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1. 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)

   Abstract 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. 

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2. 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)

   Abstract 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. 

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3. 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. 

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4. A stalagmite test of North Atlantic SST and Iberian hydroclimate linkages over the last two glacial cycles

   https://doi.org/10.5194/cp-14-1893-2018  

   Denniston, Rhawn F.; Houts, Amanda N.; Asmerom, Yemane; Wanamaker Jr., Alan D.; Haws, Jonathan A.; Polyak, Victor J.; Thatcher, Diana L.; Altan-Ochir, Setsen; Borowske, Alyssa C.; Breitenbach, Sebastian F.; et al (January 2018, Climate of the Past)

   Abstract. Close coupling of Iberian hydroclimate and North Atlantic seasurface temperature (SST) during recent glacial periods has been identifiedthrough the analysis of marine sediment and pollen grains co-deposited on thePortuguese continental margin. While offering precisely correlatable records,these time series have lacked a directly dated, site-specific record ofcontinental Iberian climate spanning multiple glacial cycles as a point ofcomparison. Here we present a high-resolution, multi-proxy (growth dynamicsandδ¹³C, δ¹⁸O, and δ²³⁴Uvalues) composite stalagmite record of hydroclimate from two caves in westernPortugal across the majority of the last two glacial cycles (∼220ka).At orbital and millennial scales, stalagmite-based proxies for hydroclimateproxies covaried with SST, with elevated δ¹³C,δ¹⁸O, and δ²³⁴U values and/or growth hiatusesindicating reduced effective moisture coincident with periods of lowered SSTduring major ice-rafted debris events, in agreement with changes inpalynological reconstructions of continental climate. While in many cases thePortuguese stalagmite record can be scaled to SST, in some intervals themagnitudes of stalagmite isotopic shifts, and possibly hydroclimate, appearto have been somewhat decoupled from SST. 

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5. Monitoring of Sierra Nevada Caves Reveals the Potential for Stalagmites to Archive Seasonal Variability

   https://doi.org/10.3389/feart.2021.781526  

   Wortham, Barbara E.; Montañez, Isabel P.; Bowman, Kimberly; Kuta, Daphne; Contreras, Nora Soto; Brummage, Eleana; Pang, Allison; Tinsley, John; Roemer-Baer, Greg (December 2021, Frontiers in Earth Science)

   In the southwestern United States, California (CA) is one of the most climatically sensitive regions given its low (≤250 mm/year) seasonal precipitation and its inherently variable hydroclimate, subject to large magnitude modulation. To reconstruct past climate change in CA, cave calcite deposits (stalagmites) have been utilized as an archive for environmentally sensitive proxies, such as stable isotope compositions (δ¹⁸O, δ¹³C) and trace element concentrations (e.g., Mg, Ba, Sr). Monitoring the cave and associated surface environments, the chemical evolution of cave drip-water, the calcite precipitated from the drip-water, and the response of these systems to seasonal variability in precipitation and temperature is imperative for interpreting stalagmite proxies. Here we present monitored drip-water and physical parameters at Lilburn Cave, Sequoia Kings Canyon National Park (Southern Sierra Nevada), CA, and measured trace element concentrations (Mg, Sr, Ba, Cu, Fe, Mn) and stable isotopic compositions (δ¹⁸O, δ²H) of drip-water and for calcite (δ¹⁸O) precipitated on glass substrates over a two-year period (November 2018 to February 2021) to better understand how chemical variability at this site is influenced by local and regional precipitation and temperature variability. Despite large variability in surface temperatures and precipitation amount and source region (North Pacific vs. subtropical Pacific), Lilburn Cave exhibits a constant cave environment year-round. At two of the three sites within the cave, drip-water δ¹⁸O and δ²H are influenced seasonally by evaporative enrichment. At a third collection site in the cave, the drip-water δ¹⁸O responds solely to precipitation δ¹⁸O variability. The Mg/Ca, Ba/Ca, and Sr/Ca ratios are seasonally responsive to prior calcite precipitation at all sites but minimally to water-rock interaction. Lastly, we examine the potential of trace metals (e.g., Mn²⁺and Cu²⁺as a geochemical proxy of recharge and find that variability in their concentrations has high potential to denote the onset of the rainy season in the study region. The drip-water composition is recorded in the calcite, demonstrating that stalagmites from Lilburn Cave, and potentially more regionally, could record seasonal variability in weather even during periods of substantially reduced rainfall. 

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