Paleoceanography of the Last Interglacial/Glacial Cycle in the Polar North Atlantic (original) (raw)
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Glacial and Oceanic History of the Polar North Atlantic Margins: An Overview
Quaternary Science Reviews, 1998
The five-year PONAM (Polar North Atlantic Margin: Late Cenozoic Evolution) programme was launched by the European Science Foundation in 1989. Its aim was to study the major climate-driven environmental variations in the Norwegian-Greenland (also Nordic) Sea and its continental margins over the last 5 milliion years. The programme has provided substantial new insights into the contrasting behaviour of the ice sheets covering the Svalbard-Barents Sea and East Greenland over the last glacial-interglacial cycle in particular. The highly dynamic Svalbard-Barents Sea Ice Sheet, after reaching the shelf edge during each stadial, almost vanished during subsequent interstadials. By contrast, the East Greenland Ice Sheet showed only minor advances confined to fjord basins or ending on the inner shelf. Although there is a striking correspondence in the timing and duration of the first post-Eemian ice advance in East Greenland and on Svalbard, their chronology and dynamics have been very different since about 65 ka. The Svalbard-Barents Sea Ice Sheet showed well-defined Middle and Late Weichselian ice advances, whereas the East Greenland Ice Sheet was characterised by a 55 kyr-long period with a relatively stable ice margin located in fjords or the inner shelf. The contrasting behaviour of the two ice sheets is probably linked to the palaeoceanographic circulation pattern in the Polar North Atlantic. East Greenland is under the influence of the cold East Greenland Current, whereas the development and behaviour of ice in the Barents Sea is influenced by the continuous, but highly variable. North Atlantic meridional current system that has resulted in a northward inflow of relatively warm waters of Atlantic origin on the eastern side of the Polar North Atlantic. Of particular interest are the so-called ''Nordway events'' in glacial stages 6 and 4 to 2. These represented periods of pronounced inflow of temperate waters from the south and an associated increase in seasonally open waters, providing moisture for ice-sheet growth. The largest of these events ended in major glaciations, which were reflected in terrestrial glacial sequences and in deep-sea records of ice-rafted debris. Differences in ice extent and dynamics around the Polar North Atlantic are expressed in the evolution and architecture of its east and west continental margins. The Svalbard-Barents Sea Ice Sheet developed much later than the East Greenland Ice Sheet, in the Late Pliocene as compared with the Middle/Late Miocene. The Svalbard-Barents Sea margin is characterised by major prograding fans, built mainly of stacked debris flows. These fans are interpreted as products of rapid sediment delivery from fast-flowing ice streams reaching the shelf break during full glacial conditions. Such major submarine fans are not found north of the Scoresby Sund Fan off East Greenland, where ice seldom reached the shelf break, sedimentation rates were relatively low and sediment transport appears to have been localised in several major deep-sea submarine channel systems. Few debris flows are present and more uniform, acoustically-stratified sediments predominate. In general, the Greenland Ice Sheet has been more stable than those on the European North Atlantic margin, which reflect greater variability in heat and moisture transfer at timescale varying from 100,000 year glacial cycles to millennial-scale fluctuations.
"Surface water conditions at the Integrated Ocean Drilling Program (IODP) Site U1314 (Southern Gardar Drift, 56º 21.8’ N, 27º 53.3’ W, 2820 m depth) were inferred using planktic foraminifer assemblages between Marine Isotope Stage (MIS) 19 and 11 (ca. 800–400 ka). Factor analysis of the planktic foraminifer assemblages suggests that the assemblage was controlled by three factors. The first factor (which explained 49% of the variance) is dominated by transitional and subpolar species and points to warm and salty surface water conditions (Atlantic water). The second factor (37%) is dominated by Neogloboquadrina pachyderma sin and has been associated with the presence of cold and low saline surface waters (Arctic water). Finally, the third factor (9%), linked to a significant presence of Turborotalita quinqueloba, reflects the closeness of the Arctic front (the boundary between Atlantic and Arctic water). The position of the Arctic and Polar fronts has been estimated across the glacial-interglacial cycles studied according to planktic foraminifer abundances from Site U1314 (and their factor analysis) combined with a synthesis of planktic foraminifer and diatom data from other North Atlantic sites. Regarding at the migrations of the Arctic front and the surface water masses distribution across each climatic cycle we determined five phases of development. Furthermore, deep ocean circulation changes observed in glacial-interglacial cycles have been associated with each phase. The high abundance of transitional-subpolar foraminifers (above 65% at Site U1314) during the early interglacial phase indicated that the Arctic front position and surface water masses distribution were similar to present conditions. During the late interglacial phase, N. pachyderma sin and T. quinqueloba slightly increased indicating that winter sea ice slightly expanded southwestwards whereas the ice volume remained stable or was still decreasing. N. pachyderma sin increased rapidly (above 65% at Site U1314) at the first phase of glacial periods indicating the expansion of the Arctic waters in the western subpolar North Atlantic. During the second phase of glacial periods the transitional-subpolar assemblage throve again in the central subpolar North Atlantic associated with strong warming events that followed ice-rafting events. The third phase of glacial periods corresponds to full glacial conditions in which N. pachyderma sin dominated the assemblage for the whole subpolar North Atlantic. This division in phases may be applied to the last four climatic cycles."
Global and Planetary Change, 2001
Three cores recovered off the northwest of Svalbard were studied with respect to glacialrinterglacial changes of clay and Ž . bulk mineralogy, lithology and organic geochemistry. The cores cover the Late Quaternary Marine Isotope Stages MIS 6-1 Ž . ca. 170,000 years and are located in the vicinity of the Polar Front which separates the warm Atlantic water of the Westspitsbergen Current and the cold Polar Water of the Transpolar Drift. Globally driven changes in the paleoenvironment like the variable advection of warm Atlantic water into the Arctic Ocean can be distinguished from regional events by means of source mineral signatures and organic geochemistry data. In particular, a combination of high organic carbon and low carbonate contents, high CrN-ratios, a particular lithology and a distinct bulk and clay mineral assemblage can be related to Svalbard ice sheet developments between 23,000 and 19,500 14 C years. This complex sediment pattern has been traced to the northwest of Spitsbergen as far north as 828N. Additionally, the same signature has been recognized in detail in upper MIS 5 sediments. The striking similarity of the history of the SvalbardrBarents Sea Ice Sheet during the late and earlyrmiddle Weichselian is elaborated. Both sediment horizons are intercalated between biogenic calcite rich core sequences which contain the so-called AHigh Productivity ZonesB or ANordway EventsB related to the increased advection of warm Atlantic water to the Arctic Ocean. This study provides further evidence that the meridional circulation pattern has been present during most of the Weichselian and that the ice cover was often reduced in the northeastern Fram Strait and above the Yermak Plateau. Our findings contradict the widely used reconstructions in modelling of the last glaciation cycle and reveal a much more dynamic system in the Fram Strait and southwestern Eurasian Basin of the Arctic Ocean. q
Three sites from Leg 151 were selected for a study of orbital-and millennial-scale climate variability during the last 140,000 years. This interval, from marine isotope Stage (MIS) 6 to the present, includes the last large climate cycle of the Quaternary. Sites 907, 909, and 910 constitute a transect, roughly north-south, from the Iceland Plateau, through the Fram Strait, to the Yermak Plateau. Sediment cores from these sites were analyzed for the abundance and diversity of planktonic foraminifers and the quantity and composition of ice-rafted debris (IRD).
Proceedings of the Ocean Drilling Program, 1996
Three sites from Leg 151 were selected for a study of orbital-and millennial-scale climate variability during the last 140,000 years. This interval, from marine isotope Stage (MIS) 6 to the present, includes the last large climate cycle of the Quaternary. Sites 907, 909, and 910 constitute a transect, roughly north-south, from the Iceland Plateau, through the Fram Strait, to the Yermak Plateau. Sediment cores from these sites were analyzed for the abundance and diversity of planktonic foraminifers and the quantity and composition of ice-rafted debris (IRD). Leg 151 drilling was successful in recovering young sediments. This is best demonstrated in Hole 907A, which has a sedimentation rate of 1.7 cm/k.y., where an 11,000-year-old volcanic ash is disseminated at a depth of 0.2 meters below seafloor (mbsf), indicating good recovery of the overlying Holocene section. The last climate cycle in Hole 907A is well defined by faunal assemblages and abundances, which indicate that mild conditions were limited to peak interglacials. Ice-rafted debris is abundant at all other times, although discrete peaks in the ratio of ice-rafted grains to foraminifers, perhaps analogous to the Heinrich events of the North Atlantic, occur only during MIS 2-4 and 6. Site 909 in the Fram Strait has a sedimentation rate of 3.4 cm/k.y., and is characterized by variability in the abundance of ice-rafted debris and clastic rock fragments. Sharp increases in the weight percentage of coarse sediment and the occurrence of detrital coal mark MIS 6, and contrast with the last (MIS 2) glaciation. Site 910 on the Yermak Plateau has a sedimentation rate of 2.7 cm/k.y., and is dominated by detrital sediments. The abundance of coarse sediment remains high with little variation throughout the study interval. Ice-rafted clastic rock fragments are relatively less important on the Yermak Plateau than in the Fram Strait, implying different glacial source areas. The similarity between the last two glacial and interglacial pairs seen on the Iceland Plateau (as in the subpolar North Atlantic) is less evident in our high latitude cores.
Quaternary Science Reviews, 1997
Oxygen isotope, magnetic susceptibility and foraminiferal distribution data are presented for a high resolution core (ENAM93-21) located at the northeast Faeroe Margin. This core recorded a rapid succession of faunistic, sedimentologic and isotopic variations which paralleled the Greenland ice core isotopic records with their typical succession of abrupt temperature rises and gradual toolings (the Dansgaard-Oeschger cycles). The most notable feature was the contemporaneous changes in surface and bottom water conditions and circulation that appeared tightly coupled with the rapid climate fluctuations. Warm episodes ('interstadials') were associated with higher sea surface temperatures and thermohaline convection in the Norwegian-Greenland Sea. The Polar Front was located north of the ENAM93-21 site. Cold episodes ('stadials') were associated with an increase in the input of melting Fennoscandian icebergs, low sea surface temperature and salinity, and no thermohaline convection in the Norwegian-Greenland Sea. Intermediate waters changed to an estuarine mode at the Faeroe Margin with a reversed flow pattern through the Faeroe-Shetland
Geo-Marine Letters, 1998
The paleoceanography in the Nordic seas was characterized by apparently repeated switching on and off of Atlantic water advection. In contrast, a continous influx of Atlantic waters probably occurred along the northern Barents Sea margin during the last 150 ka. Temporary ice-free conditions enhanced by subsurface Atlantic water advection and coastal polynyas accelerated the final ice sheet build-up during glacial times. The virtually complete dissolution of biogenic calcite during interglacial intervals was controlled mainly by CO -rich bottom waters and oxidation of higher levels of marine organic carbon and indicates intensive Atlantic water inflow and a stable ice margin.
Early and Mid-Pleistocene climate, ocean hydrography and ice sheet dynamics have been reconstructed using a high-resolution data set (planktonic and benthic d 18 O time series, faunal-based sea surface temperature (SST) reconstructions and ice-rafted debris (IRD)) record from a high-deposition-rate sedimentary succession recovered at the Gardar Drift formation in the subpolar North Atlantic (Integrated Ocean Drilling Program Leg 306, Site U1314). Our sedimentary record spans from late in Marine Isotope Stage (MIS) 31 to MIS 19 (1069-779 ka). Different trends of the benthic and planktonic oxygen isotopes, SST and IRD records before and after MIS 25 ($940 ka) evidence the large increase in Northern Hemisphere ice-volume, linked to the cyclicity change from the 41-kyr to the 100-kyr that occurred during the Mid-Pleistocene Transition (MPT). Beside longer glacial-interglacial (G-IG) variability, millennial-scale fluctuations were a pervasive feature across our study. Negative excursions in the benthic d 18 O time series observed at the times of IRD events may be related to glacio-eustatic changes due to ice sheets retreats and/or to changes in deep hydrography. Time series analysis on surface water proxies (IRD, SST and planktonic d 18 O) of the interval between MIS 31 to MIS 26 shows that the timing of these millennial-scale climate changes are related to half-precessional (10 kyr) components of the insolation forcing, which are interpreted as cross-equatorial heat transport toward high latitudes during both equinox insolation maxima at the equator.
Palaeogeography Palaeoclimatology Palaeoecology, 2002
Records of ice-rafted detritus (IRD) from Ocean Drilling Program Sites 644 and 907 in the Nordic Seas and Deep Sea Drilling Program Sites 610 and 607 in the North Atlantic Ocean are used to determine the growth and history of Northern Hemisphere glaciations spanning the interval from 3.6 to 2.4 Ma. The records document that the initiation of large-scale glaciation in the circum Atlantic region occurred stepwise between 3.5 and 2.4 Ma, with Greenland leading the other areas. The first major pulse of IRD occurs at 3.3 Ma suggesting a distinct expansion of the Greenland ice sheet. Progressive increases in IRD occur from 3.0 Ma, with a synchronous ice sheet development between the Greenland, Scandinavian and North American regions starting around 2.72^2.75 Ma. The regional records of IRD correspond to major trends in the oxygen isotope record, suggesting a tight connection between the record of global ice volume and evidence for expanding glaciers in the Northern Hemisphere. It appears as if widespread IRD distribution occurs when the global ice volume surpasses certain thresholds, similar to the late Quaternary situation. ß