1. Where is Arkhangelsk?
Arkhangelsk is a big city in northwestern Russia's Arkhangelsk Oblast, situated on the banks of the Northern Dvina River where it flows into the White Sea[^1^]. Its geographical and environmental significance derive from its strategic location at the mouth of a huge river and sea.
The shore line in the area around Arkhangelsk consists of a combination of sandy beaches, rock outcrops, and marshy areas. The persistent influence of the tides and waves of the White Sea, along with the deposition of sediment brought by the Northern Dvina River, has formed the shore line over time. In some areas, rocky cliffs jut out precipitously from the sea, offering a dramatic shoreline of oceanic landscape, while in other areas, there are gentle slopes that go on to extensive sandy beaches. The river delta mouth of Northern Dvina is a huge wetland area of great biodiversity with living places for numerous bird and fish species as well as other aquatic animals. Interior, the region is characterized by coniferous forests, particularly pine, spruce, and fir, along with sparse deciduous forests, constituting a typical taiga landscape.
For centuries, Arkhangelsk has been a commercial and cultural hub. It was among Russia's primary ports since the 16th century, functioning as a trading center between Russia and the remainder of Europe. Its location on the White Sea situated it at the hub of commerce for the trade in goods such as timber, furs, and fish, all of which were common in the surrounding regions. The city's architecture is indicative of its past, with a combination of the original wooden structures of local design and more modern structures adapted to the cold climate of the area. The city is multicultural with a mix of Russian citizens and representatives of various ethnicities, resulting in a rich cultural heritage.
2. What are the coastal currents surrounding Arkhangelsk?
The coastal currents surrounding Arkhangelsk are controlled by a variety of influences. The combination of the White Sea's saltwater and the Northern Dvina River's freshwater is one of the main factors. The large outflow of freshwater into the ocean from the river extends the salinity of the shore waters, creating a distinct mixing zone. Mixing process controls temperature, salinity, and density in the water column, which also compels the motion of the coastal currents [^2^]. The gradient in density between the salt and freshwater can force estuarine circulation systems with seaward flow of surface water and landward flow of deeper water that carry sediments, marine organisms, and nutrients.
Tidal activity also plays a crucial role in current dynamics. The White Sea experiences a semi - diurnal tidal regime with two high and two low tides per day. The compound shape of the Arkhangelsk coast and the location of the river delta along it changes the flow of these tides. Shallow coastal waters near the delta and narrowing at the river mouth are enough to make the tidal currents stronger, especially for spring tides. These tidal currents play a crucial role in the resuspension and transportation of sediments as well as in maintaining the ecological balance of the coastal ecosystem.
Wind-driven circulation is another significant component. Arkhangelsk surroundings have varied wind patterns all over the course of the entire year. High-intensity winds, particularly during autumn and winter months, are capable of pushing surface waters, resulting in surface-level currents. The wind strength and direction could suddenly change, and this would cause the surface - current patterns to change. Surface currents meet river - sea interaction and tidal force-influenced deeper - layer currents and create a dynamic and complex current system within the Arkhangelsk coastal waters.
3. How to observe the coastal water flow of Arkhangelsk?
A variety of methods can be used to monitor the coastal water current of Arkhangelsk. One such widespread method is the technique of surface drifting buoys. Scientists attach tracking devices, such as GPS receivers or radio transmitters, to buoys and then release them into the ocean. The buoys are carried by the currents, and by monitoring their movement with time, scientists can determine the direction and speed of the surface-level currents. But this is a method that can only describe the upper layer of the water column and might not actually describe the currents at deeper levels.
A second commonly used technique is the anchored ship method. An anchored ship can use a range of instruments to sample the direction and speed of the current at different depths surrounding the vessel. While more accurate sampling of the water column is possible with this compared to the buoy method, it will only be representative of the area surrounding the anchored location and not necessarily the whole spatial variability of the coastal currents in the Arkhangelsk region.
In recent years, the Acoustic Doppler Current Profiler (ADCP) method has emerged as a more advanced and economical method of monitoring coastal currents. ADCPs can simultaneously measure currents at various depths. ADCPs introduce acoustic waves into the water column that reflect off small suspended water particles such as sediment, plankton, or microorganisms. The back-scattered signals are subsequently utilized to find the present speed and direction at various points in the water column. This provides an overall indication of the water flow structure, which renders ADCPs a useful tool for probing the complex and three-dimensional nature of the coastal currents off Arkhangelsk.
4. How do Doppler principle-based ADCPs work?
ADCPs operate on the Doppler principle. They project acoustic signals into the water column. They reflect off tiny suspended particles in the water, such as sediment, plankton, or small animals, and are sent back to the ADCP as echoes. If the water is in motion, the frequency of the echo signals reflected is altered compared to the transmitted signals' frequency. This frequency change, also known as the Doppler shift, is linearly proportional to the speed of the water current.
By observing the Doppler shifts of the acoustics signals, which are recorded at different depths, the ADCP determines the current speed and direction at multiple points in the water column. With this technique, scientists can obtain a three-dimensional map of the water current, horizontal and vertical components. With this detailed information, researchers can understand the complex dynamics of the coastal currents around Arkhangelsk and utilize it for applications such as marine ecosystem management, safe navigation, and environmental research.
5. What's required for good-quality measurement of Arkhangelsk coastal currents?
For proper high - quality measurement of the coastal currents off Arkhangelsk, ADCP equipment must meet several vital requirements. Material strength is paramount. The marine environment off Arkhangelsk is characterized by fluctuating temperatures, the corroding nature of saltwater, and the added complexity of the mixing zone between freshwater and saltwater. The ADCP has to be constructed from strong and durable materials that are capable of withstanding these unfavourable conditions under long - term deployments.
The ADCP's size and weight have to be minimized. The reason for this is so that it can be easily deployed with consideration given to the shallow seas and the need to reach different parts of the Arkhangelsk coast. Whether installed on a small local fisherman research boat, on a bolted buoy, or on the sea floor, a smaller and lighter ADCP is easier to manage and maintain. Low power usage is also crucial because the location may have limited access to power in outlying areas. This allows extended deployments with no requirement for repeated battery replacement or recharging, enabling continuous data collection. It is also quite a low-cost solution, enabling several ADCPs to be deployed over an area and take a more comprehensive understanding of the complex current patterns.
The ADCP housing must be made of titanium alloy. Titanium alloy is also extremely corrosion resistant, which is key to surviving the long-term exposure to the White Sea water and the effects of mixing the freshwater and saltwater. Titanium alloy also has a high strength-to-weight ratio, which is strong enough to support the mechanical loads of the sea environment and light enough for easy transport and simple deployment in the extreme conditions off Arkhangelsk. These traits make titanium alloy an appropriate material for delivering the dependable and long-term performance of ADCPs used in the measurement of coastal currents of this country.
6. How to Choose the right equipment for current measurement?
Hardware selection of ADCP relies on the particular measurement requirements. A ship-mounted ADCP is suitable for large-scale monitoring of current behavior over the entire coastal region of Arkhangelsk and its connection with the White Sea. It can be mounted on research ships that pass through seas, collecting data as the ship goes and a large-scale picture of current systems in the region.
For long - term monitoring at fixed points, for instance, near the critical fishing grounds or environmentally critical areas, a bottom - mounted ADCP is more suitable. It can be placed on the seafloor and measure current data continuously for extended periods of time and give detailed information on local current conditions.
An ADCP mounted on a buoy is an appropriate option if mobility and flexibility are necessary. The buoy will ride the currents, providing real-time data on movement of water mass and allowing dynamic changes in currents in the Arkhangelsk coastal waters to be monitored.
The frequency of choice is also an issue of concern. 600kHz ADCP is appropriate for water depths up to 70 meters, 300kHz ADCP for depths up to 110 meters, and 75kHz ADCP for depths up to 1000 meters[^3^]. Famous ADCP companies are Teledyne RDI, Nortek, and Sontek. But for individuals looking for a budget - friendly yet top - quality alternative, the China Sonar PandaADCP is highly recommended. Being a member of the titanium alloy group, it is an economical value and highly rated for price - conscious consumers. To learn more, visit https://china - sonar.com/.
[^1^]: Facts about the placement of Arkhangelsk are obtained from official Russian geographical databases and regional tourist websites.
[^2^]: Scientific studies on river-borne freshwater and sea saltwater interaction and its contribution to the development of coastal currents may be found published in peer - reviewed marine science journals.
[^3^]: Precepts on ADCP frequency choice according to water depth are taken from standard marine instrumentation manuals.
How do we estimate coastal currents of Arkhangelsk?