Seawater carbonate chemistry and calcification during tropical reef studies at Moorea (French Polynesia), 1997

Community metabolism and air-sea carbon dioxide (CO2) fluxes were investigated in July 1992 on a fringing reef at Moorea (French Polynesia). The benthic community was dominated by macroalgae (85% substratum cover) and comprised of Phaeophyceae Padina tenuis (Bory), Turbinaria ornata (Turner) J. Agardh, and Hydroclathrus clathratus Bory (Howe); Chlorophyta Halimeda incrassata f. ovata J. Agardh (Howe); and Ventricaria ventricosa J. Agardh (Olsen et West), as well as several Rhodophyta (Actinotrichia fragilis Forskál (Børgesen) and several species of encrusting coralline algae). Algal biomass was 171 g dry weight/m**2. Community gross production (Pg), respiration (R), and net calcification (G) were measured in an open-top enclosure. Pg and R were respectively 248 and 240 mmol Co2/m**2/d, and there was a slight net dissolution of CaCO3 (0.8 mmol/m**2/d). This site was a sink for atmospheric CO2 (10 ± 4 mmol CO2/m**2/d), and the analysis of data from the literature suggests that this is a general feature of algal-dominated reefs. Measurement of air-sea CO2 fluxes in open water close to the enclosure demonstrated that changes in small-scale hydrodynamics can lead to misleading conclusions. Net CO2 evasion to the atmosphere was measured on the fringing reef due to changes in the current pattern that drove water from the barrier reef (a C02 source) to the study site.

Sediment composition in NE Greenland Fjords, Shelf, and Slope

In order to document changes in Holocene glacier extent and activity in NE Greenland (~73° N) we study marine sediment records that extend from the fjords (PS2631 and PS2640), across the shelf (PS2623 and PS2641), to the Greenland Sea (JM07-174GC). The primary bedrock geology of the source areas is the Caledonian sediment outcrop, including Devonian red beds, plus early Neoproterozoic gneisses and early Tertiary volcanics. We examine the variations in colour (CIE*), grain size, and bulk mineralogy (from X-ray diffraction of the <2 mm sediment fraction). Fjord core PS2640 in Sofia Sund, with a marked red hue, is distinct in grain size, colour and mineralogy from the other fjord and shelf cores. Five distinct grain-size modes are distinguished of which only one is associated with a coarse ice-rafting signal - this mode is rare in the mid- and late Holocene. A sediment unmixing program (SedUnMixMC) is used to characterize down-core changes in sediment composition based on the upper late Holocene sediments from cores PS2640 (Sofia Sund), PS2631 (Kaiser Franz Joseph Fjord) and PS2623 (south of Shannon Is), and surface samples from the Kara Sea (as an indicator of transport from the Russian Arctic shelves). Major changes in mineral composition are noted in all cores with possible coeval shifts centred c. 2.5, 4.5 and 7.5 cal. ka BP (±0.5 ka) but are rarely linked with changes in the grain-size spectra. Coarse IRD (>2 mm) and IRD-grain-size spectra are rare in the last 9-10 cal. ka BP and, in contrast with areas farther south (~68° N), there is no distinct IRD signal at the onset of neoglaciation. Our paper demonstrates the importance of the quantitative analysis of sediment properties in clarifying source to sink changes in glacial marine environments.

Results of bulk sediment X-ray diffraction analysis and quantification of mineral phases based on the RockJock and on the QUAX quantitative analysis

We have performed quantitative X-ray diffraction (qXRD) analysis of 157 grab or core-top samples from the western Nordic Seas between (WNS) ~57°-75°N and 5° to 45° W. The RockJock Vs6 analysis includes non-clay (20) and clay (10) mineral species in the <2 mm size fraction that sum to 100 weight %. The data matrix was reduced to 9 and 6 variables respectively by excluding minerals with low weight% and by grouping into larger groups, such as the alkali and plagioclase feldspars. Because of its potential dual origins calcite was placed outside of the sum. We initially hypothesized that a combination of regional bedrock outcrops and transport associated with drift-ice, meltwater plumes, and bottom currents would result in 6 clusters defined by "similar" mineral compositions. The hypothesis was tested by use of a fuzzy k-mean clustering algorithm and key minerals were identified by step-wise Discriminant Function Analysis. Key minerals in defining the clusters include quartz, pyroxene, muscovite, and amphibole. With 5 clusters, 87.5% of the observations are correctly classified. The geographic distributions of the five k-mean clusters compares reasonably well with the original hypothesis. The close spatial relationship between bedrock geology and discrete cluster membership stresses the importance of this variable at both the WNS-scale and at a more local scale in NE Greenland.

Raw X-ray fluorescence (XRF) scannings and radiocarbon age of sediment cores GeoB8331-4, and GeoB8322-2

Variations in the sediment input to the Namaqualand mudbelt during the Holocene are assessed using an integrative terrestrial to marine, source to sink approach. Geochemical and Sr and Nd isotopic signatures are used to distinguish fluvial sediment source areas. Relative to the sediments of the Olifants River, craton outcrops in the northern Orange River catchment have a more radiogenic Sr and a more unradiogenic Nd isotopic signature. Furthermore, upper Orange River sediments are rich in heavier elements such as Ti and Fe derived from the chemical weathering of Drakensberg flood basalt. Suspension load signatures change along the Orange River's westward transit as northern catchments contribute physical weathering products from the Fish and Molopo River catchment area. Marine cores offshore of the Olifants (GeoB8323-2) and Orange (GeoB8331-4) River mouths show pulses of increased contribution of Olifants River and upper Orange River input, respectively. These pulses coincide with intervals of increased terrestrial organic matter flux and increased paleo-production at the respective core sites. We attribute this to an increase in fluvial activity and vegetation cover in the adjacent catchments during more humid climate conditions. The contrast in the timing of these wet phases in the catchment areas reflects the bipolar behavior of the South African summer and winter rainfall zones. While rainfall in the Orange River catchment is related to southward shifts in the ICTZ, rainfall in the Olifants catchment is linked to northward shifts in Southern Hemisphere Westerly storm tracks. The later may also have increased southern Benguela upwelling in the past by reducing the shedding of Agulhas eddies into the Atlantic. The high-resolution records of latitudinal shifts in these atmospheric circulation systems correspond to late Holocene centennial-millennial scale climate variability evident in Antarctic ice core records. The mudbelt cores indicate that phases of high summer rainfall zone and low winter rainfall zone humidity (at ca. 2.8 and 1 ka BP) may be synchronous with Antarctic warming events. On the other hand, dry conditions in the summer rainfall zone along with wet conditions in the winter rainfall zone (at ca 3.3, 2 and 0.5 ka BP) may be associated with Antarctic cooling events.

Major ion chemistry of snow cores along a transect in central Dronning Maud Land, Antarctica

Among the large variety of particulates in the atmosphere, calcic mineral dust particles have highly reactive surfaces that undergo heterogeneous reactions with nitrogen oxides contiguously. The association between Ca2+, an important proxy indicator of mineral dust and NO3-, a dominant anion in the Antarctic snow pack was analysed. A total of 41 snow cores (~ 1 m each) that represent snow deposited during 2008-2009 were studied along coastal-inland transects from two different regions - the Princess Elizabeth Land (PEL) and central Dronning Maud Land (cDML) in East Antarctica. Correlation statistics showed a strong association (at 99 % significance level) between NO3- and Ca2+ at the near-coastal sections of both PEL (r = 0.72) and cDML (r = 0.76) transects. Similarly, a strong association between these ions was also observed in snow deposits at the inland sections of PEL (r = 0.8) and cDML (r = 0.85). Such systematic associations between Ca2+ and NO3- is attributed to the interaction between calcic mineral dust and nitrogen oxides in the atmosphere, leading to the possible formation of calcium nitrate (Ca(NO3)2). Forward and back trajectory analyses using HYSPLIT model v. 4 revealed that Southern South America (SSA) was an important dust emitting source to the study region, aided by the westerlies. Particle size distribution showed that over 90 % of the dust was in the range < 4 µm, indicating that these dust particles reached the Antarctic region via long range transport from the SSA region. We propose that the association between Ca2+ and NO3- occurs during the long range transport due to the formation of Ca(NO3)2. The Ca(NO3)2 thus formed in the atmosphere undergo deposition over Antarctica under the influence of anticyclonic polar easterlies. However, influence of local dust sources from the nunataks in cDML evidently mask such association in the mountainous region. The study indicates that the input of dust-bound NO3- may contribute a significant fraction of the total NO3- deposited in Antarctic snow.

Magnetic extracts of three gravity cores located at the Ceará Rise, the Mid-Atlantic Ridge and the Sierra Leone Rise

The magnetic microparticle and nanoparticle inventories of marine sediments from equatorial Atlantic sites were investigated by scanning and transmission electron microscopy to classify all present detrital and authigenic magnetic mineral species and to investigate their regional distribution, origin, transport, and preservation. This information is used to establish source-to-sink relations and to constrain environmental magnetic proxy interpretations for this area. Magnetic extracts were prepared from sediments of three supralysoclinal open ocean gravity cores located at the Ceará Rise (GeoB 1523-1; 3°49.9'N/41°37.3'W), the Mid-Atlantic Ridge (GeoB 4313-2; 4°02.8'N/33°26.3'W), and the Sierra Leone Rise (GeoB 2910-1; 4°50.7'N/21°03.2'W). Sediments from two depths corresponding to marine isotope stages 4 and 5.5 were processed. This selection represents glacial and interglacial conditions of sedimentation for the western, central, and eastern equatorial Atlantic and avoids interferences from subsurface and anoxic processes. Crystallographic, elemental, morphological, and granulometric data of more than 2000 magnetic particles were collected by scanning and transmission electron microscopy. On basis of these properties, nine particle classes could be defined: detrital magnetite, titanomagnetite (fragmental and euhedral), titanomagnetite-hemoilmentite intergrowths, silicates with magnetic inclusions, microcrystalline hematite, magnetite spherules, bacterial magnetite, goethite needles, and nanoparticle clusters. Each class can be associated with fluvial, eolian, subaeric, and submarine volcanic, biogenic, or chemogenic sources. Large-scale sedimentation patterns are delineated as well: detrital magnetite is typical of Amazon discharge, fragmental titanomagnetite is a submarine weathering product of mid-ocean ridge basalts, and titanomagnetite-hemoilmenite intergrowths are common magnetic particles in West African dust. This clear regionalization underlines that magnetic petrology is an excellent indicator of source-to-sink relations. Hematite encrustations, magnetic spherules, and nanoparticle clusters were found at all investigated sites, while bacterial magnetite and authigenic hematite were only detected at the more oxic western site. At the eastern site, surface pits and crevices were seen on the crystal faces indicating subtle early diagenetic reductive dissolution. It was observed that paleoclimatic signatures of magnetogranulometric parameters such as the ratio of anhysteretic and isothermal remanent magnetizations can be formed either by mixing of multiple sources with separate, relatively narrow grain size ranges (western site) or by variable sorting of a single source with a broad grain size distribution (eastern site). Hematite, goethite, and possibly ferrihydrite nanoparticles occur in all sediment cores studied and have either high-coercive or superparamagnetic properties depending on their partly ultrafine grain sizes. These two magnetic fractions are generally discussed as separate fractions, but we suggest that they could actually be genetically linked.

Grain entrainment and transport rates of magnetic minerals of coastal sediment samples from the Bay of Plenty, New Zealand

Heavy (magnetic & non-magnetic) minerals are found concentrated by natural processes in many fluvial, estuarine, coastal and shelf environments with a potential to form economic placer deposits. Understanding the processes of heavy mineral transport and enrichment is prerequisite to interpret sediment magnetic properties in terms of hydro- and sediment dynamics. In this study, we combine rock magnetic and sedimentological laboratory measurements with numerical 3D discrete element models to investigate differential grain entrainment and transport rates of magnetic minerals in a range of coastal environments (riverbed, mouth, estuary, beach and near-shore). We analyzed grain-size distributions of representative bulk samples and their magnetic mineral fractions to relate grain-size modes to respective transport modes (traction, saltation, suspension). Rock magnetic measurements showed that distribution shapes, population sizes and grain-size offsets of bulk and magnetic mineral fractions hold information on the transport conditions and enrichment process in each depositional environment. A downstream decrease in magnetite grain size and an increase in magnetite concentration was observed from riverine source to marine sink environments. Lower flow velocities permit differential settling of light and heavy mineral grains creating heavy mineral enriched zones in estuary settings, while lighter minerals are washed out further into the sea. Numerical model results showed that higher heavy mineral concentrations in the bed increased the erosion rate and enhancing heavy mineral enrichment. In beach environments where sediments contained light and heavy mineral grains of equivalent grain sizes, the bed was found to be more stable with negligible amount of erosion compared to other bed compositions. Heavy mineral transport rates calculated for four different bed compositions showed that increasing heavy mineral content in the bed decreased the transport rate. There is always a lag in transport between light and heavy minerals which increases with higher heavy mineral concentration in all tested bed compositions. The results of laboratory experiments were validated by numerical models and showed good agreement. We demonstrate that the presented approach bears the potential to investigate heavy mineral enrichment processes in a wide range of sedimentary settings.

Flower and seed biomass, and germination rate of arctic tundra plants in response to long term experimental warming

We provide new information on changes in tundra plant sexual reproduction in response to long-term (12 years) experimental warming in the High Arctic. Open-top chambers (OTCs) were used to increase growing season temperatures by 1-2 °C across a range of vascular plant communities. The warming enhanced reproductive effort and success in most species; shrubs and graminoids appeared to be more responsive than forbs. We found that the measured effects of warming on sexual reproduction were more consistently positive and to a greater degree in polar oasis compared with polar semidesert vascular plant communities. Our findings support predictions that long-term warming in the High Arctic will likely enhance sexual reproduction in tundra plants, which could lead to an increase in plant cover. Greater abundance of vegetation has implications for primary consumers - via increased forage availability, and the global carbon budget - as a function of changes in permafrost and vegetation acting as a carbon sink. Enhanced sexual reproduction in Arctic vascular plants may lead to increased genetic variability of offspring, and consequently improved chances of survival in a changing environment. Our findings also indicate that with future warming, polar oases may play an important role as a seed source to the surrounding polar desert landscape.