Announcements: Primary Fields of Oceanography. Weathering. Geology. Chemistry. Happy 157 th birthday, Fridtjof Nansen. Precipitation/ Dissolution

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1 Announcements: Happy 157 th birthday, Fridtjof Nansen First problem set due tonight at midnight Geology Primary Fields of Oceanography Weathering Precipitation/ Dissolution Chemistry First exam in one week Tuesday Oct 11 th Study questions posted on web page under lecture notes Review for exam on Thursday Come with questions Organic C production & degradation Nutrients Contaminants This week: Marine chemistry Physics Biology Introduction to Chemical Oceanography Part 1: Wacky water Learning objectives: Why is the ocean blue? Why is it salty? What determines the concentrations of salts and other chemicals in seawater? What is the chemical structure (chemical geometry) of the ocean? What makes water climb celery stalks? 1

2 Properties of water Polarity: Results in Hydrogen bonding 2 electron shells shown Surface tension cohesion > adhesion (E.g, Hg and glass) adhesion > cohesion Water s dipole moment Electron orbitals shown Properties of water compared to similar compounds Molecular Boiling Point C Surface Tension C Dynes cm -1 Water (H 2 O) H-sulfide (a) (H 2 S) Ammonia (a) (NH 3 ) Methanol (CH 3 OH) Ethanol (C 2 H 5 OH) Ether (C 2 H 5 OC 2 H 5 ) 2

3 Hydrogen bonding results in an open lattice structure of ice, and a maximum density at 3.98 degrees C. Cold water is denser than warm water Flickering cluster model explains the density max at ~ 4 degrees so why does ice float? Clusters: Low density structures that form more frequently as T 4 to 0 C Liquid water has a large heat capacity (1 cal/g/ o C) Hydrogen bonding and latent heat Gas At the beach, the water is cool why does the sand burn your feet? Liquid Solid 3

4 Depth (km) Depth (km) Depth (km) Effects of latent heat on global climate If water has such a high heat capacity, why do I feel so cold when I get wet? Heat is lost at the equator via evaporation (latent heat). But, net heat accumulation occurs at the equator and net loss occurs at the poles. Transport of water vapor from equator to poles and transport of water currents moderates latitudinal variation in climate. Evaporation Seawater: Effects of temperature and salinity on density & stratification Why is it easier to float in seawater than in freshwater? T-S diagram indicates major properties of water masses. Mixing of water masses along isopycnals. Ocean water can be considered a two-layer system; a surface mixed layer over a deep layer. 4

5 Why does the fish that got away always look so big? Scuba diver s mask Fish Fish appears closer and bigger than it really is. Refractive index of water relative to air is ~ 1.33 sin(i air ) / sin(i water ) ~ 1.33 = ratio of light velocity (air:water) Effects of density structure on underwater sound 1. Sound velocity increases with temperature, salinity and pressure C sound speed = (axial modulus/density) How do whales keep in touch across thousands of miles of ocean? 2. Low velocity zone at 1000 m (sofar layer) 3. Reflection and refraction of sound waves due to velocity changes creates shadow zones, important for submarine warfare. Subs can hide below the pycnocline Why was it difficult for the Allied navies in WWII keep the German submarines out of the Mediterranean Sea? 5

6 Depth Thermally stratified water column Why is the ocean blue? Salinity stratified water column Color in the ocean: Light attenuation = f(wavelength, color) Light attenuation in the ocean (Beer s Law) I Z =I 0 e -K D z The parameter K D is the light attenuation coefficient. 1/K D is one light attenuation depth. I 0 is the light intensity at the ocean surface I Z is the light intensity at depth z Light intensity (I) K D can be calculated from the Secchi depth: D Secchi =1.5/K D D Secchi Why is the ocean blue? 6

7 Why are coastal waters green? Summary Hydrogen bonding makes water a unique molecule with high heat capacity, high heat of fusion (freezing) and vaporization, anomalous density maximum at 3.98 deg C, High dipole moment of hydration Latent heat of vaporization and fusion along with global transport of water vapor moderates the earth s climate Temperature and salinity determine water density Ocean water is a two-layer system: mixed layer / deep layer Sound is reflected and refracted in these layers The ocean is blue due to differences in penetration depths of light of different wavelengths 7