FINISHEDhw6_upwelling_lab_2023
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Apr 3, 2024
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OC340 ~ Biological Oceanography
Lab 3/Homework 6 Mooring data from a coastal upwelling system
Due on Wednesday, May 17
th
(Total: 46 Points) The goal of this exercise is to understand the atmospheric and oceanic processes that characterize coastal upwelling systems.
Introduction:
The data we will be working with come from MBARI, the Monterey Bay Aquarium Research Institute, located in Moss Landing, CA (www.mbari.org).
The Biological Oceanography Group at MBARI operates several moorings in Monterey Bay, designated M1, M2 etc…
Today we’ll be working with data from the mooring called M1, located about 10 miles from shore, latitude 36.75°N, longitude 122.03°W. The following images show you what the mooring looks like.
As we learned in class, the California Upwelling system is seasonal. In the south (say, south of Santa Barbara), upwelling occurs almost year-round because winds are upwelling-favorable (equatorward) almost all year long. However, in the northern part of the upwelling system, the winds are only upwelling-favorable in the Spring and Summer. The following two images of surface chlorophyll illustrate strong upwelling with productive conditions (left) and absent upwelling conditions (right).
Today we’ll focus on data from Spring/Summer 1999 – a particularly strong upwelling year. The parameters we’ll be plotting are winds, sea surface temperature (SST), chlorophyll and sea surface CO
2
concentration.
The data:
Data were downloaded from www.mbari.org, see hw7_upwelling_lab_2021.xls
. A sample of the data is shown below:
D
a t e
N
- S
W
i n d [ m
s
- 1
]
S
S
T [ ° C
]
C
O
2
[ p p m
]
C
h l o r o p h y l l [ m
g m
- 3
]
1
5
- F
e
b
- 9
9
- 1
. 5
0
1
1
. 5
5
1
1
. 4
2
2
. 2
3
1
6
- F
e
b
- 9
9
- 1
. 9
5
1
1
. 4
6
1
8
. 0
1
2
. 1
4
1
7
- F
e
b
- 9
9
- 0
. 8
9
1
1
. 5
5
3
4
. 5
2
2
. 0
0
1
8
- F
e
b
- 9
9
- 1
. 5
1
1
1
. 5
2
3
2
. 6
5
1
. 8
4
1
9
- F
e
b
- 9
9
- 1
. 3
7
1
1
. 5
7
2
2
. 7
4
1
. 6
9
2
0
- F
e
b
- 9
9
- 1
. 4
2
1
1
. 6
0
- 6
. 8
9
1
. 6
7
2
1
- F
e
b
- 9
9
- 1
. 2
9
1
1
. 3
9
1
4
. 9
3
1
. 6
6
Let’s examine the columns.
Date
is self-explanatory.
N-S wind
is the component of the wind in the north-south direction [m s
-1
], called ‘v’.
The component in the E-W direction is ‘u’ (not shown here). Because of the orientation of the California coast, and the Coriolis force, winds are upwelling favorable when they blow towards the south (southeast actually). The more negative the N-S wind component, the greater the potential for upwelling.
SST
is simply the sea surface temperature [°C] measured by a temperature sensor at about 1m depth, which is attached to the mooring structure.
CO
2
is the difference between ocean and atmosphere CO
2
concentration, in units of parts per million [ppm]. The difference is calculated as CO
2[ocean]
– CO
2[atmosphere]
, so positive values indicate that ocean CO
2
is greater than atmospheric CO
2
.
Chlorophyll
is the concentration of chlorophyll at the surface. This could be measured by several different types of optical devices attached to the mooring, but in this case the data have been extracted from the SeaWiFS satellite. That is, an automated script was used to search the satellite data files for the chlorophyll pixels closest to the M1 location.
Your tasks:
1.
Make a plot of winds and temperature vs. time. Plot the two parameters on the same chart but with different y-axes so that you can see the variability in each, or
make two separate plots, one on top of the other. Make sure that you label the axes with the name of the parameter and its units, and make sure that the font size is large enough so that the plot will be readable in your report. (3 points)
2.
Now that we have established the relationship between winds, which drive the upwelling, and SST, which is a signature of upwelling occurring, make a plot of SST (the physical phenomenon) and chlorophyll (the biological response). (3 points) Upwelling brings the nutrients so the chlorophyll increases.
3.
Make a plot of SST and CO
2
, so that you can see how these two parameters vary (or not) together. (3 points)
4.
Finally, make a plot of Chl and CO
2
, so that you can see how these two parameters vary (or not) together. (3 points)
Questions:
1.
General trends:
What is the relationship between N-S wind strength and SST? That is, explain what a negative N-S wind vector means, what it does to the ocean, and the signal it produces in SST. (3 points)
2.
What happens to chlorophyll and CO
2
when SST starts to decrease? Explain in terms of upwelled water nutrient and CO
2
content. (2 points)
3.
What do you observe in terms of timing of the peaks (maxima) of chlorophyll and
CO
2 between March 1 and May 1, 1999? Explain the relationship between chlorophyll and CO
2
. Think about what upwelling does to CO
2
and what increased
productivity does to CO
2
. (2 points)
4.
Focusing on the period from 15-Feb-1999 to 01-May-1999, how many separate upwelling ‘events’ can you identify? Approximately when do each of them begin?
Your answers should be based on when you see the SST respond to the upwelling-favorable N-S wind. (3 points)
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