Regions of enhanced chlorophyll-a concentrations can be identified by applying a threshold to the concentration value to a forecast and observed field (or analysis). These regions can then be treated and analysed as features using diagnostic techniques to consider of the evolution of the chlorophyll-a blooms in space and time. This allows us to understand whether the biogeochemistry in the model has any skill in predicting these blooms, their location, intensity, onset, duration and demise.

We propose a probabilistic method and a new inter-class comparison metric for highlighting fronts in the Southern Ocean. We compare it with an image processing method that provides a more localised view of fronts that effectively highlights sharp jets. These two complementary approaches offer two views of Southern Ocean structure: the probabilistic method highlights boundaries between coherent thermohaline structures across the entire Southern Ocean, whereas edge detection highlights local jets.

Internal tides are responsible for surface deformations of the ocean that could affect the measurements of the forthcoming SWOT altimetric mission and need to be corrected. This study highlights the variability of the properties of internal tides based on the stratification variability only. A single methodology is successfully applied in two areas driven by different oceanic processes: the western equatorial Atlantic and the Bay of Biscay.

Research on strong El Niños has shown that they may be a result of a stronger-than-normal North Equatorial Counter Current, itself triggered by lower-than-normal sea levels that develop early in the year. A numerical model study of the 1981–1982 El Niño shows that the low sea levels are due to local winds in the west Pacific, and this is shown also to be true for the 1997–1998 and 2015–2016 El Niños. As a result, we now have a much better understanding of the mechanism causing strong El Niños.

Understanding tidal hydrodynamics is essential for water resources management in estuarine environments. In this study, we propose an analytical model to examine the fortnightly water level variations due to tidal motions alone in tide-dominated estuaries. Details of the analytical model show that changes in the mean depth or length of semi-arid estuaries affect the fortnightly tide amplitude, which has significant potential impacts on the estuarine ecosystem management.

Observations of sea level, taken manually by reading a tide pole, were carefully taken at a number of locations around Ireland in 1842 as part of the first land survey of Ireland. Our study investigates how useful this type of sea level observation is for understanding mean sea level and tidal change. We find that when carefully adjusted for seasonal, meteorological, and astronomical factors, these data can provide important insights into changing sea levels.

Here, we describe a strait that has narrow and shallow sills in both ends and is close to an amphidromic region. This generates tidally driven flows into and out of the strait, but with very different exchange rates across the entrances in both ends so that it behaves like a mixture between a strait and a fjord. Using a numerical model, we find a fortnightly signal in the net transport through the strait, generated by long-period tides. Our findings are verified by observations.

The exchange of carbon dioxide (CO₂) between the sea and the atmosphere is regulated by the gradient of CO₂ partial pressure (pCO₂) between the sea and the air. The daily variation of the seawater pCO₂ recorded at the fixed station Utö in the Baltic Sea was found to be mainly biologically driven. Calculation of the annual net exchange of CO₂ between the sea and atmosphere based on daily measurements of pCO₂ carried out using the same sampling time every day could introduce a bias of up to 12 %.

Over the past decade, understanding of the Indian Ocean has progressed through new observations and advances in theory and models of the oceanic and atmospheric circulation. This review brings together new understanding of the ocean–atmosphere system in the Indian Ocean, describing Indian Ocean circulation patterns, air–sea interactions, climate variability, and the critical role of the Indian Ocean as a clearing house for anthropogenic heat.

Non-linear tidal dynamics can produce prominent time-mean transport in coastal regions where strong tidal currents interact with topography. We investigate tidal-induced transport using a tidally driven ocean model for Lofoten–Vesterålen in northern Norway and find that both tidal pumping and tidal rectification can play an important role for time-mean transport in the region. The study emphasizes the importance of non-linear tidal dynamics for time-mean transport in complex coastal regions.

We investigated the spatial distribution pattern and diversity of phytoplankton communities in the western Pacific Ocean (WPO) in the autumn of 2016, 2017, and 2018. The regions with strong vertical stratification were more favorable for cyanobacteria, whereas weak vertical stratification was more conducive to diatoms and dinoflagellates. It is clear that physical processes control phytoplankton community structure by driving the balance of chemical elements.

The SWOT satellite will provide a step change in our ability to measure the sea surface height over large areas, and so improve operational ocean forecasts, but will be affected by large correlated errors. We found that while SWOT observations without these errors significantly improved our system, including correlated errors degraded most variables. To realise the full benefits offered by the SWOT mission, we must develop methods to account for correlated errors in ocean forecasting systems.

Waves that travel faster than the wind are called swell. Our study presents wave model statistics of swell waves in the Baltic Sea, since such statistics have not yet been reliably compiled. Our results confirm that long, high, and persistent swell is absent in the Baltic Sea. We found that the dependency between swell and wind waves differs in the open sea compared to nearshore areas. These distinctions are important for studies on how waves interact with the atmosphere and the sea floor.