Ice Core Analysis Provides Information About Past Ecosystem Dynamics

By Laura ThomsonDec 1 2021

Continental-scale impacts on ecosystems are often not extensively recorded. This article details the use of ice core retrieved from the Monte Rosa Massif in the Swiss Alps to reveal close association among vegetation, climate, pollution, agriculture, pests, and fire in the past millennium in Europe. The article looks at Brugger, S. O et al.'s paper published in Geophysical Research Letters.

Image Credit: Wim Hoek/Shutterstock.com

Knowledge about the past ecosystem dynamics and human activities is mostly attained through narrative sources by chroniclers and diarists. However, these do not allow extrapolation to an extended region. The majority of the microfossil records from lake sediments recording ecosystem change lacks chronological precision, spatial scale, temporal resolution, and ecosystem complexity.

Recently, microfossils protected in ice cores demonstrated the strength to provide vegetation and land use-reconstructions on a large spatial scale with incomparable chronological precision, but this area is hugely unexplored.

The current research is the first of its kind analysis of a glacier ice core from the European Alps. The article analyzes how human innovation, extreme weather, crop failures, and pollution molded European ecosystems and how these societies adjusted to technological advances in a highly changing world.

The ice core was collected from Colle Gnifetti in the Monte Rosa massif, located in the heart of the European continent. The Colle Gnifetti glacier saddle is an old natural ice archive. It resisted melting due to its high elevation. Microfossils such as charcoal from burning biomass, pollen from plants, and pollution particles are preserved in the ice and transported from various areas via the atmosphere (see Figure 1).

Figure 1. Study site in the Monte Rosa massif. (a) European biomes and geographical regions (Lang, 1994), as well as the study region of Monte Rosa in the European Alps (red triangle). (b) Southern view from Italy toward Monte Rosa and the Colle Gnifetti glacier saddle (red triangle; Photo: Willy Tinner). (c) Drilling camp in summer 2015 on the Colle Gnifetti glacier saddle (Photo: Michael Sigl). (d) Source sensitivity of Colle Gnifetti to different land areas are based on the atmospheric transport model FLEXPART. Source sensitivity was calculated as air mass residence time in a given grid cell divided by air density and as such is given in units (s m³ kg⁻¹). Isolines encompass areas with the largest source sensitivity that contribute the given percentage to the total source sensitivity. Image Credit: Brugger, et al., 2021

The article utilizes the information gathered to decipher land-use dynamics and large-scale vegetation in response to environmental, biological, and societal drivers, such as an invasion, succession, disturbance, pathogen infestation, climate change, and technological innovation.

A comprehensive assessment of the major environmental and ecological forcings of European ecosystem dynamics in the past 1,000 years can be evaluated. The study also evaluates the extent of ongoing global change response processes that are rooted in the past.

Methodology

The study analyzed two ice cores from Colle Gnifetti, recovered in 2003 and 2015. The ice was dated and chronology and dating of the oldest ice core section were done by independent absolute dating techniques such as carbon (¹⁴C) isotopes and nuclear dating with lead (²¹⁰Pb).

To enable microfossil analysis, the ice core was split into contiguous sections of ca. 500–1,000 g. Optical analysis of the microfossils that infer vegetation and land-use dynamics was carried out. A black carbon (BC) record and an oxygen isotopes (δ¹⁸O) record were used as an indicator of past temperatures as an additional nonspecific burning tracer.

Statistically important local pollen assemblage zones (LPAZ) were inferred with the broken stick approach. The catchment areas of the Colle Gnifetti ice core were investigated with the atmospheric transport model FLEXPART.

Results

The microfossil record showed a huge variety of pollen types and demonstrated inherent sample-to-sample noise in the pollen signal. The principal component analysis (PCA) for the pollen data shows that expansions of forest species alternated with grassland and crop plants over time.

The ice core’s stable oxygen isotope data reveal past temperature oscillations at decadal to centennial scales. This enables direct comparison and evaluation of the effect of climate dynamics and variability of the past 1,000 years across various European biomes.

The microfossil record starts in the medieval period and is indicated by the high δ¹⁸O values (see Figure 2).

Figure 2. Comparison of the Colle Gnifetti glacier record (a) with independent data (b and c). (a) Colle Gnifetti record shows the sum of nonnative plants (Nothofagus, Pterocarya, Fallopia, Heliotropium), Vitis (grapevine), Zea mays (maize), the sum of crop, tree, shrub, and herb pollen as a proxy for vegetation and land use, microcharcoal concentrations for fire activity, spheroidal carbonaceous particles (SCP) for fossil fuel combustion, black carbon for nonspecific burning averaged to the microfossil resolution and oxygen isotopes (δ¹⁸O) for temperature averaged to microfossil resolution (gray) and as a 9-point moving average (black line). 5X exaggeration for crops and 10X exaggeration before 1750 CE for microcharcoal (red). White curve in the pollen summary graph shows 5-point moving average for tree pollen percentages. (b) Vegetation and fire reconstruction from Lago di Origlio, south of the Alps (Tinner et al., 2005). (c) Gorner glacier advances (low values) and retreats (high values) ca. 5 km northwest from Colle Gnifetti (Holzhauser et al., 2005) and cumulative global volcanic aerosol forcing (Sigl et al., 2015). Gray boxes indicate palynological signals during the Black Death, volcanic eruptions 1453/1458 CE (1450s eruptions), “Megadrought,” Maunder minimum, Tambora eruption, and the grapevine pest Phylloxera. Blue vertical line delimits statistically significant local pollen assemblage zones (LPAZ 1 and 2). Vertical dashed lines delimit 200-year intervals. Image Credit: Brugger, et al., 2021

The data revealed that around 1300 CE, the LIA cooling reflected with lower values and from 1400 to 1850 CE it resulted in the decline of crop cultivation and pastoral activities. Population decline led to the demand for grain and marginal land was converted to permanent pasture or the forest (see Figures 2 and 3).

With various other findings of major volcanic eruptions, the study also identified other preindustrial fire episodes in the ice core during the medieval period.

Figure 3. Sample scores for principal component analysis (PCA) for the ice pollen record. PCA based on percentages of the pollen sum. Sample scores of the following historical events are highlighted: Black Death CE 1347–1352, the volcanic eruptions CE 1453/1458 (VE 1450s), the megadrought CE 1540, volcanic eruption (VE) Tambora CE 1815. Selected taxa scores indicate the importance of farming vs. forest over the period recorded by the ice core: temperate beech oak forests (Fagus and Quercus robur), Mediterranean evergreen oak forest (Quercus ilex), crop cultivation (Cerealia, Vitis, Zea mays), and open landscape (Poaceae). Image Credit: Brugger, et al., 2021

The ice record became much more complex after 1750 CE, with the huge energy demands reflected in the Colle Gnifetti microfossil record. The introduction of many productive and resilient new crops such as maize was noted. The ice core also preserved the devastating Tambora eruption. However, the study failed to detect Solanum tuberosum (potato). It has a weak pollen dispersal, revealing the limitations.

The ice core also provides evidence of fire signals and large-scale deforestation. The spectacular shift in pollen assemblage indicates the exchange of goods over large distances.

The data obtained revealed the scale to which preindustrial societies in Europe were impacted by climatic events and epidemics.

Eventually, the impacts from industrial land use and amplified energy consumption led to unsustainable resource exploitation and these were confirmed due to tracers such as sulfate (SO₄), ammonium (NH₄), lead (Pb), nitrate (NO₃), other heavy metals, polycyclic aromatic hydrocarbons, and radioactive isotopes in the ice core.

Conclusion

Brugger, S. O. et al.'s provides a microfossil-inferred view and reveals that acclimatization and innovation were vital in breaking the historical cycle of societal expansion. With continued acclimatizations and technological innovations, society can identify sustainable land use approaches to decrease climate warming and the threats linked to them.

Journal Reference:

Brugger, S. O., Schwikowski, M., Gobet, E., Schwörer, C., Rohr, C., Sigl, M., Henne, S., Pfister, C., Jenk, T. M., Henne, P. D., Tinner, W. (2021) Alpine Glacier Reveals Ecosystem Impacts of Europe’s Prosperity and Peril Over the Last Millennium. Geophysical Research Letters. Available online: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL095039.

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