Luminescence dating of Holocene spit deposits: An example from Skagen Odde, Denmark

Clemmensen, L. B. & Murray, A. S. 2009: Luminescence dating of Holocene spit deposits: An example from Skagen Odde, Denmark. Boreas , 10.1111/j.1502-3885.2009.00110.x. ISSN 0300-9483.
Skagen Odde is a large, active spit system in northern Denmark that started to form about 7200 years ago. Models for spit growth have usually relied on radiocarbon-dating of swale peat (Martørv). In this study, we date the spit deposits at three sites directly using Optically Stimulated Luminescence (OSL) to obtain supplementary age control on spit development. The spit deposits consist of a lowermost succession of shoreface, beach and backshore aeolian deposits topped by a swale peat and followed by an uppermost succession of aeolian sand sheet and dune deposits. The ages of the shallow marine, beach and backshore aeolian deposits at the main study site are indistinguishable, implying good resetting of the shallow marine deposits; the average age of 4640±250 years compares well with earlier model predictions based on radiocarbon-dating of swale peat. Aeolian sand extracted from the uppermost part of the swale peat at this site provides OSL ages of between 1600 and 2500 years, in good agreement with a calibrated AMS age from the same level of 2330–2200 years. The uppermost aeolian succession consists of two units separated by a thin palaeosol, and the aeolian units have OSL ages of about 1500 years and younger than 130 years. Lowermost spit deposits at the two additional sites have average ages of 5010±240 and 3730±190, respectively, supporting the existing chronology for spit growth based on radiocarbon-dating.     

Stadials and interstadials during the Weichsel glackiation on Finnmarksvidda, northern Norway

Till beds and waterlain sediments from at least 3 stadials and 2 interstadials during the Weichsel glaciation are recorded on Finnmarksvidda. The oldest, possibly Weichselian, ice-free period recorded on Finnmarksvidda is represented in one river section and is preliminary named the Vuolgamasjåkka thermomer. Its initiation is TL-dated to about 120 ka, which indicates a pre-Weichselian, possibly Eemian age. The interstadial which follows the subsequent and assumed oldest Weichsel stadial on Finnmarksvidda, the Eiravarri interstaeial, has previously been tentatively correlated lithostratigtrahically with the Peräpohojola interstadial ( sensu stricto ) in North Finland. The youngest interstadial, the Sargejåk internatiodial , is in this paper suggested to correlate with the Tärändö interstadial in North Sweden. The initial Weichselian ice movement across Finnmarksvidda is so far unknown, but locally N of Kautokeino in the W the initial (recorded) ice movement was directed towards NW-N. The regional ice movements for the two subsequent stadials on Finnmarksvidda were initially directed towards NE-ene and NNW, respectively.     

A Late Pleistocene sequence at Seitevare, Swedish Lapland

A peat layer beneath two till beds was found at Seitevare in Swedish Lapland. The pollen flora layer indicates deposition during the later part of the Eemian Interglacial. The vegetation consisted of open forests predominated by pine and birch, mixed with alder and spruce. The sedimentation took place in a small oligotrophic-dystrophic water basin with a pH about 5, according to the diatom flora. In an adjacent section, silty sediments with pollen indicating interstadial vegetation (birches, herbs) are covered by one till bed. These sediments are tentatively correlated with the Peräpohjola Interstadial in northern Finland and north-eastern Sweden. The lithostratigraphy indicates one pre-Eemian and probably three Weichselian glacial advances.     

A New Video and Digital Camera System for Studies of the Dynamics of Microtopographic Features on Tidal Flats

A newly developed video and camera system for tidal flat microtopographic studies is presented. It consists of a SONY handy cam placed in an underwater housing mounted on a frame about 70?cm above the sediment surface. A rectangular surface area of 30?×40?cm is imaged by the camera. The camera records video sequences and/or digital images at predetermined time lapses. The total number of images is about 540, and a similar number of 10-second long video sequences can be recorded. The camera is programmed with a PC before deployment, and the total deployment time depends on the time lapse between recordings. The camera is connected to an external power supply (12?volt), and a halogen projector pointing towards the sediment surface ensures that the system is operable on a 24-hours scale. The system has been tested in the Danish Wadden Sea. It has proved to be a very useful tool in studies of topographic effects of erosion and deposition sequences, and for studies of benthic organisms-sediment interactions. The test site was further equipped with sensors for water and seabed measurements, which proved to be indispensable regarding the interpretation of recorded image time-series.     

River flow regimes in a changing climate

Abstract

A river flow regime describes an average seasonal behaviour of flow and reflects the climatic and physiographic conditions in a basin. Differences in the regularity (stability) of the seasonal patterns reflect different dimensionality of the flow regimes, which can change subject to changes in climate conditions. The empirical orthogonal functions (EOF) approach can be used to describe the intrinsic dimension of river flow regimes and is also an adopted method for reducing the phase space in connection to climate change studies, especially in studies of nonlinear dynamic systems with preferred states. A large data set of monthly river flow for the Nordic countries has been investigated in the phase space reduced to the first few amplitude functions to trace a possible signature of climate change on the seasonal flow patterns. The probability density functions (PDF) of the weight coefficients and their possible change over time were used as an indicator of climate change. Two preferred states were identified connected to stable snowmelt-fed and rainfed flow regimes. The results indicate changes in the PDF patterns with time towards higher frequencies of rainfed regime types. The dynamics of seasonal patterns studied in terms of PDF renders it an adequate and convenient characterization, helping to avoid bias connected to flow regime classifications as well as uncertainties inferred by a modelling approach.     

Bryophytes from the last interglacial/glacial cycle, Jameson Land, East Greenland

Subfossil bryophyte remains from Jameson Land, central East Greenland reveal diverse moss floras from the Langelandselv interglacial and the Hugin Sø interstadial. Around 30 species are reported as new subfossils from Greenland, indicating our insufficient knowledge of earlier bryophyte floras in the area. Among the species found from the Langelandselv interglacial. Several are southern and do not reach as far north as Jameson Land today, thus indicating a slightly warmer climate than at present in the area. The climate indications for the Hugin Sø interstadial are less clear, and further studies are necessary before delinitivc conclusions can he drawn. A large proportion of the found taxa indicate mineral-rich or intermediately mineral-rich conditions. Several wetland species indicate moving water, and a few sometimes or exclusively ( Sanionia nivalis ) occur in connection with late snow beds or meltwater brooks. Abundant material or the Polytrichaceae and of Racomitrum indicates that more or less unstable soil. with sparse vascular plant cover, was relatively abundant.