methods for estimating new primary production in upwelling systems james j. bisagni university of...
TRANSCRIPT
Methods forEstimating New Primary Production
In Upwelling Systems
James J. Bisagni
University of Massachusetts, DartmouthPhysics Department &
School for Marine Science & TechnologyNew Bedford, Massachusetts, USA
Talk Outline:
I. List Some Goals
II. Provide Working Definitions
III. Summary of Model Types
IV. Model Descriptions
V. Discussion
Tentative Project Goals:
I. Describe the size of New Primary Production (NPP) in the Peru/Chile upwelling system
II. Describe the mean seasonal cycle of NPP in the Peru/Chile upwelling system
III. Describe interannual variability of NPP in the Peru/Chile upwelling system
IV. Achieve goals I-III with a model-based approach, using both satellite and in-situ data
Total Primary Production
Total primary production in the ocean may be divided into “new” and “regenerated” production based on the source of the nitrogen which is utilized.(Dugdale & Goering, 1967; Eppley & Peterson, 1979).
Allocthonous nitrogen or nitrate (NO3) is input into the euphhotic zone from horizontal and/or vertical advection and diffusion.
Autocthonous nitrogen or ammonium (NH4) is input in the euphotic zone from metabolic recycling caused by biota within the water column and sediments.
Importance of New Primary Production
It is reasonable to state that in the absence of an allocthonous nitrogen supply, any given marine ecosystem will eventually become non-sustainable due to export of nitrogen through sinking of biogenic material and harvesting activities such as fishing, and predation from migratory pelagic species.(Platt et al., 1989)
Thus, it is clear from the standpoints of the global ocean’s ability to sequester atmospheric CO2, along with a local region’s ability to maintain a sustainable ecosystem, that new primary production, rather than total primary production, is the key quantity.
Measurements of New Production
Assimilation of 15N-labeled compounds allows instantaneous estimates of uptake rates of the available nitrogen sources by phytoplankton (Dugdale and Goering, 1967) and an estimate of the so-called “f-ratio” of new production to total production, where
However, estimates of regional or global new production must be done using other techniques such as using the relationship between new and total production and remotely-sensed data in order to discern how the presence of nitrogen species within the euphotic zone varies in space and time.
f–ratio=
[NO3–]
[NO3–] +[NH4
+]
(Eppley and Peterson, 1979)
New Production Models
1) Nitrate Uptake (Shift-Up) ModelsUtilize the inverse relationship between temperature and nitrate and the physiological response of phytoplankton within the euphotic zone.===> Largely “kinetics-based”
Examples include:Dugdale et al., 1989, Northwest AfricaKudela & Dugdale, 1996, CaliforniaDugdale et al., 1997, California
2) Nitrate Bulk ModelsUtilize the inverse relationship between temperature and nitrate and a nitrate budget to account for the amount of nitrate within and entering the euphotic zone.===> Largely “physics-based”
Examples include:Waldron & Probyn, 1992, BenguelaTownsend, 1998, Gulf of MaineBisagni, in-press, Gulf of Maine
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
(After Dugdale et al., 1989)
Nitrate Uptake (Shift-Up) Model
QuickTime™ and aTIFF (Uncompressed) decompressor
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AVHRR (Only) Model (Left-Half)For Each Pixel
Satellite SSTProvides NO3
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
AVHRR (Only) Model (Left-Half)For Each Pixel
Satellite SSTProvides NO3
Satellite SSTProvides Time-Base
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
AVHRR (Only) Model (Left-Half)For Each Pixel
Satellite SSTProvides NO3
Satellite SSTProvides Time-Base
Maximum measuredspecific NO3 uptake(Vmax NO3) at time=tassuming shift-up
Shift-Up: Vmax NO3(t) = VNO3 (i) + A(t) x t
Measured acceleration of NO3 uptake, d/dt(VNO3)
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
AVHRR (Only) Model (Left-Half)For Each Pixel
Satellite SSTProvides NO3
Satellite SSTProvides Time-Base
Maximum measuredspecific NO3 uptake(Vmax NO3) at time=tassuming shift-up
Predicted VNO3 attime=t assuming shift-
up & Michaelis-Menton kinetics
Shift-Up: Vmax NO3(t) = VNO3 (i) + A(t) x t
Michaelis-Menton Kinetics:
VNO3(t) = Vmax NO3(t) x [NO3]/(Ks + [NO3])
Measured half-saturation constant
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
AVHRR (Only) Model (Left-Half)For Each Pixel
Satellite SSTProvides NO3
Satellite SSTProvides Time-Base
Maximum measuredspecific NO3 uptake(Vmax NO3) at time=tassuming shift-up
Predicted VNO3 attime=t assuming shift-
up & Michaelis-Menton kinetics
Shift-Up: Vmax NO3(t) = VNO3 (i) + A(t) x t
Michaelis-Menton Kinetics:
VNO3(t) = Vmax NO3(t) x [NO3]/(Ks + [NO3])
Variation in VNO3
versus irradiance& depth of euphotic zone measurements
(or from ocean color)
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
AVHRR (Only) Model (Left-Half)For Each Pixel
Satellite SSTProvides NO3
Satellite SSTProvides Time-Base
Maximum measuredspecific NO3 uptake(Vmax NO3) at time=tassuming shift-up
Predicted VNO3 attime=t assuming shift-
up & Michaelis-Menton kinetics
Shift-Up: Vmax NO3(t) = VNO3 (i) + A(t) x t
Michaelis-Menton Kinetics:
VNO3(t) = Vmax NO3(t) x [NO3]/(Ks + [NO3])
Variation in VNO3
versus irradiance& depth of euphotic zone measurements
(or from ocean color)
Integrate VNO3 over the euphotic zone and multiply by
PONto yield NPP
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
AVHRR (Only) Model (Left-Half)For Each Pixel
Satellite SSTProvides NO3
Satellite SSTProvides Time-Base
Maximum measuredspecific NO3 uptake(Vmax NO3) at time=tassuming shift-up
Predicted VNO3 attime=t assuming shift-
up & Michaelis-Menton kinetics
Shift-Up: Vmax NO3(t) = VNO3 (i) + A(t) x t
Michaelis-Menton Kinetics:
VNO3(t) = Vmax NO3(t) x [NO3]/(Ks + [NO3])
Variation in VNO3
versus irradiance& depth of euphotic zone measurements
(or from ocean color)
Integrate VNO3 over the euphotic zone and multiply by
PONto yield NPP
Compute f-ratio
Stored NO3
NPP is estimated using a bulk quantity termed “potential new production” (PNP) as a proxy “upper limit” for NPP where PNP has been defined in a variety of ways:
For each Benguela upwelling event:
Nitrate Bulk Models
PNP= NO3
–Ze
0
dz ×Redfieldratio×n
(Waldron & Probyn, 1992)
z= 0
z= -Ze
PNP= NO3
–Ze
0
dz ×Redfieldratio
Then sum over “n” upwelling events:
In the Gulf of Maine:
NO3 FluxTPP ×Redfieldratio=PNP
TPP
(Townsend, 1998)
z= 0
z= -Ze
===> PNP = NO3 Flux x Redfield ratio
NO3 Flux=Kz
∂NO3∂z
NO3 Flux
Stored NO3
PNP=
ddt NO3
–Ze
0dz – KZ
∂NO3∂z –Ze
×Redfieldratio
z= 0
z= -Ze
===> PNP = d/dt[Stored NO3 - NO3 Flux] x Redfield ratio
NO3 Flux
(Bisagni, in press)
In the Gulf of Maine:
Model Differences
Nitrate Uptake (Shift-Up) Models
In addition to “standard” hydrographic measurements of temperature, NO3, and PON, such kinetics-based NPP models require “rate measurements” of A(t), KS, and KE, the half saturation constant for NO3 uptake as a function of irradiance (depth). Moreover, measured 15N incubations, if available would allow verification of modeled VNO3(t) values.
Models are sensitive to slope of temperature- NO3 regression and the applied constant heating rate (may not be constant!).
Nitrate Bulk Models
Utilize “standard” hydrographic measurements of temperature and NO3 but require estimates of KZ and upwelling velocity to measure the proxy PNP.
Models are sensitive to slope of temperature- NO3 regression, KZ and upwelling velocity.
Summary & Conclusions
Models exist which are able to estimate NPP
Nitrate uptake (shift-up) models are able to make pixel-by-pixel estimates of NPP, but make some strong assumptions (heating rate) and require many in-situ rate measurements.
Nitrate Bulk Models are able to make pixel-by-pixel estimates of the upper limit of NPP through estimation of PNP as a proxy for NPP, but require some physical oceanographic quantities (KZ and w).
Choosing a model depends largely on the questions being asked and available data.
Summary & Conclusions
Models exist which are able to estimate NPP
Nitrate uptake (shift-up) models are able to make pixel-by-pixel estimates of NPP, but make some strong assumptions (heating rate) and require many in-situ rate measurements.
Nitrate Bulk Models are able to make pixel-by-pixel estimates of the upper limit of NPP through estimation of PNP as a proxy for NPP, but require some physical oceanographic quantities (KZ and w).
Choosing a model depends largely on the questions being asked and available data.
What are the available data?