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The hadal zone ranges from around 6 to 11 km (3.7 to 6.8 mi; 20,000 to 36,000 ft) below sea level, and exists in long, narrow, topographic V-shaped depressions. [ 1 ] [ 2 ] The cumulative area occupied by the 46 individual hadal habitats worldwide is less than 0.25% of the world's seafloor , yet trenches account for over 40% of the ocean's ...
Open ocean areas with no oxygen have grown more than 1.7 million square miles in the last 50 years, and coastal waters have seen a tenfold increase in low-oxygen areas in the same time. [47] Measurement of dissolved oxygen in coastal and open ocean waters for the past 50 years has revealed a marked decline in oxygen content.
From shallow waters to the deep sea, the open ocean to rivers and lakes, numerous terrestrial and marine species depend on the surface ecosystem and the organisms found there. [28] The ocean's surface acts like a skin between the atmosphere above and the water below, and harbours an ecosystem unique to this environment.
The main ocean currents involved with the North Pacific Gyre. The life processes in open-ocean ecosystems are a sink for the atmosphere’s increasing CO 2. Gyres make up a large proportion, approximately 75%, of what we refer to as the open ocean, or the area of the ocean that does not consist of coastal areas.
Dead zones are hypoxic (low-oxygen) areas in the world's oceans and large lakes. Hypoxia occurs when dissolved oxygen (DO) concentration falls to or below 2 ml of O 2 /liter. [2] When a body of water experiences hypoxic conditions, aquatic flora and fauna begin to change behavior in order to reach sections of water with higher oxygen levels.
Anoxic basins exist in the Baltic Sea, [6] the Black Sea, the Cariaco Trench, various fjord valleys, and elsewhere. [7] Eutrophication has likely increased the extent of anoxic zones in areas including the Baltic Sea, the Gulf of Mexico , [ 8 ] and Hood Canal in Washington State.
Worldwide, continental shelves occupy a total area of about 24 million km 2 (9 million sq mi), 8% of the ocean's total area and nearly 5% of the world's total area. [ 29 ] [ 30 ] Since the continental shelf is usually less than 200 metres deep, it follows that coastal habitats are generally photic , situated in the sunlit epipelagic zone .
A marine coastal ecosystem is a marine ecosystem which occurs where the land meets the ocean. Worldwide there is about 620,000 kilometres (390,000 mi) of coastline. Coastal habitats extend to the margins of the continental shelves, occupying about 7 percent of the ocean surface area.