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© GFZRemoval of a short core

Regional climate changes can be very rapid. A German-British team of geoscientists now reports that such a rapid climate change occurred in different regions with a time difference of 120 years. Investigation in the west German Eifel region and in southern Norway demonstrated that at the end of the last glaciation, about 12,240 years before the present, the climate became warmer, first recognised in the Eifel region and 120 years later in southern Norway. Nonetheless, the warming was equally rapid in both regions.

The team around Christine Lane (Oxford University) and Achim Brauer from the GFZ German Research Centre for Geosciences reports in the latest volume of Geology (vol 41, no 12, p. 1251 - 1254) that within the younger Dryas, the last about 1100-year long cold phase at the end of the last ice age, a rapid warming first was measured in the Eifel region. Sediment cores from the Meerfelder Maar lake depict a typical deposition pattern, which was also found in the sediments of Lake Krakenes in southern Norway, but with a time lag of 120 years.

But how did the researcher reveal such an accurate time marking? "12,140 years ago a major eruption of the Katla volcano occurred on Iceland," explains Achim Brauer. "The volcanic ash was distributed by strong winds over large parts of northern and central Europe and we can find them with new technologies as tiny ash particles in the sediment deposits of lakes. Through counting of annual bands in these sediments we could precisely determine the age of this volcanic ash." Therefore, this ash material reflects a distinct time marker in the sediments of the lakes in the Eifel and in Norway.

Accurate

Furthermore, lake sediments are very accurate climate archives, especially when they contain seasonal bands similar like tree rings. "It is a diligent piece of work to count and analyse thousands of these thin layers under the microscope to reconstruct climate year-by-year far back in time", illustrates Brauer.

The ash of the Katla volcanic eruption thus was deposited at the same time in the Eifel and in Norway. The sediments of the Eifel maar lake depict the rapid warming 100 years before the volcanic ash, while it is seen in the southern Norwegian lake sediment 20 years after the volcanic eruption. The same warming, but with a 120 years difference in timing between locations about 1200 km apart. Achim Brauer: "We can explain this difference with the shift of hemispheric wind systems. Climate changed in both regions very rapidly, but the polar front, that is the atmospheric boundary layer between cold polar air and the warmer air of the mid-latitudes, required more than 100 years to retreat from its glacial position at about the location of the Eifel at 50° N to its southern Norwegian position at 62° N." Hence, the study provides evidence for a rapid change that slowly moved northwards.

The result of this study has some implications on the understanding of both past and future climate change. The assumption of an everywhere and always synchronously changing climate must be questioned and climate models have to better consider such regional aspects.

Abstract

Knowledge of regional variations in response to abrupt climatic transitions is essential to understanding the climate system and anticipating future changes. Global climate models typically assume that major climatic changes occur synchronously over continental to hemispheric distances. The last major reorganization of the ocean-atmosphere system in the North Atlantic realm took place during the Younger Dryas (YD), an ~1100 yr cold period at the end of the last glaciation. Within this region, several terrestrial records of the YD show at least two phases, an initial cold phase followed by a second phase of climatic amelioration related to a resumption of North Atlantic overturning. We show that the onset of climatic amelioration during the YD cold period was locally abrupt, but time-transgressive across Europe. Atmospheric proxy signals record the resumption of thermohaline circulation midway through the Younger Dryas, occurring 100 yr before deposition of ash from the Icelandic Vedde eruption in a German varve lake record, and 20 yr after the same isochron in western Norway, 1350 km farther north. Synchronization of two high-resolution continental records, using the Vedde Ash layer (12,140 ± 40 varve yr B.P.), allows us to trace the shifting of the polar front as a major control of regional climate amelioration during the YD in the North Atlantic realm. It is critical that future climate models are able to resolve such small spatial and chronological differences in order to properly encapsulate complex regional responses to global climate change.

Citation

C.S. Lane, A. Brauer, S.P.E. Blockley, P. Dulski: "Volcanic ash reveals a time-transgressive abrupt climate change during the Younger Dryas", Geology v. 41, no. 12, p. 1251 - 1254; December 2013; doi:10.1130/G34867.1

See abstract and get paper here.

Source

This report based on a story provided by GFZ Potsdam here.