Western Pacific Warm Pool Research Articles

Mixed diversity of shifting IOD and El Niño dominates the location of Maritime Continent autumn drought.

SummaryThe Maritime Continent is a huge heat source region over the Indo-Pacific warm pool and it plays a key role in global weather/climate variations. The locations of Maritime Continent autumn droughts, linked to frequent rampant forest wildfires, are closely related to the mixed diversity of El Niño and Indian Ocean Dipole events.

Origins of Quasi-Biweekly and Intraseasonal Oscillations over the South China Sea and Bay of Bengal and Scale Selection of Unstable Equatorial and Off-Equatorial Modes

The daily outgoing longwave radiation (OLR) field in boreal summer shows significant power spectrum peaks on quasi-biweekly (10–20-day) and intraseasonal (20–80-day) timescales over the Indo–western Pacific warm pool, especially over the South China Sea and Bay of Bengal. The quasi-biweekly oscillation (QBWO) originates from off-equatorial western North Pacific, and is characterized by a northwest–southeast oriented wave train pattern, propagating northwestward. The intraseasonal oscillation (ISO), on the other hand, originates from the equatorial Indian Ocean and propagates eastward and northward. Why the equatorial mode possesses a 20–80-day periodicity while the off-equatorial mode favors a 10–20-day periodicity is investigated through idealized numerical experiments with a 2.5-layer atmospheric model. In the off-equatorial region, the model simulates, under a realistic three-dimensional summer mean flow, the most unstable mode that has a wave train pattern with a typical zonal wavelength of 6000 km and a period of 10–20 days, propagating northwestward. This is in contrast to the equatorial region, where a Madden–Julian oscillation (MJO) like mode with a planetary (wavenumber-1) zonal scale and a period ranging from 20 to 80 days is simulated. Sensitivity experiments with different initial conditions indicate that the QBWO is an intrinsic mode of the atmosphere in boreal summer in the off-equatorial Indo–western Pacific region under the summer mean state, while the MJO is the most unstable mode in the equatorial region.

Late Quaternary East Asian Summer Monsoon Variability Deduced From Lacustrine Mineral Magnetic Records of Dahu Swamp, Southern China

AbstractThe lack of long‐term and well‐preserved terrestrial archives from southern China largely impedes our understanding of past variability in the East Asian summer monsoon (EASM). In this study, we developed rainfall/precipitation‐related records by conducting a systematic mineral‐magnetic investigation on Dahu Swamp sediments over the past ~47.0 ka. The integrated magnetic results show that the magnetic minerals in the sediments were mainly catchment derived, likely reflecting hydroclimatic changes associated with EASM strength. In combination with other climatic proxies, our magnetic records reveal a relatively wet climate during the middle‐late Marine Oxygen Isotope Stage 3 and the Holocene and a relatively dry climate during the Marine Oxygen Isotope Stage 2, which broadly follow the precession‐induced summer insolation changes in the middle‐low latitudes of the Northern Hemisphere. The regional heterogeneity of the EASM rainfall evolution might be ascribed to the changes in timing and duration of Mei‐yu Front in China, which were closely associated with the El Niño/Southern Oscillation activities through its effects on the Western Pacific Subtropical High position. Long‐term climatic patterns inferred from Dahu Swamp were broadly similar to those of the Western Pacific Warm Pool region, especially during the mid‐Holocene rainfall optimum period, further supporting that the thermal mean states of the tropical Pacific associated with El Niño/Southern Oscillation modes may influence EASM precipitation. Our results highlight the coupled influence of external insolation forcing and internal low‐latitude processes on the spatial and temporal EASM variability, and understanding these influences could be critical to the prediction of future monsoon behavior under ongoing and future global warming.

CMIP5 model biases in the climatological mean state of the western Pacific warm pool

Biases in coupled general circulation models represent important limits for climate prediction. Based on historical runs of 26 coupled climate models of the Fifth Phase of the Coupled Model Intercomparison Project, the error of the climatological mean of the western Pacific warm pool (WPWP) is investigated. The results show that simulation of the morphology of the WPWP is significantly influenced by ocean currents. The upper-ocean heat budget analysis also indicates that heat advection plays a key role in determining the shape of the WPWP during the simulation. For the shrinkage of the tropical region and south section of smaller WPWPs, both the zonal heat advection bias caused by zonal ocean currents bias and meridional heat advection bias caused by the meridional sea temperature gradient bias are the crucial factors, while for the extension of larger WPWPs, the zonal heat advection bias is more important. For the northern section of WPWPs, the horizontal heat advection biases are still responsible for the shrinkage and extension in the region from 4°N to 7°N, while in the north of 7°N, the biases of WPWP are related to that of short wave radiation. In addition, in the equator and south section of the WPWP, the advective feedback plays a key role in the development of biases.

Improving the dynamical seasonal prediction of western Pacific warm pool sea surface temperatures using a physical–empirical model

AbstractThe western Pacific warm pool (WPWP) has a profound impact on the global climate. In this study, the forecast skill of ENSEMBLES model for predicting the WPWP sea surface temperature (SST) for the period 1960–2006 is evaluated, where a WPWP index (WPWPI) is defined to represent the interannual variability of WPWP SST. The result indicates that the ENSEMBLES exhibit a poor skill in predicting the WPWPI during January–April (2‐ to 5‐month forecasts starting on November 1). To improve the ENSEMBLES‐predicted WPWP SSTs during January–April, a physical–empirical (PE) model is developed based on two predictors, using the year‐to‐year increment method and the linear regression method. The two predictors include the ENSEMBLES‐predicted sea level pressure during January and the observed northern tropical Atlantic SSTs during the preceding August. The mechanisms associated with the two predictors are illuminated. The 1‐year‐out cross‐validation and the independent hindcast indicate that this PE model may notably improve the WPWPI prediction of ENSEMBLES, with a correlation coefficient (CC) above 0.6 between the PE‐model‐predicted WPWPI and the observed WPWPI during January–April. The physical mechanisms expounded in this study and the PE model utilized in this study can be considered to improve the prediction of WPWP SST of numerical models in the future.

A quantitative temperature reconstruction of the ‘Little Ice Age’ in southern China

We present a branched glycerol dialkyl glycerol tetraethers (brGDGTs)–based mean annual temperature reconstruction covering the last millennium from a subtropical lake in Guangxi Province, southern China (23°N). We demonstrate that the pattern and absolute values of mean annual temperatures reconstructed using the eastern African lake brGDGTs calibration based on the methylation of 5-methyl branched tetraethers index provided the most reliable and accurate temperature estimates from the site. The results resemble regional and Northern Hemisphere changes over this period. The pattern shows a general cool period between ca. AD 1450 and 1950, including cooling minima centred at ca. AD 1600, 1750 and 1900, coeval with the ‘Little Ice Age’ temperature fluctuations in the Northern Hemisphere, followed by a warming trend from the mid-20th century to the present. The results suggest that both solar forcing and high-latitude Northern Hemisphere climate fluctuations play a role in influencing the terrestrial temperatures in southern China, possibly on different timescales. In addition, our results support the hypothesis that changes of the East Asian summer monsoon are primarily driven by the land–sea thermal gradient change between terrestrial southern China and the Indo-Pacific Warm Pool regions during the last millennium, owing to external radiative and/or volcanic forcings.

Mixed-layer Heat Budget in Western and Eastern Tropical Pacific Ocean during El Niño Event in 2015/2016

Temporal variation of mixed-layer heat budget at two contrasting locations, namely, western Pacific (warm water pool) and eastern Pacific (cold tongue) during the extreme El Niño phenomenon in 2015/2016 is evaluated. Oceanic and atmospheric datasets, including sea surface temperature (SST), wind stress, shortwave radiation (SWR), longwave radiation, latent heat flux (LHF), and sensible heat flux are analyzed. A slight warming occurred in the eastern tropical Pacific associated with a positive SST anomaly, which reflected the weakening or reversal of the trade winds. Meanwhile, the western tropical Pacific exhibited a cooling tendency during the development phase of El Niño. Analysis of the mixed-layer heat budget shows that the net heat flux due to SWR and LHF significantly contributes to the warming of the eastern tropical Pacific. The contribution from horizontal advection was extremely small on both sides. The analysis shows that the residual term significantly contributes to cooling (warming) tendency observed in the western (eastern) tropical Pacific. This condition may suggest that residual process due to entrainment and diffusivity played an important role in the evolution of cooling (warming) process in the western (eastern) tropical Pacific.

Disappearance of the last tropical glaciers in the Western Pacific Warm Pool (Papua, Indonesia) appears imminent

The glaciers near Puncak Jaya in Papua, Indonesia, the highest peak between the Himalayas and the Andes, are the last remaining tropical glaciers in the West Pacific Warm Pool (WPWP). Here, we report the recent, rapid retreat of the glaciers near Puncak Jaya by quantifying the loss of ice coverage and reduction of ice thickness over the last 8 y. Photographs and measurements of a 30-m accumulation stake anchored to bedrock on the summit of one of these glaciers document a rapid pace in the loss of ice cover and a ∼5.4-fold increase in the thinning rate, which was augmented by the strong 2015-2016 El Niño. At the current rate of ice loss, these glaciers will likely disappear within the next decade. To further understand the mechanisms driving the observed retreat of these glaciers, 2 ∼32-m-long ice cores to bedrock recovered in mid-2010 are used to reconstruct the tropical Pacific climate variability over approximately the past half-century on a quasi-interannual timescale. The ice core oxygen isotopic ratios show a significant positive linear trend since 1964 CE (0.018 ± 0.008‰ per year; P < 0.03) and also suggest that the glaciers' retreat is augmented by El Niño-Southern Oscillation processes, such as convection and warming of the atmosphere and sea surface. These Papua glaciers provide the only tropical records of ice core-derived climate variability for the WPWP.

Teleconnection analysis of monthly streamflow using ensemble empirical mode decomposition

Streamflow is the result of complex climatic and hydrological interactions that are driven by atmosphere–ocean circulation. Teleconnection analysis of streamflow is significant for identifying the atmosphere- and climate-related indices of hydrology series. To mine the physical information of streamflow series more effectively, ensemble empirical mode decomposition (EEMD) was employed to decompose streamflow series into inherent stationary components with different periodic oscillations and a trend. In this study, important climate indices were identified based on the correlation coefficients, which were calculated using cross-correlation. According to the selected indicators, the decomposed and streamflow series were regressed using an artificial neural network (ANN) and support vector regression (SVR). In total, 130 climate phenomenon indices, pre-runoff, and 1–12-month time lags were considered as teleconnection variables. The results show that EEMD can be used to extract the period and trend of streamflow, and that the decomposed hydrology components have much stronger correlations than the original runoff with the climate phenomenon indices. The original streamflow was the most closely correlated with the series from the previous month, which is an autocorrelation. However, more physical information was obtained through the teleconnection of the sub-streamflow series. The periodic oscillations was explained by relatively diverse atmospheric circulation and sea surface temperature indices with different time lags. The low-frequency periodic series were better represented than the high-frequency series by the climate phenomenon indices. In addition, Nino 3.4, Nino 4, the Warm-pool ENSO Index, and the ENSO Modoki Index were representative of the high-frequency component; the mid-frequency signals were sensitive to the Solar Flux Index, Total Sunspot Number Index, Pacific Decadal Oscillation Index, and Southern Oscillation Index; the low-frequency series were influenced by the Atlantic Multi-decadal Oscillation Index, North African Subtropical High Area Index, North Atlantic Triple Index, etc.; and the Indian Ocean Basin-Wide Index, Atlantic Multi-decadal Oscillation Index, Western Pacific Warm Pool Strength Index, and East Pacific 850 mb Trade Wind Index expressed well the long-term trend of monthly streamflow. Meanwhile, the regression results of the decomposed series obtained by the ANN and SVR exhibited better statistical performance than those of the original series, especially for the EEMD-SVR.

Climate Variability over the Maritime Continent and Its Role in Global Climate Variation: A Review

The Maritime Continent (MC) consists of multiple islands with varying sizes and topography, and surrounding seas. It is characterized by rainfall (convection) variability on multiple spatial and temporal scales. Various large-scale atmospheric, oceanic, and coupled climate systems, such as the El Nino–Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Madden–Julian Oscillation (MJO), and cold surge, exert significant influences on the spatio-temporal complexity of the MC climate and climate variability. As a major tropical heat source located within the warmest oceanic area (the western Pacific warm pool), the MC has been identified as a region of great importance for climate variation on the global scale. However, prediction of climate variability over the MC and its surrounding areas and the relationships to large-scale atmospheric circulation patterns are big challenges, even for state-of-the-art climate models. In this paper, we provide a thorough review on current understanding of the spatiotemporal complexity and prediction of climate variability over this important region, and its influence on global climate variation.

Twofold expansion of the Indo-Pacific warm pool warps the MJO life cycle.

The Madden-Julian Oscillation (MJO) is the most dominant mode of subseasonal variability in the tropics, characterized by an eastward-moving band of rain clouds. The MJO modulates the El Niño Southern Oscillation1, tropical cyclones2,3 and the monsoons4-10, and contributes to severe weather events over Asia, Australia, Africa, Europe and the Americas. MJO events travel a distance of 12,000-20,000km across the tropical oceans, covering a region that has been warming during the twentieth and early twenty-first centuries in response to increased anthropogenic emissions of greenhouse gases11, and is projected to warm further. However, the impact of this warming on the MJO life cycle is largely unknown. Here we show that rapid warming over the tropical oceans during 1981-2018 has warped the MJO life cycle, with its residence time decreasing over the Indian Ocean by 3-4days, and increasing over the Indo-Pacific Maritime Continent by 5-6days. We find that these changes in the MJO life cycle are associated with a twofold expansion of the Indo-Pacific warm pool, the largest expanse of the warmest ocean temperatures on Earth. The warm pool has been expanding on average by 2.3×105km2 (the size of Washington State) per year during 1900-2018 and at an accelerated average rate of 4×105km2 (the size of California) per year during 1981-2018. The changes in the Indo-Pacific warm pool and the MJO are related to increased rainfall over southeast Asia, northern Australia, Southwest Africa and the Amazon, and drying over the west coast of the United States and Ecuador.

Observing Possible Thermodynamic Controls on Tropical Marine Rainfall in Moist Environments

Abstract Radar and rawinsonde data from four ground-based observing stations in the tropical Indo-Pacific warm pool were used to identify possible associations of environmental state variables and their vertical profiles with radar-derived rain rate inside a mesoscale radar domain when the column-integrated relative humidity (CRH) exceeds 80%. At CRH exceeding 80%, a wide range—from near 0 to ~50 mm day−1—in rain rate is observed; therefore, tropospheric moisture was a necessary but insufficient condition for deep convection. This study seeks to identify possible factors that inhibit rainfall when the atmosphere is sufficiently moist to support large precipitation rates. The domain-mean rain rate was highly sensitive to the areal coverage of intense, convective rainfall that occurs. There were two fundamentally different instances in which convective area was low. One was when the radar domain is primarily occupied by weakly precipitating, stratiform echoes. The other was when the radar domain contained almost no precipitating echoes of any type. While the former was dependent upon the stage of the convective life cycle seen by radar, the latter was probably dependent upon the convective environment. Areal coverage of convective echoes was largely determined by the number of individual convective echoes rather than their sizes, so changes in the clear-air environment of updrafts might have governed how many updrafts grew into deep cumulonimbi. The most likely environmental influence on convective rainfall identified using rawinsonde data was 900–700-hPa lapse rate; however, processes occurring on spatial scales smaller than a radar domain were probably also important but not investigated.

Is the Net Cloud Radiative Effect Constrained to be Uniform Over the Tropical Warm Pools?

AbstractGlobal radiative‐convective equilibrium simulations are used to investigate the hypothesis that mutual interactions among cloud albedo, sea surface temperature gradients, and atmospheric circulation constrain the net cloud radiative effect (CRE) to be similar in convective and nonconvective regions over the tropical warm pools. We perform an experiment in which convective clouds interact naturally with the ocean and atmosphere by forming over the warmest water and shading it and an experiment in which this interaction is removed by randomizing cloud shading of the ocean. Removing the cloud shading interaction enhances sea surface temperature gradients, lateral atmospheric heat transport, and large‐scale convective aggregation and produces convective clouds with much more negative net CRE. These findings support the hypothesis that feedbacks between sea surface temperature and convection are critical to obtaining similar net CRE in convective and nonconvective regions over the tropical warm pools.

Moored Observations of Transport in the Solomon Sea

AbstractThe Solomon Sea is a marginal sea in the western Pacific warm pool that contains the South Pacific low latitude western boundary currents. These low latitude western boundary currents chiefly exit the Solomon Sea through three channels (Vitiaz Strait, St. George's Channel, and Solomon Strait) and serve as the primary source water for the Equatorial Undercurrent. Simulations have shown that transport partitioning between the straits determines the water mass structure of the Equatorial Undercurrent, but the relative contributions of transport through each strait have not been observed before. As part of the Southwest Pacific Ocean Circulation and Climate Experiment, an array of moorings was deployed simultaneously in the three outflow channels of the Solomon Sea from July 2012 until March 2014 to resolve transport and water properties in each strait. Above deep isopycnals (σ0 ≤ 27.5), Vitiaz and Solomon Straits account for 54.2% and 36.2% of the mean transport, respectively, with the remaining 9.6% exiting through St. George's Channel. The strongest subinertial transport variability is observed in Solomon Strait and dominates total Solomon Sea transport variability, and a significant fraction of this variability is at intraseasonal time scales. Finally, a previously unobserved deep current at 1,500‐m depth is found to enter the Solomon Sea through Solomon Strait, with a deployment‐mean transport of 4.6 Sv (Sv ≡106 m3/s).

La Niña-driven flooding in the Indo-Pacific warm pool during the past millennium

Extreme precipitation events are one of the most consequential components of climate change for society. The El Niño-Southern Oscillation (ENSO) is the dominant mode of precipitation variability in the tropics and causes severe flooding and drought in many socioeconomically vulnerable regions. It remains unclear how tropical rainfall extremes and ENSO are changing in response to anthropogenic forcing, demanding that we investigate the relationships between precipitation, ENSO, and external forcing in the past. Lake sediment records have provided benchmark records of extreme flood events from the eastern tropical Pacific, where paleofloods have been interpreted to reflect El Niño events during the last millennium. However, the connections between flooding and ENSO variability in this region are uncertain, and the eastern Pacific can only capture precipitation events driven by El Niño, not La Niña. Thus, it is unclear how the ENSO system and tropical rainfall extremes have changed in the recent past. Here, we reconstruct flood events during the past millennium using a lake sediment record from East Java, Indonesia, which can provide insight into flooding driven by La Niña. We detect flood frequency variations in the western tropical Pacific that are highly coherent with records from the eastern part of the basin over the past millennium. Our findings demonstrate that heavy rainfall and flooding occurs more frequently on both sides of the tropical Pacific during periods of warmer Northern Hemisphere mean temperatures, implying that ENSO-driven rainfall extremes could intensify in the near future.

Nonlinear response of Northern Hemisphere stratospheric polar vortex to the Indo\u2013Pacific warm pool (IPWP) Ni\xf1o

Variations in tropical sea surface temperatures (SST) have pronounced impacts on the stratospheric polar vortex, with the role of El Niño being the focus of much research interest. However, the Indo–Pacific warm pool (IPWP), which is the warmest body of seawater in the world, has received less attention. The IPWP has been warming in recent years. This paper presents for the first time the remarkable nonlinearity in Northern Hemisphere (NH) stratospheric circulation and temperature response to IPWP warming (the so-called IPWP Niño) in boreal winter. The magnitude of NH stratospheric vortex weakening is strong and significant in case of moderate IPWP Niño, but is weak and insignificant in strong IPWP Niño case. This phenomenon is robust in both the historical simulations and observations. An idealized model experiments forced with linear varying SST forcing in the IPWP region isolate the nonlinearities arising from IPWP Niño strength. Westward extension of precipitation into the Maritime Continent drives attenuation and westward shift of extratropical waves during strong IPWP Niño events. Linear wave interference analysis reveals this leads to weak interference between the climatological and anomalous stationary waves and thereby a weak response of the stratospheric vortex. These findings imply a distinct stratospheric vortex response to the IPWP Niño, and provide extended implications for the surface climate in the NH.

Radiative Feedbacks Associated with the Madden–Julian Oscillation

AbstractRadiative kernels derived from CloudSat/CALIPSO measurements are used to diagnose radiative feedbacks induced by the Madden–Julian oscillation (MJO). Over the Indo-Pacific warm pool, positive cloud and water vapor feedbacks are coincident with the convective envelope of the MJO during its active phases, whereas the lapse rate feedback shows faster eastward propagation than the convective envelope. During phase 2/3, when the convective envelope is over the Indian Ocean, water vapor exhibits a vertically coherent response, with the largest anomalies and strongest feedback in the midtroposphere. Though spatial structures of the feedbacks vary, the most prominent difference lies in the magnitude. Cloud changes induce the largest radiative perturbations associated with the MJO. It is also found that the strength of the cloud feedback per unit of precipitation is greater for strong MJO events, suggesting that the strength of individual MJO events is largely dictated by the magnitude of cloud radiative heating of the atmosphere. In addition, stronger radiative heating due to water vapor and clouds helps the MJO survive the barrier effect of the Maritime Continent, leading to farther eastward propagation. These results offer process-oriented metrics that could help to improve model simulations and predictions of the MJO in the future.

Indonesian throughflow controlled the westward extent of the Indo-Pacific Warm Pool during glacial-interglacial intervals

Abstract The tropical atmospheric circulation is strongly influenced by the sea surface temperature (SST) of the warmest region of the world ocean, the Indo-Pacific Warm Pool (IPWP). The effect of recent anomalous Indian Ocean warming on the extent of the IPWP remains uncertain. Past SST records from the tropical Indian Ocean, associated with different temporal boundary conditions, can help shed light on how climate change impacts the IPWP and associated monsoonal processes. Here, we reconstruct the seawater temperature and precipitation changes (from Mg/Ca and δ18O of surface-dwelling planktic foraminifera Globigerinoides ruber) of the last ~184 kyr BP from the westernmost margin of the IPWP. The data is then used to reconstruct the spatial extent and intensity of the IPWP structure as well as its relationship with other regional phenomena. A consistently warmer (>28 °C) central equatorial Pacific Ocean and significantly cooler equatorial western Pacific and the Indian Ocean suggests that the warm pool extent reduced considerably during MIS6 as well as the last glacial interval, leading to a strong La-Nina like condition. The most enriched seawater δ18O (δ18Osw) during MIS6, was in the westernmost IPWP, suggesting weakened precipitation, despite La-Lina like conditions. The westernmost part of the IPWP became warmer than the threshold 28 °C during MIS5e and the early Holocene, suggesting the westward extension of the IPWP. The eastern equatorial Pacific Ocean also warmed considerably during MIS5e, suggesting a weaker Walker Circulation and a stronger El-Nino. The difference in δ18Osw decreased considerably during MIS5e and is attributed to increased precipitation/freshwater runoff in the central equatorial Indian Ocean. The increase in δ18Osw (~1.5‰) between ~55 kyr until the last glacial maximum, in a majority of the Indian Ocean records, suggests progressively weakened precipitation. A majority of the records have a uniform SST anomaly throughout the Holocene. A warmer equatorial Indian Ocean during interglacials suggests a strong modulation of the IPWP extent by the transport of warm water through the Indonesian throughflow region. The large drop in δ18Osw despite the comparable change in SST during the last glacial interval suggests that monsoon forcing has been much stronger in altering the surface hydrography in the Indian Ocean than the central Pacific Ocean.

Extracting historic cyclone data from coastal dune deposits in eastern Hainan Island, China

Understanding long-term, large cyclone activity is critical for coastal management and disaster prevention and mitigation, particularly with projected rising sea level and increasing cyclone frequency and the intensity. Here we present sedimentary evidence (cyclone overwash deposits, beachrock boulders, and cyclone-induced clastic deposits) of historic large cyclone events from coastal dune deposits on eastern Hainan Island, China. Based on luminescence dating and sedimentological analysis, eight historic tropical cyclone events (at 1095 ± 90 BCE, 900–1000 BCE, 975 ± 50 CE, 1720 ± 20 CE, 1740 ± 35 CE, 1790 ± 25 CE, 1850 ± 15 CE, and 1895 ± 10 CE) have been identified in this region. The elevation of the termination point of cyclone overwash deposit layers that represent the paleo-cyclone minimum wave run-up stage, in combination with knowledge of present-day cyclone events, was applied to assess the intensity of these extreme events. The intensity of these cyclone events was likely greater than that of cyclones in the local instrumental records. Furthermore, these large cyclone events correspond to historic records of devastating cyclones. Through comparison with regional and global climate records, we infer that the variability of large cyclones in the South China Sea was probably modulated by the El Niño-Southern Oscillation, western Pacific warm pool, and local sea surface temperatures over the past 3400 yr. These results provide an improved understanding of long-term, extreme cyclone events and their response to climate change, thereby contributing to regional planning and coastal defense strategies.

High- and low-latitude forcing on the south Yellow Sea surface water temperature variations during the Holocene

Abstract Sea surface temperature (SST) of the modern Yellow Sea (YS) is sensitive to forcing by both the East Asian monsoon and the North Pacific western boundary current, however, detailed mechanisms for explaining the Holocene SST evolution remains to be understood. Here we present two decadal sampling resolution alkenone SST records from the south YS spanning the last 8.9 kyr to understand forcing mechanisms on different timescales. The results show that the two sites from the south YS experienced SST variations on millennial timescale, displaying mean high values of 16.5 °C (A03-B) and 15.2 °C (YS01) from 7.7 to 5.9 ka, followed by low values of 16.4 °C (A03-B) and 14.8 °C (YS01) from 5.9 to 2.9 ka, then by high values of 16.9 °C (A03-B) and 15.5 °C (YS01) from 2.9 to 0.6 ka. After the entrance of the YS Warm Current at about 7.5 ka, evolution of the south YS SSTs paralleled the pattern of the main Kuroshio Current intensity, i.e., low (high) SST coeval with weak (strong) Kuroshio Current, suggesting that millennial-scale SST variations in the south YS were primarily controlled by the Kuroshio Current. Superimposing on the millennial variations, seven abrupt centennial-scale cold events were observed during the Holocene, with SST oscillations broadly coeval with those of North Atlantic ice-rafted detritus and East Asian winter monsoon rather than SSTs from the Okinawa Tough and Indo-Pacific warm pool. Hence, we propose that the East Asian winter monsoon was the top-down conveyor transmitting North Atlantic cooling signals to the south YS on centennial timescale. Thus, our study reveals both high- and low-latitude climate forcing on the evolution of the south YS SST during the Holocene, with low-latitude forcing on millennial-scale and high-latitude forcing on centennial-scale.