Final answer:
Changes in ocean salinity affect ocean circulation and climate patterns, potentially disrupting marine ecosystems and the water cycle. The rise in ocean levels due to global warming and melting glaciers threatens freshwater resources and shoreline stability.
Step-by-step explanation:
Scientists have observed a change in ocean salinity over the past fifty years, specifically with tropical and subtropical regions in the Atlantic Ocean becoming saltier and the high latitudes becoming fresher. Since salty water is denser and tends to sink, changes in the salinity can affect ocean circulation and climate. If the cooler northern ocean waters become less salty, we may see changes in climate patterns, such as alterations in global wind circulation cells which affect precipitation levels and can influence desert locations and sizes. We might also see changes in marine ecosystems, such as the productivity of organisms like phytoplankton and krill due to the disruption of upwelling zones caused by the density changes in ocean waters.
Global warming is an additional factor that can cause ocean levels to rise due to meltwater from glaciers and from the expansion of water as it warms. This leads to the inundation of shorelines and the potential disappearance of islands. The water cycle itself, including the processes of evaporation and condensation, plays a crucial role in how water varies in salinity. It ensures that oceans maintain a high salinity while freshwater resources, continually recycled through these processes, remain low in salinity. Freshwater availability is therefore crucial, as the melting and refreezing cycles of glaciers and polar regions, which have been a source of freshwater for centuries, may be jeopardized, leading to a shortage of freshwater resources.