The Canary Islands CTZ region: Ecosystem response to the interplay between upwelling filaments, eddies and island wakes
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The Canary Islands CTZ region: Ecosystem
response to the interplay between upwelling
filaments, eddies and island wakes
Javier Arístegui1, Eric D. Barton2, Pablo Sangrá1, Evan Mason1
1Facultad de Ciencias del Mar, Universidad de Las Palmas de Gran Canaria, Spain
NASE
2Instituto de Investigaciones Marinas de Vigo, CSIC, Spain
CTZ
Outline
! Zonal gradients along the Coastal Transition Zone
! The island-lee region: convergence and divergence fronts
! The eddy field south of the islands
! Biological response to cyclonic and anticyclonic eddies
NASE
! Interactions between eddies and filaments
CTZ
! Role of eddies in carbon export
! Tracking filaments: frontal structures and temporal evolution
! Modelling the mesoscale and submesocale in the Canary region
! Conclusions and way forward
The Coastal Transition Zone region
Madeira
! Transition zone between the eutrophic waters of
NASE the Canary Current Coastal Region and the
C. Ghir oligotrophic waters of the North Atlantic
Subtropical Gyre (NASE)
Canary Islands
! Region of intense mesoscale & submesoscale
C. Jubi variability, and filament-eddy exchanges
CTZ C. Bojador ! Represents a significant carbon source and
offshore pump to the open ocean
C. Blanc Africa
SST
P
The range of variation in P-E parameters is of E
the same magnitude as ranges observed in
basin-scale studies in the Atlantic Ocean.
! : 0.03 – 0.053 (mixed layer)
Pm : 0.60 – 13.02 (mixed layer)
P
Basterretxea and Arístegui 2000, MEPS E
28.5
Gran Canaria Fuerteventura
28.0
Latitude (N)
27.5 Prochlorococcus Pigment biomarkers
20
21
17 Haptophytes 25.64 44.10
19 18 14 Pelagophytes
27.0
41 Diatoms
42 Africa 12
Integrated values (mg m-2)
Prasinophytes
18 19 37 38 39 40 Cryptophytes
26.5 10
Temperature (ºC)
8
16.0 15.5 15.0 14.5 14.0 13.5 13.0 6
Longitude (W)
4
Station numbers
18 19 37 38 39 40 41 42 2
max. 3.5
0
18 19 37 38 39 40 41 42
50
Coastal-ocean replacement of diatoms
d e pth (m )
DCM
100
by smaller phytoplankton
150
200
Open Ocean (NASE) Canaries CTZ Coastal Upwelling
Summer
Strong upwelling
Spring
Weaker upwelling
Baltar et al. 2009, PiO
Summer
Strong upwelling
Larger phytoplankton
Spring
Weaker upwelling
More phytoplankton
…but smaller
Baltar et al. 2009, PiO
Cyclonic Eddy
! Wakes at the lee of the islands
! Cyclonic eddies
Wake ! Anticyclonic eddies
Filament ! Upwelling filaments
Anticyclonic
Eddy
The NW Africa-Canary CTZ region represents an exceptional laboratory to
study oceanographic processes at mesoscale and submesoscale!
Night Night Day Evening-Night
CE
Warm wake: diurnal heating cycle
Weak variability with semi-diurnal period
Barton et al. 2000, JGRNight Night Day Evening-Night
CE
Trichodesmium
Warm wake: diurnal heating cycle
Phaeocystis-like
Accumulation of positive-buoyant phytoplankton
Barton et al. 2000, JGRWind rows AVHRR sea surface temperature SAR: wind shear boundaries Field wind from SAR backscatter intensity Barton et al. 2000, JGR
Trade Winds Ekman transport Ekman transport
Section 1 Section 2
Leeward Leeward
Convergent and divergent frontal regions (with upwelling
and downwelling of 10-20 m d-1) are generated by the wind
shear zones extending from the flanks of the island
Basterretxea et al. 2002, DSRSection 1 Section 2
Leeward Leeward
Convergent and divergent frontal regions (with upwelling
and downwelling of 10-20 m d-1) are generated by the wind
shear zones extending from the flanks of the island
Basterretxea et al. 2002, DSRThe eddy field south of the Canary Islands
C F
C !Island eddies are formed by the
combination of flow-perturbation
A
F
and Ekman pumping forced at the
A
C
C wind-shearing zones
A
F
A
C A !Interaction between island-eddies
F
and the coastal jet may induce the
C A
A
development of upwelling filaments
C. Bojador
A
F SST
C A F August, 1999
C : Cyclonic eddy
A : Anticyclonic eddy
F : Upwelling filamentBiological consequences of cyclonic eddies
D’ D
Eddy center
50
100
150
200
Total chlorophyll a (!g l-1)
Depth (m)
20
40
60
80
100
Fucoxanthin (ng l-1)
20
40
60
80
100
Divinyl chlorophyll a (!g l-1)
Cyclonic eddies inject nutrients into the euphotic zone,
increasing primary production and promoting changes in
plankton community structure
Barton et al. 1998, PiOBiological consequences of cyclonic eddies
F
CE
AEBiological consequences of cyclonic eddies
Nitrate (uM)
16.2 16.0 15.8 15.6 15.4 15.2 15.0
F
CE
AEBiological consequences of cyclonic eddies
F
CE
AEContribution of cyclonic eddies to nitrate fluxes
Cyclonic eddies contribute as much
as coastal upwelling to nitrogen fluxes
Barton et al. 1998, PiOBiological consequences of anticyclonic eddies!
Canary Islands
Cyclonic
Eddy
Anticyclonic
Eddy
CZCS Chlorophyll
Anticyclonic island-eddies entrain and transport
chlorophyll-rich upwelling waters Arístegui et al., 1997, DSRBiological consequences of anticyclonic eddies!
Anticyclonic eddies accumulate and sink
down organic matter in their cores,
increasing respiration rates
Arístegui et al., 2003, AMEFrontal regions between eddies: POM distribution!
Accumulation of POC at interface layers
In the deep oceanFrontal regions between eddies!
66
66 70
70
More than 6 times increase in Bacteria at Station 66…
(front between CE and AE)Frontal regions between eddies!
H/L 64
65
0,0 0,2 0,4 0,6 0,8 1,0 1,2
66
0
67
100 68
69
200 70
300 71
72
Depth (m)
400 73
74
500
75
600 76
77
700 78
800 79
80
900 81
82
1000
83
…but they are mostly Low Nucleic-Acid Bacteria
(less active?)POC (!M)
Canary Islands
2 C. Juby
8
32 22 14
C. Bojador
Africa
SeaWIFS
Chlorophyll C. Blanc
How important is the contribution of eddies to the
global carbon export ?
(both to the deep ocean and to the open ocean)Propagation of a SWESTY (Pingree, 1994 )
SWESTY: anticyclonic Shallow subtropical subducting WEStward-propagating eddY
Sangrá et al., 2009, DSR31 Jul
Sedimentation of Chla
Centre of filament
Perihery of filament
Sea Surface Temperature (21 Aug 2009)6
4
Sedimentation of Chla
Centre of filament
Perihery of filament
Sea Surface Temperature (21 Aug 2009)
!"
,,)-'("*.*#/'"*)&00.
1)23#$)4"'5"'6
!"#$%&'()*&'(&+
Filament poleward front
convergence
#"
!"#$%&'###()"*+,-./0)1223)
Compression of planetary
vorticity tubes
anticycloneD4 D3
D6 D5 D2
D1D4 D3
D6 D5 D2
D1
Microplankton Nanoplankton PicoplanktonD4 D3
D6 D5 D2
D1Cape Guir, 1992
C. Juby, 1999
mmolO2 m-2 d-1
mmolO2 m-2 d-1
P/R
P/R
GP/R >1 GP/RCyclonic Eddy
SST
August 1993
Wake
Filament
Anticyclonic
Eddy
Near surface currents Zooplankton biomass
28.5
N
28.0
27.5
27.0
26.5
Chlorophyll a Neritic larvae
Barton et. al. 1998 26.0NW Africa UW Filaments Canary Is.
Year
Catches Larvae Catches
1993 Sardina pilchardus S. pilchardus S. pilchardus
1999 Engraulis encrasicolus E. encrasicolus E. encrasicolus
Sardinella aurita S. aurita S. aurita
2001
Sardina pilchardus S. pilchardus S. pilchardus ( ! )
Moyano et al. 2009, Fish Ocean! Large domain
" 10 years
" 11–km resolution
" Includes open Strait of
Gibraltar
! Intermediate domain
" 6 years
" 5-km resolution
! Small domain
" 2 years
" 1-1.5-km resolution! Develop a ROMS configuration for the
Canary Island region
" ROMS: 3D, primitive equation,
hydrostatic model (Shcheptekin &
McWilliams, 2005)
! Study the evolution and generation
mechanisms of eddies and upwelling
filaments
" Topographic forcing
" Wind forcing1.5-km domain: Compare low vs. high resolution wind
Climatological wind stress forcing Atmospheric model (MM5)
Mason et al. (in prep)Vorticity-1-km resolution.
1-km domain embedded
within a 3 Km domain
Side boundary forcing:TS
climatology with
geostrophic velocities
25-km SCOW wind stress
climatology and COADS
surface fluxes
Mason et al. (in prep)Conclusions & Way Forward ! The Canary region is an excellent laboratory to study the influence of submesoscale ocean dynamics on the marine ecosystem and biogeochemical cycles ! The interplay between (island) eddies and upwelling filaments enhance production and may export coastal enriched water to the open ocean through POC sedimentation and transport by an eddy corridor ! Little is known about the effects and global magnitude of submesoscale dynamics on transient productivity and carbon fluxes events ! Novel instrumentation (e.g autonomous vehicles and drifters with new generation of optical sensors) and processes-oriented studies at the submesoscale are necessary to understand the mechanisms of carbon production, exchange and transport in CTZ ! ROMS does good job of reproducing submesoscale variability in response to both topographic and wind forcing ! Biogeochemical ROMS modules should be incorporated to address productivity and carbon fluxes in the region
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