Western Caribbean Sea Research Articles

The Influence of Caribbean Current Eddies on Coastal Circulation in the Southwest Caribbean Sea

Abstract Westward-propagating Caribbean Current eddies modify the volume-integrated potential vorticity (PV) balance in the western Caribbean Sea, influencing the circulation of the Panamá–Colombia Gyre (PCG) and coastal currents hundreds of kilometers to the south of the eddies’ mean trajectory. Using 22 years of output from the Hybrid Coordinate Ocean Model, we apply a volume-integrated eddy phase-averaged 1.5-layer PV balance, showing that PV fluxes into the PCG region are balanced by frictional PV dissipation represented by linear drag along the coastline. Coastal currents in the PCG region vary by a factor of 2 in phase with the passage of a Caribbean Current eddy over the 116-day average eddy period. Flow separation at the Isthmus of Panamá results in a vortex shed from the Darien Gulf, which slows the coastal currents in the gyre region from their maximum during eddy events. An annual ensemble average PV balance in the gyre region shows that the mean PV influx to this region is higher from August to October. Correspondingly, the range of coastal currents in the gyre region over an eddy event is modestly influenced by the PV influx magnitude. Eddy-influenced reversals in the coastal current can occur between November and July at Bocas del Toro and year-round at Colón. Such coastal current reversals are important for the alongshore transport of larvae, freshwater, and chemical tracers.

First record of the bluntnose sixgill shark Hexanchus griseus (Bonnaterre, 1788) in the Guatemalan Caribbean Sea

The Guatemalan Caribbean has a deepwater fishing area close to the shore around the Cayman Trench. This study reports the first record of the bluntnose sixgill shark (Hexanchus griseus) from this fishing area. Fishery-independent surveys using longlines at ~430-465 m depth, ~11 km northeast of El Quetzalito fishing village, were conducted in 2022 and 2023. Two bluntnose sixgill sharks were captured during these surveys. The sharks were females with total lengths of 300 and 310 cm, with morphological characteristics consistent with this species. These are the first confirmed records of bluntnose sixgill sharks in the western Caribbean Sea. Expanding coastal fisheries to deeper waters presents an emerging threat to deep-sea chondrichthyans in the region. Therefore, periodic fisheries monitoring is needed to estimate their vulnerability to fishing pressure.

Microbial eukaryotic predation pressure and biomass at deep-sea hydrothermal vents.

Deep-sea hydrothermal vent geochemistry shapes the foundation of the microbial food web by fueling chemolithoautotrophic microbial activity. Microbial eukaryotes (or protists) play a critical role in hydrothermal vent food webs as consumers and hosts of symbiotic bacteria, and as a nutritional source to higher trophic levels. We measured microbial eukaryotic cell abundance and predation pressure in low-temperature diffuse hydrothermal fluids at the Von Damm and Piccard vent fields along the Mid-Cayman Rise in the Western Caribbean Sea. We present findings from experiments performed under in situ pressure that show cell abundances and grazing rates higher than those done at 1 atmosphere (shipboard ambient pressure); this trend was attributed to the impact of depressurization on cell integrity. A relationship between the protistan grazing rate, prey cell abundance, and temperature of end-member hydrothermal vent fluid was observed at both vent fields, regardless of experimental approach. Our results show substantial protistan biomass at hydrothermally fueled microbial food webs, and when coupled with improved grazing estimates, suggest an important contribution of grazers to the local carbon export and supply of nutrient resources to the deep ocean.

Factors contributing to morning rain in the upper Río Chagres Basin, Panamá

The Upper Chagres River Basin plays an important role in the stable operation of the Panama Canal. Previous studies have shown that there is a salient regional difference in the diurnal variation of precipitation in the basin. Precipitation during the rainy season peaks in the early afternoon throughout the basin, but precipitation is also observed in the morning at sites in the northern part of the basin. However, the cause of this is not clear due to limited ground observation. To address this issue, we conducted dynamical downscaling experiments with a horizontal grid spacing of 5 and 2 km and nested in a global atmospheric model with horizontal grid spacing of approximately 20 km. The results showed that the 2 km convection-permitting model successfully reproduced regional differences in observed diurnal variations. The downscaled results indicated that intensified low-level northeasterly winds over the southern Caribbean Sea triggered favorable conditions for morning rain with an orographic effect under the seaside coastal regime in the western Caribbean Sea. This is in contrast to precipitation peaks in the early afternoon under a landside coastal regime.

Rates of Future Climate Change in the Gulf of Mexico and the Caribbean Sea: Implications for Coral Reef Ecosystems

AbstractRising temperatures and ocean acidification due to anthropogenic climate change pose ominous threats to coral reef ecosystems in the Gulf of Mexico (GoM) and the western Caribbean Sea. Unfortunately, the once structurally complex coral reefs in the GoM and Caribbean have dramatically declined since the 1970s; relatively few coral reefs still exhibit a mean live coral cover of >10%. Additional work is needed to characterize future climate stressors on coral reefs in the GoM and the Caribbean Sea. Here, we use climate model simulations spanning the period of 2015–2100 to partition and assess the individual impacts of climate stressors on corals in the GoM and the western Caribbean Sea. We use a top‐down modeling framework to diagnose future projected changes in thermal stress and ocean acidification and discuss its implications for coral reef ecosystems. We find that ocean temperatures increase by 2°C–3°C over the 21st century, and surpass reported regional bleaching thresholds by mid‐century. Whereas ocean acidification occurs, the rate and magnitude of temperature changes outpace and outweigh the impacts of changes in aragonite saturation state. A framework for quantifying and communicating future risks in the GoM and Caribbean using reef risk projection maps is discussed. Without substantial mitigation efforts, the combined impact of increasing ocean temperatures and acidification are likely to stress most existing corals in the GoM and the Caribbean, with widespread economic and ecological consequences.

Planktonic Egg Masses of the Diamondback Squid Thysanoteuthis rhombus in the Western Caribbean, Honduras; a Comprehensive Review of Global Observations

The Diamondback Squid Thysanoteuthis rhombus is a globally distributed deep-sea species, one of only a few oegopsid nektonic cephalopods in which planktonic egg masses are well known. Here, we report three new T. rhombus egg masses found in the Bay Islands, Honduras, in 2020. Using the egg trace method, these egg masses provide one of the first indications that T. rhombus adults occur and spawn, and that their eggs hatch, in the Western Caribbean Sea. The first egg mass was 215 cm long and was stranded on an intertidal seagrass bed on Utila Island, from which we estimated 78,758 eggs. Two additional egg masses were photographed underwater: one in a scuba diving area near Utila Island, and one from the neighbouring Bay Island of Roatan. We reviewed possibilities that this squid could provide an alternative commercially valuable fishing and touristic resource for the Bay Islands. As part of our investigation, we conducted a comprehensive literature review plus an online search of citizen science, to provide an accurate count of egg mass observations to date, which resulted in a reference table of 108 T. rhombus egg masses known worldwide.

Sensitivity of precipitation and atmospheric low-level circulation patterns to domain size and choice of parameterization schemes in RegCM4.4 over Central America

The sensitivity of regional climate model simulations to domain size and position is becoming increasingly important for generating reliable climate scenarios. In this study, the Central America CORDEX domain (CCA) at 50 km horizontal resolution with a relaxation zone of 10° around the boundaries (CCA+) was taken as the basis to increase domain size in the RegCM4.4 model. The low-level circulation and precipitation patterns over Central America, the western Caribbean Sea, and the eastern tropical Pacific do not show strong sensitivity to domain size changes for an area increment of 18, 32, and 52% with respect to the size of CCA+. The physical configuration in RegCM4.4 has a greater impact on the representation of relevant climate characteristics and atmospheric processes. Simulated 925 hPa winds over the Caribbean low-level jet (CLLJ) region show unrealistic winter and summer intensities, especially in July. Similar issues were found in other studies for the CCA domain, using different models and physical configurations. A reduction of the critical Richardson number in the selected planetary boundary layer scheme resulted in little change in the strength of the summer component of the CLLJ. The model simulations do not completely capture key regional precipitation patterns such as the mid-summer drought, due to limitations in adequately representing low-level circulation. However, simulations using the Grell cumulus parameterization perform relatively better than those using a mixed scheme (Grell over land-Emanuel over ocean).

Ecological impacts of an invasive mesopredator do not differ from those of a native mesopredator: lionfish in Caribbean Panama

The impacts of invasive lionfish (Pterois volitans/miles) on native coral reef populations in the Western Atlantic Ocean and Caribbean Sea can be enormous. However, how much lionfish differ from native predators and whether their effects outweigh the abundant mesopredators that occupy many reefs invite continued examination. Here, we present empirical evidence from Caribbean Panama and beyond suggesting that lionfish are less abundant than native mesopredators. Furthermore, we show that their direct impacts on survivorship and size distributions of one native prey species are similar to those of a native mesopredator. These results support calls for lionfish management that considers evolving local ecological and social dynamics, including prey community composition, the roles of native mesopredators, and regional goals for conservation and fisheries. Recognition of regional context creates the potential for synergies between conservation actions aimed both at the invasion and other consequential problems such as overexploitation and climate change.

Parasitic isopods (Crustacea: Dajidae) of euphausiids (Crustacea: Euphausiacea) in the western Caribbean Sea

ABSTRACT In this work, we provide new data on the parasitic isopods infecting euphausiid species in the western Caribbean Sea, Northwestern Tropical Atlantic (NWTA). Our study was based on the examination of a total of 211 zooplankton samples obtained in 1999, 2010 and 2011 from the western Caribbean Sea (i.e. the eastern coast of the Yucatan Peninsula, off the southwest coast of Cuba and Honduras) with different sampling gears at a depth range of 0–200 m. Euphausiid species were examined to detect parasitic isopods. Three species of these parasites were identified. One of them, Heterophryxus appendiculatus G. O. Sars, 1885 has been hitherto reported exclusively as a parasite of the species of Euphausia Dana, 1852; quite unexpectedly, this species was found as a parasite of Thysanopoda aequalis Hansen, 1905, thus expanding its known host range to a different euphausiid genus. We also report the finding of two specimens of Oculophryxus bicaulis Shields and Gómez-Gutiérrez, 1996, only known as a parasite of Stylocheiron G. O. Sars, 1883. Accordingly, O. bicaulis was observed on S. affine G. O. Sars, 1883 in the western Caribbean. The third isopod species herein reported is the rare Branchiophryxus koehleri Nierstrasz & Brender à Brandis, 1931. We found only one female individual of this species attached to S. longicorne. Members of this dajid genus have been recorded only a few times and this is the first record in the NWTA. We report a new host record at the genus level of Heterophryxus appendiculatus. Oculophryxus bicaulis was confirmed as a parasite of Stylocheiron species. The rare Branchiophryxus koehleri was first recorded for the NWTA region. We presume that some of these isopods indeed have a wide distribution in tropical and subtropical areas but tend to be overlooked in routine examination of zooplankton samples.

Submarine geomorphology, tectonic features and mass wasting processes in the archipelago of San Andres, Providencia and Santa Catalina (western Caribbean)

Recent acquisition of multibeam bathymetric data in western Caribbean allowed illuminating for the first time the submarine morphology of the Archipelago of San Andres, Providencia and Santa Catalina (ASAPSC), and surrounding areas. Our results show that the nine islands of the archipelago (San Andres, Providencia, Albuquerque, Este-Sureste, Roncador, Quitasueño, Serrana, Serranilla and Bajo Nuevo) correspond to the emerged portions of a belt of volcanic edifices extending along the ASAPSC seafloor. Overall, the submarine slopes are characterized by having steep flanks that extend to depths greater than −2000 m and are frequently cut by linear gullies and canyons. The submarine volcanic buildings are aligned in specific directions, parallel to the trends of the main fault systems in the area, indicating that the genesis and evolution of the archipelago have been strongly influenced by the interplay between volcanism and tectonics. Moreover, the presence of several pull-apart basins (Providencia, Albuquerque, Nutibara, Cunas and Guambiano depressions) related to S-shaped releasing bends in the Albuquerque-Providencia, Pedro and Serrana fault systems evidences that an intraplate transtensional tectonics is currently operating in this sector of the Caribbean plate. We propose that the ASAPSC belongs to the Northwestern Caribbean Volcanic Province (NCVP), which corresponds to a province made of an oceanic crust highly affected by volcanism sandwiched between a block composed of continental crust (Upper Nicaraguan Rise) and a block underlain by a CLIP-type to normal oceanic crust (Colombia Basin). Finally, the identification of massive debris avalanche deposits and large-scale bedforms shows that mass wasting processes have been common in the most recent history of the ASAPSC. This implies that collapses of the seamount flanks and the subsequent generation of tsunamis should be considered as a new threat to the coastal zones of the western Caribbean Sea.

Two species of Carcinonemertes Coe, 1902 (Nemertea: Carcinonemertidae) infesting the Caribbean spiny lobster, Panulirus argus (Latreille, 1804) (Decapoda: Achelata: Palinuridae), in Saint Kitts, West Indies

Abstract The Caribbean spiny lobster, Panulirus argus (Latreille, 1804), is an important resource in the Western Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. A nemertean egg predator of P. argus, Carcinonemertes conanobrieniSimpson, Ambrosio & Baeza, 2017, was recorded in Florida in 2017 and Colombia in 2018. This study sought to investigate the presence of C. conanobrieni in P. argus in Saint Kitts and Nevis, eastern Caribbean Sea. Nemerteans were observed in the brood masses of P. argus. Molecular techniques confirmed its presence in the P. argus population on Saint Kitts. Egg, juvenile, and adult stages of C. conanobrieni and of an undescribed Carcinonemertes sp. were found in the brood masses of 27 of 31 (87%) ovigerous P. argus. Differences in the shape of the nemertean egg masses (string versus spherical arrangement) were confirmed as two distinct species of Carcinonemertes Coe, 1902 using molecular analyses. The juvenile stage of the undescribed Carcinonemertes sp. was detected in the gills of 72 of 320 (23%) of the P. argus individuals from Saint Kitts. The prevalence of branchial nemertean infestation was not significantly different among male and female P. argus. Female lobsters with ovaries in early stages of gonadal maturation were more likely to have branchial nemerteans relative to those with ovaries in late stages of maturation, suggestive of nemertean migration from gills to egg mass once the host oviposits. This is the first report of C. conanobrieni in the Caribbean spiny lobster from the eastern Caribbean, which is approximately 1,300 miles from Florida and 1,000 miles from Colombia. This is also the first report of an undescribed nemertean worm in P. argus. The high prevalence of Carcinonemertes spp. in P. argus raises concern for the extent to which these egg predators may be impacting P. argus in Saint Kitts, an important fishery on the island.

Large-scale environmental controls on the seasonal statistics of rapidly intensifying North Atlantic tropical cyclones

This study is concerned with the connections between the large-scale environment and the seasonal occurrence of rapid intensification (RI) of North Atlantic tropical cyclones. Physically-motivated statistical analysis using observations and reanalysis products suggests that for tropical cyclones over the open tropical North Atlantic, the interannual variability of the probability of storms undergoing RI is influenced by seasonal large-scale atmospheric and oceanic variables, but not so for storms over the Gulf of Mexico and western Caribbean Sea. We suggest that this differentiated response is due to the former region exhibiting a strong negative correlation between the seasonal anomalies of vertical wind shear and potential intensity. Differences in the mean climatology and subseasonal variations of the large-scale environment in these regions appear to play an insignificant role in the distinctive seasonal environmental controls on RI. We suggest that the interannual correlation of vertical wind shear and potential intensity is an indicator of seasonal predictability of tropical cyclone activity (including RI) across the tropics .

Molecular phylogeography of Tumidotheres maculatus (Say, 1818) and Zaops ostreus (Say, 1817) (Crustacea: Decapoda: Pinnotheridae) in the western Atlantic, with description of a new species and synonymy of Epulotheres Manning, 1993

ABSTRACTThe commensal crab genus Tumidotheres is reportedly represented along the western Atlantic coast by Tumidotheres maculatus, with populations distributed from temperate to tropical waters in North and South America. Western Atlantic populations of the related genus Zaops have been alternatively separated into the northern species Zaops ostreus and southern Zaops geddesi. We hypothesized that populations of T. maculatus comprised more than one species, much as currently accepted in Zaops. Molecular markers (COI, 16S-NADH1 complex, 12S, and histone 3) were used to infer relationships between sampled populations of Tumidotheres and Zaops. We found that most populations of Tumidotheres belonged to a single species, but that specimens from the western Caribbean Sea represented an undescribed congener, herewith described and named. Remarkably, all sequenced populations of Zaops were inseparable, leading us to question the validity of Z. geddesi as the southern counterpart of Z. ostreus. Though sequence analyses failed, we provisionally reassign Epulotheres angelae to the genus Zaops on the basis of morphological characters. Since Epulotheres is a monotypic genus, this synonymizes the genus with Zaops.

Determining keystone species complexes and macroscopic properties for improving ecosystem‐based conservation practices in coral reefs along the western Caribbean Sea (Mexico and Honduras)

Abstract Coral ecosystems have been subjected to disturbances caused by humans that threaten their health and alter their structure and functioning. Trophic models were constructed in three coral reef ecosystems along the western Caribbean Sea (Mexico and Honduras) to evaluate the structure, organization, health, and species and functional groups that play keystone roles in these ecosystems. The quantification of the macroscopic properties showed that Media Luna Reef (Honduras) is a more mature, developed, organized, and healthy ecosystem but, in turn, is less resistant to perturbations. The outcomes showed that the ecological systems with reduced human disturbances were more mature and healthy. Likewise, the keystone species complexes contributed considerably to the maturity, development, and health of such coral ecosystems. Several exploited species were integrated into the keystone species complexes, which also would increase resistance against perturbations. These findings suggest that current fisheries management strategies could be improved within a network context to achieve the sustainable usage of resources and to include management programmes to conserve the current conditions of Media Luna Reef.

Late Cretaceous–Cenozoic sequence stratigraphic and paleogeographic controls on petroleum system elements of the Nicaraguan platform, western Caribbean Sea

Late Cretaceous–to–present-day mixed carbonate–clastic deposition along the Nicaraguan platform, western Caribbean Sea, has evolved from a tectonically controlled, rifted upper Eocene shallow–to–deep-marine carbonate–siliciclastic shelf to an upper Miocene–to–present-day tectonically stable shallow-marine carbonate platform and passive margin. By integrating subsurface data of 287 two-dimensional seismic lines and 27 wells, we interpret the Cenozoic stratigraphic sequence as 3 cycles of transgression and regression beginning with an upper Eocene rhodolitic–algal carbonate shelf that interfingered with marginal siliciclastic sediments derived from exposed areas of Central America bordering the margin to the west. During the middle Eocene, a carbonate platform was established with both rimmed reefs and isolated patch reefs. A late Eocene forced regression produced widespread erosion and subaerial exposure across much of the platform and was recorded by a regional unconformity. The Oligocene–upper Miocene sedimentary record includes a southeastward prograding delta of the proto-Coco river, which drained the emergent area of what is now northern Nicaragua. The late Miocene–to–present-day period marks a period of strong subsidence with the development of small pinnacle reefs. We describe favorable petroleum system elements of the Nicaraguan platform that include (1) Eocene fossiliferous limestone source rocks documented as thermally mature in vintage exploration wells and seen as active gas chimneys emanating from inferred carbonate reservoirs; (2) upper–to–middle Eocene reservoirs in patch and pinnacle reefs, middle Eocene calcareous slumps, and Oligocene fluvial-deltaic facies documented in wells; and (3) regional seal intervals that consist of both regional unconformities and Eocene–Oligocene intraformational shale.

Outer Continental Shelf Delimitation in the Western Caribbean Sea (Nicaragua v. Colombia II)

The controversy between Nicaragua and Colombia before the ICJ now concerns maritime delimitation beyond 200 nm. One of the main legal issues in this case is whether international law allows for delimitation to take place where alternative bases of continental shelf entitlement, namely, natural prolongation and distance, are opposed. As alleged by Nicaragua, its natural prolongation extends beyond 200 nm and overlaps with Colombia’s distance-based continental shelf entitlement. Nicaragua endorses the principle of equal division and accordingly, advocates for the viability of maritime delimitation. In Colombia’s view, the distance criterion has priority and trumps natural prolongation. In this work, the author analyses the legal discourse already voiced on the occasion of the dispute in the East China Sea, in order to identify instances of parallelism and symbiotic contribution with the question of the delimitation of the continental shelf beyond 200 nm in the Western Caribbean Sea.

On the Moisture Origins of Tornadic Thunderstorms

AbstractTornadic thunderstorms rely on the availability of sufficient low-level moisture, but the source regions of that moisture have not been explicitly demarcated. Using the NOAA Air Resources Laboratory HYSPLIT model and a Lagrangian-based diagnostic, moisture attribution was conducted to identify the moisture source regions of tornadic convection. This study reveals a seasonal cycle in the origins and advection patterns of water vapor contributing to winter and spring tornado-producing storms (1981–2017). The Gulf of Mexico is shown to be the predominant source of moisture during both winter and spring, making up more than 50% of all contributions. During winter, substantial moisture contributions for tornadic convection also emanate from the western Caribbean Sea (>19%) and North Atlantic Ocean (>12%). During late spring, land areas (e.g., soil and vegetation) of the contiguous United States (CONUS) play a more influential role (>24%). Moisture attribution was also conducted for nontornadic cases and tornado outbreaks. Findings show that moisture sources of nontornadic events are more proximal to the CONUS than moisture sources of tornado outbreaks. Oceanic influences on the water vapor content of air parcels were also explored to determine if they can increase the likelihood of an air mass attaining moisture that will eventually contribute to severe thunderstorms. Warmer sea surface temperatures were generally found to enhance evaporative fluxes of overlying air parcels. The influence of atmospheric features on synoptic-scale moisture advection was also analyzed; stronger extratropical cyclones and Great Plains low-level jet occurrences lead to increased meridional moisture flux.

Regional transect across the western Caribbean Sea based on integration of geologic, seismic reflection, gravity, and magnetic data

We analyze western Caribbean structural styles and depositional controls associated with Late Cretaceous–Cenozoic deformational events using a 1600-km (994-mi)-long, regional, northwest–southeast transect extending from the Cayman Trough in Honduras to northern Colombia. Different structural provinces defined along the transect include (1) the Cayman Trough and adjacent Honduran borderlands marking the North American–Caribbean transtensional plate boundary characterized by late Eocene–Holocene fault-controlled depocenters; (2) the Nicaraguan Rise that includes continental Paleocene–Eocene rocks deposited in sag basins, which are overlain by relatively undeformed Miocene–Holocene carbonate and clastic shelf deposits of the northern Nicaraguan Rise, following a Late Cretaceous convergent phase; (3) the Colombian Basin that includes thick Miocene clastic depocenters and the localized presence of Upper Cretaceous rocks overlying the basement and where much of the subsidence is likely isostatic and flexurally driven given its proximity to the subduction zone of northern Colombia; (4) the south Caribbean deformed belt, an active, accretionary prism produced by the subduction of the Caribbean large igneous province beneath the South American plate, which has deformed the Cenozoic prism and fore-arc section and produced thrust-fault–controlled accommodation space for upper Miocene–Holocene piggyback deposits; and (5) the onshore Cesar–Rancheria Basin in northern Colombia, which has recorded the uplift of its bounding mountain ranges, the Sierra de Santa Marta massif to the west and Perija Range to the east. Plate reconstructions place the various crustal provinces along the transect into the context of the Late Cretaceous–Cenozoic deformation events that can be partitioned into strike-slip, convergent, and extensional components.

Second-stage Caribbean Large Igneous Province volcanism: The depleted Icing on the enriched Cake

A long-standing question has been whether the Lower Nicaraguan Rise in the western Caribbean Sea represents thinned continental crust or is part of the Caribbean Large Igneous Province (CLIP). During the R/V Meteor cruise M81/2, the northeastern part of the Lower Nicaraguan Rise including the Hess Escarpment was extensively sampled. Only volcanic and carbonate rocks were recovered and no metamorphic rocks or rocks with continental crustal affinities, indicating that at least the uppermost basement is volcanic and belongs to a volcanic province, probably the CLIP. We provide a comprehensive geochemical dataset, including major and trace elements and Sr-Nd-Hf-Pb double spike isotope ratios, for the volcanic rocks. The basalts are geochemically subdivided into two groups: 1) depleted and 2) enriched. The majority belong to the depleted group with 6–9 wt% MgO and highly depleted incompatible element (e.g. (La/Yb)N = 0.15–0.76, (La/Sm)N = 0.21–0.65) compositions and depleted radiogenic isotope (e.g. εNdi = 8.9–11.0, εHfi = 13.6–16.5, 206Pb/204Pbi = 18.28–18.98) ratios. The subordinate enriched group basalts have 5–8 wt% MgO and were solely recovered from the lower part of the central Hess Escarpment. These rocks possess enriched incompatible element ((La/Sm)N = 1.15–1.60, (La/Yb)N = 1.40–2.57) and isotopic (εNdi = 7.52–8.34, εHfi = 12.6–12.9, 206Pb/204Pbi = 18.87–19.07) ratios resembling E-MORB. The depleted group is distinct from Pacific and Atlantic MORB based on combined 206Pb/204Pb, 143Nd/144Nd and 176Hf/177Hf data. It is similar, but not identical to the highly depleted Gorgona komatiites, thought to be generated during the CLIP event, and depleted Galápagos hotspot track lavas accreted to the Pacific margin of Central America. Ages of ~81 Ma from rocks drilled on the Hess Escarpment postdate the main CLIP phase (95-83 Ma), and indicate that at least the northeastern part of the Nicaraguan Rise formed during a later volcanic event. Lithospheric thinning after the main CLIP phase is suggested to have triggered upwelling of still anomalously hot, partially-melted or unmelted CLIP mantle material to form the younger depleted group of lavas. Our investigations imply that second-stage melting to generate depleted compositions during formation of oceanic large igneous provinces, as has been recently proposed for the Manihiki Plateau, is a more common process than originally thought.

Basin dependence of the MJO modulating tropical cyclone genesis

The modulation of tropical cyclone (TC) genesis over the western North Pacific (WNP) and the tropical North Atlantic (ATL) by the Madden–Julian Oscillation (MJO) is investigated based on observational analysis and numerical simulations. A genesis potential index (GPI) is used to investigate relative contributions of environmental parameters associated with the MJO to TC genesis. It is found that relative humidity plays the most important role in modulating TC genesis in the WNP, the Gulf of Mexico and the western Caribbean Sea (GOM), while vertical wind shear associated with the MJO has the most significant impact on TC activities in the eastern Atlantic (EAT). To further understand the relative importance of the MJO dynamic and thermodynamic impact on TC activities, idealized numerical model experiments are conducted using the Advanced Research version of the Weather Research and Forecasting model (WRF-ARW). The results are consistent with that of observational analysis, indicating that TC activities in the WNP, the GOM and the EAT are modulated by the MJO. Specific humidity anomalies related to the MJO exert the strongest impact on TC development in the WNP and the GOM, while the vertical wind shear is the most critical factor in the EAT.