The core of the Baltic CIL: shall we introduce the Bornholm Intermediate Water?

Mapping Intimacies ◽

10.5194/egusphere-egu21-9930 ◽

2021 ◽

Author(s):

Tatiana Bukanova ◽

Olga Lobchuk ◽

Irina Chubarenko

Keyword(s):

Surface Water ◽

Baltic Sea ◽

Surface Waters ◽

Intermediate Water ◽

Cold Surface ◽

Spring Warming ◽

The Core ◽

Intermediate Layers ◽

Baltic Proper ◽

The Baltic

Cold Intermediate Layer (CIL) is apparent in the thermohaline structure of the Baltic Sea every year, typically from April to December. Within the CIL, water temperature, salinity, oxygen content, and other parameters are highly inhomogeneous in vertical, reflecting a complicated process of its formation. The core of the CIL (the layer of the coldest waters) has its T,S-index) allowing to identify the south-western part of the sea as the source of these waters. At the beginning of spring warming, a combination of environmental factors favors the subduction of the cold surface waters into the intermediate layers of the Baltic Proper, where they adjust to the density field, making up the coldest layer right above the permanent pycnocline.For spring 2006, CTD measurements from 2 expeditions of research vessels &#8220;Professor Shtokman&#8221; of the Shirshov Institute of Oceanology and &#8220;Gauss&#8221; of Leibniz Institute for Baltic Sea Research in Warnem&#252;nde (IOW) were analyzed, along with the CTD measurements from ICES open database, and meteorological information. Remote sensing data provide observations of the abrupt transformation of SST field in the Bornholm Basin in early spring 2006, when the coldest surface water occurred within the coastal zones and its temperature was close to or below the temperature of maximum density (Tmd). The beginning of spring warming in the region and further heating of the cold surface water from temperature below the Tmd induce horizontal exchange, which favors the penetration of winter-cold (1.1&#8211;2.1 &#176;C) surface waters of moderate salinity (7.6-8.1) into the intermediate layers in March. This water was observed in the Gdansk and Gotland basins in April-May 2006 as the core of the CIL. On the basis of vertical T,S-profiles and T,S-diagrams, the range of parameters of the CIL core waters in spring 2006 was determined (T: 1.4&#8211;2.1 &#176;C; S: 7.6&#8211;8.1), which corresponds to the upper mixed layer in the vicinity of the Bornholm Island in March, 2006. Since this relation has already been confirmed for other years, and having in mind the importance of the process of the CIL formation for the entire Baltic Sea conveyor belt, we suggest to term waters of the CIL core as the Bornholm Intermediate Waters (BIW). Obviously, the T,S-index of the BIW shall vary from year to year, reflecting the severity of the past winter and the conditions of the particular spring. However, the BIW location right above the pycnocline, the lowest (for the current year) temperature, and its characteristic salinity of 7.6-8.1 seem to be repeatedly confirmed by field observations in the Baltic Proper in spring.Investigations are supported by the Russian Foundation for Basic Research, grant No. 19-05-00717 (in part of the data analysis) and the State Assignment No. 0149-2019-0013 (in part of satellite data collecting and processing).

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Metagenomics Uncovers a Core SAR11 Population in Brackish Surface Waters of the Baltic Sea

Water ◽

10.3390/w12020501 ◽

2020 ◽

Vol 12 (2) ◽

pp. 501 ◽

Cited By ~ 2

Author(s):

Poorna Vidanage ◽

Seok-Oh Ko ◽

Seungdae Oh

Keyword(s):

Baltic Sea ◽

Relative Abundance ◽

Surface Waters ◽

Environmental Changes ◽

Rrna Gene ◽

The Baltic Sea ◽

Bacterial Populations ◽

The Core ◽

The Baltic ◽

Seasonal Shifts

The Baltic Sea represents one of the largest brackish ecosystems where various environmental factors control dynamic seasonal shifts in the structure, diversity, and function of the planktonic microbial communities. In this study, despite seasonal fluctuations, several bacterial populations (<2% of the total OTUs) that are highly dominant (25% of relative abundance) and highly frequently occurring (>85% of occurrence) over four seasons were identified. Mathematical models using occurrence frequency and relative abundance data were able to describe community assembly persisting over time. Further, this work uncovered one of the core bacterial populations phylogenetically affiliated to SAR11 subclade IIIa. The analysis of the hypervariable region of 16S rRNA gene and single copy housekeeping genes recovered from metagenomic datasets suggested that the population was unexpectedly evolutionarily closely related to those inhabiting a mesosaline lacustrine ecosystem rather than other marine/coastal members. Our metagenomic results further revealed that the newly-identified population was the major driver facilitating the seasonal shifts in the overall community structure over the brackish waters of the Baltic Sea. The core community uncovered in this study supports the presence of a brackish water microbiome distinguishable from other marine and freshwater counterparts and will be a useful sentinel for monitoring local/global environmental changes posed on brackish surface waters.

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Deuterium and Oxygen-18 in Surface Waters of GDR draining to the Baltic Sea

Isotopenpraxis Isotopes in Environmental and Health Studies ◽

10.1080/10256019008622436 ◽

1990 ◽

Vol 26 (12) ◽

pp. 569-573 ◽

Cited By ~ 1

Author(s):

W. Richter ◽

P. Kowski

Keyword(s):

Baltic Sea ◽

Surface Waters ◽

The Baltic Sea ◽

The Baltic

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Effects of surface current/wind interaction in an eddy-rich general ocean circulation simulation of the Baltic Sea

10.5194/os-2016-12 ◽

2016 ◽

Author(s):

H. Dietze ◽

U. Löptien

Keyword(s):

Baltic Sea ◽

Ocean Circulation ◽

Surface Waters ◽

Algal Blooms ◽

Circulation Model ◽

Transport Processes ◽

Surface Currents ◽

Wind Effects ◽

The Baltic Sea ◽

The Baltic

Abstract. Deoxygenation in the Baltic Sea endangers fish yields and favours noxious algal blooms. Yet, vertical transport processes ventilating the oxygen-deprived waters at depth and replenishing nutrient-deprived surface waters (thereby fuelling export of organic matter to depth), are not comprehensively understood. Here, we investigate the effects of the interaction between surface currents and winds (also referred to as eddy/wind effects) on upwelling in an eddy-rich general ocean circulation model of the Baltic Sea. Contrary to expectations we find that accounting for current/wind effects does inhibit the overall vertical exchange between oxygenated surface waters and oxygen-deprived water at depth. At major upwelling sites, however, as e.g. off the south coast of Sweden and Finland, the reverse holds: the interaction between topographically steered surface currents with winds blowing over the sea results in a climatological sea surface temperature cooling of 0.5 K. This implies that current/wind effects drive substantial local upwelling of cold and nutrient-replete waters.

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Nitrate source identification in the Baltic Sea using its isotopic ratios in combination with a Bayesian isotope mixing model

Biogeosciences ◽

10.5194/bg-11-4913-2014 ◽

2014 ◽

Vol 11 (17) ◽

pp. 4913-4924 ◽

Cited By ~ 25

Author(s):

F. Korth ◽

B. Deutsch ◽

C. Frey ◽

C. Moros ◽

M. Voss

Keyword(s):

Atmospheric Deposition ◽

Baltic Sea ◽

Surface Waters ◽

N2 Fixation ◽

Source Identification ◽

Agricultural Land ◽

Mixing Model ◽

The Baltic Sea ◽

Bayesian Isotope Mixing Model ◽

The Baltic

Abstract. Nitrate (NO3−) is the major nutrient responsible for coastal eutrophication worldwide and its production is related to intensive food production and fossil-fuel combustion. In the Baltic Sea NO3− inputs have increased 4-fold over recent decades and now remain constantly high. NO3− source identification is therefore an important consideration in environmental management strategies. In this study focusing on the Baltic Sea, we used a method to estimate the proportional contributions of NO3− from atmospheric deposition, N2 fixation, and runoff from pristine soils as well as from agricultural land. Our approach combines data on the dual isotopes of NO3− (δ15N-NO3− and δ18O-NO3−) in winter surface waters with a Bayesian isotope mixing model (Stable Isotope Analysis in R, SIAR). Based on data gathered from 47 sampling locations over the entire Baltic Sea, the majority of the NO3− in the southern Baltic was shown to derive from runoff from agricultural land (33–100%), whereas in the northern Baltic, i.e. the Gulf of Bothnia, NO3− originates from nitrification in pristine soils (34–100%). Atmospheric deposition accounts for only a small percentage of NO3− levels in the Baltic Sea, except for contributions from northern rivers, where the levels of atmospheric NO3− are higher. An additional important source in the central Baltic Sea is N2 fixation by diazotrophs, which contributes 49–65% of the overall NO3− pool at this site. The results obtained with this method are in good agreement with source estimates based upon δ15N values in sediments and a three-dimensional ecosystem model, ERGOM. We suggest that this approach can be easily modified to determine NO3− sources in other marginal seas or larger near-coastal areas where NO3− is abundant in winter surface waters when fractionation processes are minor.

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Dissolved iron (II) in the Baltic Sea surface water and implications for cyanobacterial bloom development

Biogeosciences Discussions ◽

10.5194/bgd-6-3803-2009 ◽

2009 ◽

Vol 6 (2) ◽

pp. 3803-3850 ◽

Cited By ~ 4

Author(s):

E. Breitbarth ◽

J. Gelting ◽

J. Walve ◽

L. J. Hoffmann ◽

D. R. Turner ◽

...

Keyword(s):

Baltic Sea ◽

Surface Waters ◽

Cyanobacterial Bloom ◽

Euphotic Zone ◽

Strong Wind ◽

Ferrous Ions ◽

The Baltic Sea ◽

High Concentrations ◽

Wind Events ◽

The Baltic

Abstract. Iron chemistry measurements were conducted during summer 2007 at two distinct locations in the Baltic Sea (Gotland Deep and Landsort Deep) to evaluate the role of iron for cyanobacterial bloom development in these estuarine waters. Depth profiles of Fe(II) were measured by chemiluminescent flow injection analysis (CL-FIA) and reveal several origins of Fe(II) to the water column. Photoreduction of Fe(III)-complexes and deposition by rain are main sources of Fe(II) (up to 0.9 nmol L−1) in light penetrated surface waters. Indication for organic Fe(II) complexation resulting in prolonged residence times in oxygenated water was observed. Surface dwelling heterocystous cyanobacteria where mainly responsible for Fe(II) consumption in comparison to other phytoplankton. The significant Fe(II) concentrations in surface waters apparently play a major role in cyanobacterial bloom development in the Baltic Sea and are a major contributor to the Fe requirements of diazotrophs. Second, Fe(II) concentrations up to 1.44 nmol L−1 were observed at water depths below the euphotic zone, but above the oxic anoxic interface. Finally, all Fe(III) is reduced to Fe(II) in anoxic deep water. However, only a fraction thereof is present as ferrous ions (up to 28 nmol L−1) and was detected by the CL-FIA method applied. Despite their high concentrations, it is unlikely that ferrous ions originating from sub-oxic waters could be a temporary source of bioavailable iron to the euphotic zone since mixed layer depths after strong wind events are not deep enough in summer time.

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Nitrogen fixation in a diazotrophic post-bloom situation in the Baltic Sea

10.5194/egusphere-egu21-911 ◽

2021 ◽

Author(s):

Christian Reeder ◽

Carolin Löscher

Keyword(s):

Climate Change ◽

Surface Water ◽

Baltic Sea ◽

The Baltic Sea ◽

Biological Fixation ◽

Community Based ◽

Iron Iron ◽

The Baltic ◽

Metal Cofactors ◽

Diazotrophic Community

The Baltic Sea is characterised as a semi-enclosed brackish Sea that has experienced increased eutrophication, hypoxia, and increased temperature over the last ~100 years making Baltic Sea one of the most severely impacted oceanic environment by climate change. Biological fixation of dinitrogen gas (N2) is an essential process to make atmospheric N2 available for marine life. This process is carried out by specialised organisms called diazotrophs and is catalysed by the energetic-consuming enzyme nitrogenase. Nitrogenases exist in three subtypes depending on their metal cofactors, (1) the most common molybdenum-dependent (Nif), (2) the vanadium-dependent (Vnf) and (3) the Iron-Iron-dependent nitrogenase (Anf). To date, the effect of climate change on those three enzyme subtypes and their potential role a future ocean is yet to be explored. The predicted ongoing oxygen loss in the ocean may limit Mo's availability and trigger a shift from the abundant Nif-type nitrogenase to Vnf or Anf and, therefore, a potential shift in the diazotrophic community. This study explored the climate change-related pressures on N2 fixation and the diazotrophic community based on nifH and vnf/anfD amplicons. At the time of sampling, we found a post-bloom high-nutrient low-chlorophyll situation. Cyanobacterial groups, Nodularia and UCYN-A, dominated the diazotrophic community and showed a horizontal where UCYN-A were the dominant fixers at 20 m. Based on alternative nitrogenases amplicons, Rhodopseudomonas was the dominating microbe in the surface water. This paper presents the first hint of active nitrogenases in surface water and further establish UCYN-A as a significant player in Baltic Sea primary production.

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