English: isopach sheet - Isopach and Depth to Basement - The isopach map depicts the thickness of unconsolidated sediment of probable Holocene age beneath the seafloor. Thicknesses are based on interpretation of high-resolution, seismic reflection profiles. Unconsolidated sediment is typically imaged on these profiles as an "acoustically transparent layer (ATL)" that either overlies bedrock or older, more consolidated sediment deposited before or during the last ice age when sea level was siginifcantly lower than at present. Where the thickness is zero or less than one meter, bedrock crops out on the sea floor or is covered by a very thin veneer of sediment.The depth to base of unconsolidated sediment map shows the depth to the base of the unconsolidated sediment layer, determined from seismic reflection profiles, by adding the water depth to the thickness of the unconsolidated sediment layer (ATL).