Geochemical composition and radiocarbon ages of cores from Lago Fugnano, Tierra del Fuego

Recent advances in the chronology and the palaeoclimatic understanding of Antarctic ice core records point towards a larger heterogeneity of latitudinal climate fluctuations than previously thought. Thus, realistic palaeoclimate reconstructions rely in the development of a tight array of well-constrained records with a dense latitudinal coverage. Climatic records from southernmost South America are critical cornerstones to link these Antarctic palaeoclimatic archives with their South American counterparts. At 54° S on the Island of Tierra del Fuego, Lago Fagnano is located in one of the most substantially and extensively glaciated regions of southernmost South America during the Late Pleistocene. This elongated lake is the largest (~110km long) and non-ice covered lake at high southern latitudes. A multi-proxy study of selected cores allows the characterisation of a Holocene sedimentary record. Detailed petrophysical, sedimentological and geochemical studies of a complete lacustrine laminated sequence reveal variations in major and trace elements, as well as organic content, suggesting high variability in environmental conditions. Comparison of these results with other regional records allows the identification of major known late Holocene climatic intervals and the proposal for a time for the onset of the Southern Westerlies in Tierra del Fuego. These results improve our understanding of the forcing mechanisms behind climate change in southernmost Patagonia.

Dinoflagellate abundance and events of ODP Site 189-1172 sediments

Palynomorphs were studied in samples from Ocean Drilling Program (ODP) Leg 189, Holes 1172A and 1172D (East Tasman Plateau; 2620 m water depth). Besides organic walled dinoflagellate cysts (dinocysts), broad categories of other palynomorphs were quantified in terms of relative abundance. In this contribution, we provide an overview of the dinocyst distribution from the Maastrichtian to lowermost Oligocene and Quaternary intervals and illustrate main trends in palynomorph distribution. The uppermost Cretaceous-lowermost Oligocene succession of Site 1172 has a confident biomagnetostratigraphy, enabling us to tie early Paleogene Southern Hemisphere dinocyst events to the geomagnetic polarity timescale for the first time. Dinocyst species from the Maastrichtian to earliest Oligocene at Site 1172 are largely endemic ("Transantarctic Flora") or bipolar; cosmopolitan taxa are present in the background as well. The Maastrichtian-early late Eocene dinocyst assemblages are indicative of shallow-marine to restricted marine, pro-deltaic conditions, closely tied to a massive siliciclastic sequence. By middle late Eocene times (~35.5 Ma), the siliciclastic sequence gave way to a thin glauconitic unit, considered to reflect the deepening of the Tasmanian Gateway. This transition coincides with the most prominent change in dinocyst associations of the Paleogene. The turnover is inferred to reflect a change from marginal marine to more offshore conditions, with increased winnowing and oxidation. Overlying pelagic carbonate ooze of middle early Oligocene and younger age is virtually barren of organic microfossils, although Quaternary assemblages have been recovered. This aspect is taken to reflect average low sedimentation rates and well-oxygenated water masses during most of the Oligocene and Neogene. The few palynologically productive samples from the Oligocene-Quaternary interval have a stronger cosmopolitan to subtropical signature, with warm-water species being common to abundant.

Middle Eocene bulk sediment, benthic and planktic foraminiferal stable isotope values, and relative weight percent CaCO3 content from ODP Site 207-1260

Major ice sheets were permanently established on Antarctica approximately 34 million years ago, close to the Eocene/ Oligocene boundary, at the same time as a permanent deepening of the calcite compensation depth in the world's oceans. Until recently, it was thought that Northern Hemisphere glaciation began much later, between 11 and 5million years ago. This view has been challenged, however, by records of ice rafting at high northern latitudes during the Eocene epoch and by estimates of global ice volume that exceed the storage capacity of Antarctica at the same time as a temporary deepening of the calcite compensation depth 41.6 million years ago. Here we test the hypothesis that large ice sheets were present in both hemispheres 41.6 million years ago using marine sediment records of oxygen and carbon isotope values and of calcium carbonate content from the equatorial Atlantic Ocean. These records allow, at most, an ice budget that can easily be accommodated on Antarctica, indicating that large ice sheets were not present in the Northern Hemisphere. The records also reveal a brief interval shortly before the temporary deepening of the calcite compensation depth during which the calcite compensation depth shoaled, ocean temperatures increased and carbon isotope values decreased in the equatorial Atlantic. The nature of these changes around 41.6 million years ago implies common links, in terms of carbon cycling, with events at the Eocene/Oligocene boundary and with the 'hyperthermals' of the Early Eocene climate optimum. Our findings help to resolve the apparent discrepancy between the geological records of Northern Hemisphere glaciation and model results that indicate that the threshold for continental glaciation was crossed earlier in the Southern Hemisphere than in the Northern Hemisphere.

Sea surface temperature record of ODP Site 202-1233

We present the first high-resolution alkenone-derived sea surface temperature (SST) reconstruction in the southeast Pacific (Ocean Drilling Program Site 1233) covering the major part of the last glacial period and the Holocene. The record shows a clear millennial-scale pattern that is very similar to climate fluctuations observed in Antarctic ice cores, suggesting that the Southern Hemisphere high-latitude climate changes extended into the midlatitudes, involving simultaneous changes in air temperatures over Antarctica, sea ice extent, extension of the Antarctic Circumpolar Current, and westerly atmospheric circulation. A comparison to other midlatitude surface ocean records suggests that this "Antarctic" millennial-scale pattern was probably a hemisphere-wide phenomenon. In addition, we performed SST gradient reconstructions over the complete latitudinal range of the Pacific Eastern Boundary Current System for different time intervals during the last 70 kyr. The main results suggest an equatorward displaced subtropical gyre circulation during marine isotope stages 2 and 4.

Microsedimentological characterization as indicators of sedimentary processes and climate changes during Lateglacial at Laguna Potrok Aike, Santa Cruz, Argentina

Palaeoclimatic and paleoenvironmental high latitude records in the Southern Hemisphere are scarce compared to the northern counterpart. However, understanding global evolution of environmental systems during sudden climate changes is inseparable from an equivalent knowledge of both Hemispheres. In this context, a high-resolution study of lacustrine sediments from Laguna Potrok Aike, Santa Cruz province, Patagonia, Argentina, was conducted for the Lateglacial period using concurrent X-Ray Fluorescence (XRF) and Scanning electron microscope analyses. Peaks of Ca/Si and Mn, and occurrences of the green alga Phacotus lenticularis have been interpreted as variations in ventilation of the water column from 13.6 to 11.1 ka cal. BP. During this interval, mild climate conditions during the Younger Dryas are characterized by relatively weak westerlies favouring the formation of a stratified water body as indicated by preserved manganese and Ca/Si peaks and high Total Organic Carbon (TOC) values. In this environment, water in the epilimnion can reach sufficiently high temperature to allow P. lenticularis to grow. Colder conditions are marked by peaks in Ca without P. lenticularis and occur during the Antarctic Cold Reversal (ACR). In this Lateglacial interval, micropumices were also detected in large amount. Image analysis of thin sections allowed the counting and size measurement of detrital particles and micropumices separately. Micropumices significantly influence the iron and titanium content, hence preventing to use them as proxies of detrital input in this interval.

Hexachlorocyclohexanes concentration in air and ocean water

Hexachlorocyclohexanes (HCHs) are ubiquitous organic pollutants derived from pesticide application. They are subject to long-range transport, persistent in the environment, and capable of accumulation in biota. Shipboard measurements of HCH isomers (a-, b- and g-HCH) in surface seawater and boundary layer atmospheric samples were conducted in the Atlantic and the Southern Ocean in October to December of 2008. SumHCHs concentrations (the sum of a-, g- and b-HCH) in the lower atmosphere ranged from 12 to 37 pg/m**3 (mean: 27 ± 11 pg/m**3) in the Northern Hemisphere (NH), and from 1.5 to 4.0 pg/m**3 (mean: 2.8 ± 1.1 pg/m**3) in the Southern Hemisphere (SH), respectively. Water concentrations were: a-HCH 0.33-47 pg/l, g-HCH 0.02-33 pg/l and b-HCH 0.11-9.5 pg/l. Dissolved HCH concentrations decreased from the North Atlantic to the Southern Ocean, indicating historical use of HCHs in the NH. Spatial distribution showed increasing concentrations from the equator towards North and South latitudes illustrating the concept of cold trapping in high latitudes and less interhemispheric mixing process. In comparison to concentrations measured in 1987-1999/2000, gaseous HCHs were slightly lower, while dissolved HCHs decreased by factor of 2-3 orders of magnitude. Air-water exchange gradients suggested net deposition for a-HCH (mean: 3800 pg/m**2/day) and g-HCH (mean: 2000 pg/m**2/day), whereas b-HCH varied between equilibrium (volatilization: <0-12 pg/m**2/day) and net deposition (range: 6-690 pg/m**2/day). Climate change may significantly accelerate the release of "old" HCHs from continental storage (e.g. soil, vegetation and high mountains) and drive long-range transport from sources to deposition in the open oceans. Biological productivities may interfere with the air-water exchange process as well. Consequently, further investigation is necessary to elucidate the long term trends and the biogeochemical turnover of HCHs in the oceanic environment.

Isotope oxygen record for ODP sediments from the Exmouth Plateau

A new composite d18O record, generated from calcareous fine-fraction and bulk sediments from the Exmouth Plateau, details long-term Cretaceous climatic change at mid-latitudes in the Southern Hemisphere. Assessment of new and previously published d18O data indicates that a mid-Cretaceous global climatic optimum was achieved sometime between the time of the Cenomanian-Turonian boundary and the middle Turonian, when surface-ocean paleotemperatures were the highest of the past 115 m.y. Periods of cooling and warming that reversed the general patterns were superimposed on long-term Aptian-Turonian warming and Turonian-Maastrichtian cooling trends, respectively. Extrapolation of Southern Hemisphere paleotemperature trends to Maastrichtian paleotemperature data from a low-latitude Pacific guyot implies that maximum mid-Cretaceous low-latitude paleotemperatures could have been in excess of 33°C.

Biogenic and terrigeneous components in Pliocene-Pleistocene sediments of the equatorial Atlantic

High-resolution analyses of sediments at equatorial Atlantic Sites 662, 663, and 664 define the accumulation rates of biogenically produced CaC03 and opal and of eolian dust from North Africa over the last 3.7 m.y. The mean flux of opal increased abruptly by 60%-70% near 2.5 Ma (2.65 to 2.3 Ma), reflecting pulses of increased opal productivity along the equator due mainly to increased upwelling. The mean winter-plume dust influx from Sahelian and Saharan Africa also increased at this time by between 35% and 75%, following smaller increases earlier in the late Pliocene. The increased opal flux implies a stronger zonal component of the southern trade winds in Southern Hemisphere winter. Consistent with this wind configuration, the stronger dust flux suggests a weaker southwesterly monsoonal flow into Africa in Northern Hemisphere summer, thus increasing Sahelian aridity and winter-plume dust fluxes. Dust fluxes to the equator may possibly have also been enhanced by stronger Northern Hemisphere winter trade winds and a more southerly position of the Intertropical Convergence Zone over Africa. These late Pliocene biogenic and terrigenous flux changes coincided with the appearance of Northern Hemisphere ice sheets, implying an ultimate causal link. The immediate control on changes in tropical circulation may, however, have been changes in the Atlantic sector of the Southern Ocean. A steady background trend of increasing winter-plume dust flux occurred from the late Pliocene until the middle Pleistocene. This may reflect a progressive, tectonically induced aridification of northern and eastern Africa because of the gradual uplift of the Tibetan Plateau.

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.

AMS 14C dating points, isotopic compositions, Mg/Ca ratios and sea surface temperatures of sediment cores GeoB10029-4 and GeoB10038-4

Quantifying the spatial and temporal sea surface temperature (SST) and salinity changes of the Indo-Pacific Warm Pool is essential to understand the role of this region in connection with abrupt climate changes particularly during the last deglaciation. In this study we reconstruct SST and seawater d18O of the tropical eastern Indian Ocean for the past 40,000 years from two sediment cores (GeoB 10029-4, 1°30'S, 100°08'E, and GeoB 10038-4, 5°56'S, 103°15'E) retrieved offshore Sumatra. Our results show that annual mean SSTs increased about 2-3 °C at 19,000 years ago and exhibited southern hemisphere-like timing and pattern during the last deglaciation. Our SST records together with other Mg/Ca-based SST reconstructions around Indonesia do not track the monsoon variation since the last glacial period, as recorded by terrestrial monsoon archives. However, the spatial SST heterogeneity might be a result of changing monsoon intensity that shifts either the annual mean SSTs or the seasonality of G. ruber towards the warmer or the cooler season at different locations. Seawater d18O reconstructions north of the equator suggest fresher surface conditions during the last glacial and track the northern high-latitude climate change during the last deglaciation. In contrast, seawater ?18O records south of the equator do not show a significant difference between the last glacial period and the Holocene, and lack Bølling-Allerød and Younger Dryas periods suggestive of additional controls on annual mean surface hydrology in this part of the Indo-Pacific Warm Pool.

Grain-size distributions and bulk chemistry of sediment core MD00-2361

The terrigenous fraction of sediments from a deep-sea sediment core recovered from the northwestern Western Australian continental slope offshore North West Cape, SE Indian Ocean, reveals a history of Western Australian climate throughout the last 550 ka. End-member modelling of a data set of grain-size distributions (n = 438) of the terrigenous sediment fraction allows to interpret the record in terms of aeolian and fluvial sediment deposition, both related to palaeo-environmental conditions in the North West Cape area. The data set can be best described by two aeolian end members and one fluvial one. Changes in the ratio of the two aeolian end members over the fluvial one are interpreted as aridity variations in northwestern Western Australia. These grain-size data are compared with bulk geochemical data obtained by XRF scans of the core. Log-ratios of the elements Zr/Fe and Ti/Ca, which indicate a terrigenous origin, corroborate the grain-size data. We postulate that the mid- to late Quaternary near North West Cape climate was relatively arid during the glacial and relatively humid during the interglacial stages, owing to meridional shifts in the atmospheric circulation system. Opposite to published palaeo-environmental records from the same latitude (20°S) offshore Chile and offshore Namibia, the Australian aridity record does not show the typical southern hemisphere climate variability of humid glacials and dry interglacials, which we interpret to be the result of the relatively large land mass of the Australian continent, which emphasises a strong monsoonal climatic system.

International Polar Year 1882-1883 the digitized meteorological data legacy

The first International Polar Year (IPY) was an international effort to perform continous meteorological and geophysical observations over a time period of two years (1882-1883). Eleven nations established twelve research stations in the Arctic along with thirteen auxilary stations. Two stations were operated on the southern hemisphere (South Georgia and Tierra del Fuego). The data were published in 26 volumes on 8700+ pages of reports, descriptions, tables and graphs in total. The list of meteorological parameters includes temperature, wind, pressure, clouds, precipitation, evaporation, humidity and radiation. In the light of Global Change and the intensification of observations and continous measurements in both polar regions, long-time series increase in importance. The observations of the first IPY from the 19th century enable us to extend the data from the 20th century even more back into the past. In the occasion of the fourth IPY (2007-2009) WDC-MARE decided to digitize the complete set of meteorological data in full hourly resolution and publish it in its reports and make it available in Open Access via the data library PANGAEA.