 that's Joan Marie Del Descio from Penn State University, and she'll be talking about topographic signatures of permafrost processes. Okay, Lawn. Okay. Be good here. Okay. Hi, everybody. I'm Joan Marie Del Vecchio. I'm a PhD student at Penn State, and I'm going to talk to you a little bit about my thoughts of landscape evolution and permafrost landscapes, and in particular, I wanted to say thanks to all the systems folks, including especially Irina Overeem for organizing permafrost hackathons that we've done prior to the annual systems meetings for the past two years, and those have given me a very observational scientist the confidence to try her hand in some numerical modeling. So in my research, I try to understand how permafrost landscapes respond to warming climates. And in particular, I'm interested in forecasting how future warming might affect sediment and carbon budgets in high latitudes. For my dissertation, I mainly use sedimentary records from postglacial warming in Alaska and Eastern North America to reconstruct how surface processes change the climate. But I want to see if I can use landscape models to explore how topography might also reflect how surface processes responded to climate change. So by observing landforms and processes in ancient and modern permafrost environments, I've developed a sense of the relative balance of hill slope and fluvial processes as a function of climate. So in Central Appalachia, close to the Laurentide Ice Margin, I observe thick colluvial deposits with distinct permafrost landforms preserved onto hill slopes into the present climate. And moving north to south in the Valley and Ridge physiographic province, sandstone ridge lines seem to get more incised in the south. This leads me to hypothesize that permafrost processes facilitate more efficient transport of hill slope sediments compared to warmer climates, while fluvial processes were more efficient under the relatively warmer conditions farther south. But it's hard to tell when I only have a snapshot of the modern landscape that integrates over multiple climate cycles. Likewise, in Alaska, we have observed rapid growth of gully networks in watersheds that are undergoing anthropogenic thaw, but it's unclear if these hollow fill an empty sort of on their own or if the channels are adjusting to some new equilibrium state. And that is why I want to explore the balance between hill slope and channel processes in numerical models. So in terms of hill slope processes, most modelers take the approach of ascribing more or less sediment flux as a function of the thermal state of the soil column. So on this slide, I'm showing you model results where I've imposed temperature variation over the past 120,000 years on a simple synthetic hill slope in land lab that accumulates sediment at its base, not unlike my field sites where we core tow slopes and quantify accumulation rates with radio carbon. My model, like these other models, produces a shark fin shaped relationship between temperature and flux with a peak at zero degrees where efficient thaw movement is optimized. Of course, the real question and the motivation of my field observations is whether to describe a higher or lower transport rate during warm climate phases. Now, of course, each landscape is going to have its own quirks that change that relationship, but it seems at least in central Appalachia, cold periods are more efficient movers of sediment than modern warm ones. But I think just important as hill slope rate constants and something that hasn't been explored nearly as much through modeling are the changes to permafrost channel networks of climate. So in this 2003 modeling experiment simulating quaternary climate change in the Netherlands, these workers showed how frozen hill slopes, restricted hill slope water storage and forced overland flow to daylight higher up on the hill slopes, causing channel networks to expand and sediment discharge to go up under cold climate conditions. You may, of course, note that this is the opposite of what I think I see in Pennsylvania and Alaska. One major difference between these specific simulated hill slopes in my landscapes is that unlike in the Netherlands, my landscape's bedrock is close enough to the surface that the change in water storage probably isn't as important, though this modeling endeavor actually maybe indirectly explains the patterns I see in Appalachia since the mantle of this relatively permeable periglacial debris is thicker up north compared to south, maybe explaining some of those latitude incision trends. But I think an additional explanation is that a realistic representation of permafrost hill slopes requires treatment of the vegetation. So in grassy, tender landscapes, moss and roots generate a highly permeable surface, tens of centimeters thick, allowing lots of water to move on the surface without ever having to interact with the mineral soil beneath. In contrast, shrubby patches lack this cohesive and permeable layer that is thought to exacerbate slope instability. In fact, shrubs preferentially colonize disturbed patches of the landscape, meaning shrub expansion might create a positive feedback loop that instigates further erosion. Indeed, when I analyzed the topography of mossy versus shrubby landscapes on the Seward Peninsula in western Alaska, controlling best as I could for rock type and climate, I found that shrubby landscapes are characterized by more defined and steep channel networks, whereas mossy hill slopes support a more gradual transition to fluvial processes. My next modeling steps then are to create a realistic representation of the tundra mat in controlling not only hill slope flux, but also the drainage area at which the landscape is likely to saturate and form channelized flow. I suspect that without such a layer, models will overestimate channel incision in permafrost landscapes. I think in general, models of permafrost landscapes underestimate the role that moisture plays alongside temperature in controlling sediment flux, which incidentally is what I think I see in my late paternity stratigraphic and pollen records as well. You've got to pair the modeling with the field observations, make them match. I'm really excited and looking forward to exploring this dynamic once I get this model worked out up and running. Stay tuned. We'll figure it out at some point. I usually use the system's annual meeting to learn all about modeling and get lots of feedback to figure out what's feasible and what's already been done. Please, I would encourage you to chat with me if you have insight for me or other questions that might help me do this project. All right. Thanks, everybody. Great. Thanks, Jo and Ray. I encourage people to put questions in the chat or raise their hand. And while we wait, I was curious how... Oh, a question already. Hold on. No, I'm right. Okay. My question is what types of observations of vegetation do you need to put different types of vegetation in the model? That's a good question. So the data set I used for this particular analysis that I did on the digital elevation models out in Seward was like a broad-based sort of remote sensing mapping. And so it's sort of like a broad picture that I'm collecting my typographic data from. But I think from at least one season of field work, I can definitely, as we dug pits in the permafrost, it was clear that the thickness of the tundra mat changed as a function of not only the geomorphology, but where you were on the landscape and the specific times of the vegetation that was growing there. It's definitely something that I need to learn a lot more about. But I know that there's lots of people thinking about tundra ecology. So I'm hoping that I can mine some of those studies for information about infiltration, thickness, the physical properties they're going to change how water would move through the landscape. Great. Then a question from Colin Rowland. Great talk. Are anthropogenic changes in the thermal regime of the soil accompanied by changes in the vegetative community? That's a good question. So definitely folks believe that they see shrub expansion in the Arctic right now. As the Arctic gets warmer, and in some cases wetter, people think that they see shrubs encroaching on landscapes that were formerly maybe too wet or sorry, too dry or too cold for them. Of course, it's not so much anthropogenic because there's sort of natural fire ignition sources, but there's also, of course, people studying how fire frequency might be going up in the changing Arctic and whether or not the same vegetation will come back after the fire is also something that people are studying. I think someday down the line I might be able to incorporate into some sort of dynamic landscape evolution model, too.