Temporal Variability in the Flux and Ratios of Trace Metals in Sinking Southern Ocean Particulate Material

Implications for Southern Ocean Productivity and the Transport of Carbon to the Ocean Interior

Supervisors

Andrew Bowie (UTas), Tom Trull (Utas)

(PhD Only)

Project Outline

Suitable for graduates with degrees in Chemistry, Oceanography/Marine Science, Earth/Environmental Science, Biology disciplines. A strong interest in the biogeochemistry of trace elements in the ocean and/or marine instrumentation would be desirable. Students should meet normal University PhD entry requirements.

Background and rationale

The formation, consumption, sinking and remineralisation of organic matter dominate the biogeochemistry of trace metals in the ocean. Conversely, their distributions regulate these processes, particularly primary production. Despite the ecological importance of trace metal assimilation by autotrophs, there are no modern measurements of the trace element content of Southern Ocean lithogenic and biogenic particles. Native organisms incorporate metals into their tissues and inorganic hard-parts, and thus represent important transport vectors in the marine ecosystem through the sinking of living and detrital organic matter. As such, knowledge of the trace metal content of particulate matter is a critical requirement for understanding the source (e.g. dust [1]) and biogeochemical cycling of trace elements in the ocean. Furthermore, for elements such as iron that are known to act as a limiting nutrients over much of the Southern Ocean [2], data on the elemental content of phytoplankton is an essential requirement for the development of biogeochemical models concerned with ecosystem structure and ocean-atmosphere CO2 exchange [3].

Methodology

Since 1997, the Antarctic Climate & Ecosystems CRC (ACE CRC) has successfully run a deep ocean mooring with automated traps in the Sub-Antarctic Zone (SAZ), and the Centre is presently developing an advanced "PULSE" mooring for this site to provide complementary sample collections from surface waters. To date, research has focused on the determination of nutrient elements (carbon, nitrogen, silica) exported in particles, and their relationship with phytoplankton primary production and the seasonal CO2 sink known to exist in SAZ waters. This project would extend current efforts by developing novel trace metal clean instrumentation and methods to collect and process suspended and sinking particulate material from the study area, for the size-fractionated analysis of iron and other trace metals. Sequential shore-based digestion and analysis will take place using high resolution inductively-coupled plasma (HR-ICPMS) techniques [4] in class-100 clean room facilities at CSIRO Marine Laboratories. Such trace metal data will greatly enhance the current suite of chemical and biological measurements made on samples collected from the traps and the PULSE mooring.

Objectives

(i) To obtain a seasonal and multi-year record of the transfer of particulate trace metals from Sub-Antarctic surface waters to the deep ocean, using moored automated sediment traps

(ii) To obtain data on the trace metal to carbon ratios (e.g. Fe:C) of sinking particles in the traps

(iii) To determine the links between the sinking particle flux and suspended particles, via correlation with size-fractionated trace metal particulate samples taken from the surface mixed layer at the mooring sites

(iv) To differentiate between the lithogenic and biogenic components of particulate trace metals through the use of geochemical tracers, cellular wash solutions and organic poisons.

Wider implications

Information on the fluxes and ratios of trace metals in Southern Ocean particles is critical to the development of realistic biogeochemical models of this oceanic region, including its role in past climate change and response to future climate change. Earlier attempts to budget the fate of iron in mesoscale fertilisation experiments were hampered by the lack of knowledge of the distribution of trace metals within the particulate pool [5]. This work will help us to obtain a more comprehensive mass balance in the climatically-important Sub-Antarctic waters south of Australia, as well as aiding in predicting the sources and strength of trace metal laden dust deposition to the region.

Training

The successful applicant will join an active team within the Antarctic Climate & Ecosystems CRC and CSIRO Marine Laboratories that is working on important aspects of trace elemental biogeochemistry in the Southern Ocean. The student will be trained in state of the art ultra-clean sampling and analytical procedures for trace elements for use both at sea and on land. The candidate will also have the opportunity to participate in related ACE CRC field programs (e.g. SAZ Dynamics [6] or VERTIGO [7]), will take part in a student focused seminar series, and will receive additional training from the Research Higher Degrees Unit at the University in the range of skills required for a successful postgraduate career.

References

[1] Jickells, T. D., L. J. Spokes (2001). Atmospheric iron inputs to the oceans, in "The Biogeochemistry of Iron in Seawater", edited by D. Turner and K. A. Hunter, Wiley, Chapter 4, p 85.

[2] Moore J. K., Doney S. C., Glover D. M., Fung I. Y. (2002). Iron cycling and nutrient-limitation patterns in surface waters of the World Ocean. Deep-Sea Research II 49, 463-507.

[3] Lancelot C., Hannon E., Becquevort S., Veth C., de Baar H.J.W. (2000). Modeling phytoplankton blooms and carbon export production in the Southern Ocean: dominant controls by light and iron in the Atlantic sector in Austral spring 1992. Deep-Sea Research I 47, 1621-1662.

[4] Cullen J.T., Sherrell R.M. (1999). Techniques for determination of trace metals in small samples of size-fractionated particulate matter: phytoplankton metals off central California. Marine Chemistry 67, 233-247.

[5] Bowie A.R. et al. (2001). The fate of added iron during a mesoscale fertilisation experiment in the Southern Ocean. Deep-Sea Research II 48, 2703-2743.

[6] http://www.acecrc.org.au/drawpage.cgi?pid=programs&sid=control_of_CO2

[7] http://www.whoi.edu/science/MCG/cafethorium/website/projects/vertigo.html

Contact

A/Prof Tom Trull or tel +61 3 6226 2988