Eastern Tropical Pacific Ocean Research Articles

The connection of the Costa Rica Coastal Current with the West Mexican Current in the Gulf of Tehuantepec

The interconnections of some ocean currents in the Eastern Tropical Pacific are still a mystery to the scientific community. In the Mexican Pacific, the West Mexican Current (WMC) and the Costa Rica Coastal Current (CRCC) are two flows that are typically considered independent; however, some evidence of a subsurface connection when the Tehuantepec Bowl (TB) moves westward suggests otherwise. With the Hybrid Coordinated Ocean Model (HYCOM), we obtained a 19 years-run in a domain encompassing the Eastern Tropical Pacific Ocean. The numerical results were validated qualitatively and quantitatively by comparing them with remote and direct observations. We found a generally good agreement between the model results and those observations. To analyze the model results, we defined four transects perpendicularly to the coast, and surface and subsurface layers; in the long-term mean, the CRCC is disconnected from the WMC, in both layers. However, during the seasonal cycle, we found a close relationship between the general structures in thermocline topography and surface and subsurface large-scale circulation. The model results confirmed that the interconnection between the CRCC and the WMC depends on the dynamics of the TB, that on its seasonal migration moves westward, allowing the CRCC to travel along the coast further west than the Gulf of Tehuantepec (GT) and to connect with the WMC during spring at a subsurface level below the thermocline.

Adaptive spatiotemporal management to reduce shark bycatch in tuna fisheries.

Purse-seine tropical tuna fishing in the eastern tropical Pacific Ocean (EPO) results in the bycatch of several sensitive species groups, including elasmobranchs. Effective ecosystem management balances conservation and resource use and requires considering trade-offs and synergies. Seasonal and adaptive spatial measures can reduce fisheries impacts on nontarget species while maintaining or increasing target catches. Identifying persistently high-risk areas in the open ocean, where dynamic environmental conditions drive changes in species' distributions, is essential for exploring the impact of fisheries closures. We used fisheries observer data collected from 1995 to 2021 to explore the spatiotemporal persistence of areas of high bycatch risk for 2 species of oceanic sharks, silky shark (Carcharhinus falciformis) and oceanic whitetip shark (Carcharhinus longimanus), and of low tuna catch rates. We analyzed data collected by fisheries scientific observers onboard approximately 200 large purse-seine vessels operating in the EPO under 10 different flags. Fishing effort, catch, and bycatch data were aggregated spatially and temporally at 1°×1° cells and monthly, respectively. When areas of high fishing inefficiency were closed the entire study period and effort was reallocated proportionally to reflect historical effort patterns, yearly tuna catch appeared to increase by 1-11%, whereas bycatch of silky and oceanic whitetip sharks decreased by 10-19% and 9%, respectively. Prior to fishing effort redistribution, bycatch reductions accrued to 21-41% and 14% for silky and oceanic whitetip sharks, respectively. Our results are consistent with previous findings and demonstrate the high potential for reducing elasmobranch bycatch in the EPO without compromising catch rates of target tuna species. They also highlight the need to consider new dynamic and adaptive management measures to more efficiently fulfill conservation and sustainability objectives for exploited resources in the EPO.

Interannual Fluctuations and Their Low-Frequency Modulation of Summertime Heavy Daily Rainfall Potential in Western Japan

Heavy rainfall under the conditions of the changing climate has recently garnered considerable attention. The statistics on heavy daily rainfall offer vital information for assessing present and future extreme events and for clarifying the impacts of global climate variability and change, working to form a favorable background. By analyzing a set of large-ensemble simulations using a global atmospheric model, this study demonstrated that two different physical processes in global climate variability control the interannual fluctuations in the 99th- and 90th-percentile values of summertime daily rainfall (i.e., the potential amounts) on Kyushu Island in western Japan. The 90th-percentile values were closely related to large-scale horizontal moisture transport anomalies due to changes in the subtropical high in the northwestern Pacific, which was usually accompanied by basin-scale warming in the Indian Ocean subsequent to the wintertime El Niño events. The contributions of the sea surface temperatures over the northern Indian Ocean and the eastern tropical Pacific Ocean showed low-frequency modulations, mainly due to the influences of the global warming tendency and the interdecadal variability in the climate system, respectively. In contrast, tropical cyclone activity played a major role in changing the 99th-percentile value. The potentials of both the tropical cyclone intensity and the existence density fluctuated, largely owing to the summertime sea surface temperature over the tropical Pacific, which can be modulated by the El Niño diversity on interdecadal timescales.

Unique Temperature Trend Pattern Associated With Internally Driven Global Cooling and Arctic Warming During 1980–2022

AbstractDiagnosing the role of internal variability over recent decades is critically important for both model validation and projections of future warming. Recent research suggests that for 1980–2022 internal variability manifested as Global Cooling and Arctic Warming (i‐GCAW), leading to enhanced Arctic Amplification (AA), and suppressed global warming over this period. Here we show that such an i‐GCAW is rare in CMIP6 large ensembles, but simulations that do produce similar i‐GCAW exhibit a unique and robust internally driven global surface air temperature (SAT) trend pattern. This unique SAT trend pattern features enhanced warming in the Barents and Kara Sea and cooling in the Tropical Eastern Pacific and Southern Ocean. Given that these features are imprinted in the observed record over recent decades, this work suggests that internal variability makes a crucial contribution to the discrepancy between observations and model‐simulated forced SAT trend patterns.

First record of the deep-sea anglerfish Ceratias uranoscopus Murray, 1877 (Lophiiformes, Ceratiidae) from the Tropical Eastern Pacific Ocean

n 1973, a specimen of the deep‑sea anglerfish Ceratias uranoscopus Murray, 1877 was collected at a depth of 1000 m off the Pacific coast of Panama. This specimen represents (1) the first verified occurrence record of this species and genus in the Tropical Eastern Pacific Ocean and (2) an extension of about 7000 km east on this species’ previously known distribution. In this contribution, we provide and discuss unpublished and comparative morphometric, meristic, and occurrence data, corroborating the identity of the specimen and species and validating the new geographic range.

Climate projections of oceanographic variables in the Exclusive Economic Zone of Ecuador: A 21st century perspective to inform impact and adaptation assessment

Climate projections of ocean variables are essential to inform adaptation strategies and plans involving open and coastal oceanic regions. Assessment of baseline and projections of sea surface temperature (SST), pH, dissolved oxygen (DO), mean sea level (MSL), waves coastal flooding within Ecuador’s Exclusive Economic Zone, including Galapagos Islands are reported herein. With different magnitudes of change, both near-future (2021–2050) and far-future projections (2051–2080) show a statistically robust increase in SST, MSL rise and a reduction in pH, a proxy for acidification. In contrast, DO decrease is only observed in surface (0–100 m) but not in subsurface waters (100–400 m). The likelihood of extreme sea level events in the coastal cities of La Libertad, Manta and Esmeraldas would remain almost unchanged for near-future projections (2026–2045) whereas, for end-of-century projections (2081–2100), historical 1 in a 100-year extreme flooding events would become yearly occurrences. The generated data product offers a state-of-the-art research and management tool for the 21st century under the combined stressors of global climate change. Since the eastern Tropical Pacific Ocean is one of the most productive and biodiverse worldwide due to the equatorial upwelling system, possible impacts on marine biodiversity, social, and economic systems are discussed.

Environmental drivers of species richness in shallow-water gorgonians (Cnidaria: Anthozoa) from the Eastern Tropical Pacific Ocean

Environmental drivers of species richness in shallow-water gorgonians (Cnidaria: Anthozoa) from the Eastern Tropical Pacific Ocean

Latitudinal diversity of planktonic copepods in the Eastern Pacific: overcoming sampling biases and predicting patterns

Gradients of latitudinal diversity are one of the biogeographic features calling the most attention in ecology and macroecology. However, in pelagic communities of the marine environment, geographic trends and patterns are poorly known. We evaluated the latitudinal variation in species richness of marine planktonic copepods in the Eastern Pacific using spatial statistical models and approaches that mitigate and account for biases in occurrence data. A Boosted Regression Tree (BRT) and regression-Kriging based models allowed us to estimate and predict alpha diversity in poorly sampled regions, whereas beta diversity patterns were assessed using generalized dissimilarity analysis (GDM). Species richness showed a bimodal pattern, with a maximum of 291 species in the Northern Hemisphere and Tropical Eastern Pacific Ocean. Particulate Organic Carbon, salinity (max), spatial autocovariate, range of salinity and temperature, and Mixed Layer Depth, explained 85.2% of the latitudinal variability of copepods. Beta diversity was structured into four macrozones associated with the main water masses of the North and South Pacific.Our analytical approaches can overcome the limitations of data gaps, predicting greater diversity in subtropical and coastal areas, while providing insights into key drivers modulating spatial diversity patterns.

Age and growth of the crocodile shark, Pseudocarcharias kamoharai, in the Eastern Tropical Pacific Ocean

ABSTRACT The age, growth, and longevity parameters of crocodile shark, Pseudocarcharias kamoharai, from Santa Rosa, Ecuador were estimated. A number of 328 organisms were analyzed, 158 females (69 to 117 cm total length, TL) and 170 males (72.5 to 110 cm TL). The relationship between the vertebra's radius and TL was moderate (r2 = 0.63), indicating a relation between structure growth and the organism's size. Females were four to 14 years old and males were four to 12 years. The multimodal approach determined that the suitable equations were: The Von Bertalanffy growth function model with a fixed L0 (45.5 cm TL), VBGM2P (L∞ = 118.4 cm cm TL, k = 0.15) for combined sexes with a weight of evidence (Wi) to its favour of 43.9%; logistic growth model (L∞ = 109.5 cm TL, k = 0.41, L0 = 33.1 cm TL) for females with Wi = 28.4% and VBGM2P (L∞ = 110.4 cm TL, k = 0.16) for males with a Wi = 39.4%. No model obtained a sufficient evidence to be declared the best adjusted. The calculated longevities were 18 years for combined sexes, 16 for females, and 14 for males.

Application of a seismic network to baleen whale call detection and localization in the Panama basin-a Bryde's whale example.

Baleen whales use sounds of various characteristics for different tasks and interactions. This study focuses on recordings from the Costa Rica Rift, in the Eastern Tropical Pacific Ocean, made by 25 ocean-bottom seismographs and a vertical array of 12 hydrophones between January and February 2015. The whale calls observed are of two kinds: more commonly, repetitive 4-5 s-long signals separated into two frequency bands centered at ∼20 and ∼36 Hz; less commonly, a series of ∼0.5 to 1.0 s-long, lower amplitude signals with frequencies between 80 and 160 Hz. These characteristics are similar to calls attributed to Bryde's whales which are occasionally sighted in this region. In this study, the repetitive calls are detected using both the short-term average/long-term average approach and a network empirical subspace detector. In total, 188 and 1891 calls are obtained for each method, demonstrating the value of the subspace detector for highly similar signals. These signals are first localized using a non-linear grid search algorithm and then further relocalized using the double-difference technique. The high-resolution localizations reveal the presence of at least seven whales during the recording period, often crossing the instrument network from southwest to northeast.

Halichoeres sanchezi n. sp., a new wrasse from the Revillagigedo Archipelago of Mexico, tropical eastern Pacific Ocean (Teleostei: Labridae).

A new labrid fish species, Halichoeres sanchezi n. sp., is described from eight specimens collected in the Revillagigedo Archipelago in the tropical eastern Pacific Ocean, off the coast of Mexico. The new species belongs to the Halichoeres melanotis species complex that is found throughout the region, differing by 2.4% in the mtDNA cytochrome c oxidase I sequence from its nearest relative, H. melanotis from Panama, and 2.9% from Halichoeres salmofasciatus from Cocos Island, off Costa Rica. The complex is distinguished from others in the region by having a black spot on the opercular flap and a prominent black area on the caudal fin of males. The juveniles and initial phase of the new species closely resemble those of H. salmofasciatus and Halichoeres malpelo from Malpelo Island of Colombia, differing in having an oblong black spot with a yellow dorsal margin on the mid-dorsal fin of initial-phase adults as well as on juveniles. In contrast, the terminal-phase male color pattern is distinct from other relatives, being vermilion to orangish brown with dark scale outlines, a white patch on the upper abdomen, and a prominent black band covering the posterior caudal peduncle and base of the caudal fin. The new species adds to the list of endemic fish species for the isolated archipelago and is an interesting case of island endemism in the region. The discovery was made during the joint 2022 collecting expedition to the archipelago, which featured a pioneering collaborative approach to an inventory of an island ichthyofauna, specifically including expert underwater photographers systematically documenting specimens in situ, before hand-collection, and then photographed fresh, tissue-sampled, and subsequently vouchered in museum collections.

Extreme fire weather in Chile driven by climate change and El Niño–Southern Oscillation (ENSO)

A string of fierce fires broke out in Chile in the austral summer 2023, just six years after the record-breaking 2017 fire season. Favored by extreme weather conditions, fire activity has dramatically risen in recent years in this Andean country. A total of 1.7 million ha. burned during the last decade, tripling figures of the prior decade. Six of the seven most destructive fire seasons on record occurred since 2014. Here, we analyze the progression during the last two decades of the weather conditions associated with increased fire risk in Central Chile (30°–39° S). Fire weather conditions (including high temperatures, low humidity, dryness, and strong winds) increase the potential for wildfires, once ignited, to rapidly spread. We show that the concurrence of El Niño and climate-fueled droughts and heatwaves boost the local fire risk and have decisively contributed to the intense fire activity recently seen in Central Chile. Our results also suggest that the tropical eastern Pacific Ocean variability modulates the seasonal fire weather in the country, driving in turn the interannual fire activity. The signature of the warm anomalies in the Niño 1 + 2 region (0°–10° S, 90° W–80° W) is apparent on the burned area records seen in Central Chile in 2017 and 2023.

Evolution of ocean circulation and water masses in the Guaymas Basin (Gulf of California) during the last 31,000 years revealed by radiolarians and silicoflagellates in IODP expedition 385 sediment cores

The high-resolution analysis of radiolarians and silicoflagellates in sediments from Holes U1545A and U1549A drilled during IODP Expedition 385 in the Guaymas Basin, in the Gulf of California provides detailed insights into the evolution of ocean circulation and water masses, and its relation to Eastern Tropical Pacific Ocean climate conditions, over the past 31,000 cal years BP (based on AMS radiocarbon dates). In the pre-Last Glacial Maximum, the Guaymas Basin experienced alternating circulation patterns of California Current Water (CCW) and Gulf of California Water (GCW), with an extended presence of the Pacific Intermediate Water (PIW) owing to: amplified jet streams; southern movement of the California Current System (CCS) and the incursion of CCW into the gulf; and increased North Pacific Intermediate Water (NPIW) formation. The Last Glacial Maximum witnessed the incursion of CCW due to the stronger CCS. The dominance of the PIW indicates the expansion and formation of NPIW. The Heinrich-I event as manifested in the core record, displays two distinct patterns, one suggesting GCW-like dominance and the other, the occurrence of CCW. The Bølling-Ållerød interstadial featured the entry of Tropical Surface Water (TSW), GCW, and CCW, linked with the northward migration of the Intertropical Convergence Zone. In the Younger Dryas, CCW dominated, transitioning to GCW as colder climatic conditions and more intense CCS. The Holocene displayed alternating periods of TSW and GCW, with a modern monsoon regime from 7,600 to 1,000 cal years BP. From 1,000 cal years BP to the present the ITCZ shifted to the south.

The El Niño Phenomenon and Its Impact on Public Health

The El Niño phenomenon (EFN) is the warm phase of the El Niño Southern Oscillation (ENSO), a major climate event global defined as an increase in sea surface temperature in the eastern tropical Pacific Ocean due to weakening trade winds. This process is related to higher concentrations of humidity and more intense precipitation

The 1991–2020 sea surface temperature normals

AbstractThe 1991–2020 climate normals for sea surface temperature (SST) are computed based on the NOAA Daily Optimum Interpolation SST dataset. This is the first time that high‐resolution SST normals with global coverage can be achieved in the satellite SST era. Normals are one of the fundamental parameters in describing and understanding weather and climate and provide decision‐making information to industry, public, and scientific communities. This product suite includes SST mean, standard deviation, count and extreme parameters at daily, monthly, seasonal and annual time scales on 0.25° spatial grids. The main feature of the SST mean state revealed by the normals is that in the Tropics, the Indo‐Pacific Ocean is dominated by the warm pool (SST ≥ 28°C) while the eastern Pacific is characterized by the cold tongue (SST ≤ 24°C); in the midlatitudes, SSTs are in zonal patterns with high meridional gradients. Daily SST standard deviations are generally small (<1.0°C) except in frontal zones (>1.5°C) mostly associated with ocean currents such as the Gulf Stream, Kuroshio and Equatorial Currents. Compared to the 1982–2011 climatology, the 1991–2020 mean SSTs increased over most global areas but obvious cooling is seen in the Southern Ocean, eastern tropical South Pacific Ocean and North Atlantic warming hole. The Indo‐Pacific warm pool (IPWP) is found to have strengthened in both intensity and coverage since 1982–2011. By a count parameter criterion of ≥300 days annually with SST ≥ 28°C, the IPWP coverage increased 33% from 1982–2011 to 1991–2020. The global mean SST of 1991–2020 is warmer than that of 1982–2011, and the warming rate over 1991–2020 doubles that over 1901–2020.

Isotopic trajectories and interspecific niche partitioning in tropical pelagic sharks

Pelagic sharks are top predators with key role in the structure and functioning of ocean ecosystems. However, little is known on their assemblage-wide trophic ecology. Specifically, fundamental data gaps exist over how trophic niches of pelagic sharks diverge both intra- and inter-specifically. To address this question, multi-tissue stable isotope analysis is a powerful tool that enables the quantification of trophic dynamics of mobile predators throughout ontogeny and across species. In this study, we utilized stable isotope analysis of carbon (δ13C) and nitrogen (δ15N) of tissues with varying turnover rates (muscle, red blood cells, liver, and plasma) to assess individual niche trajectories (i.e., temporal isotopic variation), population isotopic niche width, and isotopic niche overlap across five shark species (n = 155) in the eastern tropical Pacific Ocean: silky (Carcharhinus falciformis), blue (Prionace glauca), smooth hammerhead (Sphyrna zygaena), bigeye thresher (Alopias superciliosus), and the pelagic thresher shark (A. pelagicus). Overall, the relationship between isotopic niche trajectory length and body size was not significant, indicating that the magnitude of ontogenetic dietary variation does not increase in larger individuals. Pelagic sharks had variable feeding strategies over short-long time scales, likely reflecting species-specific responses to seasonality of prey availability and foraging location. Observed interspecific differences in isotope values indicate a degree of trophic niche partitioning across the five pelagic shark species. These data suggest ontogenetic niche shifts in pelagic sharks potentially differ from more coastal tied species and reveal species-specific ecological roles, but further studies on the diet and fine-scale habitat use are required to verify these results.

Record of the unarmored dinoflagellate Gynogonadinium aequatoriale (Ceratoperidiniaceae, Dinophyceae) in the Mediterranean Sea

Abstract The records of the unarmored dinoflagellate Gynogonadinium aequatoriale have been restricted to the western equatorial and the eastern tropical Pacific Ocean. The genus is reported for the first time in the Mediterranean Sea from the coast of Taranto, Ionian Sea. This is a distinctive taxon that can only be confused with the cosmopolitan Pseliodinium fusus (=Ceratoperidinium falcatum). A comparison of these two species is provided.

Combining otolith chemistry and genetics to infer the population structure of yellow snapperLutjanus argentiventris

AbstractDeveloping a metapopulation framework contributes to the understanding of spatial processes and structures in populations, providing basic information for conservation biology. However, the extent to which the metapopulation structure differs geographically and across life history stages is unexplored for most fishes. Here, we compared the population structure and connectivity patterns of juvenile yellow snapperLutjanus argentiventrisin mangroves of the Eastern Tropical Pacific Ocean. In both the Gulf of California and Galápagos, these fish experience an array of environmental and oceanographic conditions that produce unique otolith microchemistry signatures and genetic population structures. In the Galápagos Archipelago, we used otolith microchemistry and microsatellite DNA, while for the Gulf of California, we only used otolith microchemistry. We observed relatively small differences in the otolith microchemistry at the ecoregion spatial scale (10–100 km2) for the Galápagos and the Gulf of California (classification accuracy of 57% and 64%, respectively). At the finer mangrove spatial scale (~1 km2), we found larger differences in the otolith microchemistry among the Gulf of California mangroves (classification accuracy ~90%) than in Galápagos (classification accuracy ~24%), potentially related to a stronger environmental gradient in the former. Based on otoliths, 75% of juveniles were migrants among mangroves in the Galápagos, in contrast to only around 10% of juveniles being migrants among the Gulf of California mangroves, suggesting a metapopulation structure characterized by high rates of self‐recruitment for snappers in the Gulf of California. For Galápagos, both otolith microchemistry and genetics supported the presence of a source–sink metapopulation structure for the yellow snapper, with high levels of connectivity in mangroves within the Eastern and Western ecoregions (FST = 0.003,p < 0.05). By combining tools that assess connectivity at multiple timescales (microchemistry and genetics) at different life stages and ecosystems, we provide a more complete elucidation of metapopulation structure forL. argentiventris. The approach employed here can be applied to other tropical fishes with broad distribution ranges and ontogenetic changes across complex habitats such as mangroves, seagrasses, and coral reefs.

The biology and ecology of the Pacific sharpnose shark Rhizoprionodon longurio.

Amidst global declines in elasmobranch populations resulting predominantly from overfishing, the need to gather data regarding shark ecology is greater than ever. Many species remain data deficient or at risk of going extinct before sufficient conservation measures can be applied. In this review, we summarise existing knowledge regarding the biology and ecology of the Pacific sharpnose shark Rhizoprionodon longurio (Jordan & Hilbert, 1882), a small-bodied carcharhinid shark found in coastal waters of the Eastern Tropical Pacific Ocean that is of both commercial and ecological importance. We compare ecological parameters of this species with its closest extant relatives and identify major knowledge gaps and avenues for future research. In particular, additional studies investigating the behavioural and sensory ecology, as well as potential migratory patterns of the species are needed. Such studies will not only improve our understanding of R. longurio, but provide insight into the extent to which the numerous studies performed on a close relative-Rhizoprionodon terraenovae-provide an accurate representation of the biology and ecology of Rhizoprionodon and carcharhinids more generally.

Shifts in the Isotopic Composition of Nitrous Oxide Between El Niño and La Niña in the Eastern Tropical South Pacific

AbstractThe El Niño‐Southern Oscillation (ENSO) is a natural climate phenomenon that alters the biogeochemical and physical dynamics of the Eastern Tropical Pacific Ocean. Its two phases, El Niño and La Niña, are characterized by decreased and increased coastal upwelling, respectively, which have cascading effects on primary productivity, organic matter supply, and ocean‐atmosphere interactions. The Eastern Tropical South Pacific oxygen minimum zone is a source of nitrous oxide (N2O), a potent greenhouse gas, to the atmosphere. Here, we present the first study to directly compare N2O sources during opposing ENSO phases using N2O isotopocule analyses. Our data show that during La Niña, N2O accumulation increased six‐fold in the upper 100 m of the water column, and N2O fluxes to the atmosphere increased up to 20‐fold. N2O isotopocule data demonstrated substantial increases in δ18O up to 60.5‰ and decreases in δ15Nβ down to −10.3‰ in the oxycline, signaling a shift in N2O cycling during La Niña compared to El Niño. During El Niño, N2O production was primarily due to ammonia‐oxidizing archaea, whereas during La Niña, N2O production by incomplete denitrification supplemented that from ammonia‐oxidation, with N2O consumption likely maintaining the high site preference values (up to 26.7‰). Ultimately, our results illustrate a strong connection between upwelling intensity, biogeochemistry, and N2O flux to the atmosphere. Additionally, they highlight the combined power of N2O isotopocule analysis and repeat measurements in the same region to constrain N2O interannual variability and cycling dynamics under different climate scenarios.