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Export and remineralization of sinking, organic particles moves nutrients to denser isopyncals:. Macro-Nutrient Transport Pathways and Interactions with the Iron Cycle. Mick Follows , Stephanie Dutkiewicz , Payal Parekh : MIT Taka Ito : University of Washington

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Presentation Transcript
slide1

Export and

remineralization of

sinking, organic

particles moves

nutrients to denser

isopyncals:

Macro-Nutrient Transport Pathways and Interactions with the Iron Cycle.

Mick Follows, Stephanie Dutkiewicz, Payal Parekh: MIT

Taka Ito: University of Washington

Ric Williams: University of Liverpool

slide5

surface nitrate surface silica

Mode and intermediate waters formed equatorwards of ACC - pathway for macro-nutrients to northern basins

(Sarmiento et al., 2003)

slide7

Marshall (1997)

Residual mean flowtransports nutrients northwards to sites of mode and intermediate water formation

Ψres = ΨEkman + Ψeddy

slide8

Marshall (1997)

Residual mean flowtransports nutrients northwards to sites of mode and intermediate water formation

Ψres = ΨEkman + Ψeddy

slide9

iron limited macro-nutrient

limited

  • balance between northward residual mean advection and export sets subducted nutrient concentration
  • export sensitive to iron availability

dust

subduction

upwelling

+NO3

-Fe

NO3 (uM)

slide11

Role of eddies?

Residual mean flow

Lateral Ekman transfer into N. Atlantic subtropical gyres

Williams and Follows (1998)

Convergence of horizontal Ekman nitrate flux in N. Atlantic (10-3 mol N m-2 yr-1)

slide12

North Atlantic subtropical gyre: schematic nutrient budget

Ekman transfer significant source to subtropical bowl

(~ mol N m-2 yr-1)

organic export (Jenkins, 1988)

slide13

Connecting southern and northern hemispheres:

“nutrient stream” centred at σθ = 27.0supplies nutrients

to northern gyres (Pelegri and Csanady, 1991)

σθ = 27.0

PO4* (“conservative”) (μM) NO3 (μM)

slide14

Nutrient stream outcrops close to intergyre boundary in winter

March NO3 and σθ (10m)

World Ocean Atlas

slide15

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
slide16

Aeolian Iron Source (mmol Fe m-2 yr-1)

Luo et al (2003)

Sensitivity studies with uniform “high” and “low” aeolian iron flux...

slide17

Sensitivity of primary production to aeolian iron source

difference in primary producitivity

(high – low) aeolian iron supply (g C m-2 y-1)

More dust, higher productivity

More dust,

lower productivity

slide20

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.
slide22

Two regimes:

- iron limited upwelling regions

- macro-nutrient limited subtropical gyres + Atlantic

slide23

Export and remineralization of sinking, organic particles moves

nutrients to denser isopyncals

Atlantic basin

slide24

Pelegri and Csanady (1991): “nutrient stream”

core of stream at σθ ~ 27.0

v NO3 at 36N

slide25

Numerical model

Eulerian mean

(Ekman) upwelling

(200m)

Residual mean

upwelling (200m)