While the ocean's temperature is higher near the equator, it doesn't have that great of an effect on the dumbo octopus as is lives at such depths that it would be cold regardless.
Regions of the ocean with greater amounts of rainfall will have a lower salinity.
Within the coastline of North Carolina there is a wide range of temperatures. The Gulf Stream (orange) brings in warmer waters allowing for this variety in temperature.
Along North Carolina's coastline, different areas receive different amounts of rainfall. The areas with less rain will have a higher salinity than areas with more rain.
The dumbo octopus lives on the ocean floor. The map above shows the salinity at the ocean surface. However, since the dumbo octopus lives so deep down, its salinity as well as pressure is much higher. In general, precipitation will impact the ocean's salinity, and a greater amount of precipitation will decrease salinity. For the same reason, salinity is lower near the poles because of the melting ice caps.