Eastern Equatorial Pacific Ocean Research Articles

Pliocene Weakening of Gradients in Temperature but Not in Productivity in the Eastern Equatorial Pacific

AbstractThe modern eastern equatorial Pacific Ocean (EEP) exhibits strong upwelling, producing pronounced gradients in sea surface temperature (SST), nutrient concentration, and biological productivity between 80° and 140°W. During the globally warmer late Pliocene (3.0–3.6 Ma), the EEP may have experienced permanent El Niño‐like conditions, supported by a reduced SST gradient across the equatorial Pacific. However, the weakened east‐west SST gradient has been controversial, with disparate results depending on the proxy used to monitor Western Warm Pool SSTs. We present new Pliocene alkenone‐based SST and paleoproductivity records from four Ocean Drilling Program (ODP) cores spanning an east‐west transect across the EEP, which present an internally consistent picture of SST and productivity gradients in the modern cold tongue, resolved at orbital‐scale variability. Strong agreement between core top reconstructions and satellite estimates indicates that alkenone paleotemperature and paleoproductivity proxies are appropriate for reconstructing Pliocene EEP conditions. The average SST gradient between 90° and 120°W was reduced from the modern 1.8°C gradient to 0.9°C in the late Pliocene. Despite the weakened SST gradient, the surface productivity gradient was stronger during the late Pliocene compared to modern, based on calibrated X‐ray fluorescence biogenic opal and alkenone average accumulation rates. Contrary to modern El Niño SST and productivity patterns, reduced Pliocene surface productivity did not accompany the weakened SST gradient. Instead, strong Pliocene biogenic opal and alkenone concentration accumulation gradients in the eastern EEP suggest that subsurface tilting of the nutricline and thermocline persisted to supply vigorous upwelling of warm but nutrient‐rich subsurface waters in a warmer climate.

Iron fertilization–induced deoxygenation of eastern equatorial Pacific Ocean intermediate waters during the Paleocene–Eocene thermal maximum

Abstract The Paleocene–Eocene thermal maximum (PETM), a transient period of global warming, is considered to be an important analog for future greenhouse conditions. It was accompanied by a significant carbon cycle perturbation. Although ocean deoxygenation across the PETM is reported widely, its mechanism in the open ocean remains uncertain. Here, we present magnetic and geochemical analyses of sediments from the eastern equatorial Pacific Ocean. We found that iron fertilization during the PETM by eolian dust and volcanic eruptions fueled eastern equatorial Pacific Ocean productivity. This process led to increased organic matter degradation and oxygen consumption in intermediate waters, leading to deoxygenation. Our findings suggest that iron fertilization could be an important driver of open-ocean oxygen loss, as a side effect of global warming.

Dynamically computed characteristic adjustment time scale for Zhang–McFarlane convective parameterization scheme

AbstractCharacteristic adjustment time scale τ is an important parameter in convective parameterization scheme. In this paper, we propose a dynamic calculation formula of τ in the Zhang–McFarlane scheme based on convective available potential energy (CAPE) in order to improve the simulation of precipitation. The performance of using the new formula is tested and evaluated using the Community Atmosphere Model (CAM5) for numerical experiments. The results indicate that the root mean square errors of mean precipitation amount over the Northern Hemisphere eastern equatorial Pacific Ocean, the central Indo-Pacific Warm Pool, the Tibetan Plateau, and northern South America are reduced by 20.15, 16.40, 12.56, and 6.45% in summer, respectively, after a dynamic τ is adopted. The dynamically computed τ improves the Pacific Walker circulation by strengthening the western ascending and eastern descending, and increases the intensity of deep convective precipitation in tropical areas by at least 1 mm/day. Dynamic τ also increases the frequency of large deep convective precipitation in the equatorial Pacific by almost 50%, and decreases the frequency of light deep convective precipitation in many other regions. The dynamic τ has positive effects in the areas with large CAPE and spatiotemporal variability, and also leads to an increase in deep convective precipitation and a significant decrease in large-scale precipitation over high-altitude regions of windward slopes. Therefore, the generation of exaggerated precipitation in the highlands is reduced in the CAM5. Overall, the dynamic calculation of characteristic adjustment time scale can improve precipitation simulation.

Climate-related habitat variations of Humboldt squid in the eastern equatorial Pacific Ocean

An integrated habitat suitability index (HSI) model was developed in this study for Dosidicus gigas in the eastern equatorial waters of the Pacific Ocean to explore climate-related spatial and temporal variability in the habitat distribution pattern based on three crucial environmental variables: sea surface temperature (SST), sea surface salinity (SSS) and chlorophyll-a concentration (Chl-a). Results revealed that the HSI model could accurately predict potential habitats for D. gigas. The habitat suitability varied significantly by month, with highest suitability in April and lowest in March. Besides, from December to May, the longitudinal gravity center of the fishing grounds (LONG) and the HSI overall shifted eastward and the latitudinal gravity center shifted northward then southward. In comparison to the warm ENSO phases in 2019, the cold ENSO phases in 2018 produced increased suitable habitat from December to May, leading to a significantly higher CPUE. Prospective high-quality habitats in 2018 primarily occurred in the western regions, with the exception of December, which resulted in a more westward distribution of LONG from January to May. High-quality habitats moved northward from December to February and southward from March to May 2018, compared to minor latitudinal movement in 2019. It was inferred that annual variations in squid abundance and distribution were largely affected by the SST-related habitat pattern of D. gigas in the eastern equatorial waters. Our findings suggested that D. gigas habitats clearly varied by month and year and were greatly influenced by climate-induced environmental changes.

Predicting the interannual variability of the subtropical high over the western Pacific Ocean based on the improved information diffusion model

Because of its special location and structure, the Western Pacific Subtropical High (WPSH) influences greatly the climate and weather in East Asia, especially the summer precipitation. To clarify how the interannual variability (IAV) of the WPSH is related to anomalies in the tropical sea surface temperature (SST) and atmospheric circulation, time series of the intensity index of the WPSH are subjected to wavelet analysis, showing IAV in the index. Characteristic indexes are defined for three key sea areas and the equatorial-latitude westerly region. After a continuous wavelet transform, the oscillation period of them is similar to that of the WPSH. The cross-wavelet transform of the four regional and two WPSH indexes is used to obtain the corresponding time-delay correlation. Regarding the potential correlation, WPSH weakening leads to strengthening of the westerly wind and then affects the rise of SST in the eastern equatorial Pacific Ocean. At the same time, warm water moves eastward. This gradually increases the SST in the equatorial central Pacific and warm pool area and then strengthens the WPSH under the action of the Hadley circulation. From the above analysis, a model for predicting the IAV of the WPSH intensity index is established based on the information diffusion model improved by a genetic algorithm. An experiment is conducted to predict the IAV of the WPSH intensity index, and the results show that the prediction model is accurate in predicting the IAV trend, with good prediction for 84 months. The mean absolute percentage error is 14.44% and the correlation coefficient is 0.8507. Also, the normal and abnormal years of the WPSH are used as different starting points for different prediction experiments. However, the different starting points have little influence on the predictions, showing the stability of the model. Studying the IAV of the WPSH provides a strong theoretical and scientific basis for predicting its abnormal interannual behavior and offers the prospect of socially important disaster prevention and mitigation.

Transient Deep Ocean Cooling in the Eastern Equatorial Pacific Ocean at the Eocene‐Oligocene Transition

AbstractAt the Eocene‐Oligocene Transition (EOT), approximately 34 million years ago, Earth abruptly transitioned to a climate state sufficiently cool for Antarctica to sustain large ice sheets for the first time in tens to hundreds of millions of years. Oxygen isotope records from deep‐sea benthic foraminifera (δ18Ob) provide the foundation of our understanding of this pivot point in Cenozoic climate history. A deeper insight, however, is hindered by the paucity of independent deep‐sea temperature reconstructions and the ongoing challenge of deconvolving the temperature and continental ice volume signals embedded in δ18Ob records. Here we present records of deep‐sea temperature change from the eastern equatorial Pacific for the EOT using clumped isotope thermometry, which permits explicit temperature reconstructions independent of seawater chemistry and continental ice volume. Our records suggest that the deep Pacific Ocean cooled markedly at the EOT by 4.7 ± 0.9°C. This decrease in temperature represents the first direct and robust evidence of deep‐sea cooling associated with the inception of major Cenozoic glaciation. However, our data also indicate that this major cooling of the deep Pacific Ocean at the EOT was short‐lived (∼200 kyrs), with temperatures rebounding to values close to pre‐EOT levels by 33.6 Ma. Our calculated record of seawater δ18O suggests that this rebound in ocean temperature occurred despite the continued presence of a large‐scale Antarctic ice sheet. This finding suggests a degree of decoupling between deep ocean temperatures in the eastern equatorial Pacific Ocean and the behavior of the newly established Antarctic ice sheet.

Prediction of La Niña Events Based on BP Neural Network Model

As an extreme weather phenomenon, La Niña event will cause low water temperature in the equatorial eastern Pacific Ocean and abnormal longitudinal circulation in East Asia, resulting in widespread and continuous abnormal cooling of sea surface temperature in the eastern and central equatorial Pacific Ocean, which will cause frequent precipitation and flooding in the north and high temperature and low rainfall and frequent droughts in the south[1]. Therefore, it is particularly important to assess the damage and propose response strategies[2]. For the main countries involved in the global triple La Niña event, this paper selects four representative countries located in different regions to analyze, through descriptive analysis and graphical visualization, and selects the relevant index data of the last three years: monthly average maximum and minimum temperatures, monthly average precipitation rate, monthly average precipitation days, monthly average wind speed and monthly average water temperature, and finds that New York City and Brazil were affected by the triple La Niña event at the same time and were affected to a higher degree, and the temperature changes in Malasila and Jakara were stable, and the temperature effects brought by the triple La Niña event were smaller[3]. Then, a BP neural network model was established to predict the probability of future La Niña events in each region by modeling pressure, temperature, and salinity data, and it was found that a total of 110 regions would experience La Niña events in the future, with a general probability of 55%-60%..

Streamflow reconstruction in the Kafirnigan River, Tajikistan since 1568 CE reveals a linkage between southern Central Asian hydrological variation and ENSO

AbstractLong‐term hydroclimate change can provide reliable reference for water resources management in Central Asia. However, only a few palaeohydrological records exist in Tajikistan. To obtain a long‐term perspective on hydrological changes in Tajikistan, we developed, for the first time, a streamflow reconstruction from September of the previous year to June of the current one in the Kafirnigan River basin, based on Juniperus semiglobosa tree‐ring width indices from the Iskanderkul area in northern Tajikistan. The streamflow reconstruction explains 40% of the actual streamflow variance during the period 1939–1993. Spatial correlation analyses with gridded precipitation data indicate that our streamflow reconstruction contains a strong regional hydroclimatic signal for southern Central Asia. The high and low intervals of our streamflow reconstruction are closely related to the interdecadal variations of El Niño‐Southern Oscillation (ENSO). Our reconstructed streamflow is significantly correlated with sea surface temperatures in the eastern equatorial Pacific Ocean and northern Indian Ocean, indicate the existence of remarkable 11‐, 5.6–5.7‐, 4.3‐, 2.6‐, 2.3‐ and 2.0‐year cycles, and suggest a relationship between southern Central Asian streamflow variations and ENSO activity.

Equatorial Pacific dust fertilization and source weathering influences on Eocene to Miocene global CO2 decline

Stimulation of the biological pump by iron-bearing dust in the eastern equatorial Pacific Ocean plays an important role in long-term carbon sequestration, yet past dust fertilization and its impact on CO2 perturbations over major climate transitions remain debated. Here, we integrate proxies of dust input, source-region weathering, and biological pump activity from late Eocene to early Miocene sediments of Integrated Ocean Discovery Program Hole U1333, which includes the Eocene-Oligocene Transition (~34 million years ago) when a major ice sheet was first established on Antarctica. We find that intensified chemical weathering in the large central Asian dust source region enhanced atmospheric CO2 removal at ~34 Ma. Superimposed dust fertilization and biological pump action amplified this CO2 removal before ~34 Ma, while weakening of this amplification process helped to moderate the CO2 decline after that time. The observed inter-linked, counteracting processes with different timescales illustrate the complexity of carbon cycle feedbacks associated with major climate changes.

Tropical instability waves in a high-resolution oceanic and coupled GCM

Tropical instability waves (TIWs) are the dominant mesoscale variability in the eastern equatorial Pacific Ocean. TIWs have direct impacts on the local hydrology, biochemistry and atmospheric boundary layer, and feedback on ocean circulations and climate variability. In this study, the basic characteristics of Pacific Ocean TIWs simulated by an eddy-resolving ocean model and a coupled general circulation model are evaluated. The simulated TIW biases mainly result from the mean climatology state, as TIWs extract eddy energy from the mean potential and kinetic energy. Both the oceanic and coupled models reproduce the observed westward propagating large-scale Rossby waves between approximately 2°–8°N, but the simulated TIWs have shorter wavelengths than the observed waves due to the shallower thermocline. Meanwhile, the weak meridional shears of background zonal currents and the less-tilted pycnocline in these two models compared to the observations causes weak barotropic and baroclinic instability, which decreases the intensity of the simulated TIWs. We then contrast the TIWs from these two models and identify the roles of atmospheric feedback in modulating TIWs. The latent heat flux feedback is similar to observation in the coupled model but absent in the ocean model, contributing to the stronger standard deviation (STD) of the TIW SST in the ocean model. The ocean model is not able to capture realistic air–sea interaction processes when forced with prescribed atmospheric forcing. However, the misrepresented atmospheric feedback in the ocean model tends to decrease the sea surface height (SSH) variability, and the current feedback damping effect is stronger in the ocean model than in the coupled model. Combined with weaker barotropic conversion rate and baroclinic conversion rate in the ocean model than in the coupled model, the STD of the TIW SSH in the ocean model is weaker.

Paleoecology and evolutionary response of planktonic foraminifera to the mid-Pliocene Warm Period and Plio-Pleistocene bipolar ice sheet expansion

Abstract. The Pliocene-Recent is associated with many important climatic and paleoceanographic changes, which have shaped the biotic and abiotic nature of the modern world. The closure of the Central American Seaway and the development and intensification of Northern Hemisphere ice sheets had profound global impacts on the latitudinal and vertical structure of the oceans, triggering the extinction and radiation of many marine groups. In particular, marine calcifying planktonic foraminifera, which are highly sensitive to water column structure, exhibited a series of extinctions as global temperatures fell. By analyzing high-resolution (∼ 5 kyr) sedimentary records from the Eastern Equatorial Pacific Ocean, complemented with global records from the novel Triton dataset, we document the biotic changes in this microfossil group, within which three species displayed isochronous co-extinction, and species with cold-water affinity increased in dominance as meridional temperature gradients steepened. We suggest that these changes were associated with the terminal stages of the closure of the Central American Seaway, where following the sustained warmth of the mid-Pliocene Warm Period, bipolar ice sheet expansion initiated a world in which cold- and deep-dwelling species became increasingly more successful. Such global-scale paleoecological and macroevolutionary variations between the Pliocene and the modern icehouse climate would suggest significant deviations from pre-industrial baselines within modern and future marine plankton communities as anthropogenic climate forcing continues.

Insights into the deglacial variability of phytoplankton community structure in the eastern equatorial Pacific Ocean using [231Pa/230Th]xs and opal-carbonate fluxes

Fully and accurately reconstructing changes in oceanic productivity and carbon export and their controls is critical to determining the efficiency of the biological pump and its role in the global carbon cycle through time, particularly in modern CO2 source regions like the eastern equatorial Pacific (EEP). Here we present new high-resolution records of sedimentary 230Th-normalized opal and nannofossil carbonate fluxes and [231Pa/230Th]xs ratios from site MV1014-02-17JC in the Panama Basin. We find that, across the last deglaciation, phytoplankton community structure is driven by changing patterns of nutrient (nitrate, iron, and silica) availability which, in turn, are caused by variability in the position of the Intertropical Convergence Zone (ITCZ) and associated changes in biogeochemical cycling and circulation in the Southern Ocean. Our multi-proxy work suggests greater scrutiny is required in the interpretation of common geochemical proxies of productivity and carbon export in the EEP.

The Sediment Green‐Blue Color Ratio as a Proxy for Biogenic Silica Productivity Along the Chilean Margin

AbstractSediment cores recently collected from the Chilean Margin during D/V JOIDES Resolution Expedition 379T (JR100) document variability in shipboard‐generated records of the green/blue (G/B) ratio. These changes show a strong coherence with benthic foraminiferal δ18O, Antarctic ice core records, and sediment lithology (e.g., higher diatom abundances in greener sediment intervals), suggesting a climate‐related control on the G/B. Here, we test the utility of G/B as a proxy for diatom productivity at Sites J1002 and J1007 by calibrating G/B to measured biogenic opal. Strong exponential correlations between measured opal% and the G/B were found at both sites. We use the empirical regressions to generate high‐resolution records of opal contents (opal%) on the Chilean Margin. Higher productivity tends to result in more reducing sedimentary conditions. Redox‐sensitive sedimentary U/Th generally co‐varies with the reconstructed opal% at both sites, supporting the association between sediment color, sedimentary U/Th, and productivity. Lastly, we calculated opal mass accumulation rate (MAR) at Site J1007 over the last ∼150,000 years. The G/B‐derived opal MAR record from Site J1007 largely tracks existing records derived from traditional wet‐alkaline digestion from the south and eastern equatorial Pacific (EEP) Ocean, with a common opal flux peak at ∼50 ka suggesting that increased diatom productivity in the EEP was likely driven by enhanced nutrient supply from the Southern Ocean rather than dust inputs as previously suggested. Collectively, our results identify the G/B ratio as a useful tool with the potential to generate reliable, high‐resolution paleoceanographic records that circumvent the traditionally laborious methodology.

The effects of redistributed heat flux on ocean climate change in FAFMIP heat flux anomaly experiments

The Flux–Anomaly-Forced Model Inter-comparison Project (FAFMIP) aims to study the response of the ocean to changes in prescribed surface flux (heat, freshwater, and wind) caused by atmospheric CO2 increase. Among these surface flux perturbations, the heat flux has the greatest effect on ocean heat uptake (OHU), the Atlantic Meridional Circulation (AMOC), and sea level changes. This occurs in part because of the redistributed heat flux (Qr’), which is the component of the heat flux driven by ocean circulation changes and almost nearly doubles the initial heat flux perturbation (F) prescribed by FAFMIP in the North Atlantic (NA). In this study, we used a standalone ocean model to quantitatively investigate the impact of Qr’ on OHU and the AMOC in prescribed heat anomaly experiments (faf-heat experiment in FAFMIP). We also showed that whether the other two FAFMIP heat flux anomaly experiments (faf-heat-NA50pct and faf-heat-NA0pct) can reasonably simulate the ocean’s response to prescribed surface heat flux, especially OHU and AMOC. Our findings show that faf-heat-NA50pct is better because the redistribution-feedback (Qr’) nearly equals the initial perturbation (50%F) in the NA and thus recovers the total perturbation F in faf-heat. Although direct comparisons cannot be drawn, both faf-heat-NA50pct and faf-heat experiments with no effect of Qr’ cause AMOC weakening that is roughly comparable with the 1pctCO 2 experiments. The magnitude of simulated AMOC weakening in faf-heat-NA50pct is 3.9Sv, accounting for about 29% of the AMOC intensity in unperturbed experiment, which is closer to the faf-heat experiment (about 31%) with no effect of Qr’ relative to the faf-heat experiment. Because of negative Qr’ in all regions except the NA region especially for the Central and Eastern Equatorial Pacific and Southern Ocean, the simulated global OHU in faf-heat-NA50pct is reduced by 10% as compared to the added OHU in the faf-heat experiment. The Qr’ in the faf-heat experiment increases OHU by approximately 13% of the total OHU and further reduces AMOC intensity by 3.4 Sv, accounting for 26% of the AMOC strength in an unperturbed experiment. Faf-heat-NA0pct results in a significant reduction in OHU (approximately 26%), and the magnitude of AMOC weakening is only approximately 1.9 Sv, despite no F being added in the NA.

Asian rainfall anomaly patterns associated with interannual variations of early and peak summer rainfall over the Indochina Peninsula

AbstractThis study investigates the rainfall anomaly patterns over Asia associated with interannual variations of early summer (May–June) and peak summer (July–August) Indochina Peninsula (ICP) rainfall during 1979–2016. It is found that the early and peak summer rainfall variation in the ICP displays an out‐of‐phase relation to that in central Asia and central China, respectively. Analysis reveals that the out‐of‐phase early summer rainfall variation between the ICP and central Asia tends to occur in ENSO decaying years and the out‐of‐phase peak summer rainfall variation between the ICP and central China tends to occur in ENSO developing years. The early summer out‐of‐phase rainfall anomaly pattern between the ICP and central Asia forms due to a Rossby wave type response to anomalous heating extending from the ICP to northeast India, which is attributed to a combined influence of same sign sea surface temperature (SST) anomalies in the equatorial eastern Pacific and tropical southwestern Indian Ocean and opposite sign SST anomalies in the tropical western North Pacific. The peak summer out‐of‐phase rainfall variation between the ICP and central China forms due to a meridional atmospheric circulation pattern over East Asia and the western North Pacific, which is resulted from the combined impacts of opposite SST anomalies in the equatorial central Pacific and tropical southeastern Indian Ocean. Further analysis indicates that the out‐of‐phase rainfall variations between the ICP and central Asia in early summer and between the ICP and central China in peak summer may occur without anomalous tropical Indo‐Pacific SST forcing.

The Impact of Indonesian Throughflow Constrictions on Eastern Pacific Upwelling and Water‐Mass Transformation

The Indonesian Throughflow (ITF) is a key link in the global ocean overturning circulation. Heat gained from upwelling and watermass transformation in the eastern equatorial Pacific Ocean (PO) is transported through the ITF into the Indian Ocean, ultimately connecting to high-latitude regions of heat loss such as the North Atlantic. However, state-of-the-art General Circulation Models (GCMs) often poorly simulate upwelling, particularly in the eastern Pacific boundary regions. Recent studies have hypothesized that these difficulties may be related to biases in downstream ITF volume and heat transport, whereby insufficient warm surface water from the western PO passes through the ITF, a complex region that is hard to accurately represent in models. Here, we test this hypothesis using a coarse-resolution ocean model by artificially widening the ITF and allowing greater quantities of warm water to exit the western PO. This reduces the Indo-Pacific sea-surface height and pressure gradient biases. Using diagnostics in temperature coordinates, we trace the source of increased ITF warm-water transport to enhanced watermass transformation of cold-to-warm waters in the eastern tropical PO. Additional cool water is brought to the surface in the Cold Tongue region, resulting in an enhancement of surface flux-driven warming. However, we find only limited evidence for changes in upwelling at lower temperatures along the eastern PO margins, considerably less than hypothesized in a previous study. Our experiment provides useful insights to help understand simulated ITF mass and heat transport biases and their links with the tropical PO in GCMs.

Simulation and Scaling of the Turbulent Vertical Heat Transport and Deep-Cycle Turbulence across the Equatorial Pacific Cold Tongue

Abstract Microstructure observations in the Pacific cold tongue reveal that turbulence often penetrates into the thermocline, producing hundreds of watts per square meter of downward heat transport during nighttime and early morning. However, virtually all observations of this deep-cycle turbulence (DCT) are from 0°, 140°W. Here, a hierarchy of ocean process simulations, including submesoscale-permitting regional models and turbulence-permitting large-eddy simulations (LES) embedded in a regional model, provide insight into mixing and DCT at and beyond 0°, 140°W. A regional hindcast quantifies the spatiotemporal variability of subsurface turbulent heat fluxes throughout the cold tongue from 1999 to 2016. Mean subsurface turbulent fluxes are strongest (∼100 W m−2) within 2° of the equator, slightly (∼10 W m−2) stronger in the northern than Southern Hemisphere throughout the cold tongue, and correlated with surface heat fluxes (r2 = 0.7). The seasonal cycle of the subsurface heat flux, which does not covary with the surface heat flux, ranges from 150 W m−2 near the equator to 30 and 10 W m−2 at 4°N and 4°S, respectively. Aseasonal variability of the subsurface heat flux is logarithmically distributed, covaries spatially with the time-mean flux, and is highlighted in 34-day LES of boreal autumn at 0° and 3°N, 140°W. Intense DCT occurs frequently above the undercurrent at 0° and intermittently at 3°N. Daily mean heat fluxes scale with the bulk vertical shear and the wind stress, which together explain ∼90% of the daily variance across both LES. Observational validation of the scaling at 0°, 140°W is encouraging, but observations beyond 0°, 140°W are needed to facilitate refinement of mixing parameterization in ocean models. Significance Statement This work is a fundamental contribution to a broad community effort to improve global long-range weather and climate forecast models used for seasonal to longer-term prediction. Much of the predictability on seasonal time scales is derived from the slow evolution of the upper eastern equatorial Pacific Ocean as it varies between El Niño and La Niña conditions. This study presents state-of-the-art high-resolution regional numerical simulations of ocean turbulence and mixing in the eastern equatorial Pacific. The results inform future planning for field work as well as future efforts to refine the representation of ocean mixing in global forecast models.

The Miocene/Pliocene Boundary In The North East Java Basin, Indonesia

As a part of the LEMIGAS Research Programme on Neogene Epoch Boundaries in the Indonesian Tertiary Basins, in 1981 fiscal year is selected North East Java Basin as an object for research. In this paper we will stress our work on the Miocene/ Pliocene Boundary of the basin based on planktonic Foraminifera. More recently a lot of paleontologists have been working on the Miocene/Pliocene Boundary problem. Bandy (1963) used the first appearance of Sphaeroidinella dihescens as a boundary in the Phillipine, whereas boundary based on the initial apppearance of Globoratalia margaritae. carried out an examination of samples from the Trubi Marl of the Zanclean Sicily and came to the conclusion approximately with middle N18 of this zonal scheme. Bolli ( 1966, revision in 19/0 ) put this stage In 1969, Blow Berggren (1973) proposed the limit of this stage boundary based on the last occurrence of Globoquadrina dehiscens. Kaneps (1974) based on this observation on planktonic Foraminifera of the DSDP cores from the Eastern Equatorial Pacific Ocean came to the conclusion that the Miocene/Pliocene Boundary lies at the base of Globoratalia tumida zone. The base of this zone was placed at the horizon of the initial appearance of Globoratalia tumida while the upper boundary was placed at the horizon of reversal in coiling direction of Pulleniatina primalis from left below to right above. Pringgoprawiro and Baharuddin (1979) on the other hand proposed the initial appearance of Sphaeroidinella immatura as a boundary between these two periods. The purpose of this paper is to study the ranges of some selected important species, and to detect how far these species can be used as a tool for Miocene/Pliocene Boundary in the North East Java Basin. No radiometric age dating has been done in the area.

Evaluation of East Asian Meiyu from CMIP6/AMIP simulations

East Asian Meiyu simulated by 35 global atmospheric models from the 6th Coupled Model Intercomparison Project (CMIP6)/Atmospheric Model Intercomparison Project (AMIP) were systematically evaluated for 1998–2014. The results show that most of the CMIP6/AMIP models can hardly reproduce the observed spatial pattern and interannual variability of East Asian Meiyu. The spatial pattern is relatively better simulated over Southern Korea and Japan where 14 out of 35 models have realistically simulated precipitation, as compared with the lower reaches of the Yangtze River where only 7 out of 35 models can well reproduce the Meiyu precipitation. For the Meiyu interannual variations, GFDL-CM4 and GFDL-ESM4 have the closest variance among the models versus the TRMM observations, while 12 out of 35 models show smaller variances. We explored the relationships of Meiyu precipitation with large-scale circulation and tropical sea surface temperature (SST), and showed that these relationships from CESM2-WACCM-FV2, EC-Earth3-CC, and MPI-ESM1-2-HAM agree well with those based on TRMM precipitation, MERRA2 reanalysis-derived large-scale atmospheric fields, and observed SST. It is found that the models with a better simulation of Meiyu precipitation can capture the relationship between Meiyu precipitation and the SST in the eastern equatorial Pacific and Indian Ocean more realistically. A performance ranking of the 35 individual CMIP6/AMIP models is further provided. It is shown that the top 20% of models based on interannual variability score tend to simulate a more realistic western Pacific subtropical high than the bottom 20% of models. And the top 20% of models based on comprehensive ranking measure simulate a more realistic EAP pattern than the bottom 20% of models.

Prediction Challenges From Errors in Tropical Pacific Sea Surface Temperature Trends

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.