Warm vs Cold Water: The Differences for Freedivers

By Kirk Krack

I’m often asked by students around the world if I freedive in British Columbia where I live, as most of my work and teaching is done globally and usually in more tropical destinations. This question is really about the temperature of the water and the tidal currents that we enjoy in BC. Although for the last three years I’ve primarily been diving in 89°F (32°C) water in a 26-foot (8m) purpose-built tank, training cast and crew for the Avatar sequels, I absolutely love the waters of British Columbia. The water temperatures combined with tides and currents provide so much in-water oxygen that the amount and variation of the life both big and small (along with colours!) are second to none. Who doesn’t love flying in a tidal current, cruising by a wall covered with strawberry anemones then ascending into kelp with sealions playing, after having watched wolf eels crunch on urchins while Pacific White-sided dolphins swim nearby? Did I sell it a little thick? Well, honestly, all of these can be enjoyed in a day off Port Hardy, BC. You simply need the right equipment and procedures to make it safe and enjoyable. 

What and where?

For this article we’ll consider the difference in freediving between that of temperate oceans (cold) versus tropical (warm). Tropical oceans lie between the Tropic of Cancer (23.5° north of the equator or around Mexico and the Bahamas) and the Tropic of Capricorn (23.5° south of the equator or around lower Brazil or upper Chile). The water here remains above 68° (20°C) year-round, with little fluctuation. Temperate oceans lie between the Tropic of Cancer to the Arctic Circle in the north or the Tropic of Capricorn and the Southern Ocean in the south, with temperatures generally ranging from 50°F to 68°F (10°C to 20°C ) that can vary wildly with the seasons.

Temperature is the obvious and biggest difference. While all tropical waters are 68°F (20°C) and above, places like the Cayman Islands are typically 78°F (26°C) and sometimes reach 86°F (30°C). In the lower temperature range this may require a 3mm full suit with hood to stay comfortable for a 2-3hr session, as a slowing metabolism due to the diving reflex can make us more thermally susceptible. In the warmest part of a tropical season, a 1.5mm full suit may be a better choice. Having the two suits allows you to mix-n-match: a 3mm top and a 1.5mm bottom to satisfy all temperature ranges or styles of freediving when tropical.

The right tools

In temperate waters like British Columbia, temperatures can range significantly from 43°F (6°C) to 59°F (15°C) and occasionally warmer, with seasonal and tidal influences. When the AIDA World Freediving Championships were hosted in Vancouver in 2004 during a bright and sunny August with little tidal exchange, our Mexican and Greek teams were pleasantly surprised (as were we) to enjoy surface waters of 70°F (21°C). This was the surface water, of course. Upon reaching the thermocline during descent past 33 feet (10m), they were soon greeted by a chilly 18°F/10°C drop in temperature to 52°(11°C). So, as a freediver ‘playing’ for 2-3hrs in our local waters, a 6mm freediving wetsuit with attached hood and open cell neoprene inside, along with proper boots/socks and 3mm gloves, is important. In tropical areas any surf or scuba wetsuit may do the job, but when in temperate waters a freediving wetsuit with attached hood is an absolute must as they have no zippers (which minimizes water flow) and don’t impede flexibility. Also, the cut of the suit and materials, such as open cell neoprene, allow amazing flexibility allowing the suit ‘hug’ your body, again minimizing water flow. Brands such as Oceaner out of Burnaby, BC offer both men’s and women’s cuts, which is important. Don’t buy into the idea that freediving suits are flexible enough that a man’s suit will fit a woman. Get the right tool for the job. Since we can have such a wide swing of temperatures in temperate waters, having that 3mm for your tropical or pool training and 6mm for your cold water comes in handy again with the 6mm top and 3mm bottom being the perfect combination for that sunny and warm part of the season. Much of your time can be spent preparing on the surface in the ‘warmer’ water before the adventure in colder darker water, so playing with different combinations can be practical.

The next obvious difference between temperate and tropical is visibility. 

In tropical waters a freediver can enjoy 65+ feet (20m+) visibility. Routinely in the Cayman Islands at our training camps we start to lose sight of our target plate with camera and lights after 245 feet (75m) looking down from the surface. This visibility allows for wider visual exploration of the surrounding reefs and their geography than in temperate colder waters, where, as a result of plankton blooms and the abundance of microscopic life, visibility during certain times of the year can range from pea soup to 33 feet (10m) in the upper shallow zone (although it will sometimes open up to 100+ feet (30m+) below that). As you go deeper in temperate waters it gets dark fast, and anyone who dives in British Columbia knows that beyond 100-130 feet (30-40m) it can seem like mid-night. Because of this, freedivers in temperate waters tend to be focused more on the ocean immediately in front of them. This is where having a proper light comes into play, one that isn’t too large and bulky. Here freedivers often favour ‘pen lights’, which fit beside the mask and can help during line diving with lanyards. They make it easy to reference the line a short 3-6 feet (1-2m) away. Smaller backhand-mounted lights like Light and Motion’s Sola series are great for exploration. They allow full use of the hands while providing an amazing amount of light and are small enough that they don’t create unnecessary drag or weight. 

Freedivers in a single session may make 30-50 freedives to depth and back, whereas the scuba diver generally makes one or two. For the scuba diver, the slow descent and ample time at depth allows the diver’s night vision to adapt. For the freediver travelling at 3 feet per second (1m/s) during descent with a minute or so at depth, there never really is time for the night vision to work fully. A trick I use is to close one eye at the surface and keep it as my ‘night eye’. Then upon descent, while starting with my ‘light eye’ I then switch eyes at 65 feet (20m) when it gets darker, opening my ‘night eye’ and closing my ‘light eye’. This helps my ‘light eye’ adapt to becoming a ‘night eye’ during my further descent until such time as I’m deep enough and I open up both eyes. This way I don’t have to use my light constantly, allowing me more peripheral vision and not just vision where my light shines. Another simple trick when exploring with a buddy, is to hook a simple 33-foot (10m) line with 10-20lbs (5-10kg) of weight and a light or strobe hanging off the bottom, pointing down from your surface marker and flag. The freediver at depth can easily reference to the surface float and buddy during ascent. The 33-foot (10m) line and weights can also assist with warm-ups or forms of pulling through buoyant phases before getting into easier kicking depths. It’s also not so bulky that it’s difficult to swim with and can provide a great surface station for other equipment.

Buoyancy considerations

With a thicker wetsuit comes the obvious buoyancy considerations and associated safety implications. Regardless of the suit thickness, recreational freedivers aim to be neutral at 33 feet (10m) on a full breath—first from a safety point of view and secondly for technique. In a 3mm full suit in tropical freediving where salinity is slightly higher, it’s common to see 5-10 lbs (2-4kg) used. This may be separated evenly between a waist belt and neck weight to help with trim and balance. In temperate waters where salinity is slightly less but thermally we require a 6mm wetsuit plus socks and gloves, we’ll typically see 10-18lbs (4-8kg) used. Distribution is more likely to use a neck weight with a max 5lbs (2kg) for comfort, with the balance on the waist. (NOTE: in recreational freediving when using a neck weight that it isn’t ‘quick release’, half or less of the total weight should be used on the neck with the balance in a right-hand quick release waist belt). One aspect of thicker suits that becomes noticeable is the overall compression of the wetsuit at depth and subsequent increase in negative buoyancy, and its affects on the sink phase (the negative non-kicking part of the descent). Here you you’ll feel more negatively buoyant and your sink phase can be much faster.

Tropical pre-freedive preparation is pretty simple. Arrive, unpack gear and put the suit on. 

In temperate areas, especially if you’re freediving at the height of winter, it can be a challenge. In a 6mm wetsuit with proper gloves and socks in temperate waters I can easily (and comfortably) spend 2-3hrs if I’m active. Success really depends on the preparation prior to getting into the suit and finally in the water. First off, I dress and head to the dive site as if I’m going to be stepping out into an arctic blizzard. This usually means having adequate clothing layers plus hat and gloves and a windproof jacket with hood. Secondly, I add to my thermal mass by drinking warm water prior to arrival at the dive site and while suiting up. Thirdly, keeping my core heat prior to entry is vitally important so I try to do two things: use warm lube (water/hair-conditioner solution used to make it easier to put the wetsuit on); and bring a large cooler of warm water, in which I put my suit to soak during the travel. Then I stand in the cooler to get suited and unsuited. Once I’m suited up and ready to go, last thing I’ll do is pre-charge my wetsuit by pouring warm water into it. Feeding heat into the body via extremities such as the feet and hands can also be very effective. 

Diving reflexes

In cold water the diving reflex can come on much quicker and stronger. One response of the body to cold is to peripherally shunt blood from the extremities to the core to preserve heat and this shift of blood to the core is also a helpful diving reflex in warm water. However, in warmer water it can take longer to initiate, so this is where cold can help. After cold water durations where you experience your first shiver, your resting oxygen consumption can go up 500%. Essentially, you’re not moving, just remaining still on the surface breathing, yet every muscle is activating trying to generate heat and now you’re in a losing battle and your diving responses are quickly diminishing. We know that 68°F (20°C) on the face starts to initiate the diving reflexes faster, but there is such as thing as too cold. Below 59°F (15°C) I forgo facial immersions and below 50°F (10°C) it sometimes takes a bit of acclimatization on the face even with a mask on. I have several times felt nausea from extreme cold chilling my sinuses from near freezing water.

Safety protocols

Good safety protocols are important wherever you are diving. Poor visibility can make it easy to lose your buddy when surfacing. For the buddy on the surface, you simply disappear into the green soon after your entry. Agreeing to descend and ascend in the same area is important and this is where that small weighted line with a light can help reference the surfacing area. Your surface buddy can, at the appropriate time, descend to this ‘meeting point’ and use the light if they need to. Also, as the surface buddy you should keep active track of your partner’s dive times so you know what’s normal and what should cause concern or cause you start surveying the surface waters around you. Discussing and agreeing to these simple procedures prior to the dive is an important part of responsible buddy freediving. Most blackouts, if their going to occur, happen at the surface or in the last 15 feet (5m) at the end of the freedive. If you are properly weighted, both these zones should have you buoyant and floating on the surface for your partner to easily handle you and affect simple blacked out diver procedures. 

With peripheral circulation shunting away from the extremities, losing dexterity in numb fingers and hands can cause issues with simple things like trying to take your fins off or reseal your mask, as well as more important things like trying to activate your or your buddy’s weight belt release. Be smart and know when to call it quits. And obviously avoid getting into 2nd stages of hypothermia or beyond. Your first shivers are ‘notice’ that you should be timing your travel to the boat or shore exit. Intermittent shivers and you should be packing up and making your way to the exit. Uncontrollable shivering and loss of hand dexterity and you’re pushing a potentially dangerous situation. Play smart not hard. 

One last thing to consider in temperate waters is tides and tidal flows or currents. The further away from the equator, the larger the tides and water exchanges and therefore currents. In places with lots of inlets and islands like the Inside Passage of Vancouver Island, currents can be amazingly fun when planned properly but can also pose obvious dangers. Know how to read tide tables and current charts and be able to plan your freediving session around them.

Enjoy it, temperate waters are amazing.