Final answer:
The option NOT an example of a carbon sink among the choices provided is 'd. The vast open ocean,' as it is part of the carbon cycle where exchange of carbon happens rapidly rather than acting as a storage depot, unlike the other options which are true carbon sinks.
Step-by-step explanation:
In addressing the question of which option is NOT an example of a carbon sink, we focus on the key components of the carbon cycle and carbon sinks. A carbon sink is a natural or artificial reservoir that accumulates and stores some carbon-containing chemical compound for an indefinite period. The choices provided include many typical examples of carbon sinks: deposition of organic matter on the deep ocean floor (carbon sediments become part of the oceanic crust and store carbon for long periods), preservation of a tropical rainforest (where carbon is absorbed and stored in the trees and soil), and formation of calcium carbonate shells of marine crustaceans (which eventually contribute to the formation of geological features like limestone that act as long-term carbon stores).
However, the vast open ocean itself is not a sink for carbon. While the top layer of ocean water does dissolve some atmospheric carbon dioxide, the ocean in general is part of the carbon cycle where exchange happens quite rapidly and continuously, rather than being a storage depot. Nutrient uptake by the roots of grasses in a suburban lawn also can be considered as a carbon sink, as the grasses absorb carbon dioxide from the atmosphere during photosynthesis, contributing to the carbon storage in soil. Therefore, the option that is NOT an example of a carbon sink is 'd. The vast open ocean'.