Strong Habitat Compression by Extreme Shoaling Events of Hypoxic Waters in the Eastern Pacific

Köhn, Eike; Münnich, Matthias; Vogt, Meike; Desmet, Flora; Gruber, Nicolas

doi:10.1029/2022jc018429

Cited by 15 publications

(37 citation statements)

References 184 publications

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“…We also updated the atmospheric forcing from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA) interim (Dee et al, 2011) to ERA5 (Hersbach et al, 2020. For further details the reader is referred to Köhn et al (2022). Here we provide a summary of the simulation protocol.…”

Section: Model Hindcastmentioning

confidence: 99%

On the Vertical Structure and Propagation of Marine Heatwaves in the Eastern Pacific

Köhn,

Vogt,

Münnich

et al. 2024

JGR Oceans

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Marine heatwaves (MHWs) have been recognized as a serious threat to marine life, yet, most studies so far have focused on the surface only. Here, we investigate the vertical dimension and propagation of surface MHWs in the Eastern Pacific (EP) using results from a high‐resolution hindcast simulation (1979–2019), performed with the Regional Ocean Modeling System. We detect MHWs using a seasonally varying percentile threshold on a fixed baseline and track their vertical propagation across the upper 500 m. We find that nearly a third (∼29%) of the MHWs extend beyond the surface mixed layer depth (MLD). On average, these deep‐reaching MHWs (dMHWs) extend to 110 m below the MLD and last five times longer than MHWs that are confined to the mixed layer (184 vs. 36 days). The dMHWs can cause stronger temperature anomalies at depth than at the surface (maximum intensity of 5.0 vs. 1.9°C). This general subsurface MHW intensification even holds when scaling the temperatures with the respective local variability. A clustering of dMHWs reveals that 41% of them are block‐like, that is, continually remain in contact with the sea surface, 24% propagate downward, 20% propagate upward, while 15% appear at the surface multiple times. Although the water column MHW duration, intensity and severity are only moderately correlated with their corresponding surface‐based MHW characteristics, dMHWs have the potential to be detected from the surface. Our study can help to augment the remote sensing‐based monitoring of upper ocean exposure to MHWs.

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Section: Model Hindcastmentioning

confidence: 99%

On the Vertical Structure and Propagation of Marine Heatwaves in the Eastern Pacific

Köhn,

Vogt,

Münnich

et al. 2024

JGR Oceans

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“…On top of this general, broad-scale trend, short-term and localized extreme shoaling events of low oxygen waters can dramatically decrease tuna habitat. Termed "transient habitat reduction extreme events", they temporarily reduce the aerobic habitat by 50%-70% (Köhn et al, 2022). Habitat compression means that yellowfin tuna have less space to hunt and are more frequently in contact with their own predators, which are also restricted by the compression.…”

Section: Oxygen and Climate Changementioning

confidence: 99%

“…This notable oxygen deficiency is caused by a combination of high productivity in surface waters, a strong permanent pycnocline, and sluggish interior ocean ventilation (Fiedler & Talley, 2006). Furthermore, the aerobic habitat above the OMZ in this region is periodically compressed, particularly during La Niña conditions, as the OMZ shoals during intermittent extreme events (Köhn et al, 2022).…”

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confidence: 99%

Movement and vertical habitat use of yellowfin tuna Thunnus albacares in a vertically compressed habitat: the Galápagos Marine Reserve

Rohner

Garabato

Hearn

2023

Journal of Fish Biology

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Tropical pelagic predators are exploited by fisheries and their movements are influenced by factors including prey availability, temperature, and dissolved oxygen levels. As the biophysical parameters vary greatly within the range of circumtropical species, local studies are needed to define those species’ habitat preference and model possible behavioural responses under different climate change scenarios. Here, we tagged yellowfin tuna Thunnus albacares in the Galápagos Marine Reserve and tracked the horizontal and vertical movements of 8 individuals for 4–97 days. The tuna travelled a mean of 13.6 km d‐1 horizontally and dispersed throughout the archipelago and in offshore waters inside the Galápagos Marine Reserve and in the surrounding Ecuadorian exclusive economic zone. Vertically, they travelled a mean of 2 km d‐1, although high‐resolution data from a recovered tag suggested that transmitted data underestimated their vertical movement by a factor of 5.5. The tracked yellowfin tuna spent most of their time near the surface, with an overall mean swimming depth of 24.3 ± 46.6 m, and stayed shallower at night (12.3 ± 4.9 m) than during the day (23.8 ± 20.9 m), but on occasion dived to cold, oxygen‐poor waters below 200 m. Deep dives were commonly made during the day with a mean recovery period of 51 min between exposures to modelled limiting oxygen conditions <1.5 ml l‐1, presumably to re‐oxygenate. The depth and frequency of dives were likely limited by dissolved oxygen levels, as oxygen depleted conditions reach shallow depths in this region. The main habitat of tracked yellowfin tunas was in the shallow mixed layer which may leave them vulnerable to fishing. Vertical expansion of low‐oxygen waters under future climate change scenarios may further compress their habitat, increasing their vulnerability to surface fishing gear.This article is protected by copyright. All rights reserved.

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“…Dissolved oxygen (DO) is of great importance for elemental biogeochemical cycling (Hietanen et al, 2012;Rabalais et al, 2014;Cai et al, 2017) and marine habitats (Diaz and Rosenberg, 2008;Vaquer-Sunyer and Duarte, 2008;Stramma et al, 2010;Breitburg et al, 2018;Köhn et al, 2022). Influenced by increasing anthropogenic perturbations and natural changes, the estuarine and coastal ecosystems are experiencing eutrophication, which may eventually result in subsurface/ bottom hypoxia (Zhang et al, 2010;Howarth et al, 2011;Rabalais et al, 2014;Cui et al, 2019;Diaz et al, 2019) and associated acidification (Cai et al, 2011;Sunda and Cai, 2012;Wallace et al, 2014;Zhao et al, 2020;Kessouri et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

Spatial variability of hypoxia and coupled physical-biogeochemical controls off the Changjiang (Yangtze River) Estuary in summer

et al. 2022

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Global estuarine hypoxia is among the most acute environmental issues, yet the recognition of hypoxia variability remains patchy. The Changjiang (Yangtze River) Estuary (CE) is well known as one of the largest estuarine hypoxic systems. However, the mechanisms controlling the spatial variability and heterogeneity of summer hypoxia have been rarely examined in this region. Based on observational data in the summer of 2013, the essential linkages between physical-biogeochemical processes and spatial variability of hypoxia were revealed off the CE. The hypoxia generally occurred in a transitional region off the CE, presenting to be spatially variable and heterogeneous in its distribution and intensity. The river plume, stratification, front, upwelling and localized high phytoplankton biomass combine to shape the spatial morphology and scope of hypoxia. The spatial heterogeneity of hypoxic magnitude in horizontal direction is mainly regulated by the intensity variability of stratification and phytoplankton blooms. The position of bottom front formed by the offshore Taiwan Warm Current (TWC) and coastal water under tidal mixing controls the shoreward boundary of hypoxic zone, while the river plume front-dominated outer edge of phytoplankton blooms in upper layers plays a role in determining the seaward limit of the reach of bottom hypoxia. The stratification depth controlled by the upwelling and river plume governs the upper limit of the top reach of hypoxia, and shapes the vertical morphology of hypoxic zone. We contextualize the role of physical-biogeochemical drivers to the spatially variable hypoxia in a conceptual diagram. The findings would considerably contribute to our understanding of the spatially variable hypoxia in river plume-upwelling-front coupled estuarine systems, providing a sound basis for prediction and simulation under anticipated future conditions.

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Strong Habitat Compression by Extreme Shoaling Events of Hypoxic Waters in the Eastern Pacific

Abstract: While climate change driven long term ocean deoxygenation induces profound changes in marine ecosystems (

Cited by 15 publications

References 184 publications

On the Vertical Structure and Propagation of Marine Heatwaves in the Eastern Pacific

On the Vertical Structure and Propagation of Marine Heatwaves in the Eastern Pacific

Movement and vertical habitat use of yellowfin tuna Thunnus albacares in a vertically compressed habitat: the Galápagos Marine Reserve

Spatial variability of hypoxia and coupled physical-biogeochemical controls off the Changjiang (Yangtze River) Estuary in summer

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