Final answer:
The density of salt in surface waters can increase due to thermal expansion, melting of ice caps, ocean acidification, seasonal turnover in lakes, and changes in molecular interactions caused by high salt concentrations.
Step-by-step explanation:
The increase in the density of salt in surface waters can be attributed to a few factors. One such factor is the process known as thermal expansion, where warmer water has its density decreased, causing the same amount of water molecules to occupy a larger volume. This is significant in the context of sea level rise due to global climate change. Another factor contributing to salt density increase is the melting of glaciers and polar ice caps, which releases previously frozen freshwater into the ocean, thereby increasing the overall volume of the ocean and affecting its salinity.
Moreover, the uptake of atmospheric carbon dioxide leads to ocean acidification, which can impact the solubility and distribution of salts in ocean waters. In addition, during the spring turnover in lakes, as surface ice melts and water warms to 4 °C, this denser water sinks, displacing nutrients and potentially affecting the salinity levels in surface waters. Lastly, high amounts of salt can change how water molecules interact with other substances, such as proteins, which can lead to increased protein-protein interactions and affect the water's characteristics.