Tiger
Benjamin H.
Tiger
Benjamin H.
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ArticleZonal Indian Ocean variability drives millennial-scale precipitation changes in Northern Madagascar(American Geophysical Union, 2023-11-07) Tiger, Benjamin H. ; Burns, Stephen J. ; Dawson, Robin R. ; Scroxton, Nick ; Godfrey, Laurie R. ; Ranivoharimanana, Lovasoa ; Faina, Peterson ; McGee, DavidThe low latitude Indian Ocean is warming faster than other tropical basins, and its interannual climate variability is projected to become more extreme under future emissions scenarios with substantial impacts on developing Indian Ocean rim countries. Therefore, it has become increasingly important to understand the drivers of regional precipitation in a changing climate. Here we present a new speleothem record from Anjohibe, a cave in northwest (NW) Madagascar well situated to record past changes in the Intertropical Convergence Zone (ITCZ). U-Th ages date speleothem growth from 27 to 14 ka. δ18O, δ13C, and trace metal proxies reconstruct drier conditions during Heinrich Stadials 1 and 2, and wetter conditions during the Last Glacial Maximum and Bølling–Allerød. This is surprising considering hypotheses arguing for southward (northward) ITCZ shifts during North Atlantic cooling (warming) events, which would be expected to result in wetter (drier) conditions at Anjohibe in the Southern Hemisphere tropics. The reconstructed Indian Ocean zonal (west-east) sea surface temperature (SST) gradient is in close agreement with hydroclimate proxies in NW Madagascar, with periods of increased precipitation correlating with relatively warmer conditions in the western Indian Ocean and cooler conditions in the eastern Indian Ocean. Such gradients could drive long-term shifts in the strength of the Walker circulation with widespread effects on hydroclimate across East Africa. These results suggest that during abrupt millennial-scale climate changes, it is not meridional ITCZ shifts, but the tropical Indian Ocean SST gradient and Walker circulation driving East African hydroclimate variability.
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ArticleTropical volcanic eruptions and low frequency Indo-Pacific variability drive extreme Indian Ocean dipole events(American Geophysical Union, 2023-10-05) Tiger, Benjamin H. ; Ummenhofer, Caroline C.Volcanic eruptions can have significant climate impacts and serve as useful natural experiments for better understanding the effects of abrupt, externally forced climate change. Here, we investigate the Indian Ocean Dipole's (IOD) response to the largest tropical volcanic eruptions of the last millennium. Post-eruption composites show a strong negative IOD developing in the eruption year, and a positive IOD the following year. The IOD and El Niño-Southern Oscillation (ENSO) show a long-term damped oscillatory response that can take up to 8 years to return to pre-eruptive baselines. Moreover, the Interdecadal Pacific Oscillation (IPO) phase at the time of eruption controls the IOD response to intense eruptions, with negative (positive) IPO phasing favoring more negative (positive) IOD values via modulation of the background state of the eastern Indian Ocean thermocline depth. These results have important implications for climate risk in low-likelihood, high-impact scenarios, particularly in vulnerable communities unprepared for IOD and ENSO extremes.
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ArticleZonal control on Holocene precipitation in northwestern Madagascar based on a stalagmite from Anjohibe(Nature Research, 2024-03-06) Dawson, Robin R. ; Burns, Stephen J. ; Tiger, Benjamin H. ; McGee, David ; Faina, Peterson ; Scroxton, Nick ; Godfrey, Laurie R. ; Ranivoharimanana, LovasoaThe Malagasy Summer Monsoon is an important part of the larger Indian Ocean and tropical monsoon region. As the effects of global warming play out, changes to precipitation in Madagascar will have important ramifications for the Malagasy people. To help understand how precipitation responds to climate changes we present a long-term Holocene speleothem record from Anjohibe, part of the Andranoboka cave system in northwestern Madagascar. To date, it is the most complete Holocene record from this region and sheds light on the nature of millennial and centennial precipitation changes in this region. We find that over the Holocene, precipitation in northwestern Madagascar is actually in phase with the Northern Hemisphere Asian monsoon on multi-millennial scales, but that during some shorter centennial-scale events such as the 8.2 ka event, Anjohibe exhibits an antiphase precipitation signal to the Northern Hemisphere. The ultimate driver of precipitation changes across the Holocene does not appear to be the meridional migration of the monsoon. Instead, zonal sea surface temperature gradients in the Indian Ocean seem to play a primary role in precipitation changes in northwestern Madagascar.
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ArticleSISALv3: a global speleothem stable isotope and trace element database(Copernicus Publications, 2024-04-26) Kaushal, Nikita ; Lechleitner, Franziska A. ; Wilhelm, Micah ; Azennoud, Khalil ; Buhler, Janica C. ; Braun, Kerstin ; Brahim, Yassine Ait ; Baker, Andy ; Burstyn, Yuval ; Comas-Bru, Laia ; Fohlmeister, Jens ; Goldsmith, Yonaton ; Harrison, Sandy P. ; Hatvani, István G. ; Rehfeld, Kira ; Ritzau, Magdalena ; Skiba, Vanessa ; Stoll, Heather M. ; Szucs, Jozsef G. ; Tanos, Peter ; Treble, Pauline C. ; Azevedo, Vitor ; Baker, Jonathan L. ; Borsato, Andrea ; Chawchai, Sakonvan ; Columbu, Andrea ; Endres, Laura ; Hu, Jun ; Kern, Zoltan ; Kimbrough, Alena ; Koc, Koray ; Markowska, Monika ; Martrat, Belen ; Masood Ahmad, Syed ; Nehme, Carole ; Novello, Valdir Felipe ; Perez-Mejias, Carlos ; Ruan, Jiaoyang ; Sekhon, Natasha ; Sinha, Nitesh ; Tadros, Carol V. ; Tiger, Benjamin H. ; Warken, Sophie ; Wolf, Annabel ; Zhang, Haiwei ; SISAL Working Group membersPalaeoclimate information on multiple climate variables at different spatiotemporal scales is becoming 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 365 sites from across the globe, including 95 Mg/Ca, 85 Sr/Ca, 52 Ba/Ca, 25 U-Ca, 29 P-Ca, and 14 Sr-isotope records. The database also has increased spatiotemporal coverage for stable oxygen (892) and carbon (620) isotope records compared with SISALv2 (which consists of 673 and 430 stable oxygen and carbon records, respectively). Additional meta information has been added to improve the machine-readability and filtering of data. Standardized chronologies are included for all new entities along with the originally published chronologies. Thus, the SISALv3 database constitutes a unique resource of speleothem palaeoclimate information that allows regional to global palaeoclimate analyses based on multiple geochemical proxies, permitting more robust interpretations of past hydroclimate and comparisons with isotope-enabled climate models and other Earth system and hydrological models. The database can be accessed at https://doi.org/10.5287/ora-2nanwp4rk (Kaushal et al., 2024).