We develop a multiproxy, reduced‐dimension methodology to blend magnesium‐calcium (Mg/Ca) and alkenone (U 37k) paleo sea surface temperature (SST) records from the eastern and western equatorial Pacific, to recreate snapshots of full field SSTs and zonal winds from 10 to 2 ka B.P. in 2000 year increments. Single‐proxy reconstructions (Mg/Ca only versus U 37K′ only) reveal differences in the timing and duration of maximum cooling across the east‐central equatorial Pacific. The largest zonal temperature differences (average west Pacific SST minus average east Pacific SST) occur at 6 ka B.P. for the Mg/Ca‐only reconstruction (0.61°C) and at 10 and 4 ka for the U 37K′‐only reconstruction (0.55°C and 0.47°C, respectively). Disagreements between SST trends suggested by each proxy call for methods that can resolve the common patterns between each and have motivated the work presented in this study. In combining inferences from these proxies, we treat both Mg/Ca and U 37K′ reconstructions of SST as annual average values, but we recognize that they may be sensitive to different seasons. In the multiproxy reconstruction, the zonal SST difference is largest at 10 ka (0.26°C), with coldest SST anomalies of ∼ −0.9°C in the eastern equatorial Pacific and concurrent easterly maximum zonal wind anomalies of 7 m s−1 throughout the central Pacific. From 10 to 2 ka, the entire equatorial Pacific warms, but at a faster rate in the east than the west, and the average central Pacific easterly winds weaken gradually to approximately 2 m s−1. These patterns are broadly consistent with previous inferences of reduced El Niño‐Southern Oscillation variability associated with a “La Niña‐like” state during the early to middle Holocene.

A controversial aspect of the Pliocene climate system is a posited permanent sea surface temperature (SST) distribution resembling that during El Niño events, which is largely inferred from sea surface temperatures reconstructed from several sites in the equatorial Pacific. We utilize a reduceddimension methodology on a compilation of previously published multiproxy (Mg/Ca, U k′ 37 , TEX 86 , and foraminifer assemblages) Pliocene SST records from the equatorial Pacific to reconstruct spatial and temporal snapshots of SST anomalies and a time series of Niño indices from 5 to 1 Ma. The use of multiple proxies increases the number of study sites and thereby improves the robustness of the reconstruction. We find that the early Pliocene equatorial Pacific was characterized by a reduced zonal SST difference due to minimal change in the west and extreme warmth in the east which peaked at 4.3 Ma. The intensity of this mean El Niño-like SST state then gradually diminished toward modern conditions. We also use the Pliocene Niño 4 time series to estimate the past strength of Indian Summer Monsoon given the modern correlation of it to the Niño 4 index. Results indicate the monsoon was weaker throughout the study interval with weakest conditions (~37% less rainfall than modern) occurring at 4.3 Ma, congruent with regional proxy records. In summation, this reduced-dimension approach spatially and temporally resolves the warm mean state of the Pliocene equatorial Pacific and has numerous applications to inferences of paleoclimate conditions in distal regions teleconnected to El Niño today.

Correlations of 1 ∘ by 1 ∘ seasonal rainfall with Pacific sea surface temperatures (SSTs) reveal spatially distinct teleconnections between El Niño-Southern Oscillation (ENSO) and Indian summer monsoon rainfall over the full monsoon season, as well as three subseasons. Over the full season (June-September), Pacific SSTs correlate with rainfall in Western India more than that in Eastern India. This spatial signature shifts as the monsoon progresses through early (June), middle or peak (July-August), and late (September) subseasons. Specifically, a 1 ∘ C cooling of the central equatorial Pacific (i.e., La Niña conditions) can result in the following: ∼70-100% increase in precipitation in north central Indian and the Indo-Gangetic Plains during the early season, ∼30-80% increase peak season precipitation in south central India and northwestern Rajasthan, and ∼60-100% increase in late season precipitation in northern, northwestern, and central India. Furthermore, the spatial signatures between La Niña and El Niño are asymmetric in that for a particular location, the enhancement and suppression of rainfall associated with La Niña and El Niño conditions, respectively, are not equal. El Niño suppresses peak season rainfall in the south central and northwestern Rajasthan regions more than La Niña enhances it, but the opposite occurs during the late season in northern, northwestern, and central India. Additionally, the correspondence of minima (maxima) in anomalies of velocity potential aloft with maxima (minima) at 925 mb and with positive (negative) surface pressure anomalies suggests that anomalous subsidence (ascent) occurs in July-September during El Niño (La Niña) times. In the early season, however, patterns of velocity potential composites suggest a region of descent (ascent) over the western equatorial Indian Ocean, along with a region of ascent (descent) over the Indian subcontinent that exists only during the early season but not during the peak or late season. These patterns are consistent with the hypothesis that local Hadley cell circulation affects pressure and thus rainfall during the early season but that a larger-scale mechanism, such as eastward or westward shifts in the Walker circulation, may be more responsible for teleconnections seen throughout the remainder of the season. These findings indicate that focusing monsoon forecasting efforts on these regions and on subseasonal periods while incorporating ENSO asymmetries will yield useful and skillful regional forecasts, compared to the declining utility and skill of all-India summer monsoon rainfall.

Using a multiproxy reduced dimension methodology, we reconstruct fields of Arabian Sea summer wind stress curl and Indian monsoon rainfall anomalies since early Holocene using sea surface temperature (SST) proxies (Mg/Ca and alkenones) from 27 locations scattered across the equatorial Pacific. Reconstructions of summer wind stress curl reveal positive anomalies of ∼30% greater than present day off the coastlines of Oman and Yemen at 10 ka, suggesting enhanced ocean upwelling and an enhanced monsoon jet during this time. Positive wind stress curl anomalies in these regions continued but weakened to ∼12% greater than present day at 6 ka. Wind stress curl anomalies increased by about 8% from 6 to 4 ka but declined again until 2 ka. Positive anomalies in wind stress curl during the early to middle Holocene are consistent with greater early Holocene abundances of the upwelling indicator Globigerina bulloides in the western Arabian Sea, which accumulates most rapidly in present climates during periods of marked upwelling. Spatial rainfall reconstructions reveal the greatest difference in precipitation at 10 ka over the core monsoon region (∼20–60% greater than present day) and concurrently the greatest deficit in rainfall in North East India and on the eastern side of the Western Ghats (∼10–30% less than present day). Specifically, reconstructions for 10 ka reveal 40–60% greater rainfall than present day over northwest India. These findings advance the hypothesis that teleconnections from the equatorial Pacific contributed to, if not accounted for, greater early to middle Holocene wetness over India as recorded by various (e.g., cave, lacustrine, and discharge) paleoclimate proxies throughout the monsoon region.