Spatial variations
in respiration rates and hypoxia
on the Oregon shelf
Megan Wolf
HHMI Summer 2007 Undergraduate Research Program
Mentor: Dr. Francis Chan
Department of Zoology
Oregon State University
Hypoxia: Biological Impacts
Cascade Head
2006
Lincoln Beach
2000
100m
Newport
Seal Rock
Strawberry Hill
2006
50m
Spatial and temporal variation
in dissolved O2 concentration
May 2007
June 2007
July 2007
August 2007
Research Question:
What drives spatial
variations in hypoxia
risk and severity?
Shelf topography
interacts with coastal
currents…
Kirincich and Barth (COAS)
…To modulate water residence times and surface production
Ocean Currents
Phytoplankton
Purpose:
Determine whether spatial
hypoxia patterns are due to:
a) differences in water
residence time
100m
50m
OR
b) differences in surface
productivity
Average dissolved O2 concentration
May - August 2007
Hypothesis
H0 : Hypoxia variation driven by physics
North
Latitude
South
100m
50m
Respiration Rate
HA : Hypoxia variation driven by biology
North
Latitude
Average dissolved O2 concentration
May - August 2007
South
Respiration Rate
Methods: Sample Collection
Collected
water from
ocean floor at
various shelf
locations
Reagants added
immediately to measure
O2 concentration by
Winkler titration or…
...samples incubated and
O2 concentration
monitored over time using
Fibox
Methods: Measuring Dissolved Oxygen
Winkler Titration
Iodine proportional to dissolved oxygen
Winkler Reagents:
MnCl2
NaOH + NaI
Methods: Measuring Dissolved Oxygen
Fluorescing Membrane
Fibox 3
by Precision Sensing GmbH
Temperature compensated
oxygen meter for use with
fiber-optic oxygen sensors
Advantage: noninvasive
method for measuring
oxygen concentrations
in closed samples
Correlation between methods
Data collected:
08/16/07 from Southern Lines (SH, SR, WK)
08/17/07 from Northern Lines (NH, CH, LB)
Data collected:
08/16/07 from Southern Lines
(SH, SR, WK)
-1.2
-1
R2 = 0.6417
-0.8
-0.6
-0.4
-0.2
0
20
40
60
80
100
120
0
0.2
Depth (m)
-0.9
Data collected:
08/17/07 from Northern Lines
(NH, CH, LB)
Change in dissolved O2 concentration (ml/l) per day
Change in dissolved O2 concentration (ml/l) per day
Spatial Variation
-0.8
R2 = 0.4525
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
20
40
60
0
Depth (m)
80
100
120
Spatial variation
in respiration rates
100m
50m
Measured as change in
ml dissolved O2 per liter per day
Conclusions
• Respiration rates do not vary with latitude
–
–
Respiration decoupled from north-south
gradient in surface production
Suggests water residence times play a dominant
role in structuring the risk of hypoxia
Future Research
To determine limiting factors of respiration…
Abiotic:
•
Oxygen limitation
•
Carbon limitation
•
Temperature effects
Biotic:
•
Food web structure
– Relative abundance of microorganism size classes
– Per capita respiration rate of microorganism size classes
– Spatial and temporal variation in microorganism activity
– Factors controlling microorganism size class
distribution
Acknowledgements
Howard Hughes Medical Institute
Ray and Fran Cripps
Dr. Francis Chan
Dr. Bruce Menge
Claire Shapleigh
Kristina McCann
Dr. Kevin Ahern
North Winds: Summer Upwelling
1. Northerly winds blow
surface water offshore
1. Northerly winds blow
surface water offshore
2. Upwelling of deeper,
colder, nutrient-rich water
near coast
1. Northerly winds blow
surface water offshore
3. Phytoplankton bloom
because nutrients reach
lighted zone
2. Upwelling of deeper,
colder, nutrient-rich water
near coast
1. Northerly winds blow
surface water offshore
3. Phytoplankton bloom
because nutrients reach
lighted zone
4. Phytoplankton
sink to seafloor
2. Upwelling of deeper,
colder, nutrient-rich water
near coast
1. Northerly winds blow
surface water offshore
3. Phytoplankton bloom
because nutrients reach
lighted zone
4. Phytoplankton
sink to seafloor
2. Upwelling of deeper,
colder, nutrient-rich water
near coast
5. Microorganisms decompose phytoplankton,
consuming oxygen through respiration
1. Northerly winds blow
surface water offshore
3. Phytoplankton bloom
because nutrients reach
lighted zone
4. Phytoplankton
sink to seafloor
2. Upwelling of deeper,
Thereby lowering
colder, nutrient-rich water
oxygen
near coast
concentration at
sea floor
5. Microorganisms decompose phytoplankton,
consuming oxygen through respiration
Successive upwelling produces hypoxia
1. Northerly winds blow
surface water offshore
3. Phytoplankton bloom
because nutrients reach
lighted zone
4. Phytoplankton
sink to seafloor
2. Upwelling of deeper,
Thereby lowering
colder, nutrient-rich water
oxygen
near coast
concentration at
sea floor
5. Microorganisms decompose phytoplankton,
consuming oxygen through respiration
Successive upwelling produces hypoxia
1. Northerly winds blow
surface water offshore
3. Phytoplankton bloom
because nutrients reach
lighted zone
4. Phytoplankton
sink to seafloor
2. Upwelling of deeper,
Thereby lowering
colder, nutrient-rich water
oxygen
near coast
concentration at
sea floor
5. Microorganisms decompose phytoplankton,
consuming oxygen through respiration
Successive upwelling produces hypoxia
1. Northerly winds blow
surface water offshore
3. Phytoplankton bloom
because nutrients reach
lighted zone
4. Phytoplankton
sink to seafloor
2. Upwelling of deeper,
Thereby lowering
colder, nutrient-rich water
oxygen
near coast
concentration at
sea floor
5. Microorganisms decompose phytoplankton,
consuming oxygen through respiration