Chapter 3 Chemical and Physical Features of Seawater & The World Ocean

– Water molecules stick together with hydrogen bonds. This effect is called cohesion. – In water the hydrogen bonds are formed between hydrogen and oxygen atoms of adjacent molecules.

– Any substance on earth can occur in three different states or phases: 1)solid 2)liquid 3)gas The States of Water

-Water molecules in a gaseous state move faster than those in a liquid state. - Water molecules in a liquid state move faster than those in a solid state. - As molecules move faster they move further apart.

Density of Water -As water cools, the molecules move closer together and the volume decreases. -As the volume decreases the weight stays the same and thus the water becomes more dense. -The colder the water, the more dense. What about ice? Ice is in a crystalline structure (crystals). - molecules are more spread out than when in a liquid Floating ice acts as an insulating blanket that helps keep the water below warm.

Seawater The characteristics of seawater are due to the nature of -pure water (universal solvent) -the solids dissolved in it (solute) Solids are dissolved in seawater by -weathering -hydrothermal vents -volcanoes

Salt Composition Seawater has a lot of solutes dissolved in it. solutes - dissolved material 98% of the solutes are made up of 6 different ions. Cl , Na +, SO 4 , Mg +2, Ca +2, and K + Sodium (Na) and chloride (Cl) ions make up 85% of the solutes, that is why seawater tastes like table salt.

Salinity is the total amount of salt dissolved in seawater. Expressed in parts per thousand, which is the number of grams of salt left behind when 1000 grams (1000mL) of seawater are evaporated. Example: 1000 grams of seawater is evaporated and 35 grams of salt is left behind… what is the salinity? 35 0 / 00 (parts per thousand)

Average salinity of the ocean = 35 0 / 00 The Red Sea = 40 0 / 00 The Baltic Sea = 7 0 / 00 Hotter weather results in increased rates of evaporation causing the salinity to be higher!!

Salinity increases when water is removed by evaporation freezing [ice is almost pure water] When water freezes salt is expelled out...there is no room for salt in the CRYSTAL STRUCTURE OF WATER!!! Salinity decreases when water is added from precipitation runoff glacier melt

While salinity of seawater varies, the relative concentration of each ion does not change. The principle is called the rule of constant proportions. So, no matter which sea you are floating around in... You will always be floating in about _____% NaCl.

Density of seawater not only depends on temperature, it also depends on salinity. The saltier the water the more dense it is. The colder the water the more dense it is. Ocean temp. varies more than salinity so density is controlled more by temperature than salinity. Reversing thermometers and electronic thermometers (ie. Clinefinder) are used to take temperature at various depths. Temperature Profile = a graph that shows temperature at different depths. The vertical axis appears upside down. Salinity, Temperature and Density

Satellite images can show the temperature of the oceans surface. Real Time Sea Temp. Link

Dissolved Gasses The three most important dissolved gasses are 1)oxygen - O 2 2)carbon dioxide - CO 2 3)nitrogen - N 2 Gas Exchange = gasses in the atmosphere dissolve into the seawater at the surface or the opposite can occur. Gasses dissolve better in cold water than in warm. This is important to animals at sea.

Niskin bottles are one type of sampling bottle that can be used to take samples at depth for various tests including salinity.

Transparency Transparency is necessary for photosynthesis. Material that is suspended and or dissolved in water can limit transparency. Red light penetrates the least. That is why things that appear red on the surface appear gray or black at depth. Blue light penetrates the most.

A Secchi disk is used to measure how much light penetrates through the water column (TURBIDITY). The more light that penetrates, (or the farther down the secchi is visible) the lower the salinity of the water.

Pressure Organisms on land are under 1atmosphere (ATM) of pressure With every 10 meters of added depth 1 ATM is added. Observe how air pressure affects a rising balloon.

Organisms that are brought up from the deep can be injured due to air bladder expansion. Surface organisms that go too deep can suffer from collapsed air bladders. This limits the depth and range of marine organisms.

Surface Circulation Currents and waves are driven by the wind. Coriolis effect = because the earth is rotating anything that moves over its surface turns a little to one side instead of moving in a straight line. Observe an animation of the Coriolis effect over Earth's surface. Northern Hemisphere = coriolis effect deflects things to the right (clockwise). Southern Hemisphere = coriolis effect deflects things to the left (counter clockwise).

Winds are driven by heat energy from the sun. Warm air at the equator rises and air from adjacent areas replaces the equatorial air. The winds created are called the Trade winds - they develop between the 0  (the equator) 30° (both N & S) latitudes.

Due to the Coriolis effect, the trade winds approach the equator at about a 45° angle. The trade winds are the steadiest winds on earth.

The major currents of the open ocean are driven by the wind. Surface Currents Due to the Coriolis effect, surface water does not move in the same direction as the wind. The surface water moves at about a 45  angle from the wind.

Equatorial currents Equatorial currents move parallel to the equator. The surface currents combine into large circular systems called gyres.gyres Examine global surface currents.

Gyres regulate the temp. of the planet by warming the poles and cooling the tropics.

Waves The wind drives the waves. Crest = the highest part of the wave. Trough = the lowest part of the wave. Height = the distance between the crest and the trough. Wavelength = the distance between wave crests or troughs. Period = time it takes for a wave to go by a given point.

Faster and longer winds = larger waves. Fetch = the span of open water over which the wind blows. Larger fetch = larger waves (potentially).

Tides Tides are formed by the gravitational pull of the moon and the sun. A full tidal cycle takes 24 hours and 50 minutes.

Two forces create tides. 1)Gravitational force from the moon. 2)Centrifugal force on the opposite side of the moon.

There are three types of tide schedules. Semidiurnal = Two high tides of similar height and two low tides of similar height per day. Mixed Semidiurnal = Two high tides of differing heights and two low tides of differing heights per day. Diurnal = One high tide and one low tide per day.

The ocean is stratified (divided vertically into horizontal layers). More dense water sinks to the bottom Less dense water rises to the surface. The Three-Layered Ocean

The three main layers of the ocean are… 1)Surface layer (mixed layer) = 100 to 200 m. Often mixed by wind, waves, and currents. 2) Intermediate layer = 1,500 m. Contains the Main Thermocline, a zone of transition between the warm surface water and the cold water below. 3) Deep and Bottom Layers = below 1,500 m. Uniformly cold, less than 4°C

Stable = All the water is settled into layers according to density – with the warmer, less dense solar-heated water remaining at the surface. Unstable = The surface water is cooled by the colder air and winds, so it becomes more dense than the water below. Overturn = The displacement of the less dense lower water by the more dense surface water occurs. Stability and Overturn

During overturn, the super-oxygenated water from the surface (where photosynthesis has been occurring all summer) is exchanged with the super-nutrient-rich water of the bottom (where decomposition has been occurring all summer). This is called upwelling.upwelling.

THE END