Abstracted/indexed

This paper presents an efficient method for high-resolution ocean modelling based on a combination of the deterministic and stochastic approaches. The method utilises mathematical tools similar to those developed for data assimilation in ocean modelling. The main difference is that instead of assimilating a relatively small number of observations, the SDD method assimilates all the data produced by a parent model. The method is applied to create an operational Stochastic Model of the Red Sea.

Mesoscale eddies are an important part of the turbulent motion in the oceans, constituting coherent structures that can live for years storing physical properties anomalies. Analysis of anticyclones (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.

Little is known about the impact of chlorophyll on SST in the Bay of Bengal (BoB). Solar irradiance measured by an ocean glider and three Argo floats are used to determine the effect of chlorophyll on BoB SST during the 2016 summer monsoon. The Southwest Monsoon Current has high chlorophyll concentrations (~ 0.5 mg m⁻³) and shallow solar penetration depths (~ 14 m). Ocean mixed layer model simulations show that SST increases by 0.35 °C month⁻¹ with the potential to influence monsoon rainfall.

Experiments in the rotating tanks can simulate the earth system and help to represent the real ocean where the rotation plays an important role. We want to show the minor importance of the wind in driving the flow in the Ionian Sea. This we show by observing changes of water current in the rotating tank affected only by pumping of the dense water into the system. The flow variations are alike to what happens in the real sea confirming the scarce importance of the wind for the flow in the Ionian.

This special issue marks the 100th anniversary of the Liverpool Tidal Institute. This preface summarises how the LTI came about and the roles of its first two Directors. It also gives an overview of research on tides at the LTI. Summaries are given of the 26 papers in the special issue. The topics of many of them could be thought of as providing a continuation of the research first undertaken at the LTI. They provide a snapshot of work on tides now being made by groups around the world.

Satellite altimetry have revolutionized the ocean observation by monitoring the sea level with a very good spatio-temporal coverage. However, only the sea level anomalies are retrieved; to monitor the whole oceanic signal a temporal mean (called MDT=Mean Dynamic Topography) must be added to these anomalies. In this study we present the newly updated CNES-CLS18 MDT. An evaluation of this new solution shows significant improvements both in strong currents and coastal areas.

Six tropical areas in the Pacific, Atlantic and Indian Ocean were investigated for trends for the years since 1950 in temperature, salinity, oxygen and nutrients for the layers 50 to 300 m and 300 to 700 m depths. Generally, temperature increases, oxygen decreases while nutrients often increase. Overlain variability on the trends seem to be related to climate modes. Different trends indicate that oxygen and nutrient trends cannot by completely explained by local warming.

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 a 12 %.

In our laboratory experiments we addressed the question of how surface standing waves in a closed stratified basin are getting damped by the interaction of the flow in the bulk with a sill-like bottom obstacle reaching up to a density interface between the more saline deep layer and the freshwater layer at the top. We quantify the decay rates of the surface waves and explore what types of internal waves can be excited in this process along the internal density interface.

This study presents the three-dimensional imaging of a large ocean volume in the Gulf of Mexico. We found that the time variation barely affects imaging in the survey vessel's sailing direction, but heavily affects the imaging perpendicular to the sailing direction. Most importantly, the obtained ocean volume represents a series of snapshots of the ocean revealing the evolution of ocean structures over time. This research provides essential understanding for 3D seismic oceanography.

In support of the developing ocean renewable energy sector, and indeed all mariners, we have developed a new tidal model for Australian waters and thoroughly evaluated it using a new compilation of tide gauge and current meter data. We show that while there is certainly room for improvement, the model provides useful predictions of tidal currents for about 80 % (by area) of Australian shelf waters. So we intend to commence publishing tidal current predictions for those regions soon.

Paper concerns with developing methods for 24/7/365 monitoring of plankton while controlling key environmental conditions at precise depths. The method is based on using high-frequency acoustical device in a manner that gets it sufficiently close to the animals of interest. Such data are used to visualize the breathtaking dynamics of the sound scattering plankton and month-to-month variations of plankton diel vertical migrations and diapause displacements in the hypoxic zone of the Black Sea.

Freshwater in the Arctic Ocean plays a critical role in the global climate system by impacting ocean circulations, stratification, mixing, and emergent regimes. In this review paper we assess how the Arctic freshwater budget in the 2010s has changed relative to the 2000s. Estimates from satellites and reanalyses show a stabilization in the 2010s due to an increased compensation between a freshening of the Beaufort Gyre and a reduction in freshwater in the Amerasian and Eurasian basins.

Free sea level oscillations in stratified (baroclinic) and unstratified (barotropic) conditions were examined using numerical experiments based on a 3D hydrodynamic model of the Baltic Sea. We identified free barotropic oscillations of periods of 44, 41, 37, 29, 21, 16, and 15 h that have not been noted previously. In stratified basins both the high-frequency (daily/hourly scales) and the low-frequency free oscillations of seasonal scale have been recorded.

Atlantic Waters carry heat and salt towards Arctic. The goal of this study was to study how the heat flux changes with its journey to the north. It was shown that despite the fact that there is some connection between variability of the heat flux near the shores of Norway and heat fluxes in the northern part of the Fram Strait. There are different processes governing this variability, which results in a different tendencies in the southern and northern regions of the study.

Multi-spectral optical sensors and models are increasingly adopted to study marine systems. In this work, BOUSSOLE mooring and biogeochemical Argo float optical observations are combined with the Ocean–Atmosphere Model (OASIM) to analyse the variability of sunlight at the sea surface. We show that the model skill in simulating data varies according to the wavelength of light and temporal scale considered, and that is significantly affected by cloud dynamics.

In order to improve forecasting skills of South China Sea Operational Forecasting System operated in NMEFC of China, comprehensive updates have been conducted to the configurations of physical model and data assimilation scheme. Scientific inter-comparison and accuracy assessment has been performed by employing GODAE IV-TT Class 4 metrics. The results indicate that remarkable improvements have been achieved in the new version of SCSOFS.