Abstract. Analyzing seasonally resolved δ18O ice core data can aid the
interpretation of the climate information in ice cores, also providing
insights into factors governing the δ18O signal that cannot be
deciphered by investigating the annual δ18O data only.
However, the seasonal isotope signal has not yet been investigated in
northern Greenland, e.g., at the NEEM (North Greenland Eemian Ice Drilling)
ice core drill site. Here, we analyze seasonally resolved δ18O
data from four shallow NEEM ice cores covering the last 150 years. Based on
correlation analysis with observed temperature, we attribute about 70 and
30 % of annual accumulation to summer and winter, respectively. The NEEM
summer δ18O signal correlates strongly with summer western
Greenland coastal temperature and with the first principal component (PC1) of
summer δ18O from multiple seasonally resolved ice cores from
central/southern Greenland. However, there are no significant correlations
between NEEM winter δ18O data and western Greenland coastal
winter temperature or southern/central Greenland winter δ18O
PC1. The stronger correlation with temperature during summer and the
dominance of summer precipitation skew the annual δ18O signal
in NEEM. The strong footprint of temperature in NEEM summer
δ18O record also suggests that the summer δ18O
record rather than the winter δ18O record is a better
temperature proxy at the NEEM site. Despite the dominant signal of the North
Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO) in
the central–southern ice core data, both NAO and AMO exert weak influences
on NEEM seasonal δ18O variations. The NEEM seasonal
δ18O is found to be highly correlated with Baffin Bay sea ice
concentration (SIC) in the satellite observation period (1979–2004),
suggesting a connection of the sea ice extent with δ18O at
NEEM. NEEM winter δ18O significantly correlates with SIC even
for the period prior to satellite observation (1901–1978). The NEEM winter
δ18O may reflect sea ice variations of Baffin Bay rather than
temperature itself. This study shows that seasonally resolved
δ18O records, especially for sites with a seasonal
precipitation bias such as NEEM, provide a better understanding of how
changing air temperature and circulation patterns are associated with the
variability in the δ18O records.
Chlorophyll-a
in Antarctic Landfast Sea Ice: A First Synthesis of Historical Ice Core Data