Final answer:
The steepest change in slope in the ocean occurs at the continental slope. This zone marks the transition from the comparatively shallow continental shelf to the deeper ocean basins, characterized by a substantial change in depth and sediments.
Step-by-step explanation:
The most rapid change in slope in the ocean is found at the continental slope. This area is characterized by a sudden change to deep-water sediments such as shales, and it represents a dramatic change in depth from the continental shelf to the ocean basins. In the context of plate tectonics and earthquake patterns, the continental slope does not typically associate with the deepest earthquakes or the pattern of earthquakes from the coast to inland at subduction zones.
Most of the deep earthquakes are associated with subduction zone boundaries, where one tectonic plate is forced under another. Volcanoes are closer to the coastline near these subduction zones because partial melting of the asthenosphere above the subducting slab leads to volcanism. The rift and subduction zones in oceans are also where new oceanic crust is formed, as seen in areas like the Mid-Atlantic ridge.
Regarding the ecosystems of the ocean, the most photosynthesis is expected in the intertidal zone due to the availability of sunlight. Coral reefs are typically found in shallow ocean water where sunlight can support the symbiotic algae that live within the coral tissue. In comparison, the deepest part of the ocean, known as the abyssal zone, is devoid of sunlight and therefore lacks the photosynthetic life found in shallower regions.