1,721,025 research outputs found
Compilation of non-annually resolved Holocene proxy climate records: stacked Holocene peatland palaeo-water table reconstructions from northern Britain
No full textThe number and range of Holocene palaeoclimate reconstructions from various regions of the world have increased dramatically
over the last decade. The data density for many regions and proxies now offers the potential of robust regional-scale reconstructions
that avoid the problems of records from individual sites, and improve communication between palaeoclimate subdisciplines and
climate modellers. However, there are problems with chronological uncertainties and quantification of proxies, which make
compilation of multiple records difficult. Here we explore a ‘stacking’ and ‘tuning’ approach to the derivation of regional records
from peatland climate proxies to test its applicability to non-annually resolved terrestrial records. Twelve individual records from
northern Britain based on water table reconstructions from testate amoebae analysis were divided into four regions. Records were
detrended, normalised and compared within regions to identify clear correlative events. The original chronologies of the records
were tuned using both these events and independent age markers. The stacked record for northern Britain indicates pronounced
changes to wet conditions at 3600, 2760 and 1600 cal yr BP with more minor changes at 3060, 2050, 1260, 860, 550 and 260 cal yr BP.
The main wet phases are highly correlated with mid-European lake highstands, wider North Atlantic climate change inferred from
ocean and ice core records, and solar variability. Tuning and stacking of non-annual terrestrial palaeoclimate records is a new
approach to the compilation and reconciliation of individual records within coherent climatic regions and provides a tool for
upscaling of palaeoclimate records for climate model-data comparisons
Use of environmental magnetic measurements to characterize and correlate tephra: a case study in Iceland
No full textA set of environmental magnetic parameters (i.e. magnetic susceptibility, ?ARM, IRMs, hysteresis loops and thermomagnetic curves) has been applied to two soil sections from SE Iceland. Results demonstrate that the main magnetic minerals in the tephras are ferrimagnetic minerals (e.g. magnetite) and canted antiferromagnetic minerals (e.g. haematite), with abundant paramagnetic material also present. Cross plots of Mrs/Ms vs. (B0)cr/(B0)c and ?fd? vs. ?ARM/SIRM indicate that the main magnetic grain sizes in tephras are pseudo single domain (PSD) and multidomain (MD). Initial correlation of tephra layers was achieved, using all the measured magnetic parameters, by use of the multivariate statistical measures of Similarity Coefficient (SC) and Euclidean Distance (ED). This demonstrates that magnetic techniques can potentially assist in the identification and correlation of distal tephra
Testing a cellular modelling approach to simulating late-Holocene sediment and water transfer from catchment to lake in the French Alps since 1826
No full textThis paper describes the application of a hydrogeomorphological numerical model (CAESAR) to simulate, at hourly time steps, changes in the hydrological and sediment regime of the Petit lac d’Annecy catchment. The outputs of the model were validated in three ways. In the short term (~5 years), water discharge outputs were compared against observed instrumental data. Over the longer term, modelled sediment discharge (AD 1825–2005) was compared with proxies for detrital sediment influx (environmental magnetism) and accumulation rates discerned from a 210Pb chronology for the lake sediments.Finally, spatial validation of the modelled erosion and deposition of sediment was undertaken by comparison with a field and remotely sensed survey of catchment geomorphology. The results suggest that while minor perturbations in forest cover during the last 180 years have partially conditioned the response of the sediment system, the bulk of modelled sediment discharge and particularly the peaks in sediment discharge were controlled by flood duration and magnitude, which in turn is driven by precipitation (storms/floods) and snowmelt. Basin geometry and geomorphology of each sub-catchment (Ire and Tamie) were also important in producing differences in the modelled sediment discharge. In essence, these differences were a function of sediment accommodation space and the ability of each system to store and release sediments. Modelled sediment discharge and χpara (lake sediments) display similar histories, and thus are both interpreted as reflecting variations in detrital sediment supply. Intriguingly the style of modelled sediment discharge from the Ire, a confined mountain torrent, displays a greater similarity to and perhaps dominates the lake sediment record. These results provide partial validation of the CAESAR model and indicate that perhaps in the future it may be used as an exploratory and predictive tool in determining the impact of changes in climate, meteorology and land use on lake-catchment systems
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