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Abstract Marine heat waves (MHWs) are extreme events characterized by prolonged periods of unusually high sea surface temperatures. The North Pacific has been a focus of MHW research due to the severe ecosystem impacts of several events in the 2010s. These events are influenced by global warming and climate variability patterns like El Niño–Southern Oscillation (ENSO) and the Pacific decadal oscillation (PDO). We identify MHWs in the Community Earth System Model, version 2, large ensemble using an object-based tracking algorithm (Ocetrac) and classify them via hierarchical clustering, focusing on five dominant midlatitude types. All types are initiated by reduced wind stress, which results in suppressed ocean cooling. This initial warming is then amplified by a cloud–shortwave feedback making net surface heat flux anomalies the largest contributor to peak intensity. While this two-phase atmospheric forcing is consistent, the dominant heat flux component and large-scale precursors vary regionally. Enhanced shortwave radiation drives peak warming in the subarctic northwest Pacific (favored during negative ENSO/PDO) and northeast Pacific (favored during positive ENSO/PDO). The three other types are driven primarily by weaker cooling via reduction in evaporation. The subtropical northeast Pacific and central Pacific types are associated with positive PDO conditions, while northwest Pacific types are associated with negative phases of the PDO/ENSO. Significance StatementMarine heat waves (MHWs), prolonged periods of anomalously high sea surface temperatures, have been associated with biodiversity loss, species mortality, altered community structures, and changes in marine species’ geographical ranges. Analyzing MHWs in a large climate model dataset enables a robust characterization of different types of MHW events in the North Pacific and allows characterization of local atmospheric drivers and linkages to large-scale climate variability modes such as the Pacific decadal oscillation and El Niño–Southern Oscillation.
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The Pacific Decadal Oscillation modulated marine heatwaves in the Northeast Pacific during past decades
Abstract The Pacific Decadal Oscillation has been suggested to play an important role in driving marine heatwaves in the Northeast Pacific during recent decades. Here we combine observations and climate model simulations to show that marine heatwaves became longer, stronger and more frequent off the Northeast Pacific coast under a positive Pacific Decadal Oscillation scenario, unlike what is found during a negative Pacific Decadal Oscillation scenario. This primarily results from the different mean-state sea surface temperatures between the two Pacific Decadal Oscillation phases. Compared to the cool (negative) phase of the Pacific Decadal Oscillation, warmer coastal sea surface temperatures occur during the positive Pacific Decadal Oscillation phase due to reduced coastal cold upwelling and increased net downward surface heat flux. Model results show that, relative to the background anthropogenic global warming, the positive Pacific Decadal Oscillation in the period 2013–2022 prolongs marine heatwaves duration by up to 43% and acts to increase marine heatwaves annual frequency by up to 32% off the Northeast Pacific coast.
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- PAR ID:
- 10500422
- Publisher / Repository:
- Nature
- Date Published:
- Journal Name:
- Communications Earth & Environment
- Volume:
- 4
- Issue:
- 1
- ISSN:
- 2662-4435
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1038/s43247-023-00863-w
