Pacific Warm Pool Research Articles

Role of atmosphere-ocean interactions in supermodeling the tropical Pacific climate.

The supermodel strategy interactively combines several models to outperform the individual models comprising it. A key advantage of the approach is that nonlinear improvements can be achieved, in contrast to the linear weighted combination of individual unconnected models. This property is found in a climate supermodel constructed by coupling two versions of an atmospheric model differing only in their convection scheme to a single ocean model. The ocean model receives a weighted combination of the momentum and heat fluxes. Optimal weights can produce a supermodel with a basic state similar to observations: a single Intertropical Convergence zone (ITCZ), with a western Pacific warm pool and an equatorial cold tongue. This is in stark contrast to the erroneous double ITCZ pattern simulated by both of the two stand-alone coupled models. By varying weights, we develop a conceptual scheme to explain how combining the momentum fluxes of the two different atmospheric models affects equatorial upwelling and surface wind feedback so as to give a realistic basic state in the tropical Pacific. In particular, we propose a mechanism based on the competing influences of equatorial zonal wind and off-equatorial wind stress curl in driving equatorial upwelling in the coupled models. Our results show how nonlinear ocean-atmosphere interaction is essential in combining these two effects to build different sea surface temperature structures, some of which are realistic. They also provide some insight into observed and modelled tropical Pacific climate.

Variations in the start, end, and length of extreme precipitation period across China

ABSTRACTUsing the daily precipitation records during 1961–2013 from 686 meteorological stations across China and the atmospheric circulation indexes, this study investigates the spatio‐temporal changes in the occurrence time and length of the extreme precipitation period (EPP), as well as their influencing factors. The results show the following aspects: (1) In the last 53 years, the start dates of the extreme precipitation period (EPPS) generally advanced. The end dates of the extreme precipitation period (EPPE) are delayed, which show an increasing trend. The lengths of the extreme precipitation period (EPPL) in most of the China meteorological stations increased. (2) The spatial patterns of the trends in the occurrence time and length of the extreme precipitation period are similar and show obvious clustering. The occurrence time and length of the extreme precipitation period have obvious spatial gradient differences in their average values. In southeastern China, the average EPPS is earlier, EPPE is later than those in other regions, and their EPPL is prolonged. The EPP in northeastern China begins later and ends earlier, and its EPPL is shorter than that in other regions. (3) The western Pacific subtropical high, Northern Hemisphere polar vortex, Antarctic Oscillation, and western Pacific warm pool have significant effects on the occurrence time and length of EPP over China, and different regions show different effects.

Stable Oxygen Isotopes and Mg/Ca in Planktic Foraminifera From Modern Surface Sediments of the Western Pacific Warm Pool: Implications for Thermocline Reconstructions

AbstractMg/Ca and stable oxygen isotope compositions (δ18O) of planktic foraminifera tests are commonly used as proxies to reconstruct past ocean conditions including variations in the vertical water column structure. Accurate proxy calibrations require thorough regional studies, since parameters such as calcification depth and temperature of planktic foraminifera depend on local environmental conditions. Here we present radiocarbon‐dated, modern surface sediment samples and water column data (temperature, salinity, and seawater δ18O) from the Western Pacific Warm Pool. Seawater δ18O (δ18OSW) and salinity are used to calculate individual regressions for western Pacific surface and thermocline waters (δ18OSW = 0.37 × S‐12.4 and δ18OSW = 0.33 × S‐11.0). We combine shell δ18O and Mg/Ca with water column data to estimate calcification depths of several planktic foraminifera and establish regional Mg/Ca‐temperature calibrations. Globigerinoides ruber, Globigerinoides elongatus, and Globigerinoides sacculifer reflect mixed layer conditions. Pulleniatina obliquiloculata and Neogloboquadrina dutertrei and Globorotalia tumida preserve upper and lower thermocline conditions, respectively. Our multispecies Mg/Ca‐temperature calibration (Mg/Ca = 0.26exp0.097*T) matches published regressions. Assuming the same temperature sensitivity in all species, we propose species‐specific calibrations that can be used to reconstruct upper water column temperatures. The Mg/Ca temperature dependencies of G. ruber, G. elongatus, and G. tumida are similar to published equations. However, our data imply that calcification temperatures of G. sacculifer, P. obliquiloculata, and N. dutertrei are exceptionally warm in the western tropical Pacific and thus underestimated by previously published calibrations. Regional Mg/Ca‐temperature relations are best described by Mg/Ca = 0.24exp0.097*T for G. sacculifer and by Mg/Ca = 0.21exp0.097*T for P. obliquiloculata and N. dutertrei.

Niño4 as a Key Region for the Interannual Variability of the Western Pacific Warm Pool

AbstractThe Western Pacific Warm Pool (WPWP) plays an important role in the global climate through modulating deep convections, ENSO, monsoon onsets, etc. Due to the vast spatial range and huge heat storage of the WPWP, near‐real‐time monitoring of its three‐dimensional variations remains challenging. Based on Argo observations and three reanalysis data sets, we find that the Niño4 sea surface temperature (SST) index captures the interannual variability of the WPWP well. The Niño4 SST can explain approximately half of the variance of the WPWP heat content and almost all the variance of the east‐west migration of the WPWP. An assessment of 31 CMIP5 models also reveals that models with larger interannual spectral powers and amplitudes of the Niño4 SST tend to simulate larger variations in the heat content and east‐west migration of the WPWP. A surface heat budget analysis further shows that the Niño4 SST and WPWP are physically connected through basin‐scale horizontal advections of mean temperatures by anomalous horizontal currents, which dominate the interannual variations of both the Niño4 SST and WPWP. Our results indicate that the Niño4 SST can efficiently estimate the interannual WPWP changes and a reliable predictor of the onset time of the South China Sea summer monsoon and Bay of Bengal summer monsoon, without the need to calculate the eastern boundary location and heat content of the WPWP. Moreover, a better simulation of the SST and horizontal currents in the Niño4 region can help to reduce model bias when reproducing the WPWP's interannual variabilities.

Simulations of three natural decadal climate variability phenomena in CMIP5 experiments with the UKMO HadCM3, GFDL-CM2.1, NCAR-CCSM4, and MIROC5 global earth system models

The ability of four Earth System Models (ESMs) to simulate major attributes of sea-surface temperature (SST) manifestations of the Pacific Decadal Oscillation (PDO), the tropical Atlantic SST gradient (TAG) variability, and the West Pacific Warm Pool (WPWP) SST variability was assessed. Data from simulation experiments conducted under the CMIP5 with the CM2.1, HadCM3, MIROC5, and CCSM4 ESMs from 1861 to 2005 were used. A Multi-Model Ensemble was also formed by combining data from the four ESMs. Aerosol optical depths and solar radiation were specified in these experiments. The simulation of PDO spatial pattern, annual cycle, and preferred timescales is the closest to observed attributes in these ESMs. The simulated and observed TAG SST patterns are generally similar, but their average annual cycles are very different and simulated TAG variability does not have a preferred decadal timescale unlike observed variability. No one of the ESMs is able to simulate the WPWP SST pattern. Simulated and observed average annual cycles of the WPWP SST are similar, and the dominant timescale of WPWP variability is close to 8 years in all ESMs and observations. Simulation skills of the three phenomena fluctuate from decade to decade in all ESMs. Major volcanic eruptions substantially influence observed and simulated indices and simulation skills of the three phenomena. The mixing of net surface heat flux anomalies to 200 m depth in the tropical and mid-latitude Pacific, and the WPWP region causes a delayed and multiyear response of the PDO and WPWP indices to volcanic eruptions.

Decadal Western Pacific Warm Pool Variability: A Centroid and Heat Content Study

We examine several characteristics of the Western Pacific Warm Pool (WP) in the past thirty years of mixed interannual variability and climate change. Our study presents the three-dimensional WP centroid (WPC) movement, WP heat content anomaly (HC) and WP volume (WPV) on interannual to decadal time scales. We show the statistically significant correlation between each parameter’s interannual anomaly and the NINO 3, NINO 3.4, NINO 4, SOI, and PDO indices. The longitudinal component of the WPC is most strongly correlated with NINO 4 (R = 0.78). The depth component of the WPC has the highest correlation (R = −0.6) with NINO3.4. The WPV and NINO4 have an R-Value of −0.65. HC has the highest correlation with NINO3.4 (R = −0.52). During the study period of 1982–2014, the non-linear trends, derived from ensemble empirical mode decomposition (EEMD), show that the WPV, WP depth and HC have all increased. The WPV has increased by 14% since 1982 and the HC has increased from −1 × 108 J/m2 in 1993 to 10 × 108 J/m2 in 2014. While the largest variances in the latitudinal and longitudinal WPC locations are associated with annual and seasonal timescales, the largest variances in the WPV and HC are due to the multi-decadal non-linear trend.

Tropical and high latitude forcing of enhanced megadroughts in Northern China during the last four terminations

Understanding the origin and evolutionary history of drought events is of great significance, providing critical insight into future hydrological conditions under the changing climate. Due to the scarcity of drought proxies from northern China, the occurrence and underlying mechanisms of the drought events remains enigmatic on longer timescales. Here we utilize microbial lipid proxies to reconstruct significant drought events over the last four ice age terminations in the southernmost section (Weinan section) of the Chinese Loess Plateau. The abundance of archaeal isoprenoid GDGTs (glycerol dialkyl glycerol tetraethers) relative to bacterial branched GDGTs, measured by Ri/b and BIT indices, is diagnostic of enhanced drought conditions. The Ri/b (and BIT) indices are stable and low (high) throughout most of the loess section spanning the last 350 thousand years, but they do exhibit sharp transient peaks (valleys) during the intervals associated with the four ice age terminations, and especially Terminations II and IV. These enhanced drought events are, non-intuitively, associated with a significant decrease in the relative abundance of C4 plants, inferred by a decrease in the carbon isotope composition of bulk organic matter. Although the microbial records show some consistency with the Weinan grain size profiles, indicative of Eastern Asian winter monsoon variability, they also show some apparent difference. In fact, some features of the microbial records exhibit strong similarities with marine sediment planktonic foraminiferal δ13C records from the western Pacific warm pool, which reflect ENSO-like changes during glacial terminations. Therefore, enhanced droughts immediately before the interglacial warming in northern China could be explained, at least in part, by teleconnections in tropical ocean–atmosphere circulation via shifts in the Intertropical Convergence Zone (ITCZ) and associated Jet Stream over the Asian continent. According to our microbial biomarker data, these enhanced megadroughts are apparently different, both in terms of severity and causal mechanism, from the more commonly discussed dry conditions observed during glacial periods.

The three-dimension intensity index for western Pacific subtropical high and its link to the anomaly of rain belt in eastern China

Western Pacific subtropical high (WPSH) is a deep circulation system located at middle-lower troposphere over the East Asia. The anomalies of its position and intensity determine the shift of climates in eastern China, especially the summer rainfall belt. However, previous definitions of WPSH intensity index were limited mainly by a single threshold of 5880-gpm geopotential height contour at 500-hPa, which cannot denote the rain pattern in eastern China reasonably, in particular the floods and droughts along the Yangtze River valley. In this paper, the link between the intensity of East Asian summer monsoon (EASM) and the geopotential heights at each level were analyzed by correlation analyses. The results indicate that the significant negative correlations spread obviously from the upper to lower levels with longitude changed from west to east. At the upper levels over the Asian continent, the most significant negative correlation was found at the central region of the South Asia High (SAH). This implies that the EASM would be weaker if the SAH was stronger, and vice versa. Over the western Pacific warm pool, the most significant negative correlation was found in the middle-lower troposphere. The correlation coefficients at 500-hPa were much weaker than those at 700-hPa and 850-hPa, indicating that the EASM was easier influenced by the subtropical high at lower levels. Similar, the relationship between the WPSH and the precipitation along the Yangtze River valley was more significant at lower levels indicated by the correlation coefficient. In this study, the representativeness of the threshold of 5880 gpm at 500-hPa level over the western Pacific subtropical regions was analyzed at different grids and seasons, and the limitations of previous definitions were also discussed. Considering the three-dimension (3D) structures of the subtropical high, a new WPSH intensity index was defined by integrated the standardized geopotential heights from 500-hPa to 1000-hPa levels over the region (10°–30°N, 110°–150°E). Compared with the two traditional WPSH indices, the new 3D WPSH intensity index can better represent the subtropical summer monsoon and the precipitation along the middle and lower reaches of the Yangtze River. Although all the three indices could reflect the primary correlation patterns between WPSH and the precipitation in eastern China, only the correlation coefficient between the 3D intensity index and precipitation is significant at the 95% confidence level to pass the student t -test. Compared to the other two indices, the 3D WPSH index can better reflect the anomalous of both meridional and zonal water vapor transportation between the tropical and subtropical regions of East Asia. During the transition seasons of boreal spring and autumn, the mechanisms of anomalous precipitation are more complicated, which are obviously different from EASM. Preliminary analysis shows that even in these two transition seasons, the 3D WPSH index defined in this paper also has better link with the precipitation anomalies in eastern China. As mentioned before, the WPSH is a deep circulation system over the western Pacific. Besides its intensity, the position also impacts on the climates over East Asia, especially its west boundary and meridional axis. In the future study, the definitions of other parameters of WPSH need to be studied from its 3D structure.

Environmental modeling of occurrence of dolphinfish (Coryphaena spp.) in the Pacific Ocean off Mexico reveals seasonality in abundance, hot spots and migration patterns

AbstractDolphinfish are little known migratory fish targeted by sport, artisanal and commercial fleets. In this study, we analyzed a 10 year database of incidental catches of the tuna purse seine fleet in the Pacific Ocean off Mexico with the aim to understand the environmental determinants of the spatial distribution and seasonal migration patterns of dolphinfish. We modeled the probability of occurrence of dolphinfish as a function of spatial (geographical coordinates), temporal (month/year) and environmental variables (sea surface temperature [SST], chlorophyll [CHL] and sea surface height [SSH], inferred from satellites) using logistic Generalized Additive Models. Dolphinfish preferred waters with SST values from 23 to 28°C, low (<0.2 mg/m3) CHL values, and primarily positive SSH values. Two dolphinfish hot spots were found in the study area: one in an oceanic zone (10°–15°N, 120°–125°W), which was more defined during spring, and one on the Pacific side of the Baja California Peninsula, which became important during summer. Models suggested that dolphinfish migrated through the study area following a “corridor” that ran from the Gulf of Tehuantepec along the Equatorial Upwelling zone to the oceanic hot spot zone, which in turn connected with the hot spot off the BCP. This “migratory corridor” went around the Eastern Pacific Warm Pool, which suggested that dolphinfish avoided this high temperature‐low production zone. Dolphinfish occupied zones close to certain oceanic features, such as eddies and thermal fronts. Results suggested that the primary cause of the biological hot spots was wind‐driven upwelling, because the hot spots became more important 3–4 months after the peak in upwelling activity.

Future marine ecosystem drivers, biodiversity, and fisheries maximum catch potential in Pacific Island countries and territories under climate change

The increase in anthropogenic CO2 emissions over the last century has modified oceanic conditions, affecting marine ecosystems and the goods and services that they provide to society. Pacific Island countries and territories are highly vulnerable to these changes because of their strong dependence on ocean resources, high level of exposure to climate effects, and low adaptive capacity. Projections of mid-to-late 21st century changes in sea surface temperature (SST), dissolved oxygen, pH, and net primary productivity (NPP) were synthesized across the tropical Western Pacific under strong climate mitigation and business-as-usual scenarios. These projections were used to model impacts on marine biodiversity and potential fisheries catches. Results were consistent across three climate models, indicating that SST will rise by ≥ 3°C, surface dissolved oxygen will decline by ≥ 0.01mlL−1, pH will drop by ≥ 0.3, and NPP will decrease by 0.5gm−2 d−1 across much of the region by 2100 under the business-as-usual scenario. These changes were associated with rates of local species extinction of > 50% in many regions as fishes and invertebrates decreased in abundance or migrated to regions with conditions more suitable to their bio-climate envelope. Maximum potential catch (MCP) was projected to decrease by > 50% across many areas, with the largest impacts in the western Pacific warm pool. Climate change scenarios that included strong mitigation resulted in substantial reductions of MCP losses, with the area where MCP losses exceeded 50% reduced from 74.4% of the region under business-as-usual to 36.0% of the region under the strong mitigation scenario.

Reconstruction of oceanic circulation patterns in the tropical Pacific across the early/middle Miocene boundary as inferred from radiolarian assemblages

Although there have been attempts to infer Neogene oceanic circulation patterns in the tropical Pacific on the basis of multiple marine proxies, oceanic circulation patterns across the early/middle Miocene boundary are still poorly understood despite paleoclimate having significantly changed during this interval. In this study, we reconstruct the changes in tropical oceanic circulation patterns in the Pacific across the early/middle Miocene boundary based on radiolarian assemblages obtained at Integrated Ocean Drilling Program Site U1335 in the eastern tropical Pacific.The radiolarian upwelling taxa increased during four intervals (18.4–18.1Ma, 16.9–15.7Ma, 15.2–14.6Ma, 14.2–13.4Ma). Radiolarian temperature index (RTI) was calculated using the relative abundances of the warm water (cluster B1) and cool water taxa (cluster B2) in order to evaluate relative temperature fluctuations of the surface water. The sea surface temperature index was relatively high from 16.8 to 16.0Ma and gradually decreased from 16.0 to 14.6Ma. Subsequently, the temperature index decreased stepwise at 13.9 and 13.4Ma and became relatively low from 13.4 to 12.7Ma. Comparison of the RTI record in the eastern tropical Pacific to the climatic index based on the benthic foraminiferal δ18O record shows that variability in the two records follows a roughly similar trend from the early to the middle Miocene. However, the sea surface temperature record does not indicate a sharp increase in warmth in the eastern tropical Pacific during the mid-Miocene climatic Optimum-1 (MMCO-1), as suggested by the benthic isotopic record. This is likely because of increased upwelling of cool, nutrient-rich water at this time.Beginning in the latest early Miocene (~17Ma) radiolarian assemblages were dominated by different taxa in the eastern and western tropical Pacific. This pattern is interpreted as indicating a shallower thermocline in the east and a deeper thermocline in the west, based on the relative abundance of the upwelling taxa. There is an overall increasing trend in this difference since the latest early Miocene. We tie these events to the effective closure of the Indo-Pacific seaway and the development of a substantial western Pacific warm pool along with the development of a strong Equatorial Undercurrent.

Observational evidence of the downstream impact on tropical rainfall from stratospheric Kelvin waves

Analysis of one continuous decade of daily, high-vertical resolution sounding data from five proximate islands in the western equatorial Pacific region reveals eastward and downward propagating Kelvin waves in the tropical stratosphere, with a zonal wave number one structure and a period of ~15 days. By defining an initiation index, we find that these waves are primarily generated over the western Pacific warm pool and South America–tropical Atlantic sector, consistent with regions of frequent deep convection. The zonal phase speed of the stratospheric Kelvin waves (SKWs) is relatively slow (~10 m s−1) over the initiation region due to coupling with deep convection, and becomes much faster (~30–40 m s−1) once decoupled from the downstream troposphere. SKWs have significant impacts on downstream tropical rainfall through modulation of tropopause height. The cold phase of SKWs at tropopause leads to higher tropopause heights and more convection in tropics—with opposite impacts associated with the warm phase. Downstream tropical precipitation anomalies associated with these SKWs also propagate eastward with the same speed and zonal scale as observed SKWs. Interannual variability of the amplitude of the SKWs is shown to be associated with the Quasi-Biennial oscillation (QBO); implications for predictability are discussed.

Increased Chances of Drought in Southeastern Periphery of the Tibetan Plateau Induced by Anthropogenic Warming

The southeastern periphery of the Tibetan Plateau (SEPTP) was hit by an extraordinarily severe drought in the autumn of 2009. Overall, the SEPTP has been gripped by a sustained drought for six consecutive years. To better understand the physical causes of these types of severe and frequent droughts and thus to improve their prediction and enhance the ability to adapt, many research efforts have been devoted to the disastrous droughts in the SEPTP. Nonetheless, whether the likelihood and strength of the severe droughts in the SEPTP, such as that in the autumn of 2009, have been affected by anthropogenic climate change remains unknown. This study first identifies the atmospheric circulation regime responsible for the SEPTP droughts and then explores how human-induced climate change has affected the severe droughts in the SEPTP. It is found that the drought conditions in the SEPTP have been driven by the Indian–Pacific warm pool (IPWP) sea surface temperature (SST) through strengthening of the local Hadley circulation and anomalously cyclonic motion over the South China Sea. Ensemble simulations of climate models demonstrate a robust increase in the dry and warm meteorological conditions seen during the 2009 SEPTP autumn drought due to anthropogenic global warming. Given that warming is expected to continue into the future, these results suggest that it is likely that drought conditions will become more common in the SEPTP.

Variations in the western Pacific warm pool across the mid-Pleistocene: Evidence from oxygen isotopes and coccoliths in the West Philippine Sea

We present planktonic foraminifera oxygen isotope and Florisphaera profunda abundance data from the International Marine Global Change Study Program (IMAGES) Core MD06-3050, which was collected in the West Philippine Sea on the margin of the Western Pacific Warm Pool (WPWP). Our records reveal marked changes in the upper water structure in the Kuroshio source region as early as 1.5Ma, continuing through the mid-Pleistocene climate transition (MPT). These changes are evidenced by reconstructions of the thermocline (based on planktonic foraminiferal oxygen isotope differences) and the nutricline (based on the relative abundance of the coccolithophore species Florisphaera profunda) in the Kuroshio source region. The evolution of the thermocline/nutricline featured three prominent phases: 1) phase I (1.5–1.1Ma), which was characterized by low-amplitude variations in a shallow thermocline; 2) phase II (1.1–0.8Ma), which was characterized by high-amplitude variations in a relatively shallow thermocline/nutricline; and 3) phase III (0.8–0.5Ma), which was characterized by low-amplitude variations in a deep thermocline/nutricline. Combined with the zonal sea surface temperature gradient in the tropical Pacific, the evolution of the upper water structure can be linked to tropical climatic changes across the MPT, including the intensification of atmospheric circulation and a gradual cessation of the long-term El Niño-like state. The upper water structure of the WPWP was asymmetric before 0.8Ma, with a shallow thermocline/nutricline along the northern margin and a deep thermocline/nutricline in the center of the WPWP and South China Sea (SCS). The modern WPWP was established by approximately 0.8Ma, and the upper water structure has changed synchronously as a whole since that time. A comparison of the δ18O values derived from Globigerinoides ruber tests from the MD06–3050 core with those from other cores in the western Pacific suggests that the lower glacial/interglacial G. ruber δ18O values in MD06-3050 before 0.8Ma could be related to the enhancement of the WPWP and to changes in atmospheric circulation patterns.

Spatio-temporal variability of lightning and convective activity over South/South-East Asia with an emphasis during El Niño and La Niña

The present analysis investigates the spatio-temporal variability of the convective parameters and associated lightning flash rates during the period 1997–2013 including the El Niño and La Niña episode. It reveals that north-western and north-eastern part along the foothills of Himalayas as well as Indo-China peninsular region and South China Sea are much convective prone zones over the South/South-East Asia. The terrain/orography of the Himalayan range, the influence of cross-equatorial low-level jet and large-scale circulation during pre-monsoon and active phase of monsoon, the western Pacific Warm Pool with increased sea surface temperature as well as the solar-heating-originated local instability instigate the convective anomaly to propagate over the north-western and north eastern Indian sub-continent along with the Indo-China peninsula and South China Sea respectively. The land surfaces of the Indian sub-continent and the sea surface of South China Sea possesses significant correlation with lightning flash rates and convective parameters whereas the sea surface surrounding Indian sub-continent do not show such good correlations among them. Although, the occurrence of convective activities during the El Niño (La Niña) gets reduced (increased), the occurrence of lightning flashes gets enhanced (diminished) during this period which may be the direct consequence of warming atmosphere in relation to changing patterns of regional climate.

Nonlinear climatic sensitivity to greenhouse gases over past 4 glacial/interglacial cycles

The paleoclimatic sensitivity to atmospheric greenhouse gases (GHGs) has recently been suggested to be nonlinear, however a GHG threshold value associated with deglaciation remains uncertain. Here, we combine a new sea surface temperature record spanning the last 360,000 years from the southern Western Pacific Warm Pool with records from five previous studies in the equatorial Pacific to document the nonlinear relationship between climatic sensitivity and GHG levels over the past four glacial/interglacial cycles. The sensitivity of the responses to GHG concentrations rises dramatically by a factor of 2–4 at atmospheric CO2 levels of >220 ppm. Our results suggest that the equatorial Pacific acts as a nonlinear amplifier that allows global climate to transition from deglacial to full interglacial conditions once atmospheric CO2 levels reach threshold levels.

Characteristics of the Heinrich 1 abrupt climate event inferred from a speleothem record from Xianyun Cave, Fujian Province

The climate system of the Earth experienced a series of abrupt changes such as Heinrich events and Dansgaard-Oeschger cycles during the last glaciation. Among them, the Heinrich 1 event (H1 event) is the most prominent cold event. It was recorded in Greenland ice cores, deep sea sediments, loess, stalagmites and lacustrine sediments and was proposed to be a global climate event. During H1 event (~18–15 ka), the ice raft extended southward and large amount of cold and fresh water was integrated into the North Atlantic Ocean. It led to the reduction of the Atlantic Meridional Overturning Circulation (AMOC), cooling of the northern hemisphere, and the weakening of the East Asian summer monsoon (EASM) as the results of the southward shift of the Inter-tropical Convergence Zone (ITCZ). Pausata et al. (2011) used a numerical climate model with an embedded oxygen-isotope model to assess what caused the shifts in the oxygen-isotope signature of precipitation during a climate perturbation designed to mimic the Heinrich event. The simulations reproduced the enrichment of δ 18O over Northern India and East Asia evident in speleothem records during Heinrich events. They then concluded that changes in the δ 18O of Chinese stalagmites associated with Heinrich events reflect changes in the intensity of Indian rather than East Asian monsoon precipitations. The simulation result also shows no significant change in δ 18O in precipitation over southeastern China, where its climate is influenced by EASM only. However, there is a lack of well-dated stalagmite record covering the H1 event from the southeastern China to test this hypothesis. Here we present a high resolution stalagmite isotope record (XYⅣ-3) from Xianyun Cave in western Fujian Province to reveal the detailed precipitation history of the EASM from 16.8 to 15.2 ka BP, based on eight high-precision 230Th ages and 256 oxygen isotope data, yielding an average resolution of 7 a. This high resolution stalagmite δ 18O record constrained detailed changes of the EASM during H1 event. It is characterized by a two-step positive shift process beginning at ~16.2 ka BP with the amplitude of 1.8‰, which indicates a significant weakened monsoon period. This result does not support the model simulation which was proposed by Pausata et al. (2011) that the δ 18O of Chinese stalagmites reflected changes of the Indian Summer Monsoon rainfall. Indeed our record suggests that changes in δ 18O of Chinese stalagmites reflect changes of EASM, especially during Henrich events. Comparing with stalagmite records from Hulu Cave and Qingtian Cave, stalagmites records from all 3 caves captured the H1 abrupt climate changes within dating errors. However, changes in Xianyun Cave are more prolonged (~260 a) than the abrupt (18–19 a) changes in Qingtian and Hulu caves. We conclude that the prolonged process of the Xianyun Cave is influenced, to some extent, by ocean-atmosphere coupling processes over the tropical western Pacific Ocean. The hydroclimate of the tropical west Pacific may cause the different responses. Due to the influence of sea-surface temperature changes in the tropical western Pacific warm pool and ENSO, the response of δ 18O in precipitation in Fujian Province evident by our stalagmites to North Atlantic Ocean change would last longer than other EASM regions.

Carbon fixation in sediments of Sino-Pacific seas-differential contributions of bacterial and archaeal domains

Abstract Oceanic stretches experiencing perpetual darkness and extreme limitation of utilizable organic matter often rely on chemosynthetic carbon (C)-fixation. However, C-fixation is not limited to carbon-deplete environments alone but might also occur in varying degrees in carbon-replete locales depending on the nature and concentration of utilizable carbon, electron donors and acceptors. Quantification of microbial C-fixation and relative contribution of domains bacteria and archaea are therefore crucial. The present experiment estimates the differential rates of C-fixation by archaea and bacteria along with the effects of different electron donors. Four Sino-Pacific marine sediments from Bashi strait (Western Pacific Warm Pool), East China Sea, South China Sea and Okinawa Trough were examined. Total microbial C-uptake was estimated by doping of aqueous NaH14CO3. Total bacterial C-uptake was measured by blocking archaeal metabolism using inhibitor GC7. Archaeal contribution was estimated by subtracting total bacterial from total microbial C-uptake. Effect of electron donor addition was analyzed by spiking with ammonium, sulfide, and reduced metals. Results suggested that C-fixation in marine sediments was not the function of archaea alone, which was in contrast to results from several recent publications. C-fixing bacteria are also equally active. Often in spite of great effort of one domain to fix carbon, the system does not become net C-fixing due to equal and opposite C-releasing activity of the other domain. Thus a C-releasing bacterial or archaeal community can become C-fixing with the change of nature and concentration of electron donors.

Late Quaternary water temperature variations of the Northwest Pacific based on the lipid paleothermometers TEXH86, UK´37 and LDI

The Kuroshio Current (KC) and Oyashio Current (OC) are the two major western boundary currents of the Pacific Ocean and their interplay exerts a major control on the climate evolution of the northwestern Pacific region as well as East Asia. Although millennial scale variations in the strength and flow pattern of the KC are well documented, only little is known on the long-term evolution of this ocean current and its role in affecting regional and global climate over geological time scales. Here, we present surface and thermocline temperature records covering the last two glacial-interglacial cycles of IODP (Integrated Ocean Drilling Program) Site C0011, SE of Japan, using the lipid paleothermometers TEXH86 (tetraether index of tetraethers consisting of 86 carbon atoms), UK´37 (unsaturated ketone index) and LDI (long-chain diol index). Lower average water temperatures (20.1–20.7°C in TEXH86, 21.6–22.0°C in UK´37, and 20.7–21.9°C in LDI) during marine isotope stages (MIS) 2 and 6 are considered to indicate a reduction in warm water mass export from the Western Pacific Warm Pool (WPWP) to northern mid-latitudes via the KC due to decreased subtropical gyre circulation in the North Pacific. A synchronous southward displacement of the KC/OC interfrontal zone resulted in an overall stronger influence of colder and more polar waters at Site C0011. MIS 1, 3 and 5 are characterized by generally higher water temperatures (21.7–22.1°C in TEXH86, 23.2–24.3°C in UK´37, and 23.1–24.3°C in LDI), likely reflecting an increased northward transport of subtropical waters to the study site. Higher Holocene than Eemian water temperatures are attributed to a stronger KC and the formation of its short meander south of Japan, whereas a less strong KC during the Eemian likely favored the formation of the large meander path. Better correlations between the different lipid paleothermometers during cold MIS are considered to indicate more similar production seasons and habitat depths of the biological proxy sources with the latter factor likely driven by thermocline shoaling.

An aftereffect of global warming on tropical Pacific decadal variability

Studies have shown that global warming over the past six decades can weaken the tropical Pacific Walker circulation and maintain the positive phase of the Interdecadal Pacific Oscillation (IPO). Based on observations and model simulations, another aftereffect of global warming on IPO is found. After removing linear trends (global warming signals) from observations, however, the tropical Pacific climate still exhibited some obvious differences between two IPO negative phases. The boreal winter (DJF) equatorial central-eastern Pacific sea surface temperature (SST) was colder during the 1999–2014 period (P2) than that during 1961–1976 (P1). This difference may have been a result of global warming nonlinear modulation of precipitation; i.e., in the climatological rainy region, the core area of the tropical Indo-western Pacific warm pool receives more precipitation through the “wet-get-wetter” mechanism. Positive precipitation anomalies in the warm pool during P2 are much stronger than those during P1, even after subtracting the linear trend. Corresponding to the differences of precipitation, the Pacific Walker circulation is stronger in P2 than in P1. Consequent easterly winds over the equatorial Pacific led to a colder equatorial eastern–central Pacific during P2. Therefore, tropical Pacific climate differences between the two negative IPO phases are aftereffects of global warming. These aftereffects are supported by the results of coupled climate model experiments, with and without global warming.