The response of the Mediterranean thermohaline circulation to changes in the ocean gateway
(1)UCG, Department of Earth Sciences, Faculty of Geosciences, Utrecht University, (2)UCG, IMAU, Department of Physics and Astronomy, Utrecht University, Bahjat Alhammoud¹, Paul Th. Meijer¹ and Henk A. Dijkstra² E-mail: bahjat@geo.uu.nl
1. Background
During the Cenozoic, the convergence of Africa and Eurasia
gradually restricted the gateway(s) connecting the Mediterranean to the open ocean (Fig.1) which strongly affected the Mediterranean thermohaline circulation (MTHC) [Meijer et al. 2004].
Figure 1: Geologic records show major changes in the Atlantic-Mediterranean gateways during the Cenozoic (65-2 Ma) [Blakey: http://jan.ucc.nau.edu/rbc7].
Eocene Early-Miocene Late-Miocene
In order to investigate the effects of the gateway geometry on the
MTHC- expected to be of major importance on the basis of geological data- several experiments with different sill depths are performed.
Fig.2: (a) Model grid and topography, dashed lines indicate the position of sections, (b) Vertical section at ZZ’ of sigma levels.
2. Model setup
We used the Princeton Ocean Model [Blumberg and Mellor, 1987].
A simplified basin is used (Fig.2) with grid horizontal resolution of
1°x1°. A buffer zone and open boundary condition are applied in the Atlantic box. The Initial conditions for T-S are put to 20°C and 35 psu.
The surface forcing is reduced to uniform net evaporation (1 m/yr) and relaxation of SST to a latitudinal profile of air temperature.
These results are taken from three parallel sensitivity experiments
(SD100, REF and SD500), where we only change the sill depth.
3. Results
3.1. Model drift
Fig.3: Time series for the different simulations of (a) Kinetic energy
measure (solid line); volume transport
through the gateway (in Sv; dashed line), (b) Basin-averaged salinity S (solid line) and temperature T (dashed line),
(c) Decadal smoothed Mediterranean zonal overturning (in Sv); maximum value in the upper 1000 m (solid line); and minimum value in the lower 500 m (dashed line).
0 2 4 6 8 10 12
<KE> [m
2s
−2]*10
−30 200 400 600 800 1000
0 2 4 6 8 10 12
transport [Sv]
(a) inflow−SD500 inflow−REF inflow−SD100
KE−SD500
KE− REF KE−SD100
36 38 40 42 44
<S> [psu]
16 17 18 19 20
<T> [
oC]
(b)
T−SD500 T−REF T−SD100
S−SD500 S−REF S−SD100
−2 0 2 4 6 8 10
ψ
z[Sv]
−2 0 2 4 6 8 10
ψ
z[Sv]
(c)
min
ψ
z−SD500
min
ψ
z−REF
min
ψ
z−SD100
max
ψ
z−SD500
max
ψ
z−REF
max
ψ
z−SD100
0 200 400 600 800 1000
time [year]
3.2. Impact of sill-depth changes
Fig.4: Zonal cross-sections (at ZZ’ in Fig.1a);
of the salinity fields averaged over the last 10 years of integration for the different
experiments, (a) SD100, (c) REF, and (e) SD500.
Fig.5: Same as Fig.4 but for the zonal overturning circulation, arrows indicate the sense of the flow,
positive value corresponds the clockwise circulation.
0 500 1000 1500
Depth [m]
42.44
42.54
42.64
42.74 42.84
42.94
42.94
SD100 (a)
0 500 1000 1500
Depth [m]
37.12
37.22 37.4237.3237.52 37.62
37.62 37.62
37.72
(c) REF
0 500 1000 1500
Depth [m]
−15 −10 −5 0 5 10 15 20 25 30 35
Longitude
36.18 36.2836.38
36.38
36.48
36.48 36.48
36.48
36.58 36.58
SD500 (e)
0 500 1000 1500
Depth [m]
−1−0.5−0.5 0
0
0.5 0.5
1 1
1.5 2
3
(a)
SD100
0 500 1000 1500
Depth [m]
−1−0.5 0 0.5
0.5
1 1
1.5
1.5 2
2 2.5
2.5
3 3.5
4
(c) REF
0 500 1000 1500
Depth [m]
−15 −10 −5 0 5 10 15 20 25 30 35
Longitude
−0.5
0
0
0.5
1
1.5 1.5
2 2
2.5 2.5
3 3
3.5
3.5
4
4 4.5
5.55
SD500 (e)
34.5 36.0 37.5 39.0 40.5 42.0
Salinity [PSU] −4 −2 0 2 4 6 [Sv]ψ
40
45
Latitude
0 5 10 15 20 25 30 35
Longitude 40
45
-15 -10 -5 5 10 15 20 25 30 35
500 1000 1500
Depth [m]
-15 -10 -5 0 5 10 15 20 25 30 35
Longitude
Q E-P
DW
IW AW
MOW
40
45
Latitude
0 Longitude 5 10 15 20 25 30 35 40
45
-15 -10 -5 5 10 15 20 25 30 35
500 1000 1500
Depth [m]
-15 -10 -5 0 5 10 15 20 25 30 35
Longitude
Q E-P
DW
IW AW
MOW IW
DW
40
45
Latitude
0 5 10 15 20 25 30 35
Longitude 40
45
-15 -10 -5 5 10 15 20 25 30 35
500 1000 1500
Depth [m]
-15 -10 -5 0 5 10 15 20 25 30 35
Longitude
E-P Q
DW- IW AW
MOW
