2012 Changing Arctic Ocean 506E/497E - Lecture 5 - Woodgate

The Bering Sea/Bering Strait Relationship Bering Strait and the Chukchi Sea Exit route! ANSF= Aleutian North Slope Nutrient-rich Current From Anadyr waters To first order, BSC = Bering Stabeno, except for Slope Current Schumacher Bering Shelf - cooling & Ohtani, waters - input from Anadyr 1999 coastal waters Alaskan polynyas, (colder, Alaska(n) Coastal Current saltier, Coastal (warm, fresh, Chukchi nutrient-rich) Current seasonal) dominated by (warm, input through fresh, Siberian Bering Strait Bering seasonal) Coastal Current Shelf (cold, fresh, Export to Arctic Waters seasonal) ~ (in Input through between!) Stagnation Bering Strait By providing an exit, Bering Strait influences flow over Zones over Herald and the Bering Sea Shelf Hanna Shoals Woodgate et al, DSR, 2005, http://psc.apl.washington.edu/Chukchi.html (although the deep Bering Sea Basin may not care)

Bering Strait dominates the Chukchi Sea Woodgate et al., 2005, DSR and via http://psc.apl.washington.edu/HLD The role of Pacific waters in the Arctic

Important for Marine Life 150 150 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 Bering Strait good 500 proxy of Arctic inflow Courtesy of (and adapted from) Codispoti, Stein, Macdonald, and others, 2005

1 2012 Changing Arctic Ocean 506E/497E - Lecture 5 - Woodgate

The role of Pacific waters in the Arctic The role of Pacific waters in the Arctic

Chlorophyll from ARCTIC FRESHWATER FLUXES Significant part of SeaWifs Satellite 3 Bering Strait ~ 2500 km /yr Arctic Freshwater from NASA/Goddard Space (0.08 Sv) Flight Center and Orbimage Budget Arctic Rivers ~ 3300 km3/yr Bering Strait P-E ~ 900 km3/yr throughflow Sea ice concentration from SSMI (IABP) Fram Strait water ~ 820 km3/yr ~ 1/3rd of Arctic Fram Strait ice ~ 2790 km3/yr Freshwater Canadian Archipelago ~ 920 km3/yr (Wijffels et al, 1992; Aagaard & Carmack, 1989; Woodgate & Aagaard, 2005; Serreze et al, 2006)

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

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

2 2012 Changing Arctic Ocean 506E/497E - Lecture 5 - Woodgate

Global role of Bering Strait Paleo role of A Freshwater source for the Atlantic Ocean Bering Strait

Pacific waters exit the Arctic through the Stabilizer for World Climate? Fram Strait and (DeBoer & Nof, 2004) - if Bering Strait is open, excess through the Canadian freshwater in the Atlantic (from, for Land Bridge Archipelago Broecker, 1991 (Jones et al, 2003) example, ice sheet collapse) can for migration “vent” through the Bering Strait, of mammals Freshwater inhibits deep convection, slowing the Atlantic Ocean overturning allowing a speedy return to deep and people? circulation (see Wadley & Bigg, 2002, for a discussion) convection in the Atlantic. www.debbiemilleralaska.com Models suggest the Bering Strait throughflow also influences the deep Note: in modern times, people have swum, driven and walked across! western boundary currents & the Gulf stream separation (Huang & Schmidt, 1993)

(Woodgate et al, 2005) Seasonal cycle in water properties Bering Strait - annual mean flow ~0.8 Sv northwards, with an 3 annual cycle of 0.3 to 1.3 Sv 2 WHY CARE? Basics (1) Maximum - weekly flow reversals common (-2 Sv to +3 Sv)

SALINITY temperature in late -1 hourly flow can be over 100 cm/s Seasonally varying 31.9 to 33 psu summer - Alaskan Coastal Current (ACC) velocities can input to the Arctic be 50-100 cm/s stronger than midchannel flow (2) AutumnOcean cooling ICE - flow strongly rectilinear 1 and freshing, as 4 - tides are weak overlying- temperature layers (Roach et al, 1995; Woodgate et al, 2005) TEMPERATURE mixed- salinity down -1.8 to 2.3 deg C -volume (3) Winter at

freezing point, - equilibrium depth salinisation due to - away from boundary (~50m in summer ice formation currents, flow dominantly ~120m in winter) barotropic (Roach et al, 1995) TRANSPORT (4) Spring 0.4 to 1.2 Sv freshening-nutrient loading (due to - flow in east and west channel highly correlated ice melt) and then (30 day means) (0.95, Woodgate et al, 2005) warming

AUG APRIL

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Getting the 4-dimensional picture What Drives the Bering Strait Throughflow? Bering Strait and Chukchi Sea 2003 Velocity = “Pacific-Arctic Pressure Head” + “Wind Effects” Mean=northward Mean=northward Mean=southward

- across-strait atmospheric pressure gradient -6 MOST 10 sea surface slope gives (Coachman & Aagaard, 1981) NUTRIENTS rise to pressure gradient - local wind (Aagaard et al, 1985 and others) 23rd June IN THE between Pacific and Arctic - set-up against topography (same ref) WEST!!! 2003 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 Convention line Fluorescence - steric height difference? winds oppose the pressure head - global winds? (Nof) forcing. Thus, in Chlorophyll from SeaWifs Satellite ASSUMED constant winter, when winds from NASA/Goddard Space Flight Center & Orbimage - but why should it be? are strongest, the (Woodgate et al, 2005, DSR) northward flow is weakest. Sea surface temperature and altimeter AUG APRIL satellite data too Woodgate et al, 2005, GRL 5th – 7th July 2003

OUTFLOW FROM ARCTIC INFLOW TO ARCTIC Estimating Heat Flux 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) 2007 Bering Strait Heat is 5-6 x 1020 J/yr (20 TW) which is:

- 2 x the 2001 Bering Strait heat

- could melt 2 x 106 km2 (2 MSK) of 1m thick ice winter extent ~ 10 MSK 2006 Sept min ~ 6 MSK 2007 Sept min ~ 4 MSK

- 4 W/m2 over ½ the Arctic (ERA-40 -2 to + 10 W/m2 Serreze et al, 2007)

- greater than incoming solar into Chukchi ~ 3 to 4.5 x 1020 J/yr (data, B.Light)

- ~ 1/3rd of Fram Strait Heat ~30-50TW net, (Schauer et al, 2008) 15 Errors ~ 0.1 Sv, 1020J Woodgate et al, 2010 Schauer et al, 2002

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Nordic Seas Transports in Sv for period 1997-2000 Fram Strait Mooring Data Schauer et al., 2008, SpringerBook (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

Barents Sea Outflow Atlantic (Schauer et al, 2002, DSR) Barents Sea facts Water? - strong modification Inflow from Greenland Sea ~ 2 Sv - important fisheries 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)

Schauer et al, 2004; Schauer and Beszczynska-Moeller, 2009 Heat flux through Fram Strait - based on moorings

Annual Mean ~ 25 - 50 TW ~ 8 to 16 x 1020 J/yr

Estimates? Pathways? Loeng & Getting heat up? Drinkwater, 2007

5 2012 Changing Arctic Ocean 506E/497E - Lecture 5 - Woodgate

Nares Strait CAA and Nares 1989 Rivers! Ellesmere Greenland Strait Challenges and Hell Gate Island Units = km3/yr Cardigan Strait Measurements Issues: (and Hell Gate) Remote,ice covered, 1 Sv ~ 30,000 km3/yr WC small scale variability, strong tides, 3 BS Lancaster Baffin strong winds, compass issues, 500 km /yr ~ 0.02 Sv Sound Bay Lancaster simultaneous measurements Sound Volume is SMALL, but Science Issues: important because of Friction (ice, tides) what they carry Hydraulic Control - freshwater. Pressure Head forcing - BS= Mediated by wind - ??? - WC=WellingtonChannel Bering Strait ~ 80km wide ~ 50m deep ~ 0.8 Sv highly seasonal e.g. Melling et al, ASOF, 2008 ALL Rivers ~ 3200 km3/yr

Lancaster Sound ~ 68km wide ~ 285m deep ~ 0.7 Sv Bering Strait (seasonal 0.4Sv winter, 1.0 Sv summer) ice covered ~ 10 months ~ 2500 ± 300 km3/yr (Woodgate and Aagaard, 2005) Nares Strait ~ 38km wide ~380m deep ~ 0.8Sv (SNAPSHOT) ice bridges, very strong winds 3 P-ET ~ 2000 km /yr 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 Precipitation & Precipitation-Evapotranspiration Arctic (P-ET) Freshwater Arctic ~ 12-36 cm/year much ~ desert (< 25 cm/yr) revised 3 Seattle ~ 38 cm/year (km /yr) Serreze et al, JGR, 2006 http://arctic.atmos.uiuc.edu/ERA40/IMAGES/ era40.arctic.prec.ann.gif INFLOW - Rivers 38% - Bering Strait 30% 2006 - P-E 24%

OUTFLOW - CAA 35% - Fram St water 26% - Fram St ice 25% ~2000 km3/yr ~ 0.06 Sv

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