Which factor made the Deepwater Horizon oil spill very different from previous marine oil spills?

The factor that made the Deepwater Horizon oil spill significantly different from previous marine oil spills is that it happened at great depth below the surface. This depth, approximately 1 mile underwater in the Gulf of Mexico, presented unique challenges both in terms of containment and cleanup efforts compared to oil spills that occurred closer to the surface. The pressure and conditions at such depths affected the behavior and dispersion of the oil, making it more challenging to respond effectively.

Additionally, the deep location meant that the oil was released into a less accessible environment, complicating monitoring and recovery operations. The spill's great depth also led to the formation of underwater plumes, impacting marine ecosystems in ways that were not typically observed in other spills. This situational context highlights why the depth at which the spill occurred was a defining characteristic that influenced its consequences and the approach needed for remediation.