North-south Migrations Research Articles

Abandoning the Revolution or Weaving Peace? South-South Migration, Socialism, and Decolonial Feminist Geopolitics in South America

ABSTRACT This article presents a decolonial feminist geopolitics of Venezuelan migration to Colombia, with Venezuelans fleeing the socialist Bolivarian Revolution and then facing discrimination and violence upon settling in capitalist Colombia amid its failing peace process context. Conflicts over migration and nationality permeate our global order of sovereign nation-states, both in north-south migrations and across the global south, while the feminisation and racialisation of migrants divides the subaltern class and facilitates capitalist exploitation. However, this paper elucidates migrants’ inter-national solidarities and grassroots peace struggles. Community organisers along the Colombia-Venezuela border – the women’s empowerment organisation Tejedores de Paz and youth leadership foundation Horizonte de Juventud – unite impoverished internally-displaced Colombians and Venezuelan immigrants to create resistance territories against xenophobia, patriarchy, and poverty. Illustrating the utility of the methodology of decolonial feminist geopolitics, I trace the reconfiguration of the spirit of sociopolitical revolution in South America through migrants’ emergent form of feminist non-state socialism.

Diatom-based reconstruction of the Subantarctic Front migrations during the late Miocene and Pliocene

Abstract The Antarctic Circumpolar Current (ACC) is an influential component of the global climate system, and therefore it is essential to clarify the history of the oceanic fronts associated with it. However, there have been only a few attempts to reconstruct their history during the Neogene, as most previous studies focused on Quaternary ages. This study uses the late Miocene to Pliocene (ca. 9–3 Ma) fossil records of diatoms from the Atlantic sector of the Southern Ocean (Deep Sea Drilling Project Site 513 and Ocean Drilling Program Site 689) to reconstruct the paleo-location of the Subantarctic Front (SAF), which represents the northern limit of the ACC. The abundance of subtropical diatoms at Site 513 shows significant fluctuations during ca. 9–5 Ma, which strongly suggest that there have been repetitive north-south migrations of the SAF across Site 513 during at least ca. 9–5 Ma. In order to reconstruct the SAF migration history in more detail, changes in abundance of a typical subtropical diatom (i.e., Thalassionema nitzschioides var. parva Heiden emend. Moreno-Ruiz) recorded at Sites 513 and 689 are compared to abundance patterns of the same taxon at several drilling sites (Ocean Drilling Program Sites 697, 699, and 704) published in previous data reports. Results suggest several phases of SAF migration involving the following shifts in SAF position (direction of shift is indicated in brackets): ca. 8.5 Ma (northward), 8.0 Ma (northward), 7.0 Ma (southward), 6.1 Ma (northward), 5.4 Ma (the direction differs region by region), 4.9 Ma (northward), 4.6 Ma (southward), 3.8 Ma (northward). The results also show that SAF has experienced north-south migrations with a latitudinal amplitude of ca. 5° or more. Comparison between changes in fossil diatom assemblages at Site 689 and the inferred SAF shifts suggest that the northward/southward shift of the SAF could be induced by the cooling/warming in the high-latitude regions.

4 Migration research and analysis: Growth, reach and recent contributions

4 Migration research and analysis: Growth, reach and recent contributions

A Strong Role for the AMOC in Partitioning Global Energy Transport and Shifting ITCZ Position in Response to Latitudinally Discrete Solar Forcing in CESM1.2

Abstract Ocean circulation responses to interhemispheric radiative imbalance can damp north–south migrations of the intertropical convergence zone (ITCZ) by reducing the burden on atmospheric energy transport. The role of the Atlantic meridional overturning circulation (AMOC) in such dynamics has not received much attention. Here, we present coupled climate modeling results that suggest AMOC responses are of first-order importance to muting ITCZ shift magnitudes as a pair of hemispherically asymmetric solar forcing bands is moved from equatorial to polar latitudes. The cross-equatorial energy transport response to the same amount of interhemispheric forcing becomes systematically more ocean-centric when higher latitudes are perturbed in association with strengthening AMOC responses. In contrast, the responses of the Pacific subtropical cell are not monotonic and cannot predict this variance in the ITCZ’s equilibrium position. Overall, these results highlight the importance of the meridional distribution of interhemispheric radiative imbalance and the rich buffering of internal feedbacks that occurs in dynamic versus thermodynamic (slab) ocean modeling experiments. Mostly, the results imply that the problem of developing a theory of ITCZ migration is entangled with that of understanding the AMOC’s response to hemispherically asymmetric radiative forcing—a difficult topic deserving of focused analysis across more climate models.

Detected trematodes inside blue-winged teals (Spatula discors) give insights on north-south flow of parasites through Cuba during migration.

The Blue-winged Teal (Spatula discors) is known for engaging in long-distance North-South migrations and back in the Americas with Cuba being an important wintering ground. Teals serve as hosts for a wide range of parasite species that can be "discharged" at each end of the migration route. Here, we explore for the first time the diversity of trematodes that the Blue-winged Teal may be introducing to -or exporting from- Cuba. We found 15 digenean parasites in 65 sampled teals of which 13 represent first reports for Cuba with one species (Echinostoma revolutum) of zoonotic importance. Overall prevalence was very high (96.92%) whereas Trichobilharzia spp. resulted the most ubiquitous parasite. Highest intensities were recorded for Australapatemon sp. (arriving teals) and Levinseniella amnicolae (departing teals). Altogether, departing teals harboured the highest number of trematode species and abundance. The short development and lifespan, inside migratory birds, of adult stages of trematodes like Trichobilharzia sp., Cotylurus flabelliformis and Microphallus pygmaeus strongly suggest that the occurrence of these trematodes in the departing teals could be related to their long establishment in Cuban ecosystems. In a global scenario where parasitology, particularly wildlife parasitology, is mostly overlooked, there should be an increasing need of gathering information and increasing surveillance of wildlife diseases that might eventually become important for the health of ecosystems and of domestic animals and humans. The present study constitutes the first major attempt to explore trematode infection from S. discors in Cuba under the view of parasite flow via bird migration.

A model for simulating the active dispersal of juvenile sea turtles with a case study on western Pacific leatherback turtles.

Oceanic currents are known to broadly shape the dispersal of juvenile sea turtles during their pelagic stage. Accordingly, simple passive drift models are widely used to investigate the distribution at sea of various juvenile sea turtle populations. However, evidence is growing that juveniles do not drift purely passively but also display some swimming activity likely directed towards favorable habitats. We therefore present here a novel Sea Turtle Active Movement Model (STAMM) in which juvenile sea turtles actively disperse under the combined effects of oceanic currents and habitat-driven movements. This model applies to all sea turtle species but is calibrated here for leatherback turtles (Dermochelys coriacea). It is first tested in a simulation of the active dispersal of juveniles originating from Jamursba-Medi, a main nesting beach of the western Pacific leatherback population. Dispersal into the North Pacific Ocean is specifically investigated. Simulation results demonstrate that, while oceanic currents broadly shape the dispersal area, modeled habitat-driven movements strongly structure the spatial and temporal distribution of juveniles within this area. In particular, these movements lead juveniles to gather in the North Pacific Transition Zone (NPTZ) and to undertake seasonal north-south migrations. More surprisingly, juveniles in the NPTZ are simulated to swim mostly towards west which considerably slows down their progression towards the American west coast. This increases their residence time, and hence the risk of interactions with fisheries, in the central and eastern part of the North Pacific basin. Simulated habitat-driven movements also strongly reduce the risk of cold-induced mortality. This risk appears to be larger among the juveniles that rapidly circulate into the Kuroshio than among those that first drift into the North Equatorial Counter Current (NECC). This mechanism might induce marked interannual variability in juvenile survival as the strength and position of the NECC are directly linked to El Niño activity.

North–South migrations and the asymmetric expulsions of late capitalism: Global inequality, arbitrage, and new dynamics of North–South transnationalism

North–South migrations and the asymmetric expulsions of late capitalism: Global inequality, arbitrage, and new dynamics of North–South transnationalism

A re-interpretation of impact of the Icelandic Low and Azores High on winter precipitation over Iberian Peninsula

Several studies show that North Atlantic Oscillation (NAO) has dominant influence on the variability of climate over Iberian Peninsula. The traditional definition of the NAO index is a very simple representation of the atmospheric state of negative correlation between the Azores High and the Icelandic Low. The NAO index does not take into account the geographically extensive nature of the high and the low pressure systems and their movements. Fluctuations in both the characteristic shapes and positions of the Azores High and the Icelandic Low influence atmospheric circulation over the north Atlantic region. We study interannual variations of winter rainfall over Iberia, taking into account variations in the Azores High and the Icelandic Low pressure systems. Analysis presented in this paper shows that the north–south migrations of the Azores High exert the greatest impact on winter precipitation over Iberian Peninsula. Using NCEP/NCAR reanalysis data, this approach allows us to understand the changes in atmospheric circulation through which latitudinal shifts of the Azores High influence regional precipitation over Iberia.

Early Holocenic and Historic mtDNA African Signatures in the Iberian Peninsula: The Andalusian Region as a Paradigm.

Determining the timing, identity and direction of migrations in the Mediterranean Basin, the role of “migratory routes” in and among regions of Africa, Europe and Asia, and the effects of sex-specific behaviors of population movements have important implications for our understanding of the present human genetic diversity. A crucial component of the Mediterranean world is its westernmost region. Clear features of transcontinental ancient contacts between North African and Iberian populations surrounding the maritime region of Gibraltar Strait have been identified from archeological data. The attempt to discern origin and dates of migration between close geographically related regions has been a challenge in the field of uniparental-based population genetics. Mitochondrial DNA (mtDNA) studies have been focused on surveying the H1, H3 and V lineages when trying to ascertain north-south migrations, and U6 and L in the opposite direction, assuming that those lineages are good proxies for the ancestry of each side of the Mediterranean. To this end, in the present work we have screened entire mtDNA sequences belonging to U6, M1 and L haplogroups in Andalusians—from Huelva and Granada provinces—and Moroccan Berbers. We present here pioneer data and interpretations on the role of NW Africa and the Iberian Peninsula regarding the time of origin, number of founders and expansion directions of these specific markers. The estimated entrance of the North African U6 lineages into Iberia at 10 ky correlates well with other L African clades, indicating that U6 and some L lineages moved together from Africa to Iberia in the Early Holocene. Still, founder analysis highlights that the high sharing of lineages between North Africa and Iberia results from a complex process continued through time, impairing simplistic interpretations. In particular, our work supports the existence of an ancient, frequently denied, bridge connecting the Maghreb and Andalusia.

The use of satellite tags to redefine movement patterns of spiny dogfish (Squalus acanthias) along the U.S. east coast: implications for fisheries management.

Spiny dogfish (Squalus acanthias) are assumed to be a highly migratory species, making habitual north-south migrations throughout their northwestern Atlantic United States (U.S.) range. Also assumed to be a benthic species, spiny dogfish stock structure is estimated through Northeast Fisheries Science Center (NEFSC) bottom-trawl surveys. Recent anomalies in population trends, including a recent four-fold increase in estimated spawning stock biomass, suggest alternative movement patterns could exist for this shark species. To obtain a better understanding of the horizontal and vertical movement dynamics of this species, Microwave Telemetry pop-up satellite archival X-Tags were attached to forty adult spiny dogfish at the northern (Gulf of Maine) and southern (North Carolina) extents of their core U.S. geographic range. Reconstructed geolocation tracks ranging in lengths from two to 12 months suggest that the seasonal migration patterns appear to be local in nature to each respective northern and southern deployment site, differing from previously published migration paradigms. Differences in distance and direction traveled between seasonal geolocations possibly indicate separate migratory patterns between groups. Kernel utilization distribution models also suggest strong separate core home ranges. Significant differences in seasonal temperature and depths between the two regions further substantiate the possibility of separate regional movement patterns between the two groups. Vertical utilization also suggests distinct diel patterns and that this species may not utilize the benthos as previously thought, potentially decreasing availability to benthic gear.

Corroboration and refinement of a method for differentiating landings from two stocks of Pacific sardine (Sardinops sagax) in the California Current

Abstract Demer, D. A., and Zwolinski, J. P. 2014. Corroboration and refinement of a method for differentiating landings from two stocks of Pacific sardine (Sardinops sagax) in the California Current. – ICES Journal of Marine Science, 71: 328–335. Efforts to survey, assess and manage Pacific sardine (Sardinops sagax) in the California Current may depend on accurate differentiation of the purported two migrating stocks. The southern stock spans seasonally from southern Baja California, México to Point Conception, California; the northern stock spans seasonally from Punta Eugenia, México northwards to southern Alaska. Their seasonal north–south migrations are approximately synchronous within their respective domains, resulting in segregated spawning and different identities. A decade ago, a practical method was proposed for differentiating landings from the two stocks using concomitant measurements of sea-surface temperature (SST). Here, we corroborate and refine the method using regional indices of optimal and good potential habitat for the northern stock, and SST-based indices associated with the 99.9 and 100% confidence intervals of the potential habitat. For months when the index is <0.5, (i.e. when the minority of a fishing region probably includes potential northern stock habitat), the landings are attributed to the southern stock, and vice versa. We applied this method to regional monthly landings data from 2006–2011 and the results indicated that an average of 63–72 and 32–36% of the summertime landings at Ensenada, México and San Pedro, southern California were probably from the southern stock, respectively, depending on the index used. Allocation error could be reduced if the landings were evaluated on finer spatio-temporal scales, particularly during habitat-transition periods. Our method may be used to improve estimates of northern stock biomass, spatial and length distributions, recruitment, and mortality.

Ecosystem-level consequences of movement: seasonal variation in the trophic impact of a top predator

Spatio-temporal patterns of species abundance influence the strength of trophic interactions, while movement of individuals helps determine those patterns of abundance. Thus, understanding movement is a basis for quantifying interactions within a food web. In Puget Sound, Washington, USA, the North Pacific spiny dogfish Squalus suckleyi is an abundant top predator with a diverse, generalist diet. Coastal dogfish populations make seasonal north-south migrations, but populations in inland waters are thought to be more resident. In this study, we combined acoustic telemetry and bioenergetics modeling to determine patterns of movement and to quantify seasonal variation in the predatory impact of dogfish in Puget Sound. All tagged dogfish migrated out of Puget Sound in the winter and were absent until the following summer. Individuals that returned to Puget Sound in subsequent years showed consistent timing and duration of residence across years, but these metrics varied across individuals. Incorporating movement data into the bioenergetics model resulted in a 70% decrease in the predatory impact of dogfish in the winter and a 30 % decrease in the summer, compared to a year-round resident Puget Sound population. Incorporating metrics of movement into food web or ecosystem models will increase our understanding of species interactions and will improve our ability to predict changes in food web dynamics under various environmental and management scenarios.

Tracking apex marine predator movements in a dynamic ocean

Pelagic marine predators face unprecedented challenges and uncertain futures. Overexploitation and climate variability impact the abundance and distribution of top predators in ocean ecosystems. Improved understanding of ecological patterns, evolutionary constraints and ecosystem function is critical for preventing extinctions, loss of biodiversity and disruption of ecosystem services. Recent advances in electronic tagging techniques have provided the capacity to observe the movements and long-distance migrations of animals in relation to ocean processes across a range of ecological scales. Tagging of Pacific Predators, a field programme of the Census of Marine Life, deployed 4,306 tags on 23 species in the North Pacific Ocean, resulting in a tracking data set of unprecedented scale and species diversity that covers 265,386 tracking days from 2000 to 2009. Here we report migration pathways, link ocean features to multispecies hotspots and illustrate niche partitioning within and among congener guilds. Our results indicate that the California Current large marine ecosystem and the North Pacific transition zone attract and retain a diverse assemblage of marine vertebrates. Within the California Current large marine ecosystem, several predator guilds seasonally undertake north-south migrations that may be driven by oceanic processes, species-specific thermal tolerances and shifts in prey distributions. We identify critical habitats across multinational boundaries and show that top predators exploit their environment in predictable ways, providing the foundation for spatial management of large marine ecosystems.

South China Sea hydrological changes and Pacific Walker Circulation variations over the last millennium

The relative importance of north–south migrations of the intertropical convergence zone (ITCZ) versus El Niño-Southern Oscillation and its associated Pacific Walker Circulation (PWC) variability for past hydrological change in the western tropical Pacific is unclear. Here we show that north–south ITCZ migration was not the only mechanism of tropical Pacific hydrologic variability during the last millennium, and that PWC variability profoundly influenced tropical Pacific hydrology. We present hydrological reconstructions from Cattle Pond, Dongdao Island of the South China Sea, where multi-decadal rainfall and downcore grain size variations are correlated to the Southern Oscillation Index during the instrumental era. Our downcore grain size reconstructions indicate that this site received less precipitation during relatively warm periods, AD 1000–1400 and AD 1850–2000, compared with the cool period (AD 1400–1850). Including our new reconstructions in a synthesis of tropical Pacific records results in a spatial pattern of hydrologic variability that implicates the PWC.

The genetic structure of Quercus crispula in northeastern Japan as revealed by nuclear simple sequence repeat loci

Previous studies have reached different discussions about the genetic variation and genetic structure of Quercus crispula populations in northeastern Japan. This is a common oak species in Eastern Asia. Some studies have suggested that the populations in northeastern Japan were derived from those remaining in the southwest after the last glacial maximum (LGM), whilst other studies have found evidence that populations persisted in northeastern Japan during the LGM. Using seven highly polymorphic nuclear simple sequence repeat loci, we investigated the genetic structure of 16 Q. crispula populations along a latitudinal gradient in northeastern Japan (northern Honshu and Hokkaido), spanning about half of the species' biogeographic range in the country. Although the level of population differentiation was low (F (ST) = 0.021; [Formula: see text] = 0.090), two geographically differentiated clusters were detected by STRUCTURE analysis. The first cluster included most of the populations in Hokkaido, and may indicate continued survival throughout past glacial periods. We found a significant decrease in allelic richness with latitude, so the second cluster may represent an expansion of the lineage from Honshu during the post-glacial period. These results should enhance our understanding of historical north-south migrations of this species in northeastern Japan.

Life history of the neon flying squid: effect of the oceanographic regime in the North Pacific Ocean

The North Pacific Ocean population of the neon flying squid Ommastrephes bartramii, which un- dertakes seasonal north-south migrations, consists of autumn and winter-spring spawning cohorts. We ex- amined life history differences between the 2 cohorts in relation to the oceanographic environment. The differ- ences could be explained by seasonal north-south movements of the following 2 oceanographic zones: (1) the optimum spawning zone defined by sea surface temperatures; and (2) the food-rich zone defined by the position of the transition zone chlorophyll front (TZCF). The 2 cohorts use the food-rich zone in different phases of their life cycles. The spawning grounds for the au- tumn cohort occur within the subtropical frontal zone (STFZ), characterized by enhanced productivity in win- ter due to its proximity to the TZCF, whereas the spawning grounds for the winter-spring cohort occur within the subtropical domain, which is less productive. As the TZCF shifts northward in spring, the autumn co- hort continues to occur in the productive area north of the TZCF, whereas the winter-spring cohort remains in the less productive area to the south until it migrates into productive waters north of the TZCF in the summer or autumn. Consequently, the autumn cohort grows faster than the winter-spring cohort during the first half of its life cycle, whereas the winter-spring cohort grows faster during the second half. This growth pat- tern may be responsible for differing migration pat- terns; males of the autumn cohort do not have to migrate given their early fast growth in the STFZ, whereas those of the winter-spring cohort must mi- grate to the food-rich subarctic frontal zone to compen- sate for their slow growth. These biological and eco- logical differences between the 2 cohorts suggest flexibility of their life history response to oceanographic environments. Hatchling of the neon flying squid Ommastrephes bartramii

Schooling and migration of large pelagic fishes relative to environmental cues

A kinesis model driven by high‐resolution sea surface temperature maps is used to simulate Atlantic bluefin tuna movements in the Gulf of Maine during summer months. Simulations showed that individuals concentrated in areas of thermal preference. Results are compared to empirical distribution maps of bluefin tuna schools determined from aerial overflights of the stock during the same time periods. Simulations and empirical observations showed similar bluefin tuna distributions along fronts, although interannual variations in temperature ranges occupied suggest that additional foraging factors are involved. Performance of the model is further tested by simulating the relatively large‐scale annual north–south migrations of bluefin tuna that followed a preferred thermal regime. Despite the model’s relatively simple structure, results suggest that kinesis is an effective mechanism for describing movements of large pelagic fish in the expansive ocean environment.

Walvis Ridge barrier: its influence on palaeoenvironments and source rock generation deduced from ostracod distributions in the early South Atlantic Ocean

Abstract The early South Atlantic was subdivided latitudinally by the proto-Walvis Ridge, which separated early Cretaceous open marine conditions in the south from non-marine environments to the north. Changes in the palaeogeography, which can be monitored by the distribution of ostracod assemblages, determined the establishment of a wide variety of depositional environments, including evaporitic and total organic carbon-rich facies. Limited northward marine influxes across the barrier are postulated for mid-Aptian time, while largescale southward migrations of marine ostracods from the northern sector occurred in early Cenomanian and/or Turonian times. The latter established cosmopolitan faunas in the southern Atlantic and effectively marked the breakdown of the Walvis Ridge as a physical barrier to north-south migrations, although possible oceanographic factors militated against longitudinal faunal movements. Variations in the composition of ostracod assemblages during so called ‘oceanic anoxic events’ and the production of potential source rocks is briefly reviewed.

Juvenile hormone production and sexual maturation in true armyworm,Pseudaletia unipuncta (HAW.) (lepidoptera: noctuidae): A comparison of migratory and non-migratory populations

Previous work on North American populations of the true armyworm, Pseudaletia unipuncta, has shown that (1) ovarian development, pheromone synthesis, and the onset of calling (behavior associated with the emission of the sex pheromone) in virgin females are positively correlated with an increase in juvenile hormone (JH) production, and (2) sexual maturation is delayed under short-day, low-temperature conditions. Based on these results and on the observation that this insect is unable to survive the low temperatures of the Canadian winter, it has been hypothesized that armyworm moths undertake seasonal north-south migrations in response to predictable habitat deterioration. Recently we obtained material from the Azores, a volcanic archipelago in the Atlantic Ocean where the armyworm sustains populations all year round. We, therefore, undertook a comparative study to test the hypothesis that the earlier onset of calling behavior observed in this non-migrant population, relative to the North American population under identical conditions, was associated with an earlier induction of JH biosynthesis and a more rapid ovarian development. The results clearly supported this hypothesis: JH biosynthesis increased at a significantly younger age in Azorean females, although there were no differences in the relative proportions of the three JH homologues produced in vitro by CA of females sacrificed on their first night of calling. The early production of JH was reflected in a more rapid ovarian maturation although the data suggest that sexual maturation in the Azorean population may require a lower JH titer. The importance of the observed differences are discussed with respect to the presence or absense of migration in each population. © 1996 Wiley-Liss, Inc.

1979年夏季の西太平洋における対流圏下層の季節内変動

An effort is made in this study to explore the intraseasonal (30-60 day) oscillation of the lowertropospheric circulation over the western tropical Pacific. It is found that during the 1979 northern summer, the eastward propagation of the global-scale intraseasonal divergent mode induces quasiperiodic alternations of intraseasonal local divergent and convergent centers over the western Pacific. These alternations of intraseasonal local divergent and convergent centers result in the intraseasonal north-south migrations of the North Pacific Convergence Zone (NPCZ), i. e., the Mei Yü and Baiu fronts combined, and the South Pacific Convergence Zone (SPCZ). The regional circulations associated with the NPCZ and SPCZ also exhibit a coherent intraseasonal oscillation. With the intraseasonal local Hadley circulations and the intraseasonal streamfunction budget analysis of the lower-tropospheric circulation, it is shown that the aforementioned coherent intraseasonal oscillation is a response of the regional lower-tropospheric circulation to the eastward propagation of the global-scale intraseasonal oscillation.