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Primary Production measurements over a daily cycle in Clarks Cove. Ayan Chaudhuri, Lin Zhang, Anne-Marie Brunner MAR640 – Global Marine Biogeochemistry. The aim of this experiment. Measuring primary productivity in Clarks Cove using

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primary production measurements over a daily cycle in clarks cove

Primary Production measurements over a daily cycle in Clarks Cove

Ayan Chaudhuri, Lin Zhang,

Anne-Marie Brunner

MAR640 – Global Marine Biogeochemistry

MAR640 - Project

the aim of this experiment
The aim of this experiment
  • Measuring primary productivity in Clarks Cove using
    • Light bottle/dark bottle technique to measure O2 with a Massspectrometer
    • d18O-Method
    • Organic Carbon and Nitrogen measurements
    • Nutrient measurements
  • establishing a box model for carbon fluxes in this Cove

MAR640 - Project

clarks cove
Clarks Cove
  • It has an average water depth of 12ft (Very shallow)
  • remains well mixed by tidal and wind events year round
  • Hill, 1998 found nutrient levels lower in Buzzards Bay than in Narragansett Bay
  • Hill, 1998 for Buzzards Bay measured a primary productivity in Nov/Dec between 8-26mgC m-3h-1(his figure 18, station 6)

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measuring primary productivity the theory
Measuring Primary Productivity –The Theory
  • Light Bottle/Dark Bottle Oxygen
    • a. Light bottle O2 minus initial O2 concentration is net community production. In the absence of heterotrophs, the difference is net primary production.
    • b. Dark bottle O2 concentration minus initial O2 concentration is respiration
    • c. Light bottle minus dark bottle is gross community production.
    • Incubation time: 3hrs
    • Sampling every 3 hours during the day, 5hours at night
    • Using a massspectrometer for higher accuracy

MAR640 - Project

d18o method
  • During the incubation time the gross production produces O2 in the water with the same, enriched ratio as the water. Therefore, the ratio of 18O to 16O is enriched in the dissolved O2 pool, as the tagged O2 mixes with the large O2 pool. Thus, the change in the 18O of dissolved O2 can be used as a measurement of gross production. (Bender et al., 1987). The O2 consumed during respiration has a lower d 18O than the dissolved O2
  • 18O/16O value of a gas with a d18O value, relative to SMOW (standard mean ocean water) would be 0.002005220.

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conversion to primary productivity
Conversion to primary productivity
  • carbon (mg) * 32 * PQ = oxygen (mg) * 12;
  • where PQ = photosynthetic quotient, the ratio of moles of oxygen released to moles of carbon fixed; its value depends on whether nitrate or ammonia is available as a nitrogen source, and varies from 1.0 to 1.3; here 1.2

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measuring primary productivity the experiment
Measuring Primary Productivity –The Experiment
  • Starting at 7am on the 30th of November we conducted the first sampling. Further sampling times were at 10am, 1pm, 4pm, 9pm, 2pm and 7am.
  • Light Bottles (not at 4, 9 and 2) , Dark Bottles and initial bottles were sampled and incubated in the seawater.
  • At the first sampling, also dark and light bottles for the daylight cycle (9hrs) were incubated.
  • Bottles were labeled with 18O and some samples with 13C for incubation.

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problems during the experiment
Weather conditions were good, although cloudy, it was calm. At 2am,1st December, a storm started with increasing wind speeds and light drizzle until noontime, the second half of our experiment.

Also, our setup for our bottle measurements started to fail around 2 am, so results are questionable during that time.

Some data were lost for the bottles at 10am, 30th November.

Jellyfish were seen in the sampled water

Problems during the Experiment

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  • Light Bottle/Dark Bottle O2 measurements
  • 18O Results
  • Particulate Organic Matter Results
  • Nutrient Results

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bottle measurements
Bottle Measurements
  • Initial Bottle O2/Ar ratios, low at daybreak, moves up during the day, back to low at sunset and after.
  • Light Bottle O2/Ar ratios, rises during day, should fall to zero by sunset.
  • Dark Bottle O2/Ar ratios, falls during the day and rises after sunset

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  • GPP mostly negative
  • More respiration than production
  • Average pools all light, dark and initial bottles into respective means
  • NPP comparable to thesis by Hill

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  • System as a whole is net heterotrophic
  • very less carbon is available for fixation
  • Sources

- Tidal Inflow

- Sediment re-suspension

- atmospheric deposits


- Tidal outflow

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del o18 method
Del O18 Method
  • 450 uL of H2O enriched in 18O
  • The 18O enrichment of the dissolved O2 is taken to be a proportional measure of gross production
  • 9% enrichment – biased estimate

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pom filter results

Both Carbon and Nitrogen follow the tidal cycle, but results are biased

After the onset of the storm.

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c n ratios
C/N ratios

Results are much higher than the classical Redfield Ratio of 6.6. Also

Results behave contrariy to the tidal cycle and highest results are found

At times with highest windspeeds.

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d 13 c and d 15 n
d13C and d15N

During incoming tide, both d increase and decrease with the arrival of the ebb.

Notice the strong increase in d13C with during the high windspeed values during

1st December, 2004.

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results for the enrichment with 13 c
Results for the enrichment with 13C


A first order process is assumed to

take place and simulate the procss

Of primary productivity:

d[C]/dt = -k*t with k= 0.03809102 hrs-1

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results from a graph
Results from a graph

Carbon uptake: -8.082 mC m-3/hr

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box model results
Box Model results

Atmospheric input


Tidal flushing

Benthos, Sediment resuspension

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atmospheric deposition
Atmospheric Deposition

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  • 11mg C m-3 –hr or
  • with the light/dark bottle method, which resulted in an net primary productivity in the same range

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tidal flushing
Tidal Flushing
  • in one hour 2,357 m3 are replaced. The average Carbon Concentration during daylight hours, or the calm weather period was calculated to be 78.525 mg C m-3.
  • Tidal flushing of 1.5 days
  • strong dependence of the behavior with the tidal cycle.

MAR640 - Project


MAR640 - Project

  • Like theconcentrations of nutrients follow a daily cycle, the POM values generally coincident with a tidal cycle. However, the change of C/N values shows an opposite cycle to the tidal cycle, with incoming tides, the C/N ratio decreases, and increases with outgoing tides. The above results lead to a conclusion that the phytoplanktons carry out photosynthesis when there is available light and consume the nutrients in the seawater based on the Redfield ratio. So the concentrations of nutrients decrease during the day as we got from the experiment. But POM values didn’t increase as expected when there is photosynthesis. In the night, phytoplanktons consume O2 and release CO2, the concentrations of nutrients increased due to no consumption. There should be some productivity in the Cove from the above results.

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  • The results of quad method show some interesting differences. The O2/Ar ratio in the initial bottle increases during the day which means there is O2 released and decreases in the night which means respiration leads to a decreasing of O2. However, the ratio from light bottles is always increasing during the experiment period, indicating discrepancies during measurement. The result from dark bottles is also beyond expectation. The ratios dipped from a significant high all through the day, however steadily rising by evening. The whole results show a common trend in that the entire system seems to have more respiration than production, Which is totally opposite to the nutrients and POM analysis.

MAR640 - Project