Sea-level variability and change along the Norwegian coast between 2003 and 2018 from satellite altimetry, tide gauges and hydrography

Sea-level variations in coastal areas can differ significantly from those in the nearby open ocean. Monitoring coastal sea-level variations is therefore crucial to understand how climate variability can affect the densely populated coastal regions of the globe. In this paper, we study the sea-level variability along the coast of Norway by means of in situ records, satellite altimetry data, and a network of eight hydrographic stations over a period spanning 16 years (from 2003 to 2018). At first, we evaluate the performance of the ALES-reprocessed coastal altimetry dataset by comparing it with the sea-level anomaly from tide gauges over a range of timescales, which include the long-term trend, the annual cycle and the detrended and deseasoned sea level anomaly. We find that coastal altimetry outperforms conventional altimetry products at most locations along the Norwegian coast. We later take advantage of the coastal altimetry dataset to perform a sea level budget along the Norwegian coast. We find that the thermosteric and the halosteric signals give a comparable contribution to the sea-level trend along the Norwegian coast, except for three, non-adjacent hydrographic stations, where salinity variations affect the sea-level trend more than temperature variations. We also find that the sea-level annual cycle is more affected by variations in temperature than in salinity, and that both temperature and salinity give a comparable contribution to the detrended and deseasoned sea-level along the entire Norwegian coast.

The Notau harbour and the Kontor in Bergen

The Hanseatic Kontor in Bergen was one of the main hubs of trade in the North Sea region. This paper explores a possibility suggested in a late sixteenth-century manuscript that the Norwegian Kontor for some time was also located at Notau, a place south of Bergen. It is argued that this written source might refer to the years 1427–33 when the Hanseatic merchants withdrew from Bergen because of an on-going war between King Erik and northern German princes. Notau is mentioned several times in sources from the fifteenth century and most of these references are related to Hanseatic activity. However, viewed in a broader context, Notau stands out as an important harbour on the south-western Norwegian coast, visited both by Norwegians and Hanseatics, as well as travellers from other regions.

Northern extension of Lesueurigobius friesii (Malm, 1874) (Pisces: Gobiidae) distribution and the gobiid diversity decline along the Norwegian coast

Lesueurigobius friesii was collected in Eidsfjorden, Sognefjorden, Norway, extending its known distribution range north as the new northernmost locality of this species. Globally, the northernmost presence of gobies is along the coast of Norway. Their diversity along the Norwegian coast showed an evident latitude gradient of gobiid diversity with a clear decrease from south to north. The significant regression structural change was found at the 63/64° N latitude band followed by a 36.4% decrease in gobiid species diversity. The species traits of gobiids north of the regression breaking point and those restricted to the south of it were compared. The only significantly more frequent characteristic of species passing north of the regression breaking point is the large depth range that reach down to the shelf break. All species present north of the point, except Thorogobius ephippiatus (that barely passes it) belong to Oxudercinae (i.e. to Pomatoschistuslineage of that subfamily).

An Attempt to Observe Vertical Land Motion along the Norwegian Coast by CryoSat-2 and Tide Gauges

Present-day climate-change-related ice-melting induces elastic glacial isostatic adjustment (GIA) effects, while paleo-GIA effects describe the ongoing viscous response to the melting of late-Pleistocene ice sheets. The unloading initiated an uplift of the crust close to the centers of former ice sheets. Today, vertical land motion (VLM) rates in Fennoscandia reach values up to around 10 mm/year and are dominated by GIA. Uplift signals from GIA can be computed by solving the sea-level equation (SLE), S ˙ = N ˙ − U ˙ . All three quantities can also be determined from geodetic observations: relative sea-level variations ( S ˙ ) are observed by means of tide gauges, while rates of absolute sea-level change ( N ˙ ) can be observed by satellite altimetry; rates of VLM ( U ˙ ) can be determined by GPS (Global Positioning System). Based on the SLE, U ˙ can be derived by combining sea-surface measurements from satellite altimetry and relative sea-level records from tide gauges. In the present study, we have combined 7.5 years of CryoSat-2 satellite altimetry and tide-gauge data to estimate linear VLM rates at 20 tide gauges along the Norwegian coast. Thereby, we made use of monthly averaged tide-gauge data from PSMSL (Permanent Service for Mean Sea Level) and a high-frequency tide-gauge data set with 10-min sampling rate from NMA (Norwegian Mapping Authority). To validate our VLM estimates, we have compared them with the independent semi-empirical land-uplift model NKG2016LU_abs for the Nordic-Baltic region, which is based on GPS, levelling, and geodynamical modeling. Estimated VLM rates from 1 Hz CryoSat-2 and high-frequency tide-gauge data reflect well the amplitude of coastal VLM as provided by NKG2016LU_abs. We find a coastal average of 2.4 mm/year (average over all tide gauges), while NKG2016LU_abs suggests 2.8 mm/year; the spatial correlation is 0.58.