2
Notes for Marine Biology:
Function, Biodiversity, Ecology
By Jeffrey S. Levinton
©Jeffrey S. Levinton 2001

Geography and Bottom Features
©Jeffrey S. Levinton 2001

©Jeffrey S. Levinton 2001

• The worlds oceans: oceans and marginal seas
• Oceans cover 71% of earth’s surface
• Southern hemisphere 80%, Northern hemisphere 61%
• 84% deeper than 2000m
• Greatest depth ~ 11,000 m in Marianas
Trench

• Examples: Gulf of Mexico, Mediterranean Sea
• Affected strongly by
1. regional climate,
2. precipitation-evaporation balance,
3. river input of fresh water and dissolved solids,
4. limited exchange with the open ocean (e.g., sill partially cutting Mediterranean from
Atlantic)

2
• Often have recent history of major change
• Mediterranean: completely dry a few million years ago
• Baltic Sea: less than 11,000 years old

3
• Marginal Seas (Gulf of Mexico, Baltic Sea):
• influenced more by drainage and local climate:
•
1. River input (Baltic Sea)
•
2. Precipitation - evaporation balance
(Mediterranean)
• 3. Restricted circulation (Black Sea,
Mediterranean)
•
4. Geological history (Baltic)

• Particulate mineral matter
• Dissolved salts
• Particulate organic matter (POM)
• Dissolved organic matter (DOM)
• Atmospheric precipitation
• Volcanic sources
• Water

• Continental shelf (1° slope)
• Continental slope (2.9° slope)
• Continental Rise
• Abyssal Plain
• Submarine Canyons
• Oceanic Ridge Systems

2

Eurasian Eurasian
American
Philippine
Pacific
Cocos
Nazca
Caribbean
American
African
Arabian
Antarctic
Earth’s surface is divided into plates: borders are ridge systems, faults

The Oceanic Crust: Crust is formed at ridges, moved laterally, and destroyed by subduction , which forms trenches
Continental crust
Inactive fault
Continent
Trench
Oceanic crust
Ridge
Fault
Continental
Crust
Intermediate, deepfocus earthquakes Mantle

Seawater Properties
©Jeffrey S. Levinton 2001

• Asymmetry of charge distribution on water molecule - increases ability to form bonds with ions - makes water excellent solvent

• High heat capacity (0.9)
• High heat of evaporation (590 cal/g)
• High dissolving power
• High transparency (absorbs infrared, ultraviolet)

• In shallow shelf regions with strong seasonal temperature change - get seasonal thermocline .
Example: coastal NE United States thermocline found in summer continental shelf, with surface warmer wind-mixed layer, deeper cooler water
• Winter: vertical temperature distribution much more uniform and cold, from surface to bottom. No strong thermocline

• Definition: g of dissolved salts per 100g of seawater; units are o/oo or ppt
• Controlled by:
+ evaporation, sea-ice formation
- precipitation, river runoff
Salinity in open ocean is 32-38 o/oo

• Chlorine (19,000 mg/l)
• Sodium (10,500
• Magnesium (1,300)
• Sulfur (900)
• Calcium (400)
• Potassium (380)
• Bromine (65)
• Carbon (28 - variable)

Principle of Constant Element Ratios
• Ratios between many major elements are constant all over the ocean, even though salinity varies

Principle of Constant Element Ratios 2
• Why? Because residence time of elements is much greater than time to mix them evenly throughout ocean by water currents (ca. 1000 y)

Principle of Constant Element Ratios 3
• Residence time of Na, Cl, Sr is on the order of millions of years

Principle of Constant Element Ratios 4
• Principle does not apply to elements that cycle rapidly, especially under influence of biological processes (e.g., sulfur, phosphorous)

Measurement of Salinity
• Chlorinity : g of chlorine per 1000 ml of seawater
• Salinity = 1.81 x chlorinity
• Measured by chemical titration

Measurement of Salinity 2
• Conductivity - increases with increasing salinity, has to be corrected for temperature

Measurement of Salinity 3
• Optical refraction more salt, more refraction of light, uses refractometer

Temperature
• Oceanic range (1.9 - 40 °C) less than terrestrial range (-68.5-58 °C)
• Deep ocean is cold (2 - 4) degrees

Heat Changes in the Ocean
Additions Losses
Latitudinal gradient of solar heating
Back radiation of surface
Geothermal heating Convection of heat to atmosphere
Internal Friction Evaporation
Water Vapor
Condensation

Seawater density (mass/volume)
• Influenced by salt, no maximum density at 4 °C
(unlike freshwater)
• Density measure of seawater at temperature t
 t
= (density - 1) x 1000
 t increases with increasing salinity
 t increases with decreasing temperature
Special significance: vertical density gradients

Latitudinal salinity gradient
Excess of evaporation over ppt in mid-latitudes
Excess of ppt over evaporation at equator

Circulation in the Ocean
©Jeffrey S. Levinton 2001

Coriolis Effect - Earth’s Rotation
Latitude
Equator
Eastward Velocity
(km/h)
1670
30° N. latitude
60° N. latitude
1440
830

Coriolis Effect - Movement of fluids, in relation to earth beneath, results in deflections

Coriolis Effect and Deflection
• Surface winds move over water
• Coriolis effect causes movement of water at an angle to the wind (to right in northern hemisphere)
• Water movement drags water beneath, and to right of water above
• Result: Shifting of water movement -
Ekman Spiral (actually friction binds water together and all water moves at a right angle to wind (right of wind in n. hemisphere)

Coriolis Effect and Deflection 2
• Surface winds move over water
• Coriolis effect causes movement of water at an angle to the wind (to right in northern hemisphere)
• Water movement drags water beneath, and to right of water above
• Result: Shifting of water movement -
Ekman Spiral (actually friction binds water together and all water moves at a right angle to wind (right of wind in n. hemisphere)

Coriolis Effect and Deflection 3
• Surface winds move over water
• Coriolis effect causes movement of water at an angle to the wind (to right in northern hemisphere)
• Water movement drags water beneath, and to right of water above
• Result: Shifting of water movement -
Ekman Spiral (actually friction binds water together and all water moves at a right angle to wind (right of wind in n. hemisphere)

Coriolis Effect and Deflection 4
• Surface winds move over water
• Coriolis effect causes movement of water at an angle to the wind (to right in northern hemisphere)
• Water movement drags water beneath, and to right of water above
• Result: Shifting of water movement -
Ekman Spiral (actually friction binds water together and all water moves at a right angle to wind (right of wind in n. hemisphere)

Coastal Winds + Coriolis Effect =
Upwelling
Southern hemisphere: water moves to the left of wind

Oceanic Circulation
• Wind-driven surface circulation
• Density-driven thermohaline circulation

Wind-driven Circulation
• Driven by heating of air near equator, which rises, moves to higher latitude, falls, creating circulation cells that are affected by Earth’s rotation. Air moves surface water
• Prevailing westerlies (40°N & S latitude)
• Trade winds (toward the west)

Wind-driven Circulation 2
• Combination of wind systems and shapes of ocean basins create cyclonic flow known as gyres
• Rotation of earth tends to concentrate boundary currents on west sides of ocean
- creates concentrated currents such as
Gulf Stream

Wind-driven Circulation 3
Wind systems Surface currents
Westerlies
Subpolar gyre
Subtropical gyre
NE Tradewinds
Doldrums
SE Tradewinds
Westerlies
Subtropical gyre
West wind drift

Thermohaline Circulation
• Water in the ocean can be divided into water masses, identified by distinct temperature, salinity, and other physicochemical characteristics

Thermohaline Circulation 2
• Thermohaline circulation is movement of ocean water controlled mainly by density characteristics
• Controlled by (1) Location of formation of water, (2) density, (3) Coriolis effect to a degree

Thermohaline Circulation 3
• Water masses formed in high latitude surface waters - water is cold, often high salinity because of ice formation
• Waters sink, move at depth towards lower latitude
• Water masses each have a characteristic depth, because of their density, which is largely a function of their high latitude surface origin

Thermohaline Circulation 4
AABW=Antarctic Bottom Water; AAIW = Antarctic Intermediate
Water; NADW = North Atlantic Deep Water

Circulation Recap
• Coriolis effect - rotation of Earth, prop. to sine of latitude, Right deflection in N. hemisphere, Left deflection in S. hemisphere upwelling, deflection of currents

Circulation Recap 2
• Surface circulation - driven by planetary winds, which are controlled by heating, convection, Coriolis effect gyres, eastern boundary currents

Circulation Recap 3
• Thermohaline Circulation - driven by density, sinking, surface water brought to deep sea water masses determined by density

El Niño - Global Phenomenon
• Periodic - every few years
• Warm water moves easterward across
Pacific Ocean
• Eastern tropical and subtropical Pacific becomes warm, thermocline deepens
• Causes mortality of clams, fishes, from heat shock
• Strongly affects weather in eastern
Pacific, storms increase; droughts in western Pacific

Coastal Processes
©Jeffrey S. Levinton 2001

• Dimensions
Wave Length L
Amplitude H
Velocity V
Waves

Waves
• When depth < L/2: waves “feel bottom”
• When H/L > 1/7: wave is unstable and collapses (breaks)

Beaches
• Many beaches exposed to direct wave and erosive action
• Some sandy beaches are more protected, especially some that are very broad and dissipate wave energy at the low tide mark and only for a few meters from waterline

Beaches 2
• Profile more gentle in summer; fall and winter storms cause erosion and a steeper profile

Beaches 3
• Longshore currents, riptides are common features, causing erosion and transport of sand

Wave Refraction

Tides 1
• Gravitational attraction between ocean and moon + sun (moon has 6x the effect of the sun)

Tides 2
• Water on earth facing moon has net gravitational attraction, water facing away from earth has less attraction centrifugal force causes high tides here

Tides 3
• Water on earth surface at right angles to moon is pulled either away or toward moon - results in low tides here

Tides 4
• Spring tides - greatest tidal range, highest high and lowest low - happens when earth, moon and sun are in line
• Neap tides - least tidal range - happens when earth, moon, and sun form approximate right angle

Tides 5
Spring
Tide m
E
Neap
Tide m
E m
E = Earth m m = Moon
Sun
Sun

Tides 6
• Tides differ in different areas; function of basin shape, basin size, latitude
• Results in strong regional differences in the amplitude of tides, the evenness of the expected two high and two low tides per lunar day (e.g., in Pacific NW, there is only one strong low tide per day, while the other “low” tide is nearly as high as the high tides

Tides 7
Connecticut - even tides Washington State - uneven

Estuaries 1
• Body of water where freshwater source from land mixes with seawater
• Often results in strong salinity gradient from river to ocean
• Salinity may be higher at bottom and lower at top, owing to source of river water that comes to lay on top of sea water below, or mixes with the sea water to some degree

Chesapeake Bay with summer surface salinity. Dark blue areas: tributaries have salinity
< 10 o/oo
Estuaries 2

Estuaries - types 3
Fresh water layer
Sea water
Highly stratified estuary
10
20
Moderately stratified estuary (wind, tide mixing)
10
20
30
Vertically homogeneous estuary

Circulation in a coastal fjord
• Reduced exchange of fjord’s bottom waters, combined with density stratification and respiration results in low oxygen in bottom waters
Ocean Restricted circulation
Sill