Rapid deglacial and early Holocene expansion of peatlands in Alaska

Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, PA 18015, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 04/2010; 107(16):7347-52. DOI: 10.1073/pnas.0911387107
Source: PubMed


Northern peatlands represent one of the largest biospheric carbon (C) reservoirs; however, the role of peatlands in the global carbon cycle remains intensely debated, owing in part to the paucity of detailed regional datasets and the complexity of the role of climate, ecosystem processes, and environmental factors in controlling peatland C dynamics. Here we used detailed C accumulation data from four peatlands and a compilation of peatland initiation ages across Alaska to examine Holocene peatland dynamics and climate sensitivity. We find that 75% of dated peatlands in Alaska initiated before 8,600 years ago and that early Holocene C accumulation rates were four times higher than the rest of the Holocene. Similar rapid peatland expansion occurred in West Siberia during the Holocene thermal maximum (HTM). Our results suggest that high summer temperature and strong seasonality during the HTM in Alaska might have played a major role in causing the highest rates of C accumulation and peatland expansion. The rapid peatland expansion and C accumulation in these vast regions contributed significantly to the peak of atmospheric methane concentrations in the early Holocene. Furthermore, we find that Alaskan peatlands began expanding much earlier than peatlands in other regions, indicating an important contribution of these peatlands to the pre-Holocene increase in atmospheric methane concentrations.

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    • "We interpret this to reflect relatively high terrestrial productivity, which coincides with the latter part of the HTM in Alaska (Kaufman et al., 2004) and with the peak in sea surface temperatures in the northwest Pacific Ocean and Bering Sea (Max et al., 2012) over the last 15,000 years. Regionally, high productivity also coincides with the peak in thermokarst lake development across the circum Arctic (Walter et al., 2007) and peatland initiation across Alaska (Jones and Yu, 2010). Holocene to late Pleistocene age solifluction deposits mapped immediately north of Burial Lake (Hamilton, 2010) represent a local source of autochthonous organic matter delivered to the lake from permafrost degradation at this time. "
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    ABSTRACT: Sediment cores from Burial Lake located in the western Brooks Range in Arctic Alaska record paleoenvironmental changes that span the last 37,000 calendar years before present (cal yr BP). We identified four distinct lithologic subunits based on physical properties (dry bulk density, magnetic susceptibility), sediment composition, and geochemical proxies (organic matter, biogenic silica, C/N, organic matter δ13C and δ15N, and elemental data from scanning X-ray Fluorescence). The multi-proxy approach and relatively high temporal resolution (at multi-decadal to centennial time scales) of our proxy analysis, compared with previous studies of intermediate water depth cores from Burial Lake, provides new insights into the paleoenvironmental history of the region spanning the period prior to the Last Glacial Maximum. Relatively high lake-levels and gradually decreasing in-lake and terrestrial productivity occur during the mid-Wisconsin interstadial from 37,200 to 29,600 cal yr BP. The subsequent period is defined by falling and lower lake-levels with decreasing effective-moisture, windier conditions, and sustained low aquatic productivity throughout the LGM between 29,600 and 19,600 cal yr BP. The last deglaciation that commenced by 19,600 cal yr BP is characterized by gradual changes in several sediment physical and geochemical proxies, including increasing C/N ratios and terrestrial productivity, decreasing magnetic susceptibility and clastic sediment flux, along with rising and relatively higher lake-levels. A decrease in aeolian activity after 16,500 cal yr BP is inferred from the appearance of fine (very fine sandy silt) sediment, compared to coarse sediments through the LGM and last deglaciation. The highest levels of terrestrial inputs along with increasing and variable aquatic productivity occurs during the Lateglacial to early Holocene interval between 16,500 and 8,800 cal yr BP. The absence of multi-proxy evidence for a strong climatic reversal during the Younger Dryas from Burial Lake sediments contrasts with some paleorecords showing cooler temperatures and/or dry conditions in northern Alaska at this time. Peak levels of sediment organic content and terrestrial productivity at Burial Lake between 10,500 and 9,900 cal yr BP coincide with the early Holocene summer insolation maxima, which likely represents summertime warming and an enhanced flux of watershed derived organic matter from permafrost degradation. The remainder of the Holocene (since 8,800 cal yr BP) at Burial Lake is characterized by relatively high and stable lake levels, landscape stabilization, and relatively high and variable levels of aquatic productivity.
    Quaternary Science Reviews 08/2015; 126. DOI:10.1016/j.quascirev.2015.08.031 · 4.57 Impact Factor
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    • "We thus suggest that higher insolation-induced temperature instead of monsoondriven precipitation is more crucial in triggering the peatland initiation at orbital timescales over the past 40,000 yr. Peat and peat-like depositions might be attributed to both high summer insolation leading to increased productivity and low winter insolation leading to reduced decomposition (Fig. 3, Berger and Loutre, 1991; Jones and Yu, 2010). Also, during MIS 2 when the Asian Summer Monsoon was much weaker , the steady lacustrine condition, however, remained in the Dajiuhu region. "
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    ABSTRACT: Central China has experienced stronger summer monsoon during warm periods such as Marine Isotope Stages (MIS) 1 and 3, and weaker summer monsoon during cool periods such as MIS 2. The evolution history of Dajiuhu subalpine peatland in central China can help investigate how the expansion and shrinkage of peatland were associated with monsoonal strength over the last glacial–interglacial cycle. Here we apply bulk organic carbon and molecular biomarkers (hopane and n-alkane) to reconstruct the evolution history for the Dajiuhu peatland over the past 40,000 yr. The results indicate fluctuations between lacustrine and peat-like deposition during MIS 3, steady lacustrine deposition during MIS 2, and peatland initiation and expansion during MIS 1 in the Dajiuhu peatland. Therefore, at the glacial–interglacial scale, warmer summer and cooler winter conditions in interglacial periods are crucial to trigger peat deposition, whereas reduced evaporation in glacial period instead of decreased monsoonal-driven precipitation would have played a predominant role in the regional effective moisture balance. However, within the Holocene (MIS 1), monsoonal precipitation changes appear to be the main controller on millennial-scale variations of water-table level of the Dajiuhu peatland.
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    • "All calibrated median ages are shown as calendar years before present, where BP is equal to AD 1950, unless otherwise stated. The calibrated 2s age ranges were grouped into 500-year bins for calculating the frequency of peatland initiation (Jones and Yu, 2010; Zhao et al., 2014), and the frequencies were then added to calculate the peatland initiation cumulative percentage. Basal radiocarbon ages were used to estimate LORCA and the depth of 2 ka BP was estimated by linear interpolation between median calibrated radiocarbon dates. "
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    ABSTRACT: Peatlands contain around one third of the global soil carbon (C) and play an important role in the C cycle. In particular, the response of the productivity-decay balance to climate variability is critical for understanding both the past and future global C cycle. Most studies of peatland C dynamics have been carried out on boreal and subarctic peatlands, where climate models predict a greater increase in temperature compared to the global average. Less is known about peatlands at lower latitudes, yet there are significant peatland C stocks in these regions that may be more vulnerable to future climate change because they are closer to the climatic limit of peatland distribution. Northeast China is China's largest wetland region, with extensive peatlands in mountain regions and across the plains. Here, we used core data from 134 peatland sites to quantify the C accumulation rate over different timescales and estimate C storage across northeast China. The results show that the Holocene long-term apparent rate of C accumulation (LORCA) ranged from 5.74 to 129.31 g C m−2 yr−1, with a mean rate of 33.66 g C m−2 yr−1. The total wetland area and C storage within this region is 82,870 km2 and 4.34 Gt C, and about 80% of the C is contained in mountain peatlands. We find that total C accumulated over the last 2000 years is linearly related to photosynthetically active radiation over the growing season, supporting the hypothesis that rates of net primary productivity (NPP) are more important than decomposition rates in determining long-term C accumulation. Although peatlands in northeast China are close to the southern limit of major peatland extent, our data suggest that future warming will lead to greater future C accumulation, as long as moisture balance or cloudiness do not become limiting factors.
    Quaternary Science Reviews 05/2015; 115. DOI:10.1016/j.quascirev.2015.03.005 · 4.57 Impact Factor
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