More Like this

1. Southern hemisphere forced millennial scale Indian summer monsoon variability during the late Pleistocene

   https://doi.org/10.1038/s41598-022-14010-6  

   Band, Shraddha T. ; Yadava, M. G. ; Kaushal, Nikita ; Midhun, M. ; Thirumalai, Kaustubh ; Francis, Timmy ; Laskar, Amzad ; Ramesh, R. ; Henderson, Gideon M. ; Narayana, A. C. ( December 2022 , Scientific Reports)

   Abstract Peninsular India hosts the initial rain-down of the Indian Summer Monsoon (ISM) after which winds travel further east inwards into Asia. Stalagmite oxygen isotope composition from this region, such as those from Belum Cave, preserve the vital signals of the past ISM variability. These archives experience a single wet season with a single dominant moisture source annually. Here we present high-resolution δ 18 O, δ 13 C and trace element (Mg/Ca, Sr/Ca, Ba/Ca, Mn/Ca) time series from a Belum Cave stalagmite spanning glacial MIS-6 (from ~ 183 to ~ 175 kyr) and interglacial substages MIS-5c-5a (~ 104 kyr to ~ 82 kyr). With most paleomonsoon reconstructions reporting coherent evolution of northern hemisphere summer insolation and ISM variability on orbital timescale, we focus on understanding the mechanisms behind millennial scale variability. Finding that the two are decoupled over millennial timescales, we address the role of the Southern Hemisphere processes in modulating monsoon strength as a part of the Hadley circulation. We identify several strong and weak episodes of ISM intensity during 104–82 kyr. Some of the weak episodes correspond to warming in the southern hemisphere associated with weak cross-equatorial winds. We show that during the MIS-5 substages, ISM strength gradually declined with millennial scale variability linked to Southern Hemisphere temperature changes which in turn modulate the strength of the Mascarene High. 

   more » « less
2. Evidence for Decreased Precipitation Variability in the Yucatán Peninsula During the Mid‐Holocene

   https://doi.org/10.1029/2021PA004219  

   Serrato Marks, Gabriela ; Medina‐Elizalde, Martín ; Burns, Stephen ; Weldeab, Syee ; Lases‐Hernandez, Fernanda ; Cazares, Gabriela ; McGee, David ( May 2021 , Paleoceanography and Paleoclimatology)

   The Yucatán Peninsula (YP) has a complex hydroclimate with many proposed drivers of interannual and longer‐term variability, ranging from coupled ocean–atmosphere processes to frequency of tropical cyclones. The mid‐Holocene, a time of higher Northern Hemisphere summer insolation, provides an opportunity to test the relationship between YP precipitation and ocean temperature. Here, we present a new, ∼annually resolved speleothem record of stable isotope (δ¹⁸O and δ¹³C) and trace element (Mg/Ca and Sr/Ca) ratios for a section of the mid‐Holocene (5.2–5.7 kyr BP), before extensive agriculture began in the region. A meter‐long stalagmite from Río Secreto, a cave system in Playa del Carmen, Mexico, was dated using U–Th geochronology and layer counting, yielding multidecadal age uncertainty (median 2SD of ±70 years). New proxy data were compared to an existing late Holocene stalagmite record from the same cave system, allowing us to examine changes in hydrology over time and to paleoclimate records from the southern YP. The δ¹⁸O, δ¹³C, and Mg/Ca data consistently indicate higher mean precipitation and lower precipitation variability during the mid‐Holocene compared to the late Holocene. Despite this reduced variability, multidecadal precipitation variations were persistent in regional hydroclimate during the mid‐Holocene. We therefore conclude that higher summer insolation led to increased mean precipitation and decreased precipitation variability in the northern YP but that the region is susceptible to dry periods across climate mean states. Given projected decreases in wet season precipitation in the YP’s near future, we suggest that climate mitigation strategies emphasize drought preparation.

    

   more » « less
3. High‐Resolution, Multiproxy Speleothem Record of the 8.2 ka Event From Mainland Southeast Asia

   https://doi.org/10.1029/2023PA004675  

   Wood, Christopher T. ; Johnson, Kathleen R. ; Lewis, Lindsey. E. ; Wright, Kevin ; Wang, Jessica K. ; Borsato, Andrea ; Griffiths, Michael L. ; Mason, Andrew ; Henderson, Gideon M. ; Setera, Jacob B. ; et al ( December 2023 , Paleoceanography and Paleoclimatology)

   The 8.2 ka event is the most significant global climate anomaly of the Holocene epoch, but a lack of records from Mainland Southeast Asia (MSEA) currently limits our understanding of the spatial and temporal extent of the climate response. A newly developed speleothem record from Tham Doun Mai Cave, Northern Laos provides the first high‐resolution record of this event in MSEA. Our multiproxy record (δ¹⁸O, δ¹³C, Mg/Ca, Sr/Ca, and petrographic data), anchored in time by 9 U‐Th ages, reveals a significant reduction in local rainfall amount and weakening of the monsoon at the event onset at ∼8.29 ± 0.03 ka BP. This response lasts for a minimum of ∼170 years, similar to event length estimates from other speleothem δ¹⁸O monsoon records. Interestingly, however, our δ¹³C and Mg/Ca data, proxies for local hydrology, show that abrupt changes to local rainfall amounts began decades earlier (∼70 years) than registered in the δ¹⁸O. Moreover, the δ¹³C and Mg/Ca also show that reductions in rainfall continued for at least ∼200 years longer than the weakening of the monsoon inferred from the δ¹⁸O. Our interpretations suggest that drier conditions brought on by the 8.2 ka event in MSEA were felt beyond the temporal boundaries defined by δ¹⁸O‐inferred monsoon intensity, and an initial wet period (or precursor event) may have preceded the local drying. Most existing Asian Monsoon proxy records of the 8.2 ka event may lack the resolution and/or multiproxy information necessary to establish local and regional hydrological sensitivity to abrupt climate change.

    

   more » « less
4. A new MIS 5 to MIS 2 speleothem record from Sandkraal Cave on the South African Cape south coast

   https://doi.org/10.1017/qua.2024.3  

   Braun, Kerstin ; Bar-Matthews, Miryam ; Ayalon, Avner ; Matthews, Alan ; Zilberman, Tami ; Zolotova, Natalya ; Cowling, Richard M. ; Karkanas, Panagiotis ; Cawthra, Hayley C. ; Fisher, Erich C. ; et al ( March 2024 , Quaternary Research)

   We present new stable oxygen and carbon isotope composite records (δ¹⁸O, δ¹³C) 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 ~70 ka, changes of speleothem δ¹⁸O values at SK1 are likely related to rainfall seasonality. Variations of δ¹³C values are associated with changes of vegetation density, prior carbonate precipitation (PCP), CO₂degassing in the cave, and possibly variations of the abundance of C₃and C₄grasses in the vegetation. The relationships of δ¹⁸O with other proxies shift between ~70 and 48 ka (Marine Isotope Stages 4–3) so that both stable isotope records now reflect CO₂degassing, 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.

    

   more » « less
5. Dripwater and Calcite Geochemistry Variations in a Monitored Bahamas Cave

   https://doi.org/10.1029/2019GC008339  

   Arienzo, Monica M. ; Mehterian, Sevag ; Swart, Peter K. ; Broad, Kenneth ; Kakuk, Brian ( September 2019 , Geochemistry, Geophysics, Geosystems)

   A cave‐monitoring study in Hatchet Bay Cave on the island of Eleuthera, Bahamas, has examined the origins of variations in oxygen and carbon isotopic and minor element composition in cave calcites. Every 3 to 8 months, between 2012 and 2016, temperature, humidity, cave air (δ¹³C_CO2), dripwaters (δ¹⁸O and δ²H values, and Ca, Sr, and Mg concentrations), and the chemical composition of precipitating calcite (δ¹⁸O and δ¹³C values, and Ca, Sr, and Mg concentrations) were analyzed in two rooms in the cave. Results from the elemental analyses show that throughout the cave prior calcite precipitation was a driver of the elemental chemistry of the precipitated calcites. In addition, cave calcites show that δ¹³C and δ¹⁸O values were positively correlated with Mg/Ca ratios. The Mg/Ca ratios were also positively correlated with lower calcite precipitation rates. Therefore, water/rock interactions may also influence δ¹³C and δ¹⁸O values and Mg/Ca ratios of the calcite. Differences were observed between the two rooms, with the Main Room of the cave exhibiting increased prior calcite precipitation, more ventilation, lower calcite precipitation rates, and δ¹⁸O values, which were farther from equilibrium when compared to the more isolated portion of the cave. These results also validated previous interpretations from Pleistocene stalagmites collected from a nearby Bahamian cave suggesting that a positive covariation between Mg/Ca and δ¹³C values reflects water/rock interactions.

    

   more » « less