The Hydrosphere

The “hydrosphere” is the water component of the Earth, including both saltwater and fresh water.

“Oceanography” is the study of our saltwater oceans.

The Composition of Seawater Seawater consists of about 3.5% (by weight) dissolved minerals. Salinity refers to the total amount of solid material dissolved in water. Salinity is typically expressed in parts per thousand (‰) The average salinity of seawater is 35‰, with the major constituent being sodium chloride

The Composition of Seawater Sources of Sea Salts chemical weathering of rocks on the continents and subsequent inflow from rivers outgassing from volcanic eruptions

The Composition of Seawater Processes Affecting Seawater Salinity Variations in salinity are a consequence of changes in the water content of the solution. Processes that decrease salinity (add water) include: precipitation runoff from land icebergs melting sea ice melting

The Composition of Seawater Processes Affecting Seawater Salinity Variations in salinity are a consequence of changes in the water content of the solution. Processes that increase salinity (remove water) include: evaporation formation of sea ice

The Composition of Seawater Surface salinity in the open ocean ranges from 33‰ to 38‰.

Processes Affecting Seawater Salinity decrease seawater salinity increase seawater salinity

A desalination plant that removes salts and other chemicals from sea water to produce fresh water.

Ocean Temperature Surface water temperature varies with the amount of solar radiation received. Lower surface temperatures are found in high-latitude regions. Higher surface temperatures are found in low-latitude regions. The unique thermal properties of seawater make it resistant to temperature changes. However, global warming could eventually influence ocean temperatures.

Ocean Temperature Variation with Depth In low latitudes, there is a high temperature at the surface, with a rapid decrease in temperature with depth. This indicates the presence of a thermocline. In high latitudes, there are cooler surface temperatures with no rapid change in temperature with depth.

Variations in the Ocean’s Surface Temperature and Salinity with Latitude Figure 14.3

Ocean Density Factors affecting seawater density: Density is the amount of mass a material contains in a given volume of space. Density determines the water’s vertical position in the ocean. Factors affecting seawater density: temperature (the greatest influence) salinity

Ocean Density Variations with Depth In low latitudes, there is low density at the surface, with the density increasing rapidly with depth because of colder water. This indicates the presence of a pycnocline. In high latitudes, we find high-density (cold) water at the surface with little change in density with depth.

Ocean “Layering” Due to Density The oceans have a three-layered structure according to density. The Surface Mixed Zone is warmed by the Sun and extends to a depth of 300 meters. The Transition Zone lies under the surface mixed zone and is where the thermocline and pycnocline are found, if present. The Deep Zone in under the transition zone when where sunlight never reaches. Temperatures here are just a few degrees above freezing, and the water density is constantly high.

About one-third of the carbon dioxide gas induced into the atmosphere by humans ends up in the oceans. This results in ocean water gradually becoming more acidic. This is threatening a variety of organisms, including food-chain microbes and corals.

The Ocean in Motion Currents

Ocean Water Circulation Ocean currents are masses of water that flow from one place to another. Surface currents develop from friction between the ocean and the wind that blows across the surface. Surface circulation of the oceans are cause by many interacting “gyres”, which are large systems of rotating ocean currents, particularly those involved with large wind movements.

Ocean Water Circulation Earth’s oceanic surface circulation is made up of five main gyres. North Atlantic Gyre North Pacific Gyre South Pacific Gyre South Atlantic Gyre Indian Ocean Gyre The gyres are related to atmospheric circulation.

Idealized surface circulation pattern for the Atlantic Ocean Idealized surface circulation pattern for the Atlantic Ocean. The prevailing winds create circular-moving loops of water (gyres) at the surface in both parts of the Atlantic Ocean basin. Figure 15.2

This false-color satellite image shows sea-surface temperatures of the Gulf Stream. Warmer waters are shown in red and orange, colder waters in green, blue, and purple. As the Gulf Stream meanders northward, some of its branches pinch off to form large, circular eddies. The Gulf Stream

Average ocean surface currents from February to March Average ocean surface currents from February to March. The oceans circulation is organized into five major current gyres (large, circular-moving loops of water), which exist in the North Pacific, South Pacific, North Atlantic, South Atlantic, and Indian Oceans.

Large ships crossing the ocean have lost entire containers overboard Large ships crossing the ocean have lost entire containers overboard. if the containers release floating items, inadvertent float meters are launched that help oceanographers track ocean surface currents. The map shows the path of drifting shoes and recovery locations from a spill in 1990.

Four Main Currents Exist Within Each Gyre

Surface Circulation Gyres are caused by the Coriolis Effect, an apparent deflection of moving objects caused by the rotation of the earth and the inertia of the mass experiencing the effect. The Coriolis force is quite small, and its effects generally become noticeable only for motions occurring over large distances and long periods of time, such as large-scale movement of air in the atmosphere or water in the ocean. This force causes moving objects on the surface of the Earth to appear to veer to the right in the northern hemisphere, and to the left in the southern. Surface currents are extremely important to Earth’s climate, as they transfer warmer water from low latitudes into higher latitudes, and thereby move heat from warmer to cooler areas.

Importance of Surface Currents Ocean currents have a significant influence on climate. When currents from low-latitude regions move to higher latitudes, they transfer heat from warmer to cooler areas on Earth. This is how the Gulf Stream keeps Great Britain and northwestern Europe warmer during the winter than should be expected for their latitudes. On the other hand, as cold currents originating in cold, high-latitude regions travel toward the equator, they tend to moderate the warm temperatures of adjacent land areas. For example, the cool Benguela current off the western coast of southern Africa moderates the heat along this coast.

Importance of Surface Currents Winds can also cause vertical water movements. Upwelling is the rising of cold waters from deeper layers to replace warmer surface water. Upwelling is most characteristic along the western coasts of continents where winds blow toward the equator and parallel to the coast. These winds combined with the Coriolis effect cause surface waters to move away from the shore, being replaced by cooler water “upwelling” from below. This process brings greater concentrations of dissolved nutrients to the ocean surface.

Deep Ocean Circulation Circulation in the deeper ocean is a response to density differences of water at varying depths. Recall that two factors create a dense mass of water: cold water and increased salinity. Deep-ocean circulation is referred to as thermohaline circulation. Most water involved in deep-ocean currents begins in high latitudes at the surface A simplified model of ocean circulation is similar to a conveyor belt that travels from the Atlantic Ocean, through the Indian and Pacific Oceans, and back again