AGU Advances最新文献

Unlike in the high-latitude North Atlantic, no deep water is formed in the modern subarctic North Pacific. It has previously been suggested that during climate states different from today, this dichotomy did not endure, and the formation of North Pacific Deepwater (NPDW) occurred in the subarctic North Pacific, which supported an active Pacific meridional overturning circulation (PMOC). Here we provide new records of productivity and sedimentary redox conditions from the central subarctic North Pacific spanning the late Miocene to early Pleistocene. These reconstructions indicate greater-than-modern and temporally varying North Pacific export production across the interval of ∼2.7–6 Ma. Our time series, combined with previously published data sets and model output for Pliocene North Pacific Ocean dynamics, support the presence of an active PMOC during the Pliocene, and suggest that the characteristics of NPDW formation varied during this warmer interval of Earth's history. This finding of elevated export production at a time of deep water formation presents a conundrum when considering Quaternary North Pacific Ocean dynamics, where subarctic North Pacific productivity declines during intervals when enhanced overturning is posited to occur. We evaluate our data considering the caveats of both (i.e., Pliocene and Quaternary North Pacific circulation) hypotheses, as well as additional mechanisms unrelated to ocean circulation. Because the Pliocene is a possible analogue for near-future climate, our results and analyses have important ramifications for our understanding of regional and global climate in the coming decades as the planet continues to warm.

Snow is critically important to the energy budget, biogeochemistry, ecology, and people of the Arctic. While climate change continues to shorten the duration of the snow cover period, snow mass (the depth of the snow pack) has been increasing in many parts of the Arctic. Previous work has shown that deeper snow can rapidly thaw permafrost and expose the large amounts of ancient (legacy) organic matter contained within it to microbial decomposition. This process releases carbonaceous greenhouse gases but also nutrients, which promote plant growth and carbon sequestration. The net effect of increased snow depth on greenhouse gas emissions from Arctic ecosystems remains uncertain. Here we show that 25 years of snow addition turned tussock tundra, one of the most spatially extensive Arctic ecosystems, into a year-round source of ancient carbon dioxide. More snow quadrupled the amount of organic matter available to microbial decomposition, much of it previously preserved in permafrost, due to deeper seasonal thaw, soil compaction and subsidence as well as the proliferation of deciduous shrubs that lead to 10% greater carbon uptake during the growing season. However, more snow also sustained warmer soil temperatures, causing greater carbon loss during winter (+200% from October to May) and year-round. We find that increasing snow mass will accelerate the ongoing transformation of Arctic ecosystems and cause earlier-than-expected losses of climate-warming legacy carbon from permafrost.

The oceanic uptake and resulting storage of the anthropogenic CO₂ (C_ant) that humans have emitted into the atmosphere moderates climate change. Yet our knowledge about how this uptake and storage has progressed in time remained limited. Here, we determine decadal trends in the storage of C_ant by applying the eMLR(C*) regression method to ocean interior observations collected repeatedly since the 1990s. We find that the global ocean storage of C_ant grew from 1994 to 2004 by 29 ± 3 Pg C dec⁻¹ and from 2004 to 2014 by 27 ± 3 Pg C dec⁻¹ (±1σ). The storage change in the second decade is about 15 ± 11% lower than one would expect from the first decade and assuming proportional increase with atmospheric CO₂. We attribute this reduction in sensitivity to a decrease of the ocean buffer capacity and changes in ocean circulation. In the Atlantic Ocean, the maximum storage rate shifted from the Northern to the Southern Hemisphere, plausibly caused by a weaker formation rate of North Atlantic Deep Waters and an intensified ventilation of mode and intermediate waters in the Southern Hemisphere. Our estimates of the C_ant accumulation differ from cumulative net air-sea flux estimates by several Pg C dec⁻¹, suggesting a substantial and variable, but uncertain net loss of natural carbon from the ocean. Our findings indicate a considerable vulnerability of the ocean carbon sink to climate variability and change.

The 2015 Paris Climate Agreement and Global Methane Pledge formalized agreement for countries to report and reduce methane emissions to mitigate near-term climate change. Emission inventories generated through surface activity measurements are reported annually or bi-annually, and evaluated periodically through a “Global Stocktake.” Emissions inverted from atmospheric data support evaluation of reported inventories, but their systematic use is stifled by spatially variable biases from prior errors combined with limited sensitivity of observations to emissions (also called smoothing error), as-well-as poorly characterized information content. Here, we demonstrate a Bayesian, optimal estimation (OE) algorithm for evaluating a state-of-the-art inventory (EDGAR v6.0) using satellite-based emissions from 2009 to 2018. The OE algorithm quantifies the information content (uncertainty reduction, sectoral attribution, spatial resolution) of the satellite-based emissions and disentangles the effect of smoothing error when comparing to an inventory. We find robust differences between satellite and EDGAR for total livestock, rice, and coal emissions: 14 ± 9, 12 ± 8, −11 ± 6 Tg CH₄/yr respectively. EDGAR and satellite agree that livestock emissions are increasing (0.25–1.3 Tg CH₄/yr/yr), primarily in the Indo-Pakistan region, sub-tropical Africa, and the Southern Brazilian; East Asia rice emissions are also increasing, highlighting the importance of agriculture on the atmospheric methane growth rate. In contrast, low information content for the waste and fossil emission trends confounds comparison between EDGAR and satellite; increased sampling and spatial resolution of satellite observations are therefore needed to evaluate reported changes to emissions in these sectors.

Earth observation (EO) is undergoing a paradigm shift with the development of cloud-based analytical platforms supporting EO data collection and access, parallel processing, easier communication of results, and expanded accessibility. As the global community of users and the diversity of applications grow, there is a clear need for expanded educational capacity to leverage these developments and increase the impact of EO research and teaching. Drawing upon extensive conversations between educators, practitioners, and researchers, we propose three pillars that must be prioritized to prepare students, researchers, and professionals to take full advantage of the cloud-based EO paradigm and guide future growth.

How much terrestrial precipitation is used by vegetation and how much runs off, represents central issues in hydrologic science, ecology, climate change, and even geopolitics. We present a theory for the water balance to predict the fractional change in streamflow due to given fractional changes in temperature and precipitation. The theory involves a single parameter whose value is derived under the conditions of neither energy- nor water-limitations and, therefore, is not an adjustable parameter. By comparison with extensive data for precipitation elasticity ϵ_p at global scale, we find that the theory captures the key trends of the variations of the median value of ϵ_p with the aridity index A_I. In contrast to a shortcoming of the classical Budyko phenomenology, namely, convergence to ϵ_p = 4 for large A_I, our theory yields a value of 2 for the median value of ϵ_p for all A_I > 1, in accord with the data for major river basins, as well as with the median value of summaries of global and continental data sets. Incorporating in the theory the effects of annual changes in water storage leads to the ability to predict the range of observed values of the elasticity as a function of the aridity index, or its inverse, the humidity index, as well as the run-off ratio. When changes in storage are neglected, the theory yields more accurate predictions for major river drainages than for small watersheds, particularly if the large basin spans various climate regimes and, as such, an integration over climates tends to reduce relative changes in the storage.

Combining new constraints on future socio-economic trajectories and the climate system's response to emissions can substantially reduce the projection uncertainty currently clouding regional climate adaptation decisions—more than either constraint individually.

Earth system models (ESMs) typically simplify the representation of land surface spectral albedo to two values, which correspond to the photosynthetically active radiation (PAR, 400–700 nm) and the near infrared (NIR, 700–2,500 nm) spectral bands. However, the availability of hyperspectral observations now allows for a more direct retrieval of ecological parameters and reduction of uncertainty in surface reflectance. To investigate sensitivity and quantify biases of incorporating hyperspectral albedo information into ESMs, we examine how shortwave soil albedo affects surface radiative forcing and simulations of the carbon and water cycles. Results reveal that the use of two broadband values to represent soil albedo can introduce systematic radiative-forcing differences compared to a hyperspectral representation. Specifically, we estimate soil albedo biases of ±0.2 over desert areas, which can result in spectrally integrated radiative forcing divergences of up to 30 W m⁻², primarily due to discrepancies in the blue (404–504 nm) and far-red (702–747 nm) regions. Furthermore, coupled land-atmosphere simulations indicate a significant difference in net solar flux at the top of the atmosphere (>3.3 W m⁻²), which can impact global energy fluxes, rainfall, temperature, and photosynthesis. Finally, simulations show that considering the hyperspectrally resolved soil reflectance leads to increased maximum daily temperatures under current and future CO₂ concentrations.

Fieldwork, including work done at sea, is a key component of many geoscientists' careers. Recent studies have highlighted the pervasive harassment faced by women and LGBTQ+ people during fieldwork. However, transgender and gender diverse (TGD) scientists face obstacles which have not yet been thoroughly examined. We fill this gap by sharing our experiences as TGD people. We have experienced sexual harassment, misconduct, privacy issues, and legal and medical struggles as we conduct seagoing work. In this work, we provide recommendations for individuals, cruise leaders, and institutions for making seagoing work safer for our communities.

Geodetic positioning is the geophysical record of reference for slow slip events, but typical daily solutions limit studies of the evolution of slow slip to its long-term dynamics. Accompanying seismic low-frequency earthquakes located precisely in time and space provide an opportunity to image slow slip dynamics at subdaily time scales. Here we show that a high-resolution time history of low-frequency earthquake fault slip alone can reproduce the geodetic record of slow slip that we observe to be dominated by subdaily fault slip dynamics. However, a simple linear model cannot accommodate the complex dynamics present throughout the slow slip cycle, and an analysis of different phases of the slow slip cycle shows that the ratio of geodetic to seismic fault slip varies as a function of time. This suggests that the low-frequency earthquake source region saturates as slow slip grows in moment and area. We propose that rheological heterogeneities at the plate boundary associated with low-frequency earthquakes do not play a significant role in the slow slip rupture process, thus implying that their activity is incidental to the driving aseismic slip.