Eastern Norwegian Sea Research Articles

Intra-continental rifting inferred from the major late Carboniferous quartz-dolerite dyke swarm of NW Europe

Synopsis The late Carboniferous (Stephanian) quartz-dolerite dyke swarm of northern Britain extends eastwards from the Outer Hebrides on an arcuate trend for up to 200 km from the eastern UK coast, as far as the western margin of the Central Graben. The average trend of the swarm changes by about 45° between its western and eastern extremities. Individual dykes, which are generally up to 30 m wide onshore, attain widths of well over 1 km offshore. Magmatically and spatially, the swarm is closely related to the coeval Oslo Graben volcanic rocks and dykes of southern Norway, which lie on the extrapolation of the arcuate trend. The dyke trends point to a focus of relative tensile stress centred on the West Shetland Shelf region. Finite element modelling of the NW European area corroborates the stress-focusing hypothesis, which we interpret in the context of the major period of intra-continental rifting along the line of the proto North Atlantic (the Rockall Trough, Faeroe–Shetland Trough and eastern Norwegian Sea) at about 300 Ma. The regional distribution of Archaean and Caledonian lithosphere within Pangaea may account for the fact that both the dyke swarm and the Oslo Graben were located in northern Britain and southern Norway, rather than in the Faeroe–Shetland region.

Non-steady behaviour in the Cenozoic polar North Atlantic system: the onset and variability of Northern Hemisphere glaciations

Changes of the extent of the Arctic Ocean sea-ice cover over the past century, the geological record of the Arctic Ocean seafloor of the youngest geological past, as well as the evidence of a pre-Glacial temperate to warm Arctic Ocean during Mesozoic and Palaeogene time are witnesses of dramatic revolutions of the Arctic oceanography. The climate over northwestern Europe on a regional scale as well as the global environment have responded to these revolutions instantly over geological time scales. Results of ocean drilling in the deep northern North Atlantic document an onset of Northern Hemisphere glaciation towards the end of the middle Miocene (10-14 Ma). While the available evidence points to early glaciations of modest extent and intensity centred around southern Greenland, the early to mid-Pliocene intervals record a sudden intensification of ice-rafting in the Labrador and Norwegian Greenland seas as well as in the Arctic Ocean proper. The Greenland ice cap seems to have remained rather stable whereas the northwest European ice shields have experienced rapid and dramatic changes leading to their frequent complete destruction. Many sediment properties seem to suggest that orbital parameters (Milankovitch-frequencies) and their temporal variability control important properties of the deep-sea floor depositional environment. Obliquity (with approximately 40 ka) seems to be dominant in pre-Glacial (middle Miocene) as well as Glacial (post late Miocene) scenarios whereas eccentricity (with approximately 100 ka) only dominated the past 600-800 ka. PlioPleistocene deposits of the Arctic Ocean proper, of the entire Norwegian Greenland and of the Labrador seas have recorded the almost continuous presence of sea-ice cover with only short ‘interglacial’ intervals when the eastern Norwegian Sea was ice-free. The documentation of long-term changes of the oceanographic and climatic properties of the Arctic environments recorded in the sediment cover of the deepsea floors might also serve to explain scenarios which have no modern analog, but which might well develop in the future under the influence of the anthropogenic drift towards warmer global climates.

The decay of the Barents ice sheet as documented in nordic seas ice-rafted debris

A large, marine-based ice sheet that covered the Barents Sea and Svalbard during the height of the Weichselian Glaciation began to disintegrate at 15 ka. The decay produced enormous quantities of icebergs that drifted parallel to the Norwegian continental margin southward and northwestward into the Fram Strait. This drifttrack is reflected by a trace of ice-rafted clastic sedimentary rocks from the bottom of the Barents Sea in deep sea sediments of the Norwegian Sea and the Fram Strait.The petrographic composition of ice-rafted lithic particles (dropstones) > 0.5 mm in late Quaternary (20 ka-Recent) deep-sea sediments of the Norwegian Greenland Sea was analyzed in order to determine the source areas of the dropstones. The dropstone provenance was deciphered from the regional distribution of some precisely defined lithotypes.During the maximum glaciation between 20 and 15 ka, the Norwegian Sea received crystalline rocks primarily from western Norway, but also from Svalbard and the northwestern British Isles. The Greenland Sea was supplied with clay-, silt- and sandstones from central and northern East Greenland and rocks from circum Arctic areas.At 15 ka, a dramatic shift in provenance from crystalline rocks to clastic sedimentary rocks is recorded in the dropstone composition of the northern and eastern Norwegian Sea. This impulse was the ultimate result of the deterioration of the Barents ice sheet. The dispersal area of clastic rock fragments reaches from the Barents shelf between 72° and 76°N, and 15° and 20°E to the Vøring Plateau (eastern Norwegian Sea) at 67°N and 5°E. The main direction of iceberg drift was to the south and southeast. After an initial period of only 500 years duration and extremely high dropstone deposition rates, the influx from the Barents shelf ceased and gradually changed into the modern surface current system.

Sedimentation of pteropods in the Norwegian Sea in autumn

Pteropod vertical distribution on the Vøring Plateu (eastern Norwegian Sea) was recorded during a 3 week drifting experiment during August 1988. Parallel to sampling of hydrographical, chemical and biological properties of the water column, sediment traps recorded vertical pelagic flux at five depth strata. Pteropods ( Limacina retroversa) dominated the zooplankton and reached maximum values (>13,600 individuals m −3) in the upper 25 m of the water column; the size spectrum shifted from small (< 1 mm) towards large (> mm) specimens during the study. Vertical flux at 100 m depth increased from 600 mg dry weight m −2 day −1 to 1000 mg dry weight m −2 day −1 at the end of the experiment. Trap material during the first sampling intervals consisted primarily of phytoplankton and protozoans aggregated within pteropod feeding nets. Thereafter, the increase in flux rates was associated with empty shells of pteropods in the size class 1–3 mm indicating mortality prior to mass sinking. Particle flux during the investigation period totalled 0.2 g organic Cm −2 and 1.4 g carbonate m −2 equivalent to 8 and 15% of annual flux recorded in the area in 1988. Through their feeding, reproduction and subsequent mortality pteropods were the main contributors to vertical particle flux in the eastern Norweigian Sea during 1988.

Nordic Seas surface ice drift reconstructions: evidence from ice rafted coal fragments during oxygen isotope stage 6

Abstract Sixteen long sediment cores from the eastern Arctic Ocean, the Fram Strait and the Norwegian-Greenland Sea, documenting 200 000 years of sedimentation, were studied for their qualitative dropstone composition (&gt;500 µm-fraction). In sediments from oxygen isotope stages 1–5, coal particles are usually subordinate components of the coarse fraction. In contrast to younger deposits, coal content in oxygen isotope stage 6 (186-128 ka) varies between 20% and 65 0n the eastern Arctic Ocean and the Fram Strait and between 5% and 20 0n the Norwegian Sea. Southward decreasing coal content and similarities in maturity and petrography of the coals indicate that the coal was transported by iceberg or sea ice rafting more than 1000 km to the south. It is suggested that during intervals of oxygen-isotope stage 6 drifting ice carried abundant coal fragments from the eastern Arctic Ocean southward through the Fram Strait into the eastern Norwegian Sea. Thus, surface circulation was then opposite to that of today.

Late Quaternary carbonate sedimentation and paleo‐oceanography in the eastern Norwegian Sea

Four gravity cores from the eastern Norwegian Sea are studied. Absolute accumulation rates are quantified and variations in carbonate sedimentation and their implications for the paleo‐oceanographic history of the Norwegian Sea are described. In the eastern Norwegian Sea, interglacial, ice‐free conditions were developed during oxygen‐isotope stages 1 and 5e. Open water conditions were probably the norm during the summer season, also during glacial stages. Slightly elevated summer temperatures in periods during isotope stages 2 and 7 are demonstrated by increased contents of subpolar planktic foraminifera. The deep waters of the eastern Norwegian Sea have been well oxygenated during most of the last 250,000 years. Organic‐rich sediments and intensive carbonate dissolution in some parts of isotope stages 4 and 6 indicate corrosive bottom waters. A permanent ice cover and low saline surface waters, as found in the Arctic Ocean today, may have been developed in these periods. Well‐preserved foraminiferal assemblages from stage 2 show more oxygenated bottom waters and more effective bottom water renewal in this period than during stage 3.

A stratigraphic study of Late Quaternary sediments on the Vøring-Plateau, eastern Norwegian Sea

Four gravity cores from the Vøring Plateau, west of the Nordland coast in Northern Norway have been studied. About 250,000 yrs of continuous hemipelagic sedimentation is represented in the cores. This period has been divided into seven lithostratigraphic units and four planktonic foraminiferal assemblage zones. To improve the reliability and precision of the isotopic stratigraphy, a graphic comparison with several isotopic records previously described in the literature has been performed. A taxonomy of 36 isotopic events is established following Prell's ∗ ∗ Prell et al. (1986). technique. The majority of these events seem to be recognizable in the isotopic records from the Norwegian Sea. During the glacial stages, however, several local events are caused by influxes of isotopically light meltwater. Comparisons between the records indicate a general trend toward decreasing sedimentation rates with increasing distance from the continental margins for isotope stages 2, 3, 4 and 6. Only small variations in sedimentation rates are observed during stages 5 and 7. Comparisons with the land-based stratigraphy of Northwest Europe indicate that the main glacials and interglacials as well as the Fana and the Torvaldstad interstadials are recognizable in the marine sequences. Correlations to the Bølling and Allerød interstadials and the Younger Dryas stadial is obscured by a period of rapid influx of meltwater at about 15-14 Ka, followed by a period of high influx of clastic material.

Climatic reversal in northern North Atlantic

OVER the European arctic and subarctic seas the atmospheric circulation has recently tended towards northerly airflow, with an accompanying climatic deterioration. Since the 1950s direct northerly outbreaks have swept the Norwegian–Greenland Sea with increasing frequency, adding almost every year, particularly in the 1960s, to the severity of the climate in areas as far south as the British Isles. This change has been associated with the establishment over Greenland in the early 1950s of a persistent ridge of pressure anomaly and with its subsequent maintenance and intensification (on average) throughout the Jate 1950s and 1960s. Compared with the ‘normal’ climatic period of 1900–39 this cell represented an increase of over 3 mbar in the mean annual pressure at sea level in Greenland over the period 1956–65, but was very much more pronounced during the cold season (November–March). During the winter quarter (December–February), the increase in the mean pressure at sea level in Greenland amounted to over 7 mbar between 1900–39 and 1956–65 (Fig. 1a) and the pressure rise continued during the late 1960s. (Throughout, listed dates refer to the second year of the winter in question; thus, “winter 1956” refers to the period December 1955–February 1956.) A further increase of over 5 mbar occurred in Greenland between the winters of 1956–65 and 1966–70 (Fig. 1b). Coupled with a slight decrease of pressure over the eastern Norwegian and Barents Seas this change has resulted in “… a remarkable difference of pressure between Greenland and the eastern Norwegian Sea; this has increased since 1950 in every month of the year …”1.

International fishing surveys in the Barents Sea and eastern Norwegian Sea, 1965, 1966 and 1967

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