Polar Research (E-Journal)
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Palaeogeographic reconstructions of the Russian Boreal areas and Svalbard during the Triassic
No full textTriassic palaeogeographic and palaeoclimatic environments of the Russian Arctic Boreal Province and Svalbard are reconstructed. Multi-facies complexes of clayey, silty and sandy deposits, with various biogenic nodules, accumulated throughout the Triassic, whereas phosphate accumulation was especially characteristic of the Middle Triassic. The entire region consisted of a series of shelf palaeobasins to the south of a wide, deep-water basin that we call the Northern Basin. This was connected to the Palaeo-Pacific. The climate of the region remained warm, with variable humidity, throughout the Triassic. The Franz Josef Land Archipelago stood out for its humid sedimentation during this period. Changes in the sedimentation regime caused by tectonic activity in parts of the territory took place around the Middle–Late Triassic transition. Sharp regression occurred in adjacent areas at the end of the Triassic because of the Atlantic Ocean opening. This provides an explanation for the absence of upper Norian and Rhaetian deposits in the Barents–Kara region. The general accumulation of sediments in the region only resumed in the Early Jurassic
Arctic Ocean manganese contents and sediment colour cycles
No full textCyclical variations in colour and manganese content in sediments from the central Arctic Ocean have been interpreted to represent climatically controlled changes in the input of Mn from the Siberian hinterland, and/or variations in the intermediate and deep water ventilation of the Arctic basins, although a diagenetic origin has not been excluded. A reinvestigation of core 96/12-1pc using an Itrax X-ray fluoresence (XRF) core scanner confirms that these colour cycles are indeed controlled by variations in Mn content, although changes in the source region of the sediment may override the Mn colour signal in certain intervals. The prominent Mn cycles show no correspondence to any of the other measured elements. This decoupling of Mn and the bulk chemistry of the sediment is taken to indicate that the cycles observed are caused by variations in water column ventilation and riverine input, rather than variations in sediment source or diagenesis. We therefore conclude that the Mn maxima do represent warm phases with increased ventilation and/or riverine input, and that they therefore could be used for chronostratigraphic correlation between cores from the central Arctic Ocean, where traditional isotope stratigraphy is difficult or impossible to establish because of the lack of calcareous microfossils
Micropalaeontological evidence of brackish water conditions during deposition of the Knorringfjellet Formation, Late Triassic–Early Jurassic, Spitsbergen
No full textThe Knorringfjellet Formation is a succession of mudstones and sandstones, ranging in age from Norian to Toarcian in western and west-central Spitsbergen, and contains several unconformities with associated hiatuses. Its foraminiferal succession consists almost exclusively of agglutinated taxa, shows extremely low assemblage diversities and a dominance of small-sized species. These faunal features signalize restricted environmental conditions (in contrast to those of a normal marine shelf). Comparisons with ancient and modern analogues suggest that the main restricting factor was hyposaline conditions, to a lesser extent augmented by hypoxia in near-bottom waters. These conditions were caused by high fluvial influx creating gravity stratified water masses. The depositional area was part of an extensive but shallow shelf embayment, which had an open connection to the north to the polar ocean basin. Discontinuities recognized in the foraminiferal succession indicate depositional unconformities within the formation
Palaeomagnetism and magnetostratigraphy of the Permian and Triassic of Spitsbergen: a review of progress and challenges
No full textPermian and Triassic sediments from Svalbard provide a testing ground for evaluating concepts about the polarity and configuration of the geomagnetic field during the Palaeozoic–Mesozoic transition. This review examines existing palaeomagnetic and magnetostratigraphic data, and also re-examines the issue of partial remagnetization of these sediments. Permian and Triassic palaeomagnetic poles from Spitsbergen demonstrate a close similarity to the stable Europe apparent polar wander path. Magnetostratigraphy from the Gipsdalen and Tempelfjorden groups demonstrates the dominance of reverse polarity (the Permo-Carboniferous Reverse Superchron), with evidence for three normal magnetozones of short duration, one of which may provide a useful marker near the base of the Permian. The other two normal magnetozones in the middle and lower parts of the Kapp Starostin Formation are most likely to represent equivalent magnetozones in the Wordian and Capitanian (mid- Permian). Magnetostratigraphy of the Lower Triassic up to the lowest parts of the Upper Triassic in central and western Spitsbergen provides greater chronostratigraphic detail than has been available hitherto from biostratigraphy alone. This demonstrates the scale of a number of suspected hiatuses, and also hints at improved chronostratigraphic correlations between east and west Spitsbergen. Upper Triassic sediments provide the best palaeomagnetic properties, indicating that future magnetostratigraphic studies in this interval may improve chronostratigraphic understanding of this poorly dated interval. A persistent partial remagnetization affecting both Permian and Triassic sediments is not of a single origin. It may be both a Brunhes-age viscous remanence and a Palaeogene heating/burial-induced magnetization, or a fluid flow related remagnetization locally in western Spitsbergen. The remagnetization is often composite (Cenozoic plus older) in nature
A “critical” climatic evaluation of last interglacial (MIS 5e) records from the Norwegian Sea
No full textSediment cores from the Norwegian Sea were studied to evaluate interglacial climate conditions of the marine isotope stage 5e (MIS 5e). Using planktic forminiferal assemblages as the core method, a detailed picture of the evolution of surface water conditions was derived. According to our age model, a steplike deglaciation of the Saalian ice sheets is noted between ca. 135 and 124.5 Kya, but the deglaciation shows little response with regard to surface ocean warming. From then on, the rapidly increasing abundance of subpolar forminifers, concomitant with decreasing iceberg indicators, provides evidence for the development of interglacial conditions sensu stricto (5e-ss), a period that lasted for about 9 Ky. As interpreted from the foraminiferal records, and supported by the other proxies, this interval of 5e-ss was in two parts: showing an early warm phase, but with a fresher, i.e., lower salinity, water mass, and a subsequent cooling phase that lasted until ca. 118.5 Kya. After this time, the climatic optimum with the most intense advection of Atlantic surface water masses occurred until ca. 116 Kya. A rapid transition with two notable climatic perturbations is observed subsequently during the glacial inception. Overall, the peak warmth of the last interglacial period occurred relatively late after deglaciation, and at no time did it reach the high warmth level of the early Holocene. This finding must be considered when using the last interglacial situation as an analogue model for enhanced meridional transfer of ocean heat to the Arctic, with the prospect of a future warmer climate
Review of Global outlook for ice and snow, by United Nations Environment Programme
No full textThis book provides an excellent overview of the recent research results on the cryosphere. For the non-specialist, in particular, it is a useful introduction to the subject, and provides some of the basic facts and statistics related to the cryosphere. Each of the components of the cryosphere is reviewed in a chapter or subchapter: snow, glaciers, ice sheets, sea ice, frozen ground, and lake and river ice. These chapters include a description of the cryospheric components, geographical locations and the future outlook. In addition, most sections include discussions of how each component relates to biology, ecology and human activity. Other chapters provide a general introduction to the cryosphere, to climate models and to sea level
Lower Triassic bryozoan beds from Ellesmere Island, High Arctic, Canada
No full textIn the Sverdrup Basin (Canadian Arctic), the Lower Triassic Blind Fiord Formation, comprising siltstone and shale, overlies various Middle to Late Permian (post-Wordian) sedimentary units. This formation is subdivided into three members: the Confederation Point, Smith Creek and Svartfjeld members of, respectively, Griesbachian–Dienerian, Smithian–Spathian and Spathian ages. Lower Triassic bryozoan beds are known from many sections of Ellesmere Island, but have never been studied in detail. During the Early Triassic biotic recovery interval, immediately following the Permian/Triassic extinction event, only one new bryozoan genus evolved in the Boreal region: Arcticopora. The first lower Triassic bryozoan bed appears in the upper part of the Confederation Point Member, and is dated as late Dienerian. Succeeding bryozoan levels occur in the upper Smith Creek Member, and are late Smithian–early Spathian in age. Bryozoan beds occupy a similar stratigraphic position in Spitsbergen. There, they occur scattered in silt to coarse sandstone beds, but also in bryozoan-dominated packstone beds resembling the packstone units in the uppermost part of the Confederation Point Member of Ellesmere Island. Previously, bryozoan-rich beds of Triassic age have not been reported, and the present work fills an important time gap in the bryozoan carbonate database
Last interglacial (MIS 5e) surface water conditions at the Vøring Plateau (Norwegian Sea), based on dinoflagellate cysts
No full textSediments from the last interglacial, marine isotope stage 5e (MIS 5e), have been studied for their dinoflagellate cyst content in a core retrieved from the Vøring Plateau, Norwegian Sea. Qualitative and quantitative analyses of the data, and comparison with the surface sample and published Holocene data from the core, reveal distinct differences in hydrological surface conditions between the late Holocene and MIS 5e. A higher number of co-dominant, subordinate species in the last interglacial samples suggests there was a more pronounced seasonality of the surface water at this time. This is supported by the significant presence of Bitectatodinium tepikiense, a species that was virtually absent from the area for most of the Holocene. The seasonality signal is further substantiated by transfer-function reconstructions, which also indicates a stronger stratification of the upper water column during MIS 5e. Moreover, the assemblage data clearly show that optimal, fully marine interglacial conditions prevailed only late in MIS 5e (between ca. 117.5 and 116.5 Kya), which is in contrast with the climatic optimum early in the Holocene. Stable oxygen isotope values from planktic foraminifera for this MIS 5e optimum are comparable with the average Holocene values, but are generally ca. 0.3‰ higher than those of the earlier part of the last interglacial (sensu stricto). These higher d18O values are likely to be the result of the enhanced and prolonged influence of Saalian deglacial meltwater, thus corroborating the existence of a quite differently structured sea surface, as suggested by the dinocyst data