DIFFUSING THE ARCTIC CARBON BOMB
Connecting hydrology, climate, and biogeochemistry
Arctic tundra holds about half of the soil carbon on Earth.
As it thaws, that carbon can be released into the atmosphere as a greenhouse gas, making global warming much worse.
However, we do not yet know how much carbon is delivered from the ground to the atmosphere, partly because we do not understand how the tundra drains the water that carries that carbon.
These flowpaths are complicated because the melting ice forces the water to continually change direction.
My job is to measure and model the patterns, amounts, and rates that water drains through arctic tundra, accounting for the continual thawing and freezing of the soil.
This work will allow us to better understand how much carbon we can expect tundra to supply to the atmosphere in a future, warmer climate.
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MEASURING PERMAFROST (IN A HILARIOUS TIME-LAPSE)
To understand the permafrost, we need to measure the permafrost. We made a series of high-density grids in which we measured the depth of the ice and water. You can watch us do it, all 3 hrs plus per grid, in a great 1 minute stop-motion video attached below. The results of these surveys end up in plots like the ones to the right.
MODELING PERMAFROST (IN A HILARIOUSLY LONG AMOUNT OF TIME)
Simulating the flow of water through something that continually drains, saturates, melts, and freezes is really tough on a computer. Both the equations that solve the heat of the soil and the flow of the water in the soil are nonlinear, so the computer has to do a ton of guess and check work to get that right. Thankfully, the adept team of modelers at Oak Ridge and Los Alamos National Labs have developed a model that can handle it, the Advanced Terrestrial Simulator. A simulation of a slice of my hillslope in Alaska is shown below: it's subjected to melting and freezing cycles for 10 years.
This powerful tool lets us simulate how the tundra will respond to the rapid warming that is expected for that region.
EXTRAPOLATING OUR FINDINGS
Our ultimate goal is to take our small-scale understanding and broaden it to watersheds. We have begun those efforts using large, publicly-available datasets. The figure below shows a snapshot of groundwater flowpaths and residence times based on the soil and water level, data we collected in the field, combined with lidar.
RELEVANT PUBLICATIONS & PRESENTATIONS
O’Connor, M., Cardenas, M.B., Nicholaides, K.D., Neilson, B.T., Kling, G.W., Groundwater flow in areas of continuous permafrost: the dynamic effects of stratigraphy, thawing, and micro- and macro-topography, in review, Water Resources Research
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Neilson, B. T., Cardenas, M. B., O'Connor, M. T., Rasmussen, M. T., King, T. V., & Kling, G. W. (2018). Groundwater flow and exchange across the land surface explain carbon export patterns in continuous permafrost watersheds. Geophysical Research Letters, 45(15), 7596-7605.
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O’Connor, M., Nicholaides, K.D., Cardenas, M.B., Neilson, B.T., Coon, E.T., Jan, A.L., Ferencz, S.B., Kling, G.W, 2018, Predictabiliyt of variable arctic soil hydraulic and thermal properties, and implications of such variability on future thawt, Poster at the American Geophysical Union Fall Meeting 2018, Washington, DC
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Wu, Y., O’Connor, M., Chen, J., Kling, G., Cardenas, M., Ferencz, S., 2018, Determining the link between hydraulic properties of arctic tundra soils and inferometric synthetic aperture radar deformation measurements, Poster at the American Geophysical Union Fall Meeting 2018, Washington, DC
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Cardenas, M., Neilson, B., O’Connor, M., Rasmussen, M., King, T., Kling, G., 2018, Groundwater flow and exchange across the land surface explain carbon export patterns in a continuous permafrost watershed, Talk at the American Geophysical Union 2018 Fall Meeting, Washington, DC
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O’Connor, M., Nicholaides, K.D., Cardenas, M.B., Neilson, B.T., Coon, E.T., Jan, A.L., Ferencz, S.B., Kling, G.W, 2018, Impact of a depth-variable organic mat on thaw and groundwater flow in continuous permafrost, Talk at the Geological Society of America Fall Meeting 2018, Indianapolis, IN
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O’Connor, M., Cardenas, M.B., Neilson, B.T., Nicholaides, K.D., Kling, G.W., Groundwater Dynamics and Export from Active Layer Aquifers Overlying Permafrost, Talk at the American Geophysical Union 2017 Fall Meeting, New Orleans, LA
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Nicholaides, K.D., O’Connor, M., Cardenas, M.B., Neilson, B.T., Kling, G.W., The Effects of Different Scales of Topographic Variation on Shallow Groundwater Flow in an Arctic Watershed, Poster Presentation at the American Geophysical Union 2017 Fall Meeting, New Orleans, LA
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O’Connor, M., Cardenas, M.B., Neilson, B.T., Kaufman, M.H., Kling, G.W., 2016, Controls on shallow groundwater flow and its implications on carbon processing in an arctic watershed, Poster at International Conference on Permafrost, Potsdam, Germany
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O'Connor, M., Cardenas, M.B., Neilson, B.T., Kling, G.W., 2015, Controls on Arctic groundwater flow and its impacts on carbon processing, Talk at Geological Society of America Fall Meeting 2015, Baltimore MD
DELTAS AS NATURAL WATER 'FILTERS'
Surface water/groundwater interaction within the world's newest land
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Deltas serve as the dumping ground for the world's largest river systems, which carry a whole lot of dump. These rivers often carry large volumes of agricultural runoff, causing ocean hypoxea and massive aquatic "dead zones".
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It is unclear how significantly the surface runoff interacts with surrounding delta islands as it flows to the ocean.
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Such interactions could help limit the spreading of these dead zones.
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I measured the dominant factors that that determine those interactions.
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My measurements determined that onshore/offshore winds as well as local tide activity drove surface water/groundwater exchange, potentially amplifying the amount of nutrient filtration that can occur.
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MEASURING HYDROLOGIC FORCINGS
We implemented sensors across the delta to measure the groundwater, surface water, and meterological conditions for a year. These data were used to develop the conceptual interpretation shown below. The full investigation can be found in the paper.
RELEVANT PUBLICATIONS & PRESENTATIONS
O’Connor, M., Moffett, K., 2015, Groundwater dynamics and surface water-groundwater interactions in a prograding delta island, Louisiana, USA, Journal of Hydrology, Volume 524, Pages 15-29, ISSN 0022-1694
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O'Connor, M., Moffett, K., 2013, Controls on groundwater dynamics and root zone aeration of a coastal fluvial delta island, Wax Lake, Louisiana, Poster at American Geophysical Union Fall Meeting 2015, San Francisco, CA
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Moffett, K., Smith, B., O'Connor, M., Mohrig, D., 2014, Evolution of subaerial coastal fluvial delta island topography into multiple stable states under influence of vegetation and stochastic hydrology, Talk at American Geophysical Union Fall Meeting 2014, San Francisco, CA