The ~180-km-diameter Chicxulub peak-ring crater and ~240-km multiring basin, produced by the impact that terminated the Cretaceous, is the largest remaining intact impact basin on Earth. International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 drilled to a depth of 1335 m below the sea floor into the peak ring, providing a unique opportunity to study the thermal and chemical modification of Earth’s crust caused by the impact. The recovered core shows the crater hosted a spatially extensive hydrothermal system that chemically and mineralogically modified ~1.4 × 105 km3 of Earth’s crust, a volume more than nine times that of the Yellowstone Caldera system. Initially, high temperatures of 300° to 400°C and an independent geomagnetic polarity clock indicate the hydrothermal system was long lived, in excess of 106 years.
Marine spatial planning and conservation need underpinning with sufficiently detailed and accurate seabed substrate and habitat maps. Although multibeam echosounders enable us to map the seabed with high resolution and spatial accuracy, there is still a lack of fit-for-purpose seabed maps. This is due to the high costs involved in carrying out systematic seabed mapping programmes and the fact that the development of validated, repeatable, quantitative and objective methods of swath acoustic data interpretation is still in its infancy. We compared a wide spectrum of approaches including manual interpretation, geostatistics, object-based image analysis and machine-learning to gain further insights into the accuracy and comparability of acoustic data interpretation approaches based on multibeam echosounder data (bathymetry, backscatter and derivatives) and seabed samples with the aim to derive seabed substrate maps. Sample data were split into a training and validation data set to allow us to carry out an accuracy assessment. Overall thematic classification accuracy ranged from 67% to 76% and Cohen's kappa varied between 0.34 and 0.52. However, these differences were not statistically significant at the 5% level. Misclassifications were mainly associated with uncommon classes, which were rarely sampled. Map outputs were between 68% and 87% identical. To improve classification accuracy in seabed mapping, we suggest that more studies on the effects of factors affecting the classification performance as well as comparative studies testing the performance of different approaches need to be carried out with a view to developing guidelines for selecting an appropriate method for a given dataset. In the meantime, classification accuracy might be improved by combining different techniques to hybrid approaches and multi-method ensembles.
13Natural seabed disturbance was quantified by estimating the number of days in a year that movement of the seabed 14 occurred due to waves and currents, taking into account the seabed characteristics. Disturbance over gravel 15 substrates was based on the concept of a critical threshold for bed movement. For mud substrates disturbance was 16 assessed on the basis of bed failure under extreme hydrodynamic stress. For sand beds the disturbance frequency 17 could be calculated as a function of disturbance depth below the sediment surface by relating disturbance to the 18 occurrence of small scale bedforms using established relationships for predicting ripple and megaripple height. The 19 method was applied to the northern European Continental Shelf (48° N to 58.5° N and 10° W to 10° E) using modelled 20 annual wave and current forcing with a temporal resolution of one hour and spatial resolution of approximately 11 21 km. At the broad scale highest levels of disturbance occurred in areas of high tidal stress where dune/megaripple 22 type bedforms were predicted and in shallow regions exposed to waves with large fetch. However, the detailed 23 distribution of disturbance showed a complex relationship between water depth, tidal stress, wave fetch and grain 24size. An assessment of the uncertainty in the results was made using a simple Monte Carlo approach and in general 25 indicated a large spread in disturbance frequency values. This suggests that present predictive relationships need 26 improvement if assessments of natural disturbance are to be made with confidence. Nevertheless the results give a 27 broad understanding of the location and intensity of natural physical bed disturbance including a measure of the 28 relative intensity between different regions. This has applications to management of the seabed where human 29 impacts have to be assessed in the context of the underlying natural disturbance. Recommendations are given for 30 further research that would help decrease the uncertainty in natural disturbance prediction. 31 32
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