltration proxy has only been explored in a limited set of rainfall regimes. We present a speleothem (234U/238U)i record from Mawmluh Cave in northeast India, an area influenced by the Indian Summer Monsoon, covering 1964–2012 CE. Speleothem (234U/238U)i was relatively constant from 1964 to 1984 but then linearly increased by 0.05 over ∼15 years, a trend that does not correspond with observed rainfall changes. To evaluate potential drivers of (234U/238U)i variability, we model the evolution of water (234U/238U) in a simple karst system using an advection‐reaction model parameterized by Mawmluh Cave variables. Although varying infiltration influences modeled water (234U/238U), the larger, sustained change observed in the speleothem record can only be modeled by varying the U concentration and (234U/238U) of the weathering hostrock. This suggests that larger shifts in speleothem (234U/238U)i may result from flow path changes, bringing waters in contact with hostrock of variable U characteristics. Consideration of published Mawmluh Cave records suggests that these mechanisms may also explain variability in stalagmite (234U/238U)i on precessional timescales. Further examination of speleothems (234U/238U)i from climates characterized by high rainfall and extensive weathering is warranted to better constrain the controls on (234U/238U)i in these dynamic environments. Plain Language Summary: Chemical indicators from stalagmites are useful in reconstructing changes in monsoon systems. However, the chemical measurements typically made on stalagmites do not provide direct reconstructions of rainfall amount. We developed a record of uranium isotope variability over the last 60 years in a stalagmite from Northeast India to evaluate this potential metric of past monsoon rainfall. We use a geochemical model to evaluate the climatic and environmental controls on uranium isotopes in cave drip waters and stalagmites. Comparison of our record with measured rainfall indicates that the relationship between rainfall amount and uranium isotope ratios is opposite to that observed in arid environments. Further, a large linear increase in uranium isotopes between ∼1985 and 2000 CE does not correspond to a change in rainfall. Rather, our model suggests that large changes in uranium isotopes likely result from the opening up of new water flow paths and the dissolution of fresh hostrocks. Investigation of previously analyzed stalagmites from the cave reveals a correspondence between uranium isotopes and insolation, suggesting that sustained changes in rainfall amount, coupled with opening of new flow paths, may be recorded in stalagmite uranium isotopes over the past ∼100,000 years. Key Points: Modern record of speleothem initial uranium isotope ratios from NE India shows a linear increase that does not correspond to rainfallGeochemical model shows that dripwater U isotopes respond to changing infiltration and changing U characteristics of weathering rockLong‐term variations in speleothem U isotope ratios from NE India record infiltration with additional control of changes in flow path [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
22. A simplified isotope dilution approach for the U–Pb dating of speleogenic and other low-232Th carbonates by multi-collector ICP-MS
- Author
-
Mason, Andrew J., Vaks, Anton, Breitenbach, Sebastian F. M., Hooker, John N., and Henderson, Gideon M.
- Subjects
ComputingMethodologies_DOCUMENTANDTEXTPROCESSING ,F800 ,F600 - Abstract
We describe a new method for the measurement of U/Pb ratios by isotope dilution multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) for the dating of geologically young clean carbonates, particularly speleothems. The method is intended for materials containing little or no initial 232Th. We illustrate and validate the method with four examples ranging from 0.57 to 20 Ma. The new method is capable of applying the 235U–207Pb and 238U–234U–206Pb chronometers, common Pb and quantifiable residual 234U/238U disequilibrium permitting. These provide an alternative to the more widely used 238U–206Pb chronometer, which can be highly inaccurate for samples that are < ca. 20 million years old, owing to uncertainties in the excess initial 234U (hence, excess radiogenic 206Pb) commonly observed in speleothems.
- Published
- 2022
23. Details of analyses and analytical procedures from Speleological and environmental history of Lida Ajer cave, western Sumatra
- Author
-
Louys, Julien, Duval, Mathieu, Price, Gilbert J., Westaway, Kira, Zaim, Yahdi, Rizal, Yan, Aswan, Puspaningrum, Mika, Trihascaryo, Agus, Breitenbach, Sebastian F. M., Kwiecien, Ola, Cai, Yanjun, Higgins, Penny, Albers, Paul, de Vos, John, and Roberts, Patrick
- Abstract
Raw data and methodology
- Published
- 2022
- Full Text
- View/download PDF
24. A simplified isotope dilution approach for the U–Pb dating of speleogenic and other low-<sup>232</sup>Th carbonates by multi-collector ICP-MS
- Author
-
Mason, Andrew J., primary, Vaks, Anton, additional, Breitenbach, Sebastian F. M., additional, Hooker, John N., additional, and Henderson, Gideon M., additional
- Published
- 2022
- Full Text
- View/download PDF
25. Climate variations of Central Asia on orbital to millennial timescales
- Author
-
Cheng, Hai, Spötl, Christoph, Breitenbach, Sebastian F. M., Sinha, Ashish, Wassenburg, Jasper A., Jochum, Klaus Peter, Scholz, Denis, Li, Xianglei, Yi, Liang, Peng, Youbing, Lv, Yanbin, Zhang, Pingzhong, Votintseva, Antonina, Loginov, Vadim, Ning, Youfeng, Kathayat, Gayatri, and Edwards, R. Lawrence
- Published
- 2016
- Full Text
- View/download PDF
26. Lignin oxidation products in soil, dripwater and speleothems from four different sites in New Zealand
- Author
-
Heidke, Inken, primary, Hartland, Adam, additional, Scholz, Denis, additional, Pearson, Andrew, additional, Hellstrom, John, additional, Breitenbach, Sebastian F. M., additional, and Hoffmann, Thorsten, additional
- Published
- 2021
- Full Text
- View/download PDF
27. Speleological and environmental history of Lida Ajer cave, western Sumatra.
- Author
-
Louys, Julien, Duval, Mathieu, Price, Gilbert J., Westaway, Kira, Zaim, Yahdi, Rizal, Yan, Aswan, Puspaningrum, Mika, Trihascaryo, Agus, Breitenbach, Sebastian F. M., Kwiecien, Ola, Cai, Yanjun, Higgins, Penny, Albers, Paul C. H., de Vos, John, and Roberts, Patrick
- Subjects
ENVIRONMENTAL history ,DENTAL enamel ,CAVES ,TROPICAL forests ,PALEOECOLOGY ,FOSSIL hominids ,OXYGEN isotopes ,CARBON isotopes - Abstract
Some of the earliest evidence for the presence of modern humans in rainforests has come from the fossil deposits of Lida Ajer in Sumatra. Two human teeth from this cave were estimated to be 73–63 thousand years old, which is significantly older than some estimates of modern human migration out of Africa based on genetic data. The deposits were interpreted as being associated with a rainforest environment based largely on the presence of abundant orangutan fossils. As well as the main fossil-bearing chamber, fossil-bearing passages are present below a sinkhole, although the relationship between the different fossil deposits has only been tenuously established. Here, we provide significant new sedimentological, geochronological and palaeoecological data aimed at reconstructing the speleological and environmental history of the cave and the clastic and fossil deposits therein. Our data suggest that the Lida Ajer fossils were deposited during Marine Isotope Stage 4, with fossils from the lower passages older than the main fossil chamber. Our use of stable carbon and oxygen isotope analyses of mammalian tooth enamel demonstrates that early humans probably occupied a closed-canopy forest very similar to those present in the region today, although the fossil orangutans may have occupied a slightly different niche. This article is part of the theme issue 'Tropical forests in the deep human past'. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
28. Pacific climate reflected in Waipuna Cave drip water hydrochemistry
- Author
-
Nava-Fernandez, Cinthya, Hartland, Adam, Gázquez, Fernando, Kwiecien, Ola, Marwan, Norbert, Fox, Bethany, Hellstrom, John, Pearson, Andrew, Ward, Brittany, French, Amanda, Hodell, David A., Immenhauser, Adrian, Breitenbach, Sebastian F. M., and Publica
- Subjects
ddc:550 ,F700 ,F800 - Abstract
Cave microclimate and geochemical monitoring is vitally important for correct interpretations of proxy time series from speleothems with regard to past climatic and environmental dynamics. We present results of a comprehensive cave-monitoring programme in Waipuna Cave in the North Island of New Zealand, a region that is strongly influenced by the Southern Westerlies and the El Niño–Southern Oscillation (ENSO). This study aims to characterise the response of the Waipuna Cave hydrological system to atmospheric circulation dynamics in the southwestern Pacific region in order to assure the quality of ongoing palaeo-environmental reconstructions from this cave. Drip water from 10 drip sites was collected at roughly monthly intervals for a period of ca. 3 years for isotopic (δ18O, δD, d-excess parameter, δ17O, and 17Oexcess) and elemental (Mg∕Ca and Sr∕Ca) analysis. The monitoring included spot measurements of drip rates and cave air CO2 concentration. Cave air temperature and drip rates were also continuously recorded by automatic loggers. These datasets were compared to surface air temperature, rainfall, and potential evaporation from nearby meteorological stations to test the degree of signal transfer and expression of surface environmental conditions in Waipuna Cave hydrochemistry. Based on the drip response dynamics to rainfall and other characteristics, we identified three types of discharge associated with hydrological routing in Waipuna Cave: (i) type 1 – diffuse flow, (ii) type 2 – fracture flow, and (iii) type 3 – combined flow. Drip water isotopes do not reflect seasonal variability but show higher values during severe drought. Drip water δ18O values are characterised by small variability and reflect the mean isotopic signature of precipitation, testifying to rapid and thorough homogenisation in the epikarst. Mg∕Ca and Sr∕Ca ratios in drip waters are predominantly controlled by prior calcite precipitation (PCP). Prior calcite precipitation is strongest during austral summer (December–February), reflecting drier conditions and a lack of effective infiltration, and is weakest during the wet austral winter (July–September). The Sr∕Ca ratio is particularly sensitive to ENSO conditions due to the interplay of congruent or incongruent host rock dissolution, which manifests itself in lower Sr∕Ca in above-average warmer and wetter (La Niña-like) conditions. Our microclimatic observations at Waipuna Cave provide a valuable baseline for the rigorous interpretation of speleothem proxy records aiming at reconstructing the past expression of Pacific climate modes.
- Published
- 2020
29. SISALv2: A comprehensive speleothem isotope database with multiple age-depth models
- Author
-
Comas-Bru, Laia, Rehfeld, Kira, Roesch, Carla, Amirnezhad-Mozhdehi, Sahar, Harrison, Sandy P., Atsawawaranunt, Kamolphat, Ahmad, Syed Masood, Ait Brahim, Yassine, Baker, Andy, Bosomworth, Matthew, Breitenbach, Sebastian F. M., Burstyn, Yuval, Columbu, Andrea, Deininger, Michael, Demény, Attila, Dixon, Bronwyn, Fohlmeister, Jens, Hatvani, István Gábor, Hu, Jun, Kaushal, Nikita, Kern, Zoltán, Labuhn, Inga, Lechleitner, Franziska A., Lorrey, Andrew, Martrat, Belen, Novello, Valdir Felipe, Oster, Jessica, Pérez-Mejías, Carlos, Scholz, Denis, Scroxton, Nick, Sinha, Nitesh, Ward, Brittany Marie, Warken, Sophie, Zhang, Haiwei, and the SISAL members
- Subjects
cave, speleothem, database, age-depth model - Abstract
Characterising the temporal uncertainty in palaeoclimate records is crucial for analysing past climate change, for correlating climate events between records, for assessing climate periodicities, identifying potential triggers, and to evaluate climate model simulations. The first global compilation of speleothem isotope records by the SISAL (Speleothem Isotope Synthesis and Analysis) Working Group showed that age-model uncertainties are not systematically reported in the published literature and these are only available for a limited number of records (ca. 15 %, n = 107/691). To improve the usefulness of the SISAL database, we have (i) improved the database’s spatio-temporal coverage and (ii) created new chronologies using seven different approaches for age-depth modelling. We have applied these alternative chronologies to the records from the first version of the SISAL database (SISALv1) and to new records compiled since the release of SISALv1. This paper documents the necessary changes in the structure of the SISAL database to accommodate the inclusion of the new age-models and their uncertainties as well as the expansion of the database to include new records and the quality-control measures applied. This paper also documents the age-depth model approaches used to calculate the new chronologies. The updated version of the SISAL database (SISALv2) contains isotopic data from 691 speleothem records from 294 cave sites and new age-depth models, including age-depth temporal uncertainties for 512 speleothems. SISALv2 is available at https://doi.org/10.17864/1947.242 (Comas-Bru et al., 2020).
- Published
- 2020
30. A simplified isotope dilution approach for the U–Pb dating of speleogenic and other low-232Th carbonates by multi-collector ICP-MS.
- Author
-
Mason, Andrew J., Vaks, Anton, Breitenbach, Sebastian F. M., Hooker, John N., and Henderson, Gideon M.
- Subjects
ISOTOPE dilution analysis ,URANIUM-lead dating ,INDUCTIVELY coupled plasma mass spectrometry ,CARBONATES ,SPELEOTHEMS - Abstract
We describe a new method for the measurement of U/Pb ratios by isotope dilution multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) for the dating of geologically young clean carbonates, particularly speleothems. The method is intended for materials containing little or no initial 232 Th. We illustrate and validate the method with four examples ranging from 0.57 to 20 Ma. The new method is capable of applying the 235 U– 207 Pb and 238 U– 234 U– 206 Pb chronometers, common Pb and quantifiable residual 234U/238U disequilibrium permitting. These provide an alternative to the more widely used 238 U– 206 Pb chronometer, which can be highly inaccurate for samples that are < ca. 20 million years old, owing to uncertainties in the excess initial 234 U (hence, excess radiogenic 206 Pb) commonly observed in speleothems. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
31. Pacific climate reflected in Waipuna Cave drip water hydrochemistry
- Author
-
Nava-Fernandez, Cinthya, primary, Hartland, Adam, additional, Gázquez, Fernando, additional, Kwiecien, Ola, additional, Marwan, Norbert, additional, Fox, Bethany, additional, Hellstrom, John, additional, Pearson, Andrew, additional, Ward, Brittany, additional, French, Amanda, additional, Hodell, David A., additional, Immenhauser, Adrian, additional, and Breitenbach, Sebastian F. M., additional
- Published
- 2020
- Full Text
- View/download PDF
32. Intertropical convergence zone variability in the Neotropics during the Common Era
- Author
-
Asmerom, Yemane, primary, Baldini, James U. L., additional, Prufer, Keith M., additional, Polyak, Victor J., additional, Ridley, Harriet E., additional, Aquino, Valorie V., additional, Baldini, Lisa M., additional, Breitenbach, Sebastian F. M., additional, Macpherson, Colin G., additional, and Kennett, Douglas J., additional
- Published
- 2020
- Full Text
- View/download PDF
33. Local and Regional Indian Summer Monsoon Precipitation Dynamics During Termination II and the Last Interglacial
- Author
-
Magiera, Matthias, primary, Lechleitner, Franziska A., additional, Erhardt, Andrea M., additional, Hartland, Adam, additional, Kwiecien, Ola, additional, Cheng, Hai, additional, Bradbury, Harold J., additional, Turchyn, Alexandra V., additional, Riechelmann, Sylvia, additional, Edwards, Lawrence, additional, and Breitenbach, Sebastian F. M., additional
- Published
- 2019
- Full Text
- View/download PDF
34. The Indian Summer Monsoon from a Speleothem d18O Perspective – a Review
- Author
-
Kaushal, Nikita, Breitenbach, Sebastian F. M., Lechleitner, Franziska A., Sinha, Ashish, Tewari, Vinod C., Ahmad, Syed Masood, Berkelhammer, Max, Band, Shraddha, Yadava, Madhusudan, Ramesh, Rengaswamy, and Henderson, Gideon M.
- Subjects
earth_sciences_other - Abstract
As one of the most prominent seasonally recurring atmospheric circulation patterns, the Asian Summer Monsoon (ASM) plays a vital role for the life and livelihood of about a third of the global population. Changes in the strength and seasonality of the ASM significantly affect the region, yet the drivers of change and the varied regional responses of the ASM are not well understood. In the last two decades, there have been a number of studies reconstructing the ASM using stalagmite-based proxies such as oxygen isotopes (18O). Such reconstructions allow examination of the drivers and responses, increasing monsoon predictability. In this review paper, we focus on stalagmite 18O records from India at the proximal end of the ASM region. Indian stalagmite 18O records show well dated, high amplitude changes in response to the dominant drivers of the ASM on orbital to multi-centennial timescales and indicate the magnitude of monsoon variability in response to these drivers. We examine Indian stalagmite records collated in SISAL_v1 (version 1) database (http://researchdata.reading.ac.uk/139/) and support the database with a summary of record quality and regional climatic interpretations of the 18O record during different climate states. We highlight current debates and suggest the most useful time periods (climatic events) and locations for further work using tools such as data-model comparisons, spectral analysis methods, multi-proxy investigations and monitoring work
- Published
- 2018
35. Recurrence Plot Analysis Of Irregularly Sampled Data
- Author
-
Ozken, Ibrahim, Eroglu, Deniz, Breitenbach, Sebastian F. M., Marwan, Norbert, Tan, Liangcheng, Tirnakli, Ugur, and Kurths, Juergen
- Abstract
Irregularly sampled time series usually require data preprocessing before a desired time-series analysis can be applied. We propose an approach for distance measuring of pairs of data points which is directly applicable to irregularly sampled time series. In order to apply recurrence plot analysis to irregularly sampled time series, we use this approach and detect regime transitions in prototypical models and for an application from palaeoclimatatology. This approach might be useful for any method that is based on distance measuring, e.g., correlation sum or Lyapunov exponent estimation.
- Published
- 2018
36. Fluvio‐lacustrine sedimentation in the Agadir‐Tissint Feija (Anti‐Atlas, Morocco): A promising palaeoclimate archive for the last glacial cycle in northwest Africa
- Author
-
Nutz, Alexis, primary, Kwiecien, Ola, additional, Breitenbach, Sebastian F. M., additional, Cai, Yanjun, additional, Della Porta, Giovanna, additional, Danisch, Jan, additional, Kabiri, Lahcen, additional, and Bodin, Stéphane, additional
- Published
- 2019
- Full Text
- View/download PDF
37. A stalagmite test of North Atlantic SST and Iberian hydroclimate linkages over the last two glacial cycles
- Author
-
Denniston, Rhawn F., primary, Houts, Amanda N., additional, Asmerom, Yemane, additional, Wanamaker Jr., Alan D., additional, Haws, Jonathan A., additional, Polyak, Victor J., additional, Thatcher, Diana L., additional, Altan-Ochir, Setsen, additional, Borowske, Alyssa C., additional, Breitenbach, Sebastian F. M., additional, Ummenhofer, Caroline C., additional, Regala, Frederico T., additional, Benedetti, Michael M., additional, and Bicho, Nuno F., additional
- Published
- 2018
- Full Text
- View/download PDF
38. The Indian Summer Monsoon from a Speleothem δ18O Perspective—A Review
- Author
-
Kaushal, Nikita, primary, Breitenbach, Sebastian F. M., additional, Lechleitner, Franziska A., additional, Sinha, Ashish, additional, Tewari, Vinod C., additional, Ahmad, Syed Masood, additional, Berkelhammer, Max, additional, Band, Shraddha, additional, Yadava, Madhusudan, additional, Ramesh, Rengaswamy, additional, and Henderson, Gideon M., additional
- Published
- 2018
- Full Text
- View/download PDF
39. Cave ventilation and rainfall signals in dripwater in a monsoonal setting – a monitoring study from NE India
- Author
-
Breitenbach Sebastian F M, Lechleitner Franziska A., Meyer Hanno, Diengdoh Gregory, Mattey David, and Marwan Norbert
- Subjects
Hydrology ,Wet season ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Water flow ,sub-01 ,Speleothem ,Geology ,010502 geochemistry & geophysics ,Monsoon ,01 natural sciences ,6. Clean water ,Sink (geography) ,Cave ,13. Climate action ,Geochemistry and Petrology ,Streamflow ,Dry season ,0105 earth and related environmental sciences - Abstract
© 2015 Elsevier B.V. Detailed monitoring of subterranean microclimatic and hydrological conditions can delineate factors influencing speleothem based climate proxy data and helps in their interpretation. Multi annual monitoring of water stable isotopes air temperature relative humidity drip rates and PCO2 in surface soil and cave air gives detailed insight into dripwater isotopes temperature and ventilation dynamics in Mawmluh Cave NE India. Water isotopes vary seasonally in response to monsoonal rainfall. Most negative values are observed during late Indian Summer Monsoon (ISM) with a less than one month lag between ISM rainfall and drip response. Two dry season and two less well distinguishable wet season dynamic ventilation regimes are identified in Mawmluh Cave. Cave air temperatures higher than surface air result in chimney ventilation during dry season nights. Dry season days show reduced ventilation due to cool cave air relative to surface air and cold air lake development. Both high water flow and cooler than surface cave air temperatures result in air inflow during wet season nights. Wet season daytime ventilation is governed by river flow but is prone to stagnation and development of cold air lakes. CO2 monitoring indicates that PCO2 levels vary at diurnal to annual scale. Mawmluh Cave seems to act as CO2 sink during part of the dry season. While very likely additional data is needed to establish whether wet season cave air CO2 levels rise above atmospheric values. Drip behavior is highly nonlinear related to effective recharge dynamics and further complicated by human influence on the epikarst aquifer.
- Published
- 2015
40. Lignin oxidation products in soil, dripwater and speleothems from four different sites in New Zealand.
- Author
-
Heidke, Inken, Hartland, Adam, Scholz, Denis, Pearson, Andrew, Hellstrom, John, Breitenbach, Sebastian F. M., and Hoffmann, Thorsten
- Subjects
SPELEOTHEMS ,HIGH performance liquid chromatography ,LIGNINS ,FOREST litter ,SOILS ,VEGETATION dynamics - Abstract
Lignin oxidation products (LOPs) are widely used as vegetation proxies in climate archives, such as sediment and peat cores. The total LOP concentration, S8, provides information on the abundance of vegetation, while the ratios C / V and S / V of the different LOP groups also provide information on the type of vegetation. Recently, LOP analysis has been successfully applied to speleothem archives. However, there are many open questions concerning the transport and microbial degradation of LOPs on their way from the soil into the cave system. These processes could potentially alter the original source-dependent LOP signals, in particular the C / V and S / V ratios, and thus complicate their interpretation in terms of past vegetation changes. We analyzed LOPs in leaf litter and different soil horizons as well as dripwater and flowstone samples from four different cave sites from different vegetation zones in New Zealand using ultrahigh performance liquid chromatography coupled to high resolution mass spectrometry. We test whether the original source-dependent LOP signal of the overlying vegetation is preserved and can be recovered from flowstone samples and investigate how the signal is altered by the transport from the soil to the cave. The LOP concentrations range from mg/g in the soil to ng/g in the flowstones. Our results demonstrate that, from the soil to the flowstone, the C / V and S / V ratios both increase, while the total lignin content, S8, strongly decreases. This shows that the LOP signal is strongly influenced by both transport and degradation processes. Nevertheless, the relative LOP signal from the overlying soil at the different cave sites is preserved in the flowstone. We emphasize that for the interpretation of C / V and S / V ratios in terms of past vegetation changes, it is important to compare only samples of the same type (e.g., speleothem, dripwater or soil) and to evaluate only relative variations. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
41. Abrupt transitions in time series with uncertainties
- Author
-
Goswami, Bedartha, primary, Boers, Niklas, additional, Rheinwalt, Aljoscha, additional, Marwan, Norbert, additional, Heitzig, Jobst, additional, Breitenbach, Sebastian F. M., additional, and Kurths, Jürgen, additional
- Published
- 2018
- Full Text
- View/download PDF
42. See-saw relationship of the Holocene East Asian-Australian summer monsoon
- Author
-
Eroglu, Deniz, McRobie, Fiona H., Ozken, Ibrahim, Stemler, Thomas, Wyrwoll, Karl-Heinz, Breitenbach, Sebastian F. M., Marwan, Norbert, Kurths, Juergen, and Ege Üniversitesi
- Abstract
WOS: 000385442200001, PubMed ID: 27666662, The East Asian-Indonesian-Australian summer monsoon (EAIASM) links the Earth's hemispheres and provides a heat source that drives global circulation. At seasonal and inter-seasonal timescales, the summer monsoon of one hemisphere is linked via outflows from the winter monsoon of the opposing hemisphere. Long-term phase relationships between the East Asian summer monsoon (EASM) and the Indonesian-Australian summer monsoon (IASM) are poorly understood, raising questions of long-term adjustments to future greenhouse-triggered climate change and whether these changes could 'lock in' possible IASM and EASM phase relationships in a region dependent on monsoonal rainfall. Here we show that a newly developed nonlinear time series analysis technique allows confident identification of strong versus weak monsoon phases at millennial to sub-centennial timescales. We find a see-saw relationship over the last 9,000 years-with strong and weak monsoons opposingly phased and triggered by solar variations. Our results provide insights into centennial-to millennial-scale relationships within the wider EAIASM regime., Leibniz Association (WGL) [SAW-2013-IZW-2]; Australian Postgraduate AwardAustralian Government; TUBITAKTurkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [2214/A]; Ege UniversityEge University [2015FEN028]; European Union's Horizon Research and Innovation programme under the Marie Sklodowska-Curie grant [691037]; Open Access Fund of the Leibniz Association; Kimberley Foundation Australia, D.E. and N.M. acknowledge support by the Leibniz Association (WGL) under Grant No. SAW-2013-IZW-2. F.H.M.'s research is funded through an Australian Postgraduate Award. I.O. is financially supported from TUBITAK under 2214/A program and by Ege University under the Research Project number 2015FEN028. This study received funding from the European Union's Horizon 2020 Research and Innovation programme under the Marie Sklodowska-Curie grant agreement No 691037. The publication of this article was funded by the Open Access Fund of the Leibniz Association. K.H.W. thank Rhawn F. Denniston for his wider involvement in the northwest Australian monsoon project and the Kimberley Foundation Australia for financial support for this project and Paul Wyrwoll for helpful comments. We are also grateful to Yanjun Cai for providing the Lake Qinghai record.
- Published
- 2016
43. Tropical rainfall over the last two millennia: evidence for a low-latitude hydrologic seesaw
- Author
-
Lechleitner, Franziska A., primary, Breitenbach, Sebastian F. M., additional, Rehfeld, Kira, additional, Ridley, Harriet E., additional, Asmerom, Yemane, additional, Prufer, Keith M., additional, Marwan, Norbert, additional, Goswami, Bedartha, additional, Kennett, Douglas J., additional, Aquino, Valorie V., additional, Polyak, Victor, additional, Haug, Gerald H., additional, Eglinton, Timothy I., additional, and Baldini, James U. L., additional
- Published
- 2017
- Full Text
- View/download PDF
44. Persistent northward North Atlantic tropical cyclone track migration over the past five centuries
- Author
-
Baldini, Lisa M., primary, Baldini, James U. L., additional, McElwaine, Jim N., additional, Frappier, Amy Benoit, additional, Asmerom, Yemane, additional, Liu, Kam-biu, additional, Prufer, Keith M., additional, Ridley, Harriet E., additional, Polyak, Victor, additional, Kennett, Douglas J., additional, Macpherson, Colin G., additional, Aquino, Valorie V., additional, Awe, Jaime, additional, and Breitenbach, Sebastian F. M., additional
- Published
- 2016
- Full Text
- View/download PDF
45. Seasonality of westerly moisture transport in the East Asian summer monsoon and its implications for interpreting precipitation δ18O
- Author
-
Baker, Alexander J., Sodemann, Harald, Baldini, James U. L., Breitenbach, Sebastian F. M., Johnson, Kathleen R., van Hunen, Jeroen, and Zhang, Pingzhong
- Subjects
Climate Action ,moisture sources ,oxygen isotopes ,sub-01 ,Asian monsoon ,rainfall ,Lagrangian analysis ,Physical Geography and Environmental Geoscience ,Atmospheric Sciences - Abstract
East Asian summer monsoon (EASM) rainfall impacts the world's most populous regions. Accurate EASM rainfall prediction necessitates robust paleoclimate reconstructions from proxy data and quantitative linkage to modern climatic conditions. Many precisely dated oxygen isotope records from Chinese stalagmites have been interpreted as directly reflecting past EASM rainfall amount variability, but recent research suggests that such records instead integrate multiple hydroclimatic processes. Using a Lagrangian precipitation moisture source diagnostic, we demonstrate that EASM rainfall is primarily derived from the Indian Ocean. Conversely, Pacific Ocean moisture export peaks during winter, and the moisture uptake area does not differ significantly between summer and winter and is thus a minor contributor to monsoonal precipitation. Our results are substantiated by an accurate reproduction of summer and winter spatial rainfall distributions across China. We also correlate modern EASM rainfall oxygen isotope ratios with instrumental rainfall amount and our moisture source data. This analysis reveals that the strength of the source effect is geographically variable, and differences in atmospheric moisture transport may significantly impact the isotopic signature of EASM rainfall at the Hulu, Dongge, and Wanxiang Cave sites. These results improve our ability to isolate the rainfall amount signal in paleomonsoon reconstructions and indicate that precipitation across central and eastern China will directly respond to variability in Indian Ocean moisture supply.
- Published
- 2015
46. Rainfall variations in central Indo-Pacific over the past 2,700 y.
- Author
-
Liangcheng Tan, Chuan-Chou Shen, Löwemark, Ludvig, Chawchai, Sakonvan, Edwards, R. Lawrence, Yanjun Cai, Breitenbach, Sebastian F. M., Hai Cheng, Yu-Chen Chou, Duerrast, Helmut, Partin, Judson W., Wenju Cai, Chabangborn, Akkaneewut, Yongli Gao, Ola Kwiecien, Chung-Che Wu, Zhengguo Shi, Huang-Hsiun Hsu, and Wohlfarth, Barbara
- Subjects
INTERTROPICAL convergence zone ,RAINFALL ,WALKER circulation ,MIDDLE Ages - Abstract
Tropical rainfall variability is closely linked to meridional shifts of the Intertropical Convergence Zone (ITCZ) and zonal movements of the Walker circulation. The characteristics and mechanisms of tropical rainfall variations on centennial to decadal scales are, however, still unclear. Here, we reconstruct a replicated stalagmitebased 2,700-y-long, continuous record of rainfall for the deeply convective northern central Indo-Pacific (NCIP) region. Our record reveals decreasing rainfall in the NCIP over the past 2,700 y, similar to other records from the northern tropics. Notable centennial- to decadal-scale dry climate episodes occurred in both the NCIP and the southern central Indo-Pacific (SCIP) during the 20th century [Current Warm Period (CWP)] and the Medieval Warm Period (MWP), resembling enhanced El Niño-like conditions. Further, we developed a 2,000-y-long ITCZ shift index record that supports an overall southward ITCZ shift in the central Indo-Pacific and indicates southward mean ITCZ positions during the earlyMWP and the CWP. As a result, the drying trend since the 20th century in the northern tropics is similar to that observed during the past warm period, suggesting that a possible anthropogenic forcing of rainfall remains indistinguishable from natural variability. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
47. VENTILATION AND CAVE AIR PCO2 IN THE BUNKER-EMST CAVE SYSTEM (NW GERMANY): IMPLICATIONS FOR SPELEOTHEM PROXY DATA.
- Author
-
Riechelmann, Sylvia, Breitenbach, Sebastian F. M., Schröder-Ritzrau, Andrea, Mangini, Augusto, and Immenhauser, Adrian
- Subjects
- *
SPELEOTHEMS , *CAVES , *AIR flow , *PARTIAL pressure , *ISOTOPIC fractionation , *WIND speed , *CARBON dioxide , *ATMOSPHERIC temperature - Abstract
Cave air pCO2 (carbon dioxide partial pressure) is, along with drip rate, one of the most important factors controlling speleothem carbonate precipitation. As a consequence, pCO2 has an indirect but important control on speleothem proxy data (e.g., elemental concentrations, isotopic values). The CO2 concentration of cave air depends on CO2 source(s) and productivity, CO2 transport through the epikarst and karst zone, and cave air ventilation. To assess ventilation patterns in the Bunker-Emst Cave (BEC) System, we monitored the pCO2 value approximately 100 m from the lower entrance (Bunker Cave) at bi-hourly resolution between April 2012 and February 2014. The two entrances of the BEC system were artificially opened between 1860‒1863 (Emst Cave) and 1926 (Bunker Cave). Near-atmospheric minimum pCO2 dynamics of 408 ppmv are measured in winter, and up to 811 ppmv are recorded in summer. Outside air contributes the highest proportion to cave air CO2, while soil, and possibly also ground air, provide a far smaller proportion throughout the whole year. Cave air pCO2 correlates positively with the temperature difference between surface and cave air during summer and negatively in winter, with no clear pattern for spring and autumn. Dynamic ventilation is driven by temperature and resulting density differences between cave and surface air. In summer, warm atmospheric air is entrained through the upper cave entrance where it cools. With increasing density, the cooled air flows toward the lower entrance. In winter, this pattern is reversed, due to cold, atmospheric air entering the cave via the lower entrance, while relatively warm cave air rises and exits the cave via the upper entrance. The situation is further modulated by preferential south-southwestern winds that point directly on both cave entrances. Thus, cave ventilation is frequently disturbed, especially during periods with higher wind speed. Modern ventilation of the BEC system--induced by artificially openings--is not a direct analogue for pre-1860 ventilation conditions. The artificial change of ventilation resulted in a strong increase of δ13Cspeleothem values. Prior to the cave opening in 1860, Holocene δ13Cspeleothem values were significantly lower, probably related to limited ventilation due to the lack of significant connections between the surface and cave. Reduced ventilation led to significantly higher pCO2 values, minimal CO2 degassing from drip water and low kinetic isotope fractionation. Both modern and fossil speleothem precipitation rates are driven by water supply and carbonate saturation, and not by cave air pCO2. Today, pCO2 variability is too small to affect carbonate precipitation rates and the same is likely true for pCO2 variability prior to artificial opening of the cave. Thus, fossil speleothems from BEC System are likely more sensitive to temperature and infiltration dynamics. The Bunker-Emst Cave System, therefore, represents different ventilation patterns and their influence on speleothem proxy data in an exemplary manner, and it may serve as a template for other cave systems. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
48. Climate monitoring in the Caumont cave and quarry system (northern France) reveal near oxygen isotopic equilibrium conditions for carbonate deposition.
- Author
-
Bejarano-Arias, Ingrid, Nehme, Carole, Breitenbach, Sebastian F. M., Meyer, Hanno, Modestou, Sevasti, and Mouralis, Damase
- Subjects
- *
SPELEOTHEMS , *STALACTITES & stalagmites , *CAVES , *OXYGEN isotopes , *QUARRIES & quarrying , *ISOTOPIC fractionation , *CARBONATES , *SUMMER - Abstract
The study of modern cave deposits forming under near isotopic equilibrium conditions can potentially help disentangle the processes influencing the oxygen isotope system and suitability of stalagmites as archives of past hydrological or thermal changes. We used cave monitoring to evaluate the impact of kinetic isotope fractionation and assess the conditions under which modern cave carbonates form in the Caumont cave and quarry system, located in Normandy, northwest France. Over 20 months, we collected climatological data, dripwater, and modern carbonate samples at 2–4-week intervals at three different stations inside the Caumont cave and quarry system. We find highly stable (10.4 ± 0.3°C – 11.3 ± 0.1°C) temperature in the deeper sections of the Caumont cave and quarry system. The temporal dynamics of δ18Odrip indicates that the drip water composition in Caumont reflects the original (though subdued) signal of precipitation, rather than the impact the seasonal to inter-annual cave air temperature has on isotopic fractionation. The monitoring reveals that δ13C of modern carbonate is influenced by prior carbonate precipitation that occurs during the summer season when evapotranspiration can minimize effective infiltration. Comparison of δ18O from dripwater and modern calcite, precipitated on glass plates and collected every two to four weeks, reveals that modern calcite forms near oxygen isotope equilibrium. A Hendy test on modern carbonate deposited on a stalagmite-shaped glass flask over 20 months confirms this finding because neither does δ13C increase with distance from the apex, nor are δ13C and δ18O positively correlated. We conclude that the δ13C signal in speleothems reflect summer (and longer-term) prior carbonate precipitation in response to effective infiltration dynamics, and that the δ18O signal likely reflects annual to multi-annual changes in the composition of precipitation above the cave. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
49. See–saw relationship of the Holocene East Asian–Australian summer monsoon
- Author
-
Eroglu, Deniz, primary, McRobie, Fiona H., additional, Ozken, Ibrahim, additional, Stemler, Thomas, additional, Wyrwoll, Karl-Heinz, additional, Breitenbach, Sebastian F. M., additional, Marwan, Norbert, additional, and Kurths, Jürgen, additional
- Published
- 2016
- Full Text
- View/download PDF
50. Indian monsoon variability on millennial-orbital timescales
- Author
-
Kathayat, Gayatri, primary, Cheng, Hai, additional, Sinha, Ashish, additional, Spötl, Christoph, additional, Edwards, R. Lawrence, additional, Zhang, Haiwei, additional, Li, Xianglei, additional, Yi, Liang, additional, Ning, Youfeng, additional, Cai, Yanjun, additional, Lui, Weiguo Lui, additional, and Breitenbach, Sebastian F. M., additional
- Published
- 2016
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.