1. Arctic Ocean Freshwater:
past, present, & future
Michael Steele
Polar Science Center,
Applied Physics Laboratory,
University of Washington, Seattle WA

2. P-E “Global” sea surface salinity ? 40 35 30 25 A: Uhhh… ice melting?!
Ferrel Cell
“westerlies” (N. Hem.)
P-E
Q: Why is the Arctic Ocean fresh?
A: Uhhh… ice melting?!

3. Mackenzie River discharge” Mackenzie River discharge”
SHEBA: Beaufort Sea,
SHEBA
1997 JAS SAT anom
(NCDC)
Freshening of the upper ocean in the Arctic: Is perennial sea ice disappearing? McPhee et al. (1998)
“It was mostly
sea ice melt”
October, 1997
Connections among ice, runoff and atmospheric forcing in the Beaufort Gyre Macdonald et al. (1999)
“It was mostly
Mackenzie River discharge”
Steele et al., 2006; Rawlins et al., 2009.
“It was mostly
Mackenzie River discharge”

4. Arctic Ocean freshwater inputs …adapted from A. Jahn, Jan’09 AOMIP
FW flux (km3/year)
Woodgate et al., 2005
Russian ice camp data
FW flux (km3/year)
Total = 7700
Serreze et al., 2006
For the Arctic Ocean,
net sea ice GROWTH is a FW SINK  0.4 m/yr  7 million km2 = 2800 km3/yr
“river runoff → sea ice growth”
River Runoff
Bering Strait liquid
P-E
Total = 5870
Q: Where’s the ice term?
Arctic Ocean
GIN Sea
Steele & Flato (2000)
Aagaard and Carmack, 1989

5. Mackenzie River discharge”
SHEBA: Beaufort Sea,
SHEBA
1997 JAS SA anom
(NCDC)
Distance north from Alaska (km)
River water
Melt water
net melt
net growth
Extends to m depth!
...but mostly 0-50 m
(mixed layer)
October, 1997
halocline
surface layer
Atlantic Water layer
Surface + halocline layers
 FW layer: m
S  34.8
Connections among ice, runoff and atmospheric forcing in the Beaufort Gyre Macdonald et al. (1999)
“It was mostly
Mackenzie River discharge”

6. Getting the right stratification: The effect of “background mixing”
fresh layer
Kdiff = 0.01 cm2/s
PHC
(Canada Basin)
Kdiff = 1.25 cm2/s
Depth (meters)
Atlantic Water layer
Zhang & Steele, 2006
Salinity
“Typical” Kdiff  0.1 cm2/s; Need to reduce mixing to levels 10 times less!
…it’s ok: sea ice suppresses mixing! (D’Asaro & Morison, 1992)
…for now, anyway…

7. What is Freshwater (FW)? …adapted from A. Jahn, Jan’08 CCSM
Sref = 34.8 (Aagaard & Carmack’s mean salinity of the Arctic Ocean)

8. What is Freshwater Content (FWC)?
FWC   (Sref – S)/Sref dz
surface
layer #1
Sref
Units: meters
layer #2
zref
How deep to integrate to?
…to where S ~ constant?
What about “negative freshwater?”
…depends on your focus
S(z)
bottom

9. FWC: How to integrate?  (Sref – S)/Sref dz Sref
surface
 (Sref – S)/Sref dz
layer #1
Sref
Option 1: Integrate down to the bottom,
allowing “negative freshwater”
layer #2
…using PHC annual mean
zref 50 40 30 20 10
FWC (m)
S(z)
Chukchi Borderland
Canadian Basin
Eurasian Basin
bottom
Sref
The result: FW + bathymetry!

10. FWC: How to integrate?  (Sref – S)/Sref dz Sref
zref
surface
bottom
S(z)
freshwater layer
Atlantic Water layer
 (Sref – S)/Sref dz
Option 2: Integrate down to a fixed depth zref, allowing “negative freshwater” 50 40 30 20 10
FWC (m)
Zref = 500 m
Zref = 1000 m
freshwater layer + Atlantic Water layer

11. FWC: How to integrate?  (Sref – S)/Sref dz Sref zref
surface
 (Sref – S)/Sref dz
freshwater layer
Sref
Atlantic Water layer
zref
Option 3: Integrate down to Sref (no neg FW)
S(z) 50 40 30 20 10
FWC (m)
bottom
freshwater layer only:
Salinity
Thickness

12. FWC: Seasonal salinity vs. thickness changes
…uses option #3 (no neg FW)
(JGR, 2009)
There’s 2 seasonal maxima:
June/July:
FWC peak #1 from ice melt
 upper layer freshening
Nov/Dec/Jan:
FWC peak #2 from Ekman convergence
 upper layer deepening

13. FWC: Sref vs. zref Sref zref S(z) 1970-1990s: incr. AW inflow
surface
FW layer
FWC > 0
Sref
AW layer
FWC < 0
zref
S(z)
FW volume (km3)
Sref level rises
depth (m) s:
incr. AW inflow
more “neg FW”
Sref level rises
incr. FW outflow
less “pos FW”
 Zref method yields a higher amplitude
FW volume (km3)
Polyakov et al., 2008

14. The Mean FW Budget
…Serreze et al. (2006)
Atmos. moisture transport is the major source of FW! ?
sea surface salinity

15. The Mean FW Budget FWC (m) ?? 50 40 30 20 10
FWC (m)
Atmos. moisture transport is the major source of FW! …ie,
storms  arctic drainage basins
rivers  ocean
( ocean  sea ice )
ocean/sea ice  North Atl. Ocean ??

16. Well, no… “The Arctic is the freshest ocean!” FWC (m) 45 m! 15-20 m
Sea surface salinity
Well, no… 50 40 30 20 10
FWC (m)
45 m!
FWC  factor * steric height
Bering Strait flow
DH: Pac-Nordic = over a meter
15-20 m

17. The Mean FW Budget In this budget,
river discharge > ice growth/export i.e., ~23% of discharge  liquid ocean export
Distance north from Alaska (km)
River water
Remember the SHEBA data…
Serreze et al. (2006)

18. The Mean FW Budget River discharge mean is big!
…Serreze et al. (2006)
River discharge mean is big!
River discharge variability is small!

19. Interannual Variability
… & now for some …
Interannual Variability

20. Fall 2003: Hey Mike: “You’re invited to NASA HQ for a press conference
“Arctic sea ice melting at worrying rate: NASA”
Posted: Oct. 24, Agence France-Presse
(Papers by Comiso, others)
“Increasing River Discharge to
the Arctic Ocean”
Peterson et al., Science, Dec 2002
…Russian! Canadian decr, but total still incr
“20th Century Trends of Arctic Precipitation from Observational Data & a Climate Model Simulation”
Kattsov & Walsh, J. Climate, 2000
….increasing
“Interannual Changes in the Bering Strait Fluxes of Volume, Heat and Freshwater between 1991 and 2004”
Woodgate et al., GRL, 2006
….umm, actually, no FW incr
Mike: “What should I talk about?”
NASA Program Manager: “How about the freshening of the Arctic Ocean?”
Mike: Uhhhhhh……

21. Swift et al. , JGR 2005 (presented by K
Swift et al., JGR (presented by K. Aagaard at SEARCH mtg Seattle Oct’03) Long-term variability of Arctic Ocean waters: Evidence from a reanalysis of the EWG data set … i.e., classified Russian data
Upper 175 m gets
saltier in mid-1970s
…& stays that way…

22. Arctic Ocean FWC anomalies
…using another form of the same data…
Arctic Ocean FWC anomalies
Steele & Ermold, 2007
“fw capacitor”
Proshutinsky et al., 2002)
annual
5-yr R.M.
freshwater export in mid-1970s
…liquid ocean export after GSA?
Short time series… POSSIBLE flywheel
Cite Proshutinsky’s FW flywheel
FW loss  30 cm

23. The “Great Salinity Anomaly”:
arctic
sea ice
Dickson et al., 1988
nordic
seas
subpolar
gyre

24. Arctic Ocean FWC anomalies
Steele & Ermold, 2007
freshwater export in mid-1970s
…liquid ocean export after GSA?
Short time series… POSSIBLE flywheel
Cite Proshutinsky’s FW flywheel
GSA sea ice export
Belkin (1998):
“Great Salinity Anomalies”

25. Häkkinen and Proshutinsky, 2004
Arctic FW storage & release: 1970s vs. 1990s …from A. Jahn, Jan’09 AOMIP
Köberle and Gerdes, 2007
~7000 km3
~10,000 km3
~6500 km3
~2500 km3
Häkkinen and Proshutinsky, 2004
Jahn et al, 2009
~6500 km3
~1500 km3
Polyakov et al. 2008
~6000 km3
1990s: some agreement
1970s: little agreement!

26. Arctic liquid FW release in the 1990s: Origins
Karcher et al. GRL 2005:
“Arctic Ocean change heralds North Atlantic freshening”
Laptev Sea 
Transpolar Drift 
East Greenland Current 
Subpolar Gyre?
FWC anom (m)
1995

27. OK… so why did the Arctic Ocean get saltier over the 2nd half of the 20th century?

28. North Atlantic Oscillation18 19 20
North Atlantic Oscillation
LOW
HIGH
Arctic Oscillation
HIGH
Atmospheric
Forcing
LOW

29. Arctic Ocean get saltier? was a much smaller effect
N/AO & Arctic Ocean FW
Steele et al., 2004
…similar figs in A. Jahn et al. (2009)
High
High
Why did the
Arctic Ocean get saltier?
N/AO-:
FW storage
N/AO+:
FW release
It was the
atmospheric forcing!
(i.e., winds 
ice, ocean FW release)
(non-anthropogenic?)
Incr. river discharge
was a much smaller effect 18 19 20
LOW
HIGH
storage
release

30. What’s New? …in the 2000’s

31. Increasing Beaufort Gyre
The Beaufort Gyre
April, 2008
climatology
Increasing Beaufort Gyre
FWC
S  26!

32. Where’d this Beaufort Gyre FW come from?
April, 2008
Alaska
April, 2008
Alkire et al. (2009):
It’s mostly Eurasian River Water!
…how’d it get there?
Alaska

33. Where’s this Beaufort Gyre FW going?
deSteur et al., 2009
Davis St. FW flux
FWC (m)
BGEP
NABOS
NPEO + SY
Fram St.
Davis St.
Fram St. FW flux
Incr? Decr?
…short time series!
It’s moving through the Lincoln Sea
 a new GSA coming?

34. The Longer-Term Future?
(2006): CCSM ensembles
  Sv
  Sv
(1) FW transformation:
ice 
ocean (0.1 Sv)
(2) New FW:
R + (P-E) 
ocean export (0.04 Sv)
  Sv
Rawlins et al. 2009
Arctic Ocean (liquid) FWC
Note: The models show
late 20th century FWC increase!
  Sv

35. Mysteries: Circulation (ice? ocean?) of river water?
Future Arctic Ocean stratification / mixing?
Fate of Bering St. inflow?
When will the Arctic Ocean start freshening?

36. Thank
You