Oceanography

Though the end of the 20th century looked like we were going to see runaway temperatures around the globe, that hasn't really happened despite countries like China and Russia and Mexico and India continuing to belch CO2 into the atmosphere.

More than a dozen hypotheses have been proposed for the so-called global warming hiatus, ranging from air pollution to volcanoes to sunspots and now the University of Washington has entered the fray, saying that the heat absent from the surface is plunging deep in the north and south Atlantic Ocean, and is part of a naturally occurring cycle. 

For the first time, scientists have mapped elevation changes of Greenlandic and Antarctic glaciers.

For the new digital maps, the researchers evaluated all data by the CryoSat-2 altimeter SIRAL. Satellite altimeter measure the height of an ice sheet by sending radar or laser pulses in the direction of the earth. These signals are then reflected by the surface of the glaciers or the surrounding waters and are subsequently retrieved by the satellite. This way the scientists were able to precisely determine the elevation of single glaciers and to develop detailed maps. 


During the last ice age, a large part of North America was covered with a massive ice sheet up to 3 kilometers thick and that is a key reason why the sea level was then about 120 meters lower than it is today. 

During the cold stadial periods of the last ice age, massive ice sheets covered northern parts of North America and Europe. Strong westerly winds drove the Arctic sea ice southward, even as far as the French coast. Since the extended ice cover over the North Atlantic prevented the exchange of heat between the atmosphere and the ocean, the strong driving forces for the ocean currents that prevail today were lacking.


By Raquel Vaquer-Sunyer, Lund University

The world’s oceans are plagued with the problem of “dead zones”, areas of high nutrients (such as nitrogen and phosphorus) in which plankton blooms cause a major reduction of oxygen levels in the water. Sea creatures need oxygen to breathe just as we do, and if oxygen levels fall low enough marine animals can suffocate. This commonly happens around coastlines where fertilisers are washed from fields into rivers and the sea, but also mid-ocean, where currents trap waters in gyres (large systems of rotating ocean currents).

Interpreting snow depth records from past decades is as much art as science. Even into the 1990s, Soviets on Arctic drifting sea ice used meter sticks and handwritten logs to record snow depth. Today, things are a lot more accurate. Airborne measurements are validated by researchers on the ground using automated probes similar to a ski pole. 

Accuracy is important. The public has become concerned about what is happening at the poles, and so research led by NASA and the University of Washington combined data collected by ice buoys and NASA aircraft with historic data from ice floes staffed by Soviet scientists since the late 1950s through the early 1990s to track changes over decades. 


Between Greenland and Spitsbergen, scientists have found the scours on the sea bed left behind by gigantic icebergs - about three times the height of the Empire State Building. The five lineaments, at a depth of 1,200 meters, are the lowest-lying iceberg scours yet to be found on the Arctic sea floor, and provide insight into the dynamics and the extent of last Ice Age and the Arctic ice sheet thousands of years ago.  

"Whenever icebergs run aground, they leave scours on the seabed. Depending on their depth and location, those markings may continue to exist over long periods of time," explained Jan Erik Arndt,  Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) bathymetrician and lead author of a new paper on the subject.  


As the complex story of climate change unfolds, many of the forecasts are grim, but there are exceptions - the lowest-oxygen environments in the ocean would get now get worse, they may improve if climate change weakens the trade winds. Areas of extreme low-oxygen waters could shrink.

Warmer water contains less gas, so climate change is expected to reduce oxygen levels worldwide. Observations show this is already taking place in many places. Declines during the past 20 years in the tropical low-oxygen zones, the lowest-oxygen waters on the planet, had led to a 2008 study proposing that these zones would also get worse over time.


Mercury is a naturally occurring element and a part of human enterprises like burning coal and making cement and compact fluorescent light bulbs.

Knowing how much of both natural and unnatural mercury is bioavailable - uptaken by animals and humans— is important in international agreements to protect humans and the environment from mercury emissions and establishing public policies behind warnings about seafood consumption. Yet little is known about how much mercury in the environment is the result of human activity, or even how much bioavailable mercury exists in the global ocean.


Warming temperatures are causing Arctic lakes to release methane, a greenhouse gas that has 23X the short term warming effect of CO2, it has been said. A new paper in Nature found that Siberian lakes have actually pulled more greenhouse gases from the atmosphere than they have released into it since the last Ice Age

That is causing an overall slight cooling effect. Permafrost, especially that in the Siberian Arctic, contains significant amounts of all organic carbon found on Earth locked away in frozen soils. Warming global temperatures in the 15,000 years since the last Ice Age have begun to thaw the permafrost, leading to the widespread formation of lakes. 


As the climate warms and sea ice retreats, the North is changing. An ice-covered expanse now has a season of increasingly open water which is predicted to extend across the whole Arctic Ocean before the middle of this century. Storms thus have the potential to create Arctic swell – huge waves that could add a new and unpredictable element to the region.
A University of Washington researcher made the first study of waves in the middle of the Arctic Ocean, and detected house-sized waves during a September 2012 storm. 

"As the Arctic is melting, it's a pretty simple prediction that the additional open water should make waves," said lead author Jim Thomson, an oceanographer with the UW Applied Physics Laboratory.