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Late Holocene storm-trajectory changes inferred from the oxygen ...

Late Holocene storm-trajectory changes inferred from the oxygen ...

J PaleolimnolFig. 9 a

J PaleolimnolFig. 9 a Principalcomponent analysis of MicaLake d 18 O diatom , biogenicsilica (BSi), organic matter(OM), and dominant diatomgenera. b Stratigraphicchanges of the mostdominant diatom genera atMica Lake compared withd 18 O diatom , BSi, and OM.Three distinct stratigraphiczones were identifiedby the time-trajectoryPCA: 300–140 cm(9600–4000 cal BP);120–40 cm(4000–1000 cal BP);and 40–0 cm(1000 cal BP to present)120–40 cm (4000–1000 cal BP); and 40–0 cm(1000 cal BP to present).Oxygen isotope values of diatoms from MicaLakeForty-six downcore d 18 O diatom values from MC-2range between ?25.2 and ?29.8% (Table 3;Fig. 10a). Prior to 2.6 ka, the values range by only?2.2%. At 2.6 ka, d 18 O diatom exhibits a strong shiftto values that vary as much as ?4.6%. The youngestsample, which probably represents the last *15 year,contains the highest d 18 O diatom value at ?29.8%.Within the analytical precision of the laser-extractiontechnique (±0.2%), only one other sample, at 6.4 ka,has a comparable value. Mica Lake water, collectedduring the summers of 2006 and 2007, has an average(n = 6) d 18 O value of -13.0%; the measured123

J PaleolimnolTable 3 d 18 O diatom data from core MC-2Table 3 continuedAdjusteddepthblf (cm)Age(calBP) ad 18 O diatom (% VSMOW)Run 1 Run 2 Average SDAdjusteddepthblf (cm)Age(calBP) ad 18 O diatom (% VSMOW)Run 1 Run 2 Average SD0.25 -44 29.80.75 -18 28.61.25 7 28.41.75 32 27.03.25 107 25.9 25.7 25.8 0.13.75 132 26.2 25.9 26.0 0.24.25 156 27.34.75 181 27.45.25 206 27.312.75 563 29.213.25 586 29.013.75 609 28.714.75 652 28.115.75 696 27.616.75 738 29.022.75 967 26.524.25 1017 28.429.25 1159 26.139.25 1350 25.544.25 1422 28.749.25 1500 28.2 28.2 28.2 0.054.25 1601 28.7 28.5 28.6 0.159.25 1740 27.564.25 1916 28.2 28.3 28.3 0.169.25 2120 27.174.25 2340 25.6 24.9 25.2 0.579.25 2561 29.4 28.7 29.1 0.589.25 2955 28.9 28.7 28.8 0.299.25 3257 28.0109.25 3492 28.0119.25 3687 28.4129.25 3869 28.7138.75 4055 29.0 28.9 29.0 0.0149.75 4330 28.6168.75 5036 28.5178.75 5482 28.5180.25 5551 28.4188.25 5917 29.0198.25 6364 29.6207.25 6753 28.0 28.0 28.0 0.0217.25 7173 28.6227.25 7582 27.4247.25 8373 28.1257.25 8759 29.4266.75 9123 28.3276.75 9504 29.0a Ages based on model shown in Fig. 7Fig. 10 Oxygen isotope records from (a) Mica Lake diatomscompared to other North Pacific d 18 O records from (b)Jellybean Lake carbonate (Anderson et al. 2005) and (c) Mt.Logan ice cores. The inferred influences of climatic controlsdiscussed in the text are indicated. The climatic interpretationssuggested from model simulations by Fisher et al. (2004)explain the variability at Jellybean Lake and Mt. Logan. Age ofd 18 O diatom from Mica Lake based on age model in Fig. 7isotopic partitioning between modern water anddiatoms is ?42.8%. Similar differences betweenisotope values measured in water and diatoms fromsurface sediment have been measured at four otherlakes in south-central Alaska (Schiff 2007). Evenhigher partitioning values (?44.3%) have beenreported from marine diatoms (Juillet-Leclerc andLabeyrie 1987). However, cultured diatoms exhibitfar lesser degrees of oxygen isotopic enrichment123

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