Marine Biology Chapter 3: Chemical and Physical Features of Sea Water

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1 Marine Biology Chapter 3: Chemical and Physical Features of Sea Water The Waters of the Oceans - water accounts for 80% of the volume of most marine organisms (95% for jellyfish) - provides buoyancy and support for swimming and floating organisms - Is the medium for most chemical reactions to sustain life Unique Nature of Pure Water - H20 is composed of two Hydrogen and one Oxygen atom - the angle between the hydrogen atoms is 105 degrees - this configuration forms a dipole movement - this crates an attractive force or weak hydrogen bond between molecules - hydrogen bonding accounts for many unique properties of water Viscosity is the result of H-bonding within the fluid that tends to resist external forces that would separate these molecules - viscosity reduces the sinking tendency of some organisms - viscosity magnifies problems of drag that actively swimming animals must overcome 1

2 Surface Tension is the result of H-bonding on the surface of the water and creates a skin over the surface. Both surface tension and viscosity are temperature dependent (a decrease in temp. increases both). Three States of Matter - solid - Liquid - Gas - In liquid H20 the molecules are in constant motion and are constantly forming and reforming hydrogen bonds. - Temperature reflects the speed of the molecules. - When a H20 molecule has enough energy to break free of all surrounding H20 molecules, it moves from the liquid state to the gases state. - When energy is removed the H20 molecules move slower and pack closer together and become denser - When enough energy has been removed, the hydrogen bonds are fixed in position and solid ice forms. In this state, the volume has increased and so ice is less dense than liquid H20. This is a very important property for aquatic organisms. 2

3 latent heat of fusion / melting the amount of energy needed to convert one gram of a liquid to a solid. For water it is 80 calories. (80 cal must be removed to convert water to ice and conversely for ice to liquid at the same temp) - highest of all common natural substances - maintains a large variety of substances in solution - enhances a variety of chemical reactions Heat Capacity the quantity of heat needed to raise the temperature of 1g of a substance by 1 C (cal / g C) - high for molecular size of H20 - stabilizes body temperatures of marine organisms because water temperature does not fluctuate drastically Latent heat of vaporization the amount of energy needed to convert 1 g of H20 from the liquid state to vapor. For water it is 540 cal - highest of all common natural substances - moderates sea-surface temperatures by transferring large amounts of heat to the atmosphere through evaporation - inhibits large scale freezing in oceans 3

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5 Water as a Solvent - H20 can dissolve more things than any other natural substance (universal solvent) - the small size and polarity of H20 dissolves most naturally occurring substances especially salts - ionic bonds bond between two atoms of opposite charge salts are held together by ionic bonds - dissociate when a salt is placed in H20, the H20 molecules surround each ion insulating it from the surrounding ions. 5

6 Chemical Composition of Seawater 1. Dissolved inorganic matter 2. Dissolved gases 3. Dissolved organic matter 4. Dissolved particulate matter 1. Dissolved inorganic matter: elements or compounds that do not contain carbon in its atomic structure. Usually refers to salts including nutrients for plant growth. A. Major inorganic elements: those in concentration greater than 100 ppm or 100 mg/l Ex: chlorine, sodium, magnesium calcium, sulfur, potassium B. Minor inorganic elements: those in concentration greater than 1ppm but less than 100 ppm ex: bromine, boron, silicon, fluorine, carbon C. Trace inorganic elements: those with a concentration less than 1ppm Ex: nitrogen, phosphorous, iodine iron, zinc, molybdenum 2. Dissolved gases: the major gases in seawater are nitrogen, oxygen and carbon dioxide. The solubility (ability to go into solution) of gases depends on: A. Temperature B. Atmospheric partial pressure C. Salt concentration - Note: oxygen and carbon dioxide have variable concentrations on a daily basis not dependent on temperature, atmospheric pressure or slat concentration but rather on biologic activity 3. Dissolved organic matter: the source is excreta and dead organisms, which produce carbohydrates, fats, oils, proteins, amino acids and other man made synthetics such as DDT and PCB s. Dissolved Salts % pure water; 3.5% dissolved compounds - salinity refers to the total amount of dissolved salts in solution (35g salt / 1000g seawater) - measured in parts per thousand /oo or practical salinity units (psu) - the average seawater salinity is 35 /oo - in the open ocean salinity varies slightly but varies from 0 /oo at river mouths to over 40 /oo in some areas of the Red Sea - Today conductivity is more commonly used to measure salinity but both are equivalent - salinity is altered by evaporation, precipitation, river runoff and freezing and thawing of sea ice - regardless of salinity levels, the rule of constant proportions states that the relative amounts or the various ions in seawater are always the same - Six salts account for more 98% of all sea salts 1) Chlorine 2) Sodium 3) Sulfate 4) Magnesium 5) Calcium 6) Potassium - Chlorine and Sodium alone make up 85% of all sea salts 6

7 - Majority of the salts in the oceans come from the weathering of rock, volcanic activity or hydrothermal vents - Magnesium, calcium, bicarbonate and silica are important for the skeletal parts of marine organisms - Nitrate and phosphate are needed by plants for synthesis of organic material Salinity-Temperature-Density Relationships - density of seawater is a function of both temperature and salinity - density of seawater increases with a decrease in temp or an increase in salinity - the densest water is found at the bottom of the oceans but the processes that create this water are surface features (evaporation, freezing, cooling) - therefore dense water sinks from the surface to drive the circulation of deep ocean water currents (ex: Mediterranean and Antarctic) - thermocline is a zone of rapid temp. decrease (temperature profile) with depth (1 C/m) - pycnocline is a zone of density increase that corresponds to the thermocline - halocline is a zone of salinity change with depth (salinity profile) 7

8 Dissolved Gases and Acid/Base Buffering - for organisms in the ocean the most important gases are oxygen, carbon dioxide & nitrogen - Oxygen is not very soluble in H2O (0 8 ml O2/l of H2O with 4-6 ml O2/l of H2O the average) - Air has 210 ml O2/l of air - Oxygen levels are also effected by photosynthesis and respiration - Much of the oxygen produced by photosynthesis is released to the atmosphere at the air water interface 8

9 - carbon dioxide is abundant in the ocean (80% of all dissolved gases) - seawater can absorb large quantities of CO2 because it does not remain in the gas form but reacts chemically to form a sink for CO2. - The oceans stores 50 times the amount of CO2 as the atmosphere - CO2 combines with H2O to produce carbonic acid (H2CO3) - H2CO3 dissociates to form H+ and a bicarbonate ion H CO3 - CO2 + H2O H2CO3 (carbonic acid) H2CO3 H+ + HCO3 - (hydrogen ion) (bicarbonate ion) CO3 - H+ + CO3-2 (hydrogen ion) (carbonate ion) -this system buffers or limits the change of seawater ph - in open-ocean conditions this buffering system is very effective limiting the ph range between 7.5 to 8.4 on the ph scale 9

10 Light and Transparency - our eyes only respond to the spectrum of light between 380 and 760 nm known as the visible light - about 60 % of the light entering the water is absorbed in the first meter 80 % is gone after 10 m - only 1% of the total light is available in the clearest waters below 150 meters - photosynthetic organisms must remain in the upper regions of the ocean known as the photic zone where solar energy is sufficient to support photosynthesis - depth of the photic zone depends on the clarity of the water but ranges between meters - amount of suspended matter, plankton, etc. affect transparency - coastal waters will have a lower transparency than open oceans - below the photic zone where light prohibits photosynthesis is known as the aphotic zone 10

11 Pressure - 1 atm is the weight or pressure at sea level of the earth s atmosphere (15 lb/in 2 or lkg/cm 2 ) - for every 10 m (33 ft.) of depth the pressure increases 1atm - the deepest trenches have over 1,000 atm of pressure - most organisms can tolerate moderate changes in pressure with depth - many have adapted to extreme pressure of the deep oceans Surface Circulation - if the earth was not rotating then winds and ocean currents would follow straight paths - instead wind and ocean currents follow curved paths due to the rotation of the earth - Coriolis Effect due to Earth s rotation, deflections of large scale motions (winds and currents) move to the right in the Northern Hemisphere and to the left in the Southern Hemisphere but at the equator there is no deflection - the coriolis effect does not set winds or water in motion, it deflects them after they are in motion For ex. if a rocket at the equator is fired to the north pole, the rocket is already moving eastward at a speed of 1670 km/hr by virtue of the earth s rotation at the equator. After launch, the rocket still moves eastward at this speed. When the rocket moves northward over portions of the earth moving eastward at progressively slower speeds than the equator, the rocket is moving eastward faster than the earth beneath it if observed from the earth. An observer from the moon would see the rocket moving in a straight line, while the earth turned beneath it. Wind Patterns - heat energy from the sun drive wind patterns - the equator absorbs most of the sun s energy and the air becomes less dense and rises - air from adjacent areas is sucked in the replace the rising air and creates wind - the wind does not move in a straight line due to the coriolis effect - the three major wind belts include: a) trade winds approach equator at a 45 angle; steadiest winds over the oceans b) westerlies middle latitudes and more variable than trades; move in opposite direction to trades c) polar easterlies high latitudes and most variable of all winds 11

12 Surface Currents - Ocean surface currents occur as a result of winds blowing over the ocean - the momentum of the wind produces ocean surface currents - the surface water moved by the wind does not flow parallel to the wind direction but defects to the right at a 45 in the Northern Hemisphere and to the left in the Southern Hemisphere due to Coriolis effect - layers of water beneath top layers move slightly to the right and slower - in successive layers of water this produces a pattern called an Ekman spiral - The net result of this process is that water called the Ekman layer is transported at right angles to the wind direction 12

13 - surface currents represent large scale horizontal movements of water - eventually the water accumulates and must either flow directly back against the established current producing a countercurrent or flow as a continental boundary current in a north-south direction - when these currents meet they produce large circulating gyres - warm currents flow on the western sides of landmasses and cold currents flow in the opposite direction on eastern sides of continents - therefore ocean currents act like giant thermostat, warming the poles and cooling the tropics, regulating the climate of the earth Three-Layered Ocean - the ocean water is layered or stratified due to density differences - the surface layer is usually m in depth and is also called the mixed layer because it is mixed be wind, waves and currents - intermediate layer below the surface layer is 1,000 1,500 m deep where the main thremocline of the ocean lies as is not to be confused with the shallow seasonal thermocline - deep layer is uniformly cold and lie below 1,500 m 13

14 Stability and Overturn - stability when warm surface water is less dense than colder water beneath it, it floats on top of the denser water. How much difference exist between densities determines how stable the water column is. Wind or wave energy can mix the water column if it has a low stability (little difference in densities) - downwelling when surface waters become more dense than waters below, surface water will sink and displace water below. If mixing occurs this is know as overturn. - When downwelling is intense a large volume of water will leave the surface and not mix with surrounding waters and salinity and temperature do not change giving the water mass a finger print and this water mass can be followed and is called thermohaline circulation which produces the great ocean conveyor with waters eventually reaching the surface and helps regulate the earth s weather patterns and may even trigger ice ages. This cycle continues with a time scale of 4,000 yrs - great ocean conveyor is also important to carrying dissolved oxygen to deep sea creatures 14

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16 Waves and Tides - Waves consist of a crest and trough - A crest is the highest point of a wave - A trough is the lowest part of a wave - The vertical distance between any crest and the succeeding trough is the wave height (H) - The horizontal distance between successive crest or successive troughs is the wavelength (L) - wave period(t) is measured in seconds and is the time it takes for successive crest or trough to pass a fixed point - The wave frequency (1/T) is the number of waves that pass a fixed point in a given length of time (units are cycles / sec) - the speed of waves ( C) can be calculated from the simple relationship of C = L / T (where L = wavelength; T = wave period) - When wave height is low, crest and troughs tend to be rounded. When this happens a small boat will glide smoothly over the wave - Waves commonly break when the angle at the crest is less than 120 degrees or the ratio of wave height to wavelength is H/L 1/7 - H / L is the wave steepness and is a measure of the wave stability - waves are caused by a) wind b) seismic activity - size and energy of waves are dependent on the wind s velocity, duration and fetch - fetch is the distance over which the wind blows in contact with the sea surface 16

17 - wave reinforcement is when two crest of waves collide producing a temporarily higher wave - Types of waves a) Spilling wave with unstable top spills over the front of the wave as it moves forward b) Plunging tend to form from long gentle swells over a gentle sloping bottom Also when cycle is broken by coming in contact with bottom surfaces c) seismic (Tsunami) caused by movements of plates; have very long periods but behave like shallow water waves when passing through deep ocean ex earthquake in Aleutian Is. Caused tsunamis w/ 15 min. period and wavelength of 150 km and a wave speed of 800 km/hr Tides - Tides are the pulse of the ocean - The effects of tides are most obvious in coastal regions - Tides have an important influence on the plant and animal life in the intertidal zone - Tidal fluctuations are attributed to the gravitational effects of the sun and moon and the centrifugal force due to the rotation of the earth - Moon s gravitational attraction of water on the earth is strongest on the side of the earth closest to the moon and causes the water to bulge towards the moon - On the opposite side of the earth, the gravitational pull of the moon is weaker and water bulges in the opposite direction due to the centrifugal force of the rotating earth - This phenomena happens because the moon does not exactly rotate around the earth but rather around a common center of mass of the earth-moon system 17

18 - The time between high or low tides is the tidal period and one tidal cycle is 24hr 50 min. due to the fact that earth must turn an additional 12 to bring the earth back in line with the moon - the sun s effect on tides is about half as strong as the moon s because the sun is 400X farther away even though it is much bigger - Spring Tides happen when the moon and sun are in line with each other, which happens at new or full moon and produces the maximum amplitude variations of tidal ranges - Neap Tides when the moon and sun are at right angles their gravitational pulls partially cancel each other out, this happens during 1 st and 3 rd phases of the moon producing lower amplitude tides 18

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20 Tides in the Real World Due to the presence of continents and shape of the sea floor, tides behave differently than if the world were just covered with water tides vary depending on location, and shape and depth of basin Examination of tidal curves reveals three types based on the number of highs and lows per day, the relationship between the height of successive highs and lows and the time between corresponding high and lows. 1. Semidaily or Semidiurnal Tides have two high and two low per day but they are approximately equal in height (East coast of NA, Europe, Africa) 2. Mixed Tides or mixed semidiurnal tides has two high and two low tides per day but not equal in height ( West coast of NA & Canada) 3. Daily Tides or Diurnal Tides have one high and one low tide per day (Antarctica, Parts of Gulf of Mexico, Caribbean, Pacific) 20

21 Mixed tides have the higher of the higher of the two high tides called higher high water (HHW), the other is called lower high water (LHW) and it is similar for low tides with lower low water (LLW) and higher low water (HLW) 21

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