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Cosmogenic radionuclides (e.g., 10Be) from ice cores are a powerful tool for solar reconstructions back in time. However, superimposed on the solar signal, other factors like weather/climate and volcanic influences on 10Be can complicate the interpretation of 10Be data. A comprehensive study of 10Be records over the recent period, when atmospheric 10Be production and meteorological conditions are relatively well‐known, can improve our interpretation of 10Be records. Here we conduct a systematic study of the production and climate/volcanic signals in Antarctica and Greenland 10Be records, including a new 10Be record from the East GReenland Ice‐core Project site. Greenland and Antarctica records show significant decreasing trends (5%–6.5%/decade) for 1900–1950, which is comparable with the expected production rate inferred from sunspot observations. By comparing 10Be records with reanalysis data and atmospheric circulation patterns, 10Be records from Southern/Southeastern Greenland are significantly correlated with the Scandinavia pattern. Stacking 10Be records from different locations can enhance the production signal. However, this approach is not always straightforward as uncertainties in some records can lead to a weaker solar signal. A strategy can be employed to select records for the bipolar stack by comparing Greenland records with Antarctica records, assuming the shared signal is a production signal. Finally, we observe significant increases (36%–64%) in 10Be depositions in Greenland related to the Agung eruption. This large increase in Greenland 10Be records after the Agung eruption, could be partly explained by the enhanced air mass transport from mid‐latitudes coinciding with the decreased precipitation en‐route. Plain Language Summary: Cosmogenic radionuclides (e.g., 10Be) from ice cores are useful proxies for reconstructing the solar variability in the past. However, besides the solar signal, there are also atmospheric and volcanic signals in 10Be records measured from ice cores. It is important to understand those signals before we can reliably apply 10Be records for solar reconstructions. A study of 10Be records over the recent period, when atmospheric 10Be production and meteorological conditions are relatively well‐known, can improve our interpretation of polar 10Be records. In this study, we conduct a systematic study of the production and climate/volcanic signals in 14 10Be records, including a new 10Be record from East GReenland Ice‐core Project site. We find that simply averaging all available 10Be records to strengthen the solar signal in the composite record is not always straightforward as uncertainties (e.g., regional climate effects) in some records can weaken the solar signal. For example, 10Be records from Central and Southern Greenland are influenced by the atmospheric circulation pattern (Scandinavia pattern). Finally, we find a large increase in 10Be (>30%) depositions in Greenland after the Agung eruption, which could be partly explained by enhanced air mass transport from mid‐latitudes coinciding with decreased precipitation en‐route. Key Points: A systematic analysis of production, climate, and volcanic signals in 14 polar 10Be records over the last 100 yearsThe stacking method is not always straightforward to enhance the solar signal in 10Be records due to uncertainties in some 10Be records10Be records from Central and Southern Greenland are influenced by the Scandinavia pattern [ABSTRACT FROM AUTHOR]

The climate signal imprinted in the snow isotopic composition allows to infer past climate variability from ice core stable water isotope records. The concurrent evolution of vapor and surface snow isotopic composition between precipitation events indicates that post‐depositional atmosphere‐snow humidity exchange influences the snow and hence the ice core isotope signal. To date, however, this is not accounted for in paeleoclimate reconstructions from isotope records. Here we show that vapor‐snow exchange explains 36% of the summertime day‐to‐day δ18O variability of the surface snow between precipitation events, and 53% of the δD variability. Through observations from the Greenland Ice Sheet and accompanying modeling we demonstrate that vapor‐snow exchange introduces a warm bias on the summertime snow isotope value relevant for ice core records. In case of long‐term variability in atmosphere‐snow exchange the relevance for the ice core signal is also variable and thus paleoclimate reconstructions from isotope records should be revisited. Plain Language Summary: Ice core water isotope records are valuable climate proxies containing information about past climate. Climate reconstructions from ice cores have been based on the interpretation of the water isotope records as precipitation signal. Here we show that the humidity exchange between atmosphere and snow influences the surface snow isotopic composition in‐between precipitation events in summer. Thus, it is not the precipitation signal alone that defines the summer snow isotope signal but a combination of precipitation and post‐depositional atmospheric vapor‐snow exchange. This suggests, that climate reconstructions from ice core isotope records should account for post‐depositional processes in the interpretation of the water isotope signal, specifically when interpreting summer isotope signals. Key Points: Atmosphere‐snow exchange of water vapor is a key process for the signal formation of the snow isotopic compositionTaking into account isotopic fractionation during sublimation we explain a significant share of the observed day‐to‐day isotope variabilityAtmosphere‐snow exchange introduces a warm‐bias in the net summer snow isotope signal that is not accounted for in ice core interpretations [ABSTRACT FROM AUTHOR]