Benjamin Walther is a Postdoctoral Fellow with the Centre of Excellence based at ANU, working with Prof. Malcolm McCulloch and Prof. Mike Kingsford. He received a B.A. and a B.S. from the University of Texas at Austin in 2000. He received his Ph.D. in Biological Oceanography in 2007 from the Joint Program at the Woods Hole Oceanographic Institution and the Massachusetts Institute of Technology, under the supervision of Dr. Simon Thorrold. He spent six months teaching at the U.S. Coast Guard Academy and one year as a postdoctoral fellow in the lab of Dr. Bronwyn Gillanders at the University of Adelaide before beginning his current position.

ABSTRACT:

There are two general fields of study that examine variation in chemical signatures of biogenic carbonates. The first uses elemental and isotope ratios of stationary organisms such as scleractinian corals to reconstruct properties of the ambient environment, such as temperature, salinity, and nutrient availability. The second uses similar signatures in hard parts of mobile organisms, such as fish otoliths, to track dispersal and migration patterns. Both approaches make fundamental assumptions about spatial and temporal variability in water chemistry and require careful selection of study species, locations, chemical proxies, and analytical methods.

I will discuss both uses of biogenic carbonates with two examples. First, the migratory patterns and stock mixture dynamics of a highly migratory diadromous fish species in the North Atlantic were resolved using a suite of isotope (oxygen and strontium) and elemental (Sr:Ca and Ba:Ca) ratios. Second, my current work on the Barrier Reef compares variation in Ba/Ca ratios recorded in both fish otoliths and coral skeletons to establish a time series of pulsed upwelling events and climate shifts on local and regional scales. These examples will illustrate the potential for biogenic carbonates to yield vital information about ecological processes and population dynamics in marine systems.