Late-Holocene Lake-Level Variation in West Greenland

Situated between the North Atlantic and the Greenland ice sheet, the thousands of lakes in the Kangerlussuaq area of West Greenland (67°N) present excellent targets for paleoclimate studies. Paleoshorelines surrounding multiple closed-basin lakes in this area record fluctuations in lake level since deglaciation. Shorelines along two of these lakes, Hundeso and Lake E, were surveyed and trenched to reconstruct the history of lake-level change. The stratigraphies of the trenches were described, and a chronology has been developed using radiocarbon dating of organic material. Preliminary results indicate a highly variable hydrologic regime throughout the late Holocene. Hundeso had high-stand lake levels ~810 and 1950 14C yr. B.P., reaching elevations 4-5 meters above present lake level. Topographic data show that at these times Hundeso was joined with several neighboring lakes to form a mega lake that covered over 520 ha. Lake E also experienced high stands at the same time (830 and 1920 14C yr. B.P.), with lake levels 1-2 meters above present. This study presents the first direct evidence of Holocene lake-level variability in this region, which can be used to constrain the interpretation of other paleoclimate proxies in cores from regional lakes. Our data suggest substantial hydrologic variation during the last 2000 years, including the highest lake stands since the lakes were formed ~8000 years ago

Stratigraphy and paleohydrology of lake basins in west Greenland

Modern observations, geomorphic and sedimentary history, and water-balance modeling were integrated to study the modern and ancient hydrologic and sedimentary processes of lakes in West Greenland. These lakes are located immediately north of the Arctic Circle and are the subject of ongoing paleoclimate investigations to characterize the natural variability of the arctic climate in this region. Observed precipitation records from Kangerlussuaq, Greenland, and atmospheric variables from the NCEP/NCAR reanalysis were used in a statistical analysis to determine controls on the seasonal variation of precipitation. Three distinct patterns of correlation between precipitation and the 500-hPa geopotential height were found to represent three dominant atmospheric patterns that strongly influence precipitation for different times of the year. Spatially dependent indices were developed based on the 500-hPa geopotential height field. The correlation coefficients between precipitation and these indices range from -0.35 to 0.55. Three parasequences identified in paleoshoreline exposures, along with seismic and ground penetrating radar data, were used to reconstruct lake-level fluctuations since deglaciation (∼8000 yr BP). Immediately following deglaciation, lake-levels dropped to ∼12-15 m below modern, but quickly rose to ∼5-6 m above modern by 5700 cal. yr BP. Lake-levels remained high until ∼3000 cal yr BP, when they declined to ∼2 m above modern. Lake-levels again increased to ∼4-5 m above modern by 2300 cal. yr BP and remained high until ∼700 cal. yr BP, after which they declined to modern values. Therefore, current lake levels are the lowest of the last ∼5700 years. Seismic data also provided evidence of subaqueous mass movements, modern sediment re-working from waves, and biogenic gas formation. Water-balance modeling resulted in mean annual precipitation anomaly (ΔMAP) estimates between +80 and +170 mm from 5700 to 3600 cal. yr BP and between +40 and +80 mm from 3000 to 700 cal. yr BP. In contrast, a ΔMAP of ∼-70 mm is estimated for the post-glacial lowstand. Thus, these studies demonstrate the large range of hydrologic variability in West Greenland relative to that of the 20th century

Alternative Indices for the Warm-Season NAO and Precipitation Variability in West Greenland

Observed precipitation records from Kangerlussuaq, Greenland, and atmospheric variables from the NCEP–NCAR reanalysis were used in a statistical analysis to elucidate controls on the seasonal variation of precipitation and develop indices that may be potentially useful for analyzing precipitation variability in paleoclimate and future climate change investigations. Three distinct patterns of correlation between precipitation and the 500-hPa geopotential height were found to represent three dominant atmospheric patterns that strongly influence precipitation for different times of the year. All three patterns show a relation to the North Atlantic Oscillation signature found in the first empirical orthogonal function of the 500-hPa height field. Spatially dependent indices were developed based on the 500-hPa geopotential field. The correlation coefficients between precipitation at Kangerlussuaq and these indices range from –0.38 for winter to 0.64 for the warm season (May–September). The warm-season index herein is the first index reported in the literature that correlates significantly with precipitation during the warm season. Correlations of these indices with precipitation in Oslo, Norway, are high and are of opposite sign to west Greenland indices for the winter and summer months. This indicates that they are good representations of the atmospheric patterns associated with the North Atlantic Oscillation and the west Greenland–northern Europe “seesaw.” High correlations are also found with precipitation measured at Nuuk, Qaqortoq, and Upernavik, Greenland. Links updated November 2010