Contributors: unknown

Date: 2013-05-22

Late Quaternary...sediment core GeoTü SL143 in the central Aegean Sea and the most important...sediment core GeoTü SL143 from the central Aegean Sea. AHP: African humid...sediment discharge deduced from core MS27PT (Revel et al., 2010; Caley...late Quaternary sediment core from the central Aegean Sea. The record ...sediments of core GeoTü SL143, central Aegean Sea, combined with the occurrences...Late Quaternary North African humid periods documented in the clay mineral...sediments...sediments in the source areas....Late Quaternary...late Quaternary sediment core from the central Aegean Sea. The record ...sediment core GeoTü SL123 from the southernmost Aegean Sea (Ehrmann et ... The ratio between the clay minerals kaolinite and chlorite has been investigated in high resolution in a late Quaternary sediment core from the central Aegean Sea. The record spans the last ca. 105ka. The kaolinite/chlorite ratio was used to reconstruct the fine-grained aeolian dust influx from the North African deserts, mainly derived from desiccated lake depressions. It therewith can be used as a proxy for wind activity, aridity and vegetation cover in the source area. The data document three major humid phases in North Africa bracketing the formation of sapropel layers S4, S3 and S1. They occur at >105–95ka, 83.5–72ka and 14–2ka. The first two phases are characterised by relatively abrupt lower and upper boundaries suggesting a non-linear response of vegetation to precipitation, with critical hydrological thresholds. In contrast, the onset and termination of the last humid period were more gradual. Highest kaolinite/chlorite ratios indicating strongest aeolian transport and aridity occur during Marine Isotope Stage (MIS) 5b, at ca. 95–84ka. The long-term decrease in kaolinite/chlorite ratios during the last glacial period indicates a gradual decline of deflatable lake sediments in the source areas.

Contributors: unknown

late Quaternary clay mineral distribution in the area of the SE Mediterranean...late Quaternary sediments of core GeoTü SL112, subdivided into the glacial...Late Quaternary variations in the concentrations of smectite, illite, ...Late Quaternary...late Quaternary sediments of core GeoTü SL112, subdivided into the glacial...Late Quaternary...sedimentation rate (LSR, in cm/ka) in core GeoTü SL112. Dark grey bar ...late Quaternary and that the Nile River played a very important role in...Late Quaternary variations in the concentrations of smectite, illite, ...late Quaternary and that the Nile River played a very important role in...sediments, dust samples and marine surface sediments in the southeastern...late Holocene (48 samples). The clusters of the modern clay mineral assemblages...sediment core from the southeastern Levantine Sea spanning the last 27...sediment core GeoTü SL112. The distribution of the main clay mineral groups ... The present-day clay mineral distribution in the southeastern Levantine Sea and its borderlands reveals a complex pattern of different sources and distribution paths. Smectite dominates the suspended load of the Nile River and of rivers in the Near East. Illite sources are dust-bearing winds from the Sahara and southwestern Europe. Kaolinite is prevalent in rivers of the Sinai, in Egyptian wadis, and in Saharan dust. A high-resolution sediment core from the southeastern Levantine Sea spanning the last 27 ka shows that all these sources contributed during the late Quaternary and that the Nile River played a very important role in the supply of clay. Nile influence was reduced during the glacial period but was higher during the African Humid Period. In contrast to the sharp beginning and end of the African Humid Period recorded in West African records (15 and 5.5 ka), our data show a more transitional pattern and slightly lower Nile River discharge rates not starting until 4 ka. The similarity of the smectite concentrations with fluctuations in sea-surface temperatures of the tropical western Indian Ocean indicates a close relationship between the Indian Ocean climate system and the discharge of the Nile River.

Contributors: unknown

Date: 2001-12-11

sediment grain-size composition in three AMS radiocarbon dated Okhotsk...sediment cores...coarse-sediment fractions (>0.01 and >0.15 mm) in cores 936, V34-90 and...sediments of both cores. There are positive correlations between MS and...sedimentation regime and productivity, and to clarify the formation times...sediments in the Okhotsk Sea: implication of terrigenous, volcanogenic...sediment...sediment with very low biogenic admixture, were distinguished in a series...Late Quaternary sediment cores from the Sea of Okhotsk. Sediments were...sediment) in core V34-98, versus radiocarbon time. The age model and lithology...cores. This chronological framework allowed us to investigate climate ...sediment in core V34-90, versus time. The age model was constructed using...Late Pleistocene are shown by asterisks and triangles, respectively (Braitseva...Late Quaternary sediment cores from the Sea of Okhotsk. Sediments were ... Seven lithological units, alternating between horizons enriched in biogenic opal (diatoms) and carbonate (foraminifera) and units composed largely of terrigenous sediment with very low biogenic admixture, were distinguished in a series of Late Quaternary sediment cores from the Sea of Okhotsk. Sediments were characterised using on-board visual description, smear-slides analyses, grain-size composition and magnetic susceptibility (MS) records. Five tephra marker layers, identified as Ko, TR, K2, K3 and K4, were distinguished using petrological, mineralogical and geochemical analyses. Age models were developed by comparing lithological units, tephra stratigraphy and MS records with oxygen isotope curves and with records of biogenic CaCO3, opal content, and sediment grain-size composition in three AMS radiocarbon dated Okhotsk cores. This chronological framework allowed us to investigate climate control over the sedimentation regime and productivity, and to clarify the formation times of the lithological and tephra units.

Contributors: unknown

sedimentation. The diatom data suggest that the relative sea level associated...Late Quaternary sequences are over 25 and 35m thick. These valleys are...sediment cores studied....sediment cores....Late Quaternary environmental changes in the Pearl River mouth region,...sediment cores PK16, D13 and D6. Radiocarbon dates are shown as calendarkaBP...sedimentation in the outer part of the estuary, characterised by the high...sedimentation of a fine-sand layer in the inner part of the estuary. After...Late Quaternary sequences are over 25 and 35m thick. These valleys are...sediments. In the early Holocene, strong monsoon freshwater discharge ...Late Quaternary environmental changes in the Pearl River mouth region, ... This study presents findings concerning Late Quaternary environmental changes in the Pearl River mouth region, China based on the study of over 300 boreholes. Out of these, 35 boreholes are selected for the reconstruction of transects across the deltaic plain and estuary. 39 radiocarbon dates obtained from these boreholes are used to help define the chronology of stratigraphic units present including two terrestrial units (T1 and T2) and two marine units (M1 and M2). Diatom assemblages are studied in 6 boreholes revealing similarities and differences between the two marine units. Before the area was inundated by the last interglacial sea (MIS 5), an older terrestrial unit of sand and gravel (T2) was laid down in a number of palaeo-valleys. During the last interglacial period, an older marine unit of silt and clay (M2) was laid down which was subsequently subaerially exposed when sea-level regressed during the last glacial period (MIS 4-2) causing the uppermost section to be weathered. During the same period, a younger terrestrial unit of sand and gravel (T1) was deposited along palaeo-river channels. Around the early Holocene before 8.2cal.kaBP, the postglacial rise in sea level initiated a new phase of sedimentation in the outer part of the estuary, characterised by the high percentages of marine diatoms in the sediments. In the early Holocene, strong monsoon freshwater discharge resulted in sedimentation of a fine-sand layer in the inner part of the estuary. After 8.2cal.kaBP, rapid rises in sea level caused widespread marine inundation and sedimentation. The diatom data suggest that the relative sea level associated with the M2 and M1 units were both at similar levels. Because the M2 unit is typically recorded at altitudes of 15m and 20m below the present sea level, this is likely to be a result of long-term subsidence. Although numerical dating of the pre-M1 units has not been made in the present study, the chronology of these units can be inferred from uranium-series ages and optically stimulated luminescence dating obtained from the adjacent coastal waters of Hong Kong. The T1 unit has yielded ages of about 30.0cal.kaBP while the M2 unit has yielded ages about 130.0cal.kaBP confirming their MIS 4-2 and MIS 5 ages respectively.

Contributors: unknown

Date: 2014-02-07

sediment core...sediment sections, which are particularly important tephrostratigraphic...core...late Quaternary, dispersing tephra over vast areas. These tephra layers...sediment sections from various environments. Unless a name was already...cores, marine cores (1) can also provide important tephrostratigraphic...Late Quaternary tephrostratigraphy of southern Chile and Argentina...core/exposure location labels refer to reference numbers in Supplementary...late Quaternary (post-glacial) activity, modified from Siebert et al. ...sediment records. We address the inconsistencies in and revisions of the...late Quaternary, dispersing tephra over vast areas. These tephra layers...sediment core. Numbered references can be found in Supplementary Information...sediment sections. Numbered references can be found in Supplementary Information...late Quaternary (post-glacial) activity, modified from Siebert et al. ... The Southern and Austral Volcanic Zones of the Andes comprise 74 volcanic centres with known post-glacial activity. At least 21 of these have had one or more large explosive eruptions in the late Quaternary, dispersing tephra over vast areas. These tephra layers therefore have great potential as tephrochronological marker horizons in palaeoenvironmental studies in southern Chile and Argentina, a region that is particularly useful to study climate dynamics of the southern hemisphere. However, to date tephrochronology has rarely been fully utilised in this region as a correlation and dating tool. Here we review the existing post-glacial tephrostratigraphic record of the Southern and Austral Volcanic Zones, and compile a database of known occurrences of tephra from these volcanoes in ice and lacustrine, marine, peat, and cave sediment records. We address the inconsistencies in and revisions of the tephrostratigraphies presented in prior literature, and discuss the challenges in correlating tephras and the limitations of the tephrostratigraphic record in this area. This study highlights the many gaps that still exist in our knowledge of the eruptive histories of these volcanoes, but also reveals the largely under-utilised potential of tephra as a correlation tool in this region. This is exemplified by the severe lack of adequate geochemical analysis of tephra layers preserved in many lacustrine and peat sediment sections, which are particularly important tephrostratigraphic records in southern Chile and Argentina due to the paucity of surface preservation.

Contributors: unknown

Date: 2001-07-30

sediment cores collected adjacent to the CLSC...sediments in cores collected adjacent to the CLSC (n=40)...sediment cores collected adjacent to the CLSC, indicating the ages (ka...sediments from cores collected adjacent to the CLSC, after subtraction...Late Quaternary hydrothermal sedimentation adjacent to the Central Lau...sediment cores collected adjacent to the southward-propagating Central...sediments is mainly formed of Mn oxides containing other hydrothermally...sediments adjacent to the CLSC has been more variable than in the older...core recovery, length of core section studied (cm below seafloor) and ...sediments...sediments from the area. This may be attributed to localised hydrothermal...Sedimentation, sediment density and summary statistics for HCl soluble ... The partition geochemistry of 10 sediment cores collected adjacent to the southward-propagating Central Lau Spreading Center (CLSC) has been studied. The hydrothermal oxide component in these sediments is mainly formed of Mn oxides containing other hydrothermally associated elements (e.g., Fe, Zn, Cu, Mo and Pb). The Mn oxides represent distal plume fall-out derived from hydrothermal vents. Hydrothermal Mn accumulation rates are between 2.6 and 74.4 mg cm−2 ka−1 during the 0–30-ka period and between 2.1 and 12.8 mg cm−2 ka−1 during the 30–120-ka period. Recent (<30 ka) hydrothermal input to the sediments adjacent to the CLSC has been more variable than in the older sediments from the area. This may be attributed to localised hydrothermal activity occurring behind the propagator, and possibly to magma chamber development. Periods of enhanced hydrothermal input from the CLSC at ca. 30 ka and 175 ka appear to be contemporaneous along the CLSC; however, an enrichment in Mn at ca. 112 ka probably represents distal hydrothermal plume fall-out from increased activity on the Valu Fa Ridge in the southern Lau Basin. Hydrothermal Mn input derived from the CLSC is below that from the VFR.

Contributors: unknown

late Quaternary glacial and interglacial sediments from the southern Drake...Quaternary...sediments was inferred to be the Weddell Sea region. Sediment input from...sediments of core GC05-DP02 and marine surface-sediment samples around...sediment samples from core GC05-DP02. Concentrations in ppm....Sediment...sediment provenance and transport paths during the late Quaternary. The...sediment provenance and transport paths during the late Quaternary. The...Down-core variations in sediment facies, magnetic susceptibility (MS),...Down-core variations in trace element, rare earth element, and Nd and ...sediments. In contrast, interglacial sediments are composed of mixed sediments...sediment samples from core GC05-DP02....late Quaternary glacial and interglacial sediments from the southern Drake...core used in this study records paleoenvironmental changes during the ...Late Quaternary glacial–interglacial variations in sediment supply in ... Geochemical characteristics of marine sediment from the southern Drake Passage were analyzed to reconstruct variations in sediment provenance and transport paths during the late Quaternary. The 5.95m gravity core used in this study records paleoenvironmental changes during the last approximately 600ka. Down-core variations in trace element, rare earth element, and Nd and Sr isotopic compositions reveal that sediment provenance varied according to glacial cycles. During glacial periods, detrital sediments in the southern Drake Passage were mostly derived from the nearby South Shetland Islands and shelf sediments. In contrast, interglacial sediments are composed of mixed sediments, derived from both West Antarctica and East Antarctica. The East Antarctic provenance of the interglacial sediments was inferred to be the Weddell Sea region. Sediment input from the Weddell Sea was reduced during glacial periods by extensive ice sheets and weakened current from the Weddell Sea. Sediment supply from the Weddell Sea increased during interglacial periods, especially those with higher warmth such as MIS 5, 9, and 11. This suggests that the influence of deep water from the Weddell Sea increases during interglacial periods and decreases during glacial periods, with the degree of influence increasing as interglacial intensity increases.

Contributors: unknown

Date: 2009-03-17

sediment. Note a large difference in core depth scales....sediment (purple, panel (b) only). 14C and AAR ages (ka) are shown in ...Late Quaternary sediment transport and deposition, except for turbidites...core depth (a) and linear sedimentation rates (LSR) (b) in cores from ...sediment was deposited with sedimentation rates greatly reduced away from...Late Quaternary stratigraphy and sedimentation patterns in the western...sediment was deposited with sedimentation rates greatly reduced away from...Late Quaternary...Late Pleistocene glaciations (dotted lines). See Fig. 1 for core numbers...Late Quaternary...Sediment cores from the western Arctic Ocean obtained on the 2005 HOTRAX...Late Quaternary sedimentation rates in cm/kyr at investigated sites (including...sedimentation pattern suggests that Late Quaternary sediment transport...sediment composition that is not affected by diagenetic processes as strongly...sediment was probably delivered to the core sites by icebergs during glacial...sediment cores from the Alaskan margin to the Mendeleev Ridge: sand content...sediment stratigraphy...Sediment cores investigated for this study. ... Sediment cores from the western Arctic Ocean obtained on the 2005 HOTRAX and some earlier expeditions have been analyzed to develop a stratigraphic correlation from the Alaskan Chukchi margin to the Northwind and Mendeleev–Alpha ridges. The correlation was primarily based on terrigenous sediment composition that is not affected by diagenetic processes as strongly as the biogenic component, and paleomagnetic inclination records. Chronostratigraphic control was provided by 14C dating and amino-acid racemization ages, as well as correlation to earlier established Arctic Ocean stratigraphies. Distribution of sedimentary units across the western Arctic indicates that sedimentation rates decrease from tens of centimeters per kyr on the Alaskan margin to a few centimeters on the southern ends of Northwind and Mendeleev ridges and just a few millimeters on the ridges in the interior of the Amerasia basin. This sedimentation pattern suggests that Late Quaternary sediment transport and deposition, except for turbidites at the basin bottom, were generally controlled by ice concentration (and thus melt-out rate) and transportation distance from sources, with local variances related to subsurface currents. In the long term, most sediment was probably delivered to the core sites by icebergs during glacial periods, with a significant contribution from sea ice. During glacial maxima very fine-grained sediment was deposited with sedimentation rates greatly reduced away from the margins to a hiatus of several kyr duration as shown for the Last Glacial Maximum. This sedimentary environment was possibly related to a very solid ice cover and reduced melt-out over a large part of the western Arctic Ocean.

Contributors: unknown

Date: 2006-05-31

Late Quaternary...Late Quaternary high-sedimentation rate core (573 m water depth, Pakistan...Late Quaternary high-sedimentation rate core (573 m water depth, Pakistan...core SO90 137KA off Pakistan....Late Quaternary pteropod preservation on the Pakistan shelf and continental...sediment core 137KA off Pakistan: (a) present-day situation with shallow...core 137KA is indicated by a star....sediment samples from the Pakistan shelf and upper continental slope and...sediment samples showing good to very good preservation (LDX: 2.2 to 1.3...sediments, light grey=indistinctly laminated sediments, white=bioturbated...Late Quaternary...core 137KA indicating aragonite dissolution: (A) coarse fraction content ... Fifteen surface sediment samples from the Pakistan shelf and upper continental slope and a Late Quaternary high-sedimentation rate core (573 m water depth, Pakistan continental margin) have been analysed to improve the understanding of the factors influencing pteropod preservation. The aragonite compensation depth (ACD) is located at 250–400 m water depth, which corroborates previous observations of a very shallow ACD in the northern Arabian Sea. With the exception of the Hab transect off Karachi, the ACD coincides with the upper boundary of the OMZ located at 250 m water depth. The shell preservation index of the pteropod Limacina inflata (LDX) was applied on six surface sediment samples showing good to very good preservation (LDX: 2.2 to 1.3).

Contributors: unknown

Date: 2013-02-14

sediment core with black representing peat sediments and yellow reflecting...Late Quaternary climate dynamics...Late Quaternary vegetation history of North Stradbroke Island, Queensland...cores. NC is the code for the samples taken from Native Companion Lagoon...Late Quaternary climate dynamics...late Quaternary palaeoenvironmental variability available from the subtropics...sediment core with black representing peat sediments, brown reflecting...late deglacial of Reeves et al. (2013a) have been combined into the LGIT...sediments...late Quaternary palaeoenvironmental variability available from the subtropics ... Currently there is a paucity of records of late Quaternary palaeoenvironmental variability available from the subtropics of Australia. The three continuous palaeoecological records presented here, from North Stradbroke Island, subtropical Queensland, assist in bridging this large spatial gap in the current state of knowledge. The dominance of arboreal taxa in the pollen records throughout the past >40,000 years is in contrast with the majority of records from temperate Australia, and indicates a positive moisture balance for North Stradbroke Island. The charcoal records show considerable inter-site variability indicating the importance of local-scale events on individual records, and highlighting the caution that needs to be applied when interpreting a single site as a regional record. The variability in the burning regimes is interpreted as being influenced by both climatic and human factors. Despite this inter-site variability, broad environmental trends are identifiable, with changes in the three records comparable with the OZ-INTIMATE climate synthesis for the last 35,000 years.