scholarly journals Non-stationary analysis of water level extremes in Latvian waters, Baltic Sea, during 1961–2018

2021 ◽  
Vol 21 (4) ◽  
pp. 1279-1296
Author(s):  
Nadezhda Kudryavtseva ◽  
Tarmo Soomere ◽  
Rain Männikus
Keyword(s):  
Time Series ◽  
Baltic Sea ◽  
Water Level ◽  
Shape Parameter ◽  
Linear Trend ◽  
Significant Linear Trend ◽  
Gulf Of Riga ◽  
Baltic Proper ◽  
The Baltic ◽  
Eastern Baltic

Abstract. Analysis and prediction of water level extremes in the eastern Baltic Sea are difficult tasks because of the contribution of various drivers to the water level, the presence of outliers in time series, and possibly non-stationarity of the extremes. Non-stationary modeling of extremes was performed to the block maxima of water level derived from the time series at six locations in the Gulf of Riga and one location in the Baltic proper, Baltic Sea, during 1961–2018. Several parameters of the generalized-extreme-value (GEV) distribution of the measured water level maxima both in the Baltic proper and in the interior of the Gulf of Riga exhibit statistically significant changes over these years. The most considerable changes occur to the shape parameter ξ. All stations in the interior of the Gulf of Riga experienced a regime shift: a drastic abrupt drop in the shape parameter from ξ≈0.03±0.02 to ξ≈-0.36±0.04 around 1986 followed by an increase of a similar magnitude around 1990. This means a sudden switch from a Fréchet distribution to a three-parameter Weibull distribution and back. The period of an abrupt shift (1986–1990) in the shape parameters of GEV distribution in the interior of the Gulf of Riga coincides with the significant weakening of correlation between the water level extremes and the North Atlantic Oscillation (NAO). The water level extremes at Kolka at the entrance to the Gulf of Riga reveal a significant linear trend in shape parameter following the ξ≈-0.44+0.01(t-1961) relation. There is evidence of a different course of the water level extremes in the Baltic proper and the interior of the Gulf of Riga. The described changes may lead to greatly different projections for long-term behavior of water level extremes and their return periods based on data from different intervals. Highlights. Water level extremes in the eastern Baltic Sea and the Gulf of Riga are analyzed for 1961–2018. Significant changes in parameters of generalized-extreme-value distribution are identified. Significant linear trend in shape parameter is established at Kolka. The shape parameter changes in a step-like manner. The shape parameter of GEV has regime shifts around 1986 and 1990 in the gulf.

scholarly journals Non-stationary analysis of water level extremes in Latvian waters, Baltic Sea, during 1961–2018

2020 ◽  
Author(s):  
Nadezhda Kudryavtseva ◽  
Tarmo Soomere ◽  
Rain Männikus
Keyword(s):  
Time Series ◽  
Baltic Sea ◽  
Water Level ◽  
Shape Parameter ◽  
Extreme Value Distribution ◽  
Scale Parameters ◽  
Stationary Analysis ◽  
Gulf Of Riga ◽  
Baltic Proper ◽  
The Baltic

Abstract. Analysis and prediction of water level extremes in the eastern Baltic Sea is a difficult task because of the contribution of various drivers to the water level, the presence of outliers in time series and possibly non-stationarity of the extremes owing to the changes in the atmospheric forcing. Non-stationary modelling of extremes was performed to the block maxima of water level derived from the time series at six locations in the Gulf of Riga and one location in the Baltic proper, Baltic Sea, during 1961–2018. Several parameters of the Generalised Extreme Value distribution of the measured water maxima both in the Baltic proper and in the interior of the Gulf of Riga exhibit statistically significant changes over these years. The most considerable changes occur to the shape parameter ξ. All stations in the interior of the Gulf of Riga experienced a regime shift: a drastic abrupt drop of the shape parameter from ξ ≈ 0.03 ± 0.02 to ξ ≈ −0.36 ± 0.04 around 1986 followed by an increase of a similar magnitude around 1990. This means a sudden switch from a Fréchet distribution to a three-parameter Weibull distribution and back. The water level extremes at Liepaja in the Baltic proper and Kolka at the entrance to the Gulf of Riga reveal significant linear trends in the location and scale parameters. This pattern indicates a different course of the water level extremes in the Baltic proper and the interior of the Gulf of Riga. The described changes may lead to greatly different projections for long-term behaviour of water level extremes and their return periods based on data from different intervals.

scholarly journals Nutrient transports in the Baltic Sea – results from a 30-year physical–biogeochemical reanalysis

2017 ◽  
Vol 14 (8) ◽  
pp. 2113-2131 ◽  
Author(s):  
Ye Liu ◽  
H. E. Markus Meier ◽  
Kari Eilola
Keyword(s):  
Baltic Sea ◽  
Cross Sections ◽  
Ocean Model ◽  
Optimal Interpolation ◽  
Nutrient Concentrations ◽  
Biogeochemical Model ◽  
The Baltic Sea ◽  
Gulf Of Riga ◽  
Baltic Proper ◽  
The Baltic

Abstract. Long-term oxygen and nutrient transports in the Baltic Sea are reconstructed using the Swedish Coastal and Ocean Biogeochemical model (SCOBI) coupled to the Rossby Centre Ocean model (RCO). Two simulations with and without data assimilation covering the period 1970–1999 are carried out. Here, the weakly coupled scheme with the Ensemble Optimal Interpolation (EnOI) method is adopted to assimilate observed profiles in the reanalysis system. The reanalysis shows considerable improvement in the simulation of both oxygen and nutrient concentrations relative to the free run. Further, the results suggest that the assimilation of biogeochemical observations has a significant effect on the simulation of the oxygen-dependent dynamics of biogeochemical cycles. From the reanalysis, nutrient transports between sub-basins, between the coastal zone and the open sea, and across latitudinal and longitudinal cross sections are calculated. Further, the spatial distributions of regions with nutrient import or export are examined. Our results emphasize the important role of the Baltic proper for the entire Baltic Sea, with large net transport (export minus import) of nutrients from the Baltic proper into the surrounding sub-basins (except the net phosphorus import from the Gulf of Riga and the net nitrogen import from the Gulf of Riga and Danish Straits). In agreement with previous studies, we found that the Bothnian Sea imports large amounts of phosphorus from the Baltic proper that are retained in this sub-basin. For the calculation of sub-basin budgets, the location of the lateral borders of the sub-basins is crucial, because net transports may change sign with the location of the border. Although the overall transport patterns resemble the results of previous studies, our calculated estimates differ in detail considerably.

scholarly journals SEA LEVEL VARIATIONS AT THE LATVIAN COASTAL HYDROLOGIC STATIONS

2016 ◽  
Vol 42 (2) ◽  
pp. 31-38
Author(s):  
Diāna Haritonova
Keyword(s):  
Time Series ◽  
Baltic Sea ◽  
Sea Level ◽  
The Baltic Sea ◽  
Gulf Of Riga ◽  
Water Level Variations ◽  
Sea Level Variations ◽  
Tidal Constituents ◽  
The Baltic ◽  
Tidal Variations

The objective of this paper is to analyse water level variations of the Baltic Sea on the Latvian coast. This is important because the Baltic Sea exhibits a number of remarkable phenomena. One of them is the sea level variations due to winds, complicated by the shape of the gulfs and islands. Under this influence the range of the sea level variations can reach 3 m on the coasts of gulfs. However, the tidal variations of the Baltic Sea range in the order of centimetres only. In the frame of this study, using hourly time series of the sea level records from 7 Latvian coastal hydrologic stations and employing spectral analysis, it has become feasible to identify diurnal and semi-diurnal tide existence both in the Gulf of Riga and in the Baltic Sea at the Latvian coast. Totally 4 main tidal constituents (O1, K1, M2, S2) have been identified. Additionally, nontidal frequency of 5 cycles per day has been detected in the sea level time series of the stations located in the Gulf of Riga.

scholarly journals Nutrient cycling in the Baltic Sea – results from a 30-year physical-biogeochemical reanalysis

2016 ◽  
Author(s):  
Ye Liu ◽  
H. E. Markus Meier ◽  
Kari Eilola
Keyword(s):  
Baltic Sea ◽  
Ocean Model ◽  
Optimal Interpolation ◽  
Nutrient Concentrations ◽  
Biogeochemical Model ◽  
Phosphorus Transport ◽  
The Baltic Sea ◽  
Gulf Of Riga ◽  
Baltic Proper ◽  
The Baltic

Abstract. The long-term oxygen and nutrient cycles in the Baltic Sea are reconstructed using the Swedish Coastal and Ocean Biogeochemical model (SCOBI) coupled to the Rossby Centre Ocean model (RCO). Two simulations covering the period 1970–1999 are carried out with and without data assimilation, respectively. Here, the "weakly coupled" scheme with the Ensemble Optimal Interpolation (EnOI) method is adopted to assimilate the observed profiles in the reanalysis system. The simulation results show considerable improvements in both oxygen and nutrient concentrations in the reanalysis relative to the free run. Further, the results suggest that the assimilation of biogeochemical observations has a significant effect on the simulation of the oxygen dependent dynamics of biogeochemical cycles. From the reanalysis, nutrient transports between subbasins, between the coastal zone and the open sea, and across latitudinal and longitudinal cross sections, are calculated. Further, bottom areas of nutrient import or export are examined. Our results emphasize the important role of the Baltic proper for the entire Baltic Sea, with large net exports of nutrients into the surrounding subbasins (except the phosphorus transport into the Gulf of Riga and the nitrogen transports into the Gulf of Riga and Danish Straits). In agreement with previous studies, we found that the Bothnian Sea imports large amounts of phosphorus from the Baltic proper that are buried in this subbasin. For the calculation of subbasin budgets, it is crucial where the lateral borders of the subbasins are located, because net transports may change sign with the location of the border. Although the overall transport patterns resemble the results of previous studies, our calculated estimates differ in detail considerably.

scholarly journals Interannual and Seasonal Temperature and Salinity Variations in the Gulf of Riga and Corresponding Saline Water Inflow From the Baltic Proper

2001 ◽  
Vol 32 (2) ◽  
pp. 135-160 ◽  
Author(s):  
Urmas Raudsepp
Keyword(s):  
Baltic Sea ◽  
River Flow ◽  
Saline Water ◽  
Seasonal Temperature ◽  
The Baltic Sea ◽  
Increasing Trend ◽  
Gulf Of Riga ◽  
Baltic Proper ◽  
The Baltic ◽  
Salinity Variations

Salinity and temperature data from the Gulf of Riga, a semi-enclosed sub-basin of the Baltic Sea, were analyzed with a focus on interannual and seasonal variability. The data were compiled from measurements taken from 1973 to 1995, a period which includes the stagnation period in the Baltic Sea. Interannual and seasonal variations in the net inflow of saline water from the Baltic Proper were estimated from volume and salt conservation equations for the period 1973-90. The basic decreasing trend, superimposed interannual variations in salinity, and interannual and seasonal temperature variations in the Gulf of Riga coincided with corresponding changes above the halocline in the Baltic Proper. Seasonal salinity variations were notable in the Gulf of Riga as compared to the Baltic Proper, where variations were negligible. Estimated annual mean inflow varied between 2,000 and 5,000 m3/s (average 3,200 m3/s), with a notable increasing trend. A simultaneous increasing trend was extracted from annual mean river flow data. Short-term fluctuations (over 4-6 years) of annual mean inflow ran opposite to the fluctuations of the magnitude of river flow. The average salinity in the Gulf of Riga increased during strong inflow and weak river flow and decreased when inflow was weak and river flow was strong. Variations in the inflow of water salinity had a minor effect on salinity variations in the Gulf of Riga. Seasonal inflow was strongest in spring and autumn and weak in winter.

Taxon-specific prey response to the invasion of a pelagic invertebrate predator, revealed by comparison of pre- and post-invasion time series

2020 ◽  
Author(s):  
Heli Einberg ◽  
Riina Klais-Peets ◽  
Arno Põllumäe ◽  
Henn Ojaveer
Keyword(s):  
Time Series ◽  
Baltic Sea ◽  
Seasonal Abundance ◽  
Indigenous Species ◽  
Long Term Effects ◽  
Gulf Of Riga ◽  
Marine Realm ◽  
The Baltic ◽  
Non Indigenous Species

Abstract Quantification and attribution of the food web changes associated with the invasion of non-indigenous species in the marine realm often remain a challenge. One of the pelagic non-indigenous species of concern in the recent history of aquatic bioinvasions is the predatory cladoceran Cercopagis pengoi, which invaded the Baltic Sea in the early 1990s. While several studies have reported immediate declines in abundances of its potential prey, the long-term effects of C. pengoi on the food webs remain to be examined. Based on the long-term time series (1968–2018) in the Gulf of Riga (Baltic Sea), we found significant declines in abundance of the cladoceran Pleopis spp. and copepod Eurytemora affinis by 90 and 80%, respectively, are associated with the invasion of C. pengoi as well as significant alterations in seasonal abundance patterns of Pleopis spp., E. affinis and cladoceran Bosmina spp. The invasion of the non-indigenous predator has led to the changed prey abundance–temperature relationships. Special caution was taken in data preprocessing, to minimize the likelihood that observed changes in the zooplankton prey could be associated with factors other than the invasion of C. pengoi, such as temperature and storminess.

Physical drivers of oxygen depletion in the Central and Eastern Baltic Sea

2020 ◽  
Author(s):  
Taavi Liblik ◽  
Stella-Theresa Stoicescu ◽  
Jaan Laanemets ◽  
Oliver Samlas ◽  
Kai Salm ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Deep Layer ◽  
Oxygen Depletion ◽  
Estuarine Circulation ◽  
Gulf Of Finland ◽  
The Baltic Sea ◽  
Gulf Of Riga ◽  
Baltic Proper ◽  
The Baltic ◽  
The Gulf Of Finland

<p>Eutrophication and consequent increase in biomass production and sedimentation of organic material cause oxygen depletion of the deep layers and an increase in hypoxic bottom areas in the Baltic Sea.</p><p>The Baltic Sea – a semi-enclosed brackish sea – has restricted water exchange with the North Sea. High fresh water runoff and sporadic inflows of saline water through the Danish Straits maintain stratification. Seasonal thermocline and quasi-permanent halocline, their vertical location, shape and strength are sensitive to atmospheric forcing and influence the oxygen depletion in the near-bottom layer. Physical processes altering deoxygenation in the three sub-basins of the Baltic Sea (Baltic Proper, Gulf of Finland and Gulf of Riga) are under scope of the present overview. Permanent halocline is present in the deep Baltic Proper, while in the Gulf of Finland, it occasionally vanishes during winter. Complete mixing occurs in each winter in the shallow Gulf of Riga separated from the Baltic Proper by the sill. We show that the bathymetry, combined with physical drivers, causes distinct spatial and temporal patterns of oxygen depletion in the basins. The results presented here are a summary of in-situ measurement campaigns conducted by the research vessel, underwater glider, autonomous vertical profiler and bottom moorings in 2011–2020.</p><p>Large barotropic inflows from the North Sea temporarily ventilate the deep layer of the Central Baltic Proper, but rather intensify hypoxia in the Northern Baltic Proper and the Gulf of Finland. Wind-driven estuarine circulation alterations shape the hypoxic area and volume in the Gulf of Finland considerably. Seaward winds support estuarine circulation and the advection of hypoxic saltier water of the Northern Baltic Proper into the gulf deep layer. The landward wind can reverse estuarine circulation, the collapse of stratification and mixing of the whole water column in winter (when the seasonal thermocline is absent), thus, temporarily improving oxygen conditions in the deep layer of the gulf. Intrusion of cold saltier water of the Baltic Proper over the sill into the Gulf of Riga deep layer strengthens water column stratification and supports hypoxia formation in summer. Such a water exchange regime is related to the northerly wind forced upwelling along the eastern coast of the Baltic Proper. The role of submesoscale processes on vertical mixing and deep layer ventilation is still unclear, and the data of high-resolution in situ measurements in the Baltic Sea is limited yet. Preliminary results from the dedicated underwater glider surveys conducted at the coastal slope of Eastern Baltic Proper in 2019-2020 will be presented.</p>

scholarly journals Analysis of the Water Level Variation in the Polish Part of the Vistula Lagoon (Baltic Sea) and Estimation of Water Inflow and Outflow Transport through the Strait of Baltiysk in the Years 2008–2017

Water ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1328
Author(s):  
Michał Szydłowski ◽  
Wojciech Artichowicz ◽  
Piotr Zima
Keyword(s):  
Statistical Analysis ◽  
Numerical Model ◽  
Baltic Sea ◽  
Water Level ◽  
Vistula Lagoon ◽  
Level Variation ◽  
The Baltic Sea ◽  
Water Level Variation ◽  
The Baltic ◽  
The Vistula Lagoon

The Vistula Lagoon is located in both Poland and Russia along the southern coast of the Baltic Sea. It is connected to the Baltic Sea in the Russian part by the Strait of Baltiysk. The purpose of the paper is to identify the dominant factors underlying the water level variation mechanism at Tolkmicko in the Vistula Lagoon, revealed by a statistical analysis of the measured data and a discussion on the inflow and outflow transport variation through the strait, estimated by numerical modeling. Seawater transport is exceptionally valuable in terms of the hydrological water balance in the lagoon. Historical research on the hydrology of the lagoon shows that the water exchange in the lagoon is quite complex due to the presence of several different sources of water balance, such as seawater inflow, river inflow, groundwater inflow, precipitation, and evaporation. Unfortunately, there are no current data on seawater inflow and outflow through the Strait of Baltiysk due to the lack of continuous flow measurements in the strait. A novelty of the current work is an in-depth statistical analysis of the water level variation in the Polish part of the lagoon over a long time period and an estimation of water transport through the Strait of Baltiysk by use of a numerical model. The model reproduces well the water level variation responding to variations in the sea level outside the lagoon and the wind action over the lagoon. The years 2008–2017 were chosen as the analysis period. A two-dimensional free surface shallow water numerical model of the lagoon was adapted to simulate the water level variation in view of the wind over the lagoon and the sea level variation at one open boundary. Finally, it was concluded that the water level variation on the Polish side of the Vistula Lagoon is dominated by two factors: the water level in the Gulf of Gdańsk and the wind over the lagoon. The average annual marine water inflow into the Vistula Lagoon was estimated to be equal to 15.87 km3.

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