Question

Assume someone brings several water samples to your laboratory. His problem is that the labels are incomplete. He knows samples \(A\) and \(B\) are from the Atlantic Ocean and that one came from near the equator and the other from near the Tropic of Cancer. But, he does not know which one is which. He has a similar problem with samples \(\mathrm{C}\) and \(\mathrm{D}\). One is from the Red Sea and the other is from the Baltic Sea. Applying your knowledge of ocean salinity, how would you identify the location of each sample? How were you able to figure this out?

Short answer

Sample A is from near the equator; B from the Tropic of Cancer. Sample C is from the Red Sea; D from the Baltic Sea.

Step-by-step solution

Understand Ocean Salinity Differences

Ocean salinity varies based on geographical location. Near the equator, evaporation rates are high, leading to increased salinity. In contrast, regions such as the Tropic of Cancer can experience lower salinity due to freshwater influx from rainfall or rivers. Therefore, sample B will likely have lower salinity than sample A.

Compare Sample A and B's Salinity

Measure the salinity of samples A and B. Determine that the sample with higher salinity is from near the equator, and the one with lower salinity is from the Tropic of Cancer. This will allow you to identify each sample accordingly.

Understand Regional Seas Salinity

The Red Sea is known for having one of the highest salinities due to high evaporation and low freshwater influx. The Baltic Sea, on the other hand, has low salinity because it receives large amounts of freshwater from surrounding rivers and has less evaporation.

Compare Sample C and D's Salinity

Measure the salinity of samples C and D. The sample with significantly higher salinity is from the Red Sea, and the one with lower salinity is from the Baltic Sea. This will allow you to assign the correct origin to each sample.

Key concepts

Atlantic Ocean

The Atlantic Ocean is the second-largest ocean on Earth, and it plays a crucial role in global salinity patterns. It extends from the Arctic Circle in the north to the Southern Ocean in the south. Salinity in the Atlantic Ocean can vary significantly depending on location. Near the equator, high temperatures lead to increased evaporation, thus resulting in higher salinity levels. Conversely, in areas like the Tropic of Cancer, the salinity can be slightly lower due to the influx of freshwater from rainfall and nearby rivers. These variations in salinity can help scientists identify the origin of water samples taken from different parts of the Atlantic Ocean.

Tropic of Cancer

The Tropic of Cancer is an imaginary line located at approximately 23.5 degrees north of the equator. This area is significant because it marks the northernmost point where the sun can appear directly overhead. In terms of ocean salinity, areas around the Tropic of Cancer in the Atlantic Ocean can have different salinity levels compared to equatorial regions. Generally, the Tropic of Cancer can receive more rainfall than the equator, which can bring freshwater into the ocean. This reduces salinity levels slightly compared to regions closer to the equator. The difference in salinity between the equator and the Tropic of Cancer is an important clue in determining the origin of ocean water samples.

Red Sea

The Red Sea is a narrow strip of water that lies between the northeastern part of Africa and the Arabian Peninsula. Known for its high salinity levels, the sea's high evaporation rates coupled with minimal freshwater input contribute to this characteristic trait. It is one of the saltiest bodies of water in the world, with salinity often exceeding 40 parts per thousand.
The climate around the Red Sea is arid, with limited rainfall, thus evaporation dominates the hydrological processes. This distinct feature makes the Red Sea's salinity much higher compared to many other seas, such as the Baltic Sea. Knowing this, researchers can determine if a water sample is from the Red Sea by its extremely high salinity measure.

Baltic Sea

The Baltic Sea is an inland sea located in Northern Europe, surrounded by countries such as Sweden, Finland, and Russia. It is characterized by its low salinity levels due to the numerous rivers that flow into the sea, bringing a large amount of freshwater into the system.
Moreover, the Baltic Sea experiences less evaporation because of its cooler climate. Its salinity can be less than 10 parts per thousand, which is much lower than ocean water. This low salinity is a key identifier for water samples from the Baltic Sea, making it distinguishable from high-salinity regions like the Red Sea. Understanding these factors is crucial for correctly identifying water sample origins in scientific studies.