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2 The process of moving water out of the oceans and back to the land is called the hydrologic cycle. evaporation precipitation Run-off transpiration Water is purified, collected and distributed throughout the globe. infiltration

3 Precipitation and condensation return water to the land, causing erosion and transporting nutrients. Infiltration of water into the soil recharges groundwater. Surface runoff and groundwater eventually return water back to the ocean for the cycle to begin over. On a global scale, it rains more over land.

4 Evaporation exceeds precipitation over the ocean resulting in a net movement of water to the land by wind. On land about 90% of water vapor results from plant transpiration. More Evaporation More precipitation

5 The oceans have 97.4% of the planet’s water and cover 75% of the earth’s surface. The remaining 2.8% is divided among rivers, lakes, groundwater, aquifers, and the greatest amount is locked in glaciers and polar ice.

6 While the water cycle is a global system in equilibrium - the water budget is not. An ideally balanced yearly water budget at all locations would have an equal amount of incoming water and outgoing water. We are not running out of water, but we are not returning it to the cycle in usable condition.

7 1. Unevenly distributed populations - need for a large per capita supply. For example, China has only 7% of the world’s freshwater supply but 21% of the world’s people. 2. Seasonal factors and warming trends create droughts. Surplus water occurs in winter due to lower evaporation rates. Deficits occur in the summer. The budget may be altered by situations that create shortages:

8 3. Geography: Evaporation is greater over the ocean. Precipitation is greater over the land. Dry, cold climates have less precipitation. 4. Anthropogenic activities: pollution, over-grazing, aquifer and surface water over-drafts, cutting down vegetation and other forms of deforestation. 5. The politically dangerous issue of who will control access to surface water. Many Middle Eastern and African countries have severe water shortages.

9 Oceans moderate climate, provide habitat and resources for many species on Earth. Aquatic biomes are divided into freshwater and saltwater (marine).

Major Ocean Basins

12 N 2 and CO 2 are the most abundant dissolved gases. The oceans are called carbon sinks because of their ability to hold this gas. Oxygen is less soluble, but ocean phytoplankton produce much of the atmospheric oxygen. Dissolved salts primarily Cl - and Na + and minerals give it an average pelagic salinity of 35 0/00. Contains organic nutrients and a fairly constant pH of ~8.1 Saltwater has these characteristics:

13 The ocean water is mixed by currents, waves, and upwelling. Some ecosystems in the ocean biome are: 1. Polar seas - ocean based ecosystem in North Pole, land based ecosystems in South Pole; short, efficient food chains for marine mammals (Pinnipeds); penguins only in the southern hemisphere (except near equator in Galapagos) 2. Coral reefs - oasis in a biological desert; based on mutualistic relationships between corals and zooxanthellae; greatly affected by coastal development (runoff and nutrification).

14 3. Shallow benthic - most productive zone because of light 4. Abyssal zone - recently discovered hydrothermal vent communities, cold seeps and unusual species NOAA

15 6. Estuaries - 55% of these wetlands have been lost; serve as a nursery grounds for many species 5. Sandy and Rocky beaches - 70% are experiencing heavy erosion, human pressure and efforts to protect them are expensive