ALBERT

Description: Mesoscale ocean eddies are ubiquitous coherent rotating structures of water with radial scales on the order of 100 kilometers. Eddies play a key role in the transport and mixing of momentum and tracers across the World Ocean. We present a global daily mesoscale ocean eddy dataset that contains ~45 million mesoscale features and 3.3 million eddy trajectories that persist at least two days as identified in the AVISO dataset over a period of 1993–2014. This dataset, along with the open-source eddy identification software, extract eddies with any parameters (minimum size, lifetime, etc.), to study global eddy properties and dynamics, and to empirically estimate the impact eddies have on mass or heat transport. Furthermore, our open-source software may be used to identify mesoscale features in model simulations and compare them to observed features. Finally, this dataset can be used to study the interaction between mesoscale ocean eddies and other components of the Earth System.

Description: Naturally produced polybrominated diphenyl ethers (PBDEs) pervade the marine environment and structurally resemble toxic man-made brominated flame retardants. PBDEs bioaccumulate in marine animals and are likely transferred to the human food chain. However, the biogenic basis for PBDE production in one of their most prolific sources, marine sponges of the order Dysideidae, remains unidentified. Here, we report the discovery of PBDE biosynthetic gene clusters within sponge-microbiome-associated cyanobacterial endosymbionts through the use of an unbiased metagenome-mining approach. Using expression of PBDE biosynthetic genes in heterologous cyanobacterial hosts, we correlate the structural diversity of naturally produced PBDEs to modifications within PBDE biosynthetic gene clusters in multiple sponge holobionts. Our results establish the genetic and molecular foundation for the production of PBDEs in one of the most abundant natural sources of these molecules, further setting the stage for a metagenomic-based inventory of other PBDE sources in the marine environment.

Description: RECENT advances in 40Ar/39Ar dating1,2 have made it possible to date individual K-feldspar grains from Pleistocene tephra, a capability that greatly improves the reliability and temporal resolving power of the method. Here we apply these new techniques to the dating of a phonolite tephra from the East Eifel volcanic field in West Germany, which is sandwiched between loess and palaeosol (alfisol) deposits, and which was therefore erupted during the transition from a glacial to an interglacial period. Our age estimate for this transition is 215±4 kyr (1 σ), which has important implications for the marine δ18O timescale and for models of global climate change during the Pleistocene. The results show that single-grain dating can detect and compensate for the large quantities of xenocrystic contaminants which are found in many tephra deposits. This technique could be used to date the tephra layers found in marine sediment cores and the results could greatly enhance the reliability of the marine δ18O timescale for more rigorous Fourier analysis testing of the Milankovitch hypothesis.

Description: WHILE ammonites and all other ectocochleate cephalopods became extinct, nautiloids survived relatively unchanged from the Ordovician, suggesting that they are unusually well adapted to their niche. Here we obtain high-resolution tracks of Nautilus positions and depths, combined with telemetered jet pressures, which clarify both its lifestyle and economics. Nautilus is more active in nature than in captivity1, but its energy costs are lower than projected2,3. Viewing Nautilus as 'vertic', rather than benthic, resolves this contradiction. Records show that the cost of transport is the same in any direction within a vertical plane. Living on a reef face swept by a lateral current means that vertical movements4,5 sample large areas for chemical trails. A detected trail can be followed upcurrent in the slow-moving boundary layer, but no effort is wasted on horizontal movement without good prospects for food; long-range movements are downcurrent and made by drifting. Once fed, a Nautilus can reduce its energy costs by moving to deeper, cooler waters, where a single meal can last for months.

Description: Microorganisms produce a wealth of structurally diverse specialized metabolites with a remarkable range of biological activities and a wide variety of applications in medicine and agriculture, such as the treatment of infectious diseases and cancer, and the prevention of crop damage. Genomics has revealed that many microorganisms have far greater potential to produce specialized metabolites than was thought from classic bioactivity screens; however, realizing this potential has been hampered by the fact that many specialized metabolite biosynthetic gene clusters (BGCs) are not expressed in laboratory cultures. In this Review, we discuss the strategies that have been developed in bacteria and fungi to identify and induce the expression of such silent BGCs, and we briefly summarize methods for the isolation and structural characterization of their metabolic products.

Description: Cultivable Actinobacteria are the largest source of microbially derived bioactive molecules. The high demand for novel antibiotics highlights the need for exploring novel sources of these bacteria. Microbial symbioses with sessile macro-organisms, known to contain bioactive compounds likely of bacterial origin, represent an interesting and underexplored source of Actinobacteria. We studied the diversity and potential for bioactive-metabolite production of Actinobacteria associated with two marine lichens ( Lichina confinis and L. pygmaea ; from intertidal and subtidal zones) and one littoral lichen ( Roccella fuciformis ; from supratidal zone) from the Brittany coast (France), as well as the terrestrial lichen Collema auriforme (from a riparian zone, Austria). A total of 247 bacterial strains were isolated using two selective media. Isolates were identified and clustered into 101 OTUs (98% identity) including 51 actinobacterial OTUs. The actinobacterial families observed were: Brevibacteriaceae, Cellulomonadaceae, Gordoniaceae, Micrococcaceae, Mycobacteriaceae, Nocardioidaceae, Promicromonosporaceae, Pseudonocardiaceae, Sanguibacteraceae and Streptomycetaceae. Interestingly, the diversity was most influenced by the selective media rather than lichen species or the level of lichen thallus association. The potential for bioactive-metabolite biosynthesis of the isolates was confirmed by screening genes coding for polyketide synthases types I and II. These results show that littoral lichens are a source of diverse potentially bioactive Actinobacteria.

Description: To the Editor: We congratulate Halsey et al. for their important discussion of the random nature of P values in an earlier issue of this journal1. P values from identical experiments can differ greatly in a way that is surprising to many2, 3, 4, 5, 6. The failure to appreciate this…

Description: Hurricanes and other strong storms can cause important decreases in sea surface temperature by means of vertical mixing within the upper ocean, and by air–sea heat exchange. Here we use satellite-derived infrared images of the western North Atlantic to study sea surface cooling caused by hurricane Gloria (1985). Significant regional variations in sea surface cooling are well correlated with hydrographic conditions. The greatest cooling (up to 5°C) occurred in slope waters north of the Gulf Stream where the seasonal thermocline is shallowest and most compressed; moderate cooling (up to 3 °C) occurred in the open Sargasso Sea where the thermocline is deeper and more diffused; little or no cooling occurred in shallow coastal waters (bottom depth less than 20 m) which were isothermal before the passage of hurricane Gloria. There is a pronounced right-side asymmetry of sea surface cooling with stronger (by a factor of 4) and more extensive (by a factor of 3) cooling found on the right side of the hurricane track. These qualitative results are consistent with the notion that vertical mixing within the upper ocean is the dominant sea surface cooling mechanism of hurricanes.

Description: Large amounts of the greenhouse gas methane are released from the seabed to the water column1, where it may be consumed by aerobic methanotrophic bacteria2. The size and activity of methanotrophic communities, which determine the amount of methane consumed in the water column, are thought to be mainly controlled by nutrient and redox dynamics3–7. Here, we report repeated measurements of methanotrophic activity and community size at methane seeps west of Svalbard, and relate them to physical water mass properties and modelled ocean currents. We show that cold bottom water, which contained a large number of aerobic methanotrophs, was displaced by warmer water with a considerably smaller methanotrophic community within days. Ocean current simulations using a global ocean/sea-ice model suggest that this water mass exchange is consistent with short-term variations in the meandering West Spitsbergen Current. We conclude that the shift from an offshore to a nearshore position of the current can rapidly and severely reduce methanotrophic activity in the water column. Strong fluctuating currents are common at many methane seep systems globally, and we suggest that they affect methane oxidation in the water column at other sites, too.

Description: The ability to monitor the heat content of oceans over long distances is becoming increasingly important for understanding the role of oceans in climate change, for determining the variability of the state of the oceans, for operational ocean observing systems, and for studying large-scale ocean processes such as water-mass formation. Although the properties of the upper layers of the ocean can be routinely measured on large scales by satellite remote sensing (providing altimetric and infrared data) and with expendable probes dropped from commercial vessels, the deep interior of the ocean is more difficult to monitor. Ocean acoustic tomography1 is a promising technique for such applications, as it has the potential to provide systematic, instantaneous and repeated measurements of the ocean interior over large parts of an ocean basin. Here we demonstrate the capability of this technique for measuring the heat content across an entire (albeit small) ocean basin—the western Mediterranean Sea.

Description: The conventional model whereby plume volcanism forms linear age-progressive volcanic chains, with the youngest activity occurring nearest a spreading axis (at a 'hotspot'), has been challenged for the Easter seamount chain1–4. Whereas early work suggested the existence of a linear melting anomaly (a 'hotline')1,2, more recent studies3,4 have proposed a hotspot near Salas y Gomez island, connected with the Easter microplate spreading system by an ~800-km-long, volcanically active plume channel. Here we use geochemical, geological and geochronological data to argue that the hotspot lies close to Easter Island. Moreover, new isotopic data for lavas from the seamount chain provide evidence for bidirectional flow between the spreading axis and the plume, thus supporting geophysical and fluid-dynamical models of mantle flow in a plume/spreading axis system5–7. Material balance and flux considerations show the Easter plume to be weak and cool compared with those beneath larger features such as Iceland, Hawaii and the Galápagos islands.

Description: Climate change is altering oceanic conditions in a complex manner, and the concurrent amendment of multiple properties will modify environmental stress for primary producers. So far, global modelling studies have focused largely on how alteration of individual properties will affect marine life. Here, we use global modelling simulations in conjunction with rotated factor analysis to express model projections in terms of regional trends in concomitant changes to biologically influential multi-stressors. Factor analysis demonstrates that regionally distinct patterns of complex oceanic change are evident globally. Preliminary regional assessments using published evidence of phytoplankton responses to complex change reveal a wide range of future responses to interactive multi-stressors with 〈20–300% shifts in phytoplankton physiological rates, and many unexplored potential interactions. In a future ocean, provinces will encounter different permutations of change that will probably alter the dominance of key phytoplankton groups and modify regional productivity, ecosystem structure and biogeochemistry. Consideration of regionally distinct multi-stressor patterns can help guide laboratory and field studies as well as the interpretation of interactive multi-stressors in global models.

Description: Reflection on the rapidly growing field of ocean acidification research highlights priorities for future research on the changing ocean.

Description: Thin oceanic crust is formed by decompression melting of the upper mantle at mid-ocean ridges, but the origin of the thick and buoyant continental crust is enigmatic. Juvenile continental crust may form from magmas erupted above intraoceanic subduction zones, where oceanic lithosphere subducts beneath other oceanic lithosphere. However, it is unclear why the subduction of dominantly basaltic oceanic crust would result in the formation of andesitic continental crust at the surface. Here we use geochemical and geophysical data to reconstruct the evolution of the Central American land bridge, which formed above an intra-oceanic subduction system over the past 70Myr. We find that the geochemical signature of erupted lavas evolved from basaltic to andesitic about 10Myr ago - coincident with the onset of subduction of more oceanic crust that originally formed above the Galápagos mantle plume. We also find that seismic P-waves travel through the crust at velocities intermediate between those typically observed for oceanic and continental crust. We develop a continentality index to quantitatively correlate geochemical composition with the average P-wave velocity of arc crust globally. We conclude that although the formation and evolution of continents may involve many processes, melting enriched oceanic crust within a subduction zone - a process probably more common in the Archaean - can produce juvenile continental crust.

Description: The stomachs of most vertebrates operate at an acidic pH of 2 generated by the gastric H+/K+-ATPase located in parietal cells. The acidic pH in stomachs of vertebrates is believed to aid digestion and to protect against environmental pathogens. Little attention has been placed on whether acidic gastric pH regulation is a vertebrate character or a deuterostome ancestral trait. Here, we report alkaline conditions up to pH 10.5 in the larval digestive systems of ambulacraria (echinoderm + hemichordate), the closest relative of the chordate. Microelectrode measurements in combination with specific inhibitors for acid-base transporters and ion pumps demonstrated that the gastric alkalization machinery in sea urchin larvae is mainly based on direct H+ secretion from the stomach lumen and involves a conserved set of ion pumps and transporters. Hemichordate larvae additionally utilized HCO 3- transport pathways to generate even more alkaline digestive conditions. Molecular analyses in combination with acidification experiments supported these findings and identified genes coding for ion pumps energizing gastric alkalization. Given that insect larval guts were also reported to be alkaline, our discovery raises the hypothesis that the bilaterian ancestor utilized alkaline digestive system while the vertebrate lineage has evolved a strategy to strongly acidify their stomachs.

Description: Symbiotic relationships between phytoplankton and N-2-fixing microorganisms play a crucial role in marine ecosystems. The abundant and widespread unicellular cyanobacteria group A (UCYN-A) has recently been found to live symbiotically with a haptophyte. Here, we investigated the effect of nitrogen (N), phosphorus (P), iron (Fe) and Saharan dust additions on nitrogen (N-2) fixation and primary production by the UCYN-A-haptophyte association in the subtropical eastern North Atlantic Ocean using nifH expression analysis and stable isotope incubations combined with single-cell measurements. N-2 fixation by UCYN-A was stimulated by the addition of Fe and Saharan dust, although this was not reflected in the nifH expression. CO2 fixation by the haptophyte was stimulated by the addition of ammonium nitrate as well as Fe and Saharan dust. Intriguingly, the single-cell analysis using nanometer scale secondary ion mass spectrometry indicates that the increased CO2 fixation by the haptophyte in treatments without added fixed N is likely an indirect result of the positive effect of Fe and/or P on UCYN-A N-2 fixation and the transfer of N-2-derived N to the haptophyte. Our results reveal a direct linkage between the marine carbon and nitrogen cycles that is fuelled by the atmospheric deposition of dust. The comparison of single-cell rates suggests a tight coupling of nitrogen and carbon transfer that stays balanced even under changing nutrient regimes. However, it appears that the transfer of carbon from the haptophyte to UCYN-A requires a transfer of nitrogen from UCYN-A. This tight coupling indicates an obligate symbiosis of this globally important diazotrophic association.

Description: THE vestimentiferan tubeworm Riftia pachyptila is found around hydrothermal vent areas in the deep sea. Intracellular bacterial chemoautotrophic symbionts use the oxidation of sulphide from the effluent of the vents as an energy source for CO2 fixation. They apparently provide most or all of the nutritional requirements for their gutless hosts1–5. This kind of symbiosis has since been found in many other species from various other phyla from other habitats6–9. Here we present results that the bacteria of R. pachyptila may cover a significant fraction of their respiratory needs by the use of nitrate in addition to oxygen. Nitrate is reduced to nitrite, which may be the end product (nitrate respiration)10 or it may be further reduced to nitrogen gas (denitrification)11. This metabolic trait may have an important role in the colonization of hypoxic habitats in general by animals with this kind of symbiosis.

Description: Quasi-decadal variability in solar irradiance has been suggested to exert a substantial effect on Earth’s regional climate. In the North Atlantic sector, the 11-year solar signal has been proposed to project onto a pattern resembling the North Atlantic Oscillation (NAO), with a lag of a few years due to ocean-atmosphere interactions. The solar/NAO relationship is, however, highly misrepresented in climate model simulations with realistic observed forcings. In addition, its detection is particularly complicated since NAO quasi-decadal fluctuations can be intrinsically generated by the coupled ocean-atmosphere system. Here we compare two multi-decadal ocean-atmosphere chemistry-climate simulations with and without solar forcing variability. While the experiment including solar variability simulates a 1–2-year lagged solar/NAO relationship, comparison of both experiments suggests that the 11-year solar cycle synchronizes quasi-decadal NAO variability intrinsic to the model. The synchronization is consistent with the downward propagation of the solar signal from the stratosphere to the surface.

Description: The Water and Global Change (WATCH) forcing datasets have been created to support the use of hydrological and land surface models for the assessment of the water cycle within climate change studies. They are based on 40-yr ECMWF Re-Analysis (ERA-40) or ECMWF interim reanalysis (ERA-Interim) with temperatures (among other variables) adjusted such that their monthly means match the monthly temperature dataset from the Climatic Research Unit. To this end, daily minimum, maximum, and mean temperatures within one calendar month have been subjected to a correction involving monthly means of the respective month. As these corrections can be largely different for adjacent months, this procedure potentially leads to implausible differences in daily temperatures across the boundaries of calendar months. We analyze day-to-day temperature fluctuations within and across months and find that across-months differences are significantly larger, mostly in the tropics and frigid zones. Average across-months differences in daily mean temperature are typically between 10% and 40% larger than their corresponding within-months average temperature differences. However, regions with differences up to 200% can be found in tropical Africa. Particularly in regions where snowmelt is a relevant player for hydrology, a few degrees Celsius difference can be decisive for triggering this process. Daily maximum and minimum temperatures are affected in the same regions, but in a less severe way.

Description: Dissolved oxygen in sea water affects marine habitats and biogeochemical cycles. Oceanic zones with oxygen deficits represent 7% of the volume and 8% of the area of the oceans, and are thought to be expanding. One of the most pronounced lies in the region off Peru, where mesoscale activity in the form of fronts and eddies is strong. Here, we study the dynamics of the Peruvian oxygen minimum zone in a Lagrangian framework, using a coupled physical-biogeochemical numerical model and finite-size Lyapunov exponent fields, to evaluate the role of mesoscale activity. We find that, at depths between 380 and 600 m, mesoscale structures have two distinct roles. First, their mean positions and paths delimit and maintain the oxygen minimum zone boundaries. Second, their high-frequency fluctuations inject oxygen across the oxygen minimum zone boundaries and eddy fluxes are one order of magnitude higher than mean oxygen fluxes. We conclude that these eddy fluxes contribute to the ventilation of the Peruvian oxygen minimum zone.

Description: The symbiotic association of corals and unicellular algae of the genus Symbiodinium in the southern Persian/Arabian Gulf (PAG) display an exceptional heat tolerance, enduring summer peak temperatures of up to 36 °C. As yet, it is not clear whether this resilience is related to the presence of specific symbiont types that are exclusively found in this region. Therefore, we used molecular markers to identify the symbiotic algae of three Porites species along 〉1000 km of coastline in the PAG and the Gulf of Oman and found that a recently described species, Symbiodinium thermophilum, is integral to coral survival in the southern PAG, the world’s hottest sea. Despite the geographic isolation of the PAG, we discovered that representatives of the S. thermophilum group can also be found in the adjacent Gulf of Oman providing a potential source of thermotolerant symbionts that might facilitate the adaptation of Indian Ocean populations to the higher water temperatures expected for the future. However, corals from the PAG associated with S. thermophilum show strong local adaptation not only to high temperatures but also to the exceptionally high salinity of their habitat. We show that their superior heat tolerance can be lost when these corals are exposed to reduced salinity levels common for oceanic environments elsewhere. Consequently, the salinity prevailing in most reefs outside the PAG might represent a distribution barrier for extreme temperature-tolerant coral/Symbiodinium associations from the PAG.

Description: Global warming was reported to cause growth reductions in tropical shallow water corals in both, cooler and warmer, regions of the coral species range. This suggests regional adaptation with less heat-tolerant populations in cooler and more thermo-tolerant populations in warmer regions. Here, we investigated seasonal changes in the in situ metabolic performance of the widely distributed hermatypic coral Pocillopora verrucosa along 12 degrees latitudes featuring a steep temperature gradient between the northern (28.5 degrees N, 21-27 degrees C) and southern (16.5 degrees N, 28-33 degrees C) reaches of the Red Sea. Surprisingly, we found little indication for regional adaptation, but strong indications for high phenotypic plasticity: Calcification rates in two seasons (winter, summer) were found to be highest at 28-29 degrees C throughout all populations independent of their geographic location. Mucus release increased with temperature and nutrient supply, both being highest in the south. Genetic characterization of the coral host revealed low inter-regional variation and differences in the Symbiodinium clade composition only at the most northern and most southern region. This suggests variable acclimatization potential to ocean warming of coral populations across the Red Sea: high acclimatization potential in northern populations, but limited ability to cope with ocean warming in southern populations already existing at the upper thermal margin for corals

Description: Over the past 60 years, both average daily precipitation intensity and extreme precipitation have increased in many regions1, 2, 3. Part of these changes, or even individual events4, 5, have been attributed to anthropogenic warming6, 7. Over the Black Sea and Mediterranean region, the potential for extreme summertime convective precipitation has grown8 alongside substantial sea surface temperature increase. A particularly devastating convective event experienced in that region was the July 2012 precipitation extreme near the Black Sea town of Krymsk9. Here we study the effect of sea surface temperature (SST) increase on convective extremes within the region, taking the Krymsk event as a showcase example. We carry out ensemble sensitivity simulations with a convection-permitting atmospheric model and show the crucial role of SST increase in the extremeness of the event. The enhancement of lower tropospheric instability due to the current warmer Black Sea allows deep convection to be triggered, increasing simulated precipitation by more than 300% relative to simulations with SSTs characteristic of the early 1980s. A highly nonlinear precipitation response to incremental SST increase suggests that the Black Sea has exceeded a regional threshold for the intensification of convective extremes. The physical mechanism we identify indicates that Black Sea and Mediterranean coastal regions may face abrupt amplifications of convective precipitation under continued SST increase, and illustrates the limitations of thermodynamical bounds for estimating the temperature scaling of convective extremes.

Description: To date, the parameters that determine the rupture area of great subduction zone earthquakes remain contentious. On 1 April 2014, the Mw 8.1 Iquique earthquake ruptured a portion of the well-recognized northern Chile seismic gap but left large highly coupled areas un-ruptured. Marine seismic reflection and swath bathymetric data indicate that structural variations in the subducting Nazca Plate control regional-scale plate-coupling variations, and the limited extent of the 2014 earthquake. Several under-thrusting seamounts correlate to the southward and up-dip arrest of seismic rupture during the 2014 Iquique earthquake, thus supporting a causal link. By fracturing of the overriding plate, the subducting seamounts are likely further responsible for reduced plate-coupling in the shallow subduction zone and in a lowly coupled region around 20.5°S. Our data support that structural variations in the lower plate influence coupling and seismic rupture offshore Northern Chile, whereas the structure of the upper plate plays a minor role.

Description: Oceanic dissolved organic carbon (DOC) is an important carbon pool, similar in magnitude to atmospheric CO2, but the fate of its oldest forms is not well understood. Hot hydrothermal circulation may facilitate the degradation of otherwise un-reactive dissolved organic matter, playing an important role in the long-term global carbon cycle. The oldest, most recalcitrant forms of DOC, which make up most of oceanic DOC, can be recovered by solid-phase extraction. Here we present measurements of solid-phase extractable DOC from samples collected between 2009 and 2013 at seven vent sites in the Atlantic, Pacific and Southern oceans, along with magnesium concentrations, a conservative tracer of water circulation through hydrothermal systems. We find that magnesium and solid-phase extractable DOC concentrations are correlated, suggesting that solid-phase extractable DOC is almost entirely lost from solution through mineralization or deposition during circulation through hydrothermal vents with fluid temperatures of 212-401°C. In laboratory experiments, where we heated samples to 380°C for four days, we found a similar removal efficiency. We conclude that thermal degradation alone can account for the loss of solid-phase extractable DOC in natural hydrothermal systems, and that its maximum lifetime is constrained by the timescale of hydrothermal cycling, at about 40 million years

Description: Cold-water corals (CWC) are widely distributed around the world forming extensive reefs at par with tropical coral reefs. They are hotspots of biodiversity and organic matter processing in the world’s deep oceans. Living in the dark they lack photosynthetic symbionts and are therefore considered to depend entirely on the limited flux of organic resources from the surface ocean. While symbiotic relations in tropical corals are known to be key to their survival in oligotrophic conditions, the full metabolic capacity of CWC has yet to be revealed. Here we report isotope tracer evidence for efficient nitrogen recycling, including nitrogen assimilation, regeneration, nitrification and denitrification. Moreover, we also discovered chemoautotrophy and nitrogen fixation in CWC and transfer of fixed nitrogen and inorganic carbon into bulk coral tissue and tissue compounds (fatty acids and amino acids). This unrecognized yet versatile metabolic machinery of CWC conserves precious limiting resources and provides access to new nitrogen and organic carbon resources that may be essential for CWC to survive in the resource-depleted dark ocean.

Description: The interoceanic transfer of seawater between the Indian Ocean and the Atlantic, ‘Agulhas leakage’, forms a choke point for the overturning circulation in the global ocean. Here, by combining output from a series of high-resolution ocean and climate models with in situ and satellite observations, we construct a time series of Agulhas leakage for the period 1870–2014. The time series demonstrates the impact of Southern Hemisphere westerlies on decadal timescales. Agulhas leakage shows a correlation with the Atlantic Multi-decadal Oscillation on multi-decadal timescales; the former leading by 15 years. This is relevant for climate in the North Atlantic

Description: Sea-level rise1 is one of the most pressing aspects of anthropogenic global warming with far-reaching consequences for coastal societies. However, sea-level rise did2, 3, 4, 5, 6, 7 and will strongly vary from coast to coast8, 9, 10. Here we investigate the long-term internal variability effects on centennial projections of dynamic sea level (DSL), the local departure from the globally averaged sea level. A large ensemble of global warming integrations has been conducted with a climate model, where each realization was forced by identical CO2 increase but started from different atmospheric and oceanic initial conditions. In large parts of the mid- and high latitudes, the ensemble spread of the projected centennial DSL trends is of the same order of magnitude as the globally averaged steric sea-level rise, suggesting that internal variability cannot be ignored when assessing twenty-first-century DSL trends. The ensemble spread is considerably reduced in the mid- to high latitudes when only the atmospheric initial conditions differ while keeping the oceanic initial state identical; indicating that centennial DSL projections are strongly dependent on ocean initial conditions.

Description: Restructure data-gathering and evaluation networks to address climate change, energy, food, health and water provision, say Yonglong Lu and colleagues.

Description: Global mean surface warming has stalled since the end of the twentieth century1, 2, but the net radiation imbalance at the top of the atmosphere continues to suggest an increasingly warming planet. This apparent contradiction has been reconciled by an anomalous heat flux into the ocean3, 4, 5, 6, 7, 8, induced by a shift towards a La Niña-like state with cold sea surface temperatures in the eastern tropical Pacific over the past decade or so. A significant portion of the heat missing from the atmosphere is therefore expected to be stored in the Pacific Ocean. However, in situ hydrographic records indicate that Pacific Ocean heat content has been decreasing9. Here, we analyse observations along with simulations from a global ocean–sea ice model to track the pathway of heat. We find that the enhanced heat uptake by the Pacific Ocean has been compensated by an increased heat transport from the Pacific Ocean to the Indian Ocean, carried by the Indonesian throughflow. As a result, Indian Ocean heat content has increased abruptly, which accounts for more than 70% of the global ocean heat gain in the upper 700 m during the past decade. We conclude that the Indian Ocean has become increasingly important in modulating global climate variability.

Description: An index of water-circulation strength in the North Atlantic Ocean has been derived from sea-level measurements. This provides fresh evidence of the ocean's leading role in multidecadal climate variability. See Letter p.508

Description: Increasingly, spatial geochemical zonation, present as geographically distinct, subparallel trends, is observed along hotspot tracks, such as Hawaii and the Galapagos. The origin of this zonation is currently unclear. Recently zonation was found along the last B70 Myr of the Tristan-Gough hotspot track. Here we present new Sr–Nd–Pb–Hf isotope data from the older parts of this hotspot track (Walvis Ridge and Rio Grande Rise) and re-evaluate published data from the Etendeka and Parana flood basalts erupted at the initiation of the hotspot track. We show that only the enriched Gough, but not the less-enriched Tristan, component is present in the earlier (70–132 Ma) history of the hotspot. Here we present a model that can explain the temporal evolution and origin of plume zonation for both the Tristan-Gough and Hawaiian hotspots, two end member types of zoned plumes, through processes taking place in the plume sources at the base of the lower mantle.

Description: Increasing atmospheric CO2 concentrations are causing ocean acidification (OA), altering carbonate chemistry with consequences for marine organisms. Here we show that OA increases by 46–212% the production of phenolic compounds in phytoplankton grown under the elevated CO2 concentrations projected for the end of this century, compared with the ambient CO2 level. At the same time, mitochondrial respiration rate is enhanced under elevated CO2 concentrations by 130–160% in a single species or mixed phytoplankton assemblage. When fed with phytoplankton cells grown under OA, zooplankton assemblages have significantly higher phenolic compound content, by about 28–48%. The functional consequences of the increased accumulation of toxic phenolic compounds in primary and secondary producers have the potential to have profound consequences for marine ecosystem and seafood quality, with the possibility that fishery industries could be influenced as a result of progressive ocean changes

Description: Coexisting bacteria form various microbial communities in human body parts. In these ecosystems they interact in various ways and the properties of the interaction network can be related to the stability and functional diversity of the local bacterial community. In this study, we analyze the interaction network among bacterial OTUs in 11 locations of the human body. These belong to two major groups. One is the digestive system and the other is the female genital tract. In each local ecosystem we determine the key species, both the ones being in key positions in the interaction network and the ones that dominate by frequency. Beyond identifying the key players and discussing their biological relevance, we also quantify and compare the properties of the 11 networks. The interaction networks of the female genital system and the digestive system show totally different architecture. Both the topological properties and the identity of the key groups differ. Key groups represent four phyla of prokaryotes. Some groups appear in key positions in several locations, while others are assigned only to a single body part. The key groups of the digestive and the genital tracts are totally different.

Description: A knowledge of past changes in the biological productivity of the oceans is important for understanding the interactions between carbon cycling and climate. Phytoplankton productivity in today's oceans can be estimated from the concentrations of chlorophyll in sea water1, but chlorophyll is not preserved in the sediments. Existing proxies for past algal productivity do not represent total productivity; for example, biogenic opal2 reflects the contribution of only part of the phytoplankton community, and the organic carbon record can be subject to contamination from terrestrial inputs2,3. Although chlorins, the pigment-transformation products of chlorophyll, are widespread in Quaternary marine sediments, their potential as proxy measures of past variations in primary productivity has not been convincingly demonstrated. Here we report a high-resolution molecular stratigraphic record of chlorin concentrations over the past 350,000 years in a sediment core from the subtropical Atlantic continental margin. Maxima in the chlorin accumulation rate coincide with significant peaks in the accumulation rates of biogenic opal (at the end of glacial terminations) and organic carbon (between terminations). These results suggest that chlorins, unlike other proxies, can serve as a measure of total primary productivity variations.

Description: A sustainable global ocean observation system requires timely implementation of the framework for ocean observing. The recent Qingdao Global Ocean Summit highlighted the need for a more coherent institutional response to maintain an integrated ocean-observing system.

Description: Fossils of marine microorganisms such as planktic foraminifera are among the cornerstones of palaeoclimatological studies. It is often assumed that the proxies derived from their shells represent ocean conditions above the location where they were deposited. Planktic foraminifera, however, are carried by ocean currents and, depending on the life traits of the species, potentially incorporate distant ocean conditions. Here we use high-resolution ocean models to assess the footprint of planktic foraminifera and validate our method with proxy analyses from two locations. Results show that foraminifera, and thus recorded palaeoclimatic conditions, may originate from areas up to several thousands of kilometres away, reflecting an ocean state significantly different from the core site. In the eastern equatorial regions and the western boundary current extensions, the offset may reach 1.5 °C for species living for a month and 3.0 °C for longer-living species. Oceanic transport hence appears to be a crucial aspect in the interpretation of proxy signals.

Description: Microbiota provide their hosts with a range of beneficial services, including defense from external pathogens. However, host-associated microbial communities themselves can act as a source of opportunistic pathogens depending on the environment. Marine poikilotherms and their microbiota are strongly influenced by temperature, but experimental studies exploring how temperature affects the interactions between both parties are rare. To assess the effects of temperature, temperature stress and infection on diversity, composition and dynamics of the hemolymph microbiota of Pacific oysters (Crassostrea gigas), we conducted an experiment in a fully-crossed, three-factorial design, in which the temperature acclimated oysters (8 or 22 °C) were exposed to temperature stress and to experimental challenge with a virulent Vibrio sp. Strain. We monitored oyster survival and repeatedly collected hemolymph of dead and alive animals to determine the microbiome composition by 16s rRNA gene amplicon pyrosequencing. We found that the microbial dynamics and composition of communities in healthy animals (including infection survivors) were significantly affected by temperature and temperature stress, but not by infection. The response was mediated by changes in the incidence and abundance of operational taxonomic units (OTUs) and accompanied by little change at higher taxonomic levels, indicating dynamic stability of the hemolymph microbiome. Dead and moribund oysters, on the contrary, displayed signs of community structure disruption, characterized by very low diversity and proliferation of few OTUs. We can therefore link short-term responses of host-associated microbial communities to abiotic and biotic factors and assess the potential feedback between microbiota dynamics and host survival during disease.

Description: The useful energy services and energy density value of fossil carbon fuels could be retained for longer timescales into the future if their combustion is balanced by CO2 recapture and storage. We assess the global balance between fossil carbon supply and the sufficiency (size) and capability (technology, security) of candidate carbon stores. A hierarchy of value for extraction-to-storage pairings is proposed, which is augmented by classification of CO2 containment as temporary (〈1,000 yr) or permanent (〉100,000 yr). Using temporary stores is inefficient and defers an intergenerational problem. Permanent storage capacity is adequate to technically match current fossil fuel reserves. However, rates of storage creation cannot balance current and expected rates of fossil fuel extraction and CO2 consequences. Extraction of conventional natural gas is uniquely holistic because it creates the capacity to re-inject an equivalent tonnage of carbon for storage into the same reservoir and can re-use gas-extraction infrastructure for storage. By contrast, balancing the extraction of coal, oil, biomass and unconventional fossil fuels requires the engineering and validation of additional carbon storage. Such storage is, so far, unproven in sufficiency.

Description: Ocean islands, seamounts and volcanic ridges are thought to form above mantle plumes. Yet, this mechanism cannot explain many volcanic features on the Pacific Ocean floor and some might instead be caused by cracks in the oceanic crust linked to the reorganization of plate motions. A distinctive bend in the Hawaiian–Emperor volcanic chain has been linked to changes in the direction of motion of the Pacific Plate, movement of the Hawaiian plume, or a combination of both. However, these links are uncertain because there is no independent record that precisely dates tectonic events that affected the Pacific Plate. Here we analyse the geochemical characteristics of lava samples collected from the Musicians Ridges, lines of volcanic seamounts formed close to the Hawaiian–Emperor bend. We find that the geochemical signature of these lavas is unlike typical ocean island basalts and instead resembles mid-ocean ridge basalts. We infer that the seamounts are unrelated to mantle plume activity and instead formed in an extensional setting, due to deformation of the Pacific Plate. 40Ar/39Ar dating reveals that the Musicians Ridges formed during two time windows that bracket the time of formation of the Hawaiian–Emperor bend, 53–52 and 48–47 million years ago. We conclude that the Hawaiian–Emperor bend was formed by plate–mantle reorganization, potentially triggered by a series of subduction events at the Pacific Plate margins.

Description: Today’s predictions are tomorrow’s priors

Description: Carbon dioxide removal (CDR) from the atmosphere has been proposed as a measure for mitigating global warming and ocean acidification. To assess the extent to which CDR might eliminate the long-term consequences of anthropogenic CO2 emissions in the marine environment, we simulate the effect of two massive CDR interventions with CO2 extraction rates of 5 GtC yr(-1) and 25 GtC yr(-1), respectively, while CO2 emissions follow the extended RCP8.5 pathway. We falsify two hypotheses: the first being that CDR can restore pre-industrial conditions in the ocean by reducing the atmospheric CO2 concentration back to its pre-industrial level, and the second being that high CO2 emissions rates (RCP8.5) followed by CDR have long-term oceanic consequences that are similar to those of low emissions rates (RCP2.6). Focusing on pH, temperature and dissolved oxygen, we find that even after several centuries of CDR deployment, past CO2 emissions would leave a substantial legacy in the marine environment.

Description: High-throughput techniques based on restriction site-associated DNA sequencing (RADseq) are enabling the low-cost discovery and genotyping of thousands of genetic markers for any species, including non-model organisms, which is revolutionizing ecological, evolutionary and conservation genetics. Technical differences among these methods lead to important considerations for all steps of genomics studies, from the specific scientific questions that can be addressed, and the costs of library preparation and sequencing, to the types of bias and error inherent in the resulting data. In this Review, we provide a comprehensive discussion of RADseq methods to aid researchers in choosing among the many different approaches and avoiding erroneous scientific conclusions from RADseq data, a problem that has plagued other genetic marker types in the past.

Description: The ocean stores and transports vast quantities of heat, fresh water, carbon and other materials, and its circulation plays an important role in determining both the Earth's climate and fundamental processes in the biosphere. Understanding the development of climate and important biological cycles therefore requires detailed knowledge of ocean circulation and its transport properties. This cannot be achieved solely through modelling, but must involve accurate observations of the spatio-temporal evolution of the global oceanic flow field. Estimates of oceanic flow are currently made on the basis of space-borne measurements of the sea surface, and monitoring of the ocean interior. Satellite altimetry and acoustic tomography are complementary for this purpose1, as the former provides detailed horizontal coverage of the surface, and the latter the requisite vertical sampling of the interior. High-quality acoustic-tomographic2 and altimetric3 data are now available to test the combined power of these technologies for estimating oceanic flows. Here we demonstrate that, with the aid of state-of-the-art numerical models, it is possible to recover from these data a detailed spatio-temporal record of flow over basin-scale volumes of fluid. Our present results are restricted to the Mediterranean Sea, but the method described here provides a powerful tool for studying oceanic circulation worldwide.

Description: THE supply of dissolved inorganic carbon (DIC) is not considered to limit oceanic primary productivity1, as its concentration in sea water exceeds that of other plant macronutrients such as nitrate and phosphate by two and three orders of magnitude, respectively. But the bulk of oceanic new production2 and a major fraction of vertical carbon flux is mediated by a few diatom genera whose ability to use DIG components other than CO2, which comprises 〈 1% of total DIC3, is unknown4. Here we show that under optimal light and nutrient conditions, diatom growth rate can in fact be limited by the supply of CO2. The doubling in surface water pCO2 levels since the last glaciation from 180 to 355 p.p.m.5,6 could therefore have stimulated marine productivity, thereby increasing oceanic carbon sequestration by the biological pump.

Description: One of the most striking features of the upper North Atlantic Ocean is an extensive layer of water with temperature close to 18°C and salinity close to 36.5‰, (ref. 1). This 18°C water is formed by winter convection in the Sargasso sea2,3, but aspects of the annual rate of 18°C water formation remain obscure4. We have simulated this water mass formation by integrating a one-dimensional model along a 4-yr trajectory of a water column circulating around the Sargasso Sea. Winter convection is deep (≥200 m) in regions where the ocean suffers a net annual heat loss to the atmosphere, and shallow (≤lOOm) where the ocean gains heat each year. The origin of the thermostad (nearly isothermal layer) is a thick layer of nearly homogeneous water subducted beneath the seasonal boundary layer in the year that the water column passes through the line dividing annual cooling from annual heating. We estimate the annual production of 18°C water to be 446,000 km3 yr−1. Downstream, more stratified central water is formed each year at a rate that depends more on Ekman pumping (wind-forced convergence) than on the decreasing depth of winter convection

Description: The El Niño/Southern Oscillation (ENSO) phenomenon is the strongest natural interannual climate fluctuation1. ENSO originates in the tropical Pacific Ocean and has large effects on the ecology of the region, but it also influences the entire global climate system and affects the societies and economies of manycountries2. ENSO can be understood as an irregular low-frequency oscillation between a warm (El Niño) and a cold (La Niña) state. The strong El Niños of 1982/1983 and 1997/1998, along with the more frequent occurrences of El Niños during the past few decades, raise the question of whether human-induced 'greenhouse' warming affects, or will affect, ENSO3. Several global climate models have been applied to transient greenhouse-gas-induced warming simulations to address this question4, 6, but the results have been debated owing to the inability of the models to fully simulate ENSO (because of their coarse equatorial resolution)7. Here we present results from a global climate model with sufficient resolution in the tropics to adequately represent the narrow equatorial upwelling and low-frequency waves. When the model is forced by a realistic future scenario of increasing greenhouse-gas concentrations, more frequent El-Niño-like conditions and stronger cold events in the tropical Pacific Ocean result

Description: In this study, the impact of oceanic data assimilation on ENSO simulations and predictions is investigated. The authors’ main objective is to compare the impact of the assimilation of sea level observations and three-dimensional temperature measurements relative to each other. Three experiments were performed. In a control run the ocean model was forced with observed winds only, and in two assimilation runs three-dimensional temperatures and sea levels were assimilated one by one. The root-mean-square differences between the model solution and observations were computed and heat content anomalies of the upper 275 m compared to each other. Three ensembles of ENSO forecasts were performed additionally to investigate the impact of data assimilation on ENSO predictions. In a control ensemble a hybrid coupled ocean–atmosphere model was initialized with observed winds only, while either three-dimensional temperatures or sea level data were assimilated during the initialization phase in two additional forecast ensembles. The predicted sea surface temperature anomalies were averaged over the eastern equatorial Pacific and compared to observations. Two different objective skill measures were computed to evaluate the impact of data assimilation on ENSO forecasts. The authors’ experiments indicate that sea level observations contain useful information and that this information can be inserted successfully into an oceanic general circulation model. It is inferred from the forecast ensembles that the benefit of sea level and temperature assimilation is comparable. However, the positive impact of sea level assimilation could be shown more clearly when the forecasted temperature differences rather than the temperature anomalies themselves were compared with observations.

Description: The seasonal cycle over the tropical Pacific simulated by 11 coupled ocean–atmosphere general circulation models (GCMs) is examined. Each model consists of a high-resolution ocean GCM of either the tropical Pacific or near-global means coupled to a moderate- or high-resolution atmospheric GCM, without the use of flux correction. The seasonal behavior of sea surface temperature (SST) and eastern Pacific rainfall is presented for each model. The results show that current state-of-the-art coupled GCMs share important successes and troublesome systematic errors. All 11 models are able to simulate the mean zonal gradient in SST at the equator over the central Pacific. The simulated equatorial cold tongue generally tends to be too strong, too narrow, and extend too far west. SSTs are generally too warm in a broad region west of Peru and in a band near 10°S. This is accompanied in some models by a double intertropical convergence zone (ITCZ) straddling the equator over the eastern Pacific, and in others by an ITCZ that migrates across the equator with the seasons; neither behavior is realistic. There is considerable spread in the simulated seasonal cycles of equatorial SST in the eastern Pacific. Some simulations do capture the annual harmonic quite realistically, although the seasonal cold tongue tends to appear prematurely. Others overestimate the amplitude of the semiannual harmonic. Nonetheless, the results constitute a marked improvement over the simulations of only a few years ago when serious climate drift was still widespread and simulated zonal gradients of SST along the equator were often very weak.

Description: In steady state, the export of photosynthetically fixed organic matter to the deep ocean has to be balanced by an upward flux of nutrients into the euphotic zone1. Indirect geochemical estimates2 of the nutrient supply to surface waters have been substantially higher than direct biological and physical measurements3, particularly in subtropical regions. A possible explanation for the apparent discrepancy is that the sampling strategy of the direct measurements has under-represented episodic nutrient injections forced by mesoscale eddy dynamics, whereas geochemical tracer budgets integrate fluxes over longer time and space scales. Here we investigate the eddy-induced nutrient supply by combining two methods potentially capable of delivering synoptic descriptions of the ocean's state on a basin scale. Remotely sensed sea-surface height data from the simultaneous TOPEX/Poseidon and ERS-1 satellite missions are assimilated into a numerical eddy-resolving coupled ecosystem–circulation model of the North Atlantic Ocean. Our results indicate that mesoscale eddy activity accounts for about one-third of the total flux of nitrate into the euphotic zone (taken to represent new production) in the subtropics and at mid-latitudes. This contribution is not sufficient to maintain the observed primary production in parts of the subtropical gyre, where alternative routes of nitrogen supply will have to be considered.

Description: IN 1989, the submersible Nautile discovered one of the most active hydrothermal fields on the modern ocean floor, in the Lau back-arc basin (Fig. 1). The field contains high-temperature white and black smokers, and as we report here, its characteristics contrast strongly with those of the hydrothermal fields found at normal mid-ocean ridges. The main differences are the acidity (pH as low as 2), chemistry and temperature (up to 400 °C) of the hydrothermal fluids, the composition of the ore deposits, and the volcanic and tectonic environments. The fluids also have very high concentrations of trace metals, and primary gold is present in the accompanying mineral deposits. Our data show that these back-arc deposits in the Lau Basin are intermediate between typical mid-ocean-ridge mineralization and massive sulphide deposits of the Kuroko type.

Description: Observations of large and abrupt climate changes recorded in Greenland ice cores have spurred a search for clues to their cause. This search has revealed that at six times during the last glaciation, huge armadas of icebergs launched from Canada spread across the northern Atlantic Ocean, each triggering a climate response of global extent.

Description: ROOTH proposed that the Younger Dryas cold episode, which chilled the North Atlantic region from 11,000 to 10,000 yr BP, was initiated by a diversion of meltwater from the Mississippi drainage to the St Lawrence drainage system. The link between these events is postulated to be a turnoff, during the Younger Dryas cold episode, of the North Atlantic's conveyor-belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the North Atlantic region2. This turnoff is attributed to a reduction in surface-water salinity, and hence also in density, of the waters in the region where North Atlantic Deep Water (NADW) now forms. Here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from Orca Basin core EN32-PC4 which reveal a significant reduction in meltwater flow through the Mississippi River to the Gulf of Mexico from about 11,200 to 10,000 radiocarbon years ago. This finding is consistent with the record for Lake Agassiz which indicates that the meltwater from the southwestern margin of the Laurentide Ice Sheet was diverted to the northern Atlantic Ocean through the St Lawrence valley during the interval from ~11,000 to 10,000 years before present (yr BP).

Description: Marine organic carbon is heavier isotopically (13C enriched) than most land-plant or terrestrial organic C1. Accordingly, δ 13C values of organic C in modern marine sediments are routinely interpreted in terms of the relative proportions of marine and terrestrial sources of the preserved organic matter2,3. When independent geochemical techniques are used to evaluate the source of organic matter in Cretaceous or older rocks, those rocks containing mostly marine organic C are found typically to have lighter (more-negative) δ 13C values than rocks containing mostly terrestrial organic C. Here we conclude that marine photosynthesis in mid-Cretaceous and earlier oceans generally resulted in a greater fractionation of C isotopes and produced organic C having lighter δ 13C values. Modern marine photosynthesis may be occurring under unusual geological conditions (higher oceanic primary production rates, lower P CO2) that limit dissolved CO2 availability and minimize carbon isotope fractionation4.

Description: Natural products have been a rich source of compounds for drug discovery. However, their use has diminished in the past two decades, in part because of technical barriers to screening natural products in high-throughput assays against molecular targets. Here, we review strategies for natural product screening that harness the recent technical advances that have reduced these barriers. We also assess the use of genomic and metabolomic approaches to augment traditional methods of studying natural products, and highlight recent examples of natural products in antimicrobial drug discovery and as inhibitors of protein–protein interactions. The growing appreciation of functional assays and phenotypic screens may further contribute to a revival of interest in natural products for drug discovery.

Description: The climate record obtained from two long Greenland ice cores reveals several brief climate oscillations during glacial time. The most recent of these oscillations, also found in continental pollen records, has greatest impact in the area under the meteorological influence of the northern Atlantic, but none in the United States. This suggests that these oscillations are caused by fluctuations in the formation rate of deep water in the northern Atlantic. As the present production of deep water in this area is driven by an excess of evaporation over precipitation and continental runoff, atmospheric water transport may be an important element in climate change. Changes in the production rate of deep water in this sector of the ocean may push the climate system from one quasi-stable mode of operation to another.

Description: There is now clear evidence that changes in the Earth's climate may be sudden rather than gradual. It is time to put research into the build-up of carbon dioxide in the atmosphere on a better footing.

Description: Abrupt changes in climatic conditions have been seen at high latitudes in the North Atlantic and the Antarctic at 13 kyr BP. It is important to determine whether this abrupt change was confined to high-latitude regions or whether it was global. Here we present results demonstrating an abrupt change in the rate and character of sedimentation in the South China Sea at the close of the last glacial period. Radiocarbon dating and its position in the oxygen isotope shift suggest that this change may be coincident with the changes found at high latitudes.

Description: Abrupt changes in climatic conditions have been seen at high latitudes in the North Atlantic1 and the Antarctic2,3 at 13 kyr BP. It is important to determine whether this abrupt change was confined to high-latitude regions or whether it was global. Here we present results demonstrating an abrupt change in the rate and character of sedimentation in the South China Sea at the close of the last glacial period. Radiocarbon dating and its position in the oxygen isotope shift suggest that this change may be coincident with the changes found at high latitudes.

Description: Perhaps the most significant event in the Cretaceous record of the carbon isotope composition of carbonate1,2, other than the 1–2.5 ‰ negative shift in the carbon isotope composition of calcareous plankton at the Cretaceous/Tertiary boundary3, is the rapid global positive excursion of ~2 ‰ (13C enrichment) which took place between ~91.5 Myr and 90.3 Myr (late Cenomanian to earliest Turonian (C/T boundary event))1,4,5. This excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon (TDC) reservoir resulting from an increase in rate of burial of 13C-depleted organic carbon, which coincided with a major global rise in sea level5 during the so-called C/T oceanic anoxic event (OAE)6. Here we present new data, from nine localities, which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the C/T boundary7,8 is nearly synchronous with that for carbonate and is widespread throughout the Tethys and Atlantic basins (Fig. 1), as well as in more high-latitude epicontinental seas. The postulated increase in the rate of burial of organic carbon may have had a significant effect on CO2 and O2 concentrations in the oceans and atmosphere, and consequent effects on global climate and sedimentary facies.

Description: ALTHOUGH anthropogenic emissions of carbon dioxide have today created a greater atmospheric CO2concentration in the Northern than in the Southern Hemisphere, a comparison of interhemispheric CO2 profiles from 1980 and 1962 led Keeling and Heimann1,2 to conclude that, before the Industrial Revolution, natural CO2 sources and sinks acted to set up a reverse (south to north) gradient which drove about one gigatonne of carbon each year through the atmosphere from the Southern to the Northern Hemisphere. At steady state, this flux must have been balanced by a counter flow of carbon from north to south through the ocean. Here we present a means to estimate this natural flux by a separation of oceanic carbon anomalies into those created by biogenic processes and those created by CO2 exchange between the ocean and atmosphere. We find that before the Industrial Revolution, deep water formed in the northern Atlantic Ocean carried about 0.6 gigatonnes of carbon annually to the Southern Hemisphere, providing support for Keeling and Heimann's proposal. The existence of this oceanic carbon pump also raises questions about the need for a large terrestrial carbon sink in the Northern Hemisphere, as postulated by Tans et al.3, to balance the present global carbon budget.

Description: Crossover recombination reshuffies genes and prevents errors in segregation tha't Iead to extra or missing chromosomes (aneuploidy) in human eggs, a major cause of pregnancy failure and congenital disorders. Here we generate genome-wide maps of cro~sovers and chromosome segregation patterns by recovering all three products of single female meioses. Genotyping 〉4 millioninformative SNPs from 23 complete meioses allowed us to map 2,032 maternal and 1,342 paternal crossovers and to infer the segregation patterns of 529 chromosome pairs. We uncover a new reverse chromosome segregation pattern in which both homologsseparate their sister chromatids at meiosis I; detect selection for higher recombination rates in the female germ line by the elimination of aneuploid embryos; and report chromosomal drive against non recombinant chromatids at meiosis II. Collectively, our findings show !hat recombination not only affects homolog segregation at meiosis I but also the fate of sister chromatids at meiosis II.

Description: The response of the global climate system to smoke from burning oil wells in Kuwait is investigated in a series of numerical experiments using a coupled atmosphere–ocean general circulation model with an interactive soot transport model and extended radiation scheme. The results show a decrease in surface air temperature of ~4 °C in the Gulf region. Outside this region the changes are small and statistically insignificant. No weakening of the Indian summer monsoon is observed.

Description: A fundamental issue in marine science is the identification of the factors controlling biological uptake of CO2, in high-nitrate, low-chlorophyll regions. A recent in situ iron fertilization experiment demonstrated that iron limitation is responsible for low phytoplankton stocks in the equatorial Pacific4. Here we show that flavodoxin, a biochemical marker of iron limitation, can be used to map the degree of iron stress in natural populations. Flavodoxin assays along a 900-km east-west transect in the northeastern subarctic Pacific revealed a pronounced increase in iron stress in the region west of the 135° W meridian. Addition of dissolved iron alleviated this stress. Immunostaining of single cells from the most western station showed that flavodoxin is present specifically within the chloroplasts of diatoms. Our approach provides a rapid means of defining the extent of iron stress in the ocean5 and supports the hypothesis that diatoms are iron stressed in the northeast Pacific.

Description: Seismic tomography and the isotope geochemistry of Cenozoic volcanic rocks suggest the existence of a large, sheet-like region of upwelling in the upper mantle which extends from the eastern Atlantic Ocean to central Europe and the western Mediterranean. A belt of extension and rifting in the latter two areas appears to lie above the intersection of the centre of the upwelling region with the base of the lithosphere. Lead, strontium and neodymium isotope data for all three regions converge on a restricted composition, inferred to be that of the upwelling mantle.

Description: Thiomicrospira species are ubiquitously found in various marine environments and appear particularly common in hydrothermal vent systems. Members of this lineage are commonly classified as sulfur-oxidizing chemolithoautotrophs. Although sequencing of Thiomicrospira crunogena's genome has revealed genes that encode enzymes for hydrogen uptake activity and for hydrogenase maturation and assembly, hydrogen uptake ability has so far not been reported for any Thiomicrospira species. We isolated a Thiomicrospira species (SP-41) from a deep sea hydrothermal vent and demonstrated that it can oxidize hydrogen. We show in vivo hydrogen consumption, hydrogen uptake activity in partially purified protein extracts and transcript abundance of hydrogenases during different growth stages. The ability of this strain to oxidize hydrogen opens up new perspectives with respect to the physiology of Thiomicrospira species that have been detected in hydrothermal vents and that have so far been exclusively associated with sulfur oxidation.

Description: The identification of an exchange of nutrients and signalling molecules between a planktonic alga and a bacterium demonstrates that targeted mutualistic interactions occur across domains of life in the oceans. See Letter p.98

Description: ISOTOPE ratios and concentrations of incompatible trace elements are remarkably successful in discriminating the tectonic origin and magmatic source components for basalts1–5. But problems remain with discriminating the tectonic origin of some tholeiites, especially where field relations and other geological evidence are ambiguous. For example, the tectonic origin of basalts from the Troodos ophiolite (Cyprus) has been debated for several decades. Most workers have been unable to distinguish between an island-arc and/or back-arc origin for the ophiolite6–8. Here we use volatile, K2O and TiO2 contents from ∼250 fresh submarine volcanic glasses to discriminate between tholeiites from different tectonic regimes. K2O÷H2O ratios are lower (〈0.70) in spread ing-centre glasses than in those from island arcs and intraplate oceanic islands. Back-arc-basin basalts can generally be separated from mid-ocean-ridge basalts by their high H2O contents. Using this information, we show that some fresh glasses from the Troodos ophiolite have a clear back-arc-basin affinity.

Description: Particles in aquatic environments host distinct communities of microbes, yet the evolution of particlespecialized taxa and the extent to which specialized microbial metabolism is associated with particles is largely unexplored. Here, we investigate the hypothesis that a widely distributed and uncultivated microbial group - the marine group II euryarchaea (MGII) - interacts with living and detrital particulate organic matter (POM) in the euphotic zone of the central California Current System. Using fluorescent in situ hybridization, we verified the association of euryarchaea with POM. We further quantified the abundance and distribution of MGII 16S ribosomal RNA genes in size-fractionated seawater samples and compared MGII functional capacity in metagenomes from the same fractions. The abundance of MGII in free-living and 〈3 μm fractions decreased with increasing distance from the coast, whereas MGII abundance in the 0.8-3 lm fraction remained constant. At several offshore sites, MGII abundance was highest in particle fractions, indicating that particle-attached MGII can outnumber free-living MGII under oligotrophic conditions. Compared with free-living MGII, the genome content of MGII in particleassociated fractions exhibits an increased capacity for surface adhesion, transcriptional regulation and catabolism of high molecular weight substrates. Moreover, MGII populations in POM fractions are phylogenetically distinct from and more diverse than free-living MGII. Eukaryotic phytoplankton additions stimulated MGII growth in bottle incubations, providing the first MGII net growth rate measurements. These ranged from 0.47 to 0.54 d-1. However, MGII were not recovered in wholegenome amplifications of flow-sorted picoeukaryotic phytoplankton and heterotrophic nanoflagellates, suggesting that MGII in particle fractions are not physically attached to living POM. Collectively, our results support a linkage between MGII ecophysiology and POM, implying that marine archaea have a role in elemental cycling through interactions with particles. © 2015 International Society for Microbial Ecology. All rights reserved.

Description: Algae with secondary plastids of a red algal origin, such as ochrophytes (photosynthetic stramenopiles), are diverse and ecologically important, yet their evolutionary history remains controversial. We sequenced plastid genomes of two ochrophytes, Ochromonas sp. CCMP1393 (Chrysophyceae) and Trachydiscus minutus (Eustigmatophyceae). A shared split of the clpC gene as well as phylogenomic analyses of concatenated protein sequences demonstrated that chrysophytes and eustigmatophytes form a clade, the Limnista, exhibiting an unexpectedly elevated rate of plastid gene evolution. Our analyses also indicate that the root of the ochrophyte phylogeny falls between the recently redefined Khakista and Phaeista assemblages. Taking advantage of the expanded sampling of plastid genome sequences, we revisited the phylogenetic position of the plastid of Vitrella brassicaformis, a member of Alveolata with the least derived plastid genome known for the whole group. The results varied depending on the dataset and phylogenetic method employed, but suggested that the Vitrella plastids emerged from a deep ochrophyte lineage rather than being derived vertically from a hypothetical plastid-bearing common ancestor of alveolates and stramenopiles. Thus, we hypothesize that the plastid in Vitrella, and potentially in other alveolates, may have been acquired by an endosymbiosis of an early ochrophyte.

Description: Recent captures of two female giant squid ( Architeuthis ) off southern Australia have provided the first record of a mated female specimen of these almost mythical deepsea creatures. We found sperm packages (spermatophores) embedded within the skin of both ventral arms of the larger of the two specimens. It seems that male giant squids may use their muscular elongate penis to ‘inject’ sperm packages under pressure directly into the arms of females.

Description: The nitrogen-isotope record preserved in Southern Ocean sediments, along with several geochemical tracers for the settling fluxes of biogenic matter, reveals patterns of past nutrient supply to phytoplankton and surface-water stratification in this oceanic region. Areal averaging of these spatial patterns indicates that reduction of the CO2 'leak' from ocean to atmosphere by increased surface-water stratification south of the Polar Front made a greater contribution to the lowering of atmospheric CO2 concentration during the Last Glacial Maximum than did the increased export of organic carbon from surface to deep waters occurring further north.

Description: THE hydrothermal circulation of sea water through permeable ocean crust results in rock–water interactions that lead to the formation of massive sulphide deposits. These are the modern analogues of many ancient ophiolite-hosted deposits1–4, such as those exposed in Cyprus. Here we report results obtained from drilling a series of holes into an actively forming sulphide deposit on the Mid-Atlantic Ridge. A complex assemblage of sulphide–anhydrite–silica breccias provides striking evidence that such hydrothermal mounds do not grow simply by the accumulation of sulphides on the sea floor. Indeed, the deposit grows largely as an in situ breccia pile, as successive episodes of hydrothermal activity each form new hydrothermal precipitates and cement earlier deposits. During inactive periods, the collapse of sulphide chimneys, dissolution of anhydrite, and disruption by faulting cause brecciation of the deposit. The abundance of anhydrite beneath the present region of focused hydrothermal venting reflects the high temperatures ( 〉 150 °C) currently maintained within the mound, and implies substantial entrainment of cold sea water into the interior of the deposit. These observations demonstrate the important role of anhydrite in the growth of massive sulphide deposits, despite its absence in those preserved on land.

Description: The overflow and descent of cold dense water from the Denmark Strait sill-a submarine passage between Greenland and Iceland-is a principal means by which the deep ocean is ventilated, and is an important element in the global thermohaline circulation. Previous investigations of its variability-in particular, direct current measurements(1,2) in the overflow core since 1986-have shown surprisingly little evidence of long-term changes in now speed. Here we report significant changes in the overflow characteristics during the winter of 1996-97, measured using two current-meter moorings and an inverted echo sounder located at different depths in the fastest part of the now. The overflow warmed to the highest monthly value yet recorded (2.4 degrees C), and showed a pronounced slowing and thinning at its lower margin. We believe that the extreme warmth of the overflow caused it to run higher on the continental slope off east Greenland, so that the lower current meters and the echo sounder were temporarily outside and deeper than the fast-flowing core; model simulations appear to confirm this interpretation, We suggest that the extreme warmth of the overflow is a lagged response to a warming upstream in the Fram Strait three years earlier (caused by an exceptional amplification of the winter North Atlantic Oscillation). If this is so, over-now characteristics may be predictable.

Description: Extreme, abrupt Northern Hemisphere climate oscillations during the last glacial cycle (140,000 years ago to present) were modulated by changes in ocean circulation and atmospheric forcing. However, the variability of the Atlantic meridional overturning circulation (AMOC), which has a role in controlling heat transport from low to high latitudes and in ocean CO2 storage, is still poorly constrained beyond the Last Glacial Maximum. Here we show that a deep and vigorous overturning circulation mode has persisted for most of the last glacial cycle, dominating ocean circulation in the Atlantic, whereas a shallower glacial mode with southern-sourced waters filling the deep western North Atlantic prevailed during glacial maxima. Our results are based on a reconstruction of both the strength and the direction of the AMOC during the last glacial cycle from a highly resolved marine sedimentary record in the deep western North Atlantic. Parallel measurements of two independent chemical water tracers (the isotope ratios of 231Pa/230Th and 143Nd/144Nd), which are not directly affected by changes in the global cycle, reveal consistent responses of the AMOC during the last two glacial terminations. Any significant deviations from this configuration, resulting in slowdowns of the AMOC, were restricted to centennial-scale excursions during catastrophic iceberg discharges of the Heinrich stadials. Severe and multicentennial weakening of North Atlantic Deep Water formation occurred only during Heinrich stadials close to glacial maxima with increased ice coverage, probably as a result of increased fresh-water input. In contrast, the AMOC was relatively insensitive to submillennial meltwater pulses during warmer climate states, and an active AMOC prevailed during Dansgaard–Oeschger interstadials (Greenland warm periods).