Typical Arctic profiles

MIXED LAYER Usually thin (no wind stirring)

PACIFIC WATER High nutrients Shallow (<200m) Tmax Comparatively fresh (<33psu) Mostly only in Western Arctic

ATLANTIC WATER T>0ºC, deeper than 200m Tmax and layer below Higher Salinities Radionuclide tracers Eastern Arctic warmer

Bottom Water “the rest” Western Arctic warmer

Arctic Change 2009 – Woodgate – Wk 4 - Mon 1 Pacific and Atlantic in T-S Space

Arctic Change 2009 – Woodgate – Wk 4 - Mon 2 The watermass zoo

From Ekwurzel etal, 2001, JGR

Arctic Change 2009 – Woodgate – Wk 4 - Mon 3 Bering Strait Basics The 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- - is an integrator of the Russian border properties of the Bering Sea -ice covered from ~ January -dominates the water to April properties of the Chukchi Sea - annual mean Why does a little Strait northward flow (Coachman et al, 1975; matter so much? Woodgate et al, 2005) ~0.8 Sv

Arctic Change 2009 – Woodgate – Wk 4 - Mon 4 The Bering Sea/Bering Strait Relationship Exit route! ANSF= Aleutian North Slope Current From BSC = Bering Stabeno, Slope Current Schumacher & Ohtani, Anadyr 1999 waters (colder, Alaska(n) saltier, Coastal nutrient-rich) Current (warm, fresh, Bering seasonal) Shelf Waters (in between!) By providing an exit, Bering Strait influences flow over the Bering Sea Shelf (although the deep Bering Sea Basin may not care)

Arctic Change 2009 – Woodgate – Wk 4 - Mon 5 Bering Strait and the Chukchi Sea

Nutrient-rich Anadyr waters To first order, except for Bering Shelf - cooling waters - input from coastal Alaskan polynyas, Coastal Current (warm, fresh, Chukchi seasonal) dominated by input through Siberian Bering Strait Coastal Current (cold, fresh, Export to Arctic seasonal) ~ Input through Stagnation Bering Strait Zones over Herald and Hanna Shoals Woodgate et al, DSR, 2005, http://psc.apl.washington.edu/Chukchi.html

Arctic Change 2009 – Woodgate – Wk 4 - Mon 6 The role of Pacific waters in the Arctic

Important for 150 150 Marine Life Pacific waters 50 are the most 100 nutrient-rich 20 15 waters 50 entering the 50 Arctic (Walsh et al, 1989) 50

50 350 Primary Productivity 350 150 gC m-2 yr-1 500 Courtesy of (and adapted from) Codispoti, Stein, Macdonald, and others, 2005

Arctic Change 2009 – Woodgate – Wk 4 - Mon 7 The role of Pacific waters in the Arctic

Chlorophyll from SeaWifs Satellite from NASA/Goddard Space Flight Center and Orbimage

Sea ice concentration from SSMI (IABP)

Implicated in the seasonal melt-back of ice In summer, Pacific waters are a source of near-surface heat 20% to the Arctic 50% (Paquette & Bourke, 1981; Ahlnäs & Garrison, 1984; Woodgate et al, 2006)

Arctic Change 2009 – Woodgate – Wk 4 - Mon 8 The role of Pacific waters in the Arctic

Important for Significant part of Marine Life Arctic Freshwater Pacific waters Budget are the most Bering Strait nutrient-rich throughflow waters ~ 1/3rd of Arctic entering the Freshwater (Wijffels et al, 1992; Arctic Aagaard & Carmack, 1989; (Walsh et al, 1989) Woodgate & Aagaard, 2005; Serreze et al, 2006)

Important for Arctic Stratification Implicated in the seasonal In winter, Pacific waters (fresher melt-back of ice than Atlantic waters) form a cold In summer, Pacific waters are (halocline) layer, which insulates the a source of near-surface heat ice from the warm Atlantic water to the Arctic (Paquette & Bourke, 1981; Ahlnäs & Garrison, beneath 1984); Woodgate et al, 2006 (Shimada et al, 2001, Steele et al, 2004)

Arctic Change 2009 – Woodgate – Wk 4 - Mon 9 Special Observational Challenges of Bering Strait

- shallow (50 m), Two boundary currents but covered by ice - Alaskan Coastal Current (keels to 20 m) from (ACC) in the east present ~ January to April from ~ spring to mid- - stratified in winter (Paquette & Bourke, 1974) spring/summer - Siberian Coastal Current - split by the US- (SCC) present seasonally Russian border in some years in the west (Weingartner et al, 1999)

Eastern Bering Strait in Winter

Arctic Change 2009 – Woodgate – Wk 4 - Mon 10 Bering Strait - annual mean flow ~0.8 Sv northwards, with an Basics 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)

Arctic Change 2009 – Woodgate – Wk 4 - Mon 11 Bering Strait 2004

Moorings and CTD work show temperature, salinity and velocity structure changes rapidly and on small space scales.

To resolve the physics, we use: - high spatial resolution (here ~ 3km) - high temporal resolution (line run in ~4 hrs) - ship’s ADCP data 1st Sept 2004 5th Sept 2004

Arctic Change 2009 – Woodgate – Wk 4 - Mon 12 Getting the 4-dimensional picture Bering Strait and Chukchi Sea 2003

MOST NUTRIENTS 23rd June IN THE WEST!!! 2003

Convention line Fluorescence

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

Sea surface temperature and altimeter satellite data too 5th –7th July 2003

Arctic Change 2009 – Woodgate – Wk 4 - Mon 13 What Drives the Bering Strait Throughflow?

Velocity = “Pacific-Arctic Pressure Head” + “Wind Effects” Mean=northward Mean=northward Mean=southward

- across-strait atmospheric pressure 10-6 sea surface slope gives gradient (Coachman & Aagaard, 1981) rise to pressure gradient - local wind (Aagaard et al, 1985 and others) between Pacific and Arctic - set-up against topography (same ref) Oceans (Coachman & Aagaard, 1966; Wind explains ca. 60 % of the variance Stigebrandt, 1984) and the seasonal cycle (Roach et al, 95) But WHY? - freshwater transport from Atlantic by atmosphere? In the mean, the - steric height difference? winds oppose the pressure head - global winds? (Nof) forcing. Thus, in ASSUMED constant winter, when winds are strongest, the - but why should it be? northward flow is (Woodgate et al, 2005, DSR) weakest. AUG APRIL Woodgate et al, 2005, GRL

Arctic Change 2009 – Woodgate – Wk 4 - Mon 14 Seasonal cycle in water properties (Woodgate et al, 2005) 3 WHY CARE? 2 (1) Maximum SALINITY Seasonallytemperature varying in late 31.9 to 33 psu input summerto the Arctic (2) AutumnOcean cooling ICE 1 and freshing, as 4 overlying-temperature layers TEMPERATURE mixed- salinity down -1.8 to 2.3 deg C -volume (3) Winter at - equilibriumfreezing point, depth salinisation(~50m in summer due to ~120mice formation in winter) TRANSPORT (4) Spring 0.4 to 1.2 Sv freshening-nutrient loading (due to ice melt) and then (30 day means) Interannualwarming variability?

AUG APRIL

Arctic Change 2009 – Woodgate – Wk 4 - Mon 15 Most recent change?

+1 or 2 for stratification

+ 800 for stratification

Change in transport dominates change in heat and FW fluxes (Still only from near bottom data) In 2004 – increase driven by winds In 2007 – far field forcing?? How big are these numbers??

Arctic Change 2009 – Woodgate – Wk 4 - Mon 16 Meltback in area of Pacific Water influence Bering Strait - starts the melt (then ice-albedo feedback) 20 -gives freshwater stratification to keep solar heat shallow ~ 2-5 x 10 J/Y - winter1979source of subsurface 1985 heat 1990 1995

could melt 0.6 to 1.6 million square km of 1m thick ice

2002 2005 2007

Minimum (Sept)

Sea-ice extent 1/3 total USA

Stern, UW, Data NASA

Arctic Change 2009 – Woodgate – Wk 4 - Mon 17 Bering Strait in perspective

IMPACTS - Dominates Chukchi - Ventilation of Arctic Ocean - Nutrients, HEAT, FW for Arctic and beyond - Far field influence on MOC??

~ 0.8 Sv in annual mean - highly seasonal in T,S, vol - driving mechanisms +1 or 2 for stratification FLUXES

- VOLUME: Small, BUT rich in nutrients THUS also care about density + 800 for stratification - HEAT: maybe 1/5th of Fram Strait enough to melt significant area of ice - may kick off ice-albedo effects - may thin ice in winter

- FRESHWATER: 1/3th of input to Arctic - highly variable

Arctic Change 2009 – Woodgate – Wk 4 - Mon 18 Fram Strait ~ 350km wide ~ 2700m deep

St. Anna Trough Barents Sea - broad shelf sea with topographic Fram Strait YP banks Spitsbergen - deepest Arctic Greenland shelf sea (average Barents Sea ~ 230m deep)

Scandinavia YP= Yermak Plateau

Arctic Change 2009 – Woodgate – Wk 4 - Mon 19 Fram Strait VEINS (Variability of Exchanges in the Nordic Seas) 1997 data cf Schauer et al., 2002

Arctic Change 2009 – Woodgate – Wk 4 - Mon 20 OUTFLOW FROM ARCTIC INFLOW TO ARCTIC PW (Polar Water) SVB (svalbard branch) MAW- (Modified Atlantic Water) YPB (Yermak Plateau branch) KB- (Knipovich Branch) ?? KB+ (Knipovich Branch) DW- (Deep Water) MAW+ (Modified Atlantic Water) DW+ (Deep Water)

Schauer et al, 2002

Arctic Change 2009 – Woodgate – Wk 4 - Mon 21 Schauer etal, 2002

Arctic Change 2009 – Woodgate – Wk 4 - Mon 22 Nordic Seas Transports in Sv for period 1997-2000 (European VEINS project)

FRAM STRAIT = NORTHWARD West 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 ~ 20Sv - splits into several branches - topographically steered - wind driven?

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

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

Arctic Change 2009 – Woodgate – Wk 4 - Mon 23 Fram Strait Mooring Data Schauer et al., 2008, SpringerBook

Arctic Change 2009 – Woodgate – Wk 4 - Mon 24 Changing Atlantic Inflow

2005

Arctic Change 2009 – Woodgate – Wk 4 - Mon 25 Details of temperature change depend on which branch? (Saloranta and Haugen, 2001)

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

Max winter SST 1970s – not so good agreement South end of Svalbard Warming not as extreme as suggested. - need increase in volume too??

Schauer etal 2002, - large change in WSC Heat INFLOW VARIES Flux 1997 – 1999 - seasonally 16±12 TW to 41 ± 5 TW (ref -0.1ºC) - about half due to warming, half - interannually due to more volume

Arctic Change 2009 – Woodgate – Wk 4 - Mon 26 Barents Sea Outflow (Schauer et al, 2002, DSR)

Inflow from Greenland Sea ~ 2 Sv Blindheim, 1989; Ingvaldsen et al., 2002 Outflow St Anna ~ 2 Sv (varies seasonally) (1Sv summer, 3 Sv winter) Loeng et al, 1993 Cooled and freshened from AW Deep flow little seasonal variability, but interannual variability, esp in salinity? Schauer et al, 2002 (and others)

Arctic Change 2009 – Woodgate – Wk 4 - Mon 27 DSR 2007

- interannual variability linked to NAO - ecosystems dependent on interplay of heat from AW and cold waters from the Arctic - ecosystem sensitive to seasonal retreat of sea-ice

Arctic Change 2009 – Woodgate – Wk 4 - Mon 28 Atlantic “Branch Waters” (BW) Fram Strait (FSBW) and Barents Sea (BSBW)

FSBW – temperature max

BSBW - inflexion pt

BSBW - below or mixing into Tmax - different in Schauer et al, 2002 different years?

Arctic Change 2009 – Woodgate – Wk 4 - Mon 29 The Canadian Archipelago and

Nares Strait

Ellesmere Greenland Island

Cardigan Strait (and Hell Gate)

WC BS Lancaster Baffin Sound Bay

Bellot Strait

Fury and Hecla Strait

Davis Strait

Lancaster Sound - BS= - WC=WellingtonChannel

Arctic Change 2009 – Woodgate – Wk 4 - Mon 30 Nares Strait CAA and Nares Nares Strait Ellesmere Greenland Strait Challenges and Hell Gate Island Cardigan Strait (and Hell Gate) Measurements Issues: Remote,ice covered,

WC small scale variability, strong tides, BS Lancaster Baffin strong winds, compass issues, Sound Bay Lancaster simultaneous measurements Sound Science Issues:

Fury and Hecla Strait Friction (ice, tides) Hydraulic Control Pressure Head forcing Hudson Strait - BS=Barrow Strait Mediated by wind - WC=WellingtonChannel

Bering Strait ~ 80km wide ~ 50m deep ~ 0.8 Sv highly seasonal e.g. Melling et al, ASOF, 2008

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

Arctic Change 2009 – Woodgate – Wk 4 - Mon 31 1989 Rivers!!

Units = km3/yr

1 Sv ~ 30,000 km3/yr 500 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

Arctic Change 2009 – Woodgate – Wk 4 - Mon 32 Arctic P-ET

Serreze et al., 2006

Arctic Change 2009 – Woodgate – Wk 4 - Mon 33 Arctic Freshwater revised (km3/yr) Serreze et al, JGR, 2006

INFLOW - Rivers 38% - Bering Strait 30% -P-E 24%

OUTFLOW - CAA 35% - Fram St water 26% - Fram St ice 25%

Arctic Change 2009 – Woodgate – Wk 4 - Mon 34 Science, 2002

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

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

Bering Strait Freshwater Flux

Woodgate et al, 2006

Arctic Change 2009 – Woodgate – Wk 4 - Mon 35 PACIFIC INFLOW RIVERS ~ 0.8 Sv .. and ICE & P-ET large seasonal variability Export BARENTS SEA interannual variability ~ 2 Sv high in nutrients seasonal variability freshwater, heat fluxes Russia interannual variability arctic stratification forcing?? pressure head/wind forced In and deeper than T Max

Barents Sea E u From the ra L s o ia Atlantic FRAM STRAIT INFLOW m n From the o B n as o in (West Spitsbergen Current) Pacific so v Fram R Strait ~ 8-10Sv??

in barotropic Bering as B To the Strait n ia Atlantic seasonal variability ad an C interannual warming/strengthening Greenland much recirculation Canadian You are Archipelago T Max here To the USA Atlantic FRAM STRAIT OUTFLOW (East Greenland Current) ~ 10Sv CANADIAN ARCHIPELAGO/NARES STRAIT more Baroclinic, with eddies ~ 2 Sv, seasonal variability Recirculation pressure head/wind forced A lot of unmeasured FW? tides, ice friction, hydraulic control?

Arctic Change 2009 – Woodgate – Wk 4 - Mon 36