A Pulse of Meteoric Subsurface Fluid Discharging Into the Chukchi Sea During the Early Holocene Thermal Maximum (EHTM). (29th July 2021)

• Record Type: Journal Article
• Authors: Kim, Ji‐Hoon; Hong, Wei‐Li; Torres, Marta E.; Ryu, Jong‐Sik; Kang, Moo‐Hee; Han, Dukki; Nam, Seung‐Il; Hur, Jin; Koh, Dong‐Chan; Niessen, Frank; Lee, Dong‐Hun; Jang, Kwangchul; Rae, James William Buchanan; Chen, Meilian
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 22:Number 8(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-07-29
• Subjects: subsurface meteoric fluid discharge -- Arctic element/carbon cycle -- permafrost -- EHTM -- Chukchi Sea; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2021GC009750
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: The response of Arctic Ocean biogeochemistry to subsurface flow driven by permafrost thaw is poorly understood. We present dissolved chloride and water isotopic data from the Chukchi Sea Shelf sediments that reveal the presence of a meteoric subsurface flow enriched in cations with a radiogenic Sr fingerprint. This subsurface fluid is also enriched in dissolved inorganic carbon and methane that bear isotopic compositions indicative of a carbon reservoir modified by reactions in a closed system. Such fluid characteristics are in stark contrast with those from other sites in the Chukchi Sea where the pore water composition shows no sign of meteoric input, but reflect typical biogeochemical reactions associated with early diagenetic sequences in marine sediment. The most likely source of the observed subsurface flow at the Chukchi Sea Shelf is from the degradation of permafrost that had extended to the shelf region during the Last Glacial Maximum. Our data suggest that the permafrost‐driven subsurface flow most likely took place during the 2–3°C warming in the Early Holocene Thermal Maximum. This time scale is supported by numerical simulation of pore water profiles, which indicate that a minimum of several thousand years must have passed since the cessation of the subsurface methane‐bearing fluid flow. Plain Language Summary: The permafrost in the Arctic Ocean has repeatedly formed and thawed with global climate change through geological time with significant consequences for the marine subsurface environment. In addition to biogeochemical reactions in the sediment, global climate impacts the regional water and carbon cycles. Here we address the potential influence of permafrost dynamics on the geochemical cycles in the Chukchi Sea sediments. Pore water composition at the Chukchi Sea Shelf shows a freshwater signature indicative of a meteoric contribution. The characteristics of both pore water and gas in the shelf site were remarkably different from those observed in other areas of the Chukchi Sea. To understand why and when these unique properties developed, we simulated the pore water and gas data with a numerical model. We found that the observed freshwater signature and unique composition at the Chukchi Sea Shelf were likely caused by a paleo‐subsurface flow associated with natural permafrost thaw during the Early Holocene, when the Arctic region was at least 2–3°C warmer than today. Though the results of our study are significant, more research is needed to understand and predict the change in the marine subsurface environment as permafrost thaws in response to rapid global warming. Key Points: Pore water chemistry from the Chukchi Sea Shelf reveals meteoric subsurface flow in response to permafrost thaw at the Early Holocene Thermal Maximum Concentration and isotope data from carbon pools point to a migrating fluid input from an old carbon reservoir Subsurface flow is important for the budget of carbon and other elements related to permafrost thaw