Age determination, carbon geochemistry and palynology of section AC003

Sedimentary records from California's Northern Channel Islands and the adjacent Santa Barbara Basin (SBB) indicate intense regional biomass burning (wildfire) at the Ållerød-Younger Dryas boundary (~13.0-12.9 ka) (All age ranges in this paper are expressed in thousands of calendar years before present [ka]. Radiocarbon ages will be identified and clearly marked "14C years".). Multiproxy records in SBB Ocean Drilling Project (ODP) Site 893 indicate that these wildfires coincided with the onset of regional cooling and an abrupt vegetational shift from closed montane forest to more open habitats. Abrupt ecosystem disruption is evident on the Northern Channel Islands at the Ållerød-Younger Dryas boundary with the onset of biomass burning and resulting mass sediment wasting of the landscape. These wildfires coincide with the extinction of Mammuthus exilis [pygmy mammoth]. The earliest evidence for human presence on these islands at 13.1-12.9 ka (~11,000-10,900 14C years) is followed by an apparent 600-800 year gap in the archaeological record, which is followed by indications of a larger-scale colonization after 12.2 ka. Although a number of processes could have contributed to a post 18 ka decline in M. exilis populations (e.g., reduction of habitat due to sea-level rise and human exploitation of limited insular populations), we argue that the ultimate demise of M. exilis was more likely a result of continental scale ecosystem disruption that registered across North America at the onset of the Younger Dryas cooling episode, contemporaneous with the extinction of other megafaunal taxa. Evidence for ecosystem disruption at 13-12.9 ka on these offshore islands is consistent with the Younger Dryas boundary cosmic impact hypothesis [Firestone et al., 2007, doi:10.1073/pnas.0706977104].

Age determination and sedimentology of sediment core Lz1101 from the Melles Lake

A lacustrine sediment core from Store Koldewey, northeast Greenland, was biogeochemically, biologically and sedimentologically investigated in order to reconstruct long- and short-term climatic and environmental variability. The chronology of the uppermost 189 cm of the record is based on ten 14C AMS age determinations of aquatic mosses. The record covers almost the entire Holocene and revealed changes on multidecadal to centennial scales. Dating of the oldest mosses shows that lacustrine biogenic productivity already began at around 11 cal. kyr BP. This age pre-dates the onset of biogenic productivity in other lakes on Store Koldewey by about 2 kyr. In spite of the early onset of biogenic production organic matter accumulation remained low and minerogenic sedimentation dominated. At about 9.5 cal. kyr BP moss, sulphur, organic carbon and biogenic silica content started to increase, indicating that the environment stabilized and the biogenic production in the lake adjusted to more preferable conditions. Subsequently, the biogenic productivity experienced repeated changes and varied both on long- and short-term scales. The long-term trend shows a maximum during the early Holocene thus responding to increased temperatures during the Holocene Thermal Maximum. Superimposed on the long-term trend, biogenic productivity also experienced repeated short-term fluctuations that match partly the NGRIP temperatures. The most pronounced decrease of biogenic productivity occurred at around 8.2 cal. kyr BP. Perennial lake ice coverage resulting from low temperatures is supposed to have caused decreased lacustrine biogenic productivity. From the middle Holocene to the present repeated decreases of productivity occurred that could be related to periods with severe sea-ice conditions of the East Greenland Current. Besides the dependence on air temperature it therefore demonstrates the sensitivity of lacustrine biogenic productivity in coastal high arctic areas to short-term cold spells that are mediated by the currents emanating from the Arctic Ocean. However, the data also emphasize the difficulties associated with the interpretation of lacustrine records.

Age determination of sediment cores from the continental shelf and slope off North-West Africa

Three sediment cores from the continental shelf and slope off NW Africa (Banc d'Arguin; 52 m, 665 m and 973 m water depth) have been investigated by means of a coarse fraction analysis. The two shallower cores have been deposited during less than 10,000 years, the deeper one during the last 36,000 years. The Holocene sedimentation ( 4000 years) in the deeper part of core 79 the edge of the Banc d'Arguin is strongly influenced by reworking of Late Glacial dune sands and biogenic particles from shallower ware (<40 m), as well as eroding current influence. A decrease in grain size of silicate material and a decrease in lateral supply, correlated to a doubling of accumulation rates in the upper part of the core, indicates a more autochthonous sedimentation with less sorting influence in the youngest Holocene. The depth of provenance of the allochttonous material can be assumed in 100-300 m water depth as indicated by various biogenous particles. Small amounts of shallow water particles in the autochthonous layers indicate a supplay from shallow water, which probably occured b ythe mechanism of "particle by particle supply". None of the three cores indicates upwelling influence, although occanographers found intense upwelling in the area of the Banc d'Arguin. The Holocene climate in that area probably has been arid, small variations in terrigenous matter composition and grain size in the Early Holocene might be due to decreased wind strength or to an increase in rain fall. The Peak Glacial section (14,000-22,000 y. B.P.) of the deepest core 88 indicates a very much intensified eolian silt supply and an additional bottom supply of quartz sand In the interval 22,000-36,000 y. B.P. wind strength decreased, but probably no increase in humidity occurred. So this area in about 19° 40' N had an arid climate in the Late Holocene and in the Peak Glacial. The fragmentation of planktonic foraminifers and the abundance of aragonitic tests of pteropods in core 88 indicate an Early Holocene (8330 y. B.P.) preservation spike. Two minima in fragmentation correlated to maxima in pteropod content at about 15,700 and 21,000 y. B.P. are correlated to maxima in shallow water supply and thus do not reflect preservation conditions, but only lateral supply from the carbonate dissolution minimum zone in about 300 m water depth.

Age determination and radiometric dates of cores from Okarito Pakihi in Australia

In agreement with the Milankovitch orbital forcing hypothesis (Imbrie et al., 1993) it is often assumed that glacial-interglacial climate transitions occurred synchronously in the Northern and Southern hemispheres of the Earth. It is difficult to test this assumption, because of the paucity of long, continuous climate records from the Southern Hemisphere that have not been dated by tuning them to the presumed Northern Hemisphere signals (Lynch-Stieglitz, 2004). Here we present an independently dated terrestrial pollen record from a peat bog on South Island, New Zealand, to investigate global and local factors in Southern Hemisphere climate changes during the last two glacial-interglacial cycles. Our record largely corroborates the Milankovitch model of orbital forcing but also exhibits some differences: in particular, an earlier onset and longer duration of the Last Glacial Maximum. Our results suggest that Southern Hemisphere insolation may have been responsible for these differences in timing. Our findings question the validity of applying orbital tuning to Southern Hemisphere records and suggest an alternative mechanism to the bipolar seesaw for generating interhemispheric asynchrony in climate change.

Pollen record and age determination of a sediment core from the Kara Sea

AMS-14C dated sediment cores from the Ob and Yenisei estuaries and the adjacent inner Kara Sea were investigated to determine the siliclastic and organic carbon fluxes and their relationship to paleoenvironmental changes. The variability of sediment fluxes during Holocene times is related to the post-glacial sea-level rise and changes in river discharge and coastal erosion input. Whereas during the late/middle Holocene most of the terrigenous sediments were deposited in the estuaries and the areas directly off the estuaries, huge amounts of sediments accumulated on the Kara Sea shelf farther north during the early Holocene before about 9 Cal. kyrs. BP. The maximum accumulation at that time is related to the lowered sea level, increased coastal erosion, and increased river discharge due to the final stage of mountain deglaciation of the Putoran Massif. Increased supply of Yenisei-derived material indicated by peak magnetic susceptibility values probably occurred in climate-related pulses culminating near 11, 10, and 9 Cal. kyrs. BP. As sea level rose, the main Holocene depocenter migrated southward. Based on hydrogen index values and n-alkanes, the organic matter is predominantly of terrigenous origin. Maximum accumulation rates of 1.5 to more than 6 g/cm2/y occurred in the early Holocene sediments, suggesting more humid climatic conditions with an increased vegetation cover in the source area at that time. In general, high organic carbon accumulation rates characterize the estuaries and the inner Kara Sea as important sink for terrigenous organic carbon. A high-resolution record of Holocene variability of magnetic susceptibility (MS) in an AMS14C-dated sediment core from the northern Yenisei estuary may indicate natural variability of Arctic climate change and river discharge on a centennial to millenial time scale. Short-term maxima in MS probably related to warmer climate, enhanced precipitation, intensified weathering/erosion and increased river discharge, display a frequency of about 300 to 700 years.

Age determination and stable carbon isotope ratios of Cassidulina laevigata of sediment core Svanic90_9004

A well-dated high-resolution d13C record of the last 2400 a, based on the benthic foraminifera Cassidulina laevigata, is presented for Gullmar Fjord, Sweden. The time interval covers die Roman Warm Period (RWP), the Viking Age/Medieval Warm Period (VA/MWP), the little Ice Age (LIA) and the most recent warming. There is little variation in the d13C record until the early Viking Age (AD 800), when the d13C signal becomes significantly more negative and continues to decrease throughout the VA/MWP, The d13C signal increases both at the beginning and at the end of the LIA but is marked by more negative values during the larger part of the period. Since about 1970, the d13C values are more negative than the long-term average. This general negativity of the record may result from a higher flux of organic matter, possibly of terrestrial origin due to land-use changes together with moderate changes in stagnation periods since the VA/MWP. In most recent times, the oceanic Suess effect together with increased number of extended stagnation periods are probably the main causes of the shift towards more negative d13C values.

Chemical composition, age, and magnetic parameters of igneous rocks from the Franz Josef Land

A combined study of magnetic parameters of basalt and andesite samples has been carried out in the framework of geological investigations of the Franz Josef Land. This study has included determination of coercivity, saturation magnetization, Curie points, natural remanent magnetization (NRM), and magnetic susceptibility as well as examination of ferromagnetic minerals with a microscope. Data on chemical composition of the rocks have been obtained for all the samples, and radiological ages have been determined for the majority of the rocks. Thermomagnetic curves of the samples have been subdivided into four types depending on composition of ferromagnetic NRM carriers. Data showing multiple changes in the predominant composition of the igneous rocks have been obtained. Each stage of magmatism is characterized by a specific type of the ferromagnetic component in the rocks and, therefore, magnetomineralogical investigations can be used for differentiation and correlation of the igneous rocks.