Atlantic Side Research Articles

Strong large-scale climate response to North American sulphate aerosols in CESM

The effects of increased North American sulphate aerosol emissions on the climate of Mexico and the United States (U.S.) during 1950–1975 are investigated by using two sets of transient coupled experiments with the Community Earth System Model, one with historically evolving emissions, and a second one where North American SO2 emissions are kept at their pre-industrial levels. The 1950–1975 increase in North American sulphate aerosols is found to have regional and remote impact. Over central U.S. and northern Mexico, the strengthening and westward expansion of the North Atlantic Subtropical High and subsequent intensification of the low-level easterlies, along with local aerosol interactions with radiation and clouds, cause a cooling trend and enhance precipitation. The interaction between the enhanced moisture transport across the Gulf of Mexico and the elevated topography of central Mexico favours positive rainfall on the Atlantic side while suppressing it on the Pacific side. These continental anomalies are embedded in a hemispheric-wide upper-tropospheric teleconnection pattern over the mid-latitudes, extending from the Pacific to the Atlantic basin. Details of the underlying mechanisms—in particular the prominent role of dynamical adjustments—are provided. With SO2 emissions considerably reduced in the U.S., and the expectation of a continued global decline throughout the 21st century, this study sheds light upon possible ongoing and future regional climate responses to changes in anthropogenic forcing.

Valuation of coastal ecosystem services in the Large Marine Ecosystems of Africa

The African coastline is bordered by highly valuable marine ecosystems, but the environmental degradation due to anthropogenic pressure alter the benefits that they render to people. Our paper aims at assessing the value of ecosystem services provided by mangroves, seagrass beds, coral reefs, and kelp forests present in the Large Marine Ecosystems (LMEs) of Africa. After the mapping of coastal marine habitats, our valuation relies on the transfer of value of all ecosystem services from reference monetary unit values, extracted from the literature. A habitat functionality index based on the assumption that a higher population density and a higher demographic growth rate lead to a decrease in the functionality and services of marine habitats was then defined and incorporated into the valuation. The surveyed coastal habitats cover about 117,000 km2, with seagrass beds being by far the most extensive habitat. Present all along the coasts of Africa, their surface area represents about 62% of surveyed coastal habitats, followed by the mangroves (23%), coral reefs (15%). Kelp forests are only present in the southern Benguela Current LME. We estimated the annual value of the LME's coastal ecosystem services at 814 billion USD. Coral reefs have the highest value (588 billion USD/year), followed by seagrass beds (135 billion USD/year), mangroves (91 billion USD/year), and kelp forests (0.4 billion USD/year). The results show that ecosystem services from the four coastal habitat types had the highest value in the Agulhas Current LME, representing 38% of the total value, followed by the Red Sea LME (28%) and the Somali Coastal Current LME (10%). The three LMEs of the Atlantic side represent 15% of the total estimated value. Our paper highlighted many gaps that remain to be filled in terms of mapping and ecosystem services assessment in Africa. Nonetheless, our estimated values can facilitate dialogue between decision-makers and managers, and between countries sharing the same habitats and marine resources, toward better management of these ecosystems.

Rice-pasture agroecosystem intensification affects energy use efficiency

Sustainable rice production systems are key to food security. Diversified farming systems are essential for ecological intensification and environmental enhancement. Energy use efficiency is one of the main sustainability indicators in agroecosystems. Thus, an assessment of consumption and efficiency of energy in contrasting cropping systems can discriminate their management practices and components sustainability. The goal of this study was to evaluate the energy performance through energy return on investment (EROI) in four rice-based rotation systems that belong to a long-term experiment located in the Temperate Grassland Terrestrial Ecoregion, at the Atlantic side of South America. Rotations analyzed consisted in: a) continuous rice (Rc); b) rice-soybean (R−S); c) rice-pasture for 1.5 years (R−PS); and, d) rice-pasture for 3.5 years (R−PL). The EROI estimations considered all the inputs and outputs of energy from cradle to farm gate. The greatest EROI was observed in R–S (7.2 MJMJ−1) and the lowest energy consumption in R−PL (10,607 MJ(hayr)−1). The R−PL’s EROI (6.7 MJMJ−1) was 6.5% and 8% higher than Rc and R−PS EROI, respectively. Rotations without pastures produced 79% more energy compared with rotations including pastures. However, energy inputs of rice-pasture rotations were 40% lower than either R−S or Rc. The EROI (without animal production) of R−PS, R–S and Rc was 25%, 28% and 43% lower than the EROI of R−PL (10 MJMJ−1), respectively. For the analyzed South American ecoregion, EROI assessments of four business as usual rice production systems allowed to discriminate and hierarchize their sustainability and diversity.

Fine-scale observations of physical and biological environment along a herring feeding migration route

We observed herring horizontal and vertical distribution during feeding migration along a 128 km transect across the Arctic front of the Norwegian and Iceland seas, in early June, in relation to its physical, chemical and biological environment, distribution of prey organisms and pelagic and mesopelagic competitors. The Norwegian Spring Spawning herring is one of the largest and economically most important stocks of pelagic fish in the world and understanding what controls its feeding migration is, and has been for centuries, a major research question that also has major implications for management. High resolution ecosystem data were obtained by hull mounted multi-frequency acoustics and a towed platform undulating between 10 and 400 m equipped with multi-frequency acoustics, temperature, salinity and fluorescence sensors, an Optical Plankton Counter and a Video Plankton Recorder. Additional sampling was done by MOCNESS, Macroplankton trawl, and CTD equipped with water bottles for temperature, salinity, nutrients and chlorophyll at discrete stations along the transect. Biological characteristics and stomach content of the herring were obtained from samples at discrete trawl stations. The Arctic front proved to be an important transitional zone in zooplankton biomass, abundance and diversity. Phenology of phyto- and zooplankton also changed across the front, being somewhat delayed on the cold side. The herring were distributed all along the transect showing a shallow distribution on the warm side and both deep and shallow on the cold side, not clearly related to light and time of the day. The herring stomach content was higher on the cold side. There was no significant pattern in average age, weight, or body length of the herring along the transect. The herring were present and fed in the area of the transect during the time when the overwintering generation of Calanus finmarchicus dominated, before the development of the new generation of the year. We suggest that the phenology of C. finmarchicus can be an important driver of the herring feeding migration. While prey-availability was higher on the Arctic side of the front, light conditions for visual feeding at depth were probably better on the Atlantic side. The herring did not show classical dial vertical migration, but its prey did, and the herring's prey were probably available within the upper 100 m during the course of a 24 h cycle. With a general westward direction of migration, the herring along the transect moved towards lower temperatures and temperature did not seem to be a probable driver for migration. We conclude that fine-scale studies of herring migration and feeding can increase our understanding of the migratory processes and add to our understanding of large-scale distributional patterns, changes therein, and herring trophodynamics and ecological role. The fine-resolution parameters can also be important as input to ecosystem models.

Export of bathyal benthos to the Atlantic through the Mediterranean outflow: Sponges from the mud volcanoes of the Gulf of Cadiz as a case study

The Mediterranean is a semi-enclosed sea, with a narrow natural connection —the Strait of Gibraltar— through its western basin to the North Atlantic. Many studies have investigated how the inflow of North Atlantic Surface water into the Mediterranean shapes the faunal composition and abundance of the shallow-water benthic communities of the Western Mediterranean. However, the reverse effect remains little explored, that is, at what level the relatively deep (>200 m deep) outflow of Mediterranean water (MOW) exports bathyal Mediterranean benthos into the North Atlantic and what is the fate of the exported fauna. In this study, we have investigated that process, using the bathyal sponge fauna known from a total of 9 biogeographical areas in the Northeastern Atlantic and 9 in the Western and Central Mediterranean, which accounted for a total of 456 spp. Prior to this general analysis, an exhaustive description of the bathyal sponge fauna (82 spp.) associated to 8 mud volcanoes located in the Gulf of Cadiz (Eastern North Atlantic) was conducted. This was necessary because the bathyal sponge fauna in the North Atlantic zone adjacent to the Strait of Gibraltar remained relatively poorly studied and that situation hindered relevant comparisons with the much better known bathyal fauna of the Western Mediterranean. The results of the clustering, ordination and regression analyses first revealed that the bathyal sponge fauna described from the mud volcanoes field in the Gulf of Cadiz was not essentially different from that previously described in pre-existing studies of other bathyal environments in the Gulf of Cadiz. The large scale subsequent assessment across the Atlantic-Mediterranean biogeographical gradient revealed that the sponge faunas of all Western Mediterranean areas form a relative cohesive group, except for the idiosyncratic nature of the Tyrrhenian Sea. More importantly, the deep-sea sponge fauna of the Gulf of Cadiz (in the easternmost Atlantic side of the Atlantic-Mediterranean gradient) showed more affinity with the fauna of the Western Mediterranean than with the fauna of the remaining Northeastern Atlantic areas considered in the study (i.e., Cape Verde, Canary Islands, Madeira, the Moroccan slope, Lusitanian Banks, Southern Azores Banks and Azores). The Mediterranean area with the highest faunal similarity to the Gulf of Cadiz was the Alboran Sea, followed by the Gulf of Lion, the Strait of Sicily and, the Gulf of Taranto, sharing collectively about 17% of their species. These patterns of faunal affinities clearly illustrate the importance of the MOW in transporting components of the Mediterranean deep-sea sponge communities towards the bathyal communities of the Gulf of Cadiz. The contrasting low faunal affinity between the deep-water sponge fauna of the Gulf of Cadiz and the remaining North Atlantic areas considered in the analyses also revealed that the Mediterranean faunal export is largely circumscribed to the Gulf of Cadiz. It is likely that the North-Atlantic trajectory of the MOW, turning north after the Strait of Gibraltar and staying attached to the slope of the Iberian margin, hinders subsequent colonization of the slopes of the Macaronesia region by the deep-water Mediterranean sponges exported to the Gulf of Cadiz. The results of this study, combined with previous literature on biogeographical sponge transport by marine currents, suggest that the sponge fauna provides a useful tool to reveal the future shifts in the biogeographic patterns predicted in our man-impacted and changing ocean.

A multidisciplinary overview of the lower Miño River terrace system (NW Iberian Peninsula)

The Miño River basin represents one of the main fluvial catchments draining the Atlantic side of the Iberian Peninsula. The extensive sedimentary deposits of this basin have been documented since the 19th century, but limited research has been undertaken on these features historically, and the Quaternary record of the basin has remained understudied until recently. Research carried out over the last decade on the Spanish margin of the Miño River has enabled more detailed classification and mapping of the main fluvial landforms, as well as numerical (luminescence, electron spin resonance, cosmogenic) dating of some of the deposits associated with Palaeolithic archaeological sites. Here we synthesise the existing Quaternary fluvial record for the basin, and present new geospatial and chronological analyses for the lower catchment area. Our latest examination has enabled the identification of nine fluvial terrace levels and other regionally significant sedimentary features (e.g., alluvial fans) formed in response to tectonics, eustatic changes and associated global climate changes. The chronological data and calculated incision rates indicate that the various fluvial terraces were formed during the Early to Late Pleistocene. Numerous Palaeolithic sites have been found in association with the middle terrace levels (between +40 and +13 m above present-day river level). Primarily, these archaeological sites preserve assemblages that feature large flake Acheulean (LFA) tools, though a number of Middle Palaeolithic sites have also been documented. Direct dating of these sites, together with morphostratigraphic correlations across the terrace system, suggest that the basin has been extensively occupied by human populations during the last 300 thousand years.

Paleoenvironmental implications of the first fossil record of Cyrtograpsus angulatus (Decapoda: Brachyura: Varunidae) from the mid-holocene of Argentina (northeastern Buenos Aires)

The estuarine crab Cyrtograpsus angulatus is an important burrower found in intertidal muddy and rocky shores along the modern coasts of northern Patagonia to southern Brazil on the Atlantic side and from Chile to Perú on the Pacific side. This species is commonly associated with populations of the crab Neohelice granulata in modern sites, with variable impacts of their interactions in the environment. When they become agonistic, the latter species always wins the battle for space and burrows. The previous fossil record of crabs from the mid-Holocene of Buenos Aires was restricted to Neohelice granulata, with no mention of any fossil exoskeletal elements of C. angulatus along its distribution. Herein i describe the first unambiguous fossils of C. angulatus, comprising six almost complete to isolated specimens from the mid-Holocene of Buenos Aires, Pereyra Iraola Park, taphonomic and paleoenvironmental implications of the bispecific assemblage are discussed.

The recent colonization history of the most widespread Podocarpus tree species in Afromontane forests.

Afromontane forests host a unique biodiversity distributed in isolated high-elevation habitats within a matrix of rain forests or savannahs, yet they share a remarkable flora that raises questions about past connectivity between currently isolated forests. Here, we focused on the Podocarpus latifolius-P. milanjianus complex (Podocarpaceae), the most widely distributed conifers throughout sub-Saharan African highlands, to infer its demographic history from genetic data. We sequenced the whole plastid genome, mitochondrial DNA regions and nuclear ribosomal DNA of 88 samples from Cameroon to Angola in western Central Africa and from Kenya to the Cape region in eastern and southern Africa to reconstruct time-calibrated phylogenies and perform demographic inferences. We show that P. latifolius and P. milanjianus form a single species, whose lineages diverged during the Pleistocene, mostly between approx, 200 000 and 300 000 years BP, after which they underwent a wide range expansion leading to their current distributions. Confronting phylogenomic and palaeoecological data, we argue that the species originated in East Africa and reached the highlands of the Atlantic side of Africa through two probable latitudinal migration corridors: a northern one towards the Cameroon volcanic line, and a southern one towards Angola. Although the species is now rare in large parts of its range, no demographic decline was detected, probably because it occurred too recently to have left a genetic signature in our DNA sequences. Despite the ancient and highly fluctuating history of podocarps in Africa revealed by palaeobotanical records, the extended distribution of current P. latifolius/milanjianus lineages is shown to result from a more recent history, mostly during the mid-late Pleistocene, when Afromontane forests were once far more widespread and continuous.

A modelling study of the ice-free tidal dynamics in the Canadian Arctic Archipelago

The dynamics of M2 and K1 ocean tides in the Canadian Arctic Archipelago (CAA) have been investigated using a three-dimensional hydrodynamic model, which uses an unstructured mesh with a horizontal resolution ranging from 0.5 km in narrow channels to 10–40 km in the open ocean. The model is evaluated against observed tidal elevations and tidal currents, and the evaluation indicates that the model is able to reproduce the observations at the tidal gauge sites, particularly those in the narrow straits of the CAA. In order to examine the interactions between the Arctic and the Atlantic tides in the CAA, idealized experiments were conducted by considering tidal effects through the open boundary on the Arctic and the Atlantic sides separately. The results show that the Atlantic tide is strong throughout the CAA but deceases rapidly when it encounters the open Arctic shelf for both M2 and K1 tides; on the other hand, the Arctic tide is mainly confined to the Arctic Ocean and Amundsen Gulf; it has a minor influence in the Baffin Bay. Nonlinear interactions between the Arctic and Atlantic tides are generally weak except local areas in the southern and northern CAA, where the nonlinear contribution is able to reach 10–20% of the tidal variability. Using the model results, the tidal energy flux was also analyzed, and the analysis indicated that the Lancaster Sound and Jones Sound are main pathways of the tidal energy from the Baffin Bay to the CAA, and the energy is dissipated due mainly to the vertical diffusion and the bottom friction.

Hydrological Characteristics and Paradoxes of Mediterranean High-Mountain Water-Bodies of the Sierra-Nevada, SE Spain

Each lake complex must be understood before attempting any regional synthesis leading us to view these water-bodies as indicators of regional climate change. Therefore, in order to improve knowledge of these Mediterranean biotopes, we examined the dependence of the fringes of hygrophilous communities surrounding the water-bodies (green fringes) on their hydrological and geomorphological features. The climate of the western sector of this massif is cryo–oromediterranean, where thawing produces 53 hm3 of run-off and 11 hm3 of sub-surface flow. Part of this water is stored in 123 water-bodies located from 2480 to 3200 m a.s.l., 72 of which (58%) are located on the south-facing Mediterranean watershed. The total surface of the water sheet is approximately 170,000 m2, and volume is approximately 215,000 m3, of which 140,000 m3 (65%) are stored in the south-facing water-bodies. Green fringes surrounding 84 water-bodies have a total surface area of approximately 186,000 m2. Surprisingly, the more xeric Mediterranean watershed holds 58 such fringes (149,000 m2, 80%) while 26 are found on the Atlantic watershed (38,000 m2, 20%). Green fringes are mainly associated with small water-bodies (<5000 m3), which occupy 148,000 m2 on the Mediterranean watershed, while on the Atlantic side, green fringes occupy 31,000 m2. Sierra Nevada also has 46 times higher water-efficiency in the smaller water-bodies than in the large ones; 16.4 and 335.8 times higher on the Atlantic and Mediterranean watersheds, respectively. The differences in gradient of the massif hillsides must largely explain this uneven behaviour.

Temperature and Salinity Variability in the SODA3, ECCO4r3, and ORAS5 Ocean Reanalyses, 1993–2015

Abstract This study extends recent ocean reanalysis comparisons to explore improvements to several next-generation products, the Simple Ocean Data Assimilation, version 3 (SODA3); the Estimating the Circulation and Climate of the Ocean, version 4, release 3 (ECCO4r3); and the Ocean Reanalysis System 5 (ORAS5), during their 23-yr period of overlap (1993–2015). The three reanalyses share similar historical hydrographic data, but the forcings, forward models, estimation algorithms, and bias correction methods are different. The study begins by comparing the reanalyses to independent analyses of historical SST, heat, and salt content, as well as examining the analysis-minus-observation misfits. While the misfits are generally small, they still reveal some systematic biases that are not present in the reference Hadley Center EN4 objective analysis. We next explore global trends in temperature averaged into three depth intervals: 0–300, 300–1000, and 1000–2000 m. We find considerable similarity in the spatial structure of the trends and their distribution among different ocean basins; however, the trends in global averages do differ by 30%–40%, which implies an equivalent level of disagreement in net surface heating rates. ECCO4r3 is distinct in having quite weak warming trends while ORAS5 has stronger trends that are noticeable in the deeper layers. To examine the performance of the reanalyses in the Arctic we explore representation of Atlantic Water variability on the Atlantic side of the Arctic and upper-halocline freshwater storage on the Pacific side of the Arctic. These comparisons are encouraging for the application of ocean reanalyses to track ocean climate variability and change at high northern latitudes.

An assessment of regional sea ice predictability in the Arctic ocean

Arctic sea ice plays a central role in the Earth’s climate. Changes in the sea ice on seasonal-to-interannual timescales impact ecosystems, populations and a growing number of stakeholders. A prerequisite for achieving better sea ice predictions is a better understanding of the underlying mechanisms of sea ice predictability. Previous studies have shown that sea ice predictability depends on the predictand (area, extent, volume), region, and the initial and target dates. Here we investigate seasonal-to-interannual sea ice predictability in so-called “perfect-model” 3-year-long experiments run with six global climate models initialized in early July. Consistent with previous studies, robust mechanisms for reemergence are highlighted, i.e. increases in the autocorrelation of sea ice properties after an initial loss. Similar winter sea ice extent reemergence is found for HadGEM1.2, GFDL-CM3 and E6F, while a long sea ice volume persistence is confirmed for all models. The comparable predictability characteristics shown by some of the peripheral regions of the Atlantic side illustrate that robust similarities can be found even if models have distinct sea ice states. The analysis of the regional sea ice predictability in EC-Earth2.3 demonstrates that Arctic basins can be classified according to three distinct regimes. The central Arctic drives most of the pan-Arctic sea ice volume persistence. In peripheral seas, we find predictability for the sea ice area in winter but low predictability throughout the rest of the year, due to the particularly unpredictable sea ice edge location. The Labrador Sea stands out among the considered regions, with sea ice predictability extending up to 1.5 years if the oceanic conditions upstream are known.

A close relative of the Amazon river dolphin in marine deposits: a new Iniidae from the late Miocene of Angola.

BackgroundA few odontocetes (echolocating toothed cetaceans) have been able to independently colonize freshwater ecosystems. Although some extant species of delphinids (true dolphins) and phocoenids (porpoises) at least occasionally migrate upstream of large river systems, they have close relatives in fully marine regions. This contrasts with the three odontocete families only containing extant species with a strictly freshwater habitat (Iniidae in South America, the recently extinct Lipotidae in China, and Platanistidae in southeast Asia). Among those, the fossil record of Iniidae includes taxa from freshwater deposits of South America, partly overlapping geographically with the extant Amazon river dolphin Inia geoffrensis, whereas a few marine species from the Americas were only tentatively referred to the family, leaving the transition from a marine to freshwater environment poorly understood.MethodsBased on a partial odontocete skeleton including the cranium, discovered in late Miocene (Tortonian-Messinian) marine deposits near the estuary of the Cuanza River, Angola, we describe a new large iniid genus and species. The new taxon is compared to other extinct and extant iniids, and its phylogenetic relationships with the latter are investigated through cladistic analysis.Results and DiscussionThe new genus and species Kwanzacetus khoisani shares a series of morphological features with Inia geoffrensis, including the combination of a frontal boss with nasals being lower on the anterior wall of the vertex, the laterally directed postorbital process of the frontal, the anteroposterior thickening of the nuchal crest, and robust teeth with wrinkled enamel. As confirmed (although with a low support) with the phylogenetic analysis, this makes the new taxon the closest relative of I. geoffrensis found in marine deposits. The geographic provenance of K. khoisani, on the eastern coast of South Atlantic, suggests that the transition from the marine environment to a freshwater, Amazonian habitat may have occurred on the Atlantic side of South America. This new record further increases the inioid diversity during the late Miocene, a time interval confirmed here as the heyday for this superfamily. Finally, this first description of a Neogene cetacean from inland deposits of western sub-Saharan Africa reveals the potential of this large coastal area for deciphering key steps of the evolutionary history of modern cetaceans in the South Atlantic.

АЭРОЗОЛЬ, АТМОСФЕРНАЯ ВИХРЕВАЯ АКТИВНОСТЬ И ТУРБУЛЕНТНОСТЬ

The interaction between the cyclone coming from the Atlantic side and the anticyclone above the center of the European part of Russia depends on the stability of the anticyclone. The blocking of anticyclones is observed mainly in the summer. Blocking anticyclones are formed over Siberia too. It is shown that the vortex activity of the atmosphere, jet flows and turbulence in it are associated with inhomogeneous cellular distributions of atmospheric pollution. Part of the energy of powerful atmospheric vortex structures, such as tornadoes, cyclones and anticyclones, is generated by aerosol plasma vortices.

Ontogenetic patterns in resource use dynamics of bonefish (Albula vulpes) in the Bahamas

We used stable isotope analysis to examine ontogenetic patterns in the resource use dynamics of bonefish (Albula vulpes) collected from two locations (Banks and Atlantic) within the coastal waters of Eleuthera, The Bahamas. A marked shift in δ13C signatures between leptocephali and juveniles reflected a rapid change in resource use, likely from pelagic to alternate neritic sources of primary production. Ontogenetic shifts in habitat use were observed across bonefish from both sides of Eleuthera, but direction of the isotopic shifts varied. Bonefish from the Atlantic side demonstrated an enrichment in 13C with size, whereas the opposite pattern was observed for individuals captured from the Banks. Differences are likely to be explained by the variability of primary production sources, which dominate each side of the island (i.e., more reliance on seagrass with ontogeny on the Atlantic side, versus a shift to macroalgal-dominated foodwebs with growth on the Banks side). Enrichment in 15N with body size was observed for both locations and reflects the ability to utilize a broader range of prey items with increasing gape size. Trophic diversity (inferred through nitrogen range), however, was lower on the Banks side, suggesting that reduced prey diversity may limit the increase in dietary shifts that gape size increases typically allow. A significant positive relationship between δ13C and whole-body energy density (MJ kg-1) in adults on the Banks side was observed. Adult bonefish that forage in seagrasses likely benefit from higher energy densities from selected prey items, and may explain this result. Data from this study reinforces the importance of a diversity of habitats in supporting bonefish throughout ontogeny.

Decadal variability in the Northern Hemisphere winter circulation: Effects of different solar and terrestrial drivers

Northern Hemisphere winter circulation is affected by both solar and terrestrial forcings. El-Niño events and volcanic eruptions have been shown to produce a negative and a positive North Atlantic Oscillation (NAO) signature, respectively. Recent studies show a positive NAO signature related to both geomagnetic activity (proxy for solar wind driven particle precipitation) and sunspot activity (proxy for solar irradiance). Here the relative role of these four different drivers on the Northern Hemisphere wintertime circulation is studied using a statistical analysis of observational and reanalysis data during 1868–2014. The phase of the Quasi-Biennial Oscillation (QBO) is used to study driver signals in different stratospheric conditions. Moreover, the effects are separated for early/mid- and late winter. Our findings suggest a stratospheric mediation of the ENSO signal to the Atlantic side, which is delayed and modulated by the QBO unlike the signal in the Pacific side. The positive NAO by volcanic activity is preferentially obtained in the westerly QBO. We also find a substantial QBO modulation for geomagnetic activity and late winter sunspot activity, which favours a stratospheric pathway and the top-down mechanisms. However, signal in the North Pacific produced by early/mid-winter sunspot activity remain rather similar in different QBO phases and supports a direct forcing from the troposphere by the bottom-up sunspot mechanism.

Origin and implications of orbital-induced sedimentary cyclicity in Pliocene well-logs of the Western Mediterranean

The climatic origin of astronomically induced sedimentary cycles in the Mediterranean and adjacent areas during the late Neogene and Quaternary remains puzzling; as cycles have been linked to concomitant but seasonally opposite changes in African summer monsoon precipitation (Eastern Mediterranean sapropels) and Atlantic regulated winter-precipitation (carbonate cycles on the Atlantic side of the Mediterranean). Particularly, little is known about the cyclic sedimentation on orbital time scales in the Western Mediterranean, with the prime exception of the Messinian sapropels from the Sorbas basin (southern Spain).Here we show that regular alternations in Pliocene downhole logs from the industrial drill-site Muchamiel-1, located along the Balearic Promontory in the Western Mediterranean, are related to eccentricity (bundles) and to obliquity and precession cycles (basic meter-scale alternations). We establish an astronomically based age model for the interval between 5.33 and 2.8 Ma, by first correlating cycle bundles to eccentricity and then the basic dominantly precession-related cycles to the 65°N summer insolation of La2004. The striking bed-to-bed similarities between the Muchamiel-1 well-logs and other records from both the Atlantic margin and the Central Mediterranean suggest that the same climatic forcing was responsible for the formation of carbonate cycles across the Western Mediterranean and adjacent Atlantic. We conclude that formation of alternating carbonate-rich/carbonate-poor beds was controlled by Western Mediterranean cyclogenetic mechanisms as well as by peri-Mediterranean precipitation associated with changes in the North Atlantic System (NAS). These findings highlight the importance of peri-Mediterranean precipitation on the sedimentary cyclicity by dictating terrigenous (clay) supply and potentially on the hydrology of the basin by providing additional freshwater required for sapropel formation. Consequently, cyclic sedimentation in the Mediterranean results from the combined effect of precipitation changes driven by (i) the North African monsoon, (ii) the Atlantic system, and (iii) intrabasinal Mediterranean atmospheric dynamics.

Impacts of extratropical storm tracks on Arctic sea ice export through Fram Strait

Studies have indicated regime shifts in atmospheric circulation, and associated changes in extratropical storm tracks and Arctic storm activity, in particular on the North Atlantic side of the Arctic Ocean. To improve understanding of changes in Arctic sea ice mass balance, we examined the impacts of the changed storm tracks and cyclone activity on Arctic sea ice export through Fram Strait by using a high resolution global ocean–sea ice model, MITgcm–ECCO2. The model was forced by the Japanese 25-year Reanalysis (JRA-25) dataset. The results show that storm-induced strong northerly wind stress can cause simultaneous response of daily sea ice export and, in turn, exert cumulative effects on interannual variability and long-term changes of sea ice export. Further analysis indicates that storm impact on sea ice export is spatially dependent. The storms occurring southeast of Fram Strait exhibit the largest impacts. The weakened intensity of winter (in this study winter is defined as October–March and summer as April–September) storms in this region after 1994/95 could be responsible for the decrease of total winter sea ice export during the same time period.

Comparison of Mechanisms for Low-Frequency Variability of Summer Arctic Sea Ice in Three Coupled Models

Abstract In this study the mechanisms for low-frequency variability of summer Arctic sea ice are analyzed using long control simulations from three coupled models (GFDL CM2.1, GFDL CM3, and NCAR CESM). Despite different Arctic sea ice mean states, there are many robust features in the response of low-frequency summer Arctic sea ice variability to the three key predictors (Atlantic and Pacific oceanic heat transport into the Arctic and the Arctic dipole) across all three models. In all three models, an enhanced Atlantic (Pacific) heat transport into the Arctic induces summer Arctic sea ice decline and surface warming, especially over the Atlantic (Pacific) sector of the Arctic. A positive phase of the Arctic dipole induces summer Arctic sea ice decline and surface warming on the Pacific side, and opposite changes on the Atlantic side. There is robust Bjerknes compensation at low frequency, so the northward atmospheric heat transport provides a negative feedback to summer Arctic sea ice variations. The influence of the Arctic dipole on summer Arctic sea ice extent is more (less) effective in simulations with less (excessive) climatological summer sea ice in the Atlantic sector. The response of Arctic sea ice thickness to the three key predictors is stronger in models that have thicker climatological Arctic sea ice.

Non-indigenous species (NIS) of polychaetes (Annelida: Polychaeta) from the Atlantic and Mediterranean coasts of the Iberian Peninsula: an annotated checklist

This study provides an updated catalogue of non-indigenous species (NIS) of polychaetes reported from the continental coasts of the Iberian Peninsula based on the available literature. A list of 23 introduced species were regarded as established and other 11 were reported as casual, with 11 established and nine casual NIS in the Atlantic coast of the studied area and 14 established species and seven casual ones in the Mediterranean side. The most frequent way of transport was shipping (ballast water or hull fouling), which according to literature likely accounted for the introductions of 14 established species and for the presence of another casual one. To a much lesser extent aquaculture (three established and two casual species) and bait importation (one established species) were also recorded, but for a large number of species the translocation pathway was unknown. About 25% of the reported NIS originated in the Warm Western Atlantic region, followed by the Tropical Indo West-Pacific region (18%) and the Warm Eastern Atlantic (12%). In the Mediterranean coast of the Iberian Peninsula, nearly all the reported NIS originated from warm or tropical regions, but less than half of the species recorded from the Atlantic side were native of these areas. The effects of these introductions in native marine fauna are largely unknown, except for one species (Ficopomatus enigmaticus) which was reported to cause serious environmental impacts. In other cases, the displacement of native species or economic damages are suspected.