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:

• Most of the global dust flux is derived from deserts, which expand and contract with climate change;
• Dust production varies with the cube of the wind speed (Duce, 1995), which varies in turn with climate;
• Dust impacts Earth’s radiative budget;
• 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) may have a profound impact on biogeochemical processes in the ocean and, potentially, on climate because many sources of dust contain iron, a limiting nutrient in 30 to 40 percent of the ocean (Moore and others, 2002).

Addition of iron in these areas of the ocean 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 a flux of iron to the ocean surface 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 dust or other natural sources or from intentional anthropogenic addition, is by studying the paleoclimate record. However, such efforts are limited by a lack of long term, high-resolution records of iron 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 back tens of thousands of years or more. Possible archives for dust records that could be examined include peat bogs in coastal Alaska, marine sediment cores and(or) lake sediment cores. Any peat bogs explored would be ombrotrophic bogs, which receive all of their water and nutrients (and hence dust) from atmospheric deposition. Certainly an important component of the research will involve developing a reliable high-resolution chronology for sedimentary records. 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:

• Deriving records of dust concentration and accumulation from analyses of thorium-232 and aluminum.
• Developing a high-resolution peat chronology from AMS ¹⁴C measurements of saturated aliphatic hydrocarbons of leafwax origin (Huang and others, 1999). This approach could be pursued owing to difficulties with ¹⁴C dating of bulk organic matter, and other materials, in peat.
• Contrasting past Fe delivery to the ocean from dust with the flux from non-dust sources (is dust the main source of iron to surface waters in this region?).
• Examining the provenance of aerosol material based on geochemical or mineralogical techniques (Does the dust come from the Gobi desert? From Alaska? Does the source vary?);
• Evaluating the temporal variation in carbon accumulation rates in peats, as a function of the varying climatic conditions and comparing it with existing carbon data for the coastal Alaskan wetlands;
• Refining the chronologies;
• Relating the records of dust deposition to records of biological productivity in the North Pacific ocean.

A few words about available facilities are in order. Several appropriate peat cores are already in our possession (13–15 kyr long). Marine sediment cores are also available (up to several hundred 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 Woods Hole Oceanographic Institute's Quissett campus (where the U.S. Geological Survey [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: Brian Arnold-Renicker, (703) 648-7468, brenicke@usgs.gov

Summary of Opportunities