Bering Sea Bathymetry

BeringStrait

Nunivak

St. Lawrence

St.Matthew

Pribilof

A l e u t i a n I

s l a n d sAmukta

Pass

UnimakPass

UnAlaskaDutch HarborBowers

Ridge

BowersBasin

Kamch

atka S

trait

AleutianBasin

ShirshovRidgeKamchatka

Basin

Norton SoundGulf of Anadyr

AmchitkaPass

NearStrait

Shpanberg

StraitAnadyr

Strait

Map courtesy of NASA

BeringStrait

Nunivak

St. Lawrence

St.Matthew

Pribilof

A l e u t i a n I

s l a n d sAmukta

Pass

UnimakPass

UnAlaskaDutch HarborBowers

Ridge

BowersBasin

Kamch

atka S

trait

AleutianBasin

ShirshovRidgeKamchatka

Basin

Norton SoundGulf of Anadyr

AmchitkaPass

NearStrait

DEEP BASIN~ 3500m

- nutrient source?

PACIFIC INPUT – through a leaky Ridge

FRESHWATER FROM

ALASKA COASTAL

CURRENT

OUTFLOW TO ARCTIC

Bering Sea – as an oceanographer would see it

Shpanberg

StraitAnadyr

Strait

Map courtesy of NASA

COASTS- polynyas?

- riverine input?

SHALLOW SHELF< 200m

- atmosphere driven- mixing

- canyons for upwelling

SLOPE

- topographic steering?

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 1999 modelled

Feb 2001 observed

Feb 2001 modelled

2006

Sea Ice Extent 2006, 2007?

Courtesy of Jim Overland, PMEL

Stabeno et al, 1999

ALASKA COASTAL CURRENT

- fresh!!!, but ~ 2 Sv

(Alaska ..not Alaskan ..)

BERING SLOPE CURRENT

- turns into meanders and eddies

Aleutian North Slope Current

BERING STRAITTHROUGHFLOW

ALASKAN STREAM

~ 20 Sv

Main Currents in the Bering Sea

KAMCHATKA CURRENT

~ 10 Sv, variable (7-15 Sv)

- may recirculate BERINGSEA

SHELF

Anadyr Stra

it

ShpanbergStra

it

Aleutian Passes – “a porous boundary for fluxes of water, heat, salt and nutrients” Stabeno et al, 2005

KAMCHATKA~ 12 Sv (5-15) South

but northwarddeep flow toBering SeaDeep Water

NEAR> 10 Sv (6-12)

North

BULDIR????

AMCHITKANet ~ 2-3 Sv

North(-4 to + 4 Sv)

TOO DEEP TO MIX NUTRIENTSGOOD TO MIX NUTRIENTS

TOO SHALLOWTO MIX NUTRIENTS

ACC~ 2 SvShallowFresh

SeasonalALASKAN STREAM

~ 20 Sv

SEGUAM~0.4 SvNorth

TANGA????

AMUKTA~ 4 SvNorth

SAMALGA????

AKUTAN~ 0.1 Sv

North

UNIMAK~ 0.3 Sv

North

ALEUTIAN NORTH SLOPE CURRENT

~ 10 Sv (4Sv > 1000m)

Aleutian Passes – “a porous boundary for fluxes of water, heat, salt and nutrients” Stabeno et al, 2005

= (at least ) 10 passes= deeper in the west

= medium depth channelssource for bottom nutrients

= Flow can be bidirectional within a Pass= Barotropic important (geostrophic estimates too low)= Maybe seasonal, wind-driven?, = Meanders of Alaskan Stream= Tidal mixing very strong

FRESHNUTRIENTS??

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)

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

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

Evidence from drifter tracks

, 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

15th May 2002

14th June 200027th June 2000

7th June 2001

18th June 2001

23rd May 2002

Okkonen et al, DSR, 2004

SeaWiFs false color image of

Chlorophyll-A

Regimes and Fronts of the Bering Sea Shelf

Best Science Plan, from Kachel

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

summer = 3 layers- top – well mixed (wind)- middle – increasing density- bottom – well mixed (tides)

--------------------Slope Front-------------------------------

SLOPE WATERS- in water depths > 200m over the slope

Stabeno et al, 2001,Kachel et al, 2002Hunt et al, 2002

Tides important!!e.g. Kowalik and Stabeno, 1999, JGR

Mean Circulation~ 5 cm/s

Tidal circulation~ 30 cm/s

Rectification andtrapping

Tides over the whole shelf

Many SST fronts Belkin and Cornillon, 2005

= complex= fronts align with topography

= mostly over shelf

Best Science Plan, from Kachel

The Cold PoolStabeno et al, 2002

WINTER- ice melt- ice formation

SPRING/SUMMER- surface warming- stratification

COLD POOL

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

= Variable year to year

= Important for fish!!

M4M2

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

PDOPacific

Decadal OscillationMantua 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

WARM PHASE COLD PHASE

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

courtesy JISAO

.. recently also need Victoria

PatternBond et al, 2003

= now second EOF more important

PDO important

VP important

= different pattern of SST variability

SST = PC1(t)* EOF1(x,y) + PC2(t)* EOF2(x,y) + ..

PDO Victoria Pattern