High resolution time-space variability of satellite chlorophyll

Report
High resolution time-space
variability of satellite
chlorophyll-a in the coastal and
coastal transition zones off
central-southern Chile (33-42ºS)
PERU-CHILE CURRENT SYSTEM
Carmen E. Morales - Samuel Hormazabal
Isabel Andrade - Marco Correa-Ramírez
Universidad de Concepción
P. Universidad Católica de Valparaíso
CHILE (FONDECYT 1120504)
Bathymetry
(m)
BACKGROUND
COASTAL ZONE OFF CENTRAL-SOUTHERN CHILE
CHARACTERIZED BY HAVING A STRONG SEASONALITY
IN WIND-DRIVEN UPWELLING PROCEESES,
CHLOROPHYLL-a CONCENTRATION AND
PHOTOSYNTHETIC PRIMARY PRODUCTION.
DATA SETS FOR CHLOROPHYLL-a:
- IN SITU SNAPSHOTS FROM DIFFERENT STUDIES
- IN SITU FIXED TIME SERIES STATION (ST. 18 OFF
CONCEPCION) SINCE 2002
- REGIONAL SATELLITE TIME SERIES (100, 9, AND 4 km)
NEW TOY TO PLAY WITH:
HIGHER RESOLUTION SATELLITE DATA
MOTIVATION
CONSIDERING A HIGHER RESOLUTION DATA, WHICH ARE THE
MOST SIGNIFICANT SCALES OF TIME-SPACE VARIABILITY IN
PHYTOPLANKTON BIOMASS ALONG THE COAST AND ACROSSSHORE?
MEAN VALUES 2002-2012
SST (ºC)
Wind stress (N m-2)
wind stress curl (10-7 N m-3)
Chl-a (mg m-3)
*
*
*
APPROACHES AND METHODS
DATA - Time series satellite data: 2002-2012
Chlorophyll-a (OC3 algorithm, Werdell 2009) and SST: daily and 1X1 km
resolution, MODIS Aqua mission (http://oceancolor.gsfc.nasa.gov/).
Note: 5 d average and DINEOF interpolation (Alvera-Azcárate et al. 2007)
Surface wind: wind stress and wind stress curl: daily and 25x25 km
resolution, Cross-Calibrated Multi-Platform Surface Ocean Wind product
(CCMP); (ftp://podaac-ftp.jpl.nasa.gov/allData/ccmp/L3.0/).
ANALYSIS
Multi-Taper Method - Singular Value Decomposition- (MTM-SVD)*
 Time-space variability of the main frequencies of Chl-a or other:
• graphs of local fractional variance (LFV) and their significance
• percentage of the variance explained by each frequency in different
areas within the region of study (spatial reconstruction of the
variance)
• oscillation patterns in each frequency (phases and signal
propagation)
* Correa-Ramírez & Hormazabal, 2012 (doi:103856/vol40-issue4-fulltext-19)
MAIN FREQUENCIES OF VARIABILITY OF CHL-a
Dominant frequencies of variability in Chl-a: semi-annual,
annual, and inter-annual
Similarities in the variability of frequencies between the
coastal band (<100 km) and the whole region (coast + CTZ)
CONTRIBUTION OF THE DOMINANT FREQUENCIES OF
CHL-a VARIABILITY IN THE SPACE DOMAIN
INTER-ANNUAL
ANNUAL
SEMI-ANNUAL
ANNUAL CYCLE OF CHL-a (anomalies)
WINTER
SPRING
SUMMER
AUTUMN
MAIN FREQUENCIES OF VARIABILITY
CHL-a, SST, AND WIND
Coastal Chl-a
Coastal SST
ANNUAL CYCLE OF (anomalies)
WIND STRESS (color) AND WIND STRESS CURL (grey line)
WINTER
SPRING
SUMMER
AUTUMN
PATTERNS OF CHL-a, SST, Wind VARIABILITY - COASTAL
Chl-a
SST
Wind
forcing
NIÑO
NIÑA
NIÑO NIÑA
EL NIÑO 3.4
CONCLUSIONS
Dominant frequency of Chl-a variability in the region: annual
– associated with wind and SST variability
Higher (inter-annual) and lower (semi-annual) frequencies
also important but beyond the coastal band.
In the coastal band, the patterns of the annual phytoplankton
cycle:
i) An alongshore propagation of the Chl-a increase
ii) a strong latitudinal zonation of the Chl-a  2 breaks in
continuity (at ~37 and 40°S, two main upwelling centers).
In the CTZ, the highest mean Chl-a (>0.5 mg/m3) extended
out to ~200 km offshore in the northern region (33-38°S)
whereas it was about half that width in the southern region
(38-42°S) associated to a change in wind stress and wind
stress curl.
PUZZLE
Offshore annual cycle of Chl-a in opposite phase with
coastal Chl-a (Yuras et al., 2005). Between the coast and
the offshore, a band of ~60-80 km with no significant
annual variability  annual increase in Chl-a in the coastal
band does not propagates to offshore waters.
Implications:
Chl-a increases in the CTZ depend on in situ growth of
phytoplankton (no advection from coast) -- a process most
likely linked to eddy pumping via mesoscale eddies.
Assumption: eddy generation has no annual frequency!
IS THAT TRUE ???
OTHER EXPLANATIONS?????

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