Final answer:
The density of seawater reflects its salinity, with about 3.5% consisting of dissolved solids like NaCl. Variations in salinity, influenced by processes such as evaporation, affect water density and have wider ecological and geochemical implications.
Step-by-step explanation:
The density of seawater reflects its salinity. Seawater is comprised mostly of H2O, but about 3.5% of it consists of dissolved solids, with the majority being sodium chloride (NaCl), among other ions. Seawater's salinity is significant due to its high concentration of dissolved ions, approximately 35,000 mg per liter, which affects its density. The organic matter present in seawater, though low in concentration, also plays a crucial role ecologically and chemically. In particular, the surface of the ocean is covered with an organic film influencing gas exchange with the atmosphere.
Evaporation plays an instrumental role in the water cycle by distilling out nearly pure water and leaving behind the dissolved ions in the remaining liquid. This process creates variations in salinity in different bodies of water, from highly saline oceans to less saline freshwater systems such as rivers and lakes. The salinity affects not only the density but also the geochemistry of our planet, including natural salt deposit formation and the ecology within high salinity environments like evaporative salt ponds.
Therefore, the density of seawater not only indicates its salinity but also implicates a range of ecological, chemical, and geological phenomena.