Contributors: unknown

Date: 2001-03-23

Late quaternary...Late quaternary...sediment cores in the north-eastern polar North Atlantic. BIT=Bear Island...Down-core analyses in core NP90-38 showing: δ18O and δ13C (‰ vs. PDB) ...Down-core analyses in core NP90-36 showing: δ18O and δ13C (‰ vs. PDB) ...sediment cores...coring device for the investigated sediment cores...sediment cores ENAM93-21 (Rasmussen et al., 1996), NP90-39 and M23385 ...Down-core analyses in core NP90-39 showing: δ18O and δ13C (‰ vs. PDB) ...sediment cores from the margin and abyssal plain off western Svalbard-Barents ... We have investigated five sediment cores from the margin and abyssal plain off western Svalbard-Barents Sea in the polar North Atlantic. We discuss the palaeoceanography and its relationship to glacial history during the last interglacial–glacial cycle based on detailed stratigraphic analyses of planktic and benthic foraminiferal fauna, oxygen and carbon isotopes on foraminifera, ice-rafted debris (grains >500μm) and radiocarbon dates.

Contributors: unknown

Date: 2013-12-04

sediment cores collected at 27°S and 33°S off southeastern South America...sediment cores used in this study....late Holocene is elusive because of the lack of appropriate records. Here...Late Quaternary...sedimentation rates for marine sediment cores GeoB2107-5 and GeoB6211-...late Holocene...Late Quaternary...sediment cores....late Holocene compared to circum-Atlantic climate records. (A) Low sea...late Holocene based on marine sediment cores GeoB2107-5 and GeoB6211-1...late Holocene variability in the upper water column of the BC. Our results...sediment cores investigated in this study, and mean austral summer (A)...sediment core LO09-14 collected in the subpolar North Atlantic at 58.94...late Holocene boundary conditions. ... Our understanding of the centennial-scale variability of the Brazil Current (BC) during the late Holocene is elusive because of the lack of appropriate records. Here we used the Mg/Ca and oxygen isotopic composition of planktonic foraminifera from two marine sediment cores collected at 27°S and 33°S off southeastern South America to assess the late Holocene variability in the upper water column of the BC. Our results show in phase fluctuations of up to 3°C in sea surface temperatures (SST), and 0.8‰ in oxygen isotopic composition of surface sea water, a proxy for relative sea surface salinity (SSS). Time-series analyses of our records indicate a cyclicity with a period of ca. 730yr. We suggest that the observed cyclicity reflects variability in the strength of the BC associated to changes in the Atlantic meridional overturning circulation (AMOC). Positive (negative) SST and SSS anomalies are related to a strong (weak) BC and a weak (strong) AMOC. Moreover, periods of peak strength in the BC occur synchronously to a weak North Brazil Current, negative SST anomalies in the high latitudes of the North Atlantic, and positive (negative) precipitation anomalies over southeastern South America (equatorial Africa), further corroborating our hypothesis. This study shows a tight coupling between the variability of the BC and the high latitudes of the North Atlantic mediated by the AMOC even under late Holocene boundary conditions.

Contributors: unknown

Date: 2005-06-15

sediment cores by open and solid circles. Radiocarbon analysis was performed...Late glacial progradational deposits (Unit C; Lowstand Systems Tract, ...late glacial prodeltaic deposits and slope to basin turbidites (Lowstand...Core TH-46 location is shown with the simplified sediment description ...sediment cores from the Thermaikos Gulf shelf and slope and the Sporades...Late Quaternary...Late Quaternary...sediment fluxes...sediment core description and AMS 14C dates (yr BP) of Units A, B and ...Late Quaternary sedimentary cover in the Thermaikos Gulf consists of three...late glacial sea-level fall....Late Quaternary sedimentary cover in the Thermaikos Gulf consists of three...sediment fluxes since the last glacial in the Thermaikos Gulf and the ...sediments deposited in a shallow, high-energy, estuarine environment during ... Late Quaternary sedimentary cover in the Thermaikos Gulf consists of three seismic Units: (i) the uppermost Unit A that represents delta progradation during the last 6000 yr when the sea surface almost reached the present level (Highstand Systems Tract, HST); (ii) Unit B that includes relatively coarse-grained sediments deposited in a shallow, high-energy, estuarine environment during the post-glacial transgression (Transgressive Systems Tract, TST); and (iii) the lowest Unit C which may represent late glacial prodeltaic deposits and slope to basin turbidites (Lowstand Systems Tract, LST). Seismic units A and B overlay a well-defined unconformity which resulted from sub-aerial erosion during the late glacial sea-level fall.

Contributors: unknown

Date: 2015-12-17

sediment drifts with interglacial MIS 11, 5, and 1, respectively, suggests...late Quaternary erosional gullies, abraded surfaces, and channel-related...sediment cores. White circles represent the AEG cores, whereas black circles...Late quaternary bottom-current activity in the south Aegean Sea reflecting...sediment cores, respectively....Late Quaternary Eastern Mediterranean Transient events...cores is shown in Fig. 5....cores during the Holocene. The higher frequency of strong bottom-current...Sediment drift...core to core, and are interpreted as bottom-current deposits. The separation...Sediment core photographs illustrating examples of the identified sedimentary...late Quaternary erosional gullies, abraded surfaces, and channel-related...sediment cores analysed in this paper; these beds can be confidently correlated...sediment cores. White and black circles represent the location of the ...Late Quaternary Eastern Mediterranean Transient events...sediment drifts. Such structures provide evidence for the presence of ... The Eastern Mediterranean Transient (EMT) represents a recent (early 1990s to today) water circulation phenomenon, during which more arid climatic conditions in the Mediterranean lead to the production of very dense, surface water masses in the north Aegean Sea. The produced north Aegean dense water (NADW) sinks to seafloor, flows to the south Aegean Sea and, then, spills into the Eastern Mediterranean Sea through the Cretan Straits, contributing to the rejuvenation of the bottom water. A large dataset of vintage high-resolution seismic-reflection profiles indicates that the floors of the basins in the southwest Aegean Sea are characterised by late Quaternary erosional gullies, abraded surfaces, and channel-related sediment drifts. Such structures provide evidence for the presence of strong bottom currents, which originate from the southward propagation of NADW masses. The basins have depths of 300m to 1000m and are connected to each other by narrow (a few km) straits and sills. The dominance of abraded surfaces and erosional gullies on the northern flank of the basins and in the narrow straits/sills between them provides evidence that the southward propagation of the NADW occurs by the filling and flooding of each basin by dense water, which then spills and cascades into the next basin southward. Seismic stratigraphy suggests that the formation of the drifts started at marine isotope stage (MIS) 11 (420ka BP). The coincidence of at least three erosional surfaces within the sediment drifts with interglacial MIS 11, 5, and 1, respectively, suggests that bottom currents were mostly active during high sea-level stands and sluggish during glacial low sea-level stands. A 90–100m drop of the sea level below the current level would have resulted in the emergence of the eastern Cyclades Plateau and, thus, in the disconnection of the southwest Aegean Sea from the north Aegean Sea. Several (0.05–0.5m thick) beds of gravelly sand with algal and mollusc debris, laminated to mottled sand, and mottled mud are observed in the sediment cores analysed in this paper; these beds can be confidently correlated from core to core, and are interpreted as bottom-current deposits. The separation of these beds by hemipelagic sediments indicates that bottom-current activity in the southwest Aegean is not permanently established but episodic. Six episodes of intense bottom-current activity are recorded in the MIS 2–4 (10–80ka) sediments and they appear to correlate well with the cold and dry Younger Dryas and Heinrich 3, 4, 5, 6, and 7 events. In contrast, at least three episodes of intense bottom-current activity are recorded in the cores during the Holocene. The higher frequency of strong bottom-current episodes in the southwest Aegean Sea during the Holocene is attributed to the higher sea-level stand that makes the circulation of water masses in the Aegean Sea more sensitive to climatic changes.

Contributors: unknown

Date: 2005-06-24

sediment-dominated sections of the cores off Saurashtra–Ratnagiri, followed...cores on the western margin of India. Geology after Rao and Wagle (1997...late Quaternary...late Quaternary...Down-core variations of MS and different sedimentological parameters in...sediments of the eastern Arabian Sea: Evidence for late Quaternary climatic...sediments in GC1. (B) Down-core variations of sedimentological parameters...sediment sections of the cores...sediments were determined for 15 gravity cores recovered from the western...sediments off Indus–Gulf of Kachchh and then Mangalore–Cape Comorin....Down-core variations of MS in GC11....sediments...sediments reflect the land-derived input and, in general, are the highest...Down-core variations of MS in core GC14 and GC15. ... Rock-magnetic measurements along with grain size, acid-insoluble residue (AIR), organic carbon (OC), CaCO3 and δ18O of the planktonic foraminifers of the sediments were determined for 15 gravity cores recovered from the western continental margin of India. Magnetic susceptibility (MS) values in the surficial sediments reflect the land-derived input and, in general, are the highest in terrigenous sediment-dominated sections of the cores off Saurashtra–Ratnagiri, followed by the sediments off Indus–Gulf of Kachchh and then Mangalore–Cape Comorin.

Contributors: unknown

Date: 2007-02-16

late Holocene and is non-discharging under present-day arid climate conditions...late Pleistocene...core GeoB 8509–2 of Cap Timiris Canyon since late Pleistocene times. Note...sediment transport to the Atlantic Ocean offshore Mauritania were reconstructed...sediment core GeoB 8509–2 showing bioturbated hemipelagic sediments in...late Pleistocene, predominantly coarse-grained particles, which are interpreted...sediment deposits. Despite interbedded turbidites, the sediment cores ...sediment core GeoB 8509–2 is based on radiocarbon dates. According to ...core logs of the sediments recovered from Cap Timiris Canyon indicating...sediment core GeoB 8502–2 at the distal levee of Cap Timiris Canyon. Displayed...sediments...sediment records of Cap Timiris Canyon to monitor the climatic evolution...Late Quaternary sedimentation within a submarine channel–levee system ... Aeolian and fluvial sediment transport to the Atlantic Ocean offshore Mauritania were reconstructed based on grain-size distributions of the carbonate-free silt fraction of three marine sediment records of Cap Timiris Canyon to monitor the climatic evolution of present-day arid north-western Africa. During the late Pleistocene, predominantly coarse-grained particles, which are interpreted as windborne dust, characterise glacial dry climate conditions with a low sea level and extended sand seas that reach onto the exposed continental shelf off Mauritania. Subsequent particle fining and the abrupt decrease in terrigenous supply are attributed to humid climate conditions and dune stabilisation on the adjacent African continent with the onset of the Holocene humid period. Indications for an ancient drainage system, which was discharging fluvial mud offshore via Cap Timiris Canyon, are provided by the finest end member for early to mid Holocene times. However, in comparison to the Senegal and Niger River further south, the river system connecting Cap Timiris Canyon with the Mauritanian hinterland was starved during the late Holocene and is non-discharging under present-day arid climate conditions.

Contributors: unknown

Date: 2004-02-05

Coring profile of the early Holocene terrace H1 near Luka (village close...sediment core was taken with a percussion core from a peat bog (profile...coring FA 21 near the village of Vološča (upper part) and from wood samples...late Quaternary landscape evolution with special regard to changes in ...late Quaternary landscape evolution with special regard to changes in ...Late Pleistocene and Holocene river terraces with floodplain morphology...Late Quaternary terraces of the Dnister valley near Mikolajiv, showing...corings in the environs of Mikolajiv and Bukačivci (lower part)...Late Quaternary terraces of the Dnister valley near Mikolajiv, showing...Late quaternary landscape evolution of the upper Dnister valley, western ... The broad and flat valley of the upper Dnister in western Ukraine is characterized by a complex setting of ecotopes and a relatively natural state of floodplain dynamics. Excellent geo-archives–extended peat bogs and postglacial river terraces–document late Quaternary landscape evolution with special regard to changes in fluvial morphodynamics, vegetation and human impact. The terraces were studied by detailed geomorphological mapping as well as sedimentological and pedological analyses in connection with information from historical maps. Vegetation history was studied by palynological methods in combination with radiocarbon dating.

Contributors: unknown

late Quaternary time. A succession of paleo active-layer deposits that...coring. Coring took place in a central polygon area near (∼10 m) the ice...sedimentation model illustrating terrace formation in a permafrost terrain...sediment formation in late Quaternary time in the El'gygytgyn area....sediments and the ground ice contained therein have prominent relative...cored sediments and age model with calibrated radiocarbon ages and inferred...sediments. The rectangle marks the position of the permafrost core....sedimentation scheme for slope sediment formation in late Quaternary time...sediment formation including sites of ice wedge outcrop and frozen sediment...late Holocene time. Moreover, peaks of light soluble cation contents and...sediments archiving late Quaternary paleoenvironment and paleoclimate ...cored permafrost sediments with respect to AD 1950...sediments and age model with calibrated radiocarbon ages and inferred ...sediments with respect to AD 1950...late Quaternary time. A succession of paleo active-layer deposits that...sediment variations. These two elements of the periglacial landscape serve ... An accumulation terrace close to the El'gygytgyn Impact Crater in northeastern Siberia contains stratigraphic and periglacial evidence of the paleoenvironmental and paleoclimatic history and permafrost dynamics during late Quaternary time. A succession of paleo active-layer deposits that mirror environmental changes records periods favorable for the establishment and growth of ice-wedge polygonal networks and sediment variations. These two elements of the periglacial landscape serve as complementary paleoenvironmental archives that can be traced back to ∼14,000 cal yr BP. The slope sediments and the ground ice contained therein have prominent relative maxima and minima in properties (grain size, total organic content, oxygen isotopes). They document a regional early Holocene thermal maximum at about 9000 cal yr BP, followed by a transition to slightly cooler conditions, and a subsequent transition to slightly warmer conditions after about 4000 cal yr BP. Results from sedimentary analysis resemble morphological and geochemical (oxygen and hydrogen isotopes) results from ice wedge studies, in which successive generations of ice-wedge polygonal networks record warmer winters in late Holocene time. Moreover, peaks of light soluble cation contents and quartz-grain surface textures reveal distinct traces of cryogenic weathering. We propose a conclusive sedimentation model illustrating terrace formation in a permafrost terrain.

Contributors: unknown

Date: 2000-06-26

sediment along the tectonically active Makran continental margin off south-western...sediment supply to the Arabian Sea during the late Quaternary: the Makran...Sediment cores...sediments (n=319) in cores NIOP468–NIOP472....sediments (n=65) in cores NIOP469 and NIOP472. (C) Binary mixing of EM2...sediment composition, sedimentation rate and turbidite frequency in late...sediment fraction, NIOP469. (B) Mg/Al ratio in bulk sediment fraction,...core NIOP469 (see text for discussion). Turbidite frequency and sedimentation...sediment cores distributed along a transect from the upper slope to the...Sediment composition in core NIOP469. (A) Neogloboquadrina dutertrei δ18O...sediment composition, sedimentation rate and turbidite frequency in late ... The input of terrigenous sediment along the tectonically active Makran continental margin off south-western Pakistan (Gulf of Oman, northern Arabian Sea) is studied on the basis of sediment cores distributed along a transect from the upper slope to the abyssal plain. Spatial and temporal variations in sediment composition, sedimentation rate and turbidite frequency in late Pleistocene–Holocene time (last ∼20 14C ka) will be discussed and related to changes in sea level and climate, and tectonic activity.

Contributors: unknown

Date: 1996-10-15

sediment core...sediment, biogenic silica, organic carbon and biogenic Ba, and export ...sediment redistribution in the Ross Sea margin were enlightened from a...sediment core, collected from the western part of the continental slope...core Anta91-8...Late Quaternary fluctuations of biogenic component fluxes on the continental...sediment (6.25 dpm m−2 kyr−1)....Sediment accumulation rates ranged between 1.2 cm kyr−1 in the isotope...Quaternary Research, 27: 1–29]. Sediment accumulation rates ranged between...sediment column....core ANTA91-8. ... A sediment core, collected from the western part of the continental slope of the Ross Sea at 2380 m water depth, records events of the last two climatic cycles (250 kyr). A 230Thex-based chronology was obtained and boundaries of the isotope stages were set assuming that biological productivity was enhanced during periods of less ice cover. Then, 230Thex0, organic carbon, biogenic silica and biogenic Ba distributions were compared to the glacial–interglacial stage boundaries and corresponding ages of the δ18O record of Martinson et al. [Martinson, D.G., Pisias, N.G., Hays, J.D., Imbrie, J., Moore, T.C., Jr., Shackleton, N.J, 1987. Age dating and the orbital theory of the ice ages: development of a high-resolution 0 to 300,000-year chronostratigraphy. Quaternary Research, 27: 1–29]. Sediment accumulation rates ranged between 1.2 cm kyr−1 in the isotope stage 6 and 3.8 cm kyr−1 during the Holocene. Variations in the concentrations and fluxes of organic carbon, biogenic Ba, biogenic silica and Mn gave information on palaeoclimate changes. Processes of sediment redistribution in the Ross Sea margin were enlightened from a comparison of the measured and expected fluxes of 230Thex. Calculation of the focusing-corrected accumulation rates of biogenic Ba enabled us to evaluate the export palaeoproductivity. Corrected accumulation rates of biogenic components and calculated palaeoproductivities were low, compared to the Antarctic Polar Front in the Atlantic sector, throughout the last two climatic cycles. Glacial–interglacial changes of sea ice cover and ventilation of the Ross Sea were probably major causes of variations in biogenic particle flux and distribution of redox-sensitive elements within the sediment column.