Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Antarctic bottom waters freshening at unexpected rate

26.01.2017

Shift could disturb ocean circulation and hasten sea level rise, researchers say

In the cold depths along the sea floor, Antarctic Bottom Waters are part of a global circulatory system, supplying oxygen-, carbon- and nutrient-rich waters to the world's oceans. Over the last decade, scientists have been monitoring changes in these waters. But a new study from the Woods Hole Oceanographic Institution (WHOI) suggests these changes are themselves shifting in unexpected ways, with potentially significant consequences for the ocean and climate.


In some places along the Antarctic coast, ice formation causes seawater to grow saltier and therefore denser, so that it sinks to the sea floor. Known as the Antarctic Bottom Waters (AABW), these deep, cold waters play a critical role in regulating circulation, temperature, and availability of oxygen and nutrients throughout the world's oceans.

Photo by Alison Macdonald, Woods Hole Oceanographic Institution


WHOI researchers gathered seawater samples using an instrument called a rosette -- a rose-like array of 36 bottles that can be individually opened and closed to collect samples at different locations and depths in the ocean.

Photo by Alison Macdonald, Woods Hole Oceanographic Institution

In a paper published January 25 in Science Advances, a team led by WHOI oceanographers Viviane Menezes and Alison Macdonald report that Antarctic Bottom Water (AABW) has freshened at a surprising rate between 2007 and 2016--a shift that could alter ocean circulation and ultimately contribute to rising sea levels.

"If you change the circulation, you change everything in the ocean," said Menezes, a WHOI postdoctoral investigator and the study's lead author. Ocean circulation drives the movement of warm and cold waters around the world, so it is essential to storing and regulating heat and plays a key role in Earth's temperature and climate. "But we don't have the whole story yet. We have some new pieces, but we don't have the entire puzzle."

The puzzle itself isn't new: past studies suggest that AABW has been undergoing significant changes for decades. Since the 1990s, an international program of repeat surveys has periodically sampled certain ocean basins around the world to track the circulation and conditions at these spots over time. Along one string of sites, or "stations," that stretches from Antarctica to the southern Indian Ocean, researchers have tracked the conditions of AABW--a layer of profoundly cold water less than 0°C (it stays liquid because of its salt content, or salinity) that moves through the abyssal ocean, mixing with warmer waters as it circulates around the globe in the Southern Ocean and northward into all three of the major ocean basins.

The AABW forms along the Antarctic ice shelves, where strong winds cool open areas of water, called polynyas, until some of the water freezes. The salt in the water doesn't freeze, however, so the unfrozen seawater around the ice becomes saltier. The salt makes the water denser, causing it to sink to the ocean bottom.

"These waters are thought to be the underpinning of the large-scale global ocean circulation," said Macdonald, a WHOI senior research specialist and the study's co-author. "Antarctic Bottom Water gets its characteristics from the atmosphere--for example, dissolved carbon and oxygen--and sends them deep into the ocean. Then, as the water moves around the globe, it mixes with the water around it and they start to share each other's properties. It's like taking a deep breath and letting it go really slowly, over decades or even centuries."

As a result, the frigid flow plays a critical role in regulating circulation, temperature, and availability of oxygen and nutrients throughout the world's oceans, and serves as both a barometer for climate change and a factor that can contribute to that change.

A past study using the repeat survey data found that AABW had warmed and freshened (grown less saline) between 1994 and 2007. When Macdonald and Menezes revisited the line of stations, they measured how AABW has changed in the years since.

During the austral summer of 2016, they joined the crew of the research ship R/V Revelle and cruised north from Antarctica to Australia, braving frequent storms to collect samples every 30 nautical miles. In a shipboard lab, they analyzed the samples using data from conductivity-temperature-depth (CTD) sensors, which measure the water's salinity, temperature and other properties, with support from study co-author Courtney Schatzman of the Scripps Institution of Oceanography, who processed the raw data.

The team found that the previously detected warming trend has continued, though at a somewhat slower pace. The biggest surprise, however, was its lack of saltiness: AABW in this region has grown fresher four times faster in the past decade than it did between 1994 and 2007.

"I thought, 'Oh wow!' when I saw the change in salinity," said Menezes. "You collect the data and sometimes you spend 2 to 3 years to find something, but this time we knew what we had within hours, and we knew it was very unexpected."

Such a shift, were it global, could significantly disrupt ocean circulation and sea levels.

"The fresher and warmer the water is, the less dense it will be, and the more it will expand and take up more space - and that leads to rising sea levels," Macdonald said. "If these waters no longer sink, it could have far reaching affects for global ocean circulation patterns."

Questions remain around the cause of the shift. Menezes and Macdonald hypothesize that the freshening could be due to a recent landscape-changing event. In 2010, an iceberg about the size of Rhode Island collided with Antarctica's Mertz Glacier Tongue, carving out a more-than-1,000-square-mile piece and reshaping the icescape of the George V/Adelie Land Coast, where the AABW observed in this study is thought to form. The subsequent melting dramatically freshened the waters there, which may have in turn freshened the AABW as well. Future studies could use chemical analysis to trace the waters back to the site of the collision and calving and confirm the hypothesis.

###

This research was funded in part by the National Science Foundation and the National Oceanic and Atmospheric Administration.

The Woods Hole Oceanographic Institution is a private, non-profit organization on Cape Cod, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the ocean and its interaction with the Earth as a whole, and to communicate a basic understanding of the ocean's role in the changing global environment. For more information, please visit http://www.whoi.edu.

Media Contact

WHOI Media Office
media@whoi.edu
508-289-3340

 @WHOImedia

http://www.whoi.edu 

WHOI Media Office | EurekAlert!

More articles from Earth Sciences:

nachricht Volcanoes and glaciers combine as powerful methane producers
20.11.2018 | Lancaster University

nachricht Massive impact crater from a kilometer-wide iron meteorite discovered in Greenland
15.11.2018 | Faculty of Science - University of Copenhagen

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First diode for magnetic fields

Innsbruck quantum physicists have constructed a diode for magnetic fields and then tested it in the laboratory. The device, developed by the research groups led by the theorist Oriol Romero-Isart and the experimental physicist Gerhard Kirchmair, could open up a number of new applications.

Electric diodes are essential electronic components that conduct electricity in one direction but prevent conduction in the opposite one. They are found at the...

Im Focus: Nonstop Tranport of Cargo in Nanomachines

Max Planck researchers revel the nano-structure of molecular trains and the reason for smooth transport in cellular antennas.

Moving around, sensing the extracellular environment, and signaling to other cells are important for a cell to function properly. Responsible for those tasks...

Im Focus: UNH scientists help provide first-ever views of elusive energy explosion

Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.

Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...

Im Focus: A Chip with Blood Vessels

Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.

Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...

Im Focus: A Leap Into Quantum Technology

Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.

In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Optical Coherence Tomography: German-Japanese Research Alliance hosted Medical Imaging Conference

19.11.2018 | Event News

“3rd Conference on Laser Polishing – LaP 2018” Attracts International Experts and Users

09.11.2018 | Event News

On the brain’s ability to find the right direction

06.11.2018 | Event News

 
Latest News

Removing toxic mercury from contaminated water

21.11.2018 | Life Sciences

New China and US studies back use of pulse oximeters for assessing blood pressure

21.11.2018 | Medical Engineering

Exoplanet stepping stones

21.11.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>