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The contact with icy water starts with at least one minute of brain freeze — a sharp, biting pain across the face that eventually subsides. Remember watching the 1997 film “Titanic”? The water was estimated to be around 28 to 31 degrees when the ship sank. At that temperature, survival time without flotation could be measured in minutes. The water here is not quite that cold — typically hovering around 37 to 38 degrees in late winter — but it is cold enough to command respect.
The human body loses heat about 25 times faster in water than in air of the same temperature. The first minute can trigger what is known as the cold shock response, when breathing rate spikes and heart rate increases. That is why controlled breathing is critical. Once the initial shock passes, however, a calm sets in. The body begins to acclimate. The mind quiets. It is the same controlled calm embraced by the cold plungers known as the Marblehead Wolfpack, whose members regularly immerse themselves in icy water for the mental clarity and resilience it builds.
And then comes the reward.
Winter visibility in New England can be extraordinary because the ocean is at its clearest during the coldest months. As water temperatures drop, plankton and algae growth decline dramatically, meaning there are far fewer microscopic organisms suspended in the water column to cloud the view. Boat traffic is minimal in winter, so propellers are not constantly churning up sand and sediment from the seafloor. Cold water is denser and mixes more thoroughly, helping distribute particles rather than trapping them near the surface. The result, on the right day, is stunning 30-foot-plus visibility — clarity that can rival conditions many divers expect only in tropical waters.
There is a solitude to winter diving that is difficult to describe. The ocean feels still, uninterrupted by boating traffic or surface noise. Marine life tends to be less active in these months, but patient eyes can still spot the occasional sea star clinging to rock or a crab tucked into a crevice. Lobsters, in fact, prefer colder water and remain active even in winter.
People often ask how I stay in the water so long. The answer is an open-cell wetsuit. In freediving, an open-cell wetsuit means the interior neoprene — filled with thousands of tiny nitrogen bubbles — sits directly against the skin, creating a better seal and reducing water circulation inside the suit. That trapped layer of water warms quickly and stays warm. With a 7 mm open-cell suit, along with 7 mm gloves and booties, I can remain in the water for up to two hours in December. By peak chill in February and March, that time drops to about 45 minutes.
What ultimately limits me is not my core temperature — which stays remarkably warm — but my extremities. During breath-hold diving, the mammalian dive reflex slows the heart rate and shunts blood toward vital organs and away from the hands and feet. It is the same physiological reflex that allows seals and whales to hold their breath for extended periods underwater — though those animals tolerate cold oceans due to their natural insulation, such as blubber and fat. Even with thick gloves and booties, fingers and toes are the first to feel the cold.
In summer, during spearfishing trips, I can remain in the water for six hours or more. Winter is different. It is quieter, sharper and more elemental.
Cold-water diving is not something to approach casually. It requires training, proper thermal protection and never diving alone. But for those who are prepared, the experience offers something rare: a crystal-clear glimpse into a New England ocean most people never see — a world stripped to its essentials beneath a cold gray sky.
Ryan Park, a Marblehead resident and practicing dentist, writes Beneath the Blue, an occasional column in which he shares the experiences, challenges and discoveries of freediving in photos and words.
