OCEAN WATER AND OCEAN LIFE

15.1 The Composition of Seawater Salinity is the total amount of salt dissolved in water, expressed in parts per thousand (‰) The salinity of seawater is 3.5% or 35 ‰ Most of the salt in seawater is sodium chloride The sources of salts in seawater is from salts dissolved in runoff from the chemical weathering of rocks and elements from volcanic eruptions The salinity of seawater varies slightly from 33 ‰to 38 ‰. The processes that affect salinity are adding a large amount of fresh water from precipitation, runoff from land, and melting sea ice (decreases salinity) evaporation (increases salinity)

Ocean Temperature variation 1. Ocean temperature variation with latitude – lower sea temperatures are found at higher latitudes (closer to the poles) 2. Ocean temperature variation with depth The sun’s rays only penetrate to a depth of about 1000 meters Thermocline – the layer of water between 300 meters and 1000 meters where there is a rapid change in temperature

Ocean density variation Density is mass divided by volume Density of seawater is affected by salinity and temperature Density increases the higher the salinity and the lower the temperature Pycnocline – a layer of water between 300 meters and 1000 meters, there is little mixing between the upper less dense water and the lower more dense water

Ocean Layering Surface zone – water is warmest of uniform temperature, mixed zone Transition zone – temperature fall rapidly Deep zone – no sunlight, temperatures constant at a few degrees above freezing, pressures high, cold-high density

Classification of Marine Organisms Plankton – includes all organisms that drift with ocean currents, phytoplankton and zooplankton Phytoplankton forms the base of the marine food chain, produces much of the oxygen we breathe Nekton – free swimmers Benthos - bottom dwelling

Marine Life Zones 1. Availability of Sunlight Photic – upper part of the ocean where sunlight penetrates Euphotic – surface area where photosynthesis occurs, about 100 meters Aphotic – sunlight does not penetrate

2. Distance from Shore Intertidal zone – plants and animals must adapt to crashing waves, periodic drying out, changes in temperature, salinity and oxygen content Neritic zone – extends from the low-tide zone to the edge of the continental shelf, very productive due to nutrients from land and shallower waters Oceanic zone- beyond the continental shelf, waters have lower nutrient content

3. Water depth Pelagic zone – open ocean Benthic zone – bottom Abyssal zone – deep ocean floor with extremely high pressure

5.3 Ocean Productivity Primary Productivity is the production of organic compounds from inorganic substances through photosynthesis or chemosynthesis Photosynthesis is the use of light energy to convert water and carbon dioxide into energy rich glucose molecules Chemosynthesis is the process by which certain microorganisms create organic molecules from inorganic nutrients using chemical energy Two factors affect ocean primary productivity – availability of nutrients (nitrogen, phosphorus, and iron) and the amount of sunlight

Productivity in Polar Oceans – highly productive due to upwelling of nutrients from the bottom Solar radiation is the limiting factor Productivity of Tropical Oceans – productivity is low due to little mixing of the nutrient rich bottom waters with warm surface waters Nutrients are the limiting factor Productivity of Temperate Oceans – productivity is limited by both nutrients and availability of sunlight, varies according to season

Ocean Feeding Relationships Marine algae, plants, and bacteria are the basis of the food chain – primary producers Trophic levels – feeding levels Transfer efficiency between trophic levels is very inefficient Food chain is a sequence of organisms through which energy is transferred Primary producer → herbivore → carnivore Food web shows the feeding relationship among many organisms