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!
NASA examines Peru's deadly rainfall
24.03.2017 | NASA/Goddard Space Flight Center
Steep rise of the Bernese Alps
24.03.2017 | Universität Bern
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
24.03.2017 | Materials Sciences
24.03.2017 | Physics and Astronomy
24.03.2017 | Physics and Astronomy