Showing papers by "Oliver Heiri published in 2018"

The sedimentary and remote-sensing reflection of biomass burning in Europe

Abstract: Aim: We provide the first European-scale geospatial training set relating the charcoal signal in surface lake sediments to fire parameters (number, intensity and area) recorded by satellite moderat ...

An Empirical Perspective for Understanding Climate Change Impacts in Switzerland

Abstract: Planning for the future requires a detailed understanding of how climate change affects a wide range of systems at spatial scales that are relevant to humans. Understanding of climate change impacts can be gained from observational and reconstruction approaches and from numerical models that apply existing knowledge to climate change scenarios. Although modeling approaches are prominent in climate change assessments, observations and reconstructions provide insights that cannot be derived from simulations alone, especially at local to regional scales where climate adaptation policies are implemented. Here, we review the wealth of understanding that emerged from observations and reconstructions of ongoing and past climate change impacts in Switzerland, with wider applicability in Europe. We draw examples from hydrological, alpine, forest, and agricultural systems, which are of paramount societal importance, and are projected to undergo important changes by the end of this century. For each system, we review existing model-based projections, present what is known from observations, and discuss how empirical evidence may help improve future projections. A particular focus is given to better understanding thresholds, tipping points and feedbacks that may operate on different time scales. Observational approaches provide the grounding in evidence that is needed to develop local to regional climate adaptation strategies. Our review demonstrates that observational approaches should ideally have a synergistic relationship with modeling in identifying inconsistencies in projections as well as avenues for improvement. They are critical for uncovering unexpected relationships between climate and agricultural, natural, and hydrological systems that will be important to society in the future.

The last hornbeam forests in SW Europe: new evidence on the demise of Carpinus betulus in NW Iberia

Abstract: Carpinus betulus L. is a mesic, usually considered late-successional tree widely distributed in Europe, but almost absent from Iberia, where it is generally assumed that disappeared during the coldest stages of the Wurm. High-resolution pollen analyses were carried out in 14C dated sediments from a drowned estuary (ria) and a small mountain lake. Carpinus pollen identification was confirmed by comparative light and scanning electron microscopy. Hornbeam dynamics are interpreted using palaeoclimatic reconstructions based on independent proxies (diatoms, chironomids and dinocysts). Our results support that hornbeam declined between ca. 60,000 and ca. 9,000 cal yr bp, when multiproxy evidence suggests a major regional relative sea-level rise. Moreover, chironomid-inferred July temperatures show an increase of more than 6 °C between 15,600 and 10,500 cal yr bp, while freshwater aquatics and diatoms indicate a general tendency towards increasing precipitation and a more oceanic climate. Carpinus survived during the Wurm in a variety of habitats in coastal valleys in NW Iberia which had adequate climatic and edaphic conditions. Such habitats might be comparable to the oak-ash, ravine, and hardwood floodplain forests currently existing in other regions of Europe. Large areas of these coastal ecosystems disappeared at the onset of the Holocene, when the sea-level rose. Later hornbeam was apparently unable to compete and expand further inland. Therefore, the sea-level rise combined with the climatically-induced Holocene tree succession and the increasing human impact during the Mid and Late Holocene led to hornbeam progressively becoming a marginal tree in the area.

A quantitative comparison of microfossil extraction methods from ice cores

Abstract: Microfossil records from ice archives allow vegetation, fire and land-use activity reconstructions on broad spatial scales. Samples typically contain low microfossil concentrations. Therefore, large ice volumes are often needed for palynology. Hence, it is crucial to extract maximum microfossil numbers through appropriate physical-chemical treatments. We compare six methods covering the main water reduction procedures: evaporation, filtration and centrifugation with snow samples. Adding a known number of Lycopodium marker spores prior to sample treatment and a second marker (Eucalyptus) after laboratory processing allows a quantitative microfossil loss assessment during pollen extraction. We applied the best-performing method (average loss of 22%) to high-alpine firn cores from Colle Gnifetti glacier for validation with a natural archive containing extremely low microfossil concentrations. We conclude that samples processed with different microfossil extraction protocols may give different results for pollen concentrations, percentages and ratios between different pollen types, especially if vesiculate conifer pollen is an important pollen assemblage component. We recommend a new evaporation-based method which delivers the smallest and least variable losses among the tested approaches. Since microfossil losses are inevitable during laboratory procedure, adding markers prior to sample processing is mandatory to achieve reliable microfossil concentration and influx estimates.

Chironomid-inferred Holocene temperature reconstruction in Basa de la Mora Lake (Central Pyrenees):

Abstract: We present the first Holocene chironomid-based summer temperature reconstruction for the Iberian Peninsula. A sequence from the shallow mountain lake Basa de la Mora (1914 m a.s.l., Central Pyrenee...