As the submersible approaches the twilight zone (300m deep), what changes in light and temperature occur?

In the twilight zone, the temperature and the light conditions change. The initial 200 meters of the ocean as considered as the open ocean. There is availability of light and thriving temperature there. Butt below that, in the 'deep ocean'. The availability of light decreases and as we go further down, the light no longer reaches those parts of the ocean. Moreover, the temperatures plummet down to almost freezing conditions. In addition to this, the pressure is much more higher in the deep ocean.

allowed for the prediction of the properties of missing elements.

well first you need the sample of the temperature and gas level. i couldnt write a hypothesis unless i had some data. i think temperature changes will effect volumes of gas because gas changed into a solid or liquid at specific temperatures.