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8. Increasing hypoxia on global coral reefs under ocean warming

Author

Pezner, Ariel K., Courtney, Travis A., Barkley, Hannah C., Chou, Wen-Chen, Chu, Hui-Chuan, Clements, Samantha M., Cyronak, Tyler, DeGrandpre, Michael D., Kekuewa, Samuel A. H., Kline, David I., Liang, Yi-Bei, Martz, Todd R., Mitarai, Satoshi, Page, Heather N., Rintoul, Max S., Smith, Jennifer E., Soong, Keryea, Takeshita, Yuichiro, Tresguerres, Martin, Wei, Yi, Yates, Kimberly K., and Andersson, Andreas J.

Published
2023
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17. Coral growth along a natural gradient of seawater temperature, pH, and oxygen in a nearshore seagrass bed on Dongsha Atoll, Taiwan.

Author

Pezner, Ariel K., Courtney, Travis A., Chou, Wen-Chen, Chu, Hui-Chuan, Frable, Benjamin W., Kekuewa, Samuel A. H., Soong, Keryea, Wei, Yi, and Andersson, Andreas J.

Subjects
CORAL reefs & islands, OCEAN temperature, CORALS, PORITES, LOW temperatures, SYMBIODINIUM, SEAGRASSES
Abstract

Coral reefs are facing threats from a variety of global change stressors, including ocean warming, acidification, and deoxygenation. It has been hypothesized that growing corals near primary producers such as macroalgae or seagrass may help to ameliorate acidification and deoxygenation stress, however few studies have explored this effect in situ. Here, we investigated differences in coral growth rates across a natural gradient in seawater temperature, pH, and dissolved oxygen (DO) variability in a nearshore seagrass bed on Dongsha Atoll, Taiwan, South China Sea. We observed strong spatial gradients in temperature (5°C), pH (0.29 pH units), and DO (129 μmol O2 kg-1) across the 1-kilometer wide seagrass bed. Similarly, diel variability recorded by an autonomous sensor in the shallow seagrass measured diel ranges in temperature, pH, and DO of up to 2.6°C, 0.55, and 204 μmol O2 kg-1, respectively. Skeletal cores collected from 15 massive Porites corals growing in the seagrass bed at 4 sites revealed no significant differences in coral calcification rates between sites along the gradients. However, significant differences in skeletal extension rate and density suggest that the dynamic temperature, pH, and/or DO variability may have influenced these properties. The lack of differences in coral growth between sites may be because favorable calcification conditions during the day (high temperature, pH, and DO) were proportionally balanced by unfavorable conditions during the night (low temperature, pH, and DO). Alternatively, other factors were simply more important in controlling coral calcification and/or corals were acclimated to the prevailing conditions at each site. [ABSTRACT FROM AUTHOR]

Published
2024
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23. Probabilistic Dynamic Design Curves Optimized for High-Speed Reinforced Concrete Railway Bridges Using First-Order Reliability Method.

Author

Allahvirdizadeh, Reza, Andersson, Andreas, and Karoumi, Raid

Subjects
*BRIDGE vibration, *STRUCTURAL reliability, *RAILROAD bridges, *REINFORCED concrete, *JOINT use of railroad facilities
Abstract

Increasing the operating speed of trains in modern railway networks can induce greater actions on the infrastructure than was previously the case. This is due, in particular, to the occurrence of the resonance phenomenon in railway bridges, which is the focus of this paper and was not traditionally considered as a concern. In this context, the vibrations experienced by bridges, both vertical accelerations and displacements, are limited by design regulations to ensure that the safety of train passages over bridges and the comfort of passengers are guaranteed. However, previous studies have shown that the conventional dynamic design methods do not always result in conservative designs, nor is the achieved safety always consistent. Therefore, a probabilistic approach is adopted in this study to optimize the cross-section properties of various railway bridges in a wide design range including section types, span lengths, and number of spans. For this purpose, an iterative line search-based optimization problem is formulated to minimize the thickness of the cross-sections under consideration and consequently the linear mass of the bridges. Meanwhile, the associated failure probabilities of the above dynamic limit states are constrained to be less than the desired level of safety by incorporating them into the optimization constraint. In this regard, First-Order Reliability Method (FORM) is adopted to perform reliability analyses. Thus, the obtained results are presented in the form of design curves that may assist designers to select minimum cross-section dimensions satisfying the desired level of safety in terms of dynamic limit states. This objective can be achieved using the proposed design curves without the need to construct associated complex computational models and perform computationally expensive dynamic analyses. [ABSTRACT FROM AUTHOR]

Published
2024
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24. Dynamic behaviour of bridges under critical conventional and regular trains: Review of some regulations included in EN 1991-2.

Author

Museros, Pedro, Andersson, Andreas, and Pinazo, Benjamín

Abstract

In the field of structural analysis dedicated to the study of vibrations of high-speed railway bridges, one reference load model is the well-known HSLM-A, which limits of validity are stated in Eurocode EN 1991-2, Annex E. In a recent paper published in the Journal of Rail and Rapid Transit, the authors investigated the degree of coverage provided by HSLM-A to critical articulated trains. Now in the present article, the authors have extended those analyses to critical conventional and regular trains as well. This is an important aspect because HSLM-A as such is an articulated-type model, so it is of interest to understand how it deals with covering the various resonance phenomena generated by other train types. Therefore, the main goal of this work is to establish whether the conventional and regular trains that stem from the validity rules given in Annex E/EN 1991-2, produce vibratory effects that are duly covered by HSLM-A. Following the aforementioned validity rules, one first aspect analysed is the importance of near-to-integer wheelbase ratios in the coupled vibrations produced by conventional trains. Subsequently, seven realistic, conventional and regular high-speed train models have been synthesised; these models have been made publicly available in Mendeley Data, and comprise almost 3800 different sequences of axle loads. Finally, the response of simply-supported bridges has been analysed with a view to compare the seven synthesised models versus HSLM-A. The exceedance and required speed increase have been computed for both displacements and accelerations, in a comprehensive ensemble of spans and speeds. The results provide a diagnosis of the degree of coverage of HSLM-A with respect to those conventional and regular trains compliant with Annex E/EN 1991-2. [ABSTRACT FROM AUTHOR]

Published
2024
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35. Physical and Biological Controls on the Annual CO2 Cycle in Agua Hedionda Lagoon, Carlsbad, CA.

Author

Shipley, Kenisha, Martz, Todd, Hales, Burke, Giddings, Sarah N., and Andersson, Andreas

Subjects
LAGOONS, MARINE fishes, FISH hatcheries, SUMMER, RECREATION, MASS budget (Geophysics), HATCHERY fishes, RESPIRATION in plants
Abstract

Agua Hedionda Lagoon (AHL), a tidal estuary located on the southern California coast, supports a diverse ecosystem while serving numerous recreation activities, a marine fish hatchery, a shellfish hatchery, and the largest desalination plant in the western hemisphere. In this work, a 1-year time series of carbon dioxide data is used to establish baseline average dissolved inorganic carbon conditions in AHL. Based on a mass balance model of the outer basin of the lagoon, we propose that AHL is a source of inorganic carbon to the adjacent ocean, through advective export, at a rate of 5.9 × 106 mol C year−1, and a source of CO2 to the atmosphere of 0.21 × 106 mol C year−1 (1 mol C m−2 year−1), implying a net heterotrophic system on the order of 6.0 × 106 mol C year−1 (30 mol C m−2 year−1). Although variable with a range throughout the year of 80% about the mean, the ecosystem remained persistently heterotrophic, reaching peak rates during the summer season. Using results from the mass balance, the annual cycle of selected properties of the aqueous CO2 system (pH, pCO2, and CaCO3 saturation state) were mathematically decomposed in order to examine the relative contribution of drivers including advection, ecosystem metabolism, and temperature that act to balance their observed annual cycle. Important findings of this study include the identification of advection as a prime driver of biogeochemical variability and the establishment of a data-based estimate of mean flushing time for AHL. [ABSTRACT FROM AUTHOR]

Published
2024
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41. Understanding Ocean Acidification Impacts on Organismal to Ecological Scales

Author

Andersson, Andreas J., Kline, David I., Edmunds, Peter J., Archer, Stephen D., Bednaršek, Nina, Carpenter, Robert C., Chadsey, Meg, Goldstein, Philip, Grottoli, Andrea G., Hurst, Thomas P., King, Andrew L., Kübler, Janet E., Kuffner, Ilsa B., Mackey, Katherine R.M., Menge, Bruce A., Paytan, Adina, Riebesell, Ulf, Schnetzer, Astrid, Warner, Mark E., and Zimmerman, Richard C.

Published
2015

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