Untitled Document
Silicon and Boron isotopic signatures in marine sponges
Martin Wille1, Jill Sutton1, Andrea DeLeon1, Michael
Ellwood1, Steve Eggins1 and William Maher2
1 Research School of Earth Sciences, Building 47, Daley
Road, Australian National University, ACT 0200, Australia
2 Ecochemistry Laboratory, Institute for Applied Ecology, Faculty of
Applied Science, University of Canberra, Canberra, ACT 2601, Australia
The Southern Ocean is widely regarded as playing a key role in influencing
atmospheric pCO2 over glacial-interglacial timescales; the mechanism
by which this influence is exerted is, however, poorly constrained. Diatom
production constitutes about 40% of the total oceanic primary production,
making them key players in the modulation of atmospheric CO2 concentrations
and global climate. Additionally better understanding of changes in the
surface and deep water carbonate system (eg pH, alkalinity) would provide
invaluable insight into the driver(s) of millennial scale climate change.
Here, the boron and silicon isotope composition of biogenic silica (siliceous
sponges), is being investigated as a potential seawater pH and paleo-productivity
proxy.
Relationships were investigated between coupled sponge and seawater samples
for Si isotope fractionation compared with equivalent Si concentrations
from the water column. Our new results and the subsequent new model offers
a new perspective on what controls biological fractionation in biogenic
opal and in turn, will yield a novel interpretation of the paleo-oceanic
distribution of silicon.
Boron analysis of siliceous sponges aims to examine the nexus between
seawater pH, biogenic silica and boron, and thus the utility of boron
in siliceous organisms (namely sponges and diatoms) as a pH proxy. First
order Comparison between boron and silicon signatures obtained from the
same sponge material suggest a coupling between Silicon and Boron system
in marine sponges.