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Estimating Ocean Tidal Loading and Sea-Level Variability in the Northern Adriatic Using GNSS positioning, Tide Gauges, and GNSS Reflectometry

Geophysical Journal International - Tue, 06/09/2026 - 00:00

AbstractThe northern Adriatic Sea provides an exceptional setting for investigating tidal processes because of its shallow bathymetry, elongated basin geometry, and semi-enclosed configuration. These characteristics produce some of the largest tidal amplitudes in the Mediterranean and favor the amplification of both diurnal and semidiurnal constituents, leading to complex sea-level variability and episodic extreme events such as high stands along the coastal cities. We analyze tidal dynamics and ocean tidal loading (OTL) in the northern Adriatic using a multi-technique approach that combines tide gauge (TG) observations, interferometric reflectometry (GNSS-IR) sea-level retrievals, and GNSS precise point positioning (PPP) solutions describing crustal deformation. Tide gauge records confirm the progressive increase of semidiurnal tidal energy toward the northern end of the basin, with the M2 and S2 constituents dominating over the diurnal band. These observations broadly agree with the FES2014b ocean tide model, although local amplitude and phase deviations are observed in shallow and geometrically complex coastal environments. Sea-level time series derived from GNSS-IR at several coastal sites show a high degree of agreement with nearby tide gauges, with correlations exceeding 90%. Both diurnal and semidiurnal constituents are well resolved, and amplitude differences remain within 4-5 cm, demonstrating the potential of GNSS-IR as an effective and low-cost complement to traditional TG networks. GNSS PPP solutions further allow the estimation of three-dimensional OTL displacements at hourly temporal resolution. The vertical component is primarily controlled by the semidiurnal M2 tide and closely matches model predictions in both amplitude and phase. Larger discrepancies are observed for diurnal constituents, particularly K1, likely related to interactions with GNSS orbital periods and remaining systematic effects in the processing. Overall, this work presents the first high-temporal-resolution GNSS-based assessment of ocean tidal loading in the northern Adriatic. The strong consistency among GNSS, GNSS-IR, and TG observations highlights the capability of integrated GNSS approaches to simultaneously capture oceanographic variability and solid Earth tidal deformation, opening new perspectives for coastal sea-level monitoring, geodetic stability studies, and hazard assessment in a changing climate.

Rocket launches and reentries harm Earth's ozone layer

Phys.org: Earth science - Mon, 06/08/2026 - 22:20

The space industry is surging. In coming years, nearly 10,000 spacecraft are slated to launch into low-Earth orbit for a variety of purposes, such as global surveillance, space tourism, and satellite "megaconstellations" providing internet service.

Brazilian breadbasket's aquifers are falling, and new satellite maps show where water stress is growing

Phys.org: Earth science - Mon, 06/08/2026 - 22:00

A collaboration of scientists from NASA and Brazilian research institutions has produced a detailed picture of groundwater change across Brazil. The images reveal significant declines in some of the aquifers that are critical to one of the world's largest agricultural producers.

Study reveals north–south differences in water isotopes across North America during the last deglaciation

Phys.org: Earth science - Mon, 06/08/2026 - 21:50

The last deglaciation (between 11,000 and 20,000 years ago) was a period of dramatic natural warming on Earth. During this time, North America experienced the most extensive ice-sheet melting on the planet, which profoundly reshaped its climate and water cycle. But when scientists look at oxygen isotopes in stalagmites—a key tool for reconstructing past climate—the signals from North America have been hard to interpret. A new study now provides a physical explanation for those puzzling patterns.

New Relative Niño index introduces more robust way to measure El Niño strength

Phys.org: Earth science - Mon, 06/08/2026 - 20:30

A new El Niño index that provides a more climate-robust measure of the strength of El Niño signals has been released by the European Centre for Medium-Range Weather Forecasts (ECMWF). With the World Meteorological Organization's recent update indicating an 80% likelihood of an El Niño event during June–August 2026 and a 90% probability of this continuing until at least November, it is more important than ever to have accurate, reliable data.

Ocean collapse triggered ancient wildfires, research suggests

Phys.org: Earth science - Mon, 06/08/2026 - 19:40

Research led by the University of Alabama found that widespread wildfires during one of Earth's ancient environmental crises did not trigger an ocean collapse but were a consequence of it.