Kinematic Subduction RateOf

Labrador Sea Water

Peggy Courtois

Xianmin Hu, Yarisbel Garcia, Paul Myers

Earth and Atmospheric SciencesUniversity of Alberta

Alberta, Canada

 

Subduction Rate

h : mixed layer thickness

wb : vertical velocity at the base of the mixed layer

v. h▽ : advection terms

Aσ : outcrop area between σ and σ + δσ

σh : instantaneous mixed layer density.

* Rui Xin Huang’s book (Ocean Circulation)

2

 

Subduction Rate

ML

MLD

wb

v. h▽σh

δh/δt

Surface

Aσ(t):= [σ ≤ σh(x,t) ≤ σ+δσ]3

 

Subduction Rate

Classes:

27.68 - 27.74 kg.m-3

27.74 - 27.82 kg.m-3

27.82 - 27.92 kg.m-3

ULSW(t)

CLSW(t)

τ: integration over a year

4

Subduction Rate

MLD

Obduction

MLD(winter)

S < 0

MLD MLDSubduction

(summer)

S > 0

5

Arctic and Northern Hemisphere Atlantic (ANHA)

Model: NEMO 3.4, with LIM2 and EVP

Resolution : 1/12 degree

(LS ~ 5 km, CAA ~ 4 km)

Mesh : 1632 x 2400, 50 levels

Model Configuration

km

ANHA12

Xianmin Hu

Initialization: 3D T, S, U and V (GLORYS1v1, Jan02) Sea Ice

Atmospheric forcing (CGRF, hourly): T2, Q2, U10, V10 Precipitation Radiation (SW & LW) Snow: CORE2 (IA)

Runof: Dai and Trenberth climatology

OBC: U, V, T and S (GLORYS1v1)

NO temperature & salinity restoring

Jan 2002 – 2010

CGRF: CMC GDPS reforecasts CMC: Canadian Meteorological Centre

GDPS: Global Deterministic Prediction System GLORYS: GLobal Ocean ReanalYses and Simulations 6

Mixed Layer Depth

MLDNEMO = 2080.3 m

MLDTS = 771.9 m

Position:57.0721°N54.1838°W

January, 5th 2008

Similar method toHolte and Talley,

2009

7

Mixed Layer Depth

MLDNEMO

January, 5th 2008

MLDTS

January, 5th 2008

ARGO floats

September 2007To

May 20088

Water MassesClasses:

27.68 - 27.74 kg.m-3

27.74 - 27.82 kg.m-3

27.82 - 27.92 kg.m-3

ULSW(t)

CLSW(t)

2004, January 1st

T

S

PV

9

Subduction RateMLDNEMO

MLDTS δh/δtwb graduh gradvh

January, 5th 2008

10

Subduction Rate January, 5th 2008

MLDNEMO MLDTS

δh/δt

v. h▽wb

11

Subduction Rate

MLDNEMO

MLDTS

Subduction rate versus the density averaged over

2002-2010

12

Subduction Rate

Ann. mean

-1.3 Sv

0.8 Sv

6.8 Sv

3.9 Sv

7.9 Sv

13

MLDNEMO

Subduction Rate

Ann. mean

-0.3 Sv

1.5 Sv

4.4 Sv

1.9 Sv

4.1 Sv

14

MLDTS

Subduction Rate27.68 - 27.74 kg.m-3

27.74 - 27.82 kg.m-3

27.82 - 27.92 kg.m-3

MLDNEMO

MLDTS

Annual mean

6.4 Sv

5.6 Sv

15

Conclusion

16

Paul's team:

Nathan, Laura G, Laura CG, Tilia, Vasco, Georg,

Yongxing, Natasha, Ting, Juliana, Clark

● Large impact on the MLD over the net subduction rate when different water masses are considered

● Not a large impact on the annual mean

● Labrador Sea Water formation of 5.6 Sv and 6.4 Sv depending on the MLD

● On going: Quantifying the impact of each component on the subduction rate

Thanks!

Subduction Rate

Subduction Rate

Subduction Rate