Indian Ocean Water Research Articles

Estimation of the Agulhas ring impacts on meridional heat fluxes and transport using ARGO floats and satellite data

[1] A method that combines vertical profiles from the ARGO floats program and satellite Sea Surface Height (SSH) data is used to reconstruct the vertical structure of the Agulhas rings. All eddies shed by the Agulhas retroflection in the period between January 2005 and December 2008 were successfully reconstructed. The velocity structures obtained are tilted and phase shifted in relation to the temperature anomalies, resulting in an annual mean eddy meridional heat flux across the ring paths of 0.062 ± 0.012 PW (northward). A first order estimate indicates 0.07 PW entering the Atlantic from the Indian Ocean through Agulhas rings. The volume transport by Agulhas rings is believed to play a central role in the overturning circulation, being the main process responsible for the leakage of Indian Ocean waters to the Atlantic. The new estimates of the [time mean] ring volume transport of 9 ± 8 Sv from the Indian to the Atlantic Ocean fall in the range obtained by previous works. These estimates include a better representation of the trapped water region in the eddies. A large inter-annual variability in the volume transport was observed, with a maximum of ∼11–21 Sv in 2007. This variability is related to the number of structures shed by the Agulhas retroflexion per year. The ring shapes play a secondary, though important, role.

Johann R. E. Lutjeharms (1944–2011)

Johann R. E. Lutjeharms, South Africa's leading physical oceanographer, died at the age of 67 at his home in Stellenbosch on World Oceans Day, 8 June 2011, after a 10‐year battle with a complicated form of cancer. His work was central in the process of enlightening the oceanographic and climate system community to the global importance of the complex, energetic, eddy‐rich environment of the Agulhas Current. He aptly referred to this current system, including the transfer of Indian Ocean water into the South Atlantic, as the “Greater Agulhas System.” Johann was born on 13 April 1944 in Bloemfontein, South Africa, where he attended Grey College. At the University of Cape Town (UCT), he completed his bachelor's degree in physics followed by a M.Sc. (cum laude) in oceanography in 1971. His work there led to his first research article (on the variability of the water movement in the southwest Indian Ocean), which appeared in Nature. Many papers would follow, covering a broad range of aspects of the oceans around South Africa. His curriculum vitae lists 177 articles published in peer‐reviewed international journals, many of them in AGU's Journal of Geophysical Research (JGR) and Geophysical Research Letters, including his most frequently cited ones.

Effects of Mountains and Ice Sheets on Global Ocean Circulation*

Abstract The impact of mountains and ice sheets on the large-scale circulation of the world’s oceans is investigated in a series of simulations with a new coupled ocean–atmosphere model [Oregon State University–University of Victoria model (OSUVic)], in which the height of orography is scaled from 1.5 times the actual height (at T42 resolution) to 0 (no mountains). The results suggest that the effects of mountains and ice sheets on the buoyancy and momentum transfer from the atmosphere to the surface ocean determine the present pattern of deep ocean circulation. Higher mountains reduce water vapor transport from the Pacific and Indian Oceans into the Atlantic Ocean and contribute to increased (decreased) salinities and enhanced (reduced) deep-water formation and meridional overturning circulation in the Atlantic (Pacific). Orographic effects also lead to the observed interhemispheric asymmetry of midlatitude zonal wind stress. The presence of the Antarctic ice sheet cools winter air temperatures by more than 20°C directly above the ice sheet and sets up a polar meridional overturning cell in the atmosphere. The resulting increased meridional temperature gradient strengthens midlatitude westerlies by ~25% and shifts them poleward by ~10°. This leads to enhanced and poleward-shifted upwelling of deep waters in the Southern Ocean, a stronger Antarctic Circumpolar Current, increased poleward atmospheric moisture transport, and more advection of high-salinity Indian Ocean water into the South Atlantic. Thus, it is the current configuration of mountains and ice sheets on earth that determines the difference in deep-water formation between the Atlantic and the Pacific.

Water Origins over Central and Southern Japan during the Early Summer Rainy Season as Simulated with an Isotope Circulation Model

By applying the Japanese long-term Re-Analysis project (JRA-25) and the Japan Meteorological Agency Climate Data Assimilation System (JCDAS) data to a Rayleigh-type global one-layer isotope circulation model, we performed a long-term simulation and examined how water vapor is remotely transported to the vicinity of Japan from water source regions during the early summer rainy (Baiu) season. We validated the model outputs, comparing them with the stable hydrogen and oxygen isotope ratios (δD and δ18O) of precipitation observed at two in situ sites in southern and central Japan during the 2010 Baiu, and determined that the correlations between the simulation and observation are comparable to those in precipitation in Thailand from August to October when the Asian summer monsoon withdraws. The model results demonstrate that the Baiu is characterized by relatively low values of δD and that the δD values over central Japan are lower than those over southern Japan. When the Baiu commences, Indian Ocean water increases rapidly and then contributes substantially to the total precipitable water until the withdrawal of the Baiu, which is partially responsible for the low values of δD. Once the Baiu withdraws, alternatively, Pacific Ocean water occupies most of the total precipitable water. Another signature of its withdrawal is the decrease in land water of the Eurasian continent. It is also clear that the intrusion of the Indian Ocean water into central Japan remained until the end of August in the extremely cool summers of 1993 and 2003, which is interpreted as an extraordinary persistence of the Baiu period.

Indonesian Throughflow variability during the last 140 ka: the Timor Sea outflow

Abstract The transfer of surface and intermediate water from the Pacific to Indian Ocean through the Indonesian passages (Indonesian Throughflow: ITF) strongly influences the heat and freshwater budgets of tropical water masses, in turn affecting global climate. Here, we use combined δ 18 O and Mg/Ca analyses of surface and thermocline planktonic foraminifers to estimate variations in sea surface temperature, salinity and mixed layer thickness over the last 140 ka. Comparison of water mass properties reveals a steeper thermocline temperature gradient in the Timor Strait than in the eastern Indian Ocean during glacials, implying a decrease in ITF cool thermocline outflow. A major freshening and cooling of thermocline waters occurred at c . 9.5 ka, when sea level rose above a critical threshold, allowing establishment of a shallow marine connection from the South China Sea to the Java Sea. Comparison of benthic δ 13 C profiles ( c . 1800 to 3000 m water depth) suggests vigorous mixing of Indian Ocean and ITF outflow intermediate waters during interglacials. In contrast, deep and intermediate water masses became more stratified during glacials. Lower δ 13 C values at c . 3000 m water depth reflect a decrease in deepwater ventilation, probably related to slowdown of the global thermohaline circulation during glacials.

Decadal Variability of Thermocline and Intermediate Waters at 24°S in the South Atlantic

Abstract New data are presented from 24°S in the South Atlantic in an investigation of the decadal variability of the intermediate and thermocline water masses at this latitude. Variation of salinity on neutral density surfaces is investigated with three transatlantic, full-depth hydrographic sections from 1958, 1983, and 2009. The thermocline is seen to freshen by 0.05 between 1983 and 2009. The freshening is coherent, basinwide, and of a larger magnitude than any errors associated with the datasets. This freshening reverses a basinwide, coherent increase in salinity of 0.03 in the thermocline between 1958 and 1983. Changes in apparent oxygen utilization (AOU) are investigated to support the salinity changes. In the thermocline of the eastern basin, a correlated relationship exists between local AOU and salinity anomalies, which is consistent with the influence of Indian Ocean Water. This correlated relationship is utilized to estimate the magnitude of Indian Ocean influence on the salinity changes in the thermocline. Indian Ocean influence explains half of the salinity changes in the eastern thermocline from 1958 to 1983 but less of the salinity change in the eastern thermocline from 1983 to 2009. Antarctic Intermediate Water properties significantly warm from 1958 through 1983 to 2009. A significant salinification and increase in AOU is evident from 1958 to 1983. Changes in the salinity of AAIW are shown to be linked with Indian Ocean influence rather than changes in the hydrological cycle. Upper Circumpolar Deep Water is seen to be progressively more saline from 1958 through 1983 to 2009. Increased Agulhas leakage and the intensification of the hydrological cycle are conflicting influences on the salinity of thermocline and intermediate waters in the South Atlantic as the former acts to increase the salinity of these water masses and the latter acts to decrease the salinity of these water masses. The results presented here offer an interpretation of the salinity changes, which considers both of these conflicting influences.

Transport and scavenging of Pu in surface waters of the Southern Hemisphere Oceans

The distribution of 239Pu in Atlantic and Indian Ocean waters about four decades after their main injection from atmospheric nuclear weapons tests is discussed. Recent data obtained in the framework of the SHOTS (Southern Hemisphere Ocean Tracer Studies) projects are evaluated and compared with previous investigations. Seawater samples were collected during the round the globe BEAGLE2003 (Blue Ocean Global Expedition) along the 30°S transect in the Atlantic and the 20°S transect in the Indian Ocean. The results indicate transport of surface waters labelled with 239Pu from the western North Pacific via the Indonesian Seas to the South Indian Ocean and then to the South Atlantic Ocean. Along the whole BEAGLE2003 sampling route, the Atlantic Ocean has the lowest 239Pu content due to its particle scavenging on the long way from the western North Pacific. On the other hand, concentrations of the conservative 137Cs tracer are in all three oceanic basins comparable. The primary productivity reflected by the chlorophyll content in surface waters has similar longitudinal distribution as 239Pu. Radioactive and chlorophyll tracers revealed that the most important current system in each southern oceanic basin is represented by the Subtropical gyre. While the main streams of the gyres maintain high concentrations of tracers, inside the loops the tracer concentrations are the lowest.

137Cs water profiles in the South Indian Ocean – An evidence for accumulation of pollutants in the subtropical gyre

The 137Cs seawater transect along the 20°S latitude in the Indian Ocean, sampled during the round the globe BEAGLE2003 (Blue Ocean Global Expedition) clearly shows a presence of two cores of higher 137Cs concentrations at 100°E and 55°E in water column depths between 100 and 200 m. The subsurface maximum of 137Cs activity concentration (2.1 mBq/L) observed near 100°E is the highest level found in southern hemisphere seawater, which is comparable to the maximum 137Cs concentration observed in North Pacific surface water. This transect represents the first high density sight of 137Cs distribution in South Indian Ocean waters. The estimated 137Cs water column inventories (up to 1240 Bq/m 2), normalized for the 1000 m water depth along the 20°S latitude are by a factor of three higher than would be expected from global fallout in the South Indian Ocean. The estimated residence time of 137Cs in surface waters of the South Indian Ocean (∼30 years) is by about a factor of two higher than for the North Pacific. The 137Cs data confirm a transport of surface waters from the North Pacific via Indonesian seas to the South Indian Ocean, and to the subtropical gyre. The subtropical gyre is an important reservoir of anthropogenic pollutants that have been transported from the North Pacific and Indian Oceans to the south on a time-scale of several decades.

Shallow-water squat lobsters (Crustacea, Decapoda, Galatheidae) from Mayotte (Comoros Island), La Réunion and Madagascar, with the description of a new genus and two new species

Shallow water species of galatheid crustaceans collected in Mayotte (Comoros Island), La Réunion and Madagascar have been studied. The collection contains one species of Sadayoshia and seven species of the genus Galathea, including a new species (G. denticulata) closely related to G. amamiensis known from the Indian Ocean and western Pacific waters, a new genus (Macrothea) and species (M. bouchardi). The new genus is closely related to the genus Fennerogalathea and it is easily distinguished by the following combination of characters: (1) rostrum with 4 strong lateral teeth on each side, (2) spines present on epigastric and hepatic regions only, (3) telson completely subdivided, (4) pereiopods 2–4 dactyli sharply biunguiculate. The new genus is also close to Lauriea Baba, 1971, from which it can be differentiated, among other characters, by the shape of the endopod of uropods and the number of male gonopods.

Atlantic overturning circulation and Agulhas leakage influences on southeast Atlantic upper ocean hydrography during marine isotope stage 11

Climate dynamics during the marine isotope stage (MIS) 11 interglacial may provide information about how the climate system will evolve under the conditions of low-amplitude orbital forcing that are also found during the late Holocene. New stable isotope and alkenone data are presented from southeast Atlantic Ocean Drilling Program Site 1085, providing detailed information on interglacial climate evolution and the impacts of Atlantic meridional overturning circulation (MOC) and Agulhas leakage on the regional upper ocean hydrography. The data suggest that although warm surface ocean conditions were maintained at approximate Holocene levels for 40,000 years during MIS 11, subsurface temperature and salinity recorded by deeper-dwelling planktonic foraminifera species were maintained at their highest values for only 7000–8000 years. Surface water temperature and salinity data suggest that the interocean exchange of warm, salty waters into the southeast Atlantic Ocean was directly related to changes in the activity of the MOC during the study interval. Specifically, transient regional warming events during periods of weakened overturning circulation may have been amplified by the continuous interocean exchange of warm, salty Indian Ocean waters that primed the MOC for abrupt resumptions into a vigorous mode of operation. Conversely, a peak in interocean exchange at the end of the MIS 11 interglacial optimum may reflect enhanced trade wind forcing of surface waters whose export to the North Atlantic Ocean could have contributed to renewed ice sheet buildup during the MIS 11 to 10 glacial inception.

Glacial paleoceanography off the mouth of the Mekong River, southern South China Sea, during the last 500 ka

We have analyzed core MD01-2392, ∼ 360 km east of the Mekong River mouth in the South China Sea (SCS). Over the past 500 ka, planktonic foraminiferal oxygen-isotopic values are consistently lighter than northern SCS and open-ocean records by up to 0.5‰, indicating the influence of run-off from the Mekong River during both glacial and interglacial periods. Carbonate content is higher during interglacials; sedimentation rates were higher during glacials. Increased sedimentation rates since 30 ka imply increased run-off during the last glacial maximum and Holocene Period. Contrary to general experience, in which it is classed as a warm species for temperature estimates, the thermocline-dwelling species Pulleniatina obliquiloculata increased its numbers during glacial periods. This implies an estuarine circulation and even brackish-water caps during glacial periods, reinforcing the sense of strong run-off. In an overall decline of warm water, the thermocline shoaled stepwise, with rapid rises across the glacial terminations. We infer that the southern SCS was opened to an influx of Indian Ocean waters through southern passages at those times of rising sea levels.

On the fast decay of Agulhas rings

The Indian Ocean water that ends up in the Atlantic Ocean detaches from the Agulhas Current retroflection predominantly in the form of Agulhas rings and cyclones. Using numerical Lagrangian float trajectories in a high‐resolution numerical ocean model, the fate of coherent structures near the Agulhas Current retroflection is investigated. It is shown that within the Agulhas Current, upstream of the retroflection, the spatial distributions of floats ending in the Atlantic Ocean and floats ending in the Indian Ocean are to a large extent similar. This indicates that Agulhas leakage occurs mostly through the detachment of Agulhas rings. After the floats detach from the Agulhas Current, the ambient water quickly looses its relative vorticity. The Agulhas rings thus seem to decay and loose much of their water in the Cape Basin. A cluster analysis reveals that most water in the Agulhas Current is within clusters of 180 km in diameter. Halfway in the Cape Basin there is an increase in the number of larger clusters with low relative vorticity, which carry the bulk of the Agulhas leakage transport through the Cape Basin. This upward cascade with respect to the length scales of the leakage, in combination with a power law decay of the magnitude of relative vorticity, might be an indication that the decay of Agulhas rings is somewhat comparable to the decay of two‐dimensional turbulence.

Antarctic intermediate water at the Agulhas Current retroflection region

The inter-ocean transport of salty, warm Indian Ocean water to the Atlantic Ocean has been shown to stabilize the meridional overturning of the Atlantic. This salt and heat is mostly transported by Agulhas rings, shed at the Agulhas retroflection. To investigate the contribution of Antarctic Intermediate Water (AAIW) to this salt and heat flux, 7 hydrographic sections in the south-west Indian and south-east Atlantic Oceans were investigated using Optimum Multi-parameter Analysis. The mean contributions of AAIW from the South Indian Ocean (iAAIW) and that of the Drake Passage (dAAIW), over the density range σ n = 27.25–27.7, showed that iAAIW was the dominant AAIW type east of the Agulhas Current retroflection. The maximum contributions of iAAIW were confined to the Agulhas Current, the Agulhas Return Current and Agulhas rings. In the subdivided density ranges, iAAIW was always the dominant water type in the upper density range ( σ n = 27.25–27.4), whilst in the lower density range ( σ n = 27.4–27.7) the dAAIW/iAAIW mix was almost 50/50. West of the retroflection the mean iAAIW/dAAIW mix over the density range σ n = 27.25–27.7 was around 50/50 for the southern part of the Cape Basin. In the upper density range the average mix of dAAIW/iAAIW was 45/55, whilst for the lower density range the mix was 46/54. Section by section comparisons, however, showed considerable differences in the observed mix of dAAIW/iAAIW in both the upper and lower density ranges.

First confirmed sightings of the killer whale ( Orcinus orca) in Sri Lanka's waters

Three killer whale (Orcinus orca) sightings were recorded during the twelve month period from March 2008 to February 2009 in the northern Indian Ocean waters around Sri Lanka. This included the first sighting of this species during a dedicated cetacean survey. In the past three decades, several dedicated cetacean surveys have revealed high species richness around Sri Lanka, but no killer whale sightings were recorded. Records thus far have been limited to two, very old, unconfirmed sightings and a few specimens in the fisheries bycatch. Due to this paucity of records despite dedicated surveys, the species has been considered to be rare in these waters. It is of interest however, that three sightings were reported during a short time span of one year, when no sightings had been reported previously despite numerous dedicated cetacean surveys and opportunistic observations of cetaceans in these waters.

Association of the stramenopilan protists, the aplanochytrids, with zooplankton of the equatorial Indian Ocean

Thraustochytrids and aplanochytrids, belonging to the Labyrinthulomycetes of the Kingdom Stramenopila have been frequently reported to occur as parasites or symbionts in a number of coastal invertebrates. Given the fact that these protists are widespread in coastal and oceanic waters, it is possible that they are also associated with pelagic zooplankton. This study examines their occurrence in zooplankton of the equatorial Indian Ocean waters. A total of 171 of 2100 individual specimens of zooplankton yielded Labyrinthulomycetes in culture, the colony morphology and/or life cycles of which corresponded to aplanochytrids. SSU ribosomal DNA sequence analysis of eight of the isolates placed them in a distinct clade among aplanochytrids, but closest to Aplanochytrium yorkensis/A. kerguelensis. The eight isolates were further segregated into two clusters, corresponding to isolates obtained from two different seasons. Biotinylated probes for two isolates of A.kerguelensis from the two different seasons were developed based on the Internal Transcribed Spacer (ITS) sequences. In situ hybridization (ISH) of zooplankton using the probes with streptavidin-alkaline phosphatase showed that aplanochytrid cells fed to copepods were grazed and could subsequently be detected in the animals. ISH on natural samples of zooplankton yielded a positive, but diffuse reaction in copepods, while cells resembling aplanochytrids were detected within chaetognaths. ISH using streptavidin-peroxidase conjugate lent further support for their presence within chaetognaths. This study suggests the predominant occurrence of the aplanochytrid Aplanochytrium kerguelensis in association with mesozooplankton of the equatorial Indian Ocean, particularly with chaetognaths. Further studies are suggested to understand if genetically distinct populations of Aplanochytrium kerguelensis are associated with chaetognaths in oceanic waters and if such an association is parasitic, mutualistic or commensalistic.

Flux comparison of Eulerian and Lagrangian estimates of Agulhas leakage: A case study using a numerical model

Estimating the magnitude of Agulhas leakage, the volume flux of water from the Indian to the Atlantic Ocean, is difficult because of the presence of other circulation systems in the Agulhas region. Indian Ocean water in the Atlantic Ocean is vigorously mixed and diluted in the Cape Basin. Eulerian integration methods, where the velocity field perpendicular to a section is integrated to yield a flux, have to be calibrated so that only the flux by Agulhas leakage is sampled. Two Eulerian methods for estimating the magnitude of Agulhas leakage are tested within a high-resolution two-way nested model with the goal to devise a mooring-based measurement strategy. At the GoodHope line, a section halfway through the Cape Basin, the integrated velocity perpendicular to that line is compared to the magnitude of Agulhas leakage as determined from the transport carried by numerical Lagrangian floats. In the first method, integration is limited to the flux of water warmer and more saline than specific threshold values. These threshold values are determined by maximizing the correlation with the float-determined time series. By using the threshold values, approximately half of the leakage can directly be measured. The total amount of Agulhas leakage can be estimated using a linear regression, within a 90% confidence band of 12 Sv. In the second method, a subregion of the GoodHope line is sought so that integration over that subregion yields an Eulerian flux as close to the float-determined leakage as possible. It appears that when integration is limited within the model to the upper 300 m of the water column within 900 km of the African coast the time series have the smallest root-mean-square difference. This method yields a root-mean-square error of only 5.2 Sv but the 90% confidence band of the estimate is 20 Sv. It is concluded that the optimum thermohaline threshold method leads to more accurate estimates even though the directly measured transport is a factor of two lower than the actual magnitude of Agulhas leakage in this model.

Measurements of Sea Surface Height Variability in the Eastern South Atlantic from Pressure Sensor–Equipped Inverted Echo Sounders: Baroclinic and Barotropic Components

Abstract Variability in sea surface height (SSH) can be decomposed into two contributions: one from changes in mass in the water column (barotropic) and the other from purely steric changes (baroclinic). Both contributions can be determined from data recorded by a pressure sensor–equipped inverted echo sounder (PIES). PIES data from the Agulhas South Atlantic Thermohaline Experiment (ASTTEX) were used, collected in the Cape Basin off South Africa, along 1000 km of an eddy corridor where Agulhas eddies carry cores of warm, salty Indian Ocean waters into the South Atlantic. The paper presents in detail the method used to convert PIES measurements into barotropic, baroclinic, and total SSH, and discusses the error budget. The baroclinic contribution is geopotential height (reference 4500 dbar), which can be determined from the measured vertical acoustic travel time together with a lookup curve based on the regional hydrography. The main error source is scatter about this curve that depends on the extent to which water masses advecting along each geopotential streamline may derive from different ocean regions. The barotropic contribution can be determined from the bottom pressure measurements of the mass variation in the water column and has an uncertainty due to sensor calibration drift in two years corresponding to 1-cm water column height. The barotropic component accounts for 20% of the overall SSH variance and 47% during large signal intervals exceeding 15 cm. PIES data demonstrate via the two measurements that barotropic and baroclinic contributions may work independently or in concert in different mesoscale eddies. The combined structure need not be equivalent barotropic. In particular, deep barotropic eddies exhibit mesoscale spatiotemporal scales and may or may not be systematically tilted or aligned in space or time relative to baroclinic eddies.

Impacts of interruption of the Agulhas leakage on the tropical Atlantic in coupled ocean–atmosphere simulations

In this paper we use a coupled ocean–atmosphere model to investigate the impact of the interruption of Agulhas leakage of Indian ocean water on the tropical Atlantic, a region where strong coupled ocean–atmosphere interactions occur. The effect of a shut down of leakage of Indian ocean water is isolated from the effect of a collapse of the MOC. In our experiments, the ocean model is forced with boundary conditions in the southeastern corner of the domain that correspond to no interocean exchange of Indian ocean water into the Atlantic. The southern boundary condition is taken from the Levitus data and ensures an MOC in the Atlantic. Within this configuration, instead of warm and salty Indian ocean water temperature (cold) and salinity (fresh) anomalies of southern ocean origin propagate into the South Atlantic and eventually reach the equatorial region, mainly in the thermocline. This set up mimics the closure of the “warm water path” in favor of the “cold water path”. As part of the atmospheric response, there is a northward shift of the intertropical convergence zone (ITCZ). The changes in trade winds lead to reduced Ekman pumping in the equatorial region. This leads to a freshening and warming of the surface waters along the equator. Especially in the Cold Tongue region, the cold and fresh subsurface anomalies do not reach the surface due to the reduced upwelling. The anomaly signals are transported by the equatorial undercurrent and spread away from the equator within the thermocline. Part of the anomaly eventually reaches the Tropical North Atlantic, where it affects the Guinea Dome. Surprisingly, the main effect at the surface is small on the equator and relatively large at the Guinea Dome. In the atmosphere, the northward shift of the ITCZ is associated with a band of negative precipitation anomalies and higher salinities over the Tropical South Atlantic. An important implication of these results is that the modified water characteristics due to a shut down of the Agulhas leakage remain largely unaffected when crossing the equatorial Atlantic and therefore can affect the deepwater formation in the North Atlantic. This supports the hypothesis that the Agulhas leakage is an important source region for climate change and decadal variability of the Atlantic.

Increase in Agulhas leakage due to poleward shift of Southern Hemisphere westerlies

The transport of warm and salty Indian Ocean waters into the Atlantic Ocean-the Agulhas leakage-has a crucial role in the global oceanic circulation and thus the evolution of future climate. At present these waters provide the main source of heat and salt for the surface branch of the Atlantic meridional overturning circulation (MOC). There is evidence from past glacial-to-interglacial variations in foraminiferal assemblages and model studies that the amount of Agulhas leakage and its corresponding effect on the MOC has been subject to substantial change, potentially linked to latitudinal shifts in the Southern Hemisphere westerlies. A progressive poleward migration of the westerlies has been observed during the past two to three decades and linked to anthropogenic forcing, but because of the sparse observational records it has not been possible to determine whether there has been a concomitant response of Agulhas leakage. Here we present the results of a high-resolution ocean general circulation model to show that the transport of Indian Ocean waters into the South Atlantic via the Agulhas leakage has increased during the past decades in response to the change in wind forcing. The increased leakage has contributed to the observed salinification of South Atlantic thermocline waters. Both model and historic measurements off South America suggest that the additional Indian Ocean waters have begun to invade the North Atlantic, with potential implications for the future evolution of the MOC.

Causes of Maritime Piracy Off the Somali Coast; What Solutions Can the Regional or International Community Offer?

The International Maritime Community has been hit by ship hi-jackings carried out by Somali pirates, in the Western Indian Ocean waters off the East Coast of Africa. These acts that has surged from only about as rescently as 2006, are of great concern.world wide. The acts that include, among others, unlawful acts which threaten the safety of ships and the security of their passangers and crew; with reports of crew being kidnapped, ships being hi-jacked, deliberately run aground or blown up by explosives. Passengers were threatened and sometimes killed. Ships and crew and cargo detained until a ransome amounting to sometimes millions of dollars is paid. The pirates that are combing these waters sometimes is a group of as few as six men, in a rag-tag boat, seem to be nothing, yet they have developed a level of sophistication where modern navies patrolling the maritime region seems to fail to contain this practice. This regional interuption of maritime commercial flow is being felt world wide. Ship owners that have opted for long cuts to avoid the East African coastal waters, are footing the bill of such costly measures. This in turn has caused merchandise that pass through this shipping lane to hike up on price. What is the cause of this maritime threat? - What must the International community do to get rid of this threat? - What is causing the international community, with its modern navies, to fail to contain this threat to life, property and commerce? This work explains and looks into the causes of maritime piracy in the region. This work also offers suggestions and answers on how this problem can be solved.