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Variations in sea surface conditions and sea level through the Holocene in the Kandalaksha Bay, the White Sea, were reconstructed based on the study of core sediments from the outer Kandalaksha Bay, using the modern analog technique applied to dinocysts in addition to diatoms, TOC, δ13Corg, CaCO3, and grain size data. The chronostratigraphy of the core sediments was defined from accelerator mass spectrometry 14C dates on mollusk shells. The results indicated an increase in water depth in the outer Kandalaksha Bay and in the central Dvina Bay until the late Holocene. From about 9.5 to 7.5 cal kyr BP, the data suggested a general trend of increasing sea surface temperatures (up to 14 °C), at least in areas with inflow of Atlantic waters. The last 2.5 kyr were characterized by increased freshwater runoff to the White Sea. [ABSTRACT FROM AUTHOR]

Palynological analyses of the marine sediment core AMD0509-20 collected north of Whapmagoostui-Kuujjuarapik in Nunavik were performed to investigate past changes in climate and sea-surface conditions based on pollen and spores and dinoflagellate cysts, respectively. Our results show relatively warm sea-surface temperatures before 2600 BP, about 2 °C higher than at present in summer, in addition to higher salinity suggesting relatively low freshwater inputs, thus low precipitation over the watershed. After 2400 years BP, an abrupt drop in sea-surface temperatures was recorded, followed by a decrease in salinity particularly pronounced until ∼2000 years BP. After 1600 years BP, summer sea-surface temperatures and salinity stabilized around current values. The changes recorded in surface waters during the late Holocene can be associated with a regional shift in the hydroclimatic regime that led to a gradual decline of spruce (Picea) in pollen assemblages. • Quantitative regional sea-surface temperature assessment for the last 3000 years. • Significant cooling at ∼2400 years BP. • Salinity estimates suggest increased overall precipitation after 2000 years BP. • Hydroclimatic regime changes from warm and dry to cool and humid. [ABSTRACT FROM AUTHOR]

Climate changes over the past two millennia in the central part of the Gulf of St. Lawrence are documented in this paper with the aim of determining and understanding the natural climate variability and the impact of anthropogenic forcing at a regional scale. The palynological content (dinocysts, pollen, and spores) of the composite marine sediment core MSM46-03 collected in the Laurentian Channel was used to reconstruct oceanographic and climatic changes with a multidecadal temporal resolution. Sea-surface conditions, including summer salinity and temperature, sea-ice cover, and primary productivity, were reconstructed from dinocyst assemblages. Results revealed a remarkable cooling trend of about 4°C after 1230 cal yr BP (720 CE) and a culmination with a cold pulse dated to 170-40 cal yr BP (1780-1910 CE), which likely corresponds to the regional signal of the Little Ice Age. This cold interval was followed by a rapid warming of about 3°C. In the pollen assemblages, the decrease of Pinus abundance over the past 1700 yr suggests changes in wind regimes, likely resulting from increased southerly incursions of cold and dry Arctic air masses into southeastern Canada. [ABSTRACT FROM AUTHOR]

The Barents Sea offers a suitable location for documenting advection of warm and saline Atlantic Water (AW) into the Arctic and its impact on deglaciation and postglacial conditions. We investigate the timing, succession, and mechanisms of the transition from proximal glaciomarine to marine environment in the northwestern Barents Sea. Two studied sediment cores demonstrate diachronous retreat of the grounded ice sheet from the Kvitøya Trough (core S2528) to Erik Eriksen Trough (core S2519). Oxygen isotope records from core S2528 depict a two-step pattern, with lower δ18O values prior to the Younger Dryas (YD), and higher values afterward because of advection of the more saline, 18O-enriched AW. At this location, subsurface AW penetration increased during the Allerød and YD/Preboreal transition. In the study area, foraminiferal and dinocyst data from the YD interval suggest cold conditions, extensive sea-ice cover, and brine formation, along with the flow of chilled AW at subsurface and the development of a high-productivity polynya in the Erik Eriksen Trough. Dense winter sea-ice cover with seasonal productivity persisted in the Kvitøya Trough area during the early Holocene, whereas surface warming seems to have occurred during the middle Holocene interval. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In marine sediments of late Cenozoic age, Spiniferites is a very common genus of dinoflagellate cysts (dinocysts). Despite some taxonomical ambiguities due to large range of morphological variations within given species and convergent morphologies between different species, the establishment of an operational taxonomy permitted to develop a standardized modern database of dinocysts for the mid-high latitudes of the Northern Hemisphere. In the database that includes 1490 surface sediment samples, Spiniferites mirabilis-hyperacanthus, Spiniferites ramosus and Spiniferites elongatus were counted in addition to Spiniferites belerius, Spiniferites bentorii, Spiniferites bulloideus, Spiniferites delicatus, Spiniferites lazus and Spiniferites membranaceus. Among these taxa, Spiniferites mirabilis-hyperacanthus, Spiniferites ramosus, and Spiniferites elongatus are easy to identify and are particularly common. Spiniferites bentorii and Spiniferites delicatus also are morphologically distinct and occur in relatively high percentages in many samples. Spiniferites lazus and Spiniferites membranaceus also bear distinctive features, but occur only in a few samples. The identification of other taxa (Spiniferites belerius, Spiniferites bulloideus, notably) may be equivocal and their reported distribution has to be used with caution. The spatial distribution of Spiniferites species, with emphasis on the five most common taxa, is documented here with reference to hydrography (salinity and temperature in winter and summer, sea ice cover), primary productivity and geographical setting (bathymetry, distance to the coastline). The results demonstrate distinct ecological affinities for Spiniferites elongatus, which has an Arctic-subarctic distribution and appears abundant in low productivity environments characterized by winter sea ice and large temperature contrast between winter and summer. Spiniferites mirabilis-hyperacanthus, which occurs in warm temperate water sites, is more abundant in high salinity environments. It shares its environmental domain with Spiniferites bentorii, which appears to have a narrower distribution towards the warm and high salinity end of the Spiniferites mirabilis-hyperacanthus distribution. In contrast, Spiniferites delicatus, which occurs in warm-temperate to tropical environments, shows preference for relatively low salinity and low seasonal contrasts of temperature. Spiniferites ramosus exhibits a particularly wide distribution that overlaps both cold and warm Spiniferites taxa. Its cosmopolitan occurrence and its long-ranging biostratigraphical distribution suggest a high plasticity of the species and/or co-occurrence of several cryptic species. Hence, whereas Spiniferites elongatus and Spiniferites mirabilis-hyperacanthus are useful palaeoecological indicators despite their large morphological variability, Spiniferites ramosus is a taxon with an unconstrained ecological significance. [ABSTRACT FROM AUTHOR]

Dinoflagellate cyst (dinocyst) records from the southern Nordic Seas were compiled in order to evaluate the evolution of upper ocean conditions, on a millennial timescale and supported by a highly resolved record from the Vøring Plateau. After the transitional phase from the last deglaciation, three main phases define the Holocene. The early Holocene (>7.5 ka BP) features important numbers of cool-temperate species dominated by Nematosphaeropsis labyrinthus and Impagidinium pallidum in the west. The assemblage composition changes drastically at the transition from the early to the mid-Holocene, from when on Operculodinium centrocarpum dominates. The changeover is dated between ~6.1 and 7.5 ka BP, perhaps earlier closer to the Iceland–Scotland Ridge, and appears to be linked to the onset of a modern type of surface circulation. ‘Warmest’ assemblages occur at the Vøring Plateau shortly after the transition, when Atlantic waters also appear to have spread farthest westward. The recurrence of colder elements can be linked to cooling from ~2.4 ka BP at the Vøring Plateau and presumably earlier in the west but is difficult to date there because of the low sedimentation rates. This is a general issue in many areas of the Nordic Seas and appears to have an important effect on cyst concentrations and assemblage composition, with the possible loss of oxygenation-sensitive cysts in the older parts of the cores. Comparing dinocyst-based quantitative reconstructions with those retrieved from other plankton reveals a significantly different trend between proxies, linked to a differing autecological response to seasonal changes at their respective depth habitats. [ABSTRACT FROM AUTHOR]

Palynological and geochemical analyses were carried out on a sediment core collected in the shallow Alvarado lagoon (Veracruz, Southwestern Gulf of Mexico) in order to evaluate the impact of the significant decline in the surrounding native coastal vegetation on phytoplankton assemblages. The sedimentary sequence encompasses the last millennium and provides information on pre-industrial phytoplankton assemblages. Results highlight a recent increase of freshwater-sourced organic matter relative to marine organic matter in line with reduced total concentrations of cyst-producing dinoflagellates. These changes appear to be synchronous to the extensive conversion of wetlands into agricultural areas, with consequences on the stability and water retention capacity of the soils bordering the lagoon system. The data also show that Polysphaeridium zoharyi , a cyst produced by the potentially toxic dinoflagellate Pyrodinium bahamense , is present in high abundance in the dinoflagellate population of the lagoon. Consequently, the modern cyst bank of P. bahamense in sediment has the potential to initiate harmful blooms since surface sediments are prone to resuspension events related to strong seasonal winds and human activities. [ABSTRACT FROM AUTHOR]

Micropaleontological analyses of a sediment core raised in Disko Bugt (West of Greenland) were undertaken in order to document paleoceanographical changes in the eastern Baffin Bay during the Holocene. The modern analogue technique (MAT) applied to dinocyst assemblages provided information on paleo-sea-surface conditions, whereas isotopic analyses of benthic foraminifers aimed at documenting the ‘deep’ water mass occupying the site. During the earlier interval recorded (~10 to ~7.3 cal. kyr BP), important discharge of ice and meltwater from the Greenland Ice Sheet (GIS) margin, notably through the Jakobshavn Isbrae, resulted in harsh conditions with a dense sea-ice cover and low temperatures, productivity, and foraminiferal abundances. Postglacial conditions settled at ~7.3 cal. kyr BP, with a sharp rise in dinocyst abundance and species diversity, which led to reconstruct increase in summer temperatures. We link this transition to the advection of West Greenland Current waters in the upper part of the water column after the reduction of meltwater inputs from GIS. Optimal temperature conditions reaching up to >10°C were finally achieved in surface waters at ~6 cal. kyr BP. Slight cooling pulses were then recorded at ~4.2–4 and ~1.5–1 cal. kyr BP, and the final optimum recorded in surface temperature from ~1 to 0.8 cal. kyr BP is associated with the ‘Medieval Warm Period’. Throughout the postglacial interval, the data suggest an opposition between sea-surface temperatures and salinity, with warmer intervals being characterized by lower salinity waters, probably as a result of the higher freshwater discharge along the ice margin and notably the Jakobshavn Isbrae. [ABSTRACT FROM PUBLISHER]

Abstract: Sea ice cover extent expressed in terms of mean annual concentration was reconstructed from the application of the modern analogue technique to dinocyst assemblages. The use of an updated database, which includes 1492 sites and 66 taxa, yields sea ice concentration estimates with an accuracy of ±1.1/10. Holocene reconstructions of sea ice cover were made from dinocyst counts in 35 cores of the northern North Atlantic and Arctic seas. In the Canadian Arctic, the results show high sea ice concentration (>7/10) with little variations throughout the interval. In contrast, in Arctic areas such as the Chukchi Sea and the Barents Sea, the reconstructions show large amplitude variations of sea ice cover suggesting millennial type oscillations with a pacing almost opposite in western vs. eastern Arctic. Other records show tenuous changes with some regionalism either in trends or sea ice cover variability. During the mid-Holocene, and notably at 6 ± 0.5 ka, minimum sea ice concentration is recorded in the eastern Fram Strait, northern Baffin Bay and Labrador Sea. However, this minimum cannot be extrapolated at the scale of the Arctic and circum-Arctic. The comparison of recent observations and reconstructions suggests larger variations in the Arctic sea ice cover during the last decades than throughout the Holocene. [Copyright &y& Elsevier]

Abstract: Sea ice is an important component of the Earth system with complex dynamics imperfectly documented from direct observations, which are primarily limited to the last 40 years. Whereas large amplitude variations of sea ice have been recorded, especially in the Arctic, with a strikingly fast decrease in recent years partly attributed to the impact of anthropogenic climate changes, little is known about the natural variability of the sea ice cover at multi-decadal to multi-millennial time scales. Hence, there is a need to establish longer sea ice time series to document the full range of sea ice variations under natural forcings. To do this, several approaches based on biogenic or geochemical proxies have been developed from marine, ice core and coastal records. The status of the sea ice proxies has been discussed by the Sea Ice Proxy (SIP) working group endorsed by PAGES during a first workshop held at GEOTOP in Montréal. The present volume contains a set of papers addressing various sea ice proxies and their application to large scale sea ice reconstruction. Here we summarize the contents of the volume, including a table of various proxies available in marine sediments and ice cores, with their possibilities and limitations. [Copyright &y& Elsevier]

Abstract: Sea ice is a determinant parameter of the climate system, which acts as amplifier through positive ice-albedo feedbacks and induces deep-water formation through brine production. It is also one of the most elusive parameters in the paleoclimate record. Most proxies of sea ice provide information on its presence and extent of (e.g., diatoms or dinocysts), but do not permit assessment on its rate of formation. However, seemingly off-equilibrium, low δ 18O values in mesopelagic planktic foraminifer species, as observed today in the Arctic Ocean, are thought to relate to the production of isotopically light brines during sea ice formation, and might thus provide a clue on the rate of sea ice growth. With reference to the isotopic properties of modern planktic foraminifers in the Arctic Ocean and using multi-proxy data sets from the last glacial stage in the northwest North Atlantic, we re-examined some of the current interpretations of planktic isotope records in the glacial NW North Atlantic. The large amplitude light isotopic excursions recorded in Neogloboquadrina pachyderma left coiling during Heinrich events 1, for example, correspond to extensive sea ice cover as reconstructed from dinocysts, and do not seem unequivocally linked to low-salinity pulses. Such light isotopic excursion more likely responded to enhanced rates of sea ice formation resulting in the production and sinking of isotopically light brines. On the contrary, the isotopically heavy planktic foraminifers of the last glacial maximum (LGM) interval stricto sensu would rather suggest relatively low rates of brine production, thus low sea ice growth rates in the area. This would imply that the LGM distribution of sea ice in the North Atlantic was primarily linked to spreading and drifting from marginal and Nordic source areas and not from enhanced in situ production. At the scale of glacial–interglacial cycles, isotopic distillation processes relating to sea ice production at high latitudes could be one of the factors controlling the 18O–salinity relationship in deep ocean water masses that might deserve closer examination, as it would be independent of continental ice volume changes. [Copyright &y& Elsevier]

Abstract: In the present paper, we report on micropaleontological (dinocysts) and isotopic (18O and 13C in foraminifers) analyses performed in Holocene sediments from fifteen cores raised from the central and northwest North Atlantic. Sea-surface temperature (SST), sea-surface salinity (SSS), thus potential density, and sea-ice cover are reconstructed based on dinocyst assemblages. After proper calibration, oxygen isotope data on the mesopelagic foraminifer Neogloboquadrina pachyderma left coiled (Npl) are converted into potential density values deeper in the water column, thus allowing documentation of vertical density gradients and identification of intervals favourable for winter convection to occur with formation of intermediate Labrador Sea Water (LSW). The most important findings from this study include: (1) the existence of an early-mid Holocene thermal optimum with positive anomalies up to 6 °C above present along the main SW–NE axis of the North Atlantic Current, but no significant SST maximum at most sites along eastern Canadian margins; (2) the evidence for larger than present amplitude of annual SSTs during the early Holocene, thus for a stronger seasonality; (3) minimum sea-ice cover from 11500 to 6000 cal years BP, and a slight increase of sea-ice variability, and average seasonal duration of 0.5 to 1 month per year afterwards; (4) variable SSS during the entire Holocene, suggesting changes in the routing and rates of freshwater–meltwater discharges from the Arctic and eastern Canada; (5) the setting of conditions compatible with LSW production after 8 ka only, and likely a more steady production during the late Holocene; (6) an overall trend for a potential density increase of the Labrador Sea, throughout the Holocene, matching a decreasing trend eastward, thus suggesting a progressive enhancement of the western branch of the Atlantic Meridional Overturning with respect to its northeastern route; and (7) indication of maximum production and fast dispersal of LSW in the entire North Atlantic during recent times only, as suggested by linearly-converging δ 18O-values of Npl from all sites, towards its modern relatively homogeneous composition (∼ 2.5/2.6‰). The overall picture of the Holocene North Atlantic arising from this study is that of a basin marked by a strong regionalism with large discrepancies in hydrographical trends and high frequency oscillations, at least partly controlled by freshwater–meltwater routes and rates of export from the Arctic. [Copyright &y& Elsevier]

Palynological analyses of 60 surface sediment samples from West Greenland margin revealed high concentrations of dinoflagellate cysts (dinocysts), particularly in the Disko Bugt area, where they reach >104 cysts g−1. Dinocyst assemblages are characterized by a relatively high species diversity and are dominated by Operculodinium centrocarpum , cysts of Pentapharsodinium dalei , Islandinium minutum , Islandinium ? cezare , and Brigantedinium spp. On a regional scale, the overall assemblages show statistical relationships with sea-ice cover duration, primary productivity, salinity and summer-fall temperature. The cysts of Pentapharsodinium dalei , Operculodinium centrocarpum , and Spiniferites elongatus appear linked to high productivity and to characterize the late summer-fall bloom. Although Islandinium minutum and Islandinium ? cezare are generally associated with a seasonally sea-ice covered environment, there is no linear relationship between their relative abundance and sea-ice concentration or duration on a regional scale, along the West Greenland margin. The abundance of these taxa primarily reflects cold and low-salinity water in the study area. Radionuclide measurements (210Pb and 137Cs) allow the distinction between two categories of samples, the "modern" ones likely encompassing the interval younger than 1950 CE, and the others that may be considered "sub-modern". Statistical analyses indicate that dinocyst assemblages belonging to "modern" and "sub-modern" categories are not significantly different. Hence, the dinocyst assemblages of surface sediment samples, both "modern" and "sub-modern", represent fluxes homogenized over a relatively long time interval, which illustrates a spatial distribution corresponding to the main gradient in oceanographic conditions. Consequently, dinocyst assemblages in surface sediments can be assumed to represent the average "modern" conditions with a sufficiently high degree of confidence for their use in environmental studies and paleoclimate reconstructions. • Dinocyst assemblages show relationships with sea-ice cover, primary productivity, salinity and summer-fall temperature • Islandinium sp. reflects cold and low-salinity water in the study area • Dinocyst assemblages in surface sediments allow reconstructions of sea-surface parameters averaged over several decades [ABSTRACT FROM AUTHOR]

Paleoceanographical changes during the Holocene were reconstructed from the study of core MD95-2002 situated in the northern Bay of Biscay, which is marked by the direct influence of the northeastern return branch of the North Atlantic Drift. Palynological data, sea-surface condition estimates based on dinocyst assemblages and stable isotope measurements in planktic and benthic foraminifera reveal a strong influence of freshwater/meltwaters from both the proximal European sources and the more distal Laurentide Ice Sheet, which experienced delayed deglaciation. The data also indicate the setting of a climate optimum between 7 and 5.5 ka followed by a cooling trend, which is consistent with insolation changes and other regional records of climate changes. Superimposed on the long term trends, the reconstructions of sea-surface conditions evidence large amplitude changes at centennial to millennial time-scales, with seven episodes of cooling and low salinity since 11 ka that generally match episodes of dense sea-ice cover in the Labrador Sea. The west to east transfer of the sea-ice and/or meltwater signal across the North Atlantic evidenced from core MD95-2002 points to strong linkages between western and eastern North Atlantic, probably in relation to the North Atlantic Oscillation (NAO) mode of variability. [ABSTRACT FROM AUTHOR]

We present new surface water proxy records of meltwater production (alkenone derived), relative sea surface temperature (diatom, alkenones) and sea ice (diatoms) changes from the Disko Bugt area off central West Greenland. We combine these new surface water reconstructions with published proxy records (benthic foraminifera - bottom water proxy; dinocyst assemblages – surface water proxy), along with atmospheric temperature from Greenland ice core and Greenland lake records. This multi-proxy approach allows us to reconstruct centennial scale middle to late Holocene palaeoenvironmental evolution of Disko Bugt and the Western Greenland coastal region with more detail than previously available. Combining surface and bottom water proxies identifies the coupling between ocean circulation (West Greenland Current conditions), the atmosphere and the Greenland Ice Sheet. Centennial to millennial scale changes in the wider North Atlantic region were accompanied by variations in the West Greenland Current (WGC). During periods of relatively warm WGC, increased surface air temperature over western Greenland led to ice sheet retreat and significant meltwater flux. In contrast, during periods of cold WGC, atmospheric cooling resulted in glacier advances. We also identify potential linkages between the palaeoceanography of the Disko Bugt region and key changes in the history of human occupation. Cooler oceanographic conditions at 3.5 ka BP support the view that the Saqqaq culture left Disko Bugt due to deteriorating climatic conditions. The cause of the disappearance of the Dorset culture is unclear, but the new data presented here indicate that it may be linked to a significant increase in meltwater flux, which caused cold and unstable coastal conditions at ca. 2 ka BP. The subsequent settlement of the Norse occurred at the same time as climatic amelioration during the Medieval Climate Anomaly and their disappearance may be related to harsher conditions at the beginning of the Little Ice Age. [ABSTRACT FROM AUTHOR]