Deon Louw presentation - Benguela Current Commission

Deon Louw presentation - Benguela Current Commission

Detecting phytoplankton dynamics in the central Benguela
current upwelling ecosystem off Namibia by using in situ
chlorophyll-α measurements.
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Ministry of Fisheries and Marine Resources & Leibniz Institute for Baltic Sea Research Warnemünde
D.C. Louw
Anja Eggert
Anja van der Plas
Volker Mohrholz
Objectives
• Longterm variability of chlorophyll [ ]
• Quantifying phytoplankton blooms
• Seasonality of phytoplankton blooms/peaks
Methods/Data
0
Depth (db)
-100
-200
-300
70
60
50
40
30
Distance offshore (nm)
20
10
0
Month 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
2 30-Jan-01 2-Feb-02 1-Feb-03 27-Jan-04 11-Feb-05
28-Jan-10
3 1-Mar-01 28-Feb-02 4-Mar-03
8-Mar-05 3-Mar-06
6-Mar-08 25-Feb-09 10-Mar-10 14-Mar-11
4 3-Apr-01 No Data 15-Apr-03 28-Mar-04
28-Mar-06
13-Apr-08 1-Apr-09 8-Apr-10 12-Apr-11 16-Mar-12
5 1-May-01 29-Apr-02 13-May-03 12-May-04 12-May-05
7-May-07
28-Apr-09
No Data
6 4-Jun-01 4-Jun-02 12-Jun-03 1-Jun-04
30-May-06
28-May-08
26-May-10 17-May-11
7 3-Jul-01 9-Jul-02 1-Jul-03 29-Jun-04 30-Jun-05 4-Jul-06 10-Jul-07 1-Jul-08 29-Jun-09 12-Jul-10 7-Jul-11
8 31-Jul-01 4-Aug-02 8-Aug-03 5-Aug-04
31-Jul-08
9 5-Sep-01 3-Sep-02 4-Sep-03 31-Aug-04 2-Sep-05 28-Aug-06 3-Sep-07 5-Sep-08 20-Aug-09
8-Sep-11 4-Sep-12
10 2-Oct-01 1-Oct-02 1-Oct-03 29-Sep-04
13-Oct-08 16-Sep-09
9-Oct-12
11 6-Nov-01 29-Oct-02 4-Nov-03 2-Nov-04 8-Nov-05 1-Nov-06 6-Nov-07
30-Oct-09 27-Oct-10
6-Nov-12
12 4-Dec-01 5-Dec-02 10-Dec-03 30-Nov-04 2-Dec-05
6-Dec-07 6-Dec-08 1-Dec-09 2-Dec-10 Not Data 29-Nov-12
Temperature
(15m & 10nm station)
70nm
(15m)
40nm
10nm
Jul99
10nm Station
Jul00
Jul01
Jul02
Jul03
Jul04
Jul05
Jul06
Jul07
Jul08
Jul09
Jul10
Jul11
Jul12
Temperature (Seasonality)
Summer
• Stratified
• >16°C
• Strong thermocline
Nutrients
Upwelling
• Mixed
• < 13°C
Autum/Winter
• Mixed
• 13°-16°C
Nutrients
Summer
• Stratified
• Weak Thermocline
Nu
tri
en
ts
Chlorophyll (Stations)
Variability high
Decrease in chlorophll offshore direction
2nm station not as high as expected (mixing/turbulents/waves)
5-20nm stations simallar biomass (highest production)
30-70nm stations (lowest production)
0
10
20
30
-1
Chl a [µg L ]
40
50
•
•
•
•
•
70nm
60nm
50nm
40nm
30nm
20nm
10nm
5nm
2nm
Longterm trend/variability
0
200
400
-2
Chl a [mg m ]
600
• Interannual variability high
• not a significant trend
2001
01/02
02/03
03/04
04/05
05/06
06/07
07/08
08/09
09/10
10/11
11/12
2012
Phytoplankton Blooms (surface)
Raw Readings
Major Blooms
Minor Blooms
18.4 µg/L
12.9µg/L
Define Blooms
Constant threshold value
• Mean (12years) + 2SD´s, = MajBl
• MinBl= Remove MajBl &
recalculate as above
Constant threshold = understanding the long
term changes in biomass
(Kim et al, 2009)
Phytoplankton Blooms (surface)
Raw Readings
Major Blooms
Minor Blooms
18.4 µg/L
12.9µg/L
Constant threshold = understanding the long
term changes in biomass
Defined Blooms
Constant threshold value
• Mean + 2SD´s, above the long
term mean (12years) = MajBl
• MinBl= Remove MajBl &
recalculate as above
(Kim et al, 2009)
Climatology of Chl [ ]
Median
Major Blooms
Minor Blooms
9.96 µg/L
8.12 µg/L
LATE SUMMER PEAKS
• Larger bloom
• Spread over larger area
• Major peak is sub-surface
SPRING PEAKS
• Sub-surface
• Spread almost
homogenically
EARLY SUMMER PEAKS
• Closer to the surface
• January ????
Peaks
• April/May (summer/Autum)
• August (Spring Bloom)
• December (Beginning summer)
800
0
200
400
-2
-2
Chl a [mg m ]
600
April/May
April/May
August/September
August/September
December
December
2001
01/02 02/03 03/04 04/05 05/06 06/07 07/08 08/09 09/10 10/11
11/12
2012
Summary
•
Inshore stations showed significant similarities
• High Chl [ ] inner shelf
• Low Chl [ ] offshore
• Variability of Chl is high
Blooms
Not high frequency of major blooms as well as minor blooms (missing data)
Initiation of blooms does not end up in a Minor Bloom or Major Bloom
Seasonality
April/May Peak (Late summer)
• Not a direct consequence of upwelling but rather the breakdown of the thermocline due to
cooling of the atmospheric system
• Largest blooms
• Largest contributor to annual biomass
• Sub-surface blooms
August Peak (Upwelling)
• Directly due to upwelling
• Biomass lower
• Mixing high
• Sub-surface Chl maxima (minor bloom)
December Peak (Early Summer)
• Closer to the surface