1. What Controls Biological Productivity in the Northern Gulf of Alaska? Examining Influences of Coastally Derived Iron and Oceanic Nitrate in a Region Influenced by Ongoing Glacier Mass Loss

The waters of the Gulf of Alaska are highly productive and support numerous economically important fisheries (Denman and others, 1981; Ware and Thomson, 2005). It has become clear that the micronutrient iron limits biological productivity in much of the subarctic North Pacific (for example, Boyd and others, 2004), while nitrate typically is the limiting nutrient in the nearshore region where iron supply is abundant. Hence, high productivity might be expected in a transition zone where high concentrations of coastally derived iron mix with high concentrations of nitrate derived from deep mixing and (or) upwelling. Yet our understanding of the controls on productivity is limited by our poor quantitative understanding of the sources of iron, which include rivers (for example, Schroth and others, 2011), coastal eddies (for example, Xiu and others, 2011; Lippiatt and others, 2011), dust (for example, Crusius and others, 2011), upwelling, shelf sediment remobilization together with offshore currents,and so on. Furthermore, we know that glaciers in the region are melting rapidly (Arendt and others, 2002), yet the impacts on stratification, circulation, nutrient supply, and biological productivity are poorly known. Indeed, relatively few oceanographic observations have been made in the northern Gulf of Alaska to examine these interconnected processes.

Our understanding of the ocean is in many respects limited by our tools of observation. Such observations typically stem from oceanographic cruises, which are limited in frequency by their large cost. However, new interdisciplinary approaches are rapidly being developed that allow powerful time-series observations in the ocean needed to reveal the linkages among the processes alluded to above, and their variability over time. As new technologies emerge, an increasingly sophisticated set of physical, biogeochemical, and biological observations is possible from automated instrumentation that can be deployed in situ, offering high temporal resolution at relatively modest cost, especially in remote locations. Additional tools are emerging that allow observations from autonomous vehicles at high spatial resolution, in addition to high temporal resolution. All of these types of “observing systems” are playing an increasingly large role in oceanography.

This project will seek to improve our understanding of the controls on biological productivity in the northern Gulf of Alaska through an approach that uses high-resolution in situ measurements. Because of the important controls of iron and nitrate on this ecosystem, an additional goal could be to quantify important fluxes of iron and nitrate to the euphotic zone and to infer the biological response. This is a tremendous opportunity for a new Ph.D. to champion this approach to oceanography, to define and develop such a program, and to identify the preferred technologies to be used. We wish to encourage applicants from a diverse array of backgrounds (that is, geochemical, biological, engineering) to use their own creativity and insight to take advantage of emerging technologies to optimize such observations.

One approach might be to carry out time-series observations from one site from an oceanographic mooring. Mooring-based observations might include but are not limited to:

1. CTD measurements of S, T, chl-a (by fluorometer), particle concentration (by transmissometer/OBS);
2. Current meter measurements;
3. Measurements of “new production”, inferred from measurements of O2/N2 by a gas tension device (Emerson and others, 2001, 2002). This technique was pioneered by Emerson and has been used in several other North Pacific locations;
4. In-situ nitrate analyses;
5. Time-series, trace-metal clean water sampling. This has been carried out successfully by Ed Boyle using his MITESS system, the only proven system capable of automated collection of a time-series of trace-metal clean water samples (Bell et al., 2002).  Such samples, collected at high temporal resolution along with ancillary information, could help identify the sources of iron to this iron-limited part of the ocean and the oceanographic impact;
6. Other technologies of interest to the applicant.

Oceanographic moorings, as well as a ship to deploy them, are available through R. Campbell at the nearby Prince William Sound Science Center (Cordova, Alaska).

Another approach might be to make observations in 2-D sections using a glider (Eriksen and Perry, 2009; Nicholson and others, 2008). Glider-based observations might include CTD measurements of S, T, chl-a (by fluorometer) and particle concentration (by transmissometer/OBS); measurements of “new production” inferred from measurements of O2/N2; and (or) measurements of nitrate concentrations. While this approach might preclude sampling for iron, the high-resolution spatial coverage would nonetheless facilitate hypotheses related to iron supply that could be tested with occasional oceanographic cruises (if funding levels permit). In each of these approaches, recent oceanographic and other data are available from the region to help applicants with hypothesis generation and proposal preparation (for example, Schroth and others, 2011; Crusius and others, 2011; Lippiatt and others, 2010, J. Crusius and others, unpublished data). Whatever the approach, there are excellent opportunities for a creative scientist to select state-of-the-art tools to advance our understanding of the complex controls on biological productivity in the northern Gulf of Alaska.

References
Arendt, A.A., Echelmeyer, K.A., Harrison, W.D., Lingle, C.S., and Valentine, V.B., 2002, Rapid wastage of Alaska glaciers and their contribution to rising sea level: Science, v. 297, p. 382–386.

Bell, J., Betts, J., and Boyle, E., 2002, MITESS: A moored in situ trace element serial sampler for deep-sea moorings: Deep-Sea Research, Part I, Oceanography Research Papers, v. 49, p. 2103–2118.

Boyd, P.W., Law, C.S., Wong, C.S., Nojiri, Y., Tsuda, A., Levasseur, M., Takeda, S., Rivkin, R., Harrison, P.J., Strzepek, R., Gower, J., McKay, R.M., Abraham, E., Arychuk, M., Barwell-Clarke, J., Crawford, W., Crawford, D., Hale, M., Harada, K., Johnson, K., Kiyosawa, H., Kudo, I., Marchetti, A., Miller, W., Needoba, J., Nishioka, J., Ogawa, H., Page, J., Robert, M., Saito, H., Sastri, A., Sherry, N., Soutar, T., Sutherland, N., Taira, Y., Whitney, F., Wong, S.K.E., and Yoshimura, T., 2004, The decline and fate of an iron-induced subarctic phytoplankton bloom: Nature, v. 428, p. 549–553.

Crusius, J., Schroth, A.W., Gasso, S., Moy, C.M., Levy, R.C., and Gatica, M., 2011, Glacial flour dust storms in the Gulf of Alaska:  Hydrologic and meteorological controls and their importance as a source of bioavailable iron: Geophysical. Research. Letters, v. 38, p. L06602.

Denman, K.L., Mackas, D.L., Freeland, H.J., Austin, M.J., and Hill, S.H., 1981, Persistent upwelling and mesoscale zones of high productivity off the west coast of Vancouver Island, Canada, in Richards, F.A., ed., Coastal upwelling: Washington, D.C., American Geophysical Union.

Emerson, S., Mecking, S., and Abell, J., 2001, The biological pump in the subtropical N. Pacific Ocean: Nutrient sources, Redfield ratios, and recent changes: Global Biogeochemical Cycles, v. 15, p. 535–554.

Emerson, S., Stump, C., Johnson, B., and Karl, D.M., 2002, In situ determination of oxygen and nitrogen dynamics in the upper ocean: Deep-Sea Research, Part I, Oceanographic Research Papers, v. 49, p. 941–952.

Eriksen, C.C. and Perry, M.J., 2009, The nurturing of seagliders by the National Oceanographic Partnership Program: Oceanography, v. 22, p. 146-157.

Lippiatt, S. M., Lohan, M. C. and Bruland, K. W., 2010. The distribution of reactive iron in northern Gulf of Alaska coastal waters. Marine Chemistry 121, 187–199.

Lippiatt, S.M., Brown, M.T., Lohan, M.C. and Bruland, K.W., 2011. Reactive iron delivery to the Gulf of Alaska via a Kenai eddy: Deep-Sea Research, Part I, Oceanography Research Papers, v. 58, p. 1091–1102.

Nicholson, D., Emerson, S., and Eriksen, C.C., 2008, Net community production in the deep euphotic zone of the subtropical North Pacific gyre from glider surveys: Limnology and Oceanography, v. 53, p. 2226–2236.

Schroth, A.W., Crusius, J., Chever, F., Bostick, B.C., and Rouxel, O.J., 2011, Glacial influence on the geochemistry of riverine iron fluxes to the GoA and effects of deglaciation: Geophysical Research Letters, v. 38, L16605.

Ware, D.M. and Thomson, R.E., 2005, Bottom-up ecosystem trophic dynamics determine fish production in the North Pacific: Science, v. 308, p. 1280–1284.

Xiu, P., Palacz, A.P., Chai, F., Roy, E.G., and Wells, M L., 2011, Iron flux induced by Haida eddies in the Gulf of Alaska: Geophysical Research Letters, v. 38, L13607.

Proposed Duty Station: Seattle, WA; Woods Hole, MA

Areas of Ph.D.: Chemical or biological oceanography or engineering (candidates holding a Ph.D. in other disciplines but with knowledge and skills relevant to the Research Opportunity may be considered).

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

(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, (206) 543-6978, jcrusius@usgs.gov; Andrew Schroth, (508) 457-2295, aschroth@usgs.gov; Steve Emerson (University of Washington), (206) 543-0428, emerson@u.washington.edu; Rob Campbell (Prince William Sound Science Center), (907) 424-5800, rcampbell@pwssc.org; Ed Boyle (Massachusetts Institute of Technology), (617) 253-3388 eaboyle@mit.edu

Human Resources Office Contact: Candace Azevedo, (916) 278-9393, caazevedo@usgs.gov

Summary of Opportunities