At first you have to write the variables out which are

now you have to combine like terms


now you add these two variables and end up with answer of
1. lifeless
2. evaporation
3. seeps into
4. surface, pycnocline, deep
5. food web
6. photic
I believe your answer would be places. Because a grid system makes it easier to find a location on a map. Hope this helps!
Answer:
may be a few Chuck's don't know lol