Evidence of Upwelling at the Northern
Patagonian Shelf Break
Daniel Valla
Alberto R. Piola
SAC-D/Aquarius 10th Science Meeting,
Buenos Aires, 17-19 November 2015
SAC-D/Aquarius 10th Science Meeting,
Buenos Aires, 17-19 November 2015
Outline
Motivation
Data
Results:
•
Temporal variability at the shelf break
•
Shelf break upwelling: a case study
•
Biological impact
Summary & Conclusions
SAC-D/Aquarius 10th Science Meeting,
Buenos Aires, 17-19 November 2015
MOTIVATION
[ml/l]
Satellite-derived surface chlorophyll-a
concentration (spring)
Summer satellite-derived surface chlorophyll-a
concentration (summer)
Romero et al., J. Geophys. Res., 2006
HYPOTHESIS AND QUESTIONS
SAC-D/Aquarius 10th Science Meeting,
Buenos Aires, 17-19 November 2015
Hypothesis: increase of nutrients in the photic zone is
associated with negative temperature anomalies in the
mixed layer
What mechanisms lead to temperature variability at the
shelf break?
What is the importance of horizontal and vertical
advection in generating cool anomalies?
IN-SITU DATA
B
A
SITE B
(165 days)
SITE A
(51 days)
RESULTS: Cross-shelf Structure
SITE A
SAC-D/Aquarius 10th Science Meeting,
Buenos Aires, 17-19 November 2015
Valla and Piola, J. Geophys. Res., 2015
Temporal variability – Site A (43.8 °S)
Temperature
Salinity
SAC-D/Aquarius 10th Science Meeting,
Buenos Aires, 17-19 November 2015
Temporal variability – Site A (43.8 °S)
SAC-D/Aquarius 10th Science Meeting,
Buenos Aires, 17-19 November 2015
Temperature
Salinity
Temperature vs cross-shore velocity
Temperature vs salinity
Upwelling event – Site B (41 °S)
T
S
Cross-shore
Long-shore
SAC-D/Aquarius 10th Science Meeting,
Buenos Aires, 17-19 November 2015
Upwelling event
~500km
SAC-D/Aquarius 10th Science Meeting,
Buenos Aires, 17-19 November 2015
~500km
Upwelling event – physical mechanisms
SAC-D/Aquarius 10th Science Meeting,
Buenos Aires, 17-19 November 2015
Tm
Q0
Tm
Tm
 Tm  T H 

Um
 Vm
 W H 

t
C p H
x
y
 H

Local changes
Air-Sea heat flux
Horizontal advection
~ -1.5 °C/day
~ 0.21 °C/day
~ -0.04 °C/day
Vertical advection
W-H ~ 13 – 29 m/day
Consistent with high-res models
(Combes and Matano, JGR, 2014)
Upwelling event – physical mechanisms
SAC-D/Aquarius 10th Science Meeting,
Buenos Aires, 17-19 November 2015
Este
Norte
Schematic circulation
(source: Matano et al., Ocean Sci., 2010)
Shelf break upwelling scheme
(source: Matano and Palma, J. Phys. Oceanogr., 2008)
Biological impact of cooling events
SAC-D/Aquarius 10th Science Meeting,
Buenos Aires, 17-19 November 2015
Surface cooling decrease
from T = 14.5°C to T = 11.5°C
[NO3] increases ~ 5.5 μmol l-1
Mean [NO3] at shelf break
on January is ~6 μmol l-1
(Signorini et al., Geophys. Res.
Lett., 2006)
log10 [NO3] = -0.003999 T2 + 0.009954 T + 1.488
(after Signorini et al., NASA Tech. Memo, 2009)
Other cooling events
 Cooling events
detected as extreme
SST anomalies
 Characterized by
enhanced cooling
and positive (into the
ocean) surface heat
flux
 75 % of cooling
events are concurrent
with chlorophyll
increase
SAC-D/Aquarius 10th Science Meeting,
Buenos Aires, 17-19 November 2015
Summary
SAC-D/Aquarius 10th Science Meeting,
Buenos Aires, 17-19 November 2015
In-situ temperature, salinity and velocity data provided evidence of
shelf break upwelling during an extreme cooling event. The
surface temperature decrease extended ~500 km along the outer
shelf.
Surface heat fluxes and horizontal advection play a minor role in
generating the surface temperature decrease. A vertical velocity
of 13-29 m/day is necessary to sustain the recorded cooling
Other cooling events where detected as SST anomalies over the
outer shelf and shelf break. 75% are concurrent with surface
chlorophyll increase.
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