Middle and late Holocene climate change and human impact inferred from diatoms,algae and aquatic macrophyte pollen in sediments from Lake Montcortès (NE Iberian Peninsula)

During the middle and late Holocene, the Iberian Peninsula underwent large climatic and hydrologic changes, but the temporal resolution and regional distribution of available palaeoenvironmental records is still insufficient for a comprehensive assessment of the regional variability. The high sedimentation rate in karstic, meromictic Montcortès Lake (Catalan pre-Pyrenees) allows for a detailed reconstruction of the regional palaeoecology over the last 5,340 years using diatom analysis, aquatic pollen, sedimentological data, and historic documentary records. Results show marked fluctuations in diatom species assemblage composition, mainly between dominant Cyclotella taxa and small Fragilariales. We suggest that the conspicuous alternation between Cyclotella comta and C. cyclopuncta reflects changes in trophic state, while the succession of centric and pennate species most likely reflects changes in the hydrology of the lake. The diatom assemblages were used to identify six main phases: (1) high productivity and likely lower lake levels before 2350 BC, (2) lower lake levels and a strong arid phase between 2350 and 1850 BC, (3) lake level increase between 1850 and 850 BC, (4) relatively high lake level with fluctuating conditions during the Iberian and Roman Epochs (650 BC–350 AD), (5) lower lake levels, unfavourable conditions for diatom preservation, eutrophication and erosion triggered by increased human activities in the watershed during the Medieval Climate Anomaly (900–1300 AD), and (6) relatively higher lake levels during the LIA (1380–1850 AD) and afterwards. The combined study of diatoms, algae and pollen provides a detailed reconstruction of past climate, which refines understanding of regional environmental variability and interactions between climate and socio-economic conditions in the Pyrenees.     

Quantitative high-resolution warm season rainfall recorded in varved sediments of Lake Oeschinen,northern Swiss Alps: calibration and validation AD 1901–2008

High-resolution, well-calibrated records of lake sediments are critically important for quantitative climate reconstructions, but they remain a methodological and analytical challenge. While several comprehensive paleotemperature reconstructions have been developed across Europe, only a few quantitative high-resolution studies exist for precipitation. Here we present a calibration and verification study of lithoclastic sediment proxies from proglacial Lake Oeschinen (46°30′N, 7°44′E, 1,580 m a.s.l., north–west Swiss Alps) that are sensitive to rainfall for the period AD 1901–2008. We collected two sediment cores, one in 2007 and another in 2011. The sediments are characterized by two facies: (A) mm-laminated clastic varves and (B) turbidites. The annual character of the laminae couplets was confirmed by radiometric dating (²¹⁰Pb, ¹³⁷Cs) and independent flood-layer chronomarkers. Individual varves consist of a dark sand-size spring-summer layer enriched in siliciclastic minerals and a lighter clay-size calcite-rich winter layer. Three subtypes of varves are distinguished: Type I with a 1–1.5 mm fining upward sequence; Type II with a distinct fine-sand base up to 3 mm thick; and Type III containing multiple internal microlaminae caused by individual summer rainstorm deposits. Delta-fan surface samples and sediment trap data fingerprint different sediment source areas and transport processes from the watershed and confirm the instant response of sediment flux to rainfall and erosion. Based on a highly accurate, precise and reproducible chronology, we demonstrate that sediment accumulation (varve thickness) is a quantitative predictor for cumulative boreal alpine spring (May–June) and spring/summer (May–August) rainfall (r_MJ = 0.71, r_MJJA = 0.60, p < 0.01). Bootstrap-based verification of the calibration model reveals a root mean squared error of prediction (RMSEP_MJ = 32.7 mm, RMSEP_MJJA = 57.8 mm) which is on the order of 10–13 % of mean MJ and MJJA cumulative precipitation, respectively. These results highlight the potential of the Lake Oeschinen sediments for high-resolution reconstructions of past rainfall conditions in the northern Swiss Alps, central and eastern France and south-west Germany.     

A Review of: “Fractals in Geoscience and Remote Sensing: Proceedings of Joint JRC/EARSel Expert Meeting,Ispra, Italy, 14–15 April 1994. Report EUR 16092 EN,Image Understanding Research Series Vol I. Edited by G. G. Wilkinson,I. Kanellopoulos and J. Megier”

Geographic information systems (GIS) and spatial regression modeling techniques were used to evaluate the spatially prioritized relationships between grave density and various spatial parameters for a total of 5549 grave locations. Solar radiation was the most important predictor of grave density in the Feng‐Shui locations. Similarly, spatial clustering technology identified the fact that high concentrations of grave necessarily accompany the significantly increasing trends of solar radiation. The results of the regression analyses indicate that the grave density could be explained by the four landform parameters alone yielding R ² values of 0.751. In contrast to the typical theory, slope and aspect were not a dominant determining factor upon the dependent variable of grave density. Also, the significantly increasing trends of grave density were not observed in line with a southern direction. A clear verification has been made for the hidden assumptions in Feng‐Shui's long history that its approach is found to be more appropriate in avoiding shadow conditions, rather than exploring the ideal landform location.