| 1. |
- Adler, Ruth E., et al.
(author)
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Sediment record from the western Arctic Ocean with an improved Late Quaternary age resolution : HOTRAX core HLY0503-8JPC, Mendeleev Ridge
- 2009
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In: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 68:02-jan, s. 18-29
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Journal article (peer-reviewed)abstract
- Sediment core HLY0503-8JPC raised by the HOTRAX'05 expedition from the Mendeleev Ridge was analyzed for multiple lithological, paleontological. and stable-isotopic proxies to reconstruct paleoceanographic conditions in the western Arctic Ocean during the Late Quaternary. The core, extensively sampled in the upper 5 m, reveals pronounced changes in sedimentary environments during the ca. 250 kyr interval encompassing Marine Isotopic Stages (MIS) 1 to 7. An estimated average resolution of 500 yr/sample, at least for the last glacial cycle including the last interglacial, provides more detail than seen in other sedimentary records from the western Arctic Ocean. The age control is provided by C-14 and amino acid racemization measurements on planktonic foraminifers and correlations with the stratigraphy developed for the central Lomonosov Ridge and with glacial events at the Eurasian Arctic margin. Cyclic variations in lithology combined with foraminiferal abundance and stable-isotopic composition indicate profound changes in hydrographic and depositional environments between interglacial-type and glacial-type periods apparently reflecting a combination of 100-kyr and precessional time scales. This periodicity is complicated by abrupt iceberg- and/or meltwater-discharge events with variable (Laurentide vs. Eurasian) provenance. The proxy record from the interval identified as the last interglacial (MIS 5e), which may aid in understanding the future state of the Arctic Ocean, indicates low ice conditions and possibly enhanced stratification of the water column.
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| 2. |
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| 3. |
- Dowdeswell, J. A., et al.
(author)
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High-resolution geophysical observations of the Yermak Plateau and northern Svalbard margin : Implications for ice-sheet grounding and deep-keeled icebergs
- 2010
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 29:25-26, s. 3518-3531
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Journal article (peer-reviewed)abstract
- High-resolution geophysical evidence on the seafloor morphology and acoustic stratigraphy of the Yermak Plateau and northern Svalbard margin between 79°20′ and 81°30′N and 5° and 22°E is presented. Geophysical datasets are derived from swath bathymetry and sub-bottom acoustic profiling and are combined with existing cores to derive chronological control. Seafloor landforms, in the form of ice-produced lineations, iceberg ploughmarks of various dimensions (including features over 80 m deep and down to about 1000 m), and a moat indicating strong currents are found. The shallow stratigraphy of the Yermak Plateau shows three acoustic units: the first with well-developed stratification produced by hemipelagic sedimentation, often draped over a strong and undulating internal reflector; a second with an undulating upper surface and little acoustic penetration, indicative of the action of ice; a third unit of an acoustically transparent facies, resulting from debris flows. Core chronology suggests a MIS 6 age for the undulating seafloor above about 580 m. There are several possible explanations, including: (a) the flow of a major grounded ice sheet across the plateau crest from Svalbard (least likely given the consolidation state of the underlying sediments); (b) the more transient encroachment of relatively thin ice from Svalbard; or (c) the drift across the plateau of an ice-shelf remnant or megaberg from the Arctic Basin. The latter is our favoured explanation given the evidence currently at our disposal.
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| 4. |
- Hanslik, Daniela, et al.
(author)
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Late Pleistocene and Holocene benthic and planktonic foraminifera from the central Lomonosov Ridge
- 2007
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In: First Conference on Arctic Palaeoclimate and its Extremes (APEX).
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Conference paper (other academic/artistic)abstract
- Presently available bathymetric charts show that the area between about 88°15’–89°N and 140°–180°E of the Lomonosov Ridge is characterized by a >1000 m deep depression in the ridge morphology forming a local "intra basin". During the 2005 Beringia/Healy-Oden Trans-Arctic EXpedition (HOTRAX), a detailed investigation of this part of the Lomonosov Ridge was conducted including multibeam bathymetric mapping, subbottom profiling, hydrographic measurements and sediment coring (Darby et al., 2005). The subbottom profiles reveal an expanded sediment stratigraphy in the intra basin suggesting that the area have acted as a local sediment trap with higher sediment accumulation rates compared to the 1000 m shallower ridge crest (Björk et al., in press). Core HLY0503-18JPC, investigated in this study, was retrieved at 2598 m water depth from the floor of the intra basin. The top 68 cm of this 12 m long sediment core contain abundant calcareous nanno- and microfossils. For this study, the content of benthic and planktonic foraminifera was quantified. The number of specimens per gram sediment showed several major peaks and valleys. Peak abundances of benthic and planktonic foraminifera coincide well with each other. The largest peak occurs near the base of this 68 cm long calcareous-rich sequence. All calcareous microfossils are well preserved, showing no signs of dissolution in the larger grain size fraction (>150 m). Assemblage analyses of four samples, of the size fraction >150 m, show a dominant abundance of Neogloboquadrina pachyderma (sinistral), accounting for up to 99% of the assemblage. There is no complete age model yet established for core HLY0503-18JPC, although 14C dating made on tube worms and bryozoan mats show ages of 35.200 ± 1500 (radiocarbon yrs) at 28-29 cm core depth and 32.800 ± 1500 (radiocarbon yrs) at 39 cm indicating sedimentation rates of about 1 cm/kyr. These 14C ages are in stark contrast to the nannofossil stratigraphy where the most nannofossil rich samples found between 42 and 56 cm suggest a Holocene age (Fornaciari et al., 2006) implying several times higher sedimentation rates. Additional 14C dating will be carried out on planktonic and benthic foraminifera as a next step in this study.
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| 5. |
- Hanslik, Daniela, et al.
(author)
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Quaternary Arctic Ocean sea ice variations and deep water isolation times
- 2010
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 29:25-26, s. 3430-3441
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Journal article (peer-reviewed)abstract
- A short sediment core retrieved from a local depression forming an intra basin on the Lomonosov Ridge during the Healy-Oden Trans-Arctic Expedition 2005 (HOTRAX) contains a record of the Marine Isotope Stages (MIS) 1-3 showing exceptionally high abundances of calcareous microfossils during parts of MIS 3. Based on radiocarbon dating, linear sedimentation rates of 7-9 cm/ka persist during the last deglaciation. Last Glacial Maximum (LGM) is partly characterized by a hiatus. Planktic foraminiferal abundance variations of Neogloboquadrina pachyderma sinistral and calcareous nannofossils reflect changes in Arctic Ocean summer sea ice coverage and probably inflow of subpolar North Atlantic water. Marine reservoir ages of 1400 years or more, at least during the last deglaciation, seem plausible from calibration of the radiocarbon ages using modeled reservoir corrections from previous studies in combination with the microfossil abundance record of the studied core. Paired benthic-planktic radiocarbon dated foraminiferal samples indicate a slow decrease in age difference between surface and bottom waters from the Late Glacial to the Holocene, suggesting circulation and ventilation changes.
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| 6. |
- Hanslik, Daniela, et al.
(author)
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Quaternary Arctic Ocean sea ice variations and radiocarbon reservoir age corrections
- 2010
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 29:25-26, s. 3430-3441
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Journal article (peer-reviewed)abstract
- A short sediment core from a local depression forming an intra basin on the Lomonosov Ridge, was retrieved during the Healy-Oden Trans-Arctic Expedition 2005 (HOTRAX). It contains a record of the Marine Isotope Stages (MIS) 1-3 showing exceptionally high abundances of calcareous microfossils during parts of MIS 3. Based on radiocarbon dating, linear sedimentation rates of 7-9 cm/ka persist during the last deglaciation. The Last Glacial Maximum (LGM) is partly characterized by a hiatus. Planktic foraminiferal abundance variations of Neogloboquadrina pachyderma sinistral and calcareous nannofossils reflect changes in Arctic Ocean summer sea ice coverage and probably inflow of subpolar North Atlantic water. Calibration of the radiocarbon ages, using modeled reservoir corrections from previous studies and the microfossil abundance record of the studied core, results in marine reservoir ages of 1400 years or more, at least during the last deglaciation. Paired benthic-planktic radiocarbon dated foraminiferal samples indicate a slow decrease in age difference between surface and bottom waters from the Lateglacial to the Holocene, suggesting circulation and ventilation changes. (C) 2010 Elsevier Ltd. All rights reserved.
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| 7. |
- Jakobsson, Martin, 1966-, et al.
(author)
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An Arctic Ocean ice shelf during MIS 6 constrained by new geophysical and geological data
- 2010
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 29:25-26, s. 3505-3517
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Journal article (peer-reviewed)abstract
- The hypothesis of floating ice shelves covering the Arctic Ocean during glacial periods was developed in the 1970s. In its most extreme form, this theory involved a 1000 m thick continuous ice shelf covering the Arctic Ocean during Quaternary glacial maxima including the Last Glacial Maximum (LGM). While recent observations clearly demonstrate deep ice grounding events in the central Arctic Ocean, the ice shelf hypothesis has been difficult to evaluate due to a lack of information from key areas with severe sea ice conditions. Here we present new data from previously inaccessible, unmapped areas that constrain the spatial extent and timing of marine ice sheets during past glacials. These data include multibeam swath bathymetry and subbottom profiles portraying glaciogenic features on the Chukchi Borderland, southern Lomonosov Ridge north of Greenland, Morris Jesup Rise, and Yermak Plateau. Sediment cores from the mapped areas provide age constraints on the glaciogenic features. Combining these new geophysical and geological data with earlier results suggests that an especially extensive marine ice sheet complex, including an ice shelf, existed in the Amerasian Arctic Ocean during Marine Isotope Stage (MIS) 6. From a conceptual oceanographic model we speculate that the cold halocline of the Polar Surface Water may have extended to deeper water depths during MIS 6 inhibiting the warm Atlantic water from reaching the Amerasian Arctic Ocean and, thus, creating favorable conditions for ice shelf development. The hypothesis of a continuous 1000 m thick ice shelf is rejected because our mapping results show that several areas in the central Arctic Ocean substantially shallower than 1000 m water depth are free from glacial influence on the seafloor.
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| 8. |
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| 9. |
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| 10. |
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| 11. |
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| 12. |
- O'Regan, Matthew, et al.
(author)
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Middle to late Quaternary grain size variations and sea-ice rafting on the Lomonosov Ridge
- 2014
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In: Polar Research. - : Norwegian Polar Institute. - 0800-0395 .- 1751-8369. ; 33, s. 23672-
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Journal article (peer-reviewed)abstract
- Sea ice and icebergs are the dominant transport agents for sand-sized material to the central Arctic Ocean. However, few studies have investigated concurrent changes in the silt-sized fraction of Arctic sediments. Here we present an analysis of the coarse fraction content and silt grain size composition from middle and late Quaternary sediments recovered from the Lomonosov Ridge, in the central Arctic Ocean. A significant shift in the grain size record occurs at the marine isotope stage (MIS) 6/7 boundary, where larger amplitude variability in the sand fraction is seen in glacial and stadial periods. Below the MIS6/7 boundary, variations in the coarse fraction content are less pronounced, but prominent changes in the silt size fraction appear to define glacial and interglacial periods. Throughout the record, the percent weight of sortable silt in the fine fraction (SS % wt(fines)), sortable silt mean size, and coarse silt content all increase as the >63 mu m % wt content increases. This is consistent with observations of grain size spectra obtained from modern sea-ice samples, and indicates a strong overprint from sea ice on the silt distribution. The mechanism by which this sea-ice signal is preserved in the sediments across glacial and interglacial periods remains unclear. We suggest that the coarsening of silt-sized material during glacial periods could be attributed to either the entrainment of larger size fractions during suspension/anchor ice formation when sea levels are lowered, or diminished input and advection of fine fraction material during glacial periods.
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Sellén, Emma, et al.
(author)
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Beryllium Isotope Dating of Sediment Cores From the Alpha Ridge, Arctic Ocean
- 2007
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In: Eos, Trans. AGU, 88(52), Fall Meeting.
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Conference paper (other academic/artistic)abstract
- AB: Poor preservation of biogenic calcium carbonate and biosilica in Arctic Ocean sediments has led to large problems regarding the establishment of a reliable chronostratigraphy. There are currently two differing sedimentation rate scenarios proposed for the Arctic Ocean. The first suggests sedimentation rates on the order of mm/ka and is based on cores from the Amerasian Basin, whereas the second suggests sedimentation rates on the order of cm/ka mainly derived from Eurasian Basin cores. Here we present dating results from cores HLY0503-09JPC and HLY0503-14JPC retrieved from the Alpha Ridge during the Healy-Oden Trans-Arctic Expedition 2005 (HOTRAX). These cores have been analyzed for seawater-derived beryllium (Be) isotopes in order to establish a chronostratigraphy. The isotopes 10Be and 9Be were extracted simultaneously from sample aliquots by using a leaching procedure. The decrease of 10Be concentration (half-life = 1.51 Million years) with depth in core provides first order sedimentation rates for the sampled cores. To eliminate the dilution effect of beryllium caused by short-term changes in sedimentation rate and grain size variability, the 10Be concentration was normalized to the stable isotope 9Be. The preliminary results show low downcore 10Be concentrations in both cores from the Alpha Ridge. Plotting 10Be against depth suggests an average sedimentation rate of ~2.9 mm/ka for core HLY0503-09JPC and ~2.3 mm/ka for HLY0503- 14JPC. The calculated 10Be/9Be ratios point to even lower average sedimentation rates of ~1.9 mm/ka for core HLY0503-09JPC and ~1.6 mm/ka for HLY0503-14JPC. However, core HLY0503-14JPC shows a pronounced variability of the 10Be concentration as well as for the 10Be/9Be ratio, which results in a large uncertainty of the calculated sedimentation rates. The 10Be concentrations for this core will be compared with the grain size record in order to reduce the scatter of the data. The preliminary beryllium isotope chronostratigraphy supports lower sedimentation rates in the Amerasian Basin compared to the Eurasian Basin. A long-term solid sea ice cover in the Beaufort Gyre may explain the low 10Be concentrations, but does not explain the calculated low sedimentation rates.
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| 17. |
- Sellén, Emma, et al.
(author)
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Beryllium isotope variations in sediment cores from the Alpha Ridge, Arctic Ocean
- 2008
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In: Arctic Palaeoclimate and its Extremes (APEX). ; , s. 92-
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Conference paper (other academic/artistic)abstract
- The Healy-Oden Trans-Arctic Expedition 2005 (HOTRAX) recovered cores along a transect across the Arctic Ocean. Here we present results from measurements of seawater-derived beryllium isotopes in cores HLY0503-09JPC and HLY0503-14JPC from the Alpha-Mendeleev Ridge. The intention of measuring beryllium (Be) isotopes is to establish a chronostratigraphy as the decrease of 10Be concentration (half-life = 1.51 Million years) with depth in the cores may provide first order sedimentation rates. The isotopes 10Be and 9Be were extracted simultaneously from sample aliquots by using a leaching procedure. To eliminate the dilution effect of beryllium caused by short-term changes in sedimentation rate and grain size variability, the 10Be concentration was normalized to the stable isotope 9Be. The results show low downcore 10Be concentrations and subsequently sedimentation rates on the order of mm/ka in both cores from the Alpha Ridge. However, we note two indications suggesting that our calculated sedimentation rates from the beryllium results may not be valid and requires further analysis: 1) the decrease of 10Be down core does not follow a well defined trend; 2) a comparison with preliminary results from nannofossil studies of cores HLY0503-14JPC and HLY0503-08JPC located nearby HLY0503-09JPC indicates much higher sedimentation rates than we obtained from the 10Be data (Backman and Fornaciari pers. comm.). The pronounced decrease of 10Be with core depth may imply a stronger effect of sea ice shielding of atmospheric inputs, whereas the 9Be increase with depth may point to a stronger continental input of 9Be.
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| 18. |
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| 19. |
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| 20. |
- Sellén, Emma, et al.
(author)
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Linking stratigraphy on the Lomonosov Ridge with standard lithological units of the Amerasia Basin
- 2007
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In: First Conference on Arctic Palaeoclimate and its Extremes (APEX).
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Conference paper (other academic/artistic)abstract
- A lithological classification has been established by Clark et al. (1980), based on cores primarily from the Alpha Ridge, on the Amerasian side of the Arctic Ocean. It has since been applied to correlate sediment cores over large distances, mainly in the Amerasian Basin (Alpha Ridge, Northwind Ridge and Mendeleev Ridge), but also on the Lomonosov Ridge. Over a 310 cm long stratigraphic section, synthesized from 67 cores, 13 units were recognized and named A to M by Clark et al. (1980). An age model was developed for this lithostratigraphy that relied on the identification of the Brunhes-Matuyama paleomagnetic reversal boundary (781 000 years; Lourens et al., 2004) and the assumption of a linear sedimentation rate. However, recent studies have shown that this measured magnetic polarity change represents instead a short-time excursion within the Brunhes chron. We have investigated if it is possible to infer the lithostratigraphy (Units A-M) from the Amerasian Arctic Ocean in cores from the Lomonosov Ridge that in turn have been correlated to cores in the Eurasian Basin. The cores selected for this study were B-8 and B-24 from the LOREX ‘79 ice island drift expedition (Morris et al., 1985), PS2185-6 from the Arctic’91: ARK-VIII/3 expedition with R/V Polarstern (Spielhagen et al., 1997) and 96/12-1pc from the Arctic Ocean 96 expedition with I/B Oden (Jakobsson et al., 2001). Averaged sedimentary proxies (paleomagnetism, grain size, microfossil abundance and lithostratigraphy) from a selected set of T3 cores have been published by Clark et al. (1980) and these have been used in this study to link with the same published proxies for the included Lomonosov Ridge cores. The Lomonosov Ridge cores PS 2185-6 and 96/12-1pc have previously been correlated using paleomagnetic polarity reversals and grain size (Jakobsson et al., 2001) and the lithostratigraphic units A-M were previously inferred in core B-8 by Morris et al. (1985). In our study, the lithostratigraphic units (A to M) could not be inferred in PS2185-6 or 96/12-1pc. However, correlations between the Lomonosov Ridge and Amerasian Basin T3 cores appear to be possible using paleomagnetic and grain size data. More detailed data from the Alpha Ridge sediment stratigraphy would probably enhance our first attempted correlations using these proxies. An additional correlation between the Lomonosov Ridge cores PS2185-6 and 96/12-1pc and piston core HLY0503-18JPC, retrieved from the Lomonosov Ridge during the HOTRAX expedition (2005) with USCGC Healy, has also been made. The grain size data from core HLY0503-18JPC could easily be correlated to the older cores on the Lomonosov Ridge and will hopefully be a good link to the HOTRAX cores taken on the Alpha-Mendeleev Ridge. The correlations made here, imply higher sedimentation rates on the Lomonosov Ridge than on the Alpha Ridge, but not as much higher as previously thought. By establishing a new reliable age model for the Arctic Ocean, earlier studies on Amerasian cores could be viewed from a completely different chronostratigraphic perspective.
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| 21. |
- Sellén, Emma, et al.
(author)
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Linking Stratigraphy on the Lomonosov Ridge With Standard Lithological Units of the Amerasian Basin, Arctic Ocean
- 2006
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In: AGU Fall Meeting 2006Eos Trans. AGU, 87(52), Fall Meeting.
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Conference paper (other academic/artistic)abstract
- AB: Short sediment cores taken from the ice-island T3 between 1963 and 1973 were used by Clark et al. (1980) to establish a lithological classification for the Amerasian Basin in the Arctic Ocean. Over a 310 cm long stratigraphic section, synthesized from 67 cores, 13 units were recognized and labeled A to M. This lithostratigraphic model has since been applied to correlate sediment cores over large distances on the Amerasian side, i.e., between cores on the Alpha Ridge, the Northwind Ridge and the Mendeleev Ridge. The chronostratigraphy for this lithostratigraphic model was developed by the identification of the Brunhes- Matuyama paleomagnetic reversal boundary (781 ka) and the assumption of linear sedimentation rates in the synthesized lithologic model. However, recent studies have shown that this measured magnetic polarity change rather represents a short-time excursion within the Brunhes chron, implying an order of magnitude higher sedimentation rates than originally assumed. We have investigated whether it is possible to link the lithostratigraphy from the Alpha Ridge to cores taken on the Lomonosov Ridge which, in turn, have been linked to cores in the Eurasian Basin. The cores selected for this comparison were cores B-8 and B-24 from the LOREX ‘79 ice island drift expedition, core PS2185-6 from the ARK-VIII/3 expedition of 1991 and core 96/12- 1pc from the Arctic Ocean 96 expedition. Averaged sedimentary proxies (paleomagnetism, grain size, and microfossil abundance) from selected sets of T3 cores and published by Clark et al. (1980), have been used here to correlate the included Lomonosov Ridge cores. A lithostratigraphic connection between the Amerasian Basin and the Lomonosov Ridge stratigraphies was partly successfully established, although Clark's lithostratigraphic units A to M could not be recognized in the Lomonosov Ridge. Nevertheless, the established correlations clearly show that the Amerasian Basin is characterized by lower sedimentation rates when compared to the rates obtained from the Lomonosov Ridge and the Eurasian Basin , but that the Amerasian Basin rate are not as low as Clark and others previously suggested.
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| 22. |
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| 23. |
- Sellén, Emma, et al.
(author)
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Pleistocene variations of beryllium isotopes in central Arctic Ocean sediment cores
- 2009
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In: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 68:1-2, s. 38-47
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Journal article (peer-reviewed)abstract
- Neogene marine sediments can be dated via decay of the cosmogenic radionuclide 10Be. Two cores from theAlpha and Mendeleev Ridges in the Arctic Ocean have been analyzed for seawater-derived beryllium (Be)isotopes in order to date the sediments and to calculate sedimentation rates. The decrease of 10Be concentrationin the cores was used to calculate first order sedimentation rates. To eliminate the dilution effect of berylliumcaused by short-term changes in sedimentation rate and grain size, the 10Be concentrationswere normalized tothe terrigenous stable isotope 9Be determined in the same sample aliquot. The measured 10Be concentrationsyield low average sedimentation rates for the Alpha and Mendeleev Ridges of 2.3 mm ka−1 and 2.7 mm ka−1,respectively. Sedimentation rates calculated from the 10Be/9Be ratios result in similarly low values, rangingfrom 0.2 to 6.8 mm ka−1 for the Alpha Ridge core and from 1.9 to 6.9 mm ka−1 for the Mendeleev Ridge core.However, amino acid racemization dating for the past 150 ka of a core adjacent to the Mendeleev Ridge corestudied here indicates significantly higher sedimentation rates than calculated from the downcore decreaseof 10Be and 10Be/9Be. If such higher rates also prevailed at the locations of our cores, for which there isbiostratigraphic evidence, either the supply of 10Be was much lower than assumed or that of 9Be was muchhigher. This could imply that the signature of the deepwaters in this part of the Arctic Ocean compared to todaywas largely different for most of the past approximately one million years with a significantly lower 10Be/9Beratio. Our study also addresses the variability of beryllium isotopes in sediment cores across the Arctic Oceanthrough a comparison of previously published results. Calculated 10Be fluxes reveal low values in the AmerasianBasin and highest values in the Eurasian Basin, near the Fram Strait. The decrease of Be isotopes in the twostudied Amerasian Basin cores may thus have been caused by environmental factors such as significantlyreduced inflow of Atlantic waters in the past, reduced input of 10Be and/or increased input of 9Be from theshelves, combined with a more efficient sea ice shielding in this part of the Arctic Ocean.
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| 24. |
- Sellén, Emma
(author)
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Problems of stratigraphic correlation across the Arctic Ocean
- 2007
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Licentiate thesis (other academic/artistic)abstract
- Published articles on Arctic Ocean sedimentation rates generally falls into two categories; one suggesting mm/ka-scale sedimentation rates in the Amerasian Basin and the other cm/ka-scale rates in the Eurasian Basin. This is due to the interpretation of the first measured paleomagnetic polarity change in sediment cores as either the Brunhes-Matuyama (781 ka) reversal or as the short time magnetic excursion, Biwa II (220 ka) within the Brunhes Chron. The paleoclimatological and paleoceanographical interpretations will be greatly affected depending on which age model is applied.A “standard” lithostratigraphy was developed in 1980 for cores from the Alpha-Mendeleev Ridge in the Amerasian Basin. An age model was established for this lithostratigraphic model, based on the assumption that the Brunhes-Matuyama reversal boundary was correctly identified in the investigated cores. In this thesis I have tested if this “standard” lithostratigraphy is possible to apply to cores retrieved from the Lomonosov Ridge. The purpose has been to evaluate the two age model scenarios and the difference in sediment accumulation rates between the Amerasian and Eurasian Basins. The study is based on core-to-core correlations using averaged sedimentological proxies (paleomagnetism, grain size, lithostratigraphy, sediment color and foraminiferal abundance) from a selected set of Alpha Ridge cores that were used to establish the “standard” lithostratigraphic model, and the same set of published proxies for a selected set of Lomonosov Ridge cores. In addition, the coarse fraction, foraminifera abundance, and magnetic susceptibility have been analyzed for cores taken on the Alpha Ridge and the Lomonosov Ridge during the Healy-Oden Trans-Arctic Expedition (HOTRAX) in 2005.The results suggest that it is not possible to establish a common lithostratigraphy throughout the entire Arctic Ocean as the Amerasian Basin and the Eurasian Basin have different depositional environments. Consequently, the “standard” lithostratigraphy can only be applied to the central Amerasian Basin. The paleomagnetic polarity record, however, can be correlated between cores from the Amerasian and Eurasian Basin, indicating that the large apparent differences in sedimentation rates mainly is an artifact from different interpretations. Correlations among the HOTRAX cores using magnetic susceptibility suggest that cores from the Alpha-Mendeleev Ridge in the Amerasian Basin are possible to correlate over 550 km. Finally, grain size variations in HOTRAX core HLY0503-18JPC retrieved from a local depression in the Lomonosov Ridge can be linked to previously studied key cores from the Lomonosov Ridge crest.
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| 25. |
- Sellén, Emma, 1980-
(author)
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Quaternary paleoceanography of the Arctic Ocean : A study of sediment stratigraphy and physical properties
- 2009
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Doctoral thesis (other academic/artistic)abstract
- A Quaternary perspective on the paleoceanographic evolution of the central Arctic Ocean has been obtained in this PhD thesis by studying sediment cores from all of the Arctic’s major submarine ridges and plateaus. The included cores were mainly recovered during the Healy-Oden Trans-Arctic expedition in 2005 and the Lomonosov Ridge off Greenland expedition in 2007. One of the main thesis objectives is to establish whether different sediment depositional regimes prevailed in different parts of the central Arctic Ocean during the Quaternary and, if so, establish general sedimentation rates for these regimes. This was approached by dating key cores using the decay of the cosmogenic isotopes 10Be and 14C, and through stratigraphic core-to-core correlation using sediment physical properties. However, the Arctic Ocean sea ice complicated the use of 10Be for dating because a solid sea ice cover prevents the 10Be isotopes from reaching the seafloor, resulting in too old ages. Dating using 14C is also complicated due to uncertain marine reservoir age corrections in the central Arctic Ocean. The core-to-core correlations show five areas with different depositional regimes; the northern Mendeleev Ridge and Alpha Ridge, southern Mendeleev Ridge, Morris Jesup Rise, Lomonosov Ridge and Yermak Plateau, listed in the order of increasing sedimentation rates from ~0.5cm/ka to ~4.8 cm/ka. A detailed study of the relationship between sediment bulk density and grain sizes suggests a strong link between variations in clay abundance and bulk density. Grain size analysis of a Lomonosov Ridge core show that fine silt and clay dominates the interglacials, possibly due to increased suspension freezing of these size fractions into sea ice and/or nepheloid transport. Sediments younger than the marine isotope stage (MIS) 7 generally contain more coarse silt, attributed to a regime shift during the Quaternary with increased iceberg transport into the central Arctic Ocean from MIS 6 and onwards.
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| 26. |
- Sellén, Emma, et al.
(author)
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Sedimentary regimes in Arctic’s Amerasian and Eurasian basins : Clues to differences in sedimentation rates
- 2008
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In: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 61:3-4, s. 275-284
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Journal article (peer-reviewed)abstract
- A standard lithostratigraphic model based on cores retrieved 1963–1973 from the ice island T-3 was developed by Clark et al. (1980) for the Amerasian Basin of the Arctic Ocean. We have investigated whether or not it is possible to apply this lithostratigraphy to cores from the Lomonosov Ridge, which can be correlated to Eurasian Basin cores, for the purpose of correlating the Amerasian and Eurasian stratigraphies. Published averaged sedimentary proxies from a selected set of T-3 cores are used to correlate with the identical published proxies for the included Lomonosov Ridge cores. The standard lithostratigraphic classification could not be applied to the Lomonosov Ridge cores, which is interpreted to result from differences in sedimentary regimes in the Amerasian and Eurasian Basins. These differences also apply to the barrier between the two basins, the Lomonosov Ridge. The general sedimentation rates are three to four times lower in the Amerasian Basin than in the Eurasian Basin if the first down-core paleomagnetic inclination change is used to correlate between the two basins whereas correlation based on sediment coarse fraction suggests only two times lower rates in the Amerasian Basin.
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| 27. |
- Sellén, Emma, et al.
(author)
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Spatial and temporal ArcticOcean depositional regimes : a key to the evolution of ice and current patterns
- 2010
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 29:25-26, s. 3644-3664
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Journal article (peer-reviewed)abstract
- Sediment physical properties measured in cores from all the major ridges and plateaus in the central Arctic Ocean were studied in order to analyze the spatial and temporal consistency of sediment depositional regimes during the Quaternary. In total, six physiographically distinct areas are outlined. In five of these, cores can be correlated over large distances through characteristic patterns in sediment physical properties. These areas are (1) the southern Mendeleev Ridge, (2) the northern Mendeleev Ridge and Alpha Ridge, (3) the Lomonosov Ridge, (4) the Morris Jesup Rise and (5) the Yermak Plateau. Averaged downhole patterns in magnetic susceptibility, bulk density and lithostratigraphy were compiled to establish a composite stratigraphy for each area. In the sixth physiographic area, the Chukchi Borderland, repeated ice-grounding during recent glacial periods complicates the stratigraphy and prevents the compilation of a composite stratigraphy using the studied material. By utilizing published age models for the studied cores we are able to show that the northern Mendeleev Ridge and Alpha Ridge have the lowest average late Quaternary sedimentation rates, while intermediate sedimentation rates prevail on the southern Mendeleev Ridge and the Morris Jesup Rise. The second highest sedimentation rate is observed on the Lomonosov Ridge, whereas the average sedimentation rate on the Yermak Plateau is more than twice as high. The close correlation of physical properties within each area suggests uniform variations in sediment transport through time, at least throughout the later part of the Quaternary. The unique stratigraphic characteristics within each area is the product of similar past depositional regimes and are key for furthering our understanding of the evolution of ice drift and current patterns in the central Arctic Ocean.
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