Event Details

DATE:

Thursday, March 26, 2026


SPEAKER: 

Dr. Marisa Repasch, UNM


TITLE:  

The role of Earth surface processes in the global carbon cycle: From Arctic and

alpine landscapes to subtropical foreland basins


TIME:    

5:30 - 6:30 PM: Happy hour, dinner and drinks.

6:30 - 7:30 PM: Society business and talk.

7:30 PM: Raffle to raise money for student dinners.


LOCATION:  

Vallecito Room, Student Union Bldg., Fort Lewis College

 

COST:     

 $25/person


RESERVATION DEADLINE (Please register here on website):

Friday, March 19th by 5:00pm.


ZOOM LINK: https://fortlewis.zoom.us/j/9744025631 

Meeting ID: 9744025631. Zoom starts at 6:30pm

. 

ABSTRACT:

Earth surface processes, like erosion, weathering, and sediment transport, are a central yet under-constrained component of the global carbon cycle. Weathering and erosion in upland landscapes generate and mobilize soil and sediment, and rivers transport the associated organic carbon from mountains to ocean basins. Along this transit path, organic carbon may be oxidized and returned to the atmosphere as CO2 or buried and preserved in long-term depositional sinks. The balance between carbon burial and release governs whether landscapes act as net sources or sinks of atmospheric carbon, but the role of Earth surface processes in regulating this balance remains poorly quantified. In this talk, I examine how geomorphic, hydrologic, and geochemical processes influence the fate of carbon across diverse landscapes, from Arctic permafrost catchments and alpine headwaters to lowland subtropical foreland basins.

First, I present results from a ~1,300 km lowland river reach in the Andean foreland basin in Argentina. This reach has no tributaries, allowing us to isolate the effects of fluvial transit on the fate of particulate organic carbon (POC). We show that sediment transit time controls the magnitude of POC oxidation, while mineral stabilization of organic carbon regulates oxidation rates. We also find that lateral erosion of POC-rich floodplain soils can offset oxidation losses, implying that lateral channel migration may enhance long-term POC export and burial in downstream sedimentary basins. I then shift to northern Alaska, where permafrost thaw and hydrologic regime shifts may be influencing erosion rates, flow paths, and carbon cycle dynamics. Radiocarbon analyses from the Canning River reveal a downstream transition from bedrock-derived POC in mountainous headwaters to younger, more reactive soil carbon supplied by floodplain erosion. Complementary geochemical evidence shows that permafrost thaw may also enhance oxidation of sedimentary rock organic carbon, increasing CO2 release via bedrock weathering. Together, these results highlight how Earth surface processes regulate carbon preservation versus oxidation across climate and tectonic gradients, with important implications for carbon-climate feedbacks over both geologic and human timescales.