Late Pleistocene paleo-oceanography of the Norwegian-Greenland Sea: Benthic foraminiferal evidence

Fluctuations in benthic foraminiferal faunas over the last 130,000 yr in four piston cores from the Norwegian Sea are correlated with the standard worldwide oxygen-isotope stratigraphy. One species, Cibicides wuellerstorfi, dominates in the Holocene section of each core, but alternates downcore with Oridorsalis tener, a species dominant today only in the deepest part of the basin. O. tener is the most abundant species throughout the entire basin during periods of particularly cold climate when the Norwegian Sea presumably was ice covered year round and surface productivity lowered. Portions of isotope Stages 6, 3, and 2 are barren of benthic foraminifera; this is probably due to lowered benthic productivity, perhaps combined with dilution by ice-rafted sediment; there is no evidence that the Norwegian Sea became azoic. The Holocene and Substage 5e (the last interglacial) are similar faunally. This similarity, combined with other evidence, supports the presumption that the Norwegian Sea was a source of dense overflows into the North Atlantic during Substage 5e as it is today. Oxygen-isotope analyses of benthic foraminifera indicate that Norwegian Sea bottom waters warmer than they are today from Substage 5d to Stage 2, with the possible exception of Substage 5a. These data show that the glacial Norwegian Sea was not a sink for dense surface water, as it is now, and thus it was not a source of deep-water overflows. The benthic foraminiferal populations of the deep Norwegian Sea seem at least as responsive to near-surface conditions, such as sea-ice cover, as they are to fluctuations in the hydrography of the deep water. Benthic foraminiferal evidence from the Norwegian Sea is insufficient in itself to establish whether or not the basin was a source of overflows into the North Atlantic at any time between the Substage 5e/5d boundary at 115,000 yr B.P. and the Holocene.     

Late Quaternary carbonate sedimentation and paleo-oceanography in the eastern Norwegian Sea

Four gravity cores from the eastern Norwegian Sea are studied. Absolute accumulation rates are quantified and variations in carbonate sedimentation and their implications for the paleo-oceanographic history of the Norwegian Sea are described. In the eastern Norwegian Sea, interglacial, ice-free conditions were developed during oxygen-isotope stages 1 and 5e. Open water conditions were probably the norm during the summer season, also during glacial stages. Slightly elevated summer temperatures in periods during isotope stages 2 and 7 are demonstrated by increased contents of subpolar planktic foraminifera. The deep waters of the eastern Norwegian Sea have been well oxygenated during most of the last 250,000 years. Organic-rich sediments and intensive carbonate dissolution in some parts of isotope stages 4 and 6 indicate corrosive bottom waters. A permanent ice cover and low saline surface waters, as found in the Arctic Ocean today, may have been developed in these periods. Well-preserved foraminiferal assemblages from stage 2 show more oxygenated bottom waters and more effective bottom water renewal in this period than during stage 3.     

Surface ocean circulation in the Norwegian Sea 15,000 B.P. to present

Quantitative studies of foraminifera and radiolaria, semi-quantitative analyses of diatoms and coccoliths, and the distribution of ice-rafted sediments have been performed on cores from the southeastern Norwegian Sea. The results document large variations in sea-surface temperatures and ocean circulation, showing a strong correlation between oceanic data and palaeoclimatic data from the neighbouring coastal areas of Norway. For the first time the Allerød – Younger Dryas climatic fluctuations and the Holocene climatic optimum are shown in records from the Norwegian Sea. Starting at about 13,000 B.P. the sea surface became seasonally ice-free with productive seasons. During the Allerød a narrow wedge of temperate Atlantic water flowed into the southeastern Norwegian Sea. In Younger Dryas time the surface waters cooled by several degrees. Holocene surface conditions were relatively constant, with somewhat higher temperatures in a period possibly corresponding with Atlantic time.     

Application of brachiopods in palaeoceanographic reconstructions; Macandrevia cranium (Müller, 1776) from the Norwegian shelf

The brachiopod Macandrevia cranium (Müller, 1776) occurs in Late Weichselian and Holocene sediments from the Norwegian continental shelf. It is particularly well known from the southern Barents Sea where it is a characteristic member of the Holocene macrofpssil assemblages. The Recent biogeography of the species is established. The general distribution is not random, but is almost completely confined to the continental shelves surrounding the North Atlantic and the Norwegian-Greenland Sea. The distribution pattern is compared with information on autecology and possible limiting environmental factors. It is concluded that there is substantial evidence that the distribution of Recent M. cranium is a function of dispersal by the Gulf Stream and its continuations, e.g. the Norwegian Current and the North Cape Current. Thus the stratigraphic occurrence of M . cranium in sediments on the Norwegian continental shelf may be used as an important marker for the presence of Atlantic water. Late Weichselian records of rare specimens of the species are related to incipient influx of Atlantic water following the deglaciation. Early Holocene records of abundant specimens are related to the final intrusion of the Norwegian Current. These records also suggest that the Holocene introduction of the species is time-transgressive in a south-north direction.     

A tephra-based correlation between the Faroe Islands and the Norwegian Sea raises questions about chronological relationships during the last interglacial

Marine ash zones from the last interglacial period have been described from cores from the North Atlantic and an ash zone from the middle part of the interglacial has been observed in connection with a major cooling event. Here we present evidence for a coeval ash zone in a terrestrial site on the Faroe Islands. The investigated sediments are correlated with the upper part of oxygen isotope stage 5e and the beginning of stage 5d. The Eemian climatic optimum is represented in the lower part of the sequence close to the first occurrence of the ash zone. A tephra-based correlation suggests that the climatic optimum was synchronous with the marine record from the Norwegian Sea, but several thousand years later than in Eemian sections of west central Europe. However, many questions on the chronological relationship between the Eemian and oxygen isotope stage 5e still remain to be answered.     

A model for Scottish interstadial marine palaeotemperature 13,000 to 11,000 B.P.

From a study of molluscan assemblages it is suggested that sea temperatures, particularly in the period 12,500 to 12,000 B.P., were 3°C lower than they are today for all but surface waters, implying that the interstadial North Atlantic Drift was weaker than the present Drift where it extends into the Norwegian Sea. An early interstadial 'warm' event may relate to a period when temperatures in the Bay of Biscay exceeded those of the present day. A later 'warm' episode may correlate with the warmest part of the interstadial deduced from the deep sea succession west of Ireland.     

Norwegian sea‐surface palaeoenvironments of marine oxygen‐isotope stage 3: the paradoxical response of dinoflagellate cysts

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 δ¹⁸O 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 δ¹⁸O 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 δ¹⁸O 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.     

New faunal and isotopic evidence on the late Weichselian—Holocene oceanographic changes in the Norwegian Sea

Downcore studies of planktonic and benthonic foraminifera and δ¹⁸O and δ¹³C in the planktonic foraminifer Neogloboquadrina pachyderma (sin.) in two piston cores from the southern part of the Norwegian Sea suggest large changes in the oceanic circulation pattern at the end of oxygenisotope stage 2 and in the early part of stage 1. Prior to oxygen-isotope Termination IA (16,000–13,000 yr B.P.), an isolated watermass with lower oxygen content and temperature warmer than today existed below a low salinity ice-covered surface layer in the Norwegian Sea. Close to Termination IA, well-oxygenated deep water, probably with positive temperatures, was introduced. This deep water, which must have had physical and/or chemical parameters different from those of present deep water in the Norwegian Sea, could have been introduced from the North Atlantic or been formed within the basin by another mechanism than that which forms the present deep water of the Norwegian Sea. A seasonal ice cover in the southern part of the Norwegian Sea is proposed for the period between Termination IA and the beginning of IB (close to 10,000 yr B.P.). The present situation, with strong influx of warm Atlantic surface-water and deep-water formation by surface cooling, was established at Termination IB.     

Planktonic foraminiferal and oxygen isotopic stratigraphy and paleoclimatology of Norwegian Sea deep-sea cores

BOREAS Kellogg, T. B., Duplessy, J. C. & Shackleton, N. J. 1978 03 01: Planktonic foraminiferal and oxygen isotopic stratigraphy and paleoclimatology of Norwegian Sea deep-sea cores. Boreas. Vol. 7, pp. 61–73. Oslo. ISSN 0300–9483.
Three Norwegian Sea deep-sea cores, which penetrate to sediments at least 200,000 years old, were analyzed for oxygen isotope content, total calcium carbonate, and planktonic foraminifera. The oxygen isotopic stratigraphy was used to refine the time control for paleoclimatic and paleo-oceanographic events previously described for the region. Two pulses of relatively warm subpolar water entered the region between 124,000 B.P. and 115,000 B.P. (the last interglacial), and since about 13,000 B.P. The remaining portion of the last 150,000 years was characterized by extensive ice cover. The magnitude of the change in isotopic composition between peak glacial and peak interglacial conditions is larger than can be explained by the changing isotopic content of the oceans alone suggesting that large temperature and salinity effects are recorded in isotope curves from Norwegian Sea isotope curves. The magnitude of the isotopic change from substage 5e to 5d (greater than 1%) is attributed to a combination of changing oceanic isotopic composition combined with a large temperature effect due to a sudden sea-surface temperature decrease of about 6^oC. The persistence of heavy isotope values throughout substages 5d through 5a may be related to the sea-ice cover which prevented dilution of the isotopically heavy waters by isotopically light run-off. Sedimentation rates calculated for each of the isotope stages show large changes from one stage to another with some tendency for odd numbered stages to have higher rates.     

Foraminiferal stratigraphy, palaeoenvironments and sedimentation of the glacigenic sequence southwest of Bjørrnøya

Based on four shallow drillings in the outer part of the Bjørnøya trough, palaeoenvironments of foraminifera in glacigenic sediments are discussed. Different methods were used; detailed foraminiferal analysis, oxygen and carbon stable isotope analysis and transfer functions. Six different foraminiferal assemblage zones were found. One zone, AA, appears to be pre-Pleistocene in age and contains an abundance of reworked early Tertiary foraminifera. Four of the assemblage zones have a dominant arctic foraminiferal content; however, a marked boreal input is evident, particularly in zone B where B. marginata dominates. We suggest that B. marginata has been resedimented from pre-Eemian 'warm' deposits. Its occurrence in these older warm intervals possibly reflects a lower input of the Norwegian Current into the area and possibly an increase in the relative nutrient content of the water masses. The six zones have also differing numbers of foram./gram sediment. An assemblage zone where a boreal component of foraminifera ( E. nipponica, P. bulloides ) dominates was found, zone C. We define this particular assemblage zone to be of Eemian age (isotope substage 5e). The foraminiferal assemblage composition and the oxygen and carbon isotopes from zone C indicate that oceanographic conditions in the Barents Sea during the Eemian were slightly different from those of the present and that, possibly, Atlantic waters were more prevalent.     

Benthonic foraminifera as indicators of the paleoposition of the Subarctic Convergence in the Norwegian-Greenland Sea

A method is presented for correlating benthonic foraminiferal communities in Late Quaternary marine sediments on continental shelves and in coastal areas with the planktonic foraminiferal stratigraphy of the North Atlantic and Norwegian Sea deep-sea sediments.     

Link of ocean deep water thermohaline anomalies with atmospheric state anomalies in the Northern Atlantic

Anomalies of thermohaline characteristics of the ocean deep waters formed in the subpolar North Atlantic are shown to be controlled by the natural oscillations of the atmospheric state in the region, i.e., the North Atlantic Oscillation (NAO). A general mechanism behind the NAO effect on the deep water temperature and salinity on a decadal time scale is proposed. The main factors determining the close link of the deep water thermohaline anomalies and the NAO are the zonal extension of the subpolar gyre and the wintertime deep convection intensity in the Labrador Sea.     

A high-resolution diatom record of late-Quaternary sea-surface temperatures and oceanographic conditions from the eastern Norwegian Sea

Core MD95‐2011 was taken from the eastern Vøring Plateau, near the Norwegian coast. The section between 250 and 750 cm covers the time period from 13 000 to 2700 cal. yr BP (the Lateglacial and much of the Holocene). Samples at 5 cm intervals were analysed for fossil diatoms. A data‐set of 139 modern sea‐surface diatom samples was related to contemporary sea‐surface temperatures (SSTs) using two different numerical methods. The resulting transfer functions were used to reconstruct past sea‐surface temperatures from the fossil diatom assemblages. After the cold Younger Dryas with summer SSTs about 6°C, temperatures warmed rapidly to about 13°C. One of the fluctuations in the earliest Holocene can be related to the Pre‐Boreal Oscillation, but SSTs were generally unstable until about 9700 cal. yr BP. Evidence from diatom concentration and magnetic susceptibility suggests a change and stabilization of water currents associated with the final melting of the Scandinavian Ice Sheet at c. 8100 cal. yr BP. A period of maximum warmth between 9700 and 6700 cal. yr BP had SSTs 3–5°C warmer than at present. Temperatures cooled gradually until c. 3000 cal. yr BP, and then rose slightly around 2750 cal. yr BP. The varimax factors derived from the Imbrie & Kipp method for sea‐surface‐temperature reconstructions can be interpreted as water‐masses. They show a dominance of Arctic Waters and Sea Ice during the Younger Dryas. The North Atlantic current increased rapidly in strength during the early Holocene, resulting in warmer conditions than previously. Since about 7250 cal. yr BP, Norwegian Atlantic Water gradually replaced the North Atlantic Water, and this, in combination with decreasing summer insolation, led to a gradual cooling of the sea surface. Terrestrial systems in Norway and Iceland responded to this cooling and the increased supply of moisture by renewed glaciation. Periods of glacial advance can be correlated with cool oscillations in the SST reconstructions. By comparison with records of SSTs from other sites in the Norwegian Sea, spatial and temporal changes in patterns of ocean water‐masses are reconstructed, to reveal a complex system of feedbacks and influences on the climate of the North Atlantic and Norway.     

The Late Quaternary Skagerrak and its depositional environment

The Skagerrak is a key region for our understanding of the Late Quaternary history of the East North Sea, of the entire Baltic basin and of the adjacent Scandinavian land areas. The depositional history of the postglacial Skagerrak began after the ice margin withdrew from Jutland to close to the modern Norwegian coast around 14 ka B.P. to 13 ka B.P. The Skagerrak was immediately filled by marine waters from the Norwegian Sea, but retained a fjord-like shape until approximately 10.2 ka B.P., when a connection opened across central Sweden to the Baltic Ice Lake. This seaway closed around 9 ka B.P., but a new seaway to the Baltic basin opened subsequently (probably close to 8.5 ka B.P.) through the Danish Belts. At about 10 ka B.P. the Skagerrak 'fjord' also started to change shape due to the flooding of the large former land area under the modern North Sea. Paleo-geography and -bathymetry of these changes can now be quantified in great detail. The young Quaternary sediments of the Skagerrak consist of fine-grained clays with minor amounts of silty and sandy material and are mostly of terrigenous origin, whereas biogenic components in general make up only a minor proportion of the bulk sediment. Prior to 10 ka B.P. a major portion of these deposits originated from the Fennoscandian regions N and E of the Skagerrak, while ice-rafting contributed coarse terrigenous components to the usually fine-grained sediments and while it was filled by brackish surface and cold polar bottom waters. At approximately 10 ka B.P., more temperate waters started to fill the Skagerrak and a good portion of the sediment seems to have originated from areas to the South. The Norwegian Coastal Current can only be documented for the past 7 ka; subtle changes of the pelagic and benthic environments could also be documented for later intervals.     

Indium and yttrium in North Atlantic and Mediterranean waters: comparison to the Pacific data

Vertical profiles of dissolved indium and yttrium were determined in the eastern North Atlantic and the Mediterranean Sea to compare with those of the North Pacific reported earlier. The Y concentrations in the surface waters are 120 pmol/kg in the North Atlantic and 205 pmol/kg in the Mediterranean Sea, which are significantly higher than 80 pmol/kg in the North Pacific. The difference may be attributable to the different strength of input of Y to the oceans from fluvial and aeolian sources. In contrast, the deep water concentration of Y increases in the order of North Atlantic < Mediterranean < North Pacific. This trend is similar to that of dissolved Si, suggesting that Y is involved in the biogeochemical regeneration cycle. The vertical profiles of In are far more complex than Y. The In profile shows a systematic increase from 0.6 pmol/kg at the surface to 1.7 pmol/kg at 2100 m in the North Atlantic, whereas it is almost featureless at a mean concentration of 3.8 ± 0.6 pmol/kg in the Mediterranean Sea. The North Atlantic and Mediterranean In concentrations are considerably higher than those observed in the North Pacific (∼0.1 pmol/kg), and such a large interoceanic variation has been reported before only for Al and Ga. Like Al, the deep water In concentration that decreases in the order of Mediterranean > North > North Pacific exhibits an inverse trend of Y and nutrients. Indium is highly particle-reactive (47% association in the Mediterranean Sea), and must have a short mean oceanic residence time. However, the featureless dissolved In profile in the Mediterranean Sea is clearly different from the profiles of dissolved Al, showing increase with depth Hydes et al 1988, Measures and Edmond 1988, suggesting that significant fractionation of the two elements is taking place in the ocean.The interoceanic variations of dissolved In and Al may be ascribed to the different intensities of external input of which aeolian has been considered to be major rather than fluvial. However, the difference of In and Al concentrations in the deep waters of the above oceanic basins are significantly greater than those of other refractory elements, such as Ce, Ti, Hf, and Zr, whose major sources to the ocean are also considered to be aeolian. Furthermore, the In/Al ratios in seawater are about two orders of magnitude greater than the average crustal ratio. Thus, some additional sources, though not yet certain, may be required to explain the high concentrations of In in the Atlantic and the Mediterranean deep waters.     

Variability of the Arctic front during the last climatic cycle: application of a novel molecular proxy

In the Nordic Seas, the Arctic front (AF) marks the boundary between the waters of the North Atlantic Drift/Norwegian Current and those of the Arctic domain. Long- or short-term shifts in the position of the AF may affect climate conditions in the northern hemisphere. Arctic water masses are also the loci of modern open ocean convection; hence, defining these areas in the past is important for reconstructing and modelling ocean circulation and its variability. C₃₇ alkenones are biomarkers for some algae of the Class Prymnesiophyceae (e.g. coccolitho-phorids such as Emiliania huxleyi). These alga occur in most parts of the oceans, in ice-free conditions, and are found nowadays throughout the Nordic Seas. We have related the sedimentary abundance of the tetraunsaturated C₃₇ alkenone (C_37:4) to two types of water masses in the Nordic seas. In locations affected by Atlantic water masses percentages of C_37:4 are less than 5%, whereas in Arctic type water masses these increase to more than 5%. We propose that this observation can be used as a modern analogue to reconstruct the position of the AF in North Atlantic Quaternary sediments. Using this novel molecular proxy we can infer that the southward migration of the AF in the NE Atlantic reached ≈ 50 °N during the last glacial maximum (LGM), but perhaps only 60 °N during the Younger Dryas, and that ocean conditions free of sea ice prevailed throughout the Northern North Atlantic in summer.     

Quantitative assessment of precipitation seasonality and summer surface wetness using ombrotrophic sediments from an Arctic Norwegian peatland

Seasonality of precipitation is an important yet elusive climate parameter in paleoclimatological reconstructions. This parameter can be inferred qualitatively from pollen and other paleoecological methods, but is difficult to assess quantitatively. Here, we have assessed seasonality of precipitation and summer surface wetness using compound specific hydrogen and carbon isotope ratios of vascular plant leaf waxes and Sphagnum biomarkers extracted from the sediments of an ombrotrophic peatland, Bøstad Bog, Nordland, Norway. Our reconstructed precipitation seasonality and surface wetness are consistent with regional vegetation reconstructions. During the early Holocene, 11.5–7.5 ka, Fennoscandia experienced a cool, moist climate. The middle Holocene, 7.5–5.5 ka, was warm and dry, transitioning towards cooler and wetter conditions from the mid-Holocene to the present. Changes in seasonality of precipitation during the Holocene show significant coherence with changes in sea surface temperature in the Norwegian Sea, with higher SST corresponding to greater percentage of winter precipitation. Both high SST in the Norwegian Sea and increased moisture delivery to northern Europe during winter are correlated with a strong gradient between the subpolar low and subtropical high over the North Atlantic (positive North Atlantic Oscillation).     

Palaeoceanographic changes off North Iceland through the last 1200 years: foraminifera,stable isotopes,diatoms and ice rafted debris

Palaeoclimatic changes through the last 1200 calibrated years have been documented by high-resolution multi-proxy studies of three cores from about 400 m water depth on the North Icelandic shelf. Benthic and planktonic foraminiferal assemblages and stable isotope values, as well as ice rafted debris (IRD) concentrations, are compared with diatom-based sea-surface water temperatures and the reconstructed mean temperature for the Northern Hemisphere. Changes in surface and bottom water characteristics are mainly due to variations in the strength of the relatively warm, high-salinity Irminger Current and the cold East Icelandic Current. The time period between 1200 and around 7–800 cal. (years) BP, including the Medieval Warm Period, was characterized by relatively high bottom and surface water temperatures due to the inflow of Atlantic water masses. After that, a general temperature decrease in the area marks the transition to a period with increased influence of the East Icelandic Current and, at the sea floor, the Norwegian Sea Deep Water. This corresponds to the transition to the Little Ice Age. After about 3–400 cal. BP, the inflow of cold East Icelandic Current was further enhanced. In particular, this had a strong influence on the surface waters, while the sea floor was under some influence of Atlantic water masses, resulting in stratification of the water masses. There is no clear indication of any warming in the area during the last decades.     

Early postglacial environmental conditions in the northeastern Laptev Sea region

A comparison of the first results of a comprehensive micropaleontological analysis (pollen, spores, organic-walled microfossils, diatoms, ostracods) and radiocarbon ages (AMS¹⁴C) from sediment core recovered in the northeastern outer shelf of the Laptev Sea (51 m water depth) revealed a temporal coincidence between terrestrial and marine environmental changes that occurred between 11.2–10.3 cal ka. This interval provided evidence for a landscape transition from grass tundra to shrub tundra and the development of a freshwater estuarine basin with the strong influence of riverine discharge and a minor advection of North Atlantic waters. The establishment of a warmer and wetter climate promoted the expansion of shrub tundra habitats. The interval of 9.5–7.5 cal ka recorded a transition from a shrub tundra environment to forest-tundra vegetation. This interval also revealed a series of short-term temperature fluctuations, when summer temperatures were 3–4°C higher than today. The active advection of North Atlantic waters and the increase in salinity were also recorded by this interval.     

Circulation of water masses in the Baltic Proper revealed through iodine isotopes

Tracer technology has been used to understand water circulation in marine systems where the tracer dose is commonly injected into the marine waters through controlled experiments, accidental releases or waste discharges. Anthropogenic discharges of ¹²⁹I have been used to trace water circulation in the Arctic and North Atlantic Ocean. Here, ¹²⁹I, together with ¹²⁷I, is utilized as a tracer of water pathways and circulation in the Baltic Sea through collection of seawater depth profiles. The results indicate the presence of ¹²⁹I signatures which are distinct for each water mass and provide evidence for: (1) inflow water masses through the Drogden Sill that may reach as far as the SW of the Arkona Sea, (2) a portion of North Atlantic water in the bottom of Arkona basin, (3) cyclonic upwelling which breaks through the halocline in a pattern similar to the Baltic haline conveyor belt and (4) more influx of fresher water from the Gulf of Finland and Bothnian Sea in August relative to April. These findings provide advances in labeling and understanding water pathways in the Baltic Sea.