BIOGEOCHEMICAL BUDGET THROUGH THE STRAIT OF GIBRALTAR, A MODELLING STUDY
BIOGEOCHEMICAL BUDGET THROUGH THE STRAIT OF GIBRALTAR, A MODELLING STUDY
Macías, D. (1),, Bruno, M.(2) , Echevarría, F. (1,3), Vázquez, A.(2),García, C.M. (1)
(1) Biology Department. University of Cádiz(2) Applied Physics Department. University of Cádiz
(3) Centro Andaluz de Ciencia y Tecnología Marinas (CACYTMAR)
AREA OF STUDY
1/15
AREA OF STUDY
1/15
AREA OF STUDY
14 km250 m
2/15
ALONG STRAIT CIRCULATION
TWO LAYER FLUX OVER THE SILL
3/15
ALONG STRAIT CIRCULATION
INTERNAL WAVE GENERATION
TIDE RISING IN THE ATLANTIC
INTERFACIAL MIXINGBUDGETS ALTERATION 4/15
DIMENSION OF THE PHENOMENON
-200
-150
-100
-50
-200
-150
-100
-50
-200
-150
-100
-50
Salinidad (p.s.u.)
Temperatura (ºC)
Clorofila (mg/m3)
35
35.6
36.2
36.8
37.4
38
38.6
1313.51414.51515.51616.517
00.651.31.952.63.253.94.55
a)
b)
c)
HW+6 HW-4 HW-2 HW HW+2 HW+4 HW+6 HW-4 HW-2 HW HW+2 HW+4
1 2 3 4 5 6 7 8 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37
1 2 3 4 5 6 7 8 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37
HW+6 HW-4 HW-2 HW HW+2 HW+4 HW+6 HW-4 HW-2 HW HW+2 HW+4
1 2 3 4 5 6 7 8 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37
HW+6 HW-4 HW-2 HW HW+2 HW+4 HW+6 HW-4 HW-2 HW HW+2 HW+4
Complicate patterns on the spatio-temporal distribution of physical and biogeochemical variables
Undetermined effect of interfacial mixing on the element budgets between Mediterranean and Atlantic basins.
NECESITY OF APPROPIATED MODELS TO REPRESENT TIDAL FORCINGS AND MIXING EVENTS !!
5/15
6/15
PHYSICAL MODEL
-6 -5.8 -5.6 -5.4 -5.2 -5
35.6
35.8
36
36.2
36.4
Gibraltar
Tarifa
CeutaTanger
Data of:* Upper layer velocity* Lower layer velocity* Upper layer thickness
START POINT: 2 layer-2D hydrodynamical model (Izquierdo et al, 2001)
Main problems:* Two-layered model* Hydrostatic (no w velocities)
THREE LAYER APPROACH
Sigmoid fitting
Velocity
h1
Dep
th
u1u2
1
2
Velocity
h1
Dep
th
u1u2
1
2
3
u3
h3
The interfacial layer is the region where a steep change in the vertical velocity profile occurs (3).
PHYSICAL MODELIMPROVEMENTS OF THE MODEL …
7/15
8/15
Interface
Dep
th
Along strait distance
W E
Upper layer velocity
Lower layer velocity
Density
h1
δ
Interface
δ/2
δ/21 m
Nbefore
Ndeep
( )( )
25.0*)()(
)1(0
221
12 <−−
=ρ
ρρ gtutu
Ri
22121
21
22 ))()(()()2( tutuKg −<− ρρρρ
⎟⎟⎠
⎞⎜⎜⎝
⎛ −−+−= δ*
*4)1(
)1()(1htNN
tNtN deep
PHYSICAL MODEL
ESTIMATIONS OF MIXING AND ADVECTION
The mixing and advection estimations are made by using data from the physical model
IMPROVEMENTS OF THE MODEL …
Macias et al., 2007 (PiO)
ESTIMATIONS OF MIXING AND ADVECTION
Upper layer salinity
PHYSICAL MODEL
9/15
Modeled and measured salinity(Three layer approximation)
Time relative to HW at Tarifa
Sal
inity
(p.s
.u.)
36,0
36,5
37,0
37,5
38,0
Field data
HW+5 HW-5 HW-3 HW-1 HW+1 HW+3 HW+5 HW-5 HW-3 HW-1 HW+1 HW+3 HW+5
Two layer simulation
The fitting between the model and the field data is improved, in shape and in the correlation coefficient (R = 0.91).
PHYSICAL MODELModel results and field data comparison
Three layer simulation
10/15
N P
Z1
1)(*
hNN
K deepmix
−
PJQ pµ
pGpG)1( β−
pGβ Pmp 1hPkmix
ZkZm
z
z
+Ω−
2*)1(
ZkZm
z
z
+Ω
2*
1hZkmix
TYPE OF MODEL
BIOGEOCHEMICAL IMPLICATIONS
High physical forcing!!!Tiny differences with complex models
11/15
BIOGEOCHEMICAL IMPLICATIONSELEMENTS BUDGET
Atlantic water
Mediterranean water
Atlantic water
Mediterranean water
0.87 Sv; Low nutrients
0.83 Sv; High nutrients
Mediterranean tends to oligotrophy
Injection of nutrients in the upper layer as a function of the
tidal amplitude
Average nitrate in upper layer (mmol N/m3)
Tidal height (m)0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6
0
2
4
6
8
R = 0.71
(N)
12/15
ELEMENTS BUDGET
BIOGEOCHEMICAL IMPLICATIONS
N flux towards the Mediterranean
Days0 15 30 45 60 75 90 105120135150165180195210225240255270285300315330345360
g-at
N/s
0
1000
2000
3000
4000
5000
6000
Tidal height (m)
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
Days256 258 260 262 264 266 268 270272 274 276278 280 282 284
g-at
N/s
0
1000
2000
3000
4000
5000
6000
Tidal height
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
Neap tides
Spring tides
13/15
% of nutrient recirculation
Tidal height (m)0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6
0
10
20
30
40
50
60
R = 0.71
Average = 14%
ELEMENTS BUDGET
BIOGEOCHEMICAL IMPLICATIONS
Potential effect on CO2 sequestration and ecosystem development !
Propose future scenarios based on expected conditions of water fluxes !
14/15
CONCLUSIONS AND FINALS REMARKSTidally induced processes (interfacial mixing and water fluxes …..) are of particular importance to asses the biogeochemical budgets at the Strait of Gibraltar (i.e Mediterranean Basin)
To adequately resolve tidal forcing at the Strait it is necessary to use models as a predictive tool due to the high frequency of such processes
We know that meteorological forcing (atmospheric pressure) is of capital importance for water fluxes, internal waves generation and hydrological patterns in Alboran Sea incorporate that forcing to the model
2D coastal-channel interactions should be important in the Strait. The model is being expanded in a 2D framework following the same mixing and three layer scheme
15/15