Physical properties of seawater, light penetration and colour of the sea
Composition of seawater
Seawater is a complex mixture of water, salts, and other dissolved substances. It has a number of unique physical properties, including:
Salinity:
Salinity is a measure of the amount of dissolved salts in seawater. It is typically expressed in parts per thousand (ppt). The average salinity of seawater is about 35 ppt, but it can vary depending on location and depth.
Density:
Density is a measure of how much mass is contained in a given volume. Seawater is denser than fresh water because of the dissolved salts. The density of seawater also increases with depth due to increasing pressure.
Temperature:
The temperature of seawater varies depending on location, depth, and time of year. The average temperature of seawater at the surface is about 20°C, but it can range from below freezing to over 30°C.
pH:
pH is a measure of how acidic or alkaline a substance is. Seawater is slightly alkaline, with a pH of about 8.2. Light penetration and color of the sea
Colour of Seawater
When sunlight hits the ocean surface, some of it is reflected back into the atmosphere and some of it is absorbed by the water. The amount of light that is absorbed depends on the wavelength of the light and the clarity of the water.
Red, orange, and yellow light have longer wavelengths and are absorbed more quickly by water than blue and green light. This is why the ocean appears blue to the human eye. The clearest ocean waters can absorb up to 99% of the sunlight within the first 100 meters of depth.
The color of the ocean can also be affected by the presence of suspended particles and dissolved substances. For example, phytoplankton, which are tiny algae that live in the ocean, can absorb blue light, making the water appear more green. And sediment in the water can absorb all wavelengths of light, making the water appear brown or muddy.
Overall, the physical properties of seawater, light penetration, and the color of the sea are all interrelated. The salinity, density, temperature, and pH of seawater all affect how light interacts with the water. And the presence of suspended particles and dissolved substances can also affect the color of the water.