Seabed Mapping: A Brief History from Meaningful Words

Over the last few centuries, mapping the ocean seabed has been a major challenge for marine geoscientists. Knowledge of seabed bathymetry and morphology has significantly impacted our understanding of our planet dynamics. The history and scientific trends of seabed mapping can be assessed by data mining prior studies. Here, we have mined the scientific literature using the keyword “seabed mapping” to investigate and provide the evolution of mapping methods and emphasize the main trends and challenges over the last 90 years. An increase in related scientific production was observed in the beginning of the 1970s, together with an increased interest in new mapping technologies. The last two decades have revealed major shift in ocean mapping. Besides the range of applications for seabed mapping, terms like habitat mapping and concepts of seabed classification and backscatter began to appear. This follows the trend of investments in research, science, and technology but is mainly related to national and international demands regarding defining that country’s exclusive economic zone, the interest in marine mineral and renewable energy resources, the need for spatial planning, and the scientific challenge of understanding climate variability. The future of seabed mapping brings high expectations, considering that this is one of the main research and development themes for the United Nations Decade of the Oceans. We may expect a new higher resolution ocean seafloor map that might be as influential as The Floor of the Oceans map.

Shoreline Changes Using Seabed Bathymetric, Sediments Scan and Profiles Observations in “Zarum” Gas Field Offshore Niger Delta

Seabed bathymetry, sediment scan and profiles are relevant geological and hydrographic observations widely used in marine geology to predict shore line changes as it concerns offshore fields development in the Niger Delta. Reliefs and heterogeneous sediment distribution, both across the seabed surface and in the shallow seabed profiles below, were examined. This study of the “Zarum gas Field” in the outer shelf environment offshore eastern Niger-Delta was from the results of measurements using high fidelity onboard instrumentation: Edgetech 4600 Multibeam and Sidescan, and Edgetech Sub Bottom Profiler. These instruments were side mounted on MV Cosco and towed along survey grids, within the designed corridor with the survey speed of 3knots.Seabed features were interpreted based on the acoustic sound reflectivity and refractions. The bathymetric values were reduced to the lowest astronomical tide, LAT of Opobo River entrance and range from 20.20m-25.89m with a deepening trend from the northwest to southeast caused by seabed current regimes and storm processes affecting the shoreline zones. The sediments of the scan vary from sand, through silt to clay which are of arenitic origin. Weak seismostratigraphic layer of 30m thick was observed below the seabed, which is presently undergoing secondary lithification. The study also shows existence of depressions and sediment fill in them called spud cans which vary between 10m-40m in diameter and debris, associated with previous rig movements; jack up barges and their drags. Observed are some subsea facilities pipelines and jackets. Based on findings, recommendations have been formulated for development of this gas Field.

Past and future dynamics of the Brunt Ice Shelf from seabed bathymetry and ice shelf geometry

The recent rapid growth of rifts in the Brunt Ice Shelf appears to signal the onset of its largest calving event since records began in 1915. The aim of this study is to determine whether this calving event will lead to a new steady state in which the Brunt Ice Shelf remains in contact with the bed, or an unpinning from the bed, which could predispose it to accelerated flow or possible break-up. We use a range of geophysical data to reconstruct the sea-floor bathymetry and ice shelf geometry, to examine past ice sheet configurations in the Brunt Basin, and to define the present-day geometry of the contact between the Brunt Ice Shelf and the bed. Results show that during past ice advances grounded ice streams likely converged in the Brunt Basin from the south and east. As the ice retreated, it was likely pinned on at least three former grounding lines marked by topographic highs, and transverse ridges on the flanks of the basin. These may have subsequently formed pinning points for developing ice shelves. The ice shelf geometry and bathymetry measurements show that the base of the Brunt Ice Shelf now only makes contact with one of these topographic highs. This contact is limited to an area of less than 1.3 to 3 km2 and results in a compressive regime that helps to maintain the ice shelf's integrity. The maximum overlap between ice shelf draft and the bathymetric high is 2–25 m and is contingent on the presence of incorporated iceberg keels, which protrude beneath the base of the ice shelf. The future of the ice shelf depends on whether the expected calving event causes full or partial loss of contact with the bed and whether the subsequent response causes re-grounding within a predictable period or a loss of structural integrity resulting from properties inherited at the grounding line.