Site Introduction 

Ernesto Cave (Grotta di Ernesto) is a small cave in Northern Italy’s mountainous Trentino province. The steep, north-facing slope of the Asiago Plateau on which it is situated is covered with a forest of beech, spruce, and silver fir and overlooks the deep Sugana Valley. The cave is situated 1,167 meters above sea level and consists of a seventy-meter-long descending gallery that opens into three successive chambers: Sala del Focolare, Sala Grande, and Sala Terminale. Active stalagmites and stalactites decorate the passages, courtesy of the porous overlying Jurassic limestone. 

Ernesto Cave was discovered in the autumn of 1983, during excavations for road construction, and takes its name from the boy who was first to enter since the entrance was blocked by debris around 8,000 years ago. Inside was evidence of human activity dating to the Mesolithic period (around 9,000 years ago), including a hearth and some animal bones bearing tool marks. The cave was reclosed with an iron door to prevent disturbance by humans or animals and to preserve the natural ventilation patterns.

The forest above the cave is only around eighty years old, since the area was cleared to facilitate military operations prior to World War I. On May 15, 1916, the Asiago Plateau—located on the frontline between Austria-Hungary and Italy—was the site of a major battle, in which 25,000 people died.

Location of the Core 

The GSSP11A GSSP is a Global Boundary Stratotype Section and Point, which defines the lower boundary of a chronostratigraphic unit on the geologic time scale. It is sometimes referred to as a “golden spike”, after the marker which is, in some cases, driven into the boundary. candidate for Ernesto Cave is not a core but rather stalagmites cut from the cave floor, which grew for the last 8,500 years. Speleothems (including stalagmites, which grow up from the floor, and stalactites, which hang down like stone icicles) are formed when water filters through limestone and drips into a cave. When the water loses excess carbon dioxide, it deposits calcium carbonate—a process that, over thousands of years, forms the spikes and spires that decorate underground chambers. The annual layers of stalagmites and stalactites thus constitute extremely long-running archives. Because Ernesto Cave is relatively small, largely undisturbed (it is closed to the public), and has been well-studied since the early 1990s, the records held in its speleothems can be used to form accurate pictures of past environmental and climatic conditions.

The average rate of stalagmite growth in Ernesto Cave is around 0.1 millimeters per year, with two distinct layers: most of the growth is pale colored, being made up of translucent, non-fluorescent22Fluorescence is the emission of light and other radiation after the absorption of electrons or radiation of a different wavelength, especially ultraviolet light and x-rays. calcite (up to approximately 200 micrometers thick), and a thin, brown layer of fluorescent calcite (0.5–4 micrometers thick) forms in autumn. The fluorescence and dark color originates from soil-derived organic matter, which is flushed into the cave during autumn rainfall. Another imprint of the seasons is the sulfate content in the stalagmite: lower levels of carbon dioxide increase the pH33A measure of acidity or alkalinity on a logarithmic scale 0–14. pH 7 is neutral, lower values are acidic and higher values are alkali. Derived from the German Potenz (power) and the symbol H·, former chemical symbol for the hydrogen ion (now H+). of the drip water, which in turn increases the sulfate. Over centuries, sulfate levels also change depending on pollution inputs.

Because of the small number of comparable stalagmites at the site, it is not possible to obtain further samples containing the same material (as is possible with sediment cores), although other similar stalagmites in the cave demonstrate the reproducibility of the material. Given the extremely slow rate of growth, the total material that constitutes the Anthropocene in the Ernesto Cave stalagmites is only around five millimeters thick—therefore providing much less total material for analysis.

The Core and Results

The Ernesto Cave annually laminated stalagmites record both local and global anthropogenic signals. Whereas some signals (such as the seasonal flushing of soil-derived organic matter) are transmitted practically instantaneously, others are delayed by storage and biomineralization in the soil and vegetation. Thus, signals such as sulfate concentration or carbon-14 have a variable lag (of up to fifteen years) between the date of environmental input and the date of incorporation into the stalagmite layer. 

At around 1840, there are various changes which document the end of the Little Ice Age.44A phase between 1550 and 1850 with globally lower temperatures and increased glaciation compared to the present. There is a decrease in organic content as the warmer temperatures enabled more efficient degradation of organic matter in the soil above, as well as an increase in carbon-13 and stalagmite growth rate (caused by increased dissolution of calcium carbonate as a result of higher carbon dioxide production in the soil). At the beginning of the twentieth century, there are increased trace elements and organic matter which document the deforestation that occurred to facilitate military operations before World War I. Then, at 1960 there is another increase in stalagmite growth rate following a rise in surface temperature, as well as increased sulfur from industrial pollution. At the same time there is also a rise in the carbon-14 in response to the mid-century bomb pulse,55The sudden increase of carbon-14 in the Earth’s atmosphere due to the hundreds of atmospheric nuclear bomb tests that started in 1945 and intensified after 1950 until 1963, when the Limited Test Ban Treaty was signed by the United States, the Soviet Union and the United Kingdom. Since then 123 other states have joined the treaty. when nuclear testing increased levels of carbon-14 in the atmosphere.

Collection and Analysis 

Three active stalagmites were removed from the cave: ER76 in June 1993, ER77 in November 1995 (the forty-five-centimeter-long GSSP candidate), and ER78 in October 2000. The stalagmites were removed at their bases by chisel and hammer, and transported to the Science Museum in Trento. Each stalagmite was cut along its growth axis, and the two halves were sliced into 10–12-millimeter-long slabs, which were polished and scanned with a flatbed scanner before being cut into thin sections for geochemical analyses. Most of the pieces are now held in the geological sample collection at the Trento Science Museum. 

The stalagmite samples were subjected to various analyses, including petrography and microstratigraphy, optical fluorescence imaging, annual laminae counting, uranium-thorium dating, stable isotope analyses, radiocarbon analyses, synchrotron radiation-based and ion microprobe sulfur and trace element concentration analyses, and sulfur isotope analyses.

The Research Team 

The Ernesto Cave research team formed in 1994 when the cave was selected as a study site in the framework of the paleoclimate EU Project EV5V-CT94-0509. The initial group consisted of Silvia Frisia, who led the project, and Andrea Borsato, based at the Museo Tridentino di Scienze Naturali (MTSN; renamed in 2013 as Museo delle Scienze) in Trento, and Ian Fairchild from the University of Birmingham in the UK. Following the initial European project, the MTSN research team was supported by two grants from the Autonomous Province of Trento (1998–2005) and continued to collaborate with Fairchild in a wide range of successor projects, including an innovative soil-to-cave study of carbon dioxide levels and carbon isotopes and their potential relationship to the Anthropocene.

Following the demonstration of historical changes in sulfate abundance in Ernesto speleothems (Frisia et al. in 2005), Fairchild investigated this area in depth with a grant funded by the UK Natural Environment Research Council (NERC), employing Peter Wynn as a postdoctoral researcher (2005–7). The work involved devising new methods of isotope analysis of sulfate in calcite, experimental work, and work on parallel archives of trees near the cave site. Stimulated by Borsato et al.’s (2007) work on high-resolution trace element records, Adam Hartland carried out part of his PhD studies with Fairchild on colloid analyses in cave waters, funded by another NERC grant. 

In 2005, Ernesto Cave also became a site of German Research Foundation (DFG) Research Group 668 (DAPHNE), coordinated by the Heidelberg Academy of Sciences, which supported long-term cave and soil monitoring carried out by Frisia and Renza Miorandi. The DAPHNE project investigated in detail the influences of hydrology on the radiogenic and stable carbon isotope composition of cave drip water, as well as the radiocarbon bomb peak in stalagmite ER77 within the PhD research of Jens Fohlmeister.

In 2007, Frisia accepted a permanent position at the University of Newcastle, Australia, and the MTSN group partially dissolved. However, the research at Ernesto Cave continued, because of the unique quality of the data, which included the first description of stalagmite calcite fabrics based on environmental parameters and submicroscopic scale characteristics.

Today the group continues to evolve, with current interests focusing on calcium carbonate crystal growth and implications for climate proxy data.

Principal investigators (listed alphabetically): Andrea Borsato, University of Newcastle (Australia) and Museo delle Scienze di Trento Silvia Frisia, University of Newcastle (Australia) and Museo delle Scienze di Trento Ian Fairchild, University of Birmingham Contributing Scientists/Researchers (listed alphabetically): Massimo Bernardi, Museo delle Scienze di Trento, Stalagmite archiving Flavio Corradini, Fondazione Edmund Mach, Sulphur analyses John Craven, Edinburgh Ion Microprobe Facility, Ion microprobe analysis Anna de Momi, University of Birmingham, Environmental monitoring and sampling Jens Fohlmeister, University of Heidelberg, Potsdam Institute for Climate Impact Research, Germany Radiocarbon analysis Adam Hartland, University of Birmingham/now University of Waikato, Trace element analysis (colloids) Richard Hinton, Edinburgh Ion Microprobe Facility, Ion microprobe analysis Bernd Kromer, University of Heidelberg, Radiocarbon analysis Jonathan Lageard, Manchester Metropolitan University, Dendrochronology Nicola La Porta, Fondazione Edmund Mach, Dendrochronology Neil Loader, University of Swansea, Carbon isotope analysis Augusto Mangini, University of Heidelberg, Project co-ordination Frank McDermott, University College Dublin, Ireland, Uranium-series analyses Renza Miorandi, Museo delle Scienze di Trento, Cave environmental monitoring Manfred Mudelsee, Climate Risk Analysis, Hannover, Statistical analysis Nereo Preto, University of Padova, Statistical analysis Denis Scholz, Johannes Gutenberg University Mainz, Uranium-series analyses Andrea Schröder-Ritzrau, University of Heidelberg, Radiocarbon analysis Andrea Somogyi, European Synchrotron Radiation Facility, SR-XRF trace element analyses Christoph Spoetl, University of Innsbruck, Stable isotope analysis Jean Susini, European Synchrotron Radiation Facility, SR-XRF trace element analyses Peter Thomas, Keele University, Dendrochronology Peter Wynn, University of Birmingham and University of Lancaster, Sulphur, Sulphur isotope analysis Michele Zandonati, Museo delle Scienze di Trento, Environmental monitoring and sampling