Bering Sea Bathymetry

Bering Strait

t ai Gulf of Anadyr tr St. S Norton Sound yr Lawrence ad n A it a tr S rg e b n a p h St. S Matthew Nunivak Shirshov Kamchatka Ridge Basin Aleutian Pribilof it a Basin tr S a tk a h UnAlaska c m Bowers a Dutch Harbor Unimak K Ridge Pass s Near Bowers d Strait Amukta n Basin l a Pass I s

n i a t u l e Amchitka A Pass

Map courtesy of NASA Bering Sea – as an oceanographer would see it

OUTFLOW TO ARCTIC

Bering Strait COASTS t ai - polynyas?Gulf of Anadyr tr St. S Norton Sound yr Lawrence - riverine input? ad n A it a tr S rg e SHALLOWb SHELF n a p h - S < 200m to St. p Matthew o - atmosphere driven g S r L Nunivak- mixing ap O Shirshov h P Kamchatka Ridge i E - canyons for upwelling c Basin st AleutianDEEP BASIN ee Pribilof it Basin r a in M tr ~ 3500m S g a ? RO tk F L a h - nutrient source? UnAlaska A c R T m Bowers E a Dutch Harbor Unimak T K Ridge AS Pass A O C T s HW N Near Bowers d S A E Strait Amukta n K Basin l a RE S Pass I s F A CURR n i a AL t u l e Amchitka A PACIFIC INPUT – through aPass leaky Ridge

Map courtesy of NASA Ice coverage on the Southeast Bering Sea shelf, 1972-2006

• Decreased ice cover since late 1970s

• Very little or no ice in recent years (increase in 2006)

Courtesy of Jim Overland, PMEL Feb 1999 observed Feb 2001 observed

Feb 1999 modelled Feb 2001 modelled Sea Ice Extent 2006, 2007?

2006

Courtesy of Jim Overland, PMEL Main Currents in BERING STRAIT the Bering Sea THROUGHFLOW

t ai tr r S y t d ai a tr An S g er nb pa Sh

NT RE v) UR S C 7-15 KA ( T le ate A iab ul BERING CH ar rc - B M , v tu E SEA KA v reci rn R S ay s IN 10 m i G SHELF ~ - n S to L m O P ea E n C d U ers R R a E n N NT d T E ed RR di CU es L Sv A 2 ..) ST ~ n A ut ka CO , b las A !!! A K h ot Current S es .n rth Slope LA fr . leutian No A - ka A las (A AM TRE AN S ASK Sv AL ~ 20 Stabeno et al, 1999 Aleutian Passes – “a porous boundary for fluxes of water, heat, salt and nutrients” Stabeno et al, 2005

T RREN PE CU H SLO NORT 00m) TIAN v > 10 ACC~ 2 Sv ALEU Sv (4S ~ 10 Shallow M Fresh TREA KAN S Seasonal ALAS v ~ 20 S

SAMALGA ????

AMCHITKA KAMCHATKA NEAR BULDIR SEGUAM AMUKTA AKUTAN UNIMAK Net ~ 2-3 Sv ~ 12 Sv (5-15) South > 10 Sv (6-12) ???? TANGA ~0.4 Sv ~ 4 Sv ~ 0.1 Sv ~ 0.3 Sv but northward North North ???? North North North North deep flow to (-4 to + 4 Sv) Bering Sea Deep Water TOO SHALLOW TOO DEEP TO MIX NUTRIENTS GOOD TO MIX NUTRIENTS TO MIX NUTRIENTS Aleutian Passes – “a porous boundary for fluxes of water, heat, salt and nutrients” Stabeno et al, 2005

NUTRIENTS?? FRESH

= Flow can be bidirectional within a Pass = (at least ) 10 passes = Barotropic important (geostrophic estimates too low) = deeper in the west = Maybe seasonal, wind-driven?, = medium depth channels = Meanders of Alaskan Stream source for bottom nutrients = Tidal mixing very strong 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) Anadyr and Shpanberg Straits

et al., JGR, 1988

CSR, 1993

Generally Northward?

Must be comparable to Bering Strait

Anadyr Stronger

Summer and Winter “modes” different

Strongly related to wind - thus highly variable

NOT WELL MEASURED – what about models?? 23 year mean flow field from a model Clement et al, 2005, DSR

.. but really need data to verify it (NB simulation of Bering Strait flow ok in some senses, not ok in others) Compared to observations? (not many observations)

Overland et al, 1996, JGR - drogue-less buoy (thus wind and current driven) - 2 months from Cape Navarin to Bering Strait Weingartner et al, Website Bering Slope Current Evidence from drifter tracks

Stabeno and Reed, 1994, JPO

Johnson et al, JPO, 2004

Herman et al, 2002 adapted from Stabeno et al, 2001

= fed from Aleutian North Slope Current = initially follows slope, then appears to leave it = meandering with eddies = upwelled waters/eddies for productivity , JPO, 1975

Very tricky to get something meaningful if - eddies are important (THEY ARE!) - barotropic is important (IT IS!) Bering Sea Greenbelt

Shumacher and Stabeno, http://www.pmel.noaa.gov/np/pages/wnew_bioprod.html 18th May 2000 27th June 2000 14th June 2000

15th May 2002

7th June 2001 SeaWiFs false color image of Chlorophyll-A

18th June 2001 23rd May 2002

Okkonen et al, DSR, 2004 Regimes and Fronts of the Bering Sea Shelf

COASTAL DOMAIN - inshore of 50m depth contour summer = well mixed/weakly stratified

------Inner or Structural Front (5-30km wide)------

MIDDLE SHELF DOMAIN - between 50m and 100m depth contours summer = strongly stratified 2 layer -top –wind mixed - bottom – tidal mixed T diff > 8 deg, density set by T

------Middle Transition Zone (~ 50 km wide)------

OUTER SHELF DOMAIN - between 100m and 200m depth contours Best Science Plan, from Kachel summer = 3 layers - top – well mixed (wind) - middle – increasing density - bottom – well mixed (tides)

------Slope Front------Stabeno et al, 2001, Kachel et al, 2002 SLOPE WATERS Hunt et al, 2002 - in water depths > 200m over the slope Tides important!! e.g. Kowalik and Stabeno, 1999, JGR

Mean Circulation ~ 5 cm/s

Tidal circulation ~ 30 cm/s

Rectification and trapping Tides over the whole shelf Many SST fronts Belkin and Cornillon, 2005

= complex = fronts align with topography = mostly over shelf WINTER SPRING/SUMMER The Cold Pool -ice melt - surface warming - ice formation - stratification Stabeno et al, 2002

M4 M2

Best Science Plan, from Kachel

COLD POOL

=Cold (< 2 deg C) Water at depth, covered by warmer surface waters

= Variable year to year

= Important for fish!! Depth Averaged Temperature (°C) at M2: 2 deg C increase in winter after 2000: above freezing point. Summer 2005 warmest temperature

Data from Stabeno, courtesy of Overland WARM PHASE COLD PHASE PDO Pacific Decadal Oscillation Mantua et al, 1997

Typical wintertime Sea Surface Temperature (colors), Sea Level Pressure (contours) and surface windstress (arrows) anomaly patterns during warm and cool phases of PDO

leading principal component of North Pacific monthly sea surface temperature variability (poleward of 20N for the 1900-93 period)

courtesy JISAO .. recently also SST = PC1(t)* EOF1(x,y) + PC2(t)* EOF2(x,y) + .. need Victoria PDO Victoria Pattern Pattern Bond et al, 2003

= different pattern of SST variability

PDO important

VP important

= now second EOF more important