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Thirty years (1993–2022) of concurrent satellite and in‐situ observations show a long‐term strengthening of the equatorial Pacific upper‐ocean circulation. Enhanced southeasterly and cross‐equatorial winds have caused an annual mean, basin‐wide acceleration of the equatorial westward near‐surface currents by ∼20% and an acceleration of poleward flow north (south) of the equator by ∼60% (∼20%). Additional moored velocity data reveal a deepening of the Equatorial Undercurrent (EUC) core at 170°W and significant shoaling at 140°W and 110°W, but no significant changes in EUC core velocity. The strongest subsurface zonal velocity trends are observed above the EUC core in the central to eastern Pacific and occur before and after the seasonal maximum of EUC core velocity, causing enhanced upper‐ocean vertical current shear. Consistent with trends of the 20°C isotherm depth along the equatorial Pacific, a significant basin‐wide steepening of the equatorial thermocline is observed. Both the accelerating equatorial current system and the enhanced thermocline slope are consistent with an observed steepening of the zonal sea surface height gradient due to increased wind‐driven westward mass transport at the surface. During February‐March, both surface and subsurface currents along the equator show eastward velocity trends, in contrast to westward near‐surface current trends during the remainder of the year. The trend reversal is attributed to both a long‐term shift in equatorial Kelvin wave activity and to the impact of strong interannual variability due to El Niño Southern Oscillation and other modes of natural variability on decadal to multidecadal time scales. Plain Language Summary: Thirty years (1993–2022) of temporally overlapping satellite and in‐situ observations reveal a long‐term strengthening of the equatorial Pacific circulation in the upper 200 m. Both the west‐east (zonal) and south‐north (meridional) surface atmospheric winds typically observed in the tropical Pacific intensified. As a result, westward near‐surface currents in the central equatorial Pacific accelerated by ∼20%, while poleward currents accelerated by ∼60% (∼20%) north (south) of the equator. The strongest trends in zonal velocity are observed above the core of the Equatorial Undercurrent. While the subsurface current in the central and eastern Pacific shoaled by 12 m, it deepened in the western Pacific by 6 m, which aligns with trends of the 20°C isotherm depth. Both the accelerating equatorial currents and the steeper thermocline slope are consistent with a steepening west‐east slope of sea surface height due to increased westward water mass transport. Our results show that a shift in equatorial wave activity and strong interannual variability cause eastward velocity anomalies in the observed surface and subsurface current trends during February‐March. Between 1993 and 2022, long‐term equatorial circulation trends persist, but these trends are modified by natural events at both interannual timescales such as El Niño and La Niña events, and longer timescales. Key Points: 30 years of observations show a wind‐driven strengthening of equatorial Pacific surface zonal currents by ∼20% and poleward flow by ∼20%−60%The subsurface Equatorial Undercurrent intensified above its core depth, primarily in the central to eastern PacificLong‐term moored observations of subsurface velocity and temperature show a significant basin‐wide steepening of the equatorial thermocline [ABSTRACT FROM AUTHOR]

Using a suite of coupled climate models and an extensive set of ocean heat budget diagnostics, we address the relative roles of heat convergence and surface heat flux in driving the annual rate of ocean heat content (OHC) change in the tropical Pacific and its interannual variability. The net heat convergence is further separated into convergences associated with the large‐scale ocean circulation, (parameterized) mesoscale effects and small‐scale mixing. It is found that the heat convergence due to the large‐scale ocean circulation provides the dominant contribution to the annual OHC tendency. Interannual variations of heat convergence are larger in the tropical Pacific than in the tropical Atlantic. These heat convergence variations are linked to interannual variations of the Pacific meridional overturning circulation (PMOC), driven by the associated variations in the northward Ekman transport (EkT). Northward variations of the tropical PMOC and EkT are typically associated with heat divergence and negative annual OHC tendency in the central and eastern near‐equatorial Pacific along with heat convergence and positive annual OHC tendency in the western and northwestern tropical Pacific. In the Niño3.4 region, interannual variations of the near‐surface OHC tendency negatively (positively) correlate with interannual PMOC variations at zero lag (1 year lag, when PMOC leads OHC). Plain Language Summary: We use a suite of global climate models to show that the rate of annual temperature change in the upper tropical Pacific Ocean is primarily driven by large‐scale circulation. In particular, there is a close statistical relationship between the rate of temperature change in the tropical Pacific Ocean and the conveyor‐like "meridional overturning circulation" in the basin. The findings are expected to be particularly useful for better understanding of such phenomena as the El Nino–Southern Oscillation (ENSO), which is one of the largest sources of year‐to‐year climate variation. Key Points: Interannual variability of tropical ocean heat content (OHC) tendency and heat convergence are stronger in the Pacific than in the AtlanticInterannual variability of tropical Pacific OHC tendency is dominated by heat convergence due to large‐scale ocean circulationInterannual variations of upper OHC tendency in the Nino3.4 region negatively correlate with variations of Pacific overturning circulation [ABSTRACT FROM AUTHOR]

A 110-year ensemble simulation of an ocean general circulation model (OGCM) was analyzed to identify the modulation of salinity interdecadal variability on El Niño-Southern Oscillation (ENSO) amplitude in the tropical Pacific during 1901–2010. The simulating results show that sea surface salinity (SSS) variation in the region exhibits notable and coherent interdecadal variability signal, which is closely associated with the Interdecadal Pacific Oscillation (IPO). As salinity increases or reduces, the SSS modulations on ENSO amplitude during its warm/cold events vary asymmetrically with positive/negative IPO phases. Physically, salinity interdecadal variability can enhance or reduce ENSO-related conditions in upper-ocean stratification, contributing noticeably to ENSO variability. Salinity anomalies associated with the mixed layer depth and barrier layer thickness can modulate ENSO amplitude during positive and negative IPO phases, resulting in the asymmetry of sea surface temperature (SST) anomaly in the tropical Pacific. During positive IPO phases, SSS interdecadal variability contributes positively to El Niño amplitude but negatively to La Niña amplitude by enhancing or reducing SSS interannual variability, and vice versa during negative IPO phases. Quantitatively, the results indicate that the modulation of the ENSO amplitude by the SSS interdecadal variability is −15%–28% during negative IPO phases and −30%–20% during positive IPO phases, respectively. Evidently, the SSS interdecadal variability associated with IPO and its modulation on ENSO amplitude in the tropical Pacific are among factors essentially contributing ENSO diversity. [ABSTRACT FROM AUTHOR]

A total of 366 individuals of Lutjanus argentiventris (Peters, 1869) were collected over a 5-yr period (October 2018 to June 2022) from Acapulco Bay, Mexico. Parasite communities in Lutjanus argentiventris were quantified and analyzed to determine the main factors that generate changes in species richness and/or species composition over time. The digeneans and copepods were the best-represented parasite groups. The parasite communities were characterized by a high numerical dominance of ectoparasites, mainly isopod larvae. Species richness at the component community level (9–23 species) was similar to the reported richness in other Lutjanus spp. The parasite communities of Lutjanus argentiventris exhibited high variability in species composition, suggesting that each parasite species may respond differently to environmental changes. However, the species richness and diversity were fairly stable over time; therefore, a clear pattern of interannual variation was not observed. Variations in the community structure probably were due to factors such as host traits (e.g., feeding behavior and body size), and possible interannual differences in environmental factors amplified by the occurrence of the anomalous event of La Niña. [ABSTRACT FROM AUTHOR]

In the face of ongoing discrimination, stigma, ostracism, and violence, Pacific Islanders of Diverse Sexual Orientations, Gender Identities, Intersex Expressions, and Sex Characteristics (PIDSOGIESC+) display a marked resilience. And yet, this resilience does not come lightly, nor is it cheap. This research draws on a mixed-methods data set to explore the complicated notion of resilience among PIDSOGIESC+ communities. Through engaging in rich talanoas, along with a wide-reaching survey, a nuanced picture emerges of communities that draw on a range of indigenous cultural perspectives across the Tropical Pacific to develop creative strategies for engaging meaningfully with the world around them. Highlighting a strengths-based approach to research and service delivery, we explore the unique skillset of the PIDSOGIESC+ community, the changes they have won, and the vision of a more inclusive society they are fighting for.

Coral reefs are in global decline primarily due to climate change. Herbivory is often viewed as key to maintaining coral‐dominated reefs, and herbivore management is gaining traction as a possible strategy for promoting reef resilience. The functional impact of herbivorous fishes has typically been inferred from total biomass, but robust estimates of ecological processes are needed to better inform management targets. Here, we provide a framework to calculate rates of herbivory across Pacific reefs. We synthesized available observations of foraging metrics in relation to fish body size and found considerable variation, even among closely related species. We then applied these allometric functions to survey data and calculated rates of herbivory for acanthurids and scarines, which make up the vast majority of herbivorous fish biomass in the Pacific. Estimated rates of algal consumption, area scraped, and bioerosion varied across islands, with noticeable differences that may align with the relative influence of human population density among underlying herbivore functional groups. We found no evidence of compensatory relationships among herbivore processes whereby decreasing rates in one type of herbivory is offset by increasing rates in another. We observed nonlinear, positive relationships between fish biomass and rates of herbivory. Yet, for a given biomass, the corresponding rates of herbivory varied among regions, and we observed instances where islands with the greatest biomass did not also have the highest rates of herbivory. Islands with the largest size classes of herbivores did not consistently exhibit greater rates of herbivory, and we did not find a clear, consistent pattern between the number of fish species and corresponding rates of herbivore processes. Cropping Acanthurus spp. provided the greatest proportion of algal consumption at every island, yet no single species accounted for the majority of this process, whereas we identified parrotfish species that provided >75% of scraping or bioerosion at certain islands. Our results emphasize the importance of considering the species and size composition of herbivore assemblages when estimating processes, rather than relying on total biomass alone. Lastly, we highlight gaps in foraging observations and additional work needed to further broaden our ability to quantify the ecological processes of herbivores. [ABSTRACT FROM AUTHOR]

Maximum sea surface salinity (SSS) anomalies are found in the central Pacific during the eastern Pacific El Niño (EPEN) and located further westward during the central Pacific El Niño (CPEN), but whether these differences affect event strengths is unclear. By performing ocean general circulation model experiments via modifying freshwater flux anomalies, we find salinity effects on surface warming during both types are highly sensitive to zonal locations of SSS anomalies, with the strongest warming induced by the SSS anomalies near the international dateline. Further analysis reveals that vertical mixing and entrainment dominate this temperature sensitivity, with the strongest response to SSS anomalies occurring in the central Pacific. The central‐Pacific SSS anomalies increase EPEN warming by 0.15°C while the westward‐located SSS anomalies make little contribution to CPEN warming. Therefore, the distinct zonal structures of SSS anomalies facilitate stronger EPEN than the CPEN, increasing their difference in intensity by about 10%. Plain Language Summary: The El Niño‐Southern Oscillation (ENSO) is the strongest year‐to‐year climate variability in the planet. The central Pacific El Niño (CPEN) have been recognized in recent decades, with weaker surface warming located more westward, in contrast to the traditional eastern Pacific El Niño (EPEN). Previous studies have underscored various air‐sea processes in shaping these differences, however, the impact of salinity remains unknown. Here based on ocean model experiments, we found the salinity effect on El Niño warming is very sensitive to zonal locations of salinity anomalies. The salinity anomalies located in the central Pacific are more effective in modulating local ocean vertical stratification, weakening the colder subsurface water into the mixed layer and further enhancing the surface warming. Therefore, the central equatorial Pacific‐located salinity anomalies during EPEN contributes to its stronger warming than those west‐located salinity anomalies during CPEN, enhancing the sea surface temperature difference between the two events by about 10%. Our results provide new insight in understanding the ENSO diversity and also its low‐frequency variability, which may be helpful for interpreting more complex model simulations and for and predicting ENSO variations. Key Points: Salinity anomalies in the central Pacific induce the strongest surface warming during both types of El Niño, tapering off to the east and westThe distinct sea surface salinity zonal structures between the two El Niños amplify their difference in sea surface temperature magnitude by about 10%Salinity effects on vertical mixing and entrainment account for the different eastern Pacific and central Pacific El Niño responses [ABSTRACT FROM AUTHOR]

Bigeye tuna (BET) and yellowfin tuna (YFT) are economically important target species of pelagic fisheries worldwide, especially for tropical Pacific nations whose economies and food sources are heavily affected by commercial and sustenance tuna fishing. The El Niño‐Southern Oscillation (ENSO) has a strong effect on the oceanographic conditions in the equatorial Pacific, including BET and YFT equatorial habitat and fishing grounds. For optimal fisheries management, the effects of environmental variability such as ENSO on the stocks and on the performance of fisheries must be known and predictable. However, besides some model predictions, the effects of ENSO on these two tuna species are not well understood. In this study, I investigate the statistical relationships between past ENSO conditions and equatorial fisheries using the Multivariate ENSO Index, sea surface temperature (SST), and catch and effort records from the longline fisheries in the region. Results of this study indicate that El Niño events have both delayed and concurrent positive effects on BET and YFT catch per unit effort (CPUE). The delayed positive ENSO effect on CPUE is hypothesized to be the result of enhanced recruitment acting via different mechanisms in the west than in the east. The concurrent positive effects on CPUE could be due to catchability, abundance, and/or vertical distribution of BET and YFT relative to fishing gear and require further investigation. Further exploration of the mechanisms that may underlie the results presented here could lead to predictability of CPUE of these two tuna species. [ABSTRACT FROM AUTHOR]

The tropical Pacific Ocean is a key regulator of Earth's climate, with teleconnections that influence remote locations all around the world. Here we use partially coupled climate model experiments to show that tropical Pacific cooling related to an abrupt Atlantic Meridional Overturning Circulation (AMOC) slowdown can strengthen the AMOC by ∼25%. This tropical‐extratropical teleconnection occurs initially via atmospheric Rossby waves propagating from the tropical Pacific to the North Atlantic which alter surface climate conditions locally. These changes facilitate ocean heat loss from the subpolar gyre, favoring enhanced oceanic convection. The AMOC strengthening is subsequently enhanced by anomalous northward salt advection in the Atlantic, with a potential contribution from oceanic wave adjustment triggered by increased Southern Ocean westerly winds. These results highlight the influence of the tropical Pacific on the AMOC on multidecadal timescales and suggest that cold phases of tropical Pacific decadal variability could drive temporary strengthening of the AMOC. Plain Language Summary: Changes in the tropical Pacific sea surface temperature can exert significant remote weather and climate impacts via physical mechanisms known as teleconnections. In this study, we report unexplored teleconnections to the Atlantic basin which act in a timescale of decades. In particular we found that a mean cooling in the tropical Pacific could act to accelerate a large‐scale ocean circulation in the Atlantic basin known as the Atlantic Meridional Overturning Circulation (AMOC). This occurs via atmospheric and oceanic waves which propagate to the North Atlantic and alter local conditions, favoring the acceleration of the AMOC. Key Points: Tropical Pacific cooling can drive a strengthening of the Atlantic Meridional Overturning Circulation (AMOC)The Pacific–North Atlantic teleconnection occurs via both atmospheric and oceanic planetary waveguidesPacific–AMOC teleconnections can be induced on a multidecadal time‐scale [ABSTRACT FROM AUTHOR]

The evolution of tropical sea surface temperatures (SSTs) in response to greenhouse warming is of great societal and scientific interest. Most state‐of‐the‐art climate models predict a mean "El Niño‐like" warming pattern by century‐end, characterized by greater warming over the Pacific cold tongue compared to the western warm pool. However, it is unclear which proposed mechanism dominates in this response. Here, we present partially coupled abrupt CO2 doubling experiments in which surface wind stress and shortwave heating are overridden to values from a control simulation. Contrary to previous studies, we find that experiments with overriding of surface wind stress exhibit only 58% of the full reduction in east‐west SST contrast. When both surface wind stress and shortwave flux are overridden, only 34% of the full reduction remains, controlled by spatially‐varying evaporative cooling. These results underscore the importance of Bjerknes and shortwave feedbacks in the tropical Pacific SST response to global warming. Plain Language Summary: Sea surface temperature patterns over the tropical Pacific have an outsized impact on regional and global climates, as exemplified by the impact of present day El Niño events. As such, how tropical SST patterns will evolve under global warming has been a topic of keen scientific interest and scrutiny. While most state‐of‐the‐art climate models show a transition to a more "El Niño‐like" mean state by the end of the century, the precise reason why remains debated. Here, we present a method that estimates the contributions of changing surface winds and solar radiation to the tropical ocean warming pattern simulated by a state‐of‐the‐art climate model. While some previous studies have argued that changes in surface winds are unimportant, here we show that the weakening of surface easterly winds that maintain a colder eastern Pacific is a major factor leading to a reduced east‐west temperature contrast. Key Points: Climate models predict an eastern equatorial Pacific warming pattern in the tropical Pacific by the end of the 21st centuryWe use partially coupled climate simulations to assess contributions of wind stress, shortwave, and evaporative feedbacks to this patternWeakening of surface wind stress is found to be a major factor leading to a reduced zonal SST gradient over the tropical Pacific [ABSTRACT FROM AUTHOR]

The tropical Pacific plays an important role in modulating the global climate through its prevailing sea-surface temperature spatial structure and dominant climate modes like El Niño-Southern Oscillation (ENSO), the Madden-Julian Oscillation (MJO), and their teleconnections. These modes of variability, including their oceanic anomalies, are considered to provide sources of prediction skill on subseasonal timescales in the Tropics. Therefore, this study aims to examine how assimilating in situ ocean observations influences the initial ocean sea-surface temperature (SST) and mixed-layer depth (MLD) and their subseasonal forecasts. We analyze two subseasonal forecast systems generated with the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecast System (IFS), where the ocean states were initialized using two Observing-System Experiment (OSE) reanalyses. We find that the SST differences between forecasts with and without ocean data assimilation grow with time, resulting in a reduced cold-tongue bias when assimilating ocean observations. Two mechanisms related to air-sea coupling are considered to contribute to this growth of SST differences. One is a positive feedback between the zonal SST gradient, pressure gradient, and surface wind. The other is the difference in Ekman suction and mixing at the Equator due to surface wind-speed differences. While the initial mixed-layer depth (MLD) can be improved through ocean data assimilation, this improvement is not maintained in the forecasts. Instead, the MLD in both experiments shoals rapidly at the beginning of the forecast. These results emphasize how initialization and model biases influence air-sea interaction and the accuracy of subseasonal forecasts in the tropical Pacific. [ABSTRACT FROM AUTHOR]

Abstract: Global Climate Models (GCMs) exhibit substantial biases in their simulation of tropical climate. One particularly problematic bias exists in GCMs' simulation of the tropical rainband known as the Intertropical Convergence Zone (ITCZ). Much of the precipitation on Earth falls within the ITCZ, which plays a key role in setting Earth's temperature by affecting global energy transports, and partially dictates dynamics of the largest interannual mode of climate variability: The El Niño‐Southern Oscillation (ENSO). Most GCMs fail to simulate the mean state of the ITCZ correctly, often exhibiting a “double ITCZ bias,” with rainbands both north and south rather than just north of the equator. These tropical mean state biases limit confidence in climate models' simulation of projected future and paleoclimate states, and reduce the utility of these models for understanding present climate dynamics. Adjusting GCM parameterizations of cloud processes and atmospheric convection can reduce tropical biases, as can artificially correcting sea surface temperatures through modifications to air‐sea fluxes (i.e., “flux adjustment”). Here, we argue that a significant portion of these rainfall and circulation biases are rooted in orographic height being biased low due to assumptions made in fitting observed orography onto GCM grids. We demonstrate that making different, and physically defensible, assumptions that raise the orographic height significantly improves model simulation of climatological features such as the ITCZ and North American rainfall as well as the simulation of ENSO. These findings suggest a simple, physically based, and computationally inexpensive method that can improve climate models and projections of future climate.

Abstract Maximum sea surface salinity (SSS) anomalies are found in the central Pacific during the eastern Pacific El Niño (EPEN) and located further westward during the central Pacific El Niño (CPEN), but whether these differences affect event strengths is unclear. By performing ocean general circulation model experiments via modifying freshwater flux anomalies, we find salinity effects on surface warming during both types are highly sensitive to zonal locations of SSS anomalies, with the strongest warming induced by the SSS anomalies near the international dateline. Further analysis reveals that vertical mixing and entrainment dominate this temperature sensitivity, with the strongest response to SSS anomalies occurring in the central Pacific. The central‐Pacific SSS anomalies increase EPEN warming by 0.15°C while the westward‐located SSS anomalies make little contribution to CPEN warming. Therefore, the distinct zonal structures of SSS anomalies facilitate stronger EPEN than the CPEN, increasing their difference in intensity by about 10%.

Abstract The tropical Pacific Ocean is a key regulator of Earth's climate, with teleconnections that influence remote locations all around the world. Here we use partially coupled climate model experiments to show that tropical Pacific cooling related to an abrupt Atlantic Meridional Overturning Circulation (AMOC) slowdown can strengthen the AMOC by ∼25%. This tropical‐extratropical teleconnection occurs initially via atmospheric Rossby waves propagating from the tropical Pacific to the North Atlantic which alter surface climate conditions locally. These changes facilitate ocean heat loss from the subpolar gyre, favoring enhanced oceanic convection. The AMOC strengthening is subsequently enhanced by anomalous northward salt advection in the Atlantic, with a potential contribution from oceanic wave adjustment triggered by increased Southern Ocean westerly winds. These results highlight the influence of the tropical Pacific on the AMOC on multidecadal timescales and suggest that cold phases of tropical Pacific decadal variability could drive temporary strengthening of the AMOC.

Abstract The evolution of tropical sea surface temperatures (SSTs) in response to greenhouse warming is of great societal and scientific interest. Most state‐of‐the‐art climate models predict a mean “El Niño‐like” warming pattern by century‐end, characterized by greater warming over the Pacific cold tongue compared to the western warm pool. However, it is unclear which proposed mechanism dominates in this response. Here, we present partially coupled abrupt CO2 doubling experiments in which surface wind stress and shortwave heating are overridden to values from a control simulation. Contrary to previous studies, we find that experiments with overriding of surface wind stress exhibit only 58% of the full reduction in east‐west SST contrast. When both surface wind stress and shortwave flux are overridden, only 34% of the full reduction remains, controlled by spatially‐varying evaporative cooling. These results underscore the importance of Bjerknes and shortwave feedbacks in the tropical Pacific SST response to global warming.

Ocean salinity is an important variable that affects the ocean stratification. We compared the salinity and ocean stratification in the tropical Pacific derived from the Argo (Array for Real-time Geostrophic Oceanography data), EN4 (Ensemble 4 analysis), SODA (the Simple Ocean Data Assimilation reanalysis), IAP (Institute of Atmospheric Physics data), and ORAS4 (Ocean Reanalysis System 4) over 2005–2017. Results show that the spatial distribution of climatological mean of sea surface salinity (SSS) in all the products is consistent, and the low salinity region showed large deviation and strong dispersion. The Argo has the smallest RMSE and the highest correlation with the ensemble mean, while the IAP shows a high-salinity deviations relative to other datasets. All the products show high positive correlations between the sea surface density (SSD) and SSS with respect to the deviations of climatological mean from ensemble mean, suggesting that the SSD deviation may be mainly influenced by the SSS deviation. In the aspect of the ocean stratification, the mixed layer depth (MLD) climatological mean in the Argo shows the highest correlation with the ensemble mean, followed by EN4, IAP, ORAS4, and SODA. The Argo and EN4 show thicker barrier layer (BL) relative to the ensemble mean while the SODA displays the largest negative deviation in the tropical western Pacific. Furthermore, the EN4, ORAS4, and IAP underestimate the stability in the upper ocean at the depths of 20–140 m, while Argo overestimates ocean stability. The salinity fronts in the western-central equatorial Pacific from Argo, EN4, and ORAS4 are consistent, while those from SODA and IAP show large deviations with a westward position in amplitude of 0°–6° and 0°–10°, respectively. The SSS trend patterns from all the products are consistent in having ensemble mean with high spatial correlations of 0.95–0.97. [ABSTRACT FROM AUTHOR]

The El Niño Southern Oscillation (ENSO) has profound impacts on weather patterns across the globe, yet there is no consensus on its response to global warming. Several modelling studies find a stronger ENSO in global warming scenarios, while other studies suggest ENSO weakening. Using a broad range of models from the Coupled Model Intercomparison Project phase 6 (CMIP6) and four types of warming experiments, here we show that the majority of the models predict a stronger ENSO by century-end in Shared Social Pathway (SSP) experiments, and in idealized 1pctCO2 and abrupt 4xCO2 experiments. Several models, however, do predict no change or ENSO weakening, especially in the idealized experiments. Critically, the strongest forcing (abrupt-4xCO2) does not induce the strongest ENSO response, while differences between the models are much greater than those between warming scenarios. For the long-term response (over 1000 years) the models disagree even on the sign of change. Furthermore, changes in ENSO sea surface temperature (SST) variability are only modestly correlated with the tropical Pacific mean state change. The highest correlation for ENSO SST amplitude is found with the mean zonal SST gradient in the SSP5-8.5 experiment (R = − 0.58). In contrast, changes in ENSO rainfall variability correlate well with changes in the mean state, as well as with changes in ENSO SST variability. When evaluating the Bjerknes Stability Index for a subset of models, we find that it is not a reliable predictor of ENSO strengthening, as this index tends to predict greater stability with warming. We argue that the enhanced ENSO stability is offset by increases in atmospheric noise or/and potential nonlinear effects. However, a robust inter-model mechanism that can explain a stronger ENSO simulated with global warming is still lacking. Therefore, caution should be exercised when considering ENSO changes based on a single model or warming scenario. [ABSTRACT FROM AUTHOR]

Most current climate models predict that the equatorial Pacific will evolve under greenhouse gas--induced warm-ing to a more El Niño-like state over the next several decades, with a reduced zonal sea surface temperature gradient and weakened atmospheric Walker circulation. Yet, observations over the last 50 y show the opposite trend, toward a more La Niña-like state. Recent research provides evidence that the discrepancy cannot be dis-missed as due to internal variability but rather that the models are incorrectly simulating the equatorial Pacific response to greenhouse gas warming. This implies that projections of regional tropical cyclone activity may be incorrect as well, perhaps even in the direction of change, in ways that can be understood by analogy to historical El Niño and La Niña events: North Pacific tropical cyclone projections will be too active, North Atlantic ones not active enough, for example. Other perils, including severe convective storms and droughts, will also be projected erroneously. While it can be argued that these errors are transient, such that the models' responses to green-house gases may be correct in equilibrium, the transient response is relevant for climate adaptation in the next several decades. Given the urgency of understanding regional patterns of climate risk in the near term, it would be desirable to develop projections that represent a broader range of possible future tropical Pacific warming scenarios--including some in which recent historical trends continue--even if such projections cannot cur-rently be produced using existing coupled earth system models. [ABSTRACT FROM AUTHOR]

Most climate models simulate an intensified eastern equatorial Pacific warming in response to increasing greenhouse gas concentrations. So far, the proposed mechanisms have focused on thermodynamic aspects such as the spatial inhomogeneity of evaporative feedbacks, and future increases in upper ocean thermal stratification, partly intensified by projected Walker circulation weakening. Here we show, using earth system model freshwater perturbation experiments, that the simulated future rainfall intensification along the equator plays an important role in tropical climate change. Associated negative equatorial salinity anomalies of about −0.6 permil, which are very similar to the projected late 21st century salinity anomalies in CMIP6 SSP585 scenario, strengthen upper ocean stratification in the Pacific which leads to a flattening of the thermocline, shoaling of the equatorial undercurrent, and major shifts in tropical ocean dynamics. The resulting eastern basin equatorial warming also contributes to a marked weakening of the Pacific Walker circulation. Our analysis illustrates the importance of rainfall and salinity changes in the tropical climate system with relevance for understanding both, patterns of future climate change as well as the El Niño Southern Oscillation phenomenon. Key Points: Future increased tropical rainfall and its effect on salinity contribute to the generation of the enhanced eastern Pacific warming patternSalinity‐driven enhanced eastern Pacific warming weakens Pacific Walker circulationRainfall‐induced thermocline flattening causes a subsurface cold wedge in the western to central tropical Pacific [ABSTRACT FROM AUTHOR]

It has been recognized that salinity variability in the tropical Pacific is closely related to the Interdecadal Pacific Oscillation (IPO). Here, we use model simulations from 1900 to 2017 to illustrate obvious asymmetries of salinity variability in the tropical Pacific during positive and negative IPO phases. The amplitude of salinity variability in the tropical Pacific during positive IPO phases is larger than that during negative IPO phases, with a more westward shift of a large Sea Surface Salinity (SSS) anomaly along the equator. Salinity budget analyses show that the asymmetry of salinity variability during positive and negative IPO phases is dominated by the difference in the surface forcing associated with the freshwater flux [FWF, precipitation (P) minus evaporation (E)], with a contribution of 40%–50% near the dateline on the equator. Moreover, the relationships between the salinity variability and its budget terms also show differences in their lead-lag correlations during positive and negative IPO phases. These differences in salinity variability during different IPO phases produce asymmetric effects on seawater density which can reduce or enhance upper-ocean stratification. Therefore, the salinity effects may modulate the intensity of El Niño-Southern Oscillation (ENSO), resulting in an enhanced (reduced) El Niño but a reduced (enhanced) La Niña during positive (negative) IPO phases by 1.6°C psu−1 (1.3°C psu−1), respectively. It is suggested that the asymmetry of salinity variability may be related to the recent change in ENSO amplitude associated with the IPO, which can help elucidate ENSO diversity. [ABSTRACT FROM AUTHOR]

Algal biogeography in Hawai'i has not been studied in detail for many species. The islands are home to swift-current deep-water channels separating suitable habitats. The ability of these channels to act as barriers to dispersal has been studied in several animal lineages and is assessed here using the widespread red alga Amansia glomerata C.Agardh. A variety of analytical techniques based on 129 mitochondrial COI barcoding sequences collected across c. 2500 km were used to assess the genetic diversity of A. glomerata in Hawai'i. Haplotype network analyses demonstrated that the species is split into four main lineages which overlap in large parts of their range, yet there is insufficient support to recognize the lineages as separate species. Measures of haplotype diversity, nucleotide diversity, and neutrality tests suggest that at least three of these lineages have undergone recent population expansion. Biogeographic barriers were found to largely match those of marine animal groups in the archipelago. No evidence was found for distinct haplotypes or lineages between shallow and mesophotic reefs. A number of potential collection locations are suggested for the 1822 lectotype of the species, which was included in the molecular analyses. Potential scenarios leading to observed diversity patterns in the archipelago are presented. Amansia glomerata exhibits a high degree of haplotypic variation in Hawai'i, suggesting it may exhibit vast molecular divergences across its broader range, which extends from Hawai'i to southeastern Africa. Phylogéographie d'Amansia glomerata C.Agardh (Ceramiales, Rhodomelaceae) à Hawai'i: une seule espèce à forte divergence. La biogéographie des algues à Hawai'i n'a pas été étudiée en détail pour de nombreuses espèces. Les îles abritent des chenaux rapides d'eau profonde séparant les habitats appropriés. La capacité de ces chenaux à agir comme des barrières à la dispersion a été étudiée dans plusieurs lignées animales et est évaluée ici à l'aide de l'algue très répandue Amansia glomerata C.Agardh. Une variété de techniques analytiques basées sur 129 séquences de code-barres COI mitochondriales collectées sur environ 2500 km ont été utilisées pour évaluer la diversité génétique d'A. glomerata à Hawai'i. Les analyses du réseau d'haplotypes ont démontré que l'espèce est divisée en quatre lignées principales qui se chevauchent dans de grandes parties de leur aire de répartition, mais il n'y a pas suffisamment de soutien pour reconnaître les lignées comme plusieurs espèces. Les mesures de la diversité des haplotypes, de la diversité des nucléotides et des tests de neutralité suggèrent qu'au moins trois de ces lignées ont subi des expansions démographiques récentes. Les barrières biogéographiques correspondent largement à celles des groupes d'animaux marins de l'archipel. Aucune preuve n'a été trouvée pour des haplotypes ou des lignées distincts entre les récifs peu profonds et mésophotiques. Un certain nombre de lieux de collecte potentiels sont suggérés pour le lectotype de l'espèce de 1822, qui a été inclus dans les analyses moléculaires. Des scénarios potentiels conduisant à des modèles de diversité observés dans l'archipel sont présentés. Amansia glomerata présente un degré élevé de variation haplotypique à Hawai'i, ce qui suggère qu'il peut présenter de vastes divergences moléculaires sur son aire de répartition plus large, qui s'étend d'Hawai'i au sud-est de l'Afrique. [ABSTRACT FROM AUTHOR]

This study investigates possible mechanisms under what circumstances the North Pacific Victoria mode (VM) is more likely to trigger the eastern Pacific (EP) or central Pacific (CP) El Niño event. Results indicate that while positive VM events can provide the initiates to the onset of El Niño events via forcing initial warming of sea surface temperature (SST) anomalies to occur in the central equatorial Pacific from springtime to summer, the changes in background conditions of the equatorial Pacific at the same period also are crucial contributors to the development of VM-EP or VM-CP El Niño events. That is when we predict the spatial patterns of El Niño events in advance, the extratropical variabilities and changes in the background conditions of the tropical Pacific should be both taken into consideration, rather than considered individually. For VM-EP El Niño cases, the significantly negative SST anomalies from the eastern tropical Pacific experience a fast transition into positive. These SST anomalies are usually accompanied by sign reversal of zonal wind anomalies near the dateline, finally together supplying favorable conditions for the eastward propagation of the initial warming anomalous SST generated by VM event. For VM-CP El Niño cases, there are also negative SST anomalies in the eastern equatorial Pacific, however, they can linger much longer than the former case and transit relatively slow to positive SST anomalies, which together along with the muted anomalous westerlies around the dateline suppress the eastward propagation of the warm SST anomalies generated by VM events. The changes of subsurface water are further in accordant to the results in the sea surface. Two simple statistical models for EP and CP El Niño prediction are derived depending on evolutionary features in both north and tropical Pacific, showing high prediction skills by 2-season in advance. These findings may provide useful insights for understanding the predictability of El Niño diversity. [ABSTRACT FROM AUTHOR]

Precipitation extremes driven by the El Niño–Southern Oscillation (ENSO) are one of the critical ways in which the ENSO impacts the global climate, specifically in the tropical Pacific, where they have the potential to cause extreme weather conditions. However, existing approaches struggle to effectively identify the evolution of ENSO-related precipitation anomalies that change rapidly in spatial distribution. To address this challenge, we propose the object-oriented spatiotemporal clustering approach using remote sensing products (OSCAR) for detecting evolutions of ENSO-related precipitation anomalies. The OSCAR was validated using simulated datasets and applied to precipitation anomalies over the tropical Pacific. The simulation experiment demonstrates that the OSCAR outperforms the dual-constraint spatiotemporal clustering approach (DcSTCA) in accuracy, particularly for rapidly evolving precipitation anomaly variations. The application of the OSCAR demonstrates its ability to recognize the evolution of ENSO-related precipitation anomalies over the tropical Pacific, which may offer valuable references for global climate change research. [ABSTRACT FROM AUTHOR]

Observations suggest that the tropical Pacific Ocean has lost oxygen since the 1960s leading to the expansion of its oxygen minimum zone (OMZ). Attribution to anthropogenic forcing is, however, difficult because of limited data availability and the large natural variability introduced by the Pacific Decadal Oscillation (PDO). Here, we evaluate the PDO influence on oxygen dynamics and OMZ extent using observations and hindcast simulations from two global ocean circulation models (NEMO‐PISCES, MOM6‐COBALT). In both models, the tropical Pacific oxygen content decreases by about 30 Tmol.decade−1 and the OMZ volume expands by 1.3 × 105 km3.decade−1 during PDO positive phases, while variations of similar magnitude but opposite sign are simulated during negative phases. Changes in equatorial advective oxygen supply, partially offset by biological demand, control the oxygen response to PDO. Observations which cover 39% of the tropical Pacific volume only partially capture spatio‐temporal variability, hindering the separation of anthropogenic trend from natural variations. Plain Language Summary: Human activities cause oxygen loss in the ocean, which leads to the expansion of areas with very low oxygen concentrations located in the tropics called oxygen minimum zones (OMZ). Understanding the dynamics of OMZs is crucial because they produce greenhouse gasses and are unsuitable for the life of most large marine organisms. Quantifying the response of OMZs is however complicated by natural variability that superimposes on human‐induced changes. In the Pacific Ocean, one of the strongest natural variability phenomena is the Pacific Decadal Oscillation. We used data and numerical models to assess the magnitude of oxygen changes caused by this natural phenomena in the tropical Pacific Ocean, and show that they are comparable to that of human‐induced oxygen changes. We highlight that more oxygen data is needed to accurately separate natural variations from human‐induced changes, and that a fraction of the oxygen loss attributed to human activities in prior work could in fact be due to natural variability. Key Points: Pacific Decadal Oscillation (PDO) modulates tropical Pacific oxygen content and oxygen minimum zone volume on decadal time scalesThe PDO‐induced variations are of the same order of magnitude as the anthropogenic deoxygenation signalCurrently available data are too sparse to resolve and isolate the PDO‐induced and anthropogenic signals [ABSTRACT FROM AUTHOR]

Abstract Most climate models simulate an intensified eastern equatorial Pacific warming in response to increasing greenhouse gas concentrations. So far, the proposed mechanisms have focused on thermodynamic aspects such as the spatial inhomogeneity of evaporative feedbacks, and future increases in upper ocean thermal stratification, partly intensified by projected Walker circulation weakening. Here we show, using earth system model freshwater perturbation experiments, that the simulated future rainfall intensification along the equator plays an important role in tropical climate change. Associated negative equatorial salinity anomalies of about −0.6 permil, which are very similar to the projected late 21st century salinity anomalies in CMIP6 SSP585 scenario, strengthen upper ocean stratification in the Pacific which leads to a flattening of the thermocline, shoaling of the equatorial undercurrent, and major shifts in tropical ocean dynamics. The resulting eastern basin equatorial warming also contributes to a marked weakening of the Pacific Walker circulation. Our analysis illustrates the importance of rainfall and salinity changes in the tropical climate system with relevance for understanding both, patterns of future climate change as well as the El Niño Southern Oscillation phenomenon.

The observed sea ice concentration (SIC) over the Arctic has receded substantially in recent decades, and future model projections predict a seasonally ice-free Arctic in the second half of this century. Nevertheless, the impact of the Pacific on Arctic sea ice projections has yet to receive much attention. Observations show that summertime Arctic SIC growth events are related to the weakening of the Aleutian low and cooling events over the equatorial Pacific, and vice versa. We demonstrate that under various Coupled Model Intercomparison Project Phase 6 projections, the models in which the impact of El Niño-driven SIC loss is significantly higher than the La Niña-related SIC growth tend to turn seasonally ice-free by about 10–20 years ahead of the ensemble mean under high-emission future scenarios. We show how the non-linear impact of the El Niño Southern Oscillation (ENSO) on Arctic SIC resulted in a faster decline of summertime sea ice. The ENSO-related SIC changes in the multi-model ensemble mean of Arctic SIC are considerably lower than the internal variability and anthropogenic-driven changes. However, the asymmetric interannual ENSO effects over several decades and the resultant changes in surface heat fluxes over the Arctic lead to significant differences in the timing of sea ice extinction. Our results suggest that climate models must capture the realistic tropical Pacific–Arctic teleconnection to better predict the long-term evolution of the Arctic climate.

Abstract Observations suggest that the tropical Pacific Ocean has lost oxygen since the 1960s leading to the expansion of its oxygen minimum zone (OMZ). Attribution to anthropogenic forcing is, however, difficult because of limited data availability and the large natural variability introduced by the Pacific Decadal Oscillation (PDO). Here, we evaluate the PDO influence on oxygen dynamics and OMZ extent using observations and hindcast simulations from two global ocean circulation models (NEMO‐PISCES, MOM6‐COBALT). In both models, the tropical Pacific oxygen content decreases by about 30 Tmol.decade−1 and the OMZ volume expands by 1.3 × 105 km3.decade−1 during PDO positive phases, while variations of similar magnitude but opposite sign are simulated during negative phases. Changes in equatorial advective oxygen supply, partially offset by biological demand, control the oxygen response to PDO. Observations which cover 39% of the tropical Pacific volume only partially capture spatio‐temporal variability, hindering the separation of anthropogenic trend from natural variations.

Since the early 1990s the Pacific Walker circulation shows a multi‐decadal strengthening, which contradicts future model projections. Whether this trend, evident in many climate indices especially before the 2015 El Niño, reflects the coupled ocean‐atmosphere response to global warming or the negative phase of the Pacific Decadal Oscillation (PDO) remains debated. Here we show that sea surface temperature trends during 1980–2020 are dominated by three signals: a spatially uniform warming trend, a negative PDO pattern, and a Northern Hemisphere‐Indo‐West Pacific warming pattern. The latter pattern, which closely resembles the transient ocean thermostat‐like response to global warming emerging in a subset of CMIP6 models, shows cooling in the central‐eastern equatorial Pacific but warming in the western Pacific and tropical Indian Ocean. Together with the PDO, this pattern drives the Walker circulation strengthening in the equatorial band. Historical simulations appear to underestimate this pattern, contributing to the models' inability to replicate the Walker cell strengthening. Plain Language Summary: This paper investigates the observed changes in the tropical Pacific during the satellite era, including the recent decadal strengthening of the atmospheric zonal circulation—the Walker cell. We aim to understand the extent to which these changes represent a forced response to rising CO2 concentrations versus natural variability. We apply an approach in which we decompose the observed sea surface temperature trends into three components—a pattern associated with the Pacific Decadal Oscillation, which is part of natural variability, a uniform warming pattern, and a residual pattern. This residual pattern shows a remarkable resemblance to a forced ocean thermostat‐like transient response generated in some of the climate models, characterized by equatorial Pacific (EP) cooling, and a broad warming of the Northern Hemisphere, and the Indian Ocean and West Pacific. These results challenge studies arguing that the recent strengthening of the Pacific Walker cell can be explained simply by multi‐decadal natural variability in the tropics. Furthermore, the inability of climate models at large to fully capture this forced pattern with historical forcing puts into focus the reliability of future projections of climate change in the tropical Pacific, specifically the timing of emergence of the eastern EP warming. Key Points: A multi‐decadal strengthening of the Pacific Walker cell is observed in a wide range of indices, especially after 1990A Northern Hemisphere ‐ Indo West Pacific warming sea surface temperature pattern, which differs from the Pacific Decadal Oscillation, is evident since 1980This pattern resembles a forced response to abrupt CO2 forcing, emerging in a subset of climate models, and contributes to the Walker circulation strenthening [ABSTRACT FROM AUTHOR]

Previous studies indicated that the North Tropical Atlantic (NTA) SST can serve as a precursor for the El Niño–Southern Oscillation (ENSO) predictability and the connection of NTA-ENSO is modulated by the mid-high latitude atmospheric variability. Despite significant solar footprints being found in the North Atlantic and tropical Pacific separately, their role in the two basins’ connection is still missing. In this study, we systematically examined this point by using observational/reanalysis datasets and outputs of a pair of sensitivity experiments with and without solar forcings (SOL and NOSOL). In observations, DJF-mean NAO-like SLP anomalies have a linear covariation with the subsequent JJA-mean El Niño Modoki-like SST anomalies in the tropical Pacific in the following 1 year. This observed SLP-SST covariation shows up in the high solar activity (HS) subset and disappears in the low solar activity (LS) subset. In the HS years, positive NAO-like SLP anomalies are produced by the stronger solar-UV radiation through a “top-down” mechanism. These atmospheric anomalies can enhance the influence of the NTA on the tropical Pacific SST by triggering significant and more persistent subtropical teleconnections. Here we proposed an indirect possible mechanism that the solar-UV forcing can modulate the tropical Pacific SST variability via its impacts on the atmospheric anomalies over the North Atlantic region. However, based on the same analysis method, we found a different coupled mode of the SLP and SST anomalies in the modeling outputs. The SLP anomalies in the North Atlantic, with a triple pattern (negative SLP anomalies in the Pole and the NTA, positive SLP anomalies in the mid-latitude), have “lead-lag” covariations with the Eastern Pacific El Niño-like SST anomalies in both the SOL and NOSOL. Although the impact of the solar activity is found in the North Atlantic and the tropical Pacific respectively in the SOL, no solar effect is involved in the simulated SLP-SST coupled mode.

Abstract Since the early 1990s the Pacific Walker circulation shows a multi‐decadal strengthening, which contradicts future model projections. Whether this trend, evident in many climate indices especially before the 2015 El Niño, reflects the coupled ocean‐atmosphere response to global warming or the negative phase of the Pacific Decadal Oscillation (PDO) remains debated. Here we show that sea surface temperature trends during 1980–2020 are dominated by three signals: a spatially uniform warming trend, a negative PDO pattern, and a Northern Hemisphere‐Indo‐West Pacific warming pattern. The latter pattern, which closely resembles the transient ocean thermostat‐like response to global warming emerging in a subset of CMIP6 models, shows cooling in the central‐eastern equatorial Pacific but warming in the western Pacific and tropical Indian Ocean. Together with the PDO, this pattern drives the Walker circulation strengthening in the equatorial band. Historical simulations appear to underestimate this pattern, contributing to the models' inability to replicate the Walker cell strengthening.

A robust simulation of tropical Pacific Ocean decadal‐scale zonal wind stress trends can increase the confidence in projections of global surface temperature and regional sea level rise, yet coupled general circulation models simulate weaker trends than observed. When forced with observed sea surface temperatures, the atmospheric component of these models still simulates a weaker zonal wind stress trend during 1992–2008 (and 1992–2011) than observed. Yet, this decadal wind trend bias is not evident at the 850 hPa level. We show that the modelled wind trend bias is related to deficiencies in monthly wind stress variability. Furthermore, the strength of the connectivity between the surface and 850 hPa was also an indicator of the wind stress trend. Models that simulated a more realistic wind stress trend tend to simulate a stronger Pacific zonal sea level pressure gradient intensification than observed and a South Pacific Convergence Zone shift like that observed. Plain Language Summary: From early 1990s to late 2010, the equatorial trade winds strengthened in the Pacific Ocean. This coincided with a rapid rise in sea level in the western tropical Pacific and a slowdown in global surface temperature warming. This long‐term change in the Pacific had a large impact, but ocean‐atmosphere models cannot produce a change of a similar strength as observed. It is difficult to determine whether the ocean or atmosphere components of the model are at fault. This study looks at factors contributing to the inability of models to simulate trade wind strengthening by focusing on the atmosphere component of the model. We find that improving the month‐to‐month response of wind to sea surface temperatures may improve the strength of long‐term wind changes. Improvements in wind changes may also be made if models improve their connection between winds higher in the atmosphere and those at the surface. Models that have stronger wind changes have a better representation of south tropical Pacific rainfall changes, but also rely on a stronger than observed sea level pressure response. Key Points: Atmosphere‐only models, like coupled models, struggle to simulate tropical Pacific wind stress trends of similar magnitude to observedModels with weaker wind trends tend to have a weaker monthly wind response to sea surface temperatures and a weaker link to winds aloftModels with strong trends have a better South Pacific Convergence Zone shift but a too strong sea level pressure gradient [ABSTRACT FROM AUTHOR]

Sea surface temperature (SST) variability in the tropical Pacific (TP) has world‐wide climate and economic influences; hence, improving its prediction is of great interest. Recent modeling studies suggested that north tropical Atlantic variability can influence TP SST variability and prediction. However, models are subject to biases in both the tropical Atlantic and Pacific, and it remains an open question whether these biases affect the trans‐basin linkages and the prediction of TP SST. To investigate this issue, we apply linear inverse modeling to observations and climate models. We find that removing north tropical Atlantic forcing indeed strongly lowers TP SST multiyear prediction skills in observations and models. Models show a large spread of the Atlantic trans‐basin effect, which leads to markedly different TP SST multiyear prediction skills. Our study highlights the necessity to narrow the inter‐model spread for more reliable TP SST multiyear prediction. Plain Language Summary: Tropical Pacific (TP) sea surface temperature (SST) variability is important for climate but hard to predict. Many modeling studies argued that the variability and prediction can be influenced by north tropical Atlantic trans‐basin effect, while the reliability of this argument is influenced by strong model biases. To reveal the influence of model biases in simulating the Atlantic trans‐basin modulation on TP SST prediction, we apply a commonly used tool for prediction called linear inverse modeling. We find that prediction skills of TP SST will strongly decrease without the north tropical Atlantic forcing in both observations and models. However, striking inter‐model spread exists in the strength of the Atlantic trans‐basin effect, resulting in strong inter‐model spread in TP SST multiyear prediction skills. Therefore, more efforts are needed to reduce the inter‐model spread of the Atlantic trans‐basin effect in the future. Key Points: Observational evidence supports that north tropical Atlantic forcing substantially improve tropical Pacific (TP) sea surface temperature (SST) multiyear predictionClimate models show strong inter‐model spread in simulating north tropical Atlantic trans‐basin effectThe spread of north tropical Atlantic forcing in climate models strongly affects TP SST multiyear prediction skills [ABSTRACT FROM AUTHOR]

Abstract A robust simulation of tropical Pacific Ocean decadal‐scale zonal wind stress trends can increase the confidence in projections of global surface temperature and regional sea level rise, yet coupled general circulation models simulate weaker trends than observed. When forced with observed sea surface temperatures, the atmospheric component of these models still simulates a weaker zonal wind stress trend during 1992–2008 (and 1992–2011) than observed. Yet, this decadal wind trend bias is not evident at the 850 hPa level. We show that the modelled wind trend bias is related to deficiencies in monthly wind stress variability. Furthermore, the strength of the connectivity between the surface and 850 hPa was also an indicator of the wind stress trend. Models that simulated a more realistic wind stress trend tend to simulate a stronger Pacific zonal sea level pressure gradient intensification than observed and a South Pacific Convergence Zone shift like that observed.

The Equatorial Undercurrent (EUC) stretches across the Pacific, transporting cool waters rich in oxygen and nutrients eastward to one of the most productive regions in the ocean. As an intricate part of the global climate system, EUC dynamics are essential to understanding future climate change but are poorly represented in global coupled climate models. This study examines EUC representation and future changes in the latest generations of the Coupled Model Intercomparison Project (CMIP6 and CMIP5) and an eddy-permitting ocean model. We also examine historical and projected changes in EUC source waters, including the Mindanao Current (MC), New Guinea Coastal Undercurrent (NGCU), and interior thermocline convergence. The circulation features in the models are broadly consistent with observations and ocean reanalyses, but improvements from CMIP5 to CMIP6 are limited. In the future projections, the EUC is enhanced in the western Pacific, with less prominent changes in CMIP6, but more so in the eddy-permitting model. The western Pacific EUC enhancement is likely associated with a wind-driven redirection of waters south of the equator, in which the NGCU boundary flow increases while the interior thermocline convergence decreases. This is superimposed on an overall weakening of the North Pacific subtropical overturning cell, including the MC, interior thermocline convergence, and Ekman divergence. As EUC heat and nutrient composition is linked to its sources, these projected changes have implications for the EUC's role in air–sea feedbacks, nutrient replenishment, and oxygen minimum zone ventilation in the eastern Pacific.

Precipitation extremes driven by the El Niño–Southern Oscillation (ENSO) are one of the critical ways in which the ENSO impacts the global climate, specifically in the tropical Pacific, where they have the potential to cause extreme weather conditions. However, existing approaches struggle to effectively identify the evolution of ENSO-related precipitation anomalies that change rapidly in spatial distribution. To address this challenge, we propose the object-oriented spatiotemporal clustering approach using remote sensing products (OSCAR) for detecting evolutions of ENSO-related precipitation anomalies. The OSCAR was validated using simulated datasets and applied to precipitation anomalies over the tropical Pacific. The simulation experiment demonstrates that the OSCAR outperforms the dual-constraint spatiotemporal clustering approach (DcSTCA) in accuracy, particularly for rapidly evolving precipitation anomaly variations. The application of the OSCAR demonstrates its ability to recognize the evolution of ENSO-related precipitation anomalies over the tropical Pacific, which may offer valuable references for global climate change research.

Marine protected area (MPA) designs, including large-scale MPAs (LSMPAs; >150,000 km2), mobile MPAs (fluid spatiotemporal boundaries), and MPA networks, may offer different benefits to species and could enhance protection by encompassing spatiotemporal scales of animal movement. We sought to understand how well LSMPAs could benefit nine highly-mobile marine species in the tropics now and into the future by: 1) evaluating current range overlap within a LSMPA; 2) evaluating range overlap under climate change projections; and 3) evaluating how well theoretical MPA designs benefit these nine species. We focused on Palmyra Atoll and Kingman Reef, a 2000 km2 area within the 1.2 million km2 U.S. Pacific Remote Islands Marine National Monument (PRIMNM) that contains marine megafauna (reef and pelagic fishes; sea turtles; seabirds; cetaceans) reflecting different behaviors and habitat use. Our approach is useful for evaluating the effectiveness of the Palmyra-Kingman MPA and PRIMNM in protecting these species, and tropical LSMPAs in general, and for informing future MPA design. Stationary MPAs provided protection at varying scales. Reef manta rays (Mobula alfredi), grey reef sharks (Carcharhinus amblyrhynchos), green sea turtles (Chelonia mydas), and bottlenose dolphins (Tursiops truncatus) had overall small ranges (

In this study, we explored impacts of interannual variations of chlorophyll on seasonal predictions of the tropical Pacific by the SINTEX-F2 dynamical climate prediction system, which is highly skillful at predicting El Niño/Southern Oscillation (ENSO) and other tropical climate phenomena. We conducted twin re-forecast experiments; one system used the observed climatology of chlorophyll to compute the shortwave absorption in the upper ocean, while the other used the observed chlorophyll with year-to-year variations. Although the chlorophyll impacts on predictions of the Niño 3.4 index were limited, improvements are noticed in the predictions of sea surface temperature over the eastern edge of the Western Pacific Warm Pool. This region corresponds to the separation between warm, low-salinity waters of the warm Pool and cold, high-salinity upwelled waters of the Pacific cold tongue in the central-eastern equatorial Pacific. The improvement was very striking in the 2015 case, when a super El Nino occurred.

The size-spectrum model has been considered a useful tool for understanding the structures of marine ecosystems and examining management implications for fisheries. Based on Chinese tuna longline observer data from the central and eastern tropical Pacific Ocean and published data, we developed and calibrated a multispecies size-spectrum model of twenty common and commercially important species in this area. We then use the model to project the status of the species from 2016 to 2050 under five constant-fishing-mortality management scenarios: (1) F=0; (2) F=Frecent, the average fishing mortality from 2013 to 2015; (3) F=0.5Frecent; (4) F=2Frecent and (5) F=3Frecent. Several ecological indicators were used to track the dynamics of the community structure under different levels of fishing, including the mean body weight, slope of community size spectra (Slope), and total biomass. The validation demonstrated that size-at-age data of nine main catch species between our model predictions and those empirical data from assessments by the Western and Central Pacific Fisheries Commission matched well, with the R2>0.9. The direct effect of fishing was the decreasing abundance of large-sized individuals. The mean body weight in the community decreased by ∼1 500 g (21%) by 2050 when F doubled from Frecent to 2Frecent. The higher the fishing mortality, the steeper the Slope was. The projection also indicated that fishing impacts reflected by the total biomass did not increase proportionally with the increasing fishing mortality. The biomass of the main target tuna species was still abundant over the projection period under the recent fishing mortality, except Albacore tuna (Thunnus alalunga). For sharks and billfishes, their biomass remained at relatively higher levels only under the F=0 scenario. The results can serve as a scientific reference for alternative management strategies in the tropical Pacific Ocean. [ABSTRACT FROM AUTHOR]

Changes in ocean carbon inventory are considered the likely primary driver of declining glacial atmospheric pCO2 through the Mid‐Pleistocene Transition (MPT). Here, we present global core‐top calibrations of the "size‐normalized weight" (SNW) of planktonic foraminifera for estimating paleo‐deep‐water Δ[CO32−]. Then, we apply this approach to reconstruct deep‐water Δ[CO32−] in the western tropical Pacific since ∼1.4 Ma. At ∼1.0–0.9 Ma, a rapid weakening of North Atlantic Deep Water (NADW) resulted in a transient increase of ∼10 μmol kg−1 in deep‐water Δ[CO32−], after which deep‐water Δ[CO32−] declined at ∼0.9–0.7 Ma. Glacial and interglacial deep‐water Δ[CO32−] reveals stepwise declines of about 7 and 10 μmol kg−1, respectively, after MIS 20 (0.79–0.81 Ma) and MIS 19 (0.76–0.79 Ma), reflecting increased DIC content in the deep Pacific. We infer that a sustained increase in deep Pacific carbon storage following the MPT was linked to enhanced oceanic stratification and greater influence of CO2‐rich Southern Ocean‐sourced waters. Plain Language Summary: Cyclic continental glaciation has been a primary feature of the Earth's climate system for the past 2 million years. At around 900,000 years ago, the climate system shifted from shorter, less intense to longer, stronger cycles. This climate shift, known as the Mid‐Pleistocene Transition (MPT), was marked by a decline of atmospheric pCO2. Previous geological records have shown that atmospheric CO2 was stored in the deep Atlantic Ocean at that time. The present study provides evidence for greater carbon storage in the deep Pacific Ocean. We infer that enhanced global deep‐ocean carbon storage during the MPT was due to expansion of sea ice in the Southern Ocean. Increased sea‐ice cover reduced outgassing of CO2 from the deep ocean. CO2‐rich deep waters from the Southern Ocean were transported around the world, making the Pacific Ocean an important carbon reservoir during the MPT. Key Points: Global core‐top SNW‐Δ[CO32−] calibrations are developedGlacial and interglacial deep Pacific Δ[CO32−] decreased by 7 and 10 μmol kg−1, respectively, during the MPTDeep Pacific carbon storage increased during the MPT due to enhanced Southern Ocean stratification [ABSTRACT FROM AUTHOR]

Tropical Pacific (TP) air–sea coupling is generally accompanied by significant zonal sea surface temperature anomalies (SSTAs) gradient. Here, the wintertime zonal SSTA gradient structures were highlighted in the zonal mean departure SSTA (ZMD-SSTA) field, and separated into two orthogonal dominant components by empirical orthogonal function (EOF) analysis: the west–east dipole (EOF1, 70.7%) and the zonal tripole (EOF2, 23.0%) structure. EOF result comparisons, singular value decomposition (SVD), correlation and composite analyses shows that both the two gradient structures are highly coupled with Walker circulation (WC) but in obviously different spatiotemporal features, and together constitute the vast majority of the coupling variability. Further, the dipole structure can be largely reflected by the indices for eastern-type El Niño-Southern Oscillation (ENSO), but the central-type ENSO indices appears as a superposition of both dipole and tripole structures signals. In rare events of "uncoupled El Niño warming", the two gradient structures can further describe the weaker zonal SSTA gradient under the significant local SSTA in eastern Pacific. These implies that the dipole and tripole structures here may be beneficial to independently reflect the two distinct sea-air coupling structures and supplement the gradient information during ENSO. In addition, the dipole zonal SSTA gradient structure and air-sea feedback associated with it decay rapidly and disappear before the following summer, while the tripole one shows a longer persistence lasting until autumn. The lead–lag relationship with Niño3.4 index indicated that the wintertime tripole SSTA gradient structures precedes the development of ENSO by 1-year. [ABSTRACT FROM AUTHOR]

Sea surface temperature (SST) anomalies over the tropical Pacific, such as El Niño‐Southern Oscillation (ENSO) events, can cause intensified air‐sea couplings and different climate impacts. Although there are quite a few indices describing the event magnitude, little attention is paid to directly measuring air‐sea coupling strengths. Using Dynamical Systems Metrics, we introduce an index to quantify air‐sea coupling strengths over the tropical Pacific. This coupling index explains the relatively weak impact of the super El Niño in 2015/2016, and characterizes the ENSO diversity and asymmetry. Particularly, this index can identify several unusual neutral days with prolonged strong air‐sea couplings, where SST anomaly distributions are not as homogeneous as the ENSO events, but which have caused intense climate impacts. Our results demonstrate the close relationship among air‐sea coupling strengths, SST anomalies, and coupled feedbacks, which may promote better understandings on the events diversity related to SST anomalies over the tropical Pacific. Plain Language Summary: It is widely known that each El Niño event has its unique climate impacts. Noting that El Niño‐Southern Oscillation (ENSO) is essentially an atmosphere‐ocean coupling phenomenon, the different ENSO impacts may indicate different air‐sea coupling strengths. Taking both spatial and temporal features of the observational data sets into account, we capture the co‐variation patterns between atmospheric and oceanic meteorological fields, and present a coupling index to infer the instantaneous air‐sea coupling strength over tropical Pacific. Analyses show that the sea surface temperature (SST) anomalies exhibit diverse spatial patterns, which accompanies with different air‐sea coupling strengths and climate impacts. These differences exactly characterize the diversity of tropical Pacific SST anomalies, which exist not only in El Niño and La Niña events, but also in neutral days. Compared to the existing SST‐based Niño indices, it may be a more effective way to infer the potential SST impacts through measuring the air‐sea coupling strengths directly. Furthermore, this coupling metric may also serve as a useful tool in the study of atmosphere‐ocean coupling dynamics and extreme impacts. Key Points: Instantaneous air‐sea coupling strengths over tropical Pacific are estimated by Dynamical Systems MetricsThe air‐sea coupling strengths are linked to the El Niño‐Southern Oscillation (ENSO) diversity and climate impactsIn addition to ENSO events, the sea suface temperature anomaly patterns with strong air‐sea interactions also exist in some unusual neutral days [ABSTRACT FROM AUTHOR]

Metazoan parasite communities can experience temporal structural changes related to seasonal and/or local variations in several biotic and abiotic environmental factors. However, few studies have addressed this issue in tropical regions, where changes in water temperature are less extreme than in temperate regions, so the factors or processes that can generate variations in these parasite communities are as yet unclear. We quantified and analysed the parasite communities of 421 Lutjanus peru (Nichols & Murphy, 1922) collected from Acapulco Bay in Guerrero, Mexico, over a four-year period (August 2018 to April 2021), to identify any interannual variation due to local biotic and abiotic factors influenced by natural oceanographic phenomena, such as El Niño–Southern Oscillation, or La Niña. Twenty-five metazoan parasite taxa were recovered and identified: seven Digenea species; two Monogenea; one Cestoda; one Acanthocephala; four Nematoda; and ten of Crustacea (seven Copepoda and three Isopoda). The digeneans and copepods were the best represented parasite groups. The parasite communities were characterized by a high numerical dominance of helminth larvae. Species richness at the component community level (13 to 19 species) was similar to reported richness in other Lutjanus spp. The parasite communities of L. peru had a high variability in species composition, but low aggregate variability (e.g. species diversity), suggesting that structure of these communities may be quite stable over time. A clear interannual variation pattern was not observed, suggesting that parasite species of this host may respond differently to variations in environmental factors. Interannual variations were possibly caused by a combination of biotic (i.e. host feeding behaviour and body size) and local abiotic factors (influenced by climatic anomalies) which generated notable changes in the infection levels of several component species. [ABSTRACT FROM AUTHOR]

We show evidence that tropical atmospheric variability over the central tropical Pacific modulates the circulation over the western Arctic and the North Atlantic-European sector, impacting the summer precipitation especially over Nordic European countries (NEC). Our results, based on the ERA5 reanalysis, suggest the occurrence of a teleconnection mechanism (similar to the Pacific North American pattern) between the tropical Pacific in early spring and summer precipitation over NEC, and we propose two indices as predictors for NEC summer precipitation based on geopotential height anomalies at 500 hPa over the western tropical Pacific during March. We propose an empirical model based on both indices as predictors and assess the model’s skill with a leave-one-out cross-validation procedure. Over large portions of NEC, our proposed empirical model is able to reproduce dry, normal and wet years, defined from summer standardized precipitation anomalies, with a Heidke skill score greater than 0.9.

Models in the North American Multi-Model Ensemble (NMME) predict sea surface temperature (SST) trends in the central and eastern equatorial Pacific Ocean which are more positive than those observed over the period 1982–2020. These trend errors are accompanied by linear trends in the squared error of SST forecasts whose sign is determined by the mean model bias (cold equatorial bias is linked to negative trends in squared error and vice versa). The reason for this behavior is that the overly positive trend reduces the bias of models that are too cold and increases the bias of models that are too warm. The excessive positive SST trends in the models are also linked with overly positive trends in tropical precipitation anomalies. Larger (smaller) SST trend errors are associated with lower (higher) skill in predicting precipitation anomalies over the central Pacific Ocean. Errors in the linear SST trend do not explain a large percentage of variability in precipitation anomaly errors, but do account for large errors in amplitude. The predictions toward a too warm and wet tropical Pacific, especially since 2000, are strongly correlated with an increase in El Niño false alarms. These results may be relevant for interpreting the behavior of uninitialized CMIP5/6 models, which project SST trends that resemble the NMME trend errors.

The upper zonal oceanic circulations in the tropical Pacific play a crucial role in modulating weather and climate in the tropical Pacific Ocean. However, they are poorly simulated in state-of-the-art climate models. We apply a simple bias correction scheme by only assimilating observed sea surface temperature (SST) data into a coupled earth system model, named the Chinese Academy of Sciences Earth System Model version 2 (CAS-ESM 2.0), to better reproduce the upper zonal currents in tropical oceans. There are mainly two reasons for this usage of SST assimilating method: 1) SST has dominant effects on the air–sea interactions over the tropical region; 2) The lack of effective and long-term ocean-current observation data currently. Our results show that the SST assimilation can significantly improve the strength of the Pacific Equatorial Undercurrent (EUC), the North Equatorial Countercurrent (NECC) and the South Equatorial Current (SEC) through reducing biases in the air–sea turbulence flux. Nevertheless, the SST assimilation has limited effects on improving the simulation of the spatial structure of these zonal currents in the tropical Pacific. The improvement of the wind stress curl over the tropical Pacific region mainly contributes to the improved simulated strength of the Pacific EUC, the NECC and the SEC. It also connects to the reduced biases in atmospheric convective precipitation and sea-level pressure induced by the reduction of the SST bias.

Melt (2019), Jeff Murray’s debut novel is set in the near future of 2048. It depicts how the Anthropocene has wrought massive changes to seascapes, islandscapes, and landscapes, especially those of the tropical Pacific. The novel follows the plight of the people of Independence, a fictional low-lying Pacific island, who, due to rising sea levels and tropical storms, seek to migrate to New Zealand. However, migration is an option for rich countries, and the island community remains climate refugees on their ecologically crumbling island in a new world of mass climate migration. This paper focuses on cultural seascapes and landscapes of the Anthropocene, disruptions in human-nature relationships, and the possibility of human adaptation through climate migration. We read Melt with reference to the ecocritical theories of Cheryll Glotfelty, Lawrence Buell, and M. R. Mazumdar.

The sea surface temperature anomalies (SSTAs) in the tropical Pacific (TP) and North Atlantic (NA) are both important factors regulating the winter rainfall over southern China (SC). Our results show the combined impact of SSTAs exhibits an offset effect before 1985, after a decadal transition period, the two SSTAs patterns form an additive effect on the interannual timescale after 1995. These distinct impacts of the TP and NA result in the southward shift of the winter rainfall variability, which is associated with the decadal change of the TP and NA. Both the background modes in TP and NA show a phase transition during the period 1985–1995, accompanied by the interannual variations of the SSTAs in two ocean basins before 1985 and after 1995. Before 1985, the canonical El Niño‐related southerly winds of the anticyclone over the western North Pacific transport sufficient water vapour and enhance rainfall in SC. While the concurrent dipole NA SSTA‐related wave train propagates to Eurasia, causing a cyclone and divergence of water vapour fluxes suppressing the local rainfall. After 1995, the El Niño‐related warm SSTAs move westward and strengthen the rainfall anomalies in the Yangtze River basin. Meanwhile, a tripole mode of SSTAs replaces the dipole counterpart in NA, resulting in the anomalous cyclonic circulation over South Asia with more rainfall in the south edge of SC. The decadal changes of the TP and NA mode combination could affect the seasonal distribution and prediction of China winter rainfall. [ABSTRACT FROM AUTHOR]

In this study, sea surface salinity (SSS) indexes are derived from reanalysis and observational datasets to distinguish the two types of (Central Pacific (CP) and Eastern Pacific (EP)) El Niño events in the tropical Pacific. Based on the SSS anomalous spatial and temporal pointwise correlations with sea surface temperature (SST) indexes of two types of El Niño events, the key areas with SSS variations for EP and CP El Niño events are identified. For EP El Niño events, the key areas are located over an arcuate area centered at (0°, 130°E) and in the central equatorial Pacific covering (5°S–5°N, 175°W–158°W). For CP El Niño events, the key areas are located in the northeastern western Pacific covering (2°S–9°N, 142°E–170°E) and in the southeastern Pacific covering (20°S–10°S, 135°W–95°W). The key areas for EP and CP El Niño events in this study are not located near the dateline in the equatorial Pacific and differ from those obtained from the regression or composite methods. Accordingly, these key areas are used to construct SSS indexes, termed as the CP/EP El Niño SSS index (CSI/ESI), to distinguish EP and CP El Niño events independently. The SSS indexes are verified by different datasets over varying time periods and they can be adequately used to identify the two types of El Niño events and serve as another useful tool for monitoring ENSO. These analyses offer novel insight into how to represent the diversity of El Niño events. [ABSTRACT FROM AUTHOR]