EPICA Dronning Maud Land EDML ice core drilling protocol

We report on the EPICA Dronning Maud Land (East Antarctica) deep drilling operation. Starting with the scientific questions that led to the outline of the EPICA project, we introduce the setting of sister drillings at NorthGRIP and EPICA Dome C within the European ice-coring community. The progress of the drilling operation is described within the context of three parallel, deep-drilling operations, the problems that occurred and the solutions we developed. Modified procedures are described, such as the monitoring of penetration rate via cable weight rather than motor torque, and modifications to the system (e.g. closing the openings at the lower end of the outer barrel to reduce the risk of immersing the drill in highly concentrated chip suspension). Parameters of the drilling (e.g. core-break force, cutter pitch, chips balance, liquid level, core production rate and piece number) are discussed. We also review the operational mode, particularly in the context of achieved core length and piece length, which have to be optimized for drilling efficiency and core quality respectively. We conclude with recommendations addressing the design of the chip-collection openings and strictly limiting the cable-load drop with respect to the load at the start of the run.

Organic geochemistry of ODP Leg 104 holes

The Leg 104 organic geochemistry program consisted of monitoring (a) hydrocarbon gases, (b) organic and inorganic carbon, and (c) parameters resulting from Rock-Eval pyrolysis at three sites on the Voring Plateau. The results amplify some of those obtained earlier on Deep Sea Drilling Project (DSDP) Leg 38. In a regional sense there is an inverse correlation between amounts of hydrocarbon gas and organic carbon. For example, significant concentrations of methane are present only at Site 644 in the inner part of the plateau where organic carbon contents are always less than 1%; in contrast, at Site 642 on the outer plateau, methane concentrations are very low (ppm range) whereas amounts of organic carbon approach 2%. Only at Site 644 are the environmental conditions such that methanogenesis is an active diagenetic process. Because of the importance of routine gas analyses to the Ocean Drilling Program (ODP), a procedure was devised to improve the use of Vacutainers for collection of gas samples. Comparison of methods for determining organic carbon showed that at Sites 643 and 644 Rock-Eval TOC could be used as a measure of organic carbon, but not at Site 642. Although no liquid or solid hydrocarbons were encountered at any of the sites, a catalog of potential organic geochemical contaminants was developed in anticipation of such a discovery.

Eocene siliceous and calcareous phytoplankton, Deep Sea Drilling Project Holes 95-612 and 95-613

Eocene siliceous and calcareous phytoplankton, with emphasis on silicoflagellates, were studied in 62 samples from DSDP Sites 612 and 613 on the continental slope and rise off New Jersey. The mid-latitude assemblages correlate well with assemblages from California, Peru, and offshore of southern Brazil, but are distinctly different from high-latitude cold-water assemblages of the Falkland Plateau off southern Argentina. Coccoliths and silicoflagellates provide evidence for the presence of a fairly complete middle and upper Eocene sequence, represented by a composite of Sites 612 and 613. A major unconformity occurs at the middle Eocene to upper Eocene contact at Site 612. The genus Bachmannocena Locker is emended and proposed as a replacement for genus Mesocena Ehrenberg for ring silicoflagellates. Six new silicoflagellates and one new diatom are described: Bachmannocena apiculata monolineata Bukry, n. subsp., Corbisema amicula Bukry, n. sp., C. bimucronata elegans Bukry, n. subsp., C. hastata incohata Bukry, n. subsp., C. jerseyensis Bukry, n. sp., Dictyocha acuta Bukry, n. sp., and Coscinodiscus eomonoculus Bukry, n. sp. Also, one new replacement name, B. paulschulzn Bukry, nom. nov., and 24 new combinations are proposed for genus Bachmannocena.

Stable oxygen and carbon isotope ratios of foraminifera and test results after different sample cleaning procedures from ODP Leg 207 sediments

We report oxygen and carbon stable isotope analyses of foraminifers, primarily planktonic, sampled at low resolution in the Cretaceous and Paleogene sections from Sites 1257, 1258, and 1260. Data from two samples from Site 1259 are also reported. The very low resolution of the data only allows us to detect climate-driven isotopic events on the timescale of more than 500 k.y. A several million-year-long interval of overall increase in planktonic 18O is seen in the Cenomanian at Site 1260. Before and after this interval, foraminifers from Cenomanian and Turonian black shales have d18O values in the range -4.2 per mil to -5.0 per mil, suggestive of upper ocean temperatures higher than modern tropical values. The d18O values of upper ocean dwelling Paleogene planktonics exhibit a long-term increase from the early Eocene to the middle Eocene. During shipboard and postcruise processing, it proved difficult to extract well-preserved foraminifer tests from black shales by conventional techniques. Here, we report results of a test of procedures for cleaning foraminifers in Cretaceous organic-rich mudstone sediments using various combinations of soaking in bleach, Calgon/hydrogen peroxide, or Cascade, accompanied by drying, repeat soaking, or sonication. A procedure that used 100% bleach, no detergent, and no sonication yielded the largest number of clean, whole individual foraminifers with the shortest preparation time. We found no significant difference in d18O or d13C values among sets of multiple samples of the planktonic foraminifer Whiteinella baltica extracted following each cleaning procedure.

Lead and strontium isotopic composition of some metalliferous and pelagic sediments and basalts at DSDP Leg 70 Holes

In recent years, metalliferous sediments have been discovered overlying newly generated oceanic crust in the East Pacific, North Atlantic, Indian Ocean, Red Sea, Gulf of Aden, and elsewhere (e.g., Boström, 1973; Lalou et al., 1977; Bischoff, 1969; Boström and Fisher, 1971; Cann et al., 1977, respectively). Such material has also been recovered by drilling from sediments lying upon older oceanic crust (Boström et al., 1972, 1976; Horowitz and Cronan, 1976). Hydrothermal circulation of seawater at a spreading ridge results in the leaching of Fe, Mn, and possibly other elements from the basaltic volcanic layer and their transport and discharge into ocean bottom waters, whereupon fine-grained Fe-Mn-rich precipitates form and settle into the ambient sediment (cf. Corliss, 1971; Dasch et al., 1971; Spooner and Fyfe, 1973; Bischoff and Dickson, 1975; Heath and Dymond, 1977; Corliss et al., 1979, Edmond et al., 1979). Mn-rich crusts have also been recovered from active ridges and are inferred to have formed in the vicinity of hydrothermal discharge areas (Scott et al., 1974; Moore and Vogt, 1976; Corliss et al., 1978; Hoffert et al., 1978). The source of the trace elements in the metalliferous deposits is generally not clear. They may be derived from seawater by adsorption onto the precipitates or crusts, or from hydrothermal solutions which have leached them from the basalts. Pb, however, can be used as a geochemical tracer because of the known isotopic compositional differences between oceanic basalts and seawater. Isotopic investigations of Pb in ferruginous sediments from the East Pacific have shown that it has been derived partly or mostly from a basaltic source (Bender et al., 1971; Dasch et al., 1971; Dymond et al., 1973). In the present study, Pb isotopic analyses have been made of a suite of metalliferous sediments (nontronite, Mn-oxide crust, Mn-Fe-oxide mud), pelagic sediments, and basalts from the Galapagos mounds area. The main purposes of the Pb study were to determine the source or sources of Pb in the metalliferous sediments, and whether or not stratigraphic variations exist in the isòtopic composition of Pb in the sediments.

Static GPS measurements and elevation model in the vicinity of the EDML deep-drilling site

Interpretation of ice-core records requires accurate knowledge of the past and present surface topography and stress-strain fields. The European Project for Ice Coring in Antarctica (EPICA) drilling site (0.0684° E and 75.0025° S, 2891.7 m) in Dronning Maud Land, Antarctica, is located in the immediate vicinity of a transient and splitting ice divide. A digital elevation model is determined from the combination of kinematic GPS measurements with the GLAS12 data sets from the ICESat satellite. Based on a network of stakes, surveyed with static GPS, the velocity field around the EDML drilling site is calculated. The annual mean velocity magnitude of 12 survey points amounts to 0.74 m/a. Flow directions mainly vary according to their distance from the ice divide. Surface strain rates are determined from a pentagon-shaped stake network with one center point, close to the drilling site. The strain field is characterised by along flow compression, lateral dilatation, and vertical layer thinning.

Sediment geochemical evidence for an early-middle Gilbert (early Pliocene) productivity peak in the North Pacific Red Clay Province

Current attempts to understand climatic variability during the early to middle Pliocene require paleoceanographic information from the Pacific and Indian Oceans that may serve to test and/or constrain future circulation models. Ocean Drilling Program (ODP) Sites 885/886 are located in the central subarctic North Pacific at water depths exceeding 5700 m. Recent studies of rock magnetic properties suggest that the fine-grained Fe oxide component in sediment at Sites 885/886 experienced reductive dissolution during the early-middle Gilbert. Because such an interval in the North Pacific Red Clay Province suggests a maximum in the sedimentary flux of organic carbon and/or a minimum in bottom water dissolved O2 concentrations (and hence, a peak change in North Pacific oceanographic conditions), a geochemical investigation was conducted to test the hypothesis. Quaternary sediment at Hole 886B was subjected to an oxyhydroxide removal procedure, and chemical analyses indicate that bulk sediment concentrations of Fe and the Fe/Sc ratio decrease significantly upon reductive dissolution. Downcore chemical analyses of untreated sediment at Hole 886B demonstrate that similar depletions also occur across the proposed interval of reduced sediment. Downcore chemical analyses also indicate that a pronounced increase in the Ba/Sc ratio occurs across the interval. These results are consistent with an interpretation that abyssal sediment of the North Pacific experienced a decrease in redox conditions during the early-middle Gilbert, and that this change in oxidation state was related to a peak in paleoproductivity. If the zenith of late Miocene to middle Pliocene enhanced productivity observed at other Indo-Pacific divergence regions similarly can be constrained to the early-middle Gilbert, there exists an oceanographic boundary condition in which to test future models concerning Pliocene warmth.

Mineralogical composition, copper and d18O at DSDP Site 59-448

Alteration in a submarine remnant volcanic arc should leave an important record of (1) the mineralogy of sea water-volcanic arc rock interaction; (2) the chemistry of solid reaction products; (3) the isotopic characteristics of such reactions (Muehlenbachs and Clayton, 1972; Spooner, Beckinsale, et al , 1977; Spooner, Chapman, et al., 1977); (4) the metallogenesis within such a sequence (Mitchell and Bell, 1973); and (5) the geothermal gradient during the alteration. The volcaniclastic breccias, tuffs, and igneous units of Sites 448 (993 m) and 451 (930.5 m) on the Palau-Kyushu and West Mariana ridges, respectively, are particularly suited for such studies because the thick sequences have remained submarine throughout their history, seemingly unaffected by magmatic or hydrothermal events after cessation of volcanic activity. Also, shipboard observations indicated a change in alteration products with depth. At both sites the igneous units and volcaniclastic rocks were altered to brownish clays and zeolites near the top of the volcanic sequence; to bright blue green clays and zeolites at moderate depths; and to very dark, nearly opaque, forest green clays and zeolites at still greater depths. Native copper occurs both as disseminated pockets in the volcaniclastic breccias and vesicular basalts and as veins in the breccias; native copper is restricted to stratigraphic levels characterized by the absence of sulfides or oxides of copper and iron. Although some native copper is found in vesicles of basalts and may be orthomagmatic, most of it is clearly secondary. Near dikes and sills, higher sulfur fugacity conditions caused the precipitation of iron and copper sulfides with an absence of native copper (Garrels and Christ, 1965). The occurrence of native copper may be an initial stage of Cu metallogenesis that forms porphyry coppers in island arcs (Mitchell and Bell, 1973). This study will address primarily the possibility that hydrothermal sea water interaction with volcanic arc rocks has created the mineralogical and isotopic zonation in Leg 59 cores. Hydrothermal activity can be expected in a rapidly growing island arc and is probably the result of a high geothermal gradient prevalent during arc magmatic activity. The chemical character of the alteration is further discussed by Hajash (1981).

Age-depth relation, radiocarbon ages and tephra geochemistry of core 5022-2CP from Laguna Potrok Aike, southern Patagonia

The 106 m long composite profile from site 2 of ICDP expedition 5022 (PASADO) at Laguna Potrok Aike documents a distinct change in sedimentation patterns from pelagic sediments at the top to dominating mass movement deposits at its base. The main lithological units correspond to the Holocene, to the Lateglacial and to the last glacial period and can be interpreted as the result of distinct environmental variations. Overflow conditions might have been achieved during the last glacial period, while signs of desiccation are absent in the studied sediment record. Altogether, 58 radiocarbon dates were used to establish a consistent age-depth model by applying the mixed-effect regression procedure which results in a basal age of 51.2 cal. ka BP. Radiocarbon dates show a considerable increase in scatter with depth which is related to the high amount of reworking. Validation of the obtained chronology was achieved with geomagnetic relative paleointensity data and tephra correlation.

Mg/Ca ratios in planktonic foraminifera

The primary Mg/Ca ratio of foraminiferal shells is a potentially valuable paleoproxy for sea surface temperature (SST) reconstructions. However, the reliable extraction of this ratio from sedimentary calcite assumes that we can overcome artifacts related to foraminiferal ecology and partial dissolution, as well as contamination by secondary calcite and clay. The standard batch method for Mg/Ca analysis involves cracking, sonicating, and rinsing the tests to remove clay, followed by chemical cleaning, and finally acid-digestion and single-point measurement. This laborious procedure often results in substantial loss of sample (typically 30-60%). We find that even the earliest steps of this procedure can fractionate Mg from Ca, thus biasing the result toward a more variable and often anomalously low Mg/Ca ratio. Moreover, the more rigorous the cleaning, the more calcite is lost, and the more likely it becomes that any residual clay that has not been removed by physical cleaning will increase the ratio. These potentially significant sources of error can be overcome with a flow-through (FT) sequential leaching method that makes time- and labor-intensive pretreatments unnecessary. When combined with time-resolved analysis (FT-TRA) flow-through, performed with a gradually increasing and highly regulated acid strength, produces continuous records of Mg, Sr, Al, and Ca concentrations in the leachate sorted by dissolution susceptibility of the reacting material. Flow-through separates secondary calcite from less susceptible biogenic calcite and clay, and further resolves the biogenic component into primary and more resistant fractions. FT-TRA reliably separates secondary calcite (which is not representative of original life habitats) from the more resistant biogenic calcite (the desired signal) and clay (a contaminant of high Mg/Ca, which also contains Al), and further resolves the biogenic component into primary and more resistant fractions that may reflect habitat or other changes during ontogeny. We find that the most susceptible fraction of biogenic calcite in surface dwelling foraminifera gives the most accurate value for SST and therefore best represents primary calcite. Sequential dissolution curves can be used to correct the primary Mg/Ca ratio for clay, if necessary. However, the temporal separation of calcite from clay in FT-TRA is so complete that this correction is typically <=2%, even in clay-rich sediments. Unlike hands-on batch methods, that are difficult to reproduce exactly, flow-through lends itself to automation, providing precise replication of treatment for every sample. Our automated flow-through system can process 22 samples, two system blanks, and 48 mixed standards in <12 hours of unattended operation. FT-TRA thus represents a faster, cheaper, and better way to determine Mg/Ca ratios in foraminiferal calcite.