A team of researchers has confirmed the cliché that we know more about the surface of the Moon than we do about the bottom of the sea. They have revealed an enormous stretch of the Southern Ocean where sediments are building up at a rate that dwarfs other deep ocean locations. The discovery could greatly improve our knowledge of the world’s climate history.
Across most of the oceans the deposition of sediment is a slow process. Dr Adriana Dutkiewicz of the University of Sydney told IFLScience: “There are places at the edges of continents where it is rapid, as a result of erosion on land.” With this exception, however, rates of less than 1 centimeter (0.4 inches) per thousand years are near universal.
Nevertheless, Dutkiewicz and some colleagues decided to create a map of these rates throughout the ocean, as part of a process of learning what influences the differences. They used data from seismic profiling surveys, which bounce sound waves off the bottom of the ocean to measure the depth of sediment. The age of the crust beneath can be determined using the magnetic properties of the rocks, Dutkiewicz told IFLScience. Combine these two and it is possible to see how fast, on average, the sediment is building up.
Dutkiewicz discovered that along an enormous stretch between Australian and Antarctica, the rate is more than 5 centimeters (2 inches) per thousand years. She explained to IFLScience that the unusually powerful deep sea currents in the Southern Ocean kick up sediments from elsewhere and carry them along until they meet the Southeast Indian ridge. Just as winds drop their rain when they pass over mountains, the currents drop the sediment, which settles on the ridge.
Dutkiewicz is first author of a Geology paper exploring the implications of the discovery. The rapid settling zone stretches for 8,000 kilometers (5,000 miles), which the authors note is the distance from London to Los Angeles, yet until recently no one had any idea it existed.
The discovery does more than simply reveal our ignorance about the deep sea. It demonstrates how powerful the bottom currents are in this part of the Southern Ocean. More importantly perhaps, it represents a huge resource for climatologists. Ocean sediments contain multiple indications of the temperatures when they were laid down, but in most cases build up so slowly that the resolution is very limited – short spikes or drops in temperatures can't be detected when layers are too thin.
The rapid deposition along the ridge will provide superb resolution over the 3 to 5 million year lifespan of the local crust for anyone who braves the mighty storms of the Southern Ocean to collect core samples.
The discovery also provides a poignant illustration of how much science's horzions have shrunk in recent decades. Dutkiewicz told IFLScience the data she used was collected in the 1960s, the only time sediment depth and magnetic polarities in the area have been studied. It has been more than 40 years since humans visited the Moon, and longer still since we surveyed the floor of the Southern Ocean.
The speed of the currents in the deep southern ocean contributes to the rapid sediment build up. Dutkiewicz et al/Geology
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