11 research outputs found
Towards a dendrochronologically refined date of the Laacher See Eruption
The precise date of the Laacher See eruption (LSE), central Europeâs largest Late Pleistocene volcanic event that occurred around 12,900 years ago, is still unknown. Here, we outline the potential of combined high-resolution dendrochronological, wood anatomical and radiocarbon (14C) measurements, to refine the age of this major Plinian eruption. Based on excavated trees that were killed during the explosive LSE and buried under its pyroclastic deposits, we describe how a firm date of the eruption might be achieved, and how the resulting temporal precision would further advance our understanding of the environmental and societal impacts of this event. Moreover, we discuss the relevance of an accurate LSE date for improving the synchronization of European terrestrial and lacustrine Late Glacial to Holocene archives, and outline how the proposed, interdisciplinary dating approach can be applied to other large, yet undated, volcanic eruptions
Climate-induced severe water scarcity events as harbinger of global grain price
The severe water scarcity (SWS) concept allows for consistent analysis of the supply and demand for water sourced grain production worldwide. Thus, the primary advantage of using SWS is its ability to simultaneously accommodate the spatial extent and temporal persistence of droughts using climatic data. The SWS concept was extended here to drivers of global grain prices using past SWS events and prices of three dominant grain crops: wheat, rice and maize. A significant relation between the SWS affected area and the prices of wheat was confirmed. The past priceâSWS association was then used to project future wheat prices considering likely climate change scenarios until 2050 and expected SWS extent. The projected wheat prices increase with increasing SWS area that is in turn a function of greenhouse gas emissions. The need to act to reduce greenhouse gas emissions is again reinforced assuming the SWS-price relation for wheat is unaltered
Early anthropogenic transformation of the Danube-Black Sea system
© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 2 (2012): 582, doi:10.1038/srep00582.Over the last century humans have altered the export of fluvial materials leading to significant changes in morphology, chemistry, and biology of the coastal ocean. Here we present sedimentary, paleoenvironmental and paleogenetic evidence to show that the Black Sea, a nearly enclosed marine basin, was affected by land use long before the changes of the Industrial Era. Although watershed hydroclimate was spatially and temporally variable over the last ~3000 years, surface salinity dropped systematically in the Black Sea. Sediment loads delivered by Danube River, the main tributary of the Black Sea, significantly increased as land use intensified in the last two millennia, which led to a rapid expansion of its delta. Lastly, proliferation of diatoms and dinoflagellates over the last five to six centuries, when intensive deforestation occurred in Eastern Europe, points to an anthropogenic pulse of river-borne nutrients that radically transformed the food web structure in the Black Sea.This study was supported by grants OISE 0637108, EAR
0952146, OCE 0602423 and OCE 0825020 from the National Science Foundation and
grants from the Woods Hole Oceanographic Institution
Detecting instabilities in tree-ring proxy calibration
Evidence has been found for reduced sensitivity of tree growth to temperature in a number of forests at high northern latitudes and alpine locations. Furthermore, at some of these sites, emergent subpopulations of trees show negative growth trends with rising temperature. These findings are typically referred to as the 'Divergence Problem' (DP). Given the high relevance of paleoclimatic reconstructions for policy-related studies, it is important for dendrochronologists to address this issue of potential model uncertainties associated with the DP. Here we address this issue by proposing a calibration technique, termed 'stochastic response function' (SRF), which allows the presence or absence of any instabilities in growth response of trees (or any other climate proxy) to their calibration target to be visualized and detected. Since this framework estimates confidence limits and subsequently provides statistical significance tests, the approach is also very well suited for proxy screening prior to the generation of a climate-reconstruction network. Two examples of tree growth/climate relationships are provided, one from the North American Arctic treeline and the other from the upper treeline in the European Alps. Instabilities were found to be present where stabilities were reported in the literature, and vice versa, stabilities were found where instabilities were reported. We advise to apply SRFs in future proxy-screening schemes, next to the use of correlations and RE/CE statistics. It will improve the strength of reconstruction hindcast
Millennium-long summer temperature variations in the European Alps as reconstructed from tree rings
This paper presents a reconstruction of the summer temperatures over the Greater Alpine Region (44.05°-47.41° N, 6.43°-13° E) during the last millennium based on a network of 38 multi-centennial larch and stone pine chronologies. Tree ring series are standardized using an Adaptative Regional Growth Curve, which attempts to remove the age effect from the low frequency variations in the series. The proxies are calibrated using the June to August mean temperatures from the HISTALP high-elevation temperature time series spanning the 1818-2003. The method combines an analogue technique, which is able to extend the too short tree-ring series, an artificial neural network technique for an optimal non-linear calibration including a bootstrap technique for calculating error assessment on the reconstruction. About 50% of the temperature variance is reconstructed. Low-elevation instrumental data back to 1760 compared to their instrumental target data reveal divergence between (warmer) early instrumental measurements and (colder) proxy estimates. The proxy record indicates cool conditions, from the mid-11th century to the mid-12th century, related to the Oort solar minimum followed by a short Medieval Warm Period (1200-1420). The Little Ice Age (1420-1830) appears particularly cold between 1420 and 1820 with summers that are 0.8 °C cooler than the 1901-2000 period. The new record suggests that the persistency of the late 20th century warming trend is unprecedented. It also reveals significant similarities with other alpine reconstruction
A matter of divergence: Tracking recent warming at hemispheric scales using tree ring data
No current tree ring (TR) based reconstruction of extratropical Northern Hemisphere (ENH) temperatures that extends into the 1990s captures the full range of late 20th century warming observed in the instrumental record. Over recent decades, a divergence between cooler reconstructed and warmer instrumental large-scale temperatures is observed. We hypothesize that this problem is partly related to the fact that some of the constituent chronologies used for previous reconstructions show divergence against local temperatures in the recent period. In this study, we compiled TR data and published local/regional reconstructions that show no divergence against local temperatures. These data have not been included in other large-scale temperature reconstructions. Utilizing this data set, we developed a new, completely independent reconstruction of ENH annual temperatures (1750-2000). This record is not meant to replace existing reconstructions but allows some degree of independent validation of these earlier studies as well as demonstrating that TR data can better model recent warming at large scales when careful selection of constituent chronologies is made at the local scale. Although the new series tracks the increase in ENH annual temperatures over the last few decades better than any existing reconstruction, it still slightly under predicts values in the post-1988 period. We finally discuss possible reasons why it is so difficult to model post-mid-1980s warming, provide some possible alternative approaches with regards to the instrumental target and detail several recommendations that should be followed in future large-scale reconstruction attempts that may result in more robust temperature estimates.</p
Seasonal Reconstruction of Summer Precipitation Variability and Dating of Flood Events for the Millennium Between 3250 and 2250 Years BC for the Main Region, Southern Germany
Potential and limitation of combining terrestrial and marine growth records from Iceland
Seasonally formed, perennial growth increments of various organisms may possibly contain information about
past environmental changes, well before instrumental measurements occurred. Such annually resolved proxy
records have been mainly obtained from terrestrial archives, with a paucity of similar data originating from
marine habitats. Iceland represents ideal conditions to develop both, tree ring (dendro) and bivalve shell (sclero)
chronologies from adjacent sites. Here we introduce the first network of Icelandic birch (Betula pubescens Ehrh.)
and rowan (Sorbus aucuparia) dendrochronologies, as well as ocean quahog (Arctica islandica L.) sclerochronologies.
In order to identify the dominant external drivers of tree and shell growth, we assess the common
growth trends and growth extremes within and between the terrestrial and marine records, as well as relationships
of both archives with instrumental-based meteorological indices. Capturing a strong signal of
JuneâAugust mean air temperature, the dendrochronologies are significantly positively correlated to each other.
The sclerochronologies, however, reveal much lower growth coherency, which likely results from different
sampling strategies and growth habitats. Disagreement between the dendro- and sclerochronologies possibly
originates from unequal sample size, offset in the seasonal timing and rate of the growth, as well as varying
sensitivities to different environmental factors. Our results emphasize the importance of considering a wide
range of species and taxa to reconstruct a more complete picture of terrestrial and marine ecosystem functioning
and productivity across various spatiotemporal scales