It is high time we monitor the deep ocean Environmental Research Letters

Seafarers have navigated the ocean for millennia, but the study of the deep ocean is more recent. Global subsurface observations were first recorded 150 years ago, during the Challenger expedition (1872–1876). Deep oceanography and seafloor mapping subsequently benefited from technological developments induced by the world wars, including submarines and sonars to detect them, which led to the need to know vertical profiles of ocean sound speed (hence density). In parallel, oceanographic instruments improved: early hydrographic measurements were collected laboriously using thermometers, buckets, and the like; instruments now automatically and rapidly record conductivity, temperature, and pressure at high precision as they profile the water column, either autonomously or from an electrically-wired winch. The International Geophysical Year 1957–1958 kicked off the effort to systematically measure the deep ocean, including studies of deep water renewal and oceanographic transects throughout the North Atlantic, Arctic, Nordic Seas, and Mediterranean. Observations collected during subsequent international programs, recently the Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP), have increased our understanding of the deep ocean's value as an anthropogenic carbon and heat sink, with adverse impacts including ocean warming, acidification, and sea level rise. Grant no. NA20OAR4320278