Late Marine Isotope Stage Research Articles

Vegetation and climate during the penultimate interglacial of the northeastern Russian Arctic: the Lake El'gygytgyn pollen record

We present a high‐resolution reconstruction of the vegetation and climate dynamics during the penultimate interglacial, corresponding with Marine Isotope Stage (MIS) 7, based on detailed palynological analyses of lacustrine sediments from Lake El'gygytgyn, northeastern Siberia. The analysed sediments were deposited between 246 and 181 ka ago (late MIS 8 to early MIS 6.6). The interglacial vegetation was characterized by herb and shrub (mainly alder and birch) dominated plant communities. Pollen‐based biome reconstruction shows a dominance of the tundra (TUND) biome, thus indicating rather open vegetation. Warmer intervals (MIS 7.5, 7.3 and 7.1) were marked by an increase in the cold deciduous forest (CLDE) biome scores and a synchronous decrease in the cold steppe (STEP) biome scores. The thermal maximum occurred during MIS 7.1, as indicated by the highest CLDE biome scores occurring in this period, and lasted ~10 ka, possibly favoured by the high precession‐related summer insolation and the legacy of the preceding mild and dry stadial (MIS 7.2). In contrast, MIS 7.3 and 7.5 were characterized by shorter durations (~4 ka) and lower summer temperatures. The preceding cold glacial and stadial (MIS 8 and 7.4, respectively) might have led to an extensive distribution of permafrost that hindered vegetation development during the subsequent warm intervals. MIS 7.4 and 6.6 were cold and wet, probably triggered by low obliquity values and coevally low precession‐related summer insolation. As a result, these periods were marked by significantly reduced summer temperatures and an enhanced snow‐ice albedo feedback. The obtained reconstructions provide potential scenarios for future climate changes and allow a better understanding of the relationship between vegetation, climate and external/internal forcings in the high latitudes.

Evaluation of Mumiyo Deposits From East Antarctica as Archives for the Late Quaternary Environmental and Climatic History

AbstractMumiyo deposits form in the vicinity of snow petrel (Pagodroma nivea) nesting sites and consist of fossil stomach oil (mumiyo), guano, and minerogenic material. Here we evaluate mumiyo deposits from the inland mountain ranges of central Dronning Maud Land as high‐resolution archives for paleoenvironmental reconstructions in Antarctica. Investigation of internal structures and chemical composition shows that the lamination reflects progressive sedimentation, despite the irregular outer morphology of the deposits. Detailed radiocarbon analysis demonstrates that stratigraphies are intact: 14C ages become successively younger upwards in the deposits. Fatty acid and n‐alcohol composition was determined on samples from eight mumiyo deposits. Dominance of low molecular weight compounds (C14 to C18) points to a dietary signal; however, the relatively low proportions of unsaturated compounds compared to fresh stomach oils indicates some postdepositional degradation. We found marine diatoms in the mumiyo, which potentially provide a proxy for sea ice conditions in the foraging habitat of the petrels. Age ranges of the investigated deposits suggest occupation of the analyzed sites by snow petrels from 17 ka to >58 ka. Changes in deposition rates point to higher occupation frequency in Petermann Range from 46 to 42 ka compared to the late marine isotope stage 3 and the Last Glacial Maximum.

Anatomy of a late Quaternary carbonate island: Constraints on timing and magnitude of sea-level fluctuations, West Caicos, Turks and Caicos Islands, BWI

The data set of the island of West Caicos consists of a combination of high-resolution lidar and digital imagery, radiometric data, and amino acid racemization (AAR) D/L values as well as extraordinary preservation of sedimentary and bio-constructed deposits on the island. Together with a well-established regional stratigraphic framework from the neighboring Bahamian island chain and detailed field mapping, the West Caicos data set provides an opportunity to advance our understanding of the link between carbonate stratigraphy and the controlling parameters of sea level, sediment supply, tectonics, and climate. The exceptionally well-preserved stratigraphic record of the mid–late Pleistocene from West Caicos allows recognition of marine isotope stages (MIS) 9/11, 5e, and Holocene. The west coast of the island provides a continuous 8.4 km exposure of the MIS 5e record that enhances our understanding of the intra-MIS 5e bipartite succession in this region and supports a sea-level lowering that occurred during the last interglacial (LIG).West Caicos accreted as a series of eolian, foreshore–shoreface, barrier-reef, and fringing-reef facies. Shoreline positions for all but the MIS 7 and MIS 5a/c deposits are now captured in the sub-meter geodetic-quality topobathy lidar survey. The Star Town unit of MIS 9/11 age forms the southern margin of the island as well as the central karst-modified spine, with uranium–thorium (UTh) coral ages of between 368 and 365 thousand years ago (ka) and a D/L Glu average of >0.60. Early MIS 5e strata include the Railroad Ridge unit in the center of the island, which was previously identified as one of the older units. The Railroad Ridge unit is a north–south linear dune ridge that has a D/L Glu average of 0.52 and indicates the onset of sediment sources from the east associated with a flooded central Caicos Platform. Approximately synchronously, the early MIS 5e South Reef unit (+3.75–4 m sea-level elevation) nucleated on the western coast of West Caicos, attached to the middle Pleistocene Star Town unit. The South Reef corals yield an average coral UTh age of 126.5 ka, with an average D/L Glu from skeletal matrix of 0.46. This transitional barrier/fringing reef is unconformably overlain by the late MIS 5e Boat Cove unit. Corals in the basal transgressive phase of this upper MIS 5e Boat Cove unit yield an average 120.6 ka UTh and average D/L Glu of 0.45. Shallow-marine, foreshore, and eolian facies of the late MIS 5e rest on a wave-cut terrace that cuts the early MIS 5e South Reef unit by as much as 3 m down to a +0.5 m above present sea-level elevation. The upper MIS 5e Boat Cove unit displays a maximum of +4.5 m elevation above present-day sea level, measured from the middle of the foreshore. This estimate may be a minimum value as the exposures on the west coast are part of a forced regressive foreshore sequence. Last stages of the upper MIS 5e deposition are seen in a series of regressive dune-beach ridge deposits referred to as the Northeast Ridges unit, with sea-level positions ranging from +4.5 m early in the central part of West Caicos, to +0.5 m on the far northeast coast, eventually building down below present-day sea level. This sea-level history fits well with previously documented records in the Bahamas and globally, and the extensive erosion supports a short-lived (between 126 and 120 ka) intra-MIS 5e relative-sea-level fall. Holocene deposition on West Caicos is restricted to northern and eastern margins of the island as a combination of strandplain and dune ridge mixed skeletal–oolitic units.Using the high-resolution digital elevation model (DEM) and linked digital geologic map makes it possible to compare areas of the different Pleistocene and Holocene units quantitatively and to constrain volumetric assessments and accumulation rates on the island for different units. The peak sediment volume production/accumulation rate—between 6.5 and 8 × 106 m3 or between 2.2 and 2.7 × 106 m3 per ka—is observed in the upper MIS 5e unit. This rate is 5 times greater than the 0.5 × 106 m3 per ka estimated for the Holocene ooid dune-ridge/strandplain complex, suggesting that the combination of higher sea level, greater wave and wind energy, and warmer ocean temperatures may have fostered the higher rate of chemically precipitated sediment supply.

Vegetation and climate changes since the middle MIS 3 inferred from a Wulagai Lake pollen record, Inner Mongolia, Northeastern China

The climate conditions during Marine Isotope Stage (MIS) 3 were similar to present-day conditions, but whether humidity then exceeded present levels is debated, and the driving mechanisms of palaeoclimate evolution since MIS 3 remain unclear. Here, we use pollen data from Wulagai Lake, Inner Mongolia, to reconstruct vegetation and climate changes since the middle MIS 3. The steppe biome is reconstructed as the first dominant biome and the desert biome as the second, and the results show that the vegetation was steppe over the last 43,800 years. Poaceae, Artemisia, Caryophyllaceae and Humulus were abundant from middle to late MIS 3, indicating humid climate conditions. As drought-tolerant species such as Hippophae, Nitraria and Chenopodiaceae spread during MIS 2, the climate became arid. The Holocene is characterized by the dominance of steppe with mixed coniferous-broadleaved forests in the Greater Hinggan Range, and the desert biome retains high affinity scores, indicating that the climate was semi-arid. The climate from middle to late MIS 3 was wetter than in the Holocene; this shift was related to changes in the Northern Hemisphere's solar insolation and ice volume. The humid conditions during MIS 3 were attributed to strong ice–albedo feedback, which led to evaporation that was less than the precipitation. The enhanced evaporation caused by increased solar insolation and decreased ice volume might have exceeded the precipitation during the Holocene and resulted in low effective humidity in the Wulagai Lake basin.

Origins and genesis of loess deposits in central Spain, as indicated by heavy mineral compositions and grain‐size variability

AbstractThe formation of loess deposits strongly depends on the availability of deflatable dust‐sized material. Identification of source areas and mechanisms of dust production is essential for an appropriate characterization of related palaeoenvironmental conditions. So far, little research has been done on loess deposits in the Mediterranean region and information about mechanisms of dust production is very rare. In this context, it is not clear from where the loess deposits from the upper Tagus Basin in central Spain originated. The main objective of this study was to find out whether these loess deposits were formed primarily by mountain processes and fluvial comminution, or whether they have their origin in the weathering of Tertiary marls in the centre of the Madrid Basin. A further concern was to link the determined source areas with loess formation mechanisms and concomitant environmental contexts. Following a comprehensive approach using heavy minerals and grain‐size data, together with information on stratigraphic features and geomorphic positions, different local loess sources could be identified. This study shows that during the last 35 kyr a major proportion of the Tagus loess deposits was deflated from river floodplains, while the mountain region of the Iberian Range was identified as a significant source of respective floodplain sediments. Based on heavy mineral compositions and dating results, it was found that during Heinrich Stadial 3, sediment supply from the Iberian Range strongly increased, suggesting an environmental shift from initially warmer towards colder temperatures in late Marine Isotope Stage 3. Furthermore, it was found that grain‐size patterns clearly indicate maximum wind strengths during Heinrich Stadial 3, followed by Heinrich Stadial 2 and Heinrich Stadial 1. These results demonstrate that the formation of dust‐sized particles in this part of the Mediterranean operated similar to many other places in temperate and continental regions, and that weathering processes linked to hot and dry environments were only of minor importance.

Detecting patterns of local raw material utilization among informal lithic assemblages at the late Paleolithic site of Shuidonggou Locality 2 (China)

The apparent simplicity and the lack of changes in stone tool production during the Paleolithic in China is often explained by environmental, subsistence and demographic processes that either promoted a casual approach to lithic technological organization or impeded cultural innovation among East Asian hominin groups. This perspective stems from an assumption that complexity in lithic management is solely reflected in formalized core reduction methods, tool typology and/or the transport of non-local raw material types. In this study, by using survey to establish the baseline expectation of local raw material proportions, we demonstrate the differential treatments of locally abundant stone types at the Late Paleolithic site of Shuidonggou Locality 2. In spite of the apparent technological stasis, we observe shifting patterns of local raw material selection and transport during late Marine Isotope Stage 3. Hence our results suggest that, in basic core-and-flake assemblages, technological complexity is expressed in the selection, use and transport of lithic resources, including informal artifacts made on locally available raw material.

Late MIS 3 stabilization of dunes in the eastern Central Great Plains, USA

Abstract Extensive luminescence and 14C dating of aeolian sand dunes and sheets in the Central Great Plains (CGP) have been biased toward the western part of the region, targeted relatively large dune fields, and produced primarily Holocene (Marine Isotope Stage (MIS) 1) and latest Pleistocene (MIS 2) ages. This research luminescence dated a small discontinuous dune field perched on the high terrace of the Kansas River valley, situated on the eastern side of the CGP. These dunes have been stable since at least 30–28 ka, indicating that they are among the oldest recognizable dunes preserved in the CGP, as well as the entire North American Great Plains. The inferred stabilization of these dunes was coeval with pedogenesis and low sediment accumulation rates in upland loess, playa lunettes, and alluvial sequences in the CGP, in a time period with maximum summer insolation and relatively warm conditions. Source of the sand is presumed to have been fluvial sediments from the adjacent Kansas River, now preserved as the Buck Creek Terrace. Sand-mobilizing winds were southerly to southwesterly given that the dunes mantle only the high-terrace remnants on the north side of the valley. Long-term dune stability after MIS 3 appears to indicate that latest-Pleistocene and Holocene megadroughts were not sufficiently severe and eastward penetrating to reactivate these eastern CGP dunes.

Quaternary glaciations in the Lopu Kangri area, central Gangdise Mountains, southern Tibetan Plateau

The Gangdise Mountains are located in a transition zone between the Indian Summer Monsoon-dominated Himalaya Mountains and the Westerlies-dominated Qiangtang Plateau. The timing and extent of the paleoglaciations in the central Gangdise Mountains remain unclear. We investigated the glacial history of the southeastern slopes of Lopu Kangri using 10Be exposure dating and summarized the dating results for the western and eastern sectors of the Gangdise Mountains. Glacial events were constrained to ≥243.88 ± 25.88 ka, ≥ 43.09 ± 4.18 ka, 24.19 ± 2.29 ka, 19.78 ± 1.9 ka, 10.62 ± 1 ka, 2.75 ± 0.37 ka, 1.8 ± 0.18 ka, 0.32 ± 0.04 ka and 0.22 ± 0.04 ka, representing paleoglaciations which occurred during marine isotope stage (MIS) 8/7 or earlier, MIS 3 or earlier, early MIS 2, the global Last Glacial Maximum (LGM), the early Holocene, the Neoglacial and the Little Ice Age (LIA). Evidence of MIS 5 or earlier glaciations, and the glaciations during MIS 3, early and late MIS 2, the global LGM and the LIA, can be found in the western or eastern sectors of the Gangdise Mountains. The spatial trend in ΔELA values in the Gangdise and surrounding mountain ranges would appear to have been controlled by particular precipitation distribution patterns. The glacial events identified in the Gangdise Mountains during MIS 2, the Neoglacial and the LIA appear consistent with previously-identified cold periods. Precipitation was most likely a contributory cause of the glaciations during the MIS 3, early Holocene, the Neoglacial and the LIA.

Causes and consequences of Arctic freshwater routing into the Nordic Seas during late Marine Isotope Stage 5

In the paper of Telesiński et. al., the current affiliation of the author Maciej M. Telesiński is incorrectly listed as a footnote in the article. Authors and their affiliation should appear as: Maciej M. Telesiński1,4, Henning A. Bauch2, and Robert F. Spielhagen3 1Academy of Sciences, Humanities and Literature, Mainz, Germany 2Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany 3GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany 4Institute of Oceanology, Polish Academy of Sciences, Powstańców Warszawy 55, 81-712 Sopot, Poland.

Surface-ocean dynamics during eccentricity minima: a comparison between interglacial Marine Isotope Stage (MIS) 1 and MIS 11 on the Iberian Margin

Abstract Understanding interglacial climate variability is a key issue in the scientific community. Here we compared records from Marine Isotope Stage (MIS) 11 to those from MIS 1 (Holocene) as they are perceived to be possible analogs. Our study on the Iberian Margin, a key area to investigate surface dynamics in the Atlantic Ocean, incorporates coccolithophore assemblage and alkenone data of core MD03–2699 and their statistical analyses. Evaluating similarities between MIS 11 and MIS 1 depends on the way the two MIS are being aligned, i.e. at the deglaciation or based on the precession signal. During the deglaciation of either MIS 12 or MIS 2, the Iberian Margin was affected by abrupt decreases in SST and in coccolithophores' paleoproductivity caused by the arrival of subpolar surface waters. Just prior to the decline, in both the intervals, the Portugal Current affected the studied site, although a possible difference in upwelling strength is here suggested and related to more intense westerlies during the last glacial than the late MIS 12. Similar surface-ocean dynamics occurred at the onset of both MIS 11 and MIS 1 as indicated by the prevalence of the Iberian Poleward Current and sometimes the Azores Current, although the subtropical waters were more oligotrophic during the MIS 2 deglaciation than the MIS 12 one. Synchronizing our records according to the precession cycles aligns the early-to-mid Holocene with the second, warmer phase of MIS 11c. During both these intervals, the western Iberian Margin was mainly affected by the Iberian Poleward Current that transported more temperate-warm, mesotrophic surface waters during MIS 11c than during the early-to-mid Holocene. During the early to mid-Holocene the Iberian Margin endured incursions of colder surface waters that did not occur during MIS 11c allowing us to hypothesize that the studied site experienced, from a paleoceanographic point of view, a more stable period during MIS 11c than the early Holocene. Finally, spectral analysis suggests the role of full, half and fourth precession components in driving surface-ocean variability during MIS 11 and during the last 24 kyr BP.

First evidence for onshore marine isotope stage 3 aeolianite formation on the southern Cape coastline of South Africa

The southern Cape coast of South Africa boasts an impressive suite of Plio-Pleistocene aeolian dune deposits (aeolianite). Previous research has shown that in this region onshore dune accumulation was generally focused around interglacial sea level highstands, with the locus of coastal dune accumulation shifting onto the adjacent continental shelf during glacial sea level lowstands. Here, using new luminescence dating results, we present the first evidence for preserved onshore glacial age dunes. Specifically, on the Robberg Peninsula, a rocky headland 28 km east of Knysna, two phases of aeolianite formation are identified, corresponding to early (45–60 ka) and late (35–30 ka) marine isotope stage (MIS) 3. Subsequently, during the Holocene, all substantive dune accumulation occurred between 10.2 and 7.0 ka, forming cliff-fronting dunes and filling the limited accommodation space on the headland, including an archaeological rock-shelter. Combining these ages with bathymetric data, we infer that this distinct onshore glacial age aeolianite record reflects: 1) restricted accommodation space during sea level highstands; 2) a regional narrowing of the continental shelf, and 3) liberation of sediments lying on a prominent −45 to −60 m offshore terrace, which would have been exposed during MIS 3. This demonstrates that despite broad regional-scale trends in the timing of coastal aeolian activity - driven by commonalities in relative sea level trends and climate - distinct local variations in late Quaternary coastal evolution can be identified. This is ascribed to local controls on preservation (accommodation space) and sediment supply (shoreline position and antecedent offshore sediment supplies). Such findings may have wider implications for interpretations of site context/resource availability at several notable coastal archaeological sites, and more broadly suggest that local offshore or onshore geologic contexts can at times assume greater influence on a preserved coastal aeolianite record than the regional-scale trends in sea level and climate.

Late‐Quaternary history of ‘great lakes’ on the Tibetan Plateau and palaeoclimatic implications – A review

Geomorphic evidence suggests that shorelines of 100–200 m above the modern lake levels were common across the Tibetan Plateau during late Marine Isotope Stage (MIS) 3. The timing of this lake‐level highstand is mainly based on radiocarbon ages. Problems surrounding the ages of lacustrine sediments at or beyond the limit of the radiocarbon‐dating method have created a need for alternative geochronometers. Chronological advances during the last decade have renewed interest in the timing of events beyond the limit of radiocarbon dating. Here, we synthesize published data for elevated lacustrine landforms of 48 lakes on the Tibetan Plateau, in order to provide a thorough perspective on the timing and pattern of lake‐level changes in this alpine area during the late Quaternary. The ages of these elevated shore features reveal a long‐term trend of relative lake‐level fall from at least MIS 5, instead of a peak in MIS 3, as previously thought. Dating lacustrine terrace sequences reveals that the rate of lake‐level fall ranged from ~1 to 3 mm a−1, comparable with that of related river downcutting across the plateau. Palaeoclimatic proxy records point to a sustained drying since the Last Interglacial, suggesting that long‐term aridification might be the culprit for this widespread and progressive lake‐level fall.

Sedimentary Characteristics of the Second Marine Layer During the Late Marine Isotope Stage 3 in Southern Yellow Sea and Their Response to the East Asian Monsoon

We use the particle size of sediments in core YS01A to study the sedimentary environment of the mud deposit in the central South Yellow Sea of China during late Marine Isotope Stages 3 (MIS3; 40.5 kyr–31.3 kyr). In addition, the East Asian Monsoon and its relationship with the North Atlantic Ocean climate change are discussed based on the sensitive grain-size calculation and the spectrum analysis. The results show that during late MIS3, the muddy area in the central South Yellow Sea experienced the evolution of coastal facies, shallow marine facies, coastal facies, and continental facies, with weak hydrodynamic conditions. Compared with other climate indicators, we found that there were many century to millennium-scale climate signals documented in the muddy area sediments in the central South Yellow Sea. According to our particle size results, three strong winter monsoon events occurred at 37.6 kyr, 35.6 kyr and 32.2 kyr. The East Asian Winter Monsoon records in core YS01A are consistent with the Greenland ice core and the Hulu cave stalagmite δ18O. The millennial and centennial scale cycles, which are 55 yr, 72 yr, 115 yr, 262 yr respectively, correspond to solar activity cycles, while the 1049 yr and 2941 yr cycles correspond to the Dansgaard-Oeschger cycles. These cycles indicate that the paleoclimate evolution of the area was controlled by the solar activities, with the high-latitude driving thermohaline circulation as the main energy conveyor belt, followed by the sea-air-land amplification of the winter monsoon variation in the central Yellow Sea in the late MIS3.

Preliminary results of dating for the Lower Paleolitic sites of Ukraine (Medzhibozh 1 and Medzhibozh A, Khmelnitskii region) by electron spin resonance method

In the West of Ukraine, the Medzhibozh site complex includes two multi-layered open-air Lower Paleolithic sites sitting at 49°35′ N 27°42′ E, 270 m amsl. In Medzhibozh I’s lower alluvial cycle, Layer 16a yielded Paleolithic artefacts, mainly choppers, chopping tools, and flakes with little secondary modification, associated with likely fireplaces and bones with cutmarks left by early hominids inhabiting an ancient shoreline. Ursus deningeri, Stephanorhinus kirchbergensis , and other Middle Pleistocene fossils, as well as microtheriofauna, pollen, paleopedology data suggest that Layers 13—16 must predate 200 ka, but only one TL date has been done here. About 500 m away from Medzhibozh I, Medzhibozh A’s six archaeological layers were intercalated with sterile gravels, with analogous stone products, fauna, hearth relics . Since ESR can date mammalian enamel up to 2—4 Ma with 2—5 % precision, three cervid teeth from Layer 16a at Medzhibozh I and one from the Layer 1 in Medzhibozh A were dated by standard and isochron ESR. Sediment samples were analyzed by NAA to measure volumetrically averaged sedimentary dose rates. Using geological criteria, a ramped box model calculated time-averaged cosmic dose rates were determined. From Medzhibozh A, AT29’s standard LU age of 379±27 ka agreed best with ages estimated from the faunal analyses, but the isochron showed diffusional secondary U uptake, suggesting the age could be older. At Medzhibozh I, all teeth had >100 ppm U in their dentine, but enamel U ranged from 2,8 to 11,8 ppm. AT41’s isochron, which did not show secondary U uptake, suggested that the U uptake rate, p ~4 was the best uptake rate, yielding an age of 373±17 ka, which correlates with late Marine Isotope Stage (MIS) 11. Meanwhile, AT44’s age likely dates at 399±11 ka with p =4, and AT45’s at 396±13 ka with p =6, both of which correlate with mid MIS 11. Their isochrons suggested secondary diffusional U uptake had affected both teeth. All isochron analyses suggest that one secondary uptake event may have affected the entire site, likely due to immersion in U-rich water. If correct, AT29’s age makes Medzhibozh A’s hearths the oldest in the Ukraine, but more teeth from all the layers must be ESR dated and tested with coupled ESR— 230 Th/ 234 U to confirm the ages and p ’s.

Millennial-scale Asian monsoon variability during the late Marine Isotope Stage 6 from Hulu Cave, China

AbstractA precisely 230Th-dated stalagmite δ13C profile from Hulu Cave, China, is presented to characterize the frequency and pattern of millennial-scale Asian monsoon (AM) variability from 160.6 to 132.5 ka. Evidence for an antiphased relationship of the δ13C and δ18O on the millennial scale suggests that the δ13C is indicative of the local hydrological cycle associated with changes in AM strength. Owing to the δ13C responding to AM changes more sensitively than the δ18O, we could identify 15 strong AM events that correlate to cold intervals recorded in Antarctic ice cores within 230Th dating uncertainty. This result supports a dynamic link of AM strength and southern hemispheric climates via the cross-equatorial airflows. Power spectrum analysis shows a predominant periodicity of 1.5–2.5 ka for the δ13C profile, similar to the Dansgaard-Oeschger frequency during the last glacial period. Moreover, the AM events are characterized by rapid transitions at the onset, suggesting that the observed millennial-scale AM variability is likely forced by northern high-latitude climates via north–south shifts of the Intertropical Convergence Zone associated with the bipolar seesaw mechanism. As evidence for a common mechanism for ice age terminations, a strong AM event (~134 ka) surrounding Termination II is analogous to the Bølling-Allerød warming interval.

Causes and consequences of Arctic freshwater routing into the Nordic Seas during late Marine Isotope Stage 5

ABSTRACTSediment core PS1904 reveals continuous records of planktic and benthic foraminiferal stable isotopes (δ18O/δ13C) from the north‐eastern Greenland continental margin. The data show good comparability with other records from the Nordic Seas, allowing the stratigraphic range of PS1904 to be dated to Marine Isotope Stage (MIS) 6. Focusing on MIS 5 reveals light δ18O values during MIS 5a compared to the last interglacial peak (MIS 5e) which indicates that surface and bottom water layers were strongly affected by freshwater during the former event. We present two possible scenarios explaining the origin and routing of the freshwater: (i) drainage of a Eurasian proglacial lake coupled with the collapse of the Kara Sea Ice Sheet at the MIS 5b/a boundary, and (ii) destabilization and melting of the nearby Greenland Ice Sheet. Although both scenarios could have acted simultaneously, sediment records from the Eurasian sector of the Arctic Ocean hint at the proglacial lake system in north‐western Siberia as the largest freshwater source. Regardless of the actual source, the freshwater lowered the surface ocean salinity causing water column stratification and sea ice expansion. Increased sea‐ice abundance led to a higher albedo and probably contributed to the cooling and global ice sheet growth that occurred subsequently during MIS 4.

Calcareous plankton and the mid-Brunhes climate variability in the Alboran Sea (ODP Site 977)

Quantitative calcareous plankton analyses have been performed at the Ocean Drilling Program Site 977 in the Alboran Sea through the mid-Brunhes interval (300–540 ka). The results evidence orbital-suborbital and millennial scale climate variability which primary reflects temperature change. The patterns of increase/decrease of coccolithophore and planktonic foraminifera warm water taxa reproduce the stage and substage climate variability in the planktonic δ18O in good agreement with other planktonic isotope records from Mediterranean Sea and Atlantic Ocean. Variable conditions, characterized by alternating cool nutrient-rich or warm and stable sea-surface waters, occurred during interglacial Marine Isotope Stage (MIS) 13 in response to high amplitude oscillations of insolation during obliquity maximum and to North Africa monsoon strength, influencing distribution of taxa. MIS 13a resulted warmer than MIS 13c based on the higher abundances of warm water taxa; they increase just after insolation maxima, suggesting a primary response of calcareous plankton to precessional orbital control. Following short-term warm (MIS 11e) and more humid (MIS 11d) phases, a climate optimum lasting about 16 kyr is recognized during MIS 11c, when major tropical-subtropical water arrival into the Alboran Sea occurred as evidenced by the presence of Trilobatus sacculifer. MIS 11c records unstable climate condition that persisted up to the late MIS 11, indicating multiple pulses of southward migrations of subpolar front following the full interglacial MIS 11c. Warm and oligotrophic conditions occurred during MIS 9 as during MIS 11, especially in MIS 9e, although without a climate optimum. Reduced abundance of warm water taxa and decrease of Globorotalia inflata highlight colder surface water conditions and decreased Atlantic-Mediterranean water exchange during glacials, especially during the prominent sea-level low-stand of MIS 12. Short-term prominent peaks of the polar-subpolar Neogloboquadrina pachyderma and Coccolithus pelagicus ssp. pelagicus, and additional key taxa preferring fresher and turbid water, together with minima in total Nannofossil Accumulation Rate and enhanced coccolith reworking, sustain a correlation with the North Atlantic Heinrich-type (Ht) events Ht1, Ht1a, Ht3, Ht4-6, thus documenting the sensitiveness of the Alboran Sea in recording European and Laurentide ice-sheet dynamics. The comparable chronology of most of these cold spells in the available Balearic and Ionian calcareous plankton records highlights that Atlantic melt water entering Alboran basin through Gibraltar Strait may have reached the central Mediterranean preserving some of its original polar signature.

El Paleolítico Superior de la península ibérica

Este artículo intenta ofrecer una síntesis relativamente completa de lo que se conoce en la actualidad sobre la transición del Paleolítico medio al superior y el desarrollo de las adaptaciones humanas y de las culturas durante el último periodo en la Península Ibérica (España y Portugal, así como Andorra y Gibraltar). Los énfasis del trabajo, que es inevitablemente selectivo y se basa principalmente en la bibliografía disponible más reciente, son las condiciones ambientales, el asentamiento humano, las tecnologías, la subsistencia y la expresión artística, desde una perspectiva que subraya en que medida la naturaleza y extensión de las redes sociales han cambiado durante todo el desarrollo del Estadio Isotópico Marino 3 tardío y todo el Estadio 2. El objetivo es abarcar todas las regiones de la península, pese a sus diferentes historias de la investigación y sus desiguales densidades de yacimientos. Una conclusión general es que a pesar de las fluctuaciones climáticas del Tardiglaciar, uno puede escribir diferentes histoires de la longue durée sobre importantes unidades geográficas como la región cantábrica (atlántica septentrional) de España, la cuenca del Ebro, la España levantina (mediterránea), Andalucía, las mesetas interiores de España y las cuencas del Duero y el Tajo, y las regiones meridional y central-septentrional de Portugal. Además, en diferentes grados a través del tiempo, hubo tanto una unidad cultural peninsular, creada por redes sociales entre esas regiones, como contactos con bandas de cazadores-recolectores al norte de los Pirineos.

Single-grain OSL dating of fluvial terraces in the upper Hunter catchment, southeastern Australia

Abstract Fluvial terraces in the upper Hunter catchment, southeastern Australia provide a long-term record of river activity in response to climate change in the late Quaternary. Single-grain optically stimulated luminescence (OSL) dating of quartz was applied in this study to investigate the timing of the formation of three fluvial terraces in the upper Hunter catchment. A detailed examination of luminescence properties of individual quartz grains revealed some correlation between their OSL decay rates, intrinsic brightness and dose saturation characteristics. Some quartz grains containing a higher proportion of non-fast components exhibit low brightness in OSL signals and high dose saturation levels. Some grains with slow OSL decays pass the standard rejection criteria, but are likely to yield underestimated equivalent doses (Des) because of a higher contribution of non-fast components, which are shown to have low thermal stability. Different rejection criteria, including the fast ratio, the dose saturation level and the OSL sensitivity criteria, were tested on the single-grain De results. Application of a fast ratio rejection criterion is able to successfully identify thermally unstable grains. A new rejection criterion based on dose saturation property was also applied to improve the age of one sample with a large De. Our dating results identify multiple phases of river valley aggradation in the upper Hunter catchment since late Marine Isotope Stage (MIS) 6; at ∼ 138 ka, ∼90–94 ka, ∼65 ka, ∼26 ka and ∼18 ka. The aggradational episodes of the terraces in the upper Hunter catchment are correlated with glacial or stadial periods since MIS 6. These phases of valley-floor aggradation are inferred to be a function of increased sediment supply during the cold periods resulting from strong periglacial activities in the adjacent Australian highlands.

Paleoclimatic and paleoceanographic records through Marine Isotope Stage 19 at the Chiba composite section, central Japan: A key reference for the Early–Middle Pleistocene Subseries boundary

Marine Isotope Stage (MIS) 19 is an important analogue for the present interglacial because of its similar orbital configuration, especially the phasing of the obliquity maximum to precession minimum. However, sedimentary records suitable for capturing both terrestrial and marine environmental changes are limited, and thus the climatic forcing mechanisms for MIS 19 are still largely unknown. The Chiba composite section, east-central Japanese archipelago, is a continuous and expanded marine sedimentary succession well suited to capture terrestrial and marine environmental changes through MIS 19. In this study, a detailed oxygen isotope chronology is established from late MIS 20 to early MIS 18, supported by a U-Pb zircon age and the presence of the Matuyama–Brunhes boundary. New pollen, marine microfossil, and planktonic foraminiferal δ18O and Mg/Ca paleotemperature records reveal the complex interplay of climatic influences. Our pollen data suggest that the duration of full interglacial conditions during MIS 19 extends from 785.0 to 775.1 ka (9.9 kyr), which offers an important natural baseline in predicting the duration of the present interglacial. A Younger Dryas-type cooling event is present during Termination IX, suggesting that such events are linked to this orbital configuration. Millennial- to multi-millennial-scale variations in our δ18O and Mg/Ca records imply that the Subarctic Front fluctuated in the northwestern Pacific Ocean during late MIS 19, probably in response to East Asian winter monsoon variability. The climatic setting at this time appears to be related to less severe summer insolation minima at 65˚N and/or high winter insolation at 50˚N. Our records do not support a recently hypothesized direct coupling between variations in the geomagnetic field intensity and global/regional climate change. Our highly resolved paleoclimatic and paleoceanographic records, coupled with a well-defined Matuyama–Brunhes boundary (772.9 ka; duration 1.9 kyr), establish the Chiba composite section as an exceptional climatic and chronological reference section for the Early–Middle Pleistocene boundary.