L. and Voronina, E. 2001. Dinoflagellate cyst assemblages as tracers of sea-surface conditions in the northern North Atlantic, Arctic and sub-Arctic seas: the new 'n = 677' data base and its application for quantitative palaeoceanographic reconstruction.ABSTRACT: 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°C and ±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.
Head, M. J., Harland, R. and Matthiessen, J. 2001. Cold marine indicators of the late Quaternary: the new dinoflagellate cyst genus Islandinium and related morphotypes.ABSTRACT: Round, brown, spiny dinoflagellate cysts characterise many modern high-latitude assemblages. Abundance is often highest where summer sea-surface temperatures seldom exceed 7°C and where winter sea-surface temperatures are around 0°C, making this morphological group important for reconstructing cold intervals within marine Quaternary sequences. Our analysis of modern sediments from the Beaufort Sea of Arctic Canada, the Kara and Laptev seas of Arctic Russia, and across the Arctic Ocean, allows us to recognise the new cyst genus Islandinium along with the extant species Islandinium minutum (Harland and Reid in Harland et al., 1980) new combination (basionym: Multispinula? minuta), Islandinium? cezare (de Vernal et al., 1989 ex de Vernal in Rochon et al., 1999 new status and combination (basionym: Multispinula? minuta var. cezare) sensu lato, and Echinidinium karaense new species. Of these, the generotype Islandinium minutum is a well-known but morphologically problematic species. We have re-examined the type material from the Beaufort Sea and studied specimens from across the Arctic, and our observations clarify ambiguities in the original description of this species. The archeopyle of Islandinium minutum results from the loss of three apical plates, an unusual style among peridiniphycidean dinoflagellates. The asymmetrical location of these plates around the apex is distinctive, and probably contributed to earlier misunderstandings of the archeopyle. Previous attributions to Multispinula? and Algidasphaeridium? are unsustainable. Maps showing the distribution of Islandinium minutum are given for the Northern Hemisphere and show this species to be polar to north-temperate, whereas Islandinium? cezare s.l. and Echinidinium karaense appear to be more restricted to polar environments.
A punctuated 103.3 m thick succession of upper Palaeogene to Quaternary sediments has been recovered in a borehole from the upper Hebrides Slope, west of Britain. The borehole proved 11.2m of upper Oligocene, carbonate-rich muds at the base, unconformably overlain by 2.85 m of middle to upper Miocene, glauconitic sands. This is in turn unconformably overlain by 89.25 m of predominantly Plio-Pleistocene sands and muds, with a Holocene sea-bed veneer. The post-Miocene succession is subdivided into two units: the sand-dominated, Pliocene to lower middle Pleistocene, Lower MacLeod sequence between 89.25 and 67.82 m, and the mud-dominated, middle Pleistocene to Holocene, Upper MacLeod sequence above 67.82 m. Regional mapping indicates that these sequences are commonly associated with large-scale shelf-margin progradation and slope-front fan construction.
The borehole core provides an excellent record of the transition from pre-glacial to glacial conditions in the mid-latitude NE Atlantic Ocean. Climatic conditions warmer than present prevailed in the late Oligocene, mid- to late Miocene and Pliocene, although the influx of ice-rafted detritus in the late Pliocene marks the onset of climatic deterioration. This deterioration continued, in a fluctuating manner, until the early mid-Pleistocene (0.44 Ma) when fully glacial conditions were established on the Hebridean Margin.
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