Marine heatwaves (MHWs) are prolonged periods of anomalously warm ocean temperatures, usually detected through Sea Surface Temperature (SST). Deeply connected to climate change, these extreme events signal how global warming affects the Earth’s subsystems, driving an uptick in the corresponding impacts. Key aspects related to MHWs are (i) the understanding of the MHWs drivers, (ii) the establishment of standard and (ii) the estimation of expected impacts. Through a multi-project journey, +ATLANTIC has been investigating these topics, to contribute to filling the existing knowledge gaps and to promote the societal uptake of satellite-based MHWs geospatial information.
Regarding (i) in the scope of the Horizon Europe ObsSea4Clim project, which aims to support the GCOS with novel indicators, we have been investigating the relationship between MHWs and the large-scale climate modes that modulate the North Atlantic basin climate. In addition to SST, several ocean variables, including mixed-layer depth and ocean currents, are combined with atmospheric drivers such as air-sea heat fluxes, wind speed, and sea level pressure to describe the most severe MHWs events, recognizing how pressure systems. Preliminary results indicated the importance of stable high-pressure systems in driving air-sea heat flux anomalies, particularly net, latent and sensible heat exchanges, which lead to lower wind speeds and increased energy absorption by the ocean, modulating the intensity and persistence of MHWs over the mid-latitude regions; specifically, the Portuguese EEZ.
Regarding (ii) we propose to evolve from a pixel-wise detection to an events-based labelling algorithm that allows to distinguish noisy pixel patches from meso-scale impactful events. Within the framework of XHEAT, an ESA-funded project, we are exploring the usage of ML/AI in post-processing the traditional MHWs methods to establish a novel mechanism that allows to study of specific events as a continuous element. Furthermore, it allows us to better investigate how large-scale MHWs over the North Atlantic can lead to certain continental extremes over Europe, particularly Compound Drought-Heatwaves (CDHW). Results already suggest that by adopting such techniques, more meaningful relationship patterns emerge, paving the way for probabilistic seasonal outlook predictions.
Regarding (iii) within the ESA-funded CAREHeat, the Impact Use Cases have allowed working alongside aquaculture producers to evaluate the MHW impacts in their activities. From the conducted work, several findings can be highlighted: (1) from the consulted users, all show an interest and willingness to adopt climate data on their operations, especially where local-specific indicators may impact their decision-making on short or long-term activities; nonetheless, few are capable to using geospatial products routinely; (2) the dialogue with the Early Adopters must be kept regularly, to ensure that the objective formulation of the use cases problem is scientifically sound but resonates with their needs; and (iii) biological data available is too limited to establish statistically significant relationships that span decadal time series, which hinders our capacity to measure impacts effectively, which indicates that further effort should be employed in biological data acquisition.
How to cite: Lopes, B., Oliveira, A., Silva, F., Paixão, J., Girão, I., Cunha, R., Baeta, R., Khudinyan, M., Salge, P., Barros, L., Garcia, T., Aguiar, S., and Pereira, É.: From Marine Heat Waves Drivers to Impact Use Cases: Challenges and Opportunities , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20097, https://doi.org/10.5194/egusphere-egu25-20097, 2025.
Marine heatwaves (MHWs) were shown to have devastating impacts on marine ecosystems and to influence the atmospheric circulation changing inland temperature and precipitation. While various studies utilise model and observation based datasets to detect MHWs at the surface, little is known about the characteristics and drivers of MHWs at depth. Detecting MHWs requires continuous daily temperature records over a multi-year time period, which are only scarcely available from observations, in particular in the deep ocean. Although models provide such a temporally and spatially coherent dataset, a basin-wide detection of MHWs remains challenging due to the large number of grid points, at least in realistic high-resolution models. Additionally, model biases and unrealistic model trends (‘drift’) need to be taken into consideration.
In order to fill this knowledge gap, we investigate the impact of horizontal model resolution, the choice of the temperature baseline and the impact of spurious model trends on the characteristics of MHWs at various depths. We detect MHWs over the course of more than 40 years at all three-dimensional grid points of an eddy-rich (1/20°) ocean model, covering the entire Atlantic Ocean from 34.5°S to approximately 65°N.
Our results highlight the importance of horizontal and vertical heat transport variations within the ocean on sub-surface, but also on near-surface, MHWs. The surface heat flux is important in the mixed layer, but does not affect MHWs beyond approximately the top 100 m of the ocean. As a consequence, the temporal evolution of MHWs at depth is dominated by spurious temperature trends, if this is not adequately considered by using an extensive model spin-up, or by applying a linear temperature baseline. Independent of the baseline used, we find that ocean dynamics lead to different characteristics of MHWs along the western boundary, interior and eastern boundary of the Atlantic. Furthermore, we find sub-surface MHWs to be coherent over layers of a few 100 to 1000 m thickness. These layers are closely related to the vertical structure of the temperature field.
How to cite: Schulzki, T., Schwarzkopf, F. U., and Biastoch, A.: An Atlantic wide assessment of marine heatwaves beyond the surface in an eddy-rich ocean model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8057, https://doi.org/10.5194/egusphere-egu25-8057, 2025.
Periods of anomalously high ocean temperatures, known as ‘Marine Heatwave’ (MHW), have severely affected marine organisms’ health, function, and services they provide, causing substantial biological and socioeconomic disruptions over the past few decades. While there have been many efforts to understand sea surface MHWs, our understanding of their vertical structures is relatively limited. However, subsurface MHW can have dramatic ecological impacts, and may also influence other oceanic properties (e.g., dissolved O2, pH), causing compound ocean extremes. In this study, we evaluated MHW climatology through the upper 700m during the preindustrial and recent historical times (1982-2014) using daily temperature outputs from global simulations performed with the coupled GFDL CM4 and NCAR CESM3 climate models. We evaluated shifts in the global patterns of subsurface MHW climatology and identified the predominant driving processes from the recent decades relative to preindustrial. By comparing the simulated MHW between the two models, we also analyzed the role of different representations of ocean physics and vertical coordinate types in model performance.
Model preindustrial control simulations demonstrate errors in ocean potential temperature due to temperature anomalies relative to the first year of simulation (i.e., model drift). Given the non-negligible drift shown in previous studies, we calculated the trend in daily temperature of the piControl model runs, and corrected temperatures by removing the trend over preindustrial and historical periods. We then detected MHW characteristics based on the de-drifted temperatures and systematically analyzed the influence of model drift on simulated MHWs to identify locations where the MHW metrics are most sensitive to drift-induced trends. For example, preindustrial model drifts of GFDL CM4 lead to overestimated annual peak heat intensity up to 0.1-0.4 °C over the tropical Pacific and the mid to high latitudes of the upper 700m. This suggests the trend associated with drift can induce a shifting baseline that should also be accounted for when analyzing MHWs from climate model output. Our study contributes to understanding MHW through the water column and reveals critical factors for better MHW simulation that could benefit future projection.
How to cite: Li, X., Krasting, J., and Marques, G.: Exploring Global Upper Ocean Marine Heatwaves in Coupled GFDL and NCAR models , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7612, https://doi.org/10.5194/egusphere-egu25-7612, 2025.
Marine heatwaves (MHWs) have become a major concern due to their impact on marine ecosystems. In the Arctic Mediterranean, largely based on sea surface temperature from satellite data, the annual intensity, frequency (events per year), duration, and areal coverage of MHWs have increased significantly in recent decades. In particular, a high frequency of MHWs has been shown around the Svalbard Archipelago. Based on this, we investigate patterns in MHWs around Svalbard both at the surface and subsurface, using a regional reanalysis from TOPAZ for the period 1991-2022. Overall, we find a shift in the frequency and duration around the Svalbard Archipelago, with higher values in 2011-2022 compared to 1991-2010. Analysis of eight individual summer (June-September) MHW events lasting longer than 10 days on the western side of Svalbard indicated the presence of four shallow (≤50m) and four deep (≥200m) MHWs. All events occurred after 2010. Deep MHW events were associated with an increase in ocean heat content (down to 300m), potentially connected to changes in the temperature of Atlantic Water inflow in the region. The mean duration of each event was 29 days. In terms of spatial extent, some events extended not only along the west of Svalbard but also across the Barents Sea, covering a broader area. Understanding the characteristics of MHW events including their spatial and vertical distribution, as investigated in this study, is crucial for identifying their driving mechanisms and assessing their ecosystem impact. Furthermore, as MHWs increase, it will become essential to be able to predict such events. Hence, we also present plans to use the Norwegian Climate Prediction Model (NorCPM) to evaluate the predictive skill for MHWs in the Arctic Mediterranean.
How to cite: Williams-Kerslake, M., Langehaug, H., Samuelsen, A., Keenlyside, N., Skogseth, R., Nilsen, F., and Gonzalez, S.: Characterising Marine Heatwaves in the Svalbard Archipelago and Surrounding Seas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2165, https://doi.org/10.5194/egusphere-egu25-2165, 2025.
Marine heatwaves (MHWs) have recently been recognized as extreme climate events considering their devastating impacts on marine ecosystems. Our study explored the spatial and temporal variability of short (duration < 10 days) and long MHWs in nine sub-regions around the Australian coastal region using the original (5-day) and an updated longer duration (10-day) criteria for MHW identification based on gap-free Sea Surface Temperature (SST) analyses from 1981 to 2020. By quantitatively investigating the contribution of ocean warming to short MHWs, we could consider most of the short events as background signals of a dynamic ocean surface over the Australian region. The application of the updated definition highlights areas that are more sensitive to local internal forcings, especially over the main flow of the East Australian Current. Furthermore, the Great Barrier Reef exhibit a larger increasing trend of MHW areas after excluding the short events. By numerically and graphically evaluating the relationship between the sea level anomaly (SLA) and SST metrics over two coastal regions of Australia, it is found that longer MHWs exhibiting two variation trends of large SLA metrics are ENSO dominant in the northwest coastal region (NW), and less ENSO-dominant but geographically-impacted in the southeast coastal region (SETS). However, it is possible that most short events in these two regions are a result of local and intrinsic variability or ocean warming of the water columns rather than the remote modulation of climate modes. Moreover, SLA over the 90th percentile, which successfully observed a subsurface MHW event over the NW region in 2008, has the potential to help identify subsurface MHWs, although limited by application area. Further investigation into the applicability of these, or other similar, updates to the MHW definitions may be warranted, to draw a broadly applicable conclusion to benefit detection and prediction of strong sub-surface MHWs impacting commercial and environmental activities.
How to cite: Hu, Y., Wang, X. H., Beggs, H., and Wang, C.: Intrinsic short Marine Heatwaves from the perspective of sea surface temperature and height, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2961, https://doi.org/10.5194/egusphere-egu25-2961, 2025.
Extreme events like marine heatwaves are among the most severe impacts of climate change, profoundly affecting marine ecosystems, biogeochemical cycles, and the human communities that depend on ocean resources. When these events occur simultaneously or in close sequence with other extremes, like low pH and low oxygen extreme events, they form compound events whose impacts can intensify nonlinearly. Yet, our knowledge of these events remains limited, particularly under scenarios of both rising and declining CO₂ emissions. Using the Max Planck Institute Earth System Model driven by CO₂ emissions under the emission-driven SSP5-3.4 overshoot scenario, this study explores how ocean compound extreme events evolve along a pathway marked by initial rapid emissions increases followed by steep reductions, ultimately reaching net-negative emissions.
The emission-driven simulations incorporate an interactive carbon cycle, which in this setup allows for a prognostic computation of atmospheric CO₂ and hence enables an investigation of how the global carbon cycle and climate respond dynamically to changing emissions. Previous studies have shown that under negative emissions, the ocean may transition from a sink to a source of CO₂. However, it remains unclear how this shift could influence ocean compound extreme events, potentially altering their frequency, intensity, and duration. This is especially relevant for both surface and subsurface extremes, where responses to emission changes may vary considerably.
By focusing on the SSP5-3.4 overshoot scenario, this study provides a novel perspective on the implications of emission reductions and negative emissions for marine extreme events. Linking physical and biogeochemical extremes offers a broader understanding of compound events and their interactions with the global climate system. The findings of our research will further provide guidance for future climate adaptation and mitigation strategies that consider the ocean’s critical role in a changing climate.
How to cite: Filippou, D., Li, H., and Ilyina, T.: Ocean Compound Extreme Events Under Emission Reduction and Negative CO2 Pathways, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1719, https://doi.org/10.5194/egusphere-egu25-1719, 2025.
Vertically compounded marine heatwaves (MHW) and ocean acidity extremes (OAX) impact marine biota and contract habitable space in the epipelagic zone. On a climate trend of warming, acidification, and sea ice reduction, these extreme events pose additional risks to Antarctic and Southern Ocean ecosystems. Anomalously low seasonal sea ice diminishes a critical habitat and grazing area for zooplankton and fish larvae. Co-occurring MHW and OAX impose further thermal and physiological stress on organisms that are typically adapted to narrow environmental conditions. Using a regional ocean model hindcast (1980-2019), we analysed column-compound extreme (CCX) events in temperature and the hydrogen ion concentration. Results indicate an increasing frequency of warmer and more acidic events, particularly in the Antarctic Marine Protected Areas (MPAs). These events can span over 200 000 km2 in area and persist for more than 500 days, occurring during periods of low sea ice and the positive phase of the Southern Annular Mode (SAM). Through driver attribution, we identified two main processes driving CCX. In the Antarctic zone, buoyancy changes driven by increased Ekman drift or reduced sea ice concentration, drive CCX at varying depths. In the Subantarctic and Northern zones, surface MHW can drive co-occurring OAX at or below the surface by influencing primary production, which is modulated by nutrient limitations. Overall, CCX is the Southern Ocean is found to be predominantly driven by dynamical and biogeochemical changes. These analyses elucidate the processes leading to CCX in the Southern Ocean, establishing a basis for their future predictability.
How to cite: Wong, J., Münnich, M., and Gruber, N.: Drivers of column-compound extremes in the Southern Ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2536, https://doi.org/10.5194/egusphere-egu25-2536, 2025.
El Niño typically induces cooling in the Southwest Pacific Ocean during austral summers, usually leading to decreased marine heatwave frequency and severity. However, the 2016 extreme El Niño unexpectedly coincided with the longest and most extensive marine heatwave ever recorded in the region. This heatwave, spanning over 1.7 million square kilometers, persisting for 24 days with a peak intensity of 1.5°C, resulted in massive coral bleaching and fish mortality. This exceptional warming resulted from anomalously strong shortwave radiation and reduced heat loss via latent heat fluxes, owing to low wind speed and increased air humidity. These anomalies are attributed to a rare combined event “Madden-Julian Oscillation and extreme El Niño.” Following 10 February, the rapid dissipation of this marine heatwave results from the most intense cyclone ever recorded in the South Pacific. The hazardous ecological impacts of this extreme event highlight the needs for improving our understanding of marine heatwave–driving mechanisms that may result in better seasonal predictions.
How to cite: Dutheil, C., Lal, S., Lengaigne, M., Cravatte, S., Menkès, C., Receveur, A., Börgel, F., Gröger, M., Houlbreque, F., Le Gendre, R., Mangolte, I., Peltier, A., and Meier, H. E. M.: The massive 2016 marine heatwave in the Southwest Pacific: An “El Niño–Madden-Julian Oscillation” compound event, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16822, https://doi.org/10.5194/egusphere-egu25-16822, 2025.
The East Korea Bay (EKB), located in the northwestern the East/Japan Sea (EJS), experiences the most intense and prolonged marine heatwaves within the EJS. In this study, we examine characteristics of the MHWs in the EKB from 1982 to 2018 and explore possible physical mechanisms for long-lasting MHWs using satellite data and reanalysis products. Over the 37 years, MHWs in the EKB lasted 32% longer (17±24 days) than the long-term average of the whole EJS. Notably, two exceptionally prolonged MHWs were observed, primarily during cooling seasons (fall and winter): one lasting 161 days in 2008/9 and another for 126 days in 2017/8. During these two MHWs, ocean surface cooling, predominantly driven by latent cooling, was intensified while solar heating remained near normal, suggesting that ocean processes play a crucial role in maintaining these extended MHWs. Spatiotemporal distributions of sea surface height indicate that intensified, persistent anticyclonic eddies significantly contribute to maintaining the long-lasting MHWs. A heat budget analysis further supports that the anticyclonic eddies are the primary drivers of these extended MHWs. Our findings underscore the critical role of ocean processes, including eddies and currents, in driving extremely long-lasting MHWs in the EKB within the EJS, particularly during cooling seasons.
How to cite: Jang, C. J., Jung, H., Choi, W., and Kang, N.: Long-lasting Marine Heatwaves in the East Korea Bay in the East/Japan Sea: Characteristics and drivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10889, https://doi.org/10.5194/egusphere-egu25-10889, 2025.
Extremely warm oceanic conditions, known as Marine Heatwaves (MHWs), in the Bay of Bengal, influence monsoon rainfall and cyclones; and are linked to climatic modes. These MHWs are a result of a combination of long-term ocean warming and physical processes. In this study, we segregated this impact of long-term ocean warming, from the physical processes, to understand how long-term warming influence the MHW characteristics, by a detrending baseline approach. This approach works by removing the long-term linear trend from the temperature data, which is then used to detect MHWs. We used the Ocean Reanalysis System 5 (ORAS5) dataset in this study over the period of 1993–2020, which shows good agreement with the OISST and RAMA observation on detecting the MHWs characteristics at the upper ocean. The regions with high warming tendencies showed a smaller number of the MHWs events (1-2 events at the surface) under the warming scenario but with more intensity and duration (10-20 days per event). The spatial movement of these MHWs are seen to be accompanied by western boundary currents during spring (March–May). The westward movement of the MHWs are associated with eddies during other seasons. This study helps us understand how long-term warming puts more stress on marine ecosystems.
How to cite: Bhattacharjee, A., Gupta, H., Karmakar, N., Sil, S., and Gangopadhyay, A.: Impact of Ocean Warming on Marine Heatwaves Characteristics in the Bay of Bengal, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15182, https://doi.org/10.5194/egusphere-egu25-15182, 2025.
Globally averaged sea surface temperatures were at record levels between March 2023 and July 2024. Not only were these temperatures record-breaking but they exceeded the previous record of annually averaged SSTs from 2015/16 by 0.25°C. The nearly global extent and the magnitude of this jump prompted questions about how exceptional this event was, whether climate models can represent such record-shattering jumps in surface ocean temperatures, and if global warming has accelerated. Here, we show that the sea surface temperature jump in 2023/24 that broke the old record by 0.25°C was a 1-in-512-year event under the current long-term warming trend (1-in-205-year to 1-in-1,185-year event; 95% confidence interval) based on observation-based synthetic timeseries. Without global warming, such a large jump in sea surface temperatures would have been impossible. We further used 270 simulations from a wide range of fully coupled climate models to show that these models successfully simulate such record-shattering jumps in global sea surface temperatures. The ability of these models to simulate such jumps underlines the models’ usefulness of these models for understanding characteristics, drivers, and consequences of such events. Moreover, the sea surface temperatures in the simulated jumps stop to be record-breaking between May and October in the year after temperatures started to be record-breaking. Similarly, observed sea surface temperatures also stopped to be record-breaking in July 2024, the year after the jump started. Furthermore, sea surface temperatures return to the long-term warming trend in all cases in the years following the jump. Thus, climate model simulations suggest that the record-shattering jump in surface ocean temperatures in 2023/24 was an extreme event after which surface ocean temperatures are expected to revert to the expected long-term warming trend.
How to cite: Terhaar, J., Burger, F. A., Vogt, L., Frölicher, T. L., and Stocker, T. F.: Record-shattering jump in sea surface temperatures in 2023/24 was unlikely but not unexpected, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8278, https://doi.org/10.5194/egusphere-egu25-8278, 2025.
North Atlantic Ocean circulation and temperature patterns profoundly influence global and regional climate across all time scales, from synoptic to seasonal, decadal, multi-decadal and beyond. During 2023 an unprecedented and near basin-scale marine heatwave developed during Northern Hemisphere summer, peaking in July. The warming spread across virtually all regions of the North Atlantic, including the subpolar ocean where a cooling trend over the past 50-100 years has been linked to a slowdown in the meridional overturning circulation. Yet the mechanisms that led to this exceptional surface ocean warming remain unclear. Here we use observationally-constrained atmospheric reanalyses alongside ocean observations and model simulations to show that air-sea heat fluxes acting on an extremely shallow surface mixed layer, rather than anomalous ocean heat transport, were responsible for this extreme ocean warming event. The dominant driver is shown to be anomalously weak winds leading to strongly shoaling mixed layers, resulting in a rapid temperature increase in a shallow surface layer of the North Atlantic. In addition, solar radiation anomalies made regional-scale warming contributions in locations that approximately correspond to some of the region’s main shipping lanes, suggesting that reduced sulphate emissions could have also played a localised role. With a trend toward shallower mixed layers observed over recent decades, and projections that this will continue into the future, the severity of North Atlantic marine heatwaves is set to worsen.
How to cite: England, M. H., Li, Z., Huguenin, M. F., Kiss, A. E., Sen Gupta, A., Holmes, R. M., and Rahmstorf, S.: Drivers of the unprecedented North Atlantic marine heatwave during 2023, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7537, https://doi.org/10.5194/egusphere-egu25-7537, 2025.
Marine heatwaves are periods of extreme sea surface temperatures (SSTs) which can have serious ecological and socioeconomic impacts. From a shifting baseline perspective, future changes to marine heatwaves statistics are almost entirely a result of changes to SST variance. The projected changes to SST variance in the future climate are spatially heterogeneous, with some areas experiencing less variance in the future, and others increased variance in the current generation of climate models. Moreover, the pattern of SST variance change differs between climate models. To determine the physical mechanisms behind these changes, we used a local linear stochastic-deterministic conceptual model to attribute the projected SST variance change in the extratropics to three drivers: ocean memory, El Niño-Southern Oscillation (ENSO) teleconnections, and stochastic noise forcing. We found that climate models generally agree that ocean memory will decline, resulting in decreased SST variance. Models also generally agree that the variance of the noise forcing will increase, resulting in enhanced SST variance. Changes to the ENSO teleconnection differ greatly between models, likely as a result of the substantially different future changes to ENSO in different models.
How to cite: Gunnarson, J., Stuecker, M., and Zhao, S.: Drivers of Marine Heatwaves in a Changing Climate, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3347, https://doi.org/10.5194/egusphere-egu25-3347, 2025.
The Mediterranean Sea is one of the most sensitive marine regions to climate change, with gradual warming and intensification of marine heatwaves (MHW) causing multiple environmental and socioeconomic damage. This study provides insights into sea surface temperature (SST) variability and explores the origin of MHW trends in the basin, using SST observations spanning 1982–2023. Results reveal a basin-wide increase in both mean and extreme SST, emphasized in the eastern basin. The Adriatic, Aegean and northern Levantine Seas exhibit the highest trends of SST as well as of extreme SST percentiles, identifying them as the most vulnerable Mediterranean areas. Beyond the underlying mean warming, parts of the western and central Mediterranean Sea show increased SST variability, whereas most of the eastern basin displays decreased SST variability. Our findings indicate a basin-wide dominance of mean warming over interannual variability in driving higher maximum MHW intensities, more extreme MHWs, longer heat exposure and greater accumulation of heat stress. However, interannual variability becomes the dominant driver of mean MHW intensity trends particularly in the western and central Mediterranean areas. Notably, mean MHW intensity is sensitive to the choice of the baseline climatology, suggesting a more complex nature of this metric compared to other MHW metrics. Future work should incorporate climate models, enabling a clearer distinction between the impact of anthropogenic forcing and the effect of natural variability on extreme SST events.
How to cite: Denaxa, D., Korres, G., Darmaraki, S., and Hatzaki, M.: Sea surface temperature variability and drivers of marine heatwave trends in the Mediterranean Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7943, https://doi.org/10.5194/egusphere-egu25-7943, 2025.
In 2024,the year with the warmest global temperature since 1850 (Copernicus Climate Change Service), very high temperatures were observed at regional scale.In the Mediterranean Sea,the measured sea temperature locally displayed values that were never recorded before. Satellite and in situ observationsindicate that during 2024 the Mediterranean Sea has experienced a sequence of strong marine heat waves, occurring in the months of February, April, June, and August. Thesurface temperature anomalies with respect to the 1990-2020 climatology reached about 3° C in the Algerian and Levantine basins in February, and 4-5° C in the northern part of the western Mediterranean and in the Adriatic Sea in August. Moreover, in situ observations incoastal areas oftheTyrrhenian Sea, gathered through aCitizen Scienceactivity (MEDFEVER initiative), indicated strong warming even on the seafloor, as a result of rapid heat transfer from the sea surface to the bottom. Satellite data show that surface temperature anomalies were strongly modulated by large gyres and eddies. We find that these dynamical structures control the anomalous warming induced by air-sea interactionsin regions such as the Algerian Basin, the Tyrrhenian Sea, and the Levantine basin. Estimates of mean and eddy kinetic energy from altimeter data suggest that mesoscale structures were particularly energetic during 2024 and favored warming in regions where eddy activity was intense. Model data show that themain quasi-permanent anticyclonic structures throught the basin were very effective in transferringsurface heat anomalies into the deep layers. Finally, we analyze the 2024 Mediterranean summer temperature anomaliesin relationto local and global patterns of atmospheric circulation.
How to cite: Napolitano, E., Carillo, A., Iacono, R., Struglia, M. V., Dell'Aquila, A., De Sabata, E., Bordone, A., Marullo, S., and Palma, M.: The exceptional warming in the Mediterranean Sea during 2024 , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9969, https://doi.org/10.5194/egusphere-egu25-9969, 2025.
Marine heatwaves (MHWs) are prolonged periods of extreme ocean warming that significantly impact marine ecosystems, fisheries, and aquaculture. In August 2024, northern Norway experienced one of the most intense MHWs recorded since 2012, which coincided with a sharp rise in salmon lice infestations at aquaculture sites in the area. This study investigates the atmospheric and oceanic drivers of this event, focusing on the interaction of local meteorological and oceanic conditions with large-scale climate variability. Using a combination of ocean model hindcast data (Norkyst), atmospheric reanalysis data (ERA5), and in situ observations, we characterized the MHW and identified key contributing factors. Our analysis revealed that the MHW was driven by a combination of weakened local wind patterns, high air temperatures, and strong stratification, alongside external heat supply from northward advection of warm and fresher water, facilitated by a positive phase of the summer North Atlantic Oscillation (NAO). The positive NAO phase enhanced southwesterly winds, which transported warm and humid air masses into the region, increasing the total heat flux from the atmosphere and further intensifying local warming. The ecological impacts of this MHW included increased salmon lice abundance, posing significant challenges to wild and farmed salmon populations in a region that hosts the world’s largest salmon aquaculture industry. Understanding the drivers of MHWs in northern Norway is essential for assessing their predictability and informing management strategies to mitigate their effects. This study highlights the importance of advancing regional MHW forecasting to enhance resilience in fisheries and aquaculture sectors under a warming climate.
How to cite: Gonzalez, S., Sandvik, A., Jensen, M., Sandø, A. B., Albretsen, J., Ingvaldsen, R., Vikebø, F., and Hjøllo, S.: Role of atmospheric and oceanic factors on the August 2024 marine heatwave in northern Norway, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1692, https://doi.org/10.5194/egusphere-egu25-1692, 2025.
Marine heatwaves (MHWs) have caused devasting ecological and socioeconomic impacts worldwide. Understanding the connection of regional events to large‐scale climatic drivers is key for enhancing predictability and mitigating MHW impacts. Despite the reported connection between MHWs globally and El Niño–Southern Oscillation (ENSO), establishing statistically significant links between different types of ENSO events and MHWs remains challenging due to the limited duration of observational data. Here, we use 10,000 years of simulations from a Linear Inverse Model (LIM) to address this issue. Our findings reveal distinct connections between MHWs and ENSO, with diverging influences from different flavors of El Niño and La Niña events. In addition, under long‐lasting El Niño conditions, the likelihood of MHWs increases by up to 12‐fold in the Indian and Pacific Oceans. This study highlights the global connections between ENSO diversity and variations in MHW events.
How to cite: Gregory, C., Artana, C., Lama, S., León‐FonFay, D., Sala, J., Xiao, F., Xu, T., Capotondi, A., Martinez‐Villalobos, C., and Holbrook, N.: Global Marine Heatwaves Under Different Flavors of ENSO, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1270, https://doi.org/10.5194/egusphere-egu25-1270, 2025.
The Marine heatwaves (MHWs), defined as anomalous warm seawater events disrupting marine ecosystems and commercial fisheries, have become increasingly prolonged, frequent, and intense. While these trends are partially attributed to global warming, climate variability also plays a crucial role. Using observational datasets, this study explores how large-scale climate variability over the North Atlantic Ocean strengthens MHW in the North Sea. After removing the effects of global warming, empirical orthogonal function analysis revealed that the mechanisms driving MHWs are seasonally and regionally different. In winter, the total intensity of MHW increases significantly only when the North Atlantic Oscillation (NAO) and East Atlantic Pattern (EAP) are both in their positive phases. This combination generates southwesterly wind anomalies over the English Channel, facilitating warm water transport into the southern North Sea. Simultaneously, over the northeastern North Sea, reduced geopotential height enhances precipitation, strengthening stratification and further intensifying MHWs there. When the NAO and EAP are in negative or opposing phases, easterly wind anomalies prevail, which do not contribute to strengthened MHW. In summer, the total intensity of MHW increased (decreased) during the positive (negative) phase of the Atlantic Multidecadal Oscillation (AMO). A negative AMO phase often coincides with a positive NAO phase. Their combined effects increase cloud cover over the northern North Sea, reducing net heat flux and weakening MHW. Conversely, when AMO transitions to a positive phase, it leads to a negative NAO phase after several years, weakening their connection with MHW intensification. These findings highlight the combined influence of climate variability on MHWs in marginal seas and offer insights for improving MHW predictions.
How to cite: Lin, Y., Liu, Z., and Zhang, W.: Synergistic Impacts of Climate Variabilities over the North Atlantic Ocean on Marine Heatwaves in the North Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2006, https://doi.org/10.5194/egusphere-egu25-2006, 2025.
This study investigates the interannual variability of marine heatwaves (MHWs) in the Bay of Bengal (BOB) associated with the Indian Ocean dipole (IOD) from 1982 to 2021. The results revealed a significant positive correlation at the 95% confidence level between the IOD and MHW days in the central bay at the peak of the IOD in autumn. During positive IOD (pIOD) events, the central bay experienced more MHW days in autumn, with an average increase of 7.4 days. The increased MHW days in the central bay could be primarily attributed to the enhanced net heat flux (TQ), which is 9.7 times the contribution of ocean dynamic processes (horizontal advection+entrainment). The reduced latent heat flux loss and enhanced shortwave radiation due to the anomalous atmospheric low-level high pressure associated with the pIOD account for 63%and 50%, respectively, of the anomalous enhanced TQ, while the longwave radiation and sensible heat flux make smaller contributions of 22% and 7%. In addition, thermocline deepening in the southwestern bay, caused by this anomalous high pressure and associated anticyclonic wind anomalies, favors the occurrence and persistence of MHWs by reducing the mixed-layer cooling rate. In addition to the influence of the IOD, El Niño–Southern Oscillation mainly affects MHWs from winter to the following summer, which confirms the result of a previous study.
How to cite: Qiu, Y., Liang, K., and Lin, X.: An increase in autumn marine heatwaves caused by the Indian Ocean Dipole in the Bay of Bengal, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2067, https://doi.org/10.5194/egusphere-egu25-2067, 2025.
Marine heatwaves are characterized by extended periods of warm ocean water formation in a specific area. These catastrophic events have become more common across the global oceans in recent decades, posing a serious threat to ocean ecosystems and coastal populations. Studies have also revealed that the frequency and intensity of marine heatwaves in the Indian Ocean have increased significantly in the past few decades. Previous studies of marine heatwaves in the Indian Ocean often focused on the large-scale patterns or individual heatwave events, failing to address the regional differences in their characteristics. To fill this gap, we are employing a cluster analysis technique to identify spatially homogeneous zones in the North Indian Ocean that exhibit distinct marine heatwave patterns. In this study, we delineate marine heatwaves and characterize them based on their metrics, such as maximum intensity, duration, and frequency of occurrence of an event, using a long-term dataset of sea surface temperature. Our findings reveal a diverse regional mosaic of marine heatwave characteristics. We detect distinct clusters of regions with similar heatwave patterns and regions experiencing intense and prolonged heatwaves, pointing out areas more prone to warming episodes. The findings provide crucial insights into the underlying mechanisms driving marine heatwaves and their potential impacts on marine ecosystems and fisheries. Understanding the regional heterogeneity of marine heatwaves allows us to predict better and mitigate their consequences, producing more resilient coastal populations and marine ecosystems.
How to cite: Paul, A.: Identifying Spatially Coherent Marine Heatwave Patterns in the North Indian Ocean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1083, https://doi.org/10.5194/egusphere-egu25-1083, 2025.
This study examines how a marine heatwave in the Kuroshio Extension region influenced the sustained intensity of typhoons by analyzing oceanic and atmospheric observational data. The results indicate that the anomalously high sea surface temperatures (SSTs) provided a continuous energy supply to the typhoon. During the marine heatwave, SSTs exceeded 30°C, significantly increasing the ocean heat content beneath the typhoon. Additionally, strong warm currents and reduced vertical mixing suppressed the typhoon-induced SST cooling effect, maintaining a warm ocean environment. Atmospherically, the marine heatwave led to higher moisture content and atmospheric instability, promoting sustained deep convection. These factors collectively enabled the typhoon to maintain its super typhoon intensity at higher latitudes, beyond the typical regions favorable for typhoon development. This case study highlights the critical role of marine heatwaves in modulating typhoon intensity, especially in regions like the Kuroshio Extension where intensification is usually inhibited. The findings are significant for improving typhoon intensity prediction models, particularly in the context of global climate change where marine heatwave events may become more frequent. Understanding the interaction mechanisms between marine heatwaves and typhoons can enhance disaster warning capabilities and reduce risks for coastal communities.
How to cite: Ji, J.: A Case Study of Typhoon Intensified by the Marine Heatwave in the Kuroshio Extension Region, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1618, https://doi.org/10.5194/egusphere-egu25-1618, 2025.
Mechanistic understanding of marine heatwaves (MHWs) requires a suitable definition for their detection, an approach to characterise their evolution, and an effective method to understand their causality. Much of our recent knowledge regarding MHWs has been achieved using a point-wise statistical definition that quantitatively defines MHWs as measurable warm ocean temperature extremes relative to a given threshold. While this commonly used definition is easy to use, with MHWs readily detectable and with near-global coverage from satellite sea surface temperature data, it does not quantify the spatial scale of events, their evolution in space and time, nor the association of that evolution with the key drivers. To overcome some of these limitations, more recent studies have investigated the evolution of MHWs as objects evolving in space and time to help broaden our understanding of MHWs. Our new approach represents an important step toward mechanistically characterising the space and time evolution of MHWs – it not only builds upon and extends object-based kinematic studies of MHWs but additionally connects these spatiotemporally evolving MHWs with their key drivers. Finally, we examine the potential predictability of these MHWs based on a linear inverse modelling approach.
How to cite: Holbrook, N., Zhao, Z., Capotondi, A., Cravatte, S., Kajtar, J., and Sen Gupta, A.: Toward a mechanistic characterisation of marine heatwaves, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2652, https://doi.org/10.5194/egusphere-egu25-2652, 2025.
Marine heatwaves (MHWs) are not a phenomenon confined to local areas. Instead, they may interact with other regions through specific teleconnection patterns. Numerous studies have revealed the occurrence, variability, and future trends of MHWs. However, the connections between MHWs in different regions still require further research. This study employed observational data and combined with climate model simulation results to investigate the lead-lag teleconnections of MHW between the equatorial Western Indian Ocean and the Caribbean Sea on seasonal timescales and explain the underlying mechanisms. MHWs in the equatorial Western Indian Ocean trigger atmospheric upward motion, initiating a westward-propagating Indian Ocean-Pacific-Atlantic (IPA) wave train. Influenced by the IPA, anomalous Hadley circulation and atmospheric warming occur above the Caribbean Sea, leading to intensification through increased downward latent heat flux. The IPA facilitates a close teleconnection between the MHW processes in the two ocean basins, which enables the transfer of energy and climate signals across regions, thereby further intensifying MHWs in the Caribbean Sea region.
How to cite: Li, Z. and Li, J.: Caribbean Sea Marine Heatwaves tide to Indian Ocean Marine Heatwaves , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4233, https://doi.org/10.5194/egusphere-egu25-4233, 2025.
The SouthWestern Atlantic Ocean (SWA) is undergoing significant changes as a result of climate change, including progressive sea surface warming, altered wind patterns, the poleward migration of western boundary currents, and an increase in the frequency and intensity of climate-driven variability events. Within the SWA, the Patagonian Shelf (PS), extending from the southern tip of South America (~55°S) to the Brazil/Malvinas Confluence (~38°S), stands out as one of the most biologically productive regions and a globally relevant carbon sink. Marine heatwaves (MHWs) have doubled in frequency over recent decades, lasting longer and becoming more severe. The consequent abrupt temperature shifts can significantly impact phytoplankton community structure and productivity while disrupting essential marine biogeochemical processes such as oxygen production and respiration, carbon sequestration, and nutrient cycling. However, knowledge on MHWs in the PS is scarce.
The present study focuses on characterizing MHWs in the PS by analyzing their spatial and temporal variability. Two methodologies were applied to four daily sea surface temperature (SST) datasets to determine the most suitable approach to identify MHWs in the study area. Key metrics for MHW characterization included the frequency of occurrence (MHW/year), mean intensity (SST anomaly, °C), and duration (number of days). These metrics were analyzed in relation to regional climatology, seasonality, and long-term trends. Notably, within the PS, where SST anomalies are relatively modest, both MHW identification approaches proved to be effective. Our results reveal an increasing trend in MHW days, particularly in the northern PS, where a strong correlation between MHWs and ENSO events is observed.
How to cite: Delgado, A. L., Combes, V., and Basterretxea, G.: Marine Heatwaves on the Patagonian Shelf, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11643, https://doi.org/10.5194/egusphere-egu25-11643, 2025.
Marine heatwaves (MHWs) in the Northwest Atlantic are known to significantly impact the lifecycle of tropical cyclones, due to sustained increases in the absolute sea surface temperatures (SSTs). However, MHWs can also have a notable impact on the structure and strength of the Gulf Stream SST gradient. Recent studies have shown variations in SST gradient can promote completion of extra-tropical transition of tropical cyclones passing through the region through modulation of the air-sea differential heat flux gradient. Extra-tropical cyclones present significant threats to large populations along the east coast of North America and also in Europe, which differ from the hazards brought by tropical cyclones. This study conducts a suite of Weather Research and Forecasting model simulations of Hurricane Sandy (2012) with SSTs perturbed by anomalies typically observed during October MHW events. It is demonstrated and quantified for the first time that MHW strength, through SST gradient modulation, can have a considerable impact on tropical cyclone extra-tropical transition. As such, better understanding of MHW drivers can potentially lead to better prediction of extra-tropical transition and therefore allows society to better prepare for impacts of landfalling storms.
How to cite: Kitch, K. and Parfitt, R.: Impact of marine heatwaves on the extratropical transition of North Atlantic tropical cyclones, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14376, https://doi.org/10.5194/egusphere-egu25-14376, 2025.
Marine heatwaves (MHWs) are extreme warming events in the ocean that can significantly impact marine ecosystems and economies. While such extreme events have garnered significant research attention in recent years, most research to date took an Eulerian perspective, that is, they considered MHW as stationary objects. This disregards the fact that MHW are three dimensional objects that tend to propagate in space and time.
In this study, we overcome this limitation and employ marEX, a novel method inspired by Ocetrac, to analyze and track MHWs globally. We limit outselves here to surface MHW, but the method is designed to extend to depth. Starting from a grid-level 95th percentile threshold-based detection following (A.J. Hobday et al., 2016), this method first creates coherent two-dimensional MHW objects by detecting contiguous regions of extreme sea-temperature anomalies at each time step. These regions are then linked over time using robust criteria that account for both merging (when two or more MHW regions combine into one) and splitting (when a single MHW divides into separate regions). This is achieved by tracking each piece of an event individually while maintaining links between them. This ensures that the full lifecycle of each MHW, including interactions between different events, is accurately recorded.
We test this method using ~40 years of simulated sea-surface data from the European Eddy RIch Earth System Models (EERIE) project. We find that most MHWs tend to form and dissipate in the same regions, indicating persistent hotspots for their development and termination. But there are also a substantial number of MHWs that persist for several months and propagate substantially, akin to the North Pacific “Blob event”. While the tracked MHW have, on average, a duration of ~14 days, the longest one propagated for as long as 520 days. These findings underscore the value of tracking MHWs as dynamic events, demonstrating that their propagation pathways and lifecycles hold crucial information.
How to cite: Ferri, E., Wienkers, A., Gruber, N., and Münnich, M.: Global propagation of marine heatwaves, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12816, https://doi.org/10.5194/egusphere-egu25-12816, 2025.
Marine heatwaves (MHWs) are characterized by exceptionally high ocean temperatures that persist over extended periods, leading to abrupt and profound changes in marine biodiversity and ecosystem functioning. These events have garnered increasing attention from both the research community and societal stakeholders due to their significant implications for economic activities, including fishing and aquaculture. Over the past decades, climate change has modified the frequency, duration and intensity of MHWs in the Mediterranean Sea, urging the need for precise characterization of current and future events.
ObsSea4Clim is an EU project dedicated to improving sustained and multipurpose observations vital to European and global climate requirements. The project aims to develop new regional indicators for MHWs to enhance understanding and monitoring of marine extremes, ultimately contributing to more effective ocean management and climate adaptation strategies. Within the framework of ObsSea4Clim, the CMCC is committed to advancing knowledge on MHWs by establishing and evaluating these new indicators in reanalysis datasets, historical simulations, and projection scenarios provided by Earth System Models (ESMs). We will show preliminary results on how MHWs indicators are represented in the Mediterranean Sea across different downscaling products from the MedCORDEX initiative and their parent ESMs. In particular, we aim to highlight the added value given by such downscaling exercise in the assessment of present and future MHWs characteristics in the Mediterranean Sea. This work represents the first step in determining minimum requirements, such as resolution and frequency, necessary for accurately representing MHWs indicators in the next generation of climate models (CMIP7).
How to cite: De Rovere, F., Bonino, G., McAdam, R., Scoccimarro, E., Gualdi, S., and Masina, S.: Marine Heatwaves in the Mediterranean Sea: a comparative analysis of CMIP6 and MedCORDEX model outputs, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19797, https://doi.org/10.5194/egusphere-egu25-19797, 2025.
Marine heatwaves (MHWs) are defined as discrete periods of anomalous ocean warming. In the most commonly used MHW determination method, the threshold over which a certain temperature is considered a MHW is calculated using a fixed baseline constructed from a common climatology (1982-2001). By this definition, these phenomena have been increasing in frequency and intensity due to global warming, and it is expected to ultimately lead to a saturation point. Significant efforts have been directed towards developing new ways of defining marine heatwaves motivated by the need to differentiate between long-term temperature trends and extreme events. The Mediterranean Sea serves as an ideal backdrop for comparing different MHW detection methods due to its rapid response to climate change, with higher warming trends than the global ocean. In this work, we evaluate sea surface temperature trends in the Balearic Sea, a subregion of the western Mediterranean, and compare the fixed baseline MHW detection method with two recently developed alternative methodologies. The first alternative employs a moving climatology to adjust the baseline, while the second method involves detrending the temperature data before detecting MHWs with a fixed baseline. Our analysis reveals a statistically significant warming trend of 0.036 ± 0.001°C per year, which represents an increase of ~10% compared to previous studies in the same region due to the inclusion of two particularly warm recent years, 2022 and 2023. Regarding MHWs, all three methods identify major events in 2003 and 2022. However, the fixed baseline method indicates an increase in MHW frequency and duration over time, a tendency not detected by the other methodologies, since we are isolating the extreme events from the long-term warming trend. This study underscores the importance of selecting an appropriate MHW detection method that aligns with the intended impact assessments. Studies performed with a moving baseline or detrended data could be more appropriate to analyse species with higher adaptability, while a fixed baseline could be a better option to study species less adaptable and more sensitive to exceeding a critical temperature threshold.
How to cite: Fernandez-Alvarez, B., Barceló-Llull, B., and Pascual, A.: Tracking Marine Heatwaves in the Balearic Sea: Temperature Trends and the Role of Detection Methods , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3343, https://doi.org/10.5194/egusphere-egu25-3343, 2025.
Marine Heat Waves (MHW) are heat extrema in the ocean, with temperature significantly exceeding climatological standards. They can greatly impact ecosystems, coral reefs, and fisheries, in particular in insular economies. Polynesia is wide archipelago in the South Pacific ocean, highly dependent on marine resources for its economy, to which MHW are an increasing threat.
MHW are monitored since 2 decades using remote-sensing and in situ data, and in some cases assimilated simulations. There is already an observed trend of increased MHW frequency in various part of the world ocean. Additionnally, MHW dissipation was observed in several studied cases to be linked with strong winds and high-frequency atmospheric events (e.g. tropical cyclones). Polynesian seamounts are also active internal tides generation hotspots. Internal tides increase vertical mixing and can decrease sea surface temperature, hence tides could also locally impact MHW dynamics. However so far none of these drivers has been systematically investigated.
Here we explore the sensibility of MHW to these physical drivers, in a case study in the Polynesian archipelago and using free (non-assimilated) 3D realistic simulations with the CROCO model. Air-sea fluxes are parametrized from ERA5 atmospheric reanalysis. Tides have a significant impact on sea surface temperature, but not on the heat wave. On the other hand high-frequency atmospheric forcing is shown to greatly affect MHW regional extent and dissipation. Last, Sensitivity to model grid resolution is also investigated to assess reliability of MHW forecasting skills.
How to cite: Barboni, A., Renault, L., Conejero, C., Menkes, C., Cravatte, S., and Boucharel, J.: Marine Heat Wave sensibility to tidal and atmospheric forcing, case study in French Polynesia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9168, https://doi.org/10.5194/egusphere-egu25-9168, 2025.
Marine heatwaves (MHWs) impact aquatic respiration and contribute to oxygen depletion in marine ecosystems. Understanding the frequency, intensity, and spatial extent of MHWs is critical for predicting ecosystem health. We argue that understanding the spatio-temporal variability and long-term trends of MHWs is essential for marine conservation planning, as managing cumulative impacts would require reducing other environmental stressors from regions where higher impacts of MHWs are to be expected.
We analyze past MHW events in the Gulf of Bothnia, a subbasin of the Baltic Sea, using historical measurements starting from the beginning of the 1900s. The characteristics of the past heatwave events are compared to MHWs up to year 2100, identified from modeled future projections. The future projections are based on NEMO ocean circulation model, forced with dynamically downscaled atmospheric conditions under RCP4.5 and RCP8.5 emission scenarios. During the observational period, we see decadal variability dominate over the increasing long-term trend in mean temperature. The projections indicate that by the end of this century, the increasing temperature signal exceeds the decadal variability, leading to longer and more frequent MHW events.
How to cite: Haapaniemi, V., Siiriä, S.-M., Nummelin, A., and Haapala, J.: Marine heatwaves in the Gulf of Bothnia from historical measurements to future projections , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9732, https://doi.org/10.5194/egusphere-egu25-9732, 2025.
