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Temperature is the key variable in the study of climate changes in the past and future. Most previous studies on past temperature reconstructions, however, have focused on the mean annual temperature (MAT). Here, focusing on the seasonal temperature reconstructions in the Northern Hemisphere extratropics during the Holocene period, we show that the change in seasonal cycle of temperature reconstructions is severely underestimated in comparison with the expectation from present observations. Our study highlights the current uncertainty in seasonal temperature reconstructions in the Holocene, with an implication that the MAT simulation in current climate models may not be much biased. 

Abstract: Original datasets used in:  Shutkin et al. (2025). Modeling the impacts of climate trends and lake formation on the retreat of a tropical Andean glacier (1962–2020). The Cryosphere. https://egusphere.copernicus.org/preprints/2025/egusphere-2024-3194/ See original paper and supplement for details regarding methods and data usage.All spatial data are projected in WGS 1984 UTM Zone 18S. 

Changes in global mean sea level (GMSL) during the late Cenozoic remain uncertain. We use a reconstruction of changes in δ¹⁸O of seawater to reconstruct GMSL since 4.5 million years ago (Ma) that accounts for temperature-driven changes in the δ¹⁸O of global ice sheets. Between 4.5 and 3 Ma, sea level highstands remained up to 20 m above present whereas the first lowstands below present suggest onset of Northern Hemisphere glaciation at 4 Ma. Intensification of global glaciation occurred from 3 Ma to 2.5 Ma, culminating in lowstands similar to the Last Glacial Maximum lowstand at 21,000 years ago and that reoccurred throughout much of the Pleistocene. We attribute the middle Pleistocene transition in ice sheet variability (1.2 Ma to 0.62 Ma) to modulation of 41-thousand-year (kyr) obliquity forcing by an increase in ~100-kyr CO₂variability. 

Speleothem δ18O records from central southern China have long been regarded as a key benchmark for Asian summer monsoon intensity. However, the similar δ18O minima observed among precession minima and their link to seasonal precipitation mixing remains unclear. Here, we present a 400,000-y record of summer precipitation δ18O from loess microcodium, which captures distinct precession cycles similar to those seen in speleothem δ18O records, particularly during glacial periods. Notably, our microcodium δ¹⁸O record reveals very low-δ¹⁸O values during precession minima at peak interglacials, a feature absent in speleothem δ¹⁸O records from central southern China. This discrepancy suggests that the mixed summer and nonsummer climatic signals substantially influence the speleothem δ¹⁸O records from central southern China. Proxy-model comparisons indicate that the lack of very low-δ¹⁸O values in speleothem δ¹⁸O records is due to an attenuated summer signal contribution, resulting from a lower summer-to-annual precipitation ratio in southern China at strong monsoon intervals. Our findings offer a potential explanation for the long-standing puzzle of the absence of 100- and 41-kyr cycles in speleothem δ¹⁸O records and underscore the critical role of seasonality in interpreting paleoclimatic proxies in central southern China. These insights also have broader implications for interpreting speleothem δ¹⁸O records globally, advocating for a more multiseason interpretive framework. 

Abstract. Located in Peru's Cordillera Blanca, the Queshque Glacier (∼9.8° S) has experienced nearly continuous retreat since the mid-20th century. More recently, this trend has accelerated after the glacier transitioned from land to lake terminating. We use observations of glacier surface height change (1962–2008), bed topography, and climatology to evaluate the relative drivers of Queshque's evolution from 1962–2020. Six Open Global Glacier Model ensemble members differing in climatic sensitivity are calibrated to fit the mass balance rate of −442 ± 16 mm w.e. a−1 calculated over the 2008 glacier area between 1962–2008. The models are then used to simulate monthly glacier mass balance over the entire study period and dynamic glacier evolution from 2008 to 2020. The models reproduce a typical outer-tropical glacier mass balance regime, showing continuous ablation throughout the year that increases during the pronounced wet season. Climatological trend analyses along with coupled mass balance and ice flow simulations indicate that temperature has been the predominant driver of mass loss since 2008 and that recent precipitation amounts have caused minor dampening of this trend. The strongest negative correlation between temperature and mass balance occurs during the wet season, while a positive correlation between precipitation and annual mass balance is most pronounced during the dry season. The influence of ENSO over mass balance trends appears to decline throughout the study period except during the wettest months, suggesting that wet season Pacific sea-surface temperatures are strong predictors of outer-tropical glacier mass balance variability. Finally, frontal ablation into the newly formed lake began in 2010. This caused ice acceleration at the glacier front, an average mass loss increase of 4 %, and a significant narrowing of the model ensemble mass loss spread. We conclude that while Queshque's trajectory remained coupled to climatic forcings, the new proglacial lake exacerbated and modified the retreat pattern regardless of the model climate sensitivity. 

Abundant proxy records suggest a profound reorganization of the Atlantic Meridional Overturning Circulation (AMOC) during the Last Glacial Maximum (LGM, ~21,000 y ago), with the North Atlantic Deep Water (NADW) shoaling significantly relative to the present-day (PD) and forming Glacial North Atlantic Intermediate Water (GNAIW). However, almost all previous observational and modeling studies have focused on the zonal mean two-dimensional AMOC feature, while recent progress in the understanding of modern AMOC reveals a more complicated three-dimensional structure, with NADW penetrating from the subpolar North Atlantic to lower latitude through different pathways. Here, combining²³¹Pa/²³⁰Th reconstructions and model simulations, we uncover a significant change in the three-dimensional structure of the glacial AMOC. Specifically, the mid-latitude eastern pathway (EP), located east of the Mid-Atlantic Ridge and transporting about half of the PD NADW from the subpolar gyre to the subtropical gyre, experienced substantial intensification during the LGM. A greater portion of the GNAIW was transported in the eastern basin during the LGM compared to NADW at the PD, resulting in opposite²³¹Pa/²³⁰Th changes between eastern and western basins during the LGM. Furthermore, in contrast to the wind-steering mechanism of EP at PD, the intensified LGM EP was caused primarily by the rim current forced by the basin-scale open-ocean convection over the subpolar North Atlantic. Our results underscore the importance of accounting for three-dimensional oceanographic changes to achieve more accurate reconstructions of past AMOC. 

Abstract Proxy‐based reconstructions suggest that equilibrium changes in global mean sea surface temperature (ΔGMSST) are nearly equivalent to changes in mean ocean temperature (ΔMOT) on glacial‐interglacial timescales over the past 900,000 years. However, the underlying mechanisms responsible for this relationship remain poorly understood. Here we use simulations from Paleoclimate Modeling Intercomparison Project Phase 3 and 4 (PMIP3/4) to investigate equilibrium ΔMOT and its linkage to sea surface temperature changes between the Last Glacial Maximum (LGM, ∼21,000 years ago) and pre‐Industrial. Results show that PMIP3/4 simulations generally underestimate proxy‐based ΔMOT. Regression analysis reveals that LGM MOT is strongly modulated by mid‐latitude SST cooling, with the Southern Ocean having a greater influence compared to other oceanic regions, thus helping explain why models with similar ΔGMSSTs exhibit significantly different ΔMOTs. Additionally, we find a strong relationship between simulated Antarctic sea‐ice coverage and Southern Ocean SST changes, with implications for constraining sea‐ice reconstructions.