The sun and wind evaporate water from the surface of pools. In pools isolated from the ocean, this causes a relative increase in salinity (salt-concentration.) Upper intertidal tide pools heat up rapidly especially in the summer months. If any water is left in an upper tide pool it will probably have a very high salinity. In the image above, the tide pool has completely evaporated leaving behind the salt and other dissolved material. However, at the other extreme, these upper tide pools can experience fresh water run off from rain and snow melt causing some dilution...