Ocean deoxygenation caused non‐linear responses in the structure and functioning of benthic ecosystems

Pascal, Ludovic; Cool, Joannie; Archambault, Philippe; Calosi, Piero; Cuenca, André L. R.; Mucci, Alfonso O.; Chaillou, Gwénaëlle

doi:10.1111/gcb.16994

Cited by 3 publications

(1 citation statement)

References 88 publications

(129 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Our results should be considered in the light of the current hypoxic conditions prevalent in the deep layer of the LSLE, where water oxygen levels are as low as 1 mg O 2 /L (Jutras et al, 2023). Under these conditions, it has been suggested that particle mixing and bioturbation of sediments may be nearly absent, likely in response to changes in infauna community assemblage and a lower metabolic activity (Pascal et al, 2023). In the water column, reduced degradation of organic matter by heterotrophic communities could occur at low oxygen concentrations leading to higher export at depth (Engel et al, 2017).…”

Section: Relationship Between Apparent Oxygen Utilization and Chlorin...mentioning

confidence: 77%

Using chlorophyllic organic matter degradation in the deep St. Lawrence Estuary as an indicator of water column remineralization

Lévesque,

Lebeuf,

Starr

2024

Front. Mar. Sci.

View full text Add to dashboard Cite

Coastal hypoxia, driven by remineralization of chlorophyllic particulate organic matter (POM) in dark environments, poses a threat to deep estuarine and shelf ecosystems. To better understand the fate of POM along a depth gradient, we investigated the degradation of chloropigments, particulate organic carbon (POC), and nitrogen (PON) across the water column in the St. Lawrence Estuary, one of the largest and deepest estuarine system in the world that is facing strong persistent and increasing hypoxia. Our objectives were to establish causal relationships among suspended POM descriptors and assess the potential of a chlorophyll-based degradation index, known as the chlorin index (CI), in evaluating OM degradation within the water column. The CI, ranging from 0.2 for pure chlorophyll to almost 1 for highly degraded pigments, was initially developed for uses in the sediments. Water samples from multiple depths were collected, characterized, and statistically analyzed with a combination of variation partitioning, non-linear regressions and piecewise structural equation modeling (pSEM). We found that the combined influence of chloropigments and depth explained 84.0% of POC and 90.0% of PON variations; the pure fraction attributed to chloropigments accounted for 73.4% and 75.6% (R2adj, both with p< 0.001), respectively. The decline of chloropigments, PON, and POC with increasing depth was reflected by the concomitant increase in CI, whose rate decreases as particles sink resulting in reduced degradation due to less labile organic matter. The pSEM causal model indicated that CI increased with depth and POC concentration, while it decreased in the presence of elevated PON concentrations, known for their high reactivity. The direct effect of depth on CI could be linked to the distinct water column properties influencing particle residence time and thus the degradation potential by biotic and abiotic factors. Finally, CI explained 86% (R2) of the apparent oxygen utilization highlighting the strong connection between POM degradation and hypoxia of deep coastal ecosystems. Our study underscores the utility of the chlorin index as a simple yet robust tool for monitoring OM degradation in the water column, particularly in the St. Lawrence Estuary.

show abstract

Section: Relationship Between Apparent Oxygen Utilization and Chlorin...mentioning

confidence: 77%

Using chlorophyllic organic matter degradation in the deep St. Lawrence Estuary as an indicator of water column remineralization

Lévesque,

Lebeuf,

Starr

2024

Front. Mar. Sci.

View full text Add to dashboard Cite

show abstract

Ocean deoxygenation caused non‐linear responses in the structure and functioning of benthic ecosystems

Pascal,

Cool,

Archambault

et al. 2023

Global Change Biology

Self Cite

View full text Add to dashboard Cite

The O2 content of the global ocean has been declining progressively over the past decades, mainly because of human activities and global warming. Nevertheless, how long‐term deoxygenation affects macrobenthic communities, sediment biogeochemistry and their mutual feedback remains poorly understood. Here, we evaluate the response of the benthic assemblages and biogeochemical functioning to decreasing O2 concentrations along the persistent bottom‐water dissolved O2 gradient of the Estuary and Gulf of St. Lawrence (QC, Canada). We report several of non‐linear biodiversity and functional responses to decreasing O2 concentrations, and identify an O2 threshold that occurs at approximately at 63 μM. Below this threshold, macrobenthic community assemblages change, and bioturbation rates drastically decrease to near zero. Consequently, the sequence of electron acceptors used to metabolize the sedimentary organic matter is squeezed towards the sediment surface while reduced compounds accumulate closer (as much as 0.5–2.5 cm depending on the compound) to the sediment–water interface. Our results illustrate the capacity of bioturbating species to compensate for the biogeochemical consequences of hypoxia and can help to predict future changes in benthic ecosystems.

show abstract

Evolution of oxygen and stratification and their relationship in the North Pacific Ocean in CMIP6 Earth system models

Novi,

Bracco,

Ito

et al. 2024

Biogeosciences

View full text Add to dashboard Cite

Abstract. This study examines the linkages between the upper-ocean (0–200 m) oxygen (O2) content and stratification in the North Pacific Ocean using four Earth system models (ESMs), an ocean hindcast simulation, and an ocean reanalysis. The trends and variability in oceanic O2 content are driven by the imbalance between physical supply and biological demand. Physical supply is primarily controlled by ocean ventilation, which is responsible for the transport of O2-rich surface waters to the subsurface. Isopycnic potential vorticity (IPV), a quasi-conservative tracer proportional to density stratification that can be evaluated from temperature and salinity measurements, is used herein as a dynamical proxy for ocean ventilation. The predictability potential of the IPV field is evaluated through its information entropy. The results highlight a strong O2–IPV connection and somewhat higher (as compared to the rest of the basin) predictability potential for IPV across the tropical Pacific, where the El Niño–Southern Oscillation occurs. This pattern of higher predictability and strong anticorrelation between O2 and stratification is robust across multiple models and datasets. In contrast, IPV at mid-latitudes has low predictability potential and its center of action differs from that of O2. In addition, the locations of extreme events or hotspots may or may not differ between the two fields, with a strong model dependency, which persists in future projections. On the one hand, these results suggest that it may be possible to monitor ocean O2 in the tropical Pacific based on a few observational sites co-located with the more abundant IPV measurements; on the other, they lead us to question the robustness of the IPV–O2 relationship in the extratropics. The proposed framework helps to characterize and interpret O2 variability in relation to physical variability and may be especially useful in the analysis of new observation-based data products derived from the BGC-Argo float array in combination with the traditional but far more abundant Argo data.

show abstract

Ocean deoxygenation caused non‐linear responses in the structure and functioning of benthic ecosystems

Cited by 3 publications

References 88 publications

Using chlorophyllic organic matter degradation in the deep St. Lawrence Estuary as an indicator of water column remineralization

Using chlorophyllic organic matter degradation in the deep St. Lawrence Estuary as an indicator of water column remineralization

Ocean deoxygenation caused non‐linear responses in the structure and functioning of benthic ecosystems

Evolution of oxygen and stratification and their relationship in the North Pacific Ocean in CMIP6 Earth system models

Contact Info

Product

Resources

About