Nature Geoscience最新文献

Over the last deglaciation, global sea level rose by ~120–130 m, 10–20 m of which was attributed to a singular, catastrophic event known as Meltwater Pulse 1A (MWP-1A) that spanned at most 500 years approximately 14.6 kyr ago. Given data limitations and simplified models of Earth deformation, previous studies have struggled to determine the ice sources responsible for MWP-1A, its timing and, consequently, the impacts on global climate. With the expansion of palaeo sea-level records and growing consensus that more complex Earth deformation occurs over MWP-1A timescales, revisiting MWP-1A is timely. Here we resolve a sequence of ice loss over MWP-1A using a spatiotemporal sea-level fingerprinting approach constrained by temporal variations across sea-level data that fully models transient viscoelastic deformation, resulting in a space–time melt evolution. Our favoured sequence of ice sheet melting begins with the Laurentide contributing ~3 m (~14.6–14.2 kyr ago), followed by Eurasia and West Antarctica contributing ~7 m and ~5 m, respectively (~14.35–14.2 kyr ago). This scenario is consistent with proxy data that suggest a minimal Laurentide contribution and large retreat of the Eurasian Ice Sheet Complex. Our MWP-1A ice evolution demands the revision of global ice histories and illustrates deformation feedbacks that are relevant for modern ice collapse and sea-level rise.

Reactive organic carbon species are important fuel for atmospheric chemical reactions, including the formation of secondary organic aerosol. However, in parallel to atmospheric oxidation processes, deposition can remove compounds from the atmosphere and impact downstream environments. To understand the impact of deposition on atmospheric oxidation, we present a framework for predicting and visualizing the fate of a molecule on the basis of the physicochemical properties of compounds (Henry’s law constant, vapour pressure and reaction rate constants), which are used to estimate timescales for oxidation and deposition. By implementing our deposition rates in chemical models, we show that deposition substantially suppresses atmospheric reactivity and aerosol formation by removing early-generation products and preventing the formation of large fractions (up to 90%) of downstream, late-generation compounds. Deposition is frequently missing in the laboratory experiments and detailed chemical modelling, which probably biases our understanding of atmospheric composition.

Ocean alkalinity enhancement is a widely considered approach for marine CO₂ removal. Alkalinity enhancement sequesters atmospheric CO₂ by shifting the seawater carbonate equilibrium from CO₂ towards bicarbonate and carbonate ions. Such re-equilibration has been hypothesized to benefit calcifying organisms, whose increased calcification could strongly reduce the efficiency of alkalinity enhancement. Here we use global ocean satellite data to constrain the sensitivity of coccolithophores—an important group of calcifying phytoplankton—to natural gradients of seawater carbonate chemistry. We show that the ratio of particulate inorganic to particulate organic carbon, reflecting the balance of calcifying versus non-calcifying phytoplankton, is influenced by environmental drivers, including nutrient stoichiometry and carbon substrate within biogeochemical provinces. Across biogeochemical provinces, however, this ratio persistently correlates with carbonate chemistry through combined influences of carbon substrate availability and proton inhibition of calcification. We estimate that extreme alkalinity enhancement may promote the proliferation of coccolithophores, thereby reducing the CO₂ removal potential of ocean alkalinity enhancement by 2–29% by 2100. However, less extreme alkalinity enhancement may only mitigate for adverse acidification effects on coccolithophores. Our findings demonstrate the importance of considering large-scale biogeochemical feedbacks when evaluating the efficiency of ocean alkalinity enhancement.

The inner core has been inferred to change its rotation rate or shape over years to decades since the discovery of temporal variability in seismic waves from repeating earthquakes that travelled through the inner core. Recent work confirmed that the inner core rotated faster and then slower than the rest of Earth in the last few decades; this work analysed inner-core-traversing (PKIKP) seismic waves recorded by the Eielson (ILAR) and Yellowknife (YKA) arrays in northern North America from 121 repeating earthquake pairs between 1991 and 2023 in the South Sandwich Islands. Here we extend this set of repeating earthquakes and compare pairs at times when the inner core re-occupied the same position, revealing non-rotational changes at YKA but not ILAR between 2004 and 2008. We propose that these changes originate in the shallow inner core, and so affect the inner-core-grazing YKA ray paths more than the deeper-bottoming ray paths to ILAR. We thus resolve the long-standing debate on whether temporal variability in PKIKP waves results from rotation or more local action near the inner-core boundary: it is tentatively both. The changes near the inner-core boundary most likely result from viscous deformation driven by coupling between boundary topography and mantle density anomalies or traction on the inner core from outer-core convection.

Ocean pH is a fundamental property regulating various aspects of Earth system evolution. However, early ocean pH remains controversial, with estimates ranging from strongly acidic to alkaline. Here we develop a model integrating global carbon cycling with ocean geochemistry, and incorporating continental growth and mantle thermal evolution. By coupling global carbon cycle with ocean charge balance, and by using solid Earth processes of mantle degassing and crustal evolution to specify the history of volatile distribution and ocean chemistry, we show that a rapid increase in ocean pH is likely during the Hadean to the early Archaean eons, with pH evolving from 5 to neutral by approximately 4.0 Gyr ago. This rapid pH evolution is attributed primarily to elevated rates of both seafloor and continental weathering during the Hadean. This acceleration in weathering rates originates in the unique aspects of Hadean geodynamics, including rapid crust formation, different crustal lithology and fast plate motion. Earth probably transformed from a hostile state to a habitable one by the end of the Hadean, approximately 4.0 Gyr ago, with important implications for planetary habitability and the origin of life.