Diapycnal Nutrient Fluxes in the Cape Ghir upwelling region

Arcos-Pulido, M.; Rodríguez Santana, Ángel; Emelianov, Mikhail; Paka, V.; Aristegui, J.; Sangrá Inciarte, Pablo; Machín Jiménez, Francisco José; García Weil, Luis

Abstract

An oceanographic survey was carried out from 18 to 29 October 2010 in the Canary Basin (PROMECA project). Near Cape Ghir, in the Northwest Africa coastal upwelling, 17 CTD casts were made to obtain continuous records of conductivity and temperature with depth, and to collect waters samples for nutrients analyses. Additionally, free-fall turbulence profiles were obtained at each station. 14 Expandable bathythermographs (XBTs) were deployed between stations to increase the grid resolution of the temperature field. Velocity data were acquired with a vessel-mounted Acoustic Doppler Current Profiler (ADCP) with a vertical bin size of 8 m. Water samples for nutrients: nitrate + nitrite (N+N), phosphates and silicates, were collected from 12 depths (down to 2000 m or the maximum depth), with 12-l Niskin bottles mounted on the rosettes sampler. The first results show low to moderate concentrations of nutrients offshore, with average values in the upper 150 m of 2.45 +- 1.98, 0.37 +- 0.18 and 1.47 +- 0.94 M for N+N, phosphate and silicate, respectively. However, for stations near the Cape Ghir upwelling filament or influenced by this feature, a significant increase in the concentration of nutrients (up to 10 M of N+N at 200 m) was observed. We have estimated and compared the diapycnal nutrient flux in the region by using two different approaches. First, we used the dissipation rates of turbulent kinetic energy and thermal variance estimated from microstructure data acquired from turbulence profilers, and applied a model based on the dissipation ratio. This way we obtain net turbulence diffusivities in regions where there is an interaction of processes of double diffusion and turbulence induced by vertical shear of the flow. The second approach is based on obtaining diapycnal diffusivities with parameterizations of the gradient Richardson number and density ratio.

Diapycnal Nutrient Fluxes in the Cape Ghir upwelling region

Author: Arcos-Pulido, M.,Rodríguez Santana, Ángel,Emelianov, Mikhail,Paka, V.,Aristegui, J.,Sangrá Inciarte, Pablo,Machín Jiménez, Francisco José,García Weil, Luis

Year: 2012

Source: https://accedacris.ulpgc.es/jspui/bitstream/10553/10150/2/0680215_00000_0000.pdf

Geophysical Resea ch Abs ac s
Vol. 14, EGU2012-12760-3, 2012
EGU Gene al Assembly 2012
© Au ho (s) 2012
Diapycnal Nu ien Fluxes in he Cape Ghi upwelling egion
M. A cos-Pulido (1), A. Rod íguez-San ana (1), M. Emeliano (2), V. Paka (3), J. A ís egui (4), P. Sang à (4), F.
Machín (1), and L. Ga cía-Weil (1)
(1) Depa amen o de Física, Uni e sidad de Las Palmas de G an Cana ia, Fisica, Las Palmas de G an Cana ia, Spain
([email p o ec ed]), (2) Ins i u o de Ciencias del Ma , CSIC, Ba celona, Spain, ([email p o ec ed]),
(3) Shi sho Ins i u e o Oceanology, Kalining ad, Russia, ([email p o ec ed]), (4) Ins i u o Uni e si a io de Oceanog a ía
y Cambio Global (IOCAG), Uni e sidad de Las Palmas de G an Cana ia, Las Palmas de G an Cana ia, Spain,
([email p o ec ed])
An oceanog aphic su ey was ca ied ou om 18 o 29 Oc obe 2010 in he Cana y Basin (PROMECA p ojec ).
Nea Cape Ghi , in he No hwes A ica coas al upwelling, 17 CTD cas s we e made o ob ain con inuous eco ds
o conduc i i y and empe a u e wi h dep h, and o collec wa e s samples o nu ien s analyses. Addi ionally,
ee- all u bulence p o iles we e ob ained a each s a ion. 14 Expandable ba hy he mog aphs (XBTs) we e
deployed be ween s a ions o inc ease he g id esolu ion o he empe a u e ield. Veloci y da a we e acqui ed
wi h a essel-moun ed Acous ic Dopple Cu en P o ile (ADCP) wi h a e ical bin size o 8 m. Wa e samples
o nu ien s: ni a e + ni i e (N+N), phospha es and silica es, we e collec ed om 12 dep hs (down o 2000 m
o he maximum dep h), wi h 12-l Niskin bo les moun ed on he ose es sample . The i s esul s show low o
mode a e concen a ions o nu ien s o sho e, wi h a e age alues in he uppe 150 m o 2.45 ±1.98, 0.37 ±
0.18 and 1.47 ±0.94 µM o N+N, phospha e and silica e, espec i ely. Howe e , o s a ions nea he Cape Ghi
upwelling ilamen o in luenced by his ea u e, a signi ican inc ease in he concen a ion o nu ien s (up o 10
µM o N+N a 200 m) was obse ed.
We ha e es ima ed and compa ed he diapycnal nu ien lux in he egion by using wo di e en app oaches.
Fi s , we used he dissipa ion a es o u bulen kine ic ene gy and he mal a iance es ima ed om mic os uc u e
da a acqui ed om u bulence p o ile s, and applied a model based on he dissipa ion a io. This way we ob ain
ne u bulence di usi i ies in egions whe e he e is an in e ac ion o p ocesses o double di usion and u bulence
induced by e ical shea o he low. The second app oach is based on ob aining diapycnal di usi i ies wi h
pa ame e iza ions o he g adien Richa dson numbe and densi y a io.