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- ItemA tale of shifting relations: East Asian summer and winter monsoon variability during the Holocene([London] : Macmillan Publishers Limited, part of Springer Nature, 2021) Kaboth-Bahr, Stefanie; Bahr, André; Zeeden, Christian; Yamoah, Kweku A.; Lone, Mahjoor Ahmad; Chuang, Chih-Kai; Löwemark, Ludvig; Wei, Kuo-YenUnderstanding the dynamics between the East Asian summer (EASM) and winter monsoon (EAWM) is needed to predict their variability under future global warming scenarios. Here, we investigate the relationship between EASM and EAWM as well as the mechanisms driving their variability during the last 10,000 years by stacking marine and terrestrial (non-speleothem) proxy records from the East Asian realm. This provides a regional and proxy independent signal for both monsoonal systems. The respective signal was subsequently analysed using a linear regression model. We find that the phase relationship between EASM and EAWM is not time-constant and significantly depends on orbital configuration changes. In addition, changes in the Atlantic Meridional Overturning circulation, Arctic sea-ice coverage, El Niño-Southern Oscillation and Sun Spot numbers contributed to millennial scale changes in the EASM and EAWM during the Holocene. We also argue that the bulk signal of monsoonal activity captured by the stacked non-speleothem proxy records supports the previously argued bias of speleothem climatic archives to moisture source changes and/or seasonality.
- Item“Climatic fluctuations in the hyperarid core of the Atacama Desert during the past 215 ka”([London] : Macmillan Publishers Limited, part of Springer Nature, 2019) Ritter, Benedikt; Wennrich, Volker; Medialdea, Alicia; Brill, Dominik; King, Georgina; Schneiderwind, Sascha; Niemann, Karin; Fernández-Galego, Emma; Diederich, Julia; Rolf, Christian; Bao, Roberto; Melles, Martin; Dunai, Tibor J.Paleoclimate records from the Atacama Desert are rare and mostly discontinuous, mainly recording runoff from the Precordillera to the east, rather than local precipitation. Until now, paleoclimate records have not been reported from the hyperarid core of the Atacama Desert (<2 mm/yr). Here we report the results from multi-disciplinary investigation of a 6.2 m drill core retrieved from an endorheic basin within the Coastal Cordillera. The record spans the last 215 ka and indicates that the long-term hyperarid climate in the Central Atacama witnessed small but significant changes in precipitation since the penultimate interglacial. Somewhat ‘wetter’ climate with enhanced erosion and transport of material into the investigated basin, commenced during interglacial times (MIS 7, MIS 5), whereas during glacial times (MIS 6, MIS 4–1) sediment transport into the catchment was reduced or even absent. Pelagic diatom assemblages even suggest the existence of ephemeral lakes in the basin. The reconstructed wetter phases are asynchronous with wet phases in the Altiplano but synchronous with increased sea-surface temperatures off the coasts of Chile and Peru, i.e. resembling modern El Niño-like conditions.
- ItemCommon solar wind drivers behind magnetic storm–magnetospheric substorm dependency([London] : Macmillan Publishers Limited, part of Springer Nature, 2018) Runge, Jakob; Balasis, Georgios; Daglis, Ioannis A.; Papadimitriou, Constantinos; Donner, Reik V.The dynamical relationship between magnetic storms and magnetospheric substorms is one of the most controversial issues of contemporary space research. Here, we address this issue through a causal inference approach to two corresponding indices in conjunction with several relevant solar wind variables. We find that the vertical component of the interplanetary magnetic field is the strongest and common driver of both storms and substorms. Further, our results suggest, at least based on the analyzed indices, that there is no statistical evidence for a direct or indirect dependency between substorms and storms and their statistical association can be explained by the common solar drivers. Given the powerful statistical tests we performed (by simultaneously taking into account time series of indices and solar wind variables), a physical mechanism through which substorms directly or indirectly drive storms or vice versa is, therefore, unlikely.
- ItemYield trends, variability and stagnation analysis of major crops in France over more than a century([London] : Macmillan Publishers Limited, part of Springer Nature, 2018) Schauberger, Bernhard; Ben-Ari, Tamara; Makowski, David; Kato, Tomomichi; Kato, Hiromi; Ciais, PhilippeFrance is a major crop producer, with a production share of approx. 20% within the European Union. Yet, a discussion has recently started whether French yields are stagnating. While for wheat previous results are unanimously pointing to recent stagnation, there is contradictory evidence for maize and few to no results for other crops. Here we analyse a data set with more than 120,000 yield observations from 1900 to 2016 for ten crops (barley, durum and soft wheat, maize, oats, potatoes, rapeseed, sugar beet, sunflower and wine) in the 96 mainland French départements (NUTS3 administrative division). We dissect the evolution of yield trends over time and space, analyse yield variation and evaluate whether growth of yields has stalled in recent years. Yields have, on average across crops, multiplied four-fold over the course of the 20th century. While absolute yield variability has increased, the variation relative to the mean has halved – mean yields have increased faster than their variability. But growth of yields has stagnated since the 1990’s for winter wheat, barley, oats, durum wheat, sunflower and wine on at least 25% of their areas. Reaching yield potentials is unlikely as a cause for stagnation. Maize, in contrast, shows no evidence for stagnation.
- ItemFuture tree survival in European forests depends on understorey tree diversity(London : Nature Publishing Group, 2022) Billing, Maik; Thonicke, Kirsten; Sakschewski, Boris; Bloh, Werner von; Walz, ArianeClimate change heavily threatens forest ecosystems worldwide and there is urgent need to understand what controls tree survival and forests stability. There is evidence that biodiversity can enhance ecosystem stability (Loreau and de Mazancourt in Ecol Lett 16:106–115, 2013; McCann in Nature 405:228–233, 2000), however it remains largely unclear whether this also holds for climate change and what aspects of biodiversity might be most important. Here we apply machine learning to outputs of a flexible-trait Dynamic Global Vegetation Model to unravel the effects of enhanced functional tree trait diversity and its sub-components on climate-change resistance of temperate forests (http://www.pik-potsdam.de/~billing/video/Forest_Resistance_LPJmLFIT.mp4). We find that functional tree trait diversity enhances forest resistance. We explain this with 1. stronger complementarity effects (~ 25% importance) especially improving the survival of trees in the understorey of up to + 16.8% (± 1.6%) and 2. environmental and competitive filtering of trees better adapted to future climate (40–87% importance). We conclude that forests containing functionally diverse trees better resist and adapt to future conditions. In this context, we especially highlight the role of functionally diverse understorey trees as they provide the fundament for better survival of young trees and filtering of resistant tree individuals in the future.
- ItemAlberta wildfire 2016: Apt contribution from anomalous planetary wave dynamics([London] : Macmillan Publishers Limited, part of Springer Nature, 2018) Petoukhov, Vladimir; Petri, Stefan; Kornhuber, Kai; Thonicke, Kirsten; Coumou, Dim; Schellnhuber, Hans JoachimIn May-June 2016 the Canadian Province of Alberta suffered one of the most devastating wildfires in its history. Here we show that in mid-April to early May 2016 the large-scale circulation in the mid- and high troposphere of the middle and sub-polar latitudes of the northern hemisphere featured a persistent high-amplitude planetary wave structure dominated by the non-dimensional zonal wave number 4. The strongest anticyclonic wing of this structure was located over western Canada. In combination with a very strong El Niño event in winter 2015/2016 this favored highly anomalous, tinder-dry and high-temperature conditions at the surface in that area, entailing an increased fire hazard there. This critically contributed to the ignition of the Alberta Wildfire in May 2016, appearing to be the costliest disaster in Canadian history thus far.