Description: A multiproxy data set of an AMS radiocarbon dated 46 cm long sediment core from the continental margin off western Svalbard reveals multidecadal climatic variability during the past two millennia. Investigation of planktic and benthic stable isotopes, planktic foraminiferal fauna, and lithogenic parameters aims to unveil the Atlantic Water advection to the eastern Fram Strait by intensity, temperatures, and salinities. Atlantic Water has been continuously present at the site over the last 2,000 years. Superimposed on the increase in sea ice/icebergs, a strengthened intensity of Atlantic Water inflow and seasonal ice-free conditions were detected at ~ 1000 to 1200 AD, during the well-known Medieval Climate Anomaly (MCA). However, temperatures of the MCA never exceeded those of the 20th century. Since ~ 1400 AD significantly higher portions of ice rafted debris and high planktic foraminifer fluxes suggest that the site was located in the region of a seasonal highly fluctuating sea ice margin. A sharp reduction in planktic foraminifer fluxes around 800 AD and after 1730 AD indicates cool summer conditions with major influence of sea ice/icebergs. High amounts of the subpolar planktic foraminifer species Turborotalia quinqueloba in size fraction 150–250 µm indicate strengthened Atlantic Water inflow to the eastern Fram Strait already after ~ 1860 AD. Nevertheless surface conditions stayed cold well into the 20th century indicated by low planktic foraminiferal fluxes. Most likely at the beginning of the 20th century, cold conditions of the terminating Little Ice Age period persisted at the surface whereas warm and saline Atlantic Water already strengthened, hereby subsiding below the cold upper mixed layer. Surface sediments with high abundances of subpolar planktic foraminifers indicate a strong inflow of Atlantic Water providing seasonal ice-free conditions in the eastern Fram Strait during the last few decades.

Description: The Arctic is responding more rapidly to global warming than most other areas on our planet. Northward flowing Atlantic Water is the major means of heat advection towards the Arctic and strongly affects the sea ice distribution. Records of its natural variability are critical for the understanding of feedback mechanisms and the future of the Arctic climate system, but continuous historical records reach back only ~150 years. Here, we present a multidecadal scale record of ocean temperature variations during the last 2000 years, derived from marine sediments off Western Svalbard (79°N). We find that early-21st-century temperatures of Atlantic Water entering the Arctic Ocean are unprecedented over the past 2000 years and are presumably linked to the Arctic Amplification of global warming.

Description: The Nordic Seas are a key area at the hemispheric scale since they constitute a transitional basin between the North Atlantic and Arctic Oceans (Figure 1a). The warm and salty North Atlantic waters contribute to the poleward heat transport via the Norwegian (NwAC-W, NwAC-E) and West Spitsbergen (WSC) currents, whereas the Arctic waters carry cool and fresh waters into the Nordic Seas via the East Greenland current (EGC). The interaction between these two surface currents determines the extent of the Polar and Arctic Fronts and acts on the deep-water formation. Several studies have shown large-amplitude variations in sea-surface conditions of the Nordic Seas, during the Holocene, due to changes in the strength and/or thermal characteristics of the NwAC and EGC. However, variability along the EGC is still poorly documented contrary to the NwAC where records depict warmer conditions than present along the main axis during the early Holocene, when summer insolation was higher. Nevertheless, data are not unequivocal since they show regional differences suggesting changes in atmospheric and oceanic circulation patterns. This study aims at documenting the impact of the last deglaciation on surface water masses in the Nordic Seas by reconstructing hydrographic parameters and sea-ice along the NwAC and EGC as well as to discuss the influence of the Arctic vs. North Atlantic fluxes. Here, we report the results from centennial resolution analyses performed on cores M23323, MSM 5/5-712-2 and JM06-WP-16MC (Figure 1a). Dinocyst assemblages were used as a proxy for the reconstructions of sea-surface conditions. We employed the Modern Analogue Technique (MAT) and the Northern Hemisphere dinocyst database that includes 1429 sites. The reconstructed past sea-surface conditions include the temperatures and salinities in summer, as well as the sea-ice cover duration. Likewise, redundancy analyses were done on dinocyst assemblages and environmental parameters in order to determine the statistical weight of changes observed in the distribution of assemblages. In each core, dinocyst assemblages show a clear transition at about 6.8 cal. kyrs BP. It is characterized by assemblages dominated by Nematosphaeropsis labyrinthus accompanied by Spiniferites elongatus and Spiniferites ramosus then by assemblages almost exclusively dominated by Operculodinium centrocarpum. This transition is also confirmed by the redundancy analyses that illustrate a sign shift. Sea-surface reconstructions indicate similar variations between cores but with different orders of magnitude (Figure 1b). Data of core M23323 depict cool summer temperatures (mean of 8°C) and low salinity (〈34.5) with episodic sea-ice (up to 2 months/yr) until 6.8 cal. kyrs BP. Furthermore, this interval corresponds to relatively high concentrations of pollen grains (up to 4000 grains/cm3), which suggest high fluvial discharge from adjacent watersheds. These palynological data suggest an environment marked by a coastal influence with high terrestrial inputs causing low surface salinity and upper water mass stratification. Data of core MSM5/5-712-2 illustrate a comparable variability except that summer temperatures are colder (mean of 5°) with low summer salinity (mean of 33.5) and high seasonal sea-ice cover up to 6 months/yr. Despite very low sedimentation rate, and consequently low temporal resolution in core JM06-WP-16MC, the reconstructions point out large-amplitude oscillations associated with cool conditions (mean of 6°C in summer), a mean salinity of 34 and a seasonal sea-ice cover between 2 and 3 months/yr. After 6.8 cal. kyrs BP, reconstructions from core M23323 indicate a warming trend (≈1.5°C) and the gradual establishment of modern-like conditions with temperatures reaching 9.5°C in summer and a salinity of ~34.8, as the consequence of predominant NwAC. Reconstructions from core MSM 5/5-712-2 illustrate a more stable environment with a slight cooling trend (≈1°C) that could be due to an increase of the EGC and/or ESC fluxes. This transition is not so visible in core JM06-WP-16MC, which depicts a large cyclicity with cool conditions (mean of 7°C in summer), salinity around 34.8 and a seasonal sea-ice cover reaching up to 4 months/yr. However, a freshwater pulse (≈33.5) associated with a sea-ice cover of 4 months/yr at ca. 5.9 cal. kyrs BP is well recorded in cores MSM5/5-712-2 and JM06-WP-16-MC suggesting a strengthening of the EGC and a southward moving of the Polar-Arctic Fronts. Overall, records from these three cores point out a major reorganization of sea-surface conditions during the early-mid- Holocene transition in the Nordic Seas, and particularly in the eastern part. Also, it seems that the decoupling of the western and eastern branches of the Norwegian current as well as the WSC played a predominant role on the variability of sea-surface conditions during this time. The cool conditions reconstructed from core M23323, for the early Holocene period, contrast with warm ones observed along the main axis of the North Atlantic current as recorded, for instance, by diatoms (e.g., Berner et al., 2010) and alkenones (e.g., Calvo et al., 2002). We hypothesize here that this difference in water mass during the early Holocene was notably due to an enhanced freshwater influence from the northwestern Europe, including the Baltic Sea watershed, which lead to an intensification of coastal currents and an enhancement of the upper water mass stratification along the continental margin. Berner, K.S., Koç, N., Godtliebsen, F., 2010, High frequency climate variability of the Norwegian Atlantic Current during the early Holocene period and a possible connection to the Gleissberg cycle: The Holocene, v. 20, p. 245-255. Calvo, E., Grimalt, J., Jansen, E., 2002, High resolution U37 k sea surface temperature reconstruction in the Norwegian Sea during the Holocene: Quaternary Science Reviews, v. 21, p. 1385-1394. [Figures see online publication]

Description: EGU2011-8738 At present, the Arctic is responding faster to global warming than most other areas on earth, as indicated by rising air temperatures, melting glaciers and ice sheets and a decline of the sea ice cover. As part of the meridional overturning circulation which connects all ocean basins and influences global climate, northward flowing Atlantic Water is the major means of heat and salt advection towards the Arctic where it strongly affects the sea ice distribution. Records of its natural variability are critical for the understanding of feedback mechanisms and the future of the Arctic climate system, but continuous historical records reach back only ca. 150 years. To reconstruct the history of temperature variations in the Fram Strait Branch of the Atlantic Current we analyzed a marine sediment core from the western Svalbard margin. In multidecadal resolution the Atlantic Water temperature record derived from planktic foraminifer associations and Mg/Ca measurements shows variations corresponding to the well-known climatic periods of the last millennium (Medieval Climate Anomaly, Little Ice Age, Modern/Industrial Period). We find that prior to the beginning of atmospheric CO2 rise at ca. 1850 A.D. average summer temperatures in the uppermost Atlantic Water entering the Arctic Ocean were in the range of 3-4.5°C. Within the 20th century, however, temperatures rose by ca. 2°C and eventually reached the modern level of ca. 6°C. Such values are unprecedented in the 1000 years before and are presumably linked to the Arctic Amplification of global warming. Taking into account the ongoing rise of global temperatures, further warming of inflowing Atlantic Water is expected to have a profound influence on sea ice and air temperatures in the Arctic.

Description: The Arctic is responding more rapidly to global warming than most other areas on our planet. Northward-flowing Atlantic Water is the major means of heat advection toward the Arctic and strongly affects the sea ice distribution. Records of its natural variability are critical for the understanding of feedback mechanisms and the future of the Arctic climate system, but continuous historical records reach back only ~150 years. Here, we present a multidecadal-scale record of ocean temperature variations during the past 2000 years, derived from marine sediments off Western Svalbard (79°N). We find that early–21st-century temperatures of Atlantic Water entering the Arctic Ocean are unprecedented over the past 2000 years and are presumably linked to the Arctic amplification of global warming.