The GEBCO grid can be assumed to be relative to WGS84.
https://www.gebco.net/data_and_products/gebco_web_services/web_map_service/ https://www.gebco.net/data_and_products/gebco_web_services/web_map_service/mapserv?
Layers:
- GEBCO_Latest - shaded relief imagery
- GEBCO_Latest_2 - colour-shaded for elevation imagery
- GEBCO_Lastest_TID - imagery based on the TID grid with grid cells based on interpolation transparent
This grid is North Polar Stereo. The true scale latitude is 75 North.