Data may be quantitative or qualitative. “I am impressed by the depth of Wenjer's translation capacity.” It's clear I mean qualitative. "Wenjer masters a wide variety of languages." This width would refer to something quantitative. Usually when we use depth, instead of width, it's the qualitative aspect we are talking about. Here, we're talking about something underwater, and water is often associated with depth, not width. So in his rhetoric, the writer chooses to allow a juxtaposition of one with the other. Nevertheless, I believe it is still quantity, not quality, that the writer is talking about. In other words, "depth" here means "nemerous", "plenty", "many",etc.