Oceanic convergence zone

Recent years have seen the development of prediction tools for the transport layers of plastic litter. These tools provide the facility to follow the trajectories of clusters that may be washed ashore. Evenmally, the development of an atlas of risk sensitivity will facilitate the improvment of the management of accidental risks. However, simulations performed globally over several years help in the identification of the most sensitive zones at the global scale, such as the Mediterranean, the Atlantic and Pacific convergence areas, and the Bay of Bengal. These areas on their own should receive within 30 years between 35 and 60% of all litter at sea [LEB 11], 

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Island arc A chain of volcanic islands that are commonly associated with the subduction of an oceanic plate underneath another oceanic plate (ocean-ocean convergence zone). The Aleutian Islands of Alaska are an example of an island arc. 

Solar beating of tropical oceans warms the surface water, promoting evaporation. Where the equatorial surface waters are warmest and the northeast and southeast trade winds meet, a band of cirrostratus and cirrus clouds spreads out from convective precipitation regions. This area is known as the Intertropical Convergence Zone. 

Continental interiors are thought to be constructed from welded pieces of island arcs, metamorphosed sediments, oceanic plateaux and continental fragments (e.g. Hoffinan 1989). Modern-day analogues for this include the convergent zones of the Western Pacific (Hamilton 1979), and the South American-Caribbean plate boundary, where the Leeward Antilles arc is colliding with South America (Ave Lallemant 1997). To what extent these processes were occurring... 

INDOEX IPCC ITCZ Indian Ocean Experiment Intergovernmental Panel on Climate Change Intertropical Convergence Zone... 

Fig. 9. Size of Globigerina hulloides from E49-19 in the central subantarctic Indian Ocean (43°53.2 S and 90°06.0 E) and E48-22 in the subtropical convergence zone of the Indian Ocean (39°53.7 S and 85°24.6 E) (Cronblad Malmgren 1981).

The exchange of air between the northern and southern troposphere is caused to some extent by eddy diffusion in the equatorial upper troposphere, and by the seasonal displacement of the interhemispheric tropical convergence zone which lies north of the equator in July and south of the equator in January. The displacement is greatest in the region of the Indian Ocean, where the ITCZ is relocated over the Indian subcontinent in July. By tracing the transport of fission products from Chinese and French weapons tests, Telegadas (1972) has demonstrated the importance of monsoon systems for the interhemispheric air exchange in the Indian Ocean. 

Northern Hemisphere summer insolation during the early to mid-Holocene (Berger, 1978) resulted in increased heating over the Northern Hemisphere continents and thus intensified the thermal contrast between the land and the ocean. The increased heating over the continents resulted in the northward displacement of the intertropical convergence zone (ITCZ) and hence of the monsoon front, while the enhanced land-sea contrast increased the flux of moisture from the ocean to the continent. 

Many island arcs may have started their existence at an ocean-continent convergence zone as part of a continental arc. As the hinge line of the subduction zone retreats, the space created is filled by the upward rise and partial melting of the underlying asthenosphere. The lithosphere under the arc is hot and therefore weak, and may break off as a continental sliver at the arc, which then migrates and becomes an island arc with a back-arc basin behind it. 

A study in the tropical Atlantic by Williams et al. involved measuring acetone, methanol, acetonitrile and dimethyl sulfide within the atmospheric marine boundary layer and the upper ocean [116]. Measurements were taken on either side of the intertropical convergence zone. This zone, which sailors commonly refer to as the doldrums, is an area around the equator where the southeast and northeast trade winds meet. Consequently, it is a natural barrier to atmospheric mixing between the hemispheres. This results in hemispheric gradients for VOCs whose atmospheric lifetimes are shorter than interhemispheric mixing times... 

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