Atmospheric Explosions Research Articles

Probing atmospheric waves and the middle atmosphere dynamics using infrasound

Infrasound is defined as pressure fluctuations with frequencies between acoustic cut-off (5 min) and human-hearing frequency threshold of sound (16 Hz). Low-frequent infrasonic waves can travel long distances, ranging from hundreds to thousands of kilometres. The middle atmosphere dynamics mainly control the presence of atmospheric waveguides where energy transmission loss is low. These properties are utilized to record atmospheric explosions at highly sensitive pressure sensors (micro-barometers). A global network of 60 infrasound stations was designed as part of the International Monitoring System (IMS) for the Comprehensive Nuclear-Test-Ban Treaty. IMS infrasound stations can record small pressure fluctuations of a few millipascals, which can originate from numerous atmospheric infrasound sources, including meteorological phenomena. In this study, the capability of IMS infrasound arrays for capturing a broad spectrum of atmospheric wave phenomena is highlighted; for instance, mountain-associated infrasonic waves show features that seem to be correlated with orographic gravity waves. Moreover, the interaction of ocean waves produces quasi-continuous infrasound, so-called microbaroms. Infrasonic signatures from microbaroms can be used for probing the middle atmosphere dynamics and assessing atmospheric circulation models. For opening the unique global infrasound network of the IMS for meteorological applications, we also present open-access BGR infrasound data products of two decades and highlight selected case studies.

Comment on Rogozin et al., (2023), Morphology of Lakes of the Central Tunguska Plateau (Krasnoyarsk krai, Evenkiya): New Data on the Problem of the Tunguska Event of 1908

In a recent paper, Rogozin and coauthors present a morphologic/seismostratigraphic study of two small lakes, Lake Zapovednoye (LZ) and Lake Peyungda (LP), located 50‒60 km east from the alleged epicenter of the 1908 Tunguska Event (TE), a large explosion believed to have been caused by an extraterrestrial impact. Data presented in that paper suggest a similar (although not specified) origin of these two lakes and Lake Cheko, located close to the TE epicenter. This led Rogozin et al., to question the impact crater origin of Lake Cheko, whose depression was interpreted by Gasperini et al., as caused by the freefall of an extraterrestrial fragment, which survived an atmospheric explosion. We analyze Rogozin et al., data, focusing on similarities and differences between Lake Cheko, LZ and LP, to determine whether their findings are relevant to the TE problem.

Specific Aspects of Modeling Gas Mixture Explosions in the Atmosphere

Aspects of mathematical and physical modeling of deflagration explosions emerging during atmospheric (outdoor) accidental explosions are addressed. It has been demonstrated that when physically modeling accidental deflagration explosions, a stoichiometric mixture in the shape of a sphere or hemisphere supported by the ground should be used. This allows us to research the parameters of blast loads for the worst-case accidental scenarios or address the accident using the most conservative approach. A technique has been provided allowing one to create a mixture of a given blend composition in the shape of a sphere or hemisphere supported by the ground in outdoor conditions. It has been demonstrated that there is an ability to conduct modeling studies of accidental atmospheric explosions. We have provided examples of modeling studies of accidental atmospheric explosions; a methodology for analyzing experimental results has also been reviewed. The article discusses the mathematical modeling of outdoor (unobstructed) accidental deflagration explosions. It has been demonstrated that it is most reasonable to base computational experiments on linearized (acoustic) equations of continuum motion, as the visible flame propagation rate emerging during explosive combustion is small (compared to the speed of sound). There has been a satisfactory agreement between the numerical analysis and the experimental data.

The instability of laminar methane/hydrogen/air flames: Correlation between small and large-scale explosions

Darrieus–Landau (D-L) instability can cause significant acceleration in freely expanding spherical flames, which can lead to accidental large-scale gas explosions. To evaluate the potential of using high-pressure lab-scale experiments to predict the onset of cellular instabilities in large-scale atmospheric explosions, experimental measurements of the cellular instabilities for hydrogen and methane mixtures are conducted, in laboratory spherical explosions at elevated pressures. These measurements are compared with those from several large-scale atmospheric experiments. Comprehensive correlations of the pressure effect on a critical Karlovitz number, Kcl, together with those of strain rate Markstein number, Masr, are developed for hydrogen/air mixtures. The regime of stability reduces for all mixtures, as Masr becomes negative. Values derived from large-scale experiments closely follow the same correlation of Kcl with Masr. As a result, the extent of the regime where the laminar explosion flames become unstable can be predicted as a function of Masr and pressure.

The Argentella scandal: why French officials did not make Corsica a nuclear test site in 1960

ABSTRACT Top French officials made plans in early 1960 to transform an abandoned silver mine in Corsica, called the Argentella Massif, into an underground site for nuclear explosions. By June 1960, they had canceled these plans. This article shows how a mass movement on the Mediterranean island forced their hand, and it explains why Corsicans of diverse political affiliations took to the streets. The Argentella project—and the health, environmental, and strategic risks that it entailed—looked in Corsica like evidence that Paris saw the islanders as second-class citizens, even residents of an internal colony. French police intelligence, which maintained surveillance on the Corsican anti-nuclear movement, feared that this movement might have drawn inspiration from the contemporaneous struggle for national liberation in Algeria, where French nuclear explosions began. The Argentella protests illustrated national disagreements about French nuclear ambitions that previous scholarship, proposing official consensus, has minimized. They show how, in a nuclear-armed democracy, local officials, political activists, and ordinary citizens can shape nuclear-weapons policy. But Corsican anti-nuclear action in 1960 did not demand disarmament. These protests also illuminate a longer trajectory in French nuclear history, which involved atmospheric explosions in colonized territories in Algeria and Polynesia until the 1970s, despite local and international resistance.

The great Chinese fireball of December 22, 2020

On December 22, 2020, at about 23h 23m 33s UTC a very bright fireball was seen in the sky of southeastern China. The fireball lasted for several seconds and ended with an atmospheric explosion that was detected by US surveillance satellites. According to CNEOS’s data, the fireball moved with a mean speed of 13.6 km/s and exploded at an altitude of about 35.5 km (Lat. 31.9^{circ } N; Long. 96.2^{circ } E). In this paper we estimate the atmospheric trajectory, the heliocentric orbit and the strewn fields for different mass/section ratio of the fragments. The trajectory was about from north to south and with low inclination (5^{circ } pm 2^{circ }) with respect to the local surface. The explosion height appears consistent with a fragmented rocky body, and the heliocentric orbit supports an asteroidal origin. The probable strewn field extends between two points with coordinates (+31.3^circ N; 96.3^circ E) and (+30.3^circ N; 96.5^circ E), for a total area of about 4000 text {km}^2. This large extension is a direct consequence of the low inclination of the trajectory. Given the unknown uncertainty of the CNEOS’s data, these results should be taken with caution.

1001 Rocket Launches for Space Missions and Their Infrasonic Signature

AbstractInfrasound array processing is applied to monitor and characterize atmospheric explosions in the context of the Comprehensive Nuclear‐Test‐Ban Treaty. Anyhow, for many infrasound sources the exact location and time are initially unknown and sometimes difficult to precisely estimate afterward. In contrast, rocket launches are well‐defined ground‐truth events generating strong infrasonic signatures. During the last decade, the number of rocket launches for sending satellites into Earth’s orbit and for reaching space strongly increased. We collected ground‐truth information for 1001 rocket launches from 27 global spaceports between 2009 and mid‐2020 and were able to identify infrasound signatures from up to 73% of the launches on the International Monitoring System of infrasound stations. We use these unique data to estimate the global detectability of such events, to characterize rocket infrasound, to derive an amplitude‐energy relation, and to provide the results for further use as a ground‐truth reference in geophysical and atmospheric research.

Global Monitoring and Characterization of Infrasound Signatures by Large Fireballs

Large meteoroids can be registered in infrasound recordings during their entry into the Earth’s atmosphere. A comprehensive study of 10 large fireball events of the years 2018 and 2019 highlights their detection and characterization using global infrasound arrays of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The study focuses on the observation and event analysis of the fireballs to estimate their respective location, yield, trajectory, and entry behavior. Signal characteristics are derived by applying the Progressive Multi-Channel Correlation method as an array technique. The comparison of the events with a NASA reference database as well as the application of atmospheric propagation modeling allows to draw conclusions about infrasound-based detection capability, localization accuracy, yield estimation, and source characterization. The infrasound technique provides a time- and location-independent remote monitoring opportunity of impacting near-Earth objects (NEOs), either independent or complementary to other fireball observation methods. Additionally, insights about the detection and localization capability of IMS infrasound stations can be gained from using large fireballs as reference events, being of importance for the continuous monitoring and verification of atmospheric explosions in a CTBT context.

Numerical Study on the Whole Process of Fireball Evolution in Strong Explosion**Supported by the National Key R&D Program of China under Grant No. 2017YFA0403200, and China Postdoctoral Science Foundation under Grant No. 2018M630114

With the actual mean free path for radiation in air and a simplified nuclear device, a one-dimension simulation research on fireball phenomenon in a sea level atmosphere is carried out based on the multi-group radiation hydrodynamic codes (RDMG). It is shown that our theoretical calculations can describe the whole process of the fireball evolution for strong explosions from the early X-ray expansion stage to the shock wave propagation stage. The radius of the shock wave and the brightness of the fireball are in good agreement with the experimental results. The whole thermal radiation power curve of the fireball evolution for strong atmospheric explosion at sea level is plotted for the first time. The impact of radiation opacity of the nuclear device material on the early fireball phenomenon is also studied. It is found that trajectories of the radiation fronts and case shocks change with the opacity of equivalent device material. From our simulations, we find that only the early fireball depends on the details of the nuclear device, and after the formation of main shock, the evolution is determined by the properties of hot air for strong atmospheric explosion.

Studies of the Poltava seismic-tidal records during the period of explosions events in Balakliya and Kalynivka

The seismic-tidal records obtained at the Poltava gravimetric observatory of the IGF NAS of Ukraine (PGO) studied before, during and after events in Balaklija (March 22—23) and in Kalinovka (September 26—27) 2017 (explosions in ammunition dumps). Digital records were obtained with seismotiltmeters of compensating type and vertical seismometer (horizontal and vertical components), with thermal barograph and upgraded GS-11 gravimeter. Data analysis is performed by filtration, spectral, correlation and other methods, and the results are presented by graphs. The study of seismic deformation effects during explosions in military depots is a geophysical problem, the solution of which allows parameterize such dangerous events. However, despite its importance and social significance, it is not developed yet and needs additional studies. The analysis of the current-interval correlation functions and spectra shows that in the records up to 23:00 UTC 22.03.17 and 19:00 UTC on 26.09.17 (before the explosoins), the correlation coefficients (K) for short test correlator sections are smaller than 0.2. That is, no significant correlation on the selected interval correlators is observed. The number of pulse-wave seismic packets after a specified time, increases substantially, and seismic packets become clearer in current-interval correlation functions. They also appear in places where because of the noise they are not visible on the primary records. The correlation co-efficient between seismic packets in certain case, increases (K > 0.6 ¸ 0.8). This indicates the similarity of the pulsed wave packets and that they are generated in one place and have the same physical origin: obviously it is an explosion. The research has revealed the characteristic singularity of the seismodeformation signals during these events. A methodology for studying them has been developed. Many fundamental and applied problems have remained out-of range and must be investigated. Earth’s crust interaction — atmospheric explosion, energy of charges and their influence on spectra, residual jumps — deformations, etc. have not been investigated because of limited resources.

Transmission and Reflection of Fundamental‐ModeRgSignals from Atmospheric and Underground Explosions

Research Article| September 18, 2018 Transmission and Reflection of Fundamental‐Mode Rg Signals from Atmospheric and Underground Explosions Vanessa J. Napoli; Vanessa J. Napoli aWeston Geophysical Corp., 181 Bedford St. Suite 1, Lexington, Massachusetts 02420, vnapoli@westongeo.comdhrussell@westongeo.com Search for other works by this author on: GSW Google Scholar David R. Russell David R. Russell aWeston Geophysical Corp., 181 Bedford St. Suite 1, Lexington, Massachusetts 02420, vnapoli@westongeo.comdhrussell@westongeo.combAlso at 275 Wilson Avenue, Satellite Beach, Florida 32937. Search for other works by this author on: GSW Google Scholar Author and Article Information Vanessa J. Napoli aWeston Geophysical Corp., 181 Bedford St. Suite 1, Lexington, Massachusetts 02420, vnapoli@westongeo.comdhrussell@westongeo.com David R. Russell aWeston Geophysical Corp., 181 Bedford St. Suite 1, Lexington, Massachusetts 02420, vnapoli@westongeo.comdhrussell@westongeo.combAlso at 275 Wilson Avenue, Satellite Beach, Florida 32937. Publisher: Seismological Society of America First Online: 18 Sep 2018 Online Issn: 1943-3573 Print Issn: 0037-1106 © Seismological Society of America Bulletin of the Seismological Society of America (2018) 108 (6): 3590–3597. https://doi.org/10.1785/0120180084 Article history First Online: 18 Sep 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Vanessa J. Napoli, David R. Russell; Transmission and Reflection of Fundamental‐Mode Rg Signals from Atmospheric and Underground Explosions. Bulletin of the Seismological Society of America 2018;; 108 (6): 3590–3597. doi: https://doi.org/10.1785/0120180084 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search Abstract Rg signals measured between 1 and 5 Hz at local and near‐regional distances provide a viable method for estimating the yields of atmospheric and underground explosions. However, tested methods have been restricted to single or slowly changing source and receiver geologies, because propagation across abruptly changing geological boundaries can cause large reflections of the propagating Rg signals resulting in unacceptably large errors in yield estimates. In this article, we demonstrate how to correct for transmission and reflection across boundaries if estimates of the layered velocity, density, and attenuation structure in the different geological media are known. The methodology developed is tested using the alluvium and limestone structures analyzed in detail for the Humble Redwood (HR) III (2012) explosions conducted near Albuquerque, New Mexico. We validate the technique against the HRI (2007) and HRII (2009) atmospheric and underground explosions conducted in the same geologies as HRIII, with propagation paths crossing both alluvium and limestone. We compare synthetic estimates of yields of the HRI and HRII explosions based on earth structure to the known yield of 540 kg for these events. With no alluvium–limestone transmission correction, the estimated yield for the atmospheric explosion is 31 kg, and underground is 53 kg, which are both grossly inaccurate. The estimated yield after applying the transmission correction for the atmospheric explosion is 590 kg, and for the underground explosion is 617 kg, giving respective yield errors of 9% and 14%. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The stability of laminar explosion flames

The paper presents the results of a fundamental experimental and theoretical study of Darrieus–Landau, thermo-diffusive, instabilities in atmospheric explosions, and, on a smaller scale, in laboratory explosions in closed vessels. Pressure dependencies were sought to exploit the leading role of the Peclet number in the phenomena, so that similar Peclet numbers were achieved in both instances. However, in large atmospheric explosions large Peclet numbers were achieved by the size of the fireball, whereas in the closed vessel explosion it was achieved at a higher pressure by a much smaller flame, but because of the higher pressure, one endowed with a small laminar flame thickness. This study covers a much wider range of fuels and of pressures and the dependencies of the phenomena on both of these were carefully studied, although, for the atmospheric explosions, the data only covered propane and methane. The roles of both Markstein and Peclet numbers become clear and give rise to a more fundamental correlating parameter, a critical Karlovitz number, Kcl, for flame stability. This is based on the flame stretch rate, normalised by its multiplication by the chemical reaction time in a laminar flame. The experimentally measured dependencies of this key parameter on pressure and Markstein number are reported for the first time for so many different fuels. The critical Karlovitz number for flame stability decreases with increase in the strain rate Markstein number. As a result, it is possible to predict the extent of the unstable regime for laminar flames as a function of Masr and pressure. Such data can be used to estimate the severity of large scale atmospheric explosions. As Masr becomes highly negative, the regime of stability is markedly reduced.

Detection of Impact Points of Fragments of Spent Launch Vehicle Stages Using Infrasound Direction-Finding Methods

The paper describes the principles and techniques used to detect signals propagating in the atmosphere in the infrasonic frequency range. Such signals can be generated by different sources: ground and atmospheric explosions, as well as objects moving in the atmosphere at supersonic speed (aircraft, rockets, bolides, fragments of spent stages of launch vehicles). Portable infrasound monitoring stations are described, each of which includes three spaced infrasonic microphones. Each such station makes it possible to determine three basic parameters of the detected infrasound signal, which are subsequently used to solve the direction- finding problem: the time of arrival of an infrasonic wave, the azimuth to the source in the horizontal plane, and the wave approach angle from the source of infrasonic waves to the Earth’s surface in the vertical plane. An acoustic detector used to extract useful signals against a noise background is described. The detector is based on an algorithm similar to the STA/LTA detection algorithm known in seismology. Examples of the operation of an acoustic detector with data obtained during real measurements are given. Passive infrasound direction-finding technology is described. It is based on mathematical modeling of the of infrasonic wave propagation in the atmosphere, which are generated by objects moving along possible trajectories; comparison of theoretical signals with real ones recorded by monitoring stations; and determination of the realized trajectories. The paper gives examples of experimental verification of the effectiveness of passive infrasound direction-finding technology for determining the impact points of the first and second stages of launch vehicles. It is shown that infrasound direction-finding systems makes it possible to reduce the estimated search area for launch vehicle fragments that fall to the Earth, significantly decrease the time and costs for their search and utilization, and mitigate the negative environmental impact of the rocket and space industry.

CHARACTERIZING AND MODELLING OCEAN AMBIENT NOISE USING INFRASOUND NETWORK AND MIDDLE ATMOSPHERIC MODELS

Infrasound is one of the technologies of the International Monitoring System (IMS) supporting the verification regime of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). In the frequency band of interest to detect atmospheric explosions, ambient noise may affect detection and particularly ocean noise referred to as microbaroms. Ocean wave interactions generate acoustic noise almost continuously which can obscure signals of interest in their frequency range. The detectability of such noise strongly depends on atmospheric conditions along the propagation paths. Using ocean wave action model developed by IFREMER and considering the effects of general middle-atmospheric products delivered by ECMWF in long-range propagation, microbarom amplitudes and direction of arrivals derived from various propagation models are compared with the observations. With this study, it is expected to enhance the characterization of the ocean-atmosphere coupling. In return, a better knowledge of microbarom sources would allow to better characterize explosive atmospheric events hidden in the ambient noise.

Parameters of Acoustic Signals Generated by the Atmospheric Meteoroid Explosion over Romania on January 7, 2015

System spectral analysis of temporal variations in the level of acoustic signals recorded at a number of European infrasound stations is carried out. The prevailing periods that varied within 3–5 s are found. Initial kinetic and acoustic energies of the Romanian meteoroid and infrasound parameters are calculated: celerity (280 m/s), acoustic efficiency, and stratospheric wind velocity (about 20 m/s). Parameters of cylindrical and explosive shock waves are found: duration, characteristic size, and amplitude. The dependence of the attenuation of infrasonic waves on distance is estimated. The results of the estimates are in good agreement with the results of the observations.

Characterizing ocean ambient noise using infrasound network

The ability of the International Monitoring System (IMS) global infrasound network to detect atmospheric explosions and events of interest strongly depends on station specific ambient noise signatures which include both incoherent wind noise and real coherent infrasonic waves. To characterize the coherent ambient noise, broadband array processing was performed on historical continuous IMS recordings. Ocean wave interactions contribute to the atmospheric coherent ambient noise field, and we apply wave action models to model these microbarom sources. We use two-dimensional energy spectrum ocean wave products to build a global reference database of oceanic noise sources. Then, we compare observed and modeled directional microbarom amplitudes at several stations. The expected benefits of such studies concern the use complementary data to finely characterize the coupling mechanisms at the ocean-atmosphere interface. In return, better knowledge of ambient ocean noise sources opens new perspectives not only by enhancing the characterization of explosive atmospheric events, but also by providing additional integrated constraints on middle atmosphere dynamics and disturbances where data coverage is otherwise sparse.

Characterizing global infrasonic ocean ambient noise

The ability of the International Monitoring System (IMS) global infrasound network to detect atmospheric explosions and events of interest strongly depends on station specific ambient noise which includes both incoherent wind noise and real coherent infrasonic waves. To characterize the coherent ambient noise, a broadband array processing was performed on 10 years of continuous recordings at IMS stations. Multi-year comparisons between the observed and modeled directional microbarom amplitude variations at several IMS stations using two-dimensional wave energy spectrum ocean wave products are performed to build of a reference database of infrasound oceanic sources. Microseisms are attributed the same source processes as microbaroms, involving the interaction of standing ocean waves. To further evaluate oceanic wave action models, the infrasound analysis will be supplemented with several other approaches including microseisms collected at seismic instrumentation (single stations and arrays). The expected benefits of such studies concern the use of multi-year complementary data to finely characterize coupling mechanisms at the ocean-atmosphere interface. In return, a better knowledge of the source of the ambient ocean noise opens new perspectives by providing additional integrated constraints on the dynamics of the middle atmosphere and its disturbances where data coverage is sparse.

Automated detection and cataloging of global explosive volcanism using the International Monitoring System infrasound network

AbstractWe experiment with a new method to search systematically through multiyear data from the International Monitoring System (IMS) infrasound network to identify explosive volcanic eruption signals originating anywhere on Earth. Detecting, quantifying, and cataloging the global occurrence of explosive volcanism helps toward several goals in Earth sciences and has direct applications in volcanic hazard mitigation. We combine infrasound signal association across multiple stations with source location using a brute‐force, grid‐search, cross‐bearings approach. The algorithm corrects for a background prior rate of coherent unwanted infrasound signals (clutter) in a global grid, without needing to screen array processing detection lists from individual stations prior to association. We develop the algorithm using case studies of explosive eruptions: 2008 Kasatochi, Alaska; 2009 Sarychev Peak, Kurile Islands; and 2010 Eyjafjallajökull, Iceland. We apply the method to global IMS infrasound data from 2005–2010 to construct a preliminary acoustic catalog that emphasizes sustained explosive volcanic activity (long‐duration signals or sequences of impulsive transients lasting hours to days). This work represents a step toward the goal of integrating IMS infrasound data products into global volcanic eruption early warning and notification systems. Additionally, a better understanding of volcanic signal detection and location with the IMS helps improve operational event detection, discrimination, and association capabilities.

Characterizing infrasonic ocean ambient noise in Northwest Pacific

The ability of the International Monitoring System (IMS) infrasound network to detect atmospheric explosions and events of interest strongly depends on station specific ambient noise which includes both incoherent wind noise and real coherent infrasonic waves. To characterize the coherent ambient noise, a broadband array processing was performed with IMS continuous waveform archive from 2007 to 2016 using the Progressive Multi-Channel Correlation algorithm (PMCC). The processing parameters include a new implementation of adaptive frequency dependent window length and a logarithmic band spacing. Such configuration allows to better discriminate between interfering signals with improved accuracy in the wave parameters estimations. Multi-year comparisons between the observed and modeled directional microbarom amplitude variations at several IMS stations using two-dimensional wave energy spectrum ocean wave products are performed to build of a reference database of infrasound oceanic sources in Northwest Pacific. The expected benefits of such studies concern the use of multi-year complementary data to finely characterize coupling mechanisms at the ocean-atmosphere interface. In return, a better knowledge of the source of the ambient ocean noise opens new perspectives by providing additional integrated constraints on the dynamics of the middle atmosphere and its disturbances where data coverage is sparse.

Iodine-129, Iodine-127 and Cesium-137 in seawater from the North Sea and the Baltic Sea

In this study, new data are presented for the iodine isotopes (127I, 129I and their isotopic ratios) and Cesium (137Cs) in water samples of the North Sea and the Baltic Sea in 2005 and 2009. This study supplements and extends the study of Michel et al. (2012). Iodine isotopes were separated from their matrix by using an anion exchange method and were determined by applying ICP-MS and AMS. 137Cs in seawater was determined after cesium ion exchange procedure enrichment by gamma-spectrometry. The concentrations of 127I in seawater of the North and Baltic Sea are fairly constant in each Sea with averages of (44 ± 2) and (21 ± 1) ng g−1, respectively, depending on the salinity. However, large variations of 129I concentrations in these areas were detected, which decreased along the French, Belgian, Dutch, German, and Danish shores. 129I/127I isotope ratios in the Baltic Sea are about 10 times lower than in the North Sea in 2009. The highest isotopic ratios (2.7 × 10−6) was detected in the English Channel east of the nuclear reprocessing plant at Cap de la Hague. The results confirm the result of our early study that the sources of 129I in the North Sea are primarily the nuclear reprocessing facilities at Sellafield (UK) and La Hague (F), and that in the Baltic Sea the inflow of water from North Sea through the Danish Straits dominates the occurrence of 129I.In 2009, the activity concentration of 137Cs was at least 6 times higher in the Baltic Sea (37 Bq m−3) than in the North Sea (5.9 Bq m−3), due to release of 137Cs from sediments in the Baltic Sea, which were contaminated by the Chernobyl accident and – to a minor degree – the atmospheric explosions of atomic bombs. The results are discussed by comparing the results of our previous work and the current study demonstrating the continuing disequilibrium of 129I/127I atomic ratio in the environmental compartments.