Deep water exchange in the Baltic Proper

Kõuts, Tarmo; Omstedt, Anders

doi:10.3402/tellusa.v45i4.14895

Cited by 33 publications

(28 citation statements)

References 16 publications

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“…This could indicate that the observed statistical connection between the deep and surface layers is not caused by slow filling-up from the bottom layers. The fact that the position of the halocline also shows a seasonal cycle (Kõuts & Omstedt 1993) offers some support to the idea that the mixing between the upper and deeper layers at multiannual time scales may be strong enough. However, the statistical analysis alone cannot yield any definite answers to the questions of the coherence between salinity and oxygen and the coherence between the upper and deeper layers, but may point to subjects for future research in Baltic Sea modelling.…”

Section: Discussionmentioning

confidence: 75%

“…This is in contrast to the idea that vertical stratification effectively prevents vertical mixing at longer time scales in the Baltic Sea. Previous modelling studies (Kõuts & Omstedt 1993) seem to indicate that the waters entering the Baltic from the North Sea are distributed in much of the deep Baltic at a time scale of 6 mo to 1 yr (excluding the deepest subbasins), which could offer some explanation for the horizontal coherence of the salinity and oxygen anomalies. However, the typical time scale for salinity anomalies entering the deepest layers from the North Sea to be upwelled to the surface layers seems to be of the order of 30 yr in other models (Omstedt & Axell 1998).…”

Section: Discussionmentioning

confidence: 99%

“…Deep-layer salinity was considered using the salinity averaged below 100 m. It is known that the position and strength of the halocline varies in space and time in the Baltic Sea (e.g. Kõuts & Omstedt 1993). In prolonged stagnation periods the permanent halocline in the central Baltic and Gulf of Finland descends and becomes weaker (Matthäus 1990, Elken 1996 whereas in the Gulf of Bothnia no comparable salinity stratification exists in general, but considering that at these time scales the salinity variability seems to evolve quite coherently at all depths (see Fig.…”

Section: Deeper Layermentioning

confidence: 99%

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Dependence of salinity and oxygen concentrations in the Baltic Sea on large-scale atmospheric circulation

Zorita¹,

Laine²

2000

Clim. Res.

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ABSTRACT:The relationship between the low-frequency (annually averaged) salinity and oxygen concentrations in the last 30 yr in the Baltic Sea and the large-scale atmospheric circulation was statistically analyzed. It was found that at these time scales the evolution of salinity and oxygen is quite homogeneous in depth, i.e. deviations from the long-term mean tend to be of the same sign in the upper and deeper layers simultaneously. Moreover, the evolution of the salinity and oxygen concentrations are negatively correlated within each layer: lower than normal salinities tend to be observed simultaneously with higher than normal oxygen concentrations, and vice versa. The statistical analysis seems to indicate that the forcing by the atmospheric circulation may be responsible for this anticorrelation between salinity and oxygen. A stronger meridional sea-level-pressure (SLP) gradient over the North Atlantic, and therefore stronger westerly winds, causes positive rainfall anomalies in the Baltic Sea catchment area and increase run-off giving rise to decreased salinities at all depths. The mechanisms by which a stronger zonal atmospheric circulation enhances the oxygen concentrations may be related either to a weakened stratification through the reduced salinity (at long time scales), or by stronger or more frequent inflows of North Sea waters (at short time scales). The influence of the atmospheric circulation can explain at these time scales of the order of 60 and 40% of the variability of these hydrographic variables, respectively. The question of how salinity and oxygen in the Baltic Sea may respond to changes of the atmospheric circulation in a global climate change scenario is also addressed. For this purpose the intensities of the relevant atmospheric circulation patterns in a transient experiment with a coupled atmosphere-ocean general circulation model forced with increasing anthropogenic greenhouse gas concentrations between the years 1860 and 2099 were estimated. In this integration the change of the atmospheric circulation most relevant for salinity and oxygen in the Baltic Sea seems to be an enhancement of the meridional SLP gradient in the North Atlantic. Thus, under the assumption that the statistical relationship between SLP and the hydrographic variables also holds in the future, this trend in the atmospheric circulation would lead to decreased salinity and improved oxygen conditions in the Baltic Sea.

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Section: Discussionmentioning

confidence: 75%

Section: Discussionmentioning

confidence: 99%

Section: Deeper Layermentioning

confidence: 99%

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Dependence of salinity and oxygen concentrations in the Baltic Sea on large-scale atmospheric circulation

Zorita¹,

Laine²

2000

Clim. Res.

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“…At the same time the salinity decreases due to entrainment of ambient water. Only occasionally does the salinity of the inflowing water remain high enough to allow replacement of the deepest water (Wulff et al 1990, Matthäus & Franck 1992, Kõuts & Omstedt 1993.…”

Section: Description Of the Baltic Seamentioning

confidence: 99%

Baltic Sea ocean climate: an analysis of 100 yr of hydrographic data with focus on the freshwater budget

Winsor

Rodhe²,

Omstedt³

2001

Clim. Res.

102

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The Baltic Sea climate is analysed based upon long-term oceanographic measurements. The objective of the work is to study the natural variability of present day climate with focus on the freshwater budget. The results are designed to be used for validation of climate models and for discrimination of the significance of modelled climate change scenarios. Almost 100 yr of observations are used in the study, including data for river runoff, water exchange through the Danish Straits (as calculated from river runoff and from sea level data from the Kattegat), salinity data from the Baltic Sea and the Kattegat, and oxygen content in the deep Baltic Sea. The analyses illustrate that freshwater supply to the Baltic shows large variations on time scales up to several decades. The long-term variations in freshwater storage are closely correlated to accumulated changes in river runoff. This indicates strong positive feedback between the amount of outflowing surface water from the Baltic Sea and the salinity of the inflowing Kattegat water. One implication of the study is that climate control simulations must cover several decades, probably up to 100 yr in order to capture the natural variability of present day climate. Also, models designed to study climate change for the Baltic Sea probably need to start integrating from the present day.KEY WORDS: Baltic Sea · Climate · Salinity · Freshwater · River runoff · OxygenResale or republication not permitted without written consent of the publisher

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“…On average, new high-saline water reaches the deep layers of the Gotland Basin with a delay of up to a year (e.g. Kõuts and Omstedt 1993;Matthäus et al 2008), as can be seen also in Fig. 7.4.…”

Section: 3mentioning

confidence: 79%

Recent Change—Marine Circulation and Stratification

Elken

Lehmann

Myrberg

2015

Regional Climate Studies

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This chapter describes recent change in the circulation and stratification of the Baltic Sea. A recent warming trend in sea-surface waters has been clearly demonstrated by in situ measurements, remote sensing data and numerical models. Trends in sea-surface temperature (SST) for the past three to four decades based on remote sensing data generally agree with trends determined from in situ observations. Models suggest the current warming within the Baltic Sea lies within the range experienced during the past 500 years. The salinity and stratification of the deep waters are strongly linked to the major inflows of North Sea water that occur sporadically and bring high-saline water into the deep layers of the Baltic Sea. The major inflows normally occur during winter and spring and bring cold oxygen-rich waters into the deep basins. Since 1996, large inflows have also occurred during summer, bringing in warm low-oxygen water. IntroductionChanges in thermohaline characteristics and stratification of the water column are usually analysed on the basis of data from repeat hydrographic observations, originating from shipborne monitoring programmes and/or permanent coastal and offshore oceanographic stations. Such datasets are described in recent books by Feistel et al. (2008) and Leppäranta and Myrberg (2009). In situ observations are often irregular in space and time, especially for offshore areas; therefore, trends and variability in the ocean state can only be determined by careful pre-processing of the data to address issues such as data homogenisation and the suppression of aliasing errors. In recent decades, horizontal undersampling by in situ measurements has been partially offset by the remote sensing of sea-surface properties from satellites; with these data free of spatial aliasing errors due to their high horizontal resolution. Satellite-derived cloud-free products for sea-surface temperature (SST) have been reasonably accurate since the 1980s. Many of the papers published over the past decade that address trends and variability in the circulation and stratification of the Baltic Sea are based on remote sensing data, often in combination with in situ observations and the results of numerical modelling. Improvements in the physical and numerical features of the models, accompanied by model validation studies, have increased confidence in the realism of the model results. Models provide dynamically balanced gridded datasets over decades or longer, including information for 'noisy' variables such as currents, transport and mixing fluxes. This chapter analyses the recent peer-reviewed literature, extending the findings from earlier review (Box 7.1).

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Deep water exchange in the Baltic Proper

Cited by 33 publications

References 16 publications

Dependence of salinity and oxygen concentrations in the Baltic Sea on large-scale atmospheric circulation

Dependence of salinity and oxygen concentrations in the Baltic Sea on large-scale atmospheric circulation

Baltic Sea ocean climate: an analysis of 100 yr of hydrographic data with focus on the freshwater budget

Recent Change—Marine Circulation and Stratification

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