The spatial and temporal distribution of marine geophysical surveys

We examine how bathymetric mapping coverage varies with distance from the coastline, here a proxy for the effort involved in collecting the data. Distances to the nearest coastline were evaluated on a 1' x 1' global grid. We evaluate the density of marine survey track lines, which falls off with increasing distance from the coastline and drops off precipitously for the most remote regions. Bathymetric coverage shows a marked asymmetry between the southern and northern hemispheres, the latter having a factor of 2-4 denser coverage. We find a rapid decrease in data acquisition for previously unexplored regions beginning in 1973-1975. This rate change may reflect a transition from serendipitous exploration to more targeted investigations as the plate tectonics hypothesis became accepted, but it could also reflect the 1970s oil shocks. Coverage of the seafloor varies logarithmically with mapping resolution. At 0.5A degrees resolution, only similar to 60% of the seafloor has been mapped; the 50% mark was reached in 1979 and coverage of unexplored seafloor has since been less rapid. For comparison, at 1' resolution less than 10% of the seafloor has been mapped. Given rising fuel costs we predict the most remote areas will see a decline in future surveys. Better coordination of exploration among agencies and nations could mitigate this concern and improve global coverage, as could future altimetric mapping dedicated to bathymetric prediction.