Jaan Laanemets

A Fuzzy Logic Model to Describe the Cyanobacteria Nodularia spumigena Blooms in the Gulf of Finland, Baltic Sea

A fuzzy logic model to describe the seasonal evolution of Nodularia spumigena blooms in the Gulf of Finland was built and calibrated on the basis of monitoring data. The model includes three phosphate sources: excess phosphate after the annual spring bloom and parameterised phosphate transport to the upper mixed layer by turbulent mixing and upwelling events. Surface layer temperature and wind mixing form the physical conditions controlling the growth of N. spumigena. Model simulations revealed that phosphate input caused by turbulent mixing and upwelling have to be taken into account to achieve the best fit with observed data. Testing the fuzzy model for early prediction of maximum N. spumigena biomass about a month before the usual occurrence of blooms, gave good results. The potential use of the model for prediction of bloom risk at a certain location along the Estonian or Finnish coast was tested. The bloom transport velocities used in the fuzzy model were pre-calculated by a 3D numerical circulation model for different wind regimes.

Direct Estimates of the Lateral Eddy Diffusivity in the Gulf of Finland of the Baltic Sea (Based on the Results of Numerical Experiments with an Eddy Resolving Model)

Numerical modeling was applied to study the generation of transversal jet filaments observed in the summer of 1999 after an upwelling event off the northern coast of the Gulf of Finland. An eddy resolving model well reproduces the mesoscale coherent structures observed. It was shown that they represent manifestations of instability of alongshore baroclinic jet currents of an upwelling-downwelling origin. An estimate of the effective lateral eddy diffusivity in the mesoscale coherent structures equal to 500 m2/s was obtained as a result of statistical processing of pseudorandom model fields of the temperature and current velocity.

Upwelling Parameters From Bias-Corrected Composite Satellite SST Maps in the Gulf of Finland (Baltic Sea)

This letter proposes a method for using the operational ship of opportunity temperature data at a fixed depth for bias correction of satellite sea surface temperature (SST) images. The bias-corrected SST imagery from MODerate Resolution Imaging Spectroradiometer (MODIS) and Advanced Along-Track Scanning Radiometer (AATSR) sensors were used to calculate mean upwelling characteristics in the Gulf of Finland (GoF, Baltic Sea). First, we determined that the operational flow through temperature data at a 4-m depth can be used for validation and bias correction of satellite SST images in cases of wind speed over 5 m · s-1. The composite sea temperature maps were calculated from bias-corrected images collected during upwelling events in the GoF, in 2000-2009. Mean upwelling characteristics were estimated from composite maps for both the northern and southern coasts of the gulf.

Analysis of temporal variability of measured and modeled vertical distributions of salinity and temperature in the Gulf of Finland during 10-year period

The Gulf of Finland is the sub-basin of the Baltic Sea seriously affected by eutrophication. General Estuarine Transport Model (GETM) was used for modeling hydrophysical fields of the Gulf during the period from 1997 to 2005. The results of the hydrodynamic modeling are important input for ecosystem modeling, in which salinity and temperature variations play the most important role. An accurately simulated salinity field is to some extent a proof that the transport of passive bio-chemical tracers can also be simulated correctly. In this study validation of the results of GETM is performed and comparison with Modular Ocean Model (MOM) is provided. These two models differ in numerical schemes that are used for solving the model equations, in model setup and to some extent in forcing. At first the time series of surface and bottom temperature and salinity from GETM are visually compared with measurements. Long-term measurement data from three HELCOM monitoring stations representing western, central and eastern parts of the Gulf were used. In this study we focus on Taylor diagram that provides quick summary of the degree of patterns correspondence and allows seeing how well model simulates natural pattern. For statistical analysis the surface temperature and salinity have been given the values at a depth of 5 m, and the bottom salinity and temperature are the corresponding values at the lowest depth (about 60 m) at which measurements were carried out. The validation results were grouped similarly for both models. Modeled surface temperature showed good agreement with observed data in all three stations. Root mean square error (RMSE) was between 0.2 and 0.4, correlation coefficients between 0.94 and 0.98 and normalized standard deviations between 0.9 and 1.1 for the both models. Thus, seasonal cycles in the upper layer were reproduced well. Bottom temperatures and surface and bottom salinities were reproduced with lower quality. Bottom temperatures were better reproduced in the western and central Gulf than in the eastern Gulf. Surface salinity was simulated with the same quality in all stations by GETM, while MOM reproduced salinity better in the central Gulf compared to the eastern and western part. Bottom salinities were better simulated by MOM than by GETM. The latter showed larger variability due to higher spatial resolution.

BOOS/HIROMB-based marine forecasts in Estonia: Problems, experiences and challenges

In January 2005, a severe storm hit the Baltic Sea region. Estonian towns Pärnu and Haapsalu were flooded with the storm surge waters. Considerable damages and economic loss occurred. Due to the BOOS cooperation, numerical forecasts became available and they were convincingly much more accurate than the forecasts made by the traditional methods. Advantages of modern operational oceanography were clearly demonstrated and Estonian Center of Environmental Investments launched a project to establish HIROMB-based marine forecasts in Estonia. In winter 2006, two severe oil pollution events occurred in the Gulf of Finland. Hind- and forecasts of oil drift, done with the HIROMB/SeaTrackWeb were of great importance in the practical management of those critical situations. The presentation gives an overview of problems, experiences and challenges on the implementation of BOOS/HIROMB-based marine forecasts in Estonia. We consider also validation of forecasts and the need to apply local VHR forecast models that are linked to the Baltic-wide operational system.

Long-term high-resolution hydrodynamical model simulation in the Gulf of Finland

Gulf of Finland is described as water body with very complex hydrography. Discharge of the largest river Neva in the eastern part of Gulf is the main cause for horizontal salinity gradient. Buoyancy driven mean cyclonic circulation varies with short term wind forced currents. The 10-year (1997–2006) simulation was done with the General Estuarine Transport Model. The horizontal resolution of the model grid was 0.5 nautical miles and 25 sigma layers in the vertical direction. The model reproduced overall seasonal cycle of temperature and salinity stratification with high inter-annual variability. Annual evolution of temperature stratification followed prevailing meteorological conditions of different years. The years with extreme meteorological conditions are well resolved by the model: the warmest (2002) and coldest (1998) summer and likewise the warm ice free winters 2000/2001 and 2001/2002. Model resolves mesoscale phenomena. Average mean surface circulation showed more persistent surface currents near the southern coast of the Gulf.

Propagation of impact of the recent Major Baltic Inflows from the Eastern Gotland Basin to the Gulf of Finland.

Major Baltic Inflows (MBI) have a significant impact on physics, biogeochemistry and marine life in the Baltic Sea. Spreading of the North Sea water from the Danish Straits to the Eastern Gotland Basin has been rigorously studied in recent decades. Investigations of lateral signal propagation using in-situ measurements, which cover the area from the Eastern Gotland Basin to the Gulf of Finland, are missing. Estonian-Swedish-German-Finnish oceanographic data from January 2014 to March 2017 were merged and analyzed to fill the gap. Recent MBIs caused considerable changes in water column properties, and salinity reached the highest values of the last 40–60 years. The arrivals of MBI waters were detected as peaks in the salinity and temperature time-series in the near-bottom layer of the Gotland Deep 4–5 months after the MBI events. Similar peaks were also identified in the Faro Deep, Northern Deep and Kopu West (Northern Baltic Proper) with a further delay of 2–3 months, 3–5 months and 4–6 months, respectively. The first impact of the 2014 December MBI occurred in the Gulf of Finland in nine months as the arrival of the former Northern Baltic Proper deep layer water. Water renewal in the Faro Deep occurred as a gravity current over the sill between Faro and Gotland Deep. Deep layer water in the Northern Baltic Proper and the Gulf of Finland originated from the sub-halocline layer (110–120 m) of the Eastern Gotland Basin. The pre-condition for such mid-layer advection was a denser deep layer in the Gotland and Faro Deep. Fresh oxygen, which arrived in the Gotland Deep in April 2015 and February 2016, was consumed in the near-bottom layer within 3–6 months. Since summer 2016, oxygenated waters occurred in the Gotland Deep in the layer from the halocline to 160 m depth. This oxygen did not reach the area further in the north, except a slight sign of ventilation of the Faro Deep in February 2017. Thus, MBIs did not improve the oxygen conditions in the area north of the Gotland Deep and oxygen conditions rather worsened in the Northern Baltic Proper and the Gulf of Finland.

Observation of mesoscale eddies by using SAR data complemented with optical remote sensing and in situ measurements

Mesoscale eddies were observed in the Baltic Sea using optical remote sensing, SAR imagery and high resolution in situ measurement from an autonomous system on a passenger ferry. Comparison between SAR data and in situ measurements was carried out to analyze the manifestation of sea surface temperature differences and biological surface slicks on SAR imagery. Correlation between radar backscatter and biological parameters (chlorophyll a and turbidity) was observed. Locations of upwelling related cold eddies and low temperature areas were clearly detectable on radar imagery as well. Therefore, SAR data complemented with in situ measurements enables to observe the evolution of mesoscale eddies in case there is no optical remote sensing data available (i.e.under cloud cover).