G04_P01

Exploiting radiocarbon to investigate the fate of permafrost organic matter supply to the Canadian Beaufort Sea

Bröder L^1,2, Lattaud J¹, Juhls B³, Eulenburg A³, Priest T⁴, Fritz M³, Matsuoka A⁵, Pellerin A⁶, Bossé-Demers T⁷, Rudbäck D⁸, O'Regan M⁸, Whalen D⁹, Haghipour N¹, Eglinton T¹, Overduin P³, Vonk J²

¹Swiss Federal Institute of Technology, Zürich, Switzerland, ²Vrije Universiteit, Amsterdam, The Netherlands, ³Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Potsdam, Germany, ⁴Max-Planck-Institute for Marine Microbiology, Bremen, Germany, ⁵University of New Hampshire, Durham, USA, ⁶Université du Québec à Rimouski, Rimouski, Canada, ⁷Université Laval, Québec City, Canada, ⁸Stockholm University, Stockholm, Sweden, ⁹Natural Resources Canada, Halifax, Canada

The Canadian Beaufort Sea receives large quantities of sediment, organic carbon and nutrients from rapid coastal erosion and permafrost thaw. In addition, the Mackenzie River, the largest North American Arctic river, discharges great amounts of freshwater, dissolved solids and suspended sediments to the Beaufort Sea. Current changes in these fluxes in response to the warming climate have uncertain consequences for the carbon budget on the shelf and in the deep ocean. To investigate the movement and transformation of organic matter along the land-ocean continuum, we collected water and surface sediment samples across the Beaufort Sea during fall 2021. Sampling locations span from shallow, coastal, sites with water depths ≤ 20 m, to shelf-break and deep-water settings on the continental slope (water depths of ≥1000 m). For this study, we use radiocarbon analyses of dissolved inorganic (DIC), dissolved organic (DOC) and particulate organic carbon (POC) for surface and bottom waters, as well as surface sediments, in order to compare, contrast and constrain the relative source contributions and ages of these different forms of carbon. Our results will help to better understand the fate of permafrost organic matter in the marine environment and to ultimately improve assessments of the Canadian Beaufort Sea shelf as a carbon source or sink and its potential trajectory with ongoing environmental changes.

G04_P02

Radiocarbon age of plant remains in massive ground ice of the Barrow Permafrost Tunnel, Alaska

Iwahana G¹, Uchida M², Mantoku K², Kobayashi T²

¹University Of Alaska Fairbanks, Fairbanks, United States, ²National Institute for Environmental Studies, Tsukuba, Japan

Permafrost provides paleoenvironmental information from organic matter, gas, water, and sediment contents captured in the perennially frozen ground.  Syngenetic ice wedges that grow laterally in frost cracks of the permafrost sediments are expected to be an alternative paleoenvironmental proxy where information from nearby glacier/ice sheet core or lake sediments is unavailable. Massive ground ice found in the Barrow Permafrost Tunnel at the depth range between 3 and 7 m from the surface has been interpreted as ice-wedge and used to reconstruct environmental changes in the early Holocene. To better understand the development of the massive ground ice, we conducted Radiocarbon dating of plant remains and stable isotope analysis of the ice along with two profiles. Combining with previous results, we mapped the radiocarbon age distribution within the massive ground ice. The age distribution from our dense sampling showed two ice regions with similar ages centering 11,200 and 10,200 yBP divided by a relatively narrow region of intermediate age along with the 5-m profile parallel to the tunnel long-axis. From the other sampling profile that is perpendicular to the tunnel, the youngest age (8,451 yBP) was found from the NW end of the profile. The water stable isotopes from the profile perpendicular to the tunnel showed the lowest anomaly at the SE end, which contradicts the ice-wedge origin assumption. Our results indicate the existence of unknown processes in the massive ice growth or large randomness of cracking locations during ice-wedge development.

G04_P03

Multiple radiocarbon dating of POC, DOC, DIC, and plant remains in ground ice of Siberian permafrost

Minami M¹, Sato R¹, Iwahana G², Hiyama T¹

¹Nagoya University, Nagoya, Japan, ²University of Alaska Fairbanks, Fairbanks, USA

For understanding paleoclimate changes and hydrological environmental changes preserved in ground ice, it is important to determine the chronology of the ice formation. To examine which carbon fraction in ground ice shows the most true formation age, we performed multiple ¹⁴C dating of some carbon fractions in ground ice: particulate organic carbon (POC), dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and plant remains. The ground ice samples used are permafrost outcrops collected at Syrdakh and Churapcha, near the city of Yakutsk, Russia. The thawing samples were filtered through a 0.7-μm quartz filter, and the filtrate was ultrafiltered through a 10,000 MWCO (Molecular Weight Cut-Off) followed by a 3,000 MWCO (Vivaspin Turbo, Sartorius). The ¹⁴C ages of POC in the ground ice samples were 40−27 kyr BP, which is about 10,000 years older than the plant age of 24−22 kyr BP, while the ¹⁴C ages of DOC varied with molecular size: 28−19 kyr BP for the 0.7 μm−10,000 MW and 10,000−3,000 MW fractions, and a younger age of 18−12 kyr BP for the <3000 MW, which is similar to ¹⁴C ages for DIC.

We will discuss the result of the multiple ¹⁴C dating to determine which carbon fraction in the ground ice is most suitable for accurate dating of the ice formation.