R. Lawrence 'Larry' Edwards

A better understanding of the relative roles of internal climate variability and external contributions, from both natural (solar, volcanic) and anthropogenic greenhouse gas forcing, is important to better project future hydrologic changes. Changes in the evaporative demand play a central role in this context, particularly in tropical areas characterized by high precipitation seasonality, such as the tropical savannah and semi-desertic biomes. Here we present a set of geochemical proxies in speleothems from a well-ventilated cave located in central-eastern Brazil which shows that the evaporative demand is no longer being met by precipitation, leading to a hydrological deficit. A marked change in the hydrologic balance in central-eastern Brazil, caused by a severe warming trend, can be identified, starting in the 1970s. Our findings show that the current aridity has no analog over the last 720 years. A detection and …

Heinrich events (HEs), characterized by massive and rapid ice-rafted debris from Laurentide Ice Sheet into the Labrador Sea as far south as the Iberian Margin, are observed in some stadial periods during the last glacial, however, it is still unclear regarding to the trigger and response mechanism of the HEs. A landmark work by Wang et al.(2004) was one of the first studies to associate tropical rainfall in southern Hemisphere with HEs, showing wet periods in tropical northeastern Brazil, a region that is currently semi-arid but very sensitive to the hydroclimate changes related to the cold events occurred in the northern Hemisphere, are synchronous with HEs in the North Atlantic. After two decades, we have a new chance to study the relationship between hydroclimate in NE Brazil and cold events in the North Atlantic in the light of much more new speleothem records obtained from TBV and TBR caves, NE Brazil. Here …

In recent years, Puerto Rico has been repeatedly hit by drought and hurricane, causing severe damage to the local society and economy. Therefore, understanding the region's climate variability and predicting extreme weather has become an important scientific problem. Cave stalagmites are widely recognized as high-quality terrestrial paleoclimate proxies due to their accurate dating and high resolution. In this study, we present a stalagmite-based multi-proxy reconstruction of hurricane and hydrological changes in Central America from the island of Isla de Mona, Puerto Rico, for the mid-Holocene period (4700–6260 a BP). Our data suggest a significant influence of solar activity on rainfall patterns in Central America via changes in the mean position of the Intertropical Convergence Zone (ITCZ). Our study further shows that El Niño may have played a role in influencing hurricane development at a decadal scale …

The last glacial period is characterized by abrupt climate oscillations, also known as Dansgaard-Oeschger (D-O) cycles. However, D-O cycles remain poorly documented in climate proxy records covering the penultimate glacial period. Here we present highly resolved and precisely dated speleothem time series from Sofular Cave in northern Türkiye to provide clear evidence for D-O cycles during Marine Isotope Stage (MIS) 6 as well as MIS 2-4. D-O cycles are most clearly expressed in the Sofular carbon isotope time series, which correlate inversely with regional sea surface temperature (SST) records from the Black Sea. The pacing of D-O cycles is almost twice as long during MIS 6 compared to MIS 2-4, and could be related to a weaker Atlantic Meridional Overturning Circulation (AMOC) and a different mean climate during MIS 6 compared to MIS 2-4, leading most likely to a higher threshold for the occurrence of D …

Sulawesi speleothem carbon isotopes (δ 13 C) are found to co-vary with deglacial warming and atmospheric CO 2 measured from Antarctic ice cores. This co-variation has thus far been attributed to speleothem δ 13 C recording changes in vegetation productivity and microbial activity in the soils overlaying caves as vegetation and microbes respond to glacial-interglacial changes in temperature and atmospheric CO 2 (Kimbrough et al., 2023; Krause & Kimbrough et al., in press). However, the relationship between speleothem δ 13 C and regional environmental change is complex and deconvolving the effect of different environmental drivers is difficult. To further investigate the ecosystem response in the Indo-Pacific Warm Pool to substantial warming and CO 2 rise during the penultimate deglaciation/marine isotope stage 5e (~ 127 kyrs ago) we use complimentary geochemical proxies extracted from stalagmite …

Monocytes comprise two major subsets, Ly6C hi classical monocytes and Ly6C lo nonclassical monocytes. Notch2 signaling in Ly6C hi monocytes triggers transition to Ly6C lo monocytes, which require Nr4a1, Bcl6, Irf2, and Cebpb. By comparison, less is known...

High-precision U–Th age is the key to promoting speleothem as an important archive for paleoclimate study. Notably, obtaining reliable U–Th age primarily relies on the accurate initial 230Th correction. However, correcting the U–Th age of stalagmite with the average 232Th/238U value in the crust is sometimes not enough to eliminate the effect of the initial 230Th, using other dating methods (e.g., 14C) and referring to the characteristics of speleothem δ18O values are useful to guide its age correction and establish the chronology. This paper presents a comprehensive study of the chronology and isotopic record of a stalagmite XBL-5 from Xiaobailong Cave, Yunnan, China, using a combination of stalagmite U–Th dating, 14C dating, and δ18O wiggle match dating. The low uranium content of this stalagmite and the apparent inversion of U–Th dating prevent us from establishing the proxy profiles with reliable …

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), CO2 degassing in the cave, and possibly variations of the abundance of C3 and C4 grasses in the vegetation. The relationships of δ18O with other proxies shift between ~70 and 48 ka (Marine Isotope Stages 4–3) so …