Paleotemperature and productivity reconstruction of sediment core D11957P on the Iberian Margin

Foraminifera counts and climatic assemblages from the Tore Seamount are used to approach the glacial and interglacial changes in temperature and productivity on the Iberian Margin over the last 225 kyr. Chronostratigraphy is based on Globigerinoides ruber and Globigerina bulloides oxygen isotopes and supported by foraminifera and carbonate stadial fluctuations. Foraminifera indicate cooling from late interglacial stage 5 to the beginning of Termination I (TI). Neogloboquadnna pachyderma-s reflects cold conditions during glacial stages 4-2. In contrast, glacial stage 6 is dominated by warmer N. pachyderma-d and dutertrei and a restricted arctic assemblage. Past sea surface temperatures confirm the general cooling, reaching 4.3°C (SIMMAX.28) during stage 2. Multiple productivity proxies such as organic carbon, productivity-related foraminifera, and delta13C constrain the changes observed. A productivity increase occurs after interglacial stage 5, enhanced from late glacial stage 3 to TI Present-day satellite-detected phytoplankton plumes off Portugal would have accounted in the past glacial stages for the general productivity increase over the Tore. On top of this, welldefined peaks of organic carbon and productivity-related foraminifera correspond with Heinrich events 1-4.

(Table 2) Age determination of sediments from the Nordic Seas

A combined record of three cores spanning the last 18 kyr from the northern North Sea is investigated for content of benthic and planktonic foraminifera and stable oxygen isotopes. The paleoenvironmental development through this time period shows an early deglaciation (18-14.4 ka) and the Younger Dryas (12.7-11.5 ka) characterized by arctic/polar conditions and increased ice rafting in the Norwegian Channel. During the Bølling-Allerød period, warm sea surface temperature (9°C) conditions similar to present conditions are inferred, while bottom waters stayed cold (0-1°C) with normal salinity. The Bølling-Allerød period is interrupted twice at 13.9-13.6 ka (Older Dryas) and at 13.0-12.8 ka (Inter-Allerød Cooling Period) by reductions in sea surface temperatures and increased sea ice cover. The beginning of the Holocene period is marked by increases in surface and bottom water temperature. Superimposed on the broad climatic changes through the Holocene, a series of short-lived oscillations in the ocean circulation are recorded. The amplitude of these Holocene events appears larger in the early Holocene (prior to 8 ka) than compared with the remaining part of the Holocene. This amplification can possibly be attributed to a general increased freshwater budget in the North Atlantic at this time during the final stages of the deglaciation of the Laurentide and Scandinavian ice sheets.

Pollen data and pollen-based climate reconstruction for the KTK1 pollen record from Lake Kotokel

In this study a radiocarbon-dated pollen record from Lake Kotokel (52°47' N, 108°07' E, 458 m a.s.l.) located in southern Siberia east of Lake Baikal was used to derive quantitative characteristics of regional vegetation and climate from about 15 kyr BP (1 kyr = 1000 cal. yr) until today. Quantitative reconstruction of the late glacial vegetation and climate dynamics suggests that open steppe and tundra communities predominated in the study area prior to ca. 13.5 kyr BP and again during the Younger Dryas interval, between 12.8 and 11.6 kyr BP. The pollen-based climate reconstruction suggests lower-than-present mean January (~ -38 °C) and July (~ 12 °C) temperatures and annual precipitation (~ 270-300 mm) values during these time intervals. Boreal woodland replaced the primarily open landscape around Kotokel three times at about 14.8-14.7 kyr BP, during the Allerød Interstadial between 13.3-12.8 kyr BP and with the onset of the Holocene interglacial between 11.5 and 10.5 kyr BP, presumably in response to a noticeable increase in precipitation, and in July and January temperatures. The maximal spread of the boreal forest (taiga) communities in the region is associated with a warmer and wetter-than-present climate (Tw ~ 17-18 °C, Tc ~ -19 °C, Pann ~ 500-550 mm) that occurred ca. 10.8-7.3 kyr BP. During this time interval woody vegetation covered more than 50 % of the area within a 21x21 km window around the lake. The pollen-based best modern analogue reconstruction suggests a decrease in woody cover percentages and in all climatic variables about 7-6.5 kyr BP. Our results demonstrate a gradual decrease in precipitation and mean January temperature towards their present-day values in the region around Lake Kotokel since that time.

Geomicrobiology, bulk sediment characteristics and pore water chemistry of sediment cores from Laguna Potrok Aike, southern Patagonia

Authigenic minerals can form in the water column and sediments of lakes, either abiotically or mediated by biological activity. Such minerals have been used as paleosalinity and paleoproductivity indicators and reflect trophic state and early diagenetic conditions. They are also considered potential indicators of past and perhaps ongoing microbial activity within sediments. Authigenic concretions, including vivianite, were described in late glacial sediments of Laguna Potrok Aike, a maar lake in southernmost Argentina. Occurrence of iron phosphate implies specific phosphorus sorption behavior and a reducing environment, with methane present. Because organic matter content in these sediments was generally low during glacial times, there must have been alternative sources of phosphorus and biogenic methane. Identifying these sources can help define past trophic state of the lake and diagenetic processes in the sediments. We used scanning electron microscopy, phosphorus speciation in bulk sediment, pore water analyses, in situ ATP measurements, microbial cell counts, and measurements of methane content and its carbon isotope composition (d13C CH4) to identify components of and processes in the sediment. The multiple approaches indicated that volcanic materials in the catchment are important suppliers of iron, sulfur and phosphorus. These elements influence primary productivity and play a role in microbial metabolism during early diagenesis. Authigenic processes led to the formation of pyrite framboids and revealed sulfate reduction. Anaerobic oxidation of methane and shifts in pore water ion concentration indicated microbial influence with depth. This study documents the presence of active microbes within the sediments and their relationship to changing environmental conditions. It also illustrates the substantial role played by microbes in the formation of Laguna Potrok Aike concretions. Thus, authigenic minerals can be used as biosignatures in these late Pleistocene maar sediments.

(Table 1) Radiocarbon ages of core AB01/94 obtained in the Tromper Wiek, western Baltic Sea

In the Tromper Wiek northeast of Rügen, acoustical investigations using Air Gun, Boomer, Chirp Sonar and Sediment-Echosounder were carried out. Together with sediment core information, it allowed the identification of five seismostratigraphic units (E1 to E5). Conventional and AMS-14C-datings supported their chronostratigraphical classification. The uppermost till (E1) was incised by late glacial channels filled with glaciolacustrine sediments (E2) of the early Baltic Ice Lake stages. These were regionally overlain with a sharp unconformity by a thick (locally >20 m) sedimentary complex (E3) of acoustically laminated silts of freshwater origin. This lower part of the E3-complex (E3a) is overlain by fluvial to coastal silty fine sands (E3b) deeper towards the Arkona Basin. Fine plant debris in the uppermost part of sub-unit E3a yielded ages of 10,100 and 10,500 14C-years B.P., representing the final phase of the Baltic Ice Lake. The fine sands of sub-unit E3b were deposited after the final drainage of the Baltic Ice Lake. In the shallower central part of the bay, the silts of sub-unit E3a were covered by a younger unit (E4) of fine sand with plant debris. A sedge peat occurring at the basis of unit E4 yielded an age of 9,590 14C-years B.P. The fine sands overlying the unit E3 in the central part of Tromper Wiek were deposited in the Ancylus Lake. Their position at about 20 m below present sea level (b.s.l.) reflects the maximum highstand in this area. The character and distribution of the Early Holocene deposits at greater depth suggest a lake water level at about 30 m b.s.l. after this highstand. Below 25 m b.s.l. muddy Littorina Sea sediments are observed. The thickness of these muds and sandy muds increases gradually towards the Arkona Basin. Locally, they are found in a channel-like structure immediately north of Jasmund.

Biogeochemical, sedimentological and isotopic sediment record of Lake Dojran

A Late Glacial to Holocene sediment sequence (Co1260, 717 cm) from Lake Dojran, located at the boarder of the F.Y.R. of Macedonia and Greece, has been investigated to provide information on climate variability in the Balkan region. A robust age-model was established from 13 radiocarbon ages, and indicates that the base of the sequence was deposited at ca. 12 500 cal yr BP, when the lake-level was low. Variations in sedimentological (H2O, TOC, CaCO3, TS, TOC/TN, TOC/TS, grain-size, XRF, d18Ocarb, d13Ccarb, d13Corg) data were linked to hydro-acoustic data and indicate that warmer and more humid climate conditions characterised the remaining period of the Younger Dryas until the beginning of the Holocene. The Holocene exhibits significant environmental variations, including the 8.2 and 4.2 ka cooling events, the Medieval Warm Period and the Little Ice Age. Human induced erosion processes in the catchment of Lake Dojran intensified after 2800 cal yr BP.