hw6_upwelling_lab_2023 1
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Oregon State University, Corvallis *
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Course
201
Subject
Geography
Date
Apr 3, 2024
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Pages
8
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Biological Oceanography Lab 3/Homework 6 Mooring data from a coastal upwelling system Due on Wednesday, May 17
th
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: 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. Date
N-S Wind [m s
-1
]
SST [
°
C]
CO
2
[ppm]
Chlorophyll [mg m
-3
]
15-Feb-99
-1.50
11.55
11.42
2.23
16-Feb-99
-1.95
11.46
18.01
2.14
17-Feb-99
-0.89
11.55
34.52
2.00
18-Feb-99
-1.51
11.52
32.65
1.84
19-Feb-99
-1.37
11.57
22.74
1.69
20-Feb-99
-1.42
11.60
-6.89
1.67
21-Feb-99
-1.29
11.39
14.93
1.66
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•
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) At least three events up upwelling and three events of downwelling/relaxation. 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) -9.00
-8.00
-7.00
-6.00
-5.00
-4.00
-3.00
-2.00
-1.00
0.00
1.00
2.00
8.00
8.50
9.00
9.50
10.00
10.50
11.00
11.50
12.00
12.50
15-Feb-99
15-Mar-99
15-Apr-99
15-May-99
N-S Wind [m s-1]
SST [°C]
Dates
SST [°C] and N-S Wind [m s-1]
SST [°C]
N-S Wind [m s-1]
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) 8.00
8.50
9.00
9.50
10.00
10.50
11.00
11.50
12.00
12.50
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
15-Feb-99
15-Mar-99
15-Apr-99
15-May-99
Chlorophyll [mg m-3]
SST [°C]
SST [°C] and Chlorophyll [mg m-3]
Chlorophyll [mg m-3]
SST [°C]
8.00
8.50
9.00
9.50
10.00
10.50
11.00
11.50
12.00
12.50
-150.00
-100.00
-50.00
0.00
50.00
100.00
150.00
200.00
250.00
300.00
350.00
15-Feb-99
15-Mar-99
15-Apr-99
15-May-99
SST [°C] CO2 [ppm]
Dates
SST [°C] and CO2 [ppm]
CO2 [ppm]
SST [°C]
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) When STT decreases, this indicates to us that upwelling is taking place. When upwelling is happening, chlorophyll will then increase. We can see a lag on the graph between the decrease in the temperature and the increase in chlorophyll, however there is a lag as it takes time to show such effects. When STT is decreasing, then the CO2 is increasing. CO2 is brought to the surface from upwelling. Chlorophyll needs time to grow from the increase in nutrients, as water comes from the depths and the cells haven’t been exposed to lag in awhile, hence the delay. 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) The CO2 in the atmosphere is even higher since 1999, over 400. Less CO2 means less photosynthesis, meaning the chlorophyll get less energy. The peaks in chlorophyll lag a bit behind the peaks of CO2. This is because when there is a peak in CO2, there is upwelling. Hence, with more upwelling, comes more chlorophyll after a bit of a lag. This is because chlorophyll need time to grow and gain nutrients to then eventually reach a bloom in the end. Primary productivity and upwelling increases the CO2. 0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
-150.00
-100.00
-50.00
0.00
50.00
100.00
150.00
200.00
250.00
300.00
350.00
15-Feb-99
15-Mar-99
15-Apr-99
15-May-99
Chorophyll [mg m-3]
CO2 [ppm] Dates
CO2 [ppm] and Chorophyll [mg m-3]
CO2 [ppm]
Chlorophyll [mg m-3]
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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) We can see around three to four upwelling events, as the first one seen on the graph is seen to be pretty small. However, as seen on the last graph in the blue line, the later three are larger. We also have to take relaxation into account when looking at deciphering upwelling events. 5.
By moving your cursor over the lines you plotted in the wind/SST plot, calculate the average lag between when the winds start to become upwelling-favorable and when the response is observed in SST. (1 point) As seen in the first graph of wind and SST, the average lag between when the winds start to become upwelling-favorable is two-five days. Format of your answer to the questions such it appears as a result section (like in the literature) and not like just answers to questions: In Results, present your plots - be sure to label the axes properly, make the plots a decent size, and give each plot a figure legend that describes what it is showing. Then just answer the questions above. (2 points for overall format) Notes: Report format, answer questions and add captions to figure. Don’t include the questions. Answer what is plotted. Just results in the report and then the graphs/captions and answers to the questions. Explanation of what is in your figure. On a separate page, in addition to your report, please answer the following questions (21 points) 1.
Consider the Peruvian upwelling system
. (7 points) a)
Which direction do the upwelling-favorable winds blow to? (1 point) Equatorward, roughly from south to north. Slides 13 b)
Which direction (say roughly N, S, E or W) is the resulting Ekman transport? (1point) c)
Compare the magnitude and variability of the upwelling-favorable winds in the Peru upwelling system to those in the Canary upwelling system. (2 points) d)
If the thermocline were to become depressed (deeper) due to, say, an El Ni
ñ
o event, what might this do to the concentration of nutrients in the upwelled water (assuming upwelling is still occurring)? Explain why. (2 points) e) Which species of fish is the focus of the Peruvian fishing industry? (1 point) 2.
Consider the equatorial Pacific
: (6 points) a) Which direction do the trade winds blow to? (1 point)
b) Assuming this induces Ekman transport, in which direction (N, S, E or W) will the Ekman transport be just to the north of the equator? (1 point) c) In which direction (N, S, E or W) will the Ekman transport be just to the south of the equator? (1 point) d) What happens to the water right at the equator (as a result of your answers to 2 a-c), and how does this influence (i) phytoplankton productivity and (ii) CO
2 fluxes? Explain (i) and (ii) keeping in mind that this region is a HNLC region. (3 points). 3.
What happens during El Ni
ñ
o events at the Equator? Describe the changes that occur in (i) trade winds, (ii) upwelling, (iii) phytoplankton productivity and (iv) CO
2 fluxes. (4 points) 4.
Consider eddies in the northern hemisphere, such as those observed spinning off the Gulf Stream or in the lee of the Hawaiian Islands. (4 points) a)
Which direction does the water circulate around a warm-core eddy? (1 point) b)
Which direction does the water circulate around a cool-core eddy? (1 point) c) Which type of eddy (warm or cool) is likely to have higher productivity in the center? Why? (2 points)