Here is one way you can do it.
Go to Select --> Color Range... With the Eye Dropper tool select a sample from the ocean pixels (100k) then in the Color range dialogue box check the invert button. Click OK and all values below 100k are selected.
Next select Image --> Adjustments --> Levels, bringing up the levels dialogue box.
In the Output levels box changing 0 to 8 will shift the 99k values to 96k.
I hope this helps.