Microplastics in the marine environment

This review discusses the mechanisms of generation and potential impacts of microplastics in the ocean environment. Weathering degradation of plastics on the beaches results in their surface embrittlement and microcracking, yielding microparticles that are carried into water by wind or wave action. Unlike inorganic fines present in sea water, microplastics concentrate persistent organic pollutants (POPs) by partition. The relevant distribution coefficients for common POPs are several orders of magnitude in favour of the plastic medium. Consequently, the microparticles laden with high levels of POPs can be ingested by marine biota. Bioavailability and the efficiency of transfer of the ingested POPs across trophic levels are not known and the potential damage posed by these to the marine ecosystem has yet to be quantified and modelled. Given the increasing levels of plastic pollution of the oceans it is important to better understand the impact of microplastics in the ocean food web.     

Microplastics in the Southern Ocean

A field survey to collect microplastics with sizes < 5 mm was conducted in the Southern Ocean in 2016. We performed five net-tows and collected 44 pieces of plastic. Total particle counts of the entire water column, which is free of vertical mixing, were computed using the surface concentration (particle count per unit seawater volume) of microplastics, wind speed, and significant wave height during the observation period. Total particle counts at two stations near Antarctica were estimated to be in the order of 100,000 pieces km^? 2.     

The carbon dioxide system in the oceans

A model of the carbon dioxide system in nature is derived and is used to further our understanding of the factors which control this system in the oceans, the atmosphere, and the sediments.     

Characteristics of disturbances in the atmosphere and oceans

The characteristics of the disturbances in the atmosphere and oceans and in other stably stratified and rotating fluids are analyzed according to their phase and group velocities. It is shown that both stable stratification and rotation augment the velocity of the sound waves, and that the internal gravity waves and inertial waves are mutually exclusive when the Brunt-Väisälä frequency is different from the Coriolis parameter. It is also shown that both the barotropic and the internal Rossby waves are well separated from the gravity waves and that they can be represented accurately by the quasi-geostrophic potential vorticity equation, even close to the equator, except for the one member withn=0 which is coupled with an eastward propagating gravity wave.     

Impact of oceans on climate change in drylands

Drylands account for approximately 41% of the global total land area. Significant warming and rare precipitation in drylands result in a fragile ecology and deterioration of the living environment, making it more sensitive to global climate change. As an important regulator of the Earth's climate system, the oceans play a vital role in the process of climate change in drylands. In modern climate change in particular, the impact of marine activities on climate change in drylands cannot be neglected. This paper reviews the characteristics of climate change in drylands over the past 100 years, and summarizes the researches conducted on the impact of marine activities on these changes. The review focuses on the impact of the Pacific Decadal Oscillation(PDO), Atlantic Multidecadal Oscillation(AMO), El Ni?o and La Ni?a on climate change in drylands, and introduces the mechanisms by which different oceanic oscillation factors synergistically affect climate change in drylands.Studies have shown that global drylands have experienced a significant intensification in warming in the past 100 years, which shows obvious characteristics of interdecadal dry/wet variations. The characteristics of these changes are closely related to the oscillatory factors of the oceanic interdecadal scale. Different phase combinations of oceanic oscillation factors significantly change the land-sea thermal contrast, which in turn affects the westerly jet, planetary wave and blocking frequency, resulting in changes in the temperature and dry/wet characteristics of drylands. With the intensification of climate change in drylands, the impact of marine activities on these regions will reveal new characteristics in the future, which will increase the uncertainty of future climate change in drylands and intensify the impact of these drylands on global climate.     

A global survey of perfluorinated acids in oceans

Perfluorinated acids and their salts have emerged as an important class of global environmental contaminants. Biological monitoring surveys conducted using tissues of marine organisms reported the occurrence of perfluorooctanesulfonate (PFOS) and related perfluorinated compounds in biota from various seas and oceans, including the Arctic and the Antarctic Oceans. Occurrence of perfluorinated compounds in remote marine locations is of concern and indicates the need for studies to trace sources and pathways of these compounds to the oceans. Determination of sub-parts-per-trillion (ng/L) or parts-per-quadrillion (pg/L) concentrations of aqueous media has been impeded by relatively high background levels arising from procedural or instrumental blanks. Our research group has developed a reliable and highly sensitive analytical method by which to monitor perfluorinated compounds in oceanic waters. The method developed is capable of detecting PFOS, perfluorohexanesulfonate (PFHS), perfluorobutanesulfonate (PFBS), perfluorooctanoate (PFOA), perfluorononanoate (PFNA), and perfluorooctanesulfonamide (PFOSA) at a few pg/L in oceanic waters. The method was applied to seawater samples collected during several international research cruises undertaken during 2002–2004 in the central to eastern Pacific Ocean (19 locations), South China Sea and Sulu Seas (five), north and mid Atlantic Ocean (12), and the Labrador Sea (20). An additional 50 samples of coastal seawater from several Asian countries (Japan, China, Korea) were analyzed. PFOA was found at levels ranging from several thousands of pg/L in water samples collected from coastal areas in Japan to a few tens of pg/L in the central Pacific Ocean. PFOA was the major contaminant detected in oceanic waters, followed by PFOS. Further studies are being conducted to elucidate the distribution and fate of perfluorinated acids in oceans.     

Theoretical models for electromagnetic induction in the oceans

The different methods and techniques employed in the theory of electromagnetic induction in thin sheets are reviewed and the methods for approximation to the solution are indicated. These depend on whether the sheet is closed or finite and on whether the integrated conductivity and/or the frequency of variations is high or low.Results for induction in finite sheets which are suitable for ocean modelling are given. These include sheets of perfect conductivity and sheets of finite conductivity which is either discontinuous or continuous at the boundary. The dependence of the “coastline effect” for a global ocean on the location of the edge of the continental shelf, the period of variation of the external field and the conductivity of the underlying earth is explained.     

Absolute reconstructions of the Paleozoic oceans

The orientation of three intraplate magmatic belts—the Mongolian (from 130 to 280 m.y.), South Siberian (from 320 to 400 m.y.) and Baltic (from 365 to 400 m.y.) belts—which can be considered as hot spot tracks, are used together with apparent paleomagnetic pole wander paths to reconstruct true motions of continents during Paleozoic times. The reconstructions obtained show that the old, Late Precambrian Pangea continued to exist in the Early Paleozoic with an inner arrangement of constituent continents strongly different from that of the Late Paleozoic Pangea. The continents were constantly located in the eastern hemisphere only. The western hemisphere was occupied by the Paleo-Pacific oceans. Four oceans existed in Paleozoic times between the continents in the eastern hemisphere: (1) the Iapetus which originated in the Late Precambrian and closed before Devonian times (400 m.y.), (2) the Asiatic paleo-ocean which originated in the Late Precambrian and closed 450 m.y. ago, (3) the Uralian paleo-ocean which opened around 500 m.y. ago and closed in the latest Permian (240–230 m.y.), (4) the Paleo-Tethys which opened in the Ordovician (480–450 m.y.) and became the Mesozoic Tethys. Life duration of the oceans was 200–400 m.y. The main trend in the Earth's evolution during the Paleozoic was a break up of the old, Precambrian Supercontinent and construction of the new, Late Paleozoic Pangea.     

Martian oceans, valleys and climate

The new Mars Global Surveyor altimetry shows that the heavily cratered southern hemisphere of Mars is 5 km higher than the sparely cratered plains of the northern hemisphere. Previous suggestions that oceans formerly occupied the northern plains as evidenced by shorelines are partly supported by the new data. A previously identified outer boundary has a wide range of elevations and is unlikely to be a shoreline but an inner contact with a narrow range of elevations is a more likely candidate. No shorelines are visible in the newly acquired, 1.5 metre/pixel imaging. Newly imaged valleys provide strong support for sustained or episodic flow of water across the Martian surface. A major surprise, however, is the near absence of valleys less than 100 m across. Martian valleys seemingly do not divide into ever smaller valleys as terrestrial valleys commonly do. This could be due to lack of precipitation or lack of surface runoff because of high infiltration rates. High erosion rates and formation of valley networks supports warm climates and presence of large bodies of water during heavy bombardment. The climate history and fate of the water after heavy bombardment remain controversial.     

Microplastics as contaminants in the marine environment: a review

Since the mass production of plastics began in the 1940s, microplastic contamination of the marine environment has been a growing problem. Here, a review of the literature has been conducted with the following objectives: (1) to summarise the properties, nomenclature and sources of microplastics; (2) to discuss the routes by which microplastics enter the marine environment; (3) to evaluate the methods by which microplastics are detected in the marine environment; (4) to assess spatial and temporal trends of microplastic abundance; and (5) to discuss the environmental impact of microplastics. Microplastics are both abundant and widespread within the marine environment, found in their highest concentrations along coastlines and within mid-ocean gyres. Ingestion of microplastics has been demonstrated in a range of marine organisms, a process which may facilitate the transfer of chemical additives or hydrophobic waterborne pollutants to biota. We conclude by highlighting key future research areas for scientists and policymakers.     

Numerical modelling of floating debris in the world's oceans

A global ocean circulation model is coupled to a Lagrangian particle tracking model to simulate 30 years of input, transport and accumulation of floating debris in the world ocean. Using both terrestrial and maritime inputs, the modelling results clearly show the formation of five accumulation zones in the subtropical latitudes of the major ocean basins. The relative size and concentration of each clearly illustrate the dominance of the accumulation zones in the northern hemisphere, while smaller seas surrounded by densely populated areas are also shown to have a high concentration of floating debris. We also determine the relative contribution of different source regions to the total amount of material in a particular accumulation zone. This study provides a framework for describing the transport, distribution and accumulation of floating marine debris and can be continuously updated and adapted to assess scenarios reflecting changes in the production and disposal of plastic worldwide.     

The oceans as source of cloud-forming nuclei

Summary The number and size of salt particles produced by the bursting of air bubbles in sea water has been measured. Bubbles of diameters varying between 1/2 and 2 mm each produced about 300 nuclei the sizes of which, under the electron microscope, were mainly between 0.1 and 0.5 diameter. They appeared to consist mainly of sodium chloride, the smallest ones containing only 10^–15 g of salt.These results, together with measurements of the size distribution of salt nuclei collected over the oceans in areas of spray formation, indicate that the total concentrations of salt nuclei over the oceans in winds of up to 15 m sec^–1 probably do not exceed 100 cm^–3. The corresponding rate of production of salt nuclei at the sea surface is estimated to be 1000 cm^–2 sec^–1. It is therefore inferred that sea spray contributes perhaps only one-fifth of the nuclei involved in cloud formation, the majority being the products of combustion, either natural or man-made.     

Comments on some aspects of particulate transport in the oceans

Recent studies of dissolved and particulate concentrations of trace elements and radionuclides amply demonstrate the importance of particulate transport in the case of several elements. A significant in-situ addition (J-flux) or removal (J-efflux) occurs in the case of a number of elements. However, to date it is not clear how the particulate processes occur and how the particles themselves are transported. Some of the problems are outlined briefly.It is shown that whereas a substantial flux in the case of some elements is due to transport by consolidated fecal particles, this transport does not generally lead to any substantial in-situ addition to deep waters. Changes in the dissolved concentrations of elements within the oceans occur due to small particles (1–10 μm) which sink stochastically with a mean speed of ～10^?3 cm/s. The larger particles sinking at higher Stokes' velocities impact and carry along the small particles. The smaller particles, ～1 μm size are thus transported down rapidly by the larger particles by apiggy-back mechanism. Simple theoretical calculations are consistent with the measured vertical transport rates based on studies of radionuclides.     

Electrocoagulation/Electroflotation Process for Removal of Organics and Microplastics in Laundry Wastewater

In the present research, laundry wastewater treatment is studied using the electrocoagulation/electroflotation process. For the optimization of treatment conditions such as electrode type (Al–Al, Al–Fe, Fe–Fe, and Fe–Al), initial pH (5–9), current (0.54–2.16 A), and application time (15–60 min), response surface methodology is used. Removal efficiencies of chemical oxygen demand (COD), color, anionic surfactant, microplastic, and phosphate are studied. It is determined that the most effective removal is obtained with 2.16 A current, pH 9, and 60 min reaction time using Fe–Al electrode. Here, 91%, 94%, 100%, and 98% removal efficiencies are achieved for COD, surfactant, color, and microplastic, respectively. The operating cost of the combined process is calculated as $1.32 m^?3 for the optimum removal parameters. The adsorption kinetics study shows that the removal follows second‐order kinetics. The laboratory‐scale test results indicate that the electrocoagulation/electroflotation process is feasible for the treatment of laundry wastewater.