Seasonal variability in temperature trends and atmospheric circulation systems during the Eemian (Last Interglacial) based on n-alkanes hydrogen isotopes from Northern Finland

The Last Interglacial warm period, the Eemian (ca. 130–116 thousand years ago), serves as a reference for projected future climate in a warmer world. However, there is a limited understanding of the seasonal characteristics of interglacial climate dynamics, especially in high latitude regions. In this study, we aim to provide new insights into seasonal trends in temperature and moisture source location, linked to shifts in atmospheric circulation patterns, for northern Fennoscandia during the Eemian. Our study is based on the distribution and stable hydrogen isotope composition (δD) of n-alkanes in a lake sediment sequence from the Sokli paleolake in NE Finland, placed in a multi-proxy framework. The δD values of predominantly macrophyte-derived mid-chain n-alkanes are interpreted to reflect lake water δD variability influenced by winter precipitation δD (δDprec), ice cover duration and deuterium (D)-depleted meltwater. The δD values of terrestrial plant-derived long-chain n-alkanes primarily reflect soil water δD variability modulated by summer δDprec and by the evaporative enrichment of soil and leaf water. The δDprec variability in our study area is mostly attributed to the temperature effect and the moisture source location linked to the relative dominance between D-depleted continental and polar air masses and D-enriched North Atlantic air masses. The biomarker signal further corroborates earlier diatom-based studies and pollen-inferred January and July temperature reconstructions from the same sediment sequence. Three phases of climatic changes can be identified that generally follow the secular variations in seasonal insolation: (i) an early warming trend succeeded by a period of strong seasonality (ii) a mid-optimum phase with gradually decreased seasonality and cooler summers, and (iii) a late climatic instability with a cooling trend. Superimposed on this trend, two abrupt cooling events occur in the early and late Eemian. The Sokli δD variability is generally in good agreement with other North Atlantic and Siberian records, reflecting major changes in the atmospheric circulation patterns during the Eemian as a response to orbital and oceanic forcings.

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Katrantsiotis, K., Norström, E., Smittenberg, R.H., Salonen, J.S., Plikk, A., and Helmens, K., 2021. Seasonal variability in temperature trends and atmospheric circulation systems during the Eemian (Last Interglacial) based on n-alkanes hydrogen isotopes from Northern Finland. Quaternary Science Reviews: 273, 107250. https://doi.org/10.1016/j.quascirev.2021.107250

Major winter atmospheric circulation patterns affecting Scandinavia climate dynamics (see also paragraph 2). NAO - North Atlantic Oscillation, AO - Arctic Oscillation, H - High pressure system, L- Low pressure system. (B) Atmospheric circulation patterns over Europe during summers with the effects of EA (East Atlantic) atmospheric pattern. Paleoclimatic records discussed in the text and plotted in Fig. 8: A-Sokli, B- Korallgrottan Cave, C- Okshola Cave, D-Ocean Drilling Program ODP Site 980, E-NEEM, F-Lake Baikal, G-MD99-2202 site in the Bahamian archipelago.