Strontium isotope ratios of planktonic foraminifera from sediment samples acroos the K/T boundary

Seawater 87Sr/86Sr values increase abruptly by 28 * 10**-6 across the Cretaceous/Tertiary boundary (KTB). This small, but rapid shift is superimposed on the larger scale structure of the seawater Sr isotope curve. The time scale of radiogenic Sr addition appears to be too rapid to reconcile with sources associated with volcanism, and we show that the amount of Sr required to produce even this small increase is too large to be derived from: (1) a KT bolide of the size constrained by the Ir anomaly, (2) continental crust ejecta from the impact of such a bolide, (3) soot from global wildfires initiated by an impact, or (4) any combination of these sources. The probable source of the radiogenic Sr is enhanced continental weathering, but the high rate of increase appears to rule out processes such as sea level regression, glaciation or tectonism. A plausible mechanism for rapid addition of radiogenic Sr to the oceans is enhanced weathering associated with globally distributed acid rain (pH c. 1) which is a proposed by-product of a bolide impact (Prinn and Fegley, 1987, doi:10.1016/0012-821X(87)90046-X).

(Table 2) Uranium series results of Villars Cave stalagmite Vil-stm14

We present a new high resolution speleothem stable isotope record from the Villars Cave (SW-France) that covers part of marine isotope stage (MIS) 3. The Vil14 stalagmite grew between ~52 and 29 ka. The d13C profile is used as a palaeoclimate proxy and clearly shows the interstadial substages 13, 12 and 11. The new results complement and corroborate previously published stalagmite records Vil9 and Vil27 from the same site. The Vil14 stalagmite chronology is based on 12 Th-U dating by MC-ICP-MS and 3 by TIMS. A correction for detrital contamination was done using the 230Th/232Th activity ratio measured on clay collected in Villars Cave. The Vil14 results reveal that the onset of Dansgaard-Oeschger (DO) events 13 and 12 occurred at ~49.8 ka and ~47.8 ka, respectively. Within uncertainties, this is coherent with the latest NorthGRIP time scale (GICC05-60 ka) and with speleothem records from Central Alps. Our data show an abrupt d13C increase at the end of DO events 14 to 12 which coincides with a petrographical discontinuity probably due to a rapid cooling. As observed for Vil9 and Vil27, Vil14 growth significantly slowed down after ~ 42 ka and finally stopped ~ 29 ka ago where the d13C increase suggests a strong climate deterioration that coincides with both North Atlantic sea level and sea surface temperature drop.

Bio- and magnetostratigraphic events of ODP holes of the central Kerguelen Plateau

Neogene biostratigraphic and magnetostratigraphic data are compiled from Holes 747A, 748B, and 751A drilled on the Southern Kerguelen Plateau during Ocean Drilling Program Leg 120. Neogene sections have excellent to good magnetostratigraphic signatures in many intervals. This, in addition to minimal coring gaps and the occurrence of mixed assemblages of both calcareous and siliceous microfossil assemblages, makes these valuable biostratigraphic reference sections for intra- and extraregional correlations. This paper combines the sequence of biostratigraphic events reported from diatom, radiolarian, planktonic foraminifer, calcareous nannofossil, and silicoflagellate studies of Leg 120 sediments. It correlates microfossil datums with the geomagnetic polarity time scale to test existing age estimates and to refine biostratigraphic age controls for the southern high latitudes. Significant biostratigraphic datums are presented in a series of age-depth plots. Numerous hiatuses are clearly identified through this approach, and the positions of lesser disconformities are suggested. Most Neogene intervals are represented in at least one site, although "regional" unconformities occur in the upper Pliocene, uppermost Miocene/lowermost Pliocene, middle upper Miocene, middle middle Miocene, and at the lower/middle Miocene boundaries. The longest hiatus spanned 6 m.y., with most other hiatuses representing 1 m.y. or less. This paper compiles Leg 120 biostratigraphic and magnetostratigraphic data for use in future syntheses of southern high latitude biostratigraphy and presents an age model for Leg 120 Neogene sediments.

Planktonic foraminifera of ODP Hole 107-654A

The late Miocene sediments of the Tyrrhenian ODP Site 654 encompass a deepening sequence which begins with glauconite shallow water sands followed by a rapid transition to deep water sediments and culminates with dolomitic mudstones associated with Messinian evaporites. The sequence compares well with the so-called 'Sahelian cycle' and with post-orogenic cycles recognized in peninsular Italy and Sicily. The studied interval, consisting of 55 m thick nannofossil oozes, belongs to the Globorotalia suterae subzone and lower part of the Globorotalia conomiozea Zone, indicating late Tortonian and early Messinian age, respectively. Biomagnetostratigraphic correlation assigns the Tortonian/ Messinian boundary an age of 6.44-6.45 Ma. In addition, six main events have been recognized, based on the range of keeled globorotaliids and coiling direction changes of keeled and unkeeled globorotaliids, which have been correlated to the geomagnetic time-scale. Comparison with North Atlantic sites and land sections of the Guadalquivir basin and northern Morocco provides good correlations with the events documented in these areas. In particular, Event IV, which predates the FO of Globorotalia conomiozea, may be used to recognize the Tortonian/Messinian boundary in extra-Mediterranean areas where G. conomiozea is missing. Variations in the distribution of different species of Globigerinoides are related to changes in the surficial marine environment. Although no clear trends can be recognized on the oxygen and carbon isotope records of Globigerinoides obliquus, the parallelism between the occurrence of low salinity species (G. sacculifer) and peaks of low 5180 values, as well as that of normal salinity species (G. obliquus) and peaks of high d18O values, suggests strong local changes of environmental conditions. The high amplitude of the fluctuations of d18O values suggests important variations in the salinity of the Tyrrhenian Sea, related to a rapidly changing water budget. The major feature of the carbon isotope record is a large decrease between 7.0 and 6.95 Ma, which therefore predates the 6.2 Ma global 'carbon shift'.

Middle and late Miocene calcareous nannofossil biostratigraphy from equatorial Indian and Pacific Oceans

Selected calcareous nannofossils were investigated by means of quantitative methods in middle and upper Miocene sediments from the tropical Indian Ocean (ODP Leg 115) and equatorial Pacific Ocean (DSDP Leg 85, ODP Legs 130 and 138). Our goal was to test the reliability of the classic biohorizons used in the standard zonations of Martini (1971) and Bukry (1973) and, possibly, to improve biostratigraphic resolution in the Miocene. In a time interval of about 8 m.y., from the last occurrence (LO) of S. heteromorphus (~13.6 Ma) to the LO of D. quinqueramus (~5.5 Ma), a total 37 events were investigated, using both the conventional and some additional markers proposed in the literature. At least 17 of these events proved to be distinct biostratigraphic correlation lines between the two considered areas. This integrated biostratigraphic framework increases the biostratigraphic resolution in the middle-upper Miocene interval (of the order of about 0.5 m.y). All the investigated events were tied to the geomagnetic polarity time scale (GPTS) and compared to biomagnetostratigraphy from mid-latitude North Atlantic Site 94-608 (Olafsson, 1991; Gartner, 1992), thus obtaining further information about the biostratigraphic and biochronologic reliability of the investigated events and a significant improvement of the available nannofossil biomagnetostratigraphic model for the middle and late Miocene.

Site characteristics and ice speed at four sites on Kangiata Nunata Sermia glacier, southwest Greenland

We present subdaily ice flow measurements at four GPS sites between 36 and 72 km from the margin of a marine-terminating Greenland outlet glacier spanning the 2009 melt season. Our data show that >35 km from the margin, seasonal and shorter-time scale ice flow variations are controlled by surface melt-induced changes in subglacial hydrology. Following the onset of melting at each site, ice motion increased above background for up to 2 months with resultant up-glacier migration of both the onset and peak of acceleration. Later in our survey, ice flow at all sites decreased to below background. Multiple 1 to 15 day speedups increased ice motion by up to 40% above background. These events were typically accompanied by uplift and coincided with enhanced surface melt or lake drainage. Our results indicate that the subglacial drainage system evolved through the season with efficient drainage extending to at least 48 km inland during the melt season. While we can explain our observations with reference to evolution of the glacier drainage system, the net effect of the summer speed variations on annual motion is small (~1%). This, in part, is because the speedups are compensated for by slowdowns beneath background associated with the establishment of an efficient subglacial drainage system. In addition, the speedups are less pronounced in comparison to land-terminating systems. Our results reveal similarities between the inland ice flow response of Greenland marine- and land-terminating outlet glaciers.

Chemical concentrations and fluxes from EPICA ice cores EDML and EDC

Continuous sea salt and mineral dust aerosol records have been studied on the two EPICA (European Project for Ice Coring in Antarctica) deep ice cores. The joint use of these records from opposite sides of the East Antarctic plateau allows for an estimate of changes in dust transport and emission intensity as well as for the identification of regional differences in the sea salt aerosol source. The mineral dust flux records at both sites show a strong coherency over the last 150 kyr related to dust emission changes in the glacial Patagonian dust source with three times higher dust fluxes in the Atlantic compared to the Indian Ocean sector of the Southern Ocean (SO). Using a simple conceptual transport model this indicates that transport can explain only 40% of the atmospheric dust concentration changes in Antarctica, while factor 5-10 changes occurred. Accordingly, the main cause for the strong glacial dust flux changes in Antarctica must lie in environmental changes in Patagonia. Dust emissions, hence environmental conditions in Patagonia, were very similar during the last two glacials and interglacials, respectively, despite 2-4 °C warmer temperatures recorded in Antarctica during the penultimate interglacial than today. 2-3 times higher sea salt fluxes found in both ice cores in the glacial compared to the Holocene are difficult to reconcile with a largely unchanged transport intensity and the distant open ocean source. The substantial glacial enhancements in sea salt aerosol fluxes can be readily explained assuming sea ice formation as the main sea salt aerosol source with a significantly larger expansion of (summer) sea ice in the Weddell Sea than in the Indian Ocean sector. During the penultimate interglacial, our sea salt records point to a 50% reduction of winter sea ice coverage compared to the Holocene both in the Indian and Atlantic Ocean sector of the SO. However, from 20 to 80 ka before present sea salt fluxes show only very subdued millennial changes despite pronounced temperature fluctuations, likely due to the large distance of the sea ice salt source to our drill sites.

Holocene sedimentation rates in the Northwest Passage

Palynological, geochemical, and physical records were used to document Holocene paleoceanographic changes in marine sediment core from Dease Strait in the western part of the main axis of the Northwest Passage (core 2005-804-006 PC latitude 68°59.552'N, longitude 106°34.413'W). Quantitative estimates of past sea surface conditions were inferred from the modern analog technique applied to dinoflagellate cyst assemblages. The chronology of core 2005-804-006 PC is based on a combined use of the paleomagnetic secular variation records and the CALS7K.2 time-varying spherical harmonic model of the geomagnetic field. The age-depth model indicates that the core spans the last ~7700 cal years B.P., with a sedimentation rate of 61 cm/ka. The reconstructed sea surface parameters were compared with those from Barrow Strait and Lancaster Sound (cores 2005-804-004 PC and 2004-804-009 PC, respectively), which allowed us to draw a millennial-scale Holocene sea ice history along the main axis of the Northwest Passage (MANWP). Overall, our data are in good agreement with previous studies based on bowhead whale remains. However, dinoflagellate sea surface based reconstructions suggest several new features. The presence of dinoflagellate cysts in the three cores for most of the Holocene indicates that the MANWP was partially ice-free over the last 10,000 years. This suggests that the recent warming observed in the MANWP could be part of the natural climate variability at the millennial time scale, whereas anthropogenic forcing could have accelerated the warming over the past decades. We associate Holocene climate variability in the MANWP with a large-scale atmospheric pattern, such as the Arctic Oscillation, which may have operated since the early Holocene. In addition to a large-scale pattern, more local conditions such as coastal current, tidal effects, or ice cap proximity may have played a role on the regional sea ice cover. These findings highlight the need to further develop regional investigations in the Arctic to provide realistic boundary conditions for climatic simulations.

Age and strontium isotope composition for Cretaceous in DSDP Hole 74-525

Firm stratigraphic correlations are needed to evaluate the global significance of unconformity bounded units (sequences). We correlate the well-developed uppermost Campanian and Maestrichtian sequences of the New Jersey Coastal Plain to the geomagnetic polarity time scale (GPTS) by integrating Sr-isotopic stratigraphy and biostratigraphy. To do this, we developed a Maestrichtian (ca. 73-65 Ma) Sr-isotopic reference section at Deep Sea Drilling Project Hole 525A in the southeastern Atlantic Ocean. Maestrichtian strata can then be dated by measuring their 87Sr/86Sr composition, calibrating to the GPTS of S. C. Cande and D. V. Kent (1993, personal commun.), and using the equation Age (Ma) = 37326.894-52639.89 (87Sr/86Sr). Sr-stratigraphic resolution for the Maestrichtian is estimated as +-1.2 to +-2 m.y. At least two unconformity-bounded units comprise the uppermost Campanian to Maestrichtian strata in New Jersey. The lower one, the Marshalltown sequence, is assigned to calcareous nannofossil Zones CC20/21 (~NC19) and CC22b (~NC20). It ranges in age from ~74.1 to 69.9 Ma based on Sr-isotope age estimates. The overlying Navesink sequence is assigned to calcareous nannoplankton Zones CC25-26 (~NC21-23); it ranges in age from 69.3 to 65 Ma based on Sr-isotope age estimates. The upper part of this sequence, the Tinton Formation, has no calcareous planktonic control; Sr-isotopes provide an age estimate of 66 +- 1.2 Ma (latest Maestrichtian). Sequence boundaries at the base and the top of the Marshalltown sequence match boundaries elsewhere in the Atlantic Coastal Plain (Owens and Gohn, 1985) and the inferred global sea-level record of Haq et al. (1987); they support eustatic changes as the mechanism controlling depositional history of this sequence. However, the latest Maestrichtian record in New Jersey does not agree with Haq et al. (1987); we attribute this to correlation and time-scale differences near the Cretaceous/Paleogene boundary. High sedimentation rates in the latest Maestrichtian of New Jersey (Shrewsbury Member of the Red Bank Formation and the Tinton Formation) suggest tectonic uplift and/or rapid progradation during deposition of the highstand systems tract.

Chlorophyll and true-color maps of sediments from the intertidal zones in Winyah Bay, South Carolina, USA and List, Sylt, Germany

We used hyperspectral imaging to study short-term effects of bioturbation by lugworms (Arenicola marina) on the surficial biomass of microphytobenthos (MPB) in permeable marine sediments. Within days to weeks after the addition of a lugworm to a homogenized and recomposed sediment, the average surficial MPB biomass and its spatial heterogeneity were, respectively, 150 - 250% and 280% higher than in sediments without lugworms. The surficial sediment area impacted by a single medium-sized lugworm (~4 g wet weight) over this time-scale was at least 340 cm**2. While sediment reworking was the primary cause of the increased spatial heterogeneity, experiments with lugworm-mimics together with modeling showed that bioadvective porewater transport from depth to the sediment surface, as induced by the lugworm ventilating its burrow, was the main cause of the increased surficial MPB biomass. Although direct measurements of nutrient fluxes are lacking, our present data show that enhanced advective supply of nutrients from deeper sediment layers induced by faunal ventilation is an important mechanism that fuels high primary productivity at the surface of permeable sediments even though these systems are generally characterized by low standing stocks of nutrients and organic material.

Stable isotope record of benthic foraminifera and the planktic foraminifera Globigerinoides sacculifer from sediment core GIK13519-1, Sierra Leone Rise, eastern equatorial Atlantic

From a 10.7 m long gravity core from the Sierra Leone Rise (5°39.5' N, 19°51' W) a detailed oxygen and carbon isotope record of both planktonic and benthonic foraminifera species was obtained extending from the Recent to Jaramillo event. The analysis yielded six major results. 1. Benthos oxygen isotopes varied by 1.8-2.2 per mil from interglacial to glacial times and may indicate a synglacial cooling of North Atlantic Deep Water at 2800 m depth by 1-3°C. 2. Variable anomalies between the benthos and plankton d18O record indicate a cooling of sea-surface temperatures (SST) by up to 6 °C during some glacial stages. 3. Southerly trade winds and equatorial upwelling may excert the primary control off SST variations, in particular of extremee values of cold and warm stages and of the abrupt character of climate transitions and their leads and lags, and finally, of variable sedimentation rates. 4. The benthos d13C record correlates well with the flux and preservation of organic matter. 5. A new time scale, CARPOR, was established from the assumption that terrigenous sediment supply was ± constant bit CaCO3 varied considerably. When applied to the d18O record, three major and numerous short-term variations of sedimentation rates (0.8 to 4.0 cm/kyr) can be distinguished. 6. The climatic record was modified by bioturbation much more strongly during cold than during warm stages.

Stable and strontium isotope ratios and age determination of ODP Site 130-803

Stratigraphic information from strontium, oxygen, and carbon isotopic ratios has been integrated with diatom and planktonic foraminifer datums to refine the Oligocene to early Miocene chemostratigraphy of Site 803. The Sr isotope results are based on analyses of mixed species of planktonic foraminifer and bulk carbonate samples. 87Sr/86Sr ratios of bulk carbonate samples are, in most cases, less radiogenic than contemporaneous seawater. Estimated sediment ages based on planktonic foraminifer 87Sr/86Sr ratios, using the Sr-isotope-age relation determined by Hess and others in 1989, are in moderately good agreement with the biostratigraphic ages. Chronological resolution is significantly enhanced with the correlation of oxygen and carbon isotope records to those of the standard Oligocene section tied to the Geomagnetic Polarity Time Scale at Site 522. Ages revised by this method and other published ages of planktonic foraminifer datums are used to revise the Oligocene stratigraphy of Site 77 to correlate the stable isotope records of Sites 77 and 803. Comparison of the Cibicidoides stable isotope records of Sites 77 and 574 with paleodepths below 2500 m in the central equatorial Pacific, and Site 803 at about 2000-m paleodepth in the Ontong Java Plateau reveals inversions in the vertical d18O gradient at several times during the Oligocene and in the early Miocene. The shallower water site had significantly-higher d18O values than the deeper water sites after the earliest Oligocene 18O enrichment and before 34.5 Ma, in the late Oligocene from 27.5 to at least 25 Ma, and in the early Miocene from 22.5 to 20.5 Ma. It is not possible to ascertain if the d18O inversion persisted during the Oligocene/Miocene transition because the deeper sites have hiatuses spanning this interval. We interpret this pattern to reflect that waters at about 2000 m depth were cold and may have formed from mixing with colder waters originating in northern or southern high-latitude regions. The deeper water appear to have been warmer and may have been a mixture with warm saline waters from mid- or low-latitude regions. No apparent vertical d13C gradient is present during the Oligocene, suggesting that the age difference of these water masses was small.

Sedimentation patters in the eastern equatorial Pacific Ocean

The post-middle Miocene evolution of sedimentary patterns in the eastern equatorial Pacific Ocean has been deduced from a compilation and synthesis of CaCO3, opal, and nannofossil assemblage data from 11 sites drilled during Leg 138. Improvements in stratigraphic correlation and time scale development enabled the construction of lithostratigraphic and chronostratigraphic frameworks of exceptional quality. These frameworks, and the high sedimentation rates (often exceeding 4 cm/k.y.) provided a detailed and synoptic paleoceanographic view of a large and highly productive region. The three highlights that emerge are: (1) a middle late Miocene "carbonate crash" (Lyle et al., this volume); (2) a late Miocene-early Pliocene "biogenic bloom"; and (3) an early Pliocene "opal shift". During the carbonate crash, an interval of dissolution extending from -11.2 to 7.5 Ma, CaCO3 accumulation rates declined to near zero over much of the eastern equatorial Pacific, whereas opal accumulation rates remained substantially unchanged. The crash nadir, near 9.5 Ma, was marked by a brief shoaling of the regional carbonate compensation depth by more than 1400 m. The carbonate crash has been correlated over the entire tropical Pacific Ocean, and has been attributed to tectonically-induced changes in abyssal flow through the Panamanian seaway. The biogenic bloom extended from 6.7 to 4.5 Ma, and was characterized by an overall increase in biogenic accumulation and by a steepening of the latitudinal accumulation gradient toward the equator. The bloom has been observed over a large portion of the global ocean and has been linked to increased productivity. The final highlight, is a distinct and permanent shift in the locus of maximum opal mass accumulation rate at 4.4 Ma. This shift was temporally, and perhaps causally, linked to the final closure of the Panamanian seaway. Before 4.4 Ma, opal accumulation was greatest in the eastern equatorial Pacific Basin (near 0°N, 107°W). Since then, the highest opal fluxes in the equatorial Pacific have occurred in the Galapagos region (near 3°S, 92°W).