Water pH (water in the ocean is alkalyne, different from the varied soils we can have), water dynamics and currents (whater moves, soils do not), temperature delta (the deeper it goes, there are different temperatures), source of nutrients (carbon cycle on the different soils we have vs the ocean nutrient cycles), sunlight availability (sunlight might change based on the particulates present on the ocean, in different seasons, etc, in a higher variation than above soil), etc. Ocean dynamics is very different than continental dynamics (or island dynamics).
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Water pH (water in the ocean is alkalyne, different from soils), water dynamics and currents (whater moves, soils do not), temperature delta (the deeper it goes, there are different temperatures), source of nutrients (carbon cycle on soils vs the ocean nutrient cycles), sunlight availability (sunlight might change based on the particulates present on the ocean, in different seasons, etc, in a higher variation than above soil), etc. Ocean dynamics is very different than continental dynamics (or island dynamics).