Chapter 4:
Diving - Problems and Adaptations
The problems with going deep
- Pressure - pressure increases by 1 atmosphere for each 10 meters, in addition when one depressurizes too quickly, dissolved gases can form bubbles that lodge in critical organs, a condition called "the bends"
- Oxygen storage - some marine mammals will stay down as long as 90 minutes
- Nitrogen narcosis - air is 70% nitrogen, nitrogen can become toxic at high pressures causing a type of intoxication
- The Cold - below 200 meters water temperatures approach freezing
- Buoyancy - most mammals float
The Bathyspere - 1930 (image is from Wikipedia Commons)
How humans adapt to these problems
- Submarines, closed steal and titanium containers with small thick windows
- Compressed air, or other gas mixtures in steal containers
- Decompression chambers, diving charts, slow assents and descents
- Wet suits, insulated dry suits
- Submersibles may have thousands of pounds of lead weights attached to help them sink
Sperm Whale Diving
Marine Mammal Adaptations
The sperm whale, seen in the picture above, is the diving world champion of marine mammals. The whale can stay under water for over 90 minutes and dive to depths of nearly 10,000 ft. It has an extraordinary array of adaptations that allow it to dive so deep. Read below to see how marine mammals, in general, deal with the problems associated with going deep.
Austrailian Sea Lion
Problem 1: Pressure
When you and I go underwater, the first thing we may notice is that our ears hurt. This is because of the difference in pressure between the air in our ears and the water outside. Air (as a gas) can be compressed while water cannot. At sea level a body experiences 14.7 pounds per square inch of pressure (1 atmosphere.) For a diving marine mammal, another atmosphere of pressure is added every ten meters that they go down. Thus a male elephant seal diving to 1000 meters is experiencing 100 times the pressure that he would at the surface.
Over time, most marine mammals have lost their external ears and sinuses. Without these air chambers, a diving marine mammals does not suffer the effects of changing pressure. Sea lions and fur seals do have ears, but during a dive theirs will fill with a bloody fluid, forcing any air out.
Mammals store more air in their lungs than any other place. If you were to swimming, it would only make sense that you would take a deep breath before you went under. This is a problem for two reasons. First, air is buoyant, making diving difficult. Second, as was mentioned above, air is easily compressed, leading to a potential collapse of the lungs. Most marine mammals have lungs that are designed to collapse. They tend to be long and tubular with built-in protective rings to keep valves open. Also, unlike you and I, marine mammals exhale right before a dive. They have very muscular and effcient lungs which can exhale up to 90% of the air in their lungs in any give breath (an athletic human can do around 10%.) Thus, by removing the air from their body, a diving marine mammal has very little problems with changing pressure.
An elephant seal's heart rate during a dive (Image is from Alaska Sea Grant, used with permission)
Problem 2: Oxygen Storage
So if marine mammals exhale before they dive, how do their muscles get the oxygen they need to work? The answer is that they store oxygen in their blood and in their muscles rather than in their lungs. Marine mammals have a very high blood to body volume ratio. Mare mammas also have a higher percentage of red blood cells than most mammals (human = 36%, seals = 50%.) By comparison, this makes their blood very thick and viscous. Marine mammals also have a high concentration of hemoglobin in their blood and myoglobin in their muscles. Both of these molecules are used to store oxygen.
The mammalian diving reflex allows mammals to lower their heart rate and ultimately survive submersion in water for extended periods of time. Bradiacardia, as it is also know is triggered by cold water contact to the nerves of the face. It occurs in all mammals, but to a much greater extent in marine mammals. Wedel seals have been measured to lower their heart rate to as low as four beats per minute.
When exercising humans run out of oxygen we say that they have gone into anaerobic respiration. This is very taxing on our muscles and leads to soreness and fatigue. Most body organs marine mammals appear to switch to anaerobic respiration while diving without suffering the same effects. We still don't know exactly how they do this.
This figure shows the diving behavior of a male elephant seal. Dives lasting 20-40 minutes of nearly verticle profiles are followed by very short breaks. (Image from the National Marine Mammal Labratory)
Problem 3: Decompression Sickness (aka "the bends")
When human scuba divers come up too quickly from a dive, gases that were dissolved into their blood can come out of solution too quickly and form bubbles inside the blood vessels. These bubbles can get lodged in capillaries and migrate to critical organs, causing pain and possibly organ damage. DCS increases with intensity the deeper you go and the faster you surface. Marine mammals go very deep and surface very quickly. So why don't they have problems with "the bends?" Its simple - they exhale before they dive. No air, no problem. In addition, many marine mammals have an extensive "net" of blood vessels feeding into their brain. Its known as the "retia mirabilia," and it likely serves several functions, but one of them is capturing bubbles that may form in the blood stream.
Bowhead whales can have as much as two feet of blubber insulating acting to insulate their body
Problem 4: The Cold
Many human scuba divers have known the pain and discomfort associate with having a small hole in their wetsuit during a cold water dive. Water dissipates heat from the body much faster than air. A person who falls in water near the freezing point will be hypothermic within a few minutes, yet marine mammals dive to depths where the temperatures approach freezing. The most obvious way that marine mammals stay warm is that they tend to be large and rather "sausage shaped." This shape gives them a low surface area to volume ratio. Per unit volume, there is less of them exposed to cold moving water. Marine mammals also have a lot of blood relative to their body size. Water has a high heat capacity and does a nice job of maintaining body temperature.
Most marine mammals have a thick layer of fat know as "blubber." This fat layer also serves as calorie storage for marine mammals that undergo long periods of fasting. Smaller marine mammals tend to have highly insulated layers of fur. The extreme example of this is the sea otter. Sea otter fur is two layers thick, and very effective at trapping air to aide in insulation. Sea otters may have as many as one million hairs per square inch. That's ten times as many hairs as the average human has on their whole head.
Problem 5: Buoyancy
No part of a mammal is more buyant than the air in their lungs. For marine mammals the key to reducing this buoyancy is to exhale before diving.
Thick billed murres weigh only a pound or two yet can dive up to 100 meters, image from Wikipedia Commons)
Marine diving champions
- thick billed murres – weighing only a pound or two, they can dive up to 100 meters
- elephant seals – to 1500 meters, over 60 minutes, spend 90% of time at sea diving
- emperor penguins – up to 500 meters
- leatherback sea turtles - up to 1200 meters
- beaked whales – up to 2500 meters, staying down as long as 90 minutes
- sperm whales – up to 3200 meters
- to read more go to pbs.org - deepest divers
Questions for Research
- Listen to a narrative of the 1960 dive of the Trieste from Wired Magazine. Explain how the Trieste sunk and then floated back to the surface. Next, click link for PBS: Submersible's through time, select the Deep Flight and compare and contrast how this submersible goes down.
- Listen to an interview with Dan Costa an elephant seal researcher from UC Santa Cruz. Explain how time depth graphs are created for elephant seals. If you want, you can also look through a slide show about how to tag and elephant seal.
- Also from TOPP's webpage. Look at the map of tagged elephant seals. Look at where elephant seals are going to feed. Why do they need to be able to dive so deep.
- Examine the attached diagram of a typical fin whale feeding dive. Look at the fluking pattern (these are beats of their tail.) How hard are they swimming when they dive? How hard are they swimming when they return to the surface? When they are at the bottom of their dive, why do they alternate hard-kicking and fast swimming, with periods of very little kicking and very little motion?
- Sperm whales are not only diving champions, they are also incredibly smart. Read about what happens when sperm whales combine these two traits. Describe what you learn about how Sperm Whales Both Awe and Vex Alaskan Fishermen. If you find this interesting you can also click to see a video of a sperm whale plucking Cod off of a line.
- How do marine mammals store oxygen compared to humans? Be sure to mention the function of hemoglobin and myoglobin. Read page 82 of "Marine mammal biology: An Evolutionary Approach" for details.
- Read the description of the sperm whale from Arkive.org, explain how the spermaceti organ can help to regulate buoyancy in sperm whales.
- Go to howstuffworks.com, explain what "the bends," and from the notes above how marine mammals avoid them.
- Asking howstuffworks.com a slightly different question. Explain the difficulty of being a conscious breather, and how dolphins and whales sleep one half brain at a time because of it.
- List three ways that sperm whales deal with the huge pressure changes that come with their deep dives. You may find the attached article about this topic from Scientific American quite helpful.