skip to main content

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Latitudinal gradient in the respiration quotient and the implications for ocean oxygen availability

Climate-driven depletion of ocean oxygen strongly impacts the global cycles of carbon and nutrients as well as the survival of many animal species. One of the main uncertainties in predicting changes to marine oxygen levels is the regulation of the biological respiration demand associated with the biological pump. Derived from the Redfield ratio, the molar ratio of oxygen to organic carbon consumed during respiration (i.e., the respiration quotient,r−O2:C) is consistently assumed constant but rarely, if ever, measured. Using a prognostic Earth system model, we show that a 0.1 increase in the respiration quotient from 1.0 leads to a 2.3% decline in global oxygen, a large expansion of low-oxygen zones, additional water column denitrification of 38 Tg N/y, and the loss of fixed nitrogen and carbon production in the ocean. We then present direct chemical measurements ofr−O2:Cusing a Pacific Ocean meridional transect crossing all major surface biome types. The observedr−O2:Chas a positive correlation with temperature, and regional mean values differ significantly from Redfield proportions. Finally, an independent global inverse model analysis constrained with nutrients, oxygen, and carbon concentrations supports a positive temperature dependence ofr−O2:Cin exported organic matter. We provide evidence against the common assumption of a static biological link between the respiration of organic carbon and the consumption of oxygen. Furthermore, the model simulations suggest that a changing respiration quotient will impact multiple biogeochemical cycles and that future warming can lead to more intense deoxygenation than previously anticipated.

  more » « less
Award ID(s):
1848576 1948842
PAR ID:
10189234
Author(s) / Creator(s):
; ; ; ; ; ; ;
Publisher / Repository:
Proceedings of the National Academy of Sciences
Date Published:
Journal Name:
Proceedings of the National Academy of Sciences
Volume:
117
Issue:
37
ISSN:
0027-8424
Page Range / eLocation ID:
p. 22866-22872
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ( , Journal of The Electrochemical Society)

    A theoretical analysis on crack formation and propagation was performed based on the coupling between the electrochemical process, classical elasticity, and fracture mechanics. The chemical potential of oxygen, thus oxygen partial pressure, at the oxygen electrode-electrolyte interface (μO2OE∣El) was investigated as a function of transport properties, electrolyte thickness and operating conditions (e.g., steam concentration, constant current, and constant voltage). Our analysis shows that: a lower ionic area specific resistance (ASR),riOE,and a higher electronic ASR (reOE) of the oxygen electrode/electrolyte interface are in favor of suppressing crack formation. TheμO2OE∣El,thus local pO2, are sensitive towards the operating parameters under galvanostatic or potentiostatic electrolysis. Constant current density electrolysis provides better robustness, especially at a high current density with a high steam content. While constant voltage electrolysis leads to greater variations ofμO2OE∣El.Constant current electrolysis, however, is not suitable for an unstable oxygen electrode becauseμO2OE∣Elcan reach a very high value with a gradually increasedriOE.A crack may only occur under certain conditions whenpO2TPB>pcr.

     
    more » « less
  2. ; ; ; ; ; ; ; ; ; ; et al ( , Proceedings of the National Academy of Sciences)

    Assessment of the global budget of the greenhouse gas nitrous oxide (N2O) is limited by poor knowledge of the oceanicN2O flux to the atmosphere, of which the magnitude, spatial distribution, and temporal variability remain highly uncertain. Here, we reconstruct climatologicalN2O emissions from the ocean by training a supervised learning algorithm with over 158,000N2O measurements from the surface ocean—the largest synthesis to date. The reconstruction captures observed latitudinal gradients and coastal hot spots ofN2O flux and reveals a vigorous global seasonal cycle. We estimate an annual meanN2O flux of 4.2 ± 1.0 Tg N⋅y−1, 64% of which occurs in the tropics, and 20% in coastal upwelling systems that occupy less than 3% of the ocean area. ThisN2O flux ranges from a low of 3.3 ± 1.3 Tg N⋅y−1in the boreal spring to a high of 5.5 ± 2.0 Tg N⋅y−1in the boreal summer. Much of the seasonal variations in globalN2O emissions can be traced to seasonal upwelling in the tropical ocean and winter mixing in the Southern Ocean. The dominant contribution to seasonality by productive, low-oxygen tropical upwelling systems (>75%) suggests a sensitivity of the globalN2O flux to El Niño–Southern Oscillation and anthropogenic stratification of the low latitude ocean. This ocean flux estimate is consistent with the range adopted by the Intergovernmental Panel on Climate Change, but reduces its uncertainty by more than fivefold, enabling more precise determination of other terms in the atmosphericN2O budget.

     
    more » « less
  3. ; ; ; ; ; ; ; ; ; ( , Proceedings of the National Academy of Sciences)

    Sub-Neptunes are common among the discovered exoplanets. However, lack of knowledge on the state of matter inH2O-rich setting at high pressures and temperatures (P−T) places important limitations on our understanding of this planet type. We have conducted experiments for reactions betweenSiO2andH2O as archetypal materials for rock and ice, respectively, at highP−T. We found anomalously expanded volumes of dense silica (up to 4%) recovered from hydrothermal synthesis above ∼24 GPa where theCaCl2-type (Ct) structure appears at lower pressures than in the anhydrous system. Infrared spectroscopy identified strong OH modes from the dense silica samples. Both previous experiments and our density functional theory calculations support up to 0.48 hydrogen atoms per formula unit of (Si1−xH4x)O2 (x=0.12). At pressures above 60 GPa,H2O further changes the structural behavior of silica, stabilizing a niccolite-type structure, which is unquenchable. From unit-cell volume and phase equilibrium considerations, we infer that the niccolite-type phase may contain H with an amount at least comparable with or higher than that of the Ct phase. Our results suggest that the phases containing both hydrogen and lithophile elements could be the dominant materials in the interiors of water-rich planets. Even for fully layered cases, the large mutual solubility could make the boundary between rock and ice layers fuzzy. Therefore, the physical properties of the new phases that we report here would be important for understanding dynamics, geochemical cycle, and dynamo generation in water-rich planets.

     
    more » « less
  4. ; ; ; ; ; ( , Proceedings of the National Academy of Sciences)
    Significance

    Pyrite is oxidized during weathering to form dissolved sulfate that is carried to the ocean by rivers. This process is thought to incorporate atmosphericO2-derived oxygen; geologically preserved sulfate has thus been proposed to directly trace pastO2isotope compositions. However, this mechanism has not been thoroughly tested in modern weathering environments. We show that dissolved sulfate in Himalayan rivers is predominantly derived from pyrite, yet its oxygen isotope compositions preclude directO2incorporation. Rather, alternative oxygen sources (e.g., reactive oxygen species) may be incorporated during oxidation, prompting reconsideration of the pyrite oxidation mechanism and the interpretation of geologically preserved sulfate as a directO2tracer.

     
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al ( , Proceedings of the National Academy of Sciences)

    MXenes have demonstrated potential for various applications owing to their tunable surface chemistry and metallic conductivity. However, high temperatures can accelerate MXene film oxidation in air. Understanding the mechanisms of MXene oxidation at elevated temperatures, which is still limited, is critical in improving their thermal stability for high-temperature applications. Here, we demonstrate that Ti3C2TxMXene monoflakes have exceptional thermal stability at temperatures up to 600°C in air, while multiflakes readily oxidize in air at 300°C. Density functional theory calculations indicate that confined water between Ti3C2Txflakes has higher removal energy than surface water and can thus persist to higher temperatures, leading to oxidation. We demonstrate that the amount of confined water correlates with the degree of oxidation in stacked flakes. Confined water can be fully removed by vacuum annealing Ti3C2Txfilms at 600°C, resulting in substantial stability improvement in multiflake films (can withstand 600°C in air). These findings provide fundamental insights into the kinetics of confined water and its role in Ti3C2Txoxidation. This work enables the use of stable monoflake MXenes in high-temperature applications and provides guidelines for proper vacuum annealing of multiflake films to enhance their stability.

     
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email