Alan Reece Longhurst (5 March 1925 – 7 December 2023) was a British-born Canadian oceanographer who invented the Longhurst-Hardy Plankton Recorder,[1] and is widely known for his contributions to the primary scientific literature, together with his numerous monographs, most notably the "Ecological Geography of the Sea".

[2] He led an effort that produced the first estimate of global primary production in the oceans using satellite imagery,[3] and also quantified vertical carbon flux through the planktonic ecosystem[4] via the biological pump.

He later turned down the position of Assistant Deputy Minister of Science at the national headquarters of the Department of Fisheries and Oceans (Government of Canada) in favour of going "back to the bench" as a research scientist.

In 1997, he received the A.C. Redfield Lifetime Achievement Award[11] from the Association for the Sciences of Limnology and Oceanography "in recognition of sustained excellence in the study of marine food webs and biogeography, and of outstanding leadership in the development of international collaboration and in the administration of world-renowned oceanographic programs".

[12] The well-known Sverdrup critical depth concept for the induction of phytoplankton growth forced by local mixing and light is the starting point for the seasonal evolution of primary production, and this is very much related to regional oceanography.

By placing the typology of seasonal plankton cycles into the context of regional oceanography, characteristic features of ecology can be discerned at two hierarchical scales.

An initial proof-of-concept for the Ecological Geography of the Sea was demonstrated by estimating global primary production using satellite radiometer data partitioned into biogeochemical domains and provinces.

[3] This influential work was published in 1995 with co-authors Shubha Sathyendranath, Trevor Platt, and Carla Caverhill, and stands as the most highly cited paper in the Journal of Plankton Research.