Late glacial dynamics on the continental shelf of NE-Greenland - implications from submarine landforms

Favorable sea-ice conditions gave way to an acoustic survey offshore NE-Greenland in 2009. The acquired data set clearly depicts an area of sediment ridges in an area of at app. 18 x 9 km. The ridges are found in water depths between 270 and 350 m. The sediment ridges expand between 2,5 – 9 km, are 50 – 250 m wide and between 10 and 25 m high. In profile and without exception, these ridges are characterized by steep slopes towards West and gentle slopes towards East. Their internal structure, imaged by parametric echo-sounding data, shows that they have been deposited on a rather plain surface, thus representing positive sedimentation features rather than erosive remnant structures. Their curved shape, joint orientation and position on a basal till surface indicate their origin from glacial dynamics. We interpret these ridges as a set of terminal moraines. Since they are positioned on a basal till that extends further east, we consider these moraines to reflect short-lived re-advances during an overall recession of the ice stream. This is direct evidence for a highly dynamic behavior of an ice stream from the NE-Greenland Ice Sheet. The ages for these re-advances can be inferred from a thin sedimentary drape indicating a timing between Late Glacial and early Holocene

Zur Frage der Meeresboden-Kartographie: Die Nutzung von AutoTrace Digitizer für die Vektorisierung der bathymetrischen Daten in der Petschora-See

Actually, the problem of vectorizing paper maps comes up, when the cartographer has to convert scanned paper maps or satellite imageries in vector format. This issue is of topical interest, because there are both the satellite images and bathymetric (or topographic) maps which are still largely pa- per-based and therefore uneditable in any digital system. Bitmap to vector converting is a difficult, highly time-consuming and technical task. The ideal instrument for quick and perfect digitizing of raster images to vector ones (so called R2V vectorizing software) does not exist though for the ma- chine doesn’t understand the geomorphological features and the character of the sea floor relief. That’s why the digitizing routine requires a large share of manual labour, a lot of time and patience in several trial sessions, which will necessarily contain errors to finally find out the best parameters of procedure to make a reality of our cartographic wishes. Especially difficult and tedious is to digitize large-scaled bathymetric maps with very complicated relief and geomorphological features. And it’s not to mention that nowadays paper-based maps without digital counterpart lose their value, yet making those cost a lot of money for updating and changing the thematic information on maps. At the same time, we can’t reject the paper-based maps only because they are paper-based. A lot of thematic maps are really rare, very necessary or just are to be used in mapping, e. g. geologic or tectonic maps, since their thematic information may remain the same for centuries. So it’s clear, that using of the digitizing tools in mapping and finding out the optimal instrument for the bathyme- trical purposes are questions of great actuality and importance. In this article the experience of our work with AutoTrace is presented – a vectorizer toolkit, that is chosen among others thanks to its effectiveness and open source distribution.Heutzutage wird der Kartograph oftmals mit der Herausforderung konfrontiert, einge- scannte Papierlandkarten oder Satellitenbilder ins Vektorformat umwandeln zu müs- sen. Das Problem ist recht aktuell, weil sowohl Satellitenbilder als auch bathymetrische oder topographische Karten nach wir vor überwiegend im Papierformat vorkommen und daher in keinem Computersystem editiert werden können. Die Konvertierung von Pixeldateien in Vektordaten ist eine anspruchsvolle und zeitaufwändige Aufgabe. Das ideale Hilfsmittel für eine schnelle und genaue Digitalisierung, um aus Rasterdaten Vek- tordaten zu erhalten (sogenannte R2V-Programme), gibt es noch nicht, weil der Com- puter naturgemäß kein Verständnis für die geomorphologische Beschaffenheit des Meeresbodens hat. Eine Digitalisierungsroutine erfordert viel manuellen Einsatz, Zeit und Geduld. Die vielen Versuche, die auf dem Weg zum gewünschten Endprodukt not- wendig sind, gehen gezwungenermaßen mit Fehlern einher, bis endlich die richtigen Programmeinstellungen und der richtige Ablauf der einzelnen Arbeitsschritte gefun- den ist. Besonders schwierig ist die Digitalisierung großmaßstäbiger bathymetrischer Karten, auf denen ein kompliziertes Relief dargestellt ist. Es muss nicht erwähnt wer- den, dass heutzutage Karten, die ausschließlich papierbasiert sind, an Wert verlieren, weil es zuviel kostet, die Karten nachzuführen und die thematischen Informationen zu ergänzen. Gleichzeitig kann auf papierbasierte Karten nicht einfach verzichtet wer- den (schon gar nicht, weil sie sind wie sie sind, nämlich aus Papier). Viele thematische Karten sind äußerst selten, sehr nützlich oder immer noch in Gebrauch, weil der in ih- nen dargestellte Inhalt sich selbst in Jahrhunderten nicht ändert – beispielsweise bei geologischen oder tektonischen Karten. Es ist also klar, dass die Nutzung von Hilfsmit- teln bei der Digitalisierung in der Kartographie eine Frage von großer Aktualität und Bedeutung ist. Dabeigilt es auch, das beste Instrument für die Zwe- cke der Bathymetrie zu finden. In diesem Arti- kel wird die Erfahrung mit AutoTrace vorge- stellt, einem Hilfsmittel zur Vektorisierung, das ausgewählt wurde, weil es besonders effektiv ist und auf einer Open Source-Technologie be- ruht.info:eu-repo/semantics/publishe

Oblique nonvolcanic seafloor spreading in Lena Trough, Arctic Ocean

Passive rifting and the early non-volcanic formation of ocean basins are fundamental aspects of the plate tectonic cycle. Cenozoic plate margins where this has occurred are rare. Here we present new observations from Lena Trough in the Arctic Ocean that bear on the early phase of oceanic spreading in such rifts. Lena Trough is an oblique seafloor rift system bounding the North American and Eurasian plates, and connecting neighboring Gakkel Ridge with the rest of the global mid-ocean ridge system. Mapping and sampling show widespread mantle outcrop along two parallel basement ridges bounded by steeply dipping normal faults. Volcanism is limited to the intersection with Gakkel Ridge and to minor eruption of strongly potassic alkali basalts in a single location. Non-eruptive magmatism is shown by an increase in plagioclase-and vein-bearing lithologies over residual peridotite in the center of Lena Trough. Normal mid-ocean ridge stairstep geometry and obvious low-angle detachments as seen at other ridges are absent. Lena Trough thus is an example of a young nonvolcanic continental rift that is just now beginning the transition to oblique nonvolcanic seafloor spreading. This style of oblique rifting, without the formation of striated large-scale low-angle detachments appears to be a major mode of crust formation on ultraslow spreading ridges. The sharp transition from the continental margins on either side to nonvolcanic rifting, with mantle slab exhumation in the rift may provide a model for the early evolution of oblique continental rifts, such as the Cote d\u27Ivoire/NE Brazil conjugate margins. Copyright 2011 by the American Geophysical Union

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

[1] 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 Arctic science activities, for example, by providing constraint for ocean circulation models and the means to define and formulate hypotheses about the geologic origin of Arctic undersea features. IBCAO Version 3.0 represents the largest improvement since 1999 taking advantage of new data sets collected by the circum-Arctic nations, opportunistic data collected from fishing vessels, data acquired from US Navy submarines and from research ships of various nations. Built using an improved gridding algorithm, this new grid is on a 500 meter spacing, revealing much greater details of the Arctic seafloor than IBCAO Version 1.0 (2.5 km) and Version 2.0 (2.0 km). The area covered by multibeam surveys has increased from ∼6% in Version 2.0 to ∼11% in Version 3.0