Abstract
The Last Interglacial (Eemian, MIS 5e) can be considered a test-bed for climate dynamics under a warmer-than-present climate. In this study we present a chironomid record from the high latitude Sokli site (N Finland), where a long continuous sediment sequence from the last interglacial has been preserved from glacial erosion. The chironomid-analysis shows a diverse fauna, with dominance of warm-water indicators and shifts in assemblage composition that can be attributed to temperature, lake depth, productivity and habitat availability. Quantitative mean July paleotemperature estimates based on the chironomid data indicate overall mean July air temperatures up to 1 °C warmer than present. Two cooling events can be discerned, the Tunturi event, dated to about 127.5 ka BP, in the lower part of the sequence, and the Värriö event, dated to about 119 ka BP, associated with the beginning of a cooling trend in the upper part of the record. Warm conditions already at the onset of the interglacial contrast with a recent chironomid-based last interglacial temperature reconstruction from Denmark, which suggests a late onset of Eemian warming. The relatively small increase in inferred temperatures compared to present day temperatures at Sokli differs from other high latitude Eemian sites, and likely reflects the influence of the Atlantic Meridional Overturning Circulation in maintaining already elevated temperatures in Fennoscandia during interglacials.
Highlights
Model projections of future climate change suggest temperature increase outside the range of observational records with most pronounced warming occurring in the Arctic (IPCC 2013)
The transition from the lowermost two samples in the minerogenic sediment is characterized by a distinct increase in density of chironomid head capsules and a decrease in profundal taxa e.g. Micropectra insignilobus-type, Heterotrissocladius spp., Parakiefferiella bathophilatype, Chironomus anthracinus-type and Stichtochironomus rosenschoeldi-type from peak values (15–30%), as well as in Microtendipes pedellus-type, associated with minerogenic sediment, Orthocladius spp and Chironomini larvulae
A temperature increase of 1 °C renders a temperature at Sokli similar to the temperatures of the warmest decennium of the twentieth century (1930s) and the Holocene thermal maximum (Seppaet al. 2009), and is perhaps surprisingly low considering the difference in insolation between the Eemian and the Holocene (CAPE-Last Interglacial Project Members 2006). These results suggest that temperatures at the Sokli site, possibly slightly underestimated, followed the general pattern of the Northern Hemisphere during the Eemian, being less affected by polar amplification than other high latitude (Arctic) sites (CAPE-Last Interglacial Project Members 2006), which in turn may be a reflection of the general warming effect that the Atlantic meridional overturning circulation (AMOC) has on the Fennoscandian climate
Summary
Model projections of future climate change suggest temperature increase outside the range of observational records with most pronounced warming occurring in the Arctic (above 70°N) (IPCC 2013). Global mean summer temperatures during the Eemian climate optimum are estimated to have been approximately 0–2 °C higher than present (IPCC 2013). Reconstructed summer temperature anomalies are larger in the circum-Arctic region, approximately 4–5 °C above present for most of the Arctic, due to the various feedback mechanisms amplifying insolation-driven warming at high latitudes (CAPE-Last Interglacial Project Members 2006). Paleoclimate information from this period can contribute to our knowledge of climate dynamics and forcing under a warmer than present climate and may be used for validation of climate models. It serves as a reference for natural climate variability during all phases of an interglacial, from the deglaciation to the thermal maximum to the instability associated with the onset of glaciation
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