地球科学最新文献

The marine biological pump is crucial for removing excess carbon dioxide from the atmosphere to the ocean interior and seafloor sediments. The Late Miocene Biogenic Bloom (LMBB), marked by notable increases in biogenic components in marine sediments, provides insights into the response of the biological pump to climate change. However, understanding the timing, distribution, and cause of the LMBB remains limited. We use marine barite, a refractory mineral precipitating from the water column associated with carbon export, and other proxies to reconstruct productivity in the equatorial Indian Ocean and equatorial western Atlantic between 12 and 5 Ma. Multi-proxy records reveal the onset of the LMBB in the equatorial Indian Ocean at ∼9 Ma, primarily driven by more vigorous upwelling during global cooling. We suggest that the steepened meridional temperature gradient and the Antarctic ice sheet expansion have strengthened ocean overturning, facilitating nutrient supply and biogenic bloom in upwelling regions.

Understanding the composition of lavas erupted at the surface of the Earth is key to reconstruct the long-term history of our planet. Recent geochemical analyses of ocean island basalt samples indicate the preservation of ancient mantle heterogeneities dating from the earliest stages of Earth's evolution (Péron & Moreira, 2018, https://doi.org/10.7185/geochemlet.1833), when a global magma ocean was present. Such observations contrast with fluid dynamics studies which demonstrated that in a magma ocean the convective motions, primarily driven by buoyancy, are extremely vigorous (Gastine et al., 2016, https://doi.org/10.1017/jfm.2016.659) and are therefore expected to mix heterogeneities within just a few minutes (Thomas et al., 2023, https://doi.org/10.1093/gji/ggad452). To elucidate this paradox we explored the effects of the Earth's rapid rotation on the stirring efficiency of a magma ocean, by performing state-of-the-art fluid dynamics simulations of low-viscosity, turbulent convective dynamics in a spherical shell. We found that rotational effects drastically affect the convective structure and the associated stirring efficiency. Rotation leads to the emergence of three domains with limited mass exchanges, and distinct stirring and cooling efficiencies. Still, efficient convective stirring within each region likely results in homogenization within each domain on timescales that are short compared with the solidification timescales of a magma ocean. However, the lack of mass exchange between these regions could lead to three or four large-scale domains with internally homogeneous, but distinct compositions. The existence of these separate regions in a terrestrial magma ocean suggests a new mechanism to preserve distinct geochemical signatures dating from the earliest stages of Earth's evolution.

Tropical cyclones are among the most destructive natural disasters. However, lack of detailed observations and the simplifications inherent in operational ocean models, lead to incomplete knowledge of underlying ocean processes. Using high-fidelity large-eddy simulations and moored observations away from the storm track, we show that mutually interacting shear and convective processes, govern the evolving state of the upper ocean. Our simulation agrees well with observed sea surface temperature and sea surface salinity. Shear driven turbulence due to surface wind stress erodes stratification, deepens the ocean mixed layer and transports freshwater into the mixed layer during rain events. Concurrently, surface buoyancy loss also aids in ocean mixing via convective entrainment. The mixing efficiency and the associated eddy diffusivity shows high spatiotemporal variability throughout the water column during cyclone passage. Thus, a better insight into the upper ocean mixing mechanisms is necessary for developing improved mixing parameterizations for tropical cyclone intensity forecasts.

The Gobi Desert is a prominent dust source in Asia, where the dust storm is severe and features great interannual and seasonal variability. Previous studies have found land surface variation plausibly plays an important role in the occurrence and intensity of dust storms. However, the quantitative estimation and numerical description in current models are still limited. Here, a comprehensive study utilizing multiple observations and modeling methods to assess the influence of vegetation and snow on dust was conducted. We found that Gobi deserts exhibit substantial monthly and interannual variability in dust storms, which shows a close connection with vegetation and snow. To quantitatively understand the impact of vegetation and snow cover on dust emissions and also to better characterize such effects in numerical models, we introduced a high-resolution dynamic dust source function that incorporates the effects of vegetation and snow on erodibility. The new parameterization noticeably improved dust-related simulations, including aerosol optical thickness and PM₁₀ concentrations, and provided insights into the distinct effects of vegetation and snow on dust emissions. This study sheds light on the effects of vegetation and snow on dust storms over the Gobi Desert, highlighting the importance of dynamic representation of time-varying surface properties in dust simulation.

Climate change and disturbance threaten forested ecosystems across the globe. Our ability to predict the future distribution of forests requires understanding the limiting factors for regeneration. Forest canopies buffer against near-surface air temperature and vapour pressure deficit extremes, and ongoing losses of forest canopy from disturbances such as wildfire can exacerbate climate constraints on natural regeneration. Here we combine experimental, empirical and simulation-based evidence to show that soil surface temperatures constrain the low-elevation extent of forests in the western United States. Simulated potential soil surface temperatures predict the position of the low-elevation forest treeline, exhibiting temperature thresholds consistent with field and laboratory studies. High-resolution historical and future surface temperature maps show that 107,000–238,000 km² (13–20%) of currently forested area exceeds the critical thermal threshold for forest regeneration and this area is projected to more than double by 2050. Soil surface temperature is an important physical control on seedling survival at low elevations that will likely be an increasing constraint on the extent of western United States forests as the climate warms.

Intraseasonal variabilities (ISVs) of the western boundary currents (WBCs) east of Luzon Island were explored using acoustic Doppler current profiler (ADCP) measurements from three moorings at 18°N during 2018–2020. Besides the traditionally known surface-intensified ISV, subsurface-intensified ISV with a typical period of approximately 60 days was also detected in the currents, and the strongest signal appeared between 400 and 800 m. Further analysis indicates that they are highly associated with subsurface eddies. Based on their lifespan, subsurface eddies are classified into two categories: short-lived and medium-to long-lived eddies. The short-lived eddies are primarily generated locally near the eastern coast of Luzon Island, whereas the medium-to long-lived eddies are mainly generated away from the western boundary, in the region west of 135°E. Additional energy diagnosis suggests that baroclinic instability induced by the velocity shear of the North Equatorial Current (NEC)/subtropical countercurrent (STCC) system dominates the generation of medium-to long-lived subsurface eddies in the interior ocean, while barotropic instability and baroclinic instability play a comparable role in the generation of short-lived eddies near the eastern coast of Luzon Island.

Solar heating of the upper ocean is a primary energy input to the ocean-atmosphere system, and the vertical heating profile is modified by the concentration of phytoplankton in the water, with consequences for sea surface temperature and upper ocean dynamics. Despite the development of increasingly complex modeling approaches for radiative transfer in the atmosphere and upper ocean, the simple parameterizations of radiant heating used in most ocean models can be significantly improved in cases of near-surface stratification. There remains a need for a parameterization that is accurate in the upper meters and contains an explicitly spectral dependence on the concentration of biogenic material, while maintaining the computational simplicity of the parameterizations currently in use. Here, we assemble observationally-validated physical modeling tools for the key controls on ocean radiant heating, and simplify them into a parameterization that fulfills this need. We then use observations from 64 spectroradiometer depth casts across 6 cruises in diverse water bodies, 13 surface hyperspectral radiometer deployments, and broadband albedo from 2 UAV flights to probe the accuracy and uncertainty associated with the new parameterization. A novel case study using the parameterization demonstrates the impact of chlorophyll concentration on the structure of diurnal warm layers. The parameterization presented in this work will allow for better modeling of global patterns of sea surface temperature, diurnal warming, and freshwater lenses, without a prohibitive increase in complexity.