More Like this

1. Latitudinal gradient in the respiration quotient and the implications for ocean oxygen availability

   https://doi.org/10.1073/pnas.2004986117  

   Moreno, Allison R.; Garcia, Catherine A.; Larkin, Alyse A.; Lee, Jenna A.; Wang, Wei-Lei; Moore, J. Keith; Primeau, Francois W.; Martiny, Adam C. (August 2020, Proceedings of the National Academy of Sciences)

   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 of $r_{-O2:C}$using a Pacific Ocean meridional transect crossing all major surface biome types. The observed $r_{-O2:C}$has 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 of $r_{-O2:C}$in 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
2. Global Ocean Particulate Organic Phosphorus, Carbon, Oxygen for Respiration, and Nitrogen (GO-POPCORN)

   https://doi.org/10.1038/s41597-022-01809-1  

   Tanioka, Tatsuro; Larkin, Alyse A.; Moreno, Allison R.; Brock, Melissa L.; Fagan, Adam J.; Garcia, Catherine A.; Garcia, Nathan S.; Gerace, Skylar D.; Lee, Jenna A.; Lomas, Michael W.; et al (December 2022, Scientific Data)

   Abstract Concentrations and elemental stoichiometry of suspended particulate organic carbon, nitrogen, phosphorus, and oxygen demand for respiration (C:N:P:−O 2 ) play a vital role in characterizing and quantifying marine elemental cycles. Here, we present Version 2 of the Global Ocean Particulate Organic Phosphorus, Carbon, Oxygen for Respiration, and Nitrogen (GO-POPCORN) dataset. Version 1 is a previously published dataset of particulate organic matter from 70 different studies between 1971 and 2010, while Version 2 is comprised of data collected from recent cruises between 2011 and 2020. The combined GO-POPCORN dataset contains 2673 paired surface POC/N/P measurements from 70°S to 73°N across all major ocean basins at high spatial resolution. Version 2 also includes 965 measurements of oxygen demand for organic carbon respiration. This new dataset can help validate and calibrate the next generation of global ocean biogeochemical models with flexible elemental stoichiometry. We expect that incorporating variable C:N:P:-O 2 into models will help improve our estimates of key ocean biogeochemical fluxes such as carbon export, nitrogen fixation, and organic matter remineralization. 

   more » « less
3. Modeling Spatiotemporal Patterns of Ecosystem Metabolism and Organic Carbon Dynamics Affecting Hypoxia on the Louisiana Continental Shelf

   https://doi.org/10.1029/2019JC015630  

   Jarvis, Brandon M.; Lehrter, John C.; Lowe, Lisa L.; Hagy, James D.; Wan, Yongshan; Murrell, Michael C.; Ko, Dong S.; Penta, Bradley; Gould, Jr., Richard W. (April 2020, Journal of Geophysical Research: Oceans)

   Abstract The hypoxic zone on the Louisiana Continental Shelf (LCS) forms each summer due to nutrient‐enhanced primary production and seasonal stratification associated with freshwater discharges from the Mississippi/Atchafalaya River Basin (MARB). Recent field studies have identified highly productive shallow nearshore waters as an important component of shelf‐wide carbon production contributing to hypoxia formation. This study applied a three‐dimensional hydrodynamic‐biogeochemical model named CGEM (Coastal Generalized Ecosystem Model) to quantify the spatial and temporal patterns of hypoxia, carbon production, respiration, and transport between nearshore and middle shelf regions where hypoxia is most prevalent. We first demonstrate that our simulations reproduced spatial and temporal patterns of carbon production, respiration, and bottom‐water oxygen gradients compared to field observations. We used multiyear simulations to quantify transport of particulate organic carbon (POC) from nearshore areas where riverine organic matter and phytoplankton carbon production are greatest. The spatial displacement of carbon production and respiration in our simulations was created by westward and offshore POC flux via phytoplankton carbon flux in the surface layer and POC flux in the bottom layer, supporting heterotrophic respiration on the middle shelf where hypoxia is frequently observed. These results support existing studies suggesting the importance of offshore carbon flux to hypoxia formation, particularly on the west shelf where hypoxic conditions are most variable. 

   more » « less
4. Reconciling the importance of meiofauna respiration for oxygen demand in muddy coastal sediments

   https://doi.org/10.1002/lno.12393  

   Maciute, Adele; Holovachov, Oleksandr; Glud, Ronnie N.; Broman, Elias; Berg, Peter; Nascimento, Francisco J. A.; Bonaglia, Stefano (June 2023, Limnology and Oceanography)

   ABSTRACT Meiofauna, organisms smaller than 1 mm, are the most abundant and diverse invertebrates inhabiting the world's ocean floor but their contribution to benthic oxygen demand is still poorly constrained. This knowledge is crucial for understanding seabed respiration, global marine carbon, and oxygen cycles, which are relevant to all nutrient cycling and energy flows in the ecosystem. It is common to predict meiofauna respiration based on their biomass or volume, which are difficult to quantify, and thus meiofauna are rarely included in biogeochemistry studies. In addition, it is still unknown how well the generalized allometric relations describe all meiofauna respiration. Therefore, we used a novel approach specially developed for single meiofauna respiration measurements to derive the respiration rates of 10 meiofauna groups in two marine and one brackish coastal muddy environments under oxic and hypoxic conditions, representing natural sediment conditions. Our estimates suggest that large ostracods and juveniles of macrofauna (e.g., bivalves, trumpet worms, and priapulids) had the highest individual respiration rates. Meiofauna community as a whole contributed 3–33% to sediment oxygen uptake. However, the most important contributors to the overall sediment oxygen uptake were nematodes and foraminifera which had lower respiration rates but were highly abundant. Therefore, out of more than 22 meiofauna phyla, we recommend that nematode and foraminifera respiration, which contributes 3–30% (total 3–33%) to sediment oxygen uptake, should be taken into consideration in any estimations of benthic oxygen and carbon cycles. 

   more » « less
5. What the geological past can tell us about the future of the ocean’s twilight zone

   https://doi.org/10.1038/s41467-023-37781-6  

   Crichton, Katherine A.; Wilson, Jamie D.; Ridgwell, Andy; Boscolo-Galazzo, Flavia; John, Eleanor H.; Wade, Bridget S.; Pearson, Paul N. (April 2023, Nature Communications)

   Abstract Paleontological reconstructions of plankton community structure during warm periods of the Cenozoic (last 66 million years) reveal that deep-dwelling ‘twilight zone’ (200–1000 m) plankton were less abundant and diverse, and lived much closer to the surface, than in colder, more recent climates. We suggest that this is a consequence of temperature’s role in controlling the rate that sinking organic matter is broken down and metabolized by bacteria, a process that occurs faster at warmer temperatures. In a warmer ocean, a smaller fraction of organic matter reaches the ocean interior, affecting food supply and dissolved oxygen availability at depth. Using an Earth system model that has been evaluated against paleo observations, we illustrate how anthropogenic warming may impact future carbon cycling and twilight zone ecology. Our findings suggest that significant changes are already underway, and without strong emissions mitigation, widespread ecological disruption in the twilight zone is likely by 2100, with effects spanning millennia thereafter. 

   more » « less