In three consecutive years from 2016 to 2018, extreme ocean warming events, or marine heatwaves (MHW), occurred during boreal summers in the East China Sea (ECS) and South Yellow Sea (SYS), which was unprecedented in the past four decades based on the satellite record. In this study, we used a high-resolution hydrodynamic model based on FVCOM (Finite Volume Community Ocean Model) to simulate the evolution of these warming events. An upper ocean temperature budget (0-20m) analysis based on the model results shows that the shortwave radiation and the ocean advection anomalies jointly contributed to the anomalous warming in the three successive summers (June-August) in the SYS and the north part of the ECS. In addition, the reduction of surface wind speeds during the 2016 and 2017 summers further weakened the vertical mixing, thereby enhancing the anomalous warming in the north part of the ECS adjacent to the SYS. During the three summers, the increases of shortwave radiation were closely related to the East Asian Summer Monsoon variability, which reduced the cloud cover in the ECS and SYS, whereas the advection anomalies were mostly associated with regional wind anomalies. In summer 2018, upper ocean heat was transported into the central trough of the South Yellow Sea, accumulated in an anticyclonic eddy generated by the anomalous wind stress curls. Understanding the drivers of the MHWs can help MHW predictions in the coastal region, in order to help the fisheries and aquaculture industries to better manage the environmental risks under a warming climate.
Abstract In 3 consecutive years from 2016 to 2018, extreme ocean warming events, or marine heatwaves (MHWs), occurred during boreal summers in the East China Sea (ECS) and South Yellow Sea (SYS), which is unprecedented in the past four decades based on the satellite record. In this study, we used a high‐resolution hydrodynamic model based on Finite Volume Community Ocean Model (FVCOM) to simulate the evolution of these warming events. An upper ocean temperature budget (0–20 m) analysis based on the model results shows that the shortwave radiation and the ocean advection anomalies jointly contributed to the anomalous warming in the three successive summers (June–August) in the SYS and the north part of the ECS. In addition, the reduction of surface wind speeds during the 2016 and 2017 summers further weakened the vertical mixing, thereby enhancing the anomalous warming in the north part of the ECS adjacent to the SYS. During the three summers, the increases of shortwave radiation were closely related to the East Asian Summer Monsoon (EASM) variability, which reduced the cloud cover in the ECS and SYS, whereas the advection anomalies were mostly associated with regional wind anomalies. In summer 2018, upper ocean heat was transported into the central trough of the SYS, accumulated in an anticyclonic eddy generated by the anomalous wind stress curls. Therefore, despite the primary driver of the MHWs is the EASM variation, regional processes are critical to driving the spatial pattern of the MHW intensity in the ECS and SYS.
The growing threat of Marine heatwaves (MHWs) to ecosystems demands that we better understand their physical drivers. This information can be used to improve the performance of ocean models in predicting major events so more appropriate management decisions can be made. Air-sea heat fluxes have been found to be one of the dominant drivers of MHWs but their impact are expected to decrease for MHWs extending deeper into the water column. In this study, we examine the most extreme MHWs occurring within an upper ocean layer and quantify the relative contributions of oceanic and atmospheric processes to their onset and decay phases. The base of the upper ocean layer is defined as the local winter mixed layer depth so that summer events occurring within a shallower mixed layer are also included. We perform a local upper ocean heat budget analysis at each grid point of a global ocean general circulation model. Results show that in 78% of MHWs, horizontal heat convergence is the main driver of MHW onset. In contrast, heat fluxes dominate the formation of MHWs in 11% of cases, through decreased latent heat cooling and/or increased solar radiation. These air-sea heat flux driven events occur mostly in the tropical regions where the upper ocean layer is shallow. In terms of MHW decay, heat advection is dominant in only 31% of MHWs, while heat flux dominance increases to 23%. For the majority of remaining events, advection and air-sea heat flux anomalies acted together to dissipate the excessive heat. This shift toward a comparable contribution of advection and air-sea heat flux is a common feature of extreme MHW decay globally. The anomalous air-sea heat flux cooling is mostly due to an increased latent heat loss feedback response to upper ocean temperature anomalies. Extreme upper ocean MHWs coincided with SST MHWs consistently, but with lower intensity in extra-tropical regions, where the upper ocean layer is deeper. This suggests that the upper ocean heat accumulation may pre-condition the SST MHWs in these regions. Our analysis provides valuable insights into the local physical processes controlling the onset and decay of extreme MHWs.
Earth and Space Science Open Archive This work has been accepted for publication in Journal of Geophysical Research - Oceans. Version of RecordESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary. Learn more about preprints. preprintOpen AccessYou are viewing the latest version by default [v1]Drivers of marine heatwaves in the East China Sea and the South Yellow Sea in three consecutive summers during 2016-2018Authors Guan-dong Gao iD Maxime Marin iD Ming Feng iD Bao-shu Yin Dezhou Yang Xingru Feng Yang Ding iD Dehai Song See all authors Guan-dong GaoiDInstitute of Oceanology, Chinese Academy of SciencesiDhttps://orcid.org/0000-0002-7348-876Xview email addressThe email was not providedcopy email addressMaxime MariniDCSIROiDhttps://orcid.org/0000-0001-7209-4454view email addressThe email was not providedcopy email addressMing FengiDCorresponding Author• Submitting AuthorCSIRO Oceans and AtmosphereiDhttps://orcid.org/0000-0002-2855-7092view email addressThe email was not providedcopy email addressBao-shu YinInstitute of Oceanology, Chinese Academy of Sciencesview email addressThe email was not providedcopy email addressDezhou YangInstitute of Oceanology, Chinese Academy of Sciencesview email addressThe email was not providedcopy email addressXingru FengInstitute of Oceanology, Chinese Academy of Sciencesview email addressThe email was not providedcopy email addressYang DingiDPhysical Oceanography Laboratory/CIMST, Ocean University of China and Qingdao National Laboratory for Marine Science and TechnologyiDhttps://orcid.org/0000-0001-9778-091Xview email addressThe email was not providedcopy email addressDehai SongKey Laboratory of Physical Oceanography, Ministry of Education, Chinaview email addressThe email was not providedcopy email address
The extreme Western Australia 2011 marine heatwave had a lasting effect on the marine ecosystem and after seven years, only parts of the ecosystem have showed good signs of recovery. After the heatwave, scallop fisheries in the Abrolhos Is. and Shark Bay were closed for 3-5 years, while the Shark Bay crab fishery was closed for 18 months; these fisheries at the centre of the heatwave have shown some improvement due to better protection of spawning stock and improved environmental conditions. Also at the centre of the heatwave, Roe's abalone suffered a catastrophic mortality and has not recovered as spawning stock remains very low. The Perth abalone stock which was outside the peak heatwave area had a major stock reduction but remained opened with reduced catches. The heatwave had a marked indirect effect on brown tiger prawns in Exmouth Gulf due to loss of seagrass habitat. The heatwave also resulted in a decline in western king prawn recruitment in Exmouth Gulf, to the north of heatwave centre, but an improved recruitment in the cooler waters of Shark Bay. Western rock lobsters near the heatwave peak also appear to have been indirectly affected and have not recovered. Factors influencing the recovery rate from the heatwave appeared to be: species near their upper temperature range and/or sensitive to warming temperatures; spatial overlap between the warming event and species distribution; whether spawning stock was affected to the point of recruitment impairment; life-cycle duration of invertebrate (or habitat) species affected; and management intervention. This study provides a framework for managing the consequences of heatwaves on fisheries by highlighting the value of early identification of the event and its effect on fisheries and having flexible harvest strategies for early management intervention. This is particularly important as long-term increases in water temperatures will increase the frequency of marine heatwave events and the fisheries stocks would have less time for recovery
Abstract Major marine heatwave (MHW) events have caused catastrophic impacts on coastal marine ecosystems. However, to date there has not been a global assessment of MHWs in coastal areas where rich marine ecosystems are at risk. Here, we combine four satellite Sea Surface Temperature (SST) products to quantify the distribution, characteristics, and decadal trend of coastal MHWs, using an ensemble approach. Hotspots of MHW stress, defined as yearly cumulative intensity, were found to be concentrated in mid latitude coasts like the Mediterranean Sea, Japan Sea, and Tasman Sea, as well as the north‐eastern coast of the United States. We found a global increase in coastal MHW frequency and duration during the past 25 years by 1–2 events per decade and 5–10 days per decade, respectively, with regional distribution closely related to decadal climate variability. Increases in frequency and duration of MHWs has led to large increases of cumulative intensity and yearly cumulative intensity, particularly in mid‐latitudes and hotspot regions. Long‐term changes in mean SST were the main driver of the observed trends of coastal MHWs, while internal variability was important for explaining local decreases in MHW metrics such as along the south‐eastern Pacific coast. MHW average metrics and trends were consistent across all four products used in this analysis, giving high confidence in the results. However, important differences between products were observed for MHW mean intensity, which was well correlated to SST variability, suggesting sensitivity of this metric to the specific SST data set and demonstrating a need for an ensemble approach to MHW analysis.
Abstract Long‐term temperature changes drive coastal Marine Heatwave (MHW) trends globally. Here, we provide a more comprehensive global analysis of cross‐shore gradients of MHW and Sea Surface Temperatures (SST) changes using an ensemble of three satellite SST products during recent decades. Our analysis reveals depressed onshore SST trends in more than 2/3 of coastal pixels, including both eastern and western boundary current systems. These were well correlated with depressed trends of MHW exposure and severity, ranging from a −2 to −10 decrease in MHW days per decade and from a −2.5°C to −15°C.days per decade decrease in cumulative intensity. Results were consistent across all satellite products, indicating that these cross‐shore gradients are a robust feature of observations. ERA reanalysis data show that neither air‐sea heat fluxes nor wind driven upwelling were found to be consistent drivers. Global ocean circulation models (OFAM3 and ACCESS‐OM2) have limited ability to simulate the depressed onshore trends. A heat budget analysis performed in the Chilean coast region, where models agree with observations, showed that the gradient of temperature change was controlled by an onshore increase of longwave radiative cooling, despite an increase in upwelling. This highlights the complexity of small‐scale coastal ocean‐atmosphere feedbacks, which coarser resolution climate models do not resolve. Here, we show that global coastal regions may act as thermal refugia for marine ecosystems from aspects of climate change and pulsative (MHW) changes. Contrary to the literature, our results suggest that driving mechanisms are region dependant, stressing the necessity to improve climate models resolution.
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