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In the biochemistry book I'm reading (Box 10-1, Lehninger Principles of Biochemistry), an example is given in whales of how spermaceti (a wax located in the whale head), when at sea level is a liquid, and allows the whale to float due to its buoyancy.

As the whale dives deeper, the wax turns into a solid (due to the colder temperatures), and hence this more dense wax is less buoyant and prevents the whale from floating back up due to the greater density of the seawater at these depths.

My limited understanding is that density effects buoyancy in so far as that the weight of the object displaces an equivalent weight of water. If the quantity of the water displaced is small enough that the surface area of the object isn't completely submerged, it can float.

Now with the whale example, considering the wax is fully enclosed by the head, how would this change in local density effect the buoyancy of the whale as a whole? The weight of the wax still remains the same (in so far as the example used in the book), the only thing that changes is its density inside the whale.

So with a constant weight, and only a variable local density enclosed by an object (the head) and limited to these conditions only (as this is all the example in the book uses), how is this possible?

user438383
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user4779
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  • It's volume, not weight that matters. I assume the solid wax takes up less space, and is therefore less buoyant. – MattDMo Jul 18 '15 at 05:51
  • So even if the volume of the head remains the same, this still holds? Ie: the local change in volume of the wax effects the overall buoyancy? – user4779 Jul 18 '15 at 06:02
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    This page and its associated references seem to have your answer. It seems there are a number of hypotheses on the function of spermaceti, with buoyancy control being least likely. – canadianer Jul 18 '15 at 06:06
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    @user4779 Your right that, with mass constant, the volume of water displaced by the head would have to change to affect buoyancy. Either the hand would have to shrink or water you have to be taken inside the organ. – canadianer Jul 18 '15 at 06:08
  • @canadianer That makes sense, a change in volume of the head. Can I conclude the example in the book is misleading? I quote exactly: " When the temperature of the oil is lowered several degrees during a deep dive, it congeals or crystallizes and becomes denser. Thus the buoyancy of the whale changes to match the density of seawater." Without any further specification of any other mechanisms involved, or any reference to volume. – user4779 Jul 18 '15 at 06:16
  • @user4779 here's a different example. Say I have an airtight plastic bag filled with warm liquid wax. I toss it in cold water and it floats, because it's less dense than the water it's displacing. However, if I leave it there and the wax solidifies, it will become more dense (same weight, smaller volume) and may become either neutrally bouyant or it will sink, depending on the exact density change. This is what the example in your book was trying to get at, but apparently facts got in the way... – MattDMo Jul 18 '15 at 06:27
  • @MattDMo, interesting, that would explain it. Would this be due to a decrease in the surface area of the plastic bag, or is this irrelevant? For example if there was a large ship. Would putting all the cargo into one central spot versus spreading the cargo out, affect the buoyancy, where the surface area wouldn't change? – user4779 Jul 18 '15 at 06:40
  • @user4779 The plastic bag is irrelevant, it's just there as a container for the liquid wax. Assume it is infinitely thin and infinitely flexible, with zero effect on the overall process. Buoyancy in water is directly related to the weight of the water that is displaced by an object - if the object weighs less than the weight of the water it displaces, it will float. Remember Archimedes - he was getting into his bath, and his body displaced the water, causing it to overflow the tub. That's what made him run down the street naked yelling "Eureka!" (Greek for "I have found it!"). Supposedly. – MattDMo Jul 18 '15 at 06:55
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    If you haven't already, try reading through this. It may help. – MattDMo Jul 18 '15 at 06:57
  • The important thing is that yes, the volume of the whale would have to decrease. This is quite normal for animals, every time you urinate, your body decreases its volume, it doesn't replace the urine with an equal volume of air. The surface area is not important in itself. – Lefty Jul 18 '15 at 07:07
  • @MattDMo could you please share, how is this concept be applied to body functions? Clinical wise I found hydrotherapy. – bonCodigo Jul 18 '15 at 16:15
  • @bonCodigo could you please clarify? What body functions are you talking about? – MattDMo Jul 18 '15 at 16:52
  • What version of Lehninger do you have? I just skimmed through section 10 (Lipids) of the 6th edition and found no mention of spermaceti. – canadianer Jul 18 '15 at 17:48
  • This is for the 5th edition, page 347, part 10.1. – user4779 Jul 19 '15 at 01:44

2 Answers2

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The buoyancy theory of the function of the spermaceti organ has essentially no empirical support. On the contrary, there is overwhelming support for the idea that the spermaceti organ, together with the associated structures named the "monkey's muzzle" and the "junk" (named so by whalers) are sound producing and focusing structures. The sound production theory was originally proposed by Norris and Harvey (1972) and has gained substantial support from experimental studies within the last decades. See for example Møhl et al (2003). In brief, the sounds are produced by air being pressed through the monkey's muzzle in the front of the nose, just below the blowhole. The sound is transmitted through the spermaceti oil in spermaceti organ, reflected by a parabolic mirror created by small air-pockets on the front of the skull and transmitted forward again through spermaceti-filled 'acoustic lenses' (known as the 'junk') below the spermaceti organ and into the water as an extremely directional and powerful sound beam. Next time you happen to see a sperm whale skull in a museum, take a look at the skull and once you see it, it is very difficult to see what else could explain the strange shape of the forehead.

The buoyancy model for the spermaceti organ on the other hand has some severe shortcomings. The theory is that the whale sucks in cold water through the blowhole when it wants to dive, hereby cooling and solidifying the spermaceti. The density increases by this cooling, making the whale sink. When the whale wants to surface, it heats the spermaceti by means of warm blood, whereby it expands and the whale rises. However, this would require a massive blood supply to the nose, inconsistent with anatomy, and the experimental data gathered by data recorders on diving sperm whales have shown no indication of water being inhaled upon diving. On the contrary, observations are entirely consistent with the airways being airfilled during the dive and involved in the sound production (Wahlberg et al. 2005). See also the paper by Cranfort et al (1996) where a plausible evolutionary explanation to the origin of the spermaceti organ is proposed.

  1. Cranford, T. W., Amundin, M. and Norris, K. S. 1996. Functional morphology and homology in the odontocete nasal complex: implications for sound generation. Journal of Morphology 228:223-285.
  2. Norris, K. S. and Harvey, G. W. 1972. A theory for the function of the spermaceti organ of the sperm whale (Physeter catodon L.). Pages 397-417 Animal orientation and navigation. NASA, Washington DC.
  3. Møhl, B., Wahlberg, M., Madsen, P. T., Heerfordt, A. and Lund, A. 2003. The monopulsed nature of sperm whale clicks. Journal of the Acoustical Society of America 114:1143-1154.
  4. Wahlberg, M., Frantzis, A., Alexiadou, P., Madsen, P. T. and Møhl, B. 2005. Click production during breathing in a sperm whale (Physeter macrocephalus) (L). Journal of the Acoustical Society of America 118:3404-3407.
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    Welcome to Biology.SE. Thank you for taking the tour and putting in the effort to craft what looks to be an excellent answer. I hope we see more from you in the future! – tyersome Apr 23 '22 at 17:56
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Buoyancy is controlled by "Archimedes' principle", as described in Britannica:

... any body completely or partially submerged in a fluid (gas or liquid) at rest is acted upon by an upward, or buoyant, force, the magnitude of which is equal to the weight of the fluid displaced by the body.

Here the weight is a force, not a mass, so the force that pushes an object is related to the density and volume of the object itself. In this context, considering the spermaceti, it's the temperature of the oil that matters, because it's going to change its density, thus the buoyancy force. However, the example you are referring to is a hypothesis on the spermaceti function developed by Clarke (1978). In summarizing, he stated that sperm whales are almost neutral at the surface, so they need to control their buoyancy in order to dive. So, it's possible they change the vascularization on the head (but also the blubber!) to change the density and descend or ascend.

Still, this remains a hypothesis that has not been confirmed nor rejected. Miller et al. (2004) found data that don't support the theory proposed by Clarke, as the change in temperature and so density in the spermaceti should not be relevant for buoyancy during dives and sperm whales are not neutral at the surface; moreover, they actively swim while searching for food at the bottom, so they contrast the buoyancy force. A more studied and developed theory for the function of the spermaceti system (with the nasal apparatus) is that sound production and the change in density has a relevant role found for sound transmission.

Full references:

  1. Clarke, M. R. (1978). Buoyancy control as a function of the spermaceti organ in the sperm whale. Journal of the Marine Biological Association of the United Kingdom, 58(1), 27-71;
  2. Miller, P. J., Johnson, M. P., Tyack, P. L., & Terray, E. A. (2004). Swimming gaits, passive drag and buoyancy of diving sperm whales Physeter macrocephalus. Journal of Experimental Biology, 207(11), 1953-1967.
Cristina Marcolin
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