Part Of Marine Isotope Stage Research Articles

Palynology of the northwestern Mediterranean shelf (Gulf of Lions): First vegetational record for the last climatic cycle

Palynology has been performed for the first time on Late Quaternary sediments of the Gulf of Lions. The aim is both to tighten the chronology of seismic profiles in the region, and to elucidate the vegetation of southern France during the Last Climatic Cycle. Four cores, taken on the shelf, mostly record Marine Isotope Stages (MIS) 1 and 2 and part of MIS 3 and MIS 5. The latter sediments might have been preserved in a paleodepression on the emergent shelf between the Rhône and the Hérault rivers. It would explain their preservation against transgression and regression erosions of more recent stages. This study also provides a synthesis of palynological continental data collected during the last 40 years in southern Europe. Preliminary comparisons made between the latter and new marine data demonstrate that refugia of Picea and Abies existed in southern France during MIS 3 and MIS 2. The dynamics of Artemisia, deciduous Quercus and Corylus, Abies and finally Fagus is also reconstructed for the last deglaciation. First results obtained in the Gulf of Lions confirm and complete that synthesis.

Variations of the Last Glacial Warm Pool: Sea surface temperature contrasts between the open western Pacific and South China Sea

High‐resolution paleoceanographic records from the southern South China Sea (SCS) and the tropical open western Pacific reveal multicentennial‐ to millennial‐scale variations of the Western Pacific Warm Pool (WPWP) over the last 40 kyr. During the Last Glacial Maximum (LGM), in marine isotope stage (MIS) 2, planktonic Globigerinoides sacculifer δ18O in core NS93‐5 from the southern SCS and in core WP92‐5 from the central WPWP registered a similar average value of about −1.5‰. However, the average δ18O value was about 0.5‰ more negative in the SCS than in the central WPWP, as was their difference before and after the LGM in the later part of MIS 3 and early portion of MIS 1. These results indicate weaker monsoonal and fluvial effects on the southern SCS during the last glacial than during pleniglacial and postglacial periods owing to different oceanic circulation modes and regional topography. The calculated seasonal temperature differences of summer and winter sea surface temperatures (SSTs) between the open WPWP and the southern SCS were up to 3–4.5°C during the LGM but only slightly over 3°C in the southern SCS and less than 2°C in the open WPWP during other periods. From about 29 to 25 ka the MIS 2/3 transition was marked by a sudden SST increase in the southern SCS but a decrease in the open WPWP. Over this 4 kyr period the average annual SST appeared to be only 28°C in the central WPWP but more than 28°C in the southern SCS, indicating a shift of the central WPWP toward the far west during that time. Furthermore, our results imply a period of nearly 6 kyr from 22.5 to 16.5 ka without an apparent warm pool of 28°C in the western Pacific.

Pedosedimentary development of part of a Late Quaternary loess‐palaeosol sequence in northwest Argentina

AbstractThe field properties, magnetic susceptibility, particle size, calcium carbonate content, soil micromorphology and optical luminescence ages of the upper 6.1 m and lowermost 4.7 m of the 45 m loess–palaeosol sequence at El Lambedero in the Tafí del Valle region of Tucumán Province (Sierras Pampeanas, northwest Argentina) have been used to set up a partial stratigraphy and chronology, as well as a basic pedosedimentary model of loess accumulation, palaeosol development, reworking and erosion for the site. The minimum ages derived from the basal part of the section suggest that loess began to accumulate some time before 165 ka. A thick and well‐developed pedocomplex in the upper profile is correlated with at least the latter part of marine isotope stage (MIS) 5, whereas the overlying palaeosol may be attributable to pedogenic activity during MIS 3. The absence of material younger than 33 ka close to the surface of this rounded spur landform is probably the result of either non‐deposition or erosional stripping in response to climatic change, or episodic uplift in this seismically active region. Copyright © 2004 John Wiley & Sons, Ltd.

N2O and CH4 variations during the last glacial epoch: Insight into global processes

Greenhouse gas measurements along polar ice cores provide important insight into the former composition of the atmosphere, its natural variations, and the responses to fast climatic changes in the past. We present high‐resolution nitrous oxide (N2O) and methane (CH4) records measured along two ice cores from central Greenland covering part of Marine Isotope Stages 3 and 4 in the last glacial epoch. The N2O data confirm the hypothesis that N2O shows variations in phase to fast climatic changes observed in the Northern Hemisphere, the so‐called Dansgaard‐Oeschger (D‐O) events. Variations exist not only for events with a long duration (1500 years and more) but also for the shorter ones. The comparison with CH4 unveils interesting differences between the response of CH4 and N2O to D‐O events. While the average amplitudes of CH4 oscillations associated with D‐O events are similar to those of the Northern Hemisphere summer insolation, the magnitude of the N2O concentration change instead correlates with the duration of the D‐O events. The records give further insight into the timing of concentration changes at the beginning of D‐O events. They show that for long‐lasting events the N2O concentration starts to increase before both the sharp increase in the CH4 concentration and the temperature reconstructed for Greenland.

Magnetic susceptibility study of Late Quaternary inner continental shelf sediments in the Hong Kong SAR, China

Four cores of inner continental shelf sediment from the Hong Kong Special Administrative Region (SAR) have been measured for magnetic susceptibility. In all the cores, the upper part of Marine Isotope Stage (MIS) 1 down to about 3 m below seabed show abruptly elevated but highly variable levels of magnetic susceptibility attributable mainly to shipping contamination over the past 160 years. The uncontaminated lower MIS 1 deposits show a consistently low magnetic susceptibility above a sharp increase at the Holocene-Pleistocene boundary. This increase is accounted for by the presence of eroded palaeosol fragments enriched in iron oxides and hydroxides. Acid-sulphate soil development during MIS 2–4 on the sub-aerially exposed inner continental shelf covered by MIS 5 deposits is responsible for the formation of palaeosols. The timing is therefore the opposite of palaeosols within terrestrial loess sequences in that they were formed during the Last Glacial Period. Seventeen uncorrected conventional and accelerator mass spectrometry (AMS) radiocarbon dates of mud and shell samples from the cores indicated that the palaeosols were formed before about 9130 yr BP to 19,430 yr BP.

Marine Isotope Stage 11 as an analogue for the present interglacial

Past analogues for our present interglacial or even warmer periods have been sought in order to better understand our present and future climate. Marine Isotope Stage (MIS) 5, more precisely substage 5e, has long been considered to be a good candidate. However, there were some elements against this analogy in the data themselves [Kukla et al. Quat. Sci. Rev. 16 (6) (1997) 605], as well as in the mechanisms [Berger, 1989 Response of the climate system to CO 2 and astronomical forcings. In: Paleo-Analogs, IPCC Working Group I, Bath, 20–21 November 1989] and forcing related to both periods. Here we suggest that the period from 405 to 340 ka before present (BP), including a large part of Marine Isotope Stage 11, could be a good analogue for future climate. The insolation over this interval shows a strong linear correlation with the insolation signal over the recent past and the future. In addition, simulations using the climate model developed in Louvain-la-Neuve (LLN 2-D NH) show that both MIS 11 and the future are characterized by small amount (if any) of continental ice, with almost no variation during the whole interval. In contrast, MIS 5 is exhibiting larger variability in simulated ice volume. This confirms that the interval [405–340 ka BP] may lead to a better understanding of our present and future warm climate.

Evidence for Millennial-Scale Climate Change During Marine Isotope Stages 2 and 3 at Little Lake, Western Oregon, U.S.A.

Pollen and geochemical data from Little Lake, western Oregon, suggest several patterns of millennial-scale environmental change during marine isotope stage (MIS) 2 (14,100–27,600 cal yr B.P.) and the latter part of MIS 3 (27,600–42,500 cal yr B.P.). During MIS 3, a series of transitions between warm- and cold-adapted taxa indicate that temperatures oscillated by ca. 2°–4°C every 1000–3000 yr. Highs and lows in summer insolation during MIS 3 are generally associated with the warmest and coldest intervals. Warm periods at Little Lake correlate with warm sea-surface temperatures in the Santa Barbara Basin. Changes in the strength of the subtropical high and the jet stream may account for synchronous changes at the two sites. During MIS 2, shifts between mesic and xeric subalpine forests suggest changes in precipitation every 1000–3000 yr. Increases in Tsuga heterophylla pollen at 25,000 and 22,000 cal yr B.P. imply brief warmings. Minimum summer insolation and maximum global ice-volumes during MIS 2 correspond to cold and dry conditions. Fluctuations in precipitation at Little Lake do not correlate with changes in the Santa Barbara Basin and may be explained by variations in the strength of the glacial anticyclone and the position of the jet stream.

Periglacial fluvial systems in northwest Europe during marine isotope stages 4 and 3

Comparison of fluvial successions in river valleys dating from marine isotope (MI) Stages 4 and 3 in a west–east transect from Britain to Poland shows the spatial and temporal variation in palaeohydrological characteristics of northwest European river valleys during these stages. MI Stage 4 has been a period of deep fluvial incision. Following this erosion, most valleys were filled during MI Stage 3 with successions of gravelly river deposits (Britain) or sand/silt/peat successions (northwest European lowlands). The sedimentology of the deposits suggests strong discharge variations, caused by a nival discharge regime with pronounced spring snowmelt discharges. The MI Stage 3 climate oscillations generally cannot be traced in the fluvial record. An incision phase of Hengelo interstadial age has been found in the Netherlands, but similar incision phases related to other warming events have not been proved convincingly. The restricted reaction of the river systems is caused by the absence of geomorphologically effective vegetation changes and relatively minor variations in precipitation during MI Stage 3. Over longer time scales, silt and peat beds gradually decrease in the younger (post-Hengelo/Upton Warren) part of MI Stage 3, corresponding with evidence of aeolian activity and permafrost. This is related to the longer duration of the stadials in this part of MI Stage 3.

The Last Interglacial-Glacial cycle in NE Fennoscandia: a nearly continuous record from Sokli (Finnish Lapland)

Boreholes from the Sokli basin in Finnish Lapland have recovered a unique sequence of diamicts interlayered with fine-grained sediments that are rich in fossils. The diamicts are interpreted as till beds deposited by the Fennoscandian Ice-Sheet. The fine-grained intercalations seem to represent a series of warm stages that include one interglacial and three interstadials. The interglacial is characterized by a mixed taiga pollen assemblage and corresponds to a distinct diatom gyttja bed. The interstadials show progressively colder floras from open birch forest to arctic forest limit to shrub tundra. Their sediments comprise gyttja interlayered with wood and sand (interstadial 1); sands grading into sandy gyttja (interstadial 2); and sands overlain by laminated silt and clay (interstadial 3). The interstadial 2 and 3 deposits are underlain by diamict and are interpreted as deglaciation sequences. Silts with a tundra pollen assemblage separate the interglacial and interstadial 1 deposits. Luminescence dating evidence indicates that the interglacial bed most probably represents the NW European mainland Eemian Interglacial (marine isotope stage (MIS) 5e). The interstadial 1, 2 and 3 deposits are tentatively correlated with the Early Weichselian Brørup and Odderade Interstadials and an interstadial of Middle Weichselian age, respectively (MIS 5c, 5a and 3, respectively). The correlation implies that the easternmost part of the ice-divide zone of the Fennoscandian continental ice-sheet was deglaciated during part of MIS 3.

Warm Period Growth of Travertine during the Last Interglaciation in Southern Germany

Late-Quaternary travertine at two sites near Stuttgart formed entirely during interglacial periods. The travertine contains structures from growth induced by bacteria, and such structures have been dated by 230Th/U mass spectrometry. The resulting ages from both sites imply growth episodes of short duration, with growth rates up to 5 mm yr−1, at 99,800 ± 1300 yr B.P. (2ς; n = 8) and 105,900 ± 1300 yr B.P. (2ς; n = 7). These episodes were likely part of marine isotope stage (MIS) 5.3. Deposition of silt interrupted travertine growth at one of the sites ∼105,000 yr B.P. Likely correlatives of this silt are the St. Germain I-B stade recorded in the Grand Pile peat bog and a cold episode ∼1000 yr long recorded by δ18O values in the GRIP ice core. Travertine also formed during stage 5.5 (∼115,000 yr) and during the early Holocene. We found no evidence for travertine accumulation in stages 2, 3, 4, and 5.1. At both sites, the Sr/U ratio and the initial 234U/238U activity ratio resemble those of modern spring water. However, the sites differ in the chemical composition of spring water and in stratigraphic sequence of travertine accumulation.

East Asian monsoon climates and Gobi dynamics in marine isotope stages 4 and 3

Several thick last glacial loess sequences in the western part of the Chinese Loess Plateau and an eolian–colluvial sequence in the central Mongolian Plateau are used to understand how the summer and winter monsoons responded to global forcing factors during marine isotope stages (MIS) 4 and 3. The magnetic susceptibility data are compared with other climatic proxy data to improve the well-publicized reconstruction of the past monsoons. This study suggests that different sensitivities between the summer and winter monsoons in responding to the northern insolation resulted in transitional climates between marine isotope stages, which were characterised by cold and wet climates in the western part of Chinese Loess Plateau. After forest–steppe in MIS 5, coniferous forest emerged at the MIS 5/MIS 4 transition in cold and moist conditions. These imply that the lower latitude oceans were still capable of supplying water vapour to the continental interior, and that the Mongolian High became dominant when the northern insolation entered a stadial state (MIS 4). Coniferous forest dominated MIS 4, but thereafter deteriorated to a steppe towards the end of the MIS 4, probably because the lower latitude oceans failed to supply water vapour to the interiors. A coniferous forest emerged again at the MIS 3/MIS 2 transition after forest–steppe in MIS 3. Consequently, the southern boundary of the Gobi Desert retreated northwards during the coniferous tree-dominated periods between 73 and 60 ka and between 27 and 19 ka, and expanded to maxima between 60 and 50 ka and between 19 and 10 ka. The extent of the Gobi Desert was considerably smaller for several times (around 47 ka and 41 ka, and 27+ ka) during MIS 3 than during the Holocene, and the northern boundary retreated 5 times (around 20 ka, 24 ka, 29 ka, 31 ka, and 34 ka) in just the later part of MIS 3.

Chronology of Pleistocene glacial advances in the central Rocky Mountains

The distribution and ages of moraines in the Wyoming-type localities for pre-Pinedale Rocky Mountain glacial deposits are not well known. Through morphostratigraphic mapping, river-terrace longitudinal-profile analysis, and tephrochronology, we place the age of Sacagawea Ridge moraines in the Dinwoody Lakes type area at about 660 ka. Outwash and river terrace deposits in the Bull Lake type area, previously considered to be Sacagawea Ridge, are actually older by one or two glacial cycles. In the Bull Lake type locality, 15 individual moraines are divided into 4 groups on the basis of relative age criteria. Using 36Cl/10Be cosmogenic dating of boulders, the two older groups must be >130 ka; the younger groups are given age ranges of 130 to 100 ka and 120 to 95 ka. A terrace along Wind River can be morphostratigraphically traced to the youngest of these moraine groups; 36Cl dating of boulders on the terrace provides an age range of 125 to 100 ka. The combined relative age and cosmogenic nuclide chronology is consistent with previously published evidence from Yellowstone National Park demonstrating that mountain glaciers advanced not only prior to and during the later portion of marine isotope stage 6 but also during marine isotope stage 5d. In contrast with some other areas of the Rocky Mountains, we found no evidence for advances during marine isotope stage 4. At Bull Lake, Pinedale moraines that have a 36Cl/10Be age range of 23 to 16 ka suggest that glacial advances were limited to the later part of marine isotope stage 2. A river terrace that can be traced to these moraines has an age range of 23 to 16 ka. A possible glacial advance during early marine isotope stage 2 is indicated by a river terrace whose age range is estimated by incision-rate modeling at 46 to 28 ka, but no moraines were identified. Along Wind River, there are eight terrace levels capped with outwash that are older than Sacagawea Ridge; although the terraces are the record of early to middle Pleistocene climatic cycles, there are no correlative moraines preserved at the land surface.