## 1 Introduction  
The oceans cover 71% of the Earth's surface [1], are fundamental to sustaining life, controlling climate, facilitating commerce and they represent a vast source of resources and economic wealth. Our understanding of the ocean and natural processes occurring at the seafloor is quite limited due to the difficulties in operating in this environment, especially the fact that electromagnetic waves, (e.g., light and radar), are highly attenuated in ocean water. The suite of optical and electromagnetic sensors that are used to map, observe, and understand land topography cannot penetrate more than tens of meters at best in ocean waters. This has left the vast majority of our planet virtually unmapped, unobserved, and unexplored. Satellite measurements of ocean surface height have been used to provide a general view of the shape of the deep ocean floor through altimetry-derived predicted seafloor depths [2]. However, the phenomena referred to as the \"upward continuation\" of gravity signals from bathymetric features at depth, limits the horizontal resolution of undersea features to those greater than approximately double the regional ocean depth [3]. Considering that the recent estimate of the mean world ocean depth is \(\sim\)3.9 km [1], the average achievable resolution is on the order of 8 km. Thus, while satellite altimetry-derived bathymetry is excellent for a regional tectonic studies (e.g., [4]), it does not provide enough spatial resolution or accuracy to perform the detailed geomorphometric analyses [5] required to understand the origin and significance of, for example, bottom current features [6], submarine glacial landforms [7], benthic habitats [8; 9; 10], geohazards such as shallow faults [11; 12], pockmarks, or mass transport complexes [13]. Knowing seabed depths, (bathymetry) is of vital importance for a growing variety of uses fundamental to understanding the workings of our planet. Early echo-sounding profiles across the Atlantic Ocean enabled [PERSON] and [PERSON] to understand the relationship between mid-ocean ridges and earthquake seismicity and played an important part in the formulation of one of the most significant paradigm shifts in science--the development of the hypothesis of seafloor spreading and plate tectonics [14]. Bathymetric data are also critical for establishing the limits of the extended continental shelf under the United Nations Convention on Law of the Sea [15], play a key role in a host of military and defense applications [16], and represent a fundamental dataset for addressing the growing challenges associated with climate change [17; 18]. Recognizing the need for global bathymetric data, The General Bathymetric Chart of the Oceans (GEBCO), operating under the auspices of the International Hydrographic Organization (IHO) and the Intergovernmental Oceanographic Commission (IOC) of the United Nations Educational, Scientific and Cultural Organization (UNESCO), was initiated more than 100 years ago with the vision of providing authoritative, publicly-available bathymetry data for the world's oceans [19]. Since its initiation in 1903 through the efforts of Prince [PERSON] of Monaco and Professor [PERSON] of The University of Nancy, GEBCO, and its mostly volunteer community, has produced a series of bathymetric charts that represent the best knowledge of seafloor depths at the time of their production. While the earliest products were contour plots based on very sparse lead-line measurements [19], the most recent product of GEBCO (GEBCO_2014) is now a digital, gridded product with a cell-spacing of 30 arc sec that incorporates data derived from both single-beam and modern high-resolution multibeam echo sounders, superimposed on a base that is derived from satellite altimetry data [1] (Figure 1).