The Indian Ocean receives a large proportion of plastics, but very few studies have addressed the sources, transport pathways, and sinks. There is a scarcity of observational data for the Indian Ocean. Most plastic sources are derived from rivers, although the amount derived from fishing activity (ghost nets, discarded ropes) is unknown. The unique topographic features of the Indian Ocean that create the monsoons and reversing currents have a large influence on the transport and sinks.

We use data crossing Herald Canyon in the Chukchi Sea collected in 2008 and 2014 together with numerical modelling to investigate the circulation in the western Chukchi Sea. A large fraction of water from the Chukchi Sea enters the East Siberian Sea south of Wrangel Island and circulates in an anticyclonic direction around the island. To assess the differences between years, we use numerical modelling results, which show that high-frequency variability dominates the flow in Herald Canyon.

This study explores the Arctic sea level variability depending on different timescales and the relation to temperature, salinity and mass changes, identifying key parameters and regions that need to be observed coordinately. The decadal sea level variability reflects salinity changes. But it can only reflect salinity change at periods of greater than 1 year, highlighting the requirement for enhancing in situ hydrographic observations and complicated interpolation methods.

This study uses a global oceanic model to investigate the seasonal dynamics of the sea surface partial pressure of CO₂ (pCO₂) in the global coastal ocean. Our method quantifies the respective effects of thermal changes, biological activity, ocean circulation and freshwater fluxes on the temporal pCO₂ variations. The performance of our model is also evaluated against a data product derived from observations to identify coastal regions where our approach is most robust.

Water exchange through the Åland Sea (in the Baltic Sea) affects the conditions in the neighbouring Gulf of Bothnia. Pathways and variability of flows were studied with a high-resolution hydrodynamic model. Our analysis showed a northward transport in the deep layer and net transport towards the south in the surface layer. While on the southern edge of the Åland Sea the primary route of deep-water exchange is through Lågskär Deep, some deep water still bypasses it to the Åland Sea.

This study uses a novel satellite-independent approach to quantify the components of Arctic sea level change. The 21-year time series allows studying climate-related changes in Arctic sea level. The decomposition shows that fresh water is governing sea level change, while Arctic land ice loss contributes to a small Arctic sea level rise. The reconstruction yields good agreement with sea level observations from altimetry, despite both datasets being challenged by the harsh environment.

Atlantic Water (AW) and Levantine Intermediate Water (LIW) are important water masses that play a crucial role in the internal variability of the Mediterranean thermohaline circulation. This work aims to characterize the inter-basin and inter-annual variability of AW and LIW in the Mediterranean Sea, taking advantage of the large observational dataset provided by Argo floats from 2001 to 2019. A clear salinification and warming trend characterizes AW and LIW over the last 2 decades.

Inland seas are critical habitats for globally important fisheries, and the local food webs that support these fisheries are often limited by surface nutrient availability. In the Strait of Georgia, which supports several key northern Pacific fisheries, we identify wind-driven upwelling as a dominant source of summer surface nutrients using a high-resolution coupled ecosystem model. This newly identified underlying mechanism will inform interpretations of ecosystem variability in the region.

Turbulent mixing is crucial in the aquatic environment for regulating the water column structure and the availability of nutrients to support ecosystems. Improving our understanding of how mixing varies with changes in weather, tides, and wave conditions is therefore a key challenge. This paper examines how to avoid and, where necessary, correct for bias due to instrument motion when using a relatively new technique for making long-term observations of turbulence using a moored current meter.

The southern Indian Ocean is one of the major basins for regional heat accumulation and sea level rise. The year-to-year changes of regional sea level are influenced by water exchange with the Pacific Ocean via the Indonesian Throughflow. Using a general circulation model, we show that the spatiotemporal pattern of these changes is primarily set by local wind forcing modulated by El Niño–Southern Oscillation, while oceanic signals originating in the Pacific can amplify locally forced signals.

(1) The intensity of the longitudinal estuarine circulation kept increasing as the estuary width continued to decrease. (2) The changes in water depth were the dominant factor affecting lateral circulation intensity. (3) The changes in the estuarine circulation were dominated by the changes in the baroclinic pressure gradient force and advection.

Natural sources of atmospheric methane need to be better described and quantified. We present time series from ocean observatories monitoring two seabed methane seep sites in the Arctic. Methane concentration varied considerably on short timescales and seasonal scales. Seeps persisted throughout the year, with increased potential for atmospheric release in winter due to water mixing. The results highlight and constrain uncertainties in current methane estimates from seabed methane seepage.

Chlorophyll a (Chl a), which is the primary pigment used in photosynthesis, often retains its maximum value in the subsurface layer rather that at the surface. In this study, we integrate Chl a concentration data from recent biogeochemical floats, as well as from historical ship-based and other observations, and present global maps of subsurface Chl a concentration and seasonal and interannual variations with related variables, i.e., light intensity, nitrate concentration, and oxygen production.

A large amount of marine litter, such as plastics, is located on or around beaches. Both the total amount of this litter and its transport are poorly understood. We investigate this by training a machine learning model with data of cleanup efforts on Dutch beaches between 2014 and 2019, obtained by about 14 000 volunteers. We find that Dutch beaches contain up to 30 000 kg of litter, largely depending on tides, oceanic transport, and how exposed the beaches are.