Random thoughts 2

So I was standing in the shower, thinking about dissertation topics. It hits me that a really good way to improve phytolith analysis would be to differentiate between species better. Right now, phytolith analysis can only differentiate down to the genus level at best. Is it possible to see a difference between species? I can think of two plant taxa to look into. First, the genus Festuca (bunchgrasses). These are fairly common in the American west, and with lots of species it would be relatively easy to check them out. Since this is a grass genus, there would be lots of phytoliths in the biomass. Second, the genus Artemisia (sagebrush). Artemisia is about as cosmopolitan as you can get in the American west. It's everywhere. I'd be mostly interested in the subgenus Tridentatae, as that's where I'd find the sagebrushes. The sagebrush species are all very closely related, having diverged only a few million years ago. It may be very hard to differentiate them. If I wanted to get even more specific, I could zoom in on big basin sagebrush, Artemisia tridentata. This sagebrush has six recognized subspecies. Are there any differences in those?

I think it would be fairly easy to look at the differences in these taxa. I'd just need to go out, take some plant samples, process them, and then look at them under the microscope. I'd be looking for three things. First, does a given species display unique phytoliths, or signature shapes? If these are found, then I'd know that every time I found one of those signature shapes in a soil sample, that that given species must have been present. Second, are there any differences in the ratios of phytolith shapes? A given species produces many phytolith shapes. What is the ratio of these shapes? Is there a difference in the ratios between species? Third, how much phytoliths are present in a given plant at any one time? For example, does a large bunchgrass species with lots of biomass produce more phytoliths than a smaller species? Is this reflected in the soil? This may require a determination of the total amount of phytoliths produced by a plant over its entire lifetime.

Some random thoughts on dissertation topics

It's near the end of the semester, and I've been cranking away at term papers. If I'm not focusing on that delightful subject, I'm usually muddling through wedding planning.

Well, I'm tired of that. It's time to talk dissertation topics, bitches. You knew this was coming. No going back now. (Alright so maybe there really is no built up demand to discuss dissertations, but I needed a way to introduce this blog)

My subject area will most likely be in the Great Plains; probably centered on Nebraska. There are lots of research questions lying out there in the grass. I'm most interested in 1) paleoenvironments; 2) silica biogeochemical cycles; 3) vegetation dynamics; 4) developing new methodologies to improve paleoenvironmental reconstructions using phytoliths (but proxies in general, I suppose). Let's break these down one by one.

1) Paleoenvironments. It's always good to know what was happening in the past. There are many methods out there to determine this. I'm interested in what the vegetation of a given area was doing. If the vegetation can be determined, it can be used as a paleoclimatic proxy (for example, if I find tundra vegetation, it probably means there was a tundra climate there). For the Great Plains, it would be fairly easy to do. Phytoliths are abundant in grasslands, and they're stored in loess sections. Loess sections build up through time, so the deeper a person digs in the loess, the older the phytoliths are. So it is possible to dig out 10,000 year old phytoliths and look at them. Performing a simple phytolith analysis would be the simplest route of the four options listed. I'd probably expand on this to include some of the methods I used as a Masters student. But there is a problem with this. Just using standard methods really isn't good enough for a dissertation. I'd need to have some really interesting results, and then expand on that.

2) Silica biogeochemical cycles. This topic has interested me of late. Many papers have shown the importance of Si to the global carbon biogeochemical cycle. This would be fairly straightforward -- just quantify the flux of Si from the soil to the terrestrial biomass, and back again. It's actually kind of boring when you think about it, but it could have huge ramifications. For example, suppose during the LGM that there was very little Si emplacement into soils due to mineral weathering. This would lead to a dearth of Si export to watersheds and on to the world oceans. In the oceans is where Si does its part to sequester carbon out of the air and deposit it into sediments. Would this mean that carbon would build up in the atmosphere? On the other hand, there would be considerably less global biomass during the LGM. This would mean less Si entrained in vegetation and consequently more Si just sitting around in the soil, where it would be prone to leaching. This leaching could export large amounts of Si to the world oceans, where it could act to sequester very large amounts of carbon. This would be a positive feedback loop - cold temperatures from the ice age would ultimately lead to an even greater reduction of atmospheric CO2. Paleofluxes of Si would be a great topic to tackle. It would be a bit difficult to do, but I don't think it's beyond the realm of possibility. I'd need some way to determine how much Si was around in the soils back then. During the LGM, Nebraska presumably would have looked quite a bit like central or northern Canada. I'd need to look at a modern analog for these soils -- in Canada. This would tell me what the Si flux in these soils is now. Once I know that, I could infer that Nebraska soils during the LGM must have been similar. From that, I could estimate how much Si is being produced from mineral weathering, how much is being taken up by the biomass, and how much is being exported to the watershed. I think it would be way too ambitious to do this for the entire globe, so I think I'd stick to the Great Plains, or a section of it. Another way might be to look at the Germaniun-Silica isotope ratio to determine the chemical weathering rate.

3) Vegetation dynamics. There's many routes I could follow on this one. I could stay modern, and just see how the Great Plains vegetation is responding to climate change. Or I could look at changes in vegetation through time. This ties in with #1.

4) New methodologies. This has the most appeal. There are still many uncertainties in phytolith analysis. Namely, how does Si dissolution affect phytolith preservation? In my Masters work, I saw progressively less phytoliths as the age increased. This makes sense, since one would expect the odds are against a given phytolith of being preserved as time wears on. Si is especially reactive, so it's really quite amazing to think that any of these things last more than a few years in the soil. The preservation of phytoliths in grasslands is a testament to the aridity of the region. Many studies have shown that upon deposition, a large percentage of phytoliths dissolve. That makes sense, since they're just sitting at the top of the soil getting rained on. As the phytoliths are buried, they stand a better chance of surviving. But even then, groundwater percolation will slowly and steadily dissolve the phytoliths. I just wonder if there is some way to estimate the amount of phytolith dissolution through time. Of course, it would only be a rough estimate.

Looking at this in a reverse way, it might be possible to determine phytolith production for a given time period. This summer I'll be heading off to Nebraska to determine just this. I'll take a look at the amount of phytoliths present during different climatic events. The question I'm asking is, are there more phytoliths during cold or warm periods? A person would expect to find more phytoliths during warm periods, simply because there would be more vegetation making phytoliths. But this may not be the case, as dissolution may be more of a factor. Thus, cold times may actually be over-represented int the phytolith record, simply because there is little dissolution. Once I know how much phytoliths are present for each climatic period, I'd need to find a way to estimate the vegetation density. If this is known, I could compare it to the actual amount of phytoliths present -- thus deducing the dissolution rate! I couldn't use the phytolith proportions to infer vegetation density, as that would be circular. Another way might be to use other methods, such as stable isotopes, macrofossils, pollen analysis, or even terrestrial diatoms.

Other problem areas in phytolith analysis include bioturbation and other forms of transport. This means simply that phytoliths may not stay put upon deposition. They can move around quite a bit. I really don't see any way around this, except if there were a way to identify the ages of single phytolith grains. This is way beyond our technology at this point. As with dissolution, it would be possible to estimate phytolith movement based upon the amount of contemporary bioturbation, and ground water percolation. One would need to revise these numbers based upon climate change in the past. For example, it was much colder 15,000 years ago. How will this affect phytolith transport?

The Eye of the Storm!

Git Down Muzak

The Fiancee and I are currently picking out wedding music. Are there any suggestions?

A Clockwise Midlatitude Cyclone? Has the world gone mad?

When I woke up yesterday, I felt a disturbance in the force. Something wasn't quite right, but I couldn't put my finger on it. I shrugged it off and got ready for the day. As I sat eating my breakfast and watching the boob tube, I was stunned by what I saw. I had turned to the Weather Channel. It was showing the radar for the upper midwest. The winds were spiralling clockwise, from the southeast. And it was raining.

Yes, I know what you're thinking. This is impossible right? I mean, every first year climatology grad student is taught that northern hemisphere cyclones spiral counter-clockwise. I mean, everybody knows that, right?

What I saw on the Weather Channel confused and disturbed me. I felt my entire climatological knowledge base slipping away. Everything I know was suddenly suspect. This was a life-changing event!

In retrospect, I realize now that there were certain factors at play that I wasn't aware of. The radar playback which I had seen yesterday morning had only shown the upper midwest, not the entire continent. Had I seen this, I would have realized the true driving force behind this seemingly impossible occurrence. As you can see in the satellite image above, there was a weak midlatitude cyclone centered over Illinois and Indiana. This was creating southeasterly winds over northern Illinois and Lake Michigan and on into southern Wisconsin. The northern part of this midlatitude cyclone was bringing rainy weather to Madison at the time. Meanwhile, a frontal boundary was advancing southward from Canada. This created a low pressure trough. In the proccess, the frontal boundary overpowered the weak pressure gradient of the dying midlatitude cyclone to the south. This caused those southeasterly winds over southern Wisconsin to take a right hand turn over central Wisconsin and head northward towards the frontal boundary. Thus, we have what appears to be a clockwise spin and rainy weather.

You can all rest easy. The world has not gone mad.

A Midlatitude Cyclone for the Ages

I see that Mother Nature has screwed us over again. One look outside the Sci Hall windows and you will understand what I mean. It's April 10, and the forecast is for 8-12 inches. Of snow. And wind. And curses. Today is a day where I lament my choice to attend UW Madison and not UC Santa Barbara. Oh well, at least there are no earthquakes, landslides, overcrowding, traffic jams, smog, tsunamis, droughts, surfer dudes, wildfires, etc. etc.

On the bright side, today's weather is a classic example of a midlatitude cyclone. What is it? A midlatitude cyclone is a transient weather disturbance with a low pressure center. This low pressure center allows wind to blow inward. In the northern hemisphere, the winds spiral inward in a counter-clockwise fashion (due to the rotation of the Earth). Check out a PPT of midlatitude cyclones here. A midlatitude cyclone is much like it's low latitude big brother, the hurricane: both have low pressure centers and counter-clockwise spiraling winds. However, the hurricane tends to be more compact, and has a greater difference in air pressure from the outer reaches of the storm to the center. This is what give the hurricane its strong winds.

Midlatitude cyclones also have cold fronts and warm fronts. In other words, there are areas of the cyclone where cold air is advancing, and another area where warm air is advancing. Since the midlatiude cyclone winds spiral inward in a counter-clockwise fashion, it makes sense that cold air from the north will be pulled in towards the center of the storm on the NW and west side of the cyclone. As the storm continues to spin, the cold air will advance around the spiral towards the east. This advancing cold air is the cold front. Conversely, warm air from the south is pulled toward the center of the storm on the SE and east side of the cyclone. Thus, we usually see the warm front here.

This is the classic example of a midlatitude cyclone. Of course in reality, it may not always be this easy. Today's storm is a pretty good example (see figures). The top left figure is a satellite image from the National Weather Service. This image shows water vapor in the air, and it is easy to see the counter-clockwise spiral pattern of the midlatitude cyclone. The low pressure center is parked over eastern Iowa at this time. The top right image is also from the NWS. Here we see a radar display of precipitation. Again, note the spiral pattern, and how it extends all the way to the Gulf of Mexico. Also note that in the northern part of the storm we see alot of blues (snow) and greens (rain) in the southern parts. The third image is from weather.com, and is simply a close-up of the storm. At this time, the cold front probably extends to the south or south-southeast from the center of the cyclone. The warm front extends roughly eastward.

Midlatitude cyclones are a common occurrence for Madisonites to see. They can occur any time during the year, but are most easily recognized in the winter months, when they are better organized. In the summer, they tend to be more "discombobulated" or disorganized, probably because of increased atmospheric turbulence.