1. Methods for Estimating New Primary Production In Upwelling Systems James J. Bisagni University of Massachusetts, Dartmouth Physics Department & School for Marine Science & Technology New Bedford, Massachusetts, USA

2. Talk Outline: I. List Some Goals II. Provide Working Definitions III. Summary of Model Types IV. Model Descriptions V. Discussion

3. 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

4. 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 (NO 3 ) is input into the euphhotic zone from horizontal and/or vertical advection and diffusion. Autocthonous nitrogen or ammonium (NH 4 ) is input in the euphotic zone from metabolic recycling caused by biota within the water column and sediments.

5. 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 CO 2, 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.

6. Measurements of New Production Assimilation of 15 N-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. (Eppley and Peterson, 1979)

7. New Production Models 1) Nitrate Uptake (Shift-Up) Models Utilize 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 Africa Kudela & Dugdale, 1996, California Dugdale et al., 1997, California 2) Nitrate Bulk Models Utilize 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, Benguela Townsend, 1998, Gulf of Maine Bisagni, in-press, Gulf of Maine

8. ( After Dugdale et al., 1989 ) Nitrate Uptake (Shift-Up) Model

9. AVHRR (Only) Model (Left-Half) For Each Pixel Satellite SST Provides NO 3

10. AVHRR (Only) Model (Left-Half) For Each Pixel Satellite SST Provides NO 3 Satellite  SST Provides Time-Base

11. AVHRR (Only) Model (Left-Half) For Each Pixel Satellite SST Provides NO 3 Satellite  SST Provides Time-Base Maximum measured specific NO 3 uptake (V max NO 3 ) at time=t assuming shift-up Shift-Up: V max NO 3(t) = VNO 3 (i) + A(t) x t Measured acceleration of NO 3 uptake, d/dt(VNO 3 )

12. AVHRR (Only) Model (Left-Half) For Each Pixel Satellite SST Provides NO 3 Satellite  SST Provides Time-Base Maximum measured specific NO 3 uptake (V max NO 3 ) at time=t assuming shift-up Predicted VNO 3 at time=t assuming shift- up & Michaelis- Menton kinetics Shift-Up: V max NO 3(t) = VNO 3 (i) + A(t) x t Michaelis-Menton Kinetics: VNO 3(t) = V max NO 3(t) x [ NO 3 ] / (K s + [ NO 3 ] ) Measured half-saturation constant

13. AVHRR (Only) Model (Left-Half) For Each Pixel Satellite SST Provides NO 3 Satellite  SST Provides Time-Base Maximum measured specific NO 3 uptake (V max NO 3 ) at time=t assuming shift-up Predicted VNO 3 at time=t assuming shift- up & Michaelis- Menton kinetics Shift-Up: V max NO 3(t) = VNO 3 (i) + A(t) x t Michaelis-Menton Kinetics: VNO 3(t) = V max NO 3(t) x [ NO 3 ] / (K s + [ NO 3 ] ) Variation in VNO 3 versus irradiance & depth of euphotic zone measurements (or from ocean color)

14. AVHRR (Only) Model (Left-Half) For Each Pixel Satellite SST Provides NO 3 Satellite  SST Provides Time-Base Maximum measured specific NO 3 uptake (V max NO 3 ) at time=t assuming shift-up Predicted VNO 3 at time=t assuming shift- up & Michaelis- Menton kinetics Shift-Up: V max NO 3(t) = VNO 3 (i) + A(t) x t Michaelis-Menton Kinetics: VNO 3(t) = V max NO 3(t) x [ NO 3 ] / (K s + [ NO 3 ] ) Variation in VNO 3 versus irradiance & depth of euphotic zone measurements (or from ocean color) Integrate VNO 3 over the euphotic zone and multiply by PON to yield NPP

15. AVHRR (Only) Model (Left-Half) For Each Pixel Satellite SST Provides NO 3 Satellite  SST Provides Time-Base Maximum measured specific NO 3 uptake (V max NO 3 ) at time=t assuming shift-up Predicted VNO 3 at time=t assuming shift- up & Michaelis- Menton kinetics Shift-Up: V max NO 3(t) = VNO 3 (i) + A(t) x t Michaelis-Menton Kinetics: VNO 3(t) = V max NO 3(t) x [ NO 3 ] / (K s + [ NO 3 ] ) Variation in VNO 3 versus irradiance & depth of euphotic zone measurements (or from ocean color) Integrate VNO 3 over the euphotic zone and multiply by PON to yield NPP Compute f-ratio

16. Stored NO 3 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 (Waldron & Probyn, 1992) z= 0 z= -Z e Then sum over “n” upwelling events:

17. In the Gulf of Maine: (Townsend, 1998) z= 0 z= -Z e ===> PNP = NO 3 Flux x Redfield ratio NO 3 Flux

18. Stored NO 3 z= 0 z= -Z e ===> PNP = d/dt[Stored NO 3 - NO 3 Flux] x Redfield ratio NO 3 Flux (Bisagni, in press) In the Gulf of Maine:

19. Model Differences Nitrate Uptake (Shift-Up) Models In addition to “standard” hydrographic measurements of temperature, NO 3, and PON, such kinetics-based NPP models require “rate measurements” of A(t), K S, and K E, the half saturation constant for NO 3 uptake as a function of irradiance (depth). Moreover, measured 15 N incubations, if available would allow verification of modeled VNO 3(t) values. Models are sensitive to slope of temperature- NO 3 regression and the applied constant heating rate (may not be constant!). Nitrate Bulk Models Utilize “standard” hydrographic measurements of temperature and NO 3 but require estimates of K Z and upwelling velocity to measure the proxy PNP. Models are sensitive to slope of temperature- NO 3 regression, K Z and upwelling velocity.

20. 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 (K Z and w). Choosing a model depends largely on the questions being asked and available data.

21. 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 (K Z and w). Choosing a model depends largely on the questions being asked and available data. What are the available data?