@article {3000,
	title = {Radiocarbon dates, charcoal, and polycyclic aromatic hydrocarbon (PAH) data from Great Dismal Swamp Sites GDS-519 and GDS-520},
	year = {2021},
	publisher = {U.S. Geological Survey},
	abstract = {Sediment cores were collected in Great Dismal Swamp National Wildlife Refuge in November, 2017 to advance understanding of climate- and land-management driven changes in vegetation, hydrology, and fire regimes. Radiocarbon dates were obtained from samples in two cores (GDS-519-3-21-2017 and GDS-520-3-21-2017) to generate age models for the cores. Bulk sediment samples, charcoal, plant macrofossils, and pollen residue were selected at the USGS in Reston, Virginia and submitted to Beta Analytic, Inc. and the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) laboratories for radiocarbon dating. Those laboratories provided both radiocarbon ages and stable carbon isotope (delta 13C) results, which can be used to generate calibrated ages. Bulk density was measured for each core at the USGS in Reston, Virginia. Cores were sectioned at 1-cm increments. One cubic centimeter of wet sediment was extracted from each 1-cm increment downcore and weighed. Samples were subsequently dried at 100 degrees C for at least 24 hours to obtain dry weights, and bulk density was calculated by dividing original 1-cc volume by the dry weight. Polycyclic aromatic hydrocarbons (PAHs) and sedimentary charcoal were analyzed at the Virginia Institute of Marine Science at Gloucester Point, Virginia. PAH analysis began with freeze-drying of samples and extraction of their lipid contents using a Dionex 350 Accelerated Solvent Extractor (9:1; dicholoromethane:methanol). Total lipid extracts were separated into three fractions using silica gel columns and eluents of increasing polarity (F1: hexane, F2: 25\% toluene in hexane, F3: methanol). Combined F1 and F2 fractions were analyzed to quantify PAHs using an Agilent 7890A gas chromatograph coupled with a 5975C mass selective detector (GC-MSD). The GC was equipped with a DB-5MS capillary column (30 m length; 320 micrometres outer diameter; 0.25 micrometres film thickness), which was heated using the following temperature program: 16 degrees C/minute to 150 degrees C and 5 degrees C/minute to 300 degrees C. Flow rate was 1.1 mL/minute. Individual PAH abundances were quantified using select ion monitoring mode (SIM) and relative to an external calibration curve constructed with a PAH calibration standard (Sigma-Aldrich CRM47940). Sixteen PAHs were quantified: naphthalene (Na), acenaphthylene (Ayl), acenaphthene (Ace), anthracene (An), phenanthrene (Phe), fluoranthene (Fla), pyrene (Py), benz[a]anthracene (Ba), chrysene (Ch), retene (Ret), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), benzo[b]fluoranthene (BbF), benzo[g,h,i]perylene (Bghi), dibenzo[a,h]anthracene (DiAn), and ideno[1,2,3-cd]pyrene (IP). PAH accumulation rates were quantified using the dry sediment concentration of PAHs and the age-depth model of the sediment cores. Sedimentary charcoal analysis followed a modified version of standard methodologies for isolating and identifying sedimentary charcoal particles. Dried sediment samples were weighed and then subjected to a light chemical treatment (1:1, by volume mixture of 1M sodium hexametaphosphate solution and 2\% sodium hypochlorite solution) for 24 hours, in accordance with standard methods (Vachula et al., 2019, 2018). Samples were washed over two nested sieves (63 micrometre and 125 micrometre mesh sizes) to isolate an intermediate size fraction (63-125 micrometres), in which charcoal particles were enumerated using a dissection microscope and gridded petri dishes. Charcoal accumulation rates were quantified using the numeric concentration of charcoal particles, the bulk density of the sediments, and the age-depth model of the sediment cores. References Vachula, R.S., Russell, J.M., Huang, Y. and Richter, N., 2018. Assessing the spatial fidelity of sedimentary charcoal size fractions as fire history proxies with a high-resolution sediment record and historical data. Palaeogeography, Palaeoclimatology, Palaeoecology, 508, pp.166-175. Vachula, R.S., Russell, J.M. and Huang, Y., 2019. Climate exceeded human management as the dominant control of fire at the regional scale in California{\textquoteright}s Sierra Nevada. Environmental Research Letters, 14(10), p.104011.},
	keywords = {Climatology},
	doi = {10.5066/P90L278U},
	url = {https://www.sciencebase.gov/catalog/item/614215cad34e0df5fb947f74},
	author = {Willard, Debra A and Jones, Miriam C and Vachula, Richard S and Balascio, Nicholas L and Canuel, Elizabeth A}
}
@article {2857,
	title = {Temperature-controlled tundra fire severity and frequency during the last millennium in the Yukon-Kuskokwim Delta, Alaska},
	journal = {The Holocene},
	volume = {29},
	year = {2019},
	month = {Jan-07-2019},
	pages = {1223 - 1233},
	abstract = {Wildfire is an important disturbance to Arctic tundra ecosystems. In the coming decades, tundra fire frequency, intensity, and extent are projected to increase because of anthropogenic climate change. To more accurately predict the effects of climate change on tundra fire regimes, it is critical to have detailed knowledge of the natural frequency and extent of past wildfires and how they responded to past climate variability. We present analyses of fire frequency and temperature from a lake sediment core from the Yukon-Kuskokwim (YK) Delta. Our ca. 1000 macroscopic charcoal record shows more frequent but possibly less severe tundra fires during the first half of the last millennium, whereas less frequent, possibly more severe fires characterize the latter half. Our temperature reconstruction, based on distributional changes of branched glycerol dialkyl glycerol tetraethers (brGDGTs), shows slightly warmer conditions from ca. AD 1000 to 1500, and cooler conditions thereafter (ca. AD 1500 to 2000), suggesting that fire frequency increases when climate is relatively warmer in this region. When wildfires occur more frequently, fire severity may decrease because of limited biomass (fuel source) accumulating between fires. The data suggest that tundra ecosystems are highly sensitive to climate change, and that a warmer climate, which is predicted to develop in the near future, will result in more frequent tundra wildfires.},
	keywords = {alaska, Arctic, charcoal, glycerol dialkyl glycerol tetraethers (GDGTs), late-holocene, Paleoclimate, Paleofire},
	issn = {0959-6836},
	doi = {10.1177/0959683619838036},
	url = {http://journals.sagepub.com/doi/10.1177/0959683619838036},
	author = {Sae-Lim, Jarunetr and Russell, James M and Vachula, Richard S and Holmes, Robert M and Mann, Paul J and Schade, John D and Natali, Susan M}
}
