The average water temperature in summer is a balmy zero degrees.
Sam Vincent gets that shrinking feeling on a dip to prove his polar credentials.
In Moscow they're called "walruses", hardened bathers who brave the winter chill for a swim in the Moskva River; in Vancouver, "polar bears" have swum at English Bay every New Year's Day since 1920. And those who brave Antarctic waters? We call ourselves penguins.
I've just jumped off a pirate ship. Above me is the MY Steve Irwin, the flagship of the Sea Shepherd Conservation Society; the water I'm about to crash into is Antarctica's Ross Sea, where the average summer water temperature is a balmy zero degrees. I'm not wearing a wetsuit. Nor boardshorts. Nor budgie-smugglers.
Who said environmental activism was serious business? As an embedded journalist during Sea Shepherd's annual assault on Japan's Antarctic whaling program I'd expected non-stop action: boat rammings, propeller foulings and hosing-downs from industrial-grade super-soakers - and I do in time experience all those things. But just as Jack Sparrow enjoys a jug o' rum, these pirates know how to have fun.
It began soon after I boarded the Steve Irwin off New Zealand: dress-up parties on the bow; kick-to-kick footy games on the aft deck; an afternoon of clambering on an unseaworthy raft made of lashed-together 44-gallon drums.
By late January we had nearly reached the 70th parallel, where icebergs sit on the horizon like plump clouds and margarita-style slush is beginning to appear in patches. The air has grown cold, the mood tense.
But before the search for any whalers can begin in earnest, there is an initiation ceremony to be observed on the ship.
The idea of the Penguin Swim is to prove your polar credentials by jumping into near-frozen water and staying there just long enough to impress onlookers without sustaining hypothermia.
The engine is stopped and we drift in calm, glassy waters.
The majority of the 43-strong crew form a queue on the deck, blankets and dressing gowns covering bare skin, bikinis and boardshorts.
Just looking at the Ross Sea makes me cold: a thick mist hangs above its surface and the water itself is as black as sump oil.
One by one, "penguins" begin to dive. Reactions from the newly initiated are ominous: teeth are chattering loudly and goosebumps protrude as their owners rush below deck for a hot shower.
My turn comes and I approach the gunwale. But before I reach it two friends propose a pact: penguins don't wear swimmers, so neither will we. I yank off my shorts, jump overboard and am quickly struck by the worst ice-cream headache of my life. When I resurface, all I can think about is getting back on the boat, and I'm swept up the rope ladder on a wave of adrenalin.
I'm so overcome with cold that for a moment I forget I'm standing naked in front of a crowd of people I barely know, and though it may not be my finest hour shrinkage-wise, I take comfort in the fact I am now an official member of the Antarctic Penguin Club.
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