Cosmogenic Be dating of the Salpausselkä I Moraine in southwestern Finland

We determined in situ cosmogenic ¹⁰Be ages for nine boulders sampled on the Salpausselkä I (Ss I) Moraine. Previous dating of this moraine indicated that it formed during the Younger Dryas Stadial along the southern margin of the Scandinavian Ice Sheet in southern Finland. Our new exposure ages range from 10.9±1.0 to 13.5±1.2 ¹⁰Be ka, with an error-weighted mean age of 12.4±0.7 ¹⁰Be ka. Our results confirm four previous ¹⁰Be ages obtained 40 km northeast of our sample location. The combined data (n=13) indicate that retreat from the Ss I Moraine occurred at 12.5±0.7 ¹⁰Be ka, in excellent agreement with an age of 12.1 ka for retreat from the Ss I Moraine based on varve chronologies. These results identify the Ss I Moraine as among the best-dated margins associated with Late Quaternary ice sheets.     

Bidirectional reflectance spectrometry of gravel at the Sjökulla test field

The Sjökulla test site is used for testing and calibrating aerial images. The permanent test field is made of four types of gravel (dark gabbro, grey granite, red granite, white limestone) in two sizes (diameters 8–16 mm and 4–8 mm) set in various patterns. The bidirectional reflection properties of the targets together with their temporal changes must be known in order to carry out radiometric and spectral evaluation and calibration.The bidirectional reflectance distribution functions (BRF) of the gravel have been measured several times in the test fields using portable field goniospectrometers belonging Finnish Geodetic Institute (FGI), and once using the European Goniometic Facility (EGO) of the Joint Research Centre (JRC) at Ispra, Italy. Detailed BRFs have been obtained, showing features typical to particulate media, e.g. a small bowl shape, strong backscattering, and smooth wavelength dependence. Temporal range measurements over several years show that the black gabbro and red granite are fairly stable, while the grey granite has changed somewhat over the years and the white limestone has experienced dramatic darkening effects, requiring action to be taken.The measured BRF data have increased the usability of the test field considerably. The results are also useful in the development and validation of scattering models for particulate media. The site has proved to be a good test bench for goniospectrometric instruments, too.     

利用2012年中国北极考察现场观测数据和卫星遥感资料评估海洋2号卫星扫描辐射计数据反演北极海冰密集度的研究

A retrieval algorithm of arctic sea ice concentration(SIC) based on the brightness temperature data of "HY-2" scanning microwave radiometer has been constructed. The tie points of the brightness temperature were selected based on the statistical analysis of a polarization gradient ratio and a spectral gradient ratio over open water(OW), first-year ice(FYI), and multiyear ice(MYI) in arctic. The thresholds from two weather filters were used to reduce atmospheric effects over the open ocean. SIC retrievals from the "HY-2" radiometer data for idealized OW, FYI, and MYI agreed well with theoretical values. The 2012 annual SIC was calculated and compared with two reference operational products from the National Snow and Ice Data Center(NSIDC) and the University of Bremen. The total ice-covered area yielded by the "HY-2" SIC was consistent with the results from the reference products. The assessment of SIC with the aerial photography from the fifth Chinese national arctic research expedition(CHINARE) and six synthetic aperture radar(SAR) images from the National Ice Service was carried out. The "HY-2" SIC product was 16% higher than the values derived from the aerial photography in the central arctic. The root-mean-square(RMS) values of SIC between "HY-2" and SAR were comparable with those between the reference products and SAR, varying from 8.57% to 12.34%. The "HY-2" SIC is a promising product that can be used for operational services.     

Future fluvial erosion and sedimentation potential of cohesive sediments in a coastal river reach of SW Finland

This study aims to analyse the combined impacts of future discharges and sea levels on erosion–sedimentation potential, and its seasonal changes, in a ~43‐km‐long coastal river reach of South‐west Finland. To our knowledge, this kind of combined study has not been performed before. In addition to surveying the present erosion–sedimentation conditions, the daily erosion–sedimentation potential is simulated with a one‐dimensional hydrodynamic model for the 1971–2000 and 2070–2099 periods by applying four discharge scenarios. Different sea level stages are also employed in the simulations. All scenarios forecast increasing autumn and winter discharges, but diminishing summer discharges. This indicates increasing river channel erosion, particularly during winters and autumns. Although discharge changes have altogether a greater influence on erosion–sedimentation potential, the importance of sea level changes on sedimentation is noticeable in the estuary. The rising sea level scenarios increase the sedimentation potential. In total, by 2070–2099, the erosion potential may increase in most parts of the study area. Copyright © 2013 John Wiley & Sons, Ltd.     

River ice cover influence on sediment transportation at present and under projected hydroclimatic conditions

A large number of rivers are frozen annually, and the river ice cover has an influence on the geomorphological processes. These processes in cohesive sediment rivers are not fully understood. Therefore, this paper demonstrates the impact of river ice cover on sediment transport, i.e. turbidity, suspended sediment loads and erosion potential, compared with a river with ice‐free flow conditions. The present sediment transportation conditions during the annual cycle are analysed, and the implications of climate change on wintertime geomorphological processes are estimated. A one‐dimensional hydrodynamic model has been applied to the Kokemäenjoki River in Southwest Finland. The shear stress forces directed to the river bed are simulated with present and projected hydroclimatic conditions. The results of shear stress simulations indicate that a thermally formed smooth ice cover diminishes river bed erosion, compared with an ice‐free river with similar discharges. Based on long‐term field data, the river ice cover reduces turbidity statistically significantly. Furthermore, suspended sediment concentrations measured in ice‐free and ice‐covered river water reveal a diminishing effect of ice cover on riverine sediment load. The hydrodynamic simulations suggest that the influence of rippled ice cover on shear stress is varying. Climate change is projected to increase the winter discharges by 27–77% on average by 2070–2099. Thus, the increasing winter discharges and possible diminishing ice cover periods both increase the erosion potential of the river bed. Hence, the wintertime sediment load of the river is expected to become larger in the future. Copyright © 2015 John Wiley & Sons, Ltd.     

Lithostratigraphy and Optically Stimulated Luminescence age determinations of pre‐Late Weichselian deposits in the Suupohja area,western Finland

The lithostratigraphy of pre‐Late Weichselian sediments and OSL‐dating results from four localities in the Suupohja area of western Finland, adjacent to the centre of the former Scandinavian glaciations, are presented. The studied sections expose glacifluvial, quiet‐water, littoral and aeolian deposits overlain by Middle and/or Late Weichselian tills. Litho‐ and biostratigraphical results together with seven OSL age determinations on buried glacifluvial sediment at Rävåsen (94±15 ka) and on till‐covered littoral and aeolian sediments at Risåsen, Rävåsen, Jätinmäki and Kiviharju (79±10 to 54±8 ka), accompanied by previous datings and interpretations, suggest that the glacifluvial sediments at Risåsen were deposited at the end of the Saalian Stage (MIS 6) and those at Risåsen were deposited possibly in the Early Weichselian Substage (MIS 5d?). Palaeosol horizons and ice‐wedge casts together with the dated littoral and aeolian sediments between the Harrinkangas Formation (Saalian) and the overlying till(s) indicate that western Finland was ice‐free during most of the Weichselian time. Littoral deposits, dated to the Middle Weichselian (MIS 4–3), occur at altitudes of 50–90 m a.s.l., which indicates significant glacio‐isostatic depression. The depression resulted from expansion of the ice sheet in the west of Finland at that time.