Central-eastern Pacific Research Articles

Reintensification of the Anomalous Western North Pacific Anticyclone during the El Niño Modoki Decaying Summer: Relative Importance of Tropical Atlantic and Pacific SST Anomalies

AbstractThe El Niño Modoki–induced anomalous western North Pacific anticyclone (WNPAC) undergoes an interesting reintensification process in the El Niño Modoki decaying summer, the period when El Niño Modoki decays but warm sea surface temperature (SST) anomalies over the tropical North Atlantic (TNA) and cold SST anomalies over the central-eastern Pacific (CEP) dominate. In this study, the region (TNA or CEP) in which the SST anomalies exert a relatively important influence on reintensification of the WNPAC is investigated. Observational analysis demonstrates that when only anomalous CEP SST cooling occurs, the WNPAC experiences a weak reintensification. In contrast, when only anomalous TNA SST warming emerges, the WNPAC experiences a remarkable reintensification. Numerical simulation analysis demonstrates that even though the same magnitude of CEP SST cooling and TNA warming is respectively set to force the atmospheric general circulation model, the response of the WNPAC is still much stronger in the TNA warming experiment than in the CEP cooling experiment. Further analysis demonstrates that this difference is caused by the distinct location of the effective tropical forcing between the CEP SST cooling and TNA SST warming for producing a WNPAC. The CEP cooling-induced effective anomalous diabatic cooling is located in the central Pacific, by which the forced anticyclone becomes gradually weak from the central Pacific to the western North Pacific. Thus, a weak WNPAC is produced. In contrast, as the TNA SST warming–induced effective anomalous diabatic cooling is just located in the western North Pacific via a Kelvin wave–induced Ekman divergence process, the forced anticyclone is significant and powerful in the western North Pacific.

Impacts of Central Pacific El Niño on Southern China Spring Precipitation Controlled by its Longitudinal Position

ABSTRACT Here we investigate the response of boreal spring precipitation over southern China (SPSC) to central Pacific (CP) El Niño based on observational datasets. While there is enhanced precipitation over southern China during the decaying boreal spring of eastern Pacific (EP) El Niño events, so far no clear precipitation response has been detected during the same decaying stage for CP El Niño composites. Here we show that around half of the CP El Niño events coincide with enhanced SPSC (wet CP El Niño), while the other half are accompanied by reduced SPSC (dry CP El Niño). These two types of CP El Niño events bear dramatically different evolution features in their respective tropical sea surface temperature anomaly (SSTA) patterns. Wet CP El Niño events are characterized by an SSTA longitudinal position confined to the tropical central-eastern Pacific. In contrast, dry CP El Niño events exhibit a clear westward propagation of SSTAs during their evolution, with maximum SSTAs located to the west of the date line after their mature phase. These different longitudinal positions of positive SSTAs during their decaying phase result in distinct meridional structures of the tropical Pacific convection anomalies as well as the ENSO combination mode (C-mode) response. An anomalous low-level anticyclone is evident over the western North Pacific during wet CP El Niño events during their decaying phase, while an anomalous cyclonic circulation is found for dry CP El Niño events. We emphasize that the impacts of CP El Niño on the SPSC depend crucially on the simultaneous zonal location of warm SSTAs in the tropical Pacific.

Influence of Intraseasonal Oscillation on the Asymmetric Decays of El Niño and La Niña

Warm and cold phases of El Nino–Southern Oscillation (ENSO) exhibit a significant asymmetry in their decay speed. To explore the physical mechanism responsible for this asymmetric decay speed, the asymmetric features of anomalous sea surface temperature (SST) and atmospheric circulation over the tropical Western Pacific (WP) in El Nino and La Nina mature-to-decay phases are analyzed. It is found that the interannual standard deviations of outgoing longwave radiation and 850 hPa zonal wind anomalies over the equatorial WP during El Nino (La Nina) mature-to-decay phases are much stronger (weaker) than the intraseasonal standard deviations. It seems that the weakened (enhanced) intraseasonal oscillation during El Nino (La Nina) tends to favor a stronger (weaker) interannual variation of the atmospheric wind, resulting in asymmetric equatorial WP zonal wind anomalies in El Nino and La Nina decay phases. Numerical experiments demonstrate that such asymmetric zonal wind stress anomalies during El Nino and La Nina decay phases can lead to an asymmetric decay speed of SST anomalies in the central-eastern equatorial Pacific through stimulating different equatorial Kelvin waves. The largest negative anomaly over the Nino3 region caused by the zonal wind stress anomalies during El Nino can be threefold greater than the positive Nino3 SSTA anomalies during La Nina, indicating that the stronger zonal wind stress anomalies over the equatorial WP play an important role in the faster decay speed during El Nino.

The China Multi-Model Ensemble Prediction System and Its Application to Flood-Season Prediction in 2018

Multi-model ensemble prediction is an effective approach for improving the prediction skill short-term climate prediction and evaluating related uncertainties. Based on a combination of localized operation outputs of Chinese climate models and imported forecast data of some international operational models, the National Climate Center of the China Meteorological Administration has established the China multi-model ensemble prediction system version 1.0 (CMMEv1.0) for monthly–seasonal prediction of primary climate variability modes and climate elements. We verified the real-time forecasts of CMMEv1.0 for the 2018 flood season (June–August) starting from March 2018 and evaluated the 1991–2016 hindcasts of CMMEv1.0. The results show that CMMEv1.0 has a significantly high prediction skill for global sea surface temperature (SST) anomalies, especially for the El Nino–Southern Oscillation (ENSO) in the tropical central–eastern Pacific. Additionally, its prediction skill for the North Atlantic SST triple (NAST) mode is high, but is relatively low for the Indian Ocean Dipole (IOD) mode. Moreover, CMMEv1.0 has high skills in predicting the western Pacific subtropical high (WPSH) and East Asian summer monsoon (EASM) in the June–July–August (JJA) season. The JJA air temperature in the CMMEv1.0 is predicted with a fairly high skill in most regions of China, while the JJA precipitation exhibits some skills only in northwestern and eastern China. For real-time forecasts in March–August 2018, CMMEv1.0 has accurately predicted the ENSO phase transition from cold to neutral in the tropical central–eastern Pacific and captures evolutions of the NAST and IOD indices in general. The system has also captured the main features of the summer WPSH and EASM indices in 2018, except that the predicted EASM is slightly weaker than the observed. Furthermore, CMMEv1.0 has also successfully predicted warmer air temperatures in northern China and captured the primary rainbelt over northern China, except that it predicted much more precipitation in the middle and lower reaches of the Yangtze River than observation.

The Red-fin Goby, Evorthodus minutus Meek & Hildebrand, 1928: a new record from Santa Cruz Island, Galapagos Archipelago

The Red-fin Goby, Evorthodus minutus Meek & Hildebrand, 1928, is a coastal brackish species which is commonly distributed from Sinaloa, Mexico to Guayaquil, Ecuador and particularly abundant in mangroves of Central American eastern Pacific. We report a new record of E. minutus collected from the Santa Cruz Island, part of the Galapagos Archipelago. This new record represents a range extension and is allows for a relevant discussion about colonization pathways in the equatorial eastern Pacific of a brackish-water species.

Shark-cetacean trophic interactions during the late Pliocene in the Central Eastern Pacific (Panama)

We provide a description of the remains of a fossil whale from western Panama. The record consists of appendicular remains of a mysticete, which has been assigned to Balaenopteridae. These remains, found in the sediments of the late Pliocene Burica Formation, represent the first record of a marine mammal in the Neogene sedimentary succession of the Burica Peninsula. Two different types of shark bite marks, serrated and deep-unserrated, found on the radius and phalanges suggest scavenging by at least two white shark (Carcharodon) individuals. The deep, unserrated marks were possibly caused by continual biting by sharks. Both the morphology of the shark bite marks and their relative location on the whale limb bones constitute evidence of shark-cetacean trophic interaction. Although the specimen lacks diagnostic features that would allow a species-level identification, it does provide new information on the vertebrate fauna of a very poorly prospected Central Eastern Pacific exposure, thus opening an opportunity for exploring the marine fauna during a critical episode in Earth history, the Plio-Pleistocene transition. Dirley Cortes. Redpath Museum, McGill University, 859 Sherbrooke St. W., Montreal QC H3A 0C4, Canada. Smithsonian Tropical Research Institute, Balboa-Ancon 0843-03092, Panama, Panama. dirley.cortes@mail.mcgill.ca Carlos De Gracia. Smithsonian Tropical Research Institute, Balboa-Ancon 0843-03092, Panama, Panama. degraciac@gmail.com Jorge D. Carrillo-Briceno. Palaontologisches Institut und Museum, Karl-Schmid-Strasse 4, 8006 Zurich, Switzerland. Smithsonian Tropical Research Institute, Balboa-Ancon 0843-03092, Panama, Panama. jorge.carrillo@pim.uzh.ch Gabriel Aguirre-Fernandez. Palaontologisches Institut und Museum, Karl-Schmid-Strasse 4, 8006 Zurich, Switzerland. gabriel.aguirre@pim.uzh.ch Carlos Jaramillo. Smithsonian Tropical Research Institute, Balboa-Ancon 0843–03092, Panama, Panama. ISEM, U. Montpellier, CNRS, EPHE, IRD, Montpellier, France. JaramilloC@si.edu Aldo Benites-Palomino. Smithsonian Tropical Research Institute, Balboa-Ancon 0843-03092, Panama, Panama. Departamento de Paleontologia de Vertebrados, Museo de Historia Natural, Universidad Nacional Mayor de San Marcos; Avenida Arenales 1256, Lima 14, Peru. aldomar1955@gmail.com Joaquin Enrique Atencio-Arauz. Colegio Punta Burica, Chiriqui Province, Panama. juniormurcie@latinmail.com Keywords: Mysticeti; shark bite marks; Neogene; late Pliocene; Central America; trophic interaction

Isotopic evidence for twentieth-century weakening of the Pacific Walker circulation

The strength of the Pacific Walker circulation (WC) over the historical period is uncertain and strongly debated, largely due to the limited length of reliable instrumental records. Tropical Pacific corals provide continuous, highly-resolved records that can be used to overcome the limitations of the instrumental records. Here we combine coral δ18O records from the western Pacific Warm Pool (WPWP) and tropical central-eastern Pacific (CEP) to develop a coral WC index back to 1886. Our coral WC index is in good agreement with post-1950 instrumental records, justifying both a direct comparison with earlier instrumental records and an evaluation of twentieth century WC trends. Our results show that pre-1950 instrumental records appear to underestimate WC variability. The coral WC index reveals a significant weakening of the WC over the twentieth century in response to development of El Niño like SST pattern in the tropical Pacific and enhanced hydrological cycle over the CEP under greenhouse warming. Our results provide new evidence for twentieth century WC variability and offer an observational constraint for improving models and their prediction of future WC behavior.

Identification Standard for ENSO Events and Its Application to Climate Monitoring and Prediction in China

The El Nino–Southern Oscillation (ENSO) reflects anomalous variations in the sea surface temperature (SST) and atmospheric circulation over the tropical central–eastern Pacific. It remarkably impacts on weather and climate worldwide, so monitoring and prediction of ENSO draw intensive research. However, there is not yet a unique standard internationally for identifying the timing, intensity, and type of ENSO events. The National Climate Center of China Meteorological Administration (NCC/CMA) has led the effort to establish a national identification standard of ENSO events, which was officially endorsed by the National Standardization Administration of China and implemented operationally in NCC/CMA in 2017. In this paper, two key aspects of this standard are introduced. First, the Nino3.4 SST anomaly index, which is well-recognized in the international ENSO research community and used operationally in the US, has replaced the previous Nino Z index and been used to identify the start, end, and peak times, and intensity of ENSO events. Second, two new indices—the eastern Pacific ENSO (EP) index and the central Pacific ENSO (CP) index, based on the SST conditions in Nino3 and Nino4 region respectively, are calculated to first determine the ENSO type before monitoring and assessing the impacts of ENSO on China’s climate. With this standard, all historical ENSO events since 1950 are consistently re-identified; their distinct properties are diagnosed and presented; and the impacts of ENSO events under different types on China’s climate are re-assessed. This standard is also employed to validate the intensity, grade, and type of the ENSO events predicted by the NCC/CMA operational ENSO prediction system. The new standard and the thus derived unified set of re-analyzed historical ENSO events and associated information provide a good reference for better monitoring and prediction of future ENSO events.

A Mechanism for Pacific Interdecadal Resonances

AbstractPacific interdecadal variability (PIV) is an important large‐scale climate phenomenon. There is growing evidence that PIV contains three spectral resonances: a decadal (13 ± 1‐year) spectral peak, bidecadal (20 ± 5‐year) resonance, and a pentadecadal (60 ± 10‐year) resonance. Although much has been clarified about mechanisms behind PIV, there are still many open questions about the origin of these resonant modes (especially the pentadecadal mode). We describe dynamics in the Pacific basin by a toy (delayed oscillator) model that sheds light on the nature of these resonant peaks. The model suggests that unlike the bidecadal resonance, which results from local atmosphere‐ocean coupling in the extratropics, the pentadecadal and possibly also decadal resonances result from atmospheric and oceanic teleconnections between the extratropics and tropics. We show that a tiny coupling between extratropics and tropics through the ocean tunnel is sufficient to trigger the pentadecadal oscillation in the Pacific basin. Our model also explains (a) the observed three‐period locking between the bidecadal and pentadecadal modes and (b) the synchronization of anomalies in the central eastern tropics and central North Pacific with the opposite relative sign. We conclude that the role of oceanic teleconnections is probably underestimated in the current literature on PIV.

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.

Spatiotemporal variability in bigeye vertical distribution in the Pacific Ocean

Bigeye tuna are targeted by longliners and caught incidentally by purse seiners in the tropical Pacific. The spawning biomass has been reduced significantly from unexploited levels, necessitating management action in both the western and central Pacific and eastern Pacific. Stock assessments of bigeye tuna rely primarily on data from the fisheries; however, the vulnerability of the stock to these gears, and its spatiotemporal variability, remains poorly understood, requiring simplifying assumptions to be made in the stock assessments. We analyzed the vertical behavior of 65 bigeye tuna (estimated size range 48–130 cm fork length) tracked with archival tags in the equatorial Pacific Ocean and the Coral Sea, and found that fish depth shows a clear gradient with longitude, becoming progressively shallower from west to east. Additive mixed models were used to explore potential relationships of the depth behavior during both day and night to several life history and environmental variables. Swimming depths were most clearly related to the thermocline depth, the intensity of temperature stratification of the water column and fish size. The model predictions suggest strong relationships between fish depth and fisheries catch-per-unit-effort (CPUE) both spatially and temporally. In particular, we propose that El Niño-Southern Oscillation-driven changes in oceanography have a major influence on fish depth and longline CPUE, which could have substantial implications for stock assessments where longline CPUE is used as an index of abundance.

Quantitative palaeobiogeographical analysis of South American Neogene Chioninae (Bivalvia: Veneridae)

Chionine bivalves are one of the most important components of Neogene and Recent molluscan faunas in southern South America, but it was not until recently that their phylogenetic relationships has been explored quantitatively. Based on this robust framework, we analyzed the palaeobiogeographical history of the group. The geographic areas used in this analysis were discretized using a multivariate K-means cluster analysis based on the palaeocoordinates of chionine-bearing localities. Statistical comparison of quantitative, event-based biogeography models using likelihood suggests that our data best fits models that include long-distance jump dispersal (+J), with a slight preference for a model that also gives increased weight to vicariance. The ‘Chione’ clade (including the genera Chione, Anomalocardia, and Chionopsis) is mainly a Caribbean and central Eastern Pacific lineage with expansions to California and the southern Western Atlantic coast. The ‘Protothaca’ clade (including Protothaca, Nioche, Austrovenus, and Chionista) is mainly an Eastern Pacific lineage–with a proposed southern South American origin–with occasional dispersals to the western Pacific (Oceania and East Asia). A new alternative dispersal route is proposed across the North Pacific from California and the north Eastern Pacific to East Asia and Oceania, as shown by Austrovenus stutchburyi, Tuangia crassicosta, and Protocallithaca adamsii. The ‘Ameghinomya’ clade (including all Ameghinomya species) is a southern South American lineage–south Eastern Pacific origin–that subsequently dispersed into the southern Western Atlantic. The ‘Protothaca’ and ‘Ameghinomya’ clades show opposite histories, the former being mainly Pacific and the latter mainly Atlantic. The distribution of both clades on both sides of South America may have been allowed by the opening of the Drake Passage Gateway around the Oligocene-Miocene boundary.

Trophic niche partitioning of pelagic sharks in Central Eastern Pacific inferred from stable isotope analysis.

As the apex predators of the open ocean ecosystems, pelagic sharks play important roles in stabilizing the marine food web through top-down control. Stable isotope analysis is a powerful tool to investigate the feeding ecology. The carbon and nitrogen isotope ratios can be used to trace food source and evaluate the trophic position of marine organisms. In this study, the isotope values of 130 pelagic sharks from 8 species in Central Eastern Pacific were analyzed and their trophic position and niche were calculated to compare the intra/inter-specific resource partitioning in the Central Eastern Pacific ecosystem. The results exhibited significant differences in both carbon and nitrogen isotope values among the shark species. The trophic levels ranged from 4.3 to 5.4 in the Central Eastern Pacific shark community. The trophic niche of blue sharks and shortfin mako sharks showed no overlap with the other shark species, exhibiting unique ecological roles in the open ocean food web. These data highlighted the diverse roles among pelagic sharks, supporting previous findings that this species is not trophically redundant and the trophic niche of pelagic sharks can not be simply replaced by those of other top predator species.

Atmospheric Dynamic and Thermodynamic Processes Driving the Western North Pacific Anomalous Anticyclone during El Niño. Part I: Maintenance Mechanisms

The western North Pacific anomalous anticyclone (WNPAC) is an important low-level circulation system that connects El Niño and the East Asian monsoon. In this study, the mechanisms responsible for the formation and maintenance of the WNPAC are explored. Part I of this study focuses on the WNPAC maintenance mechanisms during El Niño mature winter and the following spring. Moisture and moist static energy analyses indicated that the WNPAC is maintained by both the remote forcing from the equatorial central-eastern Pacific via the atmospheric bridge and the local air–sea interactions. Three pacemaker experiments by a coupled global climate model FGOALS-s2, with upper-700-m ocean temperature in the equatorial central-eastern Pacific restored to the observational anomalies plus model climatology, suggest that about 60% (70%) intensity of the WNPAC during the winter (spring) is contributed by the remote forcing from the equatorial central-eastern Pacific. The key remote forcing mechanism responsible for the maintenance of the WNPAC is revealed. In response to El Niño–related positive precipitation anomalies over the equatorial central-eastern Pacific, twin Rossby wave cyclonic anomalies are induced to the west. The northern branch of the twin cyclonic anomalies advects dry and low moist enthalpy air into the tropical western North Pacific, which suppresses local convection. The suppressed convection further drives the WNPAC.

Interdecadal change on the relationship between the mid-summer temperature in South China and atmospheric circulation and sea surface temperature

South China suffers from high temperature frequently in mid-summer and this study aims to explore the interdecadal change of interannual variation of the mid-summer temperature in South China. It is revealed that the relationship between South China temperature and atmospheric circulation and sea surface temperature anomaly (SSTA) experiences an interdecadal change around the early 1990s. Before the early 1990s, warmer summer in South China is associated with the mid-latitude teleconnection featured by higher pressure over the Ural Mountains and the Korean Peninsula and lower pressure around the Lake Baikal. South China is located at the southern flank of an anomalous high pressure. After the early 1990s, South China temperature is prominently influenced by the tropical SSTA, and meanwhile the mid-latitude teleconnection becomes much weaker. Warmer summer is associated with higher pressure centered over South China and the El Nino to La Nina transition phase. The higher pressure influencing South China is located more southwards after the early 1990s, and it is favored by the tropical SSTA. The warmer SST in summer over the western tropical Pacific enhances the local convection and triggers an anomalous local Hadley cell with stronger subsidence over South China, directly leading to higher pressure over South China. Moreover, the colder SST over the central–eastern Pacific induces an anomalous Walker circulation and further strengthens the convection over the western tropical Pacific, exerting an indirect impact on the higher pressure over South China. The relative role of the western Pacific warming and central–eastern Pacific cooling is verified by CAM4 simulations. The intimate relationship between the tropical SSTA and South China temperature occurs during the El Nino to La Nina transition phase, which is the case after the early 1990s and suggests higher predictability for South China temperature in the recent decades.

The tropical Pacific–Indian Ocean associated mode simulated by LICOM2.0

Oceanic general circulation models have become an important tool for the study of marine status and change. This paper reports a numerical simulation carried out using LICOM2.0 and the forcing field from CORE. When compared with SODA reanalysis data and ERSST.v3b data, the patterns and variability of the tropical Pacific–Indian Ocean associated mode (PIOAM) are reproduced very well in this experiment. This indicates that, when the tropical central–western Indian Ocean and central–eastern Pacific are abnormally warmer/colder, the tropical eastern Indian Ocean and western Pacific are correspondingly colder/warmer. This further confirms that the tropical PIOAM is an important mode that is not only significant in the SST anomaly field, but also more obviously in the subsurface ocean temperature anomaly field. The surface associated mode index (SAMI) and the thermocline (i.e., subsurface) associated mode index (TAMI) calculated using the model output data are both consistent with the values of these indices derived from observation and reanalysis data. However, the model SAMI and TAMI are more closely and synchronously related to each other.

Distribution of Dibranchus species (Pisces: Ogcocephalidae) from the Eastern Central Pacific and their relationship with environmental factors

The geographic and bathymetric distribution of the genus Dibranchus throughout the Eastern Central Pacific was analyzed, using historical distribution records and results from bottom trawls undertaken from 11 research cruises performed in the Mexican Pacific (TALUD project). A total of three species were collected: Dibranchus hystrix (nine specimens, six trawls), Dibranchus spinosus (25 specimens, nine trawls) and Dibranchus spongiosa (134 specimens, 19 trawls). The greatest density of specimens was confined to 800–1200 m depth, but they were caught together in a small number of trawls (D. hystrix-D. spinosus, three trawls; D. hystrix-D. spongiosa, one trawl). This work extends the known latitudinal ranges of D. hystrix by 230 km, and of D. spongiosa by 650 km and provides the first records for D. spinosus and D. spongiosa in the Gulf of California, and for D. hystrix in the Central Gulf of California. Also, the shallowest depth and maximum sizes records of D. hystrix (865 m, 148 mm SL) and D. spongiosa (479 m, 156 mm SL) were extended. Dibranchus spongiosa inhabits the shallowest and warmer sites, almost only within the OMZ; while both, D. hystrix and D. spinosus, are able to live in a wide range of DO concentrations, mainly in the deeper and oxygenated zone. These environmental preferences could be related to their distinct geographical ranges throughout the Eastern Pacific.

Stalked Crinoids Collected off California with Descriptions of Three New Genera and Two New Species of Hyocrinidae (Echinodermata)

Five species of stalked crinoids collected at depths from 1,693 to 4,135 m off the California coast, chiefly on seamounts, are described. Four were photographed in situ and collected during Monterey Bay Aquarium and Research Institute cruises using ROV Tiburon . Four specimens with intact crowns are attributed to Bathycrinus equatorialis A. H. Clark, 1908 a , previously known from a single stalk with basal ring collected in the central eastern Pacific. Parahyocrinus claguei Roux, n. gen., n. sp., here described from a growth series of six specimens, is closely related to Hyocrinus biscoitoi Roux, 2004 (herein transferred to Parahyocrinus Roux, n. gen.), from the East Pacific Rise, but differs in features of the tegmen, pinnules, and stalk articulations. The single, finely ornamented specimen of Tiburonicrinus ornatus Roux, n. gen., n. sp., displays an original arrangement of characters suggesting affinities with Thalassocrinus alvinae from the Gorda Ridge. Gephyrocrinus messingi Roux & Lambert, 2011, known from off British Columbia and California, is transferred as type species to Lamberticrinus Roux, n. gen., after a reexamination of its pinnule architecture. Specimens of the fifth species, Bathycrinus complanatus A. H. Clark, 1908 b , were trawled off California by R/V New Horizon .

The seasonal march of the equatorial Pacific upper-ocean and its El Niño variability

Based on two modern data sets, the climatological seasonal march of the upper-ocean is examined in the equatorial Pacific for the period 2004–2014, because of its large contribution to the total variance, its relationship to El Niño, and its unique equatorial wave phenomena. Argo provides a broadscale view of the equatorial Pacific upper-ocean based on subsurface temperature and salinity measurements for the period 2004–2015, and satellite altimetry provides synoptic observations of the sea surface height (SSH) for the period 1993–2015. Using either 11-year (1993–2003/2004–2014) time-series for averaging, the seasonal Rossby waves stands out clearly and eastward intraseasonal Kelvin wave propagation is strong enough in individual years to leave residuals in the 11-year averages, particularly but not exclusively, during El Niño onset years. The agreement of altimetric SSH minus Argo steric height (SH) residuals with GRACE ocean mass estimates confirms the scale-matching of in situ variability with that of satellite observations. Surface layer and subsurface thermohaline variations are both important in determining SH and SSH basin-wide patterns. The SH/SSH October-November maximum in the central-eastern Pacific is primarily due to a downward deflection of the thermocline (∼20m), causing a warm subsurface anomaly (>1°C), in response to the phasing of downwelling intraseasonal Kelvin and seasonal Rossby waves. Compared with the climatology, the stronger October-November maximum in the 2004–2014 El Niño composites is due to higher intraseasonal oscillations and interannual variability. Associated with these equatorial wave patterns along the thermocline, the western warm/fresh pool waters move zonally at interannual timescales through zonal wind stress and pressure gradient fluctuations, and cause substantial fresh (up to 0.6psu) and warm (∼1°C higher than the climatology) anomalies in the western-central Pacific surface-layer during the El Niño onset year, and of the opposite sign during the termination year. These El Niño-related patterns are then analyzed focusing on the case of the onset of the strong 2015/2016 episode, and are seen to be around two times larger than that in the 2004–2014 El Niño composites. The present work exploits the capabilities of Argo and altimetry to update and improve the description of the physical state of the equatorial Pacific upper-ocean, and provides a benchmark for assessing the accuracy of models in representing equatorial Pacific variability.

Variation of the Tropical Cyclone Season Start in the Western North Pacific

The variation of the tropical cyclone (TC) season in the western North Pacific (WNP) was analyzed based on the percentiles of annual TC formation dates. The results show that the length of the TC season is highly modulated by the TC season’s start rather than its end. The start of the TC season in the WNP has large interannual variation that is closely associated with the variation of the sea surface temperature (SST) in the Indian Ocean (IO) and the central-eastern Pacific (CEP). When the SSTs of the IO and CEP are warm (cold) in the preceding winter, anomalous high (low) pressure and anticyclonic (cyclonic) circulation are induced around the WNP TC basin the following spring, resulting in a late (early) start of the TC season. These results suggest that a strong El Niño in the preceding winter significantly delays the TC season start in the following year.