This project applies new high-resolution micro-analytical techniques to speleothems from Soreq Cave (Israel). The climate goal is to examine hydrological seasonality as recorded in cave deposits during periods of climatic change such as the last glacial maximum (LGM), the transition from the LGM to the interglacial (including Heinrich event H1,Bølling-Allerød, and the Younger Dryas), and other extreme wet and drought events during the Holocene.
The analytical goal of the project is to develop annual to sub-annual time resolution in the isotope and trace element records across multiple time intervals since the LGM. Specifically, the researcher and his colleagues will employ an ion microprobe to analyze stable isotope ratios (Oxygen & Carbon) and trace elements at sub-annual resolution; confocal laser fluorescent microscopy to image annual growth bands; and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-mass spectrometry) to determine the age of calcite precipitation.
The primary broader impacts involve exploring new analytical tools for climate research, examining climate forcing and impacts in arid regions, supporting a graduate student, and promoting strong international collaborations.
Carbonate cave deposits (e.g. stalagmites and stalactites, or "speleothems") preserve a geochemical record of local climate as they grow. Groundwater transmits chemical signatures of rainfall dynamics and surface vegetation into the cave, where those signatures are recorded in the mineral structure of speleothems. Given the widespread distribution of caves on Earth and the slow growth-rate of cave carbonates, speleothems provide valuable, long-lived records of past climate changes on a global scale. Before this research, however, most chemical records of past climate from speleothems had a temporal resolution of several decades or centuries; seasonal or annual climate change signals were averaged and information was lost. Here, we applied new high-resolution micro-analytical techniques in order to reveal records of rapid and seasonal climate change preserved in a suite of speleothems from Soreq Cave, Israel – a superb natural laboratory that has been studied for more than 25 years. We used the WiscSIMS ion microprobe at the University of Wisconsin-Madison to measure three geochemical properties in Soreq speleothems at high spatial resolution. Spot measurements of the stable isotope ratios of oxygen (d18O) and carbon (d13C), in addition to trace elements were made in four Soreq samples (e.g. Figure 1). The diameter of each spot measured by ion microprobe ranged from 7-15 mm, which allowed us to make multiple sequential measurements in the annual growth bands observed in each sample. Confocal laser fluorescent microscopy was used to image fluorescent annual growth bands. The ages of the samples were determined by radiometric dating and show that the samples grew between 34 ky ago and today, a timespan that includes important climatic changes that occurred during the transition out of the last glacial period. These changes are arguably the most important climate events for hypothesizing and modeling future climate dynamics. Results of our analyses indicate that seasonal climate in the Eastern Mediterranean region changed significantly at least twice since the last glacial period. Most notably, the more recent change appears to have occurred in response to atmospheric changes during the rapid warming at the end of the Younger Dryas cold period (approx. 12,000 years ago). Simultaneous changes in both the pattern of fluorescent annual banding and annual geochemical variability in a Soreq speleothem indicate a shift from a climate regime where rainfall can occur year-round to the pattern of distinct wet and dry seasons that is seen in the region today (Figure 2). Application of our micro-analytical method to a speleothem that grew in Soreq over the last 25 years, when instrumental records of rainfall amount and chemistry are available from above the cave, demonstrated remarkable transmission of a climate signal at seasonal resolution. We discovered a reliable geochemical indicator for annual rainfall amount above the cave, and observed a series of marked geochemical changes in response to the onset of a prolonged regional drought in 1999. Applied to samples from other caves and/or from different time periods, our analytical approach could access untapped high-resolution records of continental climate change. This project stimulated a fruitful international collaboration between scientists in Israel and the US and contributed to the training of two PhD-candidate graduate students in the fields of stable isotope geochemistry and paleoclimatology. These studies inspired the first Workshop on High Resolution Proxies of Paleoclimate that was hosted at the University of Wisconsin in June 2013 (Figure 3), see: www.geology.wisc.edu/~wiscsims/Paleoclimate_Workshop/index.html
