Late Weichselian and Holocene environments of lake Endletvatn, Andφya, northern Norway: as evidenced primarily by chemostratigraphical data

A 6.5 m long sediment succession (18.5-2.2 ka BP) from the northern sub-basin of lake Endletvatn was analysed lithologically, palynologically and chemically. The chemical analyses were performed at about 10 cm depth intervals for the following parameters: total organic C, N, P, Fe, Mn, Mg, Na, K, Ca and S, in addition to water content, dry density, and pH. Two main lithostratigraphical units can be distinguished, which also differ substantially in chemical characters. Five chemostratigraphical main units were distinguished. The two lowermost units 1-2 (18.5-12.9 ka BP) correspond to the lower lithostratigraphical main unit and are characterized by minerogenous sediments with low C and N, and high Fe, Mg and K. P is low, partly because of a scarcity of P in parent rocks. Chemostratigraphical unit 3 (12.9-9.6 ka BP) is characterized by increasing C and N and a high N/P ratio (10-20) culminating in the early part of the Younger Dryas, indicating abundant N available for bio-production. The Fe, Mg, and K content is still high, but decreasing, indicating decreasing glacial and kryogenic erosion and allogenic deposition until c. 10.5 ka BP. A hiatus represented by a sand layer covers most of the time-span 10.5-9.6 ka BP. Chemostratigraphical unit 4 (9.6-5.3 ka BP) represents the Holocene thermal optimum in three subunits. In the time interval 9.6-9.1 ka BP, Fe, Mg and K decrease to a minimum and P shows a pronounced increase. The megathermal period c. 8200-5300 BP, is characterized by maxima of C, N and P and a minimum of Fe. The katathermal period after 5.3 ka BP is characterized primarily by increased Fe precipitation, increasing Fe/Mn ratio, and P, C and N at a constantly lower level than during the megathermal. A stable C/N ratio of about 10, of the sediment interval younger than 12.9 ka BP characterizes the sediments as transitional between gyttja and dy. The Holocene lake type varied between weakly oligohumic and mesohumic. Stagnant bottom waters (reducing conditions) occur in the periods 12.9-11.5 ka BP and c. 7.5-5.3 ka BP. The climatic development and other environmental implications of the joint chrono-, chemo-, litho- and biostratigraphical data set are discussed.     

Late Quaternary history of northern Russia and adjacent shelves — a synopsis

This synopsis highlights some of the main results presented in this issue of Boreas. The collection of papers deals with ice sheet reconstruction in space and time, isostatic and eustatic response to deglaciation, land to shelf sediment interaction, and Eemian and Holocene environmental variations. The most significant new results are that the last glacial maximum of the Kara Sea and Barents Sea ice sheets were both much smaller and much older than in most previous hypotheses. This puts new constraints on, for example, climate and ice sheet linkages, ice sheet interactions (Scandinavian-Barents Sea-Kara Sea), and land-ocean riverine input through time.     

Factors controlling the chemical evolution of travertine‐depositing rivers of the Barkly karst,northern Australia

Groundwaters feeding travertine‐depositing rivers of the northeastern segment of the Barkly karst (NW Queensland, Australia) are of comparable chemical composition, allowing a detailed investigation of how the rate of downstream chemical evolution varies from river to river. The discharge, pH, temperature, conductivity and major‐ion concentrations of five rivers were determined by standard field and laboratory techniques. The results show that each river experiences similar patterns of downstream chemical evolution, with CO₂ outgassing driving the waters to high levels of calcite supersaturation, which in turn leads to widespread calcium carbonate deposition. However, the rate at which the waters evolve, measured as the loss of CaCO₃ per kilometre, varies from river to river, and depends primarily upon discharge at the time of sampling and stream gradient. For example, Louie Creek (Q = 0·11 m³ s^?1) and Carl Creek (Q = 0·50 m³ s^?1) have identical stream gradients, but the loss of CaCO₃ per kilometre for Louie Creek is twice that of Carl Creek. The Gregory River (Q = 3·07 m³ s^?1), O'Shanassy River (Q = 0·57 m³ s^?1) and Lawn Hill Creek (Q = 0·72 m³ s^?1) have very similar gradients, but the rate of hydrochemical evolution of the Gregory River is significantly less than either of the other two systems. The results have major implications for travertine deposition: the stream reach required for waters to evolve to critical levels of calcite supersaturation will, all others things being equal, increase with increasing discharge, and the length of reach over which travertine is deposited will also increase with increasing discharge. This implies that fossil travertine deposits preserved well downstream of modern deposition limits are likely to have been formed under higher discharge regimes. Copyright © 2002 John Wiley & Sons, Ltd.     

The influence of diurnal temperatures on the hydrochemistry of a tufa‐depositing stream

At‐a‐station diurnal variations in carbonate hydrochemistry were measured during four observation periods at Davys Creek, a tufa‐depositing stream in central NSW, Australia. Major ion concentrations and continuously logged measurements of specific conductivity, pH and temperature showed that changes in the amount of CaCO₃ deposited upstream of the study reach were directly related to changes in diurnal water temperatures, which control the rate of CO₂ efflux to the atmosphere. The greatest upstream losses occurred during the mid‐afternoon water temperature peak, whereas the lowest upstream losses occurred at sunrise, when water temperatures were at their lowest. Cloudy days at all times of the year produced small diurnal water temperatures ranges (c. 2–5°C) and, consequently, relatively small changes in upstream CaCO₃ loss (23–50 mg L^?1) through the day. Clear sunny days, especially during summer months, produced large diurnal water temperature changes (up to c. 11°C), which in turn triggered diurnal changes in upstream CaCO₃ loss of up to 100 mg L^?1. By implication, the active reach of tufa deposition must advance downstream and increase in length during the evening and vice versa during the day. Given that the temperature of Davys Creek waters are a function of insolation, changes in the reach of tufa deposition under baseflow conditions are a direct function of the prevailing weather. This has implications for the palaeoclimatic interpretation of fossil tufa deposits. Copyright © 2003 John Wiley & Sons, Ltd.     

Palynodebris analysis of a shallow core from the Barents Sea

A quantitative study of palynomorphs and palynodebris in a shallow core from the central part of Bjørnøyrenna, western Barents Sea, is presented. The core could be subdivided into a lower part characterized by a complete dominance of reworked plant debris of Mesozoic age and an upper part with considerable input of first cycle algal debris and dinoflagellate cysts. Two hypotheses are suggested to explain this radical change in palynodebris composition. Either it represents a transition from a situation with permanent ice to normal marine conditions, or the absence of first cycle plant debris in the lower part of the core is caused by a masking of this component due to extremely high input of glacially eroded material from the bordering shallow parts of the Barents Sea. The present study shows that palynodebris analysis may contribute important information to the study of composition and depositional environment of Quaternary marine sediments in the area.     

The Late Quaternary Skagerrak and its depositional environment

The Skagerrak is a key region for our understanding of the Late Quaternary history of the East North Sea, of the entire Baltic basin and of the adjacent Scandinavian land areas. The depositional history of the postglacial Skagerrak began after the ice margin withdrew from Jutland to close to the modern Norwegian coast around 14 ka B.P. to 13 ka B.P. The Skagerrak was immediately filled by marine waters from the Norwegian Sea, but retained a fjord-like shape until approximately 10.2 ka B.P., when a connection opened across central Sweden to the Baltic Ice Lake. This seaway closed around 9 ka B.P., but a new seaway to the Baltic basin opened subsequently (probably close to 8.5 ka B.P.) through the Danish Belts. At about 10 ka B.P. the Skagerrak 'fjord' also started to change shape due to the flooding of the large former land area under the modern North Sea. Paleo-geography and -bathymetry of these changes can now be quantified in great detail. The young Quaternary sediments of the Skagerrak consist of fine-grained clays with minor amounts of silty and sandy material and are mostly of terrigenous origin, whereas biogenic components in general make up only a minor proportion of the bulk sediment. Prior to 10 ka B.P. a major portion of these deposits originated from the Fennoscandian regions N and E of the Skagerrak, while ice-rafting contributed coarse terrigenous components to the usually fine-grained sediments and while it was filled by brackish surface and cold polar bottom waters. At approximately 10 ka B.P., more temperate waters started to fill the Skagerrak and a good portion of the sediment seems to have originated from areas to the South. The Norwegian Coastal Current can only be documented for the past 7 ka; subtle changes of the pelagic and benthic environments could also be documented for later intervals.