Chemical measurements from the EPICA Dome C core

Sea ice and dust flux increased greatly in the Southern Ocean during the last glacial period. Palaeorecords provide contradictory evidence about marine productivity in this region, but beyond one glacial cycle, data were sparse. Here we present continuous chemical proxy data spanning the last eight glacial cycles (740,000 years) from the Dome C Antarctic ice core. These data constrain winter sea-ice extent in the Indian Ocean, Southern Ocean biogenic productivity and Patagonian climatic conditions. We found that maximum sea-ice extent is closely tied to Antarctic temperature on multi-millennial timescales, but less so on shorter timescales. Biological dimethylsulphide emissions south of the polar front seem to have changed little with climate, suggesting that sulphur compounds were not active in climate regulation. We observe large glacial-interglacial contrasts in iron deposition, which we infer reflects strongly changing Patagonian conditions. During glacial terminations, changes in Patagonia apparently preceded sea-ice reduction, indicating that multiple mechanisms may be responsible for different phases of CO2 increase during glacial terminations. We observe no changes in internal climatic feedbacks that could have caused the change in amplitude of Antarctic temperature variations observed 440,000 years ago.

First results from stable-istope measurements on ice cores from Dronning Maud Land

The European Project for Ice Coring in Antarctica (EPICA) focuses on the drilling of two deep ice cores, the first at Dome C and the second at Kohnen station (75°00' S, 0°04' E) in Dronning Maud Land (DML). This paper deals with stable-isotope records from ice cores drilled in DML. In the first season, the deep EPICA DML core reached a depth of 450 m, recovering ice approximately 7000 years old. Generally, the d18O record indicates a stable Holocene climate and shows low variability. However, during the last 4000 years (based on a preliminary time-scale) the d18O values decrease continuously by about 0.6%, and the deuterium excess values increase by about 0.5%. The correlation between d18O and the deuterium excess d is investigated for a 50m long core section and the near-surface snow. High-pass filtered profiles are positively correlated, whereas the correlation between low-pass filtered profiles is negative. A post-depositional effect due to diffusion processes can be seen in a sub-annually resolved profile from snow-pit samples. Changes in the seasonality of the evolution of the snow cover and the consequences for stable-isotope content are demonstrated with data from ice core B31.

Data from the EPICA Dome C ice core EDC

The Antarctic Vostok ice core provided compelling evidence of the nature of climate, and of climate feedbacks, over the past 420,000 years. Marine records suggest that the amplitude of climate variability was smaller before that time, but such records are often poorly resolved. Moreover, it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records. Here we report the recovery of a deep ice core from Dome C, Antarctica, that provides a climate record for the past 740,000 years. For the four most recent glacial cycles, the data agree well with the record from Vostok. The earlier period, between 740,000 and 430,000 years ago, was characterized by less pronounced warmth in interglacial periods in Antarctica, but a higher proportion of each cycle was spent in the warm mode. The transition from glacial to interglacial conditions about 430,000 years ago (Termination V) resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases, but there are significant differences in the patterns of change. The interglacial stage following Termination V was exceptionally long - 28,000 years compared to, for example, the 12,000 years recorded so far in the present interglacial period. Given the similarities between this earlier warm period and today, our results may imply that without human intervention, a climate similar to the present one would extend well into the future.

Age model of ODP Hole 107-654A

It has long been speculated that glacio-eustatic sea level drop may have caused or contributed to the isolation and consequent desiccation of the Mediterranean in the late Miocene (the 'Messinian salinity crisis'). Ocean Drilling Program site 654 on the Sardinia margin of the Tyrrhenian Sea is the first deep-sea drill site to penetrate through upper Messinian evaporites into lower Messinian/upper Tortonian open marine sediments, and thus offers a unique opportunity to date the onset of the salinity crisis. A reexamination of the magnetostratigraphic, biostratigraphic, and stable isotope-stratigraphic constraints on the preevaporite sediments of site 654 has yielded two possible ages for the contact between salinity crisis sediments and the underlying normal marine sediments. One magnetostratigraphic interpretation plus the biostratigraphically determined position of the Tortonian/Messinian boundary imply a date of about 6.2 Ma for the youngest presalinity crisis sediments. An alternative magnetostratigraphic interpretation plus the carbon isotope stratigraphy imply a date of about 5.2 Ma. The younger of these dates coincides with a delta18O spike in open ocean sediments [Keigwin, 1987 doi:10.1029/PA002i006p00639], which is attributed to increased ice volume.

Age estimates of Discoaster datums and corresponding isotope stages (Table 2)

High-resolution records (2 7 kyr) of Upper Pliocene Discoaster abundances obtained from six ODP/DSDP sites are assessed independently using oxygen isotope stratigraphy. Four Atlantic Ocean sites (DSDP Sites 552 and 607, and ODP Sites 659 and 662) comprise a transect from 56°N to 1°S and provide a record of latitudinal variations in Diseoaster biogeography. Low-latitude sites in the Atlantic (ODP Site 662), Pacific (ODP Site 677), and Indian (ODP Site 709) oceans provide additional information about variability in Discoaster abundance patterns within the equatorial region. A common chronology, based on the astronomical time scale developed for ODP Site 677, has been established for all the sites. By integrating oxygen isotope data and Discoaster abundance records at each site we are able to independently evaluate the temporal and spatial distribution of D. brouweri and D. triradiatus in the 500 kyr prior to the extinction of the discoasters near the base of the Olduvai subchron. Major decreases in abundance are evident during some of the more intense late Pliocene glacial events. In particular, glacial isotope stages 82, 96, 98 and 100 are associated with distinct abundance minima. At these times, large-scale changes in surface hydrographic conditions appear to have suppressed Discoaster numbers on a global scale. The increase in abundance of D. triradiatus, which precedes the extinction of the discoasters by around 200 kyr, may also be related to the intensification of environmental pressures that accompanied the build-up of Northern Hemisphere ice sheets during the late Pliocene. In spite of contrasting geographic and oceanographic settings, the various D. brouweri and D. triradiatus records are remarkably similar. This demonstrates that the acme and extinction events are excellent biostratigraphic datums. The simultaneous extinction of D. brouweri and D. triradiatus at 1.95 Ma were synchronous events at both a regional scale within the Atlantic, and on a global scale between the three major oceans. However, the start of the D. triradiatus acme appears to have been diachronous, occurring some 40 kyr earlier in the Atlantic than in the Indo-Pacific, and hence the stratigraphic usefulness of this datum is regional rather than global.

Age determination of sediments from Kilkeel and sediment core Y69-71P

Evidence from the Irish Sea basin supports the existence of an abrupt rise in sea level (meltwater pulse) at 19,000 years before the present (B.P.). Climate records indicate a large reduction in the strength of North Atlantic Deep Water formation and attendant cooling of the North Atlantic at this time, indicating a source of the meltwater pulse from one or more Northern Hemisphere ice sheets.Warming of the tropical Atlantic and Pacific oceans and the Southern Hemisphere also began at 19,000 years B.P. These responses identify mechanisms responsible for the propagation of deglacial climate signals to the Southern Hemisphere and tropics while maintaining a cold climate in the Northern Hemisphere.

(Table 1) Ice thickness at lake Nam Co, Tibet, during 2008-2009

Lake ice change is one of the sensitive indicators of regional and global climate change. Different sources of data are used in monitoring lake ice phenology nowadays. Visible and Near Infrared bands of imagery (VNIR) are well suited for the observation of freshwater ice change, for example data from AVHRR and MODIS. Active and passive microwave data are also used for the observation of lake ice, e.g., from satellite altimetry and radiometry, backscattering coefficient from QuickSCAT, brightness temperature (Tb) from SSM/I, SMMR, and AMSR-E. Most of the studies are about lake ice cover phenology, while few studies focus on lake ice thickness. For example, Hall et al. using 5 GHz (6 cm) radiometer data showed a good relationship between Tb and ice thickness. Kang et al. found the seasonal evolution of Tb at 10.65 GHz and 18.7 GHz from AMSR-E to be strongly influenced by ice thickness. Many studies on lake ice phenology have been carried out since the 1970s in cold regions, especially in Canada, the USA, Europe, the Arctic, and Antarctica. However, on the Tibetan Plateau, very little research has focused on lake ice-cover change; only a small number of published papers on Qinghai Lake ice observations. The main goal of this study is to investigate the change in lake ice phenology at Nam Co on the Tibetan Plateau using MODIS and AMSR-E data (monitoring the date of freeze onset, the formation of stable ice cover, first appearance of water, and the complete disappearance of ice) during the period 2000-2009.

Age determination and stable oxygen isotope record of ODP Hole 167-1017E

Oxygen isotopic (d18O) climatic stratigraphy and radiocarbon chronology, at high resolution, have been used to establish an age model for Ocean Drilling Program Hole 1017E, a continuous 25-m sequence of hemipelagic sediments from the continental slope (956 m water depth), east of Point Arguella, Southern California. The upper part of Hole 1017E from ~33 ka (7.445 mbsf) was dated using 13 calendar-corrected radiocarbon ages of mixed planktonic foraminiferal assemblages. Benthic oxygen isotopic stratigraphy records a continuous 130-k.y. sequence ranging from marine isotope Stage 6 to the present day. The benthic d18O curve, representing the last two interglacial and glacial cycles, closely resembles the well-dated, deep-sea reference sequence, providing a detailed chronologic framework. Sedimentation rates remained relatively constant throughout the sequence at ~18 cm/k.y. and were sufficiently rapid to provide considerable potential for high-resolution paleoceanographic/paleoclimatic investigations. Planktonic foraminiferal oxygen isotopic stratigraphy based on the surface-dwelling form Globigerina bulloides defines an almost complete sequence of interstadial/stadial oscillations (Dansgaard/Oeschger cycles [D/O]). Combined use of radiocarbon chronology, deep-sea oxygen isotopic datums, and visual pattern matching has enabled us to identify the sequence of D/O cycles as described for the Greenland (GRIP2) ice core. This has strengthened the stratigraphic framework for the last 60 k.y. in the sequence as a basis for further paleoenvironmental investigations.

CaCO3 content, terrigenous components, foraminifera abundance and age of sediment core MD95-2006, Barra Fan, UK

Lithology, lithic petrology, planktonic foraminiferal abundances, and clastic grain sizes have been determined in a 30 m-long core recovered from the Barra Fan off northwest Scotland. The record extends back to around 45 kyr B.P., with sedimentation rates ranging between 50 and 200 cm/kyr. The abundance of ice-rafted debris indicates 16 glacimarine events, including temporal equivalents to Heinrich events 1-4. Enhanced concentrations of basaltic material derived from the British Tertiary Province suggest that the glacimarine sediments record variations in a glacial source on the Hebrides shelf margin. Glacimarine zones are separated by silty intervals with high planktonic foraminifera concentrations that reflect an interstadial circulation regime in the Rockall Trough. The results suggest that the last British Ice Sheet fluctuated with a periodicity of 2000-3000 years, in common with the Dansgaard-Oeschger climate cycle.

Age determination of hornblende in ODP Site 188-1165 and DSDP Hole 28-268

Sediments from Ocean Drilling Program Site 1165 in the Indian Ocean sector of the Southern Ocean (off Prydz Bay) contain a series of layers that are rich in ice-rafted debris (IRD). Here we present evidence that IRD-rich layers at Site 1165 at 7, 4.8, and 3.5 Ma record short-lived, massive discharges of icebergs from Wilkes Land and Adélie Land, more than 1500 kilometers to the east of the depositional site. This distant source of icebergs is clearly defined by the presence of IRD hornblende grains with 40Ar/39Ar ages of 1200-1100 Ma and 1550-1500 Ma, ages that are not found on the East Antarctic continent in locations closer to Site 1165. This observation requires enormous amounts of detritus-carrying drifting icebergs, most likely in the form of large icebergs. These events probably reflect destabilization, surge, and break-up of ice streams on the Wilkes Land and Adélie Land margins of the East Antarctic Ice Sheet, in the vicinity of the low-lying Aurora and Wilkes Basins. They occurred under warming conditions, but each coast seems to have produced ice-rafting events independently, at different times. The data presented here constitute the first evidence of far-traveled icebergs from specific source areas around the East Antarctic perimeter. Launch of these icebergs may have happened during quite dramatic events, perhaps analogous to "Heinrich Events" in the North Atlantic.

Age determinations on 4 sediment cores off Iceland

The north Icelandic shelf is partly distinguished by the Tjörnes Fracture Zone featuring numerous active basins in a mud-dominated shelf environment. Late Glacial and Holocene high-resolution sedimentary records from this area have been studied with tephrochronology as the main tool for correlation and for exact timing of palaeoceanographic events in the area. Data from three new piston cores from the shelf demonstrate the importance of tephra markers for the first chronological evaluation and correlation of the cores. The correlation is extended with lithological logs and with magnetic susceptibility records. A detailed multidisciplinary study (including biostratigraphy and tephrochronology) of a late Holocene record of predominantly muddy sediments at the same location demonstrates that marked variations in the distribution of water masses occurred repeatedly through the last 4500 cal. yr. Of special interest is the exact timing of a marked drop in sea-surface temperature in the area, indicated by ice rafting debris concentration, to about 50 years before the Hekla 3 eruption, which occurred at 2980 cal. yr BP. This appears to predate most records of a general cooling event in NW Europe by a couple of centuries. Two different possible age models, one based on 14C dates combined with tephra markers and one based on tephra markers alone, are discussed in context with the problem of different marine reservoir ages of the water masses in the area.