Description: Sea-surface conditions in northeastern Fram Strait since the last glacial maximum (LGM) were reconstructed from cores MSM5/5-712-2 and PS2863/1-2 based on palynological assemblages, ecological preferences of dinocysts and application of the modern analog technique. Dinocyst in LGM sediments are sparse, but their assemblages reflect mild summer conditions. Given the regional context and evidence from other tracers, the dinocyst assemblages of the LGM could relate to regional fluxes of dinocysts during exceptional mild summers. From 19 to 14.7 ka, dinocyst data suggest very cold conditions with extensive sea-ice cover, while abundant reworked palynomorphs indicate intense glacial erosion. An abrupt transition at 14.7-14.5 ka was marked by a peak in summer temperatures coinciding with a rapidly deposited sediment layer related to a regional meltwater plume event in western Svalbard. From 14.7 to 12.6 ka, large seasonal temperature contrasts with mild summers and cold winters together with low salinity indicate continuous melting of the Svalbard Barents Sea ice sheet fostered by warm climate. At 12.6 ka, the regional onset of the Younger Dryas was marked by cooling and increased salinity. On a regional scale, the 12.6-12 ka interval corresponds to an important transition involving enhanced circulation of Arctic waters around Svalbard and establishment of coastal fronts along its northern and western margins. Modern-like oceanic conditions with relatively high salinity and low seasonal temperature contrast developed at about 7.6 ka. Since then, a slight cooling is observed, especially in winter. This study offers a comprehensive picture of the deglacial phases in eastern Fram Strait with unique data on the sea-surface salinity, which controls surface water stratification and plays an important role in ocean circulation.

Description: Process length variation of cysts of the dinoflagellate Protoceratium reticulatum (Claparède et Lachmann) Bütschli in surface sediments from the North Pacific was investigated. The average process length showed a significant inverse relation to annual seawater density: σt annual = −0.8674 × average process length + 1029.3 (R2 = 0.84), with a standard error of 0.78 kg m−3. A sediment trap study from Effingham Inlet in British Columbia revealed the same relationship between average process length and local seawater density variations. In the Baltic–Skagerrak region, the average process length variation was related significantly to annual seawater density: σt annual = 3.5457 × average process length − 993.28 (R2 = 0.86), with a standard error of 3.09 kg m−3. These calibrations cannot be reconciled, which accentuates the regional character of the calibrations. This can be related to variations in molecular data (small subunit, long subunit and internal transcribed spacer sequences), which show the presence of several genotypes and the occurrence of pseudo-cryptic speciation within this species.

Description: Geochemical and micropaleontological analyses were carried out on a 35 cm box core (CR06-TCE) spanning the last 6000 years in the Esquiman Channel, a northeast arm of the Laurentian Channel in the Gulf of St. Lawrence. A 0.6‰ decrease of δ18O in benthic foraminifer Globobulimina auriculata shells characterizes the upper 10 cm of the core and suggests a warming of the bottom waters. This change is concomitant with increased percentages of the low-oxygen tolerant benthic foraminifer species Brizalina subaenariensis and the Atlantic water species Oridorsalis umbonatus. Although a precise timing cannot be established, notably because of the smoothing effect of bioturbation, the amplitude of the trend recorded in the Esquiman Channel is coherent with that of the regional warming observed in the bottom water of the main axis of the Laurentian Channel over the last century. Warm bottom water conditions, however, are not exclusive to the recent time interval as shown by data from the lower part of the core, which are also characterized by low δ18O values in G. auriculata and occurrence of both B. subaenariensis and O. umbonatus. Such data suggest the existence of low-oxygen and relatively high temperature conditions in the bottom water of the Esquiman Channel about 4 to 6 kyrs ago likely related to enhanced inflow of Atlantic water in the Gulf of St. Lawrence through the Cabot Strait and the Laurentian Channel. These results highlight the sensitivity of bottom water properties in the Gulf of St. Lawrence to changes in the western North Atlantic circulation.

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: We attempt to assess the Holocene surface-subsurface seawater density gradient on millennial time scale based on the reconstruction of potential density (σθ) by combining data from dinoflagellate cyst assemblages and planktic foraminiferal (Neogloboquadrina pachyderma (s)) stable oxygen isotopes (δ18Oc). Following several calibration exercises, the likeliness of favorable seasonal preconditioning to open ocean convection is evaluated. The reconstructed σθ values reveal unfavorable conditions for vertical convection in the western Nordic Seas prior to ~7–6.5 ka B.P., with a westward increase and persistence of surface water buoyancy. Active overturning became more likely after 6.5 ka B.P. as suggested by a reduced and recurrently inverted vertical σθ gradient, while intermittent eastward spreading of lower density surface waters continued to modulate the area of potential overturning. Despite some reservation regarding the accuracy of the σθ values reconstructed, the documentation of relative changes of σθ gradients through time and space is suggested as a helpful tool for the appraisal of past overturning likeliness.

Description: Marine sediment records of dinoflagellate cyst, foraminiferal and ice rafted debris content and stable isotopes from the Nordic seas and Labrador Sea were used to reconstruct the evolution of the surface circulation in the (sub)arctic North Atlantic during the Last Interglacial. Average global temperatures of this time interval, known as Marine Isotope subStage (MIS) 5e, are believed to have been higher than those of the present Holocene interglacial period. However, the abundance peak of warm dinoflagellate cyst taxa and subpolar planktic foraminifera in the eastern Nordic seas during late MIS 5e would suggest that the development of upper ocean interglacial conditions in that area was delayed with respect to the temperate latitudes, and the marine optimum in the eastern Nordic seas with a surface circulation comparable to the modern one was not reached until late MIS 5e. While the lack of a modern type of surface circulation during much of the early MIS 5e probably prevented the formation of Labrador Sea Water (Hillaire-Marcel et al., 2001), our data furthermore suggest that only with the establishment of this intensified modern-type of northward heat transport, an interglacial surface ocean environment also developed in the northern Nordic seas. Hence, our findings illustrate the importance of a correct (stratigraphic) context placement of those last interglacial records from the high Arctic pointing out overall warmer conditions with respect to the Holocene, as these might represent only specific phases of MIS 5e. Hillaire-Marcel, C., de Vernal, A., Bilodeau, G., Weaver, A.J., 2001. Absence of deep-water formation in the Labrador Sea during the last interglacial period. Nature 410, 1073-1077.

Description: Sediments from the last interglacial (MIS 5e) were studied for their dinoflagellate cyst (dinocyst) content from cores across the North Atlantic and Nordic seas, in order to trace changes in the interaction between the warm water masses of the northward flowing Gulf Stream/North Atlantic Drift current system and the cold water masses of the East Greenland/Labrador Current. Supported by stable isotope, IRD and planktic foraminiferal data, the qualitative and quantitative analysis of the dinocyst assemblages illustrates the stepwise development of interglacial conditions from late MIS 6 and Termination II towards a MIS 5e optimum and back to the colder MIS 5d stadial. It is shown that the development of the MIS 5e optimum occurred only late during MIS 5e in the eastern Nordic seas, as a consequence of a delayed intensification of the northernmost limb of the Gulf Stream/North Atlantic Drift. While prolonged deglacial processes presumably had hindered this northward protrusion of warm surface waters during early MIS 5e, its intensification during late MIS 5e in turn caused a reorganisation of the cold surface current system.

Description: We document climate conditions from the last interglacial optimum (LIO) or marine isotope stage 5e (MIS 5e) from terrestrial and oceanic sedimentary archives. Terrestrial climate conditions are reconstructed from pollen assemblages, whereas sea-surface temperature and salinity conditions are estimated from dinocyst assemblages and foraminiferal data (both assemblages and stable isotope composition of carbonate shells). LIO data from the eastern Canadian Arctic and northern Labrador Sea led to reconstruct much higher summer air temperature and seasurface temperature than at present by about 5°C. Data from southeastern Canada and southern Labrador Sea also suggest more thermophilic vegetation and warmer conditions although the contrast between LIO and the Holocene is of lesser amplitude. On the whole, the terrestrial and marine data sets from the northwest North Atlantic and adjacent lands suggest limited influence of southward flow from Arctic waters through the east Greenland and Labrador Currents as compared to the modern situation. The compilation of sea-surface reconstructions from the northwest and northeast North Atlantic indicate much reduced longitudinal contrasts of temperatures than at present, thus a more zonal pattern of circulation. The reconstructions also indicate a lower sea-surface salinity than at present, thus stronger stratification of upper water masses, which would be compatible with a reduced North Atlantic deep-water formation.

Description: Recent observations of enhanced oceanic heat transfer into the Arctic concomitant with the rapid sea-ice decrease temptingly suggest a direct relationship between both features. However, except for marginal areas of the Arctic Ocean where warm and saline Atlantic Water (AW) reaches the surface, the majority of AW heat is presently isolated from the sea-ice cover by a cold and fresh halocline layer. No evidence has been found to suggest a weakening of the halocline across the central Arctic basins that would enhance the AW heat transfer to the surface. A more direct link between sea-ice reduction and AW inflow is, however, seen in the inflowing Barents Sea branch in both historical and observational time series. In this presentation the AW advection into the Arctic Ocean and its influence on sea-ice variability will be reviewed from a geological point of view. Records from the geologic past are of great value as the time span of modern observations and historical data is often too short to comprehend long-term trends and causes of AW variability, changes in the marginal ice zone, and the vertical structure of the Arctic water column. Paleoceanographic studies from the recent interglacial indirectly suggest that the strength of AW advection and its propagation into the Arctic interior is effective in melting sea ice in combination with other factors such as insolation, sea level, freshwater input, and upper water mass stratification. However, to date, very little paleoceanographic work in the Arctic has focused on how the strength and position of the halocline has changed during previous interglacial periods. More direct reconstructions of the Arctic’s vertical stratification in the geologic past are needed to provide a longer-term view on the stability of the halocline, and more generally, the role of Atlantic Water inflow on the stability of sea ice in the interior basins.