The Atlantic Meridional Overturning Circulation (AMOC) quantifies the impact of the ocean on climate and climate change. Here we show that a high-resolution ocean model is able to realistically simulate ocean currents. While the mean representation of the AMOC depends on choices made for the model and on the atmospheric forcing, the temporal variability is quite robust. Comparing the ocean model with ocean observations, we able to identify that the AMOC has declined over the past two decades.

In this work we used a concept called geochemical fingerprinting, with isotopes of neodymium and lead as tools to recognize the main sources and the physical processes responsible for the transport and deposition of sediments on a large area of the South Atlantic margin. Distinct sources, such as Antarctica, the Andean Cordillera, the Río de la Plata basin, and old rocks from the Brazilian shield, are identified.

Mesoscale eddies are an important part of the turbulent motion in the oceans, constituting coherent structures that can live for years and store physical property anomalies. Analysis of anticyclone (clockwise-rotating eddies) tracks in the eastern Levantine Basin revealed statistical patterns over 19 years of data, in particular the presence of an anticyclone attractor above the Eratosthenes Seamount, with a strong heat content signature.

On top of forced changes such as human-caused global warming, unforced climate variability exists. Most multidecadal variability (MV) involves the oceans, but current climate models use non-turbulent, coarse-resolution oceans. We investigate the effect of resolving important turbulent ocean features on MV. We find that ocean heat content, ocean–atmosphere heat flux, and global mean surface temperature MV is more pronounced in the higher-resolution model relative to higher-frequency variability.

Due to the need to obtain a greater amount of data in less time in areas with little in situ hydrographic data, an algorithm based on cluster analysis is proposed. This algorithm allows real-time quality control of Argo data which has patterns similar to data in delayed mode. To test this, a study area of high scientific interest but with little concentration of in situ data was chosen. In this area 80 % of the data normally discarded because of salinity drifts was recovered.

Acoustic and satellite observations of turbulent ship wakes show that ships can mix the water column down to 30 m depth and that a temperature signature of the wake can last for tens of kilometres after ship passage. Turbulent wakes deeper than 12 m were frequently detected, which is deeper than previously reported. The observed extent of turbulent ship wakes implies that in areas with intensive ship traffic, ship mixing should be considered when assessing environmental impacts from shipping.

Oxygen-poor regions in the open ocean restrict marine habitats. Global climate simulations show large uncertainties regarding the prediction of these areas. We analyse the representation of the simulated oxygen minimum zones in the Arabian Sea using 10 climate models. We give an overview of the main deficiencies that cause the model–data misfit in oxygen concentrations. This detailed process analysis shall foster future model improvements regarding the oxygen minimum zone in the Arabian Sea.

In the North Atlantic, ocean currents carry warm surface waters northward and return cooler deep waters southward. This type of ocean circulation, known as overturning, is important for the Earth’s climate. This overturning has been measured using a mooring array at 26° N in the North Atlantic since 2004. Here we use these mooring data and global satellite data to produce a new method for monitoring the overturning over longer timescales, which could potentially be applied to different latitudes.

The bluebottle (Physalia physalis), or Portuguese man o' war, is well known for the painful stings caused by its tentacles. Its drifting dynamics have not been widely explored, with previous studies using simple assumptions to calculate its drift. Considering similarities with a sailboat, we present a new theoretical model for the drifting speed and course of the bluebottle in different wind and ocean conditions, providing new insights into the parameterization of its complex drifting dynamics.

Recent work has highlighted the dominant role of the Irminger and Iceland basins in the production of North Atlantic Deep Water. From our analysis, we find that air–sea fluxes and the ocean surface density field are both key determinants of the buoyancy-driven transformation in the Iceland Basin. However, the spatial distribution of the subpolar mode water (SPMW) transformation is most sensitive to surface density changes as opposed to the direct influence of the air–sea fluxes.

Significant trends of sea ice in Hudson Bay have led to a considerable increase in shipping activity. Therefore, understanding sea level variability is an urgent issue crucial for safe navigation and coastal infrastructure. Using the sea level, atmospheric and river discharge data, we assess environmental factors impacting variability of sea level at Churchill. We find that it is dominated by wind forcing, with the seasonal cycle generated by the seasonal cycle in atmospheric circulation.

The Equatorial Undercurrent (EUC) is a key influence on upwelling of nutrient-rich waters associated ecosystems off Peru. To quantify this influence, we backtrack upwelling waters in a computer model of ocean currents, annually, over 1989–2007. The EUC influence varies from year to year, dominating in warm El Niño years, when the EUC extends much closer to the Peruvian coast. In other years, more local upwelling is associated with coastal winds, coincident with major key population shifts.

A narrow tidal strait often leads to net transport in one direction, and the water flowing through the strait is not the same as the water that is drawn back into the strait when the tidal flow turns. We investigated this process by simulating the transport through tidal straits of different lengths and widths. A simple theory is established that describes the net transport. The theory can be applied to real coastlines when predicting spreading of pollution and other substances in the ocean.

A suspended particulate matter distribution against a hydrographical background was studied along an oceanographic transect across the Equatorial Atlantic in the year 2000. Alongside the general agreement with the three-layer model of the ocean suspended particulate matter distribution, there was a massive area with high SPM concentrations above the Sierra Leone Rise and local SPM maxima in the bottom layer within Antarctic Bottom Water.

Satellite measurements of sea surface salinity (SSS) are compared with measurements in the ocean to verify the quality of the satellite data. SSS satellites measure average values over a footprint with size of ~100 km, whereas ocean values are usually taken at a single point in space and time. Using SSS data from a network of buoys across the global tropics, we estimate the size of the mismatch between satellite and in situ measurements to better understand the error structure of the satellite.

The Gulf Stream and the Kuroshio are major currents of the North Atlantic and North Pacific, respectively. They transport warm water northward and are key components of the Earth climate system. For this study, we looked at how they affect the sea level of the coasts of Japan, the USA and Canada. We found that the inshore sea level co-varies with the north-to-south shifts of the Gulf Stream and Kuroshio. In the paper, we discuss the physical mechanisms that could explain the agreement.

We characterized the pattern and magnitude of decadal sea-level variability in the Australasian Mediterranean Sea by using high-resolution ocean models. Our results suggest low-frequency ENSO variations and PDO-related changes as a primary source of variability. Sensitivity experiments indicate that anomalies are primarily driven by wind stress fluctuation but are also amplified by local heat and freshwater fluxes. Intrinsic variability is relevant in the South China Sea.

The large oxygen minimum zones in the tropical Pacific Ocean are still not well represented by typical climate models. We analyze a set of ocean models and highlight the fact that an oxygen concentration that is too low at intermediate depth in the subtropical regions associated with a sluggish representation of the intermediate equatorial current system may be responsible for the overly large extension of the modeled oxygen minimum zones, potentially hampering future projections.

In 2018, the Canadian Coast Guard approved a science team to sample in tandem with its ice-breaking and ship escorting operations. This collaboration provided the first mixing observations during winter that covered the largest spatial extent of the St. Lawrence Estuary and the Gulf of St. Lawrence ever measured in any season. Contrary to previous assumptions, we demonstrate that fluvial nitrate inputs from upstream (i.e., Great Lakes) are the most significant source of nitrate in the estuary.