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We address here the specific timing and amplitude of sea-surface conditions and productivity changes off SW Greenland, northern Labrador Sea, in response to the high deglacial meltwater rates, the Early Holocene maximum insolation and Neoglacial cooling. Dinocyst assemblages from sediment cores collected off Nuuk were used to set up quantitative records of sea ice cover, seasonal sea-surface temperature (SST), salinity (SSS), and primary productivity, with a centennial to millennial scale resolution. Until similar to 10 ka BP, ice-proximal conditions are suggested by the quasi-exclusive dominance of heterotrophic taxa and low dinocyst concentrations. At about 10 ka BP, an increase in species diversity and abundance of phototrophic taxa marks the onset of interglacial conditions at a regional scale, with summer SST reaching up to 10 degrees C between 8 and 5 ka BP, thus in phase with the Holocene Thermal Maximum as recorded in the southern Greenlandic areas/northern Labrador Sea. During this interval, low SSS but high productivity prevailed in response to high meltwater discharge and nutrient inputs from the Greenland Ice Sheet. After similar to 5 ka BP, a decrease in phototrophic taxa marks a two-step cooling of surface waters. The first started at similar to 5 ka BP, and the second at similar to 3 ka BP, with a shift toward colder conditions and higher SSS suggesting reduced meltwater discharge during the Neoglacial. This second step coincides with the disappearance of the Saqqaq culture. The gap in human occupation in west Greenland, between the Dorset and the Norse settlements from 2000 to 1000 years BP, might be linked to high amplitude and high frequency variability of ocean and climate conditions.

Centennial‐to‐millennial temperature records of the past provide a context for the interpretation of current and future changes in climate. Quaternary climates have been relatively well studied in north‐east North America and the adjacent Atlantic Ocean over the last decades, and new research methods have been developed to improve reconstructions. We present newly inferred reconstructions of sea surface temperature for the north‐western Atlantic region, together with a compilation of published temperature records. The database thus comprises a total of 86 records from both marine and terrestrial sites, including lakes, peatlands, ice and tree rings, each covering at least part of the Holocene. For each record, we present details on seasons covered, chronologies and information on radiocarbon dates and analytical time steps. The 86 records contain a total of 154 reconstructions of temperature and temperature‐related variables. Main proxies include pollen and dinocysts, while summer was the season for which the highest number of reconstructions were available. Many records covered most of the Holocene, but many dinocyst records did not extend to the surface, due to sediment mixing, and dendroclimate records were limited to the last millennium. The database allows for the exploration of linkages between sea ice and climate and may be used in conjunction with other palaeoclimate and palaeoenvironmental records, such as wildfire records and peatland dynamics. This inventory may also aid the identification of gaps in the geographic distribution of past temperature records thus guiding future research efforts.

Palynological and sedimentological analyses were performed on the sediment core HH16-1205-GC retrieved from the central Isfjorden, West Spitsbergen. The sequence, which spans the last 7000 years, revealed an overall cooling trend with an important climate shift between 4.4 and 3.8 cal. ka BP, in addition to millennial-scale oscillations. Sea-surface reconstruction from dinocyst assemblages indicates a decrease in summer sea-surface temperature, from 2.5 to 1.5 °C, and primary productivity, from 750 to 650 gC m−2 a−1 over the last 7000 years. From around 6.8 to 5.8 cal. ka BP, the sedimentological and palynological data suggest a predominant sediment supply from the inner part of the fjord, ice rafting, dense sea ice cover, strongly stratified water masses and high primary productivity. The interval from 4.4 to 3.8 cal. ka BP is marked by a layer of coarser material and a significant decrease in the grain-size mode. Our geochemical data show large-amplitude fluctuations after 2.0 cal. ka BP, while an increase in the dinocysts Impagidinium pallidum and Spiniferites elongatus from 2.0 to 1.2 cal. ka BP suggests enhanced Atlantic Water inflow. The dinocyst-based reconstructions also reveal large-amplitude millennial fluctuations in sea ice cover, summer sea-surface temperature and salinity. Wavelet analysis and cross-wavelet analysis on K/Ti ratio coupled with sea-ice estimates confirm a strong signal with a periodicity of 1200–1500 years.

Cysts belonging to the benthic dinoflagellate Bysmatrum subsalsum were recovered from palynologically treated sediments collected in the Alvarado Lagoon (southwestern Gulf of Mexico). The cysts are proximate, reflecting the features of the parent thecal stage, and their autofluorescence implies a dinosporin composition similar to the cyst walls of phototrophic species. This finding is important for our understanding of B. subsalsum life cycle transitions and ecology. Encystment may play an important role in the bloom dynamics of this species as it can enable the formation of a sediment cyst bank that allows reinoculation of the water column when conditions become favorable. This is the first report of a fossilized cyst produced by a benthic dinoflagellate recovered from sub-recent sediments.

Paleoenvironments during the late Younger Dryas through early Holocene retreat of the Greenland Ice Sheet from the outer shelf in the Disko Trough system of central West Greenland were investigated via lithofacies, foraminifera, dinocysts and sediment provenance analyses in radiocarbon-dated sediment cores from the upper slope (JR175-VC35) and outer shelf (JR175-VC20 and HU2008029-070CC). Core data show that the ice margin retreated rapidly from the outer shelf by calving, beginning by 12.2k cal a BP under cold paleoceano- graphic conditions with up to 11 months of sea-ice. Ice retreat into Disko Bugt was well underway by 10.9k cal a BP. Enhanced ice-sheet ablation in Disko Bugt and elsewhere along the West Greenland coast is inferred from cold glacial marine conditions associated with high sedimentation rates between 10.9 and 9.5k cal a BP on the outer shelf. Glacial marine conditions are recorded on the outer shelf until 7.8k cal a BP. Detrital carbonate-bearing sediments rich in >2-mm clasts deposited between 11.6 and 10.6k cal a BP indicate that icebergs calved from northern Baffin Bay ice margins were melting and releasing sediments along West Greenland while the Greenland Ice Sheet margin was retreating into Disko Bugt. Copyright # 2013 John Wiley & Sons, Ltd.

The cyst–theca relationship of Protoperidinium fukuyoi n. sp. (Dinoflagellata, Protoperidiniaceae) is established by incubating resting cysts from estuarine sediments off southern Vancouver Island, British Columbia, Canada, and San Pedro Harbor, California, USA. The cysts have a brown-coloured wall, and are characterized by a saphopylic archeopyle comprising three apical plates, the apical pore plate and canal plate; and acuminate processes typically arranged in linear clusters. We elucidate the phylogenetic relationship of P. fukuyoi through large and small subunit (LSU and SSU) rDNA sequences, and also report the SSU of the cyst-defined species Islandinium minutum (Harland & Reid) Head et al. 2001. Molecular phylogenetic analysis by SSU rDNA shows that both species are closely related to Protoperidinium americanum (Gran & Braarud 1935) Balech 1974. Large subunit rDNA phylogeny also supports a close relationship between P. fukuyoi and P. americanum. Three subgroups in total are further characterized within the Monovela group. The cyst of P. fukuyoi shows a wide geographical range along the coastal tropical to temperate areas of the North-east Pacific, its distribution reflecting optimal summer sea-surface temperatures of ~14–18 °C and salinities of 22–34 psu.

Process length variation of cysts of the dinoflagellate Protoceratium reticulatum (Claparede et Lachmann) Butschli in surface sediments from the North Pacific was investigated. The average process ...

Climate archives available from deep sea and marine shelf sediments, glaciers, lakes, and ice cores in and around Greenland allow us to place the current trends in regional climate, ice sheet dynamics, and land surface changes in a broader perspective. We show that, during the last decade (2000s), atmospheric and sea surface temperatures are reaching levels last encountered millennia ago, when northern high latitude summer insolation was higher due to a different orbital configuration. Records from lake sediments in southern Greenland document major environmental and climatic conditions during the last 10,000 years, highlighting the role of soil dynamics in past vegetation changes, and stressing the growing anthropogenic impacts on soil erosion during the recent decades. Furthermore, past and present changes in atmospheric and oceanic heat advection appear to strongly influence both regional climate and ice sheet dynamics. Projections from climate models are investigated to quantify the magnitude and rates of future changes in Greenland temperature, which may be faster than past abrupt events occurring under interglacial conditions. Within one century, in response to increasing greenhouse gas emissions, Greenland may reach temperatures last time encountered during the last interglacial period, approximately 125,000 years ago. We review and discuss whether analogies between the last interglacial and future changes are reasonable, because of the different seasonal impacts of orbital and greenhouse gas forcings. Over several decades to centuries, future Greenland melt may act as a negative feedback, limiting regional warming albeit with global sea level and climatic impacts. 2012 John Wiley & Sons, Ltd. How to cite this article

Micropaleontological and geochemical analyses of a sediment core collected in the Laurentian Trough of the Gulf of St. Lawrence were carried out to reconstruct temporal variations in pelagic productivity and benthic environmental conditions. Dinoflagellate cyst assemblages reveal relatively stable pelagic productivity over the last two centuries. Similarly, geochemical (organic C, Corg:N) and isotopic (d13Corg, d15N) data reveal that organic matter fluxes to the seafloor have been relatively constant over the same period. In contrast, significant changes are recorded in the benthic foraminifer assemblages. A sediment surface peak in the abundance of Cassidulina laevigata and Brizalina subaenariensis is consistent with the recent record of oxygen depletion in the bottom water. A decrease in the relative abundance of Nonionellina labradorica, concomitant with a relatively higher occurrence of Oridorsalis umbonatus in the upper part of the core, reflects a significant warming of the bottom water. Changes in bottom-water properties are further constrained by a negative trend of the d18 Oi n Bulimina exilis carbonate shells over the last century, corresponding to a warming of about 2uC. These results strongly suggest that the recent oxygen depletion in the bottom waters of the Gulf of St. Lawrence is due to changes in water masses that have led to increased bottom-water temperatures and, to some extent, a resultant increase in organic matter respiration rates.

Dinosterol (4a,23,24-trimethyl-5a-cholest-22E-en-3b-ol) is frequently used as an alternative to dinoflagellate cyst (dinocyst) counting in paleoceanography to assess dinoflagellate inputs to marine sediments. However, recent studies have shown poor correlation between these two proxies in continental-margin sediments. We reevaluated the relationship and expanded it to include a suite of biogeochemical transformation products of the parent dinosterol (dinosterone, dinostanone, and dinostanol). These dinoflagellate-specific 4a,23,24-trimethyl steroidal species (Sdinosterol) are compared to dinocyst counts in sediments from the western Mexican margin (375– 3,500 m). Samples were taken from subsurface (3–6 cm) and down core (16–27 cm) to reflect widely contrasting organic carbon content and redox conditions. A strong correlation was found between the sum of all dinoflagellate-derived sterols, Sdinosterols, and total dinocyst counts, highlighting the importance of including diagenetic alteration products of the parent molecule when exploiting organic biomarkers in paleoceanographic studies. In low-energy environments and for well-preserved samples, such as those studied in this work, both methods provide robust, internally consistent data, suggesting that when diagenetic transformation products of dinosterol are taken into account, gas chromatography and optical microscopy could be used interchangeably to estimate dinoflagellate inputs to marine sediments.

High-resolution marine palynological data have been obtained from two very long sediment cores (MD952009 and MD952010) retrieved from the southern Norwegian Sea. The dinoflagellate cyst assemblages show pronounced fluctuations in composition, which correlate strongly with magnetic susceptibility records and also mimic the δ 18 O signal of the GISP2 Greenland ice-core. If focusing on the period from 48 to 30 cal. kyr BP, this correlation suggests a paradoxical response of the sea-surface environments to the atmospheric conditions over Greenland: when the Greenland δ 18 O signal reflects warm interstadial conditions, the Norwegian Sea depicts cold sea- surface temperatures with quasi-perennial sea-ice cover (based on dinoflagellate cysts). In contrast, when the Greenland δ 18 O records cold stadial periods, the Norwegian Sea-surface temperatures are warm (based on dinoflagellate cysts), probably linked to inflow of the North Atlantic Drift. These results, similar in both cores, are contrary to those of previous studies and shed light on a possible decoupling of Norwegian sea surface-water conditions and atmospheric conditions over Greenland. This decoupling could be linked to an atmosphere-ocean system behaving similar to that which the Northern Hemisphere is experiencing at present, i.e. strongly variable owing to the North Atlantic Oscillation. Copyright  2002 John Wiley & Sons, Ltd.

The distribution of dinoflagellate cyst (dinocyst) assemblages in surface sediment samples from 677 sites of the northern North Atlantic, Arctic and sub-Arctic seas is discussed with emphasis on the relationships with sea-surface parameters, including sea-ice cover, salinity and temperature of the coldest and warmest months. Difficulties in developing a circum-Arctic data base include the morphological variation within taxa (e.g. Operculodinium centrocarpum, Islandinium? cezare and Polykrikos sp.), which probably relate to phenotypic adaptations to cold and/or low salinity environments. Sparse hydrographical data, together with large interannual variations of temperature and salinity in surface waters of Arctic seas constitute additional limitations. Nevertheless, the use of the best-analogue technique with this new dinocyst data base including 677 samples permits quantitative reconstruction of sea-surface conditions at the scale of the northern North Atlantic and the Arctic domain. The error of prediction calculated from modern assemblages is ±1.3 ° Ca nd±1.8 °C for the temperature of February and August, respectively, ±1.8 for the salinity, and ±1.5 months yr −1 for the sea-ice cover. Application to late Quaternary sequences from the western and eastern subpolar North Atlantic (Labrador Sea and Barents Sea) provide reconstructions compatible with those obtained using the previous dinocyst data base (n = 371), which mainly included modern data from the northern North Atlantic. Copyright  2001 John Wiley & Sons, Ltd. Journal of Quaternary Science

PETA J. MUDIE,1∗ REX HARLAND,2 JENS MATTHIESSEN3 and ANNE DE VERNAL4 1 Geological Survey of Canada (Atlantic), PO Box 1006, Dartmouth, Nova Scotia, B2Y 4A2, Canada 2 DinoData Services, 50 Long Acre, Bingham NG13 8AH, England 3 Alfred Wegener Institute for Polar and Marine Research, Columbusstrasse, D27568 Bremerhaven, Germany 4 GEOTOP, Universite du Quebec a Montreal, C.P. 8888, Montreal, Quebec H3C 3P8 Canada

Palynological analyses were performed on 52 surface sediment samples from the eastern part of the Bering Sea and Chukchi Sea in order to document the regional distribution of dinoflagellate cyst assemblages and their relationship with sea-surface conditions. The assemblages present a relatively high species diversity (20 taxa are recovered routinely), especially in the Bering Sea, where they are dominated by Operculodinium centrocarpum and the cyst of Pentapharsodinium dalei accompanied mainly by Spiniferites elongatus s.l., Spiniferites ramosus, Impagidinium pallidum, Brigantedinium spp., Islandinium minutum, Selenopemphix quanta, Selenopemphix nephroides, Quinquecuspis concreta and the cyst of Polykrikos kofoidii. The percentages of the main taxa vary with latitude, and principal component analysis shows that the distribution of assemblages is closely related to hydrographic conditions, notably the seasonal duration of sea-ice cover and the sea-surface temperature in February. The dinoflagellate cyst assemblages from the Bering Sea differ significantly from those of subarctic seas of the North Atlantic, with respect to their species composition and relationships with sea-surface conditions. In particular, the occurrence of the cyst of Polykrikos kofoidii and Quinquecuspis concreta and the positive correlation between the percentages of Operculodinium centrocarpum and the extent of sea-ice, constitute peculiar features in the Bering Sea assemblages. Copyright  2001 John Wiley & Sons, Ltd. Journal of Quaternary Science

Investigation of organic-walled dinoflagellate cyst distribution in 118 surface sediments from the Southern Ocean documents the relatively high diversity of cyst taxa (46 species) and distinct cyst assemblages in relation to surface water masses and temperature gradient. The Antarctic Water is characterised by the dominance of Selenopemphix antarctica accompanied by Brigantedinium spp. and Impagidinium pallidum. The Subantarctic Water association consists mainly of Nematosphaeropsis labyrinthus, Impagidinium paradoxum and Impagidinium sphaericum, whereas the Subtropical Water association is dominated by Operculodinium centrocarpum and Spiniferites membranaceus. Multivariate analyses (non-metric multidimensional scaling) demonstrate the relationships with sea-surface conditions and enable the application of the best analogue method on the Southern Ocean dinoflagellate cyst data base for reconstructing past sea-surface conditions. The dinoflagellate cyst record from DSDP 594 (45°31.41'S, 174°56.88'E; 1204 m, southern margin of the Chatham Rise) shows important fluctuations in species composition from glacial to interglacial over the last 140 000 yr. Reconstruction of winter and summer SSTs reveals much lower temperature than present by 6 to 10 °C during marine oxygen isotope stages 6, 4 and 2, and higher temperature by 2-3 °C during substage 5e. Copyright  2001 John Wiley & Sons, Ltd. Journal of Quaternary Science

Palynomorphs were analysed in two sediment cores from the southeastern Barents Sea representing the past 8.3 and 4.4 kyr. High dinocyst contents and species diversity enabled the application of the best analogue method to quantitatively reconstruct sea-surface salinities, temperatures and ice cover using 677 modern reference sites from the North Atlantic and Arctic seas, including new data from the Barents Sea reported here. At the southern core site, where waters are affected by the Atlantic inflow, sea-surface conditions were relatively warm and stable between ca. 8000 and 5000 calendar yr BP. In contrast, the past 5 kyr had periods with cooler temperatures and extended ice cover, fluctuating mostly at 1–1.5 kyr frequencies at both sites. Most pronounced coolings occurred around 8.1, 5, 3.5–3.2 and 2.5 ka. The northern site additionally shows younger cooling events, tentatively dated to 1.4, 0.3 and 0.1 ka. Identified variations in sea-surface conditions indicate changes in Atlantic water inputs to the Barents Sea. Our results generally correlate to palaeoclimatic reconstructions from northwestern Eurasia, exemplified by palynological records from Karelia. This correlation suggests that sea-surface variations in the Barents Sea reflect large-scale changes in atmospheric and oceanic interactions between the North Atlantic and the Arctic. Copyright © 2001 John Wiley & Sons, Ltd.

The artificial neural network (ANN) method was applied to dinoflagellate cyst (dinocyst) assemblages to estimate palaeoceanographical conditions. The ANN method was adapted to three distinct data bases covering the northern North Atlantic (N = 371), plus the Arctic seas (N = 540) and the Bering Sea (N = 646). The relative abundance of 23 dinocyst taxa was calibrated against hydrographic variables (sea-surface temperature, salinity and density in February and August, and seasonal extent of sea-ice cover) using ANNs. The estimation of hydrographical parameters based on an ANN yields high coefficients of correlation between observations and reconstructions for each variable selected. The validation tests performed on the different data bases suggest more accurate calibration at the scale of the North Atlantic and Arctic (N = 540) than on a multibasin scale, i.e. when including the subpolar North Pacific (N = 646). The ANN calibrations and the modern analogue technique (MAT) have been applied to two sequences from the northwest North Atlantic spanning the past 25 000 yr for the purpose of comparison. Both approaches yielded similar results, generally within the range of their respective uncertainties, demonstrating their suitability. The main discrepancies generally correspond to assemblages with poor modern analogues for which we have to admit a higher degree of uncertainties in the reconstruction, whatever the approach used. Copyright © 2001 John Wiley & Sons, Ltd.

A sediment sequence from the eastern Laptev Sea shelf (Siberian Arctic, Russia) has been studied for dinoflagellate cysts in order to reconstruct sea-surface conditions during the late Holocene. Variability of assemblage composition and derived sea-surface temperature estimates indicate that the neoglacial cooling was not a gradual climate change from 2510 to 900 cal. yr BP. Relatively stable conditions, with temperatures that were warmer than today, were punctuated by a few cooling events in summer on centennial time-scales. During these events temperatures reached modern values. This suggests that modern conditions may have been established abruptly within a short period in the past 1000 yr, which is not documented in our record. Copyright © 2001 John Wiley & Sons, Ltd.

The analysis of cores collected in northernmost Baffin Bay, from within the area of the North Water Polynya, permits definition of a composite sedimentary sequence ca. 12 m thick spanning the last 10 000 14 C yr, with only a few discontinuities. Palynological analyses were performed in order to reconstruct changes in surface water conditions and biogenic production. Transfer functions, using dinocyst assemblages, were applied to estimate sea-surface temperature (SST) and salinity, as well as the seasonal duration of sea ice cover. At the base of the record, prior to 9300 14 C yr BP, dinocysts and organic linings of benthic foraminifers are sparse, indicating harsh conditions and low productivity. After ca. 9300 14 C yr BP, the increased concentration of benthic foraminifers (up to 10 3 linings cm -3 ) and dinocyst fluxes (10 2 -10 3 cysts cm -2 yr -1 ) reveals high biological productivity related to open-water conditions. The early to middle Holocene, from ca. 9000 to ca. 3600 14 C yr BP, is marked by relatively high species diversity in dinocyst assemblages and the significant occurrence of autotrophic taxa such as Spiniferites elongatus, Pentapharsodinium dalei and Impagidinium pallidum. This assemblage suggests conditions at least as warm as at present. From ca. 6400 to ca. 3600 14 C yr BP, transfer functions indicate warmer conditions than at present, with SST in August fluctuating up to 5.5°C. After 3600 14 C yr BP, the dinocyst record suggests a trend of decreasing temperature toward modern values, marked by recurrent cooling events. Copyright © 2001 John Wiley & Sons, Ltd.