BL
2
0
4
2
0
4
2
0
BL
BL
4
2
0
4
2
0
4
2
0
4
2
0
4
2
0
4
2
0
Interannual variability of dense water
formation
in the Mediterranean
sea
AF65 433m
AF65 433m 25002500
AF65 433m
2500
AF70 1883m
AF75 1199m 2000
2000
AF80 2562m
AF86 1333m
CTRL 2601m 15001500
AF70 1883m
AF70 1883m
AF75 1199m
AF75 1199m
AF80 2562m
AF80 2562m
AF86 1333m
AF86 1333m
CTRL 2601m
CTRL 2601m
MLDmax , m
MLDmax , m
MLDmax , m
M. Herrmann, S. Somot, F. Sevault,2000
J. Beuvier. LEGOS, CNRM, MERCATOR
Open-sea convection occurring in the northwestern
Mediterranean basin (NWMED) is at the origin
1500
of the formation of Western Mediterranean Deep
Water
(WMDW),
1000 one of the main Mediterranean
1000
1000
water masses. During winter 2004–2005, a spectacular convection event occurred, observed by several
500
500 with an exceptionally
500
experimental oceanographers. It was associated
large convection area and
unusually warm and salty WMDW.
0
5
0
0
5
5
0
V( > 29.10), 10 m
3
4
13
13
13
V( > 29.10), 10 m
3
V( > 29.10), 10 m
3
AF65 0.06 Sv
Explanations were proposed tentatively, relating the
AF70unusual
0.54 Sv
4
4
AF75
0.10 Sv
characteristics of this event to the Eastern Mediterranean
Transient
AF80 1.63 Sv
(EMT) that occured two decades earlier in the Eastern
basin,
AF86 0.08or
Sv to 3
3
CTRL 1.16 Sv
the atmospheric conditions during winter 2004–2005 in the 2
2
NWMED. They could, however, not be supported
until now. Here
we used numerical modeling to understand
what
drove this 1
1
3000
convection event.
0
3
AF65 0.06 Sv
AF65 0.06 Sv
AF70 0.54 Sv
AF70 0.54 Sv
AF75 0.10 Sv
AF75 0.10 Sv
AF80 1.63 Sv
AF80 1.63 Sv
AF86 0.08 Sv
AF86 0.08 Sv
CTRL 1.16 Sv
CTRL 1.16 Sv
2
1
01/09 0
01/10
01/11
01/12
01/01
01/02
01/09
01/10
01/11
01/12
01/01
01/02
01/12
01/01
01/02
01/03
01/04
MLDmax ,m
01/09
01/10
01/11
The control simulation performed with
2000 NEMOMED8 for the
3
VDW , m x1013
of dense water volume
period 1961–2006 reproduces correctly the long-term evolution of Evolution
13 3
(10
m
)
with
initial conditions of
the Mediterranean Sea circulation, the 1000
EMT, and the NWMED
autumn 2004 and atmospheric
convection event of 2004–2005. Sensitivity simulations were
forcing
of years 65 to 86 (AF..)
0
performed to assess the respective contributions
of atmospheric
and
01/12/04
01/01/05
01/02/05
01/03/05
and 2004-05
(CTRL) 01/04/05
oceanic conditions to this event. They show that winter buoyancy
13
x 10
loss is the major factor driving the
4
CTRL
intensity of deep convection, and that
3 NEMT
the initial autumn stratification of the
CI65
water column is a second order factor.
2 CI70
CI75
The weakness of the winter buoyancy
1 CI80
loss since 1988 in the NWMED
CI86
prevented strong convection to occur
0
01/12/04
01/01/05
01/02/05
01/03/05
01/04/05
during the 1990s, enabling heat and
13
3
salt contents to increase in this region.
Evolution of dense water volume (10 m ) with atmospheric
This resulted in the change of WMDW conditions of winter 2004-05 and initial conditions of years 65 to
characteristics observed in 2005. The
86 (CI..), 2004-05 (CTRL) and not taking EMT into account.
strong buoyancy loss of winter 2004–
2005 was responsible for the intensity of the convection observed this winter in terms of depth and
volume of newly formed WMDW. The EMT did not fundamentally modify the convection process but
potentially doubled this volume by inducing a deepening of the heat and salt maximum that weakened
the preconvection stratification.
Read more about this study : Herrmann et al. (2010). What induced the exceptional 2005 convection
event in the northwestern Mediterranean basin? Answers from a modeling study, J. Geophys. Res., 115,
C12051, doi:10.1029/2010JC006162.
Read also :
Beuvier et al. (2010). Modelling the Mediterranean Sea interannual variability over the last 40 years:
focus on the Eastern Mediterranean Transient (EMT). J. Geophys. Res., 115, C08017,
doi:10.1029/2009JC005950
Schroeder et al. (2010). Abrupt warming and salting of the Western Mediterranean Deep Water:
atmospheric forcings and lateral advection. J. Geophys. Res., 115, C08029, doi:10.1029/2009JC005749
Herrmann et al. (2008). Impact of interannual variability and climate change on dense water cascading
in the Gulf of Lions. Continental Shelf Research, 28 (15), 2092-2112, doi:10.1016/j.csr.2008.03.003