TY - JOUR
T1 - A 2000 year record of climatic change at Ongoke Lake, southwest Alaska
AU - Chipman, Melissa L.
AU - Clarke, Gina H.
AU - Clegg, Benjamin F.
AU - Gregory-Eaves, Irene
AU - Hu, Feng Sheng
N1 - Funding Information:
Acknowledgments This research is part of the ARCSS 2kyr project. Funding was provided by NSF grants ATM 03-18404 and ARC 04-55102 to FSH. This paper is based on the Master’s thesis research of MLC, who was supported by a Minority Recruitment Scholarship from the Graduate College of the University of Illinois. We thank Tom Brown at the Lawrence Livermore Laboratory for radiocarbon dating. We are grateful to three anonymous reviewers for their constructive comments and to Nicole Davi, Darrell Kaufman, Nick McKay, Michael Loso, and Greg Wiles for allowing the use of their data for comparison with our record. Special thanks to several current and former members of the Hu Lab Group (Andrew Henderson, Carolyn Barrett, David Nelson, Denise Devotta, Kevin Wolfe, Ryan Kelly, and Susanne Nagi) for their comments on earlier drafts of this paper.
PY - 2009/1
Y1 - 2009/1
N2 - We analyzed sediments of the past 2000 years from Ongoke Lake, southwest Alaska, for organic carbon, organic nitrogen, biogenic silica (BSi), and diatom assemblages at decadal to centennial resolution to infer limnological changes that may be related to climatic variation in southwestern Alaska. The chronology is based on a 210Pb profile from bulk sediments and nine AMS 14C ages from terrestrial plant macrofossils. Four of the 14C ages span a core depth interval of 60.5 cm but are statistically indistinguishable from one another with a mean of ~1300 AD, which compromises the determination of temporal trends at Ongoke Lake and comparison with other paleoclimate records. The diatom record suggests changes in the duration of ice cover and strength of thermal stratification that are probably related to temperature variation. This variation includes a cold interval around the first millennium cooling (FMC) and a warm interval spanning the medieval climate anomaly (MCA). However, the lake-sediment record shows no clear signals of temperature variation for the period of the Little Ice Age (LIA) or the twentieth century. Climatic changes during these periods may have been manifested through effective-moisture (precipitation minus evapotranspiration) variation in the Ongoke Lake area. We estimate water depths and infer effective-moisture fluctuations by applying a regional transfer function to our diatom record. Together with inferences from diatom autecologies, this water-depth reconstruction suggests that effective moisture increased steadily from 50 BC to 350 AD, which was followed by relatively dry conditions between 550 and 750 AD and relatively wet conditions between 750 and 1450 AD. Effective moisture was low from ~1450 to 1850 AD, coinciding with the LIA; an alternative age model places this interval between ~1315 and 1850 AD. During the past 150 years, effective moisture increased, with estimated water depths reaching peak values in the second half of the twentieth century. This study offers the first paleolimnological record for inferring centennial-scale climatic variation over the past two millennia from southwestern Alaska.
AB - We analyzed sediments of the past 2000 years from Ongoke Lake, southwest Alaska, for organic carbon, organic nitrogen, biogenic silica (BSi), and diatom assemblages at decadal to centennial resolution to infer limnological changes that may be related to climatic variation in southwestern Alaska. The chronology is based on a 210Pb profile from bulk sediments and nine AMS 14C ages from terrestrial plant macrofossils. Four of the 14C ages span a core depth interval of 60.5 cm but are statistically indistinguishable from one another with a mean of ~1300 AD, which compromises the determination of temporal trends at Ongoke Lake and comparison with other paleoclimate records. The diatom record suggests changes in the duration of ice cover and strength of thermal stratification that are probably related to temperature variation. This variation includes a cold interval around the first millennium cooling (FMC) and a warm interval spanning the medieval climate anomaly (MCA). However, the lake-sediment record shows no clear signals of temperature variation for the period of the Little Ice Age (LIA) or the twentieth century. Climatic changes during these periods may have been manifested through effective-moisture (precipitation minus evapotranspiration) variation in the Ongoke Lake area. We estimate water depths and infer effective-moisture fluctuations by applying a regional transfer function to our diatom record. Together with inferences from diatom autecologies, this water-depth reconstruction suggests that effective moisture increased steadily from 50 BC to 350 AD, which was followed by relatively dry conditions between 550 and 750 AD and relatively wet conditions between 750 and 1450 AD. Effective moisture was low from ~1450 to 1850 AD, coinciding with the LIA; an alternative age model places this interval between ~1315 and 1850 AD. During the past 150 years, effective moisture increased, with estimated water depths reaching peak values in the second half of the twentieth century. This study offers the first paleolimnological record for inferring centennial-scale climatic variation over the past two millennia from southwestern Alaska.
KW - Alaska
KW - Biogenic silica
KW - Diatoms
KW - First millennium cooling
KW - Late Holocene paleoclimate
KW - Little Ice Age
KW - Medieval climate anomaly
KW - Water-depth reconstruction
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U2 - 10.1007/s10933-008-9257-8
DO - 10.1007/s10933-008-9257-8
M3 - Article
AN - SCOPUS:58349084863
SN - 0921-2728
VL - 41
SP - 57
EP - 75
JO - Journal of Paleolimnology
JF - Journal of Paleolimnology
IS - 1
ER -