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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.
The Organization is the originator of the Convention on the protection of the Underwater Cultural Heritage, the Global Ocean Observing System and UNESCO global geoparks. Around 1 800 quantifiable and monetary pledges totaling $108 billion have been obtained since 2017 for the UN Ocean Conference and the Our Ocean Conference. [65] [66] [67] [68]
Warm-water coral reefs face near-term threats to their survival, but research on observed and projected impacts is very advanced. [ 67 ] Anthropogenic climate change has exposed ocean and coastal ecosystems to conditions that are unprecedented over millennia (high confidence2 15 ), and this has greatly impacted life in the ocean and 16 along ...
The ocean is a major driver of Earth's water cycle. Ocean water represents the largest body of water within the global water cycle (oceans contain 97% of Earth's water). Evaporation from the ocean moves water into the atmosphere to later rain back down onto land and the ocean. [69] Oceans have a significant effect on the biosphere.
These systems contrast with freshwater ecosystems, which have a lower salt content. Marine waters cover more than 70% of the surface of the Earth and account for more than 97% of Earth's water supply [3] [4] and 90% of habitable space on Earth. [5] Seawater has an average salinity of 35 parts per thousand of water.
Warm water corals are clearly in decline, with losses of 50% over the last 30–50 years due to multiple threats from ocean warming, ocean acidification, pollution and physical damage from activities such as fishing, and these pressures are expected to intensify. [98] [83]: 416
Environmental degradation is one of the ten threats officially cautioned by the High-level Panel on Threats, Challenges and Change of the United Nations. The United Nations International Strategy for Disaster Reduction defines environmental degradation as "the reduction of the capacity of the environment to meet social and ecological objectives ...
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nutrient-rich upwelled water stimulates the growth and reproduction of primary producers such as phytoplankton.