Pollen profile of sediment core Dethlingen, Germany

To better understand the environmental variability during the Holsteinian interglacial, we have palynologically analyzed a new core from Dethlingen, northern Germany, at a decadal resolution. Our data provide insights into the vegetation dynamics and thus also climate variability during the meso- to telocratic forest phases of the interglacial. Temperate mixed forests dominated the regional landscape throughout the Holsteinian. However, changes in the forest composition during the younger stages of the interglacial suggest a climatic transition towards milder conditions in winter. The strong presence of boreal floral elements during the older stages of the Holsteinian interglacial suggests a high seasonality. In contrast, during the younger stages the development of sub-Atlantic and Atlantic floral elements suggests increasingly warm and humid climatic conditions. Peak warming during the younger stage of the Holsteinian is marked by the maximum pollen abundances of Buxus, Abies, and Quercus. Although the vegetation dynamics suggest a general warming trend throughout the Holsteinian interglacial, abrupt as well as gradual changes in the relative abundances of temperate plants indicate considerable climatic variability. In particular, two marked declines in temperate taxa leading to the transient development of boreal and sub-temperate forests indicate short-term climatic oscillations that occurred within full interglacial conditions. The palynological signatures of these two regressive phases in vegetation development differ with regard to the expansion of pioneer trees, the abundances and rates of change of temperate taxa, and the presence of frost-sensitive taxa. These differences point to different mechanisms responsible for the individual regressive phases. Assuming a correlation of the interglacial at Dethlingen with Marine Isotope Stage (MIS) 11, our data suggest that temperate forests prevailed in northern Germany during the younger parts of MIS 11c.

87Sr/86Sr ratios of middle Miocene to Pleistocene planktonic foraminifers from ODP Site 117-722 (Table 3)

Continuous magnetostratigraphy and biostratigraphy made it possible to construct a detailed late Neogene record of 87Sr/86Sr isotopic ratios of ocean water, as measured in the tests of planktonic foraminifers. Sediments recovered during Leg 117, in the western Arabian Sea, provide a continuous, high resolution sedimentary record from the early Miocene to present. The late Miocene to Recent is marked by rapidly increasing 87Sr/86Sr ratios in seawater, which results in a chronostratigraphical resolution varying from 0.2 Ma to 1.5 Ma. The 87Sr/86Sr seawater curve has a stepwise character similar to the one determined by DePaolo on Site 590B, in the Tasman Sea, and to the one determined by McKenzie on Site 653A, in the Mediterranean, confirming its use as a chronostratigraphic tool for this time span. Periods of rapid increase in the 87Sr/86Sr isotopic ratio of seawater are correlated with important changes in tectonic and climatic conditions. Experiments showed that bulk carbonate sediment samples have differing 87Sr/86Sr ratios from those of planktonic and benthic foraminifers from the same depth.

Pliocene-Pleistocene stable isotope record of ODP Site 107-653

Planktonic foraminiferal oxygen and carbon isotope analyses from Tyrrhenian Sea Ocean Drilling Program (ODP) Site 653 provide a continuous record of the Pliocene-Pleistocene paleoceanographic history of the Mediterranean. Long-term trends in oxygen isotopes primarily reflect changes in global climatic conditions, with a more local or regional signal superimposed on this record. For example, significant enrichments in 18O due to decreases in surface water temperature and/or increases in continental ice volume occurred at 3.1, 2.7, 2.1, 1.6, and 0.4 Ma. In contrast to most open-ocean results, the early Pliocene 6lsO record of Site 653 exhibits high-amplitude fluctuations indicative of very unstable climatic conditions in this region. Another unique aspect of this Mediterranean d18Orecord is the pronounced cooling at the Pliocene/Pleistocene boundary. The carbon isotope record for Site 653 also exhibits high-amplitude variability throughout the Pliocene-Pleistocene. This variability most probably reflects changes in the carbon isotopic composition of the source of Mediterranean surface waters.

Beryllium-10, mineralogy and grain size distribution of DSDP Hole 68-502B (Table 1)

We present a high-resolution 10Be profile from deep sea sediments (sampled from Hole 502B in the Caribbean sea) that strongly resembles the 10Be record in ice core profiles, particularly the Vostok core from Antarctica. This high-resolution profile revealed occurrences of enhanced 10Be concentrations at about 23-24, 37-39 and 60-65 ka. The excellent match between these peaks appearing in a georeservoir profile other than in polar ice, strengthens the implications that can be inferred from 10Be and provide global markers for chronological correlation of climatic events. The position at low latitude of the studied sediment section is, unlike the case with the high latitude polar regions, excellent for exposing causes of modulation in 10Be production. We interpret the source of the pattern and enhancements, particularly the 37-39 ka peak, of 10Be to be global and do not strictly relate to climatic conditions and/or production rates specific to the polar regions.

(Fig. 9) Pollen analysis of sediment core GIK16017-2

The improved understanding of the pollen signal in the marine sediments offshore of northwest Africa is applied to deep-sea core M 16017-2 at 21°N. Downcore fluctuations in the percentage, concentration and influx diagrams record latitudinal shifts of the main northwest African vegetation zones and characteristics of the trade winds and the African Easterly Jet. Time control is provided by 14C ages and 180 records. During the period 19,000-14,000 yr B.P. a compressed savanna belt extended between about 12 ° and 14-15°N. The Sahara had maximally expanded northward and southward under hyperarid climatic conditions. The belt with trade winds and dominant African Easterly Jet transport had not shifted latitudinally. The trade winds were strong as compared to the modern situation but around 13,000 yr B.P. the trade winds weakened. After 14,000 yr B.P. the climate became less arid south of the Sahara and a first spike of fluvial runoff is registered around 13,000 yr B.P. Fluvial runoff increased strongly around 11,000 yr B.P. and maximum runoff is recorded from about 9000-7800 yr B.P. Around 12,500 yr B.P. the savanna belt started to shift northward and became richer in woody species: it shifted about 6° of latitude, reached its northernmost position during the period of 9200-7800 yr B.P. and extended between about 16° and 24°N at that time. Tropical forest had reached its maximum expansion and the Guinea zone reached as far north as about 15°N, reflecting very humid climatic conditions south of the Sahara. North of the Sahara the climate also became more humid and Mediterranean vegetation developed rapidly. The Sahara had maximally contracted and the trade winds were weak and comparable with the present day intensity. After about 7800 yr B.P. the southern fringe of the Sahara and accordingly the savanna belt, shifted rapidly southward again.

Miocene microflora and palaeoclimate reconstructions from three sites in Bulgaria

In this study we reconstruct quantitatively the Middle to Upper Miocene climate evolution in the southern Forecarpathian Basin (Central Paratethys area, Northwest Bulgaria) by applying the coexistence approach to 101 well-dated palynofloras isolated from three cores. The climatic evolution is compared with changes in vegetation and palaeogeography. The Middle Miocene was a period of a subtropical/warm-temperate humid climate with mean annual temperature (MAT) between 16 and 18°C and mean annual precipitation (MAP) between 1100 and 1300 mm. Thereby, during the entire Middle Miocene a trend of slightly decreasing temperatures is observed and only small climate fluctuations occur which are presumably related to palaeogeographic reorganisations. The vegetation shows a corresponding trend with a decrease in abundance of palaeotropic and thermophilous elements. The Upper Miocene is characterised by more diverse climatic conditions, probably depending on palaeogeographic and global climatic transformations. The beginning of this period is marked by a slight cooling and a significant drying of the climate, with MAT 13.3-17°C and MAP 652-759 mm. After that, fluctuations of all palaeoclimate parameters occur displaying cycles of humid/dryer and warmer/cooler conditions, which are again well reflected in the vegetation. Our study provides a first quantitative model of the Middle-Upper Miocene palaeoclimate evolution in Southeastern Europe and is characterised by a relatively high precision and resolution with respect to the climate data and stratigraphy.

Paleoclimate reconstruction from Miocene macroflora in Kazakhstan compiled from various publications

25 datasets (13 fossil leaf and pollen assemblages, 12 quantitative palaeoclimatic datasets) are provided in order to analyse Early Miocene palaeoclimate in Kazakhstan. The rich fossil record in Kazakhstan documents that during the Oligocene and Early Miocene this area in Central Eurasia was densely forested with warm-temperate deciduous trees and shrubs of the so-called "Turgayan flora". 29 fossil floras from 13 localities have been selected for a quantitative analysis of the Aquitanian (early Early Miocene) climate situation in Kazakhstan. The assessed mean annual temperatures generally place around 15 °C, while values of mean annual precipitation are of about 1000 mm. In combination with several other climate parameters estimated (temperatures of warmest and coldest months, precipitation rates of wettest, driest and warmest months), these data reflect uniform climatic conditions over several thousands of square kilometres. Data of temperature parameters show slight spatial differentiations, with generally cooler mean annual temperatures and higher seasonality (i.e. warmer summers and colder winters) in the north-eastern part of the study area compared with the south-western area around Lake Aral. As compared with palaeoclimate estimates for the European and East Asian Aquitanian, the central part of the Eurasian continent reveals evident signals of higher seasonality and slightly increased continentality.

Neodymium and Strontium chemistry of Arctic Ocean sediments

The early oceanographic history of the Arctic Ocean is important in regulating, and responding to, climatic changes. However, constraints on its oceanographic history preceding the Quaternary (the past 1.8 Myr) have become available only recently, because of the difficulties associated with obtaining continuous sediment records in such a hostile setting. Here, we use the neodymium isotope compositions of two sediment cores recovered near the North Pole to reconstruct over the past ~5 Myr the sources contributing to Arctic Intermediate Water, a water mass found today at depths of 200 to 1,500 m. We interpret high neodymium ratios for the period between 15 and 2 Myr ago, and for the glacial periods thereafter, as indicative of weathering input from the Siberian Putoranan basalts into the Arctic Ocean. Arctic Intermediate Water was then derived from brine formation in the Eurasian shelf regions, with only a limited contribution of intermediate water from the North Atlantic. In contrast, the modern circulation pattern, with relatively high contributions of North Atlantic Intermediate Water and negligible input from brine formation, exhibits low neodymium isotope ratios and is typical for the interglacial periods of the past 2 Myr. We suggest that changes in climatic conditions and the tectonic setting were responsible for switches between these two modes.

Geochemical analysis of two sediment cores from the southern Mendeleev Ridge

We present results of an inorganic geochemical pore water and sediment study conducted on Quaternary sediments from the western Arctic Ocean. The sediment cores were recovered in 2008 from the southern Mendeleev Ridge during RV Polarstern Expedition ARK-XXIII/3. With respect to sediment sources and depositional processes, peaks in Ca/Al, Mg/Al, Sr/Al and Sr/Mg indicate enhanced input of both ice-rafted (mainly dolomite) and biogenic carbonate during deglacial warming phases. Distinct and repetitive brown layers enriched in Mn (oxyhydr)oxides occur mostly in association with these carbonate-rich intervals. For the first time, we show that the brown layers are also consistently enriched in scavenged trace metals Co, Cu, Mo and Ni. The bioturbation patterns of the brown layers, specifically well-defined brown burrows into the underlying sediments, support formation close to the sediment-water interface. The Mn and trace metal enrichments were probably initiated under warmer climate conditions. Both river runoff and melting sea ice delivered trace metals to the Arctic Ocean, but also enhanced seasonal productivity and organic matter export to the sea floor. As Mn (oxyhydr)oxides and scavenged trace metals were deposited at the sea floor, a co-occurring organic matter "pulse" triggered intense diagenetic Mn cycling at the sediment-water interface. These processes resulted in the formation of Mn and trace metal enrichments, but almost complete organic matter degradation. As warmer conditions ceased, reduced riverine runoff and/or a solid sea ice cover terminated the input of riverine trace metal and fresh organic matter, and greyish-yellowish sediments poor in Mn and trace metals were deposited. Oxygen depletion of Arctic bottom waters as potential cause for the lack of Mn enrichments during glacial intervals is highly improbable. While the original composition and texture of the brown layers resulted from specific climatic conditions (including transient Mn redox cycling at the sediment-water interface), pore water data show that early diagenetic Mn redistribution is still affecting the organic-poor sediments in several meters depth. Given persistent steady state diagenetic conditions, purely authigenic Mn-rich brown layers may form, while others may completely vanish. The degree of diagenetic Mn redistribution largely depends on the depositional environment within the Arctic Ocean, the availability of Mn and organic matter, and seems to be recorded by the Co/Mo ratios of single Mn-rich layers. We conclude that brown Arctic sediment layers are not necessarily synchronous features, and correlating them across different parts of the Arctic Ocean without additional age control is not recommended.

Sedimentology on two cores from Scoresby Sund, Greenland

Reconstruction of the postglacial palaeoenvironmental evolution was the main objective of marine geological investigations in the Scorcsby Sund fjord system. For this purpose, samples of marine sediments, taken on RV Polarstern cruises ARK-V/3b and ARK-VII/3b in 1988 and 1990, have been analysed. All investigated fjord sediments are paratills. However, remarkable changes in sediment fabric and composition occur with depth in cores. They are attributable to different modes of sediment deposition. Therefore, a subdivision of the postglacial palaeoenvironmental history into periods of considerably different sedimentary conditions is feasible. The change of sedimentary fades with time is interpreted by deposition under changing climatic conditions during the postglacial. Displacements of cyclonic and anticyclonic centers in the atmosphere change amount of precipitation at the east coast of Greenland. Precipitation strongly influences extension of local ice caps of coastal areas and duration of coverage of the fjords by sea ice. These factors again control the sedimentary regime in the fjord system.

FTIR-inferred biogeochemical properties for the past 3.6 Myr in the sediment record of core ICDP5011-1 in Lake Elgygytgyn, NE Russia

A number of studies have shown that Fourier transform infrared spectroscopy (FTIR) can be applied to quantitatively assess lacustrine sediment constituents. In this study, we developed calibration models based on FTIR for the quantitative determination of biogenic silica (BSi; n = 420; gradient: 0.9-56.5%), total organic carbon (TOC; n = 309; gradient: 0-2.9%), and total inorganic carbon (TIC; n= 152; gradient: 0-0.4%) in a 318 m-long sediment record with a basal age of 3.6 million years from Lake El'gygytgyn, Far East Russian Arctic. The developed partial least squares (PLS) regression models yield high cross-validated (CV) R2CV = 0.86-0.91 and low root mean square error of cross-validation (RMSECV) (3.1-7.0% of the gradient for the different properties). By applying these models to 6771 samples from the entire sediment record, we obtained detailed insight into bioproductivity variations in Lake El'gygytgyn throughout the middle to late Pliocene and Quaternary. High accumulation rates of BSi indicate a productivity maximum during the middle Pliocene (3.6-3.3 Ma), followed by gradually decreasing rates during the late Pliocene and Quaternary. The average BSi accumulation during the middle Pliocene was ~3 times higher than maximum accumulation rates during the past 1.5 million years. The indicated progressive deterioration of environmental and climatic conditions in the Siberian Arctic starting at ca. 3.3 Ma is consistent with the first occurrence of glacial periods and the finally complete establishment of glacial-interglacial cycles during the Quaternary.

Alkenone unsaturation index and alkenones in ODP Hole 161-977A

A number of essential elements closely related to each other are involved in the Earth's climatic system. The temporal and spatial distribution of insolation determines wind patterns and the ocean's thermohaline pump. In turn, these last two are directly linked to the extension and retreat of marine and continental ice and to the chemistry of the atmosphere and the ocean. The variability of these elements may trigger, amplify, sustain or globalize rapid climatic changes. Paleoclimatic oscillations have been identified in this thesis by using fossil organic compounds synthesized by marine and terrestrial flora. High sedimentation rate deposits at the Barents and the Iberian peninsula continental margins were chosen in order to estimate the climatic changes on centennial time resolution. At the Barents margin, the sediment recovered was up to 15,000 years old (unit ''a'', from latin ''annos'') (M23258; west of the Bjørnøya island). At the Iberian margin, the sediment cores studied covered a wide range of time spans: up to 115,000 a (MD99-2343; north of the Minorca island), up to 250,000 a (ODP-977A; Alboran basin) and up to 420,000 a (MD01-2442, MD01-2443, MD01-2444, MD01-2445; close to the Tagus abyssal plain). At the northern site, inputs containing marine, continental and ancient reworked organic matter provided a detailed reconstruction of climate history at the time of the final retreat of the Barents ice sheet. At the western Barents continental slope, warm climatic conditions were observed during the early Holocene (~from 8,650 a to 5,240 a ago); in contrast, an apparent long-term cooling trend occurred in the late Holocene (~from 5,240 a to 760 a ago), in consistence with other paleoarchives from northern and southern European latitudes. The Iberian margin sites, which were never covered with large ice sheets, preserved exceptionally complete sequences of rapid events during ice ages hitherto not studied in such great detail: during the last glacial (~from 70,900 a to 11,800 a ago), the second glacial (~from 189,300 a to 127,500 a ago), the third ice age (~from 278,600 a to 244,800 a ago) and the fourth (~from 376,300 a to 337,500 a ago). In this thesis, crucial research questions were brought up concerning the severity of different glacial periods, the intensity and rates of the recorded oscillations and the long distance connections related to rapid climate change. The data obtained provide a sound basis to further research on the mechanisms involved in this rapid climate variability. An essential point of the research was the evidence that, over the past 420,000 a, at the whole Iberian margin, warm and stable long periods similar to the Holocene always ended abruptly in few centuries after a gradual deterioration of climate conditions. The detailed estimate of past climate variability provides clues to the natural end of the present warm period. Returning to an ice age in European lands would be exacerbated by a number of factors: a lack of differential solar heating between northern and southern north Atlantic latitudes, enhanced evaporation at low latitudes, and an increase in snowfall or iceberg discharges at northern regions. It must be emphasized that all climatic oscillations observed in this thesis were caused by forces of nature, i.e. the last two centuries were not taken into consideration.

Pollen and macrofossil profiles from six cores in Illinois, U.S.A

Pollen analysis of Wisconsinan sediments from eleven localities in northern and central Illinois, combined with the results of older studies, allows a first general survey of the vegetational changes in Illinois during the last glaciation. In the late Altonian (after 40,000 B.P.), pine was already the most prevalent tree type in northern Illinois. Probably because of the influence of the last Altonian ice advance to northern Illinois, pine migrated to the south and reached south-central Illinois, which was at that time a region of prairie, with oak and hickory trees in favorable sites. Likewise in the late Altonian, spruce appeared in northern Illinois. Spruce also expanded its area to the south during the Wisconsinan, reaching south-central Illinois only after 21,000 B.P., in the early Woodfordian. Deciduous trees (predominantly oak) were present in south-central Illinois throughout the Wisconsinan. Their prevalence decreased to the north. The vegetation during the different subdivisions of the last glacial period in Illinois was approximately as follows: Late Altonian: Pine/spruce forest with some deciduous trees in northern and central Illinois; prairie and oak/hickory stands in south-central Illinois; immigration of pine. Farmdalian: Pine/spruce forest in central Illinois; deciduous trees and pine in south-central Illinois, with areas of open vegetation, perhaps similar to the present-day transition of prairie to forest in the northern Great Plains. Woodfordian: Northern and central Illinois ice covered; in south central Illinois, spruce and oak as dominant tree types, but also pine and grassland. During the Woodfordian, pine and spruce disappeared again from south-central Illinois, and oak/hickory forest and prairie again prevailed. The ice-free areas of northern Illinois become populated temporarily with spruce, but later there is proof of deciduous forest in this region. Pollen investigations in south-central Illinois have shown convincingly that deciduous trees could survive relatively close (less than 60 km) to the ice margin. Therefore the frequently presented view that arctic climatic conditions prevailed in North America during the last glaciation far south of the ice margin can be refuted for the Illinois area, confirming the opinion of other authors resulting from investigations of fossil mollusks and frost-soil features. The small number of localities investigated still permits no complete reconstruction of the vegetation zones and their possible movements in Illinois. During the Altonian and Farmdalian in Illinois, a vegetational zonation probably existed similar to that of today in North America. As the ice pushed southward as far as 39° 20' N. lat in the early Woodfordian, this zonation was apparently broken up under the influence of a relatively moderate climate. In any case, the Vandalia area, which was only about 60 km south of the ice, was at that time neither in a tundra zone nor in a zone of boreal coniferous forest.

(Table 1) Nd isotope ratios of ODP Leg 208 samples

We present new Nd isotope records from Walvis Ridge Ocean Drilling Program (ODP) sites 1262-1264 (southeastern Atlantic) spanning the past 24 Ma to investigate the Neogene evolution of Atlantic thermohaline circulation. The new data indicate that deepwater epsilon-Nd(t) values from ODP Site 1262 decrease from -11.0 at 10.6 Ma to -12.5 by 7.3 Ma. This decrease parallels the Nd isotope trends contained in Fe-Mn crust records from the northwestern Atlantic; however, the shift at ODP Site 1262 (4755 m water depth) occurred up to ~6 Ma earlier than the corresponding changes in crust records from the Atlantic and earlier than any Atlantic site shallower than 2700 m paleowater depth. Recent interpretations of the rapid decrease in Fe-Mn crust Nd epsilon-Nd(t)ss values invoke changes in weathering inputs to the Labrador Sea region rather than a fundamental change in deepwater convection in the Labrador Sea. However, the new evidence for significant depth stratification of the Nd isotope signal in the southeastern Atlantic between 10.6 and 7.3 Ma suggests that the onset of deepwater convection in the Labrador Sea may have played a role in the deepwater decrease in Nd isotopic composition. Climatic conditions during the middle to late Miocene likely favored an increase in the importance of glacially induced mechanical weathering, while at the same time promoting deep convection in the Labrador Sea.

(Table 1) Major element composition of core 5022-2CP, Laguna Potrok Aike, southern Patagonia

Total organic carbon, total inorganic carbon, biogenic silica content and total organic carbon/total nitrogen ratios of the Laguna Potrok Aike lacustrine sediment record are used to reconstruct the environmental history of south-east Patagonia during the past 51 ka in high resolution. High lake level conditions are assumed to have prevailed during the Last Glacial, as sediments are carbonate-free. Increased runoff linked to permafrost and reduced evaporation due to colder temperatures and reduced influence of Southern Hemispheric Westerlies (SHW) may have caused these high lake levels with lake productivity being low and organic matter mainly of algal or cyanobacterial origin. Aquatic moss growth and diatom blooms occurred synchronously with southern hemispheric glacial warming events such as the Antarctic A-events, the postglacial warming following the LGM and the Younger Dryas chronozone. During these times, a combination of warmer climatic conditions with related thawing permafrost could have increased the allochthonous input of nutrients and in combination with warmer surface waters increased aquatic moss growth and diatom production. The SHW were not observed to affect southern Patagonia during the Last Glacial. The Holocene presents a completely different lacustrine system because (a) permafrost no longer inhibits infiltration nor emits meltwater pulses and (b) the positioning of the SHW over the investigated area gives rise to strong and dry winds. Under these conditions total organic carbon, total organic carbon/total nitrogen ratios and biogenic silica cease to be first order productivity indicators. On the one hand, the biogenic silica is influenced by dissolution of diatoms due to higher salinity and pH of the lake water under evaporative stress characterizing low lake levels. On the other hand, total organic carbon and total organic carbon/total nitrogen profiles are influenced by reworked macrophytes from freshly exposed lake level terraces during lowstands. Total inorganic carbon remains the most reliable proxy for climatic variations during the Holocene as high precipitation of carbonates can be linked to low lake levels and high autochthonous production. The onset of inorganic carbon precipitation has been associated with the southward shift of the SHW over the latitudes of Laguna Potrok Aike. The refined age-depth model of this record suggests that this shift occurred around 9.4 cal. ka BP.