Conventional wisdom has long held that corals -- whose calcium-carbonate skeletons form the foundation of coral reefs -- are passive organisms that rely entirely on ocean currents to deliver dissolved substances, such as nutrients and oxygen. But now scientists at MIT and the Weizmann Institute of Science (WIS) in Israel have found that they are far from passive, engineering their environment to sweep water into turbulent patterns that greatly enhance their ability to exchange nutrients and dissolved gases with their environment.

Usually there’s some sort of payoff to diving in near-freezing conditions — a magnificent wreck perhaps, or a unique geological feature. I wasn’t so lucky. When I first dived in 37-degree water, in a shallow lake outside London, there was nothing. Well, that’s not quite accurate: At one point I think I spotted a traditional British black taxi through the murk. But I couldn’t be sure — with visibility of only 20 feet, it was hard to tell.

It was so cold, I could barely think. This was problematic because I was there to make the open-water dives for my PADI Dry Suit Diver qualification and needed my wits about me. The water temperature at Wray Bury Dive Centre’s 15-acre lake is always on the chilly side — this is England, after all — but 37 degrees was unusual. A cold snap the week before caused the surface of the lake to freeze, though it had begun to melt by the time of my visit.

Taking my first steps into the lake was just about bearable. It was when my hands — protected by only 3 mm of neoprene — touched the water that I got a sense of just how hard this was going to be. But that was nothing compared to the brain freeze that struck as I made my first descent. I’m a confident, experienced diver, not prone to panic, but the feeling of ice-cold water surrounding my head and neck was too much. I motioned desperately to the instructor that I needed to surface, and came up, my breathing shallow and hurried.

He helped me to calm down, and we soon rejoined the rest of the group on a platform at 22 feet to complete the skill tests. That dive, and the follow-up that afternoon, were kept to just 20 minutes’ bottom time due to the cold. Even so, I had such limited feeling in my fingers by the time I came up for the skill tests that basic tasks — like undoing the clips on my BC or disconnecting and reconnecting my dry suit second stage — were enormously challenging. It took several attempts, with a great deal of motivational support from my instructor, to demonstrate the skills successfully.

Writing about the experience today while I’m warm and dry, it’s hard to even conjure that unexpectedly extreme environment. They are still the hardest dives I’ve ever made.

It's true what they say, getting narced is fun — of a certain kind. Similar to drinking way too much, then driving waaay too fast. As in, "Whoa, dude, you almost hit that tree! Hahahaha!"

Which should indicate the downside. Not to sound like your mother here, but nitrogen narcosis is, in fact, drunk diving. Though you hear a lot about decompression illness, getting narced should probably be a bigger worry, at least when you dive below 100 feet. At that depth, nitrogen narcosis becomes more likely than a DCI hit, and when it occurs it is more dangerous because it attacks your most important piece of life-support equipment: your brain. That, not DCI, is the primary reason for the traditional recreational depth limit of 130 feet. But there's good news too: You can manage this risk and still dive safely below 100 feet.

What Is Nitrogen Narcosis?

You probably know the term "rapture of the deep" and have heard stories of divers offering their regs to fish and so on. Inappropriate euphoria and general silliness are the best known symptoms of nitrogen narcosis, though narcosis can also trigger anxiety, even terror. The exact mechanism is not well understood, but it's probably no coincidence that the usual symptoms resemble the early stages of general anesthesia. Compare, for example, the effects of the common dental anesthetic nitrous oxide, called laughing gas. "The same kinds of mechanisms are involved," says Dr. Peter B. Bennett, author of the chapter on inert gas narcosis in Alfred Bove's Diving Medicine. "General anesthesia and nitrogen narcosis both occur when a given anesthetic gas — and I would include nitrogen as one — reaches a certain critical molar concentration." In fact, nitrogen narcosis "may be considered as a state of impending general anesthesia" according to the authors of Diving and Subaquatic Medicine. Not the best mental state, probably, with 100 feet of water over your head.

Nitrogen narcosis has also been compared to alcoholic intoxication, the so-called "Martini Law" — each 50 feet of descent is equivalent to drinking one martini. Your thinking slows down. Your inhibitions and self-control are reduced, allowing euphoria or anxiety to emerge. Perceptual narrowing and a tendency to become fixed on one idea are common. Nitrogen narcosis, like alcohol, also impairs your motor control and memory. If it progresses far enough, you become unconscious. Precisely which mental functions are impaired, in what order and to what degree are debated by researchers, and studies have yielded conflicting results. What everyone agrees on, however, is that nitrogen narcosis degrades your ability to react quickly to a crisis and reason your way out of it.

Not You? You Wish

You've been below 100 feet many times and you've never been narced? Maybe. Divers, like drinkers, vary widely in their susceptibility, and you may in fact be more resistant to narcosis than some others. But it's hard to know that for sure based on your subjective feelings. "One of the biggest effects of nitrogen narcosis is an amnesia of what happened when you were down there," says Bennett. "Divers don't even remember what they were like." So you may have been more narced than you remember. Add forgetfulness to overconfidence and recklessness, other important effects of nitrogen narcosis, and you're like the guy leaving the party after a few too many who insists he's OK to drive. He has done it before and may do it again, but only if he's not called upon to react to a sudden emergency like a sharp curve and a stout tree.

Nitrogen narcosis is related to the partial pressure of the nitrogen in your gas mix, so narcosis becomes more likely as you go deeper. You may as well say nitrogen narcosis is caused by going deep. The threshold for significant narcosis on air is often said to be 100 feet, but that's only a rough guide. Actually, narcosis probably begins to appear as soon as you leave the surface. For example, a Navy test found slight but measurable effects at only 33 feet. It's a lot like asking what blood alcohol level constitutes drunk driving. The law states a number, though everyone knows there is some effect on your reaction time at lower levels.

Nitrogen and alcohol are different in some ways too. Serious, noticeable narcosis comes on more quickly whenever you reach your personal threshold depth. Studies show it reaches a peak within two minutes, and does not get worse even after three hours at that depth. It goes away very quickly as you ascend, and totally disappears before you reach the surface. As far as anyone knows, nitrogen narcosis, unlike alcohol abuse, does not do long-term harm and leaves no hangover. However, it's not what narcosis itself does to you that you should worry about, it's the harm you can do yourself because you're too narced to think clearly.

Many Unknowns

Different divers feel different amounts of narcosis at the same depth. The same diver may feel different amounts of narcosis at the same depth on different days. Narcosis takes different forms, too. Just as there are happy drunks, sad drunks and angry drunks, some divers are euphoric when narced, but some are terrified and some are just confused.

Some of the variables affecting all divers are:

• Interaction with drugs. It is well-known that several drugs can interact in surprisingly intense ways, so that 1 + 1 equals 3. Some drugs, including anti-motion sickness pills, may interact with nitrogen to increase your narcosis susceptibility and intensity. Not much research has been done, but Bennett suggests that if a drug would increase the effect of alcohol, it's a reasonable assumption that it might increase nitrogen narcosis.

 

• Interaction with alcohol. Drinking and diving is never a good idea, of course, and some experts think the nitrogen/alcohol interaction may be especially strong because they have similar effects on your nervous system--1 + 1 may equal 5, in other words. Even a hangover can potentiate nitrogen narcosis.

 

 

• Interaction with carbon dioxide. Among the intensifiers of nitrogen narcosis, "carbon dioxide is a big one," says Bennett. "High levels of carbon dioxide in your blood are going to work with nitrogen to make narcosis worse." Elevated carbon dioxide levels generally result from rapid, heavy breathing. You may be working hard--finning into a current, for example--or sucking on a poorly performing regulator. Anxiety is another cause of rapid breathing and therefore high carbon dioxide.

 

 

• Fatigue. Doing heavy work at depth seems to bring on nitrogen narcosis, though whether that's because of the elevated carbon dioxide that usually goes with hard work or is an independent effect of being tired is not clear.

 

 

• Task-loading, time stress. Trying to do too many things, or trying to do too much in a short time, also increases the narcosis effect. Again, whether this is a carbon dioxide effect caused by the anxiety of trying to cope with too many tasks or an independent effect is not clear.

 

 

• Cold. Being cold is often mentioned as a contributing cause of nitrogen narcosis. The reasons aren't known, but some of the effects of hypothermia are similar to those of narcosis, including mental dulling, sluggishness and amnesia.

 

In addition to the variables that affect all divers, some divers seem to be more susceptible to nitrogen narcosis than others. Obviously the relaxed, healthy diver with good breathing habits and a low air consumption rate has an advantage over the nervous, heavy breather. Also, some experts think highly intelligent and emotionally stable divers are less susceptible to nitrogen narcosis.

Adaptation to Narcosis

Most divers who regularly go very deep on air are convinced that they become adapted to it and after a while have less trouble with nitrogen narcosis. Is it true physical adaptation (meaning the divers are actually less narced) or have the divers just learned to compensate better for it? That's another unknown. The adaptation, if that's what it is, is temporary. Most say it wears off in about five days.

In any event, common practice among divers who must go very deep using air is to work up to the depth by making the first dive of each day progressively deeper. In 1989, Bret Gilliam set a depth record on air of 452 feet, and worked down to the depth with more than 600 dives, at least 100 of them deeper than 300 feet. As a result, Gilliam was not so narced at 452 feet that he could not do a series of math problems and, more to the point, return to the surface alive.

How Deep Is Too Deep?

Gilliam's 452 feet on air is off the chart for the rest of us. Various studies have described the narcotic effect of air at 300 feet as "stupefaction," "severe narcosis," "marked impairment of practical ability and judgment," and even unconsciousness. Other reports: "severe impairment of intellectual performance" at 230 feet; "sleepiness, illusions, impaired judgment" at 165 feet; and "idea fixation, perceptual narrowing and overconfidence" in the 100- to 132-foot range. Probably the customary 130-foot limit for recreational diving in the U.S. is a good one until you know better your personal susceptibility to nitrogen narcosis and have trained yourself in coping with it. For diving much deeper than that, trimix (in which most of the nitrogen is replaced with less-narcotic helium) is probably a safer gas.

How To Tell If You Are Narced

That's tough because your judgment, the faculty you depend on to tell you if you are affected, is the first to be attacked by the narcosis. Returning to the analogy to alcohol, it's like asking how you can tell if your driving is affected after you've had a few drinks. In both cases, you should probably just assume it.

Some divers experienced with deep water like Gilliam have developed their own versions of roadside sobriety tests. Not foolproof, but better than nothing:

• Every few minutes, check your depth and tank pressure, and write them on your slate. Check your buddy's depth and pressure and write them on your slate. Your buddy does the same on his slate. Now each of you has to point to your own and your buddy's numbers on both slates, and the slates have to agree. This test automatically compares both divers, which can be valuable if one diver is narced and the other is not.

 

• Every few minutes, hold up a number of fingers to your buddy (say, three fingers). He has to respond with the same number plus one (four fingers).

 

These "roadside" tests aren't foolproof because many of the effects of mild to moderate nitrogen narcosis can be overcome, or at least masked, if you try hard enough. Your mind can be impaired, but if you devote all your diminished resources to one job, you can do it well. This can drive researchers crazy. In one case, subjects in a chamber at a "depth" where they should have been narced performed the tests better than at the surface. In other studies, narced divers have often been able to attain good accuracy at the expense of speed, or vice versa. This means you might be able to perform the match-slates test or the count-fingers test and still be narced. So watch your responses (and your buddy's) for both accuracy and speed.

You are like the drunk driver who, by fierce concentration, is able to keep his car between the white lines. Obviously, the greater danger for both of you is the unexpected, not the routine. It's the entanglement or a regulator free-flow, the sharp curve and the tree. So leave the nitrogen party early and dive carefully. Mom's right: There is such a thing as too much fun.

How To Beat Narcosis

Start by assuming you will be narced if you go deeper than 100 feet. You can't prevent nitrogen narcosis entirely, but you can minimize it and compensate for it.

• Be clean and sober. Avoid over-the-counter meds like Sudafed and Dramamine if you can, because they may potentiate the narcotic effect. It goes without saying that you shouldn't drink and dive, but even a hangover from last night's drinking can make narcosis worse and reduce your ability to cope with it.

 

• Be rested and confident. Fatigue and anxiety may help trigger narcosis, and certainly are stresses that diminish your ability to solve problems.

 

 

• Use a high-quality regulator in good condition. High breathing resistance elevates your carbon dioxide level, which potentiates narcosis.

 

 

• Avoid task-loading. Don't try to do too much, because that causes stress and anxiety. Your first excursion below 100 feet is not the time to figure out a new camera housing, for example, because it will divert your diminished mental capacity from what's most important—diving safely. Keep it simple, stupid, because stupid you will be.

 

 

• Be overtrained. Most of us never practice the basic safety skills like air sharing and weight dumping because they seem so simple. But under the influence of narcosis, the simplest tasks become more difficult. If you have to think about it, you may not be able to do it, and your repertoire of skills may be stripped down to those made automatic by frequent rehearsal.

 

 

• Approach limits gradually. Don't go to 130 feet until you've been to 110 a few times, seen how you react and become comfortable with the depth. And descend slowly, as there is some evidence that rapid compression makes narcosis more severe.

 

 

• Use a slate. Don't depend on remembering the dive plan or the camera controls; write them down. That frees up mental RAM for coping with the dive itself. And a slate is useful for narcosis tests like writing down depth and tank pressure.

 

 

• Schedule gauge checks and buddy checks. Don't check your tank pressure only when you think of it. Plan to check at stated intervals, say every two minutes. Likewise, plan to look for your buddy and make eye contact on a schedule, like every minute. Discipline helps keep you focused, and if either of you consistently misses appointments, suspect narcosis.

 

 

• Be positive and motivated. Experiments have shown that divers who want to conquer narcosis and believe they can, actually do. At recreational depths, narcosis is fairly mild and controllable. The key is to be optimistic but prepared, confident but prudent.

I have spent much of the last 30 years underwater. I’ve explored the deep on thousands of scuba dives and numerous submersible trips to 18,000 feet [5,500 meters] below the surface. Yet during all these journeys, I have only rarely encountered some of the ocean’s biggest mysteries: deep-sea sharks.

Twenty-seven years ago, a small cable outfit broadcast a week of television all about sharks. In the many years since, while the Discovery Channel’s Shark Week has not shied away from controversial shows depicting attacks, it has also brought sharks into the public consciousness and educated the public about their importance to our oceans.

The casual fan of Shark Week can probably name the big three: the great white, tiger and bull sharks. They are the DiCaprio, Clooney and Pitt of the shark world. As important as these are, they are just three members of the shark family, which includes over 400 species. To me, the most amazing sharks are the little-known species that lurk in the deep sea.

Over the years, we’ve learned quite a bit about shallow-water sharks because they’re in the reef — in the dive zone where we can see them. Deep-sea sharks seem almost alien to us because they’re so deep in the ocean that it’s hard to get there and observe them. The pressure is extremely high, temperatures are extremely low and only in the last several decades have we had underwater vehicles, robots and submarines that can get down into these depths.

Here are some of the few things that we do know about them:

Goblin shark: One of the strangest-looking fish in the ocean, very few specimens have been caught and studied. It was first found in Japan, but is probably widely distributed in the deep sea. Frill shark: This true example of a living fossil is typically never found in shallow water; when it is, it’s usually in distress. Eel-like in shape, and up to 6 feet [1.8 meters] long, they can distend their mouths open and eat things that are more than half their body length.

Bluntnose sixgill shark: This shark can grow up to 16 feet [5 meters] long and 1,300 pounds and can attack like a great white shark, but with a stronger bite. Though primarily a deep-sea species, some make trips to the shallows at night, allowing for the unsuspecting night-diver to chance upon them.

Greenland shark: This is one of the largest sharks in the world, reaching up to 24 feet [7.3 meters] in length. It is probably the most northern-ranging of shark species, living mainly in deep, very cold water of the high North Atlantic and Arctic Oceans The species has been found at a depth of more than 7,000 feet [2,130 meters], yet stomachs of some specimens have contained polar bear, pieces of horse and even an entire reindeer. Whether those animals were eaten at the surface or scavenged from the bottom is not known.

Megamouth shark: This species was only first discovered in the ocean in 1976; with only about 50 sightings worldwide, it remains one of the poorly known sharks. This species filters plankton from the water, a feeding mode that it may have evolved independently from the two other known filter-feeding sharks, the basking shark and whale shark.

We know that all sharks are important to human well-being. Some evidence of this is well-proven; other potential benefits remain unstudied. We know that sharks keep the food web in check and are a vital part of healthy fisheries. They boost local economies through ecotourism, have the potential to cure a variety of diseases, are a vital part of the carbon cycle and inspire smart design in items ranging from swimsuits to mechanisms that harness wave energy.

Studying deep-sea sharks in particular could bring us valuable knowledge. Science is on the cusp of understanding the power of genomes in nature. These deep-sea sharks, along with other specialized deep-sea organisms, including bacteria and worms that live on the seafloor, contain an infinite encyclopedia of genetic knowledge that has allowed them to survive in the most extreme environment on our planet. Their evolutionary secrets could open doors to understanding our own existence and survival on Earth.

One thing we do know is that sharks in all parts of the ocean are under pressure from human activity. Overfishing and unsustainable practices, like shark finning, account for the death of an estimated 100 million sharks per year. Even these deep-water dwellers face these threats.

The oceans’ depths are no doubt hiding many more secrets that human beings have yet to lay eyes upon. The Megalodon — an extinct shark the size of a school bus — may be gone, but there is still a whole range of deep-sea sharks in our oceans waiting to be studied, with probably others waiting to be discovered. As long as we can give them the same attention and protection we give to great white, tiger and bull sharks, I know there is much we can learn from them about how our oceans work.

Noise pollution has now become one of the common themes of human-generated impacts on the ocean. Shipping noise, military sonar, and seismic airgun surveys are increasingly becoming part of the public discussion in marine conservation. These noises are easy for us to understand; they are loud, ubiquitous, and they are all in the range of human hearing. We can all imagine what it must be like having an expressway of supertankers and cargo vessels plying the shipping lanes over our heads, or being subjected to ear-piercing tactical sonar signals.

But there is a flood of noises creeping into the ocean that, while we humans can’t hear them, may prove equally as insidious as the loud noises that we can hear. Dolphins, porpoises, beaked whales, and sperm whales – the “toothed whales”–use high frequency bio-sonar, so their sound frequency sensitivities reach well above the frequencies that we humans can hear.

Some of their fish prey can also hear these higher frequencies as an adaptive measure against predation. And while we don’t yet have evidence of seals using bio-sonar, we do know that many seals also hear sounds well above the highest frequencies that humans can hear.

While marine technologists don’t seem to be giving it a lot of thought, our sonar technologies are increasingly crowding out these higher frequency bands with underwater acoustical beacons, echo sounders, and underwater communication systems. The spectrogram below (and the ones accompanying the sound examples) is a method of visualizing sound with time on the horizontal “x” axis, and frequency on the vertical “y” axis. The lower frequencies are closer to the bottom.

This particular spectrogram from NEPTUNE Canada displays a year of sound near the sea floor in the ocean off of Vancouver Island.

In the figure there is a thick cyan line just between the 30 kHz and 40 kHz index lines going across the entire year. This is from an upward-looking echo-sounder used to measure ocean currents. This signal is way above our hearing range, so we call it “ultrasound.” But this sound is right in the middle of the hearing range of orcas, dolphins, and porpoises.

The echo-sounder signal is not complex, but it is persistent. Communication signals on the other hand are necessarily complex and can sound quite obnoxious (these examples are in the human auditory range).

Increasingly, these types of sounds are being used to control equipment, report on sensor conditions, and even monitor the movement of tagged sharks. Given that some of these high frequency signals are designed to broadcast up to 10 kilometers (6 miles), the increasing density of these signals in the ocean may be cropping up as a problem for the animals that can hear them.

Yet relief may be within reach. While the ocean is getting louder with the sounds of mechanization and technology, it was not necessarily quieter before the industrialization of shipping. The ocean was probably a pretty noisy place before the 20th century due to biological noise. Since the industrialization of whaling and fishing millions of whales and perhaps 90% of all fish have been pulled out of the sea–along with all of their noises.

The difference, of course, is that these “legacy noises” were natural. This may or may not be significant with the broad-band mechanical noises of ships or the loud pulsing of seismic surveys, but it is possible that technical communication signals could be crafted to sound more like animal communication sounds, and less like the antagonistic sounds currently in use.

We know that some of these community animals can be quite loud, and that for the last 30 million years they have been swimming around in large groups. If technical communication signals sounded more like animal communication signals they may fit right in!

Subsea telemetry acoustic transceivers used in offshore oil operations (Illustration: Nautronix)

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Michael Stocker on Alaska Bowpicker

Michael is the founding director of Ocean Conservation Research, a scientific research and policy development organization focused on understanding the impacts of, and finding technical and policy solutions to the growing problem of human-generated ocean noise pollution. He is a technical generalist conversant in physics, acoustics, biology, electronics, and cultural history, with a gift for conveying complex scientific and technical issues in clear, understandable terms.

He has written and spoken about marine bio-acoustics since 1992, presenting in national and regional hearings, national and international television, radio and news publications, and in museums, schools and universities.

His book titled “Hear Where We Are: Sound, Ecology, and Sense of Place” is published by Springer. The book reveals how humans and other animals use sound and sound perception to establish their placement in their environment, and communicate that placement to others.