Macro-Nutrient Transport Pathways and Interactions with the Iron Cycle. Export and remineralization...
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Transcript of Macro-Nutrient Transport Pathways and Interactions with the Iron Cycle. Export and remineralization...
![Page 1: Macro-Nutrient Transport Pathways and Interactions with the Iron Cycle. Export and remineralization of sinking, organic particles moves nutrients to denser.](https://reader035.fdocuments.in/reader035/viewer/2022062720/56649f125503460f94c2651b/html5/thumbnails/1.jpg)
Macro-Nutrient Transport Pathways and Interactions with the Iron Cycle.
Export and remineralization of sinking, organic particles moves nutrients to denser isopyncals:
Mick Follows, Stephanie Dutkiewicz, Payal Parekh: MITTaka Ito: University of Washington
Ric Williams: University of Liverpool
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Return of macro-nutrients to euphotic zone requires diapycnal transfer
Atlantic basin
![Page 3: Macro-Nutrient Transport Pathways and Interactions with the Iron Cycle. Export and remineralization of sinking, organic particles moves nutrients to denser.](https://reader035.fdocuments.in/reader035/viewer/2022062720/56649f125503460f94c2651b/html5/thumbnails/3.jpg)
Return of macro-nutrients to euphotic zone requires diapycnal transfer
Pacific basin
![Page 4: Macro-Nutrient Transport Pathways and Interactions with the Iron Cycle. Export and remineralization of sinking, organic particles moves nutrients to denser.](https://reader035.fdocuments.in/reader035/viewer/2022062720/56649f125503460f94c2651b/html5/thumbnails/4.jpg)
Atlantic basin
Upwelling in Southern Ocean major return pathway...
![Page 5: Macro-Nutrient Transport Pathways and Interactions with the Iron Cycle. Export and remineralization of sinking, organic particles moves nutrients to denser.](https://reader035.fdocuments.in/reader035/viewer/2022062720/56649f125503460f94c2651b/html5/thumbnails/5.jpg)
Mode and intermediate waters formed equatorwards of ACC - pathway for macro-nutrients to northern basins
(Sarmiento et al., 2003)
surface nitrate surface silica
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Mode waters Hanawa and Talley (2001)
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Residual mean flow transports nutrients northwards to sites of mode and intermediate water formation
Marshall (1997)
Ψres
= ΨEkman
+ Ψeddy
![Page 8: Macro-Nutrient Transport Pathways and Interactions with the Iron Cycle. Export and remineralization of sinking, organic particles moves nutrients to denser.](https://reader035.fdocuments.in/reader035/viewer/2022062720/56649f125503460f94c2651b/html5/thumbnails/8.jpg)
Residual mean flow transports nutrients northwards to sites of mode and intermediate water formation
Marshall (1997)
Ψres
= ΨEkman
+ Ψeddy
![Page 9: Macro-Nutrient Transport Pathways and Interactions with the Iron Cycle. Export and remineralization of sinking, organic particles moves nutrients to denser.](https://reader035.fdocuments.in/reader035/viewer/2022062720/56649f125503460f94c2651b/html5/thumbnails/9.jpg)
NO3 (uM)
upwelling+NO
3
-Fe
dust
iron limited macro-nutrient limited
subduction
● balance between northward residual mean advection and export sets subducted nutrient concentration
● export sensitive to iron availability
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Macro-nutrient supply to the subtropical gyres.
WOCE A20 North Atlantic
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Convergence of horizontal Ekman nitrate flux in N. Atlantic (10-3 mol N m-2 yr-1)
Lateral Ekman transfer into N. Atlantic subtropical gyres
Williams and Follows (1998)
Role of eddies? Residual mean flow
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North Atlantic subtropical gyre: schematic nutrient budget
Ekman transfer significant source to subtropical bowl
(~ mol N m-2 yr-1) organic export (Jenkins, 1988)
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Connecting southern and northern hemispheres:“nutrient stream” centred at σ
θ = 27.0 supplies nutrients
to northern gyres (Pelegri and Csanady, 1991)
σθ = 27.0
PO4* (“conservative”) (μM) NO
3 (μM)
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Nutrient stream outcrops close to intergyre boundary in winter
March NO3 and σ
θ (10m)
World Ocean Atlas
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Illustration in a global biogeochemical model:
regulation of macro-nutrient pathways by aeolian iron source (Dutkiewicz et al., 2005)
Modeled Surface Chl (mg m-3)● Explicit, coupled phosphorus, silica and iron cycles
● Two phytoplankton classes: Diatoms and "other" phytoplankton
● Single grazer
● Prescribed aeolian iron source
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Aeolian Iron Source (mmol Fe m-2 yr-1)
Luo et al (2003)
Sensitivity studies with uniform “high” and “low” aeolian iron flux...
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difference in primary producitivity(high – low) aeolian iron supply (g C m-2 y-1)
Sensitivity of primary production to aeolian iron source
More dust, higher productivity
More dust, lower productivity
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Pacific basin reflects regulation of intergyre exchange
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Atlantic productivity reflects southern ocean surface macro-nutrient utilization
Atlantic
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Summary
● Lateral transfer in surface ocean is significant route for diapycnal return of macro-nutrients to light isopycnals. (Southern Ocean, inter-gyre boundaries)
● Advection by residual mean flow (Ekman + eddy) is key physical process
● Balance between residual mean advection and iron stress regulates the lateral fluxes of macro-nutrients.
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Two regimes:
- iron limited upwelling regions - macro-nutrient limited subtropical gyres + Atlantic
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Export and remineralization of sinking, organic particles moves nutrients to denser isopyncals
Atlantic basin
![Page 24: Macro-Nutrient Transport Pathways and Interactions with the Iron Cycle. Export and remineralization of sinking, organic particles moves nutrients to denser.](https://reader035.fdocuments.in/reader035/viewer/2022062720/56649f125503460f94c2651b/html5/thumbnails/24.jpg)
Pelegri and Csanady (1991): “nutrient stream”
core of stream at σθ ~ 27.0
v NO3 at 36N
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Numerical model
Eulerian mean(Ekman) upwelling(200m)
Residual meanupwelling (200m)