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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
.
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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)
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)
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)
Results:
^ Fig. 1 – We can see in Figure 1 of at least three events of upwelling and three events of downwelling/relaxation. As seen in Figure 1, a negative N-S wind vector suggests that there will be southerly winds, which may trigger coastal upwelling. Winds force surface waves away from the beach, allowing cold, nutrient-rich water to come to the surface from deeper depths. This may result in a decline in SST along the coast. SST changes, on the other hand, are influenced by a number of factors, including ocean currents, atmospheric conditions, and geographical location. While a negative N-S wind vector might contribute to coastal upwelling and lower SST along the coast, other factors that influence SST patterns in a given region must also be taken into account.
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^ Fig. 2 – We can see in Figure 2 the relationship between SST and Chlorophyll. It seems like an inverse relationship. As the SST decreases in temperature, we can see an increase in chlorophyll mass.
Upwelling brings the nutrients so the chlorophyll increases.
When STT declines, it implies that upwelling is occurring. When there is upwelling, chlorophyll levels rise. On the graph in Figure 2, there is a lag between the fall in temperature and the increase in chlorophyll, but there is a lag because such effects take time to appear. When STT decreases, CO2 increases; CO2 is delivered to the surface through upwelling. Because water originates from the depths and the cells haven't been exposed to lag in a long time, chlorophyll requires time to thrive from the increase in nutrients, hence the delay. ^ Fig. 3 – We can see in Figure 3 the relationship between SST and CO2. A period of upwelling when we have the CO2 of the ocean is larger than the amount of CO2 in the atmosphere.
Since 1999, the amount of CO2 in the atmosphere has increased by 400%. Less CO2 equals less photosynthesis, which means less energy for chlorophyll. The chlorophyll peaks are slightly behind the CO2 peaks. This is because there is upwelling when CO2 levels are high. As a result, more upwelling results in more chlorophyll after a
slight delay. This is because chlorophyll requires time to develop and absorb nutrients before blooming. CO2 levels rise due to increased primary output and upwelling.
^ Fig. 4 – We can see in Figure 4 the relationship between CO2 and Chlorophyll. The trend seems to be relatively similar to each other in their increases and decreases in trend lines, however not exactly. In Figure 4, we can see three to four upwelling events, as the first one seen on the graph is quite modest. The latter three, however, are larger, as seen on the last graph in the blue line. When attempting to comprehend upwelling phenomena, we must also consider relaxation. As seen in the first graph of Figure 1 comparing the wind and SST, the average lag between when the winds start to become upwelling-favorable is two-five days.
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, flowing from south to north as seen in Case Study 2 in the notes. b)Which direction (say roughly N, S, E or W) is the resulting Ekman transport? (1point) It is going away from the shore, so West as seen in the diagram in our notes. 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)
The Canary has the strongest yet variable winds with a mini “spring bloom” between wind events, while Peru is the most consistent with low wind speed variability, 50% weaker than the Canary winds. d)If the thermocline were to become depressed (deeper) due to, say, an El Niño event, what might this do to the concentration of nutrients in the upwelled water (assuming upwelling is still occurring)? Explain why. (2 points)
In El Ni
ñ
o conditions, there would be decreased productivity, meaning less nutrients, as thermocline variability impacts source waters. There
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would be a deep Z
MLD
. We can also see there is less chlorophyll and fish.
e) Which species of fish is the focus of the Peruvian fishing industry? (1 point) The Peruvian anchoveta, Engraulis ringens is 4% of Peruvian GDP, however there’s a huge decrease during El Nino. 2.
Consider the equatorial Pacific
: (6 points)
a) Which direction do the trade winds blow to? (1 point) For the equatorial Pacific, they blow from East to West.
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)
It will cause an Ekman spiral, and will be to the right, or East of the wind direction in the Northern Hemisphere. c) In which direction (N, S, E or W) will the Ekman transport be just to the south of the equator? (1 point) The Ekman transport will be to the left of the wind direction when
just South of the equator, so slightly towards the West. 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). There would be equatorial upwelling, and a divergence at the surface. It brings nutrient-rich waters from the deep ocean to the
surface for the phytoplankton, increasing the productivity for them and the other organisms above them, as well as promoting carbon dioxide uptake leading to increased CO2 fluxes and potential carbon sequestration in the deep ocean. There is also an increase of iron from the upwelling for the phytoplankton to use to carry out photosynthesis.
3.
What happens during El Niño 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)
In the Equatorial Pacific, some of the changes from El Ni
ñ
o are ~20-fold change in productivity, a huge impact on CO2 flux processes, and a detectable impact on global CO2 levels; as a result, the supply of nutrients to the surface waters is reduced during El Niño events. El Niño disrupts the normal upwelling process in the equatorial Pacific. The weakened trade winds reduce the strength of the upwelling, leading to a decrease in the upwelling of nutrient-rich waters from the deep ocean to the surface. As a result, the supply of nutrients to the surface waters is reduced during El Niño events. During El Niño, the trade winds weaken or even reverse.
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) In warm core eddies (anticyclonic), they spin clockwise. b)
Which direction does the water circulate around a cool-core eddy? (1 point) In a cool-core eddy (cyclonic), the water circulates counterclockwise.
c) Which type of eddy (warm or cool) is likely to have higher productivity in the center? Why? (2 points)
The cool eddy since the warm core ring ones have low chlorophyll content, meanwhile the cold core rings (cyclonic) have high productivity and more nutrients coming up from the
depths into the euphotic zone, with phytoplankton using these
nutrients. Within a warm/anticyclonic eddy, nutricline becomes deeper leading to less productivity. Falkowski et al showed that eddies in general enhance productivity.