What describes nutrient cycling in marine ecosystems?

Nutrient cycling in marine ecosystems primarily involves the recycling of nutrients through various biological processes that sustain productivity within these ecosystems. This includes the uptake of nutrients by primary producers, such as phytoplankton and seaweeds, which use them to grow and reproduce. When these organisms are consumed by herbivores, the nutrients are transferred within the food web. Upon death or excretion, decomposers break down the organic material, returning these nutrients to the water column, where they can be re-assimilated by primary producers. This cycle is crucial for maintaining the health and productivity of marine ecosystems, allowing them to support diverse forms of marine life.

In contrast, the other choices describe scenarios that do not accurately reflect the complex processes of nutrient cycling in marine environments. While nutrients can be deposited on the ocean floor or derived from oceanic currents, these actions do not encompass the entirety of nutrient cycling, which is fundamentally about the continuous movement and recycling of nutrients through living organisms and ecosystems.