What does the expression “75 meters per second southeast” best describe?

Every second this thing moves 75 meters in the southeast direction. So, 2 secons will be 150 meters, 4 seconds will be 300 meters, etc.

Southeast means something in the middle between the south direction and the east direction, maybe about -45 degrees. We can apply Pythagorean theorem:

L1^2+L2^2=hip^2=(75m/s)^2

If East velocity is equal to the south velocity, both legs will be equal:

2L^2=(75m/s)^2

L^2=(75m/s)^2/2

L = square root [(75m/s)^2/2] = (75m/s)/[square root (2) ] = 53m/s

So the object is moving about 53m/s to the east and 53m/s to the south.

above statement is not a true statement about the open ocean because the open ocean has low levels of nutrients. most of the photosynthetic activity on earth occurs in the open ocean within the photic zone. organisms in the deep ocean are exposed to frigid temperatures and total darkness but it does not begin at the low-tide mark.