Pacific Warm Research Articles

Rapid surface water warming and impact of the recent (2013–2016) temperature anomaly in shallow coastal waters at the eastern entrance of the Gulf of California

Anthropogenically-induced global warming is increasing surface seawater temperatures (SST) worldwide. Furthermore, the Northeastern Tropical Pacific is affected by seasonal, interannual (El Niño – Southern Oscillation, marine heatwaves), and decadal variabilities (Pacific Decadal Oscillation). Here we analyzed a long-term (1973–2016) SST time-series from the Mazatlán coastal zone, at the eastern entrance of the Gulf of California (Mexico) to record the warming trend and to examine the effect of the 2013–2016 North Pacific SST positive anomaly. This SST time-series can be useful to better understand the interplay of surface water masses in the region (Tropical Surface Water, Gulf of California Water, and California Current Water) and their transport mechanisms. Variability analysis was focused on 2007–2016, for which a 10-year climatology was established. During this period, two La Niña and El Niño events, and a regional marine heatwave occurred in the Northeast Pacific. There was a significant positive correlation between the Oceanic Niño Index (ONI) and SST anomalies. La Niña events caused large negative anomalies (up to 4 °C) in maximum SST, and El Niño events caused large positive anomalies (up to 7 °C) in the minimum SST. The 2013–2014 regional marine heatwave was preceded by a previously unreported anomalous regional warming at the entrance of the Gulf of California (2012–2013), which caused positive anomalies of 4 °C in minimum SST. Since then, each winter showed increasing minimum SST anomalies until reaching a 7 °C maximum in 2016. Minimum SST positive anomalies were caused by i) the inhibition of coastal upwelling of cold waters, and ii) a limited penetration of California Current cold waters. For the past 40 years, we estimated a mean warming trend of 0.57 ± 0.01 °C per decade in the study area, which is larger than the global ocean increasing trend. This relatively fast warming rate could be caused by i) local effects caused by shallowness and coastal dynamics, ii) an increasing influence of warmer Tropical Surface Water transported by the Mexican Coastal Current, iii) the transport and upwelling of warmer waters from the Western Pacific Warm Pool during El Niño events, and iv) global warming, as increasing SST can induce stronger and longer-lasting thermoclines, especially in regions commonly affected by upwelling events. If this trend persists, a simple linear extrapolation would indicate that the mean SST from 1977 to 2100 would increase by 7 °C. This extrapolation should be taken with caution, but such an increase would have profound effects on the coastal ecosystems, so possible adaptation strategies merit urgent attention by scientists and coastal zone managers to dynamically adapt to coastal global warming and marine heatwaves. This methodology can be used in other coastal zones worldwide where enough field and satellite data are available.

Distinct Surface Warming Response Over the Western and Eastern Equatorial Pacific to Radiative Forcing

AbstractThis study examines regional characteristics of atmospheric and oceanic feedback processes in the western and eastern equatorial Pacific, by applying a localized surface heating in the respective region in a hierarchy of climate models. A western Pacific forcing is largely offset by a negative shortwave cloud radiative effect and damping via wind‐evaporation‐SST feedback. In contrast, an eastern Pacific forcing, while being partially compensated for by ocean dynamical adjustments, induces an amplified warming extending to the central Pacific due to weak local damping mechanisms. As for the inter‐model spread of the future tropical Pacific surface warming pattern, the ocean heat uptake response in the east can explain much of the spread both on fast (<5 years) and slow (>100 years) timescales. Our results suggest that an “El Niño‐like” warming pattern is probable in response to increasing greenhouse gases owing to the strong negative feedback intrinsic to the western Pacific.

Possible Causes of the Occurrence of a Rare Antarctic Sudden Stratospheric Warming in 2019

A minor Antarctic sudden stratospheric warming (SSW) with the strongest circulation changes since the first major SSW over the Antarctic was recorded in 2002 occurred in early September 2019. The diagnosis demonstrates two possible causes of this SSW. First, the tropical central Pacific warming is identified, which enhanced the amplitude of tropospheric planetary wavenumber 1 (W1) in the extratropics on the seasonal time scale. Second, the impact of intraseasonal convection anomalies similar to previous studies is also suggested here. The enhanced deep convection over the South Pacific Convergence Zone (SPCZ) in late August–early September excited a Rossby wave train to deepen an anomalous ridge, which significantly and persistently strengthened the tropospheric W1. The central Pacific warming and intraseasonal convection anomalies jointly provided the conditions for the occurrence of the Antarctic SSW in 2019 on different time scales. On the other hand, the difference of the stratospheric state between the Antarctic SSWs in 2019 and 2002 may be an important reason why the 2019 event did not meet the major SSW criteria. The stratospheric state before the 2019 SSW event is somewhat not as ideal as that of the 2002 event. Vertical planetary waves are, hence, more difficult to enter into the polar stratosphere, making it more difficult to trigger major events.

Dissimilarity among Ocean Reanalyses in Equatorial Pacific Upper-Ocean Heat Content and Its Relationship with ENSO

Dissimilarity among Ocean Reanalyses in Equatorial Pacific Upper-Ocean Heat Content and Its Relationship with ENSO

Impact of the Western Pacific Warm Pool and Kuroshio Dynamics in the Okinawa Trough During the Holocene

Impact of the Western Pacific Warm Pool and Kuroshio Dynamics in the Okinawa Trough During the Holocene

A storyline view of the projected role of remote drivers on summer air stagnation in Europe and the United States

Storylines of atmospheric circulation change, or physically self-consistent narratives of plausible future events, have recently been proposed as a non-probabilistic means to represent uncertainties in climate change projections. Here, we apply the storyline approach to 21st century projections of summer air stagnation over Europe and the United States. We use a Climate Model Intercomparison Project Phase 6 (CMIP6) ensemble to generate stagnation storylines based on the forced response of three remote drivers of the Northern Hemisphere mid-latitude atmospheric circulation: North Atlantic warming, North Pacific warming, and tropical versus Arctic warming. Under a high radiative forcing scenario (SSP5-8.5), models consistently project increases in stagnation over Europe and the U.S., but the magnitude and spatial distribution of changes vary substantially across CMIP6 ensemble members, suggesting that future projections are not well-constrained when using the ensemble mean alone. We find that the diversity of projected stagnation changes depends on the forced response of remote drivers in individual models. This is especially true in Europe, where differences of ∼2 summer stagnant days per degree of global warming are found amongst the different storyline combinations. For example, the greatest projected increase in stagnation for most European regions leads to the smallest increase in stagnation for southwestern Europe; i.e. limited North Atlantic warming combined with near-equitable tropical and Arctic warming. In the U.S., only the atmosphere over the northern Rocky Mountain states demonstrates comparable stagnation projection uncertainty, due to opposite influences of remote drivers on the meteorological conditions that lead to stagnation.

Central Equatorial Pacific Warming and Freshening in the Twentieth Century: Insights From a Coral Ensemble Approach

AbstractThe tropical Pacific influences climate patterns across the globe, yet robust constraints on decadal to centennial‐scale climate variations are difficult to extract from sparse instrumental observations in this region. Oxygen isotope (δ18O) records from long‐lived corals enable the quantitative reconstruction of tropical Pacific climate variability and trends over the twentieth century and beyond, but such corals are exceedingly rare. Here, we use multiple short coral δ18O records to create a coral ‘ensemble’ reconstruction of twentieth century climate in the central tropical Pacific. Ten U/Th‐dated fossil coral δ18O records from Kiritimati Island (2°N, 157°W) span 1891 CE to 2006 CE, with the younger samples enabling quantitative comparison to a large ensemble of modern coral records and instrumental sea surface temperature. A composite record constructed of modern and fossil Kiritimati coral δ18O records shows a shift toward warmer and fresher conditions from 1970 CE onward, consistent with previously published records in this region.

Warm and Cold Episodes in Western Pacific Warm Pool and Their Linkage With ENSO Asymmetry and Diversity

AbstractThis study investigates the role of temperature anomalies over the western Pacific warm pool (WPWP) in the asymmetry and diversity of El Niño‐Southern Oscillation. Based on observations, we select 12 cold and 13 warm WPWP episodes averaged over July to October. Using composite analyses, we reveal that the occurrence probability of El Niño events is much larger following the cold episodes than that of La Niña events related to warm episodes. The main reason for the different frequencies is that the westerlies associated with cold episodes are stronger and located eastwards than the easterlies for warm episodes, exerting more effective influences on the sea surface temperature in central‐eastern equatorial Pacific through Bjerknes feedback. As for intensity, the El Niño events tend to be stronger when the cold anomalies over WPWP are stronger, evidenced by both observations and Coupled Model Intercomparison Project Phase 6 simulations. The warming rate from July to October for El Niño events following cold episodes is three times greater than that of other historical events, denoting a prominent contribution from WPWP to the quick development of El Niño. Furthermore, we highlight the implication of WPWP on El Niño diversity with a greater probability of EP‐type El Niño under a colder WPWP state and successive westerly wind bursts. As such, the cold state of WPWP can provide an effective modification for the earlier operational prediction on El Niño intensity and flavors. On the contrary, the warm WPWP state may not be useful for future La Niña alerts.

Pacific Warming Pattern Diversity Modulated by Indo‐Pacific Sea Surface Temperature Gradient

AbstractThe multi‐model ensemble mean sea surface temperature (SST) of CMIP5 models shows an El Niño‐like Pacific warming (PW) trend, contradictory with the observational result which manifests a La Niña‐like PW pattern. Here, we demonstrate that these two SST PWs coexist in the CMIP5 models and they are largely determined by the model's tropical Indo‐Pacific SST gradient. When the Pacific warms faster than the Indian Ocean (IO), the model tends to project an El Niño‐like PW pattern. In contrast, a La Niña‐like warming trend prevails if a more rapid IO warming is simulated. We suggest that the PW pattern in an individual model is nonstationary and may transform from a La Niña‐like to an El Niño‐like when its interbasin SST gradient changes with more robust warming in the Pacific, and vice versa. Our conclusions shed great light on the future SST PW pattern change projected by the coupled models.

Asymmetric impacts of El Niño and La Niña on the Pacific–North American teleconnection pattern: the role of subtropical jet stream

The asymmetric impacts of El Niño and La Niña on the Pacific–North American teleconnection pattern in boreal winter have important implications for the surface air temperature and precipitation anomalies in North America. Previous studies have shown that the varying tropical convective heating contributes to the zonal shift of the teleconnection pattern during different El Niño/Southern Oscillation phases. In this study, using reanalysis, atmospheric general circulation model (AGCM) simulations, and a linear baroclinic model, we further present that the discrepancy of the subtropical jet stream (STJ) during El Niño and La Niña also contributes to the asymmetry. The atmospheric anomalies readily extract kinetic energy and effectively develop at the exit of the STJ. During El Niño (La Niña) years, as the central-eastern tropical Pacific warms up (cools down), the meridional temperature gradient in central subtropical Pacific increases (decreases), leading to the eastward (westward) shift of the STJ. The movement of the STJ leads to the shift of the location where disturbance develops most efficiently, ultimately contributing to the asymmetry of the teleconnection pattern.

Variation of Hourly Extreme Precipitation in the Three Gorges Reservoir Region, China, from the Observation Record

Extreme hourly precipitation is amongst the most prominent driving factors of flash floods and geological disasters. Based on the hourly precipitation data of 35 stations in the Three Gorges Reservoir Region (TGRR) from 1998 to 2020, we analyzed the spatiotemporal variation characteristics of hourly extreme precipitation indexes. The selected indicators included the frequency, intensity, period, annual maximum, trend of hourly heavy precipitation (20–50 mm/h) and hourly extreme heavy precipitation (≥50 mm/h) in the TGRR. Closely related climatic factors such as the Western Pacific Subtropical High Intensity (WPSHI) were also discussed. The results showed that in 2010–2020, the cumulative frequency of heavy precipitation magnitude between 25 and 40 mm/h slightly increased, while the corresponding frequency for magnitudes ≥50 mm/h decreased. In summer, the frequency of both heavy and extreme heavy precipitation increased in June and decreased in August, indicating a shift of extreme events to an earlier time in the flood season. The cumulative frequency of heavy precipitation in July had a period of about 7a, and that of extreme heavy precipitation had a period of 3a. The annual average intensity of heavy precipitation and extreme heavy precipitation in the TGRR was 28.9 mm/h and 61.4 mm/h per station, respectively, and both fluctuated and insignificantly decreased from 1998 to 2020. The annual maximum hourly precipitation center in the TGRR moved downstream from west to northeast. The frequency of heavy precipitation was relatively small along the main stream of the river valley. Both the frequency and total amount of heavy precipitation in southeast of the TGRR were significantly higher than those in other regions. Heavy precipitation in the majority of stations with high elevation (higher than 500 m) showed a decreasing trend. The cumulative frequency of precipitation with an intensity of 20–50 mm/h was closely correlated with the Western Hemisphere Warm Pool (WHWP) Index in February and the WPSHI Index in January, and especially, the abnormal large annual frequency (top 20%) showed strong correlation with the two indexes, implying highly predictable factors for extreme events. The frequency of precipitation intensity above 50 mm/h was correlated with the Western Pacific Warm Pool (WPWP) Area Index in January and the WPWP Intensity Index in November of last year. The research results provide a strong and refined factual basis for the assessment and prediction of extreme precipitation, and for disaster prevention and mitigation, in the TGRR.

Enhanced North Pacific subtropical gyre circulation during the late Holocene

The North Pacific Subtropical Gyre circulation redistributes heat from the Western Pacific Warm Pool towards the mid- to high-latitude North Pacific. However, the driving mechanisms of this circulation and how it changed over the Holocene remain poorly understood. Here, we present alkenone-based sea surface temperature reconstructions along the Kuroshio, California and Alaska currents that cover the past ~7,000 years. These and other paleorecords collectively demonstrate a coherent intensification of the boundary currents, and thereby the basin-scale subtropical gyre circulation, since ~3,000–4,000 years ago. Such enhanced circulation during the late Holocene appears to have resulted from a long-term southward migration of the Intertropical Convergence Zone, associated with Holocene ocean cooling. Our results imply that the North Pacific Subtropical Gyre circulation could be weakened under future global warming.

Climatic Drivers of Deglacial SST Variability in the Eastern Pacific

AbstractWe explore the response of northeastern Pacific sea surface temperature (SST) to deglacial (16–7 ka) climate variability as recorded in ‐based SST reconstructions spanning 65°N to 10°S. Included in the analysis is a new 23 kyr SST record from core NH8P from the northwest Mexican Margin. We isolate spatiotemporal patterns in regional SSTs with trend empirical orthogonal function (TEOF) analysis. The dominant TEOF mode reflects deglacial warming associated with rising . Tropical and subtropical SSTs correlated most strongly with this mode, suggesting that the thermodynamic response of the tropical eastern Pacific to greenhouse gas forcing was the dominant driver of regional SST change during deglaciation. The second TEOF mode reflects millennial‐scale variability and is most strongly expressed in subpolar SSTs. The synchronous timing between North Pacific and North Atlantic SST oscillations is evidence for the rapid transmission of millennial‐scale climate perturbations between the basins, likely through an atmospheric teleconnection. SSTs at NH8P have no correlation with either leading TEOF mode as there is minimal change in SST at this site after 20 ka. A model simulation of the LGM indicates that glacial cooling was muted in much of the Eastern Pacific Warm Pool (EPWP), in which NH8P lies, due to reductions in latent heat flux. This suggests that the wind‐evaporation‐SST feedback was responsible for the attenuation of EPWP cooling. Overall, this study highlights the distinct latitudinal trends in the Pacific's response to deglaciation.

Tropical Western Pacific Hydrology During the Last 6,000 Years Based on Wildfire Charcoal Records From Borneo

AbstractThe forcing of multicentennial climate variability in the Western Pacific Warm Pool (WPWP) region is not fully understood. Here, we generated 6‐kyr‐long continuous charcoal records from five peatlands in Borneo. Every several hundred years, peaks of charcoal influx were identified in the composite record, indicating that the peatlands repeatedly experienced dry conditions and wildfires. Major fire events were identified at ∼5.4, 4.7, 4.4, 3.7, 3.2, 2.7, 2.4, 2.2, 1.7, 1.1, 0.6, and 0.3 ka. Most of these coincided with the maxima of Borneo speleothem δ18O and occurred in the high solar activity periods following the solar minima. This suggests that the higher solar activity decreased rainfall, increasing dryness and wildfire frequency. This result challenges the hypothesis that high solar activity intensifies atmospheric convection in the WPWP area.

An Overview of Oligocene to Recent Sediments of the Western Pacific Warm Pool (WPWP) (International Ocean Discovery Program-IODP Exp. 363) Using Warm and Cool Foraminiferal Species

We use the excellent sediment recovery of International Ocean Discovery Program (IODP) Exp. 363, in the Western Pacific Warm Pool (WPWP) to assess down-core variations in the abundance of warm versus cool benthic foraminiferal species through a warm benthic foraminifers (WBF) curve. The total percentage of the “warm” shallower species group (Laticarinina pauperata, Cibicidoides kullenbergi, C. robertsonianus, Cibicidoides sp., Hoeglundina elegans, and Bulimina aculeata) and of the “cool” species group from deep waters (Pyrgo murrhina, Planulina wuellerstorfi, Uvigerina peregrina, and Globobulimina hoeglundi, Hopkinsina pacifica) at all sites is used to assess paleo temporal and spatial variations in preservation and marine temperature. Our study sites span water depths ranging from 875 m to 3421 m and our results indicate that well-preserved living and fossil foraminifera characterize mudline and core sediments at all water depths attesting the wide environmental tolerance of these species to temperature and pressure. Using magneto-and biostratigraphy datum, these sediments are of Oligocene age. Our low-resolution study showed that with the exception of core 1486B which the linear tendency of warmer species is toward cool sediments in old times, all of them show that older sediments indicate warmer periods than today, which is expected from Miocene to Recent. Our results provide evidence for the preservation potential of deeply buried sediments, which has implications on climate reconstructions based on the population dynamics of calcareous benthic foraminifera.

Influences of central Pacific warming on synoptic-scale wave intensity over the northwest Pacific

Influences of central Pacific warming on synoptic-scale wave intensity over the northwest Pacific

Coupled Mg/Ca and Clumped Isotope Measurements Indicate Lack of Substantial Mixed Layer Cooling in the Western Pacific Warm Pool During the Last ∼5 Million Years

AbstractThe Indo‐Pacific Warm Pool (IPWP) plays a crucial role in influencing climate dynamics both in the tropics and globally. Yet, there is an ongoing controversy concerning the evolution of surface temperatures in the IPWP since the Pliocene, which is fueled by contradictory proxy evidence. Temperature reconstructions using TEX86 indicate a gradual cooling by ∼2°C from the Pliocene to today while Mg/Ca‐based studies using planktonic foraminifera do not report any long‐term trends. A bias in Mg/Ca records due to seawater chemistry changes has been suggested as an explanation for this proxy mismatch. Here, we present data from two independent foraminifera‐based temperature proxies, Mg/Ca and clumped isotopes (Δ47), measured on the same samples from IODP Site U1488 in the IPWP. We reconstructed mixed layer and subsurface temperatures and find very good agreement among Mg/Ca and Δ47 when applying a minor correction for changing Mg/Ca ratios of seawater. Diagenetic effects could influence Δ47 but the evaluation of foraminifera preservation at Site U1488 suggests that this effect is unlikely to have masked a long‐term trend in the data. While remaining uncertainties prevent us from fully ruling out particular hypotheses, our study adds evidence that mixed layer temperatures likely did not cool substantially, while subsurface temperatures cooled more strongly since the Pliocene. The substantial Pleistocene cooling previously observed in TEX86 data is consistent with this finding when interpreting it as a combined surface and subsurface signal.

Interdecadal variation of summer rainfall in the Greater Mekong Subregion and its possible causes

This paper investigates the interdecadal variation in summer rainfall over the Greater Mekong Subregion (GMS) during 1981–2020 and its possible causes, using Climate Hazards Group Infrared Precipitation with Station rainfall datasets, European Centre for Medium-range Weather Forecasts Reanalysis fifth generation data and the atmospheric general circulation model ECHAM6. The dominant mode of summer rainfall in the GMS features a seesaw pattern with an increase in rainfall over the central–southern GMS and a decrease in rainfall in northwestern Myanmar–Yunnan. The dominant mode of the GMS summer rainfall shows a change in regime around 2001/2002. Interdecadal variability in rainfall is largely related to sea surface temperature anomalies (SSTAs) over the Western Pacific Warm Pool (WPWP). Warmer SSTAs in the WPWP lead to interdecadal variation in summer rainfall in the GMS by exciting an anomalous cyclone in the lower troposphere over the southern GMS–South China Sea. This is accompanied by anomalous ascending motions in the central–southern GMS and anomalous descending motions in northern Myanmar–Yunnan. The Matsuno–Gill mechanism, which links SSTAs with interdecadal variations in the GMS summer rainfall, is further confirmed by numerical experiments.

Eastern equatorial Pacific warming delayed by aerosols and thermostat response to CO2 increase

Understanding the tropical Pacific response to global warming remains challenging. Here we use a range of Coupled Model Intercomparison Project Phase 6 greenhouse warming experiments to assess the recent and future evolution of the equatorial Pacific east–west temperature gradient and corresponding Walker circulation. In abrupt CO2-increase scenarios, many models generate an initial strengthening of this gradient resembling an ocean thermostat, followed by a small weakening; other models generate an immediate weakening that becomes progressively stronger, establishing a pronounced eastern equatorial Pacific warming pattern. The initial response in these experiments is a strong predictor for the intensity of this pattern simulated in both abrupt and realistic warming scenarios, but not in historical simulations showing no multi-model-mean warming trend in this region. The likely explanation is that the recent CO2-driven changes in the tropical Pacific are masked by aerosol effects and a potential ocean-thermostat-related delay, while the eastern equatorial Pacific warming pattern will emerge as greenhouse gases overcome aerosol forcing.

A unique infaunal foraminiferal species tolerance to physical pressure in recent and past sediments of the Western Pacific Warm Pool (IODP, WPWP, Exp. 363)

A unique infaunal foraminiferal species tolerance to physical pressure in recent and past sediments of the Western Pacific Warm Pool (IODP, WPWP, Exp. 363)