Pollen record and age determination of sediment core Fersina 2

Pollen analysis of samples taken from the core of the water well Fersina 2 (Adige Valley, Prov. Trento, NE Italy) did not reveal any indication of an interglacial or Holocene age of the uppermost 190 m in the sediment sequence deposited in the over-deepened Adige River Valley. The sediment sequence dates entirely from late-glacial times. Four radiocarbon ages of pieces of wood indicate that about 165 m of the upper part of the profile are of Younger Dryas age. The lower part of the sequence dates from the Allerød or Bølling/Allerød and a preceding cold phase, probably the Oldest Dryas. Accordingly the deposition of the sequence took about 2500 or 3500 years and was completed long before the onset of the Neolithic. Our results are in excellent agreement with findings in other formerly glaciated alpine valleys (e.g. the Traun, Salzach and Enns valleys in the Northern Alps). The final depth of the Fersina 2 well is 190 m. It is very likely that the sediment sequence found below this level in the nearby 423 m deep Fersina 1 well was also deposited after the deglaciation of the Adige Valley at the end of the last glacial period.

Grain size composition and age of ODP Hole 167-1017E sediments

Siliciclastic sedimentation at Ocean Drilling Program Site 1017 on the southern slope of the Santa Lucia Bank, central California margin, responded closely to oceanographic and climatic change over the past ~130 ka. Variation in mean grain-size and sediment sorting within the ~25-m-thick succession from Hole 1017E show Milankovitch-band to submillenial-scale variation. Mean grain size of the "sortable silt" fraction (10-63 µm) ranges from 17.6 to 33.9 µm (average 24.8 µm) and is inversely correlated with the degree of sorting. Much of the sediment has a bimodal or trimodal grain-size distribution that is composed of distinct fine silt, coarse silt to fine sand, and clay-size components. The position of the mode and the sorting of each component changes through the succession, but the primary variation is in the presence or abundance of the coarse silt fraction that controls the overall mean grain size and sorting of the sample. The occurrence of the best-sorted, finest grained sediment at high stands of sea level (Holocene, marine isotope Substages 5c and 5e) reflect the linkage between global climate and the sedimentary record at Site 1017 and suggest that the efficiency of off-shelf transport is a key control of sedimentation on the Santa Lucia Slope. It is not clear what proportion of the variation in grain size and sorting may also be caused by variations in bottom current strength and in situ hydrodynamic sorting.

Mid-Miocene planktonic foraminifera of the Kerguelen Plateau, Antarctica

Miocene deep-sea sediments from ODP Site 744 (Kerguelen Plateau, southern Indian Ocean) contain abundant and diverse planktonic foraminiferal assemblages. Their analysis led to the identification of the interval between 17.0 and 14.2 Ma as a time of mid-Miocene warmth, which is investigated here in detail. This investigation includes reconstruction of trends in foraminiferal faunal composition and diversity through time, as well as in morphology and coiling direction within Globorotalia praescitula and Globorotalia zealandica plexi. These two large-globorotaliid plexi constitute the most characteristic component of the mid-Miocene foraminiferal faunas at ODP Site 744. Selected benthic (Cibicidoides sp.) and planktonic foraminifera were also analyzed for delta18O and delta13C ratios. Distinctive planktonic assemblages were the basis for identification of three foraminiferal biofacies between 17.0 and 14.2 Ma. The most prominent faunal changes took place between Biofacies 2 and 3 (15.5-15.0 Ma). Six of 11 macroperforate planktonic foraminifera from the >150-µm size fraction occur principally within Biofacies 3. Three other taxa are present throughout the interval analyzed. Moreover, both aforementioned globorotaliid plexi exhibit an increase in morphological diversity between Biofacies 2 and 3. Within the same interval, the G. zealandica plexus shows a switch from random coiling (50% sinistral) to clearly sinistral-dominated coiling. The faunal changes recognized are interpreted as the result of foraminiferal immigrations (increase in faunal diversity) and evolutionary trends (increase in morphological variability and change in coiling mode among the globorotaliid plexi). The stable isotopic results allow paleoenvironmental interpretation of these faunal changes. According to the delta18O values, no significant change in sea-surface temperature occurred between 17.0 and 14.2 Ma. However, the same data suggest an increase in ecological distance between various niches, which is expressed by a rising delta18O gradient recorded between various planktonic taxa upward within the section. This trend suggests niche-space availability as a likely factor responsible for the faunal changes recognized. Changes in the shape and depth of the thermocline, as well as in seasonality and eutrophication are considered as possible causes. Among these an increase in seasonality appears to have been responsible for the increase in species and morphological diversities between 15.5 and 15.0 Ma. The proposed scenario suggests that changes in seasonality may be an important factor driving faunal migrations and evolution. Variable seasonality may also affect the oxygen isotopic record of planktonic foraminiferal taxa.

Age and chemical composition of volcanic rocks and minerals from the Vityaz Ridge

This paper reports results of geological studies carried out during two marine expeditions of R/VAkademik M.A. Lavrent'ev (Cruises 37 and 41) in 2005 and 2006 at the underwater Vityaz Ridge. Dredging has yielded various rocks from the basement and sedimentary cover of the ridge within three polygons. On the basis of radioisotope age determinations, petrochemical, and paleontological data all the rocks have been subdivided into the following complexes: volcanic rock of Paleocene, Eocene, Late Oligocene, Middle Miocene, and Pliocene-Pleistocene; volcanogenic-sedimentary rocks of Late Cretaceous - Early Paleocene, Paleogene (undifferentiated), Oligocene - Early Miocene, and Pliocene-Pleistocene. Determinations of age and chemical composition of the rocks have enabled to specify formation conditions of the complexes and to trace geological evolution of the Vityaz Ridge. Presence of young Pliocene-Pleistocene volcanites allows to conclude about the modern tectono-magmatic activity of the central part of the Pacific slope of the Kuril Islands.

Chemical and isotope composition of rocks from the Omgon Range, Western Kamchatka coastal area

Hypabyssal rocks of the Omgon Range, Western Kamchatka that intrude Upper Albian-Lower Campanian deposits of the Eurasian continental margin belong to three coeval (62.5-63.0 Ma) associations: (1) ilmenite gabbro-dolerites, (2) titanomagnetite gabbro-dolerites and quartz microdiorites, and (3) porphyritic biotite granites and granite-aplites. Early Paleocene age of ilmenite gabbro-dolerites and biotite granites was confirmed by zircon and apatite fission-track dating. Ilmenite and titanomagnetite gabbro-dolerites were produced by multilevel fractional crystallization of basaltic melts with, respectively, moderate and high Fe-Ti contents and contamination of these melts with rhyolitic melts of different compositions. Moderate- and high-Fe-Ti basaltic melts were derived from mantle spinel peridotite variably depleted and metasomatized by slab-derived fluid prior to melting. The melts were generated at variable depths and different degrees of melting. Biotite granites and granite aplites were produced by combined fractional crystallization of a crustal rhyolitic melt and its contamination with terrigenous rocks of the Omgon Group. The rhyolitic melts were likely derived from metabasaltic rocks of suprasubduction nature. Early Paleocene hypabyssal rocks of the Omgon Range were demonstrated to have been formed in an extensional environment, which dominated in the margin of the Eurasian continent from Late Cretaceous throughout Early Paleocene. Extension in the Western Kamchatka segment preceded the origin of the Western Koryakian-Kamchatka (Kinkil') continental-margin volcanic belt in Eocene time. This research was conducted based on original geological, mineralogical, geochemical, and isotopic (Rb-Sr) data obtained by the authors.

Rare earth and other element contents and speciations in samples from Core AKO26-35, Pacific Ocean, Southwest Basin

Ferromanganese micro- and macronodules in eupelagic clays at Site AKO26-35 in the Southwest Pacific Basin were studied in order to check REE distribution during ferromanganese ore formation in non-productive zones of the Pacific Ocean. Host sediments and their labile fraction, ferromanganese micronodules (in size fractions 50-100, 100-250, 250-500, and >500 ?m) from eupelagic clays (horizons 37-10, 105-110, 165-175, and 189-190 cm), and buried ferromanganese micronodules (horizons 64-68, 158-159, and 165-166 cm) were under study. Based on partition analysis data anomalous REE enrichment in eupelagic clays from Site AKO26-35 is related to accumulation of rare earth elements in iron hydroxophosphates. Concentration of Ce generally bound with manganese oxyhydroxides is governed by oxidation of Mn and Ce in ocean surface waters. Micronodules (with Mn/Fe from 0.7 to 1.6) inherit compositional features of the labile fraction of bottom sediments. Concentrations of Ce, Co, and Th depend on micronodule sizes. Enrichment of micronodules in hydrogenic or hydrothermal matter is governed by their sizes and by a dominant source of suspended oxyhydroxide material. The study of buried ferromanganese micronodules revealed general regularities in compositional evolution of oxyhydroxide matrices of ferromanganese micro- and macronodules. Compositional variation of micro- and macronodules relative to the labile fraction of sediments in the Pacific non-productive zone dramatically differs from the pattern in bioproductive zones where micronodule compositions in coarser fractions are similar to those in associated macronodules and labile fractions of host sediments due to more intense suboxidative diagenesis.

Stable isotope record of sediment cores from the North Atlantic

Abrupt and short climate changes, such as the Younger Dryas, punctuated the last glacial-to-interglacial transition (Ruddiman and McIntyre, 1981 doi:10.1016/0031-0182(81)90097-3; Duplessy et al., 1981 doi:10.1016/0031-0182(81)90096-1; Oeschger et al. 1984; Broecker et al., 1985 doi:10.1038/315021a0). Broecker et al. (1988 doi:10.1029/PA003i001p00001) proposed that these may have been caused by an interruption of thermohaline circulation as inputs of glacial meltwater freshened the surface waters of the North Atlantic. The finding (Fairbanks, 1989 doi:10.1038/342637a0) that meltwater discharge was minimal during the Younger Dryas, however, led to the suggestion that the surface-water salinity drop might have been caused instead by changes in the freshwater budget (the difference between precipitation and evaporation), accompanied by a reduction in poleward advection of saline subtropical water. Here we use micropalaeontological and stable-isotope records from foraminifera in two cores from the North Atlantic to generate two continuous, high-resolution records of sea surface temperature and salinity changes over the past 18,000 years. Despite the injection of glacial meltwater during warm episodes, we find that sea surface salinity and temperature remain positively correlated during deglaciation. Cold, low-salinity events occurred during the early stages of deglaciation (14,500-13,000 years ago) and the Younger Dryas, but the minor injections of meltwater at high latitudes during these events are insufficient to account for the observed salinity changes. We conclude that an additional feedback from changes in the hydrological cycle and in advection was necessary to trigger changes in thermohaline circulation and thus in climate. This feedback did not act when the meltwater injection occurred at low latitude.

Surface exposure ages of samples obtained from Reedy Glacier, Antarctica

Fresh deposits above the margins of Reedy Glacier show that maximum ice levels during the last glaciation were several hundred meters above present near the glacier mouth and converged to less than 60 m above the present-day surface at the head of the glacier. Exposure ages of samples from five sites along its margin show that Reedy Glacier and its tributaries thickened asynchronously between 17 and 7 kyr BP At the Quartz Hills, located midway along the glacier, maximum ice levels were reached during the period 17-14 kyr BP. Farther up-glacier the ice surface reached its maximum elevation more recently: 14.7-10.2 kyr BP at the Caloplaca Hills; 9.1-7.7 kyr BP at Mims Spur; and around 7 kyr BP at Hatcher Bluffs. We attribute this time-transgressive behavior to two different processes: At the glacier mouth, growth of grounded ice and subsequent deglaciation in the Ross Sea embayment caused a wave of thickening and then thinning to propagate up-glacier. During the Lateglacial and Holocene, increased snow accumulation on the East Antarctic Ice Sheet caused transient thickening at the head of the glacier. An important result of this work is that moraines deposited along Reedy Glacier during the last ice age cannot be correlated to reconstruct a single glacial maximum longitudinal profile. The profile steepened during deglaciation of the Ross Sea, thinning at the Quartz Hills after 13 kyr BP while thickening upstream. Near its confluence with Mercer Ice Stream, rapid thinning beginning prior to 7-8 kyr BP reduced the level of Reedy Glacier to close to its present level. Thinning over the past 1000 years has lowered the glacier by less than 20 m.

Helium isotope ratios and sedimentation rate models of ODP holes

A continuous age model for the brief climate excursion at the Paleocene-Eocene boundary has been constructed by assuming a constant flux of extraterrestrial 3He (3He[ET]) to the seafloor. 3He[ET] measurements from ODP Site 690 provide quantitative evidence for the rapid onset (120 kyr) of global warming and of the associated disturbance to the Earth's surficial carbon budget at this time. These observations support astronomically calibrated age models indicating extremely rapid release of isotopically light carbon, possibly from seafloor methane hydrate, as the proximal cause of the event. However, the 3He[ET] technique indicates a previously unrecognized and extreme increase in sedimentation rate coincident with the return of climate proxies to pre-event values. The 3He[ET]-based age model thus suggests a far more rapid recovery from the climatic perturbation than previously proposed or predicted on the basis of the modern carbon cycle, and so may indicate additional or accelerated mechanisms of carbon removal from the ocean-atmosphere system during this period. 3He[ET] was also measured at ODP Site 1051 to test the validity of the Site 690 chronology. Comparison of these data sets seems to require removal of several tens of kyr of sediment within the climatic excursion at Site 1051, an observation consistent with sediment structures and previous age modeling efforts. The Site 1051 age model shows a ~30 kyr period in which climate proxies return toward pre-event values, after which they remain invariant for ~80 kyr. If this rise represents the recovery interval identified at Site 690, then the 3HeET-based age models of the two sites are in good agreement. However, alternative interpretations are possible, and work on less disrupted sites is required to evaluate the reliability of the proposed new chronology of the climate excursion. Regardless of these details, this work shows that the 3HeET technique can provide useful independent evidence for the development and testing of astronomically calibrated age models.

Deep water formation in the North Pacific and deglacial CO2 rise

Deep water formation in the North Atlantic and Southern Ocean is widely thought to influence deglacial CO2 rise and climate change; here we suggest that deep water formation in the North Pacific may also play an important role. We present paired radiocarbon and boron isotope data from foraminifera from sediment core MD02-2489 at 3640 m in the North East Pacific. These show a pronounced excursion during Heinrich Stadial 1, with benthic-planktic radiocarbon offsets dropping to ~350 years, accompanied by a decrease in benthic d11B. We suggest this is driven by the onset of deep convection in the North Pacific, which mixes young shallow waters to depth, old deep waters to the surface, and low-pH water from intermediate depths into the deep ocean. This deep water formation event was likely driven by an increase in surface salinity, due to subdued atmospheric/monsoonal freshwater flux during Heinrich Stadial 1. The ability of North Pacific Deep Water (NPDW) formation to explain the excursions seen in our data is demonstrated in a series of experiments with an intermediate complexity Earth system model. These experiments also show that breakdown of stratification in the North Pacific leads to a rapid ~30 ppm increase in atmospheric CO2, along with decreases in atmospheric d13C and D14C, consistent with observations of the early deglaciation. Our inference of deep water formation is based mainly on results from a single sediment core, and our boron isotope data are unavoidably sparse in the key HS1 interval, so this hypothesis merits further testing. However we note that there is independent support for breakdown of stratification in shallower waters during this period, including a minimum in d15N, younging in intermediate water 14C, and regional warming. We also re-evaluate deglacial changes in North Pacific productivity and carbonate preservation in light of our new data, and suggest that the regional pulse of export production observed during the Bølling-Allerød is promoted by relatively stratified conditions, with increased light availability and a shallow, potent nutricline. Overall, our work highlights the potential of NPDW formation to play a significant and hitherto unrealized role in deglacial climate change and CO2 rise.

Occurrence of metazoans, and gut pigments and fatty acid composition of Acartia bifilosa in ice and under-ice water samples from Santala Bay

A field study was conducted in Santala Bay with weekly samplings during February and March 2000. Ice thickness was 20-28 cm, snow cover 0-1 cm. The under-ice water column was stratified with a cold (-0.3 - 0.2°C) and less saline (S = 2.1-4.9) interface layer. Concentrations of particulate organic carbon (0.5-5.8 mg POC/l) and algal pigments (0.3-18.2 µg chlorophyll a/l) were higher in the ice than in the water (0.2-0.5 mg POC/l, 1.6-7.1 µg chlorophyll a/l) and peaked mostly in the bottom part of the ice. The thin ice and almost lacking snow cover had favoured an early ice-algal and phytoplankton bloom. The diversity of metazoans was low, with six species in the ice and eight species in the under-ice water. The rotifer Synchaeta cf. littoralis dominated both in ice and water, with maximum abundances of 230 individuals/l in the bottom part of the ice. Rotifer eggs were also observed in the ice. Baltic sea ice seems to be a suitable habitat for rotifers. Nauplii and copepodids of the calanoid Acartia longiremis in the under-ice water showed some herbivorous feeding (<0.1-0.23 ng gut pigment/individual), but analysis of fatty acids, fatty alcohols and biomarker ratios indicated a more omnivorous/carnivorous diet. Despite low temperatures, this copepod showed growth and development below the ice, doubling in numbers (mainly CI, CII) from 118 to 230 individuals m during the third week of March.

Geochemistry on manganese nodules from Timor

Fossil Mn nodules of Cretaceous age from western Timor exhibit chemical, structural and radioisotope compositions consistent with their being of deep-sea origin. These nodules show characteristics similar to nodules now found at depths of 3,500-5,000 m in the Pacific and Indian Oceans. Slight differences in the fine structure and chemistry of these nodules and modern deep-sea nodules are attributed to diagenetic alteration after uplift of enclosing sediments.

Origin and evolution of Cycladophora davisiana (Radiolaria) in DSDP Hole 19-192, Northwest Pacific

This paper documents the evolutionary history of Cycladophora davisiana Ehrenberg from an uppermost Miocene to Pleistocene sedimentary record in the high-latitude Northwest Pacific. It apparently evolved from C. sakaii Motoyama through a series of intermediates. C. sakaii has a relatively large shell with an external spongy layer. The evolutionary transition is characterized by a relatively rapid decrease in thorax size with a reduction of the spongy appendage. This change occurred during about 0.4 m.y. from 2.8 to 2.4 Ma without cladogenesis. Following this interval, a decrease in thorax size continued gradually up to the Recent, resulting in a very small morphology. Although the population of C. davisiana first appeared at about 2.5 Ma, some morphotypic specimens may occur in earlier periods as indistinguishable very small endmembers in the C. sakaii populations. Timing of the first appearance events both of morphotypic specimens and of a population of C. davisiana in Site 192 and previously reported cores does not disprove the idea that C. davisiana evolved first in the Northwest Pacific region, and later migrated into other regions of the world ocean. Biometrics clearly indicate no direct phylogenetic relationships between C. davisiana and C. cornutoides Kling in the studied core. Thus, the latter species, which was originally described as a variation and later elevated to a subspecies of the former species, is separated from the former species and raised to the species rank.

40Ar/39Ar single-crystal dating of detrital muscovite and K-feldspar of ODP Holes 116-717A and 116-718C

Detrital K-feldspars and muscovites from Ocean Drilling Program Leg 116 cores that have depositional ages from 0 to 18 Ma have been dated by the 40Ar/39Ar technique. Four to thirteen individual K-feldspars have been dated from seven stratigraphic levels, each of which have a very large range, up to 1660 Ma. At each level investigated, at least one K-feldspar yielded an age minimum which is, within uncertainty, identical to the age of deposition. One to twelve single muscovite crystals from each of six levels have also been studied. The range of muscovite ages is less than that of the K-feldspars and, with one exception, reveal only a 20-Ma spread in ages. As with the K-feldspars, each level investigated contains muscovites with mineral ages essentially identical to depositional ages. These results indicate that a significant portion of the material in the Bengal Fan is first-cycle detritus derived from the Himalayas. Therefore, the significant proportion of sediment deposited in the distal fan in the early to mid Miocene can be ascribed to a significant pulse of uplift and erosion in the collision zone. Moreover, these data indicate that during the entire Neogene, some portion of the Himalayan orogen was experiencing rapid erosion (<= uplift). The lack of granulite facies rocks in the eastern Himalayas and Tibetan Plateau suggests that very rapid uplift must have been distributed in brief pulses in different places in the mountain belt. We suggest that the great majority of the crystals with young apparent ages have been derived from the southern slope of the Himalayas, predominantly from near the main central thrust zone. These data provide further evidence against tectonic models in which the Himalayas and Tibetan plateaus are uplifted either uniformly during the past 40 m.y. or mostly within the last 2 to 5 m.y.

Abiotic characteristics and diatom abundance and biomass in different sectors of the Argentinien Shelf and antartic waters

A large spatial scale study of the diatom species inhabiting waters from the subantarctic (Argentine shelf) to antarctic was made for the first time in order to understand the relationships between these two regions with regard to the fluctuations in diatom abundances in relation with environmental features, their floristic associations and the effect of the Polar Front as a biogeographic barrier. Species-specific diatom abundance, nutrient and chlorophyll-a concentration were assessed from 64 subsurface oceanographic stations carried out during the austral summer 2002, a period characterized by an anomalous sea-ice coverage corresponding to a ''warm year". Significant relationships of both diatom density and biomass with chlorophyll-a (positive) and water temperature (negative) were found for the study area as a whole. Within the Subantarctic region, diatom density and biomass values were more uniform and significantly (in average: 35 and 11 times) lower than those of the Antarctic region, and did not correlate with chlorophyll-a. In antarctic waters, instead, biomass was directly related with chlorophyll-a, thus confirming the important contribution of diatoms to the Antarctic phytoplanktonic stock. A total of 167 taxa were recorded for the entire study area, with Chaetoceros and Thalassiosira being the best represented genera. Species richness was maximum in subantarctic waters (46; Argentine shelf) and minimum in the Antarctic region (21; Antarctic Peninsula), and showed a significant decrease with latitude. Floristic associations were examined both qualitatively (Jaccard Index) and quantitatively (correlation) by cluster analyses and results allowed differentiating a similar number of associations (12 vs. 13, respectively) and two main groups of stations. In the Drake Passage, the former revealed that the main floristic change was found at the Polar Front, while the latter reflected the Southern ACC Front as a main boundary, and yielded a higher number of isolated sites, most of them located next to different Antarctic islands. Such differences are attributed to the high relative density of Fragilariopsis kerguelensis in Argentine shelf and Drake Passage waters and of Porosira glacialis and species of Chaetoceros and Thalasiosira in the Weddell Sea and near the Antarctic Peninsula. From a total of 84 taxa recorded in antarctic waters, only 17 were found exclusively in this region, and the great majority (67) was also present in subantarctic waters but in extremely low (< 1 cell/l) concentrations, probably as a result of expatriation processes via the ACC-Malvinas Current system. The present results were compared with those of previous studies on the Antarctic region with respect to both diatom associations in regular vs. atypically warm years, and the distribution and abundance of some selected planktonic species reported for surface sediments.