Abstract
Stable water isotopologues in paleoclimate archives ( δ 18 O ) have been widely used as an indicator to derive past climate variations. The modern observed spatial δ 18 O -temperature relation in the middle and high latitudes has been used to infer the paleotemperatures changes from ice core data. However, various studies have shown that the spatial slope is larger than the temporal slope at the drill site by a factor of 2. Physically, the different spatial and temporal slope has been suggested to result from the amplified local surface air temperature cooling in the polar region at Last Glacial Maximum (LGM), according to the slope ratio equation derived in our previous study. To explicitly confirm the “polar amplification” effect in understanding the differences between temporal and spatial isotope–temperature relations, here we use the same isotope-enabled atmospheric general circulation model with a moisture-tracing module embedded to quantitatively estimate the contributions of different sources to the precipitated heavy oxygen isotopes in the middle and high latitudes. Our results show that the major sources of δ 18 O in precipitation over middle and high latitudes are from oceans where the sea surface temperature cooling at Last Glacial Maximum (LGM) is less than −2 ° C , while the local moisture sources with a higher cooling can be also relevant for polar regions, such as north Greenland. Additionally, the neglect of the strengthened local inversion layer strength at LGM could be the main cause for the overestimated source temperature cooling by the slope ratio equation, especially for the polar regions in the Northern Hemisphere.
Highlights
The ratio of stable oxygen isotopes 18 O/16 O in paleoclimate archives has been established as a well-recognized, most useful tool in deriving essential information of past climate changes during the last 22,000 years
By implementing stable water isotopes in atmospheric general circulation models (AGCMs), the reduced temporal slope relative to spatial slope in the local region can be qualitatively interpreted by the changes of precipitation in seasonality [8,11], moisture sources [12,13,14], atmospheric circulation and meteorological processes [15,16,17] and evaporation recharge processes over ocean [8]
After using the zonal mean spatial slope, the source temperature cooling for polar sub-regions is close to the results of quantitatively, the slope ratio equation implies an overestimated source temperature cooling by ~5 °C
Summary
The ratio of stable oxygen isotopes 18 O/16 O (hereafter δ18 O) in paleoclimate archives (i.e., ice cores, speleothems) has been established as a well-recognized, most useful tool in deriving essential information of past climate changes during the last 22,000 years. By implementing stable water isotopes in atmospheric general circulation models (AGCMs), the reduced temporal slope relative to spatial slope in the local region can be qualitatively interpreted by the changes of precipitation in seasonality [8,11], moisture sources [12,13,14], atmospheric circulation and meteorological processes [15,16,17] and evaporation recharge processes over ocean [8]. The contributions of different moisture source changes to the local precipitated isotopic content at middle and high latitudes in the LGM and present days were not quantified in our previous study. AGCM to quantify the isotopic contributions from different pre-defined moisture sources to the precipitated isotopic content over middle and high latitudes and further investigate how polar amplification of the SAT correlated to the temperature–oxygen relation based on slope ratio equation theory.
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