Process length variation in cysts of the dinoflagellate Protoceratium reticulatum,from surface sediments of the Baltic–Kattegat–Skagerrak estuarine system: a regional salinity proxy

Mertens, K. N., Dale, B., Ellegaard, M., Jansson, I.‐M., Godhe, A., Kremp, A. & Louwye, S. 2010: Process length variation in cysts of the dinoflagellate Protoceratium reticulatum, from surface sediments of the Baltic–Kattegat–Skagerrak estuarine system: a regional salinity proxy. Boreas, 10.1111/j.1502‐3885.2010.00193.x. ISSN 0300‐9483. Results are presented from a regional comparison of average process length variation in cysts of Protoceratium reticulatum and Lingulodinium polyedrum, extracted from surface sediments in the Skagerrak–Kattegat–Baltic estuarine system, with the environmental variables of seawater temperature and salinity. Although too few cysts of Lingulodinium polyedrum were recovered from the sediments to make reliable correlations, cysts of Protoceratium reticulatum were well represented, and average process length was correlated significantly with both salinity and temperature. Owing to dominant summer surface production, and regional covariation between salinity and density, we propose the use of the significant correlation with summer sea surface salinity (SSS_summer) by the equation SSS_summer=3.16 × average process length ?0.84 (R²=0.8). Application of this equation down‐core in Limfjord (northern Denmark) shows its usefulness as a regional palaeosalinity proxy.     

The challenge of dating early pleistocene fossil teeth by the combined uranium series–electron spin resonance method: the Venta Micena palaeontological site (Orce,Spain)

The palaeontological site of Venta Micena (Orce, Andalusia, Spain) lies in the eastern sector of the Guadix–Baza basin, one of the best documented areas in Europe for Plio‐Pleistocene biostratigraphy. The combination of biochronological and palaeomagnetic results, combined with the radiometric data obtained for Atapuerca Sima del Elefante, indicated that the Venta Micena stratum was formed between the Jaramillo and Olduvai palaeomagnetic events, most likely between 1.22 and 1.77 Ma. Five fossil teeth from two outcrops (sites A and B) were selected to assess the potential of combined uranium series–electron spin resonance (US‐ESR) dating of Early Pleistocene sites. Although the US‐ESR results of the first outcrop showed a large scatter between the three teeth, the mean age of 1.37 ± 0.24 Ma can be considered a reasonable age estimate for Venta Micena. The mean ESR age of 0.62 ± 0.03 Ma obtained for site B seems to be a severe underestimation when compared with the independent age control. This underestimation is attributed to a relative recent U‐mobilization event that led to some U‐leaching. The results show that any ESR age calculations of old samples are extremely sensitive to variations in the measured ²³⁰Th/²³⁴U ratios in dental tissues. Although the results demonstrate that ESR can in principle be applied to Early Pleistocene sites, they also reveal the complexity of dating such old teeth. It is necessary to continue research in several directions, such as study of the behaviour of ESR signals in old teeth and understanding recent U‐mobilization processes, to improve the reliability of the combined US‐ESR dating method applied to Early Pleistocene times, a period for which the number of available numerical dating techniques is very limited. Copyright © 2011 John Wiley & Sons, Ltd.     

Optical dating of sand wedges and ice‐wedge casts from Qinghai Lake area on the northeastern Qinghai‐Tibetan Plateau and its palaeoenvironmental implications

Sand wedges and ice‐wedge casts in the Qinghai Lake area on the northeastern Qinghai‐Tibetan Plateau (QTP) occur within alluvial gravel or river terrace deposits. In this study, we report the results of quartz Optically Stimulated Luminescence (OSL) dating of the infill of five relict sand wedges and one ice‐wedge cast. Combining our dating results with previously published luminescence ages of permafrost wedges in the Qinghai Lake area, we show that sand/ice wedges formed at c. 62 ka, c. 45 ka and between 30 and 15 ka, and that the mean annual air temperature (MAAT) was depressed by at least ～3°C relative to present during the sand/ice‐wedge formation periods. This new work is partially corroborated by post‐LGM proxy records from lakes and aeolian deposits reported from the northeastern QTP. It also significantly extends the palaeoenvironmental record in the region in the period before the LGM, when other proxy records are rare, allowing a better understanding of the palaeoenvironmental conditions on the northeastern QTP.     

Effects of different operational modes on the flood‐induced turbidity current of a canyon‐shaped reservoir: case study on Liuxihe Reservoir,South China

Suspended matter is an important indicator of water quality in freshwater systems. The flood‐induced turbidity current plays a dominant role in the seasonal dynamic of suspended matter in the Liuxihe Reservoir (23°45′50″N; 113°46′52″E), a large, stratified reservoir at the Tropic of Cancer in southern China. Field measurements show that loading and distribution of suspended matter in the reservoir differ in typical wet, dry and medium years, as a result of different discharge volumes and water level variation patterns. Using historical data and the practical demand for water supply and flood control, we generalized two feasible reservoir operational modes: flood impounding mode (drawing down the reservoir to a low level before flood events to impound inflow during the flooding season) and moderate level change mode (drawing down the reservoir to a moderate level before flood events, then keeping the level within the flood control level during runoff events). To examine the effects of different operational modes and outlet depths on the reservoir's flood‐induced turbidity current, a numerical simulation model was applied in three types of hydrological conditions. The results show that the mode with moderate drawdown and recharge processes can decrease loading of suspended matter in spring and promote turbidity current release during flood events, and upper withdrawal can improve the effects of turbid water release. We suggest that more attention should be focused on water quality management in the reservoir operation stage, severe artificial water level fluctuation being avoided and selective withdrawal becoming an optional management measure. Copyright © 2012 John Wiley & Sons, Ltd.     

Holocene migration of oceanic front systems over the Conrad Rise in the Indian Sector of the Southern Ocean

There has been limited previous research about Holocene climate variability in the Indian Sector of the Southern Ocean. Here we examine centennial‐scale changes in diatom assemblages and stable isotopic ratios since 10 000 cal a BP in a high‐accumulation‐rate sediment core from the Conrad Rise. Although abundances of dominant diatom taxa (Fragilariopsis kerguelensis and Thalassiothrix antarctica) are comparatively constant, relative abundances of secondary taxa fluctuate. Before c. 9900 cal a BP, winter sea‐ice and cold water covered the Conrad Rise. Following deglaciation the sea‐ice retreated from the Conrad Rise, lagging that of the Atlantic and eastern Indian Sectors by about 1500 a. The Polar Front moved southward during the early Holocene optimum and north Antarctic Zone waters covered the Conrad Rise for about 650 a. After 9300 cal a BP, solar insolation strongly influenced sea surface temperature and primary productivity in the Southern Ocean. In the high‐latitude Indian Sector, productivity increased 1500 a after the onset of late Holocene neoglaciation. Periodic δ¹⁸O and cold‐water diatom taxa spikes (at intervals of 200 and 300–500 a, respectively) occurred after 9300 cal a BP, probably associated with solar activity. Fluctuations in short‐term sea surface temperature and cold‐water taxa are synchronous with changes in δD observed in an east Antarctic ice core. Copyright © 2011 John Wiley & Sons, Ltd.     

Assessment of future runoff trends under multiple climate change scenarios in the Willamette River Basin,Oregon, USA

We investigated trends in future seasonal runoff components in the Willamette River Basin (WRB) of Oregon for the twenty‐first century. Statistically downscaled climate projections by Climate Impacts Group (CIG), eight different global climate model (GCM) simulations with two different greenhouse gas (GHG) emission scenarios, (A1B and B1), were used as inputs for the US Geological Survey's Precipitation Runoff Modelling System. Ensemble mean results show negative trends in spring (March, April and May) and summer (June, July and August) runoff and positive trends in fall (September, October and November) and winter (December, January and February) runoff for 2000–2099. This is a result of temperature controls on the snowpack and declining summer and increasing winter precipitation. With temperature increases throughout the basin, snow water equivalent (SWE) is projected to decline consistently for all seasons. The decreases in the centre of timing and 7‐day low flows and increases in the top 5% flow are caused by the earlier snowmelt in spring, decreases in summer runoff and increases in fall and winter runoff, respectively. Winter runoff changes are more pronounced in higher elevations than in low elevations in winter. Seasonal runoff trends are associated with the complex interactions of climatic and topographic variables. While SWE is the most important explanatory variable for spring and winter runoff trends, precipitation has the strongest influence on fall runoff. Spatial error regression models that incorporate spatial dependence better explain the variations of runoff trends than ordinary least‐squares (OLS) multiple regression models. Our results show that long‐term trends of water balance components in the WRB could be highly affected by anthropogenic climate change, but the direction and magnitude of such changes are highly dependent on the interactions between climate change and land surface hydrology. This suggests a need for spatially explicit adaptive water resource management within the WRB under climate change. Copyright © 2010 John Wiley & Sons, Ltd.     

Prediction of depth‐integrated fluxes of suspended sediment in the Amazon River: particle aggregation as a complicating factor

Large rivers have been previously shown to be vertically heterogeneous in terms of suspended particulate matter (SPM) concentration, as a result of sorting of suspended solids. Therefore, the spatial distribution of suspended sediments within the river section has to be known to assess the riverine sedimentary flux. Numerous studies have focused on the vertical distribution of SPM in a river channel from a theoretical or experimental perspective, but only a few were conducted so far on very large rivers. Moreover, a technique for the prediction of depth‐integrated suspended sediment fluxes in very large rivers based on sediment transport dynamics has not yet been proposed. We sampled river water along depth following several vertical profiles, at four locations on the Amazon River and its main tributaries and at two distinct water stages. Depending on the vertical profile, a one‐ to fivefold increase in SPM concentration is observed from river channel surface to bottom, which has a significant impact on the ‘depth‐averaged’ SPM concentration. For each cross section, a so‐called Rouse profile quantitatively accounts for the trend of SPM concentration increase with depth, and a representative Rouse number can be measured for each cross section. However, the prediction of this Rouse number would require the knowledge of the settling velocity of particles, which is dependent on the state of aggregation affecting particles within the river. We demonstrate that in the Amazon River, particle aggregation significantly influences the Rouse number and renders its determination impossible from grain‐size distribution data obtained in the lab. However, in each cross section, the Rouse profile obtained from the fit of the data can serve as a basis to model, at first order, the SPM concentration at any position in the river cross section. This approach, combined with acoustic Doppler current profiler (ADCP) water velocity transects, allows us to accurately estimate the depth‐integrated instantaneous sediment flux. Copyright © 2010 John Wiley & Sons, Ltd.     

A generalized additive model for the spatial distribution of snowpack in the Spanish Pyrenees

A generalized additive model (GAM) was used to model the spatial distribution of snow depth in the central Spanish Pyrenees. Statistically significant non‐linear relationships were found between distinct location and topographical variables and the average depth of the April snowpack at 76 snow poles from 1985 to 2000. The joint effect of the predictor variables explained more than 73% of the variance of the dependent variable. The performance of the model was assessed by applying a number of quantitative approaches to the residuals from a cross‐validation test. The relatively low estimated errors and the possibility of understanding the processes that control snow accumulation, through the response curves of each independent variable, indicate that GAMs may be a useful tool for interpolating local snow depth or other climate parameters. Copyright © 2005 John Wiley & Sons, Ltd.