Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI Arctic Ocean Freshwater: past, present, & future Michael Steele Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle WA Arctic Ocean Freshwater: past, present, & future Michael Steele Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle WA

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI “Global” sea surface salinity Ferrel Cell “westerlies” (N. Hem.) P-E ? ? ? ? Q: Why is the Arctic Ocean fresh? A: Uhhh… ice melting?!

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI SHEBA: Beaufort Sea, Freshening of the upper ocean in the Arctic: Is perennial sea ice disappearing? McPhee et al. (1998) “It was mostly sea ice melt” 1997 JAS SAT anom (NCDC) 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., “It was mostly Mackenzie River discharge” SHEBA October, 1997

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI Arctic Ocean freshwater inputs …adapted from A. Jahn, Jan’09 AOMIP River Runoff Bering Strait liquid P-E Aagaard and Carmack, 1989 FW flux (km 3 /year) Woodgate et al., 2005 Russian ice camp data FW flux (km 3 /year) Total = 7700 Serreze et al., 2006 Total = 5870 For the Arctic Ocean, net sea ice GROWTH is a FW SINK  0.4 m/yr  7 million km 2 = 2800 km 3 /yr “river runoff → sea ice growth” Q: Where’s the ice term? Arctic Ocean GIN Sea Steele & Flato (2000)

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI SHEBA: Beaufort Sea, JAS SA anom (NCDC) Connections among ice, runoff and atmospheric forcing in the Beaufort Gyre Macdonald et al. (1999) “It was mostly Mackenzie River discharge” SHEBA 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

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI “Typical” K diff  0.1 cm 2 /s; Need to reduce mixing to levels 10 times less! …it’s ok: sea ice suppresses mixing! (D’Asaro & Morison, 1992) …for now, anyway… Getting the right stratification: The effect of “background mixing” K diff = 1.25 cm 2 /s Salinity PHC (Canada Basin) Depth (meters) Zhang & Steele, 2006 K diff = 0.01 cm 2 /s fresh layer Atlantic Water layer

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI What is Freshwater (FW)? …adapted from A. Jahn, Jan’08 CCSM S ref = 34.8 ( Aagaard & Carmack’s mean salinity of the Arctic Ocean )

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI What is Freshwater Content (FWC)? FWC   (S ref – S)/S ref dz Units: meters How deep to integrate to? …to where S ~ constant? What about “negative freshwater?” …depends on your focus S ref z ref surface bottom S(z) layer #1 layer #2

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI FWC: How to integrate?  (S ref – S)/S ref dz FWC (m) Chukchi Borderland Eurasian Basin Canadian Basin Option 1: Integrate down to the bottom, allowing “negative freshwater” The result: FW + bathymetry! S ref z ref surface bottom S(z) layer #1 layer #2 …using PHC annual mean S ref

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI FWC: How to integrate?  (S ref – S)/S ref dz FWC (m) Option 2: Integrate down to a fixed depth z ref, allowing “negative freshwater” S ref z ref surface bottom S(z) freshwater layer Atlantic Water layer Z ref = 500 m Z ref = 1000 m freshwater layer + Atlantic Water layer

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI FWC: How to integrate?  (S ref – S)/S ref dz Option 3: Integrate down to S ref ( no neg FW ) S ref z ref surface bottom S(z) freshwater layer Atlantic Water layer freshwater layer only: Salinity Thickness FWC (m)

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI FWC: Seasonal salinity vs. thickness changes (JGR, 2009) June/July: FWC peak #1 from ice melt  upper layer freshening June/July: FWC peak #1 from ice melt  upper layer freshening …uses option #3 (no neg FW) There’s 2 seasonal maxima: Nov/Dec/Jan: FWC peak #2 from Ekman convergence  upper layer deepening Nov/Dec/Jan: FWC peak #2 from Ekman convergence  upper layer deepening

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI FWC: S ref vs. z ref S ref z ref surface S(z) AW layer S ref level rises FW layer Polyakov et al., 2008 FWC < 0 FWC > s: incr. AW inflow more “neg FW” S ref level rises incr. FW outflow less “pos FW”  Z ref method yields a higher amplitude FW volume (km 3 ) depth (m)

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI The Mean FW Budget …Serreze et al. (2006) 1) Atmos. moisture transport is the major source of FW! ? ? ? ? sea surface salinity

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI The Mean FW Budget Atmos. moisture transport is the major source of FW! …ie, 1)storms  arctic drainage basins 2)rivers  ocean ( ocean  sea ice ) 3)ocean/sea ice  North Atl. Ocean FWC (m) ??

“The Arctic is the freshest ocean!” Well, no… Sea surface salinity FWC (m) 45 m! FWC  factor * steric height Bering Strait flow m

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI The Mean FW Budget Serreze et al. (2006) 2)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…

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI The Mean FW Budget …Serreze et al. (2006) River discharge mean is big! River discharge variability is small!

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI Interannual Variability … & now for some …

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI 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, 2003 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 “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…… “20 th Century Trends of Arctic Precipitation from Observational Data & a Climate Model Simulation” Kattsov & Walsh, J. Climate, 2000 ….increasing

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI Swift et al., JGR 2005 ( 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…

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

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

Arctic Ocean FWC anomalies freshwater export in mid-1970s …liquid ocean export after GSA? Steele & Ermold, 2007 GSA sea ice export Belkin (1998): “Great Salinity Anomalies”

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI Arctic FW storage & release : 1970s vs. 1990s …from A. Jahn, Jan’09 AOMIP ~6500 km 3 ~2500 km 3 Häkkinen and Proshutinsky, 2004 Köberle and Gerdes, 2007 ~7000 km 3 ~10,000 km 3 Polyakov et al ~6000 km 3 Jahn et al, 2009 ~6500 km 3 ~1500 km s: some agreement 1970s: little agreement!

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI 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)

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI OK… so why did the Arctic Ocean get saltier over the 2 nd half of the 20 th century?

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI Arctic Oscillation LOW HIGH North Atlantic Oscillation LOW HIGH Atmospheric Forcing

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

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI What’s New? …in the 2000’s

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI The Beaufort Gyre April, 2008 climatology Increasing Beaufort Gyre FWC S  26!

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI Where’d this Beaufort Gyre FW come from? Where’d this Beaufort Gyre FW come from? Alkire et al. (2009): It’s mostly Eurasian River Water ! …how’d it get there? Alaska April, 2008

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI Where’s this Beaufort Gyre FW going? Where’s this Beaufort Gyre FW going? Fram St. FW flux Davis St. FW flux Incr? Decr? …short time series! FWC (m) deSteur et al., 2009 It’s moving through the Lincoln Sea  a new GSA coming? BGEP NABOS NPEO + SY Fram St. Davis St.

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI   Sv   Sv   Sv   Sv (1) FW transformation: ice  ocean (0.1 Sv) (2) New FW: R + (P-E)  ocean export (0.04 Sv) Rawlins et al Arctic Ocean (liquid) FWC Note : The models show late 20 th century FWC increase! (2006): CCSM ensembles The Longer-Term Future?

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI Mysteries : 1.Circulation (ice? ocean?) of river water ? 2.Future Arctic Ocean stratification / mixing? 3.Fate of Bering St. inflow? 4.When will the Arctic Ocean start freshening ?

Michael Steele Polar Science Center / APL University of Washington Oct 20, 2009 WHOI Thank You Thank You