Major Ocean Basins Research Articles

Intensification and spatial homogenization of coastal upwelling under climate change.

The timing and strength of wind-driven coastal upwelling along the eastern margins of major ocean basins regulate the productivity of critical fisheries and marine ecosystems by bringing deep and nutrient-rich waters to the sunlit surface, where photosynthesis can occur. How coastal upwelling regimes might change in a warming climate is therefore a question of vital importance. Although enhanced land-ocean differential heating due to greenhouse warming has been proposed to intensify coastal upwelling by strengthening alongshore winds, analyses of observations and previous climate models have provided little consensus on historical and projected trends in coastal upwelling. Here we show that there are strong and consistent changes in the timing, intensity and spatial heterogeneity of coastal upwelling in response to future warming in most Eastern Boundary Upwelling Systems (EBUSs). An ensemble of climate models shows that by the end of the twenty-first century the upwelling season will start earlier, end later and become more intense at high but not low latitudes. This projected increase in upwelling intensity and duration at high latitudes will result in a substantial reduction of the existing latitudinal variation in coastal upwelling. These patterns are consistent across three of the four EBUSs (Canary, Benguela and Humboldt, but not California). The lack of upwelling intensification and greater uncertainty associated with the California EBUS may reflect regional controls associated with the atmospheric response to climate change. Given the strong linkages between upwelling and marine ecosystems, the projected changes in the intensity, timing and spatial structure of coastal upwelling may influence the geographical distribution of marine biodiversity.

Analysis of remineralisation, lability, temperature sensitivity and structural composition of organic matter from the upper ocean

Organic carbon (OC) synthesised by plankton is exported out of the surface layer as particulate (POC) and dissolved (DOC) organic carbon. This “biological pump” constitutes a major pathway in the global marine carbon cycle, each year exporting about 10PgC into the ocean interior, where it is subsequently remineralised via biological decomposition. Remineralised inorganic nutrients and carbon are, ultimately, again brought to the surface by advection and turbulent mixing which closes the OC-cycle in the upper ocean. Thus, remineralisation rates of OC are a critical component of the biological pump. These rates are regulated by the lability of the material and the environmental conditions in the ambient water. Temperature is particularly important in regulating the rate of microbial respiration and, thus, remineralisation rates. A significant temperature dependence of the microbial metabolic activity in the ocean interior is expected, as this is a feature observed elsewhere in the biosphere. Such temperature dependence of microbial remineralisation of POC and DOC will alter the amount of material available for transport by the biological pump to the deep ocean. Very few studies on the lability of OC and temperature sensitivity of microbial degradation processes in the mesopelagic zone (∼100–1000m) have, to date, been carried out. Here, we present a comprehensive new experimental data set from all major ocean basins and quantify remineralisation rates of OC and their temperature sensitivity in long-term incubations of water from the upper 350m. Microbial respiration was measured by non-invasive oxygen optodes and oxygen consumption was used as a constraint for determining the remineralisation rates and temperature sensitivity by two complementary methods. First, we analysed the oxygen consumption from a multi-component OC-model where the concentration, remineralisation rates and temperature sensitivity of two bio-available (labile) pools of organic carbon were fitted to the data via a non-linear fitting procedure. Thereafter, a continuous OC-model was fitted to the data through an inverse method and information about lability, temperature sensitivity and structural composition of the OC-pool was analysed together with the results from the two-pool solutions. Median values of remineralisation rates from all experiments on material characterising sinking POC were found to be 0.6 and 0.05days−1 for the two decomposable pools corresponding to turnover times of 2 and 21days, respectively. Accordingly, solutions from the continuous model resulted in median turnover times between 6 and 11days. Similar analyses were carried out for the OC-pool characterising DOC. A significant bio-available OC-pool was found to be present in the surface layer with a median value from all experiments of 30μM TOC. The median values of all remineralisation rates from the two bio-available OC-pools were found to be 0.2 and 0.02days−1, corresponding to turnover times of 5 and 56days, respectively, in good agreement with previous studies. The corresponding temperature sensitivities, characterised by a Q10-value, were found to be about 1.9 for the POC-fraction whereas the DOC fraction was characterised with values above 2.8 for the continuous OC-models. The analysis of the structural composition indicated that the TOC distribution in the surface layer was characterised by more heterogeneous material in terms of lability compared with the POC material sampled from the upper 350m. Finally, we analyse the potential impact of the calculated temperature sensitivity on the general OC-cycling in the upper ocean and show that the implied reduction in OC-flux in a warmer ocean may have significant impact on nutrient cycling in general and also tends to reduce future ocean carbon uptake significantly.

Analysis of sailfish (Istiophorus platypterus) population structure in the North Pacific Ocean

The global genetic population structure of sailfish is not well understood, nor has it been well characterized in any of the major ocean basins. In this study, we surveyed the pattern of genetic differentiation of sailfish in the North Pacific Ocean using 307bp of sequence of the mtDNA control region I and five tetra-nucleotide microsatellite loci for 92 sailfish representing three North Pacific localities. We report significant genetic differentiation with both mitochondrial and nuclear markers between the western North Pacific Ocean collection from Taiwan (n=39) and the eastern North Pacific Ocean collections from Mexico (n=37) and Costa Rica (n=16), the latter of which were not significantly different from each other. These results corroborate genetic heterogeneity in the North Pacific previously observed using restriction fragment length polymorphisms (RFLPs) of mtDNA, and three microsatellite loci, and indicate that sailfish from the eastern and the western North Pacific Ocean belong to distinct populations. Consistent with the levels of mtDNA variation reported in other marine species, sailfish in the eastern Pacific Ocean displayed significantly (p<0.05) less variation than in the western Pacific Ocean. In future studies, sample sizes and geographic coverage should be increased to resolve the population structure throughout the entire Pacific Ocean.

The distribution of the chaetognath population and its interaction with environmental characteristics in the Bay of Bengal and the Arabian Sea

The Bay of Bengal (BoB) and the Arabian Sea (AS), the two major ocean basins in the north Indian Ocean, share similarities in geographical and meteorological characteristics but differ in hydrographic characteristics and biological production. The BoB is traditionally considered a less productive region than the AS. Chaetognatha, a major taxon of carnivorous mesozooplankton, often rank second in abundance to copepods and thus play a pivotal role in the pelagic food web of this region. We studied the influence of environmental variables on the distribution and the diversity of chaetognaths in these two ocean basins. Of the 21 species observed during the study, Flaccisagitta enflata dominated in the mixed layer to the thermocline, Decipisagitta decipiens from the bottom of the thermocline to 500 m and Eukrohnia fowleri below 500 m. Mesoscale and basin-scale processes such as eddies, gyres and upwelling had a profound influence on the abundance in the upper layer, while the presence of an oxygen minimum zone in the mid-depth layers had a crucial effect on the vertical distribution of the chaetognath population. Despite the variation in the controlling factors on chaetognath populations in the BoB and AS, the patterns of depth-specific abundance were similar.

Seismic waves in 3-D: from mantle asymmetries to reliable seismic hazard assessment

A global cross-section of the Earth parallel to the tectonic equator (TE) path, the great circle representing the equator of net lithosphere rotation, shows a difference in shear wave velocities between the western and eastern flanks of the three major oceanic rift basins. The low-velocity layer in the upper asthenosphere, at a depth range of 120 to 200 km, is assumed to represent the decoupling between the lithosphere and the underlying mantle. Along the TE-perturbed (TE-pert) path, a ubiquitous LVZ, about 1,000-km-wide and 100-km-thick, occurs in the asthenosphere. The existence of the TE-pert is a necessary prerequisite for the existence of a continuous global flow within the Earth. Ground-shaking scenarios were constructed using a scenario-based method for seismic hazard analysis (NDSHA), using realistic and duly validated synthetic time series, and generating a data bank of several thousands of seismograms that account for source, propagation, and site effects. Accordingly, with basic self-organized criticality concepts, NDSHA permits the integration of available information provided by the most updated seismological, geological, geophysical, and geotechnical databases for the site of interest, as well as advanced physical modeling techniques, to provide a reliable and robust background for the development of a design basis for cultural heritage and civil infrastructures. Estimates of seismic hazard obtained using the NDSHA and standard probabilistic approaches are compared for the Italian territory, and a case-study is discussed. In order to enable a reliable estimation of the ground motion response to an earthquake, three-dimensional velocity models have to be considered, resulting in a new, very efficient, analytical procedure for computing the broadband seismic wave-field in a 3-D anelastic Earth model.

A global climatology of extreme rainfall rates in the inner core of intense tropical cyclones

The localized rain rate maxima (RM) of the inner core region of intense tropical cyclones (TCs) are investigated using Version 6 of the Tropical Rainfall Measuring Mission Multi-satellite Precipitation Analysis data-set from 1998 to 2010. Specifically, this study examines the probabilities of RM exceeding 25 mm h−1 (P25) in intense TCs. The 25 mm h−1 RM is the 90th percentile of all RM observations during the study period. The descending order of P25 observed from intense TCs for the six major ocean basins is: the North Indian Ocean, the Atlantic Ocean, the Northwest Pacific Ocean, the South Pacific Ocean, the South Indian Ocean, and the East-central Pacific Ocean. The six major basins have been subdivided into 29 sub-basins to discern regional variability of RM. P25 increases with increasing TC category in all major basins, except for the South Pacific. Sub-basins with intense TCs that produce extreme rainfall rate maxima include the Bay of Bengal, the South Philippine Sea, the East China Sea, the north coast of Australia, southeast Melanesia, and the Northwest Atlantic. Sub-basins with a higher proportion of category 5 (CAT5) observations than category 3 (CAT3) observations tend to have a greater P25 beyond 60 km from the storm center.

Periodicity and patterns of ocean wind and wave climate

AbstractThe Climate Forecast System Reanalysis (CFSR) provides a wealth of information spanning 1979–2009 for investigation of ocean wind and wave climate. Preprocessing of the data is necessary to remove the dominant seasonal signals and to create time series of semimonthly averaged wind speed and significant wave height over a 0.5° global grid. We perform an empirical orthogonal function (EOF) analysis to extract the dominant space‐time patterns. The results for the three major ocean basins show strong zonal structures in the winds and saturation of the swells corroborating prior works with various data sets. We reexamine the CFSR data in the frequency domain to identify periodic signals associated with published climate indices. The Fourier transform of the preprocessed time series generates spectra ranging from 1 month to 15 years period for an EOF analysis. The results demonstrate the spatial structures and periods of climate phenomena. The Arctic Oscillation dominates the Atlantic basin with a broad range of intra‐annual signals off the European coasts. The Indian and Pacific Oceans are strongly influenced by inter‐annual cycles of the El Niño Southern Oscillation (ENSO) and the Antarctica Oscillation. The Indian Ocean also has strong intra‐annual components ranging from 50 to 80 days period. The ENSO proves to be a ubiquitous signal around the globe, and in particular, saturates the Pacific with strong influences in the equatorial region and the Southern Hemisphere Westerlies. A commonality of all basins is that the magnitude and the spatial structure of the intra‐annual and inter‐annual signals are similar suggesting a wide range of periods in each of the climate cycles examined.

Iron deficiency increases growth and nitrogen-fixation rates of phosphorus-deficient marine cyanobacteria.

Marine dinitrogen (N2)-fixing cyanobacteria have large impacts on global biogeochemistry as they fix carbon dioxide (CO2) and fertilize oligotrophic ocean waters with new nitrogen. Iron (Fe) and phosphorus (P) are the two most important limiting nutrients for marine biological N2 fixation, and their availabilities vary between major ocean basins and regions. A long-standing question concerns the ability of two globally dominant N2-fixing cyanobacteria, unicellular Crocosphaera and filamentous Trichodesmium, to maintain relatively high N2-fixation rates in these regimes where both Fe and P are typically scarce. We show that under P-deficient conditions, cultures of these two cyanobacteria are able to grow and fix N2 faster when Fe deficient than when Fe replete. In addition, growth affinities relative to P increase while minimum concentrations of P that support growth decrease at low Fe concentrations. In Crocosphaera, this effect is accompanied by a reduction in cell sizes and elemental quotas. Relatively high growth rates of these two biogeochemically critical cyanobacteria in low-P, low-Fe environments such as those that characterize much of the oligotrophic ocean challenge the common assumption that low Fe levels can have only negative effects on marine primary producers. The closely interdependent influence of Fe and P on N2-fixing cyanobacteria suggests that even subtle shifts in their supply ratio in the past, present and future oceans could have large consequences for global carbon and nitrogen cycles.

Re–Os isotopic and platinum group elemental constraints on the genesis of the Xiadong ophiolitic complex, Eastern Xinjiang, NW China

The Xiadong ultramafic complex, Eastern Xinjiang, NW China, was tectonically emplaced in Proterozoic rocks of the Middle Tianshan Terrane in the Central Asian Orogenic Belt. It consists of harzburgite, dunite and websterite and is associated with amphibolite. The amphibolite is interpreted as metamorphosed oceanic crust, and contains igneous zircon grains with an age of 368±3Ma.All of the ultramafic rocks have highly variable PGE contents. Both the harzburgite and dunite have high PGEs but low Cu and Ni, whereas the dunite and websterite show significant depletion of Ir and Pt. The dunite and harzburgite generally have low 187Re/188Os ratios (0.074–0.81) with relatively uniform 187Os/188Os ratios from 0.1320 to 0.1375, slightly higher than the primitive upper mantle (PUM) value (0.1296), except for one harzburgite sample with much higher 187Re/188Os (24.6) and 187Os/188Os ratios (0.4581). The websterite has significantly high 187Re/188Os (202–1661) and radiogenic 187Os/188Os (1.166–19.90) ratios relative to the dunite and harzburgite.PGE patterns and Re–Os isotopic compositions clearly indicate that the Xiadong complex is a part of an ophiolitic mantle sequence, and the PGE geochemistry suggests a relatively reduced mantle source. Rocks from the complex may have undergone two stages of formation; early partial melting at a mid-ocean ridge generated a depleted mantle sequence with low Re/Os ratios. The harzburgite represents the residuum after partial melting of the lherzolite, whereas the dunite was formed by later melt/rock interaction. The websterites are cumulates derived from SSZ magmas above an intra-oceanic subduction zone during the second stage of formation. This second stage of magmatism resulted in metasomatism and enrichment of Re/Os ratios and 187Os/188Os isotope ratios of the mantle rocks. Our new data suggest that the Xiadong complex records the former presence of a major ocean basin between the Tarim Block and the Middle Tianshan Terrane at ~368Ma. The ophiolite was emplaced shortly after the second stage of magmatism.

Contourites and associated sediments controlled by deep-water circulation processes: State-of-the-art and future considerations

The contourite paradigm was conceived a few decades ago, yet there remains a need to establish a sound connection between contourite deposits, basin evolution and oceanographic processes. Significant recent advances have been enabled by various factors, including the establishment of two IGCP projects and the realisation of several IODP expeditions. Contourites were first described in the Northern and Southern Atlantic Ocean, and since then, have been discovered in every major ocean basin and even in lakes. The 120 major contourite areas presently known are associated to myriad oceanographic processes in surface, intermediate and deep-water masses. The increasing recognition of these deposits is influencing palaeoclimatology & palaeoceanography, slope-stability/geological hazard assessment, and hydrocarbon exploration. Nevertheless, there is a pressing need for a better understanding of the sedimentological and oceanographic processes governing contourites, which involve dense bottom currents, tides, eddies, deep-sea storms, internal waves and tsunamis. Furthermore, in light of the latest knowledge on oceanographic processes and other governing factors (e.g. sediment supply and sea-level), existing facies models must now be revised. Persistent oceanographic processes significantly affect the seafloor, resulting in large-scale depositional and erosional features. Various classifications have been proposed to subdivide a continuous spectrum of partly overlapping features. Although much progress has been made in the large-scale, geophysically based recognition of these deposits, there remains a lack of unambiguous and commonly accepted diagnostic criteria for deciphering the small-scaled contourite facies and for distinguishing them from turbidite ones. Similarly, the study of sandy deposits generated or affected by bottom currents, which is still in its infancy, offers great research potential: these deposits might prove invaluable as future reservoir targets. Expectations for the forthcoming analysis of data from the IODP Expedition 339 are high, as this work promises to tackle much of the aforementioned lack of knowledge. In the near future, geologists, oceanographers and benthic biologists will have to work in concert to achieve synergy in contourite research to demonstrate the importance of bottom currents in continental margin sedimentation and evolution. • Bottom current-controlled features are ubiquitous in marine basins. • Updated, comprehensive review of the topic “contourites” and associated sediments • History, significance, occurrence, oceanography, geometry, sediments, perspectives • As much objective as possible, with our own synthesis and conclusions • Text equipped with 26 colour figures, 1 table and an exhaustive reference list

On the dynamics of the Hadley circulation and subtropical drying

Changes in subtropical precipitation and the Hadley circulation (HC) are inextricably linked. The original Halley–Hadley model cannot explain certain aspects of the Earth’s meridional circulation in the tropics and is of limited use in understanding regional changes in precipitation. Here, we expand on previous work on the regional and seasonal aspects of the HC, in particular how land–sea temperature contrasts contribute to the strength and width of the HC. We show that the Earth’s HC is well described by three regionally distinct cells along the eastern edges of the major ocean basins with opposite circulations elsewhere. Moreover, comparable summertime hemisphere cells emerge in each region. While it has been recognized that continents modify the meridional pressure gradient, we demonstrate that a substantial part of the Earth’s HC is driven by zonal pressure gradients (ZPGs) that only exist due to continental heating and air–sea interaction. Projected changes in land–sea temperature contrasts in a warming climate due to the relatively low thermal capacity of land will also affect ZPGs and thus HC strength and width, with implications for extremes in hydroclimate and freshwater resources across the increasingly vulnerable subtropics.

On the Importance of Surface Forcing in Conceptual Models of the Deep Ocean

Abstract In the major ocean basins, diapycnal mixing upwells dense Antarctic Bottom Water, which returns southward and closes the deepest cell of the meridional overturning circulation (MOC). This cell ventilates the deep ocean and regulates the partitioning of CO2 between the atmosphere and the ocean. The oceanographic community's conceptual understanding of the deep stratification and MOC has evolved from classic “abyssal recipes” arguments to a more recent appreciation of along-isopycnal upwelling in the Southern Ocean, consistent with a weakly mixed ocean interior. Both the deep stratification and the deep MOC are shown here to be sensitive to the form of the surface buoyancy forcing in a two-dimensional model that includes a circumpolar channel and northern basin. For a fixed surface buoyancy condition, the deep stratification is essentially prescribed, whereas for a fixed surface buoyancy flux, the deep stratification varies by orders of magnitude over the range of diapycnal diffusivity κ observed in the ocean. These cases also produce different scalings for the deep MOC with κ, in both weak and strong κ regimes. In addition, these scalings are shown to be sensitive not only to the type of surface boundary condition, but also to the latitudinal structure of the surface fluxes. This latter point is crucial as buoyancy budgets and dynamical features of the circulation are poorly constrained along the Antarctic margins. This study emphasizes the need for caution in the interpretation of simple conceptual models that, while useful, may not include all mechanisms that contribute to the MOC’s strength and structure.

Predicting current and future global distributions of whale sharks

The Vulnerable (IUCN) whale shark spans warm and temperate waters around the globe. However, their present-day and possible future global distribution has never been predicted. Using 30years (1980-2010) of whale shark observations recorded by tuna purse-seiners fishing in the Atlantic, Indian and Pacific Oceans, we applied generalized linear mixed-effects models to test the hypothesis that similar environmental covariates predict whale shark occurrence in all major ocean basins. We derived global predictors from satellite images for chlorophyll a and sea surface temperature, and bathymetric charts for depth, bottom slope and distance to shore. We randomly generated pseudo-absences within the area covered by the fisheries, and included fishing effort as an offset to account for potential sampling bias. We predicted sea surface temperatures for 2070 using an ensemble of five global circulation models under a no climate-policy reference scenario, and used these to predict changes in distribution. The full model (excluding standard deviation of sea surface temperature) had the highest relative statistical support (wAICc =0.99) and explained ca. 60% of the deviance. Habitat suitability was mainly driven by spatial variation in bathymetry and sea surface temperature among oceans, although these effects differed slightly among oceans. Predicted changes in sea surface temperature resulted in a slight shift of suitable habitat towards the poles in both the Atlantic and Indian Oceans (ca. 5°N and 3-8°S, respectively) accompanied by an overall range contraction (2.5-7.4% and 1.1-6.3%, respectively). Predicted changes in the Pacific Ocean were small. Assuming that whale shark environmental requirements and human disturbances (i.e. no stabilization of greenhouse gas emissions) remain similar, we show that warming sea surface temperatures might promote a net retreat from current aggregation areas and an overall redistribution of the species.

An assessment of global Ocean Thermal Energy Conversion resources under broad geographical constraints

Rates of Ocean Thermal Energy Conversion (OTEC) are assessed with a high-resolution (1° × 1°) ocean general circulation model when broad geographical restrictions are imposed on the OTEC implementation area. This may correspond to practical or legal limitations, such as the cost of long submarine power cables or the extent of Exclusive Economic Zones. Because some environmental effects predicted under large-scale OTEC scenarios exhibit a strong asymmetry among major oceanic basins, numerical experiments where the OTEC domain is restricted to such specific areas are also conducted. Results suggest that in all cases, a rate of about 0.2 TW per Sverdrup of OTEC deep cold seawater is sustained when overall OTEC net power peaks. At that juncture, temperature profiles in the OTEC implementation areas are affected in similar ways, while the strength of the Thermohaline Circulation roughly doubles. Overall geographical constraints simply defined by distance to shore, given the model's 1° horizontal resolution, produce global OTEC net power maxima of 12–14 TW. In such cases, OTEC net power density approximately increases in inverse proportion to the OTEC implementation area. Limiting OTEC development to the Indo-Pacific yields results similar to the global case with a maximum proportional to the implementation area (12 TW), but simulations restricted to the Atlantic behave quite differently. In the latter case, OTEC net power peaks a little over 5 TW. It is estimated that producing half the predicted power maxima would substantially limit large-scale environmental temperature changes in each case.

Sperm whale coda repertoires in the western Pacific Ocean

Sperm whales are social cetaceans that live in matrilineal family units, and inhabit all major ocean basins from the tropics to polar regions. They produce stereotyped patterns of 3 to 40 broadband clicks, termed “codas,” that typically occur within a period of less than 3 s. Coda repertoires can be assigned to a “vocal clan,” a type of social group used to define sperm whale population structure. Extensive studies of vocal clans have been conducted in the eastern tropical Pacific (ETP); however, little is known about sperm whale coda repertoires in the western Pacific. We reviewed codas recorded from independent sperm whale groups that were acoustically and visually encountered during two marine mammal surveys conducted in the Northern Mariana Islands (10 groups) and Palau region (3 groups), in 2007 and 2012, respectively. Three bioacousticians qualitatively classified codas to type, which indicated the presence of the “+1” and “regular” vocal clan. These data are now being analyzed using multivariate methods described by Rendell and Whitehead (2003) to quantitatively classify codas from each group. The identification of vocal clans within this region has implications for understanding the culturally linked stock distribution of sperm whales across the Pacific Ocean.

Revision of the Manefish GeneraCaristiusandPlatyberyx(Teleostei: Percomorpha: Caristiidae), with Descriptions of Five New Species

The family Caristiidae, commonly known as manefishes or veilfins, includes several species of mesopelagic, oceanic fishes found throughout the major ocean basins of the world. We present herein the second part of our revision of the family, including all of the “large-mouth” species, which are distinguished from other members of the family by having a narrow suborbital space and a long upper jaw that extends to mid-orbit or beyond and which is visible externally, not covered by the thin bones of the suborbital series. This group, which is comprised of the genera Platyberyx and Caristius, is described in full, including descriptions of five new species. The genus Platyberyx, which includes six species, three of which are newly described, is distinguished from all other caristiid genera by the presence of a conspicuous lateral line with large scales. The genus Caristius, with four species, two of which are newly described, is distinguished from Platyberyx by the absence of a conspicuous lateral line and by ...

Genetic variation in brown trout Salmo truttaacross the Danube, Rhine, and Elbe headwaters: a failure of the phylogeographic paradigm?

BackgroundBrown trout Salmo trutta have been described in terms of five major mtDNA lineages, four of which correspond to major ocean basins, and one, according to some authors, to a distinct taxon, marbled trout Salmo marmoratus. The Atlantic and Danubian lineages of brown trout meet in a poorly documented contact zone in Central Europe. The natural versus human mediated origin of the Atlantic lineage in the upper Danube is a question of both theoretical and practical importance with respect to conservation management. We provide a comprehensive population genetic analysis of brown trout in the region with the aim of evaluating the geographic distribution and genetic integrity of these two lineages in and around their contact zone.ResultsGenetic screening of 114 populations of brown trout across the Danube/Rhine/Elbe catchments revealed a counter-intuitive phylogeographic structure with near fixation of the Atlantic lineage in the sampled portions of the Bavarian Danube. Along the Austrian Danube, phylogeographic informative markers revealed increasing percentages of Danube-specific alleles with downstream distance. Pure Danube lineage populations were restricted to peri-alpine isolates within previously glaciated regions. Both empirical data and simulated hybrid comparisons support that trout in non-glaciated regions north and northeast of the Alps have an admixed origin largely based on natural colonization. In contrast, the presence of Atlantic basin alleles south and southeast of the Alps stems from hatchery introductions and subsequent introgression. Despite extensive stocking of the Atlantic lineage, little evidence of first generation stocked fish or F1 hybrids were found implying that admixture has been established over time.ConclusionsA purely phylogeographic paradigm fails to describe the distribution of genetic lineages of Salmo in Central Europe. The distribution pattern of the Atlantic and Danube lineages is extremely difficult to explain without invoking very strong biological mechanisms.The peri-alpine distribution of relict populations of pure Danubian lineage brown trout implies that they colonized headwater river courses post-glacially ahead of the expansion of the Atlantic lineage. The recognition of natural as opposed to anthropogenic introgression of the Atlantic lineage into Danubian gene pools is of fundamental importance to management strategies.

The oceanic mass balance of copper and zinc isotopes, investigated by analysis of their inputs, and outputs to ferromanganese oxide sediments

The oceanic biogeochemical cycles of the transition metals have been eliciting considerable attention for some time. Many of them have isotope systems that are fractionated by key biological and chemical processes so that significant information about such processes may be gleaned from them. However, for many of these nascent isotopic systems we currently know too little of their modern oceanic mass balance, making the application of such systems to the past speculative, at best. Here we investigate the biogeochemical cycling of copper (Cu) and zinc (Zn) isotopes in the ocean. We present estimates for the isotopic composition of Cu and Zn inputs to the oceans based on new data presented here and published data. The bulk isotopic composition of dissolved Cu and Zn in the oceans (δ65Cu ∼+0.9‰, δ66Zn ∼+0.5‰) is in both cases heavier than their respective inputs (at around δ65Cu=+0.6‰ and δ66Zn=+0.3‰, respectively), implying a marine process that fractionates them and a resulting isotopically light sedimentary output. For the better-known molybdenum isotope system this is achieved by sorption to Fe–Mn oxides, and this light isotopic composition is recorded in Fe–Mn crusts. Hence, we present isotopic data for Cu and Zn in three Fe–Mn crusts from the major ocean basins, which yield δ65Cu=0.44±0.23‰ (mean and 2SD) and δ66Zn=1.04±0.21‰. Thus for Cu isotopes output to particulate Fe–Mn oxides can explain the heavy isotopic composition of the oceans, while for Zn it cannot. The heavy Zn in Fe–Mn crusts (and in all other authigenic marine sediments measured so far) implies that a missing light sink is still to be located. These observations are some of the first to place constraints on the modern oceanic mass balance of Cu and Zn isotopes.

Detecting an external influence on recent changes in oceanic oxygen using an optimal fingerprinting method

Abstract. Ocean deoxygenation has been observed in all major ocean basins over the past 50 yr. Although this signal is largely consistent with oxygen changes expected from anthropogenic climate change, the contribution of external forcing to recent deoxygenation trends relative to natural internal variability is yet to be established. Here we conduct a formal optimal fingerprinting analysis to investigate if external forcing has had a detectable influence on observed dissolved oxygen concentration ([O2]) changes between ∼1970 and ∼1992 using simulations from two Earth System Models (MPI-ESM-LR and HadGEM2-ES). We detect a response to external forcing at a 90% confidence level and find that observed [O2] changes are inconsistent with internal variability as simulated by models. This result is robust in the global ocean for depth-averaged (1-D) zonal mean patterns of [O2] change in both models. Further analysis with the MPI-ESM-LR model shows similar positive detection results for depth-resolved (2-D) zonal mean [O2] changes globally and for the Pacific Ocean individually. Observed oxygen changes in the Atlantic Ocean are indistinguishable from natural internal variability. Simulations from both models consistently underestimate the amplitude of historical [O2] changes in response to external forcing, suggesting that model projections for future ocean deoxygenation may also be underestimated.

Resilience of marine turtle regional management units to climate change

Enhancing species resilience to changing environmental conditions is often suggested as a climate change adaptation strategy. To effectively achieve this, it is necessary first to understand the factors that determine species resilience, and their relative importance in shaping the ability of species to adjust to the complexities of environmental change. This is an extremely challenging task because it requires comprehensive information on species traits. We explored the resilience of 58 marine turtle regional management units (RMUs) to climate change, encompassing all seven species of marine turtles worldwide. We used expert opinion from the IUCN-SSC Marine Turtle Specialist Group (n=33 respondents) to develop a Resilience Index, which considered qualitative characteristics of each RMU (relative population size, rookery vulnerability, and genetic diversity) and non climate-related threats (fisheries, take, coastal development, and pollution/pathogens). Our expert panel perceived rookery vulnerability (the likelihood of functional rookeries becoming extirpated) and non climate-related threats as having the greatest influence on resilience of RMUs to climate change. We identified the world's 13 least resilient marine turtle RMUs to climate change, which are distributed within all three major ocean basins and include six of the world's seven species of marine turtle. Our study provides the first look at inter- and intra-species variation in resilience to climate change and highlights the need to devise metrics that measure resilience directly. We suggest that this approach can be widely used to help prioritize future actions that increase species resilience to climate change.