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Environmental Monitoring


April 2011 Issue

Huge Flux of Gas, Oil During BP Well Blowout, Study Says
Up to 500,000 tons of gaseous hydrocarbons were emitted into the deep ocean during Deepwater Horizon Gulf of Mexico oil discharge, researchers reported in February in Nature Geoscience.

Such a large gas discharge—which generated concentrations 75,000 times the norm—could result in small-scale zones of "extensive and persistent depletion of oxygen" as microbial processes degrade the gases, the scientists said. The Macondo well blowout discharged not only liquid oil, but also hydrocarbon gases, such as methane and pentane, which were deposited in the water column.

Gases are normally not quantified for oil spills, but the researchers said documenting the amount of hydrocarbon gases released in the BP oil spill is critical to understanding the fate of the released hydrocarbons and potential impacts on the deep oceanic systems.

The researchers explained that the 1,480-meter depth of the blowout is significant because deep-sea processes entrapped the released gaseous hydrocarbons in a deep layer of the water column.

The gases likely will remain deep in the water column and be consumed by microbes in oxidation, which en masse can lead to low-oxygen waters, said Samantha Joye, who led the study and is professor of marine sciences at the University of Georgia.

Joye's team examined samples from 70 sites around the leaking wellhead during a research cruise aboard the RV Walton Smith during late May and early June of 2010. They combined their data with estimates of the volume of oil released to quantify the gas discharge in terms of equivalent barrels of oil: either 1.6 to 1.9 or 2.2 to 3.1 million barrels of oil, depending on the method used.

These calculations increase accepted government estimates by about one third, co-author Ian MacDonald said.

Joye cautioned that although microbes feast on methane, they also need nutrients that are scarce in the Gulf's deep waters. When the nutrients are depleted, the microbes will cease to grow, regardless of how much methane is available. For more information, visit www.nature.com/ngeo/index.html.

Arctic Blooms Come Early As Temperatures Rise, Ice Melts
Warming temperatures and melting ice in the Arctic may be behind a progressively earlier bloom of a crucial annual marine event, a shift that could hold consequences for the food chain and carbon cycling in the region.

Scientists plotted the yearly spring bloom of phytoplankton—tiny plants at the base of the ocean food chain—in the Arctic Ocean and found the peak timing of the event has been progressing earlier each year for more than a decade.

An analysis of satellite data depicting ocean color and phytoplankton production showed that the spring bloom has come up to 50 days earlier in some areas during the decade, the researchers report in the March 9 edition of Global Change Biology.

The earlier Arctic blooms have roughly occurred where sea ice has dwindled, creating gaps that allow early blooms to occur, researchers said.

During the one- to two-week spring bloom, a major influx of new organic carbon enters the marine ecosystem through a massive peak in phytoplankton photosynthesis, which converts carbon dioxide into organic matter.

Phytoplankton blooms stimulate production of zooplankton which become a food source for fish. It is not clear if the fish, zooplankton and bottom-dwelling animals that consume phytoplankton are able to match the earlier blooms and avoid disruptions of their critical life-cycle stages, said Mati Kahru, the lead author of the study and a research oceanographer for the Scripps Institution of Ocean?ography at the University of California, San Diego.

Such a match or mismatch in timing could explain much of the annual variability of fish stocks in the region. For more information, visit www.wiley.com/bw/journal.asp?ref=1354-1013.

Flow Rates, Fates of Gulf Spill Contaminants Assessed From Air
Scientists have found a way to use air chemistry measurements taken hundreds of feet above last year's BP Deepwater Horizon oil spill to estimate how fast gases and oil were leaking from the reservoir thousands of meters underwater.

The researchers also determined the fate of most of those gas and oil compounds, according to an analysis accepted for publication in Geophysical Research Letters.

They say their new methods using atmospheric measurements could be applied to future oil spills.

"We found that the spilled gases and oil (spilled fluid) obeyed a simple rule: whether a compound can dissolve or evaporate determines where it goes in the marine environment," said Tom Ryerson, lead author of the report, from NOAA's Earth System Research Laboratory in Boulder, Colorado.

Using this method on a single day in June 2010, researchers calculated that at least 32,600 to 47,700 barrels of liquid gases and oil poured out of the breached reservoir.

Because this method used atmospheric data, it could not measure gases and oil that remain trapped deep underwater. For more information, visit www.agu.org/journals/gl/.

Tsunami Approaching Canada Sensed by NEPTUNE
When an 9.0-magnitude earthquake centered in the ocean near the northeast coast of Japan's Honshu Island generated a deadly tsunami in March, real-time data from an undersea cabled ocean network helped predict its arrival on Canada's western coast.

The Northeast Pacific Time-Series Undersea Networked Experiments (NEPTUNE) Canada, an undersea cabled network owned and operated by the University of Victoria, allowed scientists to determine the timing and size of the approaching tsunami. The network detected the tsunami at its pressure sensors across the Juan de Fuca tectonic plate. The tsunami first registered on a sensor 220 kilometers offshore as a 15-centimeter wave. Less than 10 minutes later, a sensor about 120 kilometers offshore recorded the wave as it passed. The wave arrived at a sensor near the coast as a 40 centimeter wave about 40 minutes later. For more information, visit www.neptunecanada.ca.


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