Here's why:
* Seawater is a solution: Seawater is a mixture of water and dissolved salts, with magnesium chloride being one of the major dissolved salts.
* Solubility: Magnesium chloride is highly soluble in water.
* Abundance: Magnesium chloride is the third most abundant dissolved salt in seawater after sodium chloride and sodium sulfate.
Therefore, magnesium chloride is not only present in seawater, but it's also dissolved within it.
