The investigation of future marine heatwave (MHW) trends in a changing climate is seriously hindered by the inability of current-generation global climate models (GCMs) to accurately reproduce high-frequency sea surface temperature (SST) variations. This limitation of GCMs is due to their coarse resolution and lack of parameterization for important small-scale processes. In this study, we introduce a novel hybrid model that combines low-frequency GCM simulation data with a machine learning (ML) component to incorporate realistic high-frequency SST variations. The ML model component is trained on 42 years of historical ERA5-reanalysis data. The hybrid model serves as a computationally inexpensive add-on to incorporate realistic high-frequency SST variability into existing GCM ensemble simulations or other low-frequency SST products. We demonstrate that the hybrid model yields MHW statistics that more closely align with past observations compared to data derived solely from MPI-ESM1.2-LR, a commonly used GCM. In particular, the well-known bias of GCMs towards longer and less frequent MHWs vanishes entirely in the hybrid model. We then utilize the hybrid model to examine the temporal evolution of MHW statistics on the North-West European Shelf (NWES) from 1850 to 2100, across multiple state-of-the-art CMIP6 scenarios. MHW statistics are projected to saturate in the future, leading to a counterintuitive decrease in event frequency. A return period analysis reveals that extremely long-lasting MHWs are expected to become 100 times more likely by the end of the century, with cumulative intensities reaching levels that were virtually impossible during pre-industrial times.

The Kuroshio intrusion into the South China Sea (SCS) through the Luzon Strait (LS) exhibits three different paths-looping, leaping, and leaking. In this study, a high-resolution Oceanic Regional Circulation and Tide Model is employed to investigate these pathways by calculating the Kuroshio SCS Index (KSI), coupled with a comprehensive diagnostic analysis of the vorticity balance to explore the controlling dynamic mechanisms. The results reveal that the KSI exhibits seasonal variations, with the leaping path predominantly occurring in summer, the looping path primarily prevailing in winter, and the leaking path mainly emerging in spring and autumn. The spatial distribution of the advection of geostrophic potential vorticity (APV) transport reveals two key regions within the LS that are critical to the Kuroshio intrusion into the SCS. The Joint Effect of Baroclinicity and Relief (JEBAR), serving as the dominating forcing term, balancing the APV term; its intensity is significantly affected by upstream Kuroshio transport (KT) via modulating the local horizontal density gradient: stronger KT homogenizes the water mass, weakening JEBAR and favoring the formation of the leaping path, while weaker KT enhances density-topography coupling, strengthens JEBAR, and promotes the formation of the looping path; intermediate conditions give rise to the leaking path. This study provides a general dynamic framework for understanding the multiple pathways of Kuroshio intrusion, offering insights into the circulation in the SCS.

Long-term reanalysis data from the Bluelink ReANalysis 2020 (BRAN2020) are used to investigate temperature variability from 2010 to 2020 in the Jailolo Strait-Halmahera Sea, which is part of the Indonesian Throughflow (ITF) eastern route. The analysis shows that net surface heat flux (NSHF) mainly affects semiannual mixed layer temperature (MLT) variability. Vertical turbulent mixing cools the mixed layer from below, while the vertical and horizontal advection have less impact on the MLT heat budget. In the upper thermocline (40-100 m), two temperature minima occur: one in April due to outflow to the Pacific Ocean, and another in August due to uplifted water. Different cooling processes mark the dominant annual variation in the mid thermocline (100-150 m depth) and the lower thermocline (150-200 m). The cooling process is mainly associated with the transport from the Pacific Ocean into the Indonesian Seas (inflow) in the mid-thermocline, while it is generally related to the outflow transport in the lower thermocline. Interannual temperature variation is marked by the relatively colder (warmer) sea surface temperature and shallowing (deepening) thermocline during the El Nino (La Nina) period, which is associated with the upwelling (downwelling) Rossby wave propagation. It is also found that the colder (warmer) temperature in the upper 200 m during the El Nino (La Nina) period correlates with the weaker (stronger) inflow from the Pacific Ocean into the Indonesian Seas.

The potential impact of the future mean sea level rise (SLR) on residence times in back-reef lagoons remains uncertain. This study employs a hydrodynamical model and a tracer model to investigate the repercussions of SLR on residence times. Two scenarios are considered: one with a growing fringing reef, maintaining a semi-closed lagoon, and the other where the fringing reef overflows due to SLR, facilitating direct cross-reef ocean water exchange. The results reveal a nuanced picture of how SLR-induced changes in fringing reef dynamics influence residence times. In the growing reef scenario, where the lagoon remains semi-closed, a decrease in residence time of less than 10% is projected under SLR scenarios. However, in the non-growing scenario with overflow, allowing direct cross-reef exchange, a substantial 20%–40% decrease in residence time compared to the present state is observed. The probability density distribution of residence times throughout the year exhibits significant differences between the two scenarios. Particularly, the non-growing reef case displays a higher probability of residence time less than 10 h. Seasonal variability in cross-reef exchange contributions is attributed to coastal monsoon winds. The onset of the summer monsoon introduces an inter-annual variability in the contribution of cross-reef exchange to lagoon-ocean water exchange. This finding has broader implications for similar coastal back-reef lagoon systems, offering insights into estimating future global changes in residence times. In summary, this study emphasises the pivotal role of SLR-induced reef changes in shaping the dynamics of lagoon-ocean water exchange. The intricate interplay between fringing reef growth and overflow under SLR scenarios significantly influences residence times, with potential implications for the broader understanding of coastal back-reef lagoon systems. The findings contribute valuable insights into the complex interactions between climate-induced sea level changes and coastal ecosystems, guiding future assessments of global residence time variations.

In order to implement successful coastal management and protect corals, it is imperative to understand the Nha Trang Bay’s coastal processes and take adequate measures to protect corals and reef structure. This paper aimed to analyze whether sudden variations in physical parameters, such as temperature, could be potentially harmful to coastal coral reefs, in addition to anthropogenic factors such as pollution and intensive fishing. In this paper, the first long-term observation (2008–2019) of temperatures, not only from SST data, but also in situ in coral reefs (10 and 18 m depth) at Nha Trang Bay, South Central Vietnam, was investigated. The data showed that wind-induced upwelling during summer mainly govern the coastal region. In contrast, wind-induced downwelling was found during winter, visible in all three investigated water layers (SST, 10 and 18 m). In winter, the vertical mixing is strong and there is virtually no time-lag between the layers. In summer a scattering layer was formed, the phenomenon where a layer of water with different properties (such as temperature or salinity) is formed, blocking the sinking of water. In summer, correlations with air temperature were not significant, nor were correlations with night cooling, thus having implications for the distribution of nutrients and the health of the coral reefs. However, this was only the situation near the coast. Wavelet analysis shows that the short-term variability is significantly more substantial, caused by the shallow depth of the thermocline, which is much stronger affected by tidal and weather events than in winter. As a result of the combination of large yearly temperature variations (21oC to 31oC) plus increased sediment deposition in the rainy seasons, reefs close to the shore are generally not well-developed. This paper strongly advocates for science-based monitoring of coral reef conditions and underscores the need for law enforcement within the Marine Protected Area of Nha Trang Bay.

The cross-shelf carbon transports across a section along the 100 m isobath from Taiwan to Cheju are estimated based on carbon concentration observations and ocean currents simulated by a regionally zoomed ocean-atmosphere coupled model. Results show that the net cross-shelf particulate organic carbon, dissolved organic carbon, and dissolved inorganic carbon transports are in the offshore direction at 1.81 +/- 0.22, 51.8 +/- 2.85, and 783 +/- 58.9 TgC yr-1, respectively, which are high in spring and summer and low in winter and fall following the seasonality of the offshore volume transport. The carbon is transported into the East China Sea (ECS) mainly by the Taiwan Warm Current and the Yellow Sea Warm Current, whereas they are carried out of the ECS mainly by the East China Sea Current extension and the recirculation north of Taiwan. Assuming steady biological activity, future net total organic carbon transports are projected to increase by 5%similar to 19% offshore at the end of the 21st century, with the maximum increase in winter, in a high greenhouse gas emission scenario of RCP8.5. The increased carbon transports are due to the increased offshore volume transport, transferring more carbon-rich coastal water away from the shelf in the warming future than at present. The results quantify cross-shelf carbon burial in the ECS in the background of global warming. Carbon transport due to water exchange between the continental shelf and the open ocean is one of the most important components of the world ocean carbon budgets. In this study, the cross-shelf carbon transport in the East China Sea (ECS) is estimated based on in situ carbon concentration observations and simulated ocean currents by an ocean-atmosphere coupled model. The use of the simulated currents is to avoid a bogus volume surplus in the estimates of the carbon transports. The offshore and the onshore volume transports, with significantly different carbon concentrations, are found to have a strong seasonal cycle and increase in the background of global warming, both of which are much larger than their difference, a.k.a. the net volume transport. As a result, the net cross-shelf carbon transports are in the offshore direction and are high in spring and summer and low in winter and fall. The organic carbon transports are projected to increase due to the ongoing global warming. These changes in the carbon burial need to be considered when assessing the impact of human activities and warming on the global carbon cycle. Our work would provide scientific evidence for increasing carbon sinks in the ECS in the warming future. Carbon transports across the ECS shelf were estimated based on carbon concentration observations and simulated currentsOffshore carbon transports are found induced by the ECSC from the inner shelf to the shelf breakThe organic carbon transports are projected to increase with the global warming at the end of the 21st century

Features and mechanism of intraseasonal cyclonic and anticyclonic eddy generation in the northeastern Bay of Bengal (NE-BoB) are investigated using satellite observations, ocean reanalysis, and related wind forcing data. Our results suggest that the intraseasonal cyclonic (anticyclonic) eddies generated in the NE-BoB can be primarily attributed to intraseasonal easterly (westerly) wind anomalies in the equatorial Indian Ocean, which provokes the upwelling (downwelling) Kelvin wave (KW) traveling along the equator and subsequently the eastern boundary through the Preparis Channel into the NE-BoB. Anomalous equatorial zonal wind can result in a strong intraseasonal subsurface flow along the KW waveguide located on the continental slope, and this KW-associated subsurface flow is essential to the formation process of both anticyclonic and cyclonic eddies in the NE-BoB. A seasonal difference in the response of sea level anomaly (SLA) to the KW-associated subsurface flow is revealed, which can be explained by the seasonal variability of stratification along the waveguide. The eddy related SLA shows a considerable correlation coefficient of -0.58 with the accumulated transport caused by KW-associated subsurface flows through the Preparis Channel when it lags 18 days, indicating a possible eddy generation mechanism that the KW-associated subsurface flow dominated net horizontal inflow (outflow) causes vertical stretching (shrinking) of the subsurface layer, which in turn triggers an anticyclonic (cyclonic) eddy.

Phthalate esters (PAEs) have been investigated in paired air and seawater samples collected onboard the research vessel SONNE in the South China Sea in the summer of 2019. The concentrations of ∑7PAEs ranged from 2.84 to 24.3 ng/m3 with a mean of 9.67 ± 5.86 ng/m3 in air and from 0.96 to 8.35 ng/L with a mean of 3.05 ng/L in seawater. Net air-to-seawater deposition dominated air-sea exchange fluxes of DiBP, DnBP, DMP, and DEP, while strong water-to-air volatilization was estimated for bis(2-ethylhexyl) phthalate (DEHP). The estimated net atmospheric depositions were 3740 t/y for the sum of DMP, DEP, DiBP, and DnBP, but DEHP volatilized from seawater to air with an average of 900 t/y. The seasonally changing monsoon circulation, currents, and cyclones occurring in the Pacific can significantly influence the concentration of PAEs, and alter the direction and magnitude of air-sea exchange and particle deposition fluxes. Consequently, the dynamic air-sea exchange process may drive the transport of PAEs from marginal seas and estuaries toward remote marine environments, which can play an important role in the environmental transport and cycling of PAEs in the global ocean.

Organophosphate esters (OPEs) have become one group of chemicals with emerging concern in the marine environment. In this work, we investigated OPEs in the air and seawater of the South China Sea in summer 2019. The concentrations of ∑10OPEs in the atmosphere ranged from 66 to 550 pg/m3, with TCIPP, TNBP, TPhP, and TEP predominating in the air. The total dissolved OPE concentrations (∑10OPEs without TEP) measured in high-volume water samples ranged from 300 to 3600 pg/L, with a mean concentration of 1180 ± 910 pg/L. TEP was measured with liquid-liquid extraction (LLE), and it showed the highest concentration (average 2000 ± 1450 pg/L) among the selected OPEs. Total suspended matter associated OPEs accounted for less than 4.7% of the sum of OPE concentrations in seawater. Fugacity fractions and air-sea exchange fluxes showed that TCEP, TCIPP, TIBP, TEHP, TPhP, and EHDPP were favored to volatilize, TEP dominated the deposition, while TPrP and TNBP varied between volatilization and deposition. Atmospheric particle deposition fluxes ranged from 5 to 71 ng/m2/day with an average of 17 ± 15 ng/m2/day. The input of ∑OPEs to the entire South China Sea via atmospheric particle deposition was estimated to be 22 ± 19 tons/year, while the net air-sea exchange fluxes of OPEs were volatilization from seawater to air with an average of 44 ± 33 tons/year. This work suggests that air-sea exchange and atmospheric particle deposition are significant processes interfering with the transport of OPEs in the marine environment.

The Indonesian Seas play an important role in the marine global environment, from the oceanographic point of view as well as from the bioenvironmental perspective, since a large population of nearly 400 million people is living directly or indirectly in contact with these waters affecting the marine environment. In this chapter, we describe the history of oceanographic research in this region, the role of the Indonesian Seas in the global circulation, the most important features of the regional circulation, the distribution of tides, water exchange rates, and freshwater sources and sinks for certain subregions, and the effect of global warming as it is detectable nowadays already. Furthermore, we explain how satellite-derived data in connection with biooptical in situ measurements can support the investigation of the marine environment in a vast region, especially in coastal waters with respect to river discharge, transport of suspended matter, and primary production. Perairan Indonesia memegang peranan penting dalam lingkungan laut global, mulai dari sisi oseanografis hingga ke perspektif lingkungan hidupnya, karena hampir 400 juta orang hidup berinteraksi baik secara langsung maupun tidak langsung dengan perairan yang berdampak pada lingkungan laut. Dalam bab ini dijelaskan sejarah penelitian oseanografi di wilayah ini, peran perairan Indonesia dalam sirkulasi global, fitur paling penting dari sirkulasi regional, distribusi pasang surut, percampuran air dan sumber air tawar dan pengurangannya untuk sub-daerah tertentu, serta efek dari pemanasan global yang sudah dapat dideteksi saat ini. Selanjutnya, kami menjelaskan bagaimana data satelit yang berhubungan dengan pengukuran in situ bio-optik dapat mendukung penelitian lingkungan laut di wilayah yang luas, terutama di perairan pesisir dengan adanya debit sungai, pengangkutan bahan-bahan tersuspensi dan produksi primer.

The operational principle of offshore wind farms (OWF) is to extract kinetic energy from the atmosphere and convert it into electricity. Consequently, a region of reduced wind speed in the shadow zone of an OWF, the so-called wind-wake, is generated. As there is a horizontal wind speed deficit between the wind-wake and the undisturbed neighboring regions, the locally reduced surface stress results in an adjusted Ekman transport. Subsequently, the creation of a dipole pattern in sea surface elevation induces corresponding anomalies in the vertical water velocities. The dynamics of these OWF wind-wake induced upwelling/downwelling dipoles have been analyzed in earlier model studies, and strong impacts on stratified pelagic ecosystems have been predicted. Here we provide for the first time empirical evidence of the existence of such upwelling/downwelling dipoles. The data were obtained by towing a remotely operated vehicle (TRIAXUS ROTV) through leeward regions of operational OWFs in the summer stratified North Sea. The undulating TRIAXUS transects provided high-resolution CTD data which enabled the characterization of three different phases of the ephemeral life cycle of a wind-wake-induced upwelling/downwelling dipole: development, operation, and erosion. We identified two characteristic hydrographic signatures of OWF-induced dipoles: distinct changes in mixed layer depth and potential energy anomaly over a distance < 5 km and a diagonal excursion of the thermocline of ~10–14 m over a dipole dimension of ~10–12 km. Whether these anthropogenically induced abrupt changes are significantly different from the corridor of natural variability awaits further investigations.

A three-dimensional baroclinic nonlinear numerical model—the Hamburg Shelf Ocean Model (HAMSOM)—was applied to investigate the effects of the Indonesian throughflow (ITF), river runoff, and tidal forcing on circulation during the southeast monsoon period (July 2004) north of the Aru Islands by conducting different sensitivity runs. It was found that the Ekman transport over the continental slope of the Sahul Shelf was the main factor that causes upwelling north of the Aru Islands, and this was suggested to be one of the main factors behind the surface water in the research area being relatively colder and saltier than the surrounding waters. The influence of South Pacific Subtropical Water (SPSW) on the surface water was indicated by the high surface salinity of waters within the internal salinity maximum layer. The results also suggested that onshore subsurface currents over the slope were induced not only by offshore surface currents over the slope but also by the ITF. By considering the eastern ITF route, river runoff and tidal forcing were also found to contribute significantly to the erosion of the salinity maximum (approx. 0.25) within the Halmahera Sea, thereby reducing sea surface salinity north of the Aru Islands. Furthermore, it was proposed that river runoff from the western coast of Papua Island contributed to intensified cross-shelf circulation over the continental slope. These conditions were related to enhancing vertical viscosity forces in the surface waters induced by stronger stratification as an impact of river inclusion in the simulation.

The cross-shelf exchange between the Yellow and East China Seas (YECS) with the Kuroshio is important for vorticity, freshwater, and effluence balances of the regional and global oceans, the responses of which to future climate changes are estimated based on Max-Planck coupled model simulations under one historical (20C, 1970–2005) and two representative concentration pathway scenarios of global warming (RCP4.5 and RCP8.5) from 2006 to 2099. The results of the 20C simulation have shown prominent cross-shelf transports in the YECS, with annual mean outflow (OVT) and inflow (IVT) volume transports across the 100 m isobath of 3.97 Sv and 2.86 Sv (1 Sv = 106 m3 s−1), respectively. These annual mean OVTs (and their equivalent IVTs) are projected to increase by 0.42 Sv and 0.48 Sv from 2006 to 2099, at rates of 11.0% and 12.8% from the 2006–2016 means, under the RCP4.5 and RCP8.5 scenarios, respectively. The maximum rates of increase are found in winter to be at 13.2% and 19.9%, respectively. Analyses suggest that the winter monsoon has a long-term southwesterly change, forcing coastal currents to flow into the Yellow Sea along the China coasts to compensate for the increase of the southeastward surface Ekman transport. Due to increases of the Tsushima Strait and upper-layer Kuroshio transports, both the OVT and IVT across the 200 m isobath have onshore changes, resulting in net onshore transport increments of 0.30 Sv and 0.57 Sv under the RCP4.5 and RCP8.5 scenarios, respectively. The enhanced cross-shelf exchanges under future warming scenarios in the YECS suggest their potential importance in carbon transportation and storage.

The characteristics and variability of intraseasonal internal coastal Kelvin waves (CKWs) along the Bay of Bengal (BoB) waveguide are investigated in the context of global warming by employing a regional ocean model. The analyzed period covers 120 years from 1980 to 2099, which includes the historical scenario and the RCP8.5 scenario. CKW information is successfully extracted from the temperature anomalies along the pycnocline by applying a newly developed methodology. The analysis reveals that intraseasonal CKWs in the BoB are highly in accordance with the intraseasonal zonal wind stress in the western equatorial Indian Ocean; the downwelling CKW lags the equatorial intraseasonal westerly winds, and the upwelling CKW lags the equatorial intraseasonal easterly winds. The CKWs significantly affect subsurface characteristics at the eastern BoB boundary, and the weakening of CKWs near the Irrawaddy Delta tip is a general feature occurring in the subsurface. With respect to the long-term scale, the occurrence of significant CKWs is predicted to be more frequent in the future under the high emissions pathway. Remarkably, the monthly climatology of CKWs varies over time; unlike the first two 30-yr analyzed periods, significant CKWs are predicted to mainly occur around August during the last two 30-yr periods due to the corresponding variabilities in the equatorial wind field, suggesting that the BoB characteristics may greatly deviate from the current climatological state.

The physical and hydrodynamic conditions in the Banda and Northern Arafura Seas (BAS) during northwest monsoon (February 2014) were investigated using a three-dimensional baroclinic nonlinear numerical model—the Hamburg Shelf Ocean Model (HAMSOM). This study found that northwesterly winds induced eastward surface currents that transported relatively fresh water from the Flores Sea to the Arafura Sea via the Banda Sea. It was also found that the westerly surface currents carried relatively cold water induced by upwelling along the northern coast of the Lesser Sunda Islands. Furthermore, the simulation results revealed that relatively saline surface water from the Indian Ocean intruding through the Ombai Strait and Timor Passage contributed to the surface water of the Eastern Banda Sea and Aru Basin being more saline than the surrounding water. Part of the surface water sank as a result of downwelling in the Arafura Sea. The BAS had higher salinity than the Makassar Strait at a depth of 75–300m. The simulation results suggested that the higher salinity was due to the influence of the South Pacific Subtropical Water (SPSW) that entered the Indonesian Seas primarily through the Halmahera Sea.

The physical and hydrodynamic conditions in the Banda and Northern Arafura Seas (BAS) during northwest monsoon (February 2014) were investigated using a three-dimensional baroclinic nonlinear numerical model—the Hamburg Shelf Ocean Model (HAMSOM). This study found that northwesterly winds induced eastward surface currents that transported relatively fresh water from the Flores Sea to the Arafura Sea via the Banda Sea. It was also found that the westerly surface currents carried relatively cold water induced by upwelling along the northern coast of the Lesser Sunda Islands. Furthermore, the simulation results revealed that relatively saline surface water from the Indian Ocean intruding through the Ombai Strait and Timor Passage contributed to the surface water of the Eastern Banda Sea and Aru Basin being more saline than the surrounding water. Part of the surface water sank as a result of downwelling in the Arafura Sea. The BAS had higher salinity than the Makassar Strait at a depth of 75 –300m. The simulation results suggested that the higher salinity was due to the influence of the South Pacific Subtropical Water (SPSW) that entered the Indonesian Seas primarily through the Halmahera Sea.

Climate change affects the marine environment on many levels with profound consequences for numerous biological, chemical, and physical processes. Benthic bioturbation is one of the most relevant and significant processes for benthic-pelagic coupling and biogeochemical fluxes in marine sediments, such as the uptake, transport, and remineralisation of organic carbon. However, only little is known about how climate change affects the distribution and intensity of benthic bioturbation of a shallow temperate shelf sea system such as the southern North Sea. In this study, we modelled and projected changes in bioturbation potential (BPp) under a continuous global warming scenario for seven southern North Sea key bioturbators: Abra alba, Amphiura filiformis, Callianassa subterranea, Echinocardium cordatum, Goniada maculata, Nephtys hombergii, and Nucula nitidosa. Spatial changes in species bioturbation intensity are simulated for the years 2050 and 2099 based on one species distribution model per species driven by bottom temperature and salinity changes using the IPCC SRES scenario A1B. Local mean bottom temperature was projected to increase between 0.15 and 5.4 °C, while mean bottom salinity was projected to moderately decrease by 1.7. Our results show that the considered benthic species are strongly influenced by the temperature increase. Although the total BP remained rather constant in the southern North Sea, the BPp for four out of seven species was projected to increase, mainly due to a simultaneous northward range expansion, while the BPp in the core area of the southern North Sea declined for the same species. Bioturbation of the most important species, Amphiura filiformis and Echinocardium cordatum, showed no substantial change in the spatial distribution, but over time. The BPp of E. cordatum remained almost constant until 2099, while the BPp of A. filiformis decreased by 41%. The northward expansion of some species and the decline of most species in the south led to a change of relative contribution to bioturbation in the southern North Sea. These results indicate that some of the selected key bioturbators in the southern North Sea might partly compensate the decrease in bioturbation by others. But especially in the depositional areas where bioturbation plays a specifically important role for ecosystem functioning, bioturbation potential declined until 2099, which might affect the biochemical cycling in sediments of some areas of the southern North Sea.

This study investigates climate-induced changes in height, frequency and duration of storm surges in the German Bight. The regionally coupled climate model system MPIOM-REMO with a focus on the North Sea has been utilized to dynamically downscale 30 members of the global climate model system MPI-ESM1.1-LR for the historical period 1950–2005 and a continuation until 2099 with the RCP8.5 scenario. Results of all members have been collected into the historical (1970–1999) and the rcp85 (2070–2099) data pools amounting to 900 years of the corresponding climate state. The global mean sea level rise was not considered. Nevertheless, the mean ensemble German Bight SSH trend amounts to about 13 ± 1 cm/century (PI control: 3 cm/century) due to adaptation of the ocean circulation to the changing climatic conditions. Storm surges were defined as SSH above mean high tidal water plus 1.5, 2.5, 3.5 m for “regular”, heavy, extreme storm surges, and then clustered to events. Our simulated storm surge events show a clear location-dependent increase in frequency (6–11%), median duration (4–24%), and average duration (9–20%) in the German Bight. Only along the central German Bight coast (Cuxhaven), longer lasting events gain more relevance. Heavy storm surge events show also a strong increase in frequency (7–34%) and average duration (10–22%). Maximum sea levels during storm events increase strongest and most significant along the northern German Bight and Danish coasts with more than 30 cm/century for the 60-year return period at Hörnum and 10–15 cm/century for shorter return periods. Levels of return periods shorter than a few years significantly increase everywhere along the southern German Bight coasts (around 5 cm/century for the 2-year return period). Highest SSH maxima do not change, and consequently, extreme storm surge events show hardly any response to climate change. Furthermore, our results indicate a shift of seasonality from the last to the first quarter of a year. As the main driver for the encountered alteration of German Bight storm surge characteristics, we identified a change in wind conditions with a pronounced increase of frequency of strong westerly winds.

Climate change is a global threat for marine ecosystems, their biodiversity and consequently ecosystem services. In the marine realm, marine protected areas (MPAs) were designated to counteract regional pressures, but they might be ineffective to protect vulnerable species and habitats, if their distribution is affected by global climate change. We used six Species Distribution Models (GLM, MARS, FDA, RF, GBM, MAXENT) to project changes in the distribution of eight benthic indicator and key species under climate change in the North Sea MPAs for 2050 and 2099. The projected distribution area of most species will be stable or even increase within the MPAs between 2001 and 2050. Thereafter, the distribution area decreased, especially within MPAs in the central North Sea by 2099, and some key species even disappeared from the MPAs. Consequently, the monitoring and protection of benthic species might not be possible within static MPA borders under climate change.

Lead–lag correlations between the subsurface temperature and salinity anomalies in the Bay of Bengal (BoB) and the Indian Ocean Dipole (IOD) are revealed in model results, ocean synthesis, and observations. Mechanisms for such correlations are further investigated using the Hamburg Shelf Ocean Model (HAMSOM), mainly relating to the salinity variability. It is found that the subsurface salinity anomaly of the BoB positively correlates to the IOD, with a lag of 3 months on average, while the subsurface temperature anomaly correlates negatively. The model results suggest the remote forcing from the equatorial Indian Ocean dominates the interannual subsurface salinity variability in the BoB. The coastal Kelvin waves carry signals of positive (negative) salinity anomalies from the eastern equatorial Indian Ocean and propagate counterclockwise along the coasts of the BoB during positive (negative) IOD events. Subsequently, westward Rossby waves propagate these signals to the basin at a relatively slow speed, which causes a considerable delay of the subsurface salinity anomalies in the correlation. By analyzing the salinity budget of the BoB, it is found that diffusion dominates the salinity changes near the surface, while advection dominates the subsurface; the vertical advection of salinity contributes positively to this correlation, while the horizontal advection contributes negatively. These results suggest that the IOD plays a crucial role in the interannual subsurface salinity variability in the BoB.