Data heterogeneity and oldness, two difficulties to overcome for the world seabed sediment mapping

A global seabed sediment map has been developed since 1995 to provide a necessary tool for different needs. This project is not completely original since it had already been done in 1912 when the French hydrographic Office and the University of Nancy produced sedimentary maps of the European and North American coasts. Seabed sediments is one of the last geographical domains which can’t benefit of satellite data. Without this contribution, sediment maps need to use very old data mixed with the new ones to be able to reach the goal of a global map. In general, sediment maps are made with the latest available techniques and are replaced after a few decades, thus generating new cartographic works as if all the previous efforts had become useless. Such approach underestimates the quality of past works and prevents to have maps covering large areas. The present work suggests to standardize all kind of sedimentary data from different periods and from very different acquisition systems and integrate them into a single product. This process has already been done for bathymetric data of marine charts, we discuss in this article of the application of this method at a global scale for sediment data.

Effects of Hypoxia on the Distribution of Calanoid Copepod Eggs in the Seabed Sediments of the Eutrophic Masan Bay, Korea

In this study, we investigate the distribution of calanoid copepod eggs in the sediments of Masan Bay (South Sea, Korea), in which hypoxic conditions occur every summer. In August (2011), hypoxia was observed at all stations, while normoxia was observed in April (2012). The pH and hydrogen sulphide concentration at the sediment-water interface in the inner bay during August were 7.7 and >20 mol L−1, respectively, and there was no significant difference between the stations in April. The abundance of eggs in the sediment ranged from 0.69 to 1.49 × 106 eggs m−2 in August, and from 0.59 to 1.08 × 106 eggs m−2 in April. Notably, the proportion of abnormal eggs was high (a maximum of 77.1%) in August, and a uniform distribution of normal eggs (>80%) was observed in April. A generation of abnormal eggs hatched with deformed nauplii in Masan Bay during the summer, and a failure to hatch was likely due to the high H2S concentration and low pH caused by hypoxia. In this paper, we discuss the effects of hypoxia and seabed environments on the hatching success of calanoid copepod eggs.

Comprehensive detection device and physical testing for mechanical properties of seabed sediments and shallow gas

In this paper, a comprehensive detection device for the mechanical properties of seabed sediments and shallow gas is designed, which is mainly composed of the seabed sediment mechanical properties detection part, the shallow gas detection part and the ultrasonic wireless transmission part. The mud water gas separation structure of the shallow gas detection part separates the shallow gas from the mud water, and then the methane concentration in the shallow gas is measured by the non-dispersive infrared methane sensor, which realizes the collection of the submarine shallow gas and the automatic real-time monitoring of the concentration. The measurement of the mechanical properties of seabed sediments realizes the real-time measurement of the three parameters of cone resistance, sidewall friction and pore water pressure, which characterize the mechanical properties of seabed sediments, through strain-sensitive elements. The ultrasonic wireless data transmission part is mainly for the data detected by the mechanical properties of the seabed sediments to be wirelessly transmitted to the sensor placement room through the ultrasonic transducer across the mud-water-gas separation structure. Finally, the data measured by the two parts are transmitted to the mother ship through the cable located in the sensor placement room. The experimental results show that it has the ability to comprehensively detect the mechanical properties of seabed sediments and shallow gas, and has strong operability.

Predicted Mapping of Seabed Sediments Based on MBES Backscatter and Bathymetric Data: A Case Study in Joseph Bonaparte Gulf, Australia, Using Random Forest Decision Tree

Predictive mapping of seabed sediments based on multibeam bathymetric (BM), and backscatter (BS) data is effective for mapping the spatial distribution of the substrate. A robust modeling technique, the random forest decision tree (RFDT), was used to predict the seabed sediments in an area of the Joseph Bonaparte Gulf, Northern Australia, using the multibeam data and seabed sediment samples collected simultaneously. The results showed that: (1) Using multibeam bathymetry data in addition to multibeam backscatter data improves the prediction performance of the RFDT. In comparison to only multibeam backscatter data, the prediction performance achieved a ~10% improvement in sediment properties; it achieved a ~44.45% improvement of overall accuracy in sediment types, and a ~0.55 improvement in Kappa. (2) The underlying relationships between sediment properties and multibeam data show that there is an opposite non-linear correlation between sediment property-BS and sediment property-BM. For example, there is an obvious negative relationship between %mud-BS at incidence angles of 13° and 21°, but the relationship between %mud-BM is positive. As such, the RFDT is a useful and well-performing method in predicting the relationship between sediment properties and multibeam data and in predicting the distribution of sediment properties and types. However, the sediment prediction method in deep-water areas with high gravel content needs to be further evaluated.

Mineralogy and Geochemistry of Seabed Sediments of the Chiloé–Taitao Area, Southern Chile, and Implications for Ore Deposits

The oceanic seabed contains a variety of mineral resources related exclusively to submarine environments. Limited information has been documented for the seabed offshore of Chile, which is particularly interesting due to its geodynamic context and large area. Mineralogical and geochemical analyses of 16 sites within the Chiloé–Taitao area, from 83 to 3388 m in depth, were carried out. The most abundant minerals are quartz, feldspars, pyroxenes, amphiboles, epidote, and biotite, with lower quantities of zircon, white mica, olivine, pyrite, magnetite, ilmenite, and hematite. Framboidal pyrites are mainly present at >900 m depth, and could be associated with methane hydrates, which have been reported in the area and its surroundings. Tenorite, sphalerite, tennantite, cordierite, birnessite, and tellurobismuthite were revealed by XRD analysis at low concentrations but at many sites. Birnessite, a Fe–Mn nodule-forming mineral, was widely detected, and Pearson correlations showed elemental associations related to the presence of Mn oxides. Samples did not evidence Fe–Mn nodules, probably due to the redox and depth conditions. Nonetheless, it is probable that to the west, polymetallic nodules are present in deeper zones. In the southern part of the area, reflective grains were identified, with up to 58.3 wt.% Cu; these grains might be derived from the continent or formed by in situ diagenetic precipitation.