DIMES:  Diapycnal  and  Isopycnal  Mixing  Experiment  in  the  Southern  Ocean  

•   A  US+UK  experiment  •   Diapycnal  diffusion  and  isopycnal  dispersion  and  eddy  fluxes  •   Improve  eddy  parameteriza>ons  in  models  of  the  MOC  for  climate  variability  

WHOI

FSU

SIO

UW/APL

UEA

BAS

NOC Southampton

SAMS (Scotland) Read all about it: http://dimes.ucsd.edu/

Why K? Dominant momentum balances:

V = net meridional volume flux, τo = wind stress η = layer thickness, p = pressure, pb = bottom pressure

Surface -fV1 = τo

-fV2 = η'1p'1x - η'2p'2x

-fV3 = - hpbx “blocked” layer

ρ1

ρ2

ρ3

…adapted from Olbers

Side view of the ACC

zonally open

τo

Why K? Dominant momentum balances:

V = net meridional volume flux, τo = wind stress η = layer thickness, p = pressure, pb = bottom pressure

Surface -fV1 = τo

-fV2 = η'1p'1x - η'2p'2x ≈ K dq/dy

-fV3 = - hpbx

zonally open

“blocked” layer

ρ1

ρ2

ρ3

…adapted from Olbers

Side view of the ACC τo

DIMES  Overview  

X X

UK2.5

The  tracer  

•  Trifluoromethyl-­‐sulphur-­‐pentafluoride.  

•  Inert,  non-­‐toxic.  •  1  milligram  is  detectable  in  a  cubic  kilometer  of  seawater,  by  gas  chromatography  with  electron  capture  detec>on.    

CF3SF5

Ledwell Watson

R/V Revelle, 5 Jan to 1 Mar 2009

US1  Cruise  Track  and  Deployments  

Sound sources

Tracer release

CTD surveys Float deployments

SoSo large blue Solo small blue Rafos black CTD red

Injec>on  patch  on  P18  Sec>on  

Mean  Concentra>on  versus  Depth  (using  mean  density  vs  depth  from  CTD)  

Tracer  Simula>on  22  Feb  2010  

Now wait a year… …but follow the evolution of the tracer with altimetry

X

Cruise  Track  R/V  Thompson  15  Jan–5  Mar  2010  

US2

Tracer  Transects  Column  Integral  

Horizontal structure

Ini>al  &    12-­‐month  profiles  

kz = 0.13 cm2/s

Vertical structure

Sco>a  Sea  

RRS  James  Cook  UK2 Dec 2010 – Jan 2011

JC054  Sta>ons  

2 years later

Average  Profiles  

0 500 1000 1500 2000 2500 3000 3500 4000 4500 -1800

-1700

-1600

-1500

-1400

-1300

West of DP

East of DP

US2

Normalized Concentration

DP kz ~ 1 cm2/s

DIMES  Floats  

•  11  sound  sources  for  acous>c  array  •  ~  150  Argos  and  Iridium  Rafos  floats  

R/V Revelle, 5 Jan to 1 Mar 2009

US1  Cruise  Track  and  Deployments  

Sound sources

Tracer release

CTD stations (red) Float deployments in triplets

SoSo large blue Solo small blue Rafos black CTD red

Neutral  Density  Sec>on  at  105  W  Deployment  on  2  isopycnal  surfaces  

X

DIMES  Floats  as  of  Sept  2011  

US1 1

US1 2US1 3

US1 4

US1 5

US1 6UK1 1

UK1 2UK1 3

UK1 4

110oW 100oW 90oW 80oW 70oW 60oW 50oW

65oS

60oS

55oS

50oS

Dimes Trajectories (43) Orsi fronts

Drake  Passage  Fronts  and  Floats  

SOSE mean speed AVISO 7 yr mean speed + real floats + bathymetry

100oW

90oW 80oW 70oW

60oW

60o S

55o S

50o S

1000 2000 3000 4000 5000 6000Depth (m)

Tracer-­‐Float  Spreading  

All stations Deep float surfacings

60 50 40 30 20 10 0 10 200

1

2

3

4

5

6

7

SSH(cm)

Num

ber o

f Par

ticle

s

Starting DF

100 80 60 40 20 0 20 400

1

2

3

4

5

6

SSH(cm)

Num

ber o

f Par

ticle

s

Ending DF

PDFs  

Kdiff = σ2/2Δt = (400km)2/4yrs ≈ 1200 m2/s Also, d<X2>/dt ~ 1000m2/s and dKSSH/dz <0

−120 −100 −80 −60 −40 −20 0 20 40 600

100

200

300

400

500

600

700

800

900

1000

1100

SSH (cm)

Column Integral (pmol/m2) & Floats

Year 2

Tracer: blue Floats: green

Ver>cal  Structure  

Klocker et al; Speer et al.

i-----------------------------I

Ver>cal  Structure  

Klocker et al

1000 K 0

Conclusions  1.  Deep  isopycnal  mixing  in  the  ACC  is    

-­‐  about  1200  m2/s  (uncertain>es  TBD)  -­‐  associated  with  f/H  -­‐  weaker  away  from  topography?  

 2.  DIMES  float  trajectories  will  provide  direct  but  limited  

diffusivity  es>mates  and  other  quan>>es,  state  es>mates  necessary  

 3.  Need  to  observe  ver>cal  structure  of  mixing  to  discriminate  

theories    4.  Flow  spligng  and  merging:  braided  jets