Characterising turbulent ship wakes from an environmental impact perspective

The world’s oceans, especially coastal areas, are intensively trafficked by ships. All these ships exert pressure on the marine environment, through emission to the atmosphere, discharges of pollutants to the water, and physical disturbance through energy input. Of these impacts, energy pollution from shipping has received the least attention. Especially the impact of ship-induced turbulence in the wake, which is induced by the hull friction and propeller, and remains for up to 15 minutes. The turbulent wake can impact the spread of contaminants, affect air-sea gas exchange, physically disturb plankton, and potentially impact local biogeochemistry through increased entrainment and vertical mixing. To assess these impacts, an understanding of the turbulent wake development and interaction with surface ocean stratification, is essential. However, characterisation of the turbulent wake development in time and space, especially in stratified conditions, is challenging and requires an interdisciplinary approach.\ua0\ua0 The aim of this thesis is to advance the understanding of turbulent wake development from an environmental impact perspective. The intensity and spatiotemporal extent of the turbulent wake, and its impact, have been investigated through a combination of in situ and ex situ observations, and Computational Fluid Dynamic (CFD) modelling of ships in full-scale. The unique dataset of several hundred in situ turbulent wake observations, showed large variation in spatiotemporal extent and intensity. Wake depths can reach down to 30 m, and the turbulent intensities in the near wake are 1–3 orders of magnitude higher than generally observed in the upper ocean surface layer. In addition, during stratified conditions ship-induced turbulence entrain water from below the pycnocline, with implications for local nutrient input and primary production in the ocean surface layer. In addition, ship-passages were observed to frequently trigger large methane emissions in an estuarine shipping lane. The results highlight the importance of addressing ship-induced turbulence in marine environmental management. Intensively trafficked coastal areas should be considered anthropogenically impacted, even unnatural, with respect to turbulence. The interdisciplinary approach applied in this thesis, is a first step towards a holistic assessment of the environmental impact of the turbulent wake

Turbulent ship wakes and their spatiotemporal extent

Shipping activities occur in almost every part of the global oceans and in intensely trafficked shipping lanes there can be up to one ship passage every ten minutes. All these ships impact the marine environment in different ways through pollution or physical disturbance. This thesis is focused on the turbulent ship wake, a physical disturbance from ships and previously overlooked as an environmental impact. When a ship moves through water, the turbulence induced by the propeller and hull, will create a turbulent wake that remains and expands after the ship passage. The turbulence in the wake will govern the spread of contaminants and affect gas exchange in the wake water, physically perturb plankton, and potentially impact local biogeochemistry through increased vertical mixing.To be able to assess the environmental impact of ship-induced turbulence in areas with intense ship traffic, knowledge of the spatiotemporal extent and development of the turbulent wake is necessary. The aim of this thesis is to increase that knowledge, by conducting in situ observations of turbulent ship wakes, which can be used to estimate the spatiotemporal extent of the turbulent wake. By using a collection of methods, the thesis work has resulted in a first estimate of the spatiotemporal extent of the turbulent ship wake, based on more than 200 field observations of different real-size ships in natural conditions. The observed turbulent wakes showed large variation in their spatiotemporal extent, and further studies are needed to fully disentangle how environmental conditions and vessel specifications affect the intensity and extent of the turbulent wake. The results and experiences gained from the in situ observations, give an indication of the complexity entailed in characterising the development of the turbulent wake, and provide valuable input regarding the relevant parameters and spatiotemporal scales to include in future studies. The work of this thesis constitutes the first step in addressing the knowledge gap regarding the environmental impact of ship-induced turbulence and can be used as a road map for further studies within the field

Deep learning for deep waters: An expert-in-the-loop machine learning framework for marine sciences

Driven by the unprecedented availability of data, machine learning has become a pervasive and transformative technology across industry and science. Its importance to marine science has been codified as one goal of the UN Ocean Decade. While increasing amounts of, for example, acoustic marine data are collected for research and monitoring purposes, and machine learning methods can achieve automatic processing and analysis of acoustic data, they require large training datasets annotated or labelled by experts. Consequently, addressing the relative scarcity of labelled data is, besides increasing data analysis and processing capacities, one of the main thrust areas. One approach to address label scarcity is the expert-in-the-loop approach which allows analysis of limited and unbalanced data efficiently. Its advantages are demonstrated with our novel deep learning-based expert-in-the-loop framework for automatic detection of turbulent wake signatures in echo sounder data. Using machine learning algorithms, such as the one presented in this study, greatly increases the capacity to analyse large amounts of acoustic data. It would be a first step in realising the full potential of the increasing amount of acoustic data in marine sciences

In situ observations of turbulent ship wakes and their spatiotemporal extent

In areas of intensive ship traffic, ships pass every 10ĝ€\uafmin. Considering the amount of ship traffic and the predicted increase in global maritime trade, there is a need to consider all types of impacts shipping has on the marine environment. While the awareness about, and efforts to reduce, chemical pollution from ships is increasing, less is known about physical disturbances, and ship-induced turbulence has so far been completely neglected. To address the potential importance of ship-induced turbulence on, e.g., gas exchange, dispersion of pollutants, and biogeochemical processes, a characterisation of the temporal and spatial scales of the turbulent wake is needed. Currently, field measurements of turbulent wakes of real-size ships are lacking. This study addresses that gap by using two different methodological approaches: in situ and ex situ observations. For the in situ observations, a bottom-mounted acoustic Doppler current profiler (ADCP) was placed at 32ĝ€\uafm depth below the shipping lane outside Gothenburg harbour. Both the acoustic backscatter from the air bubbles in the wake and the dissipation rate of turbulent kinetic energy were used to quantify the turbulent wake depth, intensity, and temporal longevity for 38 ship passages of differently sized ships. The results from the ADCP measurements show median wake depths of 13ĝ€\uafm and several occasions of wakes reaching depths >ĝ€\uaf18ĝ€\uafm, which is in the same depth range as the seasonal thermocline in the Baltic Sea. The temporal longevity of the observable part of the wakes had a median of around 10ĝ€\uafmin and several passages of >ĝ€\uaf20ĝ€\uafmin. In the ex situ approach, sea surface temperature was used as a proxy for the water mass affected by the turbulent wake (thermal wake), as lowered temperature in the ship wake indicates vertical mixing in a thermally stratified water column. Satellite images of the thermal infrared sensor (TIRS) onboard Landsat-8 were used to measure thermal wake width and length, in the highly frequented and thus major shipping lane north of Bornholm, Baltic Sea. Automatic information system (AIS) records from both the investigated areas were used to identify the ships inducing the wakes. The satellite analysis showed a median thermal wake length of 13.7ĝ€\uafkm (nCombining double low line144), and the longest wake extended over 60ĝ€\uafkm, which would correspond to a temporal longevity of 1ĝ€\uafh 42ĝ€\uafmin (for a ship speed of 20ĝ€\uafkn). The median thermal wake width was 157.5ĝ€\uafm. The measurements of the spatial and temporal scales are in line with previous studies, but the maximum turbulent wake depth (30.5ĝ€\uafm) is deeper than previously reported. The results from this study, combined with the knowledge of regional high traffic densities, show that ship-induced turbulence occurs at temporal and spatial scales large enough to imply that this process should be considered when estimating environmental impacts from shipping in areas with intense ship traffic

Effects of seawater scrubbing on a microplanktonic community during a summer-bloom in the Baltic Sea

The International Maritime Organization (IMO) has gradually applied stricter regulations on the maximum sulphur content permitted in marine fuels and from January 1, 2020, the global fuel sulphur limit was reduced from 3.5% to 0.5%. An attractive option for shipowners is to install exhaust gas cleaning systems, also known as scrubbers, and continue to use high sulphur fuel oil. In the scrubber, the exhausts are led through a fine spray of water, in which sulphur oxides are easily dissolved. The process results in large volumes of acidic discharge water, but while regulations are focused on sulphur oxides removal and acidification, other pollutants e.g. polycyclic aromatic hydrocarbons, metals and nitrogen oxides can be transferred from the exhausts to the washwater and discharged to the marine environment. The aim of the current study was to investigate how different treatments of scrubber discharge water (1, 3 and 10%) affect a natural Baltic Sea summer microplanktonic community. To resolve potential contribution of acidification from the total effect of the scrubber discharge water, “pH controls” were included where the pH of natural sea water was reduced to match the scrubber treatments. Biological effects (e.g. microplankton species composition, biovolume and primary productivity) and chemical parameters (e.g. pH and alkalinity) were monitored and analysed during 14 days of exposure. Significant effects were observed in the 3% scrubber treatment, with more than 20% increase in total biovolume of microplankton compared to the control group, and an even greater effect in the 10% scrubber treatment. Group-specific impacts were recorded where diatoms, flagellates incertae sedis, chlorophytes and ciliates increased in biovolume with increasing concentrations of scrubber water while no effect was recorded for cyanobacteria. In contrast, these effects was not observed in the “pH controls”, a suggestion that other parameters/stressors in the scrubber water were responsible for the observed effects

Effects of scrubber washwater discharge on microplankton in the Baltic Sea

In 2020, the global cap of maximum allowable sulphur content in marine fuel will be reduced from the current 3.5% to 0.5%. Another way to reduce the sulphur emissions is to install a seawater scrubber that cleans exhausts but instead release acidic water containing nutrients and contaminants back to the marine environment. In the current study, scrubber washwater was tested on a Baltic Sea microplankton community. A significant increase in chlorophyll a, particulate organic phosphorus (POP), carbon (POC) and nitrogen (PON) were observed when the community was exposed to 10% scrubber washwater for 13 days as compared to the control. A laboratory experiment with the filamentous cyanobacteria Nodularia spumigena and the chain-forming diatom Melosira cf. arctica showed negative responses in photosynthetic activity (EC10 = 8.6% for N. spumigena) and increased primary productivity (EC10 = 5.5% for M. cf. arctica), implying species-specific responses to scrubber washwater discharge

Modellering av omblandning i fartygs k\uf6lvatten, f\uf6r \uf6kad f\uf6rst\ue5else av belastning p\ue5 havsmilj\uf6n till f\uf6ljd av utsl\ue4pp fr\ue5n fartyg

6stersj\uf6n \ue4r ett av v\ue4rldens mest intensivt trafikerade omr\ue5den och i vissa delar sker en fartygs\uadpassage i genomsnitt var tolfte minut. Fartygen kan betraktas som flytande industrier som sl\ue4pper ut f\uf6roreningar, f\uf6rsurande och \uf6verg\uf6dande \ue4mnen som produceras i olika ombordssystem, s\ue5som svart-, gr\ue5-, ballast-, l\ue4ns-, kyl- och skrubbervatten, giftiga b\ue5tbottenf\ue4rger och propellerhylsolja. De senaste \ue5rens \uf6kade f\uf6rst\ue5else f\uf6r att sj\uf6fartens utsl\ue4pp inte \ue4r negligerbara f\uf6r havsmilj\uf6n belyses i Milj\uf6m\ue5lsberedningens bet\ue4nkande Havet och m\ue4nniskan (2020), d\ue4r det bland annat f\uf6resl\ue5s att Havs- och vattenmyndigheten b\uf6r f\ue5 i uppdrag att integrera \uf6vervakning av sj\uf6fartens p\ue5verkan p\ue5 havsmilj\uf6n i sin verksamhet. F\uf6r att kunna g\uf6ra detta p\ue5 ett effektivt s\ue4tt \ue4r det n\uf6dv\ue4ndigt att f\uf6rst\ue5 hur f\uf6roreningar som sl\ue4pps ut fr\ue5n fartyg sprids vidare i havsmilj\uf6n. Med utg\ue5ngspunkt fr\ue5n denna kunskap kan milj\uf6\uf6vervakningsprogram utformas och i f\uf6rl\ue4ngningen \ue5tg\ue4rder vidtas f\uf6r att minska p\ue5verkan fr\ue5n sj\uf6fart p\ue5 havsmilj\uf6n, exempelvis genom f\uf6rbud mot utsl\ue4pp eller omledning av farleder i k\ue4nsliga omr\ue5den.I befintliga modelleringar av utsl\ue4pp fr\ue5n fartyg g\uf6rs antagandet att utsl\ue4ppen sker i ytan, vilket f\ue5r till f\uf6ljd att ber\ue4kningen av spridningen i milj\uf6n i stor utstr\ue4ckning kommer att styras av r\ue5dande vind- och str\uf6mf\uf6rh\ue5llanden i ytskiktet. Detta kan vara acceptabelt, exempelvis vid modellering av l\ue4ttare oljeprodukter, men f\uf6r andra \ue4mnen \ue4r det n\uf6dv\ue4ndigt att f\uf6rst\ue5 hur omblandningen i k\uf6lvattnet sker f\uf6r att mer korrekt kunna ber\ue4kna hur f\uf6roreningarna sprider sig i milj\uf6n; str\uf6m\uadf\uf6rh\ue5llanden kan variera avsev\ue4rt i b\ue5de riktning och styrka p\ue5 5–10 m djup, j\ue4mf\uf6rt med i ytan.Syftet med den h\ue4r f\uf6rstudien var att unders\uf6ka f\uf6ruts\ue4ttningarna att kombinera ber\ue4kningsstr\uf6m\uadningsdynamik (Computational Fluid Dynamics (CFD)) som vanligtvis anv\ue4nds f\uf6r att g\uf6ra h\uf6guppl\uf6sta 3D modelleringar av str\uf6mningen runt skrov och propeller p\ue5 fartyg, med regionala oceanografiska modeller. Anv\ue4ndningen av den h\uf6guppl\uf6sta 3D Reynolds- Medelv\ue4rdesbildad Navier-Stokes (3D RANS) modellen \ue4r dock ber\ue4kningsintensiv och brukar endast anv\ue4ndas f\uf6r att modellera n\ue4rvaken, upp till n\ue5gon fartygsl\ue4ngd akter om fartyget. F\uf6r att kunna brygga \uf6ver skalorna i fj\ue4rrvaken (ca 0,8–3 km) akter om fartyget \ue4r det d\ue4rf\uf6r l\ue4mpligt att f\uf6rs\uf6ka f\uf6renkla ber\ue4kningarna, vilket kan g\uf6ras genom semi-empirisk modellering och 2D modellering av ett tv\ue4rsnitt av vaken \uf6ver tid, vilka i begr\ue4nsad omfattning validerats mot 3D RANS resultaten. Vidare har in-situ m\ue4tningar med en Acoustic Doppler Current Profiler (ADCP) anv\ue4nts f\uf6r att validera utbredningen av det turbulenta vakomr\ue5det.Resultaten av f\uf6rstudien, b\ue5de fr\ue5n modellering och f\ue4ltm\ue4tningarna, visar tydligt att utsl\ue4pp i fartygsvaken kan spridas p\ue5 olika djup och i olika riktning som en effekt av omblandningen som sker i vaken. Vidare \ue4r hydrografin viktig f\uf6r hur och var spridningen i vaken sker och f\ue4ltm\ue4tningarna indikerar att n\ue4r det finns en stark skiktning kommer det omblandade vattnet i fartygsvaken att spridas i sidled, l\ue4ngs med skiktningen, ist\ue4llet f\uf6r ned\ue5t mot botten. Ur milj\uf6\uf6vervakningsperspektiv \ue4r det d\ue4rf\uf6r viktigt att k\ue4nna till skiktningen och djupet i relation till farledernas placering, d\ue5 det f\ue5r konsekvenser f\uf6r spridningen av f\uf6roreningar fr\ue5n farleden och d\ue4rmed \ue4ven var provtagning b\uf6r ske.Slutsatsen fr\ue5n f\uf6rstudien \ue4r att det f\uf6reslagna ramverket, kombinationen av olika teoretiska modeller och in-situ m\ue4tningar, har stor potential f\uf6r att kunna leverera indata till regionala oceanografiska modeller, f\uf6r att kunna modellera den storskaliga spridningen av f\uf6roreningar fr\ue5n fartyg och farleder. Denna information \ue4r ocks\ue5 kritisk f\uf6r utformning av \uf6vervakningsprogram, d\ue4r det \ue4r avg\uf6rande att m\ue4tningar g\uf6rs d\ue4r f\uf6roreningar fr\ue5n fartyg kan f\uf6rv\ue4ntas att \ue5terfinnas

Trajectories of functional limitation in early rheumatoid arthritis and their association with mortality

This study aimed to identify subgroups with distinct trajectories of functional (HAQ) progression over 10 years following diagnosis of RA and identify baseline characteristics associated with the trajectories and their prognostic value for mortality.Peer reviewe