Ocean acidification: the oceans are becoming more acidic ph: stable at -8. 2. How many oceans: historically four: pacific, atlantic, indian and artic. In recent years a fifth is sometimes added: the southern ocean. Salinity: number of grams of salts dissolved in 1000g of water, expressed as parts per thousand. In decreasing order of abundance cl, na, so, mg, ca, k, etc. Surface water salinity averages 35: higher salinity - from evaporation and sea-ice formation, lowe salinity - from rainfall, glacial melt, and river input. Salinity becomes more inform with depth: halocline: zone of rapid salinity change. Temperature: quite variable: surface range: ~28 c/83 f (tropics) ~0 c/32 f, average sea surface temperature: ~17 c/63 f, seasonal variations: Temperature versus depth: surface water is warm -> doesn"t want to sink, below 300 m in the tropics: near freezing (polar water is always near freezing, abrupt t change is called the thermocline.