Northern Peatland Climate Archives Show Moisture Shifts with Carbon Cycle Implications
Establishing a longer perspective for climate change is important in northern peatlands where carbon sequestration plays a major role in the global carbon cycle. Whether peatlands have always been the carbon sink they are today is critical for understanding future sinks and sources of carbon. Subarctic Alaskan peatlands are particularly sensitive to climate change, where alterations to the biogeochemical and hydrological cycles are affected by the vegetational shifts taking place. As part of a coastal regional Alaskan transect we analyzed a 2.5 meter sediment core at 2-cm intervals for fossil pollen, spores, and macrofossils over the last 14,000 years, utilizing plant macrofossils for accelerator mass spectrometry (AMS) carbon-14 dating. This record gives us the Kenai climate since the last ice age, which is then comparable to sites westward (Kodiak, the Alaskan Peninsula) and southeastward (Icy Cape, Yakutat).
Results show that peat initiation began on the Kenai Peninsula around 14,000 years ago, and cool temperatures resulted in shrubs dominating until the Holocene warming, which favored tree growth. Complexity in the Alaskan Younger Dryas cooling is indicated by the expansion of dwarf birch on the Kenai, while other Alaskan sites show declines in shrubs and increases in herbs. Possible explanations include either birch dominance due to increased snowfall which would have favored nutrient enrichment, or enhanced permafrost which may have created palsas and a drier habitat. A remarkable fern dominance that followed for about 3000 years (11,500-8500 years ago) shows high moisture in the region. This wetter interval is in contrast to drier conditions at Icy Cape and Yakutat to the southeast. This fern interval suggests a possible re-positioning of the Aleutian Low with increased rainfall, followed by a drier interval with high seasonality and enhanced glacial melt on the Kenai.
These moisture shifts dramatically affected peat preservation, with enhanced peat preservation in the wetter interval and more decomposition in the drier regimes. Trees entered the local area as the climate warmed, and subsequent shifts in first cooling, then drying and volcanic activity between 5000 and 3500 years ago were followed by the cool, moist climate resulting in Neoglaciation up to the present. Mountain hemlock trees expanded after about 1500 years ago in response to cooler, moist conditions, a pattern typical of areas both to the west and southeast.
Jones, M.C., D.M. Peteet, D. Kurdyla, and T. Guilderson 2009: Climate and vegetation history from a 14,000-year peatland record, Kenai Peninsula, Alaska. Quaternary Res., 72, 207-217, doi:10.1016/j.yqres.2009.04.002.
Please address all inquiries about this research to Dr. Dorothy Peteet.