Variation of the Euphotic Zone Depth in the South China Sea and the Tropical Pacificis there any con

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Variation of the Euphotic Zone Depth in the South
China Sea and the Tropical Pacific-is there any
connection?
Workshop on Western Tropical Pacific, Guangzhou,
2007

• Shaoling Shanga, Zhongping Leeb
• a State Key Laboratory of Marine Environmental
  Science, Xiamen University,Xiamen 361005, China
  slshang_at_xmu.edu.cn slshang_at_gmail.com
• b Naval Research Lab, Code 7333, Stennis Space
  Center, MS 39529, USA
• zplee_at_nrlssc.navy.mil

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• Introduction
• Measurements of the Euphotic Zone Depth (Ze)
• Validation of Remote Sensing Ze
• Seasonal change of Ze in the South China Sea and
  the tropical Pacific
• Interannual change of Ze in the South China Sea
  and the tropical Pacific
• Concluding remarks

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Introduction
Where light is sufficient for phytoplankton
production by photosynthesis to exceed the loss
of material that takes place through respiration

• Euphotic Zone depth (Ze)
• -a cumulative measure of biogeochemical
  properties of the upper-water column
• Will changes of Ze depict
  environmental patterns, especially those
  associated with the climate?

ecosystem dynamics, air-sea interaction
(transfer of either heat or materials, such as
CO2)
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• There have been some reports on the changes in
  the SCS associated with ENSO-
• Warm event Wang et al., 2002
• Cold tongue Liu et al., 2004
• Upwelling Xie et al., 2003 Tang et
  al., 2007
• -based on SST, SSH, wind, Chl
• Our target is to see if there is any change of Ze
  in the South China Sea (SCS) and the tropical
  Pacific (TP) and if there is any connection
  between them.

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2. Measurements of the Euphotic Zone Depth (Ze)

• Practical definition of Ze
• -the depth at which PAR (photosynthetic
  available radiation) value is 1 of the surface
  value
• In situ
• Ze3.05 x Secci depth
• rPAR(z)/PAR(0), when r0.01, zZe
• Remote sensing
• Empirical Zef(Chl) e.g.
  Morel, JGR,1988
• Semi-analytical Zef(IOP) Lee et al.,
  JGR, 2007

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Ze34.0x (Chl)-0.39 Morel
Comparison of empirical algorithms
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Kvis(Ze) Ze4.605
4.605/Zek1k2/(1Ze)0.5
Ze
a, bb
Lee et al., JGR, 2007
QAA
Rrs
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3. Validation of the Euphotic Zone Depth
Validation in the Gulf of Mexico, the Arabian Sea
and the Monterey Bay
Upper empirical Chl centered approach Bottom
semi-analytical IOP centered approach
Lee et al., JGR, 2007
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Validation over the China Sea
The East China Sea
The Taiwan Strait
The South China Sea
Chen et al., Proceedings of SPIE, 2007
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Comparison between in situ Ze and Lee-approach
results in the East China Sea (aspring ,
bautumn)
IOP
Chl
Comparison between in situ Ze and Chl-approach
results in the East China Sea (aspring ,
bautumn)
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Chl
IOP
Comparison between in situ Ze and IOP and
Chl-approach results in the Taiwan Strait
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IOP
winter
summer
Comparison between in situ Ze and IOP- and
Chl-approach results in the South China Sea
in winter and summer
Chl
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Comparison between the Ze derived from Rrs and in
situ Ze from PAR profiles in different seas
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4. Seasonal change of Ze in the South China Sea
and the Tropical Pacific
Data used- 1) Sep.1997-Sep.2007, 9 km
resolution SeaWiFS monthly mean Rrs (L2) derived
Ze (IOP approach) SeaWiFS monthly mean Chl
(L3) 2) Jan. 1997-Dec.2006, 9 km resolution AVHRR
monthly mean SST (L3)
Western Tropical Pacific (WTP)
Eastern Tropical Pacific (ETP)
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01
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Monthly Climatology of Ze in the South China Sea
(1998-2006)
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01
03
03
08
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Monthly Climatology of Ze in the tropical Pacific
(1998-2006)
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The South China Sea (SCS)
Mean values Patterns Magnitude of change
All different
Comparison of the Ze monthly changes among the
three regions
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Comparison of the Chl monthly changes among the
three regions
ETP relatively productive, weak seasonality
e.g. Pennington et al., 2006 SCS productive
in winter e.g. Tseng et al., 2005 WTP low
production, strong seasonality e.g. Bricaud et
al., 2002
Ze is determined by the extinction coefficient
(K). K is affected by the amount of CDOM,
detritus and Chl Lalli Parsons, 1993. That
why we see the differences of Ze in the three
regions.
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5. Interannual change of Ze in the South China
Sea and the Tropical Pacific
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Monthly change of Ze in the SCS
Annual mean change of Ze in the SCS
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See different patterns in the 1997-1998 and the
2006-2007!
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6. Concluding remarks

• Ze calculate from Rrs was compared with in situ
  data to evaluate the accuracy of IOP-centered
  approach in the Gulf of Mexico, the Arabian Sea,
  the Monterey Bay and the China Sea. The
  IOP-centered approach has higher accuracy
  compared to Chl-approach, thus has great
  advantages.
• SeaWiFS Ze time series in the SCS and the TP were
  thus derived from this IOP-centered approach.
  Different seasonal patterns in the SCS and the
  tropical Pacific are revealed.
• Changes of Ze in the SCS and the TP during the
  two El Nino events 1997-1998 and 2006-2007 are
  quite different. It seems that there are links
  between the changes of these two regions but the
  mechanism may be different in different periods.

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• Thank you!