The oceans, which began to be scientifically explored 200 years ago,hold the key to how the Earth works. For example, the ocean’s sediments provide a record of climatic signals over the last 200 million years. Although our improving knowledge of the oceans has revolutionised our understanding of the planet as a whole (the best example being the sea-g
oing expeditions after World War 2, which led to the theory of plate tectonics in the late 1960s) much more remains to be discovered – not only in the use of oceans to the benefit of humankind and the environment, but also in mitigating hazards around the continental margins. About 21% of the world’s population, 1147 million people, live within 30km of a coastline. Within the framework of plate tectonics, the birth of a new ocean spreading centre often involves the rupturing of a continent and this leads to the production of a pair of rifted continental margins (like opposing sides of the Atlantic Ocean today). Ocean floor is generated continuously at the global system of spreading ridges, and the ocean crust moves away from the ridge. After its journey across the deep ocean basin, seafloor may disappear at an ocean trench, where the oceanic plate is subducted, often beneath a continent – as around the Pacific Ocean today. Therefore, most of the scientific questions of OCEAN are related to spreading ridges and continental margins, whether created by rifting (Atlantic) or subduction (Pacific).
oing expeditions after World War 2, which led to the theory of plate tectonics in the late 1960s) much more remains to be discovered – not only in the use of oceans to the benefit of humankind and the environment, but also in mitigating hazards around the continental margins. About 21% of the world’s population, 1147 million people, live within 30km of a coastline. Within the framework of plate tectonics, the birth of a new ocean spreading centre often involves the rupturing of a continent and this leads to the production of a pair of rifted continental margins (like opposing sides of the Atlantic Ocean today). Ocean floor is generated continuously at the global system of spreading ridges, and the ocean crust moves away from the ridge. After its journey across the deep ocean basin, seafloor may disappear at an ocean trench, where the oceanic plate is subducted, often beneath a continent – as around the Pacific Ocean today. Therefore, most of the scientific questions of OCEAN are related to spreading ridges and continental margins, whether created by rifting (Atlantic) or subduction (Pacific). The ocean cover nearly 71% of the earth's surface,but hemispherewise, the extent is 81% in the southern hemisphere and 61% in the northern. the average depth of the oceans is of the order of $ km though the deep trenches go down to a depth of more than 10km. atmosphere and oceanic process are inter connected. winds, waves and weather, are sun-powered and ther is profound interaction at the land-air and land-sea interfaces. the distribution and juxtaposition of the oceans and land masses have intimate relationship with the climatic pattern
How do the lithosphere, hydrosphere and biosphere interact at mid-ocean ridges, and what role did these interactions play in the origin of life on Earth?
Huge cracks in the Earth’s surface are formed when the tectonic plates that make up our planet’s outer shell move apart. These cracks run mostly through the ocean basins, forming a 60,000km globe-encircling volcanic syst
em known as mid-ocean ridges. With only one exception (Iceland) this volcanic belt is completely hidden from view beneath two to four kilometres of ocean. Nevertheless, it is along these ridges that molten rock (“magma”) generated at depths between 20 to 80km within the Earth rises and erupts on the seafloor, slowly resurfacing vast areas of our planet as that seafloor spreads away from these ridges. The results are bizarre landscapes (strictly speaking, “bathyscapes”), of toxic hot springs and an abundance of life thriving independently of sunlight, all of which are constantly being remodeled by volcanic eruptions and earthquakes. This is an interesting and largely unknown part of our planet for sure, but how important is this volcanic activity and the life it supports to the world as a whole? What part does it play, for example, in the production of mineral deposits, in controlling the chemical composition of the oceans, in the deep-sea food chain, and in the origin of life? In view of the enormous length of the ridges and their relative inaccessibility, answering these questions has required - and still requires - a global, coordinated international scientific collaboration. Science programme A panel of 20 eminent geoscientists from all parts of the world decided on a list of nine broad science themes -Groundwater, Hazards,Earth& Health, Climate, Resources, Megacities,Deep Earth, Ocean, and Soils.The next step is to identify substantive science topics with clear deliverables within each broad theme.A ‘key-text’ team has now been set up for each, tasked with working out an Action Plan. Each tea will produce a text that will be published as a theme prospectus like this one. A series of Implementation Groups will then be created to set the work under the nine programmes in motion. Every effort will be made to involve specialists from countries with particular interest in (and need for) these programmes. Mid-ocean ridges are the site of the most active volcanism and frequent earthquakes on our planet
Recent effort has shown just how important the ridges are for the deep ocean and potentially for humankind. The energy released by the cooling volcanic rock at the ridges is equal to about half of what is generated by the human race through burning fossil fuels and from nuclear power. At present this energy dissipates on and near the seafloor, driving the circulation of vast amounts of seawater through the oceanic crust. The output of this circulation is hot (up to 400°C) and acidic hydrothermal fluids, which carry dissolved metals and are laden with dissolved gases such as methane and hydrogen sulphide. When they vent on the seafloor, reactions between the hot, metalladen vent fluids and the surrounding cold deep-sea water lead to the precipitation of metal sulphides, a reaction that has generated some of the largest metal ore bodies on Earth. Hot,
sulphide and metal-laden fluids do not sound like the ideal place for life to thrive, but it is precisely around these vents that the highest concentrations of biomass in the deep sea are found. The animals found at the hydrothermal vents are often quite strange by our standards, including giant worms without guts that feed by relying on bacteria in their tissues that in turn harness the energy from the normally toxic chemical, hydrogen sulphide. These and numerous other unique vent animals have much to teach us about how they can withstand, and even flourish in, the dynamic and hostile environment they inhabit. Furthermore, the microbes found in hydrothermal vents can live in even more extreme environments, and we have just begun to explore the enormous diversity of metabolic pathways (chains of biochemical reactions) found in bugs both above and below the seafloor. We already know that some can live at temperatures greater than any other form of life on the planet can tolerate, and in fact many scientists believe that it was in places like this that life first evolved on Earth. Mid-ocean ridges are the site of the most active volcanism and frequent earthquakes on our planet.
As such they provide a unique natural laboratory for long-term monitoring of the interaction between submarine volcanoes, earthquakes, and changes in physical conditions in the deep ocean. For example, recent studies have indicated that moderate-sized earthquakes along the oceanic transform faults (which offset the spreading ridges) appear to be associated with much higher numbers of foreshocks but lower numbers of aftershocks in comparison to continental counterparts. Moreover, changes in ocean tides appear to have triggered seismicity in the vicinity of submarine volcanoes. New knowledge obtained from studying the way the rocky shell of the Earth (lithosphere) interacts with the hydrosphere in the mid-ocean ridge volcanic-tectonic system has important implications for applied research and the forecasting of volcanic and earthquake hazards on land. Volcanic, tectonic, and hydrothermal processes at mid-ocean ridges also control the chemical composition of the Earth’s oceanic lithosphere (the rocks that form the ocean floor) and the landscape of the vast abyssal plains.
Beneath fast-spreading ridges, such as the East Pacific Rise, a steady-state lens of magma is often imaged, providing molten rock for the relatively frequent intrusion of magma sheets (dykes) and for the seafloor eruption events that they feed. The magma lens also supplies heat to drive hot-water (hydrothermal) circulation in the ocean crust. At the slow and ultraslow ridges, such as the Mid-Atlantic Ridge and the Gakkel Ridge under the Arctic Ocean, however, magmatic events are much less frequent and the tectonic extension of the lithosphere by faulting is a significant component of seafloor spreading. We are only at the early stage of understanding what controls the cycles of magmatic/tectonic events at mid-ocean ridges. Mid-ocean ridges and hotspots, such as Iceland, the Azores, and Galapagos islands, exhibit the greatest flow of heat from the Earth’s mantle to the bottom of the oceans. The effects of such hotspots are manifested by shallowing and even emergence of the ocean floor (the two most dramatic ca
ses being Hawaii in the Pacific ocean basin and Iceland at the Mid-Atlantic Ridge), increases in the thickness of the oceanic crust, changes in the style and intensity of seafloor volcanism, and evolving geometry of the seafloor spreading centres. When a hotspot interacts with a mid-ocean ridge spreading centre, the lava that erupts on the ocean floor (and on the hotspot islands) also contains important information on the chemical composition of Earth’s mantle. However, we do not yet know whether most of the hotspots found on the ocean basins have deep roots inside Earth’s lower mantle, or are caused by anomalies in Earth’s upper mantle.
