Benthic foraminiferal stable isotope record for the equatorial Pacific

Stable oxygen and carbon isotope (d18O and d13C) values measured in foraminiferal calcite are one of the primary tools used in paleoceanography. Diagenetic recrystallization of foraminiferal calcite can act to reset primary isotopic values, but its effects are typically poorly quantified. Here we test the impact of early stage diagenesis on stable isotope records generated from a suite of drill sites in the equatorial Pacific Ocean recovered during Ocean Drilling Program Leg 199 and Integrated Ocean Drilling Program Expedition 320. Our selected sites form paleowater and burial depth transects, with excellent stratigraphic control allowing us to confidently correlate our records. We observe large intersite differences in the preservation state of benthic foraminiferal calcite, implying very different recrystallization histories, but negligible intersite offsets in benthic d18O and d13C values. We infer that diagenetic alteration of benthic foraminiferal calcite (in sedimentary oozes) must predominantly occur at shallow burial depths (<100 m) where offsets in both the temperature and isotopic composition of waters in which the foraminifera calcified and pore waters in which diagenesis occurs are small. Our results suggest that even extensive recrystallization of benthic foraminiferal calcite results in minimal shifts from primary d18O and d13C values. This finding supports the long-held suspicion that diagenetic alteration of foraminiferal calcite is less problematic in benthic than in planktic foraminifera and that in deep-sea sediments routinely employed for paleoceanographic studies benthic foraminifera are robust recorders of stable isotope values in the fossil record.

Age and chemical composition of dredged igneous rocks from the Vityaz Ridge, Pacific slope of the Kuril Island Arc

Original results of igneous rock studies are presented. The rocks were dredged during a marine expedition (cruise 37 of R/V Akademik M.A. Lavrent'ev in August-September, 2005) in the region of the submarine Vityaz Ridge and the Kuril Arc outer slope. Several age complexes (Late Cretaceous, Eocene, Late Oligocene, Miocene, and Pliocene-Pleistocene) are recognizable on the Vityaz Ridge. These complexes are characterized by a number of common geochemical features since all of them represent formations of island arc calc-alkali series. At the same time, they also have individual features reflecting different geodynamic settings. The outer slope of the Kuril Arc demonstrates submarine volcanism. Pliocene-Pleistocene volcanic rocks dredged here are similar to volcanites of the Kuril-Kamchatka Arc frontal zone.

Annotated record of the detailed examination of Mn nodules recovered from the VA04 expedition (R/V Valdivia) in the Pacific Ocean

Twenty-four manganese nodules from the surface of the sea floor and fifteen buried nodules were studied. With three exceptions, the nodules were collected from the area covered by Valdivia Cruise VA 04 some 1200 nautical miles southeast of Hawaii. Age determinations were made using the ionium method. In order to get a true reproduction of the activity distribution in the nodules, they were cut in half and placed for one month on nuclear emulsion plates to determine the alpha-activity of the ionium and its daughter products. Special methods of counting the alpha-tracks resolution to depth intervals of 0.125 mm. For the first time it was possible to resolve zones of rapid growth (impulse growth) with growth rates, s > 50 mm/106 yr and interruptions in growth. With few exceptions the average rate of growth of all nodules was surprisingly uniform at 4-9 mm/10 yr. No growth could be recognized radioactively in the buried nodules. One exceptional nodule has had recent impulse growth and, in the material formed, the ionium is not yet in equilibrium with its daughter products. Individual layers in one nodule from the Indian Ocean could be dated and an average time interval of t = 2600±400 yr was necessary to form one layer. The alternation between iron and manganese-rich parts of the nodules was made visible by colour differences resulting from special treatment of cut surfaces with HCl vapour. The zones of slow growth of one nodule are relatively enriched in iron. Earlier attempts to find paleomagnetic reversals in manganese nodules have been continued. Despite considerable improvement in areal resolution, reversals were not detected in the nodules studied. Comparisons of the surface structure, microstructure in section and the radiometric dating show that there are erosion surfaces and growth surfaces on the outer surfaces of the manganese nodules. The formation of cracks in the nodules was studied in particular. The model of age-dependent nodule shrinkage and cracking surprisingly indicates that the nodules break after exceeding a certain age and/or size. Consequently, the breaking apart of manganese nodules is a continuous process not of catastrophic or discontinuous origin. The microstructure of the nodules exhibits differences in the mechanism of accretion and accretion rate of material, shortly referred to as accretion form. Thus non-directional growth inside the nodules as well as a directional growth may be observed. Those nodules with large accretion forms have grown faster than smaller ones. Consequently, parallel layers indicate slow growth. The upper surfaces of the nodules, protruding into the bottom water appear to be more prone to growth disturbances than the lower surfaces, immersed in the sediment. Features of some nodules show, that as they develop, they neither turned nor rolled. Yet unknown is the mechanism that keeps the nodules at the surface during continuous sedimentation. All in all, the nodules remain the objects of their own distinctive problems. The hope of using them as a kind of history book still seems to be very remote.

Response of spring diatoms to CO2 availability in the Western North Pacific as determined by next-generation sequencing

Next-generation sequencing (NGS) technologies have enabled us to determine phytoplankton community compositions at high resolution. However, few studies have adopted this approach to assess the responses of natural phytoplankton communities to environmental change. Here, we report the impact of different CO2 levels on spring diatoms in the Oyashio region of the western North Pacific as estimated by NGS of the diatom-specific rbcL gene (DNA), which encodes the large subunit of RubisCO. We also examined the abundance and composition of rbcL transcripts (cDNA) in diatoms to assess their physiological responses to changing CO2 levels. A short-term (3-day) incubation experiment was carried out on-deck using surface Oyashio waters under different pCO2 levels (180, 350, 750, and 1000 µatm) in May 2011. During the incubation, the transcript abundance of the diatom-specific rbcL gene decreased with an increase in seawater pCO2 levels. These results suggest that CO2 fixation capacity of diatoms decreased rapidly under elevated CO2 levels. In the high CO2 treatments (750 and 1000 µatm), diversity of diatom-specific rbcL gene and its transcripts decreased relative to the control treatment (350µatm), as well as contributions of Chaetocerataceae, Thalassiosiraceae, and Fragilariaceae to the total population, but the contributions of Bacillariaceae increased. In the low CO2 treatment, contributions of Bacillariaceae also increased together with other eukaryotes. These suggest that changes in CO2 levels can alter the community composition of spring diatoms in the Oyashio region. Overall, the NGS technology provided us a deeper understanding of the response of diatoms to changes in CO2 levels in terms of their community composition, diversity, and photosynthetic physiology.

Seawater carbonate chemistry and Pacific oyster (Crassostrea gigas) biological processes during experiments, 2011

Ocean acidification, due to anthropogenic CO2 absorption by the ocean, may have profound impacts on marine biota. Calcareous organisms are expected to be particularly sensitive due to the decreasing availability of carbonate ions driven by decreasing pH levels. Recently, some studies focused on the early life stages of mollusks that are supposedly more sensitive to environmental disturbances than adult stages. Although these studies have shown decreased growth rates and increased proportions of abnormal development under low pH conditions, they did not allow attribution to pH induced changes in physiology or changes due to a decrease in aragonite saturation state. This study aims to assess the impact of several carbonate-system perturbations on the growth of Pacific oyster (Crassostrea gigas) larvae during the first 3 days of development (until shelled D-veliger larvae). Seawater with five different chemistries was obtained by separately manipulating pH, total alkalinity and aragonite saturation state (calcium addition). Results showed that the developmental success and growth rates were not directly affected by changes in pH or aragonite saturation state but were highly correlated with the availability of carbonate ions. In contrast to previous studies, both developmental success into viable D-shaped larvae and growth rates were not significantly altered as long as carbonate ion concentrations were above aragonite saturation levels, but they strongly decreased below saturation levels. These results suggest that the mechanisms used by these organisms to regulate calcification rates are not efficient enough to compensate for the low availability of carbonate ions under corrosive conditions.

Neodymium isotopic characterization of Ross Sea Bottom Water and its advection through the southern South Pacific, POLARSTERN cruise ANT-XXVI/2

Since the inception of the international GEOTRACES program, studies investigating the distribution of trace elements and their isotopes in the global ocean have significantly increased. In spite of this large-scale effort, the distribution of neodymium isotopes (143Nd/144Nd) and concentrations ([Nd]) in the high latitude south Pacific is still understudied. Here we report dissolved Nd isotopes and concentrations from 11 vertical water column profiles from the south Pacific between South America and New Zealand. Results suggest that Ross Sea Bottom Water (RSBW) is represented by an epsilon-Nd value of ~ -7, and is thus more radiogenic than Circumpolar Deep Water (epsilon-Nd ~ -8). RSBW and its characteristic epsilon-Nd signature can be traced far into the SE Pacific until progressive mixing with ambient Lower Circumpolar Deep water (LCDW) dilutes this signal north of the Antarctic Polar Front (APF). The SW-NE trending Pacific-Antarctic Ridge restricts the advection of RSBW into the SW Pacific, where bottom water density, salinity, and epsilon-Nd values of -9 indicate the presence of bottom waters of an origin different from the Ross Sea. Neodymium concentrations show low surface concentrations and a linear increase with depth north of the Polar Front. South of the APF, surface [Nd] is high and increases with depth but remains almost constant below ~1000 m. This vertical and spatial [Nd] pattern follows the southward shoaling density surfaces of the Southern Ocean frontal system and hence suggests supply of Nd to the upper ocean through upwelling of Nd-rich deep water. Low particle abundance dominated by reduced opal production and seasonal sea ice cover likely contributes to the maintenance of the high upper ocean [Nd] south of the APF. The reported data highlights the use of Nd isotopes as a water mass tracer in the Southern Ocean, with the potential for paleocenaographic reconstructions, and contributes to an improved understanding of Nd biogeochemistry.

(Table 3) Age determination of sediment cores from the SW Pacific Ocean

Eight- to ten-point depth profiles (from 1200 to 4800 m water depth) of oxygen and carbon isotopic values derived from benthic foraminifera, averaged over selected times in the past 160 ka, are presented. The data are from 10 sediment cores off eastern New Zealand, mainly North Chatham Rise. This lies under the Deep Western Boundary Current in the Southwest Pacific and is the main point of entry for several water masses into the Pacific Ocean. The benthic isotopic profiles are related to the structure of water masses at present and inferred for the past. These have retained a constant structure of Lower Circumpolar Deep Water-Upper Circumpolar Deep Water/North Pacific Deep Water-Antarctic Intermediate Water with no apparent changes in the depths of water mass boundaries between glacial and interglacial states. Sortable silt particle size data for four cores are also examined to show that the vigour of the inflow to the Pacific, while variable, appears to have remained fairly constant on average. Among the lowest Last Glacial Maximum values of benthic d13C in the world ocean (-1.03 per mil based on Cibicidoides wüllerstorfi) occurs here at ~2200 m. Comparable values occur in the Atlantic sector of the Southern Ocean, while those from the rest of the Pacific are distinctly higher, confirming that the Southern Ocean was the source for the unventilated/nutrient-enriched water seen here. Oxygen and carbon isotopic data are compatible with a glacial cold deep water mass of high salinity, but lower nutrient content (or better ventilated), below ~3500 m depth. This contrasts with the South Atlantic where unventilated/nutrient-enriched water extends all the way to the sea bed. Comparison with previous studies also suggests that the deeper reaches of the Antarctic Circumpolar Current below ~3500 m are not homogeneous all around the Southern Ocean, with the Kerguelen Plateau and/or the Macquarie-Balleny Ridges posing barriers to the eastward spread of the deepest low-d13C water out of the South Atlantic in glacials. These barriers, combined with inferred high density of bottom waters, restricted inter-basin exchange and allow three glacial domains dominated by bottom waters from Weddell Sea, Adelie Coast and Ross Sea to be defined. We suggest that the Ross Sea was the main source of the deep water entering the Pacific below ~3500 m.

Diatom abundance in surface sediments of the northern North Pacific

In order to map the modern distribution of diatoms and to establish a reliable reference data set for paleoenvironmental reconstruction in the northern North Pacific, a new data set including the relative abundance of diatom species preserved in a total of 422 surface sediments was generated, which covers a broad range of environmental variables characteristic of the subarctic North Pacific, the Sea of Okhotsk and the Bering Sea between 30° and 70°N. The biogeographic distribution patterns as well as the preferences in sea surface temperature of 38 diatom species and species groups are documented. A Q-mode factor analysis yields a three-factor model representing assemblages associated with the Arctic, Subarctic and Subtropical water mass, indicating a close relationship between the diatom composition and the sea surface temperatures. The relative abundance pattern of 38 diatom species and species groups was statistically compared with nine environmental variables, i.e. the summer sea surface temperature and salinity, annual surface nutrient concentration (nitrate, phosphate, silicate), summer and winter mixed layer depth and summer and winter sea ice concentrations. Canonical Correspondence Analysis (CCA) indicates 32 species and species groups have strong correspondence with the pattern of summer sea surface temperature. In addition, the total diatom flux data compiled from ten sediment traps reveal that the seasonal signals preserved in the surface sediments are mostly from spring through autumn. This close relationship between diatom composition and the summer sea surface temperature will be useful in deriving a transfer function in the subarctic North Pacific for the quantitative paleoceanographic and paleoenvironmental studies. The relative abundance of the sea-ice indicator diatoms Fragilariopsis cylindrus and F. oceanica of >20% in the diatom composition is used to represent the winter sea ice edge in the Bering Sea. The northern boundary of the distribution of F. doliolus in the open ocean is suggested to be an indicator of the Subarctic Front, while the abundance of Chaetoceros resting spores may indicate iron input from nearby continents and shelves and induced productivity events in the study area.

Grain size and chemical composition of the surface sediment layer from the Pacific Ocean

The book is devoted to results of studies of Pacific sediment composition, regularities of their distribution and processes of sedimentation in the Pacific Ocean. Materials obtained by Soviet expeditions are the main part of the book.

Particle flux at mooring sites in the Pacific Ocean (Table 1)

In order to understand the vertical transport of particulate matter, suspended and settling particles were collected along a meridional transect between 46°N and 35°S and an equatorial longitudinal transect between 135°E and 175°E in the Pacific. The low COrganic/N atomic ratios (<8.2) of suspended particulate organic matter (OM) and good correlation between particulate organic carbon (OC) and chlorophyll-a confirmed that the suspended particulate OM in the surface water was mainly produced by phytoplankton. Only 0.1-3.2% of primary production was transported to 1.3 km water depth in the boreal central Pacific. All data on settling particles (excluding deep trap data) showed strongly positive correlation between total mass and OM fluxes with high correlation factor of 0.93. Biogenic opal-producing plankton, mainly diatoms were responsible for most of the vertical transport of particulate OM in association with higher COrganic/CCarbonate ratios in the subarctic and equatorial hemipelagic regions in the Pacific. This vertical transport of settling particles potentially works as a sink of CO2. In the transition zone during the May 1993, large difference between PCO2 (<300 µatm) in the surface water and pCO2 (340 µatm) in the atmosphere was actually due to enhanced particulate OM flux. Since the deep water of the Pacific is enriched in CO2 and nutrients, upwelled seawater may tend to release CO2 to the atmosphere. However, higher production of particulate matter could reduce the partial pressure of CO2 in the surface water. Also terrestrial nutrients' inputs in the western equatorial Pacific have potential for the reduction of CO2 in the surface water.

(Plate 3) Manganese nodules and deep-sea sediment core from Pacific Ocean

A synoptic review of the studies of well-known occurrences of palagonite tuffs is presented. Included are palagonite tuffs from Iceland, and pillow-lava palagonite complexes from Columbia River basalts and from the central Oregon coast. Additional petrologic and x-ray defraction data for selected samples are presented. Petrologic evidence shows that basaltic glass of aqueous tuffs and breccias consists of sideromelane, which is susceptible to palagonitization. It is shown that palagonitization is a selective alteration process, involving hydration, oxidation and zeolitization. Some of the manganese nodules dredged from the Pacific Ocean floor contain nucleus of palagonite-tuff breccias or of zeolite. A brief megascopic and microscopic description of nodules from the south Pacific, the Mendocino ridge and the 'Horizon' Nodule from the north Pacific is presented. Petrographic studies of palagonite-tuff breccias of manganese nodules and other palagonites suggest that migration and segregation of metallic elements occur during and subsequent to palagonitization. During the palagonitization of sideromelane, nearly 30 percent of sea water is absorbed. The hydration of sideromelane is also accompanied by oxidation of iron and other elements. These oxides may be released either in colloidal form or in true solution and tend to precipitate first from the unstable palagonite.

Chemical composition of a manganese nodule from the Tiki Basin, Touamotou Archipelago, Pacific Ocean

The text studies the deep-sea red clays in the East-Central Pacific ocean (Tahiti-Touamotou Archipelago), their authigenic formation, transport and diagenetic character in particular through their composition in REE.

Age, 232Th, 230Th, 238U, CaCO3, organic carbon, lithogenic fraction and opal concentrations of 4 sediment cores from the southwest Pacific, with calculated 230Th-normalized mass flux

No clear scenario has yet been able to explain the full carbon drawdown that occurred during the Last Glacial Maximum (LGM); however, increased export production (EP) in the Subantarctic Zone (SAZ) of the Southern Ocean due to iron (Fe) fertilisation has been proposed to have provided a key mechanism affecting the air-sea partitioning of carbon. We chronicle changes in marine EP based on four sediment cores in Subtropical Waters (STW) and SAZ around New Zealand since the LGM. For the first time in this region, we present 230-Thorium normalised fluxes of biogenic opal, carbonate (CaCO3), excess Barium (xsBa), and organic Carbon (Corg). In STW and SAZ, these flux variations show that EP did not change markedly since the LGM. The only exception was a site in the SAZ close to the STF, where we suggest the STF shifted over the core site, driving increased EP. To understand why EP was mostly low and constant we investigated dust deposition changes by measuring lithogenic fluxes at the four sites. These data are coherent with an increased dust deposition in the southwest Pacific during the LGM. Additionally, we infer an increased lithogenic material discharge from erosion and glacier melts during the deglaciation, limited to the Campbell Plateau. Therefore, we propose that even though increased glacial dust deposition may have relieved Fe limitation within the SAZ, the availability of silicic acid (Si(OH)4) limited any resultant increase in carbon export during the LGM. Consequently, we infer low Si(OH)4 concentrations in the SAZ that have not significantly changed since the LGM. This result suggests that both Si(OH)4 and Fe co-limit EP in the SAZ around New Zealand, which would be consistent with modern process studies.