Temperature and salinity variability of the Atlantic Water in the Eastern Eurasian

Basin between 1991 and

2011

Meri Korhonen

R/V Akademik Fedorov, August 24th, 2013

Atlantic Water in the Arctic Ocean

• Defined as a subsurface layer with temperature above 0 ºC

• Located between ~200-800 dbar• Freshwater flux results in strong

upper ocean stratification and restricts vertical mixing

30 31 32 33 34 35-2

-1

0

1

2

Pot

enti

al te

mpe

ratu

re [ C

]

2525

25

2626

26

2727

27

2828

28

24 26 28 30 32 34 36

0

200

400

600

800

1000

Salinity

Dep

th [

dbar

]Nansen BasinAmundsen BasinMakarov BasinNorth Canada BasinSouth Canada Basin

-2 -1 0 1 2

0

200

400

600

800

1000

Potential temperature [C]

Dep

th [

dbar

]

Circulation of Atlantic Water

• Two main inflow passages to the Arctic Ocean from the North Atlantic: the Fram Strait and the Barents Sea

• Mixing of the two branches north of the Kara Sea

• The Arctic Atlantic water leaving the Arctic Ocean (AAW) through the Fram Strait is colder than the entering Atlantic water (AW)

Schauer et al., 2008

The Fram Strait branch

• Northward flow through the Fram Strait 6.6 Sv

• ~3 Sv of water with temperature above 2 ºC (Mauritzen et al., 2011; Beszczynska-Möller et al., 2012)

• Heat from the Atlantic Water keeps the area north of Svalbard ice free through out the year; the ice melt mixes with AW and creates cold and relatively fresh surface layer

North of the Franz Josef Land the Fram Strait branch is attached to the

slope.

FSB

FSB

The Barents Sea branch

• Initially warm, 4-6 ºC, with salinities higher than 35.05• Includes less saline, 34.3, Norwegian Coastal Current• Heat is lost to atmosphere, salinity decreases because of

net precipitation -> colder and less saline water than the Atlantic Water north of Svalbard

• Inflow through the Barents Sea is estimated to be equal to the Fram Strait branch, 3.2-3.3 Sv

BSB located on the shelf and slope

The water masses formed in the Barents SeaFSB AW

densest BSB contribution

FSB return flow

intermediate contribution

BSB AW?

surface/halocline waters

Conditions in the St. Anna and Voronin troughs 1996

Influence of the Barents Sea branch to the intermediate and deep waters

Barents Sea branch water that has entered the deep basin directly at the St. Anna Trough

The Barents Sea branch mixes with

the boundary current between the

Kara and Laptev seas

Major cooling of the boundary current appears to result from the inflow from the Barents Sea.

Variability: the 1990s warming

• Warm pulse through the Fram Strait in the mid 1980s (Quadfasel et al., 1991), consisted until the mid 1990s (Schauer et al., 2002)

• Spreading along the continental slope– North of Laptev Sea– Amundsen and Makarov

basins (Carmack et al., 1995)

– Canada Basin by 2005 (Shimada et al., 2004; McLaughlin et al., 2009)

Variability: 2000s cooling

• Cooling in the Fram Strait in 1997 (Rudels et al., 2000)

• Reduced temperatures observed north of Laptev Sea in 2002 (Polyakov et al., 2005; Dmitrenko et al., 2008)

• 1990s warm pulse was observed to circulate the Makarov Basin: it was partly returning towards Siberia along the Lomonosov Ridge (Kikuchi et al., 2005)

• Cooling on the Barents Sea was due to predominant winds from the deep basins towards the shelves -> longer cooling on the shelf (Dmitrenko et al., ?)

• On the Amundsen Basin side of the Lomonosov Ridge the cooler pulse was propagating towards Greenland-> pronounced horizontal temperature difference between the Amundsen and Makarov basins

Variability:2000s warming

• Warming in the Fram Strait in 1998 (Schauer et al., 2004)

• Sudden warming observed north of Laptev Sea in 2004 (Polyakov et al., 2005; Dmitrenko et al., 2008)

• Further warming in the Fram Strait since 2002 with maximum temperatures observed in 2006 (Beszczynska-Möller et al., 2012)

• Warming north of the Laptev Sea (Polyakov et al., 2010)

2007

2011

The Eastern Arctic Ocean in 2007

The heat loss takes place

mainly in the lower AW layer (orange).

The freshening takes place

mainly in the lower AW layer (orange).

The Eastern Arctic Ocean in 2007

The warm core of the FSB is diluted

and located far from the slope.

The Eastern Arctic Ocean in 2011

The saline signalof the Fram Strait

branch has disappearead north

of the Laptev Sea.

The Eastern Arctic Ocean in 2011

Solid blue lines indicate the BSB at the slope and dashed lines possible BSB return flow

The water columns in the Makarov and Canada basins compared to the two inflow branchesThe properties of

the Atlantic core (the temperature maximum at ~300 dbar) are closer to the properties of the Barents Sea branch than the Fram Strait branch.

The intermediate and deep waters (below ~1000 dbar) have become more saline and warmer due to shelf-slope convection.

Temperature variability in the central basins

Salinity variability in the central basins

Conclusions• Between 1991 and 1996 the temperature was increasing in

all basins• Salinity in the Nansen Basin was increasing together with the

salinity increase in the Fram Strait (Rudels et al., 2000), but the salinity in the Amundsen and Makarov basins was decreasing

-> changes must have taken place in the Barents Sea

• In the 2000s the warming and salinification was restricted to the Nansen Basin

• Mixing with the Barents Sea branch would explain both, reduction in temperature and salinity beyond the Nansen Basin

• Thus the pulses of warm Atlantic Water beyond the Gakkel Ridge would be signs of variability in the Barents Sea branch rather than the Fram Strait branch