Intense El Nino-Southern Oscillation Research Articles

The role of sea surface salinity in ENSO forecasting in the 21st century

Significant strides have been made in understanding El Niño-Southern Oscillation (ENSO) dynamics, yet its long-lead prediction remains challenging, especially for the El Niño events after 2000. Sea surface salinity (SSS) is known to affect ENSO development and intensity by influencing ocean stratification and heat redistribution and therefore, when combined with sea surface temperature (SST) data, can potentially enhance ENSO forecast skill. In this study, we develop a deep learning (DL) model that incorporates a multiscale-pyramid structure and spatiotemporal feature extraction blocks, and the model successfully extends effective ENSO forecast lead time to 24 months for 2000–2021 with reduced effect of the spring predictability barrier (SPB). Interpretable methods are then applied to reveal the time-dependent roles of SST and SSS in ENSO forecast. More specifically, SST is critical for short-medium lead forecasts (<1 year), while SSS is important for medium-long lead forecasts (>6 months). Furthermore, we track global SST and SSS spatiotemporal shifts related to subsequent ENSO development, highlighting the importance of ocean inter-basin and tropics-extratropics interactions. With increasing availability of satellite SSS observations, our findings unveil unprecedented potential for advancing ENSO long-lead forecast skills.

The Pacific Meridional Mode Influences ENSO by Inducing Springtime Near-Equatorial TCs in the Western North Pacific

Abstract Previous research has shown that tropical cyclones in the near-equatorial western North Pacific (NE-WNP TCs) in boreal spring are associated with the onset of El Niño–Southern Oscillation (ENSO). However, the cause of these TCs is unclear. Here, we find that the interannual activity of the springtime NE-WNP TCs is insensitive to the simultaneous ENSO intensity but is closely related to the springtime Pacific meridional mode (PMM). The lead–lag correlation between PMM and NE-WNP TCs is high from January to April, and the evolution of the SST anomaly associated with the NE-WNP TCs strongly manifests the seasonal footprint of the PMM. Analysis using AGCM experiments confirms that the positive PMM tends to reduce the vertical shear of zonal wind and sea level pressure and to increase vertical velocity in the middle atmosphere and surface humidity in the WNP. All of these conditions are favorable for NE-WNP TC genesis. We conducted CGCM experiments to validate that the NE-WNP TCs significantly influence ENSO development. A statistical regression model with respect to the impact of PMM on NE-WNP TCs and further on ENSO intensity was also conducted. The results imply that modulating the springtime NE-WNP TCs is another effective way in which the PMM influences ENSO. Significance Statement Some studies have found that springtime near-equatorial western North Pacific (NE-WNP) tropical cyclones (TCs) heavily impact ENSO development. Using observations and AGCM experiments, we showed that the genesis of these TCs is closely associated with the Pacific meridional mode (PMM), presumably because the PMM provides favorable conditions for TC genesis. We further showed that including the PMM-induced NE-WNP TCs in a CGCM leads to an El Niño–like response. The linkage between the PMM and NE-WNP TCs not only supplements the existing theories about tropical–subtropical interactions but also provides a new way to improve ENSO simulation and prediction.

ENSO skewness hysteresis and associated changes in strong El Niño under a CO2 removal scenario

El Niño-Southern Oscillation (ENSO) sea surface temperature (SST) anomaly skewness encapsulates the nonlinear processes of strong ENSO events and affects future climate projections. Yet, its response to CO2 forcing remains not well understood. Here, we find ENSO skewness hysteresis in a large ensemble CO2 removal simulation. The positive SST skewness in the central-to-eastern tropical Pacific gradually weakens (most pronounced near the dateline) in response to increasing CO2, but weakens even further once CO2 is ramped down. Further analyses reveal that hysteresis of the Intertropical Convergence Zone migration leads to more active and farther eastward-located strong eastern Pacific El Niño events, thus decreasing central Pacific ENSO skewness by reducing the amplitude of the central Pacific positive SST anomalies and increasing the scaling effect of the eastern Pacific skewness denominator, i.e., ENSO intensity, respectively. The reduction of eastern Pacific El Niño maximum intensity, which is constrained by the SST zonal gradient of the projected background El Niño-like warming pattern, also contributes to a reduction of eastern Pacific SST skewness around the CO2 peak phase. This study highlights the divergent responses of different strong El Niño regimes in response to climate change.

Study Variability of the Land Surface Temperature of Land Cover during El Niño Southern Oscillation (ENSO) in a Tropical City

The World Health Organization has reported numerous fatalities, primarily among urban residents, during El Niño events. This study employed remote sensing technology to investigate the influence of the El Niño Southern Oscillation on temperature. The objective was to analyze the effect of ENSO on temperature across different land cover types using Landsat satellite data. Pre-processing was applied to the satellite data before converting numerical values into surface temperatures. The findings revealed that RS technology effectively captured the impact of varying ENSO intensity levels on surface temperatures. ENSO strength influenced temperature variations in the study areas. During El Niño events, urban areas exhibited higher land surface temperatures compared to vegetation, wetlands, and water bodies, a pattern consistent during La Niña. Specifically, there was a 2.5 °C temperature increase in the urban land cover area during El Niño events between 2016 and 1997. Water bodies, vegetation, and wetlands experienced respective temperature increases of 0.17 °C, 0.17 °C, and +0.7 °C during ONI value 1 events between 2016 and 1997. These findings are crucial for local authorities, providing spatial information on hot spots to enhance vigilance against potential El Niño temperatures.

Understanding the delayed Amundsen Sea low response to ENSO

Although the El Niño-Southern Oscillation (ENSO) affects West Antarctica via teleconnection, it is delayed by a season, because the Amundsen Sea Low (ASL) anomaly in response to the ENSO is the strongest in May. However, the process and mechanism of the delay has not been fully elucidated yet. In this study, we examined the formation of the ENSO-driven teleconnection in each month from January to May by analyzing the kinetic energy conversion and Rossby wave propagation. The flow perturbed by the ENSO gains energy from the basic state by energy conversion, but the perturbation does not reach the high latitudes until April. In May, although the ENSO intensity becomes weak, the development of the subtropical jet induces waves to propagate further south, resulting in the anticyclonic circulation anomaly over the ASL region. Numerical experiments that account for the decay of the ENSO forcing and the monthly varying basic state also indicate that the formation of the teleconnection is the strongest in May. The results reveal that the configuration of the basic state is crucial for the teleconnection in response to the ENSO to reach West Antarctica.

Why could ENSO directly affect the occurrence frequency of Arctic daily warming events after the late 1970s?

Arctic winter daily warming events have sparked growing interest, particularly in recent years, when Arctic daily temperatures have approached melting point several times. This analysis reveals that the impact of the El Niño-Southern Oscillation (ENSO) on the frequency of Arctic daily warming events experienced an obvious change around the late 1970s, which may be attributed to changes in ENSO intensity. Since the late 1970s, due to stronger ENSO intensities, ENSO has induced a stronger Rossby wave; then, El Niño (La Niña) has deepened (weakened) the Aleutian Low and strengthened anomalous northerlies (southerlies) over the North Pacific, thereby decreasing (increasing) the frequency of Arctic daily warming events. In contrast, before the late 1970s, the ENSO did not have an apparent direct impact on the frequency of Arctic daily warming events due to its weaker intensity. Our findings provide a potential relationship between the equator and the Arctic to improve the prediction accuracy of extreme Arctic daily warming events. By analyzing Coupled Model Intercomparison Project phase-6 models, we confirm that the potential relation may be strengthened under the global warming scenario.

Centennial-scale variability of the Indian Summer Monsoon during the middle to late Holocene and its links with ENSO activity

Relatively little is known about the relationship between the Indian summer monsoon (ISM) and the El Niño-Southern Oscillation (ENSO) on the centennial timescale during the Holocene. We present a well-dated high-resolution X-ray fluorescence (XRF) scanning record from a sediment core from Lake Qionghai on the southeastern Tibetan Plateau, which reveals the impact of ENSO activity on ISM variability. The results indicate a gradual drying of the regional climate on the sub-orbital timescale, which is in broad agreement with ISM changes controlled by Northern Hemisphere summer insolation. Additionally, centennial-scale drought events occurred at around 6230–5740, 4620–4250, 3820–3540, 3210–2440, 2180–1320, and 1000–615 cal yr B.P. and are consistent with enhanced ENSO activity, documenting the occurrence of ENSO-related drought events in the Holocene. Both ISM oscillations and ENSO variability show significant 350-yr, 500-yr, and 800-yr cyclicities, and there is a highly significant negative relationship between the ISM and ENSO at these cyclicities, indicating that a weak ISM was related to increased ENSO intensity, and vice versa. Our findings provide evidence for the modulation of ISM intensity by ENSO variability on the centennial timescale during the Holocene.

The Interdecadal Change of the Relationship Between North Indian Ocean SST and Tropical North Atlantic SST

AbstractThe summertime North Indian Ocean (NIO) and tropical North Atlantic (TNA) sea surface temperature (SST) anomalies exert important impacts on atmospheric circulation and climate variation. Little attention is paid on the interdecadal change of NIO–TNA SST connection. This study reveals that the NIO–TNA SST relationship experiences an obvious interdecadal change around the early 2000s. The NIO and TNA SST correlation is positive and significant before the early 2000s, while this connection becomes weak and insignificant after that. This interdecadal change is closely associated with the changes in the El Niño‐Southern Oscillation (ENSO) intensity. During 1980–2001, strong ENSO forces a sustained SST warming in the southwest Indian Ocean, which further warms the summertime NIO via inducing antisymmetric circulation and reducing the upward surface latent heat flux. Meanwhile, strong ENSO forces a summertime TNA warming via arousing the Pacific North American (PNA) teleconnection. The PNA weakens the TNA trade winds, then reduces the upward surface heat flux and consequently warms the TNA. Thus, NIO and TNA SST connection is established via ENSO events during 1980–2001. In contrast, during 2002–2020, the summertime NIO SST anomaly is still related to ENSO. However, the connection between the TNA SST anomaly and ENSO is interrupted due to the weak ENSO intensity. Such weak ENSO yields a much weaker PNA teleconnection, which is inefficient to generate the TNA warming. Further analysis shows that the TNA warming during 2002–2020 is generated mainly by the negative North Atlantic Oscillation. Therefore, the connection between NIO and TNA SST anomalies collapses under the weak ENSO condition.

Unraveling forced responses of extreme El Niño variability over the Holocene.

Uncertainty surrounding the future response of El Niño–Southern Oscillation (ENSO) variability to anthropogenic warming necessitates the study of past ENSO sensitivity to substantial climate forcings over geological history. Here, we focus on the Holocene epoch and show that ENSO amplitude and frequency intensified over this period, driven by an increase in extreme El Niño events. Our study combines new climate model simulations, advances in coral proxy system modeling, and coral proxy data from the central tropical Pacific. Although the model diverges from the observed coral data regarding the exact magnitude of change, both indicate that modern ENSO variance eclipsed paleo-estimates over the Holocene, albeit against the backdrop of wide-ranging natural variability. Toward further constraining paleo-ENSO, our work underscores the need for multimodel investigations of additional Holocene intervals alongside more coral data from periods with larger climate forcing. Our findings implicate extreme El Niño events as an important rectifier of mean ENSO intensity.

Zonal Structure of Tropical Pacific Surface Salinity Anomalies Affects ENSO Intensity and Asymmetry

AbstractPrevious studies have revealed the potential importance of salinity in El Niño‐Southern Oscillation (ENSO) asymmetry, but the responsible mechanisms remain unclear. Here, we investigate how the zonal structure of surface salinity anomalies affects ENSO intensity and asymmetry by modifying freshwater flux in ocean general circulation model simulations. Results show that the amplitudes of El Niño and La Niña are both highly sensitive to zonal patterns of salinity anomalies, with the strongest sea surface temperature change occurring when maximum salinity anomalies are located near 170°W. Furthermore, the effect of salinity anomalies in the central Pacific on El Niño warming is larger than those in the western Pacific on La Niña cooling. Thus, the asymmetric salinity anomalies strengthen the temperature asymmetry between El Niño and La Niña. Temperature budget analysis shows that vertical mixing and entrainment due to salinity‐induced changes in stratification are a major response to different zonal patterns of freshwater flux forcing.

ENSO feedback drives variations in dieback at a marginal mangrove site

Ocean–atmosphere climatic interactions, such as those resulting from El Niño Southern Oscillation (ENSO) are known to influence sea level, sea surface temperature, air temperature, and rainfall in the western Pacific region, through to the north-west Australian Ningaloo coast. Mangroves are ecologically important refuges for biodiversity and a rich store of blue carbon. Locations such as the study site (Mangrove Bay, a World Heritage Site within Ningaloo Marine Park and Cape Range National Park) are at the aridity range-limit which means trees are small in stature, forests small in area, and are potentially susceptible to climate variability such as ENSO that brings lower sea level and higher temperature. Here we explore the relationship between mangrove dieback, and canopy condition with climatic variables and the Southern Oscillation Index (SOI)—a measure of ENSO intensity, through remote sensing classification of Landsat satellite missions across a 29 year period at a north-west Australian site. We find that the SOI, and seasonal mean minimum temperature are strongly correlated to mangrove green canopy (as indicator of live canopy) area. This understanding of climate variations and mangrove temporal heterogeneity (patterns of abundance and condition) highlights the sensitivity and dynamics of this mangrove forest and recommends further research in other arid and semi-arid tropical regions at mangrove range-limits to ascertain the extent of this relationship.

Paleolimnological evidence for lacustrine environmental evolution and paleo-typhoon records during the late Holocene in eastern Taiwan

The late Holocene lacustrine environmental evolution and paleo-typhoon records are poorly understood around lowland Liyu Lake and mountain Tunlumei Pond in eastern Taiwan. In this study, we use records of diatom populations, magnetic susceptibility, total organic carbon, carbon-to-nitrogen ratio, and δ13C from two lacustrine sediment cores in eastern Taiwan to reconstruct the paleoenvironment and the paleo-typhoon records during the late Holocene. Significant changes in lithology and in multi-proxy data in the record from lowland Liyu Lake (LYL) show that LYL became hydrologically isolated by 2850 cal BP, possibly as a result of landslide-induced alluvial fan formation. Synchronous increases of the diatom-inferred lake level proxy for LYL and regional precipitation proxies reflect a strengthened East Asia summer monsoon since 1600 cal BP. Eutrophication of the water in LYL is also inferred, and this is interpreted to be related to agricultural activities, which provides evidence for changes in land use during the past 200 years. The occurrence of diatom valves in sediment of the mountain Tunlumei Pond (TLM) indicates that the pond area has been stable since 760 cal BP, which reflects an increase in the local precipitation. The decrease of diatom-inferred pH indicates an increase in the input of acid runoff from the watershed during typhoon-triggered heavy rainfall. Both lacustrine records suggest that the typhoon intensity increased during the early Little Ice Age. The sediment records in northeastern Taiwan also suggest an increase in typhoon activity during the late Little Ice Age. The asymmetric pattern of typhoon intensity during the last 1000 years is interpreted to reflect the control exerted by anomalies in both global temperature and the El Nino-Southern Oscillation intensity on typhoon tracks over several centuries.

El Niño/Southern Oscillation during the 4.2 ka event recorded by growth rates of corals from the North South China Sea

The 4.2 ka event that occurred during the period from 4 500–3 900 a BP was characterized by cold and dry climates and resulted in the collapse of civilizations around the world. The cause of this climatic event, however, has been under debate. We collected four corals (Porites lutea) from Yongxing Island, Xisha Islands, South China Sea, dated them with the U-series method, and measured the annual coral growth rates using X-ray technology. The dating results showed that the coral growth ages were from 4 500–3 900 a BP, which coincide well with the period of the 4.2 ka event. We then reconstructed annual sea surface temperature anomaly (SSTA) variations based on the coral growth rates. The growth rate-based SSTA results showed that the interdecadal SSTA from 4 500–3 900 a BP was lower than that during modern times (1961–2008 AD). A spectral analysis showed that the SSTA variations from 4 500–3 900 a BP were under the influence of El Nino-Southern Oscillation (ENSO) activities. From 4 500–4 100 a BP, the climate exhibited La Nina-like conditions with weak ENSO intensity and relatively stable and lower SSTA amplitudes. From 4 100–3 900 a BP, the climate underwent a complicated period of ENSO variability and showed alternating El Nino- or La Nina-like conditions at interdecadal time scales and large SSTA amplitudes. We speculate that during the early and middle stages of the 4.2 ka event, the cold climate caused by weak ENSO activities largely weakened social productivity. Then, during the end stages of the 4.2 ka event, the repeated fluctuations in the ENSO intensity caused frequent extreme weather events, resulting in the collapse of civilizations worldwide. Thus, the new evidence obtained from our coral records suggests that the 4.2 ka event as well as the related collapse of civilizations were very likely driven by ENSO variability.

The Relationship Between South Pacific Atmospheric Internal Variability and ENSO in the North American Multimodel Ensemble Phase‐II Models

AbstractDespite substantial progress made in the theoretical understanding and practical prediction of the El Niño‐Southern Oscillation (ENSO), accurate predictions of particular ENSO characteristics (e.g., evolution, intensity, and spatial pattern) remain challenging. Using two models from the North American Multimodel Ensemble (NMME) Phase‐II hindcasts, we find that the austral winter atmospheric internal variability is a key determinant of how the South Pacific atmospheric circulation responds to concurrent tropical Pacific sea surface temperature anomalies. While this internal variability may not trigger ENSO onsets, it regulates the southeasterly trades and contributes to thermodynamic feedbacks that grow into an ENSO‐like structure during the following austral summer. The difference in the simulation of South Pacific atmospheric variability amongst ensemble members appears to be a significant source of the inter‐member spread in ENSO predictions. Monitoring South Pacific atmospheric variability provides an opportunity to improve the prediction of ENSO intensity and flavor with about a two‐season lead time.

A multi-proxy μ-XRF inferred lake sediment record of environmental change spanning the last ca. 2230 years from Lake Kanono, Northland, New Zealand

Reliable interpretation of annual-resolution climate proxies for wind, precipitation, and detrital influx are required for identifying the onset and periodicities of climatic events. In particular, this is essential for the evaluation of inter-annual, decadal, and centennial trends driven by shifting positions of the Southern Westerly Winds (SWW) and subsequent storm belts associated with the Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO). Here we present a quasi-annual data set of μ-XRF time series spanning ca. 2230 years from lake sediment cores from Lake Kanono, Northland, New Zealand. The μ-XRF time series were interpreted using a combination of principal component analysis (PCA) and cluster analysis, then verified with comparison to regionally averaged empirical rainfall and wind climate station data. Our results show that the wavelet patterns align with the PCA results allowing the μ-XRF time series to be classified into: Group I (detrital) and Group II (biological productivity and normalized climate proxies). The normalized Group II μ-XRF time series wavelet analyses displayed periodicities in the 2–16 year frequency, likely associated with ENSO, from ca. 237 BCE – 1330 CE. The data show clear evidence of both Polynesian and European settlement phases in this part of northern New Zealand, and that Polynesian settlement impact was coeval with changes in ENSO intensity and a phase shift in SAM ca. 1350 CE. The Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) appear in the μ-XRF time series data as separate clusters. This data suggests that the MCA is associated with windy/dry conditions with intermittent storminess. During the LIA, the 2–16 year periodicity associated with ENSO decreased and centennial to multi-decadal length periodicities increase, which may be an indication of an underlying SAM signal within the data. European settlement also had a direct impact on the lake basin via increased detrital influx, likely from farming activities and intensification of local forestry operations.

Prominent Precession Band Variance in ENSO Intensity Over the Last 300,000 Years

AbstractThree transient National Center for Atmospheric Research Community Climate System Model, version 3 model simulations were analyzed to study the responses of El Niño–Southern Oscillation (ENSO) and the equatorial Pacific annual cycle (AC) to external forcings over the last 300,000 years. The time‐varying boundary conditions of insolation, greenhouse gases, and continental ice sheets, accelerated by a factor of 100, were sequentially added in these simulations. The simulated ENSO and AC amplitudes change in phase, and both have pronounced precession band variance (~21,000 years). The precession‐modulated slow (orbital time scales) ENSO evolution is dominated linearly by the change of the coupled ocean‐atmosphere instability, notably the Ekman upwelling feedback and thermocline feedback. In contrast, the greenhouse gases and ice sheet forcings (~100,000‐year cycles) are opposed to each other as they influence ENSO variability through changes in AC amplitude via a common nonlinear frequency entrainment mechanism. The acceleration technique could dampen and delay the precession signals below the surface ocean associated with ENSO intensity.

Tropical cyclones act to intensify El Ni\xf1o

Tropical cyclones (TCs), some of the most influential weather events across the globe, are modulated by the El Niño–Southern Oscillation (ENSO). However, little is known about the feedback of TCs on ENSO. Here, observational and modelling evidence shows that TC activity in the southeastern western North Pacific can affect the Niño-3.4 index 3 months later. Increased TC activity in July–September can significantly contribute to the intensity of ENSO in October–December by weakening the Walker circulation and enhancing eastward-propagating oceanic Kelvin waves in the tropical Pacific. Thus, the greater the accumulated cyclone energy, the stronger (weaker) the El Niño (La Niña). A new physics-based empirical model for ENSO is constructed that significantly outperforms current models in predicting ENSO intensity from July to December and addressing the problem about the target period slippage of ENSO. Results suggest that TCs may provide significant cross-scale feedback to ENSO.

ENSO Normals: A New U.S. Climate Normals Product Conditioned by ENSO Phase and Intensity and Accounting for Secular Trends

AbstractClimate normals are traditionally calculated every decade as the average values over a period of time, often 30 years. Such an approach assumes a stationary climate, with several alternatives recently introduced to account for monotonic climate change. However, these methods fail to account for interannual climate variability [e.g., El Niño–Southern Oscillation (ENSO)] that systematically alters the background state of the climate similar to climate change. These effects and their uncertainties are well established, but they are not reflected in any readily available climate normals datasets. A new high-resolution set of normals is derived for the contiguous United States that accounts for ENSO and uses the optimal climate normal (OCN)—a 10-yr (15 yr) running average for temperature (precipitation)—to account for climate change. Anomalies are calculated by subtracting the running means and then compositing into 5 ENSO phase and intensity categories: Strong La Niña, Weak La Niña, Neutral, Weak El Niño, and Strong El Niño. Seasonal composites are produced for each of the five phases. The ENSO normals are the sum of these composites with the OCN for a given month. The result is five sets of normals, one for each phase, which users may consult with respect to anticipated ENSO outcomes. While well-established ENSO patterns are found in most cases, a distinct east–west temperature anomaly pattern emerges for Weak El Niño events. This new product can assist stakeholders in planning for a broad array of possible ENSO impacts in a changing climate.

How does the Asian summer precipitation-ENSO relationship change over the past 544 years?

The secular change of the Asian monsoon (AM)-El Niño–Southern Oscillation (ENSO) relationship has been recognized as a specter for seasonal forecast. The causes of such changes have not been well understood. How the monsoon-ENSO relationship underwent secular changes beyond instrumental period has rarely been discussed. Here we explore the multidecadal to centennial changes of the AM-ENSO relationship with the recently compiled Reconstructed Asian summer Precipitation (RAP) dataset (1470–2013) and multiple ENSO proxy indices. During the past five centuries, two leading modes of interannual variability of RAP are found to be associated with the ENSO developing and decaying phases, respectively. The mechanisms behind the modern monsoon-ENSO relationship can reasonably well explain the past monsoon behavior. In response to a developing ENSO, precipitation anomalies from the Maritime Continent (MC) via India to northern China are in phase, and this “chain reaction” tends to be largely steady since around 1620 AD when the Indian summer monsoon abruptly strengthened. Further, the strengthening of the link between developing-ENSO and Indian-northern China rainfall since 1620 AD concurred with a phase reversal of the Pacific Decadal Oscillation. During the decaying phase, however, the summer rainfall-ENSO relationship over the Yangtze River Valley-southern East China (YRV-SEC), the MC and central Asia, has gone through large multidecadal to centennial changes over the past five centuries. A remarkable reversal of sign in the AM-decaying ENSO relationship occurred roughly from 1740 to 1760 over the YRV-SEC and MC, which may be associated with the long-term strengthening of ENSO intensity. Future research should continue focusing on revealing the possible causes of the low-frequency changes in the monsoon-ENSO relationship using general circulation models and paleoclimate proxy reconstructions.

Seasonal and interannual variability of the mixed layer heat budget in the Caribbean Sea

Abstract The long-term mean annual cycle and interannual variability of the mixed layer heat budget in the Caribbean Sea are quantified by using high resolution oceanic and atmospheric reanalysis products (the GLobal Ocean ReanalYsis and Simulations, GLORYS2V4, and ERA-Interim) for the period spanning from January 1993 to December 2015. In this region the mixed layer depth (MLD) is relatively shallow, oscillating spatially from 10 to 90 m, with maximum values observed during the dry season (December to March), and minimum values during the main rainy season (September to November). The highest MLD values are found in the northwestern part of the basin and the lowest in the Central and northern South American coastal region. The strength and location of greater MLD oscillations over the Caribbean Sea depend on the intensity of the zonal winds and the location of the Caribbean-Low Level Jet (CLLJ). At interannual timescales, reanalysis data shows that the MLD anomalies are associated with extreme phases of the El Nino Southern Oscillation (ENSO); however, low statistical correlation suggests that other factors, such as a Quasi-Biennial Oscillation (QBO), or a weak ENSO cycle with a 2-year periodicity, could influence this region, and induce changes in the depth of the mixed layer and in the heat budget within it. The seasonal ocean heat balance within the mixed layer ranges between −315 and 393 W m−2 in the Caribbean region (monthly means around ±60 W m−2 averaged over the entire domain). The net air-sea heat flux varies seasonally around ±60 W m−2. Analysis of this term shows that during the dry season (rainy season), when the MLD is deep (shallow) the region loses (gains) heat, with net short wave radiation being the main gain, and the latent heat the main loss at seasonal and interannual timescales. The advection term is an order of magnitude less (monthly means from −2 to 7.5 W m−2) but has the highest values during the dry season in the northwest Caribbean Sea, when the winds and surface currents are intense. This term tends to provide small interannual heat variability (up to ±2 W m−2). The entrainment is almost negligible in its contribution to the budget. At interannual timescales this flux reduces the stored heat by up to ±1 W m−2. It is noted that although the MLD is not so clearly related with ENSO, the heat stored in this layer is significantly modulated by El Nino/La Nina remote forcing, especially during the period spanning from 1992 to 2001 when intense ENSO events occurred and affected the air-sea fluxes, and the advection. The CLLJ influences both the MLD and the heat budget in the Caribbean Sea. This jet is being modulated by ENSO and other long-term oscillations.