Structure and evolution of the cold intermediate layer in the southeastern part of the Baltic Sea by the field measurement data of 2004–2008

Stepanova, Natalia; Chubarenko, Irina; Щука, С. А.

doi:10.1134/s0001437015010154

Cited by 12 publications

(4 citation statements)

References 7 publications

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“…Cold intermediate layer forms in winter due to mixing by convection and wind stirring of the previous year intermediate water and the upper layer (Stepanova et al, 2015). Erosion of the halocline contributes to the formation of intermediate layer water mass as well during storm events due to wind stirring (Lass et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Stratification Has Strengthened in the Baltic Sea – An Analysis of 35 Years of Observational Data

Liblik

Lips

2019

Front. Earth Sci.

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Stratification of the water column, consisting of the three layers (upper, intermediate, and deep layer) separated by the seasonal thermocline and the permanent halocline, respectively, is an important factor for the functioning of the brackish Baltic Sea. In the present work, changes in the vertical structure of temperature and salinity, as well as heat content, salt mass, and stratification conditions were estimated on the basis of in situ and remote sensing data in 1982-2016. The seasonal thermocline and the halocline have strengthened in most of the sea by a rate of 0.33-0.39 and 0.70-0.88 kg m −3 , respectively, during 35 years. The upper layer has warmed by 0.03-0.06 • C year −1 and sub-halocline deep layer 0.04-0.06 • C year −1 in most of the sea. The total warming trend in the whole Baltic has been 1.07 • C for 35 years, being approximately twice higher compared to the upper 100 m in the Atlantic Ocean. Average upper layer warming of the sea from May to September has been 0.07-0.08 • C year −1 while in winter, trends were mostly statistically not significant. More rapid warming during summers has occurred in shallower, closed-end areas of gulfs if compared to the rest of the sea. Possible reasons for high warming there might be shallow depths and limited water exchange, stronger stratification, and/or higher turbidity. Sea surface temperature trends estimated by in situ and satellite data agree well. Trends of freshening (−0.005 to −0.014 g kg −1 year −1 ) of the upper layer and increasing salinity (0.02 to 0.04 g kg −1 year −1 ) in the sub-halocline deep layer were detected. Increased salinity in the deep layer is likely caused by the increased lateral import of saltier water from the North Sea. Changes in the upper layer salinity might not be related to the accumulated river runoff only, but decadal changes of vertical salt flux might also contribute. The vertically distinct changes cancel each other and no significant trend in the mean salinity of the Baltic Sea was detected. No remarkable changes have occurred in the cold intermediate layer. In conclusion, different dominating processes have caused distinct long-term trends in the three layers of the Baltic Sea.

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Section: Introductionmentioning

confidence: 99%

Stratification Has Strengthened in the Baltic Sea – An Analysis of 35 Years of Observational Data

Liblik

Lips

2019

Front. Earth Sci.

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“…Since river discharge is concentrated in the east and the gulf is connected to the Baltic Proper in the west, there is a mean longitudinal salinity gradient in the upper layer from approximately 0 g kg −1 at the easternmost end to 6 g kg −1 in the west (Alenius et al, 1998). Also, mean salinity in the upper layer is lower on the northern coast than the southern (e.g., Kikas and Lips, 2016) due to the mean cyclonic circulation in the upper layer and prevailing westward current along the northern coast (Palmen, 1930;Rasmus et al, 2015;Stipa, 2004). Free water exchange between the gulf and the Baltic Proper means that there is a quasi-permanent halocline and saltier deep layer in the gulf.…”

Section: Introductionmentioning

confidence: 99%

The winter stratification phenomenon and its consequences in the Gulf of Finland, Baltic Sea

et al. 2020

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Abstract. Stratification plays an essential role in the marine ecosystem, with a shallow mixed layer being one of the preconditions for enhanced primary production in the ocean. In the Baltic Sea, the general understanding is that the upper mixed layer (UML) is well below the euphotic zone in winter. In this study, we demonstrate that wintertime shallow stratification is common in the Gulf of Finland and it forms at a depth comparable to the euphotic zone in January–February. The onset of restratification is likely associated with the annual cycle of westerly winds, which ease off in late January–early February. Stratification is first invoked along the northern coast by the westward advection of riverine water forced by easterly winds and is expanded to the south when the prevailing wind direction changes from an easterly to a westerly direction. Haline stratification emerges approximately 1 month later in the southern part of the gulf. Winter restratification can occur in the entire gulf and also in the absence of ice; thus, it is a regular seasonal feature in the area. Interannual variations in the wintertime UML correspond with variations in the North Atlantic Oscillation. Chlorophyll a concentrations in winter can be comparable to mid-summer; the limiting factor for phytoplankton bloom in winter is likely insufficient solar radiation.

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“…The temperature typically passes the Tmd in the northern and eastern part of the Baltic Sea during the cooling period (Karlson et al, 2016;Liblik et al, 2013) while it is not always the case in the offshore areas in the southern Baltic Sea (e.g. Stepanova et al, 2015). Lateral haline buoyancy flux can compensate the thermal convection and stabilization of the shallow upper layer in spring can 60 occur at temperatures already below Tmd (Eilola, 1997;Eilola and Stigebrandt, 1998;Stipa et al, 1999).…”

Section: Introduction 20mentioning

confidence: 99%

Winter stratification phenomena and its consequences in the Gulf of Finland, Baltic Sea

Liblik¹,

Väli²,

Lips³

et al. 2020

Preprint

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Abstract. Stratification plays an essential role in the marine system. The shallow mixed layer is one of the preconditions for the enhanced primary production in the ocean. The general understanding is that the mixed layer is well deeper than the euphotic zone in the Baltic Sea during winter. In this work, we demonstrate the wintertime stratification is a common phenomenon in the Gulf of Finland. Shallow haline stratification at the depth comparable to the euphotic zone depth forms in late January–early February. Stratification is evoked by the positive buoyancy flux created by the westward advection of riverine water along the northern coast of the gulf. Fresher water and haline stratification appeared approximately one month later in the southern part of the gulf. The phenomena can occur in the whole gulf and also without ice. Chl a concentration and phytoplankton biomass in winter can be comparable to mid-summer. The limiting factor for phytoplankton bloom in winter is likely insufficient solar radiation.

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Structure and evolution of the cold intermediate layer in the southeastern part of the Baltic Sea by the field measurement data of 2004–2008

Cited by 12 publications

References 7 publications

Stratification Has Strengthened in the Baltic Sea – An Analysis of 35 Years of Observational Data

Stratification Has Strengthened in the Baltic Sea – An Analysis of 35 Years of Observational Data

The winter stratification phenomenon and its consequences in the Gulf of Finland, Baltic Sea

Winter stratification phenomena and its consequences in the Gulf of Finland, Baltic Sea

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