Ocean Models

The Ocean Model Intercomparison Project (OMIP) aims to provide a framework for evaluating, understanding, and improving the ocean and sea-ice components of global climate and earth system models contributing to the Coupled Model Intercomparison Project Phase 6 (CMIP6). OMIP addresses these aims in two complementary manners: (A) by providing an experimental protocol for global ocean/sea-ice models run with a prescribed atmospheric forcing, (B) by providing a protocol for ocean diagnostics to be saved as part of CMIP6. We focus here on the physical component of OMIP, with a companion paper (Orr et al., 2016) offering details for the inert chemistry and interactive biogeochemistry. The physical portion of the OMIP experimental protocol follows that of the interannual Coordinated Ocean-ice Reference Experiments (CORE-II). Since 2009, CORE-I (Normal Year Forcing) and CORE-II have become the standard method to evaluate global ocean/sea-ice simulations and to examine mechanisms for forced ...

Purpose of Review Assessment of the impact of ocean resolution in Earth System models on the mean state, variability, and future projections and discussion of prospects for improved parameterisations to represent the ocean mesoscale. Recent Findings The majority of centres participating in CMIP6 employ ocean components with resolutions of about 1 degree in their full Earth System models (eddy-parameterising models). In contrast, there are also models submitted to CMIP6 (both DECK and HighResMIP) that employ ocean components of approximately 1/4 degree and 1/10 degree (eddy-present and eddy-rich models). Evidence to date suggests that whether the ocean mesoscale is explicitly represented or parameterised affects not only the mean state of the ocean but also the climate variability and the future climate response, particularly in terms of the Atlantic meridional overturning circulation (AMOC) and the Southern Ocean. Recent developments in scale-aware parameterisations of the mesoscale are being developed and will be included in future Earth System models. Summary Although the choice of ocean resolution in Earth System models will always be limited by computational considerations, for the foreseeable future, this choice is likely to affect projections of climate variability and change as well as other aspects of the Earth System. Future Earth System models will be able to choose increased ocean resolution and/or improved parameterisation of processes to capture physical processes with greater fidelity.

Purpose of Review Assessment of the impact of ocean resolution in Earth System models on the mean state, variability, and future projections and discussion of prospects for improved parameterisations to represent the ocean mesoscale. Recent Findings The majority of centres participating in CMIP6 employ ocean components with resolutions of about 1 degree in their full Earth System models (eddy-parameterising models). In contrast, there are also models submitted to CMIP6 (both DECK and HighResMIP) that employ ocean components of approximately 1/4 degree and 1/10 degree (eddy-present and eddy-rich models). Evidence to date suggests that whether the ocean mesoscale is explicitly represented or parameterised affects not only the mean state of the ocean but also the climate variability and the future climate response, particularly in terms of the Atlantic meridional overturning circulation (AMOC) and the Southern Ocean. Recent developments in scale-aware parameterisations of the mesoscale...

A theory for the exchange between a rotating, buoyancy-forced marginal sea and an ocean is developed and tested numerically. Cooling over the marginal sea leads to sinking and sets up a two-layer exchange flow, with a warm surface layer entering from the ocean and a cool layer exiting at depth. The connecting strait is sufficiently narrow and shallow to cause the exchange flow to be hydraulically controlled. The incoming surface layer forms a baroclinically unstable boundary current that circles the marginal sea in a cyclonic sense and feeds heat to the interior by way of eddies. Consistent with the overall heat and volume balances for the marginal sea, there is a continuous family of hydraulically controlled states with critical flow at the most constricted section of the strait. Included in this family is a limiting "maximal-exchange" solution with two sections of hydraulic control in the strait and with fixed layer depths at the most constricted section. The state of exchange for a given forcing is predicted using a theory that assumes energy conservation over a certain path connecting the strait to the marginal sea or, in some cases, the ocean. Depending on the configuration of the exchange, long-wave information may be blocked from entering the strait from the marginal sea, from the open ocean, or both. The scenario that holds determines what is predicted and what needs to be input. Numerical tests of the prediction for the temperature difference and the state of exchange are carried out for straits with a pure contraction in width and for a constant width strait with a topographic sill. The comparison is reasonable in most cases, though the numerical model is not able to reproduce cases of multiple states predicted by the theory for certain forcing values. The analytical model is an alternative to the Price and Yang and Siddall et al. models of a marginal sea outflow.

Observations suggest that enhanced turbulent dissipation and mixing over rough topography are modulated by the transient eddy field through the generation and breaking of lee waves in the Southern Ocean. Idealized simulations also suggest that lee waves are important in the energy pathway from eddies to turbulence. However, the energy loss from eddies due to lee wave generation remains poorly estimated. This study quantifies the relative energy loss from the time-mean and transient eddy flow in the Southern Ocean due to lee wave generation using an eddy-resolving global ocean model and three independent topographic datasets. The authors find that the energy loss from the transient eddy flow (0.12 TW; 1 TW 5 10 12 W) is larger than that from the time-mean flow (0.04 TW) due to lee wave generation; lee wave generation makes a larger contribution (0.12 TW) to the energy loss from the transient eddy flow than the dissipation in turbulent bottom boundary layer (0.05 TW). This study also shows that the energy loss from the time-mean flow is regulated by the transient eddy flow, and energy loss from the transient eddy flow is sensitive to the representation of anisotropy in small-scale topography. It is implied that lee waves should be parameterized in eddy-resolving global ocean models to improve the energetics of resolved flow.

Understanding the dynamics of the coastal oceans is important for managing coastal ecosystems, and hence for protecting lives and planning sustainable development. Among other countries in the southwest Indian Ocean, Mozambique has a greater number of environmental problems to solve. These problems include the landing of tropical cyclones 1 along the coast and associated heavy rain and flooding events which cause loss of life, infrastructural damage, coastal erosion, incident droughts, water pollution, overexploitation of marine and coastal resources, and weather and climate change and extremes. 2,3 Many of these problems can be monitored, so that remedial action can be taken, by conducting sustainable institutional collective research. 4 Therefore Mozambican institutions should attain adequate capacity of human resources in strategic research areas (e.g. weather and climate extremes, mitigating harmful effects of climate change, and conservation and sustainable management of marine and coastal resources). 5 It was because of the aforementioned problems that, for the first time, an initiative developed by a Mozambican research group to focus on oceanic and atmospheric dynamics was established.

We investigated the effect of the assimilation of altimeter satellite data in the third-generation ocean wave model WAM. We used a sequential method, where analyzed significant wave height fields are created by optimum interpolation, and the analyzed values are then used to construct the analyzed wave spectrum. The method provides also an estimate of the surface stress showing the possibility of using the analysis of the wave spectrum to derive an analyzed surface stress field. In a first set of numerical experiments, the data, provided by the Seasat altimeter, have been assimilated in the WAM model for 1-• days. The comparison between model results and satellite data during the continuation of the run shows a positive and persistent impact of the assimilation. In a second set of numerical experiments, Geosat altimeter data were assimilated for 10 days and the resulting analysis was compared with buoy data. Although the assimilation improves the model results, it is not capable of compensating the differences between model and buoys. Some failures are clearly derived from the absence in the satellite data of the high-wave events that were reported by the buoys. Other failures may be the consequence of an excessive swell attenuation in the WAM model, which compromises the effect of a previous correction. In fact, the comparison of WAM model results with altimeter data suggests that there is a tendency of the model to overevaluate initially the wind sea, and successively to overestimate the decay of the wave energy, when the waves leave the area of the storm.

Enhanced decadal variability in sea surface temperature (SST) centered on the Kuroshio Extension (KE) has been found in the Community Climate System Model version 3 (CCSM3) as well as in other coupled climate models. This decadal peak has higher energy than is found in nature, almost twice as large in some cases. While previous analyses have concentrated on the mechanisms for such decadal variability in coupled models, an analysis of the causes of excessive SST response to changes in wind stress has been missing. Here, a detailed comparison of the relationships between interannual changes in SST and sea surface height (SSH) as a proxy for geostrophic surface currents in the region in both CCSM3 and observations, and how these relationships depend on the mean ocean circulation, temperature, and salinity, is made. We use observationally based climatological temperature and salinity fields as well as satellite-based SSH and SST fields for comparison. The primary cause for the excessive...

Three simulations of the circulation in the Gulf of Mexico (the “Gulf”) using different numerical general circulation models are compared with results of recent large-scale observational campaigns conducted throughout the deep (>1500 m) Gulf. Analyses of these observations have provided new understanding of large-scale mean circulation features and variability throughout the deep Gulf. Important features include cyclonic flow along the continental slope, deep cyclonic circulation in the western Gulf, a counterrotating pair of cells under the Loop Current region, and a cyclonic cell to the south of this pair. These dominant circulation features are represented in each of the ocean model simulations, although with some obvious differences. A striking difference between all the models and the observations is that the simulated deep eddy kinetic energy under the Loop Current region is generally less than one-half of that computed from observations. A multidecadal integration of one o...

In the regions of flat immobile landfast ice (shallow Siberian Seas with depths less than 25-30 m), the models generally overestimate both the total observed sea ice thickness and rates of September and October ice growth from observations by more than 4 times and more than one standard deviation, respectively. The models do not reproduce conditions of fast ice formation and growth. Instead, the modeled fast ice is replaced with pack ice which drifts, generating ridges of increasing ice thickness, in addition to thermodynamic ice growth. Considering all observational data sets, the better correlations and smaller differences from observations are from the Estimating the Circulation and Climate of the Ocean, Phase II and Pan-Arctic Ice Ocean Modeling and Assimilation System models.

The generation of trapped and radiating internal tides around Izu-Oshima Island located off Sagami Bay, Japan, is investigated using the three-dimensional Stanford Unstructured Nonhydrostatic Terrain-following Adaptive Navier-Stokes Simulator (SUNTANS) that is validated with observations of isotherm displacements in shallow water. The model is forced by barotropic tides, which generate strong baroclinic internal tides in the study region. Model results showed that when diurnal K 1 barotropic tides dominate, resonance of a trapped internal Kelvin wave leads to large-amplitude internal tides in shallow waters on the coast. This resonance produces diurnal motions that are much stronger than the semidiurnal motions. The weaker, freely propagating, semidiurnal internal tides are generated on the western side of the island, where the M 2 internal tide beam angle matches the topographic slope. The internal wave energy flux due to the diurnal internal tides is much higher than that of the semidiurnal tides in the study region. Although the diurnal internal tide energy is trapped, this study shows that steepening of the Kelvin waves produces high-frequency internal tides that radiate from the island, thus acting as a mechanism to extract energy from the diurnal motions.

Understanding the dynamics of the coastal oceans is important for managing coastal ecosystems, and hence for protecting lives and planning sustainable development. Among other countries in the southwest Indian Ocean, Mozambique has a greater number of environmental problems to solve. These problems include the landing of tropical cyclones 1 along the coast and associated heavy rain and flooding events which cause loss of life, infrastructural damage, coastal erosion, incident droughts, water pollution, overexploitation of marine and coastal resources, and weather and climate change and extremes. 2,3 Many of these problems can be monitored, so that remedial action can be taken, by conducting sustainable institutional collective research. 4 Therefore Mozambican institutions should attain adequate capacity of human resources in strategic research areas (e.g. weather and climate extremes, mitigating harmful effects of climate change, and conservation and sustainable management of marine and coastal resources). 5 It was because of the aforementioned problems that, for the first time, an initiative developed by a Mozambican research group to focus on oceanic and atmospheric dynamics was established.

The stability of baroclinic Rossby waves in large ocean basins is examined, and the quasigeostrophic (QG) results of LaCasce and Pedlosky are generalized. First, stability equations are derived for perturbations on large-scale waves, using the two-layer shallow-water system. These equations resemble the QG stability equations, except that they retain the variation of the internal deformation radius with latitude. The equations are solved numerically for different initial conditions through eigenmode calculations and time stepping. The fastest-growing eigenmodes are intensified at high latitudes, and the slower-growing modes are intensified at lower latitudes. All of the modes have meridional scales and growth times that are comparable to the deformation radius in the latitude range where the eigenmode is intensified. This is what one would expect if one had applied QG theory in latitude bands. The evolution of large-scale waves was then simulated using the Regional Ocean Modeling Sy...

The recently released NCEP Climate Forecast System Reanalysis (CFSR) is used to examine the response to ENSO in the northeast tropical Pacific Ocean (NETP) during 1979–2009. The normally cool Pacific sea surface temperatures (SSTs) associated with wind jets through the gaps in the Central American mountains at Tehuantepec, Papagayo, and Panama are substantially warmer (colder) than the surrounding ocean during El Niño (La Niña) events. Ocean dynamics generate the ENSO-related SST anomalies in the gap wind regions as the surface fluxes damp the SSTs anomalies, while the Ekman heat transport is generally in quadrature with the anomalies. The ENSO-driven warming is associated with large-scale deepening of the thermocline; with the cold thermocline water at greater depths during El Niño in the NETP, it is less likely to be vertically mixed to the surface, particularly in the gap wind regions where the thermocline is normally very close to the surface. The thermocline deepening is enhanc...

We use the method of least squares with Lagrange multipliers to fit an ocean general circulation model to the Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface (MARGO) estimate of near sea surface temperature (NSST) at the Last Glacial Maximum (LGM; circa 23–19 thousand years ago). Compared to a modern simulation, the resulting global, last-glacial ocean state estimate, which fits the MARGO data within uncertainties in a free-running coupled ocean–sea ice simulation, has global-mean NSSTs that are 2°C lower and greater sea ice extent in all seasons in both the Northern and Southern Hemispheres. Increased brine rejection by sea ice formation in the Southern Ocean contributes to a stronger abyssal stratification set principally by salinity, qualitatively consistent with pore fluid measurements. The upper cell of the glacial Atlantic overturning circulation is deeper and stronger. Dye release experiments show similar distributions of Southern Ocean source waters i...

The ability of paleoceanographic tracers to constrain rates of transport is examined using an inverse method to combine idealized observations with a geostrophic model. Considered are the spatial distribution, accuracy, and types of tracers required to constrain changes in meridional transport within an idealized single-hemisphere basin. Measurements of density and radioactive tracers each act to constrain rates of transport. Conservative tracers, while not of themselves able to inform regarding rates of transport, improve constraints when coupled with density or radioactive observations. It is found that the tracer data would require an accuracy one order of magnitude better than is presently available for paleo-observations to conclusively rule out factor-of-2 changes in meridional transport, even when assumed available over the entire model domain. When data are available only at the margins and bottom of the model, radiocarbon is unable to constrain transport while density remai...

Understanding the dynamics of the coastal oceans is important for managing coastal ecosystems, and hence for protecting lives and planning sustainable development. Among other countries in the southwest Indian Ocean, Mozambique has a greater number of environmental problems to solve. These problems include the landing of tropical cyclones 1 along the coast and associated heavy rain and flooding events which cause loss of life, infrastructural damage, coastal erosion, incident droughts, water pollution, overexploitation of marine and coastal resources, and weather and climate change and extremes. 2,3 Many of these problems can be monitored, so that remedial action can be taken, by conducting sustainable institutional collective research. 4 Therefore Mozambican institutions should attain adequate capacity of human resources in strategic research areas (e.g. weather and climate extremes, mitigating harmful effects of climate change, and conservation and sustainable management of marine and coastal resources). 5 It was because of the aforementioned problems that, for the first time, an initiative developed by a Mozambican research group to focus on oceanic and atmospheric dynamics was established.

The upper ocean circulation near the western margin of the South Atlantic Ocean is dominated by the southward flow of the warm and salty Brazil Current and the northward flow of the cold and relatively fresh Malvinas Current. The collision, near 38 o S, of the two jets produces a strong frontal zone known as the Brazil-Malvinas Confluence (BMC). The BMC is populated with eddies and meanders and is known to be one of the most energetic areas of the world oceans (Chelton et al) [1] . In this article we describe the numerical strategies used to implement a regional, eddy resolving, three-dimensional numerical model of the BMC. The numerical experiments consisted of integrations using idealized set-ups and experiments with a realistic basin configuration. The experiments in idealized basins were used to test the numerical implementation of open boundary conditions in a dynamical setting that includes both passive and active lateral boundaries. The simulations in a realistic basin ere fo...

The evolution of the oceanic free-surface is responsible for the propagation of fast surface gravity waves, which approximatively propagate at speed √ gH (with g the gravity and H the local water depth). In the deep ocean, this phase speed is roughly two orders of magnitude faster than the fastest internal gravity waves. The very strong stability constraint imposed by those fast surface waves on the time-step of numerical models is handled using a mode splitting between slow (internal / baroclinic) and fast (external / barotropic) motions to allow the possibility to adopt specific numerical treatments in each component. The barotropic mode is traditionally approximated by the vertically integrated flow because it has only slight vertical variations. However the implications of this assumption on the stability of the splitting are not well documented. In this paper, we describe a stability analysis of the mode splitting technique based on an eigenvector decomposition using the true (depth-dependent) barotropic mode. This allows us to quantify the amount of dissipation required to stabilize the approximative splitting. We show that, to achieve stable integrations, the dissipation usually applied through averaging filters can be drastically reduced when incorporated at the level of the barotropic time stepping. The benefits are illustrated by numerical experiments. In addition, the formulation of a new mode splitting algorithm using the depth-dependent barotropic mode is introduced.

The evolution of the oceanic free-surface is responsible for the propagation of fast surface gravity waves, which approximatively propagate at speed √ gH (with g the gravity and H the local water depth). In the deep ocean, this phase speed is roughly two orders of magnitude faster than the fastest internal gravity waves. The very strong stability constraint imposed by those fast surface waves on the time-step of numerical models is handled using a mode splitting between slow (internal / baroclinic) and fast (external / barotropic) motions to allow the possibility to adopt specific numerical treatments in each component. The barotropic mode is traditionally approximated by the vertically integrated flow because it has only slight vertical variations. However the implications of this assumption on the stability of the splitting are not well documented. In this paper, we describe a stability analysis of the mode splitting technique based on an eigenvector decomposition using the true (depth-dependent) barotropic mode. This allows us to quantify the amount of dissipation required to stabilize the approximative splitting. We show that, to achieve stable integrations, the dissipation usually applied through averaging filters can be drastically reduced when incorporated at the level of the barotropic time stepping. The benefits are illustrated by numerical experiments. In addition, the formulation of a new mode splitting algorithm using the depth-dependent barotropic mode is introduced.

What most clearly distinguishes near-shore and offshore currents is their dominant spatial scale, O (1-30) km near-shore and O (30-1000) km offshore. In practice, these phenomena are usually both measured and modeled with separate methods. In particular, it is infeasible for any regular computational grid to be large enough to simultaneously resolve well both types of currents. In order to obtain local solutions at high resolution while preserving the regional-scale circulation at an affordable computational cost, a 1-way grid embedding capability has been integrated into the Regional Oceanic Modeling System (ROMS). It takes advantage of the AGRIF (Adaptive Grid Refinement in Fortran) Fortran 90 package based on the use of pointers. After a first evaluation in a baroclinic vortex test case, the embedding procedure has been applied to a domain that covers the central upwelling region off California, around Monterey Bay, embedded in a domain that spans the continental U.S. Pacific Coast. Long-term simulations (10 years) have been conducted to obtain mean-seasonal statistical equilibria. The final solution shows few discontinuities at the

ROMSTOOLS, a collection of global datasets and a series of Matlab programs collected in an integrated toolbox, generates the grid, surface forcing, initial condition, open boundary conditions, and tides for climatological and inter-annual ROMS ocean simulations. ROMSTOOLS generates also embedded models, realtime coastal modeling systems, as well as experiments including biology. Tools for visualization, animations and diagnostics are also provided.

In the regions of flat immobile landfast ice (shallow Siberian Seas with depths less than 25-30 m), the models generally overestimate both the total observed sea ice thickness and rates of September and October ice growth from observations by more than 4 times and more than one standard deviation, respectively. The models do not reproduce conditions of fast ice formation and growth. Instead, the modeled fast ice is replaced with pack ice which drifts, generating ridges of increasing ice thickness, in addition to thermodynamic ice growth. Considering all observational data sets, the better correlations and smaller differences from observations are from the Estimating the Circulation and Climate of the Ocean, Phase II and Pan-Arctic Ice Ocean Modeling and Assimilation System models.

Understanding the dynamics of the coastal oceans is important for managing coastal ecosystems, and hence for protecting lives and planning sustainable development. Among other countries in the southwest Indian Ocean, Mozambique has a greater number of environmental problems to solve. These problems include the landing of tropical cyclones 1 along the coast and associated heavy rain and flooding events which cause loss of life, infrastructural damage, coastal erosion, incident droughts, water pollution, overexploitation of marine and coastal resources, and weather and climate change and extremes. 2,3 Many of these problems can be monitored, so that remedial action can be taken, by conducting sustainable institutional collective research. Therefore Mozambican institutions should attain adequate capacity of human resources in strategic research areas (e.g. weather and climate extremes, mitigating harmful effects of climate change, and conservation and sustainable management of marine and coastal resources). It was because of the aforementioned problems that, for the first time, an initiative developed by a Mozambican research group to focus on oceanic and atmospheric dynamics was established.

The shores of Cape Verde hosts one of the most important nesting populations of the loggerhead turtle Caretta caretta in the world, as well as important feeding grounds for hawksbill Eretmochelys imbricata and green turtles Chelonia mydas . In the past few years, a number of scientific studies have demonstrated the relevance of the waters and beaches of this archipelago for the conservation of these endangered marine megavertebrates. This article aims to bring together the most relevant scientific information published on the subject so far. In addition, we will provide an overview of the current situation of sea turtles in Cape Verde, their conservation status and their importance in an international context.

The ability of individuals to actively control their movements, especially during the early life stages, can significantly influence the distribution of their population. Most marine turtle species develop oceanic foraging habitats during different life stages. However, flatback turtles (Natator depressus) are endemic to Australia and are the only marine turtle species with an exclusive neritic development. To explain the lack of oceanic dispersal of this species, we predicted the dispersal of post-hatchlings in the Great Barrier Reef (GBR), Australia, using oceanographic advection-dispersal models. We included directional swimming in our models and calibrated them against the observed distribution of post-hatchling and adult turtles. We simulated the dispersal of green and loggerhead turtles since they also breed in the same region. Our study suggests that the neritic distribution of flatback post-hatchlings is favoured by the inshore distribution of nesting beaches, the local wate...

The ability of individuals to actively control their movements, especially during the early life stages, can significantly influence the distribution of their population. Most marine turtle species develop oceanic foraging habitats during different life stages. However, flatback turtles (Natator depressus) are endemic to Australia and are the only marine turtle species with an exclusive neritic development. To explain the lack of oceanic dispersal of this species, we predicted the dispersal of post-hatchlings in the Great Barrier Reef (GBR), Australia, using oceanographic advection-dispersal models. We included directional swimming in our models and calibrated them against the observed distribution of post-hatchling and adult turtles. We simulated the dispersal of green and loggerhead turtles since they also breed in the same region. Our study suggests that the neritic distribution of flatback post-hatchlings is favoured by the inshore distribution of nesting beaches, the local wate...

The ability of individuals to actively control their movements, especially during the early life stages, can significantly influence the distribution of their population. Most marine turtle species develop oceanic foraging habitats during different life stages. However, flatback turtles (Natator depressus) are endemic to Australia and are the only marine turtle species with an exclusive neritic development. To explain the lack of oceanic dispersal of this species, we predicted the dispersal of post-hatchlings in the Great Barrier Reef (GBR), Australia, using oceanographic advection-dispersal models. We included directional swimming in our models and calibrated them against the observed distribution of post-hatchling and adult turtles. We simulated the dispersal of green and loggerhead turtles since they also breed in the same region. Our study suggests that the neritic distribution of flatback post-hatchlings is favoured by the inshore distribution of nesting beaches, the local wate...

Previous studies have shown that loggerhead sea turtles (Caretta caretta), monitored by satellite telemetry, complete long-distance migration between the western and eastern Mediterranean basins following a seasonal pattern. This study investigated if these migration routes may be inXuenced by surface currents by superimposing the tracks of three loggerhead turtles (curved carapace length >55 cm), migrating from the western to the eastern Mediterranean basin, on Lagrangian data of current developed into pseudo-eulerian speed Welds. The average travel speed of the turtles was 1.6 km h ¡1 and did not depend on the current speed or direction. We observed a connection between surface currents and the turtles' migration routes, although not a conclusive one. These observations show that neritic stage loggerhead turtles conduct migration in two distinct alternate phases: the Wrst characterized by high and constant speed of travel both when swimming with or against currents and the second typiWed by low travel speeds and a good concurrence between the trailed routes and the course of the currents. These two phases corresponded to two types of movements, one where the turtle migrates actively to reach a speciWc destination (either neritic foraging, wintering or nesting ground) and the other, where the turtle drifts with the mesoscale current and forages pelagically. It seemed thus, that the inXuence of currents on a turtle's movements depends on the turtle's momentary behaviour and location of residence. Communicated by R. Cattaneo-Vietti.

Austronesians colonized the islands of Rapa Nui, Hawaii, the Marquesas and Madagascar. All of these islands have been found to harbor Austronesian artifacts and also, all of them are known nesting sites for marine turtles. Turtles are well known for their transoceanic migrations, sometimes totalling thousands of miles, between feeding and nesting grounds. All marine turtles require land for nesting. Ancient Austronesians are known to have had outstanding navigation skills, which they used to adjust course directions. But these skills will have been insufficient to locate tiny, remote islands in the vast Indo-Pacific oceans. We postulate that the Austronesians must have had an understanding of the marine turtles' migration patterns and used this knowledge to locate remote and unknown islands. The depth and speed at which marine turtles migrate makes following them by outrigger canoes feasible. Humans have long capitalized on knowledge of animal behavior. ß 2015 Acadé mie des sciences. Published by Elsevier Masson SAS. All rights reserved. R E ´ S U M E ´ Les Austroné siens ont colonisé des ı ˆles e ´ loigné es, comme Rapa Nui, Hawaii ou les Marquises, ainsi que Madagascar. Des arté facts austroné siens ont e ´ té dé couverts sur ces ı ˆles, qui sont aussi des sites de nidification pour les tortues de mer, qui sont connues pour effectuer de longues migrations transocé aniques, parfois de milliers de kilomè tres, entre les sites de reproduction et les pâtures océ aniques. Les anciens Austroné siens sont connus pour leur maıˆtrise de la navigation hauturiè re ; cependant, ces compé tences sont insuffisantes pour localiser de petites ı ˆles dans les vastes océ ans Pacifique et Indien. Nous postulons que les Austroné siens ont dû comprendre la migration des tortues de mer et

Understanding the movements of turtle hatchings is essential for improved understanding of dispersal behaviour and ultimately survivorship, life history strategies and population connectivity. Yet investigation of in-water movement has been hampered by the small size of hatchlings relative to the size of available tracking technologies. This has resulted in the use of labour intensive visual tracking methods, or active tracking methods with high transmitter to body weight ratios. These methods are confounded by the presence of the observer, the size of the tag, usual small treatment sample sizes and studies that are constrained to daylight hours when turtles hatch predominantly at night. Passive acoustic monitoring using new miniature tags can overcome these limitations. We tested the effectiveness of active and passive acoustic tracking in monitoring turtle hatchling movement in order to measure the influence of artificial light on newly hatched turtles once they enter the water. A Vemco VR2W Positioning System (VPS) comprising an array of 18 VR2W receivers was deployed in the surf zone to detect signals from acoustic-coded transmitters (1.14 ± 0.06% of body mass) attached to 26 flatback turtle hatchlings released into the array. A total of 1328 detections were recorded for 22 hatchlings with turtles spending a mean of 16.63 ± 5.89 min in the array. The test detection range for this technology in the surf-zone was 50-100 m and was influenced by wave noise and shallow deployment. Cyclonic conditions hampered the experiment and resulted in an inconclusive test of light effects. Three additional instrumented flatback hatchlings were followed in a small boat using a mobile acoustic receiver and directional hydrophone up to 2 km from shore. Passive acoustic monitoring is a viable technology for tracking small marine animals and removes many of the confounding effects of other telemetry methods. It has great potential to examine natural and anthropogenic factors influencing orientation and behaviour during a crucial stage in turtle life historytheir initial movement from the beach through predator-rich, near shore waters. While the data obtained by passive acoustic monitoring is limited in its spatio-temporal coverage, being constrained by the size of the array, active acoustic tracking can be applied over larger scales. Such studies will be particularly important for assessing the impacts of anthropogenic pressures that have changed the natural light, noise or wave environments and for providing behavioural data to improve and validate bio-physical models of the migration and dispersal of young turtles.

Dispersal during juvenile life stages drives the life-history evolution and dynamics of many marine vertebrate populations. However, the movements of juvenile organisms, too small to track using conventional satellite telemetry devices, remain enigmatic. For sea turtles, this led to the paradigm of the ‘lost years' since hatchlings disperse widely with ocean currents. Recently, advances in the miniaturization of tracking technology have permitted the application of nano-tags to track cryptic organisms. Here, the novel use of acoustic nano-tags on neonate loggerhead turtle hatchlings enabled us to witness first-hand their dispersal and behaviour during their first day at sea. We tracked hatchlings distances of up to 15 km and documented their rapid transport (up to 60 m min−1) with surface current flows passing their natal areas. Tracking was complemented with laboratory observations to monitor swimming behaviours over longer periods which highlighted (i) a positive correlation between swimming activity levels and body size and (ii) population-specific swimming behaviours (e.g. nocturnal inactivity) suggesting local oceanic conditions drive the evolution of innate swimming behaviours. Knowledge of the swimming behaviours of small organisms is crucial to improve the accuracy of ocean model simulations used to predict the fate of these organisms and determine resultant population-level implications into adulthood.

The movements of some long-distance migrants are driven by innate compass headings that they follow on their first migrations (e.g., some birds and insects), whilst the movements of other first time migrants are learnt by following more experienced conspecifics (e.g., baleen whales). However, the overall roles of innate, learnt and social behaviors in driving migration goals in many taxa are poorly understood. To look for evidence of whether migration routes are innate or learnt for sea turtles, here for 42 sites around the World we compare the migration routes of > 400 satellite tracked adults of multiple species of sea turtle with c.45,000 Lagrangian hatchling turtle drift scenarios. In so doing, we show that the migration routes of adult turtles are strongly related to hatchling drift patterns, implying that adult migration goals are learnt through their past experiences dispersing with ocean currents. The diverse migration destinations of adults consistently reflected the diversity in sites they would have encountered as drifting hatchlings. Our findings reveal how a simple mechanism, juvenile passive drift, can explain the ontogeny of some of the longest migrations in the animal kingdom and ensure that adults find suitable foraging sites.


Read More: http://www.esajournals.org/doi/abs/10.1890/13-2164.1

Some animals migrate huge distances in search of resources with locomotory mode (flying/swimming/walking) thought to drive the upper ceilings on migration distance. Yet in cross-taxa comparisons, upper ceilings on migration distance have been ignored for one important group, sea turtles.
Using migration distances recorded for 407 adult and 4715 juvenile sea turtles across five species, we show that for adult cheloniid turtles, the upper ceiling on species migration distances between breeding and foraging habitats (1050–2850 km across species) is similar to that predicted for equivalent-sized marine mammals and fish.
In contrast, by feeding in the open ocean, adult leatherback turtles (Dermochelys coriacea) and juveniles of all turtle species can travel around 12 000 km from their natal regions, travelling across the widest ocean basins. For juvenile turtles, this puts their maximum migration distances well beyond those expected for equivalent-sized marine mammals and fish, but not those found in some similar sized birds.
Post-hatchling turtles perform these long-distance migrations to juvenile foraging sites only once in their lifetime, while adult turtles return to their breeding sites every few (generally ≥2) years. Our results highlight the important roles migration periodicity and foraging mode can play in driving the longest migrations, and the implications for Marine Protected Area planning are considered in terms of sea turtle conservation.