of, related to or located in the deeper part of the sea
2020 May 20, Industry Insider, “An online boost for freight”, in Rail, page 68:
At the time, international deep-sea shipping remained a loose cargo operation, although BR did seek to influence conversion to unit loads by providing a containerised short sea shipping service between Harwich and Rotterdam in 1968.
(of a port) able to accommodate the largest ships.
2019 November 6, Rail, page 60:
In addition to the long-standing relationship with Felixstowe (GBRf now carries a third of all containerised rail traffic arising from that port), operations have expanded at two other deep-sea ports - Southampton and Thames Gateway.