biogeochemical budget through the strait...

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