Carbon Dioxide Content of the Icelandic Mantle

Carbon emitted in volcanically-active regions provides insight into volatile fluxes, interactions between magmatic and crustal reservoirs, and the nature of deep carbon reservoirs and how they contribute to the global carbon cycle.

Carbon emitted in volcanically-active regions provides insight into volatile fluxes, interactions between magmatic and crustal reservoirs, and the nature of deep carbon reservoirs and how they contribute to the global carbon cycle. Iceland represents an ideal setting to investigate deep carbon due to its unique geological setting, marking the intersection of plume-related magmatism with the mid-Atlantic Ridge. New research from Barry et al. [1] suggests that the carbon dioxide (CO2) content of the Icelandic mantle overlaps with previous estimates from the upper-mantle, even though Iceland bears the ubiquitous high 3He/4He fingerprint of the lower-mantle. In addition, CO2 fluxes along the Icelandic neovolcanic zones may be larger than expected, due to higher crustal production rates in Iceland compared to submarine spreading centers. The team, based at Scripps Institution of Oceanography, report new CO2 abundance and isotope data for 71 geothermal gases and fluids from both high- and low-temperature geothermal systems located throughout Iceland and 47 subglacial basaltic glasses from the rift zones. This impressive carbon compilation reveals important information about carbon sources and fluxes as well as the overall extent of degassing.

“This study of carbon in Iceland represents one of the most comprehensive investigations reported to date and the findings reveal important information about carbon sources, fluxes, as well as the overall extent of degassing in Iceland” said lead author Dr. Peter Barry (now at the University of Tennessee, Knoxville).

Using an equilibrium-degassing model, Barry et al. estimate that pre-eruptive basaltic melts beneath Iceland are in good agreement with olivine-hosted melt inclusions [2] and estimates of depleted MORB mantle (DMM) CO2 source values [3]. Using these representative samples, the CO2 flux from Iceland was then estimated to be 0.1–10% of the estimated global ridge flux [4]. These findings suggest that the upper- and lower-mantle may be homogenized with respect to carbon. This work represents an important calibration point for future carbon studies in plume-influenced regions.

Image: Peter Barry: Geysir, Iceland – the type locality for geothermal manifestations known as geysers (spouting hot springs that intermittently boil and disperse water and steam into the air). It represents the first geyser described in a printed source and the first identified by modern Europeans. It is located in southwestern Iceland, in the Haukadalur valley.

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