Bathymetric elevation in meters.

Elevations can be assumed to be relative to mean sea level. However, in
some shallow water areas, the grids include data from sources having a
vertical datum other than mean sea level. We are working to understand
how best to fully assimilate these data.

=== Original Data Source ===
General Bathymetric Chart of the Oceans (GEBCO) Grid 2023

The GEBCO_2023 Grid is a global terrain model for ocean and land,
providing elevation data, in meters, on a 15 arc-second interval
grid of 43200 rows x 86400 columns, giving 3,732,480,000 data
points. The data values are pixel-centre registered i.e. they refer
to elevations, in meters, at the centre of grid cells.

The grid was published in April 2023 and is the fifth GEBCO grid
developed through The Nippon Foundation-GEBCO Seabed 2030
Project. This is a collaborative project between the Nippon
Foundation of Japan and GEBCO. The Seabed 2030 Project aims to bring
together all available bathymetric data to produce the definitive
map of the world ocean floor and make it available to all.

Citation:
GEBCO Compilation Group (2023) GEBCO 2023 Grid
(doi:10.5285/f98b053b-0cbc-6c23-e053-6c86abc0af7b)

Citation URL:
https://www.gebco.net/data_and_products/gridded_bathymetry_data/