An 800-year multiple-proxy record of atmospheric circulation, climate change, and aquatic productivity from Kepler Lake, South-Central Alaska
Dates
Year
2009
Citation
Gonyo, Andrew William, 2009, An 800-year multiple-proxy record of atmospheric circulation, climate change, and aquatic productivity from Kepler Lake, South-Central Alaska: Lehigh University.
Summary
A multiple-proxy investigation was undertaken on two short cores (85 cm and 101 cm long) from Kepler Lake, an evaporation-insensitive, groundwater-fed marl lake in South-Central Alaska, with the goal of reconstructing climate and environmental changes in recent centuries. The proxies employed in this study include: calcite Carbon-Oxygen isotopes, organic matter (OM) Carbon-Nitrogen isotopes, and loss on ignition (LOI) analysis. An 800-year chronology for two cores was established based on four calibrated AMS 14 C dates on terrestrial macrofossils, 210 Pb analysis and core-to-core correlations using LOI results. δ18 O VPDB values of inorganic calcite range from -17.0[per thousand] to -15.7[per thousand], with the highest values occurring [...]
Summary
A multiple-proxy investigation was undertaken on two short cores (85 cm and 101 cm long) from Kepler Lake, an evaporation-insensitive, groundwater-fed marl lake in South-Central Alaska, with the goal of reconstructing climate and environmental changes in recent centuries. The proxies employed in this study include: calcite Carbon-Oxygen isotopes, organic matter (OM) Carbon-Nitrogen isotopes, and loss on ignition (LOI) analysis. An 800-year chronology for two cores was established based on four calibrated AMS 14 C dates on terrestrial macrofossils, 210 Pb analysis and core-to-core correlations using LOI results. δ18 O VPDB values of inorganic calcite range from -17.0[per thousand] to -15.7[per thousand], with the highest values occurring during the period of 1450 to 1850 AD, a time coeval to the Little Ice Age (LIA). The high δ18 O values during the cold LIA contrast with the conventional temperature interpretation using O isotopes and are interpreted to reflect a shift in atmospheric circulation. A weakening of the wintertime Aleutian Low (AL) pressure system residing over the Gulf of Alaska would result in 18 O-enriched winter precipitation as well as a colder winter climate in SC Alaska during the LIA. We propose that elevated CaCO3 contents of >80% during the LIA reflect enhanced seasonality (warmer summer and colder winter), as calcite precipitation in freshwater lakes is primarily a function of peak summer temperature. This interpretation is also supported by high δ13 C values, likely reflecting high aquatic productivity. The enhanced seasonality during the LIA may explain some complex moisture and temperature changes inferred from studies of glacier, lake and tree-ring records. Since 1850 an increase of 6[per thousand] in δ 15 N from ca. +2[per thousand] to +8.0[per thousand] is interpreted to be caused by atmospheric transport of 15 N enriched N-containing pollutants to the lake since the European Industrial Revolution. Through the use of multiple proxies complex relationships between climate change (shifts in the strength and/or position of the AL) and anthropogenic change (atmospheric deposition of nitrogen) can be examined in the context of aquatic ecosystems in order to yield a more complete understanding of paleo-environmental change during the late Holocene.