Regional circulation patterns inducing coastal upwelling in the Baltic Sea

Abstract

Atmospheric feedback involved in the occurrence of coastal upwelling in a small semi-enclosed sea basin, i.e., the Baltic Sea, was analysed, and the regional circulation conditions triggering upwelling in different coastal sections were identified. Upwelling in the summer season (June–August, years 1982–2017) was recognized on the basis of sea surface temperature patterns. Circulation conditions were defined using (1) the established daily indices of zonal and meridional airflow and (2) the synoptic situation at sea level distinguished by applying rotated principal component analysis to sea level pressure data. The 12 daily synoptic patterns differed substantially in the intensity and location of their pressure centres. The mean seasonal frequency of upwelling was generally higher along the western Baltic shores than along the meridionally oriented eastern shores and varied from less than 10 to over 30% along the more predestined coastal sections, i.e., the northwestern coast of the Gulf of Bothnia, the northern Gulf of Finland and the southern Swedish coast. Due to the variable orientations of coastlines, upwelling could occur under almost any prevailing wind direction, and thus, each of the classified synoptic patterns could induce upwelling in some coastal sections. As deduced from the pressure fields for each circulation pattern, mostly alongshore winds triggered upwelling, which is in line with the Ekman rule. With time, upwelling could also be induced by the stress of normal to the coastline seaward winds.

Upwelling characteristics in the Gulf of Riga (Baltic Sea): multiple data source approach

“…events in the GoR in 2010-2022 is 9 events/per year on average. Previous results obtained via satellite data (e.g., Bednorz et al, 2021) and model data (e.g., Myrberg and Andrejev, 2003) suggest that upwellings are more frequent on the W coast of the GoR rather than the E coast, which is in accordance with our acquired results based on coastal measurements. Even if we consider the previously mentioned no measurement data from Skulte and Roja and apply the correction based on the average number of events/per year, the total amount of upwelling events in the W coast would yield 71 events as opposed to 55 events in the E coast, with a ratio of 56%:44% in 2010-2022.…”

“…Based on the main upwelling regions in the Baltic Sea derived by Bychkova et al (1988) in relation to weather conditions, the previous studies have shown that upwelling frequency (%) in the GoR is lower (e.g., Lehmann et al, 2012;Bednorz et al, 2021). Our study adds that a quantitative measure for the number of upwelling…”

“…Previous investigations regarding upwelling in the GoR have been considered mainly in the context of the whole BS region based on satellite data (e.g., Uiboupin and Laanemets, 2015;Dabuleviciene et al, 2018;Zhang et al, 2022), model data (e.g., Myrberg and Andrejev, 2003;Wu et al, 2019), or a combination of both (e.g., Lehmann et al, 2012;Gurova et al, 2013;Kowalewska-Kalkowska and Kowalewski, 2019). In addition to that, more detailed investigations have been performed concentrating on specific gulfs (e.g., Kikas and Lips, 2016-the Gulf of Finland), parts, or regions (Bednorz et al, 2018 andBednorz et al, 2019-South-Eastern Baltic Sea) of the Baltic Sea and explore various aspects of upwelling-related topics, e.g., atmospheric forcing (Bednorz et al, 2021), submesoscale structures (Väli et al, 2017), surface transport (Delpeche-Ellmann et al, 2017 andSoomere, 2018), excess of phosphorus in surface layer (e.g., Laanemets et al, 2011;Väli et al, 2011), chlorophyll a variability (Dabuleviciene et al, 2020), and heat waves (Suursaar, 2020). Previous studies of the GoR region have been general and descriptive (e.g., Bychkova et al, 1988;Lehmann et al, 2012;Bednorz et al, 2021), focused on identifying the main upwelling areas and giving frequency estimates.…”

Impact of Thermohaline Conditions on Vertical Variability of Optical Properties in the Gulf of Finland (Baltic Sea): Implications for Water Quality Remote Sensing

“…However, the conclusions cannot be automatically expanded to the other basins of the Baltic Sea as the vertical distribution of IOPs differ between basins of the Baltic Sea (Berthon and Zibordi, 2010;Soja-Woźniak et al, 2017;Kratzer and Moore, 2018). However, upwelling is a frequent process also in other basins of the Baltic Sea (Lehmann et al, 2012;Dabuleviciene et al, 2018Dabuleviciene et al, , 2020Bednorz et al, 2021), therefore future research is needed to quantify the effect of upwelling on the remote sensing signal/retrievals in the other basins of the Baltic Sea.…”