Current
Research Interests
Hot Spring Sinter Formation
It is now well established that there is a close association between
the different types of hot spring sinter and the microorganisms growing
in the overlying mat community. However, what remains lacking is a full
understanding of how different microbial assemblages form the unique biosedimentary
features (i.e., morphology, fabric) intrinsic to each sinter. Working on
the hot springs at Krisuvik, Iceland, we examined in detail the columnar
microstromatolites forming at temperatures between 30-40
oC.
Several important findings were made (Konhauser et al. 2001).
First, we showed that cyanobacterial silicification contributed significantly to the overall
sinter formation, with nearly 50% of the structure comprising biomineralized
cells. Second, the microstromatolites were laminated, with the cyclicity
related to seasonal variations in microbial activity. Third, recolonization
of the solid silica surface occurred by free living bacteria: cell motility
was not responsible for the laminations. Fourth, and most surprisingly,
this work also demonstrated that insufficient light penetrates deep within
the sinter to support photosynthesis, yet culturable populations of cyanobacteria
were recovered. This meant that those cyanobacteria living in the deeper
layers either changed their mode of metabolism, they became inactive or
they no longer were the dominant microorganisms. Recent work in New Zealand
has also shown that silicification in silica-supersaturated hot springs
can be extremely rapid (on the order of hours to days) and that the microbes
appear well preserved with their general morphology, diameter, length,
and presence/absence of septa being readily apparent. However, most
of the silicified microbes lack any key features that would allow accurate
comparisons with extant taxa. Moreover, the presence of collapsed filaments
and pseudo-fossils complicate any efforts to relate the extant silicified
cells to ancient microfossils (Jones et al., 2004; Jones et al., 2005).
I am now in the process of continuing this work in Yellowstone National
Park, USA with Dr. Bill Inskeep (Montana State) to ascertain the microbial
influences on both silica and iron hydroxide precipitation under varying
geothermal conditions. Natural sinter and effluent samples have been collected
to characterize the dominant microflora, their activities and their relative
importance in constructing the various sinter fabrics via biomineralization
and growth patterns. This work will be linked to current studies on the
origins of laminations in Archean stromatolites and on the mechanisms responsible
for the fossilization of Archean microbial mats.