1. Ms. Halbohm Marine Biology
Chapter 4 Section 4
Ms. Halbohm
Marine Biology

2. Ocean Layers and Ocean Mixing
Characteristics of ocean layers
depth m (330 feet): warmed by solar radiation, well mixed
100-1,000 m: temperature decreases
thermocline – zone of rapid temperature change
halocline: salinity increases 0-1,000 m
pycnocline: 100-1,000 m, where changes in temperature and salinity create rapid increases in density
seasonal thermoclines

3. Figure 4-18 (a) Changes In Temperature, Salinity, And Density Of Seawater With Depth.

4. Figure 4-18 (b) Changes In Temperature, Salinity, And Density Of Seawater With Depth.

5. Figure 4-18 (c) Changes In Temperature, Salinity, And Density Of Seawater With Depth.

6. Figure 4-19 Seasonal Changes And Vertical Mixing.

7. Water column stabilizes
Fall
Air temperature
cools
Surface water
cools, displaces
less dense
water
Colder denser
water
Summer
Warm surface water
Thermocline
Isopycnal
Wind
Winter
Water column unstable
Spring
Air temperature warms
Surface water warms
Colder denser
water
Thermocline
Water column stable
Storms drive surface
water deeper
Water column stabilizes
Stepped Art
Fig. 4-19, p. 86

8. Ocean Layers and Ocean Mixing
Horizontal mixing
higher density causes water at 30o N to form a curved layer that sinks below less-dense equatorial surface water and then rises to rejoin the surface at 30o S
even denser water curves from 60o N to 60o S below other surface waters
winter temperatures and increased salinity owing to freezing result in very dense water at the poles, which sinks toward the ocean floor

9. Ocean Layers and Ocean Mixing
Vertical mixing
vertical overturn results when denser water at the top of the water column sinks while less-dense water rises
isopycnal—stable water column that has the same density from top to bottom
vertical mixing allows water exchange between surface and deep waters
nutrient-rich bottom water is exchanged for oxygen-rich surface water

10. Figure 4-20 Vertical Overturn.

11. Ocean Layers and Ocean Mixing
Upwelling and downwelling
equatorial upwelling
water from currents on either side of the equator is deflected toward the poles, pulling surface water away to be replaced by deeper, nutrient-rich water
coastal upwelling
Ekman transport moves water offshore, to be replaced by deeper, nutrient-rich water
coastal downwelling
coastal winds force oxygen-rich surface waters downward and along the continental shelf

12. Figure 4-21 Upwelling And Downwelling Zones.

13. Ocean Layers and Ocean Mixing
Deepwater circulation
differences in density, not wind energy, cause water movement in deep oceans
densest water of all is Antarctic Bottom Water, mostly formed in winter in the Weddell Sea
dense Antarctic water sinks to the bottom and moves slowly toward the Arctic
some North Atlantic Deep Water moves into the North Atlantic via a channel east of Greenland
high-salinity Mediterranean Deep Water flows through the Strait of Gibraltar into the Atlantic Ocean