M.F. Sánchez Goñi

High resolution palynological record off the Iberian margin: direct land-sea correlation for the Last Interglacial complex

Abstract We present high resolution pollen, dinocyst and isotopic data for the Last Interglacial complex from marine core MD952042 (southwestern margin of the Iberian Peninsula; 37°48′N; 10°10′W; 3148 m). Direct land-sea correlation from this core indicates that during this period, North Atlantic sea surface temperatures were in phase with Iberian climate. Our palynological analysis suggests a Younger Dryas-like event at the Marine Isotope Stage (MIS)-6/5 transition. The analysis also indicates that the Eemian spans from the lightest isotopic values of MIS-5e (ca. 126 ky BP) to the heavier isotopic values towards the MIS-5e/5d transition. Therefore, the Eemian is not entirely equivalent to MIS-5e. Pollen analysis identifies four climatic phases of low amplitude during the Eemian. A Mediterranean climate in southwestern Europe is gradually replaced by oceanic conditions. The middle of the Eemian is characterized by an increase in precipitation on the land and ocean, associated with a slight cooling. This seems to be the result of a displacement of the Polar Front as far south as southern Europe during this period. After the Eemian, three relatively short climatic phases on land (Melisey I, St. Germain Ia and Montaigu cold event) occurred contemporaneously with three shifts of sea surface temperatures. The Montaigu event, first identified in terrestrial pollen sequences, is, therefore, also recorded in core MD952042 on the basis of pollen, dinocyst and planktonic isotopic data. Our results also show that the warm periods of MIS-5 are not characterized by similar climatic conditions on land.

Holocene biomass burning and global dynamics of the carbon cycle

Fire regimes have changed during the Holocene due to changes in climate, vegetation, and in human practices. Here, we hypothesise that changes in fire regime may have affected the global CO2 concentration in the atmosphere through the Holocene. Our data are based on quantitative reconstructions of biomass burning deduced from stratified charcoal records from Europe, and South-, Central- and North America, and Oceania to test the fire-carbon release hypothesis. In Europe the significant increase of fire activity is dated approximately 6000 cal. yr ago. In north-eastern North America burning activity was greatest before 7500 years ago, very low between 7500-3000 years, and has been increasing since 3000 years ago. In tropical America, the pattern is more complex and apparently latitudinally zonal. Maximum burning occurred in the southern Amazon basin and in Central America during the middle Holocene, and during the last 2000 years in the northern Amazon basin. In Oceania, biomass burning has decreased since a maximum 5000 years ago. Biomass burning has broadly increased in the Northern and Southern hemispheres throughout the second half of the Holocene associated with changes in climate and human practices. Global fire indices parallel the increase of atmospheric CO2 concentration recorded in Antarctic ice cores. Future issues on carbon dynamics relatively to biomass burning are discussed to improve the quantitative reconstructions.

25. Climate variability of the last five isotopic interglacials: Direct land-sea-ice correlation from the multiproxy analysis of North-Western Iberian margin deep-sea cores

Abstract The last five isotopic interglacials (marine isotope stages 11, 9, 7, 5 and 1) were investigated in Iberian margin deep-sea cores, using terrestrial (pollen) and marine (planktic foraminifera assemblages, benthic and planktic oxygen isotopes) climatic indicators. This work shows that the climatic variability detected on the continent is contemporaneously recorded in the ocean, but temperature changes are not in phase with ice volume variations. The comparison of the different marine isotope stages highlights a common pattern within these stages. They are characterized by three major climatic cycles, related to orbital cyclicity, on which suborbital climatic fluctuations are superimposed. Particularly, suborbital events interrupt the deglacial warming associated with Terminations IV to I and the second major warm period of each isotopic interglacial as well as the transitions towards glacial marine isotope stages. MIS 7 displays a short first warm period (8kyr) followed by a striking cold and dry period succeeded by a new strong warmth. In contrast, MIS 11 presents the longest period (31kyr) of the last 450000 years.

Holocene environmental changes in the Gallocanta lacustrine basin, Iberian Range, NE Spain

The sedimentological and palynological study of the Gallocanta lake sediments, in the NE of Spain, has allowed the Holocene environmental evolution of this lacustrine basin to be established, and several changes in the hydrological balance to be interpreted. The chronology of the sequence is based on new radiocarbon datings and 210Pb radiometric techniques. Ten facies have been characterized, which have been grouped into five sedimentary units: two (Units A and B) are interpreted as deposited in alluvial areas, and three (Units C, D and E) in lacustrine environments. Moreover five pollen zones have been established for this succession. From the stratigraphic correlation of the cores extracted in this lake, three stages in the basin evolution have been interpreted. Stage 1 was characterized by a broad development of alluvial fans during the Fullglacial or Lateglacial times. The sediments of this stage are lacking in pollen as they were exposed for most of the time. Stage 2 started around 10 100 yr BP and is characterized by the establishment of a brackish lake linked to a decrease in alluvial supplies and a more positive water balance. The maximum lake level would have been reached around 8010 yr BP coinciding with the relatively moist period of the beginning of the Holocene recorded in some Spanish lakes, although this dating would not match that of other areas of the Iberian Peninsula, in which the maximum lake levels have been recorded around 6000 yr BP. A sharp decrease in the lacustrine level has been registered at 3405 yr BP, which may be correlated to a change to more arid conditions. Nevertheless, the lake level recovered later. Stage 3 was linked to the development of an ephemeral shallow lake. An age of AD 1840 yr has been calculated for this palaeogeographical change. The data obtained suggest that the main vegetation changes during stage 2 were more related to climate variability, whereas during stage 3 the anthropogenic impact became more significant.