Lecture 16- Ocean Primary Production 2 Flashcards
primary production are exceptionally low year round in
subtropical gyres (on a per meter square basis) due to persistent lens of warm water
Low surface layer nutrients
present through all seasons
Subtropical gyres
exhibit very little seasonal variation
Equatorial pacific
exhibits very little seasonal variability in primary production
Proximity of the thermocline near the surface in the east
enhances upwelling of cold and nutrient rich deep water to the lighted region and thus enhances biological productivity in this area
Tidal mixing
occurs in shallow continental shelf regions year-round
coastal upwelling
- results from wind/Ekman offshore transport
- seasonally variable
- greatly enhances upward movement of deep water that is rich in nutrients
coastal upwelling primary production
- high year round
- exceptionally high during upwelling periods in certain regions
large seasonal increase in primary production occurs in the North Atlantic during
the spring season due to deep water mixing and strong springtime stratification
mixing in winter
- mixing is below the critical depth (due to cold winter storms)
- NPP is negative
mixing in spring
- mixing is above the critical depth (due to shallow thermocline)
- NPP is positive
what determines if NPP is positive and if phytoplankton blooms will occur?
changes in mixing depth relative to the critical depth
mixing in westerly wind region
- deep vertical mixing in winter
- brings high levels of nutrients to surface
- causes phytoplankton to mix below the critical depth so NPP is light limited (deep water- no light)
polar ocean regions
same as temperate oceans but melting of ice shelf enhances stratification
global NPP
104 GT C/year
