Seasonal variability of sea surface height in the coastal waters and deep basins of the Nordic Seas

Sea surface height measured by the Envisat radar altimeter over open ocean and from leads in sea ice are combined to generate a complete view of variability in the Nordic Seas, geographically and seasonally. The observed seasonal variability is decomposed using empirical orthogonal functions, and is consistent with seasonal variations in steric and dynamic forcing. Wintertime increase in sea surface height on the east Greenland shelf is hypothesised to be caused by wind-forced downwelling, which provides direct evidence for the regional play of coastal dynamics. High levels of eddy kinetic energy around the sea ice edge in Fram Strait, and off east Greenland and Svalbard are consistent with the interaction of the wind with the ice edge

Altimetry for the future: Building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ‘‘Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

Altimetry for the future: building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the “Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

Long-term variability of near-bottom oxygen, temperature, and salinity in the Southern Baltic

Bottom conditions in deep sea basins are strongly connected to the health of marine ecosystems. Due to its enclosed location and shallow bathymetry, the Baltic Sea is very sensitive to eutrophication and climate change. The primary objective of this study is to describe long-term variability of near-bottom oxygen concentration, salinity, and temperature in three basins of the Southern Baltic: the Bornholm Basin (BB), Slupsk Furrow (SF), and Gdansk Deep (GD) based on the analysis of historical hydrographic data, and to demonstrate the impact of inflow events on deep ventilation in those basins. Mean bottom oxygen concentration in the period 1946–2016 was very similar in the deep basins (1.2–1.4 ml l−1), and much higher in the shallower SF (3.2 ml l−1) due to the water mass modification occurring between BB and SF. SF was found to contribute to the ventilation of GD with a 1–3-month lag. The results indicate that vertical mixing in SF and the eastward advection of ventilated waters towards GD directly influence bottom water properties in GD. Therefore, next to Major Baltic Inflows (MBIs), also weaker barotropic and baroclinic inflows are important for the bottom ventilation in this area. The long-term trends are very similar in all of the basins. Near-bottom oxygen gradually decreased from 1946, reaching a minimum in 2000. This coincided with salinity and temperature minimums and was linked to reduced frequency and volume of barotropic inflows due to their decadal variability. Oxygen concentrations have been slowly recovering in all three basins since 2000. At the end of the record, their 5-year mean values were approximate to the levels from the 1970's. In the period 1946–2016, hypoxia (oxygen concentration below 2 ml l−1) occurred more frequently in BB (78%) than in GD (73%). Although the results show slow recovery of dissolved oxygen concentrations based on 5-year long mean values, the occurrence of hypoxia increased over the last two decades, reaching 85% in BB and GD and 24% in SF. Mean and decadal variability of the seasonal cycle of near-bottom water properties were analysed. Mean annual cycles of bottom oxygen in three basins are approximately sinusoidal, with the highest values occurring in March, and lowest in September. The range of the mean oxygen seasonal cycle decreases eastward from 1.6 ml l−1 in BB, through 1.3 ml l−1 in SF, to 1.2 ml l−1 in GD. Furthermore, between 1946–1980 and 1995–2016, the range of the mean DO seasonal cycle decreased by 0.2 ml l−1 in BB, 0.6 ml l−1 in SF, and 0.4 ml l−1 in GD. In BB and SF, minimum bottom temperatures occur in summer, and maximum in winter. The strongest annual temperature variation (3 °C) occurs in SF, and is smaller in BB (1.5 °C) and GD (1 °C). The amplitude of the seasonal salinity variation is approximately 0.5 psu in all basins. In BB and GD, a drop in salinity is observed in autumn