Barcelona
España

Saltwater

Escrito por Peces y Corales

Saltwater

 españaVersión en español

 

ARTICLE TABLE OF CONTENTS
What is it?
Origin
Composition
Salinity
Electrical conductivity
Density
Ph
Gases

 

What is it?

Seawater or saltwater is a solution made or based on water that composes the oceans and seas of the Earth. It is salty by the concentration of dissolved mineral salts containing, a 35 ‰ (3.5% or 35 g/L) as average. The average surface density is 1.025 g/ml, being denser than fresh water and pure water. A higher salt content lowers its freezing point, so seawater converts to ice under −2 °C, although a current in Antarctica has been recorded at −2.6 °C. The ocean contains 97.25% of the total water that forms the hydrosphere.

Origin

Scientific theories behind the seawater origins began with Edmond Halley in 1715. He proposed that salt and other minerals came into the sea from the rivers in the continents. And these came into the rivers from the continuous washing of the terrestrial minerals through the rain. Once reaching the ocean, these salts have been concentrating more and more on the oceans through the hydrological cycle. Halley also realized that those lakes that had no exit to the sea (such as the Dead Sea or the Caspian Sea) had high saline concentrations. Halley called this process the "Continental Weathering" process.

Composition

El agua de mar es una disolución en agua (H2O) de muy diversas sustancias. Hasta los 2/3 de los elementos químicos naturales están presentes en el agua de mar, aunque la mayoría sólo como trazas. Seis componentes, todos ellos iones, dan cuenta de más del 99 % de la composición de solutos.

WANT TO KNOW MORE? REMAIN IN ACUAPEDIA
The ocean
Speciation
Evaporation
Salt

Salinity

The study of the composition is simplified by the fact that the proportions of the components are always approximately the same, although the joint concentration of all of them is enormously variable. We refer to this total concentration as salinity, which is usually expressed as per thousand (‰). Thanks to the universality of its composition, salinity is usually estimated from the measurement of a single parameter, such as electrical conductivity, refractive index or concentration of one of its components, usually the chloride ion (Cl-). Salinity presents variations when one compares the watersheds, the different latitudes or the different depths. It favours a higher salinity the most intense evaporation of the tropical latitudes, especially on the surface, and a lower salinity due to the proximity of river mouths and high precipitations.

Electrical conductivity

Saltwater has a high electrical conductivity, which contributes to the polarity of the water and to the abundance of dissolved ions. Salts in water dissociate themselves into ions. An ion is an atom positively or negatively charged and, therefore, exchanges electrons with the medium. They can absorb and release electrons to neighbouring particles. The conductivity varies especially with temperature and salinity (at higher salinity, greater conductivity), and its measurement allows, with controlled temperature, to know the salinity.

Density

The density of seawater is one of its most important properties. Its variation causes currents. It is determined using the international equation of seawater state at atmospheric pressure, which is formulated by UNESCO (UNESCO Technical Papers in Marine Science, 1981) from the work done throughout this century to know the relationships among the thermodynamic variables of seawater: density, pressure, salinity, and temperature. The density of the typical seawater (saltwater with 3.5% of dissolved salts) is usually 1.02819 kg/L at − 2 °C, 1.02811 at 0 °C, 1.02778 at 4 °C, etc.

Ph

The ocean water is slightly alkaline, and the pH value is between 7.5 and 8.4 and varies depending on the temperature. If it increases, pH decreases and tends to acidity. It can also vary depending on salinity, pressure or depth and the vital activity of marine organisms.

Gases

In well-mixed surface oceanic waters, the typical composition of dissolved gases includes 64% nitrogen (N2), 34% oxygen (O2) and 1.8% carbon dioxide (CO2), far above the latter of 0.04% in the open air. Oxygen (O2) abounds mainly on the surface, where photosynthesis predominates on respiration and tends to present its minimum to 400 m deep, where the effects of diffusion from the air and photosynthesis no longer reach, but where it is still high density of consumer organisms, which deplete it. The temperature, lower in the deep bottoms, affects the solubility of the carbonates.

 

Categoría: