Ocean energies (OEs) are referred to as a group of renewable energies attached to (这是按照你的字面意思翻译的,我觉得改为contained in较好) the oceanic water.Through a variety of physical processes,the ocean recieves,stores(reserves),and emits energies in the forms of tide,wave,temperature difference,salinity gradient,and ocean flow,etc.
The earth's surface area is about 5.1×10^8km^2,including 1.49×10^8km^2 land surface area (account for 29%) and 3.61×10^8km^2 ocean surface area.Land mean altitude is around 840m with sea surface as a referrence,while the mean depth and volume of the ocean are 380 m and 1.37×10^9km^3,respectively.The endless ocean can not only provide people with shipping(transportation),water resource,and rich minerals,but also can store solar energy and the derived wind energy in the forms of thermal energy and mechanical energy,and these energies are not easy to loss as those in the land or air.
OEs have the following features：
1.OEs have large storage in the total water in the ocean,however,the energy contained in per volume,per area,and per length is low.This is to say,large energy only can be obtained from large volume of oceanic water.
2.OE has renewability.It derives from solar radiation and gravitation between celestial bodies such as the sun,the moon,therefore,OE is renewable and inexhaustible as long as the celestial bodies coexsist with the earth.
3.OEs can be divided into relative stable energies and instable energies.The former include temperature difference energy,salinity gradient energy,and ocean flow energy,while the latter also can be subdivided into two groups as regular instable energies (eg.tidal energy and tidal current energy) and irregular energies (eg.wave energy).People can compile timeto-time and day-by-day tide and ocean flow prediction everywhere to predict tide scale and ocean flow according to tide and ocean flow dynamics（可选词汇:fluctuations,changing rules）.Tidal power stations and ocean flow power stations may arrange for their generations according to the prediction.
4.OEs belong to clean energies,that is to say,they cause almost none environmental pollution once belong exploered （可替换词汇是developed,但是这里我觉得用给出的比较好）.