Suboxic and anoxic conditions in the Gdansk basins’ deep water (the Baltic sea)

Variability of oxygen and hydrogen sulphide concentrations in the Gdansk basins deep water of the Baltic Sea for the last 25 years was analyzed. It was shown that suboxic and anoxic conditions in deep water were mainly determined by Baltic inflow frequency and intensity. Oxygen concentration in the bottom layer of the Gdansk basins increased strongly in 13 months after Major Baltic Inflow events (MBI). There were three periods of strong increasing of dissolve oxygen concentration in deep water since 1992 till 2018 after MBI in 1993, in 2003 and 20142016. It was shown that at the bottom of the Gdansk basins hydrogen sulphide was detected during 79 months till 22.5 years after MBI. Quality evaluation of dissolved oxygen distribution reanalysis was also conducted in this work. It can be noted good reproduction of field data by the reanalysis in its quality part; however, in most cases the observable maximum concentrations in dissolved oxygen distribution are understated, sometimes even several times.

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Suboxic and Anoxic Conditions of Deep Waters in the Gdansk Basin of the Baltic Sea

Oceanology ◽

10.1134/s0001437019050011 ◽

2019 ◽

Vol 59 (5) ◽

pp. 639-647

Author(s):

K. V. Artamonova ◽

A. N. Demidov ◽

O. A. Zuev

Keyword(s):

Baltic Sea ◽

The Baltic Sea ◽

Anoxic Conditions ◽

Deep Waters ◽

The Baltic

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A model of the deep water flow into the Baltic Sea

Tellus A Dynamic Meteorology and Oceanography ◽

10.1034/j.1600-0870.1992.t01-4-00005.x ◽

1992 ◽

Vol 44 (5) ◽

pp. 414-424 ◽

Cited By ~ 7

Author(s):

LARS GIDHAGEN ◽

BERTIL HAKANSSON

Keyword(s):

Baltic Sea ◽

Water Flow ◽

Deep Water ◽

The Baltic Sea ◽

The Baltic

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Bathymetric Properties of the Baltic Sea

10.5194/os-2019-18 ◽

2019 ◽

Cited By ~ 1

Author(s):

Martin Jakobsson ◽

Christian Stranne ◽

Matt O'Regan ◽

Sarah L. Greenwood ◽

Bo Gustafsson ◽

...

Keyword(s):

High Resolution ◽

Baltic Sea ◽

Ocean Circulation ◽

Deep Water ◽

Water Exchange ◽

The Baltic Sea ◽

Resolution Mapping ◽

Baltic Proper ◽

Southern Side ◽

The Baltic

Abstract. Marine science and engineering commonly require reliable information about seafloor depth (bathymetry), e.g. for studies of ocean circulation, bottom habitats, fishing resources, sediment transport, geohazards and site selection for platforms and cables. Baltic Sea bathymetric properties are analysed here using the using the newly released Digital Bathymetric Model (DBM) by the European Marine Observation and Data Network (EMODnet). The analyses include hypsometry, volume, descriptive depth statistics, and km-scale seafloor ruggedness, i.e. terrain heterogeneity, for the Baltic Sea as a whole as well as for 17 sub-basins defined by the Baltic Marine Environment Protection Commission (HELCOM). We compare the new EMODnet DBM with IOWTOPO, the previously most widely used DBM of the Baltic Sea which has served as the primary gridded bathymetric resource in physical and environmental studies for nearly two decades. The area of deep water exchange between the Bothnian Sea and the Northern Baltic Proper across the Åland Sea is specifically analysed in terms of depths and locations of critical bathymetric sills. The EMODnet DBM provides a bathymetric sill depth of 88 m at the northern side of the Åland Sea and 60 m at the southern side, differing from previously identified sill depths of 100 and 70 m respectively. High-resolution multibeam bathymetry acquired from this deep water exchange path, where vigorous bottom currents interacted with the seafloor, allows us to assess what we are missing in presently available DBMs in terms of physical characterisation and our ability to then interpret seafloor processes and highlights the need for continued work towards complete high-resolution mapping of the Baltic Sea seafloor.

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Tracking the spatiotemporal variability of the oxic–anoxic interface in the Baltic Sea with broadband acoustics

ICES Journal of Marine Science ◽

10.1093/icesjms/fsaa153 ◽

2020 ◽

Author(s):

Elizabeth Weidner ◽

Christian Stranne ◽

Jonas Hentati Sundberg ◽

Thomas C Weber ◽

Larry Mayer ◽

...

Keyword(s):

Dissolved Oxygen ◽

Baltic Sea ◽

Water Column ◽

Acoustic Scattering ◽

Spatiotemporal Variability ◽

Coastal Zones ◽

Anoxic Zone ◽

The Baltic Sea ◽

Impedance Contrast ◽

The Baltic

Abstract Anoxic zones, regions of the water column completely devoid of dissolved oxygen, occur in open oceans and coastal zones worldwide. The Baltic Sea is characterized by strong salinity-driven stratification, maintained by occasional water inflows from the Danish Straights and freshwater input from rivers. Between inflow events, the stratification interface between surface and deep waters hinders mixing and ventilation of deep water; consequently, the bottom waters of large regions of the Baltic are anoxic. The onset of the anoxic zone is closely coincident with the depth of the halocline and, as a result, the interface between oxic and anoxic waters corresponds to a strong impedance contrast. Here, we track acoustic scattering from the impedance contrast utilizing a broadband split-beam echosounder in the Western Gotland Basin and link it to a dissolved oxygen level of 2 ml/l using ground truth stations. The broadband acoustic dataset provides the means to remotely observe the spatiotemporal variations in the oxic–anoxic interface, map out the extent of the anoxic zone with high resolution, and identify several mechanisms influencing the vertical distribution of oxygen in the water column. The method described here can be used to study other systems with applications in ongoing oceanographic monitoring programs.

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Ventilation of the Northern Baltic Sea

10.5194/os-2019-48 ◽

2019 ◽

Author(s):

Thomas Neumann ◽

Herbert Siegel ◽

Matthias Moros ◽

Monika Gerth ◽

Madline Kniebusch ◽

...

Keyword(s):

Sea Ice ◽

Baltic Sea ◽

Deep Water ◽

Bottom Water ◽

Ice Core ◽

Winter Season ◽

The Baltic Sea ◽

The Baltic ◽

Bothnian Bay ◽

Bothnian Sea

Abstract. The Baltic Sea is a semi-enclosed, brackish water sea in northern Europe. The deep basins of the central Baltic Sea regularly show hypoxic conditions. In contrast, the northern parts of the Baltic Sea, the Bothnian Sea and Bay, are well oxygenated. Lateral inflows or a ventilation due to convection are possible mechanisms for high oxygen concentrations in the deep water of the northern Baltic Sea. Owing to the high latitudes of the northern Baltic, this region is regularly covered by sea ice during the winter season. In March 2017, the RV Maria S. Merian was for two days in the Bothnian Bay collecting ice core samples, brine water, and CTD profiles. The bulk sea ice salinity was on average 0.6 g/kg and in brine samples, a salinity of 11.5 g/kg and 17.8 g/kg have been measured. At one station, the CTD profiles indicated a recent ventilation event of the deep water. A water mass analysis showed that the ventilation is most probably due to mixing of Bothnian Sea and Bothnian Bay surface water which results in sufficient dense water able to replace older bottom water. However, the high salinity of brine provides the potential for forming dense bottom water masses as well.

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