Invertebrates from the Low Head Member (Polonez Cove Formation, Oligocene) at Vaureal Peak, King George Island, West Antarctica

Eight taxa of marine invertebrates, including two new bivalve species, are described from the Low Head Member of the Polonez Cove Formation (latest early Oligocene) cropping out in the Vaureal Peak area, King George Island, West Antarctica. The fossil assemblage includes representatives of Brachiopoda (genera Neothyris sp. and Liothyrella sp.), Bivalvia (Adamussium auristriatum sp. nov., ?Adamussium cf. A. alanbeui Jonkers, and Limatula (Antarctolima) ferraziana sp. nov.), Bryozoa, Polychaeta (serpulid tubes) and Echinodermata. Specimens occur in debris flows deposits of the Low Head Member, as part of a fan delta setting in a high energy, shallow marine environment. Liothyrella sp., Adamussium auristriatum sp. nov. and Limatula ferraziana sp. nov. are among the oldest records for these genera in King George Island. In spite of their restrict number and diversification, bivalves and brachiopods from this study display an overall dispersal pattern that roughly fits in the clockwise circulation of marine currents around Antarctica accomplished in two steps. The first followed the opening of the Tasmanian Gateway at the Eocene/Oligocene boundary, along the eastern margin of Antarctica, and the second took place in post-Palaeogene time, following the Drake Passage opening between Antarctic Peninsula and South America, along the western margin of Antarctica.

Sediment properties of IODP Holes 303-U1302A and 303-U1305C

Episodes of ice-sheet disintegration and meltwater release over glacial-interglacial cycles are recorded by discrete layers of detrital sediment in the Labrador Sea. The most prominent layers reflect the release of iceberg armadas associated with cold Heinrich events, but the detrital sediment carried by glacial outburst floods from the melting Laurentide Ice Sheet is also preserved. Here we report an extensive layer of red detrital material in the Labrador Sea that was deposited during the early last interglacial period. We trace the layer through sediment cores collected along the Labrador and Greenland margins of the Labrador Sea. Biomarker data, Ca/Sr ratios and d18O measurements link the carbonate contained in the red layer to the Palaeozoic bedrock of the Hudson Bay. We conclude that the debris was carried to the Labrador Sea during a glacial outburst flood through the Hudson Strait, analogous to the final Lake Agassiz outburst flood about 8,400 years ago, probably around the time of a last interglacial cold event in the North Atlantic. We suggest that outburst floods associated with the final collapse of the Laurentide Ice Sheet may have been pervasive features during the early stages of Late Quaternary interglacial periods.

Mineralogy, and composition of turbidites and background samples at ODP Sites 166-1003 and 166-1007

The lower slope and toe-of-slope sediments of the western flank of the Great Bahama Bank (Sites 1003 and 1007) are characterized by an intercalation of turbidites and periplatform ooze. In general, turbidites form up to 12% of the total mass of the sedimentary column. Based primarily on data from the Bahamas, it has been postulated that steep-sided carbonate platforms shed most of their sediments into the basin during sea-level highstands when the platforms are flooded. This highstand shedding is assumed to be less pronounced along platforms with a ramp-like depositional profile where sediment production is not restricted to sea-level highstand. Miocene to Pliocene sediments recovered in five drill holes during Leg 166 at the western margin of the Great Bahama Bank reveal that turbidite distribution follows a complex pattern that is dependent on several factors such as sedimentation rates, sea-level changes, and slope morphology. To identify the depositional sequences in the cores, the depths of seismic-sequence boundaries were used. The distribution of turbidites within sedimentary sequences varies strongly. Generally, turbidites are clustered at the upper and/or lower portions of the sequences indicating deposition of carbonate turbidites during both highstand and lowstand of sea level. Analyses of the Miocene turbidites show that (1) during high sea level, 60% of all turbidites were deposited at Site 1003 (309 out of 518 turbidites), while during low sea level, two thirds of all turbidites were deposited at Site 1007 (332 out of 486 turbidites); (2) the average thickness of highstand turbidites is 1.5 times higher than the average thickness of lowstand turbidites; and (3) the turbidites display slight differences in composition and sorting. In general, highstand turbidites are less sorted and contain an abundant amount of shallow-water constituents such as green algae, red algae, shallow-water benthic foraminifers (miliolids), and intraclasts. The lowstand turbidites are better sorted and contain abundant planktonic foraminifers and micrite. To complicate matters, highstand and lowstand turbidites seem to be deposited at different locations on the slope. At the lower slope (Site 1003), more turbidites were deposited during highstands, while at the toe of the slope, turbidites were dominantly deposited during sea-level lowstands. The result is a slope section with laterally discontinuous turbidite lenses within periplatform ooze, which is controlled by the interplay of sea-level changes, sediment production, and platform morphology.

Mineral XRD peak areas and ratios of ODP Site 184-1146 clays, South China Sea

Site 1146 (19°27.40'N, 116°16.37'E) was drilled in ~2092 m water depth in a rift basin on the continental slope of the South China Sea. A total of 607 m of sediment was cored in Hole 1146A, and a composite section from three holes extends down to 640 meters composite depth (mcd). Three stratigraphic sedimentary units were recognized at this site: late Pliocene to Pleistocene nannofossil clay (Unit I), middle Miocene to late Pliocene foraminifer and nannofossil clay mixed sediment (Unit II), and early to middle Miocene nannofossil clay (Unit III). This study reports the mineralogy from the late Miocene through early Pleistocene, 150-440 mcd.

Peak areas and heights for minerals of ODP Leg 113-696B (Table 1)

Seismic data acquired over the eastern shelf and margin of the South Orkney microcontinent, Antarctica, have shown a high-amplitude reflection lying at a sub-bottom two-way traveltime (TWT) of 0.5-0.8 s. There appear to be two causes for the reflection which apply in different parts of the shelf. The more widespread cause of the reflection is a break-up unconformity associated with the opening of Jane Basin to the east. This is clearly seen where reflections in the underlying sequence are discordant. In contrast, in Eotvos Basin and the southeastern part of Bouguer Basin, the high-amplitude reflection in places cuts across bedding and is interpreted to be caused by silica diagenesis. A post-cruise analysis of core samples from Site 696 in Eotvos Basin by X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed the presence of a silica diagenetic front at 520-530 mbsf. The position of the unconformity at this site is uncertain, but probably coincides with a change of detrital input near 548 mbsf. Fluctuations of physical properties related to the depth of the diagenetic front are difficult to separate from those related to the variation of detrital composition over the same depth interval. Correlation of the drilling record with the seismic record is difficult but with a synthetic seismogram it is demonstrated that diagenesis is the probable cause of the high-amplitude reflection. In Bouguer Basin at Site 695 the depth of the high-amplitude reflection was not reached by drilling; however, the reflection is probably also caused by silica diagenesis because of the biogenic silica-rich composition of the sediments cored. The estimated temperatures and ages of the sediments at the depths of the high-amplitude reflections at Sites 695 and 696 compare favorably with similar data from other diagenetic fronts of the world. The high-amplitude reflection in Bouguer Basin is commonly of inverse polarity, possibly caused either by interference between reflections from several closely-spaced reflecting layers, such as chert horizons, or by free gas trapped near the diagenetic front.

Biostratigraphy, magnetostratigraphy, granulometry, isotopes and clay mineral composition of ODP Site 188-1165

During Ocean Drilling Program Leg 188 to Prydz Bay, East Antarctica, several of the shipboard scientists formed the High-Resolution Integrated Stratigraphy Committee (HiRISC). The committee was established in order to furnish an integrated data set from the Pliocene portion of Site 1165 as a contribution to the ongoing debate about Pliocene climate and climate evolution in Antarctica. The proxies determined in our various laboratories were the following: magnetostratigraphy and magnetic properties, grain-size distributions (granulometry), near-ultraviolet, visible, and near-infrared spectrophotometry, calcium carbonate content, characteristics of foraminifer, diatom, and radiolarian content, clay mineral composition, and stable isotopes. In addition to the HiRISC samples, other data sets contained in this report are subsets of much larger data sets. We included these subsets in order to provide the reader with a convenient integrated data set of Pliocene-Pleistocene strata from the East Antarctic continental margin. The data are presented in the form of 14 graphs (in addition to the site map). Text and figure captions guide the reader to the original data sets. Some preliminary interpretations are given at the end of the manuscript.

Stable isotope record, opal accumulation rate and geochemistry of middle Miocene sediments of IODP Site 321-U1338

During the middle Miocene, Earth's climate transitioned from a relatively warm phase (Miocene climatic optimum) into a colder mode with re-establishment of permanent ice sheets on Antarctica, thus marking a fundamental step in Cenozoic cooling. Carbon sequestration and atmospheric CO2 drawdown through increased terrestrial and/or marine productivity have been proposed as the main drivers of this fundamental transition. We integrate high-resolution (1-3 k.y.) benthic stable isotope data with XRF-scanner derived biogenic silica and carbonate accumulation estimates in an exceptionally well-preserved sedimentary archive, recovered at Integrated Ocean Drilling Program Site U1338, to reconstruct eastern equatorial Pacific productivity variations and to investigate temporal linkages between high- and low-latitude climate change over the interval 16-13 Ma. Our records show that the climatic optimum (16.8-14.7 Ma) was characterized by high amplitude climate variations, marked by intense perturbations of the carbon cycle. Episodes of peak warmth at (southern hemisphere) insolation maxima coincided with transient shoaling of the carbonate compensation depth and enhanced carbonate dissolution in the deep ocean. A switch to obliquity-paced climate variability after 14.7 Ma concurred with a general improvement in carbonate preservation and the onset of stepwise global cooling, culminating with extensive ice growth over Antarctica at ~13.8 Ma. We find that two massive increases in opal accumulation at ~14.0 and ~13.8 Ma occurred just before and during the final and most prominent cooling step, supporting the hypothesis that enhanced siliceous productivity in the eastern equatorial Pacific contributed to CO2 drawdown.

Shotgun proteomics reveals physiological response to ocean acidification in Crassostrea gigas

Background. Ocean acidification as a result of increased anthropogenic CO2 emissions is occurring in marine and estuarine environments worldwide. The coastal ocean experiences additional daily and seasonal fluctuations in pH that can be lower than projected end of century open ocean pH reductions. Projected and current ocean acidification have wide-ranging effects on many aquatic organisms, however the exact mechanisms of the impacts of ocean acidification on many of these animals remains to be characterized. Methods. In order to assess the impact of ocean acidification on marine invertebrates, Pacific oysters (Crassostrea gigas) were exposed to one of four different pCO2 levels for four weeks: 400 µatm (pH 8.0), 800 µatm (pH 7.7), 1000 µatm (pH 7.6), or 2800 µatm (pH 7.3). At the end of 4 weeks a variety of physiological parameters were measured to assess the impacts of ocean acidification: tissue glycogen content and fatty acid profile, shell micromechanical properties, and response to acute heat shock. To determine the effects of ocean acidification on the underlying molecular physiology of oysters and their stress response, some of the oysters from 400 µatm and 2800 µatm were exposed to an additional mechanical stress and shotgun proteomics were done on oysters from high and low pCO2 and from with and without mechanical stress. Results. At the end of the four week exposure period, oysters in all four pCO2 environments deposited new shell, but growth rate was not different among the treatments. However, micromechanical properties of the new shell were compromised by elevated pCO2. Elevated pCO2 affected neither whole body fatty acid composition, nor glycogen content, nor mortality rate associated with acute heat shock. Shotgun proteomics revealed that several physiological pathways were significantly affected by ocean acidification, including antioxidant response, carbohydrate metabolism, and transcription and translation. Additionally, the proteomic response to a second stress differed with pCO2, with numerous processes significantly affected by mechanical stimulation at high versus low pCO2 (all proteomics data are available in the ProteomeXchange under the identifier PXD000835). Discussion. Oyster physiology is significantly altered by exposure to elevated pCO2, indicating changes in energy resource use. This is especially apparent in the assessment of the effects of pCO2 on the proteomic response to a second stress. The altered stress response illustrates that ocean acidification may impact how oysters respond to other changes in their environment. These data contribute to an integrative view of the effects of ocean acidification on oysters as well as physiological trade-offs during environmental stress.