Day 2 at the American Geophysical Union (AGU) Meeting was fantastic. I spent the morning browsing some posters about megafloods and also spoke with a researcher looking at the relationship of tectonics and sedimentation to kelp forests offshore of southern California. Just like terrestrial ecosystems are viewed within the framework of the landscape they are in (e.g., river ecology), understanding submarine ecosystems will require more multidisciplinary research to identify the important relationships. I foresee such work exploding in the coming decade as more and better data about the seafloor are acquired.
I then had a nice lunch with a friend from graduate school I haven't seen in some time. While the science at conferences like this are the main event, the socializing and catching-up aspects of conferences are really important.
I spent all afternoon in oral sessions. The early afternoon session was called Quantifying Present and Ancient Rates of Earth Surface Processes and included several interesting talks. A session like this tends to attract those that are working on the nuts-and-bolts of new methods and/or new applications of existing methods. Many of the talks dealt with innovative uses of various isotopes, a lot of the details of which were beyond my expertise. But I was able to keep up (mostly).
One talk that stood out was about using U-Th (Uranium-Thorium) series isotopes for investigating sediment residence times. Being able to constrain the time it takes sediment to move from one part of a system to another -- for example, from upland tributary rivers to a coastal plain delta -- would be a huge advance in fundamental understanding. Quantifying the rates of sediment transfer through the system would have implications for understanding the transfer of other materials, including pollutants and terrestrial carbon.
In this case, the researchers are taking advantage of U-Th fractionation during water-rock interactions and using as a tracer/chronometer of weathering. What they are doing is essentially constraining the timing and duration of weathering and drawing conclusions about sediment transfer from that. The details of the fractionation and the decay of these isotopes is not straightforward (at least to me) but progress is being made.
The later afternoon session was called The Morphodynamics of Big Rivers: What Do and Don't We Know and was very well attended. The objective of the session was to explore the big rivers of our planet and discuss their origin and evolution (and, yes, defining what 'big' means is part of it). Gary Parker gave the first talk and had the room laughing at his entertaining and informative presentation style. He talked about how our current numerical expressions for sediment transport and their relationship to river morphology don't account for 'natural armoring' of the banks. Tree branches, slumped material, and other 'junk' (as Gary put it) play a huge role in armoring the bank and protecting it from erosion. He then showed some preliminary work into developing a better numerical understanding of this armoring.
There was a great talk looking at the planform morphology of the Amazon River. If you are reading this then you've seen this pattern already (hint: look at the header image of this blog).
There were several informative talks in this session. The final talk discussed issues of what types of rivers are preserved in the long-term geologic record. Is there a morphology that is preserved preferentially and, thus, makes up most of the stratigraphic record? If so, then our conceptual and numerical understanding of longer-term river evolution as derived from preserved deposits might be significantly affected. Some commentary from people in the audience following this talk nicely set up the companion poster session, which is tomorrow morning.
A great day, I look forward to more tomorrow!
