Understanding Earth’s Water Systems: Oceans, Inland Waters, and the Water Cycle
Dynamic Oceanica
Marine Currents: redistribute the heat received from the Sun, accounting for differences in solar radiation by latitude. They are crucial heat delivery mechanisms for the Earth. Surface ocean currents (eddies are produced in the oceans as cyclonic or anticyclonic formations). Deep sea currents (occur due to differences in water density).
Tides: Deformations of sea level are caused by the gravitational attraction exerted on the Earth by the Moon, and to a lesser extent, the Sun. As the Earth rotates, the sea water rises and falls. Each point on the coast experiences high tide when aligned with the Moon or Sun, and low tide when positioned otherwise. As the Moon aligns, there are typically two high tides and two low tides for each point on Earth.
Inland Water Distribution
Surface Waters: are formed by the confluence of rivers originating from streams. These streams, in turn, form rivers, creating a structure similar to a tree, where the main river is the trunk and its tributaries are the branches. Drainage Network (the set of streams that drain into a river). Catchment (the land surface occupied by a drainage network, i.e., the surface area from which groundwater flows into the same river).
Groundwater: forms when water from rivers, lakes, or seas infiltrates the earth through pores in rocks and sediments. This water can move or be stored, forming groundwater. Key features of these rocks include: Porosity (the ratio between voids and the total volume of the rock) and Permeability (the ability of a rock to allow water to circulate).
Water Cycle
The water cycle is a closed circuit where water flows through interconnected compartments of the hydrosphere. The phases of the water cycle are:
Evapotranspiration: Continental and oceanic water evaporates due to solar energy, entering the atmosphere as water vapor. Living organisms also contribute water vapor through transpiration. The sum of these two processes is evapotranspiration.
Precipitation: Water evaporated from the sea and rivers accumulates in the upper atmosphere as water vapor, leading to precipitation in the form of rain, snow, etc.
Runoff: Water returns to the oceans through various paths: Surface runoff (rivers, streams…) or Underground runoff (water infiltrates into the soil and descends to reach the sea).
-> Water Balance: The relationship between water entering (rains) and leaving (evapotranspiration).
Ocean Waters
Salinity, temperature, and density are the most important chemical and physical parameters that determine the behavior of ocean water:
Salinity: The total dissolved substances in a fixed amount of water, usually expressed in grams of salt per kilogram of sample (parts per thousand). Salinity is controlled by the balance between evaporation and precipitation.
Temperature: Varies with latitude in surface waters and also with the depth of the ocean.
Density: Depends on salinity and temperature. The density of ocean waters is directly proportional to salinity and inversely proportional to temperature.