SEAWATER 101 Seawaters Amazing Physical and Chemical Properties

SEAWATER 101 Seawater’s Amazing Physical and Chemical Properties Introductory Oceanography Ray Rector - Instructor

The Nature of Water Topics To Be Covered n n n n n Elements of Water Chemical Bonding The Water Molecule Hydrogen Bonding Thermal Properties Water’s Affect on Climate Light and Sound in Water Seawater Surface Conditions Seawater Density

Physical Properties of Water’s Key Concepts 1) Water is a strongly polar compound made up of 2 hydrogen atoms covalently bonded to 1 oxygen atom 2) Water exists in all three physical states on Earth 3) Water’s amazing physical and chemical properties are mainly attributed to it’s relatively strong inter-molecule hydrogen bonds 4) The Earth’s blanket of liquid water and ice act as a great global climate moderator – thanks to its unique thermal properties a) High heat capacity b) High latent heats 5) Seawater density is controlled by 1) temperature and 2) salinity 6) The ocean’s water column is density stratified into 3 horizontal layers: surface zone, pycnocline, and deep zone

Structure of Atoms Three Major Components ü Protons ü Neutrons ü Electrons Nucleus üElemental atoms have equal numbers of + charged protons and – charged electrons üElectrons are grouped into energy shells üAtoms are 99. 9% space Electron Energy Shells

Periodic Table of Elements üElements are arranged in columns according to the number of valence electrons in the outer shell üElements are arranged in rows according to the number of electron energy levels (shells)

Electrons in Outermost Shell

Types of Chemical Bonding Between Atoms to Form Molecules Ionic Bonding ü Electrostatic bonding ü Relatively weak bond ü Type of bond in salts Covalent Bonding ü Electron sharing bonding ü Relatively strong bond ü Type of bond in water

Water - Bonds in H 2 O 1) Two hydrogen atoms each share an electron with the same single oxygen atom 2) Mutual sharing of electrons completes the electron shell of all three atoms 3) Resultant covalent bonds are very strong 4) Water molecule has 105 degree bend 5) H 2 O charged at ends: 1+ at H’s and 2 - at O +1 +1 -2

Water Hydrogen Bonds Key Concepts n Water is a polar compound made up of 2 hydrogen atoms covalently bonded to 1 oxygen atom n Many of water’s amazing properties are attributed to the polar electrostatic bonding between water molecules Termed “Hydrogen bonds” Ø Positively charged hydrogen atoms of one water molecule attracted to negatively-charged oxygen atom of another water molecule Ø

Hydrogen Bonding – Water’s “Magic” Hydrogen Bonding has a Strong Influence on Water’s Nature ü High Heat Capacity ü Viscosity ü High Boiling and Freezing Points ü Large Latent Heats of Fusion and Vaporization

Three Physical States of Water Gas Liquid Solid

Unique Density Properties of Water Density-Temperature Graph Ice Crystal Lattice ü Water is unique - liquid water is the densest phase ü Ice floats on liquid water due to hydrogen bonds

Thermal Properties of Water n Heat Capacity – Measure of heat required to raise the n Water has a very high heat capacity – it can absorb temperature of 1 gram of a substance by 1 degree Celsius (or release) large amounts of heat without changing much in temperature

Thermal Properties of Water n Latent Heat of Fusion – Amount of heat gained (or loss) to n Latent Heat of Vaporization – Amount of heat gained (or change a water’s state from a solid to a liquid (or liquid to a solid) without raising (or lowering) the substance’s temperature (80 calories/gram) loss) to change a water’s state from a liquid to a gas (or gas to a liquid) without raising (or lowering) the substance’s temperature (540 calories/gram) § Water has very high latent heats

Global Thermostatic Effects of Water Thermostatic Properties of Water q Water absorbs the Sun’s energy without great temperature changes Ocean’s Great Thermal Inertia q Ocean-Air masses moderate the temperature of the land masses q Thermal moderation takes place on many scales – from local to global

Global Thermostatic Effects of Water Ocean’s Great Thermal Inertia = A Very Comfortable Place to Live

Light in the Ocean

Sound in the Ocean Water travels five times faster in water than air – 1500 m/s n Speed of sound in ocean varies according to depth n Minimum sound speed occurs at around 1200 meters; termed the Sofar Layer n Measuring speed of sound along sofar layer used to accurately calculate the ocean’s water temperature n

Seawater Temperature-Salinity-Density Relationships Density of seawater is function of temperature and salinity n Two samples of seawater can have same density at different combinations of temperature and salinity n Seawater tends to form stable density layers n n Coldest saltiest at the bottom Warmest, least saltiest at the surface Changes in ocean temperature and salinity are primarily controlled by surface processes

Ocean Surface Temperature Sea Surface Temperature (Annual mean temperature ( C) at the surface) o – Warmest in low-latitudes – Coldest in high latitudes

Ocean Surface Salinity Sea Surface Salinity (Annual mean salinity (PSS) at the surface) – Saltiest in mid-latitude Atlantic, Pacific and Mediterranean – Freshest in high latitudes

Density Structure of the Ocean n Ocean divided into three horizontal density layers or zones n n Surface Zone n n Warmest, least dense Typically extends down to 150 meters Makes up only 2% of ocean Pycnocline n n Surface Zone Pycnocline Deep Zone Density increases with increasing depth Isolates the surface zone from the deep zone Makes up about 18% of ocean Deep Zone n n n Top is at about 1000 meters down Coldest, densest Contains about 80% of ocean

Temp – Salinity - Density Profiles of the Major Oceans Comparing the Major Oceans n Pacific Ocean Water n n Atlantic Ocean Water n n Lowest Avg Salinity Intermediate temp variation Least dense Highest Avg Salinity Greatest temp variation Most dense Indian Ocean Water n n n Intermediate Avg Salinity Least temp variation Intermediate density

Review of Seawater’s Physical Properties Discussion of Topics Covered n n n n n Elements of Water Chemical Bonding The Water Molecule Hydrogen Bonding Thermal Properties Water’s Affect on Climate Light and Sound in Water Seawater Surface Conditions Seawater Density

Seawater Chemistry Got Salt?

Seawater’s Chemical Properties Topics of Interest üWater’s Dissolving Power üChemical Make-up of Seawater üSalinity üMeasuring Salinity üSources and Sinks of Ocean Salts üDissolved Gasses in Seawater üResidence Times of Ocean Salts üSeawater Acid-Base Balance üSeawater Chemistry and Life

Seawater's Chemical Properties The Major Points 1) Water is a strongly polar compound of 2 hydrogens bonded to 1 oxygen. 2) Water’s amazing properties are attributed mostly to the hydrogen bonds. 3) Seawater is a solution: a mix of water, dissolved ions and gases. 4) Salinity = amount of dissolved ions and gases in water – in parts per 1000 5) Salinity has 7 major, 14 minor, and numerous trace element constituents. 6) Dissolved salts recycle through ocean via numerous sources and sinks. 7) Ocean is in chemical equilibrium – both in total salinity and the proportion of the major constituents 8) Seawater has 3 major dissolved gases: nitrogen, oxygen, carbon dioxide. 9) Sources of dissolved gases are from atmosphere, ocean, and seabottom 10) Dissolved oxygen derived from photosynthesis processes – 11) Seawater is chemically buffered – broad swings in p. H are naturally limited.

Water – The Universal Solvent + Salt Water Mineral Salts and Gasses from Several Sources Dissolve Readily in Seawater Dissolving Power of H 2 O = Salty Ocean Water

Seawater “Earth Soup” Major Components of Seawater Based on 3. 44% salinity Major Constituents (ppt) Minor Constituents (ppm) Chloride Bromine Sodium Strontium Sulfate Boron Magnesium Fluorine Calcium Trace Elements (ppb) Potassium • Fe, Al, Mn, Cu, Ni, P, Zn, Pb, REE’s Bicarbonate

Seawater Salinity - Defined Definition of Salinity Total amount of dissolved solids (ions) and gasses in one kilogram of sea water. Routinely measured in parts per thousand ( %0 ) Methods Used to Measure Salinity 1) Derive from Seawater Density and Temperature 2) Refractometry 3) Chlorinity 4) Conductivity

Measuring Salinity Various Types of Salinometers

Find Temperature and Density to Determine Salinity Temp Density ü Measure seawater temperature ü Measure seawater density ü Use TSD graph to determine salinity Hydrometer

Measuring Salinity with a Refractometer ü Hand-like device ü Measures bending of light from air into seawater to indicate density and salinity ü Place seawater sample on plate ü Close clear gate and view gauge panel ü Density on the left ü Salinity on the right ü Value where blue & white fields meet

Seawater Salinity - Quantifying Salinity Based on Chlorinity and Conductivity 1. Salinity = 0. 03 + 1. 805 Cl where chlorinity Cl is defined as "the mass of silver required to precipitate completely the halogens in 0. 328 523 4 kg of the seawater sample. 2. Salinity= 0. 0080 - 0. 1692 R 1/215 + 25. 3851 RT + 14. 0941 R 3/2 T -7. 0261 R 2 T + 2. 7081 R 5/2 T + DSRT= C (S, T, 0) / C (KCl, T, 0)(6. 4 b)DS =[(T - 15) / (1 + 0. 0162(T - 15))] + 0. 0056 R 1/2 T - 0. 0066 RT - 0. 0375 R 3/2 T + 0. 636 R 2 T - 0. 0144 R 5/2 T 2 £ S £ 42 where C (S, T, 0) is the conductivity of the sea-water sample at temperature T and standard atmospheric pressure, and C (KCl, T, 0) is the conductivity of the standard potassium chloride (KCl) solution at temperature T and standard atmospheric pressure.

Measure Seawater Conductivity to Determine Salinity CTD ü Most widely used method for measuring seawater salinity ü Conductivity (CTD) meter used to measure seawater conductivity ü CTD measure conductivity, temperature, and depth ü CTD’s can measure continuously in real time in water column ü Typically installed on a water sampling rosette instrument rack ü Need a conductivity-temperature chart to calculate to salinity

Levels of Salinity of Various Waters

Seawater “Chemical Equilibrium” The Ocean is in Chemical Equilibrium 1) Ocean salinity nearly constant (billions of years) Ø Amount of each constituent going into ocean (from sources) appears to equal the amount going out (to sinks) 2) Major constituents in constant ratio with each other Ø Principle of Constant Proportionality Ø Examples: Chloride and Sodium 3) Acid-base (p. H) balance of ocean is very stable

Sources for Dissolved Solids in Seawater CO 2, H 2 O, H 2 S, HCl, and SO 2 § Land Erosion (via rivers, wind Salt Sources glaciers and groundwater) Fe++ + Mg++ + Si. O 4 + K+ + Na+ + Ca+ + HCO 3 - + SO 42 + PO 42 - § Volcanic eruptions § Hydrothermal Seafloor Venting § Bottom Sediment Dissolution Ca++ + SO 4= --> Ca. SO 4 Mg++ + Basalt + H 2 O --> Mg(OH)Si. O 3 + H+

Sinks for Dissolved Solids in Seawater Salt Sinks § Ocean Bottom Sediments § Deep Sea Hydrothermal Systems § Biological Processes § Subduction of Ocean crust

Seawater – “Residence Time” n Residence Time - defined Amount of element/ion in the ocean Rate at which the element/ion is added (or removed from) the ocean = n Mixing Time of Ocean n Conservative Constituents n n Calculated to be 1, 600 years Based on steady state conditions and effective mixing processes Occur in constant proportions Have very long residence times Examples: Chloride and Sodium Nonconservative Constituents n n n Tied to seasonal or biological cycles Have short residence times Examples: Iron and Aluminum

Seawater – Dissolved Gasses Major Gases in Seawater and Air Sinks for Gases Leaving the Ocean Sources of Gases Entering the Ocean 1. Atmosphere (N 2, O 2) 2. Volcanic Activity (H 2 S) 3. Chemical Processes (CO 2 ) Fossil Fuel Burning 4. Biological Processes (O 2, CO 2 ) 1. Atmosphere (N 2, O 2 , CO 2 ) 2. Chemical Processes (CO 2 ) Dissolved Carbonate Ions Calcium Carbonate Precipitates Dissolved Sulfate Ions 3. Biological Processes (O 2, CO 2 ) Photosynthesis Respiration

Seawater – Dissolved Gasses Sources of Gases Entering Ocean 1. Atmosphere (N 2, O 2) 2. Volcanic Activity (H 2 S) 3. Chemical Processes (CO 2 ) Fossil Fuel Burning 4. Biological Processes (O 2, CO 2 ) Sinks for Gases Leaving Ocean 1. Atmosphere (N 2, O 2 , CO 2 ) 2. Chemical Processes (CO 2 ) Dissolved Carbonate Ions Calcium Carbonate Precipitates Dissolved Sulfate Ions 3. Biological Processes (O 2, CO 2 ) Photosynthesis Respiration

Seawater Temperature-Salinity-Density Relationships Density of seawater is function of temperature and salinity n Two samples of seawater can have same density at different combinations of temperature and salinity n Seawater tends to form stable density layers n n Coldest saltiest at the bottom Warmest, least saltiest at the surface Changes in ocean temperature and salinity are primarily controlled by surface processes

Ocean Surface Temperature Sea Surface Temperature (Annual mean temperature ( C) at the surface) o – Warmest in low-latitudes – Coldest in high latitudes

Ocean Surface Salinity Sea Surface Salinity (Annual mean salinity (PSS) at the surface) – Saltiest in mid-latitude Atlantic, Pacific and Mediterranean – Freshest in high latitudes

Density Structure of the Ocean n Ocean divided into three horizontal density layers or zones n n Surface Zone n n Warmest, least dense Typically extends down to 150 meters Makes up only 2% of ocean Pycnocline n n Surface Zone Pycnocline Deep Zone Density increases with increasing depth Isolates the surface zone from the deep zone Makes up about 18% of ocean Deep Zone n n n Top is at about 1000 meters down Coldest, densest Contains about 80% of ocean

Temp – Salinity - Density Profiles of the Major Oceans Comparing the Major Oceans n Pacific Ocean Water n n Atlantic Ocean Water n n Lowest Avg Salinity Intermediate temp variation Least dense Highest Avg Salinity Greatest temp variation Most dense Indian Ocean Water n n n Intermediate Avg Salinity Least temp variation Intermediate density

Seawater Acid-Base Balance ü Ocean p. H average is 8 ü Ocean gets more acidic with depth Ocean’s Carbonate Buffer System § Helps maintain a steady p. H balance § Three step acid-base buffer system Step One: CO 2 + H 2 O Step Two: H 2 CO 3 The p. H Acid-Base Scale Step Three: HCO 3 - + H+ H 2 CO 3 HCO 3 - + H + CO 32 - +2 H+

Seawater Chemistry Summary n Water a Remarkable Molecule n n n Important Chemical Properties n n n Strongly Polar Hydrogen Bonding Nature’s Strongest Solvent Saline Solution Major, Minor, and Trace Constituents Methods of Measuring Salinity Sources and Sinks of Sea Salts Ocean in Chemical Equilibrium n n Stable Salinity Constant Proportionality Density Stratified Ocean controlled by Seawater Temperature and Salinity Buffered p. H-balance