| 2. Current Flow and Motion: |
| Learning Objectives: |
- Appreciation that western boundary currents can meander and swirl
- Understanding of possibilites for vertical movement of water
- Recognition of the characteristics of areas of upwelling and convergence
|
| Eddies, Meanders and Rings: |
- Meanders in western boundary currents
- e.g. Gulf Stream
- to north, cold water, to south, warm water
- can become isolated to form rings
- 100 - 300 km across
- detached from current
- may be resorbed, detached several times and persist for years.
|
| Convergence and Divergence: |
- Surface water movement:
- away from upwelling: divergence
- gatherings of water masses are convergences.
- Permanent Zones:
- tropical convergence at equator
- subtropical convergences at 30 - 40°N
- S, Arctic and Antarctic convergences at about 50°N and S.
- Seasonal Zones:
- created by change in wind direction
- leads to seasonal upwelling
|
3. Vertical Circulation:
|
Learning Objectives:
|
- Understanding of the structural features in individual
oceans
- Recognition of the characteristics of different water
masses
|
Density-driven Circulation:
|
- Thermohaline circulation
- convective exchange and vertical circulation;
- controlled by temperature and salinity
- seasonal temperature changes create seasonal thermocline
- affect surface density
- can form sinking water masses, or freshwater lid.
- Sigma-t (s
t): measure of seawater density
- defined as (density - 1) x 1000.
- 1.02677 becomes 26.77
st
|
Movement of Water:
|
- Upwelling: ascending water masses
- Downwelling: sinking water masses
- maintain continuity of flow, vertical movement (0.1
- 1.5m/day)
- Sinking waters may take 1000 years to reach great
depths.
- Horizontal water movement:
- convergence (meeting) and divergence (spreading out).
|
Structure of Oceanic
Waters:
|
- Atlantic and Arctic Oceans:
- cooling at high N. latitudes produces North
Atlantic Deep Water
- NADW (2 - 4°C, 34.9‰)
- sinks, moves southward.
- in South Atlantic:
- Antarctic Intermediate W
ater (AAIW; 5°C, 34.4%o)
- Antarctic Bottom Water
(AABW; 0.5°C, 34.8%o).
- Surface waters: 25°C, 36.5%o
.
- Arctic Ocean controlled by salinity.
- surface low salinity waters
- affected by seasonal ice formation.
- at intermediate depths: Norwegian and Greenland
currents
- Pacific Ocean:
- no counterpart of NADW, isolated from Arctic
- no source of deep water, sluggish deep water circulation
- subtropical lens of warm, salty water.
- Indian Ocean:
- isolated from Arctic, no source of deep water
- sluggish deep water circulation
- Mediterranean:
- Mediterranean Intermediate Water
(MIW, 13°C, 37.3%o)
- outflows at depth, mixes in Atlantic
- Red Sea:
|
Temperature and Salinity
Relationships:
|
- T-S Curves:
- depth distribution of temperature and salinity are
distinctive
- plot of temperature vs. salinity forms a T-S diagram
- depth plots are T-S curves
- T-S Curves and Water Masses:
- T-S curves for large areas of the ocean are vertically
similar
- define water masses by depth and location
- water masses are related by density.
|
| 4. Global Circulation Changes and Measurement of
Currents: |
| Learning Objectives: |
-
- Understanding that deep water movement is distinct from
surface waters
- Recognition of approaches used to determine current directions and
velocities
|
| Global Conveyor: |
- Deep water movement distinct from movement of surface water
- deep water (NADW)
- formed near Iceland
- moves southward, mixes with AABW
- moves eastward into Pacific
- warmed and returns via Indian Ocean to Atlantic
- controlled by topography
- deep circulation acts as conveyor belt
- changes in deep water flow can cause major climate change.
|
| Measuring Currents: |
- Follow a moving water parcel:
- drift bottles, buoys, or flotsam:
- Determine current flow at fixed points using current meters
|
