Glacial-interglacial vegetation dynamics in South Eastern Africa coupled to sea surface temperature variations in the Western Indian Ocean

Glacial-interglacial fluctuations in the vegetation of South Africa might elucidate the climate system at the edge of the tropics between the Indian and Atlantic Oceans. However, vegetation records covering a full glacial cycle have only been published from the eastern South Atlantic. We present a pollen record of the marine core MD96-2048 retrieved by the Marion Dufresne from the Indian Ocean similar to 120 km south of the Limpopo River mouth. The sedimentation at the site is slow and continuous. The upper 6 m (spanning the past 342 Ka) have been analysed for pollen and spores at millennial resolution. The terrestrial pollen assemblages indicate that during interglacials, the vegetation of eastern South Africa and southern Mozambique largely consisted of evergreen and deciduous forests. During glacials open mountainous scrubland dominated. Montane forest with Podocarpus extended during humid periods was favoured by strong local insolation. Correlation with the sea surface temperature record of the same core indicates that the extension of mountainous scrubland primarily depends on sea surface temperatures of the Agulhas Current. Our record corroborates terrestrial evidence of the extension of open mountainous scrubland (including fynbos-like species of the high-altitude Grassland biome) for the last glacial as well as for other glacial periods of the past 300 Ka

Contrasting sea-surface responses between the western Mediterranean Sea and eastern subtropical latitudes of the North Atlantic during abrupt climatic events of MIS 3

EuroCLIMATE project RESOLuTIONInternational audienceAbstract Dinoflagellate cyst (dinocyst) analysis was conducted on two cores from the SW Iberian margin and central Alboran Sea from which high quality records of Marine Isotope Stage 3 have been previously derived. Our aim in this study is to compare the dinocyst signature between 50 and 25 ka BP with existing datasets of foraminiferal and geochemical proxies related to hydrological parameters. Quantitative reconstructions of sea-surface temperatures (SSTs) and salinities (SSS) based on dinocysts are performed for the first time in this area. The results are compared to SSTs derived from planktonic foraminifera and alkenone measurements, and to SSS calculated from planktonic δ18O and foraminiferal SST. Significant oscillations related to Dansgaard-Oeschger cycles are recorded in both cores. Dinocyst-derived hydrological parameters exhibit synchronous fluctuations and similar values to those derived from the other methods, in particular when considering quantitative reconstructions for February based on foraminifera and dinocysts. Our study shows that the influence of subpolar waters was felt during each Greenland Stadial (GS) off Portugal, and that the amplification of the Heinrich Stadial cooling in the Alboran Sea was related to the penetration of subpolar waters through the Strait of Gibraltar. During Greenland Interstadials (GI), we provide evidence for the occurrence of warm and nutrient-rich sea-surface waters in the Alboran Sea, probably due to gyre-induced upwelling. Finally, the difference between August and February dinocyst SST estimates suggests higher seasonal contrasts during GS compared to GI at the two core sites. Additionally, precession appears to have an imprint on dinocyst-derived long-term seasonality record. However, this observation needs to be confirmed by longer records. Research Highlights ► We provide new dinocyst data on core MD95-2043 (Alboran Sea) during MIS 3. ► Quantitative dinocyst sea-surface parameters (SST, SSS) are reconstructed. ► A multi-proxies compilation (microfossils, alkenones, isotopes) is established. ► This dataset has been compared with the one of a SW Iberian margin core. ► Millennial-scale climatic variability is perfectly apparent from each side of Gibraltar

CH4 and δ18O of O2 records from Antarctic and Greenland ice: A clue for stratigraphic disturbance in the bottom part of the Greenland Ice Core Project and the Greenland Ice Sheet Project 2 ice cores

The suggestion of climatic instability during the last interglacial period (Eem), based on the bottom 10% of the Greenland Ice core Project (GRIP) isotopic profile, has been questioned because the bottom record from the neighboring Greenland Ice Sheet Project 2 (GISP2) core (28 km away) is strikingly different over the same interval and because records of the δ18O of atmospheric O2 from both cores showed unexpected rapid fluctuations. Here we present detailed methane records from the Vostok (Antarctica), GRIP, and GISP2 cores over the relevant intervals. The GRIP and GISP2 data show rapid and large changes in methane concentration, which are correlative with variations of the δ18O of the ice, while the Vostok record shows no such variations. This discrepancy reinforces the suggestion that the bottom sections of the Greenland records are disturbed. By combining the methane data with measurements of δ18O of O2 in the same samples, we attempt to constrain the nature of the stratigraphic disturbance and the age of the analyzed ice samples. Our results suggest that ice layers from part of the last interglacial period exist in the lower section of both ice cores and that some of the apparent climate instabilities in the GRIP core would be the result of a mixture of ice from the last interglacial with ice from the beginning of the last glaciation or from the penultimate glaciation. Copyright 1997 by the American Geophysical Union

Factors controlling frequency of turbidites in the Bengal fan during the last 248 kyr cal BP: Clues from a presently inactive channel

International audienc

Increasing vegetation and climate gradient in Western Europe over the Last Glacial Inception (122-110 ka): data-model comparison

High-resolution terrestrial (pollen) and marine (planktic and benthic isotopes, coarse fraction, and N. pachyderma (s)) analyses have been performed in the Marine Isotope Stage (MIS) 5 interval of IMAGES core MD99-2331 retrieved in the northwestern Iberian margin. This study shows the occurrence of a Zeifen Interstadial/Stadial succession on land and in the ocean during the first part of MIS 5e. In northwestern Iberia, the Eemian is marked from 126 to 122 ka by the development of deciduous Quercus forest at the same time as Mediterranean forest colonised southern Iberia, and deciduous Quercus-Corylus forest occupied northernmost European regions. From 121 to 115 ka Carpinus betulus forest developed in NW Iberia indicating a winter cooling by 2degreesC on land and an increase in annual precipitation by 100-200 min along with a Sea Surface Temperature (SST) decreasing trend off Iberia. A similar cooling has been documented at the same time in northern Germany (52degreesN) by the replacement of deciduous forest by coniferous (Abies-Picea) formations, implying a southward displacement of the deciduous tree line between similar to60degreesN and 50degreesN as early as 120 ka. The southward migration of the tree line between 72degreesN and 58degreesN simulated by the Earth Model of Intermediate Complexity MoBidiC from 122 and 120 ka and considered as a major process to initiate the last glaciation is, therefore, compatible with data. Between 115 and 110 ka, the substantial ice accumulation in northern high latitudes (MIS 5e/5d transition) was synchronous with successive drops, C26 and C25, in northeastern Atlantic SST. In northwestern Iberia Abies-Pinus trees developed at the expense of Quercus-Carpinus forest. A tundra-like environment occupied northern Germany, marking the end of the interglacial in northwestern Europe at 115 ka, and boreal forest likely colonised northeastern France. The first displacement of the vegetation belts at 121 ka was enhanced at 115 ka indicating an amplification of the vegetation and climate gradients in northeastern Atlantic and European borderlands probably related with the well-developed ice caps at that time. The comparison between the general trend in the estimated and simulated MoBidiC winter and summer temperatures for latitudes between 35 and 45degreesN, shows that both follow quite straightforwardly the precession signal although the simulated and reconstructed temperatures agree better in the South than North of 40degreesN. Annual precipitation is exhibiting opposite trend in the data and in the model. This contradiction is likely the fact that the zonal climate simulated by the model may not accurately represent the regional climate features, as reconstructed from the pollen. (C) 2004 Elsevier B.V All rights reserved

Factors controlling frequency of turbidites in the Bengal fan during the last 248 kyr cal BP: Clues from a presently inactive channel

International audienc

Is vegetation responsible for glacial insolation inception during periods of muted changes?

The Marine Isotope Stage 11 interglacial, centred at similar to 400 ka, appears to be the best candidate for understanding climatic changes in the context of low insolation forcing such as that of our present interglacial. Direct correlation between terrestrial (pollen) and marine climatic indicators and ice volume proxy from deep-sea core MD01-2447 (off northwestern Iberia) shows for the first time the phase relationship between southwestern European vegetation, sea surface temperatures in the northeastern Atlantic mid-latitudes and ice volume during MIS 11. A warmest 32,000 years-long period and three following warm/cold cycles occurred synchronously on land and ocean. The end of the warmest period sees the glacial inception which coincides with the replacement of warm deciduous forest by conifer (pine-fir) expansion in northwestern Iberia and, consequently, with the southward migration of the tree line in high latitudes in response to declining summer insolation. As weak insolation changes alone cannot account for ice growth, the associated vegetation changes must now be considered as a potential major feedback mechanism for glaciation initiation during MIS 11. (c) 2005 Elsevier Ltd. All rights reserved

The Bengal fan: external controls on the Holocene Active Channel turbidite activity

International audienceThe eastern levee of the Active Channel in the Bengal fan has been investigated in order to better understand the history of turbidite activity in this channel during the Holocene in the context of Ganges-Brahmaputra source-to-sink' system. A robust C-14-based chronostratigraphy provides high temporal resolution for reconstructing sediment accumulation history on the eastern levee of the Active Channel. Integration of this study with previous work in the area suggests that the Bengal fan has remained continually connected with the Ganges-Brahmaputra fluvial system through the Holocene, feeding through the main canyon, the Swatch of No Ground (SoNG). An intense turbidite activity occurred during a transgressive wet period from 14.5 to 9.2 ka cal. BP, followed by an abrupt shift in sedimentation at 9.2 ka cal. BP, probably due to the high sea level leading to a partial disconnection between massive river discharges and the deep turbidite system. During the last 9.2 ka cal. BP, turbidite activity is still present but irregular, likely modulated by a combination of various forcings such as monsoon variability and river migration. In total, three phases are distinguishable during this period: 9.2-5.5, 5.5-4, and 4 ka cal. BP to modern, according to the turbidite record. Unexpectedly, the Indo-Asian monsoon does not appear to be the only predominant forcing on the establishment of the Bengal fan during the Holocene because of the combination of different forcings directly affecting transfers between the Ganges-Brahmaputra and the Bengal fan as well as river migrations, delta construction, and potentially anthropogenic impact

A tentative reconstruction of the last interglacial and glacial inception in Greenland based on new gas measurements in the Greenland Ice Core Project (GRIP) ice core

The disturbed stratigraphy of the ice in the lowest 10% of the Greenland GRIP ice core prevents direct access to climatic information older than 110 kyr. This is especially regretful since this period covers the previous interglacial corresponding to marine isotopic stage 5e (MIS 5e, 130-120 kyr B.P.). Here we present a tentative reconstruction of the disturbed GRIP chronology based on the succession of globally well mixed gas parameters. The GRIP δ18Oice chronological sequence is obtained by comparing a new set of δ18O of atmospheric O2 and CH4 measurements from the bottom section of the GRIP core with their counterpart in the Vostok Antarctic profiles. This comparison clearly identifies ice from the penultimate glacial maximum (MIS 6, 190-130 kyr B.P.) in the GRIP core. Further it allows rough reconstruction of the last interglacial period and of the last glacial inception in Greenland which appears to lay its Antarctic counterpart. Our data suggest that while Antarctica is already entering into a glaciation, Greenland is still experiencing a warm maximum during MIS 5e. © 2003 by the American Geophysical Union