Geophysical Research Letters最新文献

Modern observations reveal that large-scale ocean-atmosphere circulation (OAC) is drifting toward higher latitudes under global warming. Paleoclimate proxies indicate that similar OAC drifts occurred on orbital timescale as well. However, the characteristics and underlying mechanisms remain unclear. Here, by conducting simulations with different Earth's orbits, we investigate how changes in Earth-Sun distance affect the OAC. We find that a closer Earth-Sun distance (perihelion) causes a poleward drift of OAC. This drift in circulation is dynamically consistent with displacement of meridional temperature gradient. Precession alters the perihelion season on orbital timescales, leading to a seasonal poleward drift in OAC. This drift is amplified during the hemispheric summer, reaching magnitudes of $��\sim �$10° under high eccentricity. The identified OAC drifts reshape the seasonality of precipitation and temperature over land, as well as ocean upwelling and downwelling, ultimately affecting the distribution of Earth's terrestrial and marine ecosystems.

The origin of enriched mantle 1 (EM1) endmember, characterized by low ²⁰⁶Pb/²⁰⁴Pb and ¹⁴³Nd/¹⁴⁴Nd ratios in ocean island basalts, has long been debated. This is because melting of surrounding peridotite, together with the EM1 component, can dilute the “EM1 fingerprints” in these rocks. Here, we present barium isotope data for well-characterized EM1-type continental basalts from northeast China to constrain their nature and origin. Our results show that these basalts have δ^138/134Ba values ranging from −0.1‰ to 0.08‰, which are lower than the depleted MORB mantle. Correlations between δ^138/134Ba and K/U, Ba/Th, U/Pb, ε_Nd and ²⁰⁶Pb/²⁰⁴Pb suggest a heterogeneous source involving binary mixing between the lithospheric mantle and an EM1 component. The EM1 component, characterized by light δ^138/134Ba and low ²⁰⁶Pb/²⁰⁴Pb ratios, can be attributed to the addition of recycled ancient sediments to the source. This study indicates that Ba isotopes have potential to trace crustal material recycling into Earth's deep mantle.

This study aims to understand the mechanisms of the activation and evolution of the marine heatwave (MHW) that occurred in the Gulf of Mexico (GoM) during summer 2023. We quantified contributions of the thermodynamic processes that transformed surface waters in the GoM into an unprecedented large volume of extremely warm water $��\left(��>�31.8�°�C��\right)�$. Through water mass transformation analysis of reanalyses data, we find that the genesis of this MHW was due to the compounding effect of anomalously warm winter surface water priming the region for a MHW, coupled with greater exposure to strong solar radiation. Transformation due to total surface fluxes (sensible and latent heat, solar and longwave radiation) contributed to the MHW volume at a peak rate of 17.0 Sv ($��{10}^6�$ $��m^3�$ $��s^{�-�1�}�$ = Sv), while the residual term (including mixing) countered the effect by 22.3 Sv at its peak. Total transformation during this 2023 MHW peaked at 4.9 Sv.

Asymmetrical ocean carbon responses to La Niña and El Niño complicate global carbon budget estimation. Using multiple ocean CO₂ data products and an advanced ocean biogeochemical model, we identified significant asymmetries in ocean carbon magnitude, spatial distribution, and duration in the tropical Pacific Ocean. La Niña enhances ocean CO₂ outgassing (0.1–0.2 PgC/yr) with a broader poleward extension (15°S–15°N) for up to 3 years, while El Niño reduces outgassing (0.2–0.4 PgC/yr) with a narrower poleward extension (10°S–10°N) for up to 1 year. The air-sea carbon flux anomaly shifts westward during La Niña and eastward during El Niño. These asymmetries are attributed to differing wind, precipitation, and ocean circulation anomalies between La Niña and El Niño. Additionally, the cumulative carbon flux remains slightly imbalanced, impacting the global ocean carbon sink balance. This study provides deeper insights into ocean carbon sink variability and highlights the need for enhanced monitoring of asymmetrical ocean carbon dynamics.

Early detection of emerging agricultural drought conditions is challenging but crucial for ensuring sustainable agriculture and global food security. Existing drought early warning systems utilize hydrometeorological or greenness-based vegetation indicators. We propose that spaceborne measurements of solar-induced chlorophyll fluorescence (SIF) yield (SIFyield), which is SIF normalized by absorbed photosynthetically active radiation (APAR), have the potential for early detection of emerging crop stress conditions. We evaluate meteorological (Standardized Precipitation Evapotranspiration Index (SPEI)), hydrological (root zone soil moisture (RZSM)), and physiological (SIF, and SIFyield) vegetation stress indicators to monitor the onset of crop stress indicated by reductions in gross primary productivity (GPP). Empirical Orthogonal Function and causal analysis indicate SIFyield has the strongest positive correlation with GPP, lagging by 1–2 months compared to other indicators. With its long lead time, space-borne SIFyield can serve as an early indicator for agricultural drought onset, aiding global agricultural management efforts.

Ocean evaporation (E_o) is the major source of atmospheric water vapor and precipitation. While it is widely recognized that E_o may increase in a warming climate, recent studies have reported a diminished increase in the global water vapor since ∼2000s, raising doubts about recent changes in E_o. Using satellite observations, here we show that while global E_o strongly increased from 1988 to 2017, the upward trend reversed in the late 2000s. Since then, two-thirds of the ocean have experienced weakened evaporation, leading to a slight decreasing trend in global-averaged E_o during 2008–2017. This suggests that even with saturated surface, a warmer climate does not always result in increased evaporation. The reversal in E_o trend is primarily attributed to wind stilling, which is likely tied to the Northern Oscillation Index shifting from positive to negative phases. These findings offer crucial insights into diverse responses of global hydrological cycle to climate change.

The Precambrian history of the Lhasa terrane, southern Tibet is intensely debated, which hinders global plate tectonic reconstructions throughout the Proterozoic. Previous research on Precambrian basement has suggested that the Lhasa terrane originated from India or Africa, although the paucity of exposed pre-Neoproterozoic rocks in the North Lhasa terrane (NL) has led to significant uncertainty. We document newly identified Neoarchean granites and Mesoproterozoic Guomangtso Suite from the NL. These pre-Neoproterozoic rocks reveal a 2.62 Ga anorogenic rifting event and a 1.30–1.10 Ga transition from subduction to back-arc extension, related to the 2.7–2.6 Ga rifting of the Pilbara Craton and the Proterozoic assembly between the North and West Australian Cratons, respectively. However, these tectono-magmatic events have no equivalents in the South Lhasa terrane (SL). These observations suggest that the NL originated from Western Australia, and the NL and SL may have distinct origins.

Ongoing Amazon deforestation has raised concerns about forest dieback via induced precipitation changes. Previous studies have found that complete deforestation reduces evapotranspiration, contributing to low precipitation rates that would limit the regrowth of the forest, but such studies have used climate models with convective parameterization and/or fixed large-scale circulation. For the first time, we simulate a complete Amazon deforestation scenario without convective parameterization, allowing full interaction between convection and large-scale circulation, for 3 years. Our results show no significant reduction in annual mean precipitation. Changes in the 700 hPa circulation and associated moisture convergence compensate for the reduction in evapotranspiration. These changes also lead to a north-south dipole pattern in the precipitation response during the dry and wet seasons. The uncovered dynamics suggest that Amazon mean precipitation may be more resilient to land surface perturbations than previously thought.

The Lorenz energy cycle was often used to analyze energy conversions related to instabilities in planetary atmospheres using zonal means as basic states. Alternatively, the bred vector (BV) energy equations use the control run as basic states and detect longitudinal dependency of the energy conversions. Additionally, it quantifies contributions from baroclinic and barotropic instabilities separately. We apply this method to understand energy conversions of the Venus atmosphere. BVs are obtained from breeding cycles emphasizing perturbation growths in the cloud layer. The BV potential energy in the pressure coordinate is newly derived. Energy conversions at different latitudes in the cloud layer are examined. Results show that baroclinic conversions are stronger at higher latitudes and exceed barotropic conversions at mid- to high-latitudes. Thermal tides increase energy conversions in the morning hemisphere at mid-latitudes. This study offers new insights into energy conversions of the Venus atmosphere, with potential applications to other planetary atmospheres.

Many sea-ice models formulate sea-ice rheology by a viscous-plastic approach with an elliptical yield curve and a normal flow rule. However, it remains uncertain whether this formulation is suitable for finer-resolution climate models in the warming Arctic. We analyze sea-ice deformation using half-hourly Global Positioning System (GPS) data initially spaced approximately 100 m to 10 km apart from March–July 2020 and 2022 in the Beaufort Gyre. Our findings show the prevalence of shear-dominated deformation and the greater capacity for persistence in the convergence-dominated deformation compared to divergence-dominated deformation. The former supports the sine-lens yield curve, while the latter supports the teardrop yield curve. Our results examine the validity of the elliptical yield curve during sea-ice breakup and advocate the need for a combination of sine-lens and teardrop yield curves from data-supported arguments.