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Ocean Research


May 2012 Issue

Researchers Sample Pacific to Study Fukushima Radiation
A team of scientists researching the amount, spread and impacts of radiation released into the ocean from nuclear reactors in Fukushima, Japan, has found that the concentration of several radionuclides was elevated but varied widely across the study area. The reactors at the Fukushima Dai-Ichi nuclear power plant were severely damaged in the Tohoku earthquake and tsunami last year.

Although radioactivity levels in marine life sampled during the cruise were well below levels of concern for humans and organisms, the researchers still question whether radioactive materials are accumulating on the seafloor sediments and, if so, whether these might pose a long-term threat to the marine ecosystem. Among the materials released were cesium-134 and -137, two radioactive isotopes that do not occur naturally in the ocean. The results of the 15-day cruise were published in the Proceedings of the National Academy of Sciences in April.

The group departed Yokohama, Japan, in June aboard the RV Ka'imikai-o-Kanaloa and sailed a sawtooth pattern that began 600 kilometers offshore and came as close as 30 kilometers from the power plant. Along the way, the group conducted water sampling from the surface to as deep as 1,000 meters and made more than 100 net tows to collect samples of phytoplankton, zooplankton and small fish. They also released two dozen drifters.

The group found that the Kuroshio acted as a barrier that prevented the movement of radionuclides to the south. Aside from the samples taken from within sight of the reactors, the samples with highest levels of radionuclides were those taken much further south along the coast of Ibaraki. The drifter tracks showed an eddy had formed in the area and hugged the coast, drawing in contaminated water. For more information, click here.

Challenger, Argo Data Show Ocean Warming Over 100 Years
A study published in April contrasting ocean temperature readings of the 1870s with temperatures of the modern seas reveals an upward trend of global ocean warming spanning at least 100 years.

The research, led by Scripps Institution of Oceanography physical ocean'ographer Dean Roemmich, shows a .33° C average increase in the upper portions of the ocean to 700 meters depth. The increase was largest at the ocean surface, .59° C, decreasing to .12° C at 900 meters depth.

The report is the first global comparison of temperature between the HMS Challenger (1872 to 1876) voyage and modern data obtained via the Argo float program. Scientists have previously determined that nearly 90 percent of the excess heat added to Earth's climate system since the 1960s has been stored in the oceans. The new study pushes the ocean warming trend back much earlier.

'The significance of the study is not only that we see a temperature difference that indicates warming on a global scale, but that the magnitude of the temperature change since the 1870s is twice that observed over the past 50 years,' Roemmich said. 'This implies that the timescale for the warming of the ocean is not just the last 50 years but at least the last 100 years.'

Although the Challenger data set covers only some 300 temperature soundings (measurements from the sea surface down to the deep ocean) around the world, the information sets a baseline for temperature change in the world's oceans, which are sampled continuously with 3,500 free-drifting, profiling Argo floats that each collect a temperature profile every 10 days. For more information, click here.

Dead Sea Nearly Dried Up 100,000 Years Ago, TAU Says
Rapidly dropping water levels of the Dead Sea, the lowest point on the earth's surface heralded for its medicinal properties, has been a source of ecological concern for years. Now a drilling project led by researchers from Tel Aviv University (TAU) and Hebrew University reveals that water levels have risen and fallen by hundreds of meters over the past 200,000 years.

Directed by professor Zvi Ben-Avraham of TAU's Minerva Dead Sea Research Center and professor Mordechai Stein of the Geological Survey of Israel, researchers drilled 460 meters beneath the sea floor and extracted sediments spanning 200,000 years. The material recovered revealed the region's past climatic conditions and may allow researchers to forecast future changes.

Layers of salt indicated several periods of dryness and very little rainfall, causing water to recede and salt to gather at the center of the lake. During the last interglacial period, approximately 120,000 years ago, the sea came close to drying up entirely, the researchers found, with another period of extreme dryness taking place about 13,000 years ago.

Today, the Dead Sea lies 426 meters below sea level and is receding rapidly. Despite this historical precedent, there is still cause for concern, said Ben-Avraham. In the past the change was the result of natural conditions. Today, the lake is threatened by human activity, as water is increasingly being taken from rivers for irrigation before it reaches the Dead Sea, preventing the refilling of the sea. For more information, click here.

Researchers Use Crowdsourcing App to Track Fish Mortalities
Scientific and educational organizations led by Woods Hole Group have developed a free smartphone app to study fish deaths in Buzzards Bay in Massachusetts.

The Buzzards Bay Fish Mortality app utilizes collected data from citizens who encounter dead fish at Buzzards Bay. The goal is to collect enough data to verify reports of large numbers of fish mortality in the area. The app utilizes mCrowd, a crowdsourcing platform developed by the University of Massachusetts Amherst. It is available for iPhone and iPad users, and an Android version is expected to launch this summer.

Drop-down and multiple-choice menus allow the user to input the date and time they encountered the fish, the approximate number of dead fish observed, the species and the location. Users can also upload photos and leave additional comments. The information is sent to a database at Woods Hole Group where a team of scientists will compile it, analyze it over time and try to understand whether the deaths are natural or indicative of stressors in the waters. For more information, click here.


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