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Registros recuperados: 13
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Independent tephrochronological evidence for rapid and synchronous oceanic and atmospheric temperature rises over the Greenland stadial-interstadial transitions between ca. 32 and 40 ka b2k ArchiMer
Berben, Sarah M.p.; Dokken, Trond M.; Abbott, Peter M.; Cook, Eliza; Sadatzki, Henrik; Simon, Margit H; Jansen, Eystein.
Understanding the dynamics that drove past abrupt climate changes, such as the Dansgaard-Oeschger (DO) events, depends on combined proxy evidence from disparate archives. To identify leads, lags and synchronicity between different climate system components, independent and robust chronologies are required. Cryptotephrochronology is a key geochronological tool as cryptotephra horizons can act as isochrons linking disparate and/or distant records. Here, we investigated marine sediment core MD99-2284 from the Norwegian Sea to look for previously identified Greenland ice core cryptotephra horizons and define time-parallel markers between the archives. We explored potential secondary transport and depositional mechanisms that could hamper the isochronous...
Tipo: Text Palavras-chave: Quaternary; Paleoclimatology; Paleoceanography; North Atlantic; Sedimentology; Marine cores; Ice cores; Cryptotephrochronology; DO-Events; Synchronization.
Ano: 2020 URL: https://archimer.ifremer.fr/doc/00622/73391/72606.pdf
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Rapid reductions and millennial-scale variability in Nordic Seas sea ice cover during abrupt glacial climate changes ArchiMer
Sadatzki, Henrik; Maffezzoli, Niccolò; Dokken, Trond M.; Simon, Margit H; Berben, Sarah M. P.; Fahl, Kirsten; Kjær, Helle A.; Spolaor, Andrea; Stein, Ruediger; Vallelonga, Paul; Vinther, Bo M.; Jansen, Eystein.
Constraining the past sea ice variability in the Nordic Seas is critical for a comprehensive understanding of the abrupt Dansgaard-Oeschger (D-O) climate changes during the last glacial. Here we present unprecedentedly detailed sea ice proxy evidence from two Norwegian Sea sediment cores and an East Greenland ice core to resolve and constrain sea ice variations during four D-O events between 32 and 41 ka. Our independent sea ice records consistently reveal a millennial-scale variability and threshold response between an extensive seasonal sea ice cover in the Nordic Seas during cold stadials and reduced seasonal sea ice conditions during warmer interstadials. They document substantial and rapid sea ice reductions that may have happened within 250 y or...
Tipo: Text Palavras-chave: Sea ice; Nordic Seas; Dansgaard-Oeschger events; Abrupt climate change.
Ano: 2020 URL: https://archimer.ifremer.fr/doc/00659/77066/78374.pdf
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A signal of persistent Atlantic multidecadal variability in Arctic sea ice ArchiMer
Miles, Martin W.; Divine, Dmitry V.; Furevik, Tore; Jansen, Eystein; Moros, Matthias; Ogilvie, Astrid E. J..
Satellite data suggest an Arctic sea ice-climate system in rapid transformation, yet its long-term natural modes of variability are poorly known. Here we integrate and synthesize a set of multicentury historical records of Atlantic Arctic sea ice, supplemented with high-resolution paleoproxy records, each reflecting primarily winter/spring sea ice conditions. We establish a signal of pervasive and persistent multidecadal (~60–90 year) fluctuations that is most pronounced in the Greenland Sea and weakens further away. Covariability between sea ice and Atlantic multidecadal variability as represented by the Atlantic Multidecadal Oscillation (AMO) index is evident during the instrumental record, including an abrupt change at the onset of the early twentieth...
Tipo: Text Palavras-chave: Sea ice.
Ano: 2014 URL: https://archimer.ifremer.fr/doc/00291/40199/39229.pdf
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Water mass properties and exchange between the Nordic seas and the northern North Atlantic during the period 23-6 ka: Benthic oxygen isotopic evidence ArchiMer
Meland, Marius Y.; Dokken, Trond M.; Jansen, Eystein; Hevroy, Kjersti.
Twenty benthic oxygen isotope records from different water depths in the Nordic seas and the North Atlantic are compared. During the Last Glacial Maximum, brine formation on continental shelves produced Brine Shelf Water (BSW), sinking below 1500 m in the Nordic seas. Open- ocean convection in the Nordic seas produced Glacial North Atlantic Intermediate Water (GNAIW). GNAIW overflowed the Greenland-Scotland Ridge and entrained depths above and at least partly below 2000 m in the North Atlantic. During the early deglaciation, BSW-enriched intermediate water masses in the Nordic seas were formed. These overflowed the Greenland-Scotland Ridge and influenced the North Atlantic intermediate and deepwater masses. In the Bolling-Allerod ( BA), open-ocean...
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Ano: 2008 URL: https://archimer.ifremer.fr/doc/00237/34873/33188.pdf
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Evidence for northward expansion of Antarctic Bottom Water mass in the Southern Ocean during the last glacial inception ArchiMer
Govin, Aline; Michel, Elisabeth; Labeyrie, Laurent; Waelbroeck, Claire; Dewilde, Fabien; Jansen, Eystein.
We investigated deep water changes in the Southern Ocean during the last glacial inception, in relationship to surface hydrology and global climatology, to better understand the mechanisms of the establishment of a glacial ocean circulation. Changes in benthic foraminiferal delta(13)C from three high-resolution cores are compared and indicate decoupled intermediate and deep water changes in the Southern Ocean. From the comparison with records from the North Atlantic, South Atlantic, and the Southern Ocean, we show that the early southern deep water delta(13)C drop observed at the MIS 5.5-5.4 transition occurred before any significant reduction of North Atlantic Deep Water ventilation. We propose that this drop is linked to the northward expansion of poorly...
Tipo: Text Palavras-chave: Isotope substage 5E; Ice core; Interglacial period; Climate variability; Deep ocean; Atlantic; Sea; Circulation; Temperature; Hemisphere.
Ano: 2009 URL: https://archimer.ifremer.fr/doc/00208/31952/30375.pdf
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Abrupt climate changes for Iceland during the last millennium: Evidence from high resolution sea ice reconstructions ArchiMer
Masse, Guillaume; Rowland, Steven J.; Sicre, Marie-alexandrine; Jacob, Jeremy; Jansen, Eystein; Belt, Simon T..
A high resolution account of Icelandic sea ice over the last millennium has been constructed using a novel proxy based on the presence in sediments of a biomarker (IP25) produced by sea ice algae. Comparison with historical sea ice records demonstrates a strong correlation between documented sea ice Occurrences and the IP25 proxy. An excellent agreement is also observed between the IP25 record and a diatom-based sea surface temperature reconstruction obtained from the same core and the Crowley and Lowery Northern Hemisphere temperature reconstruction. Using this approach, we provide new historical sea ice data for periods where records are scarce or absent and evidence for abrupt changes to sea ice and/or climate conditions around Iceland during the Little...
Tipo: Text Palavras-chave: Highly branched isoprenoid alkenes; Sea ice; Iceland; Sediments.
Ano: 2008 URL: https://archimer.ifremer.fr/doc/00237/34839/33273.pdf
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Mid to late Holocene strengthening of the East Greenland Current linked to warm subsurface Atlantic water ArchiMer
Perner, Kerstin; Moros, Matthias; Lloyd, Jeremy M.; Jansen, Eystein; Stein, Ruediger.
The relatively fresh and cold East Greenland Current (EGC) connects the Arctic with the subpolar North Atlantic Ocean. Its strength and influence on the freshwater balance in the North Atlantic affects both the Subpolar Gyre dynamics and deep convection in the Labrador Sea. Enhanced freshwater and sea-ice expansion in the subpolar North Atlantic is suggested to modify the northward heat transport within the North Atlantic Current. High-resolution palaeoceanographic reconstructions, based on planktic and benthic foraminifera assemblage data, from the central East Greenland shelf (Foster Bugt) reveal distinct centennial to millennial-scale oceanographic variability that relates to climatic changes during the mid to late Holocene (the last c. 6.3 ka BP). Our...
Tipo: Text Palavras-chave: Foraminifera; East Greenland Current; Return Atlantic Current; Subpolar gyre; Polar front; Subpolar north Atlantic; Mid to late Holocene.
Ano: 2015 URL: https://archimer.ifremer.fr/doc/00496/60725/83614.pdf
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Which is the better proxy for paleo-current strength: Sortable-silt mean size (SS) or sortable-silt mean grain diameter (d SS)? A case study from the Nordic Seas ArchiMer
Tegzes, Andrea D.; Jansen, Eystein; Telford, Richard J..
The coarseness of the 10-63 m terrigenous silt (i.e., sortable-silt) fraction tends to vary independently of sediment supply in current-sorted muds in the world's oceans, with coarser sediments representing relatively greater near-bottom flow speeds. Traditionally, the coarseness of this size fraction is described using an index called sortable-silt mean size ( SS), which is an arithmetic average calculated from the differential volume or mass distribution of grains within the 10-63 m terrigenous silt fraction, where the relative weights of the individual size bins become increasingly disproportionate, with respect to the actual number of grains within those size bins, toward the coarse end of the size range. This not only increases the absolute value of...
Tipo: Text Palavras-chave: Ocean circulation; Paleo-current reconstructions; Sortable-silt mean size; Sortable-silt mean grain size; Coulter Counter.
Ano: 2015 URL: https://archimer.ifremer.fr/doc/00496/60728/65240.pdf
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Early Holocene temperature variability in the Nordic Seas: The role of oceanic heat advection versus changes in orbital forcing ArchiMer
Risebrobakken, Bjorg; Dokken, Trond; Smedsrud, Lars Henrik; Andersson, Carin; Jansen, Eystein; Moros, Matthias; Ivanova, Elena V..
The separate roles of oceanic heat advection and orbital forcing on influencing early Holocene temperature variability in the eastern Nordic Seas is investigated. The effect of changing orbital forcing on the ocean temperatures is tested using the 1DICE model, and the 1DICE results are compared with new and previously published temperature reconstructions from a transect of five cores located underneath the pathway of Atlantic water, from the Faroe-Shetland Channel in the south to the Barents Sea in the north. The stronger early Holocene summer insolation at high northern latitudes increased the summer mixed layer temperatures, however, ocean temperatures underneath the summer mixed layer did not increase significantly. The absolute maximum in summer mixed...
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Ano: 2011 URL: https://archimer.ifremer.fr/doc/00227/33800/32547.pdf
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Tephra horizons identified in the western North Atlantic and Nordic Seas during the Last Glacial Period: Extending the marine tephra framework ArchiMer
Rutledal, Sunniva; Berben, Sarah M.p.; Dokken, Trond M.; Van Der Bilt, Willem G.m.; Cederstrøm, Jan Magne; Jansen, Eystein.
Geochemically distinct volcanic ash (tephra) deposits are increasingly acknowledged as a key geochronological tool to synchronize independent paleoclimate archives. Recent advances in the detection of invisible (crypto) tephra have led to the ongoing establishment, development and integration of regional tephra lattices. These frameworks offer an overview of the spatial extent of geochemically characterized tephra from dated eruptions – a valuable tool for precise correlation of paleorecords within these areas. Here, we harness cryptotephra analysis to investigate the occurrence of two well-known tephra markers from the Last Glacial Period (i.e. FMAZ II-1 (26.7 ka b2k) and NAAZ II (II-RHY-1) (55.3 ka b2k)), in marine sediment cores from the Nordic,...
Tipo: Text Palavras-chave: Tephrochronology; Cryptotephra Tephrostratigraphy; Tephra isochrons; FMAZ II; NAAZ II; Geochemistry; Paleoceanography; Marine sediment cores Quaternary; North Atlantic Ocean.
Ano: 2020 URL: https://archimer.ifremer.fr/doc/00614/72659/71665.pdf
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Inception of the Northern European ice sheet due to contrasting ocean and insolation forcing ArchiMer
Risebrobakken, Bjorg; Dokken, Trond; Ottera, Odd Helge; Jansen, Eystein; Gao, Yongqi; Drange, Helge.
About 115,000 yr ago the last interglacial reached its terminus and nucleation of new ice-sheet growth was initiated. Evidence from the northernmost Nordic Seas indicate that the inception of the last glacial was related to an intensification of the Atlantic Meridional Overturning Circulation (AMOC) in its northern limb. The enhanced AMOC, combined with minimum Northern hemisphere insolation, introduced a strong sea-land thermal gradient that, together with a strong wintertime latitudinal insolation gradient, increased the storminess and moisture transport to the high Northern European latitudes at a time when the Northern hemisphere summer insolation approached its minimum.
Tipo: Text Palavras-chave: Glacial inception; Nordic Seas; Northern European ice sheets; Palco-reconstruction; OGCM; AMOC; Insolation; Insolation gradient.
Ano: 2007 URL: https://archimer.ifremer.fr/doc/00233/34441/82768.pdf
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Sea ice variability in the southern Norwegian Sea during glacial Dansgaard-Oeschger climate cycles ArchiMer
Sadatzki, Henrik; Dokken, Trond M.; Berben, Sarah M. P.; Muschitiello, Francesco; Stein, Ruediger; Fahl, Kirsten; Menviel, Laurie; Timmermann, Axel; Jansen, Eystein.
The last glacial period was marked by pronounced millennial-scale variability in ocean circulation and global climate. Shifts in sea ice cover within the Nordic Seas are believed to have amplified the glacial climate variability in northern high latitudes and contributed to abrupt, high-amplitude temperature changes over Greenland. We present unprecedented empirical evidence that resolves the nature, timing, and role of sea ice fluctuations for abrupt ocean and climate change 32 to 40 thousand years ago, using biomarker sea ice reconstructions from the southern Norwegian Sea. Our results document that initial sea ice reductions at the core site preceded the major reinvigoration of convective deep-water formation in the Nordic Seas and abrupt Greenland...
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Ano: 2019 URL: https://archimer.ifremer.fr/doc/00484/59606/62620.pdf
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A continuous tephrostratigraphic record from the Labrador Sea spanning the last 65 ka ArchiMer
Rutledal, Sunniva; Haflidason, Hafkidi; Berben, Sarah Mp; Griem, Lisa; Jansen, Eystein.
Volcanic ash preserved in marine sediment sequences is key for independent synchronization of palaeoclimate records within and across different climate archives. Here we present a continuous tephrostratigraphic record from the Labrador Sea, spanning the last 65.5 ka, an area and time period that has not been investigated in detail within the established North Atlantic tephra framework. We investigated marine sediment core GS16]204] 22CC for increased tephra occurrences and geochemically analysed the major element composition of tephra shards to identify their source volcano(es). In total we observed eight tephra zones, of which five concentration peaks show isochronous features that can be used as independent tie]points in future studies. The main...
Tipo: Text Palavras-chave: Marine tephra; North Atlantic; Quaternary; Tephra isochrons; Tephrochronology.
Ano: 2020 URL: https://archimer.ifremer.fr/doc/00648/76044/76980.pdf
Registros recuperados: 13
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