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Wood formation consumes around 15% of the anthropogenic CO₂ emissions per year and plays a critical role in long-term sequestration of carbon on Earth. However, the exogenous factors driving wood formation onset and the underlying cellular mechanisms are still poorly understood and quantified, and this hampers an effective assessment of terrestrial forest productivity and carbon budget under global warming. Here, we used an extensive collection of unique datasets of weekly xylem tissue formation (wood formation) from 21 coniferous species across the Northern Hemisphere (latitudes 23 to 67°N) to present a quantitative demonstration that the onset of wood formation in Northern Hemisphere conifers is primarily driven by photoperiod and mean annual temperature (MAT), and only secondarily by spring forcing, winter chilling, and moisture availability. Photoperiod interacts with MAT and plays the dominant role in regulating the onset of secondary meristem growth, contrary to its as-yet-unquantified role in affecting the springtime phenology of primary meristems. The unique relationships between exogenous factors and wood formation could help to predict how forest ecosystems respond and adapt to climate warming and could provide a better understanding of the feedback occurring between vegetation and climate that is mediated by phenology. Our study quantifies the role of major environmental drivers for incorporation into state-of-the-art Earth system models (ESMs), thereby providing an improved assessment of long-term and high-resolution observations of biogeochemical cycles across terrestrial biomes.

This paper reviews recent progress made by Chinese scientists on the pathways of influence of the Northern Hemisphere mid-high latitudes on East Asian climate within the framework of a “coupled oceanic-atmospheric (land-atmospheric or sea-ice-atmospheric) bridge” and “chain coupled bridge”. Four major categories of pathways are concentrated upon, as follows: Pathway A—from North Atlantic to East Asia; Pathway B—from the North Pacific to East Asia; Pathway C—from the Arctic to East Asia; and Pathway D—the synergistic effects of the mid-high latitudes and tropics. In addition, definitions of the terms “combined effect”, “synergistic effect” and “antagonistic effect” of two or more factors of influence or processes and their criteria are introduced, so as to objectively investigate those effects in future research.

Regime shifts are characterized by sudden, substantial and temporally persistent changes in the state of an ecosystem. They involve major biological modifications and often have important implications for exploited living resources. In this study, we examine whether regime shifts observed in 11 marine systems from two oceans and three regional seas in the Northern Hemisphere (NH) are synchronous, applying the same methodology to all. We primarily infer marine pelagic regime shifts from abrupt shifts in zooplankton assemblages, with the exception of the East Pacific where ecosystem changes are inferred from fish. Our analyses provide evidence for quasi-synchronicity of marine pelagic regime shifts both within and between ocean basins, although these shifts lie embedded within considerable regional variability at both year-to-year and lower-frequency time scales. In particular, a regime shift was detected in the late 1980s in many studied marine regions, although the exact year of the observed shift varied somewhat from one basin to another. Another regime shift was also identified in the mid- to late 1970s but concerned less marine regions. We subsequently analyse the main biological signals in relation to changes in NH temperature and pressure anomalies. The results suggest that the main factor synchronizing regime shifts on large scales is NH temperature; however, changes in atmospheric circulation also appear important. We propose that this quasi-synchronous shift could represent the variably lagged biological response in each ecosystem to a large-scale, NH change of the climatic system, involving both an increase in NH temperature and a strongly positive phase of the Arctic Oscillation. Further investigation is needed to determine the relative roles of changes in temperature and atmospheric pressure patterns and their resultant teleconnections in synchronizing regime shifts at large scales.

The interpretation of stalagmite δ18O in terms of reflecting Asian summer monsoon (ASM) precipitation is still elusive. Here, we present high‐resolution stalagmite trace element ratios (X/Ca, X = Mg, Sr, Ba) records from southwest China covering 116.09 to 4.07 ka BP. δ18O, δ13C, and X/Ca values exhibit clear precessional cycles, with δ18O values reflecting ASM circulation/intensity, while X/Ca ratios capture local precipitation or evapotranspiration variations. Our results show that Northern Hemisphere summer insolation (NHSI) is the main driver of ASM intensity and precipitation phase variation, but global ice volume modulates the response magnitude of summer precipitation to insolation. During the Last Glacial Maximum, high ice volumes caused significant monsoon precipitation to decrease. In contrast to modern observations of the tripolar distribution of precipitation in China, our record is consistent with paleo‐precipitation records in southern and northern China. Plain Language Summary While it is well known that global changes have led to variations in the intensity and spatial distribution of Asian monsoon precipitation, the mechanisms behind this are not well understood. Paleoclimate records are essential for revealing the drivers behind monsoon variation. However, speleothem records from the Asian monsoon region rarely provide direct information on the amount of rainfall. Here we report on multiple indicator data sets from a stalagmite in southwestern China. It could help explore the variation of monsoon precipitation over the last ∼100,000 years. We find that the increase/decrease of Northern Hemisphere summer insolation controls the increase/decrease of Asian summer monsoon rainfall. In addition, global ice volume moderates the magnitude of rainfall response to insolation, and precipitation decreases significantly during high ice volume periods. Based on the present paleo‐precipitation records evidence, the existence of the spatial pattern of increasing/decreasing rainfall in central China corresponding to decreasing/increasing rainfall in northern and southern China remains ambiguous on the orbital scales, although the feature has been captured by some of the model simulations. Key Points Stalagmite trace elements are indicators of regional hydrological environmental variations in Southwestern China Northern Hemisphere summer insolation and global ice volume modulate the phase and amplitude variations of regional hydrological environment The meridional tripolar spatial pattern of precipitation in monsoon region in China on the orbital scale remains ambiguous

Part of the Northern Hemisphere has experienced widespread autumn cooling during the most recent decades despite overall warming, but how this contrasting temperature change has influenced the ecosystem carbon exchange remains unclear. Here, we show that autumn cooling has occurred over about half of the area north of 25° N since 2004, producing a weak cooling trend over the period 2004–2018. Multiple lines of evidence suggest an increasing net CO2 release in autumn during 2004–2018. In cooling areas, the increasing autumn CO2 release is due to the larger decrease of gross primary productivity (GPP) growth than total ecosystem respiration (TER) growth suppressed by cooling. In the warming areas, TER increased more than GPP because the warming and wetting conditions are more favourable for TER growth than GPP increase. Despite the opposite temperature trends, there has been a systematic increase in ecosystem carbon release across the Northern Hemisphere middle and high latitudes.Despite overall warming, many regions in the Northern Hemisphere have been cooling in autumn. This cooling resulted in an increasing release of net CO2 2004–2018 as primary production decreased more than respiration in cooling and respiration increased more than production in warming areas.

Sea-level rise resulting from the instability of polar continental ice sheets represents a major socioeconomic hazard arising from anthropogenic warming, but the response of the largest component of Earth’s cryosphere, the East Antarctic Ice Sheet (EAIS), to global warming is poorly understood. Here we present a detailed record of North Atlantic deep-ocean temperature, global sea-level, and ice-volume change for ∼2.75 to 2.4 Ma ago, when atmospheric partial pressure of carbon dioxide (pCO₂) ranged from presentday (>400 parts per million volume, ppmv) to preindustrial (<280 ppmv) values. Our data reveal clear glacial–interglacial cycles in global ice volume and sea level largely driven by the growth and decay of ice sheets in the Northern Hemisphere. Yet, sea-level values during Marine Isotope Stage (MIS) 101 (∼2.55 Ma) also signal substantial melting of the EAIS, and peak sea levels during MIS G7 (∼2.75 Ma) and, perhaps, MIS G1 (∼2.63 Ma) are also suggestive of EAIS instability. During the succeeding glacial–interglacial cycles (MIS 100 to 95), sea levels were distinctly lower than before, strongly suggesting a link between greater stability of the EAIS and increased land-ice volumes in the Northern Hemisphere. We propose that lower sea levels driven by ice-sheet growth in the Northern Hemisphere decreased EAIS susceptibility to ocean melting. Our findings have implications for future EAIS vulnerability to a rapidly warming world.

Reconstruction of the seawater carbonate system is essential for an improved understanding of glacial‐interglacial oceanic carbon cycling and climate change. However, continuous high‐resolution ocean carbonate chemistry data are generally lacking for the Plio‐Pleistocene. Here, we present a deep Pacific carbonate ion saturation state (Δ[CO32−]) record spanning the last 5.1 Myr, reconstructed from the size‐normalized shell weight of planktonic foraminifer in the western tropical Pacific. Deep Pacific Δ[CO32−] has been modulated primarily by orbital obliquity since 5.1 Ma, during which it has exhibited in‐phase behavior with the 40‐Kyr obliquity cycle. Significantly, the amplitude of the 40‐Kyr Δ[CO32−] cycles has responded linearly to obliquity forcing throughout the Plio‐Pleistocene, independent of the late Pliocene intensification of Northern Hemisphere glaciation. We speculate that the obliquity signal in the deep Pacific Δ[CO32−] record reflects an ocean‐atmosphere circulation feedback mediated by migration of the Southern Hemisphere Westerlies. Plain Language Summary The ocean has played an important role in controlling glacial‐to‐interglacial atmospheric pCO2 variation through changes in its carbon inventory. To decipher the patterns and drivers of the oceanic carbon cycle and climate change through glacial cycles, we provide a continuous Plio‐Pleistocene deep Pacific carbonate ion saturation state (Δ[CO32−]) at orbital time scales. The deep PacificΔ[CO32−] has been modulated by orbital forcing since 5.1 Ma, a time interval during which it has exhibited in‐phase behavior with the 40‐Kyr obliquity cycle as well as a linear response of Δ[CO32−] amplitude to obliquity range. We speculate that Plio‐Pleistocene glacial cycles of the deep Pacific carbon storage were linked to variation in Southern Hemisphere upwelling rates yoked to meridional migration of the Westerlies. Key Points Deep Pacific Δ[CO32−] has been modulated primarily by orbital obliquity since 5.1 Ma 40‐Kyr Δ[CO32−] cycles were in‐phase with and responded linearly to 40‐Kyr band obliquity forcing Plio‐Pleistocene glacial cycles of deep Pacific carbon storage were linked to meridional migration of the Southern Hemisphere Westerlies