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Quantifying competing carbon pathways in mesoscale upwelling filaments off NW Africa. (or the pitfalls of seawater CO 2 inversions). Nick Hardman-Mountford (CSIRO), Carol Robinson (UEA), Ricardo Torres, Tim Smyth, Ian Brown, Vasilis Kitidis, P. Nightingale, C. Widdicombe (PML).

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quantifying competing carbon pathways in mesoscale upwelling filaments off nw africa

Quantifying competing carbon pathways in mesoscale upwelling filaments off NW Africa

(or the pitfalls of seawater CO2 inversions)

Nick Hardman-Mountford (CSIRO), Carol Robinson (UEA), Ricardo Torres, Tim Smyth, Ian Brown, Vasilis Kitidis, P. Nightingale, C. Widdicombe (PML)

what is relative contribution of different co 2 pathways air sea flux vs export production
What is relative contribution of different CO2 pathways: air-sea flux vs. export production?

NCP = E

slide3

Lagrangian study: plume tracking with SF6 and drifters

SOLAS-ICON+(D338)

  • 3 patches seeded
  • P1 & P3 filaments tracked
  • P2 subducted

Rees et al. 2011

+The impact of coastal upwelling on the air-sea exchange of climatically important gases

slide4

Sampling

Rosette bottle samples

Deck incubations

Physics:

CTD, MVP, ADCP, micro-turbulence, wirewalker, optics

Surface drifters:

T, S, fCO2

Underway:

T, S, fCO2, O2, Fl

slide5

Spatial structure – satellite view

Patch 1: freshly upwelled, followed for 9 days

Patch 3: ~10 days old, followed for 8 days

slide9

Controls on CO2 dynamics

Shadwick et al. 2010

?

Horizontal diffusion flux

Vertical entrainment (ventilation)

Horizontal advection

Sea-air Flux

Vertical diffusion flux

NCP

Daily DIC change

  • Assume advection/diffusion terms negligible because lagrangianexpt, i.e. tracking water patch.
  • Supported by lack of relationship between salinity and DIC within patch
  • Salinity normalise DIC to make sure
  • Focus on NCP, F and V?
dic calculations
DIC calculations
  • Need continuous DIC
  • Use discrete TA / S relationship to calculate continuous TAs
  • Calculate DIC from TAs and measured underway fCO2 in CO2SYS
  • Salinity normalise calculated DIC = nDIC
daily n dic calculation
Daily δnDIC calculation

Time

δnDICday+night

δnDICday

nDIC

δnDICnight

depth integrated NCPt = Zeut(max DICt- max DICt-1) – Ft (– Vt)

slide12

A. Daily nDIC change

Patch 1

  • Daily DIC reduction
  • Night time DIC increase
  • production/respiration signal
  • Patch 1 has larger signals and is more variable than Patch 3

Patch 3

slide13

B. Sea-air CO2 fluxes

Patch 1

Calculated using Nightingale et al. (2000)

Winds 6-14 m s-1 P1, 8-14 m s-1 P3

ΔpCO2 20-100 µatm P1, 60-110 µatm P3

Patch 1 sea-air flux starts high and reduces as seawater pCO2 reduces

Increase on 25-26/4 from ventilation?

Patch 3 sea-air flux higher on average, more gradual decline, driven by seawater pCO2 decline

Patch 3

slide14

C. Depth Integrated NCP* vs. sea-air flux

Patch 1

Patch 1

Louicades et al. 2011

Patch 3

slide15

C. Depth Integrated NCP* vs. sea-air flux

Patch 1

Patch 1 is net autotrophic and NCP* dominates over sea-air flux

Patch 3 shifts from autotrophic to heterotrophic between days

In ~trophic balance over all

NCP* dominates the signal but overall sea-air flux is greater

Patch 3

slide16

Water masses

NACW>50%

Max(80%,75m)

Patch 1

SACW>50%

Max(95%,300m)

Patch 3

SACW<50%

Max(40%,150m)

(NACW or BDA shelfwater)

SACW>50%

(Max 100%)

slide17

D. NCP vs. entrainment/ventilation vs. sea-air flux

Use change in nutricline depth and DIC gradient over nutricline

NCP (residual) has to increase with ventilation

Accounting for ventilation increases estimate of autotrophy - Is it real?

preliminary conclusions
Preliminary conclusions
  • Biogeochemistry different between filaments:
    • phytoplankton, CO2dynamics, [nutrients]
    • Water masses or age?
  • Variable influence of NCP vs Sea-Air Flux
    • Patch 1: net autotrophic, NCP dominates; sea-air CO2 flux has minor influence
    • Patch 3:trophic status looks neutral but depends on external sources of DIC; sea-air CO2 flux may be dominant over time
  • Method
    • Ventilation calculation critical for determining NCP?
    • Method needs testing / refining for a lagrangian/sub-mesoscale framework
next steps
Next steps
  • Consider sub-mesoscale physics to calculate ventilation fluxes
  • Compare results with DOC, C14 PP, O18 R, N-flux estimates
  • Look at heterotrophic dynamics (diurnal variability in grazing?)
slide20

Thank you!

Acknowledgements: UK-SOLAS ICON team, National Marine Facilities staff, Captain and crew of RRS Discovery. Funding: UK Natural Environment Research Council (NERC). Satellite images provided by NEODAAS, UK.

slide21

B. Sea-air CO2 fluxes

Units on time plots legend!!!