Maps and acoustic profiles of free gas distribution, Western Baltic Sea and Kattgat-Skagerrak area

A shallow gas depth-contour map covering the Skagerrak-western Baltic Sea region has been constructed using a relatively dense grid of existing shallow seismic lines. The digital map is stored as an ESRI shape file in order to facilitate comparison with other data from the region. Free gas usually occurs in mud and sandy mud but is observed only when sediment thickness exceeds a certain threshold value, depending on the water depth of the area in question. Gassy sediments exist at all water depths from approx. 20 m in the coastal waters of the Kattegat to 360 m in the Skagerrak. In spite of the large difference in water depths, the depth of free gas below seabed varies only little within the region, indicating a relatively fast movement of methane in the gas phase towards the seabed compared to the rate of diffusion of dissolved methane. Seeps of old microbial methane occur in the northern Kattegat where a relatively thin cover of sandy sediments exists over shallow, glacially deformed Pleistocene marine sediments. Previous estimates of total methane escape from the area may be correct but the extrapolation of local methane seepage rate data to much larger areas on the continental shelf is probably not justified. Preliminary data on porewater chemistry were compared with the free gas depth contours in the Aarhus Bay area, which occasionally suffers from oxygen deficiency, in order to examine if acoustic gas mapping may be used for monitoring the condition of the bay.

Clay mineralogy on five NBP cores

During 2006, the SHALDRIL program recovered cores of Eocene through Pliocene material at four locations in the northwestern Weddell Sea, each representing a key period in the evolution of the Antarctic Peninsula ice cap. The recovered cores are not continuous, yet they provide a record of climate change with samples from the late Eocene, late Oligocene, middle Miocene, and early Pliocene and represent the only series of samples recovered from the northwestern Weddell Sea and spanning the Cenozoic and the initial growth of the peninsula ice cap. Late Eocene sediments sampled in the James Ross Basin are typically characterized by very dark greenish-gray muddy fine sand with some preserved burrowing and are interpreted to represent a shallow water continental shelf setting. Rare dropstones, primarily of well-cemented sandstones and minor ice-rafted material consisting of angular grains with glacially influenced surface features record the onset of mountain glaciation, the earliest such evidence in the region. The remaining cores were collected on the Joinville Plateau to the north of the James Ross Basin. The late Oligocene sediments consist of dark gray sandy mud with some clay lenses and many burrows, likely representing a distal delta or shelf setting. This core contains only very few and small dropstones, and the individual grains show decreased angularity and fewer glacial surface features relative to late Eocene deposits. The middle Miocene strata are composed of pebbly gray diamicton, representing proximal glacimarine sediments. The lower Pliocene section also contains many ice-rafted pebbles but is dominated by sandy units rather than diamicton and is interpreted to represent a current-winnowed deposit, similar to the modern contour current-influenced sediments of the region.