Typical Arctic profiles

Potential Temperature= cold at surface= small subsurface Tmax(only in western Arctic)= deep subsurface Tmax(in all the Arctic)= cooler below

Salinity= fresh at surface (fresher in western Arctic)= S always increases with depth= most salinity change in top few 100ms

Density (Sigma-0)= looks like salinity= most stratification is top few 100ms(i.e., away from surface, ~ barotropic)

Typical Arctic profiles

Bottom Water“the rest”

Western Arctic warmer

ATLANTIC WATERT>0ºC, deeper than 200m

Tmax and layer belowHigher Salinities

Radionuclide tracersEastern Arctic warmer

PACIFIC WATERHigh nutrients

Shallow (<200m) TmaxComparatively fresh (<33psu)Mostly only in Western Arctic

MIXED LAYERUsually thin (no wind stirring)

Pacific and

Atlantic in T-S Space

The watermass

zoo

From Ekwurzel etal, 2001, JGR

Bering Strait BasicsThe only Pacific gateway

to the Arctic Ocean

~ 85 km wide

~ 50 m deep

-divided into 2 channels by the Diomede Islands

- split by the US-Russian border

-ice covered from ~ January

to April

- annual mean northward flow

~0.8 Sv

- is an integrator of the properties of the

Bering Sea

-dominates the water properties of the

Chukchi Sea(Coachman et al, 1975;Woodgate et al, 2005)

Why does a little Strait matter so much?

The Bering Sea/Bering Strait RelationshipANSF= Aleutian

North Slope Current

BSC = Bering Slope Current

From Stabeno,

Schumacher & Ohtani,

1999

Alaska(n) Coastal Current (warm, fresh,

seasonal)

Anadyr waters (colder, saltier,

nutrient-rich)

Bering Shelf

Waters (in

between!)

Exit route!

By providing an exit, Bering Strait influences flow over the Bering Sea Shelf

(although the deep Bering Sea Basin may not care)

Bering Strait and the Chukchi SeaNutrient-rich

Anadyr waters

Bering Shelf waters

Alaskan Coastal Current

(warm, fresh, seasonal)

Siberian Coastal Current

(cold, fresh, seasonal)

Stagnation Zones over Herald and

Hanna Shoals

To first order, except for- cooling

- input from coastal

polynyas,

Chukchi dominated by input through Bering Strait

Export to Arctic ~

Input through Bering Strait

Woodgate et al, DSR, 2005, http://psc.apl.washington.edu/Chukchi.html

Important for Marine Life

Pacific waters are the most nutrient-rich

waters entering the

Arctic(Walsh et al, 1989)

Primary Productivity gC m-2 yr-1

Courtesy of (and adapted from) Codispoti, Stein, Macdonald, and others,

2005

500

50

50

350 150 350

150

15

50

50

50

150

20 100

The role of Pacific waters in the Arctic

20%50%

The role of Pacific waters in the Arctic

Implicated in the seasonal melt-back of ice

In summer, Pacific waters are a source of near-surface heat

to the Arctic(Paquette & Bourke, 1981; Ahlnäs & Garrison,

1984; Woodgate et al, 2006)

Chlorophyll from SeaWifs Satellite

from NASA/Goddard Space Flight Center and Orbimage

Sea ice concentration from SSMI (IABP)

The role of Pacific waters in the Arctic

Important for Arctic StratificationIn winter, Pacific waters (fresher than Atlantic waters) form a cold

(halocline) layer, which insulates the ice from the warm Atlantic water

beneath(Shimada et al, 2001, Steele et al, 2004)

Pacific winter waters

The role of Pacific waters in the Arctic

Significant part of Arctic Freshwater

BudgetBering Strait throughflow

~ 1/3rd of Arctic Freshwater(Wijffels et al, 1992;

Aagaard & Carmack, 1989; Woodgate & Aagaard, 2005;

Serreze et al, 2006)

ARCTIC FRESHWATER FLUXES

Bering Strait ~ 2500 km3/yr(0.08 Sv)

Arctic Rivers ~ 3300 km3/yrP-E ~ 900 km3/yr

Fram Strait water ~ 820 km3/yrFram Strait ice ~ 2790 km3/yr

Canadian Archipelago ~ 920 km3/yr

Bering Strait Basics

- annual mean flow ~0.8 Sv northwards, with an annual cycle of 0.3 to 1.3 Sv

- weekly flow reversals common (-2 Sv to +3 Sv)-1 hourly flow can be over 100 cm/s

- Alaskan Coastal Current (ACC) velocities can be 50-100 cm/s stronger than midchannel flow

- flow strongly rectilinear- tides are weak

(Roach et al, 1995; Woodgate et al, 2005)

- away from boundary currents, flow dominantly barotropic (Roach et al, 1995)

- flow in east and west channel highly correlated

(0.95, Woodgate et al, 2005)

Getting the 4-dimensional pictureBering Strait and Chukchi Sea 2003

Convention line Fluorescence

Chlorophyll from SeaWifs Satellitefrom NASA/Goddard Space Flight Center & Orbimage

23rd June2003

5th – 7th July 2003

Sea surface temperature and altimeter satellite data too

MOST NUTRIENTS

IN THE WEST!!!

What Drives the Bering Strait Throughflow?Velocity = “Pacific-Arctic Pressure Head” + “Wind Effects”Mean=northward Mean=northward Mean=southward

10-6 sea surface slope gives rise to pressure gradient

between Pacific and Arctic Oceans (Coachman & Aagaard, 1966;

Stigebrandt, 1984)

But WHY?- freshwater transport from Atlantic by atmosphere?- steric height difference?

- global winds? (Nof)

ASSUMED constant- but why should it be?

(Woodgate et al, 2005, DSR)

- across-strait atmospheric pressure gradient (Coachman & Aagaard, 1981)

- local wind (Aagaard et al, 1985 and others)

- set-up against topography (same ref)

Wind explains ca. 60 % of the varianceand the seasonal cycle (Roach et al, 95)

In the mean, the winds oppose the

pressure head forcing. Thus, in

winter, when winds are strongest, the northward flow is

weakest.

Woodgate et al, 2005, GRL

AUG APRIL

Seasonal cycle in water properties (Woodgate et al, 2005)

SALINITY31.9 to 33 psu

TEMPERATURE-1.8 to 2.3 deg C

TRANSPORT0.4 to 1.2 Sv

(30 day means)

(1) Maximum temperature in late

summer

(2) Autumn cooling and freshing, as overlying layers

mixed down

(3) Winter at freezing point,

salinisation due to ice formation

(4) Spring freshening (due to ice melt) and then

warming

ICE1

2

3

4

AUG APRIL

WHY CARE?

Seasonally varying input to the Arctic

Ocean

- temperature- salinity-volume

- equilibrium depth(~50m in summer~120m in winter)

-nutrient loading

Interannual variability?

InterannualVariability

(up to 2004)

Since 2001

- increasing flow

- warming and some freshening

Woodgate et al, 2006, GRL

Velocity(cm/s)

Transport(Sv,

=106m3/s)

Salinity(psu)

Temperature(degC)

InterannualVariability

(up to 2004)

Increasing flow since 2001 mostly attributable to changes in local wind

Woodgate et al, 2006, GRL

Transport change significant

0.7 Sv in 2001 1 Sv in 2005

(long term mean 0.8 Sv)

AnnualMean Wind

(m/s)(NCEP)

Bering Strait Heat Flux

2004 largest heat flux observed

Increasing flow accounts for

50% of the heat flux increases

Woodgate et al, 2006

The Alaskan Coastal Current is~ 1/3 Bering Strait heat

BUT is not yet properly measured

IN PERSPECTIVE:

Extra heat since 2001 could melt an area 800km by 800km of 1m thick ice(Coincidentally, this is

about the same as the ice area lost in this time)

Bering Strait heat flux is ~ 1/5 of Fram Strait heat flux

IN PERSPECTIVE:

Extra freshwater since 2001 is about ¼ of annual mean

river run off(Bering Strait significant

source of Arctic freshwatervariability?)

Bering Strait freshwater flux is ~ 1/3 of Arctic

freshwater input

Bering Strait Freshwater Flux

Woodgate et al, 2006

Alaskan Coastal Current (ACC) carries ~ 10% of freshwater entering the Arctic!

~ 1/4 Bering Strait FWBUT is not yet properly measured

Increasing freshwater flux 2001-2004, but not record high

Increasing flow accounts for 80% of the

freshwater flux increases

Due to more sea water, not more

river water

The Pacific Arctic Gateway

ICE1

23

4

Bering and Chukchi- indicator of

hydrography and change

Arctic- Most nutrient-rich, - 1/3rd of freshwater, - source of heat and

halocline waters

Globally- influences Atlantic

overturning circulation

Why is Bering Strait important?

Northward flowing, daily/weekly flow reversals

Large seasonal cycles in input to Arctic Ocean,

including equilibrium depth

Interannual variability, suggesting freshening and

warming in recent years

Bering Strait Basics

http://psc.apl.washington.edu/BeringStrait.html

Fram Strait ~ 350km wide~ 2700m deep

Barents Sea- broad shelf sea with topographic

banks- deepest Arctic

shelf sea (average ~ 230m deep)

Barents Sea

St. Anna Trough

YP

YP= Yermak Plateau

Fram Strait

Spitsbergen

Scandinavia

Greenland

Fram StraitVEINS (Variability of Exchanges in the Nordic

Seas) 1997 data cf Schauer et al., 2002

Schauer et al, 2002

INFLOW TO ARCTICSVB (svalbard branch)YPB (Yermak Plateau branch)KB+ (Knipovich Branch)MAW+ (Modified Atlantic Water)DW+ (Deep Water)

OUTFLOW FROM ARCTICPW (Polar Water)MAW- (Modified Atlantic Water)KB- (Knipovich Branch) ??DW- (Deep Water)

Schauer etal, 2002

Nordic Seas (European VEINS project)

Transports in Sv for period 1997-2000

FRAM STRAIT= NORTHWARDWest Spitsbergen Current- warm, salty- estimated 0-7 Sv (Rudels, 1989)- large barotropic component- lots of eddies- varies seasonally- T min in winter, Vol max in winter- splits into several branches- topographically steered- wind driven?

= SOUTHWARDEast Greenland Current- significant velocity shear- lower kinetic energy- eddies more dominant than wind- NOT seasonal

NB East Greenland Current inGreenland Sea MUCH stronger (~ 20Sv),recirculating, wind driven, seasonal

~ 20Sv

Details of temperature change depend on which branch?

(Saloranta and Haugen, 2001)

Max winter SST

South endof Svalbard

1980s and 1990s – agree with Fram Strait- coherent with NAO

1970s – not so good agreement

Warming not as extreme assuggested. - need increase in volume too??

Schauer etal 2002,- large change in WSC Heat

Flux 1997 – 199916±12 TW to 41 ± 5 TW (ref -0.1ºC)

- about half due to warming, half due to more volume

INFLOW VARIES- seasonally

- interannually

Barents Sea Outflow(Schauer et al, 2002, DSR)

Inflow from Greenland Sea ~ 2 SvBlindheim, 1989; Ingvaldsen et al., 2002

Outflow St Anna ~ 2 Sv (varies seasonally)(1Sv summer, 3 Sv winter)

Loeng et al, 1993Cooled and freshened from AWDeep flow little seasonal variability, butinterannual variability, esp in salinity?

Schauer et al, 2002 (and others)

Atlantic “Branch Waters” (BW) Fram Strait (FSBW) and

Barents Sea (BSBW)

FSBW – temperature max

BSBW - inflexion pt

Schauer et al, 2002

BSBW- below or mixing

into Tmax- different in

different years?

~ 2 Sv,likely seasonal

CAA and NaresStrait ChallengesGreenlandEllesmere

Island

Davis Strait

Nares Strait

Lancaster Sound

BaffinBay

Hudson Strait

Fury and Hecla Strait

Bellot Strait

Cardigan Strait(and Hell Gate)

WCBS

Lancaster Sound- BS=Barrow Strait

- WC=WellingtonChannel

Nares Strait

LancasterSound

Cardigan Straitand Hell Gate

Davis Strait ~ 360km wide ~ 1000m deep ~ 2Sv NETalso northward inflow from Atlantic (~ 2Sv northward, 4Sv southward)

Lancaster Sound ~ 68km wide ~ 285m deep ~ 0.7 Sv(seasonal 0.4Sv winter, 1.0 Sv summer) ice covered ~ 10 months

Nares Strait ~ 38km wide ~380m deep ~ 0.8Sv (SNAPSHOT)ice bridges, very strong winds

Cardigan Strait and Hells Gate ~12km wide ~180m deep ~ 0.3 Sv very variable, seasonal not clear, VERY strong (2m/s) tides

Bering Strait ~ 80km wide ~ 50m deep ~ 0.8 Sv highly seasonal e.g. Melling et al, ASOF, in press

Measurements Issues:Remote,ice covered,

small scale variability, strong tides,strong winds, compass issues,simultaneous measurements

Science Issues:Friction (ice, tides)Hydraulic Control

Pressure Head forcingMediated by wind

Rivers!!1989

Units = km3/yr

1 Sv ~ 30,000 km3/yr500 km3/yr ~ 0.02 Sv

- only care about rivers as they are freshwater.

ALL Rivers ~ 3200 km3/yr

Bering Strait ~ 2500 ± 300 km3/yr(Woodgate and Aagaard, 2005)

P-ET ~ 2000 km3/yr

Science, 2002

Woodgate et al, 2006

Bering Strait Freshwater Flux

~ 60 year river change ~= uncertainty of Bering Strait FW

<< Bering Strait interannual change

??????pathways (as fresh, not mixed)

USA

Greenland

Russia

FramStrait

Barents Sea

Bering Strait

Eurasian Basin

Lomonosov R

Canadian Basin

CanadianArchipelago

From theAtlantic

From thePacific

To theAtlantic

To theAtlantic

You arehere

PACIFIC INFLOW~ 0.8 Sv

large seasonal variabilityinterannual variability

high in nutrientsfreshwater, heat fluxes

arctic stratificationpressure head/wind forced

CANADIAN ARCHIPELAGO/NARES STRAIT~ 2 Sv, seasonal variabilitypressure head/wind forced

tides, ice friction, hydraulic control?

BARENTS SEA~ 2 Sv

seasonal variabilityinterannual variability

forcing??In and deeper than T Max

FRAM STRAIT INFLOW(West Spitsbergen Current)

~ 8-10Sv??barotropic

seasonal variabilityinterannual warming/strengthening

much recirculationT Max

FRAM STRAIT OUTFLOW(East Greenland Current)

~ 10Svmore Baroclinic, with eddies

Recirculation????