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The surface salinity of the ocean is a key variable in the climate system when studying the global water cycle, ocean–atmosphere exchanges and ocean circulation, all vital components transporting heat, momentum, carbon and nutrients around the world. [84] Cold water is more dense than warm water and salty water is more dense than freshwater.
While marine pollution can be obvious, as with the marine debris shown above, it is often the pollutants that cannot be seen that cause most harm.. Marine pollution occurs when substances used or spread by humans, such as industrial, agricultural and residential waste, particles, noise, excess carbon dioxide or invasive organisms enter the ocean and cause harmful effects there.
Mercury can enter seas and the open ocean as a result of the down stream movement and re-deposition of contaminated sediments from urban estuaries. [12] For example, high total Hg content up to 5 mg/kg and averaging about 2 mg/kg occur in the surface sediments and sediment cores of the tidal River Mersey, UK, due to discharge from historical industries located along the banks of the tidal ...
Driven by this sinking and the upwelling that occurs in lower latitudes, as well as the driving force of the winds on surface water, the ocean currents act to circulate water throughout the sea. When global warming is factored in, changes occur, particularly in areas where deep water is formed. [50]
Debris on beach near Dar es Salaam, Tanzania Debris collected from beaches on Tern Island in the French Frigate Shoals over one month. Researchers classify debris as either land- or ocean-based; in 1991, the United Nations Joint Group of Experts on the Scientific Aspects of Marine Pollution estimated that up to 80% of the pollution was land-based, [5] with the remaining 20% originating from ...
Over time, the water returns to the ocean, to continue the water cycle. The ocean plays a key role in the water cycle. The ocean holds "97% of the total water on the planet; 78% of global precipitation occurs over the ocean, and it is the source of 86% of global evaporation". [2]
Changes in ocean circulation triggered by ongoing climate change could also add or magnify other causes of oxygen reductions in the ocean. [11] Anthropogenic causes include use of chemical fertilizers and their subsequent presence in water runoff and groundwater, direct sewage discharge into rivers and lakes, and nutrient discharge into ...
The rising temperatures in the oceans also cause a reduced solubility of oxygen in the water, which can explain about 50% of oxygen loss in the upper level of the ocean (>1000 m). Warmer ocean water holds less oxygen and is more buoyant than cooler water.