2018 workshop - ocb · verdy and mazloff (2017), a data assimilating model for estimating southern...
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Ariane Verdy, Matt Mazloff
Data assimilation of carbon and other biogeochemical constraints
Lynne Talley, Sharon Escher, Bruce Cornuelle, Isa Rosso, Natalie Freeman, Joellen Russell, Jorge Sarmiento, Ken Johnson, Emmanuel Boss, Matt Long, John Dunne, Eric Galbraith
OCB CMIP
6 Work
shop
2018
Southern Ocean Climate and Carbon Observations and Modelling
bgc-Argo: oxygen, nitrate, pH, optics
OCB CMIP
6 Work
shop
2018
State estimationmodels are used to hindcast the ocean state (T, S, V, SSH)
using inputs: initial conditions & atmospheric forcing
adjust those inputs to bring the model closer to observations of the actual ocean state
minimize the “cost function” :
Σ (weighted model-observations misfit)2 + Σ (weighted adjustment to inputs)2
B-SOSE: biogeochemical + physical state optimized together
* *
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o
e.g. Southern Ocean 2013-2017e.g. T & S from Argo maps, winds & air temp, etc. from ECMWF e.g. from Argo profiles, satellites, …
4D-Var, “adjoint” method
new estimate1st guess
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ecco.jpl.nasa.gov
Biogeochemical model
pCO2
pH
Fe
ALK
DIC phytoplankton community production
carbon system
chlBlg Bsm DOP
O2
NO3PO4
light temperature
scavenging
sediments
dust
remineralization
air-sea flux air-sea flux
DON
Bdia
all and variables are estimated; can be compared / constrained to observationsprognostic diagnostic
“N-bling”
B-SOSE product2008-2012, 1/3 degree
Verdy and Mazloff (2017), A data assimilating model for estimating Southern Ocean biogeochemistry, JGR-Oceans
2013-2017 in production (with SOCCOM floats constraints)
pCO2
DIC ALK pH NO3
PO4
O2
O2
pH Fe
No
rma
lize
d c
ost
0
5
10
15
20
25
30
35
40
SOCATv4 GLODAPv2 Argo GoShip GEOTRACES
prior
B-SOSE
B-SOSE indep
B-SOSE vs climatologywith SOCCOM float observations
B-SOSE vs climatologywith SOCCOM float observations
Comparisons with in situ observations* Argo profiles (T,S)* calibrated bgc-Argo (O2)* SOCCOM floats
* SOCAT (pCO2)* GLODAPv2 (carbon, nutrients)* CTD (T, S, O2, chl)* XBT, MEOP, PIESGEOTRACES
Comparisons with gridded products* ocean color (chl, POC)* altimetry* microwave SST* sea ice Argo monthly mapped productGLODAPv2, WOA13, SOCAT climatologiesLandschützer monthly mapped product
Validation* = assimilated
mean difference
standard dev. difference
Comparisons with in situ observations7 m O2 in B-SOSE 2013-2017 is compared to bgc-Argo
2008 2009 2010 2011 2012 2013
pC
O2 (µ
atm
)
320
340
360
380
400
420 SOCATv4B-SOSEB-SOSE subsampled
Monthly-averaged pCO2 in Drake Passage (75°W to 55°W, south of 50°S) from SOCATv4 observations (black) [Bakker et al., 2016; Munro et al., 2015a, 2015b], and from B-SOSE (area average in pink; subsampled at the location of observations in red). Summer months are shaded gray.
pCO2 in Drake Passage
Assimilating ocean color observationscost function = surface chlorophyll from VIIRS satellite, 2013
red = where adding iron would reduce the misfit with observations
Higher resolution, multi-grid assimilation
Budgets
Rosso et al. (2017), Space and time variability of the Southern Ocean carbon budget. JGR-Oceans.
DIC in the top 650 m, 2008-2012
mol
/m2 /y
r
DIC
NO
330-40°S
40-50°S
50-60°S
60-70°S
70-80°S
as a tool for explaining observed C:N ratios
surface top 150m
Budgets
plots show seasonal variability of DIC and NO3 in B-SOSE (black) and SOCCOM floats (red) in latitude bands
arrows between seasonal averages = tendencies from DIC and NO3 budgets
budget analysis shows how different mechanisms are contributing to the tendency
30-40°S 40-50°S 50-60°S
60-70°S 70-80°S
(1) dilution is dominant at high latitudes (sea ice)(2) gas exchange is important in mid-latitudes(3) ocean dynamics (advection + mixing) is non-negligible
What explains deviations from Redfield?
Getting the products
B-SOSE output: sose.ucsd.edu+ validation+ documentation
MITgcm BLING model and adjoint: github.com/MITgcm/MITgcm
use model + observations to estimate carbon system over the past ~10 years
multi-year estimate = a continuous model run, which has closed budgets for mass / heat / salt / BGC tracers (DIC, O2, NO3, …)
the output is available online (sose.ucsd.edu) for analysis and comparisons with modelsSnapshot of the simulated dissolved inorganic
carbon (DIC) concentration at 100 m on 2/1/09
summary