An ocean–ice coupled response during the last glacial: a view from a marine isotopic stage 3 record south of the Faeroe Shetland Gateway (original) (raw)
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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
Quaternary Science Reviews, 2016
Five sediment cores from the Lomonosov Ridge and the Morris Jesup Rise north of Greenland show the history of sea-ice coverage and primary productivity over the last two glacial cycles. Variations in Manganese content, benthic and planktonic foraminifera, bioturbation, and trace fossil diversity are interpreted to reflect differences in sea-ice cover and sediment depositional conditions between the identified interglacials. Marine Isotope Stage (MIS) 1 and MIS 2 are represented by thin (<<5 cm) sediment units while the preceding interglacial MIS 5 and glacial MIS 6 are characterized by thick (10 e20 cm) deposits. Foraminiferal abundances and bioturbation suggest that MIS 1 was generally characterized by severe sea-ice conditions north of Greenland while MIS 5 appears to have been considerably warmer with more open water, higher primary productivity, and higher sedimentation rates. Strengthened flow of Atlantic water along the northern continental shelf of Greenland rather than development of local polynyas is here suggested as a likely cause for the relatively warmer marine conditions during MIS 5 compared to MIS 1. The cores also suggest distinct differences between the glacial intervals MIS 2 and MIS 6. While MIS 6 is distinguished by a relatively thick sediment unit poor in foraminifera and with low Mn values, MIS 2 is practically missing. We speculate that this could be the effect from a paleocrystic sea-ice cover north of Greenland during MIS 2 that prevented sediment delivery from sea ice and icebergs. In contrast, the thick sequence deposited during MIS 6 indicates a longer glacial period with dynamic intervals characterized by huge drifting icebergs delivering ice rafted debris (IRD). A drastic shift from thinner sedimentary cycles where interglacial sediment parameters indicate more severe sea-ice conditions gave way to larger amplitude cycles with more open water indicators was observed around the boundary between MIS 7/8. This shift is in agreement with a sedimentary regime shift previously identified in the Eurasian Basin and may be an indicator for the growth of larger ice sheets on the Eurasian landmass during the penultimate glacial period.
A mid-Holocene shift in Arctic sea-ice variability on the East Greenland Shelf
The Holocene, 2002
Records of iceberg-rafting and palaeohydrography from two East Greenland shelf cores (JM96-1206/1-GC and JM96-1207/1-GC) are reported. Benthic foraminifera, stable isotopes and IRD uxes indicate a shift toward colder, lower-salinity 'polar' conditions c. 5 cal. ka. A new proxy of iceberg-rafting on the East Greenland Shelf is the ux of calcium carbonate (TIC) thought to be derived from glacial erosion of Cretaceous calcareous mudstones. A change in the regularity and spacing of carbonate ux peaks at c. 4.7 cal. ka in JM96-1207 coincides with the onset of Neoglacial cooling in the Renland ice core d 18 O record. We propose that the carbonate ux peaks between 4.7 and 0.4 cal. ka are related to sea-surface coolings associated with increased ux of polar water and sea ice in the East Greenland Current. These peaks are synchronous with sea-surface coolings interpreted from North Atlantic deep-sea cores, but additional peaks centred around 2.4 and 3.8 cal. ka in JM96-1207 suggest that the shelf site captures higher-frequency events. The data indicate that severe Arctic sea-ice events began in the Neoglacial interval, and that earlier-Holocene cool events in deep-sea records are associated with other processes, such as release of meltwater from residual glacier ice and glacial lakes.
The synchronization of palaeoclimatic events in the North Atlantic region during Greenland Stadial 3
Two high resolution marine sediment cores located 83 km apart in the NE Atlantic have been studied: MD95-2006 (Barra Fan; 57˚01.82 N, 10˚03.48 W; 2120m water depth) and MD04-2822 (Rockall Trough; 56˚50.54 N, 11˚22.96 W; 2344m water depth). The records are anchored to the NGRIP ice core stratigraphy and GICC05 chronology by the presence of geochemically characterized Fugloyarbanki tephra. Replicated sea surface temperature (SST) records show evidence for an abrupt and short-lived warming within Greenland Stadial (GS) 3, to which we tentatively assign an age of ca. 25 ka GICC05 b2k. Post-dating this warming event, but prior to the onset of Heinrich Event (HE) 2, SSTs are warmer than during the early stages of GS-3. Equally, abrupt warming in SSTs post-dating GS-3 coincides with Greenland Interstadial (GIS) 2; both cores resolving the double-warming associated with GIS-2 in Greenland ice-core records. Based on these and other marine palaeoclimate records from the Ib...
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).
1995
Eight time slices of surface-water paleoceanography were reconstructed from stable isotope and paleotemperature data to evaluate late Quaternary changes in density, current directions, and sea-ice cover in the Nordic Seas and NE Atlantic. We used isotopic records from 110 deep-sea cores, 20 of which are accelerator mass spectrometry (AMS)-14C dated and 30 of which have high (>8 cm/kyr) sedimentation rates, enabling a resolution of about 120 years. Paleotemperature estimates are based on species counts of planktonic foraminifera in 18 cores. The •5180 and •513C distributions depict three main modes of surface circulation: (1) The Holocene-style interglacial mode which largely persisted over the last 12.8 •4C ka, and probably during large parts of stage 3. (2) The peak glacial mode showing a cyclonic gyre in the, at least, seasonally ice-free Nordic Seas and a meltwater lens west of Ireland. Based on geostrophic forcing, it possibly turned clockwise, blocked the S-N flow across the eastern Iceland-Shetland ridge, and enhanced the Irminger current around west Iceland. It remains unclear whether surface-water density was sufficient for deepwater formation west of Norway. (3) A meltwater regime culminating during early glacial Termination I, when a great meltwater lens off northern Norway probably induced a clockwise circulation reaching south up to Faeroe, the northward inflow of Irminger Current water dominated the Icelandic Sea, and deepwater convection was stopped. In contrast to circulation modes two and three, the Holocene-style circulation mode appears most stable, even unaffected by major meltwater pools originating from the Scandinavian ice sheet, such as during •80 event 3.1 and the B611ing. Meltwater phases markedly influenced the European continental climate by suppressing the "heat pump" of the Atlantic salinity conveyor belt. During the peak glacial, melting icebergs blocked the eastward advection of warm surface water toward Great Britain, thus accelerating buildup of the great European ice sheets; in the early deglacial, meltwater probably induced a southward flow of cold water along Norway, which led to the Oldest Dryas cold spell. Introduction The circulation regime in the Nordic Seas has a strong impact on the climate of the adjacent continents. Today, the warm waters of the North Atlantic Drift, the Irminger Current, Paper number 95PA01453. 0883-8305/95/95PA-01453 $10.00
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.
Marine Geology, 2007
A sediment record from the practically unknown southernmost part of the Lomonosov Ridge off North Greenland/Ellesmere Island has been studied. GreenICE core 10 encompasses marine isotope stages (MIS) 7-1 and reveals changing paleoceanographic conditions and land-ocean connections during the last two glacial-interglacial cycles. The isotope record of planktic foraminifera Neogloboquadrina pachyderma (s) show large similarities to other Arctic Ocean key records, supporting that the pattern reflect over-regional changes of the halocline structure. The relatively low δ 18 O values of subpolar foraminifera Turborotalita quinqueloba in the last interglacial unit support that the specimens represent local production, related to warm interglacial conditions and a reduced sea ice cover in the interior Arctic Ocean. Enhanced deposition of coarse ice-rafted debris took place during the MIS 8/7 transition, periods of MIS 6, MIS 6/5 transition, MIS 5d, MIS 4, and late MIS 3 (30-40 14 C kyr BP). In MIS 2, IRD flux was low in the area. The IRD contains detrital carbonate similar to other Amerasia Basin records. The occurrence of finegrained, calcite-rich detrital carbonate layers at glacial-interglacial transitions, seems unique to this area. We suggest that detrital carbonate was transported and deposited from nepheloid flows during deglaciations of Ellesmere Island, when the Atlantic Water boundary current along the continental margin was gaining strength.
2009
The evolution and dynamics of the last British-Irish Ice Sheet (BIIS) have hitherto largely been reconstructed from onshore and shallow marine glacial geological and geomorphological data. This reconstruction has been problematic because these sequences and data are spatially and temporally incomplete and fragmentary. In order to enhance BIIS reconstruction, we present a compilation of new and previously published ice-rafted detritus (IRD) flux and concentration data from high-resolution sediment cores recovered from the NE Atlantic deep-sea continental slope adjacent to the last BIIS. These cores are situated adjacent to the full latitudinal extent of the last BIIS and cover Marine Isotope Stages (MIS) 2 and 3. Age models are based on radiocarbon dating and graphical tuning of abundances of the polar planktonic foraminifera Neogloboquadrina pachyderma sinistral (% Nps) to the Greenland GISP2 ice core record. Multiple IRD fingerprinting techniques indicate that, at the selected locations, most IRD are sourced from adjacent BIIS ice streams except in the centre of Heinrich (H) layers in which IRD shows a prominent Laurentide Ice Sheet provenance. IRD flux data are interpreted with reference to a conceptual model explaining the relations between flux, North Atlantic hydrography and ice dynamics. Both positive and rapid negative mass balance can cause increases, and prominent peaks, in IRD flux. First-order interpretation of the IRD record indicates the timing of the presence of the BIIS with an actively calving marine margin. The records show a coherent latitudinal, but partly phased, signal during MIS 3 and 2. Published data indicate that the last BIIS initiated during the MIS 5/4 cooling transition; renewed growth just before H5 (46 ka) was succeeded by very strong millennial-scale variability apparently corresponding with Dansgaard-Oeschger (DO) cycles closely coupled to millennial-scale climate variability in the North Atlantic region involving latitudinal migration of the North Atlantic Polar Front. This indicates that the previously defined ''precursor events'' are not uniquely associated with H events but are part of the millennial-scale variability. Major growth of the ice sheet occurred after 29 ka with the Barra Ice Stream attaining a shelf-edge position and generating turbiditic flows on the Barra-Donegal Fan at w27 ka. The ice sheet reached its maximum extent at H2 (24 ka), earlier than interpreted in previous studies. Rapid retreat, initially characterised by peak IRD flux, during Greenland Interstadial 2 (23 ka) was followed by readvance between 22 and 16 ka. Readvance during H1 was only characterised by BIIS ice streams draining central dome(s) of the ice sheet, and was followed by rapid deglaciation and ice exhaustion. The evidence for a calving margin and IRD supply from the BIIS during Greenland Stadial 1 (Younger Dryas event) is equivocal. The timing
Quaternary International, 2012
The records are anchored to the NGRIP ice core stratigraphy and GICC05 chronology by the presence of geochemically characterized Fugloyarbanki tephra and further tested by radiocarbon age control. Replicated sea surface temperature (SST) records show evidence for an abrupt and short-lived warming within Greenland Stadial (GS)-3, to which we tentatively assign an age of ca 25.6e24.8 kyr GICC05 b2k. Based on these and another marine palaeoclimate record (LINK17) from the Faroe-Shetland Channel, we propose a new threefold event stratigraphy for GS-3 within the North East Atlantic region. The recognition of this warming event within GS-3 in NE Atlantic SST records demonstrates that such events may not readily be identified within the coldest stadials of the Greenland ice cores, highlights the need for carefully constructed event stratigraphies (independently tested by the use of tephra isochrones and radiocarbon) and illustrates pervasive millennial-scale climate variability of the North Atlantic region (Dansgaard-Oeschger (D/O) events) is deeply embedded in the dynamics of Atlantic Meridional Overturning Circulation (AMOC).