Saburo Sakai

Age constraints on the origin and growth history of a deep-water coral mound in the northeast Atlantic drilled during Integrated Ocean Drilling Program Expedition 307

Sr isotope stratigraphy provides a new age model for the first complete section drilled through a deep-water coral mound. The 155-m-long section from Challenger Mound in the Porcupine Sea-bight, southwest of Ireland, is on Miocene siliciclastics and consists entirely of sediments bearing well-preserved cold-water coral Lophelia pertusa. The 87Sr/86Sr values of 28 coral specimens from the mound show an upward-increasing trend, correspond to ages from 2.6 to 0.5 Ma, and identify a significant hiatus from ca. 1.7 to 1.0 Ma at 23.6 m below seafloor. The age of the basal mound sediments coincides with the intensification of Northern Hemisphere glaciations that set up the modern stratification of the northeast Atlantic and enabled coral growth. Mound growth persisted throughout glacial-interglacial fluctuations, reached a maximum rate (24 cm/k.y.) ca. 2.0 Ma, and ceased at 1.7 Ma. Unlike other buried mounds in Porcupine Seabight, Challenger Mound was only partly covered during its growth interruption, and growth restarted ca. 1.0 Ma.

Earliest Known Use of Marine Resources by Neanderthals

Numerous studies along the northern Mediterranean borderland have documented the use of shellfish by Neanderthals but none of these finds are prior to Marine Isotopic Stage 3 (MIS 3). In this paper we present evidence that gathering and consumption of mollusks can now be traced back to the lowest level of the archaeological sequence at Bajondillo Cave (Málaga, Spain), dated during the MIS 6. The paper describes the taxonomical and taphonomical features of the mollusk assemblages from this level Bj19 and briefly touches upon those retrieved in levels Bj18 (MIS 5) and Bj17 (MIS 4), evidencing a continuity of the shellfishing activity that reaches to MIS 3. This evidence is substantiated on 29 datings through radiocarbon, thermoluminescence and U series methods. Obtained dates and paleoenvironmental records from the cave include isotopic, pollen, lithostratigraphic and sedimentological analyses and they are fully coherent with paleoclimate conditions expected for the different stages. We conclude that described use of shellfish resources by Neanderthals (H. neanderthalensis) in Southern Spain started ∼150 ka and were almost contemporaneous to Pinnacle Point (South Africa), when shellfishing is first documented in archaic modern humans.

Cold water coral mounds revealed

The discovery of mounds and reefs hosting cold-water coral ecosystems along the northeastern Atlantic continental margins has propelled a vigorous effort over the past decade to study the distribution of the mounds, surface sediments, the ecosystems they host, and their environments [Hovland et al., 1994; Freiwald and Roberts, 2005].This effort has involved swath bathymetry, remotely operated vehicle deployments, shallow coring, and seismic surveys. Global coverage is difficult to gauge, but studies indicate that cold-water corals may cover as large an area as the better known warm-water corals that form shallow reefs (284,300 square kilometers) [Freiwald et al., 2005]. Cold-water corals occur in a variety of forms and settings, from small isolated colonies or patch reefs to giant mound structures such as those found west of Ireland.

Large changes in seasonal sea ice distribution and productivity in the Sea of Okhotsk during the deglaciations

Changes in the surface environment of the central Sea of Okhotsk were reconstructed using TEX86 paleothermometry, facilitated by the BIT index, in order to investigate paleoenvironmental changes during the glacial-interglacial cycles. The core top TEX86-derived temperature is the same as the present-day summer sea surface temperature (SST), suggesting that TEX86 records seasonal rather than annually averaged SSTs in this region. The TEX86 record reveals ∼3°C lower summer SST during glacial maxima than during interglacial periods and significant warming during the deglaciations (15–10 ka and 136–130 ka). This is consistent with previous inferences of more expanded and persistent seasonal sea ice during the glacial periods than the present-day and its substantial retreat during the deglaciation. Timing of the deglacial warming also coincided with a distinct increase in coccolithophorid productivity, suggesting a causal relationship between sea surface warming and coccolithophorid blooms during the deglaciations. The relationship could reflect an increase in the supply of fresh and warm water from the Amur River during deglaciation, which significantly impacted hydrology by facilitating sea surface stratification, which in turn promoted production of coccolithophids.

Pliocene cooling enhanced by flow of low-salinity Bering Sea water to the Arctic Ocean

Warming of high northern latitudes in the Pliocene (5.33–2.58 Myr ago) has been linked to the closure of the Central American Seaway and intensification of North Atlantic Deep Water. Subsequent cooling in the late Pliocene may be related to the effects of freshwater input from the Arctic Ocean via the Bering Strait, disrupting North Atlantic Deep Water formation and enhancing sea ice formation. However, the timing of Arctic freshening has not been defined. Here we present neodymium and lead isotope records of detrital sediment from the Bering Sea for the past 4.3 million years. Isotopic data suggest the presence of Alaskan glaciers as far back as 4.2 Myr ago, while diatom and C37:4 alkenone records show a long-term trend towards colder and fresher water in the Bering Sea beginning with the M2 glaciation (3.3 Myr ago). We argue that the introduction of low-salinity Bering Sea water to the Arctic Ocean by 3.3 Myr ago preconditioned the climate system for global cooling.

Correlation of Virgulinella fragilis Grindell & Collen (benthic foraminiferid) with near-anoxia in Aso-kai Lagoon, central Japan

The distribution of Virgulinella fragilis and the hydro-environment of Aso-kai Lagoon, central Japan, were studied to clarify the foraminifer’s adaptation to low-oxygen conditions. The hypolimnion of the lagoon is oxygen-poor during much of the year. Two faunas (A and B) are recognized, based on cluster analysis. Cluster A fauna consists of species common in brackish lagoons, such as the genera Trochammina and Ammonia, and occurs in seasonally oxygenated waters. Virgulinella fragilis, the predominant species of Cluster B fauna, dominates the central part of the lagoon. This species can tolerate more severe oxygen deficiencies than the typical brackish foraminifers (e.g. Trochammina spp.) and can adapt to long periods of oxygen-poor conditions in coastal lagoon environments, as well as in pelagic to hemi-pelagic settings. In order to survive in the near-anoxia of Aso-kai Lagoon, V. fragilis may have adapted to environments in which little reactive iron is available in the sediment, leaving pore-water and bottom-water sulphide available for symbionts, or may utilize sulphur denitrification processes.

Sources of Dissolved Inorganic Carbon in Two Small Streams with Different Bedrock Geology: Insights from Carbon Isotopes

Radiocarbon natural abundances ( Δ 14 C ) are being increasingly used to trace carbon cycling in stream ecosystems. To understand the ultimate sources of carbon, we determined the stable carbon isotope ratios (δ 13 C) and Δ 14 C values of dissolved inorganic and organic carbon (DIC and DOC, respectively) and of particulate organic carbon (POC) in two small streams in central Japan, one of which flows over limestone bedrock (Seri) and the other does not (Fudoji). Investigations over four seasons revealed that the Δ 14 C values of the DIC (from –238‰ to –174‰ for Seri and –23‰ to +10‰ for Fudoji) were less variable than those of the other carbon fractions (DOC: from –400‰ to –138‰ for Seri and –2‰ to +103‰ for Fudoji; POC: from –164‰ to –60‰ for Seri and –55‰ to +37‰ for Fudoji). Based on mass balance calculations using the δ 13 C and Δ 14 C values, the proportions of carbon in the DIC originated from (1) atmospheric CO 2 were 47% to 57% for Seri and 74% to 90% for Fudoji, (2) organic matter degradation were 29% to 35% for Seri and 4% to 21% for Fudoji, and (3) carbonate rock were 14% to 22% for Seri and 4% to 6% for Fudoji. We compared the results with previous studies that had been conducted in larger rivers and showed that in small streams, the dissolution of atmospheric CO 2 and weathering of carbonate rock are more important factors in the carbon cycling than the biological degradation of organic matter. DOI: 10.2458/azu_rc.57.18348

Brucite chimney formation and carbonate alteration at the Shinkai Seep Field, a serpentinite‐hosted vent system in the southern Mariana forearc

Brucite-carbonate chimneys were discovered from the deepest known (∼5700 m depth) serpentinite-hosted ecosystem – the Shinkai Seep Field (SSF) in the southern Mariana forearc. Textural observations and geochemical analysis reveal three types (I-III) of chimneys formed by the precipitation and dissolution of constitutive minerals. Type I chimneys are bright white to light yellow, have a spiky crystalline and wrinkled surface with microbial mat and contain more brucite; these formed as a result of rapid precipitation under high fluid discharge conditions. Type II chimneys exhibit white to dull brown coloration, tuberous textures like vascular bundles, and are covered with grayish microbial mats and dense colonies of Phyllochaetopterus. This type of chimney is characterized by inner brucite-rich and outer carbonate rich zones and is thought to have precipitated from lower fluid discharge conditions than type I chimneys. Type III chimneys are ivory colored, have surface depressions and lack living microbial mats or animals. This type of chimney mainly consists of carbonate, and is in a dissolution stage. Stable carbon isotope compositions of carbonates in the two types (I and II) of active chimneys are extremely 13C-enriched (up to +24.1‰), which may reflect biological 12C consumption under extremely low dissolved inorganic carbon concentration in alkaline fluid. Type III chimneys have 13C compositions indicating re-equilibration with seawater. Our findings demonstrate for the first time that carbonate chimneys can be form below carbonate compensation depth and provide new insights about linked geologic, hydrologic, and biological processes of the global deep-sea serpentinite-hosted vent systems. This article is protected by copyright. All rights reserved.

Micropowder collecting technique for stable isotope analysis of carbonates.

Micromilling is a conventional technique used in the analysis of the isotopic composition of geological materials, which improves the spatial resolution of sample collection for analysis. However, a problem still remains concerning the recovery ratio of the milled sample. We constructed a simple apparatus consisting of a vacuum pump, a sintered metal filter, electrically conductive rubber stopper and a stainless steel tube for transferring the milled powder into a reaction vial. In our preliminary experiments on carbonate powder, we achieved a rapid recovery of 5 to 100 µg of carbonate with a high recovery ratio (>90%). This technique shortens the sample preparation time, improves the recovery ratio, and homogenizes the sample quantity, which, in turn, improves the analytical reproducibility.

Evaluation of the δ18O Value of the Submarine Cavernicolous Micro-Bivalve Carditella iejimensis as a Proxy for Palaeotemperature

Abstract. The micro-bivalve Carditella iejimensis is less than 3.5 mm in shell height and lives in the surface sediment within a submarine cave at Ie Island, Okinawa Islands, Japan. A previous study interpreted that &dgr; 18O-derived temperature obtained from C. iejimensis shells indicates the water temperature between May and July of each year. This interpretation is based mainly on a statistically significant correlation between shell size and &dgr; 18O values obtained from empty shells. To assess the validity of this interpretation, we performed high-resolution isotopic analyses on 19 empty shells with the aim of examining ontogenetic variation in &dgr; 18O values. The results reveal no systematic variation in &dgr; 18O values, inconsistent with the previous interpretation. Our data indicate little or no influence of growth duration (shell size) on the &dgr; 18O values of shells greater than 1 mm in height.