A new paper describes the slowly rotting skeleton of a whale on the seafloor near the South Sandwich Islands, between South America and Antarctica. Why is such a thing exciting to geologists? There are a couple of reasons.
When whales die, they drop dead wherever they happen to be. If they beach themselves first, their corpses lie on the beach, but most whales pass away at sea and sink. Once on the seafloor, their decomposing bodies, called “whale falls,” amount to a winning lottery ticket for a host of creatures, which gather around the corpses and settle in to live off them. The flesh goes first, then come the fat-filled bones. The biological communities that arise may last for decades, perhaps centuries, depending on the local conditions.
Biologists are interested in whale falls as lovely self-contained examples of oceanic food chains. Geologists see whale falls as a rich study in taphonomy, their name for everything that happens to organisms as they become fossilized.
If you think about the exquisite fossils you see in museums, the marvel is how clean they are, as if a taxidermist had prepared them for burial. But nature is a lousy taxidermist. For every perfect museum skeleton there are drawers backstage stuffed with thousands of bony fragments, incomplete and imperfect in many ways. But what the fossil collector sees as lamentable damage, the paleontologistspecifically the taphonomistsees as possible environmental data. Everything from the tooth marks of scavengers to the scrapes made by construction-site bulldozers is the kind of evidence that geology prizes for insight into the living world of the deep past.
Some of the first whale falls studied by scientists were found by the U.S. Navy while they were searching for something they’d dropped. Most whale-fall research, however, is done on carcasses that are towed away from beaches and deliberately placed on the seafloor. That kind of research is quite young, though, and to learn about the late stages of whale-fall existence we need natural examples that are older. It is way too expensive to just dive down and look around for them, so we have to grab the opportunities that arise while we’re looking for other things.
The new paper was published in the journal Deep Sea Research Part II: Topical Studies in Oceanography in January (read it online). The British research ship James Cook was surveying a blown-out seafloor volcano full of hydrothermal vents (white smokers) when it spotted whale bones. The scientists alertly carried out a state-of-the-art study using the ship’s underwater roving vehicle Isis, making a thorough video survey and grabbing some bone samples. It is only the sixth time that a natural whale fall has been examined in this much detail, and the first case from the Southern Ocean where whales are most abundant.
The paper is full of the kind of information that can be applied to fossils as we get our bearings in this field. The different stages of life on a whale fall leave different signs in the bones. The subject is complex, but that’s what science is for. And the Bay Area’s younger rocks, especially in the Santa Cruz area, are full of whale fossils. Modern whale falls can inform our understanding of the ancient times in which those whales lived and died around here.
Another thing that interests geologists, especially students of evolution, about whale falls is their role in the deep sea environment. Hospitable places in the deep sea are stepping stones for life, like oases in a desert or gas stations in Nevada. Many of the same species on whale falls also live on hydrothermal vents, which exist only in places where tectonic plates are spreading apart. Whale falls are scattered more randomly and allow the vent species to “island hop,” keeping the seafloor a unified biome.
These matters are relevant to how Earth operates. The deep seafloor can be a source of new species when mass extinctions strike the surface world, and vice versa. How did this work before whales existed? Are there signs in the fossil record, or in the genetic records of living species, of this process at work in the past? Those are the scientific topics that this new set of whale bones will help us address.