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Michael Steele Polar Science Center / APL University of Washington. The circulation of summer Pacific Water in the Arctic Ocean. Michael Steele, Jamie Morison, Wendy Ermold, Ignatius Rigor, & Mark Ortmeyer

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slide1

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)

slide2

Michael Steele

Polar Science Center / APL

University of Washington

Lateral extent of summer Pacific water

slide3

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)

slide4

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

slide5

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
slide6

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?
slide7

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

slide8

Michael Steele

Polar Science Center / APL

University of Washington

Lateral extent of summer Pacific water

slide9

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)

slide10

Michael Steele

Polar Science Center / APL

University of Washington

1993 Summer Pacific water: vs.

sBSW

ACW

ACW

sBSW

Tmax

z

slide11

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

slide12

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

slide13

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

slide14

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
slide15

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…
slide16

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.

slide17

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

slide18

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.

slide19

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…

slide20

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
slide21

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

slide22

…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)
switchyard slope section 03

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
switchyard slope section 0325
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
slide27

Michael Steele

Polar Science Center / APL

University of Washington

The

End…

Thanks to colleagues at

PSC, IOS, & elsewhere for

data and ideas!