Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

The striking deep current reversal in the tropical Pacific Ocean

14.11.2006
The ocean's immense heat storage capacity means that it has a dominant role in the regulation of heat exchange and of the Earth's climate. And it is the ocean's currents that drive thermal exchanges between ocean and atmosphere and contribute to climate balance.

This they do in transporting warm- and cold-water masses from the Equator to the poles. The near-surface currents are generated essentially by the winds, whereas the deeper ones (known as thermohaline currents) result from water density variations induced by differences in temperature and salinity between the distinct masses.

The prevailing winds in the tropical Pacific, the trade winds, blow from the American continent towards Asia, causing the warm surface waters to drift in a general East-West direction. As they approach the Asian continent, these waters accumulate, then change direction, part of them turning North and feeding the Kuroshio (the equivalent in the Pacific of the Gulf Stream), part going South to join up with the East Australian current, another portion flowing at depth and feeding the Equatorial Undercurrent (EUC), which runs at between 100 and 150 m below the surface. The EUC flows along the Equator, from Papua New Guinea to the Galapagos Islands, counter to the trade winds. That current extends over a width of nearly 300 km and transports a large mass of water eastwards (1), at a maximum velocity of around 2 knots (1 m/s or 3.6 km/h).

Scientists are currently seeking to describe ocean circulation and improve on data acquired, aiming to identify the physical mechanisms that regulate climate variability. The impact of the ENSO (El Niño-Southern Oscillation) event on the climatic situation in the southern Pacific Ocean is still not well known, for instance. In two oceanographic cruises run in October 1999 and April 2000 as part of the IRD's ECOP programme, the Institute's researchers were able to study this region and, in particular, the ENSO. The latter has a determinant effect on the distribution of ocean water masses, ocean/atmosphere exchanges in the tropical southern Pacific and many anomalies of climate that occur on the continents that border the Pacific. Physical determinations of currents and masses of water under transport were made from the surface down to 1 200 m over a large area, 1700 km in length, along the Equator (between the Equator and 10° S latitude, between 165° and 180° E longitude), using a Lowered Acoustic Doppler Current Profiler (L- ADCP) (2) installed aboard R/V Alis, the IRD oceanographic research vessel.

These series of measurements give a well-defined picture of the tropical circulation in this zone, for two specific dates. They show up in particular the horizontal alternation of bands of currents of opposing directions between the Equator and 10° S latitude, from the surface to 1200 m. Essentially, however, they reveal a surprising variability of intermediate equatorial currents (the equatorial intermediate current (EIC) and the lower equatorial intermediate current (LEIC)), which plunge at the Equator under the Equatorial Undercurrent and flow in the same direction, between about 300 and 1200 m (see Figure). Between October 1999 and April 2000, these equatorial intermediate currents changed direction, between 2° S latitude and the Equator, over the 1 700 km of the zone investigated. This reversal is already known, but its amplitude in this case is striking. The resulting variation in water mass transport is considerable, around 100 Sv (50 Sv towards the West in October 1999 and 50 Sv towards the East in April 2000). The question is, what causes this change-about? One hypothesis put forward involves the passage of an oceanic instability wave, but no disturbance of the EUC was detected during the research cruises and the reversal remains unexplained. Further current measurement campaigns in the future should shed light on this event and bring clues for unravelling the dynamics of these currents. At present, such a change in ocean water mass transport must be taken into account in studies on the mass balance that exists in the equatorial Pacific Ocean. Mathematical models of ocean circulation are needed so that the variations in water transport can be reproduced, and thereby facilitate assessment of their impact on the climate variability, whether a seasonal, inter-annual or decennial temporal scales.

Marie Guillaume-Signoret | EurekAlert!
Further information:
http://www.ird.fr

More articles from Earth Sciences:

nachricht Algorithm provides early warning system for tracking groundwater contamination
14.08.2018 | DOE/Lawrence Berkeley National Laboratory

nachricht Artificial Glaciers in Response to Climate Change?
10.08.2018 | Universität Heidelberg

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

Im Focus: The “TRiC” to folding actin

Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.

Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...

Im Focus: Lining up surprising behaviors of superconductor with one of the world's strongest magnets

Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way -- a finding that could help direct the search for materials that can perfectly conduct electricity at room temperatur

What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that...

Im Focus: World record: Fastest 3-D tomographic images at BESSY II

The quality of materials often depends on the manufacturing process. In casting and welding, for example, the rate at which melts solidify and the resulting microstructure of the alloy is important. With metallic foams as well, it depends on exactly how the foaming process takes place. To understand these processes fully requires fast sensing capability. The fastest 3D tomographic images to date have now been achieved at the BESSY II X-ray source operated by the Helmholtz-Zentrum Berlin.

Dr. Francisco Garcia-Moreno and his team have designed a turntable that rotates ultra-stably about its axis at a constant rotational speed. This really depends...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

2018 Work Research Conference

25.07.2018 | Event News

 
Latest News

'Building up' stretchable electronics to be as multipurpose as your smartphone

14.08.2018 | Information Technology

During HIV infection, antibody can block B cells from fighting pathogens

14.08.2018 | Life Sciences

First study on physical properties of giant cancer cells may inform new treatments

14.08.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>