Description: Foraminiferal Mg/Ca-ratios have proven to be valuable proxies for reconstructing past water temperatures and salinities especially in subtropical to tropical regions. However, recent studies have expanded the temperature range of the proxy to include subarctic and arctic environments. In this study we aim to reconstruct the temperatures of the inflowing Atlantic Water mass on the European arctic and subarctic margins from late glacial to the present using Mg/Ca-ratios measured on planktic and benthic foraminiferal tests. The Atlantic Water is carried towards the Arctic by the North Atlantic Current and its meriodinal extension the West Spitsbergen Current. Both currents are important components of the meridional overturning circulation system of the North Atlantic. Furthermore, these currents contribute to the relatively milder climate along their paths. The subarctic paleorecord is based on two adjacent cores from ca. 500 m water depth in the Andfjorden, North Norway covering an Allerød - present sequence constrained by 15 AMS datings. SiZer analysis indicates variable chilled bottom water temperatures during Allerød and Younger Dryas, before a significant multistep temperature increase mark the onset of the Holocene. Stable relatively high temperatures prevail throughout the Holocene with a significant but modest decline at around 3.500 cal yr B.P. The arctic paleorecord is based a core from ca. 1500 m water depth on the West Spitsbergen slope. The core covers an Allerød - present sequence constrained by 13 AMS datings. SiZer analysis indicates no significant sea surface temperatures (SSTs) during the Late Glacial/Holocene boundary presumably linked to prevailing severe sea ice conditions and melt water influence in the area. Significant SST decline is observed from the early Holocene to ca. 6.000 cal yr B.P. SST remain remains low and stable until ca. 3000 cal yr B.P. after which a significant temperature increase initiates and continues toward the present.

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: EGU2011-407 The spatial and temporal distribution of sea ice in the subpolar North Atlantic is mainly controlled by the advection of warm Atlantic Water via the Norwegian and West Spitsbergen Current in eastern Fram Strait. Simultaneously, polar water and sea ice from the Arctic Ocean is transported southward by the East Greenland Current. Hence, variations in the strength of this oceanic circulation regime may either stimulate or reduce the sea ice extent. Based on organic geochemical studies of a high-resolution sediment core from eastern Fram Strait we provide new evidence for the highly variable character of the sea ice conditions in this area. The combination of the sea ice proxy IP25 (Belt et al., 2007) with phytoplankton derived biomarkers (e.g. brassicasterol, dinosterol; Volkman 2006) enables a reliable reconstruction of sea surface and sea ice conditions, respectively (Müller et al., 2009; 2010). By means of these biomarkers, we trace gradually increasing sea ice occurrences from the Mid to the Late Holocene – consistent with the neoglacial cooling trend. Throughout the past ca. 3,000 years (BP) we observe a significant short-term variability in the biomarker records, which points to rapid advances and retreats of the sea ice cover at the continental margin of West Spitsbergen. The co-occurrence of IP25 and phytoplankton markers, however, suggests that the primary productivity benefits from these sea ice surges. As such, higher amounts of open-water phytoplankton biomarkers together with peak abundances of IP25 indicate recurring periods of enhanced ice-edge phytoplankton blooms at the core site. To what extent a seesawing of temperate Atlantic Water may account for these sea ice fluctuations requires further investigation. Concurrent variations in Siberian river discharge (Stein et al., 2004) or Norwegian glacier extents (Nesje et al., 2001), however, strengthen that these fluctuations may be assigned to variations in the North Atlantic/Arctic Oscillation (NAO/AO) and (hence) a weakened/accelerated Atlantic Water input and Arctic sea ice export.

Description: The Atlantic Water inflow through Eastern Fram Strait - a major pathway of warm and saline water to the Arctic Ocean – plays an essential role for the Arctic Ocean heat budget (Schauer et al., 2004). Atlantic Water (AW) has been continuously present since ca 20,000 years in the Eastern Fram Strait (Rasmussen et al., 2007). However, the conditions of the AW inflow through the Fram Strait have varied much throughout the Holocene. From two sediment cores from the West Spitsbergen continental margin we present multiproxy evidence of variations of the Atlantic Water inflow and the position of the sea ice margin during the past ca 10,000 cal kyr BP. Maximum occurrence of the subpolar planktic foraminifer species T. quinqueloba suggests warmest temperatures of the Atlantic Water - bearing West Spitsbergen Current during the early part of the Holocene (10 to 8 cal ka BP). However, low planktic d13C values indicate limited ventilation of the AW layer that most likely submerged beneath a relatively thick surface layer of sea ice and lower salinity. A second warming pulse between 5 and 6 ka was accompanied by higher planktic d13C values pointing to the AW layer appearing at the surface. In the second half of the Holocene, increased IRD contents indicate a neoglacial trend found in many records of the North Atlantic realm (e.g. Koç and Jansen, 2002). Despite of the decreasing solar insolation planktic foraminiferal assemblages suggest a return of slightly strengthened Atlantic Water advection around 3 to 2 ka and a strong warming event in the present, anthropogenically influenced period.

Description: The last interglacial (Eemian), the first interval in marine isotope stage 5 (MIS 5) is often considered as a possible analog for future climate conditions forced by anthropogenic greenhouse gas emissions. The reason lies in decades of research on the Eemian which have shown that in many areas in the northern hemispheric mid-latitudes hypsithermal Eemian climate conditions were warmer than at any time in the Holocene. In the Atlantic sector, northward Atlantic Water transport is the major means of heat transfer to the northern high latitudes. As a possible explanation for Eemian-Holocene differences, one may thus propose a stronger and warmer Atlantic Water advection to the Arctic for the peak Eemian than for the Late Holocene. Since surface-near water mass properties are reflected in the oxygen and carbon isotope composition of planktic foraminifers, a comparison of such values from Eemian and Holocene sediments can give hints on possible differences in Arctic Ocean environments in these intervals. While there is a dense coverage of isotope values from planktic foraminifers in sediment surface samples available for large parts of the Arctic Ocean and the northern Nordic Seas, the number of suitable Eemian isotopic records is still rather limited. The situation is complicated by meltwater influences on surface- near waters in the MIS 6/5 transition and by the generally rather low sedimentation rates in the Arctic which often restrict Eemian deposits to a few centimeters. Comparison of available records, mostly from the Fram Strait and Eastern Arctic Ocean, show ca. 0.5‰ higher oxygen isotope values in the Eemian than in the Late Holocene. Carbon isotope differences are variable but the number of sites with slightly lower values in the Eemian is dominating. The results may be interpreted in several and partly contrasting ways, involving differences in river run-off, salinity, temperature, ice-coverage, and main habitats of the planktic foraminifers.