Abstract
Two > 5-m-long sediment cores from Cascade Lake (68.38° N, 154.60° W), Arctic Alaska, were analyzed to quantify their paleomagnetic properties over the past 21,000 years. Alternating-field demagnetization of the natural remanent magnetization, anhysteretic remanent magnetization, isothermal remanent magnetization, and hysteresis experiments reveal a strong, well-defined characteristic remanent magnetization carried by a low coercivity magnetic component that increases up core. Maximum angular deviation values average < 2°, and average inclination values are within 4° of the geocentric axial dipole prediction. Radiometric ages based on 210Pb and 14C were used to correlate the major inclination features of the resulting paleomagnetic secular variation (PSV) record with those of other regional PSV records, including two geomagnetic field models and the longer series from Burial Lake, located 200 km to the west. Following around 6 ka (cal BP), the ages of PSV fluctuations in Cascade Lake begin to diverge from those of the regional records, reaching a maximum offset of about 2000 years at around 4 ka. Several correlated cryptotephra ages from this section (reported in a companion paper by Davies et al., this volume) support the regional PSV-based chronology and indicate that some of the 14C ages at Cascade Lake are variably too old.
Highlights
In paleoclimate and paleo-environmental studies of lake sediments, a firm chronological framework is needed to place observations and corresponding interpretations into regional and global contexts
Unit L2 exhibits a spike in magnetic parameters relative to unit L3, with kLF exhibiting a low of 4.50 x 10-5 at 382 cm to a high of 1.06 x 10-4 SI at 361 cm, anhysteretic remanent magnetization (ARM) acquisition at 100 mT alternating field (AF) exhibits a low of 7.89 x 10-3 at 381, to a high 2.95 x 10-2 A m-1 at 363 cm), and IRM0.3T at 0 mT AF exhibits a low of 4.81 x 10-1 at 380, to a high 2.03 A m-1 at 355 cm) and saturation isothermal remanent magnetization (SIRM) at 0 mT AF exhibits a low of 8.97 x 10-1 at 380, to a high 2.35 A m-1 at 355 cm. (Fig. 2)
Up-core of this interval, IRM0.3T does not cleanly decrease in intensity with higher AF suggesting that the SQUID electronics are unable to keep up with the change in counts resulting in artifacts within the subsequent magnetic measurements
Summary
In paleoclimate and paleo-environmental studies of lake sediments, a firm chronological framework is needed to place observations and corresponding interpretations into regional and global contexts. Dating Quaternary lake sediments in the Arctic using 14C can be problematic due to scarcity of terrestrial macrofossils, and the inheritance of “old carbon” eroded 25 from the surrounding landscape (Gaglioti et al, 2014). 30 The latest geomagnetic field models provide estimates of site-specific inclination, declination, and field intensity for the past 10 kyr (CALS10k.1b; Korte et al, 2011) and 9 kyr (pfm9k.1b; Nilsson et al, 2014) These models are not perfectly constrained for the Alaskan Arctic and they are inherently smoothed both spatially and temporally, their major directional and intensity features can be used for age control by correlation with site-level records (e.g., Barletta et al, 2010). In addition to correlations afforded by field models, individual site-level paleomagnetic records supported by well-constrained
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