In Eumaeus, a chapter filled with allusions to shipwrecks, frequent mentions of ice are perhaps the first clue that Joyce may be evoking the sinking of a famous Irish vessel in April 1912. A reference, about halfway through the chapter, to "collisions with icebergs" certainly strengthens this hypothesis.

JH 2019

Photograph taken by chief steward M. Linoenewald of the liner Prinz Adalbert early on 15 April 1912,  hours after the Titanic struck an iceberg in the same area, with a note observing that red paint was "plainly visible" on the iceberg, apparently made by the "scraping of a vessel" on it. Titanic had a large stripe of red paint just above the waterline. Source:

Photograph of a growler taken on 12 April 1912 with handwritten notation, "Blue berg taken by Captain Wood S. S. Etonian 12/4/12 in Lat 41º50W Long 49º50N Titanic struck 14/4/12 and sank in three hours." Source:

Photographic image distinguishing a "growler" from smaller "bergy bits," both of them technical terms at sea.  Source:

Lookouts in the crow's nest of the Titanic, about 15 meters above the forecastle deck. Source: