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- Title
Using Water Table Depths Inferred From Testate Amoebae to Estimate Holocene Methane Emissions From the Hudson Bay Lowlands, Canada.
- Authors
Davies, M. A.; McLaughlin, J. W.; Packalen, M. S.; Finkelstein, S. A.
- Abstract
Wetlands are the largest natural source of methane, yet the roles of source region and paleoclimate in explaining the variability in Holocene atmospheric methane concentrations remain poorly constrained. The Hudson Bay Lowlands (HBL) is one of the world's largest continuous peatland regions and a significant source of methane. We present here, using a novel proxy‐based approach, Holocene methane fluxes for the HBL. Paleo‐methane fluxes were quantified based on water table depth (WTD), inferred from testate amoeba assemblages in nine peat records. WTDs were reconstructed using a North American transfer function and were used to estimate paleo‐methane flux through a linear regression model of contemporary growing season methane fluxes and WTDs from 88 sites across the region. Following HBL peatland initiation in the Middle Holocene, total methane flux is closely related to the increasing area of land emerging from below sea level, controlled by rapid rates of glacial isostatic adjustment. In the Late Holocene, rates of uplift slowed, but methane fluxes remained high due to lower evapotranspiration in a wetter and cooler climate. We estimate that 4.8 ± 1.6 Pg C has been released from HBL peatlands to the atmosphere as CH4 over the last 8,000 years, with an average annual methane emission of 1.1 Tg CH4 yr−1 in the Late Holocene. The values estimated here are broadly consistent with those calculated from other independent methods, on modern and Holocene timescales, demonstrating that testate amoeba records provide an effective approach for scaling local processes to regional paleo‐methane emissions. Plain Language Summary: Northern peatlands are an important part of the global carbon cycle, as they both store a third of the soil carbon pool and are a significant natural methane source to the atmosphere. Therefore, understanding long‐term carbon uptake and release in these ecosystems is important for understanding their role in future climate change. Here, we use the paleoecological record preserved in peat cores up to 8,000 years old to analyze how methane emissions varied in the past in response to paleoclimate and landscape changes. We focus on the Hudson Bay Lowlands (HBL), one of the world's largest continuous peatland regions. We analyzed testate amoebae (single‐celled protists) in a series of nine peat cores. These organisms preserve well as microscopic fossils, and they are highly sensitive to waterlogging. Using statistical models, we use assemblages of fossil testate amoebae to quantify the changes in surface wetness over the past 8,000 years. Those changes in wetness were then used to infer summer‐season methane fluxes using available contemporary methane flux measurements under different conditions of waterlogging. The results show a link between total methane emissions and land available for the early part of the record and show potential for increased methane fluxes under wetter climates. Key Points: Novel proxy‐based approach used to estimate total Holocene methane emissions from Hudson Bay Lowlands peatlands (0.01–1.3 Tg CH4 yr−1)Holocene emissions are related to land availability, controlled by changing glacial isostatic adjustment rates, and hydroclimateDrier conditions and lower methane fluxes in the Middle Holocene coincide with regionally lower lake levels and warmer temperatures
- Subjects
HUDSON Bay Lowlands (Canada); METHANE &; the environment; WATER table -- Climatic factors; GROUNDWATER mounding; HOLOCENE Epoch
- Publication
Journal of Geophysical Research. Biogeosciences, 2021, Vol 126, Issue 2, p1
- ISSN
2169-8953
- Publication type
Article
- DOI
10.1029/2020JG005969