The circulation of summer Pacific Water in the Arctic Ocean

1. Michael Steele Polar Science Center / APL University of Washington The circulation of summerPacific Water in the Arctic Ocean Michael Steele, Jamie Morison, Wendy Ermold, Ignatius Rigor, & Mark Ortmeyer Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, WA 98105 USA Koji Shimada Jamstec Marine Science and Technology Center, Yokosuka, Japan surface layer summer Pacific water S T Atlantic layer SCICEX’96 (cast 43)

2. Michael Steele Polar Science Center / APL University of Washington Lateral extent of summer Pacific water

3. Michael Steele Polar Science Center / APL University of Washington Why do we care about Pacific water? • Global freshwater circulation • Major component of the Arctic Ocean halocline • “Nutrient river” through the Arctic Ocean Nutrients! North Water Polynya Tremblay et al. (2002)

4. Michael Steele Polar Science Center / APL University of Washington Water masses in the Bering Strait region …following Coachman et al. (1975) & others Bering Sea Water (BSW) Alaska Coastal Water (ACW) Siberian Coastal Current (SCC) Alaska LDI BDI Russia Gulf of Anadyr Water (GAW) Bering Shelf Water (BSW) BSW : colder, salty, high nut’s ACW : warmer, fresher, low nut’s

5. Michael Steele Polar Science Center / APL University of Washington “BSW” There are 2 types of summer Pacific water in the Arctic Ocean! S T …Shimada et al., 2001 • ACW: AlaskanCoastalWater • sBSW: summerBeringSeaWater

6. Michael Steele Polar Science Center / APL University of Washington How far downstream can we detect a summer Pacific water Tmax ? NPEO = North Pole Environmental Observatory • At least as far as the Ellesmere Island Shelf Break... • …but is this true for all years? • …and what exactly is getting there: sBSW? ACW?

7. Michael Steele Polar Science Center / APL University of Washington Hydrographic surveys http://psc.apl.washington.edu/northpole Twin Otter tent Years 2000/03 stations CTD & bottle obs …NPEO also includes drifting buoys + moorings

8. Michael Steele Polar Science Center / APL University of Washington Lateral extent of summer Pacific water

9. Michael Steele Polar Science Center / APL University of Washington Summer Pacific water: The view from 1993 1993 cruise data (SCICEX/Larsen/Melling/ ARKIX/4, Newton&Sotirin)

10. Michael Steele Polar Science Center / APL University of Washington 1993 Summer Pacific water: vs. sBSW ACW ACW sBSW Tmax z

11. Michael Steele Polar Science Center / APL University of Washington Schematic circulation of summer Pacific water in 1993 BSW ACW sBSW …a “separated flow regime” w.r.t. Pacific water

12. Michael Steele Polar Science Center / APL University of Washington Positive AO index: Chukchi Sea -> Ellesmere Island: ~3 years And now, for the obligatory Arctic Oscillation discussion… positive AO index neutral negative The sea ice response Negative AO index: Chukchi Sea -> Ellesmere Island: ~6 years

13. Michael Steele Polar Science Center / APL University of Washington The area north of Ellesmere Island: Iceshelf(Newton & Sotirin, 1997) + NPEO(Steele et al., 2003) sBSW Tmax north of Ellesmere Island

14. Michael Steele Polar Science Center / APL University of Washington sBSW sBSW ACW ACW Summer Pacific Water circulation: Low (1980’s) vs. High (early-mid 1990’s) AO index • Mixed summer Pacific water regimes throughout the Arctic Ocean …including in outflows through the western Canadian Archipelago? • Old (i.e., no Tmax) sBSW north of E.I. • Separated summer Pacific water regimes in some of the Arctic Ocean …including through western/ eastern Canadian Archipelago channels? • New (i.e., warm Tmax) sBSW at EISB

15. Michael Steele Polar Science Center / APL University of Washington A new look at T(z) profiles in the Canadian Basin of the Arctic Ocean, especially under AO+ conditions. • There’s 3 Pacific water types: • ACW • Summer BSW • Winter BSW • …is there “winter ACW?” • T & S data say “no” • T, S, O2 data (Itoh & Shimada, 2003) say maybe…

16. Michael Steele Polar Science Center / APL University of Washington What about interannual source variability?! Aagaard, Woodgate, & Weingartner http://psc.apl.washington.edu/HLD/Bstrait/bstrait.html There’s a lot of it! …not to mention variations in the Chukchi Sea.

17. Michael Steele Polar Science Center / APL University of Washington Why don’t we see this in our data, downstream from this (highly varying) source? high variance low variance

18. Michael Steele Polar Science Center / APL University of Washington ACW 1996 + 1997 1993 warmer? Why don’t we see this in our data, downstream from this (highly varying) source? (Part 2) There’s some evidence for source variability downstream in the Arctic Ocean, but: Our observations are explainable mostly by changes in circulation, rather than by changes in the character of the inputs.

19. Michael Steele Polar Science Center / APL University of Washington What about chemical tracers? Pacific water (%) in the upper 30 m (using the N/P ratio). 50% ’93 – ‘96 50% ’00 – ‘01 K. Falkner, OSU Jones et al. (1998) AO index drops through the latter 1990’s  Transpolar Drift Stream has less Pacific influence Confirms our T/S data. But there’s more to do…

20. Michael Steele Polar Science Center / APL University of Washington sBSW sBSW ACW ACW What’s the role of the North American boundary undercurrent? • Lots of question marks… • Limited evidence suggests a deep eastward current, with interannually varying vertical shear in the halocline. • This  high interannual variability in the transport of halocline water masses within the current

21. Large-scale sections Boundary current section …based on Jones et al. (1998); Steele & Boyd (1998); Proshutinsky et al. (2002); Rigor et al. (2002) The “freshwater switchyard”: A good place to detect the origins of freshwater that’s about to leave the Arctic Ocean • 3 project components: • Large-scale hydrochemical sections (Schlosser + Smethie) • Boundary current section at the shelf break (Steele) • Sea ice transport studies (Kwok) Obs: spring 2003-2007

22. …modified from Newton & Sotirin (1997) Details Alert-NP survey: Twin Otter aircraft, 6-9 stations “THICR” = THrough-Ice CTD-Rosette, measuring T, S, O2, oxygen isotopes, tritium/3He, CFC’s, barium, & nutrients. Samples to be drawn at Alert. Boundary current survey: helicopter, 6-9 stations CTD-O, XCP, surface layer bottles. • Sea ice transport studies: satellites • uice: AMSR passive μwave, ENVISAT SAR; • hice: altimeters on IceSAT (laser) & ENVISAT, CryoSAT (radar)

23. Switchyard’03

24. Continental shelf Switchyard slope section’03 • The isopycnals are flat as a pancake! •  very little vertical shear • …I need to look at the wind/ice stress forcing

25. Switchyard slope section’03 BSW / ACW ? • Summer Pacific water Tmax: • It’s recovered, but still cool • S ~ 32 on the slope • S > 32 on either side • NPEO station #6 Tmax slope Tmax’s

26. Switchyard and NPEO sections

27. Michael Steele Polar Science Center / APL University of Washington The End… Thanks to colleagues at PSC, IOS, & elsewhere for data and ideas!