Periodic Reporting for period 2 - GyroSCoPe (Geomorphic and Sedimentary responses to Climate Periodicity)
Período documentado: 2021-12-01 hasta 2023-05-31
Under the threat of ongoing global warming, predictions concerning how much temperatures will rise and precipitation will change are undergoing continual improvement, but the spatial distribution of predicted changes and their impacts on Earth-surface processes, notably erosion and sedimentation, are subject to great uncertainty. Such processes have immediate consequences for people living along alluvial or “transport-limited” rivers, which constitute the majority of rivers on Earth, yet their evolution in response to external forcing conditions is not well understood. In the GyroSCoPe project, we address these knowledge gaps through an innovative approach that focuses on how periodic changes in climate affect Earth-surface processes. Specifically, because the dominant forcing frequencies have changed through time (notably at the Mid-Pleistocene Transition, MPT, which occurred around 1 million years ago), and the frequency of each forcing period likely dictates how far downstream in alluvial channels impacts are felt, it should be possible to decipher the impacts of individual periodic forcings in the geologic record. To do this, we are applying novel tools to decipher erosion histories in mountainous regions, and we are investigating alluvial fans and terraces in the context of a new numerical model developed by my group. These data will allow us to interpret the impact of a change in the dominant forcing period on hillslope erosion rates, track how this sediment propagates across landscapes through alluvial rivers, and thus provide a wealth of data that can be used to calibrate landscape-evolution and alluvial-channel models. This improved understanding of the fundamental impacts of the magnitude and frequency of periodic forcing on erosion rates and sediment transport through rivers will in turn enable (1) the use of terraces and fans as paleoclimate proxies, which can be used to test climate models and (2) predicting Earth-surface responses to ongoing and future climate changes.
WP1: Impacts of periodic climate forcing in the Tien Shan, Kyrgyzstan
Thermochronology samples and an initial set of river terrace sampleswere collected during field expeditions in August 2021 and July 2022. Despite delays in obtaining shipping permits, all of the samples have arrived in Germany, and sample processing has started. We anticipate that the first results from both sets of samples will be available in March or April 2023.
WP2: Impacts of periodic climate forcing in the Central Andes, NW Argentina
Due to international travel restrictions during the pandemic, one Masters project was redesigned to focus on calibration of our alluvial-channel model with modern data published from the Central Andes. This work represents the first attempt to perform a field calibration of the model, which is critical for application of the model to other sites where my team is collecting new data. The student then used the calibrated model together with information from fluvial terraces (past sediment flux and past channel slope) to infer paleo-water discharge values.
Post-doctoral researcher PD2 has submitted a manuscript on his approximate analytical solutions to our alluvial-channel model to Geophysical Research Letters. With his analytical approximations, he was able to make precise predictions of how forcing with frequencies over several orders of magnitude not only affect cut-and-fill cycles and sediment-discharge signals along channels, but also predict how the amplitudes of response vary downstream, and by how much of a time lag exists between the timing of forcing and the timing of the channel response. These predictions have already helped us to better define our field sampling sites to most effectively test the model predictions. If the predictions are supported by our field observations, they will have major implications for interpreting river terraces and sedimentary archives with regards to past climate forcing, as well as enabling predictions of how future climate change will affect river-channel geometry.
Samples from the Central Andes have been processed and analyzed; a manuscript on these results will be prepared within the coming year.
WP3: Impacts of periodic climate forcing in the Patagonian Andes
Thermochronology samples and a set of river terrace samples were collected on a field expedition in March 2022, associated with projects for one PhD student and one post-doctoral researcher. Approximately 20% of the samples have been processed, and we received results that are consistent with our hypothesis that river-channel incision started around 1 million years ago. We anticipate that the next large batch of results will arrive in March or April 2023.
WP4: Project coordination, management, synthesis and outreach
The PI published a manuscript in Geochronology with a new thermal model designed for interpreting regional thermochronology datasets. The model incorporates sample-specific information in a way that makes it a powerful approach to determining exhumation rates over wide regions. Moreover, it is the only thermal model that is designed to do so efficiently on regional scales. The model has been made freely available on Zenodo as both a Matlab script and a Python script, to ensure broad access to the model. This new model will play a key role in my team's efforts to use regional thermochronology datasets to assess how and where Quaternary climate change, and specifically the Mid-Pleistocene Transition, has impacted sites in the Kyrgyz Tien Shan and the Patagonian Andes.
Thermochronology samples and an initial set of river terrace sampleswere collected during field expeditions in August 2021 and July 2022. Despite delays in obtaining shipping permits, all of the samples have arrived in Germany, and sample processing has started. We anticipate that the first results from both sets of samples will be available in March or April 2023.
WP2: Impacts of periodic climate forcing in the Central Andes, NW Argentina
Due to international travel restrictions during the pandemic, one Masters project was redesigned to focus on calibration of our alluvial-channel model with modern data published from the Central Andes. This work represents the first attempt to perform a field calibration of the model, which is critical for application of the model to other sites where my team is collecting new data. The student then used the calibrated model together with information from fluvial terraces (past sediment flux and past channel slope) to infer paleo-water discharge values.
Post-doctoral researcher PD2 has submitted a manuscript on his approximate analytical solutions to our alluvial-channel model to Geophysical Research Letters. With his analytical approximations, he was able to make precise predictions of how forcing with frequencies over several orders of magnitude not only affect cut-and-fill cycles and sediment-discharge signals along channels, but also predict how the amplitudes of response vary downstream, and by how much of a time lag exists between the timing of forcing and the timing of the channel response. These predictions have already helped us to better define our field sampling sites to most effectively test the model predictions. If the predictions are supported by our field observations, they will have major implications for interpreting river terraces and sedimentary archives with regards to past climate forcing, as well as enabling predictions of how future climate change will affect river-channel geometry.
Samples from the Central Andes have been processed and analyzed; a manuscript on these results will be prepared within the coming year.
WP3: Impacts of periodic climate forcing in the Patagonian Andes
Thermochronology samples and a set of river terrace samples were collected on a field expedition in March 2022, associated with projects for one PhD student and one post-doctoral researcher. Approximately 20% of the samples have been processed, and we received results that are consistent with our hypothesis that river-channel incision started around 1 million years ago. We anticipate that the next large batch of results will arrive in March or April 2023.
WP4: Project coordination, management, synthesis and outreach
The PI published a manuscript in Geochronology with a new thermal model designed for interpreting regional thermochronology datasets. The model incorporates sample-specific information in a way that makes it a powerful approach to determining exhumation rates over wide regions. Moreover, it is the only thermal model that is designed to do so efficiently on regional scales. The model has been made freely available on Zenodo as both a Matlab script and a Python script, to ensure broad access to the model. This new model will play a key role in my team's efforts to use regional thermochronology datasets to assess how and where Quaternary climate change, and specifically the Mid-Pleistocene Transition, has impacted sites in the Kyrgyz Tien Shan and the Patagonian Andes.
Progress beyond the state of the art:
The new thermal model for interpreting thermochronology data advances the field of thermochronology beyond the state of the art, as no other thermal model previously available was designed to calculate exhumation rates in an unbiased manned from regional to global datasets. The model development was unplanned, but my motivation for creating the model arose from my recognition of the limits of currently available models for interpreting regional datasets.
The finding of an onset of incision for two large Patagonian rivers at ca. 1 million years ago is a major finding, and supports the initial hypothesis that the Mid-Pleistocene Transition had a major impact on erosion and landscape evolution in the Andes.
The submitted manuscript by project member Dr. Fergus McNab is a major advance in modeling the details of how periodic climate forcing will affect cut-and-fill cycles in river channels and how the amount of sediment transported downstream will vary over time (considering temporary storage and release of sediment along the channel). The model makes clear predictions that can be tested in the field, which we are planning to do with our field-based projects.
Expected results until the end of the project:
The work on using hyperspectral images to assist in mapping terraces is not yet complete (our first scenes should be delivered in early 2023), nevertheless, the Landsat-based analyses already show great promise. If we are able to improve upon the mapping further with hyperspectral imagery, this will clearly mark a major advance in using remotely-sensed imagery to map out geomorphic surface and provide a "weathering metric" that could be calibrated to infer absolute ages of surfaces.
A majority of the results of new sample collection from the Patagonian Andes and the Kyrgyz Tien Shan will be obtained in 2023. One additional field sampling campaign to Patagonia will take place in March 2023, with the aim of collecting 4 more thermochronology samples, more river-terrace samples, and performing in situ spectral measurements of terrace surfaces using a field spectrometer.
The work on alluvial-channel modeProgress beyond the state of the art and expected results until the end of the project
ling has continued, with the model framework now expanded to include not only single-thread channels (which reasonably charcterize the rivers we are studying in the Patagonian Andes), but also complex channel networks with a multitude of tributaries, which better characterizes the rivers we are studying in the Kyrgyz Tien Shan and the Central Andes. Fundamental differences in model predictions will be tested with the terrace ages and mapped distribution from both field sites.
The new thermal model for interpreting thermochronology data advances the field of thermochronology beyond the state of the art, as no other thermal model previously available was designed to calculate exhumation rates in an unbiased manned from regional to global datasets. The model development was unplanned, but my motivation for creating the model arose from my recognition of the limits of currently available models for interpreting regional datasets.
The finding of an onset of incision for two large Patagonian rivers at ca. 1 million years ago is a major finding, and supports the initial hypothesis that the Mid-Pleistocene Transition had a major impact on erosion and landscape evolution in the Andes.
The submitted manuscript by project member Dr. Fergus McNab is a major advance in modeling the details of how periodic climate forcing will affect cut-and-fill cycles in river channels and how the amount of sediment transported downstream will vary over time (considering temporary storage and release of sediment along the channel). The model makes clear predictions that can be tested in the field, which we are planning to do with our field-based projects.
Expected results until the end of the project:
The work on using hyperspectral images to assist in mapping terraces is not yet complete (our first scenes should be delivered in early 2023), nevertheless, the Landsat-based analyses already show great promise. If we are able to improve upon the mapping further with hyperspectral imagery, this will clearly mark a major advance in using remotely-sensed imagery to map out geomorphic surface and provide a "weathering metric" that could be calibrated to infer absolute ages of surfaces.
A majority of the results of new sample collection from the Patagonian Andes and the Kyrgyz Tien Shan will be obtained in 2023. One additional field sampling campaign to Patagonia will take place in March 2023, with the aim of collecting 4 more thermochronology samples, more river-terrace samples, and performing in situ spectral measurements of terrace surfaces using a field spectrometer.
The work on alluvial-channel modeProgress beyond the state of the art and expected results until the end of the project
ling has continued, with the model framework now expanded to include not only single-thread channels (which reasonably charcterize the rivers we are studying in the Patagonian Andes), but also complex channel networks with a multitude of tributaries, which better characterizes the rivers we are studying in the Kyrgyz Tien Shan and the Central Andes. Fundamental differences in model predictions will be tested with the terrace ages and mapped distribution from both field sites.