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

Ocean Layers and Ocean Mixing Characteristics of ocean layers depth 0-100 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

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

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

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

Figure 4-19 Seasonal Changes And Vertical Mixing.

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

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

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

Figure 4-20 Vertical Overturn.

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

Figure 4-21 Upwelling And Downwelling Zones.

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