Tomas Remenyi

Quantifying the impact of dust deposition to the Southern Ocean using dissolved aluminium
concentrations

Supervisors: Dr Andrew Bowie (ACE CRC, UTAS) and Dr Ed Butler (CMAR)

Background Project

It is becoming increasingly important to understand the role that aeolian deposition plays in supplying trace elements to the surface ocean, and consequentially the role that such episodic supply plays in moderating biological processes. Periodic input of dust laden with iron, an element essential for photosynthesis, is thought to stimulate phytoplankton growth, resulting in a shift in the dominant phytoplankton species composition and an increase in carbon fixation, with consequent effects on atmospheric C02. This coupling is particularly evident in the iron-deficient Southern Ocean, where there is mounting evidence that dust particles from the arid Australian desert provide a vital link in the planet's climate control system, and provide a key climate feedback loop linking the lithosphere, atmosphere and ocean. Indeed, the polar ice core record shows that during the last ice age, average dust input to the oceans was tenfold greater than today, with high dust periods being closely associated with abnormally low atmospheric C02 and temperature. Despite being the most abundant metallic element in the Earth's crust (8.1% by weight), oceanic aluminium (Al) concentrations are extremely low predominantly due to its extremely short residence time (2-5 yr). A knowledge of its surface water distribution is thus extremely useful in that it can be used to identify the location and magnitude of inputs of continentally derived dusts to the ocean. Vertical profiles of Al are probably controlled by dissolution of dust particles (at the sea-surface) and bottom sediments (at the ocean depths) balanced against scavenging by particulate matter. Recent work has also shown Al distributions to show large inter-ocean variability.

Methodology

To map Al distributions on a large scale requires the development of analytical methodology that is sensitive, precise, rapid, minimises the risk of sample contamination and operable onboard research vessels. Through this project, the candidate will initially develop and optimise a shipboard analytical method for the determination of Al in seawater. Recent successful methods have coupled flow injection analysis (FIA) with in-line preconcentration and fluorometric detection, and thus this approach will be an obvious starting point. FIA methods for Al have been based on the well-documented lumogallion and the preconcentration abilities of resin-immobilised 8-hydroxyquinoline. SUB-nanomolar detection limits have been achieved. The optimised system will be tested against a series of archived Southern Ocean and Atlantic samples. The validated method will then be deployed alongside other shipboard analytical methods for trace elements on major Southern ocean research expeditions, for the real-time determination of Al.