
==== Front
Sci Adv
Sci Adv
sciadv
advances
Science Advances
2375-2548
American Association for the Advancement of Science

adp7855
10.1126/sciadv.adp7855
Research Article
Earth, Environmental, Ecological, and Space Sciences
SciAdv r-articles
Climatology
Geochemistry
Climatology
Triple oxygen isotope reveals insolation-forced tropical moisture cycles
Triple oxygen isotope reveals moisture cycles
https://orcid.org/0000-0002-6003-2157
Sha Lijuan Conceptualization Data curation Formal analysis Funding acquisition Investigation Methodology Resources Validation Visualization Writing - original draft Writing - review & editing 1
https://orcid.org/0000-0002-1320-4761
Dang Haowen Conceptualization Formal analysis Funding acquisition Investigation Methodology Visualization Writing - original draft Writing - review & editing 2 *
https://orcid.org/0000-0002-2733-6220
Wang Yue Investigation Methodology Visualization Writing - original draft Writing - review & editing 2
https://orcid.org/0000-0002-0698-5459
Wassenburg Jasper A. Funding acquisition Writing - review & editing 3 4
https://orcid.org/0000-0002-7070-7365
Baker Jonathan L. Conceptualization Investigation Writing - original draft Writing - review & editing 1 5
https://orcid.org/0000-0002-7915-9828
Li Hanying Formal analysis Software Visualization 1
https://orcid.org/0000-0001-5700-2451
Sinha Ashish Visualization 6
https://orcid.org/0000-0003-3098-7339
Ait Brahim Yassine Conceptualization Supervision Validation Visualization Writing - original draft 7
https://orcid.org/0000-0002-9327-9957
Wu Nanping Methodology Writing - review & editing 8 9
https://orcid.org/0000-0002-5911-7110
Lu Zhengyao Funding acquisition Validation Writing - review & editing 10
https://orcid.org/0000-0001-8310-6115
Yang Ce Resources 11
https://orcid.org/0000-0002-7611-0244
Dong Xiyu Conceptualization Writing - original draft 1
Lu Jiayu Formal analysis Investigation 12
https://orcid.org/0000-0002-0855-1283
Zhang Haiwei Writing - original draft Writing - review & editing 1
Mahata Sasadhar Data curation Investigation Methodology Resources Validation 1
https://orcid.org/0000-0001-7063-5050
Cai Yanjun Conceptualization Visualization Writing - review & editing 1
https://orcid.org/0000-0002-2037-3539
Jian Zhimin Conceptualization Supervision 2
https://orcid.org/0000-0002-5305-9458
Cheng Hai Conceptualization Funding acquisition Project administration Supervision Writing - original draft Writing - review & editing 1 13 *
1 Institute of Global Environmental Change, Xi’an Jiaotong University, Xi’an, China.
2 State Key Laboratory of Marine Geology, Tongji University, Shanghai, China.
3 Center for Climate Physics, Institute for Basic Science, Busan, Republic of Korea.
4 Pusan National University, Busan, Republic of Korea.
5 Institute of Geology, University of Innsbruck, Innrain 52, Innsbruck 6020, Austria.
6 Department of Earth Sciences, California State University Dominguez Hills, Carson, CA, USA.
7 International Water Research Institute, Mohammed VI Polytechnic University, Ben Guerir, Morocco.
8 Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences, Hainan, China.
9 School of Earth, Atmosphere and Environment, Monash University, Clayton, VIC 3800, Australia.
10 Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden.
11 State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an, China.
12 Jiangsu Coastal Development Research Institute, Yancheng Teachers University, Yancheng, China.
13 State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an, China.
* Corresponding author. Email: cheng021@xjtu.edu.cn (H.C.); hwdang@tongji.edu.cn (H.D.)
13 9 2024
11 9 2024
10 37 eadp785511 4 2024
06 8 2024
Copyright © 2024 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).
2024
The Authors
https://creativecommons.org/licenses/by-nc/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial license, which permits use, distribution, and reproduction in any medium, so long as the resultant use is not for commercial advantage and provided the original work is properly cited.

Tropical oceans are the main global water vapor and latent heat sources, but their responses to radiative forcing remain unclear. Here, we investigate oceanic moisture dynamics of the western tropical Pacific (WTP) over the past 210,000 years through an approach of planktonic foraminiferal triple oxygen isotope (Δ′17O). The Δ′17O record is dominated by the precession cycles (~23,000 years), with lower values reflecting higher humidity in concert with higher Northern Hemisphere summer insolation. Our empirical and modeling results, combined with other geological archives, suggest that the enhanced moisture convergence over the WTP largely intensifies changes in the meridional and zonal hydrological cycles, affecting rainfall patterns in East Asia and northern South America. We propose that the insolation-driven WTP moisture dynamics play a pivotal role in regulating tropical hydroclimate.

Triple oxygen isotope record reveals insolation-forced changes in atmospheric moisture dynamics over the tropics.

http://dx.doi.org/10.13039/501100001809 National Natural Science Foundation of China 42488201 http://dx.doi.org/10.13039/501100001809 National Natural Science Foundation of China 42103005 http://dx.doi.org/10.13039/501100001809 National Natural Science Foundation of China 42222603 http://dx.doi.org/10.13039/501100001809 National Natural Science Foundation of China 41976047 http://dx.doi.org/10.13039/501100001809 National Natural Science Foundation of China 42202218 http://dx.doi.org/10.13039/501100004359 Vetenskapsrådet 2022-03617 http://dx.doi.org/10.13039/501100010446 Institute for Basic Science IBS-R028-Y2 Shanghai Pilot Program for Basic Research N/A Shanghai Pilot Program for Basic Research N/A
==== Body
pmcINTRODUCTION

The global hydrologic cycle, i.e., exchanges of moisture and energy among the atmosphere, ocean, and land, has strengthened and becomes increasingly volatile, especially precipitation extremes in tropical regions under anthropogenic warming (1, 2). The atmospheric convection and moisture convergence over the warm tropical oceans, particularly the “warm pool” in the western tropical Pacific (WTP) (3), have a global impact through the Hadley and Walker cells (4, 5). A comprehensive characterization of the dynamic processes, from sea-surface evaporation, moisture transport to continental rainfall, is thus essential for understanding the hydrological cycle in the tropics. However, most proxy-based studies of tropical hydroclimate to date have relied on reconstructions of precipitation (e.g., speleothem isotopes, seawater salinity, and terrigenous inputs) (6–8), with little information available about long-term changes in vapor dynamics and the role of radiative forcing in modulating the WTP moisture variability (9, 10). This limitation stems from the absence of direct proxies for evaporation and humidity, making the development of a reliable method to reconstruct total changes in atmospheric water vapor content over the WTP crucial for understanding tropical hydroclimate.

The 17O anomalies of water inferred from triple oxygen isotope (Δ′17O = δ′17O − 0.528 × δ′18O; Materials and Methods and Supplementary Text) are the result of fractionations among three oxygen isotopes (18O/16O and 17O/16O reported as δ18O and δ17O, respectively) during water phase changes, mainly controlled by relative humidity during the evaporation process (11, 12). Recent advances in mass spectrometric analysis enable high-precision measurements on triple oxygen isotope in carbonates (13–15), which have the potential to record the triple oxygen isotope compositions of parent waters. This innovation provides a useful approach to reconstructing atmospheric humidity in water vapor source regions beyond the instrumental observation era, facilitating constraints on this key physical component of the hydrological cycle.

Here, we present the first set of Δ′17O data obtained from the mixed-layer dwelling planktonic foraminifera, Globigerinoides ruber (white, sensu stricto), taken from a central WTP sediment core (MD10-3340). This dataset enables the estimation of both relative and specific humidity (Supplementary Text and Fig. 1) spanning the past 210 ka (thousand years) at the global moisture centroid region, to tackle one of the most poorly understood factors in hydroclimate studies: the atmospheric water vapor content. By combining the Δ′17O record with proxy-reconstructed sea surface temperature (SST) and δ18Osw-ive (the surface seawater δ18O calibrated from planktonic foraminiferal δ18O after correcting the Mg/Ca-based SST and the ice-volume effects; Materials and Methods) over the WTP (11), and model simulations, we provide insights into the tropical moisture dynamics in response to the orbital insolation forcing.

Fig. 1. Precession dominated changes in Δ′17O and δ18Osw-ive records.

(A) Δ′17O (blue circles with error bars showing the measurement uncertainty; see Materials and Methods) and δ18Osw-ive (black, the surface seawater δ18O calibrated from planktonic foraminiferal δ18O after correcting the Mg/Ca-based SST and the ice-volume effects, linearly resampled from the original data using a 0.6-ka step; see Materials and Methods) (10) on the mixed-layer dwelling planktonic foraminifera G. ruber from MD10-3340, compared with the precession parameter (esinω; red) (70). Four replicate samples (dark blue symbols) for the carbonate triple oxygen isotope experiments are used to assess the reproducibility. (B) The Δ′17O-estimated relative humidity (gray with squares) and specific humidity (benzo blue with circles), compared with the precession parameter (red) (70). Error bars denote each sample’s SD (1σ SD). (C) Gaussian filtering on the precession band (frequency, 0.0435; bandwidth, 0.01) of Δ′17O (blue), δ18Osw-ive (black), and the precession parameter (red) (70). B.P., before the present; VSMOW, Vienna standard mean ocean water. (D to F) Cross-spectral analyses of Δ′17O versus δ18Osw-ive (D), δ18Osw-ive versus precession (E), and Δ′17O versus precession (F). Spectral powers are normalized and shown in corresponding colors. Gray shadings denote the coherence, and the purple line segments the phase (in degrees) at the frequency of precession. Spectral analyses are performed by Blackman–Tukey spectrum using a Tukey window on AnalySeries (71), with an error of the power by 0.53 < ∆Power/Power < 2.73 and a significance level of coherence of >0.5.

RESULTS

Modern hydrological analyses

The Halmahera Sea, where core MD10-3340 was retrieved, is situated at a critical conduit for the westward transport of warm equatorial Pacific waters and, hence, can plausibly represent the hydroclimatic conditions of the WTP (16). We analyzed the modern hydrology of the tropical Pacific. On a seasonal scale, moisture-trajectories for site MD10-3340 show a large alternation between northeasterly (southeasterly) winds and rainfall minima (maxima) in boreal winter (summer) (figs. S1 and S2), following the seasonal migration of the Inter-Tropical Convergence Zone (ITCZ; figs. S2 and S3). In addition, our air mass back-trajectory reanalysis from 1988 to 2015 indicates that during the summer months (June to September), moisture contributions from the southwest Pacific Ocean dominate (58.72%), whereas during the boreal winter months (November to February) moisture from the northeast Pacific Ocean is more prominent (41.28%) (fig. S2). On an interannual scale, moisture convergence in the WTP varies in association with the El Niño Southern Oscillation (ENSO) (fig. S3C). During the La Niña (El Niño) phase, more (less) evaporated water from the open tropical Pacific converges by stronger (weaker) surface easterly trade winds toward the WTP, concomitant with higher (lower) relative humidity over the WTP (fig. S1, D and E) and a strengthened (weakened) Walker circulation (fig. S3C). In sum, changes in the humidity in our study area are closely related to the intensity of water vapor convection and convergence around the rising limbs of the meridional Hadley cell and the zonal Walker cell (figs. S3 and S4) (17). Local rainfall amount and relative humidity over the WTP are thus positively correlated (fig. S4).

Variations of foraminiferal Δ′17O and Δ′17O-based reconstruction

The foraminiferal carbonate Δ′17O record of MD10-3340 shows a large range from −106 to −64 per meg [1 per meg = 10−3 per mil (‰) = 10−6] on orbital timescales with associated errors between 1 and 10 per meg (1σ, SD; Fig. 1A, fig. S5, and table S1), manifesting a dominant ~23-ka periodicity apparently linked to Earth’s precession cycle (esinω; Fig. 1). The precession minima and maxima are marked by negative and positive Δ′17O excursions, respectively, with an amplitude of 20 to 40 per meg (Fig. 1A). On the basis of the triple oxygen isotopic fractionation between carbonates and seawater (Materials and Methods), these foraminiferal Δ′17O can be calculated back into seawater Δ′17O of the WTP surficial waters, averaging from −23 to 20 per meg (fig. S6).

To reconstruct the relative humidity, we developed an isotopic mass-balance calculation model for our G. ruber Δ′17O record, incorporating the oceanic flows and evaporation-precipitation over the WTP (detailed in Supplementary Text; Fig. 2). The reconstructed relative humidity values increase (decrease) by ~20 to 40% with associated uncertainties ranging from 4 to 10% (1σ, SD) at the precession minima [corresponding to the maxima of Northern Hemisphere summer insolation (NHSI)], relative to precession maxima (i.e., the NHSI minima) (Fig. 1B and fig. S5). Our Δ′17O-based estimate of relative humidity for the late Holocene (73 ± 5%; Fig. 1B and table S1) agrees within error with the observed annual mean relative humidity over the WTP (~75%; fig. S1C), providing a test on the validation of our method.

Fig. 2. The schematic representation of the triple oxygen isotope systematics for planktonic foraminiferal shells in the WTP.

(A) Schematic view of steady-state evaporation, and diagrammatic representation of the Craig-Gordon isotope evaporation model over the Pacific surficial seawater. F represents the various fluxes of water in terms of the mass of the major water isotope, including FI, the inflow flux, which is the averaged velocity of the westward mixed layer flows (particularly South Equatorial Current that dominates upper waters near the coring site); FO, the outflow flux, which is the horizontal velocity of eastward-flowing North Equatorial Countercurrent; FE and FP, the evaporation and precipitation flux, respectively. RI, RO, RE, and RP are the isotope ratios of the inflow, outflow, and water loss by evaporation and precipitation (table S3), respectively. (B) A schematic presentation of δ17O-δ18O-Δ′17O systematics for carbonates during the calcification of planktonic foraminiferal shells (G. ruber). The fractionation exponents for carbonate-water equilibrium, equilibrium vapor, diffusion, and condensation processes are 0.525 (60, 61), 0.529 (11), 0.518 (12), and 0.529 (11), respectively. The blue dashed line indicates the global meteoric water line (GMWL) (slope of 0.528) (11). δ′17O = 1000 × ln(1 + δ17O/1000) and δ′18O = 1000 × ln(1 + δ18O/1000). RH, relative humidity.

Besides relative humidity, we further estimated specific humidity from our Δ′17O record on the basis of vapor pressure and SST (Supplementary Text and fig. S5) (18, 19), with values fluctuating between 12.35 and 21.97 g/kg over the past 210 ka (Fig. 1B). The observed precession cycles in our Δ′17O-based reconstruction of the WTP humidity (Fig. 1) are supported by the simulated boreal summer season [July to September (JAS)]–specific humidity changes over the WTP (10°S to 10°N, 100°E to 150°W) from the Goddard Institute for Space Studies of the US (GISS_ModelE2-R model; Materials and Methods) and the National Center for Atmospheric Research Community Climate System Model 3 (NCAR-CCSM3 model; Materials and Methods) (Fig. 3D and fig. S7) (20). The disparity in absolute values observed between the two models can be attributed to variations in parameterization and the inclusion of continental ice-sheet forcing in the NCAR-CCSM3 model, as opposed to its absence in the GISS_ModelE2-R (Materials and Methods).

Fig. 3. Model simulated and proxy reconstructed changes in specific humidity.

(A to C) Averaged anomalies at precession minima relative to precession maxima (Pmin minus Pmax) of vertically integrated water vapor content (shading, positive values for moisture convergence and negative values for moisture divergence), and 850-hPa wind (black vectors) for the annual mean [ANN (A)], boreal summer [July to September (JAS) (B)], and winter [January to March (JFM) (C)], respectively, from transient experiment by Goddard Institute for Space Studies of the US (GISS_ModelE2-R model; see Materials and Methods). (D) Specific humidity of our Δ′17O-derived record (symbols) and from the GISS (red) and NCAR-CCSM3 (blue) model outputs (boreal summer, July to September, 11-point running average). The gray dashed line shows the 21 July insolation (70) at core MD10-3340 (0.5°S).

DISCUSSION

Δ′17O-derived moisture content changes

As a typical mixed-layer dwelling planktonic foraminifera, G. ruber has been used as an indicator of surface-water properties (21), and oxygen isotope compositions of G. ruber in MD10-3340 theoretically inherit the signals from meteoric water near the center of the WTP. Analysis of scanning electron microscopy (SEM) on foraminiferal samples shows no evident signs of dissolution or secondary recrystallization (Supplementary Text and fig. S8). Moreover, the triple oxygen isotope of foraminiferal carbonates remains unaffected by geochemical postdepositional effects, and kinetic effects did not substantially influence their calcification process (see details in Supplementary Text). Triple oxygen isotope compositions of well-preserved G. ruber principally maintained a quasi-equilibrium with the ambient seawater (see details in Supplementary Text), and the reconstructed paleo-seawater Δ′17O values align with existing data of the seawater and meteoric water in modern times (fig. S6). Hence, our G. ruber Δ′17O can serve as a faithful proxy for reconstructing hydroclimate over the WTP.

On the other hand, the reconstructed paleo-seawater data exhibit a −0.79 per meg/% slope of Δ′17O with respect to relative humidity (fig. S9), intermediary to that for precipitation (−1.04 per meg/%) (11) and atmospheric water vapor (−0.64 per meg/%) (22). This intermediate slope supports the notion that the Δ′17O signatures inferred by the planktonic foraminifera G. ruber reflect a composite signal of hydrological processes over the WTP, inclusive of both evaporation and precipitation dynamics. Moreover, the Δ′17O and δ18Osw-ive of MD10-3340 are anticorrelated at precession minima (maxima) under high (low) NHSI (Fig. 1). Mechanistically, at higher (lower) NHSI, lower (higher) Δ′17O suggests enhanced (reduced) humidity over the moisture-source region arising from increased (decreased) evaporation, and higher (lower) δ18Osw-ive indicates increased (decreased) evaporation relative to precipitation, causing more 18O enrichment (depletion) in surface seawater (Fig. 1A) (10, 23, 24). Climate model simulations also show an enhanced (reduced) evaporation minus precipitation (E-P) over a broad part of the open tropical Pacific (10, 25) at high (low) NHSI. This coherence is captured by Δ′17O and δ18Osw-ive records from the WTP (fig. S10), despite the differences in amplitudes and extreme values between model simulations and proxy reconstructions possibly induced by uncertainties in both of them. Therefore, the δ18Osw-ive proxy and model simulations lend robust support to the significance of our foraminiferal Δ′17O, affirming its role as indicators of the hydrological balance in the WTP, a balance that includes both evaporation and precipitation processes.

Because G. ruber growth in the WTP has a seasonal preference for July to October (26), and the specific humidity in the boreal summer season largely regulates its annual mean at site MD10-3340 (Fig. 3), our Δ′17O record can be used to deduce the variations in the specific humidity of the summer and the integrated atmospheric water vapor content at the moisture source region (18, 19).

Low-latitude insolation and glacial-interglacial cycles

Our Δ′17O-based reconstruction of the WTP humidity (Fig. 1) is consistent with the simulated specific humidity (Fig. 3D) and the rainfall deuterium excess (dexcess = δD − 8 × δ18O) derived from the GISS_ModelE2-R model (Fig. 4D), all exhibiting a tight correlation with precession. This phasing is seemingly contradictory to the SST changes in the tropical oceans, which mainly manifest as an ~100-ka cycle of the global glacial-cycle signal (fig. S11) (27, 28), stemming from the waxing and waning of atmosphere pCO2 and the northern high-latitude ice sheets (7, 29). By affecting saturation vapor pressure (fig. S5, E and F), local SST has important impacts on low-latitude evaporation and precipitation (30, 31).

Fig. 4. Comparison of GISS-modeled rainfall deuterium compositions over the WTP with Δ′17O, deuterium excess (dexcess), and dln from the Antarctic ice cores.

From top to bottom: (A) Original 150-ka ice core Δ′17O dataset of Vostok (light blue thin line) (35) and its 2000-year running average (dark blue thick line), and the eccentricity with a ~100-ka periodicity (gray dashed line) (70). (B) The rainfall dln {dln = ln[1 + δD] + 2.85 × 10−2 × [ln(1 + δ18O)]2 – 8.47 × ln[1 + δ18O]} from GISS_ModelE2-R model over the WTP and the precession (esinω; gray dashed line). (C) Antarctic ice core dln records from Vostok (cyan) and EPICA Dome C (light yellow) (36), and the eccentricity (gray dashed line) (70). (D) GISS_ModelE2-R simulated WTP rainfall dexcess and the precession (gray dashed line) (70). (E) Antarctic ice core dexcess records from Vostok (light blue) and EPICA Dome C (brown), and the eccentricity (gray dashed line). Proxy records shown through (B) to (C) are their 11-point running averages. (F to H) Spectral analyses of ice core Δ′17O dataset of Vostok (dark blue) and eccentricity (black) (F), Vostok (cyan) and EPICA Dome C (light yellow) dln dataset and eccentricity (black) (G), modeled rainfall dln records of WTP (purple) and precession (black) (H), and their coherences (light blue shading, all above 80% confidence level), respectively.

The recent proxy-derived and model-simulated upper (0 to 200 m) ocean heat content (upper-OHC) over the Indo-Pacific Warm Pool exhibits a precession-dominated variation (Fig. 5G) (10, 32), which is consistent with the key hydrological reconstructions in low latitudes (8, 16, 33), including the Asian monsoon speleothem δ18O records (Fig. 5D) (6, 29). In essence, this provides an energetic pathway in which the precession-driven seasonal insolation variations, rather than SST, are essential to modulating variability in the evaporation and moisture convection processes over the WTP.

Fig. 5. Schematic representation of the oceanic thermal state (left) and comparison of results from MD10-3340 with speleothem and other marine records (right).

(A and B) The hypothetical meridional and zonal atmospheric circulations in the Pacific under precession minimum [La Niña–like state (A)] and precession maximum [El Niño–like state (B)]. From top to bottom in the right panel: (C) Reconstructed specific humidity with errors; (D to F) speleothem δ18O from East Asian Sanbao Cave (D) (6), Western Amazonian Cueva del Diamante Cave (E) (43), and El Peñon municipality in the eastern Colombian (Cordillera Caracos Cave) (F) (44); (G) the proxy reconstruction in the upper ocean heat content (upper-OHC) over the Indo-Pacific Warm Pool (10); (H) composite SST difference between the western and eastern tropical Pacific (ΔSSTW-E) (detailed in table S2). Thin lines and symbols display the results, and the thick curves show the Gaussian filtering on the precession band (frequency, 0.0435; bandwidth, 0.01). The dotted gray lines show the precession parameter (esinω; ~23 ka) (70). WEP, western equatorial Pacific; VPDB, Vienna Pee Dee belemnite.

However, the proxy-reconstructed upper-OHC of the Warm Pool exhibits anomalous spikes at the peak interglacials Marine Isotope Stage 1 (MIS1) and MIS5e, which were suggested to be partly related to global ocean heat increases owing to ice-sheet melting (10). These spikes are absent, however, in our Δ′17O-reconstructed humidity records (Fig. 5C) and the pan-Pacific speleothem δ18O records (Fig. 5D) (6). Our Δ′17O and estimated relative and specific humidity show smaller amplitudes of changes during ~60 to 40 ka and the 200 to 140 ka and large amplitudes from MIS6 to MIS5e (~140 to 100 ka) (Fig. 3D), likely indicating the amplitude-modulation effect of eccentricity on precessional insolation changes. As such, our WTP Δ′17O record implies a rather small effect of high-latitude processes on tropical atmospheric moisture. In other words, the tropical hydroclimate is suggested to be primarily controlled by precessional insolation changes (25, 34).

To examine this hypothesis, we compare our WTP Δ′17O record with the Δ′17O (35) and dexcess (36) records from Antarctic ice cores (Vostok and EPICA Dome C, where the dexcess is expressed, consistent to Δ′17O, in its logarithmic delta values as dln = ln(1 + δD) + 2.85 × 10−2 × [ln(1 + δ18O)]2 –8.47 × ln(1 + δ18O); Fig. 4, A to C) (36, 37). Notably, dln adjusts for the local temperature effects as recorded by δ18O in ice cores and preserves information regarding water vapor origin with minimal alteration (36, 37). In contrast to the precession-dominated variations in our WTP Δ′17O record, the Δ′17O and dln record from the Vostok ice core are characterized by a notable glacial-interglacial variability with a strong ~100-ka cycle (Fig. 4, F to G). This divergence between low- and high-latitude records reveals that the moisture dynamics in these two regimes are sensitive to different forcings (20). In the southern high latitudes, the moisture dynamics are dominated by glacial-interglacial changes in sea-surface temperatures, sea-ice extents, and meridional insolation gradients (36, 38); while, in the low-latitude WTP, precessional insolation changes overwhelm the glacial-interglacial cycle in driving the moisture dynamics, as seen in our WTP Δ′17O record. Such different low- and high-latitude moisture dynamics in response to orbital forcings suggest a dual nature of the hydrodynamic systems of the ice sheet and the monsoon systems, shedding light to corroborate the recent “Cheng hypothesis” (25), which combines the Milankovitch theory and the Kutzbach orbital monsoon hypothesis (34).

WTP moisture dynamics

Our Δ′17O-derived reconstruction of moisture dynamics further demystifies the orbital-scale hydroclimate variations over the WTP. In general, the specific humidity in the WTP is sensitive to insolation forcing as a fast-response component of the tropical hydroclimate (39). This is related to the associated evaporation and condensation of water vapor that amplifies the effect of solar insolation (10, 39) through their influence on the vertical stability of the atmosphere. Hence, we suggest that moisture dynamics over the tropical ocean are causally linked to NHSI variations: High (low) NHSI drives enhanced (reduced) E-P over the broad low-latitude Pacific and strengthens (weakens) the moisture convergence/fluxes, thus increasing (decreasing) the water vapor content over the WTP.

The in-phase correlation of the NHSI with both marine Δ′17O record and speleothem δ18O records from the East Asian continent suggests that the moisture flux over the low-latitude oceans and the overall rainfall in the East Asian summer monsoon (EASM) domain are propelled by a common orbital forcing of insolation (29, 34, 40, 41). Enhanced NHSI increases summer E-P over the tropical WTP and strengthens the ocean-land thermal gradient, thus increasing the oceanic moisture flux and its transport to the East Asian continent via the summer monsoon circulations (34). This dynamic link intensifies the EASM and overall continental precipitation (figs. S3 and S4). In other words, when evaporation and specific humidity increase (decrease) in the WTP at high (low) NHSI, the related atmospheric circulations in NH low latitudes strengthen (weaken), which then intensify (weaken) the EASM due to northward (southward) shifts of both the meridional Hadley cell and ITCZ following changes of the low-latitude interhemispheric insolation gradient (25, 40, 41). A larger amount and stronger transport of the moisture from the WTP across the marginal seas toward the East Asian Continent (Fig. 5A) at high NHSI ultimately result in the observed broad patterns of more rainfall with stronger depleted speleothem δ18O over the continental part of the EASM regime (42).

On the other hand, our Δ′17O record shows an antiphase relationship with the terrestrial speleothem δ18O records from the western Amazon (Fig. 5E) (43) and northern South America (Fig. 5F) (44), suggesting that, at the precession minima (maxima), the enhanced (reduced) atmospheric moisture flux and specific humidity over the WTP concurred with intensified (weakened) air descending motion and reduced (increased) precipitation in northern South America adjacent to the eastern equatorial Pacific (EEP). It has been proposed that ENSO-like changes across the Equatorial Pacific are also dominated by precession cycles, as revealed by orbital-forced model simulations (20, 45, 46). The proxy-reconstructed zonal SST gradient (ΔSSTW-E) and thermocline-depth across the western equatorial Pacific and the EEP (Fig. 5H) consistently exhibit a larger (smaller) zonal ΔSSTW-E and a deeper (shallower) thermocline in the WTP than in the EEP (fig. S10, F and G), imitating a La Niña–like (El Niño–like) state (Fig. 5, A and B) (47, 48) at the precession minima (maxima). Our results further indicate that, at the precessional band, an antiphase hydrological response occurred between the WTP and northern South America adjacent to the EEP, manifesting an ENSO-like teleconnection, in line with both proxy records and model results (41, 47, 49).

Our triple oxygen isotope dataset of planktonic foraminifera provides a better understanding of past changes in summer monsoon and ENSO-like shifts, emphasizing the role of atmospheric convergence and oceanic moisture convection over the WTP in shaping the pan-Pacific hydroclimate under solar radiative forcing. These records offer insights into the moisture budget between the WTP and the pan-Pacific monsoonal lands, especially their long-term responses to radiative forcing, confirming that the spatially integrated moisture dynamic from the WTP to East Asia and South America is primarily influenced by precessional insolation changes. Nearly 70 years ago, Cesare Emiliani (1955) revolutionized the field of paleoceanography by using the oxygen isotope 18O and 16O ratio (or δ18O) of planktonic foraminifera from the Pacific and Atlantic Oceans (50) that led to a much deeper understanding of Earth’s climate change at orbital scales, particularly at high latitude. Now, our findings, by using the triple oxygen isotope of planktonic foraminifera, provide further insights into the key moisture mechanisms that drive the low-latitude hydroclimate changes following that orbital insolation forcing.

MATERIALS AND METHODS

Core MD10-3340 and age model

Core MD10-3340 (00°30.98′S, 128°43.47′E, water depth of 1094 m, total core length of 34.10 m) is retrieved from the Halmahera Sea, a minor marginal basin in the western equatorial Pacific (fig. S1), ensuring a relatively high sedimentation rate with abundant terrigenous input and hence better preservation of foraminiferal shells compared to that in the open Pacific (16). The specific basin configuration has remained sufficiently stable over the past 200 ka, allowing us to confidently interpret the terrigenous input and hydroclimate reconstructions based on the sediment records from core MD10-3340. The age model for core MD10-3340 is developed using accelerator mass spectrometry (AMS) 14C dating (with a regional reservoir age of 309 years) and benthic foraminiferal δ18O, by extending the AMS 14C-dated chronological features of benthic δ18O downcore (16). Such a method makes the age uncertainties of core MD10-3340 much less than those derived from benthic δ18O stratigraphic correlation (several thousand years), ensuring the robustness of detecting changes on the precessional band.

High-precision Δ′17O measurements of marine carbonate

All G. ruber samples (n = 35) were collected from the 250- to 350-μm-size fraction of sediment core MD10-3340. The triple oxygen isotope measurements were performed at the Institute of Global Environmental Change of Xi’an Jiaotong University (China). To precisely measure the δ17O and Δ′17O values of the acid-extracted CO2 of G. ruber shells, the O2-CO2 Pt-catalyzed oxygen-isotope equilibrium technique (13, 51) was used, and the major steps include the following: (i) each sample (~5 to 7 mg) was digested using phosphoric acid (H3PO4, 1.92 g/ml, ~104%) to extract the CO2 gas from carbonates; (ii) equilibration of the extracted CO2 and O2 of known isotopic composition for 30 min under Pt-catalyzation at 750°C; (iii) cryogenic separation of two post-equilibration gases; and (iv) measurement of the equilibrated O2 using a MAT-253 isotope ratio mass spectrometer and calculation of the δ17O and Δ′17O values of the CO2 extracted from carbonates.

Analytical errors of O2 isotope ratios were estimated using the standard error of the mean (1σ/n); hereafter SE, where n (90 cycles, the number of repeat measurements) is multiplied by the Student’s t factor (t = 1.96) for 95% confidence limit (SE*t) (13, 51). The uncertainties of δ18O and δ17O of steady-state O2 measurements by Thermo Scientific MAT 253 isotope ratio mass spectrometer were typically 0.004‰ and 0.005‰, respectively (SE*t, 95% confidence limit). The δ18O values of the CO2 gases from acid digestion of carbonate samples were measured for eight cycles to attain a precision of ~0.01‰ or better (SE*t, 95% confidence limit). The uncertainty for each carbonate Δ′17O value is represented by the SD (1σ SD) of repeated measurements, with each sample undergoing at least three repeated measurements. In addition, we incorporate the errors propagated from δ18O into the calculations of triple oxygen isotope ratios in paleo-seawater using the Monte Carlo method. To ensure reproducibility, we analyzed four replicate samples at ages of 6.2, 80, 150.1, and 196.6 ka in our carbonate triple oxygen isotope experiments (fig. S5 and table S1). The consistent results across these replicates confirm the accuracy of our high-precision Δ′17O measurements in marine carbonates.

Normalization was applied to the δ18O and δ17O values, and the normalized values were then used to calculate Δ′17O (fig. S5B). All analytical results presented here have been calibrated against the high-precision published values of the standards NBS18 and IAEA603 on the Vienna Standard Mean Ocean Water-Standard Light Antarctic Precipitation scale, as reported by Wostbrock et al. (52), using a two-point linear normalization method (53).

SST and δ18Osw-ive reconstruction

Mg/Ca (685 samples, with each sample weighing ~0.3 mg) and δ18O (1141 samples; each weighing ~0.05 mg) analyses on G. ruber (white, sensu stricto) from MD10-3340 (250 to 350 μm) were performed by an inductively coupled plasma mass spectrometry (Thermo VG-X7, with a measurement reproductivity of 2.4%) and a Finnigan-MAT253 mass spectrometer (measurement accuracy < 0.07‰), respectively (10). The sampling interval for Mg/Ca and δ18O analyses ranged from 2 to 4 cm. For our records of MD10-3340, the uncertainty of foraminiferal shell δ18O is 0.07‰ and that of Mg/Ca is estimated by 108 replicate samples (aliquots of well-mixed shell fragments of the same sample) with an SD of 2.4% (0.11 mmol/mol). Mg/Ca was converted to SST by the calibration, Mg/Ca = 0.34 ± 0.08 exp (0.102 ± 0.010 T) (54). The uncertainty of the Mg/Ca-derived SST (1σ) is 1.0°C for MD10-3340, estimated by error propagation using the uncertainties of our replicate Mg/Ca measurements and the coefficients in the Mg/Ca-temperature calibration. δ18Osw-ive was calculated by subtracting the temperature and global mean ice-volume effects from the δ18O of G. ruber (δ18Oc) using the equation (55) of T (°C) = 16.9 + 4.38 × (δ18Oc − δ18Ow) + 0.1 × (δ18Oc − δ18Ow)2 and the mean sea-level reconstruction (56). The uncertainty of sea-level reconstruction, as converted to seawater δ18O, averages 0.11‰ (1σ). The uncertainty of δ18Osw-ivc is estimated by error propagation to be 0.32‰. An offset of 0.27‰ between the Vienna Pee Dee belemnite and Vienna standard mean ocean water standards was corrected.

Calculations of triple oxygen isotope ratios in paleo-seawater

Generally, the fractionation of δ18O during the calcification of planktonic foraminiferal shells is considered to be in quasi-equilibrium with the surrounding seawater (fig. S12) (16, 49). Consequently, the δ17O (or Δ′17O) values in planktonic foraminiferal carbonates are primarily dictated by quasi-equilibrium processes similar to δ18O, attributed to the inherent mass-dependent fractionation of carbonates (Fig. 2) (13–15). The measured δ18O and δ17O values of CO2 extracted from carbonates were calculated using a fractionation exponent (θ) of 0.523 for the oxygen fractionation between CO2 and carbonate during the phosphoric acid digestion process at 25°C (57). The fractionation factors used were 1.01025 for 18αCO2/carbonate (58) and 1.00535 for 17αCO2/carbonate (57). The values for 18αcarbonate/water and 17αcarbonate/water are necessary to back-calculate the triple oxygen isotope composition of paleo-seawater via a carbonate proxy. Previous studies suggest that different carbonate minerals (e.g., calcite and aragonite) should have very similar θcarbonate/water values. Theoretical predictions for θcarbonate/water are 0.525 at 25°C (59). Experiment results showed similar values to theoretical predictions, in which analysis of O2 derived from fluorination of the modern marine brachiopod shells resulted in a value of 0.52486 and 0.52515 at 0° and 30°C, respectively (60, 61). Although this parameter was predicted to have a potentially minor (62, 63) or moderate (64) temperature sensitivity between 0° and 40°C (14), the main source of uncertainty on the calculated parent-water triple oxygen isotope compositions is derived from analytical errors, rather than the potential temperature effect on θcarbonate/water value. This study calculates paleo-seawater oxygen-isotope values using the θcarbonate/water value of 0.525 and temperature-specific 18αcarbonate/water values (65). The temperature is based on the SST reconstruction. The triple oxygen isotope compositions of paleo-seawater are calculated with a Monte Carlo method (MC = 1000) in combination with statistical estimates of uncertainty (fig. S5C). The error calculation includes uncertainties in temperature estimation (0.1°C), carbonates δ18O (0.010‰), and triple oxygen isotope exponent between carbonate and water (0.0001 for 18αcarbonate/water and 0.0002 for θcarbonate/water).

The reconstructed δ18O and δ17O values of paleo-seawater are consistent with data from oceanic and meteoric waters, and the slope (λ) of the triple oxygen isotope plot of the reconstructed paleo-seawater is 0.523 (fig. S13), closely resembling the slopes observed for Mariana Trench waters (0.521 ± 0.003) (66) and Pacific deep waters (λ = 0.521 ± 0.001) (11). This suggests that our paleo-seawater Δ′17O values can be used as a proxy for past hydroclimate (detailed in Supplementary Text).

Time series analysis

Cross-spectral analyses were performed with the Blackman–Tukey approaches using AnalySeries (17), with an error of the power by 0.53 < ∆Power/Power < 2.73 and a significance level of coherence of >0.5. All spectra used a Bartlett window and a 30% (n/3) lag, where n is the number of series data points. For model-proxy comparisons, the bandwidth is 0.0167, nonzero coherence is >0.3844, and the error estimation on the power spectrum is 0.6255. For proxy comparisons, the bandwidth is 0.0127, nonzero coherence is >0.3844, and the error estimation on the power spectrum is 0.6255.

Model simulations

Our transient experiment was performed with a water isotope (δ18O)–enabled air-sea coupled climate model from the Goddard Institute for Space Studies of the US (GISS_ModelE2-R model). Water isotope tracers (1H216O, “normal” water; 2H1H16O or HDO, reported as δD; and 1H218O, δ18O) were incorporated into the atmosphere, land surface, sea ice, and ocean. Water isotopes were tracked through all stages of the hydrologic cycle and were advected throughout the model. At each phase change, a fractionation was applied that explicitly determines equilibrium fractionation, with parameterizations accounting for kinetic fractionations. This model has a horizontal resolution of 4° latitude × 5° longitude, with 20 vertical layers in the atmosphere (up to 0.1 hPa) and 13 vertical layers in the Russell ocean model (67, 68). As a spin-up, the model was run for 200 model years under fixed orbital parameters and greenhouse gases (GHGs) at 300 ka BP, with all other boundary conditions (but neglecting ice sheet changes) set for their values in 1950 CE. Then, the model was integrated for 3000 model years with the transient orbital insolation forcing and GHG forcing of the past 210,000 years, in which orbital parameters and GHG were both advanced by 100 years at the end of each model year (34). This transient experiment was called GISS_ghg and its outputs for the past 3000 model years were used in our analysis. Orbitally forced hydrological changes between the Asian continent and tropical ocean were illustrated by regression coefficients of annual mean specific humidity against the normalized time series of the precessional parameter. Regionally averaged time series of specific humidity for the annual mean and summer months (JAS) were also calculated.

To compare with GISS_ModelE2-R results, we analyzed another transient climate simulation of the past 210,000 years using the NCAR-CCSM3. NCAR-CCSM3 was incorporated with active atmosphere, land, ocean, and sea ice components (20, 69), although without water isotope tracers. The atmospheric model component has a horizontal resolution of T31 (~3.75°) and 26 vertical levels. The transient simulation was initialized from preindustrial conditions and subjected to transient orbital parameters, GHGs, and continental ice sheets forcings spanning the past 210,000 years. The past 210,000-year output of hydroclimate evolution was used for analysis for this study.

Acknowledgments

We thank E. Barkan, B. Luz, H. P. Affek, Y. F. Ning, Y. R. Tian, B. Y. Zong, and P. Z. Duan for invaluable assistance in laboratory work. We also thank Y. Lin, H. Yan, J. H. Du, L. J. Tian, J. W. Wang, and A. F. Li for critical manuscript discussions, as well as Y. Ren and Z. W. Zeng for taking the SEM images of foraminiferal shells.

Funding: Funding information is listed as follows: National Natural Science Foundation of China, grants 42488201 (H.C.), 42103005 (L.S.), 42222603 (H.D.), 41976047 (Y.W.), and 42202218 (Z.L.); Institute for Basic Science (IBS), Republic of Korea, under IBS-R028-Y2 (J.A.W.); Shanghai Pilot Program for Basic Research (Tongji University) (H.D. and Y.W.); and Swedish Research Council Vetenskapsrådet, under grant no 2022-03617 (Z.L.).

Author contributions: Conceptualization: H.C., H.D., Z.J., and L.S. Methodology: L.S., H.C., H.D., and Y.W. Investigation: L.S., Y.W., Z.L., C.Y., and J.L. Formal analysis: L.S., H.L., and A.S. Visualization: L.S., H.D., J.L.B., H.L., and J.L. Supervision: H.C., Z.J., and H.D. Writing—original draft: L.S. and H.D. Writing—review and editing: L.S., H.D., H.C., Y.W., J.A.W., Z.J., J.L.B., A.S., Y.A.B., N.W., Z.L., X.D., H.Z., S.M., and Y.C.

Competing interests: The authors declare that they have no competing interests.

Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials.

Supplementary Materials

This PDF file includes:

Supplementary Text

Figs. S1 to S14

Tables S1 to S3

References
==== Refs
REFERENCES AND NOTES

1 IPCC, in Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (Cambridge Univ. Press, 2021), pp. 2391.
2 J. D. Neelin, C. Martinez-Villalobos, S. N. Stechmann, F. Ahmed, G. Chen, J. M. Norris, Y. H. Kuo, G. Lenderink, Precipitation extremes and water vapor. Curr. Clim. Change Rep. 8 , 17–33 (2022).
3 X. H. Yan, C. R. Ho, Q. Zheng, V. Klemas, Temperature and size variabilities of the Western Pacific Warm Pool. Science 258 , 1643–1645 (1992).17742536
4 W. Cai, L. Wu, M. Lengaigne, T. Li, S. McGregor, J. S. Kug, J. Y. Yu, M. F. Stuecker, A. Santoso, X. Li, Y. G. Ham, Y. Chikamoto, B. Ng, M. J. McPhaden, Y. Du, D. Dommenget, F. Jia, J. B. Kajtar, N. Keenlyside, X. Lin, J. J. Luo, M. Martín-Rey, Y. Ruprich-Robert, G. Wang, S. P. Xie, Y. Yang, S. M. Kang, J. Y. Choi, B. Gan, G. I. Kim, C. E. Kim, S. Kim, J. H. Kim, P. Chang, Pantropical climate interactions. Science 363 , eaav4236 (2019).30819937
5 T. Schneider, T. Bischoff, G. H. Haug, Migrations and dynamics of the intertropical convergence zone. Nature 513 , 45–53 (2014).25186899
6 H. Cheng, R. L. Edwards, A. Sinha, C. Spötl, L. Yi, S. Chen, M. Kelly, G. Kathayat, X. Wang, X. Li, X. Kong, Y. Wang, Y. Ning, H. Zhang, The Asian monsoon over the past 640,000 years and ice age terminations. Nature 534 , 640–646 (2016).27357793
7 S. C. Clemens, A. Holbourn, Y. Kubota, K. E. Lee, Z. Liu, G. Chen, A. Nelson, B. Fox-Kemper, Precession-band variance missing from East Asian monsoon runoff. Nat. Commun. 9 , 3364 (2018).30135494
8 K. Tachikawa, O. Cartapanis, L. Vidal, L. Beaufort, T. Barlyaeva, E. Bard, The precession phase of hydrological variability in the Western Pacific Warm Pool during the past 400 ka. Quat. Sci. Rev. 30 , 3716–3727 (2011).
9 P. Knippertz, H. Wernli, A Lagrangian climatology of tropical moisture exports to the Northern Hemispheric extratropics. J. Climate 23 , 987–1003 (2010).
10 Z. Jian, Y. Wang, H. Dang, M. Mohtadi, Y. Rosenthal, D. W. Lea, Z. Liu, H. Jin, L. Ye, W. Kuhnt, X. Wang, Warm pool ocean heat content regulates ocean–continent moisture transport. Nature 612 , 92–99 (2022).36261525
11 B. Luz, E. Barkan, Variations of 17O/16O and 18O/16O in meteoric waters. Geochim. Cosmochim. Acta 74 , 6276–6286 (2010).
12 E. Barkan, B. Luz, Diffusivity fractionations of H216O/H217O and H216O/H218O in air and their implications for isotope hydrology. Rapid Comm. Mass Spectrom. 21 , 2999–3005 (2007).
13 L. Sha, S. Mahata, P. Duan, B. Luz, P. Zhang, J. Baker, B. Zong, Y. Ning, Y. A. Brahim, H. Zhang, R. L. Edwards, H. Cheng, A novel application of triple oxygen isotope ratios of speleothems. Geochim. Cosmochim. Acta 270 , 360–378 (2020).
14 B. H. Passey, H. Hu, H. Ji, S. Montanari, S. Li, G. A. Henkes, N. E. Levin, Triple oxygen isotopes in biogenic and sedimentary carbonates. Geochim Cosmochim Acta 141 , 1–25 (2014).
15 B. H. Passey, N. E. Levin, Triple oxygen isotopes in meteoric waters, carbonates, and biological apatites: Implications for continental paleoclimate reconstruction. Rev. Mineral. Geochem. 86 , 429–462 (2021).
16 H. Dang, Z. Jian, C. Kissel, F. Bassinot, Precessional changes in the western equatorial Pacific Hydroclimate: A 240 kyr marine record from the Halmahera Sea, East Indonesia. Geochem. Geophys. Geosyst. 16 , 148–164 (2015).
17 R. Suwarman, K. Ichiyanagi, M. Tanoue, K. Yoshimura, S. Mori, M. Yamanaka, F. Syamsudin, H. Belgaman, El Niño Southern Oscillation signature in atmospheric water isotopes over maritime continent during wet season. J. Meteorol. Soc. JPN. 95 , 49–66 (2017).
18 D. Bolton, The computation of equivalent potential temperature. Mon. Weather Rev. 108 , 1046–1053 (1980).
19 O. A. Alduchov, R. E. Eskridge, Improved magnus form approximation of saturation vapor pressure. J. Appl. Meteorol. 35 , 601–609 (1996).
20 Z. Lu, Z. Liu, G. Chen, J. Guan, Prominent precession band variance in ENSO intensity over the last 300,000 years. Geophys. Res. Lett. 46 , 9786–9795 (2019).
21 J. Murray, On the distribution of the pelagic foraminifera at the surface and on the floor of the ocean. Nat. Sci. 11 , 17–27 (1897).
22 R. Uemura, E. Barkan, O. Abe, B. Luz, Triple isotope composition of oxygen in atmospheric water vapor. Geophys. Res. Lett. 37 , 307–328 (2010).
23 D. W. Oppo, G. A. Schmidt, A. N. LeGrande, Seawater isotope constraints on tropical hydrology during the Holocene. Geophys. Res. Lett. 34 , L13701 (2007).
24 A. N. LeGrande, G. A. Schmidt, Global gridded data set of the oxygen isotopic composition in seawater. Geophys. Res. Lett. 33 , 12604 (2006).
25 H. Cheng, H. Li, L. Sha, A. Sinha, Z. Shi, Q. Yin, Z. Lu, D. Zhao, Y. Cai, Y. Hu, Q. Hao, J. Tian, G. Kathayat, X. Dong, J. Zhao, H. Zhang, Milankovitch theory and monsoon. Innovation 3 , 100338 (2022).36353675
26 H. Kawahata, A. Nishimura, M. K. Gagan, Seasonal change in foraminiferal production in the western equatorial Pacific warm pool: Evidence from sediment trap experiments. Deep Sea Res. 2 Top Stud. Oceanogr. 49 , 2783–2800 (2002).
27 D. W. Lea, D. K. Pak, H. J. Spero, Climate impact of late quaternary equatorial pacific sea surface temperature variations. Science 289 , 1719–1724 (2000).10976060
28 K. A. Dyez, A. C. Ravelo, Late Pleistocene tropical Pacific temperature sensitivity to radiative greenhouse gas forcing. Geology 41 , 23–26 (2013).
29 H. Cheng, H. Zhang, Y. Cai, Z. Shi, L. Yi, C. Deng, Q. Hao, Y. Peng, A. Sinha, H. Li, J. Zhao, Y. Tian, J. Baker, C. Perez-Mejías, Orbital-scale Asian summer monsoon variations: Paradox and exploration. Sci. China Earth Sci. 63 , 529–544 (2021).
30 J. He, N. C. Johnson, G. A. Vecchi, B. Kirtman, A. T. Wittenberg, S. Sturm, Precipitation sensitivity to local variations in tropical sea surface temperature. J. Climate 31 , 9225–9238 (2018).
31 P. Good, R. Chadwick, C. E. Holloway, J. Kennedy, J. A. Lowe, R. Roehrig, S. S. Rushley, High sensitivity of tropical precipitation to local sea surface temperature. Nature 589 , 408–414 (2021).33106670
32 M. Rajeevan, M. J. McPhaden, Tropical Pacific upper ocean heat content variations and Indian summer monsoon rainfall. Geophys. Res. Lett. 31 , 10.1029/2004GL020631 (2004).
33 Y. Wang, Z. Jian, P. Zhao, D. Xiao, J. Chen, Relative roles of land- and ocean-atmosphere interactions in Asian-Pacific thermal contrast variability at the precessional band. Sci. Rep. 6 , 28349 (2016).27381940
34 J. E. Kutzbach, X. Liu, Z. Liu, G. Chen, Simulation of the evolutionary response of global summer monsoons to orbital forcing over the past 280,000 years. Climate Dynam. 30 , 567–579 (2008).
35 A. Landais, E. Barkan, B. Luz, Record of δ18O and 17O-excess in ice from Vostok Antarctica during the last 150,000 years. Geophys. Res. Lett. 35 , doi.org/10.1029/2007GL032096 (2008).
36 A. Landais, B. Stenni, V. Masson-Delmotte, J. Jouzel, A. Cauquoin, E. Fourré, B. Minster, E. Selmo, T. Extier, M. Werner, F. Vimeux, R. Uemura, I. Crotti, A. Grisart, Interglacial Antarctic–Southern Ocean climate decoupling due to moisture source area shifts. Nat. Geosci. 14 , 918–923 (2021).
37 B. R. Markle, E. J. Steig, C. Buizert, S. W. Schoenemann, C. M. Bitz, T. J. Fudge, J. B. Pedro, Q. Ding, T. R. Jones, J. W. C. White, T. Sowers, Global atmospheric teleconnections during Dansgaard–Oeschger events. Nat. Geosci. 10 , 36–40 (2017).
38 F. Vimeux, V. Masson, J. Jouzel, M. Stievenard, J. R. Petit, Glacial–interglacial changes in ocean surface conditions in the Southern Hemisphere. Nature 398 , 410–413 (1999).
39 R. T. Pierrehumbert, The hydrologic cycle in deep-time climate problems. Nature 419 , 191–198 (2002).12226673
40 M. Biasutti, A. Voigt, W. R. Boos, P. Braconnot, J. C. Hargreaves, S. P. Harrison, S. M. Kang, B. E. Mapes, J. Scheff, C. Schumacher, A. H. Sobel, S.-P. Xie, Global energetics and local physics as drivers of past, present and future monsoons. Nat. Geosci. 11 , 392–400 (2018).
41 W. R. Boos, R. L. Korty, Regional energy budget control of the intertropical convergence zone and application to mid-Holocene rainfall. Nat. Geosci. 9 , 892–897 (2016).
42 E. Huang, Y. Chen, E. Schefuß, S. Steinke, J. Liu, J. Tian, G. Martínez-Méndez, M. Mohtadi, Precession and glacial-cycle controls of monsoon precipitation isotope changes over East Asia during the Pleistocene. Earth Planet. Sci. Lett. 494 , 1–11 (2018).
43 H. Cheng, A. Sinha, F. W. Cruz, X. Wang, R. L. Edwards, F. M. d’Horta, C. C. Ribas, M. Vuille, L. D. Stott, A. S. Auler, Climate change patterns in Amazonia and biodiversity. Nat. Commun. 4 , 1411 (2013).23361002
44 V. M. Ramirez, F. W. Cruz, M. Vuille, V. F. Novello, N. M. Stríkis, H. Cheng, J. P. Bernal, W. J. Du, A. Ampuero, M. Deininger, C. M. Chiessi, E. Tejedor, Y. A. Brahim, R. L. Edwards, Summer insolation controlled movements of Intertropical Convergence Zone during last glacial cycle in northern South America Commun . Earth Environ. 4 , 495 (2023).
45 A. C. Clement, R. Seager, M. A. Cane, Orbital controls on the El Niño/Southern Oscillation and the tropical climate. Paleoceanography 14 , 441–456 (1999).
46 A. Timmermann, S. J. Lorenz, S.-I. An, A. Clement, S.-P. Xie, The effect of orbital forcing on the mean climate and variability of the tropical pacific. J. Climate 20 , 4147–4159 (2007).
47 S. Zhang, Z. Yu, X. Gong, Y. Wang, F. Chang, G. Lohmman, Y. Qi, T. Li, Precession cycles of the El Niño/Southern oscillation-like system controlled by Pacific upper-ocean stratification. Commun. Earth Environ. 2 , 239 (2021).
48 P. J. Webster, T. N. Palmer, The past and the future of El Niño. Nature 390 , 562–564 (1997).
49 H. Dang, Z. Jian, Y. Wang, M. Mohtadi, Y. Rosenthal, L. Ye, F. Bassinot, W. Kuhnt, Pacific warm pool subsurface heat sequestration modulated Walker circulation and ENSO activity during the Holocene. Sci. Adv. 6 , eabc0402 (2020).33055161
50 C. Emiliani, Pleistocene temperatures. J. Geol. 63 , 538–578 (1955).
51 L. Sha, S. Mahata, P. Duan, B. Zong, Y. Ning, P. Zhang, J. Wang, Y. Cai, H. Cheng, Preparation of high-precision CO2 with known triple oxygen isotope for oxygen isotope analysis. Isotopes Environ. Health Stud. 57 , 443–456 (2021).34383572
52 J. A. G. Wostbrock, E. J. Cano, Z. D. Sharp, An internally consistent triple oxygen isotope calibration of standards for silicates, carbonates and air relative to VSMOW2 and SLAP2. Chem. Geol. 533 , 119432 (2020).
53 D. Paul, G. Skrzypek, I. Fórizs, Normalization of measured stable isotopic compositions to isotope reference scales: A review. Rapid Commun. Mass Spectrom. 21 , 3006–3014 (2007).17705258
54 P. Anand, H. Elderfield, M. H. Conte, Calibration of Mg/Ca thermometry in planktonic foraminifera from a sediment trap time series. Paleoceanography 18 , doi.org/10.1029/2002PA000846 (2003).
55 J. R. O’Neil, R. N. Clayton, T. K. Mayeda, Oxygen isotope fractionation in divalent metal carbonates. J. Chem. Phys. 51 , 5547–5558 (1969).
56 C. Waelbroeck, L. Labeyrie, E. Michel, J. C. Duplessy, J. F. McManus, K. Lambeck, E. Balbon, M. Labracherie, Sea-level and deep water temperature changes derived from benthic foraminifera isotopic records. Quat. Sci. Rev. 21 , 295–305 (2002).
57 J. A. G. Wostbrock, U. Brand, T. B. Coplen, P. K. Swart, S. J. Carlson, A. J. Brearley, Z. D. Sharp, Calibration of carbonate-water triple oxygen isotope fractionation: Seeing through diagenesis in ancient carbonates. Geochim. Cosmochim. Acta 288 , 369–388 (2020).
58 T. B. Coplen, C. Kendall, J. Hopple, Comparison of stable isotope reference samples. Nature 302 , 236–238 (1983).
59 W. Guo, C. Zhou, Triple oxygen isotope fractionation in the DIC-H2O-CO2 system: A numerical framework and its implications. Geochim. Cosmochim. Acta 246 , 541–564 (2019).
60 J. R. Kelson, T. E. Huth, B. H. Passey, N. E. Levin, S. V. Petersen, P. Ballato, E. J. Beverly, D. O. Breecker, G. D. Hoke, A. M. Hudson, H. Y. Ji, A. Licht, E. J. Oerter, J. Quade, Triple oxygen isotope compositions of globally distributed soil carbonates record widespread evaporation of soil waters. Geochim. Cosmochim. Acta 355 , 138–160 (2023).
61 T. E. Huth, B. H. Passey, J. E. Cole, M. S. Lachniet, D. McGee, R. F. Denniston, S. Truebe, N. E. Levin, A framework for triple oxygen isotopes in speleothem paleoclimatology. Geochim. Cosmochim. Acta 319 , 191–219 (2022).
62 X. Cao, Y. Liu, Equilibrium mass-dependent fractionation relationships for triple oxygen isotopes. Geochim. Cosmochim. Acta 75 , 7435–7445 (2011).
63 E. D. Young, A. Galy, H. Nagahara, Kinetic and equilibrium mass-dependent isotope fractionation laws in nature and their geochemical and cosmochemical significance. Geochim. Cosmochim. Acta 66 , 1095–1104 (2002).
64 A. Pack, D. Herwartz, The triple oxygen isotope composition of the Earth mantle and understanding Δ17O variations in terrestrial rocks and minerals. Earth Planet. Sci. Lett. 390 , 138–145 (2014).
65 S.-T. Kim, J. R. O’Neil, Equilibrium and nonequilibrium oxygen isotope effects in synthetic carbonates. Geochim. Cosmochim. Acta 61 , 3461–3475 (1997).
66 Y. Lin, N. Wu, K. Ta, A. Landais, X. Peng, Triple oxygen isotopic compositions of ocean water from the Mariana Trench. ACS Earth Space. Chem. 5 , 3087–3096 (2021).
67 G. A. Schmidt, M. Kelley, L. Nazarenko, R. Ruedy, G. L. Russell, I. Aleinov, M. Bauer, S. E. Bauer, M. K. Bhat, R. Bleck, V. Canuto, Y.-H. Chen, Y. Cheng, T. L. Clune, A. Del Genio, R. de Fainchtein, G. Faluvegi, J. E. Hansen, R. J. Healy, N. Y. Kiang, D. Koch, A. A. Lacis, A. N. LeGrande, J. Lerner, K. K. Lo, E. E. Matthews, S. Menon, R. L. Miller, V. Oinas, A. O. Oloso, J. P. Perlwitz, M. J. Puma, W. M. Putman, D. Rind, A. Romanou, M. Sato, D. T. Shindell, S. Sun, R. A. Syed, N. Tausnev, K. Tsigaridis, N. Unger, A. Voulgarakis, M.-S. Yao, J. Zhang, Configuration and assessment of the GISS ModelE2 contributions to the CMIP5 archive. J. Adv. Model. Earth Syst. 6 , 141–184 (2014).
68 S. C. Lewis, D. Karoly, The role of anthropogenic forcing in the record 2013 Australia-wide annual and spring temperatures [in “explaining extreme events of 2014 from a climate perspective”]. Bull. Amer. Meteor. Soc. 95 , S31–S34 (2014).
69 S. Yeager, C. Shields, W. Large, J. Hack, The low-resolution CCSM3. J. Climate 19 , 2545–2566 (2006).
70 J. Laskar, P. Robutel, F. Joutel, M. Gastineau, A. C. M. Correia, B. Levrard, A long-term numerical solution for the insolation quantities of the Earth. Astron. Astrophys. 428 , 261–285 (2004).
71 D. Paillard, L. Labeyrie, P. Yiou, Macintosh program performs time-series analysis. Eos. Trans. 77 , 379–379 (1996).
72 D. Herwartz, Triple oxygen isotope variations in Earth’s crust. Rev. Mineral. Geochem. 86 , 291–322 (2021).
73 S. J. Bergel, E. Barkan, M. Stein, H. P. Affek, Carbonate 17Oexcess as a paleo-hydrology proxy: Triple oxygen isotope fractionation between H2O and biogenic aragonite, derived from freshwater mollusks. Geochim. Cosmochim. Acta 275 , 36–47 (2020).
74 Y. Uechi, R. Uemura, Dominant influence of the humidity in the moisture source region on the 17O-excess in precipitation on a subtropical island. Earth Planet. Sci. Lett. 513 , 20–28 (2019).
75 T. Toyofuku, M. Y. Matsuo, L. J. de Nooijer, Y. Nagai, S. Kawada, K. Fujita, G.-J. Reichart, H. Nomaki, M. Tsuchiya, H. Sakaguchi, H. Kitazato, Proton pumping accompanies calcification in foraminifera. Nat. Commun. 8 , 14145 (2017).28128216
76 L. J. de Nooijer, H. J. Spero, J. Erez, J. Bijma, G. J. Reichart, Biomineralization in perforate foraminifera. Earth Sci. Rev. 135 , 48–58 (2014).
77 B. E. Bemis, H. J. Spero, J. Bijma, D. W. Lea, Reevaluation of the oxygen isotopic composition of planktonic foraminifera: Experimental results and revised paleotemperature equations. Paleoceanography 13 , 150–160 (1998).
78 S. A. Katz, N. E. Levin, D. T. Rodbell, D. P. Gillikin, P. G. Aron, B. H. Passey, P. M. Tapia, A. R. Serrepe, M. B. Abbott, Detecting hydrologic distinctions among Andean lakes using clumped and triple oxygen isotopes. Earth Planet. Sci. Lett. 602 , 117927 (2023).
79 J. R. Kelson, S. V. Petersen, N. A. Niemi, B. H. Passey, A. N. Curley, Looking upstream with clumped and triple oxygen isotopes of estuarine oyster shells in the early Eocene of California, USA. Geology 50 , 755–759 (2022).
80 S. He, D. Jackisch, D. Samanta, P. K. Y. Yi, G. Liu, X. Wang, N. F. Goodkin, Understanding tropical convection through triple oxygen isotopes of precipitation from the maritime continent. J. Geophys. Res. Atmos. 126 , e2020JD033418 (2021).
81 J. Surma, S. Assonov, D. Herwartz, C. Voigt, M. Staubwasser, The evolution of 17O-excess in surface water of the arid environment during recharge and evaporation. Sci. Rep. 8 , 4972 (2018).29563523
82 H. A. J. Meijer, W. J. Li, The use of electrolysis for accurate δ17O and δ18O isotope measurements in water. Isotopes Environ. Health Stud. 34 , 349–369 (1998).
83 Y. Nyamgerel, Y. Han, M. Kim, D. Koh, J. Lee, Review on applications of 17O in hydrological cycle. Molecules 26 , 4468 (2021).34361621
84 P. G. Aron, N. E. Levin, E. J. Beverly, T. E. Huth, B. H. Passey, E. M. Pelletier, C. J. Poulsen, I. Z. Winkelstern, D. A. Yarian, Triple oxygen isotopes in the water cycle. Chem. Geol. 565 , 120026 (2021).
85 H. Craig, L. I. Gordon, in Stable Isotope in Oceanographic Studies and Paleotemperatures (V. Lischi e Figli, 1965), p. 122.
86 R. E. Criss, Principles of Stable Isotope Distribution (Oxford Univ. Press, 1999).
87 S. Gao, T. Qu, X. Nie, Mixed layer salinity budget in the tropical Pacific Ocean estimated by a global GCM. J. Geophys. Res. Oceans 119 , 8255–8270 (2014).
88 L. Gimeno, A. Drumond, R. Nieto, R. M. Trigo, A. Stohl, On the origin of continental precipitation. Geophys. Res. Lett. 37 , doi.org/10.1029/2010GL043712 (2010).
89 J. L. Conroy, K. M. Cobb, D. Noone, Comparison of precipitation isotope variability across the tropical Pacific in observations and SWING2 model simulations. J. Geophys. Res. Atmos. 118 , 5867–5892 (2013).
90 J. L. Conroy, K. M. Cobb, J. Lynch-Stieglitz, P. J. Polissar, Constraints on the salinity–oxygen isotope relationship in the central tropical Pacific Ocean. Mar. Chem. 161 , 26–33 (2014).
91 J. L. Conroy, N. K. Murray, G. S. Patterson, A. I. G. Schore, I. Ikuru, J. E. Cole, D. Chillagana, F. Echeverria, Equatorial undercurrent influence on surface seawater δ18O values in the Galápagos. Geophys. Res. Lett. 50 , e2022GL102074 (2023).
92 J. Surma, S. Assonov, M. Staubwasser, Triple oxygen isotope systematics in the hydrologic cycle. Rev. Mineral. Geochem. 86 , 401–428 (2021).
93 J. R. Gat, The stable isotope composition of Dead Sea waters. Earth Planet. Sci. Lett. 71 , 361–376 (1984).
94 J. Horita, D. J. Wesolowski, Liquid-vapor fractionation of oxygen and hydrogen isotopes of water from the freezing to the critical temperature. Geochim. Cosmochim. Acta 58 , 3425–3437 (1994).
95 L. Merlivat, J. Jouzel, Global climatic interpretation of the deuterium-oxygen 18 relationship for precipitation. J. Geophys. Res. 84 , 5029–5033 (1979).
96 C. D. Cappa, M. B. Hendricks, D. J. DePaolo, R. C. Cohen, Isotopic fractionation of water during evaporation. J. Geophys. Res. 108 , 4525 (2003).
97 J. Horita, K. Rozanski, S. Cohen, Isotope effects in the evaporation of water: A status report of the Craig-Gordon model. Isotopes Environ. Health Stud. 44 , 23–49 (2008).18320426
98 E. Barkan, B. Luz, High precision measurements of 17O/16O and 18O/16O ratios in H2O. Rapid Commun. Mass Spectrom. 19 , 3737–3742 (2005).16308852
99 R. Adler, G. Huffman, A. Chang, R. Ferraro, P. Xie, J. Janowiak, B. Rudolf, U. Schneider, S. Curtis, D. Bolvin, A. Gruber, J. Susskind, The Version-2 Global Precipitation Climatology Project (GPCP) monthly precipitation analysis (1979-present). J. Hydrometeorol. 4 , 1147–1167 (2003).
100 E. Kalnay, M. Kanamitsu, R. Kistler, W. Collins, D. Deaven, L. Gandin, M. Iredell, S. Saha, G. White, J. Woollen, Y. Zhu, M. Chelliah, W. Ebisuzaki, W. Higgins, J. Janowiak, K. C. Mo, C. Ropelewski, J. Wang, A. Leetmaa, R. Reynolds, R. Jenne, D. Joseph, The NCEP/NCAR 40-year reanalysis project. Bull. Am. Meteorol. Soc. 77 , 437–471 (1996).
101 R. Draxler, G. Hess, An overview of the HYSPLIT 4 modelling system for trajectories. Aust. Met. Mag. 47 , 295–308 (1998).
102 H. Hersbach, B. Bell, P. Berrisford, S. Hirahara, A. Horányi, J. Muñoz-Sabater, J. Nicolas, C. Peubey, R. Radu, D. Schepers, A. Simmons, C. Soci, S. Abdalla, X. Abellan, G. Balsamo, P. Bechtold, G. Biavati, J. Bidlot, M. Bonavita, G. De Chiara, P. Dahlgren, D. Dee, M. Diamantakis, R. Dragani, J. Flemming, R. Forbes, M. Fuentes, A. Geer, L. Haimberger, S. Healy, R. J. Hogan, E. Hólm, M. Janisková, S. Keeley, P. Laloyaux, P. Lopez, C. Lupu, G. Radnoti, P. de Rosnay, I. Rozum, F. Vamborg, S. Villaume, J.-N. Thépaut, The ERA5 global reanalysis. Q. J. R. Meteorol. Soc. 146 , 1999–2049 (2020).
103 E. Brady, S. Stevenson, D. Bailey, Z. Liu, D. Noone, J. Nusbaumer, B. L. Otto-Bliesner, C. Tabor, R. Tomas, T. Wong, J. Zhang, J. Zhu, The connected isotopic water cycle in the Community Earth System Model version 1. J. Adv. Model. Earth Syst. 11 , 2547–2566 (2019).
104 Z. Jian, Y. Wang, H. Dang, D. W. Lea, Z. Liu, H. Jin, Y. Yin, Half-precessional cycle of thermocline temperature in the western equatorial Pacific and its bihemispheric dynamics. Proc. Natl. Acad. Sci. U.S.A. 117 , 7044–7051 (2020).32179673
105 M. Hollstein, M. Mohtadi, Y. Rosenthal, P. M. Sanchez, D. Oppo, G. M. Méndez, S. Steinke, D. Hebbeln, Stable oxygen isotopes and Mg/Ca in planktic foraminifera from modern surface sediments of the Western Pacific Warm Pool: Implications for thermocline reconstructions. Paleoceanography 32 , 1174–1194 (2017).
106 T. Bolliet, A. Holbourn, W. Kuhnt, C. Laj, C. Kissel, L. Beaufort, M. Kienast, N. Andersen, D. Garbe-Schönberg, Mindanao Dome variability over the last 160 kyr: Episodic glacial cooling of the West Pacific Warm Pool. Paleoceanography 26 , doi.org/10.1029/2010PA001966 (2011).
107 H. B. Shaari, M. Yamamoto, T. Irino, T. Oba, Nutricline shoaling in the eastern Pacific warm pool during the last two glacial maxima. J. Oceanogr. 70 , 25–34 (2014).
108 L. D. Pena, I. Cacho, P. Ferretti, M. A. Hall, El Niño–Southern Oscillation–like variability during glacial terminations and interlatitudinal teleconnections. Paleoceanography 23 , doi.org/10.1029/2008PA001620 (2008).
109 L. J. de Nooijer, T. Toyofuku, H. Kitazato, Foraminifera promote calcification by elevating their intracellular pH. Proc. Natl. Acad. Sci. U.S.A. 106 , 15374–15378 (2009).19706891
