Early Holocene Temperature Oscillations Exceed Amplitude of Observed and Projected Warming in Svalbard Lakes

Abstract

Arctic climate is uniquely sensitive to ongoing warming. The feedbacks that drive this amplified response remain insufficiently quantified and misrepresented in model scenarios of future warming. Comparison with paleotemperature reconstructions from past warm intervals can help close this gap. The Early Holocene (11.7-8.2 ka BP) is an important target because Arctic temperatures were warmer than today. This study presents centennially resolved summer temperature reconstructions from three Svalbard lakes. We show that Early Holocene temperatures fluctuated between the coldest and warmest extremes of the past 12 ka, exceeding the range of instrumental observations and future projections. Peak warmth occurred~10 ka BP, with temperatures 7°C warmer than today due to high radiative forcing and intensified inflow of warm Atlantic waters. Between 9.5 and 8 ka BP, temperatures dropped in response to freshwater fluxes from melting ice. Facing similar mechanisms, our findings may provide insight into the near-future response of Arctic climate. Plain Language SummaryThe Arctic warms much faster than the global average. This amplified response can trigger feedbacks that affect the trajectory of future change. In areas formerly covered by ice, darker open water or rocks reflect less solar heat, enhancing warming. However, freshwater from melting ice may slow ocean circulation, leading to cooling. The climate impact of these mechanisms remain insufficiently understood, restricting efforts to predict future change. To reduce uncertainty, our research uses geological information from the most recent past period when the Arctic was warmer than the present, the Early Holocene, which lasted from 11,700 to 8,200 years ago. We analyzed fats from algae preserved in Svalbard lakes that yield information about past summer temperatures. Our findings show that the Early Holocene was characterized by the coldest and warmest extremes experienced since the last Ice Age. During peak warmth, summer temperatures were 7°C warmer than today as more solar radiation and warm water reached the Arctic. However, Early Holocene warming was much slower than today. But warming was interrupted when freshwater pulses from melting Ice Sheets lowered temperatures. As we face a warmer Arctic with a melting Greenland Ice Sheet, our findings provide a rare window into the region's future.

Arctic glaciers record wavier circumpolar winds

“…2b). We focus on the months June, July and August (JJA) as fluctuations in the summer melt rate cause the greatest year-to-year variability in the annual mass balances of both regions (75% for ACN and 68% for SVA) 11,17,18 (Extended Data Fig. 3).…”

“…As ACN is situated east and SVA west of the Greenland Ice Sheet, both regions have been influenced by more frequent blocking conditions in recent years 15,16 .Temperatures in Svalbard are projected to rise by 6-7 °C until 2100 under the IPCC scenario representative concentration pathway (RCP) 4.5 and up to 10 °C under business-as-usual conditions (RCP 8.5) compared with 1971-2000 17 . Precipitation is said to increase by 45-65% and to contain a progressively lower fraction of snowfall, causing unchanged or more snow storage under RCP 4.5 and less snow for RCP 8.5 over most of Svalbard (50-100% in many places) 17 . Combined with a shorter accumulation season 18 , the overall SMB will become increasingly negative.…”

Lake Dynamics Modulate the Air Temperature Variability Recorded by Sedimentary Aquatic Biomarkers: A Holocene Case Study From Western Greenland

“…Modern observations of lake SPM and surface sediments suggest 𝐴𝐴 U K 37 -temperature sensitivity is constant across Group I species (D'Andrea et al, 2016;Longo et al, 2016), supporting the reconstruction of Holocene temperature variations based on downcore Harning et al, 2020;Longo et al, 2020;Richter et al, 2021;van der Bilt et al, 2018van der Bilt et al, , 2019. For all currently published in situ Group I calibrations, 𝐴𝐴 U K 37 -temperature slopes are within error, albeit with different intercepts (D'Andrea et al, 2016;Longo et al, 2016Longo et al, , 2018.…”

“…Modern observations of lake SPM and surface sediments suggest $${\mathrm{U}}_{37}^{\mathrm{K}}$$‐temperature sensitivity is constant across Group I species (D’Andrea et al., 2016; Longo et al., 2016), supporting the reconstruction of Holocene temperature variations based on downcore $${\mathrm{U}}_{37}^{\mathrm{K}}$$ variations in the sediments of freshwater Arctic lakes (D’Andrea et al., 2011, 2012; Harning et al., 2020; Longo et al., 2020; Richter et al., 2021; van der Bilt et al., 2018, 2019). For all currently published in situ Group I calibrations, $${\mathrm{U}}_{37}^{\mathrm{K}}$$‐temperature slopes are within error, albeit with different intercepts (D’Andrea et al., 2016; Longo et al., 2016, 2018).…”

“…The site‐specific seasonality of $${\mathrm{U}}_{37}^{\mathrm{K}}$$‐inferred temperatures is typically determined according to the seasonal temperatures controlling the timing and water temperatures of modern ice out and inferred haptophyte bloom, as sediment traps show highest alkenone fluxes early in the ice‐free season during ice melt and isothermal mixing periods (D’Andrea et al., 2011, 2016; Longo et al., 2018). As a result, Arctic alkenone records have been interpreted to reflect winter/spring (Longo et al., 2020; Richter et al., 2021), early summer (D’Andrea et al., 2011), or average summer (JJA) temperature changes (D’Andrea et al., 2012; Harning et al., 2020; van der Bilt et al., 2018, 2019).…”