Deep ocean currents - 7 Flashcards
What is thermohaline circulation?
A density driven flow of water generated by differences in water temperature and salinity
Water at the surface is expose to more rapid changes in…
- Salinity: evaporation and precipitation
- Temperature: cooling and heating
Based on depth below the surface, water masses can be broadly classified as …
- Central waters: 0-1 km
- Intermediate waters: 1-2 km
- Deep and bottom waters: >2 km
Where does deep and bottom water originate?
At the surface where it is cooled and/or density increases until it sinks
Where is deep water the youngest?
North Atlantic (200 years)
Where is deep water the oldest?
North Pacific (1200 years)
Where is water >10ºC confined?
Between 45ºN and 45ºS
‘Climate change affects thermohaline circulation’, true or false?
True … increased freshwater influx to the North Atlantic would prevent NADW from downwelling, thereby chasing weather patterns in Europe and North America
Which ocean has the most complex stratification?
The Atlantic ocean
What water masses are found in the Atlantic ocean?
- Antarctic bottom water (ABW)
- Antarctic deep water (ADW)
- North Atlantic deep water (NADW)
- Arctic Intermediate water (AIW)
- Mediterranean Intermediate water (MIW)
Where does Antarctic bottom water form? where does it flow?
The Weddel Sea … Northward into the Atlantic
What is the densest water mass in the ocean?
ABW
What is Antarctic deep water?
A less saline, slightly warmer mass formed off the coast of Antartica
How does the ADW flow?
Flows along the surface to the Antarctic convergence where it sinks and becomes sandwiched between ABW and NADW
What is North Atlantic Deep Water?
A cold, salty water mass formed off the coast of Greenland. It flows southward along the bottom until it encounters the ABW and rides over this
What is Arctic Intermediate Water?
A water mass formed in subarctic regions and flows southward between surface water of the Sargasso Sea and NADW
What is Mediterranean Intermediate Water?
A water war, highly saline water mass that flows out of the Mediterranean Sea
To what depth does MIDW sink?
1 km … spreads westward across the Atlantic
What is Common Water?
The Pacific Oceans main water mass, formed by a blending of ABW and NADW in the Antarctic Circumpolar Current.
How does Common Water flow?
Injected into the Pacific basin and flows northward to 10ºS where it encounters Pacific Subarctic Water
Which waters dominate the Pacific ocean above 2000 metres?
North Pacific Intermediate Water and Antarctic Intermediate Water
Which ocean has the simplest stratification?
The Indian Ocean
Which water mass dominates the Indian ocean?
Common Water
What 3 water masses are found in the Indian ocean?
- Common Water
- Antarctic Intermediate Water
- Red Sea Intermediate water
What is the Red Sea Intermediate Water?
A warm, highly saline (40ppm) water mass formed in the Red Sea that sinks to 3000m in the Indian Ocean basin
Where does Atlantic water flow into the Mediterranean basin?
Across the Straits of Gibraltar at the surface
As water flows eastward in the Mediterranean basin …
- salinity increases due to increase evaporation
- the sea surface slopes eastward creating a pressure gradient
How is Mediterranean water formed?
Sinking, warm but highly saline (38ppm) water sinks in the east of the basin and flows along the bottom until it enters the Atlantic ocean
What temperature is MIW and at what depth does it flow?
13ºC and flows at 1km depth
What are surface water conditions in the Black Sea?
Surface waters are brackish (excess precipitation and river inflow from the Danube)
What prevents mixing in the Black Sea?
A strong halocline and thermocline
What is water like below the pycnocline in the Black Sea?
- Anoxic
- Rich in dissolved hydrogen sulphide gas
What is the turnover time of the Black Sea?
Approx 3000 years
What % of the ocean has a temperature of 0-5ºC?
75%
