Geophysical Research Abstracts
Vol. 18, EGU2016-PREVIEW, 2016
EGU General Assembly 2016
© Author(s) 2016. CC Attribution 3.0 License.
Estimates of volume, heat and freshwater budgets for the Arctic
Mediterranean and North Atlantic in relation to the main physical
processes: Insight from the EU-NACLIM observations
Bert Rudels (1), Bogi Hansen (2), Johannes Karstensen (3), Gerard McCarthy (4), and Detlef Quadfasel (5)
(1) Finnish Meteorological Institute, Ocean Research, Helsinki, Finland ([email protected]), (2) Faroe Marine Research
Institute, Torshavn, Faroe Islands, (3) Geomar, Helmholz Centre for Ocean Research Kiel, Kiel, Germany, (4) National
Oceanography Centre, University of Southampton, Southampton, UK., (5) Institute of Oceanography, University of Hamburg,
Hamburg, Germany
The EU NACLIM (North Atlantic Climate) project aims to understand the forcing of the North Atlantic circulation
and its importance for the climate of northwestern Europe. NACLIM comprises extensive modelling studies of the
atmosphere, ocean and climate, but here mainly the oceanographic observations are presented. The core observation areas are the North Atlantic Subpolar Gyre and the Greenland-Scotland Ridge, separating the North Atlantic
from the Arctic Mediterranean Sea. These are the areas, where the waters of the lower limb of the Meridional
Overturning Circulation (MOC) are formed and sink into the deep North Atlantic to return southward, mainly
in the Deep Western Boundary Current (DWBC). The exchanges across the Greenland-Scotland Ridge, both the
northward flowing Atlantic and the returning dense waters, have been monitored over decades, as have the circulation in the Subpolar gyre and the convection and mode water formation in the Labrador Sea. These studies are
extended southward to the RAPID array located in the Subtropical gyre at 26oN to capture the MOC further south,
and northward into the Arctic Mediterranean Sea and the formation area of the densest water in the DWBC. In the
Subtropical gyre the ocean circulation is mainly forced by the wind, while in the Subpolar gyre the atmospheric
influence, in addition to wind forcing, also has a large thermodynamic component, changing the characteristics of
the water masses and the density structure of the gyre. The importance of cooling and freshwater input increases
in the Arctic Mediterranean Sea. Variability and a recent declining trend of the MOC strength have been observed
in the Subtropical gyre at the RAPID array. By contrast, both the northward flow across the Greenland-Scotland
Ridge and the overflows have remained steady during the observation periods. An increased atmospheric freshwater flux does not appear to affect the dense water formation in the Arctic Mediterranean, mainly because the
low salinity upper layer is separated from the cooling area in the Norwegian Sea and the Barents Sea. A warmer
climate could reduce the cooling and the density increase in the Atlantic water, unless it is compensated by higher
initial salinity of the northward flowing Atlantic water. Ice drifting over and melting on the warm, saline Atlantic
water might, however, create an upper layer that prevents further cooling of the Atlantic core below. The sea ice
extent and volume are presently declining and such sea ice flux is not expect to happen, The possibility is rather
that not enough ice is available to create the low salinity upper layer in the Nansen Basin. Should this upper layer
disappear, it could actually lead to more overflow water being produced. Almost all of the atmospheric freshwater
that is added to the North Atlantic flow south in the lower limb of the MOC. This implies that the freshwater is
eventually mixed into and contributes to the mode waters that are formed in the Labrador Sea and the Irminger Sea
and flow south in the DWBC.
Estimates of volume, heat and freshwater budgets for the Arctic Mediterranean and the North Atlantic in relation to the main physical processes:
Insights from the EU-NACLIM observations.
B. Rudels1, B. Hansen2, J. Karstensen3 ,
M. Korhonen1 G. McCarthy4 & D. Quadfasel5
& the CT2 members
1 FMI, Helsinki, Finland
2 FMRI, Torshavn, Faroe Islands
3 GEOMAR, Kiel, Germany
4 NOC, Southampton, UK
5 ZMAW, Hamburg, Germany
1.25SvSvNCC
NCCwater
water+ +
1.25
0.64SvRR
RRenter
enteracross
across
0.64Sv
4
5
the
Laptev
shelf
the Laptev shelf
Bering Strait inflow  0.8 Sv
Bering Strait inflow  0.8 Sv
Slope
Slope
convection
Density separation &
convection
Density separation &
double estuary
4
1.5
Sv
uPDW
double
estuary
5
Freshwater
1.5
Sv
uPDW
circulation
Freshwater
circulation
accumulation
Ice melt Ice melt &
accumulation
Ice melt Ice melt &
& FSB
seasonal
&
FSB
Barocline & barotrop pressure gradients
seasonal
recirc.
Baroclinic & barotropic pressure gradients
ice cover
recirc.
ice cover
Ice formation &
Ice formation &
dense water
dense water
production
production
Cooling
Cooling
WSC:
6.6
Sv
6
EGC: 8.8Sv, WSC: 6.6 Sv
74TW
9
7
NS 0.7Sv10 EGC: 8.8Sv, AW 4.5 Sv,
74TW
NS 0.7Sv 4 upper 1.8Sv, AW 4.5 Sv6,
8
JS
0.3Sv
7
LS 0.5Sv8 JS 0.3Sv9 0.4Sv deep5 upper 1.8Sv, heat transport
BSO:
Net
AW
inflow
1.8Sv,
NCC
1.8Sv
0.4Sv deep AAW 1.8Sv, heat transport
LS 0.5Sv
BSO: Net AW inflow 1.8Sv, NCC
1.8Sv
4
AAW 1.8Sv, 25TW? 5
low salinity return flow 0.3Sv5
low salinity return flow 0.3Sv
RAW 1.5Sv, 25TW? 5,6
RAW 1.5Sv, 4
uPDW 1,5Sv.4 Convection: Cooling
uPDW 1,5Sv. Convection: Cooling6
124TW7
0.5Sv
upper
124TW
GIS melting
0.5Sv
upper
GIS melting
water to AIW
can weaken
water to AIW
can weaken
GSDW

EBDW
the baroclinic
GSDW  EBDW
the baroclinic
outflow
outflow
?
3
11
Eastern
overflows
DS
overflow
Davis Strait net outflow
3
12
Eastern
overflows
DS
overflow
Davis
Strait net
outflow
10
4
Atlantic inflows: 3.8Sv west and 2.7Sv net east of
1.611 to 1.9 Sv5
3.4Sv
0.5Sv?
1.6 to 1.9 Sv
1.3Sv polar 3.4Sv
0.5Sv?2Sv
Atlantic
inflows
across
GSR:
0.9Sv
westheat
of transport
the
Faroes.
Slope
Current
3.5Sv
Total
1.3Sv polar
2Sv
2, 3.8Sv west and 2.7Sv net east
outflow
2,3
Iceland
0.9
Sv
230TW.
.
West
of Iceland 0.8Sv ca. 25TW
outflow
0.2Sv
0.2Sv
3,4. Total heat transport 254TW.2,3.
of
the
Faroes
Spilljet
Spilljet
Convection
Entrainment doubles the
Unknown inflow east of Shetland
Convection
Entrainment doubles the
transfers
Unknown
inflow
east
of
Shetland
transfers
brings 3-4 Sv IC
overflow contribution
– 1Sv ??
brings 3-4 Sv IC
polar water overflow contribution
–
1Sv
??
polar
water
water + 3 Sv low
water + 3 Sv low
to the IC
to the IC
salinity water
Expanding SPG,
salinity water12
Expanding
SPG,
into the deep13
cold & fresh
into the deep
Expanding STG,
cold & fresh
Expanding STG,
SPG warm & saline
All fw (37mSv)
SPG warm & saline
All fw (37mSv)
added north of
added
north of
o
26oN is exported
26 N is exported
in the AMOC. This
14
and
sea
level
slope
in the AMOC. This Potential energy gradients13
Potential energy gradients14 and sea level slope15
implies that most
force the interactions between the two gyres
implies that most
of the polar water force the interactions between the two gyres
of the polar water
is convected in the
is convected
in the
15
SPG16
SPG
16,17
How wide is the DWBC as it passes from the SPG to and flows under the STG?
How wide is the DWBC as it passes from the SPG and flows under the STG?17,18
The Rapid Array at 26ooN: cable, direct current measurements, geostrophic velocity and Ekman drift:. 35Sv
The Rapid Array at 26 N: cable, direct current measurements, geostrophic velocity and Ekman drift:. 35Sv
northward with 17Sv recirculating in the subtropical gyre (>1100m) and 18 returning in the AMOC circulation.
northward with 17Sv recirculating in the subtropical gyre (>1100m) and 18 returning in the AMOC circulation. 1
AMOC decreasing 2 Sv in the last three years, mostly in the densest layer. Northward heat transport 1.25PW.1
AMOC decreasing 2 Sv in the last three years, mostly in the densest layer. Northward heat transport 1.25PW.
Acknowledgement:
The background image has been produced by Martin Jakobsson, Stockholm University, Sweden
The research leading to these rsesults has been funded by the EU NACLIM Project, Grant No. 308299.
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