For several decades, scientists have been baffled by a mysterious hole in Antarctic ice that opens and gapes at times, leading to the exposure of its cold and dark water underneath. It appears that the last puzzle pieces have finally been uncovered.
Antarctic Sea Ice Hole
In the sea ice that crusts over the Antarctic Weddell Sea, which is close to Maud Rise, which is a submerged peak, there is a massive hole that opens and gapes at times. This led to the exposure of its cold and dark waters beneath.
The hole was first seen in 1974 and does not appear each year. Because of this, scientists have been wondering about the conditions necessary for it to be produced.
Antarctic sea ice holes, called polynyas, can be frequently seen near the shore. Marine mammals, such as whales and seals, use them for catching their breath.
These holes are less common across the sea. In fact, the Maud Rise polynya has baffled scientists since it was first seen in a satellite image 50 years ago. It was found in 1974 to be roughly the size of New Zealand. It returned in both 1975 and 1976. However, after this, its return was only brief anduntik. This was until scientists thought that it could be permanently gone.
However, things took a turn in 2016 and 2017 when it came back as a hole as big as Maine. Since the 1970s, the 2017 Maud Rise polynya was the longest-lived and largest example of such a phenomena.
Now, since it reappeared in 2016 and 2017, a solution has been uncovered. With the help of floating autonomous instruments, satellite imagery, seals that wear hats, and computational modeling, scientists were able to find that the missing piece involved wind that drags water layers in order to produce what is called an Ekman spiral.
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Mystery of the Giant Sea Ice Hole
Alberto Naveira Garabato, an oceanographer from the University of Southampton in the UK, says that Ekman transport was the vital missing piece necessary for boosting salt balance and sustaining the mix of heat and salt towards surface water.
Data taken from various sources showed that different factors contributed to the hole. All of them had to align in just the right way in order for the polynya to be produced.
One of the factors was the Weddell Sea's circular current. This was quite strong in 2016 and 2017, leading to the upwelling of warm and notably salty water.
Fabien Roquet, an oceanographer from the University of Gothenburg, explains that such an upwelling helps shed light on the melting of sea ice. However, with the melting of sea ice, this results in the surface waters freshening. This, in turn, must stop the mixing. Hence, there should be a different process that is happening in order for the polynya to persist. An additional salt input must be coming from somewhere else.
Salt is capable of lowering water's freezing point significantly. Hence, if the polynya's water is quite saline, this could explain the persistence of the hole. Hence, the team revisited the data and the ocean computation models in order to find out where the added salt was from.
They found that rough eddies that were generated as the current of Weddell Sea flows around Maud Rise ends up transporting salt to the seamount top.
Ekman transport then takes over from this point. This happens when wind blows over the surface of the ocean making a drag. Water does not just end up getting pulled along. Rather, it gets deflected sideways, similar to a boat wake, leading to the spiraling of the water like a screw. As the water's top layer moves with the wind, water from beneath goes up in order to replace it.
For the Maud Rise polynya's case, the upwelling water carries a salt buildup that hovers around the Maud Rise. This prevents the hole from freezing over.
This is crucial to helping scientists know what will happen to the sea ice of Antarctica in the future. This could also lead to implications for the oceans of the world.
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