Fill This Form To Receive Instant Help

Help in Homework
trustpilot ratings
google ratings

Homework answers / question archive / Chemical Oceanography Problem #1

Chemical Oceanography Problem #1


Chemical Oceanography
Problem #1.– Nutrient limitation


Aerosols generated from local forest fires are deposited in the surface waters of a nearby oligotrophic marine bay, raising dissolved concentrations of sea surface phosphate to 0.5 µM and nitrate to 10 µM. A cyanobacteria bloom of Synechoccocus grows as a result until the phytoplankton become macronutrient limitation.


a. Calculate the expected concentrations of dissolved inorganic phosphorous, dissolved inorganic nitrogen, dissolved inorganic carbon (DIC), and O2 in these surface waters at the end of the bloom. State all assumptions used.



b. Provide a quantitative estimate of how much [CO32-] changed by the end of the bloom. Do the surface water conditions at the end of the bloom favor or disfavor calcite precipitation relative to pre-bloom conditions?


Problem #2.  – Organic matter remineralization


Organic matter containing 0.02 moles of C is added to a 1 liter sample of deep water from the North Pacific. The bacteria in the sample respond and consume the organic matter drawing on the oxygen in the sample (100 µM O2).  If we assume Redfield ratios:


a. Which will run out first, C or O2?


b. How much CO2 will be produced?


c. How much dissolved inorganic nitrogen and dissolved inorganic phosphorous will be produced?


d. After measuring the final concentration of NO3, you find these are lower than your estimates of how much NO3 was produced. What process may account for that difference?

Problem #3.  – Nitrogen budget


When O2 concentrations are very low, organisms that depend on respiration cannot grow and continue to oxidize organic matter. Some marine bacteria and archaea can use NO3- as an electron acceptor to oxidize organic matter in place of O2, producing N2 and CO2 as end products. This process, termed ‘denitrification’ is one of the main removal mechanisms of fixed nitrogen from the ocean.


a. Fill in the remaining stoichiometric coefficients in the following overall denitrification reaction.


4HNO3 + 5CH2O à __CO2 + __H2O + __N2


b. You measure the concentration of dissolved NO3- in an oxygen minimum zone off of the Oregon Coast. Although you expect to find 40µM NO3- based on estimates from apparent oxygen utilization, you only measure 30µM NO3-. You expect that this deficit of 10µM NO3- is due to denitrification. Using the stoichiometries above, estimate the change in DIC in these waters due to denitrification.


c. Expected phosphate concentrations in these waters were 2µM prior to denitrification. Calculated the dissolved phosphate concentration in the oxygen minimum zone after denitrification took place (Assume Redfield ratio, i.e. that the organic matter degradation releases 1 mole of phosphate per 106 moles of DIC).


d. Soon after you make your measurements, waters in the OMZ upwell to the surface, supplying nutrients to the photic zone that drive a phytoplankton bloom. What nutrient is expected to limit the net productivity of the bloom? Provide calculations that justify your answer.



Problem #4. - Characteristics of Marine Snow


Measurements of sinking particles in the surface tropical Pacific (temperature of 25 oC, density of 1025 kg/m3) reveal they have an average settling velocity of 200 meters per day and an average diameter of 0.2 mm. 


a. Using Stoke’s Law, calculate the density of the average particle.


b. Knowing that on a volume basis the particles are made up of 90% seawater and 10% solid material (mixture of organic matter, carbonate, opal), calculate the density of the solid component.


c. Knowing that organic matter has a density of 1050 kg/m3 and that calcite and opal have a density of 2500 kg/m3, calculate the contributions of biominerals (calcite + opal) and organic matter to the solid particle mass.


d. Chemical analyses reveal the particles contain organic carbon and inorganic carbon in a 2:1 mole ratio. Knowing that organic matter is on average 50% C by mass and that calcite is 12% C by mass, calculate the contributions of calcite and opal to the solid component.  Express the contributions of organic matter, calcite and opal as a mass fraction (% of total solid mass).


Option 1

Low Cost Option
Download this past answer in few clicks

19.99 USD


Already member?

Option 2

Custom new solution created by our subject matter experts