Sea Water vs. Fresh Water

　　In our pursuit to unravel the distinctive characteristics and far-reaching effects of Earth’s primary aquatic entities, we’re zeroing in on the contrast between sea water and fresh water. What are the pivotal differences that set them apart, and how do these distinctions influence our ecosystems and daily routines? Let’s explore these disparities and the indispensable roles each water body plays.

　　Interviewer: "Let’s begin with the most recognizable trait of the ocean—it’s its salinity. Can you explain the fundamental elements that contribute to the saltiness of seawater?"

　　Expert: "Well, the ocean’s salinity is primarily composed of sodium and chloride, which together make up what we commonly know as table salt. Seawater salinity is measured by the ratio of salt to a liter of water, with an average of 35 grams of dissolved salts per liter, denoted as 35‰. However, this isn’t consistent across all oceanic regions; the salinity can vary due to weather patterns, with areas of high and low salinity much like areas of high and low pressure in meteorology."

　　Interviewer: "That’s interesting. How does the salinity differ across the various ocean basins?"

　　Expert: "The Atlantic Ocean is typically the saltiest among the five ocean basins. There’s a noticeable drop in salinity near the equator and at the poles, but for varying reasons. Near the equator, heavy tropical rainfall introduces freshwater into the ocean, diluting the surface water salinity. Moving towards the poles, rainfall decreases, and with more sunshine, evaporation rates rise. Also, the freshwater from melting ice reduces surface salinity at the poles."

　　Interviewer: "Can you elaborate on the processes that contribute to these variations?"

　　Expert: "Certainly. Freshwater evaporates from the ocean’s surface and moves into the atmosphere, leading to higher salinity in areas with less rainfall. Conversely, at the poles, melting ice introduces more freshwater, again lowering salinity. The saltiest ocean waters are found in regions with high evaporation rates or in bodies of water without an outlet to the ocean, like the Red Sea and the Persian Gulf, which can have salinity levels around 40‰."

　　Interviewer: "Now, let’s compare sea water and fresh water directly. How do their salt concentrations stack up?"

　　Expert: "If you were to evaporate a cubic foot of seawater, you’d be left with roughly 2.2 pounds of salt. Compare that to a cubic foot of water from one of North America’s Great Lakes, where only about 0.01 pounds of salt remains, or roughly one-sixth of an ounce. This means the sea is approximately 220 times saltier than our major freshwater sources."