Tree-ring isotope and satellite records of vegetation changes reveal transition from cold to hot degassing in the Yellowstone Plateau volcanic field
Magmatic degassing often provides the earliest clues to changes in magmatic systems, yet detection and characterization of the escaping gases is challenging. Recent work suggests that satellite-based normalized difference vegetation index (NDVI) calculations may provide an indirect method for detecting changes in degassing. Here, we use tree ring δ 13 C , δ 18 O , and radiocarbon ( 14 C) data to assess NDVI as a proxy for diffuse magmatic degassing and to better understand the development of the Tern Lake thermal area (TLTA) in the Yellowstone Plateau volcanic field, USA. We measured δ 13 C , δ 18 O , and 14 C in wood from four TLTA trees and two control trees. The 14 C data indicate that TLTA trees were exposed to significant magmatic CO 2 degassing during the 1990s, corroborating satellite-based NDVI changes observed at a time when no other indications of degassing existed. Magmatic degassing also increased water availability for trees closest to the degassing center, as indicated by decreasing δ 13 C and δ 18 O values relative to background throughout the 1980s and 1990s. Increased H 2 S degassing in the early 2000s impaired stomatal functioning, increasing δ 13 C and δ 18 O values. These isotope values were strongly correlated with NDVI, demonstrating that ground- and satellite-based approaches yield similar conclusions. Together, the satellite and isotope datasets suggest that TLTA degassing was characterized by cold CO 2 emissions with minimal H 2 S until the early 2000s, when it transitioned to a high-temperature system with significant CO 2 and H 2 S emissions. These results add to a growing body of evidence that vegetation responses can be an effective proxy for magmatic degassing.