OC3230 Winter 05
Study Topics, Exam 1
You should be familiar with the following concepts or tasks. Use them to guide your review of the notes
from this material.
Early Oceanography
Age of Explorers
15th and 16th Century
Columbus (1492), Magellan (1521), etc.
(Exceptions=Vikings in 11th and 12th Century,
Greeks in 600-400 B.C.)
Early Scientific Beginnings
18th Century (late 1700s)
Relatively young field compared with math, physics, biology, etc.
Benjaman Franklin's map of the Gulf Stream (1769)
Matthew Maury (1841)
Navy Officer, injured in stagecoach accident
began regular sampling, 1st textbook, 1st conference
Challenger Expedition (1872-76)
Specifically for scientific study of oceans
Most oceans covered: 68,000 miles
All types of data collected: physical, chemical, biological
Results in 50 volumes over 23 years
de-bunked Forbes' theory of no life in deep ocean
Fram Expedition (1893-96)
Fridtjof Nansen, frozen in arctic ice
Meteor Expedition (1925-27)
T-S survey of South Atlantic
Morphology of Ocean Basins (Geology)
Distribution of land and sea
Northern Hemisphere 60% water (“Continental”)
Southern Hemisphere 80% water (“Maritime”)
Mean ocean depths = 3800m
Deepest depths in trenches ~11,500m
Comparable to highest mountain elevations
Marginal and Adjacent Seas depths typically 1200m
Continental Margin
Continental Shelf
Part of continental crust under water
Width varies around the world
East coast ~100km, west coast ~10km
Important to commerce, fisheries, recreation, etc.
May have unique circulation compared with deep ocean
Continental Shelf Break
Offshore location where depth begins to change rapidly
Typically at about 130m water depth
Actual boundary between continental crust and ocean crust
Continental Slope
Continental Rise
Submarine Canyons
Cut through continental shelf/slope/rise from deep ocean
Common along coast
Can be large (cf Grand Canyon/Monterey Submarine Canyon)
No certain explanation for orgin in some cases
Abyssal Plain
Depths typically 4000m – 5000m
Extremely flat, thick sediment cover from biological production above
Includes seamounts and ridges
Vertical Exaggeration
Idea that aspect ratio (Vertical:Horizontal) in the ocean is very small
Use expanded scale to plot data versus depth
Plate Tectonics
Combination of “Continental Drift” and “Sea Floor Spreading” theories
Wegener (1912) suggested Continental Drift
Shape of continents observed to match up
Harry Hess (Navy Officer; 1960) suggested Sea Floor Spreading
Oceanic Crust more dense but thinner (~7km)
Continental Crust less dense but thicker (~40km)
Oceanic Crust produced at mid-ocean ridges and consumed at trenches
along active margins
Passive margins (e.g. U.S. East Coast) are not plate boundaries
>>Know how to diagram the difference: active vs. passive
Evidence for Plate Tectonics
Earthquakes occur primarily along plate boundaries
Magnetic anomalies align in bands parallel to mid ocean ridges
Age increases in bands parallel to mid ocean ridges
Heat flow decreases in bands parallel to mid ocean ridges
Thickness of sediment cover increases in bands parallel to ridges
Hot Spots
Fixed location (relative to Lat/Lon) where magma rises
e.g. Hawaiian Island/Emperor Seamount chain; Yellowstone
Useful for tracking history of plate motions
Properties of Water
Water is a very unique substance relative to other compounds
High Heat Capacity
Hydrogen bonds lead to temp of max density at 4 ˚C
Hydrogen bonds lead to different crystalline structure of ice
Ice is less dense than water, floats
Very good solvent (high dielectric constant)
Salinity
Amount of dissolved material in grams in one kilogram of water
Measured as parts per thousand, ppt or ‰
Origin of Salinity in Seawater
From output of mid ocean ridges (not rivers)
Salinity probably in chemical equilibrium
Salinity probably same since beginning of oceans
Most (99%) of salinity made up from 6 major constituents
Major constituents always found in constant proportion to each other
Absolute Salinity, SA, comes from 1.80655 x Chlorinity
(contrast with Pracitcal Salinity Units, psu, from conductivity)
Minor constituents not in constant proportions and not conserved
Important for biological and chemical reactions
Important as tracers for physical circulation
Salinity changes the freezing point, boiling point, and temp of max density
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Colligative Properties
At S=24.7‰ freezing point and temp of max density are equal
For typical ocean ranges (>34‰) no temp of max density
Density
Mass per unit volume (e.g. Kg/m3)
Range in ocean is small (~3%) from about 1000–1030 Kg/m3
Often neglect changes in density but important for circulations
Know: specific volume, specific volume anomaly, thermosteric anomaly,
sigma-T, density anomaly
Equation of State
Relates density to state variables: T,S,P
No simple equation for seawater (cf ideal gas: P=RT)
Potential Temperature
Account for pressure effect on temperature
Should use in deep ocean calculations (>500m)
Potential density if derived using Potential-T,S,P
Sound in the Oceans
Travels as a longitudinal wave (also called compression wave)
c = f, wave equation relating phase speed, frequency, and wavelength
c depends on compressibility and density of fluid
c ~ 1500 m/sec in seawater; c ~ 350 m/sec in air
Sound refraction bends sound waves toward region with lower c
c+ for T+, S+, and P+
Temperature and pressure are most important effects in ocean
Decreasing temperature combined with increasing pressure lead to
minimum in sound speed around 1500m in the oceans (except at high
latitudes)
SOFAR or sound channel
Propagate sound around the world
Useful for mapping bottom depths and sediment/rock layers (depending on frequency)
Useful for tracking things (like submarines)
Profile of sound speed may lead to shadow zones
Attenuation
Absorption by medium
Energy goes to heat
In seawater, additional energy goes to break up MgSO4
Difference for fresh vs. seawater is “relaxation”
Spreading
Spherical (normal case) vs. cylindrical (sound channel case)
Scattering
Deflection by particles
Reflection conditions for sound between two medium depend on acoustic impedence
Imporant to active sensing
Z = c
Reflectivity: R = ( (Z1-Z2)/(Z1+Z2) ) x 100
Matched impedences (Z1 ~ Z2) gives mostly transmission
Mis-matched gives mostly reflection
Ambient Noise
Important to passive sensing
Listen to naturally produced sounds and relate to processes (e.g. wind, rain)
Acoustic Tomography
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Equivalent to catscan where inverse methods used to determine sound speed
Distribution of Properties
Ranges found in ocean
T: 0-6 ˚C; S: 34-35‰ accounts for 75%
Ave-T = 3.5 ˚C; Ave-S = 34.7‰
Mostly zonal distributions (vary north to south more than east to west)
T follows “sun”, S follows “E-P”
T max at equator, S max in tropics under trade winds
Vertical gradients >> Horizontal gradients
Methods of data plotting
1) Profiles, 2) Horizontal (contour) maps, 3) Vertical Sections
Thermocline/halocline/pycnocline
Permanent versus seasonal
Strong seasonal cycle in mid latitudes near surface
No seasonal cycle below permanent thermocline
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