What feature is typically used to indicate deep water on a nautical chart?

Soundings are the measurements of water depth indicated on nautical charts. This information is crucial for navigation, as it allows mariners to determine whether they are in deep enough water to safely navigate their vessels. Soundings are usually shown in feet or meters and can help identify areas of deep water, along with features such as channels or basins.

While contour lines provide an effective visual representation of underwater topography, indicating the shape and depth of the seabed, they are not specifically used to mark deep water as soundings do. Buoys and markers serve primarily to provide navigational aids and warning signals, but they do not directly signify water depth in a nautical chart context. Therefore, soundings serve as the primary feature for indicating deep water, making this answer the most appropriate choice.