Download so, where would you predict the highest primary productivity?

high productivity in the
mid- to high latitudes. Why?
low productivity in the
low latitude open ocean;
subtropical gyres are
“biological deserts” Why?
Amazon River
coastal upwelling
equatorial upwelling
so, where would you predict the
highest primary productivity?
along continental margins,
especially in coastal waters
Georges Bank
“north wall” of the Gulf Stream
What relationship,
if any, do you
see between
chlorophyll
abundance
(top panel)
and sea surface
temperature
(bottom panel)?
Northern Hemisphere summer
subtropical gyre
“Sargasso Sea”
cooler sea surface
temperatures =
higher productivity
cooler sea surface
temperatures =
weaker thermocline
1
Low Latitudes
High Latitudes
Temperature
cold
32
41
50
59
68
77
86 °F
0
5
10
15
20
25
30 °C
0
41
50
59
68
77
86 °F
0
5
10
15
20
25
30 °C
0
EUPHOTIC ZONE
summer
100
200
PHOTIC ZONE
winter
strong thermocline 100
= strong density
gradient & barrier
to nutrient diffusion
200
the presence or absence of a strong
thermocline (including the
development of a seasonal
thermocline in the mid-latitudes)
seasonal changes in solar
radiation (angle of incidence)
weak thermocline
= weak density
gradient which does not
obstruct nutrient diffusion
NUTRIENTS
NUTRIENTS
(from decomposition
of organic matter
by bacteria)
300
300
400
(from decomposition
of organic matter
by bacteria)
400
The thermocline can be an effective barrier to diffusion and vertical advection
of nutrients between nutrient-rich deep waters and the sunlit surface waters
High Latitudes (Polar)
Temperature
cold
high productivity
solar-limited
(in meters)
solar-limited
warm
32
41
50
59
68
77
86 °F
0
5
10
15
20
25
30 °C
think of the thermocline as a
“density doorway”
Mid-Latitudes (Temperate)
high
0
(short-lived peak)
Water Depth
Biomass
(abundance of organisms)
high
seasonal factors that influence
primary production across latitude
100
weak thermocline
year-round
(even in summer)
200
Biomass
(in meters)
Water Depth
EUPHOTIC ZONE
Seasonality
warm
32
high
productivity
spring "bloom"
solarlimited
nutrientlimited
(low sun
angle)
(thermocline)
Temperature
cold
0
renewed
productivity
warm
32
41
50
59
68
77
86 °F
0
5
10
15
20
25
30 °C
winter
(weak
thermocline)
(in meters)
warm
(abundance of organisms)
cold
Water Depth
Temperature
100
spring
& fall
summer
(strong
thermocline)
200
low
low
winter
spring summer
fall
300
productivity is not limited by nutrients
“density doorway” is open
productivity is limited by available solar radiation
angle of solar incidence too low for much of the year
short-lived episode of productivity when solar
radiation is available 24 hours/day
winter
spring summer
fall
300
winter: nutrients are available (doorway open),
but not enough solar radiation
spring: nutrients and solar radiation are
available = high productivity (“spring bloom”)
summer: solar radiation available, but nutrients
cut-off by seasonal thermocline (doorway closed)
fall: break-down of thermocline = renewed
productivity
2
Low Latitudes (Tropics)
warm
41
50
59
68
77
86 °F
0
5
10
15
20
25
30 °C
Mid-latitude seasonal cycle
nutrient-limited
year-round
(except where there is
upwelling)
(in meters)
Water Depth
0
(abundance of organisms)
Biomass
high
Temperature
cold
32
100
200
strong
thermocline
year-round
low
300
winter
spring summer
fall
always enough solar radiation, but nutrients cut-off
from below by the strong thermocline (“density
doorway” closed tight)
except where upwelling occurs (coastal & near equator)
coral reefs are an exception – despite very low
nutrients in the water, high productivity is driven
by highly efficient nutrient recycling
Angle of solar radiation controls the development
of the seasonal thermocline and the depth of light
penetration for photosynthesis.
Jan.Jan.-March (1978(1978-1986)
Nutrient Cycling
organic matter in the ocean:
rain of organic matter from the surface waters
terrigenous organic matter from the continents
AprilApril-June (1978(1978-1986)
heterotrophic bacteria break down the
organic matter
nutrients are recycled back to there useable
inorganic form
these regenerated nutrients become “trapped”
in the deep waters below the pycnocline
(thermocline)
except where upwelling occurs
upwelling provides a mechanism to deliver
nutrients back to the sunlit surface waters.
3
Overview of nutrient distribution
Continental Margin
Open Ocean Surface Waters
scarce nutrients = low biomass
moderate to abundant nutrients
= moderate to high biomass
(except where upwelling)
(especially where coastal upwelling)
warm, nutrient-depleted
surface waters
Continental Margin
moderate to abundant nutrients,
moderate to high biomass
(especially where/when
coastal upwelling occurs)
Continental
Shelf
scarce nutrients, low biomass
(except areas of upwelling)
(food for benthic
organisms)
Co
shelf edge
Open Ocean Surface Waters
rain of
organic matter
oceanic divergence and
upwelling: abundant nutrients,
high biomass
Continental Margin
coastal upwelling
results in
abundant nutrients,high biomass
Wa ter
Depth
(in meters)
0
photic zone
aphotic zone
(no light below
about 200 m)
nti
lo
lS
nta
ne
terrigenous sediments
mixed with organic matter
(food for benthic organisms)
pe
Spreading Center
Co
ntin
enta
l
Pycnocline
(Thermocline)
cold, nutrient-rich
deep waters
("nutrient sink", "storehouse")
100 note change
500 in scale
1000
2000
3000
4000
5000
Ri se
Abyssal Pla ins
Annual mean sea surface temperature
6000
Marine life is concentrated in sunlit surface waters where
photosynthesis occurs; however, vast areas of the surface ocean are
depleted in nutrients required for photosynthesis due to the presence
of a pycnocline (thermocline) - except where upwelling occurs
The subtropical
gyres are
“biological
deserts”
very little
dissolved
nutrients make
it out into the
open ocean
surface waters
Annual mean phosphate at the surface
Note the scarcity of nutrients where
surface waters are warm and well
stratified (the thermocline is a barrier
to nutrient diffusion to surface waters).
Annual mean nitrate at the surface
Bay of
Fundy,
film:
“Where the
Bay Meets
the Sea”
4