Yngve Kristoffersen

The International Bathymetric Chart of the Arctic Ocean (IBCAO) Version 3.0

The International Bathymetric Chart of the Arctic Ocean (IBCAO) released its first gridded bathymetric compilation in 1999. The IBCAO bathymetric portrayals have since supported a wide range of Arc ...

The Cenozoic palaeoenvironment of the Arctic Ocean

The history of the Arctic Ocean during the Cenozoic era (0–65 million years ago) is largely unknown from direct evidence. Here we present a Cenozoic palaeoceanographic record constructed from >400 m of sediment core from a recent drilling expedition to the Lomonosov ridge in the Arctic Ocean. Our record shows a palaeoenvironmental transition from a warm ‘greenhouse’ world, during the late Palaeocene and early Eocene epochs, to a colder ‘icehouse’ world influenced by sea ice and icebergs from the middle Eocene epoch to the present. For the most recent ∼14 Myr, we find sedimentation rates of 1–2 cm per thousand years, in stark contrast to the substantially lower rates proposed in earlier studies; this record of the Neogene reveals cooling of the Arctic that was synchronous with the expansion of Greenland ice (∼3.2 Myr ago) and East Antarctic ice (∼14 Myr ago). We find evidence for the first occurrence of ice-rafted debris in the middle Eocene epoch (∼45 Myr ago), some 35 Myr earlier than previously thought; fresh surface waters were present at ∼49 Myr ago, before the onset of ice-rafted debris. Also, the temperatures of surface waters during the Palaeocene/Eocene thermal maximum (∼55 Myr ago) appear to have been substantially warmer than previously estimated. The revised timing of the earliest Arctic cooling events coincides with those from Antarctica, supporting arguments for bipolar symmetry in climate change.

Extinct triple junction south of Greenland and the Tertiary motion of Greenland relative to North America

Geophysical data collected by R/V Vema during cruises from 1960 to 1973 in the area south of Greenland were used to establish details of the magnetic lineation pattern and the basement morphology associated with an extinct triple junction. The sequence of magnetic anomalies 20 to 24 (49 to 60 m.y. B.P.) is continuous from the western flank of the Reykjanes Ridge into the Labrador Sea north and south of the triple junction and defines a period of simultaneous sea-floor spreading in the Norwegian Sea, the North Atlantic, and the Labrador Sea. At the time of anomaly 20 (49 m.y. B.P.) a major slowdown in the rate of spreading of the Labrador Sea Ridge occurred, and it met with extinction prior to the time of anomaly 13 (∼40 m.y. B.P.). The magnetic lineation pattern shows the amount of opening in the Labrador Sea between the interval spanned by anomalies 13 to 21 and that spanned by anomalies 21 to 23. An independent estimate of the relative motion between Greenland and North America was obtained from the difference in the opening between Greenland and Europe and that between North America and Europe. This second estimate predicts more opening of the Labrador Sea than is observed. Bounds can nevertheless be placed on the early Tertiary relative motion between Greenland and North America, and this motion compares well with the history of tectonic deformation in the Canadian Arctic islands during the Eurekan orogeny.

Lomonosov Ridge—A double-sided continental margin

The first two traverses of marine multichannel seismic data across the Lomonosov Ridge (central Arctic), by the German research icebreaker Polarstern and the Swedish icebreaker Oden , demonstrate a prograded margin toward the Amerasian side and fault-bounded half grabens toward the Eurasian side of the ridge. Nearly 450 m of undisturbed flat-lying strata have been deposited on top of the peneplaned ridge since it rifted from the Barents-Kara Sea margin and subsided below sea level in early Tertiary time (64-56 Ma).

The Crary Fan: A trough-mouth fan on the Weddell Sea continental margin, Antarctica

Abstract Multichannel seismic investigations show the presence of a large trough-mouth fan deposit on the continental margin in the southern Weddell Sea. A characteristic feature of the fan is relatively few, but large canyons and/or channels which appear to have been stable for long periods. Levees associated with the channels may reach thicknesses of more than 1 km. Drilling during ODP Leg 113 recorded the presence of glaciers in East Antarctica since early Oligocene time, and the seismic stratigraphic evidence suggests that the submarine fan is largely composed of glacigenic sediments. The channel-levee systems and complexes indicate several growth phases, apparently controlled by glacial/interglacial climate fluctuations, with maximum fan growth during glacial periods. The present interglacial period is characterized by strong and erosive flow of Ice Shelf Water running down the western slope of the fan and carrying only minor amounts of suspended matter. The fan is essentially sediment starved during interglacial periods. The dimensions of the channel-levee complexes and the persistent loci of sediment supply suggest that turbidite sedimentation resulted from melting of wet-based glaciers at or near the shelf edge, which has consequently prograded 70–80 km seaward.

Sea-floor spreading and the early opening of the North Atlantic

Abstract We have examined available magnetic and gravity data bearing on the initiation of sea-floor spreading in the North Atlantic between Ireland and Newfoundland. The change in character of the magnetic field on the continental margin on either side of the Atlantic from a landward magnetic quiet zone to a seaward “noisy”, magnetic signature is postulated to be related to a change from continental to oceanic crust. Sea-floor spreading between Ireland and Newfoundland was initiated during the long normal geomagnetic polarity interval in the Late Cretaceous. Rockall Trough may have opened at this time. At the end of the normal polarity interval (Late Santonian) the ridge axis jumped westward to bypass Rockall Trough and the related offset initiated the Charlie Gibbs fracture zone. A reconstruction is presented for the relative position between North America and Europe prior to the initiation of sea-floor spreading in the Late Cretaceous.

Late Cretaceous magnetic anomalies in the North Atlantic

Abstract An identification of anomalies 31–34 is presented for the North Atlantic. North of the Azores-Gibraltar Ridge this implies a revision of the identification of the magnetic anomalies older than anomaly 26. DSDP site 10 in the western North Atlantic appears to be located on the old end of anomaly 33. The relative spacings of anomalies 29–34 in the North and South Atlantic, North and South Pacific and Indian Oceans are compared and the estimated relative widths of the magnetic polarity intervals in the Late Cretaceous are revised.

Deformation of the Baltic continental crust during Caledonide intracontinental subduction: Views from seismic reflection data

Deep seismic profiling in Norway and Sweden provides documentation of the amount and style of deformation of the Baltic crust in response to Caledonian intracontinental subduction. The seismic data demonstrate that the preserved Caledonide allochthon in central Scandinavia is 15 to 20 km thick, considerably greater than the 2 to 5 km predicted from surface geologic data. Much of the thickness of allochthonous rocks results from imbrication of the Baltic basement within a thin-skinned-style thrust complex. Seismic data across the Skardora antiform, one of the basement windows in the central Caledonides, indicate that the window represents an antiformal stack of thrust sheets involving basement and cover rocks. These data suggest that many of the basement windows in the Scandinavian Caledonides may result from similar thrust culminations and that the basement windows do not expose autochthonous Baltic basement. Documentation of the response of the Baltic crust during intracontinental subduction provides new constraints on reconstructions of the Scandinavian Caledonides and insights into the style of deformation occurring in other collisional orogens.

Physiographic provinces of the Arctic Ocean seafloor

The International Bathymetric Chart of the Arctic Ocean (IBCAO) grid model has been used to define the first-order physiographic provinces of the Arctic Ocean, which in this study is taken to consist of the oceanic deep Arctic Ocean Basin; the broad continental shelves of the Barents, Kara, Laptev, East Siberian, and Chukchi Seas; the White Sea; and the narrow continental shelves of the Beaufort Sea and the Arctic continental margins of the Canadian Arctic Archipelago and northern Greenland. The first step in this classification is an evaluation of seafloor gradients contained in a slope model that was derived from the IBCAO grid. The evaluation of this slope model, which emphasizes certain process-related seafloor features that are reflected in the bathymetric information, is subsequently used along with the bathymetry to classify the first-order physiographic provinces. The areas of the provinces so classified are individually calculated, and their morphologies are subsequently discussed in the context of the geologic evolution of the Arctic Ocean Basin as described in the published literature. In summary, this study provides a physiographic classification of the Arctic Ocean seafloor according to the most up-to-date bathymetric model, addresses the geologic origin of the prominent features, and provides area computations of the defined first-order physiographic provinces and of the most prominent second- order features.

Seismic investigations in the Weddell Sea Embayment

Abstract Seismic multi-channel data collected during Norwegian Antarctic Research Expeditions in 1976–1977 and 1978–1979 outline aspects of the Cenozoic depositional environment in the Weddell Sea Embayment. Acoustic basement, probably representing the East Antarctic craton, is exposed in a 50–100 km wide swath along the ice barrier between 78°S–75.5°S on the eastern side of the Crary Trough. The shelf prograded westward and northward from the craton into a subsiding basin colinear with the Transantarctic Mountain Range. Measured sediment thicknesses exceed 5 km. During middle and late Tertiary times a submarine fan complex—the Crary Fan—developed on the southeastern margin of the Weddell Sea Embayment. The glacially eroded Crary Trough is located at the contact between the craton and a sedimentary basin to the west. The entire sedimentary section is undisturbed by faulting or folding, which indicates that any movements related to Cenozoic uplift of the Trans-Antarctic Mountains and/or relative motion of East Antarctica had little effect in the area north of the Filchner Ice Shelf east of 41°W.