Expedition 302 summary

The first scientific drilling expedition to the central Arctic Ocean was completed in September 2004. Integrated Ocean Drilling Program Expedition 302, Arctic Coring Expedition (ACEX), recovered sediment cores to 428 meters below seafloor (mbsf) in water depths of ~1300 m, 250 km from the North Pole. Expedition 302’s destination was the Lomonosov Ridge, hypothesized to be a sliver of continental crust that broke away from the Eurasian plate at ~56 Ma. As the ridge moved northward and subsided, marine sedimentation occurred and continues to the present, resulting in what was anticipated from seismic data to be a continuous paleoceanographic record. The elevation of the ridge above the surrounding abyssal plains (~3 km) ensured that sediments atop the ridge were free of turbidites. The primary scientific objective of Expedition 302 was to continuously recover this sediment record and to sample the underlying sedimentary bedrock by drilling and coring from a stationary drillship. The biggest challenge during Expedition 302 was maintaining the drillship’s location while drilling and coring in 2–4 m thick sea ice that moved at speeds approaching 0.5 kt. Sea-ice cover over the Lomonosov Ridge moves with one of the two major Arctic sea-ice circulation systems, the Transpolar Drift, and responds locally to wind, tides, and currents. Until now, the high Arctic Ocean Basin, known as “mare incognitum” within the scientific community, had never before been deeply cored because of these challenging sea-ice conditions. Initial results reveal that biogenic carbonate is present only in the Holocene–Pleistocene interval. The upper 198 mbsf represents a relatively high sedimentation rate record of the past 18 m.y. and is composed of sediment with ice-rafted debris and dropstones, suggesting that ice-covered conditions extended at least this far back in time. Details of the ice type (e.g., iceberg versus sea ice), timing, and characteristics (e.g., perennial versus seasonal) await further study. A hiatus occurs at 193.13 mbsf, spanning a 25 m.y. interval from the early Miocene to the middle Eocene between ~18 Ma and 43 Ma. The sediment record during the middle Eocene is of dark, organic-rich biosiliceous composition. Isolated pebbles, interpreted as ice-rafted dropstones, are present down to 239 mbsf, well into this middle Eocene interval. Around the lower/middle Eocene boundary an abundance of Azolla spp. occurs, suggesting that a fresh and/or low-salinity surface water setting dominated the region during this time period. Although predrilling predictions based on geophysical data had placed the base of the sediment column at 50 Ma, drilling revealed that the uppermost Paleocene to lowermost Eocene boundary interval, well known as the Paleocene/Eocene Thermal Maximum (PETM), was recovered. During the PETM, the temperature of the Arctic Ocean surface waters exceeded 20°C. Drilling during Expedition 302 also penetrated into the underlying sedimentary bedrock, revealing a shallow-water depositional environment of Late Cretaceous age

Optically Stimulated Luminescence Dating Supports Central Arctic Ocean CM-scale Sedimentation Rates

This paper presents new results from Optically Stimulated Luminescence (OSL) dating on a sediment core raised from the crest of the Lomonosov Ridge in the central Arctic Ocean. There has been much debate about dating sediment cores from the central Arctic Ocean and by using an independent absolute dating technique we aim to test whether or not relatively fast, cm-scale/ka, sedimentation rates were typical of Arctic’s Pleistocene depositional mode. On the basis of mainly paleomagnetic reversal stratigraphy, many previous studies suggest mm-scale/ka sedimentation rates. A common feature in these studies is that the first down core paleomagnetic negative inclination is consistently interpreted as the Brunhes/Matuyama boundary at about 780 ka. Our OSL dating results indicate that this assumption is not generally valid, and that the first encountered negative inclination represents younger age excursions within the Brunhes Chron, implying reinterpretation of many published core studies where paleoenvironmental reconstructions have been made for the central Arctic Ocean. Our dating results furthermore corroborates a correlation of the uppermost 2–3 m of the Lomonosov Ridge cores to a well-dated core located off the Barents-Kara Sea margin that in turn is correlated to cores in the Fram Strait. Valuable information on the paleoceanographical evolution in the Arctic Ocean from MIS 6 to the Holocene is given through this correlation of records from the central Arctic Ocean to records off the Eurasian continental margin

Climatic cyclicity at Site 806; the GRAPE record

We used the continuous saturated bulk density records collected by the gamma-ray attenuation porosity evaluator (GRAPE) at Ocean Drilling Program Site 806 on the top of the Ontong Java Plateau to evaluate the continuity of the recovered cores and to splice together a complete section from the multiple holes drilled at the site (for the upper 165 m, this is equivalent to approximately 0-5 Ma). The lack of offset in core breaks (between the 9.5-m-long, successive cores) from hole to hole made splicing difficult, and the results are not unambiguous. The composite section was converted to a time series by using biostratigraphy and supplementing this with oxygen-isotope datums for the interval between 2 and 5 Ma. Evolutionary spectra generated from the composite section clearly indicate the presence of Milankovitch frequencies throughout the record. We chose a final age model that was most consistent with a Milankovitch model but have not, as yet, spectrally tuned the data. The GRAPE (saturated bulk density) changes at Site 806 are the result of changes in grain size, with density decreasing as grain size increases. We attribute this to the removal of fine particles by winnowing, leaving a greater percentage of large hollow foraminifers behind— the winnowing effect. This is in contrast to the dissolution effect, which breaks up large hollow foraminifers into fragments but merely transfers intraparticle porosity to interparticle porosity and thus shows significant changes in grain size without significant changes in density. A 300-k.y. piston core record reveals that during this time interval increased winnowing has been associated with glacials and 100-k.y. cyclicity. For the time interval from 5 to 2 Ma, enhanced winnowing continues to be associated with isotopically heavy intervals dominated by 41-k.y. (obliquity) variance. In this band, the winnowing record is highly correlated with the ice-volume record, particularly since the onset of Northern Hemisphere glaciations. Before that time, the grain-size record continues to show variance in the obliquity band whereas the oxygen isotope record shows a shift to the dominance of precessional frequencies. We suggest that the winnowing signal is a response to increased thermohaline circulation and benthic storm activity associated with enhanced north-south thermal gradients during times of climatic degradation

Evolution of Pliocene climate cyclicity at Hole 806B (5-2 Ma); oxygen isotope record

A detailed Pliocene oxygen isotope record from the Ontong Java Plateau, based on measurements of the surface-dwelling planktonic foraminifer Globigerinoides sacculifer, was produced for the period from 5 to 2 Ma. The record documents major long and short-term climate changes. The results show periods of enhanced ice volume at 4.6 to 4.3 Ma and after 2.85 Ma, a long-term warming trend from 4.1 to 3.7 Ma, and a distinct cooling trend that was initiated at 3.5 Ma and progressed through the initiation of large-scale Northern Hemisphere glaciation after 2.85 Ma (according to the time scale of Shackleton and others proposed in 1990). Periods of high average ice volumes also show the highest δ 1 8 amplitudes. The pattern of climate cyclicity changed markedly at about 2.85 Ma. Earlier times were marked by high-frequency variability at the precessional frequencies or even higher frequencies, pointing to low-latitude processes as a main controlling factor driving planktonic δ 1 8 variability in this period. The high-frequency variability is not coherent with insolation and points to strong nonlinearity in the way the climate system responded to orbital forcing before the onset of large scale Northern Hemisphere glaciation. After 3 Ma, stronger 41-k.y. cyclicity appears in the record. The shift in pattern is clearest around 2.85 Ma (according to the time scale proposed by Shackleton and others in 1990), 100-200 k.y. before the most dramatic spread of Northern Hemisphere ice sheets. This indicates that high-latitude processes from this point on began to take over and influence most strongly the δ 1 8 record, which now reflects ice-volume fluctuations related to the climatic effects of obliquity forcing on the seasonality of high-latitude areas, most probably in the Northern Hemisphere. The general Pliocene trend is that high-latitude climate sensitivity and instability was increasing, and the causal factors producing the intensified glacial cyclicity during the Pliocene must be factors that enhance cooling and climate sensitivity in the subarctic areas

Paleomagnetic Chronology of Arctic Ocean Sediment Cores: Reversals and Excursions -The Conundrum

Chronologies of Arctic Ocean sediment cores are mainly based on interpretation of paleomagnetic inclination records. The first paleomagnetic chronology assigned zones with negative inclinations to polarity reversals (Steuerwald et al, 1968) because geomagnetic excursions at that time were a novel observation and had only been reported from lavas. Arctic Ocean sedimentation rates were thus established to be in the mm/ka-range. A general recognition of excursions as real features of the geomagnetic field emerged more than three decades later, and presently there is still no consensus regarding the number (or name), duration and age of global synchronous excursions within the Brunhes Chron. Assigning inclination records to polarity reversals or excursions is an ambiguous exercise without independent age information. Based on independently derived time frames, 11 negative inclination intervals in core 96/12-1pc from the Lomonosov Ridge were assigned to reported excursions resulting in cm/ka deposition rates (Jakobsson et al, 2000). However, the detail of the excursional stratigraphy in this core is problematic. The absence of two (three?) excursions in the upper 2 m of core (base MIS5) was tentatively suggested to reflect pDRM-erasing in this sandy part of the core, while the short extent of the inferred pre-Brunhes Matyuama Chron remains unaccounted for. We have recently retrieved a relative paleointensity record from a parallel core (96/B6-1pc) for alternative dating control and assessment of stratigraphic completeness and uniformity of deposition. This study indicated the presence of a hiatus of the order of 200 ka (Løvlie et al 2002). We present a paleointensity record from core 96/12-1pc and will address identification of depositional hiatuses and their significance in understanding the paleomagnetic record in Arctic Ocean core

Estimation of liquidus temperatures in silicate glasses

Two models for estimating liquidus temperature from composition are presented and compared with thermodynamically calculated temperature as well as primary phase. Α simple polynomial model is given for high silica glasses, while a model covering a wide composition range and several primary phase fields is more complex. Thermodynamic calculations generally give too high liquidus temperatures in the devitrite field and too low in the primary field for Na2O · 2 CaO · 3 SiO2. In the wollastonite field the values are scattered, but in general too high

Rates of Sedimentation in the Central Arctic Ocean

The Arctic Ocean is presently undergoing geoscientific investigations of the type that occurred during the late 1940\u27s through 1960\u27s in the Atlantic, Indian and Pacific oceans. Seismic reflection and refraction data are scarce in the Arctic Ocean and large areas are virtually unsampled with respect to piston or gravity coring. The vast majority of available cores are less than10 m in length and largely lack biostratigraphically useful calcareous and siliceous microfossils. No drill cores exist from the ridges or deep basins in the central Arctic Ocean. Considering the limited geophysical and geological data available, it is not surprising that current concepts about Arctic Ocean sedimentation rates are diverging. The main point of difference is whether or not strongly subdued rates of sedimentation persisted in the central Arctic Ocean during Plio-Pleistocene times. The low sedimentation rate scenario is based on age models suggesting Plio-Pleistocene rates that vary between about 0.04 and 0.4 cm/ka. This scenario is chiefly derived from cores raised from ridges in the Amerasian Basin and implies that the majority of cores presently available extend well into, or encompass the entire, Pliocene. The contrasting high sedimentation rate scenario is based on age models suggesting rates that vary from about one to a few cm/ka, derived from cores from ridges and basins in both the Amerasian and Eurasian parts of the central Arctic Ocean. The latter scenario implies that most short cores rarely extend beyond the Pleistocene. Early paleomagnetic chronologies of sediment cores retrieved from the Amerasian Basin were based on the assumption that zones with negative inclination represented genuine polarity reversals. The first encountered down-core zone with negative inclination was interpreted to be the Brunhes/Matuyama boundary. This approach yielded mm-scale Plio-Pleistocene sedimentation rates. Biostratigraphy, cyclostratigraphy, and OSL dating, subsequently have indicated that many of these negative inclination changes represent Brunhes geomagnetic excursions, thus providing cm-scale Pleistocene sedimentation rates. All longer-term, Cretaceouos through Cenozoic, sedimentation rates derived from seismic reflection and tectonic models of bedrock age are on the order of cm/ka

Sub-series and sub-epochs are informal units and should continue to be omitted from the International Chronostratigraphic Chart

In June 2016 the Paleogene, Neogene, and Quaternary subcommissions (ISPS, SNS, SQS) of the International Commission on Stratigraphy (ICS) voted on whether to formalize sub-series and their geochronologic equiva-lents, sub-epochs. The vote required a 60 percent major-ity for the proposal to be forwarded to the ICS for further consideration. That majority was not achieved, albeit by a narrow margin, hence sub-series and sub-epochs are currently to be regarded as informal, and if used should carry a lower case modifier, as in lower Miocene and early Pleistocene. To accompany the vote, those who favoured continuation of informal usage were asked to prepare a short summary of the main arguments in support of their viewpoint, as were the proponents of the formalization case. Although this statement was not originally intended for publication, it is reproduced here at the request of the Former Chair of the ICS, so as to put it on record

Response to chemoradiatiotherapy in squamous cell carcinoma of the esophagus: evaluation of some prognostic factors

Dag Stockeld1, Ursula Falkmer2, Sture Falkmer3, Lars Backman1, Lars Granström1, Jan Fagerberg41Department of Surgery, Danderyd Hospital, Stockholm, Sweden; 2Department of Oncology; 3Department of Pathology, University Hospital, Trondheim, Norway; 4Department of Oncology, Radiumhemmet, Karolinska Hospital, Stockholm, SwedenObjective: To evaluate the predictive values of the expression of factor VIII, CD-34, p53, bcl-2, and DNA ploidy regarding the response to chemoradiation of squamous cell carcinoma of the esophagus.Design: Retrospective analysis of pretreatment biopsies with immunohistochemistry and flow cytometry. The results were correlated to tumor response (complete vs. noncomplete) following chemoradiation with three cycles of 5-FU and cisplatin combined with 40–64 Gy of radiation.Subjects: 44 consecutive patients with squamous cell carcinoma of the esophagus treated with chemoradiation with a curative intent from 1992–2000.Main outcome measures: Treatment response.Results: No correlations were found between the expressions of p53, bcl-2, or DNA ploidy and tumor response to chemoradiation. A positive correlation was found between factor VIII expression and a complete tumor response (p = 0.0357). However the other marker for angiogenesis, CD-34, showed a negative correlation (p = 0.0493). Both markers indicate blood vessel density meaning that, in this study, many vessels indicated a favorable response if measured with factor VIII, but a poor response if measured with CD-34. Conclusion: It is not possible to predict tumor response to our chemoradiation protocol through the analysis of pretreatment expression of p53, bcl-2 or DNA ploidy in biopsy specimens. In spite of significant correlations between complete tumor responses and the expressions of the markers for angiogenesis this significance may be questionable since one of the two markers, factor VIII had a positive and the other, CD-34, a negative correlation to tumor response.Keywords: chemoradiation, response, prognostic factor, apoptosis, p-53, angiogenesis, DNA ploid