3. Exploring the relationship between past atmospheric dust deposition, climate, and biological productivity in the North Pacific ocean

Dust deposition is directly related to climate in a number of ways in that:

1. most of the global dust flux is derived from deserts, which expand and contract with climate change;
2. dust production varies with the cube of the wind speed (Duce, 1995), which varies in turn with climate;
3. dust impacts earth’s radiative budget;
4. dust removal from the atmosphere occurs by both wet and dry deposition (Hand and others, 2004), such that the amount of precipitation can influence the distance dust is transported (up to thousands of kilometers).

The portion of global dust deposition that reaches the ocean (roughly one quarter of global production) (Jickells and others, 2005) can have a profound impact on biogeochemical processes in the ocean, and potentially on climate. This is because many sources of dust contain iron, a limiting nutrient in 30–40% of the ocean (Moore and others, 2002).

Addition of iron-containing dust in these areas can cause phytoplankton blooms and uptake of CO₂ from the ocean surface. It is not known whether iron addition to the ocean leads to significant long-term removal of CO₂ from the atmosphere (Buesseler and Boyd, 2003), but this is an active area of research. Indeed, John Martin proposed many years ago that iron addition to the ocean, during glacial periods, may have contributed to the large reduction in atmospheric CO₂ at that time. This question is not fully resolved. Furthermore, researchers and private companies alike are asking whether iron addition to the modern-day ocean might help to sequester CO₂ from the atmosphere, although this process is not well understood. It is possible that deposition of iron-bearing dust could serve as a negative feedback on climate, leading to a reduction in atmospheric CO₂ and in global temperature.

One of the best ways we can evaluate possible future impacts of iron addition to the ocean surface, be it from natural dust sources or intentional, anthropogenic addition, is by studying the paleoclimate record. However, such efforts are limited by a lack of long term, high-resolution records of dust deposition to iron-limited regions of the ocean. This opportunity seeks to address this limitation of our current understanding.

A primary goal of this opportunity is to develop one or more well-dated, high-resolution records of atmospheric dust deposition in the North Pacific region extending, if possible, back to the last deglaciation. One available archive for dust records includes cores from ombrotrophic peat bogs in coastal Alaska. These are bogs which receive all of their water and nutrients (and hence dust) from atmospheric deposition. This opportunity would involve deriving records of dust concentration and accumulation from analyses of thorium-232 and aluminum. Another important component of the research will involve developing a reliable high-resolution chronology based on AMS C-14 measurements on saturated aliphatic hydrocarbons of leafwax origin (Huang and others, 1999). This approach will be pursued due to difficulties with C-14 dating of bulk organic matter, and other materials, in peat. This record of dust deposition will be related to other climate proxies, including pollen records (developed by D. Peteet) that will be available from these cores. Beyond the basic scope outlined above, this Mendenhall fellow could pursue any of several possible research directions, depending on the interests and talents of the candidate, including, but not limited to:

1. examining the provenance of aerosol material based on isotopic or other techniques. (Does the dust come from the Gobi desert, from AK or does the source vary??);
2. examination of the iron content, and the solubility of iron, in dust from different possible source regions;
3. evaluating the temporal variation in carbon accumulation rates in the peats, as a function of the varying climatic conditions and comparing it with existing carbon data for the coastal Alaskan wetlands;
4. refining the chronology using tephra, Pb-210 and Cs-137;
5. relating the records of dust deposition to available records of biological productivity in the North Pacific ocean.

A few words about available facilities are in order. Note that several appropriate peat cores are already in our possession (13–15 kyr long). Opportunities may arise to collect additional records, as well. A new clean lab exists for the preparation of the peat samples for ²³²Th, Al, Fe and isotopic analysis. Both high-resolution and multi-collector icp-ms instruments exist on the WHOI Quissett campus (where USGS is located), and at the Denver USGS lab. AMS 14C measurements would be made at the adjacent NOSAMS facility (http://www.nosams.whoi.edu/) following sample preparation in Eglinton’s lab.

References

Buesseler, K.O., and Boyd, P.W., 2003, Climate change: Will ocean fertilization work?: Science, v. 300, no. 5616, p. 67.

Duce, R.A., 1995, Direct radiative forcing by anthropogenic airborne mineral aerosols, in Charlson, R.J., and Heintzenberger, J., eds., Aerosol forcing of climate: Chicester, England, Wiley, p. 43–72.

Hand, J.A., Mahowald, N.M., Chen, Y., Siefert, R.L., Luo, C., Subramaniam, A., and Fung, I., 2004, Estimates of atmospheric-processed soluble iron from observations and a global mineral aerosol model: Biogeochemical implications: Journal of Geophysical Research, v. 109, no. D17205, doi:10.1029/2004JD004574.

Huang, Y., Li, B., Bryant, C., Bol, R., and Eglinton, G., 1999, Radiocarbon dating of aliphatic hydrocarbons: A new approach for dating passive-fraction carbon in soil horizons: Journal of the Soil Science Society of America, v. 63, p. 1181–1187.

Jickells, T.D., An, Z.S., Andersen, K.K., Baker, A.R., Bergametti, G., Brooks, N., Cao, J.J., Boyd, P.W., Duce, R.A., Hunter, K.A., Kawahata, H., Kubilay, N., laRoche, J., Liss, P.S., Mahowald, N., Prospero, J.M., Ridgwell, A.J., Tegen, I., and Torres, R., 2005, Global iron connections between desert dust, ocean biogeochemistry, and climate: Science, v. 308, no. 5718, p 76–71.

Moore, J.K., Doney, S.C., Glover, D.M., and Fung, I.Y., 2002, Deep Sea Research, Part II: Topical Studies in Oceanography, v. 49, no. 1-3, p. 463–507.

Proposed Duty Station: Woods Hole, MA

Areas of Ph.D.: Chemical oceanography, geochemistry, marine biogeochemistry, geology

Qualifications: Applicants must meet one of the following qualifications: Research Chemist, Research Oceanographer, Research Geologist

(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Research Advisor(s): John Crusius, (508) 457-2353, jcrusius@usgs.gov; Dorothy Peteet (Lamont-Doherty Earth Observatory of Columbia University), (845) 365-8624, peteet@ldeo.columbia.edu; Tim Eglinton (Woods Hole Oceanographic Institution), (508) 289-2627, teglinton@whoi.edu

Human Resources Office contact: Kathy McDuffie, (703) 648-7408, kmcduffie@usgs.gov

Summary of Opportunities