When glaciers are growing larger, the concentration of the heavier oxygen isotope in sea water increases?

TRUE

Explanation: Oxygen has two isotopes namely, ¹⁶O (being the lighter oxygen) and ¹⁸O (being the heavier oxygen). Both this isotopes plays a significant role.

The water-ice that accumulates at the glaciated region are derived from the seas and oceans. The ocean and sea water when heated, gets vaporized and rises up, being rich in ¹⁶O, whereas the ¹⁸O, being the heavier isotope does not get vaporize and so it remains in the oceans.

This lighter oxygen isotopes ¹⁶O are then carried to the atmosphere which subsequently falls back as snow in the glacial covered region and consecutively forms ice undergoing compaction.

This, is the reason why ¹⁶O are rich in the glaciated region, whereas the ocean waters are rich in ¹⁸O.

Thus, the above given statement is true, i.e when glaciers become large in size and quantity, then the concentration of heavier oxygen isotope also increases in the ocean and sea water.