Ice cores from Greenland provide science with valuable data about the past. The substances and materials trapped in the ice provide information about processes that had also taken place in distant regions. These include volcanic eruptions. One of the most famous of these is the eruption of Mount Vesuvius near Naples. Researchers had discovered layers in an ice core in 2013 that they attributed to the eruption at the time, which became hugely important in dating other layers. But now an international team with Swiss participation has called this result into question.
According to the scientists led by authors Professor Gill Plunkett of Queen’s University in Belfast and Professor Michael Sigl of the Oeschger Center for Climate Change Research at the University of Bern, the tephra layers (deposits of volcanic ash) from the ice core are not from Mount Vesuvius, but probably from a volcanic eruption in the Aleutian Islands. This had probably taken place unobserved, but was in no way inferior to the eruption of Vesuvius in its violence. The research team also concludes that the eruption on the Aleutian Islands also does not fall within the same time frame as the eruption of Mount Vesuvius in 79 AD, but probably occurred in the winter of 87-88 AD.
The deposits that led to the original result about the connection of Vesuvius to Greenland came from ice cores produced by the first large-scale drilling project in Greenland, GRIP. At the time, an Italian-Danish research team had examined the deposits and concluded that they must have come from the famous eruption of Mount Vesuvius in 79 AD.
The new results come from ice cores taken in 2011 in the northwestern part of Greenland. In addition to the sulfate deposits, the international team also examined the particles from the layers of high sulfate concentrations. The main and trace element analysis of the particles showed that they could not be originally from Italy, since both the chemical and chronological examinations did not correspond to the eruption of Vesuvius. Rather, the data pointed to an eruption from the Aleutian Islands region. Modeling showed that the strength of the eruption, which may have ejected about 0.5 cubic kilometers of material over a 12-hour period, was large enough to propel the particles to the appropriate altitude, from where they were subsequently transported toward Greenland and redeposited.
One problem that the researchers, led by Gill Plunkett and Michael Sigl, have is that there is no accurate record of the eruption. The Aleutian Islands are volcanically very active, but only sparsely populated. And the inhabitants of that time only knew the oral tradition. However, it is known that the Aleutian Islands have always had violent eruptions, such as those of the volcano Okmok in the years 45 and 43 BC. These had been so violent that climatic changes had occurred as far away as the Mediterranean. Incidentally, Plunkett and Sigl also discovered these results in ice cores. But when it came to these findings, the team was unable to determine the exact location of the eruption. According to the authors, the chemical composition of the particles suggests that the Aniakchak volcano is a possible source.
Ice cores are actually like libraries in which information from different times is stored as layers at different depths. Therefore, it is important to assign known events whose time is known to the corresponding depths. The results of the 2013 study helped greatly, as volcanic eruptions had rarely been observed in ancient times, and had been even less accurately documented. It was therefore fortunate for further research that the deposits in this core were assigned to the date of the eruption handed down by Pliny the Younger. But other work and results from research on ice cores taken from other parts of Greenland had already called the Italian-Danish team’s conclusions into question. The insights now gained with this new work by Professors Plunkett and Sigl may be further fuel to the fire of the heated debate over the frigid data from the far reaches of the Greenland ice sheet.
Dr Michael Wenger, PolarJournal
Link to the current study: Plunkett, G., Sigl, M., Schwaiger, H. F., Tomlinson, E. L., Toohey, M., McConnell, J. R., Pilcher, J. R., Hasegawa, T., and Siebe, C.: No evidence for tephra in Greenland from the historic eruption of Vesuvius in 79 CE: implications for geochronology and paleoclimatology, Clim. Past, 18, 45-65, https://doi.org/10.5194/cp-18-45-2022, 2022
Link to Vesuvius study: Barbante, C., Kehrwald, N. M., Marianelli, P., Vinther, B. M., Steffensen, J. P., Cozzi, G., Hammer, C. U., Clausen, H. B., and Siggaard-Andersen, M.-L.: Greenland ice core evidence of the 79 AD Vesuvius eruption, Clim. Past, 9, 1221-1232, https://doi.org/10.5194/cp-9-1221-2013, 2013.
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