Zigzagging in the Arctic

Rebecca Woodgate Polar Science Center,

University of Washington, Seattle, USA

in collaboration withKnut Aagaard (UW), Jim Swift (Scripps), Bill Smethie (LDEO), Kelly Falkner (OSU),Tom Weingartner (UAF) and many others

Funded by NSF and ONRWith thanks to the crews of

USCGC Polar Star, USCGC Healy, RV Helix, CCGS Laurier

The Magic of Observations?

D.G.Barton, 1992

CBL cruise, 2002

CBL cruise, 2002

Helix cruise, 2004

The Magic of the Arctic

Arctic Ocean Basics

Arctic Ventilation by Pacific Waters –

smoking guns in T-S space

Tracing Atlantic waters in the Arctic by double diffusive

ZigZags

Where are we in the Global Ocean?

Broecker, 1991

The Great Arctic Ocean

Welcome to the Arctic Ocean

You arehere

About the size of the USA!

USA

Greenland

Russia

Fram Strait

Barents Sea

Bering Strait

Eurasian Basin

Lomonosov R

Canadian Basin

Chart from IBCAO

CanadianArchipelago

Broad, Shallow Shelves

Deep Basins

Shallow entrance from the Pacific

Medium and Deep connections to the Atlantic

From theAtlanticFrom the

Pacific

To theAtlantic

To theAtlantic

What makes the Arctic “hot”?

Pink=1979-2000 mean minimumNSIDC, 2006

Stroeve et al, 2005, GRL

Local communities subsistence

Arctic Shipping Routes?

Oil/Gas Exploration

Links to Global Climate

Decreasing Ice cover

UN Environ Prog

Arctic Ice Circulation

AMSR, by Agnew, http://www.socc.ca/seaice/sea_ice_motion.cfm

International Arctic Buoy Program, Rigor et al,

What makes the Arctic FUN?

USA

Greenland

Russia

Fram Strait

Barents Sea

Bering Strait

From thePacific

Eurasian Basin

Lomonosov R

Canadian Basin

Chart from IBCAO

ICE

Weak stratification (away from surface), low energy.

Cold

Thus – traditionally small terms are important, viz thermobaric, double diffusion etcetctc

A Challenge to measure

Arctic Ocean Circulation

Surface/Pacific water circulation “similar to ice motion”

Atlantic water circum-Arctic Boundary current following topography

EDDIES!

Pacific Water in the Arctic

Steele et al, 2004

Rich in Nutrients

Source of heat, freshwater, stratification ... and upper ocean ventilation

Pathways dependent on atmospheric

state

Pacific and

Atlantic Tracers?

Mixing in T-S Space

TEM

PER

ATU

RE

SALINITY

Mechanical mixing in TS space creates straight lines between water masses

Thus, straight lines in TS space suggest mechanical mixing

Influence of shelf waters

Use silicate to track Pacific Water

in the Chukchi Borderland

Along the Chukchi Shelf, upwelling and diapycnal mixing of

lower halocline waters and Pacific waters

(Note ventilation by polynya waters

couldn’t give this T-S structure)

Woodgate et al, 2005

Atl

Pac

Pacific Nutrient Max

Atlantic layer warming of the 1990s

Follow the warming by tracing the temperature maximum

Some suggestions of slight cooling following the warming Mooring and CTD Data, Woodgate etal, 2001; Scicex data, Gunn & Muench, 2001

Karcher et al, 2003

‘80

‘99

‘95

‘96

‘93

‘91

‘84

‘87

1993 Larsen - 1 deg warmer on the Mendeleev Ridge- inversions in temperature and salinity

Carmack et al, ‘95, and McLaughlin et al, ‘96

The Warming of the 1990s

Atlantic Water zigzags AOS94

Line up/ Nest all throughthe Arctic

Angles of the Zigzags match double diffusive theory

Carmack et al, 1997

Salinity (psu)

Pote

ntia

l Tem

pera

ture

(deg

C)

Mixing and Double Diffusion in T-S Space

TEM

PER

ATU

RE

SALINITY

Mechanical mixing in TS space creates straight lines between water masses

TEM

PER

ATU

RE

SALINITY

In double diffusive processes,heat diffuses faster than salt.

So, in TS space resultant waters are not on a straight line between the parent water masses

Zigzags - things we know

Line up throughout the Arctic (Carmack et al)

NOT isopycnal, but double diffusive

Theories for formation, and for growing to a large

amplitude steady state(Turner, Ruddick, Toole,

Georgi, McDougall, Walsh, Carmack, Rudels, May … )

Salt fingeringRegime

Warm Salty / Cold Freshunstable in salt

Diffusive ConvectionRegime

Cold Fresh / Warm Saltyunstable in temperature

Warming in the

Chukchi Borderland

cf Shimada et al, 2004;Woodgate et al, in press

‘93

‘97

‘02

‘00

‘99‘96

‘94

‘98‘95

warming progressing through the

Chukchi Borderland

Structure in the Atlantic Water core

- very different T-S structures

- very sharp fronts

1) The temperature maximum is very dependent on location

2) Why are the structures so different?

3) Can we follow pathways using the T-S structure?

Pacific Nutrient Max

Woodgate et al, in press

Zigzags – what else can they tell us?

Form within the envelope of the parent water masses?

SMALL Zigzags - parents similar

Points of Zigzags contain least altered

waters

NEW??

OLD??

BIG Zigzags - parents different

Zigzags – do tracers agree with this??NEW??

OLD??

NEW??

OLD??

NEW??

OLD??

% Oxygen Saturation

CFC-11 Higher Oxygen and CFCs in the

warmer, saltier part of the zigzags

Temperature Salt Oxygen CFC-11

Tracking waters with Zigzags

BIG ZIGZAGS- medium Oxygen- middle/low CFCs

- Interleaving of boundary current

with old basin waters

Temperature

Oxygen

CFC-11

Temperature

Oxygen

CFC-11

SMALL ZIGZAGS- high Oxygen- high CFCs

New boundary current interleaving

with recent basin waters

Temp

Oxyg

CFC-11

RAGGED ZIGZAGS- Low Oxygen- Low CFCs

Relic waters isolated in the Northwind

Abyssal Plain

Temp

Oxyg

CFC-11

POINT AND BUMP- Medium/high

Oxygen- High CFCs

Core of Boundary Current

Woodgate et al, in press

Temp

Oxyg

CFC-11

SMOOTH TEMPERATURE

MAXIMUM- Low Oxygen

- Medium CFCs

Shelf-influenced waters

Chukchi Borderland Atlantic Water

CirculationOnly shown Fram

Strait Branch Water, but Barents Branch very similar

http://psc.apl.washington.edu/HLD

Woodgate et al, in press, JGR

http://psc.apl.washington.edu/HLD

Using T-S Zigzags to trace Atlantic Water pathways

Pacific/Atlantic diapycnal mixing via upwelling on the Chukchi Shelf

NEW

OLD

Arctic from TS-Space