A Holocene sediment sequence from Lake Igelsjön, south central Sweden, was studied by stable oxygen- and carbon-isotope analyses of different carbonate components. The deposit, which covers the time-span from ca 11,500calBP to the present, was laid down in a small, kettle-hole lake, the hydrological balance of which is presently dominated by groundwater flow. Isotopic records obtained on bulk carbonates originating mainly from summer-produced, calcitic algal encrustations exhibit several rapid shifts of more than 2‰, likely reflecting pronounced hydrological variations. Corresponding isotopic data obtained on calcitic gastropod opercula from parts of the profile show subdued responses to major climatic shifts, probably related to an extended calcification season. The isotopic records were complemented by studies of modern isotope hydrology, and our interpretations are based on a simplistic climate-hydrology model in which variations in groundwater generation within the lake catchment produce changes in groundwater level and related adjustments of lake level and surface/volume ratio of the basin during the ice-free season. Assumed periods of decreased lake volume in a relatively dry climate (low lake level) are characterised by enrichment in 18O and 13C resulting from increased evaporation/inflow ratio and atmospheric equilibration, respectively. In clear contrast to this situation, intervals of more humid climatic conditions give rise to increased lake volume (high lake level), possibly surface over flow, and relatively depleted isotopic ratios. Relatively humid conditions, which may correlate to a wide-spread cooling event recorded by various proxies across the North Atlantic region, are indicated by distinct isotopic shifts at ca 8300 and 8000calBP, bracketing a period of 18O-depletion. The period between ca 8000 and 4000calBP was characterised by relatively dry and stable climatic conditions, whereas the subsequent part of the Holocene experienced a more humid and variable climate following marked and coherent depletions in 18O and 13C at ca 4000calBP.

A multi-technique approach has been used to study a Pliocene shallow water marine deposit, designated the Île de France Formation, in North-East Greenland. The sequence is correlated on the basis of 87Sr–86Sr ratios in shells and palaeomagnetic studies with the Gauss normal polarity chron, which is dated to between 2.60 and 3.58 Ma years BP. This dating is in accordance with amino acid epimerisation and evidence from dinoflagellates, foraminifers and molluscs. Sediments, marine molluscs and foraminifers show that the sequence was deposited on the inner shelf, below storm wave base. Seawater temperatures were much higher than today, as demonstrated by the occurrence of a number of southern extra-limital species. The same applies to air temperature, and the few remains of land plants may indicate a forested upland with Picea and Thuja. A number of extinct taxa are present, including Nucula jensenii that is erected as a new species.

Ikka Fjord in southwest Greenland is the type locality for ikaite, a metastable hexahydrate of calcium carbonate. Here, ikaite forms submarine tufa columns rising up to 18 m above the fjord bottom. The columns are spectacular examples of abiogenic carbonate precipitation in a cold seawater environment and so far represent the only known formation of ikaite in seawater. We have analyzed the H-2, C-13, C-14, O-18 and Sr-87 contents and major-element and minor-element compositions of ikaite and of the different water types in and around Ikka Fjord in order to understand the formation of the Ikka columns. Water from inside the columns is fresh but alkaline, rich in ions of sodium, bicarbonate, and carbonate, and has a stable-isotope composition identical to precipitation falling on the nearby Gronnedal-Ika igneous complex, and we conclude that the tufa columns form over submarine springs issuing from the bottom of Ikka Fjord, Dissolution of unidentified sodium carbonate minerals in carbonatites in the igneous complex probably accounts for the peculiar chemistry of the springs. Ikaite supersaturation and precipitation is controlled by mixing of spring water and seawater at the cold (< 6C) fjord bottom, and precipitation is accelerated by the formation of hydrated CaCO(3)degrees (aq) ion pairs, while phosphate ions in the spring water act as inhibitor for precipitation of anhydrous carbonates, We propose that the spring water seeps in Ikka Fjord literally create their own conduits in the form of the vertical, chimney-like columns with ikaite forming continuously at the tops of the columns. The only limits to upward growth are winter ice and the fresh-water layer capping the fjord during summer.

The Kap København Formation, North Greenland, is a 100-m thick succession of predominantly shallow marine nearshore sediments, dated to c. 2.4 ma. The abundant well preserved remains of mosses, land plants, foraminifers, ostracodes, insects, cladocers, molluscs, and a few vertebrates enable a detailed reconstruction of terrestrial and marine environments and climate. The sediments indicate a complex sea-level history implying combined glacioisostatic and -eustatic control. This is supported by the faunal and floral development from arctic to subarctic and boreal conditions, and the record probably reflects the demise of the first major Cenozoic ice sheet, the Praetiglian, over the area, and the onset of the succeeding Tiglian A interglacial. The record ends with the attainment of the interglacial sea-level highstand and climate optimum when forest tundra reached the world’s northernmost coasts. It is inferred that the duration of sedimentation was a half obliquity cycle, i.e. 20,000 yr, at the most.

Corals from the Seychelles Islands, Indian Ocean, occur mainly as small coralline algae–vermetid remnants found in cavities adhering to the rock surface, and they rarely attain more than 2 m2in area. Samples ofGoniastreaandPoritesfrom elevations between 1.7 and 6 m above present mean sea level were dated by TIMS238U–234U–230Th techniques. The ages from well-preserved corals lie between 131,000 and 122,000 yr B.P., in agreement with most other observations of the last-interglacial sea level. Field evidence and dating from high marine limestones from two sections at La Digue Island indicate a period of coral buildup until 131,000 yr B.P., followed by a drop in sea level between 131,000 and 122,000 yr B.P.

U-Th ages of Holocene lacustrine sediments from southern Sweden have been determined to assess the reliability of this technique for dating climatic events from the last interglacial-glacial-interglacial cycle, and for calibration of the14C dating method. The sediments are organic- and carbonate-rich, and they are shown to be very well suited to high precision238U-234U-230Th dating by thermal ionisation mass spectrometry (TIMS). Twenty-one samples from 2.58 m of sediment from Lake Igelsjön, southern Sweden, yield ages between 3058 ± 89 and 9426 ± 262 yr (2σ error). The sediments consist of hydrogenous calcium carbonate (50–90%), organic matter (5–50%), and siliceous residue (< 5%). The high U contents of the lake sediments (between 6 and 76 ppm) are in contrast to the low concentrations in the lake- and groudwater (1.9 and 3.2 ppb, respectively), and mass balance calculations based on U content of water and sediments can be used to calculate a lakewter residence time of 24 days which is close to the residence time calculated using hydrologic data. Recent ground and lakewater ((234U/238U) = 0.920) is enriched in 234U compared to soils from the catchment area ((234U/238U= 0.587), and (234U/238U) in the lake sediments shows a marked decrease with time from 0.958 at 9426 yr BP to 0.919 at 3058 yr BP. This is attributed to progressive leaching of U from soils which have experienced a previous history of recoil-related U loss, and it indicates that the assumption of constant initial (234U/238U) ratios may be a source of significant error in the calculation of (234U/238U) ages for continental deposits.

was collected from the pelagic cap and the suprabasaltic clay cover at Limalok (Site 871), Lo-En (Site 872), Wodejebato (Sites 873 and 874), MIT (Site 878), and Seiko (Sites 879 and 880) guyots. Shipboard analyses of water samples included determinations of salinity, pH, alkalinity, chlorinity, calcium, magnesium, sulfate, fluoride, silica, ammonium, sodium, potassium, strontium, rubidium, and lithium (Premoli Silva, Haggerty, Rack, et al., 1993, p. 23). The chemical composition of the interstitial fluids from the pelagic caps showed few modifications with depth, and most samples had a composition close to that of modern seawater. This suggested either contamination with modern seawater during drilling or pore-water flushing by advection of recent seawater through the highly porous pelagic caps. Shore-based stable isotope analyses (hydrogen, oxygen, and strontium isotopes) of the Leg 144 interstitial water samples were then conducted to clarify the character of this phenomena. Surface seawater samples were collected at each site and analyzed for comparison. This report presents the results of the isotopic analyses. Further discussion of the pore-water history for selected sites will be given in Israelson et al. (this volume).

Strontium isotopes were used to evaluate the subsidence and sedimentation history of Limalok and Lo-En guyots in the western Pacific Ocean. We found that the Sr-isotope data from pelagic sediments deposited after the drowning of the guyots not only reflect the variations in seawater isotopic composition during the Neogene but also the amount of sediment reworking. At Site 871 (Limalok Guyot), analyses from the complete pelagic cap were obtained; however, at Site 872 (Lo-En Guyot), only the lowermost 50 m of the pelagic cap was analyzed. Limalok Guyot subsided and started to accumulate pelagic sediments about 20 Ma; Lo-En Guyot started at about 27 Ma. Sediment accumulation was not continuous, and sediments were considerably reworked at several intervals. In general, sediment reworking occurs during the initial pelagic sedimentation. On Limalok Guyot, another interval of sediment reworking as well as large erosional intervals from 14.2 to 2.4 Ma were identified.

Pelagic sediments accumulated on Limalok and Lo-En guyots as they sank below the wave base. Limalok Guyot contains 140 m of pelagic sediments that range in age from the early Miocene to the Holocene. Lo-En Guyot contains approximately 150 m of pelagic sediments of late Oligocene to Holocene age. Ten different geochemical parameters were measured in an attempt to evaluate the potential use of the sediments as a geochemical recorder of the environment. It was found that, although the pelagic caps consist of well-preserved planktonic foraminifers, mixing of sediments during or shortly after deposition precludes high- resolution paleoceanographic studies. The original pore-water composition is modified by interactions with the sediment and possibly by seawater at a postdepositional time. The purpose of the present study is to evaluate pelagic caps on western Pacific guyots as geochemical recorders and to assess their suitability for paleoceanographic studies. The guyots studied are Limalok and Lo-En guyots, which belong to the Marshall Island group of seamounts. Pelagic sediments accu- mulated on these guyots as they slowly sank below the wave base after the drowning of the carbonate platform. This means that the pelagic sediments were deposited well above the carbonate compen- sation depth (CCD) and consist almost solely of planktonic foramin- ifers and nannofossil ooze with a very low clay content. Four kinds of geochemical parameters were studied in these sedi- ment samples: carbonate concentration, element ratios (Sr/Ca, Mg/ Ca), stable isotopes (δ18θ and δ13C), and radiogenic isotopes (87Sr/ 86Sr). Furthermore, four kinds of parameters were studied in the pore water samples: element concentration, stable isotopes (δ'8O and δ2H), radiogenic isotopes (87Sr/86Sr), and short-chain organic acids.

The first major Weichselian ice advance in Scoresby Sund, during the Aucellaelv stage, deposited thick till beds along the coast of Jameson Land between > 107 ka and 140 ka. and is correlated with isotope substage 5d in the marine record. This is shown by stream‐cut sections at the mouth of the Aucellaelv. Jameson Land, which contain a scquence of shallow marine, fluvial and glacigene sediments extending from the Scoresby Sund glaciation (≅Saalian) to the Flakkerhuk stade (Late Weichselian). The sequence is dated by palaeoceanographic correlation with the deep‐sea record, U/Th and luminescence dating, and correlated with the record in adjacent areas by mapping of marker horizons, and by mollusc fauna assemblages and amino acid analyses.

Oxygen and carbon isotope composition of arctic bivalve shells are used in an attempt to reconstruct surface water temperature and salinities in Scoresby Sund, East Greenland. The oxygen isotope compositions of Mya truncata, Hiatella arctica and Tridonta borealis have been compared with present day hydrological parameters. Modern shells yield oxygen isotope values that, on the whole, reproduce the environmental temperature and sea water isotopic composition. Furthermore, it is possible to estimate the living depth of the analysed specimens. Analyses of growth increments from single shells show that there are large variations from year to year in temperature and oxygen isotope composition of the surface waters of Scoresby Sund and that these variations decrease with depth. Analyses of Holocene shells indicate that the Polar Current water, which flows from north to south along the East Greenland coast was also present during the Holocene climatic optimum 8000-7000 yr B.P. Analyses of bivalve shells from the last interglacial show that Scoresby Sund during that time was well circulated and that meltwater from the Greenland ice sheet and sea ice meltwater was important for the temperature, salinity and isotopic composition of the surface waters.

The UPb dating of carbonate offers considerable potential for accurate and direct dating of sedimentary rocks. Here we show that carbonate concretions from the Upper Cambrian black shales in southern Scandinavia have remarkably high U to Pb ratios (238U204Pb up to 288,000) permitting precise geochronology. A fine-crystalline early diagenetic concretion yields an age of 509.8 ± 5.1 Ma, providing an accurate age for the late Cambrian, whereas a coarse ‘cone-in-cone’ concretion has yielded an age of 478.2 ± 4.9 Ma, defining the final stage of sediment compaction and indicating a protracted dewatering and diagenetic history. These results demonstrate the power of this method for directly calibrating the geological time scale and constraining diagenetic histories.