Central Baltic Research Articles

High-resolution characterization of the development and decay of seasonal hypoxia in the Gulf of Riga, Baltic Sea

The Gulf of Riga is a shallow basin in the eastern Baltic Sea connected to the Central Baltic Sea via shallow straits. Seasonal oxygen depletion occurs in the deep layer of the gulf. We conducted hourly measurements of dissolved oxygen, temperature, and salinity in the deep layer (50 m) of the gulf and observed the full cycle of development and relaxation of hypoxia in 2021. Hypoxia (<2.9 mg l-1) first occurred on 27 June and was observed for 71 days until its complete decay on 22 October. Average oxygen decline of 0.10 mg l-1 d-1 from saturation in mid-April until mid-July and 0.04 mg l-1 d-1 onwards until the end of August were observed. This seasonal pattern was superimposed by short-term variability in time scales from hours to days and was probably caused by inertial oscillations, (sub)mesoscale processes, deep layer currents, and pycnocline movements. Ventilation events with a relatively low impact and duration of up to ten days occurred in the deep layer due to the inflows of the saltier water from the Central Baltic. The inflowed water originated from the upper layer in winter and the thermocline in summer and was almost saturated in oxygen. Mostly mixing with existing oxygen-depleted water in the Gulf of Riga, but also local consumption declined the oxygen levels in the inflow water before it arrived at the observing station. Monthly standard deviations in oxygen varied from 0.3 to 2.8 mg l-1 and illustrated the added value of Eulerian measurements to complement the conventional monitoring.

THE INFLUENCE OF NATURAL FACTORS ON THE EMERGENCE OF LARGE SCYTHIAN SETTLEMENTS AND THE DEVELOPMENT OF TRADE ROUTES

This article considers the impact of changes in the natural environment on historical processes that took place in the steppe and forest-steppe zones of Ukraine in the XI—V centuries BC. It is determined that one of the main reasons for the emergence of large Scythian settlements was a natural factor. Changes in climatic conditions in the steppe zone led to the almost complete outflow of population from its territory in the XI—V centuries BC. The establishment of a more favorable climate in the south of Ukraine, which began in the VII century BC, led to an increase in the population in the forest-steppe zone and the emergence of large Scythian settlements on its territory.
 The article also considers the question of the emergence and functioning of the main trade routes that existed in the Northern Black Sea region at that time. South Bug, Dnieper and Don rivers were used as trade routes beginning ХV century BC. The Scythian penetration to forest-steppe zone and the construction of big sites of settlements started before the start opening the north coastal Black Sea territory by Greek colonists. The Scythians appeared in the forest-steppe zone in the first half to mid- VII century, and the Greek opening of the coastal areas starts at the end of VII century BC. That time the South Bug, Dnieper and Don rivers became waterways connecting North Black sea area with central East Europe and Baltic countries. It were the estuaries of these rivers where appeared the biggest early Greek settlements: Berezan at the Bug and Dnieper estuary’s conjunction and Taganrog at the Don estuary. In the VII—V centuries South Bug was the main trade route. This point is supported by the fact that the Olvia state capital-Olvia city was established on the right bank of the Bug estuary.
 The Greek centers exported to these areas, possibly ceramics, vine, olive oil, jewelry etc. These are the ceramic residuals which make it possible to determine the big Scythian settlements lifetime. Greek traders as reported ancient authors imported from forest-steppe areas, where these settlements were established, cattle, slaves, copper, furs, wax, salted fish, amber etc. The climate improvement at the North Black Sea area started opening of these unsettled steppe areas. This process resulted in gradual decadence of big Scythian settlements. The Grate Scythian center moves to the lower reach of Dneaper river, which followed by main trade route transfer to that exact river. So the natural factor seriously influenced the South Black Sea areas historical processes in the VII—V centuries BC.

Robust, ecological–economic multispecies management of Central Baltic fishery resources

Abstract The Baltic fisheries are in distress. In the Central Baltic, fisheries management is challenged by reduced cod stock productivity, and altered species interactions. Here, we use an age-structured, ecological–economic multispecies model, which includes latest biological and economic knowledge, to advance our understanding of optimal fisheries management and related trade-offs between user groups under such altered conditions. We contribute to the scientific discussion (i) by showing that the economic importance and optimal stock size of cod largely decreased under prevailing conditions, while clupeids increased in importance. (ii) We challenge the current MSY management objective in a multispecies setting (MMSY) and suggest that an economic multispecies management objective (MMEY) might be more useful for setting future management targets. (iii) We identify new trade-offs and synergies by including a consumer perspective: There is a win–win situation for ecological conservation, and profits in the fishery, while fishery management faces trade-offs between these two on the one hand, and consumer surplus on the other hand. (iv) Finally, we suggest an easy to implement new management approach, called robust management, which is capable of better dealing with variability and time-trends in recruitment, as observed for cod, in order to safeguard the Central Baltic fishery resources.

Cleaning up seas using blue growth initiatives: Mussel farming for eutrophication control in the Baltic Sea

Eutrophication is a serious threat to aquatic ecosystems globally with pronounced negative effects in the Baltic and other semi-enclosed estuaries and regional seas, where algal growth associated with excess nutrients causes widespread oxygen free “dead zones” and other threats to sustainability. Decades of policy initiatives to reduce external (land-based and atmospheric) nutrient loads have so far failed to control Baltic Sea eutrophication, which is compounded by significant internal release of legacy phosphorus (P) and biological nitrogen (N) fixation. Farming and harvesting of the native mussel species (Mytilus edulis/trossulus) is a promising internal measure for eutrophication control in the brackish Baltic Sea. Mussels from the more saline outer Baltic had higher N and P content than those from either the inner or central Baltic. Despite their relatively low nutrient content, harvesting farmed mussels from the central Baltic can be a cost-effective complement to land-based measures needed to reach eutrophication status targets and is an important contributor to circularity. Cost effectiveness of nutrient removal is more dependent on farm type than mussel nutrient content, suggesting the need for additional development of farm technology. Furthermore, current regulations are not sufficiently conducive to implementation of internal measures, and may constitute a bottleneck for reaching eutrophication status targets in the Baltic Sea and elsewhere.

Late Weichselian to Holocene history of the Baltic Sea as reflected in ostracod assemblages

The study presents the first description and analysis of ostracod records from three sites cored in different parts of the Baltic Sea during the IODP Expedition 347, Baltic Sea Paleoenvironment. Our data present the first high‐resolution ostracod records from the Late Weichselian and Holocene sediments collected across the Baltic Sea Basin. Using published data on modern ostracod species ecology of the Baltic Sea, we were able to provide ostracod‐based palaeoreconstructions of the history of the region. The stratigraphical framework for the sites is based on radiocarbon‐based age models. The three studied sites reveal different ostracod assemblage successions that reflect environmental changes in the study area. Site M0060, located in the Kattegat area, contains the oldest ostracod assemblages that document a marine environment with very high sedimentation rates during the most recent deglaciation. Between ~13 000 and 7500 cal. a BP a modern‐like near‐shore environment developed. Site M0059 in the southwestern Baltic Sea, Little Belt area, contains assemblages reflecting the transition from a freshwater lake to the brackish Littorina Sea between ~7500 and 7300 cal. a BP. Site M0063 is the deepest location in the central Baltic, Landsort Deep, and yielded very limited ostracod data, but comparison with our organic carbon data allowed us to distinguish the Yoldia Sea, Ancylus Lake and Littorina Sea intervals. The ostracod record correlates well with the organic carbon record with alternation between periods of hypoxia and periods of low oxygen that still supported ostracods.

Candling and Field Atlas of Early Egg Development in Common Eiders Somateria Mollissima in the Central Baltic

Abstract Here we present the results of candling 258 eggs from 50 nests of Common Eiders Somateria mollissima in a colony in the central Baltic. Of these, 223 (86%) had a developing foetus. Among the 35 (14%) failed eggs, 15 were unfertilized and 20 contained a dead embryo. The prevalence of failed eggs is similar to the average proportion of failed eggs reported previously by the Christiansø Scientific Field Station during 1998–2014. The reason for the high percentage of failed eggs is unknown; however, low pre-incubation body mass and energetic stress is likely to be the main factor. In addition, we incubated 8 eggs in the laboratory from day 0 to hatch in order to follow the development and foetal morphology. This resulted in a field atlas from which it is possible to estimate date of incubation start using candling in early incubation (days 1–12). The atlas is a new possibility for field biologists to estimate the first day of incubation of breeding eiders and the prevalence of unfertilized and rotten eggs, which is important for studying their biology and population dynamics.

Remote sensing of chlorophyll in the Baltic Sea at basin scale from 1997 to 2012 using merged multi-sensor data

Abstract. A 15-year (1997–2012) time series of chlorophyll a (Chl a) in the Baltic Sea, based on merged multi-sensor satellite data was analysed. Several available Chl a algorithms were sea-truthed against the largest in situ publicly available Chl a data set ever used for calibration and validation over the Baltic region. To account for the known biogeochemical heterogeneity of the Baltic, matchups were calculated for three separate areas: (1) the Skagerrak and Kattegat, (2) the central Baltic, including the Baltic Proper and the gulfs of Riga and Finland, and (3) the Gulf of Bothnia. Similarly, within the operational context of the Copernicus Marine Environment Monitoring Service (CMEMS) the three areas were also considered as a whole in the analysis. In general, statistics showed low linearity. However, a bootstrapping-like assessment did provide the means for removing the bias from the satellite observations, which were then used to compute basin average time series. Resulting climatologies confirmed that the three regions display completely different Chl a seasonal dynamics. The Gulf of Bothnia displays a single Chl a peak during spring, whereas in the Skagerrak and Kattegat the dynamics are less regular and composed of highs and lows during winter, progressing towards a small bloom in spring and a minimum in summer. In the central Baltic, Chl a follows a dynamics of a mild spring bloom followed by a much stronger bloom in summer. Surface temperature data are able to explain a variable fraction of the intensity of the summer bloom in the central Baltic.

Reply to Pardo et al. 2015 on ‘Reply to comment on Couto‐Mendoza et al. 2014. More complexity does not always mean more accuracy: the case of IBMWP and METI in NW Spain’ Ecohydrology DOI: 10.1002/eco.1660

AbstractThe manuscript “More complexity does not always mean more accuracy: the case of IBMWP and METI in NW Spain” compares the behaviour of one multimetric index (METI), proposed for NW Spain rivers, and the IBMWP, excluded from the Spanish Water Planning Instruction for NW Spain rivers, under the same conditions in the Miño‐Sil Basin District (DHMS) in the NW Spain. The conclusion of that assay is that both indices are useful tools for evaluating the ecological status of the running‐water ecosystems in the NW Spain, and emphasises the use of the IBMWP, because it may be better (more practical) than the METI, which has already been proposed for the same goal in this region. Another topic to deal with in the report was the number of established reference sites in the DHMS. Pardo et al. () give 5 replies to 5 criticisms that question the use of the METI in the NW Spain. Pardo et al. (2015) mention that those criticisms are contained in Couto‐Mendoza et al. (). Overall, Pardo et al. () highlight the validity of the METI as a method for assessing the ecological status because, unlike the IBMWP that they reject, it has been intercalibrated in the European exercise in the Central Baltic Rivers GIG. Each reply to the criticisms selected by Pardo et al. () is discussed. Copyright © 2015 John Wiley & Sons, Ltd.

Nonlinear Properties of the Gotland Deep – Baltic Sea

AbstractThe properties of the nonlinear phenomenon in water, including sea water, have been well known for many decades. The feature of the non homogeneous distribution of the speed of sound along the depth of the sea is very interesting from the physical and technical point of view. It is important especially in the observation of underwater area by means of acoustical method (Grelowska et al., 2013; 2014). The observation of the underwater space has been carried out for more than hundred years. In the second half of the twentieth century we observed very intense trend of development of the measuring methods of underwater sound speed. It was done mainly in the linear sound propagation aspect. At the end of 20th century nonlinear devices were invented. Thus, from this point of view, knowledge on the nonlinear properties of the sea water is the matter of interest. The phenomenon of nonlinear distortion of elastic waves, and the same the efficiency of nonlinear transfer of energy from the primary wave to the higher harmonic components depend on properties of the medium, especially on the material constant known as the nonlinearity parameter B/A. The Baltic Sea is a specific reservoir with untypically low salinity and low depth (Grelowska, 2000). In the paper results of investigation of nonlinear properties of the South and the Central Baltic by means of thermodynamic method are presented.

Fresh oxygen for the Baltic Sea — An exceptional saline inflow after a decade of stagnation

The ecological state of the Baltic Sea depends crucially on sufficiently frequent, strong deep water renewal on the periodic deep water renewal events by inflow of oxygen rich saline water from the North Sea. Due to the strong density stratification these inflows are the only source for deep water ventilation. Since the early eighties of the last century the frequency of inflow events has dropped drastically from 5 to 7 major inflows per decade to only one inflow per decade. Wide spread anoxic conditions became the usual state in the central Baltic. The rare major Baltic inflow (MBI) events in 1993 and 2003 could interrupt the anoxic bottom conditions only temporarily. After more than 10years without a major Baltic inflow events, in December 2014 a strong MBI brought large amounts of saline and well oxygenated water into the Baltic Sea. Based on observations and numerical modeling, the inflow was classified as one of the rare very strong events. The inflow volume and the amount of salt transported into the Baltic were estimated to be with 198km3 and 4Gt, respectively. The strength of the MBI exceeded considerably the previous 2003 event. In the list of the MBIs since 1880, the 2014 inflow is the third strongest event together with the MBI in 1913. This inflow event will most probably turn the entire Baltic deep water from anoxic to oxic conditions, with substantial spread consequences for marine life and biogeochemical cycles.

Gross Value Added per Person Analyses of Transportation Companies of new European Union countries in 2005 – 2011

The objective is to analyse the labour productivity of new European Union (EU) Member States from Central and Eastern Europe (CEE-8) and Baltic States or former Soviet-bloc countries in Europe in 2005 to 2011, with emphasis labour productivity by gross value added per person employed and employee, with emphasis the Baltic States. The aim is to analyse labour productivity of transportation and storage companies before and after the economic crisis, and to compare them on the EU and Russia and Ukraine level. We will look at how the economic crisis has affected the labour productivity of transportation companies. What are the lessons learned from the economic crisis? How ex-post-socialist countries have been the economic crisis? The literature review shows in short the history and economy of the former USSR or ex-post-socialist countries and the crisis theory. It is concerned with explaining the recession, depression and business cycle in economics. We will make a short view of the financial crisis. Based on this and previous publications, we will offer a number of generalized suggestions.

Seasonal dynamics of early life stages of invasive and native ctenophores give clues to invasion and bloom potential in the Baltic Sea

Recently, both the invasive ctenophore Mnemiopsis leidyi and the arctic Mertensia ovum were discovered in the Baltic Sea but their range expansion remains unclear due to misidentification of their larval stages. Supported by molecular species verification we describe seasonal abundance and distribution of larvae and eggs of these two species. We show that their occurrence is significantly but inversely related to salinity. Mertensia ovum was present year round throughout the brackish Baltic Sea but also occurred in high-saline areas during cold seasons. Larvae of M. leidyi occurred throughout all seasons in high-saline areas but never extended further into the central Baltic. Highest ctenophore egg abundances were observed in high-saline areas during summer along with the first appearance of M. leidyi adults. The M. leidyi population peaked 2 months after the first occurrence of adults in high-saline areas, suggesting these areas as a source for lower saline regions. Low larvae abundances and a reduced transitional-to-adult ratio in the southern Baltic point to reduced or no active recruitment, suggesting that drift of animals from high-saline into lower saline regions sustains the M. leidyi population in the southern Baltic such as the Arkona and Bornholm basins.

Long-term changes in Secchi depth and the role of phytoplankton in explaining light attenuation in the Baltic Sea

Secchi depth, as a proxy of water transparency, provides valuable information on the availability of light to the underwater ecosystems. Changes in water transparency have also been widely linked to eutrophication and phytoplankton biomass. This study aimed to describe the development of water transparency in the Baltic Sea through a unique century-long set of Secchi depth observations. Furthermore, the aim was to explain the role of phytoplankton in determining water transparency in these optically complex waters. Water transparency in the open Baltic Sea has decreased during the last one hundred years. The development differs between the sub-basins of the Baltic Sea. The decrease has been most profound in the north-eastern Baltic sub-basins, but apparent also in parts of the Southern and Central Baltic. In many of the northern areas the decrease has accelerated during the last decades, whereas in the Southern Baltic a recent increase was observed. The analysis of simultaneous chlorophyll a observations during the period from 1972 to 2006 revealed that during summer time, 13–17% of the light attenuation can be attributed to phytoplankton. In spring, the average proportion is between 31 and 42%, with great variation between observations. We find Secchi depth a suitable indicator of eutrophication, integrating various organic matter related features. It should always be applied with sufficient background information of the optical properties of the water mass, and complemented by other indicators.

The effect of damming on biological quality according to macroinvertebrates in some Estonian streams, Central—Baltic Europe: A pilot study

AbstractThe effect of damming on the structure of the macroinvertebrate community and biological quality was studied in nine (the 3–6th order) lowland streams of Estonia, Central—Baltic ecoregion of Europe. Four habitats—reservoirs with accumulated fine sediments, reservoirs with hard bottom, and two corresponding below‐dam areas (both fast‐flowing)—were compared to study whether and how significantly the bottom substrata in dammed areas affected macroinvertebrates and biological quality downstream of dams. The standard kick‐net samples (1.25 m2, complemented with qualitative sample) were collected in autumn 2005—spring 2006. The multimetric biological quality, based on five macroinvertebrate indices (total taxa richness, EPT taxa richness, Average Score Per Taxon, Danish Stream Fauna Index, Shannon diversity) was estimated and compared with reference values. Biological quality in reservoirs with hard bottom and their downstream reaches corresponded to good, or even high quality. Conversely, damming affected biological quality significantly and negatively, above the dam if fine sediments were accumulated. The effect was the strongest within muddy reservoirs themselves (revealing moderate quality only). However, some harmful consequences of mud were observed also downstream of dams. The results also demonstrated that the indices of estimation of organic pollution and/or general quality were able to reflect significant changes in stream flow. Copyright © 2010 John Wiley & Sons, Ltd.

Analysis of bacterial core communities in the central Baltic by comparative RNA–DNA-based fingerprinting provides links to structure–function relationships

Understanding structure-function links of microbial communities is a central theme of microbial ecology since its beginning. To this end, we studied the spatial variability of the bacterioplankton community structure and composition across the central Baltic Sea at four stations, which were up to 450 km apart and at a depth profile representative for the central part (Gotland Deep, 235 m). Bacterial community structure was followed by 16S ribosomal RNA (rRNA)- and 16S rRNA gene-based fingerprints using single-strand conformation polymorphism (SSCP) electrophoresis. Species composition was determined by sequence analysis of SSCP bands. High similarities of the bacterioplankton communities across several hundred kilometers were observed in the surface water using RNA- and DNA-based fingerprints. In these surface communities, the RNA- and DNA-based fingerprints resulted in very different pattern, presumably indicating large difference between the active members of the community as represented by RNA-based fingerprints and the present members represented by the DNA-based fingerprints. This large discrepancy changed gradually over depth, resulting in highly similar RNA- and DNA-based fingerprints in the anoxic part of the water column below 130 m depth. A conceivable mechanism explaining this high similarity could be the reduced oxidative stress in the anoxic zone. The stable communities on the surface and in the anoxic zone indicate the strong influence of the hydrography on the bacterioplankton community structure. Comparative analysis of RNA- and DNA-based community structure provided criteria for the identification of the core community, its key members and their links to biogeochemical functions.

Egg mortality: predation and hydrography in the central Baltic

Abstract Voss, R., Hinrichsen, H-H., Stepputtis, D., Bernreuther, M., Huwer, B., Neumann, V., and Schmidt, J. O. 2011. Egg mortality: predation and hydrography in the central Baltic. – ICES Journal of Marine Science, 68: 1379–1390. Cod and sprat are the dominant fish species in the Baltic pelagic ecosystem, both of great economic importance and ecologically strongly interlinked. Management of both species is challenged by highly variable recruitment success. Recent studies have identified predation and hydrographic conditions during the egg phase to be of critical importance. Two years of extensive field investigations in the Bornholm Basin, central Baltic Sea, were undertaken. In 2002, a typical stagnation situation characterized by low salinity and poor oxygen conditions was investigated, and in early 2003, a major inflow of North Sea water completely changed the hydrographic conditions by increasing salinity and oxygen content, thereby altering ecological conditions. The goal was to quantify egg mortality caused by predation and hydrography, and to compare these estimates with independent estimates based on cohort analysis. Results indicated high intra-annual variability in egg mortality. Cod and sprat egg mortality responded differently to the major Baltic inflow: mortality related to hydrographic conditions increased for sprat and decreased for cod. On the other hand, predation mortality during peak spawning decreased for sprat and increased for cod.

Central Baltic Zone

Acta ArchaeologicaVolume 82, Issue 1 p. 233-233 D) CENTRAL BALTIC ZONE First published: 29 December 2011 https://doi.org/10.1111/j.1600-0390.2011.00477.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume82, Issue1December 2011Pages 233-233 RelatedInformation

Physical aspects of extreme storm surges and falls on the Polish coast

Extreme sea levels – storm-generated surges and falls – on the Polish coast are usually the effects of three components: the volume of water in the southern Baltic (the initial level preceding a given extreme situation), the action of tangential wind stresses in the area (wind directions: whether shore- or seaward; wind velocities; and wind action duration), and the sea surface deformation produced by deep, mesoscale baric lows moving rapidly over the southern and central Baltic that generate the so-called baric wave. Among these factors, the baric wave is particularly important for, i.e. the water cushion underneath the baric depression, moving along the actual atmospheric pressure system over the sea surface.

Spatio-temporal overlap of the alien invasive ctenophore Mnemiopsis leidyi and ichthyoplankton in the Bornholm Basin (Baltic Sea)

In 2007 the alien invasive ctenophore Mnemiopsis leidyi A. Agassiz 1865 was recorded for the first time in the Bornholm Basin, an area which serves as important spawning ground for Baltic fish stocks. Since M. leidyi is capable of preying upon early life stages of fish and further might act as food competitor for fish larvae, it is of major concern to investigate the potential threat that this non-indigenous species poses to the pelagic ecosystem of the Baltic Sea. The present study investigates the temporal and spatial overlap of M. leidyi with eggs and larvae of Baltic cod (Gadus morhua L.) and sprat (Sprattus sprattus L.) in order to assess the potential impact of this new invader on two of the most important Baltic fish stocks. Results show variable inter-seasonal distribution and overlap dynamics and thus different seasonal threat-scenarios for the early life stages of cod and sprat. The spatial overlap between M. leidyi and ichthyoplankton was low for most of the period observed, and we conclude that M. leidyi presently does not have a strong impact. However, we detected situations with high overlaps, e.g. for sprat larvae and cod eggs in spring. As the population dynamics of M. leidyi in the central Baltic are not yet fully understood, a future population explosion of the alien ctenophore with possible effects on fish recruitment cannot be ruled out. Furthermore, a possible shift in peak spawning of cod to the early season, when ctenophore abundances were relatively high, might increase the impact of M. leidyi on cod.

Spatial and interannual variations of seasonal sea surface temperature patterns in the Baltic Sea

Onthebasisofmonthlyaveragedsatellitedata,thisstudyexaminedhowtheannual cycleofthe BalticSeasurfacetemperature(SST) variedspatially andtemporally duringtheperiod1986–2005. Weconcludethattherearetwomainthermalseasons intheBalticSeaseparatedonlybyshorttransitionalperiods–springlastingabout one month, and autumn lasting two months. Generally speaking, summer covers thepartofthe yearfromJunetoOctoberwiththehighestmonthlymeanSSTin August. Winter,withaminimummonthlymeanSSTinFebruaryinshallowwaters orin Marchin deeper areas,lasts fromDecember to April. As aresultof climate changes over the Baltic Sea region, strong positive trends in SST occur in the summermonths. Inconsequence,theperiodwithextremelyhighseasurfacewater temperatures has become slightly longer in the central Baltic. In the last decade winter changes in SST display zero or even negativetendencies. The investigated period was characterized by an annual increase in mean temperatures of about 0.03–0.07 ◦ C. However, the rates of monthly mean SST changes were sometimes morethanthreetimes ashigh.