Open Ocean

Question 1

Ocean basin circulation

Answer 1

Major surface ocean currents are driven by combined effect of:
- Major global wind patterns
- Latitudinal variation in the Coriolis force
Ekman spiral forms resulting in ekman transport

Question 2

Gyres

Answer 2

N clockwise
S anti
Warm SSTs
Tend to have high surface salinity

Question 4

Eddies

Answer 4

Warm and cold core eddies have different temperature and nutrient characteristics
Different ecosystems with their own temperature, nutrients and plankton

Question 5

Meso-scale eddies

Answer 5

Weather of the ocean
Satellite altimetry, SS heights
Eddies affect top 150m
Pump nutrient rich waters from depth
Stimulate new production

Question 6

Nutrients and PP

Answer 6

New nutrients enter euphotic zone from outside gyre
New nutrients support new PP
Regenerated nutrients are recycled within the euphotic zone.
Regenerated nutrients supported regenerated production
F-ratio, ratio of nitrate uptake by phytos to total inorganic and organic uptake by phytos

Question 7

Subtropical gyre production, old

Answer 7

Considered to be oceanic deserts, biomass and production v low.
Inefficient ecosystems with nutrient-limited growth
F-ratios are low ~0.1
New production 10% of total

Question 8

Subtropical gyre, current view

Answer 8

Dynamic systems, important for production
Episodic nutrient inputs increase annual f ratio to 0.3-0,5
Clearly defined vertical structure
- deep waters, blooms during winter due to mixing and nitrate inputs
Upper waters, blooms in late summer based on N fixing

Question 9

Deep sub surface chlorophyll maximum

Answer 9

Upper nutrient-limited, light rich, based on regenerated nutrients, f-ratio low 0.1-0.3
Deep light limited, nutrient rich, based on new nutrients, high f 0.4-0.6.

Question 10

Biogeography of phytoplankton

Answer 10

Regions with different nutrient levels
Chlorophyll maximum at different depths and sub-tropical gyres
Vertical structure of water column and cellular response to different light levels
Small phytoplankton in regions where nutrient levels are low, regeneration
Large phyto species in regions with high levels of nutrients, no need for regeneration

Question 11

N Fixation

Answer 11

If system has no inputs from other sources
n fixing can supply 60-90% of N required
Carried out by N fixing organisms, cyanobacteria
Trichodesmium is the dominant N fixer

Question 12

Vertical migration

Answer 12

Can bring nitrate up from depth
Cyanobacteria may migrate between upper and deep waters to mine deep inorganic phosphorous pools

Question 13

Subtropical gyre food web

Answer 13

Both the microbial loop and classical food chains are present
Under nutrient limitation, microbial dominates
When there is nutrient input, classical dominates briefly
6 trophic levels
Small pelagic forage fish are intermediate
High trophic levels include fast predators, mammals and birds
Low levels of regenerated production are continuously grazed by zooplankton
Top down and bottom up control

Question 14

Microbial loop

Answer 14

Bacterial production, important food webs
Inputs dissolved OM from plankton
Small heterotrophic zooflagellates link to classic food chain
Mixotrophy is common
Important for remineralization and nutrient cycling, nutrient limiting open ocean