Western Tropical North Research Articles

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.

Formation and Evolution of a Freshwater Plume in the Northwestern Tropical Atlantic in February 2020

AbstractIn February 2020, a 120‐km‐wide freshwater plume was documented by satellite and in situ observations near the Demerara Rise (7°N/54°W‐56°W). It was initially stratified in the upper 10 m with a freshwater content of 2–3 m of Amazon water distributed down to 40 m. On February 2nd, ship transects indicate an inhomogeneous shelf structure with a propagating front in its midst, whereas minimum salinity close to 30 pss was observed close to the shelf break on February 5th. The salinity minimum eroded in time but was still observed 13–16 days later with 33.3 pss minimum value up to 400 km from the shelf break. At this time, the mixed layer depth was close to 20 m. The off‐shelf flow lasted 10 days, contributing to a plume area extending over 100,000 km2 and associated with a 0.15 Sv (106 m3 s−1) freshwater transport. The off‐shelf plume was steered northward by a North Brazil Current ring up to 12°N and then extended westward toward the Caribbean Sea. Its occurrence followed 3 days of favorable wind direction closer to the Amazon estuary, which contributed to north‐westward freshwater transport on the shelf. Other such events of freshwater transport in January–March are documented since 2010 in salinity satellite products in 7 out of 10 years, and in 6 of those years, they were preceded by a change in wind direction between the Amazon estuary and the Guianas favoring the north‐westward freshwater transport toward the shelf break.

Interannual Variability of Tropical Atlantic-to-Pacific Moisture Transport Linked to ENSO, Atlantic Niño, and Freshwater Budget in the Northwestern Tropical Atlantic

AbstractMoisture transport from the Atlantic to Pacific is important for basin-scale freshwater budget and the formation of meridional ocean circulation. Although the climatological tropical Atlantic-to-Pacific moisture transport (TAPMORT) has been well investigated, few studies have focused on its variability. Here we investigate the interannual variability of TAPMORT based on the atmospheric reanalysis data sets. The TAPMORT interannual variability is dominated by the variations of trans-basin winds across Central America, and peaks in late boreal summer and late boreal winter. 1) In late summer, a developing El Niño and a mature Atlantic Niña set up an interbasin sea-surface temperature (SST) gradient that strengthens the low-level jet across Central America and therefore TAPMORT (with weakened TAPMORT for opposite signed events). This process typically occurs from July to September, with a peak in August. 2) In late winter, the strengthened southern North American center of the Pacific-North American-like pattern intensifies the TAPMORT variations. Although atmospheric interannual variability dominates these variations, extreme El Niño events are also important for the teleconnections. This process shows a single peak in February, in contrast to the persistent peak in late summer. We further demonstrate that the persistent TAPMORT variability in late summer dominates the moisture divergence over the northwestern tropical Atlantic and modulates freshwater flux there. Thus, our study improves the understanding of how TAPMORT interannual variability and the related interbasin SST gradient regulate the northwestern tropical Atlantic freshwater budget and the related salinity variability.

Equatorial Moisture Dynamics of the Quasi‐Biweekly Oscillation in the Tropical Northwestern Pacific During Boreal Summer

AbstractThe pronounced summertime quasi‐biweekly oscillation (QBWO) in the tropical northwestern Pacific usually originates from equatorial convective anomalies (ECAs) in the western Pacific. In this study, ECAs in relation to the QBWO are investigated in terms of the equatorial moisture dynamics. The results show that the development of ECAs is preconditioned by significant moisture anomalies associated with zonal moisture advection along the equator. Prior to initiation, an equatorially westward‐moving moisture precursor at a speed of approximately 5° longitude per day could be traced back to 140°W. A moisture budget analysis indicates that the successive westward movement of the moisture precursor is primarily due to the interaction between the zonal gradient of moisture anomalies and the mean easterly trade winds. The equatorial moisture dynamics likely maintain the quasi‐biweekly variability of ECAs regarding the QBWO in the tropical northwestern Pacific.

Role of the South China Sea in Southern China rainfall: meridional moisture flux transport

The South China Sea (SCS) serves as the main source of moisture for rainfall in Southern China (SC) and the meridional moisture transport to SC is dominated by wind changes during the first rainy season (April–June). El Niño-Southern Oscillation (ENSO) and Tropical Northwestern Pacific (TNWP) variability modulate the SC rainfall through anomalous anticyclonic circulation over the western North Pacific by strengthening the SCS meridional moisture transport to SC. However, our study indicates that the SCS is not only the intermediary in which ENSO or the TNWP affects the SC rainfall but also plays an independent role in the modulation of the SC rainfall. Notably, the SCS meridional moisture transport has a lower impact on the SC rainfall during the second rainy season (July–September), especially in July. At that time, the main cause of the SC rainfall is the southward moisture flux anomaly across its northern boundary with the anomalous cyclone over SC. This cyclone suppresses the moisture flux out of SC and leads to moisture convergence in SC. Moreover, we present a new concept by analyzing internal differences of moisture circulation during the second rainy season. Either strengthening the meridional moisture flux into SC across its southern boundary or suppressing the moisture flux out of SC across its northern boundary is important depending on whether or not the moisture from the SCS can converge in SC, which is mainly determined by the amplitude of moisture transport fluxes in SC.

The Annual Cycle of Air-Sea Fluxes in the Northwest Tropical Atlantic

In this article we analyze 11 years of near-surface meteorology using observations from an open-ocean surface mooring located in the Northwestern Tropical Atlantic (51°W, 15°N). Air-sea fluxes of heat, freshwater, and momentum are derived from these observations using the Coupled Ocean–Atmosphere Response Experiment (COARE) bulk parameterization. Using this dataset, we compute a climatology of the annual cycle of near-surface meteorological conditions and air-sea fluxes. These in situ data are then compared with three reanalyses: the National Centers for Environmental Prediction-Department of Energy [NCEP-DOE (hereafter referred to as NCEP-2)], the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim and the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) reanalyses. Products from the Clouds and the Earth’s Radiant Energy System (CERES) and the Tropical Rainfall Measuring Mission (TRMM) are also used for comparison. We identify the agreements and characterize the discrepancies in the annual cycles of meteorological variables and the different components of air-sea heat fluxes (latent, sensible, shortwave, and longwave radiation). Recomputing the reanalyses fluxes by applying the COARE algorithm to the reanalyses meteorological variables results in better agreement with the in situ fluxes than using the reanalyses fluxes directly. However, the radiative fluxes (longwave and shortwave) from some of the reanalyses show significant discrepancies when compared with the in situ measurements. Longwave radiation from MERRA-2 is biased high (too much oceanic heat loss), and NCEP-2 longwave does not correlate to in situ observations and other reanalyses. Shortwave radiation from NCEP-2 is biased low in winter and does not track the observed variability in summer. The discrepancies in radiative fluxes versus in situ fluxes are explored, and the potential regional implications are discussed using maps of satellite and reanalyses products, including radiation and cloud cover.

Hyperiid amphipod vertical distribution and community structure in the upper 100 m of the northwestern Caribbean Sea

The community structure and variability of the hyperiid amphipods of the Northwestern Tropical Atlantic (NWTA) remain largely unknown. We described and analyzed the hyperiid nictemeral, vertical, and horizontal distribution and the influence of environmental variables in the upper 100 m of the northwestern Caribbean Sea. We examined 196 zooplankton samples obtained during both day and nighttime at four depth strata from 49 sampling stations in January 2007. Up to 82 hyperiid species including 14 new regional records were identified and quantified. Both day/night and some interstrata differences were significant, particularly in reference to the uppermost and deepest strata. The local hyperiid community structure appeared to be profiled by the frequency and abundance variations of the two most abundant species, Lestrigonus bengalensis and Brachyscelus crusculum, both being most abundant in the uppermost (0–25 m) stratum. The horizontal distribution of the highest hyperiid abundance and diversity appears to be related to the influence of mesoscale processes like upwelling and cyclonic eddies. The Gulf of Honduras area had relatively low hyperiid abundances. The principal component analysis revealed density and temperature as the main factors explaining the local environmental variability. The canonical analysis of principal coordinates (CAP) showed that salinity and temperature strongly influenced the variability of the local hyperiid community. Overall, the two middle vertical strata (25–75 m) were relatively uniform; the main differences were found only between the uppermost and deepest strata. This study is the first to provide information regarding small-scale vertical distribution of hyperiid amphipods in the NWTA.

Effects of perturbation type on tropical cyclone size over tropical North Western Pacific and Atlantic

In authors’ previous studies, the role of distinctive mean states in the western North Pacific (WNP) and North Atlantic (NA) in affecting tropical cyclone (TC) size was investigated. In this study, the effect of different synoptic scale perturbation types in the two basins on TC size is further investigated. Numerical model experiments with an initial synoptic wave train (SWT) and easterly wave (EW) environmental condition show that the former (latter) leads to the development of a larger (smaller) TC at an equilibrium state. The physical mechanism responsible for the difference is revealed. Compared with the EW, the surface wind speed of the SWT is larger. Therefore, the SWT generates more moisture in the outer region than EW through surface evaporation process. This favors the development of stronger convection in the outer region. The enhanced convection leads to greater diabatic heating, which lower the local sea level pressure (SLP), which changes surface radial pressure gradients in the inner-core and outer-core of the vortex. On the one hand, the falling of the SLP decreases the surface radial pressure gradient in the inner-core. As a result, the radial wind is weakened and then the radius of maximum wind (RMW) extends outwards after initial contraction. On the other hand, the lower SLP increases the radial pressure gradient in the outer region, strengthening the radial wind outside. The wind convergence favors stronger development of convection in the outer region. Through this positive feedback, inflow in the outer region is further strengthened. This accelerates local tangential wind and thus enlarges the TC size.

Impact of Assimilation of Moored Velocity Data on Low‐Frequency Current Estimation in Northwestern Tropical Pacific

AbstractThis study investigates the impact of assimilation of Northwestern Tropical Pacific Ocean (NWTPO) moored currents observation system on low‐frequency (over a period of more than 90 days) current estimation. A low‐frequency scale‐selective ensemble optimal interpolation (EnOI) scheme is designed to assimilate the horizontally sparse moored currents into an eddy‐permitting ocean model. In this assimilation scheme, low‐frequency current signals are selected by removing intraseasonal signals in both observation and ensemble data, and a horizontal spatial filter is implemented to match the model forecast to the low‐frequency ensemble and observation. The assimilation of currents efficiently resolves simulated low‐frequency current displacements, especially for the Equatorial Undercurrent (EUC), the North Equatorial Countercurrent (NECC), and the North Equatorial Current (NEC). More realistic intensities of the NWTPO low‐frequency currents are also reproduced. With respect to the moored velocity profiles, the root‐mean‐square error (RMSE) of the simulated low‐frequency zonal velocity above a 500‐m depth is reduced from 10.9 to 5.8 cm/s using this low‐frequency EnOI scheme. The low‐frequency variation of NWTPO currents is reproduced by correcting the structures of different baroclinic modes. The increments of zonal velocities mainly correspond to the first baroclinic mode for the NECC and NEC, while for the EUC, they correspond to the leading three and higher‐order baroclinic modes. The improvements of the simulated stratification and pressure gradient remark the role of the assimilation of moored currents in adjusting available potential energy.

Moisture sources associated with heavy rainfall over the Limpopo River Basin, southern Africa

Moisture sources and pathways over the Limpopo River Basin (LRB) in southern Africa were identified using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model applied to NCEP II (2.5° × 2.5°) reanalysis data for 1981–2016. The 10-day air parcel backward trajectories were produced for the extended wet season (October–April) as well as the early and late summer. Analysis of a 36-year climatology of air parcel trajectories indicated seven moisture source regions for the LRB; namely, local continental, tropical southeast Atlantic Ocean, midlatitude South Atlantic Ocean, tropical northwest Indian Ocean, tropical southwest Indian Ocean, subtropical southwest Indian Ocean, and the Agulhas Current. The results have shown that important differences in moisture source regions and pathways exist between early (October–December) and late (January–April) summers, with the tropical northwestern Indian Ocean and the northern Agulhas Current sources more prominent during JFMA than OND. On interannual time scales, there are notable differences in moisture source regions between anomalously wet and dry summers, with the South Indian Ocean moisture contribution and transport over the LRB smaller during dry summers than wet summers. Changes in specific humidity for trajectory linked to heavy daily rainfall events (defined from CHIRPS data) showed that subtropical South Indian Ocean source is more extensive for the heavy rainfall than for the moderate case. Generally, moisture source regions and transport pathways for LRB tend to be influenced by both the regional summer season circulation and the synoptic setting.

Host plant affiliations of aphid vector species found in a remote tropical environment

The Ord River Irrigation Area (ORIA) produces annual crops during the dry season (April to October), and perennial crops all-year-round, and is located in tropical northwestern Australia. Sandalwood plantations cover 50 % of the ORIA’s cropping area. Aphids cause major crop losses through transmission of viruses causing debilitating diseases and direct feeding damage. During 2016–2017, in both dry and wet seasons a total of 3320 leaf samples were collected from diverse types of sites on cultivated and uncultivated land and 1248 (38 %) of them were from aphid-colonized plants. In addition, aphids were found at 236 of 355 sampling sites. The 62 plant species sampled came from 23 families 19 of which contained aphid-colonized species. Aphid hosts included introduced weeds, Australian native plants, and volunteer or planted crop plants. Six aphid species were identified by light microscopy and CO1 gene sequencing, but there was no within species nucleotide sequence diversity. Aphis nerii, Hysteroneura setariae, Rhopalosiphum maidis and Schoutedenia ralumensis each colonized 1–3 plant species from a single plant family. A. craccivora colonized 14 species in five plant families. A. gossypii was the most polyphagous species colonizing 19 species in 11 plant families. A. gossypii, A. craccivora, A. nerii and S. ralumensis were found in both wet and dry seasons. Because of A. craccivora’s prevalence and high incidences on understory weeds and host trees, sandalwood plantations were important reservoirs for aphid spread to wild and crop plant hosts growing in cultivated and uncultivated land. Alternative hosts growing in rural bushland, irrigation channel banks, vacant or fallow land, and orchard plantation understories also constituted significant aphid reservoirs. This study provides new knowledge of the ecology of aphid vector species not only in the ORIA but also in tropical northern Australia generally. It represents one of relatively few investigations on aphid ecology in tropical environments worldwide.

Recent changes in the precipitation-driving processes over the southern tropical Andes/western Amazon

Analyzing December–February (DJF) precipitation in the southern tropical Andes—STA ($$12^{\circ }\,\hbox {S}$$–$$20^{\circ }\,\hbox {S}$$; > 3000 m.a.s.l) allows revisiting regional atmospheric circulation features accounting for its interannual variability over the past 35 years (1982–2018). In a region where in-situ rainfall stations are sparse, the CHIRPS precipitation product is used to identify the first mode of interannual DJF precipitation variability (PC1-Andes). A network of 98 rain-gauge stations further allows verifying that PC1-Andes properly represents the spatio-temporal rainfall distribution over the region; in particular a significant increase in DJF precipitation over the period of study is evident in both in-situ data and PC1-Andes. Using the ERA-Interim data set, we found that aside from the well-known relationship between precipitation and upper-level easterlies over the STA, PC1-Andes is also associated with upward motion over the western Amazon (WA), a link that has not been reported before. The ascent over the WA is a component of the meridional circulation between the tropical North Atlantic and western tropical South America—WTSA ($$80^{\circ }\,\hbox {W}$$–$$60^{\circ }\,\hbox {W}$$; $$35^{\circ }\,\hbox {S}$$–$$10^{\circ }\,\hbox {N}$$). Indeed, the precipitation increase over the last 2 decades is concomitant with the strengthening of this meridional circulation. An intensified upward motion over the WA has moistened the mid-troposphere over WTSA, and as a consequence, a decreased atmospheric stability between the mid- and the upper troposphere is observed over this region, including the STA. We further show that, over the last 15 years or so, the year-to-year variability of STA precipitation (periodicity < 8 years) has been significantly associated with upward motion over the WA, while upper-level easterlies are no longer significantly correlated with precipitation. These observations suggests that the STA have experienced a transition from a dry to a wet state in association with a change in the dominant mode of atmospheric circulation. In the former dominant state, zonal advection of momentum and moisture from the central Amazon, associated with upper-level easterlies, is necessary to develop convection over the STA. Since the beginning of the 21st century, DJF precipitation over the STA seems to respond directly and primarily to upward motion over the WA. Beyond improving our understanding of the factors influencing STA precipitation nowadays, these results point to the need of exploring their possible implications for the long-term evolution of precipitation in a context of global warming.

Four times more species of sea spiders (Arthropoda: Pycnogonida) in Martinique Island (Lesser Antilles)

The marine biodiversity of the tropical northwestern Atlantic (TNWA) has been explored by many great naturalist expeditions. After more than one century of marine exploration, how well do we know its biodiversity? As a poorly studied taxon, sea spiders (Arthropoda: Pycnogonida Latreille, 1810) are excellent candidates to address this issue. Here, we report the results from the Madibenthos Survey conducted by the Museum national d’Histoire naturelle (Paris) on the coasts of Martinique during Fall 2016, where sea spiders were collected during 138 sampling events by different methods. A total of 67 pycnogonid species, including 13 species probably new to science, were distinguished during this survey, whereas only 20 species were previously known from Martinique. Relying on an extensive and intensive sampling, the collection of pycnogonids from the Madibenthos Survey is one of the richest for TNWA. DNA barcoding based on 172 new CO1 sequences helped to discriminate species with inconspicuous diagnostic characters and pointed out 11 additional possible cryptic species. Richness estimators and species rarity indicate that the diversity of Martinique still remains underestimated. Results suggest that Martinique is not a hot spot for sea spiders and that similar levels of biodiversity might be expected in most other islands of the TNWA if similar sampling methods were applied. Finally, we show that the Caribbean and Atlantic coasts of Martinique harbor different sea spider faunas.

Interannual Anomaly in Tropical Cyclone Frequency Around Korea by Western North Pacific Monsoon

ABSTRACT In this study, the correlation between the frequency of summer tropical cyclones (TC) affecting areas around Korea over the last 37 years and the western North Pacific monsoon index (WNPMI) was analyzed. A clear positive correlation existed between the two variables, and this high positive correlation remained unchanged even when excluding El Nino-Southern Oscillation (ENSO) years. To investigate the causes of the positive correlation between these two variables, ENSO years were excluded, after which the 8 years with the highest WNPMI (strong WNPM phase) and the 8 years with the lowest WNPMI (weak WNPM phase) were selected, and the average difference between the two phases was analyzed. In the strong WNPM phase, TCs usually occurred in the eastern waters of the tropical and subtropical western North Pacific, and tended to pass the East China Sea on their way north toward Korea and Japan. In the weak WNPM phase, TCs usually occurred in the western waters of the tropical and subtropical western North Pacific, and tended to pass the South China Sea on their way west toward the southeastern Chinese coast and the Indochina peninsula. Therefore, TC intensity was higher in the strong WNPM phase, during which TCs are able to gain sufficient energy from the sea while moving a long distance to areas nearby Korea. TCs also tended to occur more often in the strong WNPM phase. In the difference between the two phases regarding 850 hPa and 500 hPa streamline, anomalous cyclones were reinforced in the tropical and subtropical western North Pacific, while anomalous anticyclones were reinforced in mid-latitude East Asian areas. Due to these two anomalous pressure systems, anomalous southeasterlies developed in areas near Korea, with these anomalous southeasterlies playing the role of anomalous steering flows making the TCs head toward areas near Korea. Also, due to the anomalous cyclones developed in the tropical and subtropical western North Pacific, more TCs could occur in the strong WNPM phase.

Eulimids (Gastropoda, Eulimidae) on the Sea Cucumber Holothuria mexicana (Ludwig, 1875) (Holothuroidea, Holothuriidae) in Belize

This study presents new records for 4 eulimid species (Gastropoda, Eulimidae) including Melanella eburnea (Megerle von Mühlfeld, 1824), Melanella hypsela (Verrill &amp; Bush, 1900), Melanella sp., and Eulimostraca encalada Espinosa, Ortea &amp; Magaña, 2006 found on the body wall of the sea cucumber Holothuria mexicana in Belize. Three of these records (M. hypsela, M. eburnea, and E. encalada) represent a first for the Western Caribbean ecoregion and close a distributional gap for these species in the Caribbean. The geographic distribution of M. eburnea is thereby expanded by ~800 km; M. hypsela by ~1,200 km and E. encalada by ~970 km in the Tropical Northwestern Atlantic province. This article presents for the first time H. mexicana as a new host record for E. encalada.

Tropical Cyclone Projections: Changing Climate Threats for Pacific Island Defense Installations

Abstract Potential changing climate threats in the tropical and subtropical North Pacific Ocean were assessed, using coupled ocean–atmosphere and atmosphere-only general circulation models, to explore their response to projected increasing greenhouse gas emissions. Tropical cyclone occurrence, described by frequency and intensity, near islands housing major U.S. defense installations was the primary focus. Four island regions—Guam and Kwajalein Atoll in the tropical northwestern Pacific, Okinawa in the subtropical northwestern Pacific, and Oahu in the tropical north-central Pacific—were considered, as they provide unique climate and geographical characteristics that either enhance or reduce the tropical cyclone risk. Guam experiences the most frequent and severe tropical cyclones, which often originate as weak systems close to the equator near Kwajalein and sometimes track far enough north to affect Okinawa, whereas intense storms are the least frequent around Oahu. From assessments of models that simulate well the tropical Pacific climate, it was determined that, with a projected warming climate, the number of tropical cyclones is likely to decrease for Guam and Kwajalein but remain about the same near Okinawa and Oahu; however, the maximum intensity of the strongest storms may increase in most regions. The likelihood of fewer but stronger storms will necessitate new localized assessments of the risk and vulnerabilities to tropical cyclones in the North Pacific.

Subsurface structure and variability of the zonal currents in the Northwestern Tropical Pacific Ocean

Seven subsurface moorings were deployed between 0°N and 7.5°N at 142°E in the western Pacific during August 2014–October 2015, obtaining unprecedented high-quality measurements of the North Equatorial Countercurrent (NECC) between 60 and 200 m and the underlying Northern Subsurface Countercurrent (NSCC) and North Equatorial Subsurface Current (NESC) between 300 and 600 m. During the observation period, the eastward-flowing NSCC showed a mean velocity of 5–15 cm s−1 between 2°N and 4°N, while the NESC manifested as intermittent westward currents of < 5 cm s−1 between 4°N and 6°N. Temporal variabilities in the NSCC and NESC are documented for the first time. Both the NSCC and NESC were strengthened when the NECC shifted to the south in boreal fall. The 2015–2016 El Niño induced significant strengthening of the NECC and weakening of the NESC. Further analysis combining ocean reanalysis data suggests that seasonal variations are likely coherent between the upper and lower (300–600 m) layers and associated with the meridional migration of the NECC. Seasonal variations of the three currents are likely first-mode baroclinic Rossby wave responses to basin-wide wind forcing. By contrast, interannual variations of the NSCC and NESC have more complicated vertical structure. El Niño events generally cause the strengthening and southward migration of the NECC and the weakening of the NESC. Ocean reanalysis products however show difficulties in realistically representing the observed subsurface structure and variability of the three currents, remarking the necessity of enhancing ocean in-situ observation systems.

Shark and ray diversity in the Tropical America (Neotropics)-an examination of environmental and historical factors affecting diversity.

We present the first comprehensive review of the present and past shark and ray diversity in marine waters of Tropical America, examining the patterns of distribution in the Eastern Central Pacific (EP) and Western Central Atlantic (WA) realms. We identified the major regions of diversity and of endemism, and explored the relations to physical variables. We found a strong relationship between shark and ray diversity with area and coastal length of each province. The Tropical Northwestern Atlantic Province is characterized by high diversity and greater occurrence of endemic species, suggesting this province as the hotspot of sharks and rays in Tropical America. The historical background for the current biogeography is explored and analyzed. Referential data from 67 geological units in 17 countries, from both shallow and deep-water habitats, across five time-clusters from the Miocene to the Pleistocene were studied. New data include 20 new assemblages from six countries. The most diverse Neogene and extant groups of shark and ray are Carcharhiniformes and Myliobatiformes, respectively. The differentiation between Pacific and Atlantic faunas goes to at least the middle Miocene, probably related with the increasing closure of the Central American Seaway acting as a barrier. The highest faunal similarity between the assemblages from the EP and the WA at the early Miocene could be related to the lack of a barrier back then, but increased sampling is needed to substantiate this hypothesis.

Targeted observation analysis of a Northwestern Tropical Pacific Ocean mooring array using an ensemble-based method

An important supplement for ocean observing systems, the Northwestern Tropical Pacific Ocean (NWTPO) mooring array including 15 moorings equipped with Acoustic Doppler Current Profilers (ADCP) devices was developed by the Chinese Academy of Sciences and deployed in 2013. This study assessed the performance of this mooring array in monitoring the intra-seasonal and low-frequency (above 91 days) variability of oceanic currents by conducting targeted observation analyses using an ensemble-based method. Key regions for monitoring intra-seasonal variability of the NWTPO circulation are the equator, Indonesian throughflow (ITF), headstream of the North Equatorial Countercurrent (NECC), and Subtropical Countercurrent (STCC). For monitoring intra-seasonal variability, the range of each mooring is confined to a local scale. Therefore, NWTPO moorings cannot adequately resolve intra-seasonal variability in areas of the ITF, the headstream of the NECC, and STCC due to location constraints of the moorings. For monitoring low-frequency variability of NWTPO circulation, the key regions are the Western Boundary Current (WBC), NECC, and the Equatorial Undercurrent (EUC). NWTPO moorings performed relatively well in monitoring the low-frequency variability, as indicated by the strong background correlations between each of the currents. The NWTPO mooring array plays an important role in monitoring the location and intensity of background currents. Because moorings are costly and require a high-density distribution for optimal performance, understanding the multi-timescale dynamical nature of the NWTPO current system is critical for the deploying future moorings in this region.

Notes on Halicyclops (Copepoda, Cyclopoida, Cyclopidae) from Colombia and the western Caribbean: a new record with a key to species of Group “B” sensu Rocha (1991)

Three species of brackish waters microcrustaceans are herein recorded; they belong to the cyclopoid copepod genus Halicyclops and were collected from a coastal system in northern Colombia: H. exiguus Kiefer, 1934, H. venezuelaensis Lindberg, 1954, and H. hurlberti Rocha, 1991. The former has intraspecific variations that deserve further study. The finding of the latter species, previously known from the Eastern Tropical Pacific, represents a new record for Colombia and the Caribbean Sea Basin in the Northwestern Tropical Atlantic. With the finding of H. hurlberti the number of species of Halicyclops known from the Neotropical region and Colombia increases to 20 and 5, respectively. The regional diversity of the genus is probably underestimated. A key to species of the genus belonging to group “B” sensu Rocha (1991) is also provided.