Isotherm Depth Research Articles

Strengthening of the Equatorial Pacific Upper‐Ocean Circulation Over the Past Three Decades

AbstractThirty years (1993–2022) of concurrent satellite and in‐situ observations show a long‐term strengthening of the equatorial Pacific upper‐ocean circulation. Enhanced southeasterly and cross‐equatorial winds have caused an annual mean, basin‐wide acceleration of the equatorial westward near‐surface currents by ∼20% and an acceleration of poleward flow north (south) of the equator by ∼60% (∼20%). Additional moored velocity data reveal a deepening of the Equatorial Undercurrent (EUC) core at 170°W and significant shoaling at 140°W and 110°W, but no significant changes in EUC core velocity. The strongest subsurface zonal velocity trends are observed above the EUC core in the central to eastern Pacific and occur before and after the seasonal maximum of EUC core velocity, causing enhanced upper‐ocean vertical current shear. Consistent with trends of the 20°C isotherm depth along the equatorial Pacific, a significant basin‐wide steepening of the equatorial thermocline is observed. Both the accelerating equatorial current system and the enhanced thermocline slope are consistent with an observed steepening of the zonal sea surface height gradient due to increased wind‐driven westward mass transport at the surface. During February‐March, both surface and subsurface currents along the equator show eastward velocity trends, in contrast to westward near‐surface current trends during the remainder of the year. The trend reversal is attributed to both a long‐term shift in equatorial Kelvin wave activity and to the impact of strong interannual variability due to El Niño Southern Oscillation and other modes of natural variability on decadal to multidecadal time scales.

Structural modelling of subsurface geologic structures in Anambra and adjoining Bida Basins using aeromagnetic data: Implications for mineral explorations.

Aeromagnetic data over parts of the Northern Anambra and Southern Bida basins have been evaluated with emphasis on the subsurface geologic structures controlling mineralization and delineating the geomorphology of the basin. Four aeromagnetic data sheets (246 (Kabba), 247 (Lokoja), 266 (Auchi), and 267 (Idah)) were acquired through purchase, assemblage, analysis, and interpretation using integrated processing techniques of Euler deconvolution, analytical signal (AS), source parameter imaging (SPI), and 3D magnetic inversion model. The data are collected laterally in a series of NW-SE trajectories spaced 2 km apart, with an average flight altitude of approximately 150 m, and tielines occurring at approximately 20 km intervals. Qualitative observation of TMI and RAM shows that the research region is greatly fractured, with structures orienting in the E-W direction. The spectral analysis result shows that the sedimentary infillings range from 0.60 to 4.03 km. 3D model and curie isotherm depth subsurface maps reveal deeper curie depths at Kabba, Adavi, and Itakpe zones (28.0–40.0 km) and shallow curie depths at Auchi, Osara, Idah, and Anyigba areas (18.0–27.0 km). The result from the heat flow model shows an inverse relationship with the Curie isotherm depth. The contact depth sources calculated from Euler depth assessments show that the majority of these contact sources are trending in the E-W directions. The overall structural geomorphology of the research region conforms to the general pattern of structural trends within the research region. Most of the structures are trending NNE-SSW, NNW-SSE, and NE-SW, while the minor structures trend in the E-W direction. 3D inversion results show a discrete subsurface geologic structure that may house minerals within the region.

A preliminary assessment of regional CO2 storage potential in the onshore northern Perth Basin

The Geological Survey of Western Australia (GSWA) is creating a new carbon dioxide (CO2) geological storage atlas for Western Australia. The atlas will incorporate the latest state-wide datasets to provide a regional assessment of the potential for CO2 sequestration across the Perth, Southern Carnarvon, Northern Carnarvon (onshore and State waters), Canning and Officer basins. Multi-1D modelling of subsurface temperature in the northern Perth Basin incorporates newly collated temperature data, updated regional depth maps, and stratigraphic revisions. This modelling captures lateral subsurface temperature variations that are incorporated into isothermal depth and temperature maps identifying reservoir units within the optimum temperature–pressure window for CO2 storage. Isopach maps of associated sealing units indicate where they are of adequate thickness to contain CO2. Modelled present-day temperature maps of seven key reservoir units reveal promising CO2 storage prospectivity, with all postulated reservoir units having significant extents within optimum CO2 storage temperature and pressure ranges. Whereas older reservoir units are prospective for CO2 storage towards the margins of the basin, younger reservoir units in the shallower part of the succession are only prospective in or near the Dandaragan Trough, the deepest part of the basin. The critical upper temperature limit of 31.1°C is shallower in the north and west of the basin, where the modelled geothermal gradient is higher. All state-wide raw and interpreted datasets including temperature and depth maps will be published and available for download on the GSWA Western Australian Petroleum and Geothermal Information Management System website.

Understanding the crustal architecture beneath the Bangui magnetic anomaly and its interactions with central African tectonic megastructures based gravity and magnetic analysis

The Bangui magnetic anomaly (BMA) in Central Africa is one of the largest continental magnetic anomalies on Earth in terms of amplitude and lateral size. Determining the sources of the BMA can lead to an increased understanding of the crustal dynamic in the Central African sub-region and the African continent as a whole. Magnetic and gravity analysis-based derivative, two-dimensional forward modelling and a Curie isothermal depth, showed that (a) the bottoms of the magnetic sources were between 15 and 35 km; (b) the BMA is a coalescence of several anomalies that trend E-W and roughly NE-SW. These directions coincide with regional Pan African-aged shear zones along the Central African orogenic belt and to thrust sheets at the northern edge of the Congo Craton. The depth of magnetization does not exceed 35 km with the amplitude of magnetization becoming smaller in the Central African Republic. The potential magnetic susceptibility sources have an average density of 2850 kg/m3 and magnetic susceptibilities between 0.06 and 0.25 SI. The BMA is interpreted to be a combination of middle and lower crustal bodies that are not continuous and consist of magnetic mineral rich granulites and banded iron formations. The gravity and magnetic modelling indicate that the entire crust was involved in the Pan African collisional event similar to what is seen in the Mozambique belt in East Africa. Combined with geological and geochemical studies, the models add evidence that one or two subduction zones were involved in accreting terranes on the northern edge of the Congo Craton. The tectonic accretions caused a crustal remobilization along major shear zones that has locally contributed to a probable circulation of fluids enriched in ferromagnesian minerals during late Neoproterozoic magmatism that created the BMA sources.

A negative biological Indian Ocean dipole event in 2022

The biological dipole mode index (BDMI) showed a negative biological Indian Ocean dipole (BIOD) event occurred in the Equatorial Indian Ocean with the corresponding BIOD index BDMI(Ratio) at − 0.31 in October 2022. The chlorophyll-a (Chl-a) ratio (or Chl-a anomaly) between Chl-a in October 2022 and October Chl-a climatology from the Visible Infrared Imaging Radiometer Suite (VIIRS) showed negative dipolar features with the depressed and enhanced Chl-a in the east and west IOD zones, respectively. During this negative BIOD event, Chl-a ratio dropped to ~ 0.4–0.5 in the offshore region of the west Sumatra Coast in the east IOD zone, while it increased to ~ 1.5–1.6 in the northern west IOD zone. Temporal variations of the longitudinal averaged Chl-a ratio and the 20 °C isothermal (ISO20) depth anomaly generally coincided and collocated with each other. The positive and negative BIOD events in 2019 and 2022, respectively, were attributed to the nutrient dynamics driven by the physical dynamics in these two phases of IOD events. In the negative BIOD event in 2022, the depressed Chl-a in the east IOD zone was attributed to low sea surface nutrient levels due to dampened upwelling and deepened thermocline, while anomalously high Chl-a in the west IOD zone were driven by higher sea surface nutrient concentrations caused by the surface water divergence and shoaling thermocline.

Assessment of thermocline depth bias in the Seychelles-Chagos Thermocline Ridge of the Southwestern Indian Ocean simulated by the CMIP6 models

The Seychelles-Chagos Thermocline Ridge (SCTR, 5°S-10°S, 50°E-80°E) is a unique open-ocean upwelling region in the southwestern Indian Ocean. Due to the negative wind stress curl between the equatorial westerlies and southeasterly trade winds, SCTR is known as a strong upwelling region with high biological productivity, providing a primary fishing zone for the surrounding countries. Given its importance in shaping the variability of the Indian Ocean climate by understanding the sea-air interaction and its dynamics, the simulation of SCTR is evaluated using outputs from the Coupled Model Intercomparison Project Phase Sixth (CMIP6). Compared to observations, 23 out of 27 CMIP6 models tend to simulate considerably deeper SCTR thermocline depth (defined as the 20°C isotherm depth (D20))– a common bias in climate models. The deep bias is related to the easterly wind bias in the equatorial to southern Indian Ocean, which is prominent in boreal summer and fall. This easterly wind bias produces a weak annual mean Ekman pumping, especially in the boreal fall. Throughout the year, the observed Ekman pumping is positive and is driven by two components: the curl term, is associated with the wind stress curl, leads to upwelling during boreal summer to fall; the beta term, is linked to planetary beta and zonal wind stress, contributes to downwelling during boreal spring to fall. However, the easterly wind bias in the CMIP6 increases both the positive curl and negative beta terms. The beta term bias offsets the curl term bias and reduces the upwelling velocity. Furthermore, the easterly wind bias is likely caused by the reduced east-west sea surface temperature (SST) difference associated with a pronounced warm bias in the western equatorial Indian Ocean, accompanied by the east-west mean sea level pressure gradient over the Indian Ocean. Furthermore, this study finds local wind-induced Ekman pumping to be a more dominant factor in thermocline depth bias than Rossby waves, despite CMIP6 models replicating Rossby wave propagation. This study highlights the importance of the beta term in the Ekman pumping simulation. Thus, reducing the boreal summer-to-fall easterly wind bias over the Indian Ocean region may improve the thermocline depth simulation over the SCTR region.

Influence of the in-situ heat treatment during manufacturing on the microstructure and properties of DED-LB/M manufactured maraging tool steel

Due to high productivity, additive manufacturing (AM), and especially Directed Energy Deposition using laser and metallic powder (DED-LB/M) is attractive for manufacturing tools with integrated functionalities. This investigation was dedicated to DED-LB/M manufacturing of experimental maraging tool steel, characterization of the build microstructure with advanced electron microscopy and evaluation of hardness properties. High printability and low porosity of the final builds were observed, relative density was not lower than 99.5% for specimens manufactured with 600 W and 800 W, but microstructure and properties of the build had a gradient along the height. The characteristic hardness profile and microstructure, which were dependent on the manufacturing parameters, were observed. The top layers of manufactured maraging steel samples had a structure of martensite with precipitates presumably formed during solidification. The top layers were therefore softer to the depth of the austenitization isotherm. The higher hardness was measured in the inner regions which was a result of an in-situ heat treatment that the manufactured material was subjected to during layer-by-layer manufacturing. Thermal cycles during manufacturing resulted in precipitation hardening effect in the inner regions. Scanning and transmission electron microscopy confirmed the formation film-like and round particles in the as-build material, in top and inner regions. However, the quasicrystalline nano-sized R′-phase precipitates were observed only in the inner regions. The formation of the R′-phase precipitated during manufacturing as a result of the in-situ heat treatment was discussed as a reason for higher hardness (440 – 450 HV1) measured in the inner regions.

A Simple Model of Sea-Surface Cooling under a Tropical Cyclone

A major ocean response to tropical cyclone (TC) wind is the mixing of warm sea-surface water with cool subsurface water, which decreases the sea-surface temperature (SST). The decreased SST (δT) under the TC (rather than the cooled water in the wake after the storm has passed) modifies the storm’s intensity and is of interest to TC intensity studies. Here, the author shows that δT (non-dimensionalized by some reference temperature) is linearly related to Ψ, a dimensionless (nonlinear) function of TC and ocean parameters: the TC maximum wind, radius, and translation speed, as well as the ocean’s 26 °C and 20 °C isothermal depths (Z26 and Z20). The Ψ can be estimated from observations. The modelled δT is validated against sea-surface cooling observed by satellites, δTo, for typhoons during the May–December 2015 period in the western North Pacific. The result yields a best-fit, linear relation between δTo and Ψ that explains ~60% of the observed variance: r2 ≈ 0.6 (99% confidence). Tests show that the cube of the TC maximum wind and the ocean’s Z26 account for 46% and 7%, respectively, of the observed variance, indicating their predominant influence on TC-induced cooling. Contributions from other parameters are less but not negligible.

The ocean response to El Nino Southern Oscillation (ENSO) in the Bali Sea: a model study

The Bali Sea (BS) is connected to the Java Sea and Makassar Strait in the north and is one of the main outflow straits of the Indonesian Throughflow (ITF) in Lombok Strait (LS). Local ocean dynamics and their variability may be controlled significantly by the ITF. This study aims to investigate the interannual variation of circulation, mixed layer depth, and isotherm of 20°C, by performing a simulation of fine- a resolution 1/84° ocean circulation model of CROCO between 2010-2020 with a focus on El Nino 2015 (EN2015) and La Nina 2020 (LN2020) events. The model validation reproduces well the satellite-derived SST and SSH dataset with a correlation coefficient of >0.9. The model demonstrated an anti-clockwise circulation of the ITF in the BS, entering via the northern and exiting into the LS via the southern area. This circulation changes drastically during the ENSO event, where the ITF transport inflow is weaker and shallower during EN2015, compared to a much stronger and deeper ITF inflow during LN2020. Accordingly, shallower mixed layer depth and depth of isotherm of 20°C are found during EN2015, and vice versa. Coherence of these parameters with NINO3.4 is very significant (>-0.89) with a phase lag of 1.7 months.

NOAA's operational satellite ocean heat content products

ABSTRACT NOAA generates a suite of Ocean Heat Content (OHC) products for the North Atlantic and the North and South Pacific basins on a daily basis. Knowledge of the upper Ocean Heat Content is a critical aid in assessing the ocean's impact on Tropical Cyclones (TCs) and weather events. In-situ and satellite measurements of Sea Surface Temperature (SST) and Sea Surface Height Anomaly (SSHA) are used to generate the OHC product suite. The evaluated suite includes the 20°C (D20) and 26°C (D26) isotherm depths, the mixed layer depth (MLD) and mapping errors. Two cases are presented within the context of situational awareness showing the underling oceanic variability during the lifecycles of TC's Irma and Dorian.

Unexpected limitation of tropical cyclone genesis by subsurface tropical central-north Pacific during El Niño

The vast tropical Pacific is home to the majority of tropical cyclones (TCs) which threaten the rim countries every year. The TC genesis is nourished by warm sea surface temperatures (SSTs). During El Niño, the western Pacific warm pool extends eastward. However, the number of TCs does not increase significantly with the expanding warm pool and it remains comparable between El Niño and La Niña. Here, we show that the subsurface heat content change counteracts the favorable SSTs in the tropical central-north Pacific. Due to the anomalous positive wind stress curl, the 26 °C isotherm shoals during El Niño over this region and the heat content diminishes in the tropical central-north Pacific, even though warm SST anomalies prevail. This negative correlation between SST and 26 °C isotherm depth anomalies is opposite to the positive correlation in the tropical eastern and western Pacific. This is critical because quantifying the dynamics of the subsurface ocean provides insight into TC genesis. The trend in TC genesis continues to be debated. Future projections must account for the net effect of the surface-subsurface dynamics on TCs, especially given the expected El Niño-like pattern over the tropical Pacific under global warming.

Asymmetries in the ENSO phase space

El Niño Southern Oscillation (ENSO) dynamics are best described by the recharge oscillator model, in which the eastern tropical Pacific sea surface temperatures (T) and subsurface heat content (thermocline depth; h) have an out-of-phase relationship. This defines a 2-dimensional phase space diagram between T and h. In an idealized, stochastically forced damped oscillator, the mean phase space diagram should be a perfectly symmetrical circle with a clockwise propagation over time. However, the observed phase space shows strong asymmetries. In this study we illustrate how the ENSO phase space can be used to discuss the phase-dependency of ENSO dynamics. A normalized spherical coordinate system allows the definition of phase-depending ENSO growth rates and phase transition speeds. Based on these we discuss the implications of the observed asymmetries with regards to the dynamics and predictability of ENSO; with a particular focus on the variations in the growth rate and coupling of ENSO along the oscillation cycle. Using linear and non-linear recharge oscillator models we will show how dynamics and noise are driving ENSO at different phases of the ENSO cycles. The results illustrate that the ENSO cycle with positive phase transitions is present in all phases but has strong variations in its strength. Much of these variations result from presenting the ENSO phase space with estimates of h based on the iso-thermal depth, that is not ideal as it is not out-of-phase with T. Future work should address how h can be estimated better, including aspects such as the vertical temperature gradients and the meridional or zonal range. We further illustrated that a non-linear growth rate of T can explain most of the observed non-linear phase space characteristics.

Biological dipole mode indices: New parameters to characterize the physical and biological processes of the Indian Ocean Dipole event

The Indian Ocean Dipole (IOD) is a basin-wide ocean–atmosphere phenomenon that has profound impacts on the global climate, land, and ocean. The Dipole Mode Index (DMI), which is defined as the difference of the sea surface temperature (SST) anomaly in the east IOD zone and the west IOD zone has long been used to characterize and quantify the strength of IOD events. In this study, we propose biological dipole mode indices (BDMIs) based on the dipolar observations of chlorophyll-a (Chl-a) anomalies (difference and relative difference) in the east and west IOD zones during the IOD event. The two BDMIs, which are based on Chl-a difference and relative difference, not only represent the dipolar biological activities in the Equatorial Indian Ocean, but also reflect the thermocline dynamics in the east IOD zone and west IOD zone. The in situ measurements in the east and west IOD zones show the clear linkage between the BDMIs and the dynamics of the 20°C isothermal depth. This linkage is attributed to the changes of the nutrient supplies driven by the various ocean physical processes in the IOD event, thus the BDMIs could also act as the surrogate for the thermocline dynamics in the two IOD zones. The BDMIs from satellite ocean color observations show that they can identify and characterize all the major IOD events in the last two and half decades. The SST-based DMI and Chl-a-based BDMIs may depict some different aspects of the IOD events (e.g., surface versus subsurface properties). The performance comparison between the two BDMIs and DMI also shows that the BDMIs and traditional DMI can effectively detect IOD signal for the major IOD events. Indeed, the BDMIs and DMI are complementary for characterizing the IOD events, and the combination of these indices can provide a better understanding of the atmosphere and ocean processes for both surface and subsurface, as well as biological processes in the Equatorial Indian Ocean.

Lithospheric Thermal Structure in Jinggangshan City: Implications for High Geothermal Background

Jinggangshan City, which is located in the southwestern part of Jiangxi Province, is rich in hot springs. However, lack of geothermal studies has limited the exploration and utilization of the geothermal resources in this city. This study estimated the terrestrial heat flow in Jinggangshan City through well logging and analyses of rock thermal conductivity and heat production. Based on this and the surrounding geoscience transect and the Crust 1.0 model, this study constructed a one-dimensional lithospheric thermal structure by solving the steady-state heat conduction equation. Furthermore, the deep temperature distribution in Jinggangshan City was obtained to better understand the geodynamic condition of the geothermal resources in this city. The results show that the heat flow in this city is around 83.52 mW/m2, indicating the high heat background for the formation of geothermal resources. According to the lithospheric thermal structure of Jinggangshan City, the mantle contributes more to the terrestrial heat flow (qm/qc > 1) than the crust. The temperature of the Mohorovicic discontinuity (the Moho) is 671.7°C, which is consistent with that below the Tanlu deep fault (620–690°C). Moreover, the calculated depth of the Curie surface (585°C) is 27 km, which is consistent with the Curie isotherm depth estimated from aeromagnetic data. This consistency verifies the validity of the lithospheric thermal structure of Jinggangshan City constructed in this study. In summary, the high heat background plays an important role in the formation of geothermal resources in Jinggangshan City.

Interannual Variability of Yellowfin Tuna (Thunnus albacares) and Bigeye Tuna (Thunnus obesus) Catches in the Southwestern Tropical Indian Ocean and Its Relationship to Climate Variability

This study investigated the interannual variability of yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus) catches in the southwestern tropical Indian Ocean (SWTIO) over 25 years and its relationship to climate variability. The results indicate that the catch amount in the northern SWTIO exhibits a significant relationship with the temperature, salinity, and current variability in the upper ocean (< 400 m), associated with a significant subsurface upwelling variability, which is prominent only in the northern region. An increase of the tuna catches in the northern region is associated with the deepening of the thermocline depth and 20°C isotherm depth of the Seychelles–Chagos Thermocline Ridge, indicating suppression of the subsurface upwelling. Further analysis reveals that the catch amounts in the SWTIO tend to increase during the positive phase of the Indian Ocean Dipole. However, the catch variability in the northern SWTIO is more closely related to the El Niño–Southern Oscillation than the Indian Ocean Dipole. Favorable conditions for catches seem to develop in the northern region during El Niño years and continue throughout the following years. This relationship suggests the potential predictability of catch amounts in the northern SWTIO, an energetic region with strong subsurface upwelling variability.

Linearized Bayesian estimation of magnetization and depth to magnetic bottom from satellite data

SUMMARY Estimating the depth to magnetic bottom (DTB) from magnetic data is one of the most important and difficult potential field inversion problems. Since DTB can often be linked to the Curie isotherm depth of magnetite (∼580 °C), it could provide crucial constraints on heat flow, even in remote or inaccessible areas. Spectral methods are the most popular approach to estimate DTB, but their reliability has been challenged on many grounds. In contrast, space-domain methods have received relatively little attention, even though they might avoid some of the limitations of spectral methods. Furthermore, many DTB estimation methods are to some extent ad hoc, which makes uncertainty estimation and effective communication of the results difficult. In this work, we develop a Bayesian approach to estimate susceptibility and DTB from magnetic data. We describe the subsurface in terms of tesseroids and use a two-step inversion procedure that consists of a Monte Carlo Markov Chain hyperparameter optimization and a linearized inversion. This way, the uncertainties due to unknown hyperparameter are rigorously propagated to the final maps of susceptibility and DTB. Additionally, pointwise constraints based on heat flow measurements can be easily included into the inversion. Synthetic tests are used to determine the accuracy and reliability of the new algorithm. We find that heat flow constraints are necessary to achieve reliable results, although already a small number of points is sufficient. Finally, we apply the algorithm to the Australian continent and demonstrate applicability to real data.

Interannual variability of the thermocline depth in the south‐central Indian Ocean: Respective influences of IOD and ENSO

AbstractThe respective influences of the Indian Ocean dipole (IOD) and El Niño‐Southern Oscillation (ENSO) on the thermocline depth (represented by the 20°C isotherm depth, D20) variability in the south‐central Indian Ocean (SCIO) are investigated for the period of 1960–2020. The results show that pronounced interannual variations in D20 mainly occur in the SCIO and display a close relationship with the two tropical climate modes, with positive (negative) phase being associated with SCIO D20 deepening (shoaling). The D20 anomalies (D20A) induced by IOD and ENSO events have the same intensities but present different spatial–temporal features, as demonstrated by partial regression analysis. The IOD‐related D20A occurs during the mature phase of the event and behaves as a local response to anomalous wind stress curl induced by IOD, while the ENSO signature, dominated by the westward‐propagating oceanic Rossby waves, lasts much longer and extends further west.

Fire behaviour and design of hybrid fibre reinforced high-performance concrete columns subjected to uniaxial bending

This paper presents an experimental programme and a fire design model on hybrid fibre reinforced high-performance concrete (HPC) columns under ISO 834 heating curve. To date, there are very few experimental works on HPC columns subjected to eccentric loading under fire conditions. Therefore, a total of six specimens are tested to investigate the effects of load eccentricity and slenderness ratio on spalling and structural behaviour of HPC columns. Material properties including compressive strength, residual flexural strength and spalling behaviour under unstressed state but subject to transient heating are presented to get an overview of the performance of HPC. Following that, the test results of column specimens are discussed in terms of temperature distribution, mid-height deflection, axial deformation, failure mode and fire endurance. No spalling is observed in all the specimens owing to the synergistic effect of hybrid polypropylene and steel fibres. Test results show that mid-height deflection and axial contraction increase with an increase of load eccentricity. A simplified fire design model incorporating fibre reinforced concrete design is adopted based on 500 °C isotherm method. The model is verified with test data and it shows that 400 °C isotherm depth could provide safe and accurate predictions for HPC columns.

Tropical Cyclone Heat Potential (TCHP) from the NCMRWF NEMO based global ocean analysis and forecast system

In this study, the Nucleus European Modelling of Ocean (NEMO) based global ocean analysis and forecast system configured at National Centre for Medium Range Weather Forecasting (NCMWRF) is used to compute the upper ocean heat content up to 26° isotherm depth called as Tropical Cyclone Heat Potential (TCHP). NCMRWF has the real-time TCHP monitoring capability on daily basis. It is produced in real time using the global ocean forecast system up to 10 days using the ocean only model and up to 15 days using the coupled atmosphere-ocean model for monitoring the upper ocean and also for research purpose mainly for Tropical Cyclone (TC) study. Four pre-monsoon TCs with category above cyclonic storms in which two from Arabian Sea and two from Bay of Bengal are also examined. The Sea Surface Temperature drop is much more over the regions where the surface wind stress anomaly is strong. In both regions, various small scale warm and cold eddies are observed during TCs. TCHP anomaly is positive/negative over the region where Sea Surface Height (SSH) anomaly is positive/negative. From TCHP, it is manifest that the magnitude of TCHP anomaly is higher in BoB than AS region during TCs.

Modelling Marine Predator Habitat Using the Abundance of Its Pelagic Prey in the Tropical South-Western Pacific

Understanding the ecological mechanisms underpinning distribution patterns is vital in managing populations of mobile marine species. This study is a first step towards an integrated description of the habitats and spatial distributions of marine predators in the Natural Park of the Coral Sea, one of the world’s largest marine-protected areas at about 1.3 million km2, covering the entirety of New Caledonia’s pelagic waters. The study aims to quantify the benefit of including a proxy for prey abundance in predator niche modelling, relative to other marine physical variables. Spatial distributions and relationships with environmental data were analysed using catch per unit of effort data for three fish species (albacore tuna, yellowfin tuna and dolphinfish), sightings collected from aerial surveys for three cetacean guilds (Delphininae, Globicephalinae and Ziphiidae) and foraging locations identified from bio-tracking for three seabird species (wedge-tailed shearwater, Tahiti petrel and red-footed booby). Predator distributions were modelled as a function of a static covariate (bathymetry), oceanographic covariates (sea surface temperature, chlorophyll-a concentration and 20 °C-isotherm depth) and an acoustically derived micronekton preyscape covariate. While distributions were mostly linked to bathymetry for seabirds, and chlorophyll and temperature for fish and cetaceans, acoustically derived prey abundance proxies slightly improved distribution models for all fishes and seabirds except the Tahiti petrel, but not for the cetaceans. Predicted spatial distributions showed that pelagic habitats occupied by predator fishes did not spatially overlap. Finally, predicted habitats and the use of the preyscapes in predator habitat modelling were discussed.