Reading Questions
Lavery et al. 2010. Iron defecation by sperm whales stimulates carbon export in the southern
ocean. Proceedings of the Royal Society B 277: 3527-3531.
1) The first line of the paper reads, “The balance between photosynthesis and
respiration…determines whether the ocean acts as a sink or source of atmospheric
carbon.” In your own words, restate what the authors mean. Try to make answer no
longer than one paragraph.
a. Answer will vary slightly. Basic idea: The ratio of photosynthesis (the removal of
atmospheric C-CO2 by marine organisms) to respiration (the release of C-CO2
back to the atmosphere by marine organisms) will determine if oceans remove or
add more C to the atmosphere.
2) Why is deep ocean storage of carbon important?
a. Deep ocean storage is a long-term form of carbon storage and for the most part
can only re-enter the biosphere via tectonic activity. In comparison, carbon stored
in organisms (e.g. trees) is considered short-term storage. From a global climate
change perspective long-term storage is ideal to balance our use of fossil fuels
(i.e. using a long-term stored type of C very quickly).
3) The authors state that the southern oceans are ideal for studying the effects of iron
fertilization because of abundant nitrogen. Why is the abundance of nitrogen
important in these studies (reference Hungate et al. paper from reading for ideas)?
a. C and N do not cycle independently. For organisms to uptake and metabolize C
they must have a supply of N in part to support the required enzyme production.
4) Why is it important that the authors are studying iron defecation in the photic zone
as opposed to greater depths for example where zooplankton remove waste?
a. Because phytoplankton meet their C demands via photosynthesis a light requiring
reaction.
5) The authors acknowledge that their calculations are equivalent to the removal of
only 0.05% of the carbon added via fossil fuel burning annually. It is fair to assume
that this is insignificant from a global perspective. However, at the end of the paper
the authors mention that the wide-scale harvesting of whales has reduced iron
inputs by 450 tonnes annually. If we assume that 486 tonnes (450 + 36) of iron once
persisted in the photic zone how much more fossil fuel-derived carbon could be
account for? To try and answer this question you will need to try and perform some
creative math; but, keep it simple. Hint: try and use some of the numbers provided
for by the authors at the end of the Results section and beginning of the Discussion.
There are multiple ways to initially investigate this question.
a. Answers will vary
b. Useful information: Molecular weight of Iron = 55.5 g/mole and 1 Tonne = 1,000
kg
c. One example: Authors state: 3x1010 moles C export with 106 moles Fe persistent
in photic zone. Assume 486 (from above) is persistent = 486000000 g Fe =
8.7x106 moles.
d. This example calculation would not significantly raise the amount of fossil fuel
carbon that could be sequestered.
6) Is this increase enough to consider the conservation of ocean mammals important
for carbon sequestration and climate change?
a. Answers will vary.