Urmas Raudsepp

Comparing reconstructed past variations and future projections of the Baltic sea ecosystem first results from multi model ensemble simulations

Multi-model ensemble simulations for the marine biogeochemistry and food web of the Baltic Sea were performed for the period 1850‐2098, and projected changes in the future climate were compared with the past climate environment. For the past period 1850‐2006, atmospheric, hydrological and nutrient forcings were reconstructed, based on historical measurements. For the future period 1961‐2098, scenario simulations were driven by

On the estuarine transport reversal in deep layers of the Gulf of Finland

The Gulf of Finland is a 400-km long and 48–135-km wide tributary estuary of the Baltic Sea featuring the longitudinal two-layer estuarine flow modified by transverse circulation. Longitudinal volume transport in the deep layer is investigated by decomposing it into an averaged, slowly changing estuarine component (due to large-scale density gradients, river discharge and mean wind stress) and wind-driven fluctuating component. The derived expression relates the total deep-layer transport to the projection of wind stress fluctuation to a site-specific direction. The relationship is tested and calibrated by the results from numerical experiments carried out with the three-dimensional baroclinic circulation model. For the entrance to the Gulf of Finland, winds from northeast support standard estuarine circulation and winds from southwest work against the density-driven and riverine flow. The deep estuarine transport may be reversed if the southwesterly wind component exceeds the mean value by 4–5.5 m s−1. According to the data from hydrographic observations in the western Gulf of Finland, an event of advective halocline disappearance was documented in August 1998. Comparison of the deep-water transport estimates calculated from the wind data in 1998 with the observed salinity variations showed that the events of rapid decay of estuarine stratification were coherent with the estimated reversals of deep-layer volume transport, i.e. events of salt wedge export from the gulf.

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.

The Copernicus Marine Environment Monitoring Service Ocean State Report

ABSTRACT The Copernicus Marine Environment Monitoring Service (CMEMS) Ocean State Report (OSR) provides an annual report of the state of the global ocean and European regional seas for policy and decision-makers with the additional aim of increasing general public awareness about the status of, and changes in, the marine environment. The CMEMS OSR draws on expert analysis and provides a 3-D view (through reanalysis systems), a view from above (through remote-sensing data) and a direct view of the interior (through in situ measurements) of the global ocean and the European regional seas. The report is based on the unique CMEMS monitoring capabilities of the blue (hydrography, currents), white (sea ice) and green (e.g. Chlorophyll) marine environment. This first issue of the CMEMS OSR provides guidance on Essential Variables, large-scale changes and specific events related to the physical ocean state over the period 1993–2015. Principal findings of this first CMEMS OSR show a significant increase in global and regional sea levels, thermosteric expansion, ocean heat content, sea surface temperature and Antarctic sea ice extent and conversely a decrease in Arctic sea ice extent during the 1993–2015 period. During the year 2015 exceptionally strong large-scale changes were monitored such as, for example, a strong El Niño Southern Oscillation, a high frequency of extreme storms and sea level events in specific regions in addition to areas of high sea level and harmful algae blooms. At the same time, some areas in the Arctic Ocean experienced exceptionally low sea ice extent and temperatures below average were observed in the North Atlantic Ocean.

Environmental monitoring of water quality in coastal sea area using remote sensing and modeling

Coastal sea of the southern Gulf of Finland is under heavy anthropogenic stress due to development of harbors and increase of ship traffic. During dredging operations, the increase of suspended particulate matter (SPM) concentration in seawater is inevitable. Water transparency decreases with an increased SPM concentration, which leads to worsening of underwater light conditions. Diminishing of light intensity that penetrates to the sea bottom has negative effect on the growth of benthic macroalgae, which is an indicator of water quality in the coastal zone. Monitoring of SPM transport and distribution along with the estimation of dredging impact on marine environment is crucial especially when sensitive and critical marine areas are close to dredging site. The monitoring system that combines satellite remote sensing and numerical modeling and is supported by measurements is presented. The modeling part consists of hydrodynamic model, particle transport model and benthic macroalgae growth model. A simple approach is followed in the formulation of the system and on the determination of required relationships that are based on the measurements. The monitoring system was applied to Pakri Bay during dredging in Paldiski North harbor, which lasted a one and half year. Comparison of SPM distributions from remote sensing images and numerical model results showed qualitatively similar patterns. Quantitative comparison allowed separating SPM concentrations due to dredging operations from background values of natural origin. Underwater light conditions were the most affected close to the harbor and in the coastal sea. Estimations of the changes of macroalgae biomass due to diminishing underwater light intensity showed minor effect, as the dredging was carried out mainly from late autumn until early spring when macroalgae growth is limited by water temperature.

Simulation of Wave Damping Near Coast due to Offshore Wind Farms

Abstract ALARI, V. and RAUDSEPP, U., 2012. Simulation of wave damping near coast due to offshore wind farms. Two hundred wind turbines with an annual productivity of 2.3 TWh, which could produce up to 30% of the energy Estonia needs, are scheduled to be constructed on separate shallows in the NW Estonian coastal waters (the Baltic Sea), 5–20 km off shore. With numerical modeling, we have established a potential impact of the wind farms on wave heights. We concluded that the impact exists in terms of the reduction of significant wave height, but it is very marginal, not more than 1% below 10-m isobaths. This is due to a very small ratio between the turbine diameter and dominant wavelength and the favorable setup of turbines with respect to each other and the coast.

Use of lightweight on-line GPS drifters for surface current and ice drift observations

A family of lightweight (less than 15 kg), long-life (up to 3–4 months) and low-cost drifters are developed in the Tallinn University of Technology and local engineering companies. Such buoys have a rugged and simple housing construction with the diameter of 11 cm and length of 1 m. The buoys are equipped with GPRS based two-way communication and they are programmable during the mission. The data are transferred in real time into one or several FTPs for the operational use in circulation and ice models for data assimilation and/or model validations. The buoys are used also for the estimation of oil drift and ice dynamics properties, e.g. ice drift, compacting, ridging, etc. Real-time (on-line) data transfer is performed via the GPRS protocol with a typical time interval of 15 minutes, but it can be programmed otherwise. The data received in FTP are ready to be used for model assimilation and in different operational applications and services like the drift of surface objects, ice and oil drift. It is possible to view the buoy data in real time via a special web solution. Two major measurement campaigns have been performed using light drifters. Firstly, the validation of High Resolution Operational Model for the Baltic Sea (HIROMB) surface currents in Estonian coastal waters in 2007 and secondly, the study of dynamic ice drift. In both cases the light on-line drifters showed good performance and stability for long-life operation. The percentage of fault positioning was higher in water, reaching up to 20%, and was mainly caused by the reflections of GPS signal from the waves, since a very small part of the buoy remains above the sea surface. In ice the fault positioning was lower, less than 10%. In the case of an ice covered sea, the buoys were from time to time pushed under ice for some period during which the positioning systems failed to transfer the signal. In 2007 during the period from August till November 17 experiments were carried out with surface drifters released in small coastal bays and the open sea of the Gulf of Finland. The longest period when a buoy was drifting lasted for 8 days. It moved across the Gulf of Finland covering a little less than 50 miles. In accordance with the drifter experiments the drifter trajectories that imitate oil spill drift were calculated from HIROMB currents and wind. The calculations were carried out with a different wind factor between 0–3%. The results of modeling showed close agreement with drifter data in some cases, but no unique wind factor suitable for the Gulf of Finland could be identified. In March-April 2010, an extensive ice drifter experiment was conducted in the eastern part of the Gulf of Finland. The development of light on-line GPS drifters continues. The platform of data logging and transfer allows adding a number of parameters to be measured by the drifter and transmitted on-line. To begin with, water temperature and salinity sensors will be added.

Detection of oil spills on SAR images, identification of polluters and forecast of the slicks trajectory

SAR images from the Estonian coastal area were analyzed to identify oil spills. Slicks were detected on five images in February and March 2008. The analysis showed that the slicks occurred on the ship track. Seatrack Web model (SMHI) that includes ship automatic identification (AIS) data provides a possibility to identify the polluters. In two cases the hindcast model together with AIS information system enabled to detect the possible polluters.

Oil Spill statistics from SAR images in the North Eastern Baltic Sea ship route in 2007–2009

A large number of illegal oil pollutions impose considerable threat to marine environment especially in marginal seas like the Baltic Sea. Illegal spills are mainly detected on essential navigation routes. The monitoring of Oil Spills (OS) using remote sensing imagery (SAR data) was performed on the northeastern Baltic Sea ship route. The pre-analyzed satellite images for detecting marine pollution were provided to marine surveillance agency in Estonia. Out of 137 detected potential pollutions 76 were confirmed by aerial surveillance missions within two-year period. OS were mainly of low confidence, had small area, low contrast with surrounding water and smeared edges. The entrance to the Gulf of Finland was classified as the area where illegal spills of oil and bilge water take place, mainly. Between 30–50% of actual oil pollutions are not detected by SAR.

Validation of GETM model simulated long-term salinity fields in the pathway of saltwater transport in response to the Major Baltic Inflows in the Baltic Sea

The hydrodynamic model GETM was used to simulate the hydrographic conditions in the Baltic Sea for the hindcast period from 1966 to 2005. Time series of surface and bottom salinity and bottom temperature at four monitoring stations belonging to the Bornholm Basin, Gotland Basin, the Gulf of Finland and the Gulf of Riga were used for model validation. The model has reproduced realistic conditions through the simulation period that was characterized by stagnation period in the 80s and numerous Major Baltic Inflow events. The simulated salinity and temperature at different depths were in good agreement with measurements. Also, the sea level and maximum ice extent were compared with observations.