Why Antarctic Oceans Turn Sperm Whales Into Giants

The water here reaches -1.8 degrees Celsius and holds that temperature year-round, varying by less than 1.5 degrees regardless of season. Not uncomfortable — that word belongs somewhere warmer. The Southern Ocean, south of the Antarctic Convergence, is a different kind of cold: permanent, physiologically consequential, and organised around a single physical property that changes everything living inside it. You already know the mechanism. Cold water holds dramatically more dissolved oxygen than warm water. Near the Antarctic surface, concentrations run to around 9 milligrams per litre. Near the equator, closer to 4. That difference, roughly two-fold, is what Gauthier Chapelle and Lloyd Peck of the British Antarctic Survey formalised in Nature in May 1999, after analysing length data for 1,853 species of benthic amphipod crustaceans from 12 globally distributed sites. Maximum potential size, they found, was limited by oxygen availability. Cold polar water relaxed the constraints on oxygen delivery that set the ceiling for body size in warmer seas. The mechanism had a name: polar gigantism.