Iceberg Scars on Seafloor Offer Clues to the Past

Posted by on Mar 28, 2017

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Many people know the phrase “tip of the iceberg,” which acknowledges that most of the iceberg sits underwater, but few know what the bottom of an iceberg is capable of. Scientists recently found scars in the North Falkland Basin, north of the Falkland Islands, created by icebergs when they plowed into the seafloor. Known as scours, these u-to-v shaped scars can inform researchers about the Earth’s past in terms of climate, geography and ocean currents. Christopher Brown et al. recently published a paper on the topic in the journal Marine Geology, presenting their latest findings.

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Scours recently found in the North Falkland Basin (Source: Marine Geology).

In the paper, the researchers note that the icebergs responsible for the scours in the North Falkland Basin likely calved from glaciers in the Antarctic Peninsula. The size of the icebergs must have been immense in order for them to travel 2,000 kilometers and still leave marks on the seafloor hundreds of meters below. Given the freshness and reworking of the scours in the North Falkland Basin, researchers believe they likely formed during the Last Glacial Maximum (LGM), the time period when glacier and ice sheets dominated the globe and Antarctica was larger than it is today.

Christopher Brown et al. later found and analyzed the scours using five high-quality 3-D seismic data sets covering an area of 1550 km². From analyzing the curvature of the scours, researchers can determine what kind of tides and currents were active thousands of years ago. Scours can also inform scientists about southern hemisphere climatology and ocean patterns.

In the North Falkland Basin, Christopher Brown et al. found scours at depths ranging from 280 to 460 meters below sea level, while the depth of the basin reaches up to 2,500 meters. The researchers also located scours measuring nearly 10 meters deep, 38 kilometers long, and one kilometer wide. These scours may have meandered due to the rotation of the iceberg’s keel, or underside, when pushing into the seafloor. External forces that may have also caused a direction change can include ocean currents, tidal changes, subglacial calving, subglacial drainage and storms. Analyzing the location, curvature and orientation of scours provides scientists with insight into the Earth’s past.

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Diagram of an iceberg forming a scour (Source: Creative Commons).

For example, the icebergs in the North Falkland Basin were likely carried by the East Falkland Current, an important northward current along the east side of Argentina that brings fresh, cold water north from Antarctica. This suggests that the current was active in the LGM and sheds light on the ocean-climate interactions in the southern hemisphere’s past.

Christopher Brown et al. determined that a collection of icebergs may have even formed an iceberg “graveyard,” suggesting there may have been an ice bridge from Argentina to the Falkland Islands at some point in time. This means that the icebergs would have traveled on the east side of the Falkland Islands in order to get to the basin.

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A map of currents in the waters between Antarctica and South America (Source: Marine Geology).

In the northern hemisphere, scour marks have been found far away from where they were sourced, in the low-to-mid latitudes along the southern Atlantic United States coast, for example. In the southern hemisphere, few iceberg scours have been found outside of Antarctica, particularly in the mid-latitudes. The recent findings in the North Falkland Basin support the idea that icebergs could travel into warmer waters farther north of 50°S, the approximate location of the Falkland Islands. Rarely have icebergs been recorded north of the Falklands, but a few mega icebergs were spotted between 1979 and 2003.

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A large iceberg (Source: Pal Lter/Flickr).

With much of the ocean floor still unexplored, there are likely more scours yet to be discovered that can tell scientists more about the planet’s past. As the scours in the North Falkland Basin suggest, scours can be useful in unlocking information about climate, oceans and geography from thousands of years ago, by leaving marks at great distances, providing valuable clues to our planet’s history.

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