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Recently discovered, ocean submesoscales have attracted considerable attention due to their ability to change the upper ocean stratification, affect vertical transport, and induce a downscale cascade of energy toward dissipation. Here, we highlight the effect of submesoscale fronts and filaments on surface layer properties and dynamics during storm events, extending previous idealized simulations toward real-ocean applications. We use the Baltic Sea as a natural laboratory to study the rich submesoscale activity of this system with the help of realistic high-resolution numerical simulations. These simulations reveal a wealth of cold submesoscale filaments characterized by sharp lateral buoyancy gradients, strong surface convergence, and high vertical velocities. We show that highly heterogeneous Mixed Layer Depth (MLD) modulations are associated with these features, maintaining locally reduced MLDs even during storm events due to vigorous submesoscale restratification. The interaction of near-surface turbulence and submesoscale restratification results in strong and highly efficient mixing inside the submesoscale fronts.&nbsp, The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Semi-enclosed marginal seas like the Baltic Sea are often characterized by permanently anoxic deep layers, and may therefore serve as important model systems to study the causes and consequences of the predicted global expansion of oxygen minimum zones. Here, we focus on the role and potential of physical transport processes in ventilating the deep anoxic bottom water of the central Baltic Sea. Based on long-term deployments of an autonomous profiling system in the central Baltic Sea, we show that small scale oxic mid-water intrusions, that are advectively transported, are ubiquitous features, providing an important oxygen source. The turbulent transport of oxygen was measured by a novel combination of fast optodes with shear microstructure data and show strongly increased transport rates during the autumn and winter months as well as a confinement to the basin boundaries, caused by boundary mixing. On the long-term average, mid-water intrusions were shown to inject about 15 Gmol of oxygen per year into the deep-water region below the permanent halocline, turbulent mixing contributes with about 23 Gmol. This is about one order of magnitude larger than the average amount of oxygen imported during the massive deep-water inflow events (Major Baltic Inflows) that occur on an approximately decadal time scale. These results emphasize that a precise understanding of the oxygen transport pathways is fundamental for a projection of the state of the Baltic Sea in a changing climate., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Meereswissenschaftliche Berichte No 107 2018 - Marine Science Reports No 107 2018, Die Arbeit beschreibt die hydrographisch-hydrochemischen Bedingungen in der westlichen und zentralen Ostsee für das Jahr 2017. Basierend auf den meteorologischen Verhältnissen werden die horizontalen und vertikalen Verteilungsmuster von Temperatur, Salzgehalt, Sauerstoff/ Schwefelwasserstoff und Nährstoffen mit saisonaler Auflösung dargestellt. Für den südlichen Ostseeraum ergab sich eine Kältesumme der Lufttemperatur an der Station Warnemünde von 31,7 Kd. Im Vergleich belegt der Winter 2016/17 den 15. Platz der wärmsten Winter seit Beginn der Aufzeichnungen im Jahr 1948 und wird als mild klassifiziert. Mit einer Wärmesumme von 159,5 Kd rangiert der Sommer im Mittelfeld der 70jährigen Datenreihe und reiht sich auf Platz 28 der wärmsten Sommer ein. Das Langzeitmittel liegt bei 153,4 Kd. Auf der Grundlage von satellitengestützten Meeresoberflächentemperaturen (SST) war 2017 das elft- wärmste Jahr seit 1990 und mit 0,24 K etwas über dem langfristigen SST-Mittel. März, April und Oktober - Dezember trugen durch ihre positiven Anomalien zum Durchschnitt bei. Juli und August waren durch negative Anomalien gekennzeichnet. Die Anomalien erreichten Höchstwerte von +2 K und -3 K. Die Situation in den Tiefenbecken der Ostsee war im Wesentlichen geprägt durch bodennah einsetzende Stagnation im östlichen Gotland Becken und Belüftung der mittleren Wassersäule oberhalb 150 m im Zuge kleinerer Einströme. Zu Jahresbeginn wurde das im nördlichen Zentralbecken gelegene Farö Tief erstmals innerhalb der aktuellen Einstromphase belüftet. Im Jahresverlauf 2017 wurden zwei weitere schwache Einströme mit Volumina zwischen 210 km³ und 188 km³ im Februar sowie Oktober registriert. Zusammenfassend kann gesagt werden, dass die Auswirkungen der seit 2014 beobachten Phase von verstärkten Wasseraustauschprozessen mit entsprechenden Konsequenzen für die biogeochemischen Kreisläufe abklingen., The article summarizes the hydrographic-hydrochemical conditions in the western and central Baltic Sea in 2017. Based on meteorological conditions, the horizontal and vertical distribution of temperature, salinity, oxygen/hydrogen sulphide and nutrients are described on a seasonal scale. For the southern Baltic Sea area, the “cold sum” of the air temperature of 31.7 Kd in Warnemünde amounted to a mild winter in 2014/15 and ranks as 15th warmest winter since the beginning of the record in 1948. The summer “heat sum” of 159.5 Kd ranks on 28th position of the warmest summers over the past 70 years and is slightly above the long-term average of 153.4 Kd. Based on satellite derived Sea Surface Temperature (SST) 2017 was the eleventh-warmest year since 1990 and with 0.24 K slightly above the long-term SST average. March, April and October - December contributed to the average by their positive anomalies. July and August were characterized by negative anomalies. The anomalies reached maximum values of +2 K and -3 K. The situation in the deep basins of the Baltic Sea was mainly coined by beginning stagnation at bottom-near water depths of the eastern Gotland Basin and ongoing ventilation of the upper part 5 of the deep-water above 150 m as a consequence of weak inflows. For the first time within this phase of intensified inflow activity, starting in 2014, the ventilation of the Farö Deep at the Northern Central Basin was registered at the beginning of the year. In the course of 2017 two weak inflows showing total volumes of 210 km³ (February) and 188 km³ (October) were registered. In conclusion, the impact of the observed phase of intensified water exchange processes with subsequent consequences for the biogeochemical cycles is weakening.

Meereswissenschaftliche Berichte No 104 2017 - Marine Science Reports No 104 2017, The article summarizes the hydrographic-hydrochemical conditions in the western and central Baltic Sea in 2015. Based on meteorological conditions, the horizontal and vertical distribution of temperature, salinity, oxygen/hydrogen sulphide and nutrients are described on a seasonal scale. For the southern Baltic Sea area, the “cold sum” of the air temperature of 63.5 Kd in Warnemünde amounted to a mild winter in 2014/15 and ranks as 27th warmest winter since the beginning of the record in 1948. The summer “heat sum” of 267 Kd is ranked in the “top ten” over the past 69 years and ranks on place 6 of the warmest summers. The situation in the deep basins of the Baltic Sea was mainly coined by ongoing inflow activity of moderate Major Baltic Inflows (November 2015, January-February 2016) following the Major Baltic Inflow of December 2014, which was the third largest ever observed. Since mid of January, the deep layer in the eastern Gotland Basin was ventilated again. The November 2015 MBI reached the bottom, whereas the following event only water depths between 100-200 m had ventilated. In 2016, furthermore three smaller inflow events with estimated volumes between 171 km³ and 184 km³ occurred in the timespan October to December. In conclusion, the observed phase of intensified water exchange processes with subsequent consequences for the biogeochemical cycles is going on since 2014., Die Arbeit beschreibt die hydrographisch-hydrochemischen Bedingungen in der westlichen und zentralen Ostsee für das Jahr 2016. Basierend auf den meteorologischen Verhältnissen werden die horizontalen und vertikalen Verteilungsmuster von Temperatur, Salzgehalt, Sauerstoff/Schwefelwasserstoff und Nährstoffen mit saisonaler Auflösung dargestellt. Für den südlichen Ostseeraum ergab sich eine Kältesumme der Lufttemperatur an der Station Warnemünde von 63,5 Kd. Im Vergleich belegt der Winter 2015/16 den 27. Platz der wärmsten Winter seit Beginn der Aufzeichnungen im Jahr 1948 und wird als mild klassifiziert. Mit einer Wärmesumme von 267 Kd rangiert der Sommer in den „Top Ten“ der 69jährigen Datenreihe und reiht sich auf Platz 6 der wärmsten Sommer ein. Die Situation in den Tiefenbecken der Ostsee war im Wesentlichen geprägt durch weitere Salzwassereinbrüche von mittlere Intensität (November 2015, Januar-Februar 2016), die dem großen Salzwassereinbruch vom Dezember 2014 folgten. Seit Mitte Januar wurde das östliche Gotland Becken erneut belüftet. Während der MBI November 2015 erneut den Boden erreichte, wurden vom nachfolgenden Ereignis nur Wassertiefen zwischen 100-200 m belüftet. Im Jahr 2016 wurden drei weitere kleinere Einströme mit Volumina zwischen 171 km³ und 184 km³ im Zeitraum Oktober bis Dezember registriert. Zusammenfassend kann gesagt werden, dass die seit 2014 beobachte Phase von verstärkten Wasseraustauschprozessen mit entsprechendenKonsequenzen für die biogeochemischen Kreisläufe weiterhin andauert.

METEOR-Berichte

The expedition MSM050 K��NO INTERFACE (Coastal benthic environments in North and Baltic Sea: Evaluation of processes and transports at the sediment-water interface) was a joint activity of the BMBF-funded projects NOAH and SECOS to increase the understanding of biogeochemical, biological and physical processes along the sediment-water interface in the North and Baltic Sea. The core program of the cruise was dedicated to the completion of seasonal data in these regions, with the main focus on the determination of biogeochemical functions, their control mechanism for the relevant benthic habitat types and turbulence measurements of near bottom water layers as well as accumulation of organic pollutants, heavy metals in the sediments. At five NOAH stations in the North Sea, sediment samples were taken by MUC and van Veen grab, along with CTD measurements and the use of the IOW benthic chamber lander and dredge. During the passage of Skagerrak and Kattegat, in addition to the classical oceanographic examination, benthic fauna samples were taken at 19 stations for comparison with historical data. During the passage, a ship-bound current meter recorded physical effects on the turbulence of finest sediment particles by mini-turbulences. In the Baltic Sea, five SECOS stations were investigated for geological, biological and biogeochemical analysis of sediments by using moorings. During the waiting time, microstructure measurements (MSS) of the surrounding water body were performed., MARIA S. MERIAN-Berichte

Meereswissenschaftliche Berichte No 101 2016 - Marine Science Reports No 101 2016, The article summarizes the hydrographic-hydrochemical conditions in the western and central Baltic Sea in 2015. Based on meteorological conditions, the horizontal and vertical distribution of temperature, salinity, oxygen/hydrogen sulphide and nutrients are described on a seasonal scale. For the southern Baltic Sea area, the “cold sum” of the air temperature of 19.8 Kd in Warnemünde amounted to a very warm winter in 2014/15 and ranks as 7th warmest winter since the beginning of the record in 1948. The summer “heat sum” of 182.3 Kd is in the upper midrange over the past 68 years and ranks on place 21 of the warmest summers. The situation in the deep basins of the Baltic Sea was mainly coined by the Major Baltic Inflow of December 2014 which was the third largest ever observed. In May 2015, the layer between 140 m and the bottom in the eastern Gotland Basin was completely ventilated. In 2015, inflow events with estimated volumes between 141 and 270 km³ occurred on five occasions. In conclusion, intensified water exchange processes were recorded in the last two years and some inflow pulses were able to reach the bottom water of the central Baltic Sea fostering the large Major Baltic Inflow of December 2014 with subsequent consequences for the biogeochemical cycles., Die Arbeit beschreibt die hydrographisch-hydrochemischen Bedingungen in der westlichen und zentralen Ostsee für das Jahr 2015. Basierend auf den meteorologischen Verhältnissen werden die horizontalen und vertikalen Verteilungsmuster von Temperatur, Salzgehalt, Sauerstoff/Schwefelwasserstoff und Nährstoffen mit saisonaler Auflösung dargestellt. Für den südlichen Ostseeraum ergab sich eine Kältesumme der Lufttemperatur an der Station Warnemünde von 19,8 Kd. Damit war der Winter 2014/15 sehr warm und belegt den 7. Platz der wärmsten Winter seit Beginn der Aufzeichnungen im Jahr 1948. Mit einer Wärmesumme von 182,3 Kd rangiert der Sommer im oberen Bereich der 68jährigen Datenreihe und reiht sich auf Platz 21 der wärmsten Sommer ein. Die Situation in den Tiefenbecken der Ostsee war im Wesentlichen geprägt durch den großen Salzwassereinbruch vom Dezember 2014, der der drittgrößte jemals beobachtete war. Im Mai 2015 war die gesamte Wasserschicht im östlichen Gotlandbecken zwischen 140 m und dem Boden belüftet. Im Jahr 2015 wurden fünf weitere Einströme mit Volumina zwischen 141 und 270 km³ registriert. Zusammenfassend kann gesagt werden, dass in den letzten beiden Jahren verstärkt Wasseraustauschprozesse beobachtet wurden. Einige dieser Einströme erreichten die zentrale Ostsee und unterstützten die Effekte des großen Salzwassereinbruchs vom Dezember 2104 mit entsprechenden Konsequenzen für die biogeochemischen Kreisläufe.

This report is based on preliminary data. Ventspils (Latvia). 01-02 March 2015 and 07-09 March 2015 Purpose of the cruise The original scientific goal of this cruise, conducted in the framework of the WGL/Pakt project ILWAO-II, was the investigation of the role of internal waves for basin-scale vertical mixing in the deep basins of the Baltic Sea. In agreement with IOW’s board, however, it was decided to devote a substantial part of the cruise time to the observation of one of the rare major saline inflow events that reached the central Baltic Sea exactly at the time of this cruise. In addition to the physical measurements, microbiological and chemical investigations were conducted, focusing on the role of methane-oxidizing bacteria in pelagic redoxclines.

Meereswissenschaftliche Berichte No 96 2015 - Marine Science Reports No 96 2015, The winter of 2013/14 in the southern Baltic Sea area was a mild one, with a cold sum at Warnemünde of 65.8 Kd, a value that falls well short of the long-term average of 104.5 Kd. The winter of 2013/14 is thus the twenty-seventh warmest winter since the comparative record began in 1948. This cold sum was due exclusively to the month of February; all other months had a cold sum of 0 Kd. The coldest winter in the observation series was that of 1962/63 with a cold sum of 395.2 Kd. With a warm sum of 236.9 Kd, recorded at Warnemünde, 2014 comes in tenth place in the time series that began in 1948, forcing 2013’s value of 230.4 Kd into eleventh place. The 2014 value far exceeds the long-term average of 150 K d, and exceeds the standard deviation. 2014 can therefore again be classed as a particularly warm year, even if average monthly temperatures in June and August were slightly below the long-term average, and April and October were balanced. In comparison, May, July and September present warm sums that are twice as high; they are exceptionally warm months that come eighth, fourth, and sixth respectively in the time series since 1948. In terms of Sea Surface Temperature, 2014 was the warmest year since 1990, and was about 1.2 K above average for 1990-2014; it was 0.4 K higher than 2008, formerly the warmest year. Except for February and June, all other months, and especially July and August in the north of the Baltic Sea, contributed to that value. The western Baltic Sea exceeded long-term mean values by +1 to +3 K in every month except February. After a mild start to the year, a cold spell starting around 20 January produced strong cooling until the beginning of February. Nevertheless, the monthly average for January exceeded the long-term averages for 1990-2014 by +2 K; January was the second-warmest month in the western Baltic since 2007. February lay in the range of long-term averages, and in the Arkona Sea and Gulf of Bothnia was the coldest month of the year. As usual, March developed into the coldest month of the year in the Gotland Sea. From March to May throughout the Baltic Sea, and even from March to December in its western section, anomalies of +1 to +3 K were recorded. Inflow events with estimated volumes between 100 and 400 km³ occurred in the Baltic Sea on four occasions in 2014. In February, an inflow volume of 141 km³ was calculated based on changes in sea level at Landsort Norra. After a brief outflow phase, another inflow occurred in March with an estimated volume of 203 km³. In combination with the earlier effects of hurricane ‘Xaver’ in December 2013 (inflow volume of 147 km³) and the long phase of westerly winds from the end of October to the beginning of November 2013, both these events produced a complex interaction that resulted in water spilling over Stolpe Channel in late April / early May. These water masses reached the Gotland Deep in late May and oxygenated its deep water for the first time since 2003. Although none of these three events fulfilled the typical characteristics of a Major Baltic Inflow, combined they imported comparably large amounts of water, salt, and oxygen into the deep water of the Baltic Sea (a novel form of deep-water ventilation that was described for the first time). In August, another inflow phase with a volume of some 164 km³ was detected. In terms of ventilation of the deep basins, its effects were more restricted to the Arkona Basin and the Bornholm Basin. A very large inflow began on 13 December; it had a volume of 358 km³, of which 198 km³ was saline water bearing around 4 Gt salt. According to latest estimates, this event represents the third-largest salt-water inflow into the Baltic Sea since the beginning of the record in 1880. The annual cycle of oxygen saturation in the surface water was again typical in 2014. As a result of the dominance of oxygen-consuming processes and low productivity, the surface water in February in all sea areas was slightly undersaturated at 95 % to 96 %. In March, too, undersaturation continued to be observed in all sea areas except the Arkona Basin where saturation levels were 104.3 %. The peak of the 2014 spring bloom occurred in all sea areas in May: in the Bornholm Basin and in the eastern Gotland Basin, saturation values between 120 % and 125 % were determined. Summer presented a familiar picture with saturation values around 105 %. Only in the eastern Gotland Basin did saturation values around 115 % indicate an intensive cyanobacteria bloom. In the autumn, intensified degradation processes again led to undersaturation. Overall it can be concluded that the annual range of variation for saturation was relatively small, as in previous years. This indicates a healthy oxygen balance in the surface water. Oxygen conditions in the deep water of the basins of the central Baltic Sea are primarily influenced by the occurrence or absence of strong barotropic and/or baroclinic inflows. The Bornholm Basin is the westernmost of the deep basins, and inflows are often able to ventilate its deep water. As described above, the inflow events of autumn 2013, and February and March 2014 led in the spring to a lasting improvement in oxygen conditions in the deep water of the Bornholm Basin, where at the end of April 5.65 ml/l oxygen was measured. Once these water masses had spilled over Stolpe Sill, they advanced into the Gotland Basin whose deep water they repeatedly - if briefly - ventilated for the first time since 2003. At the same time, this meant that towards the end of the year relatively low concentrations of hydrogen sulphide were measured in the eastern Gotland Basin. Usually at the end of a long period of stagnation, values between− 5 ml/l and −7 ml/l are found, as was the case at the beginning of the year. By the end of 2014, therefore, favourable conditions had developed for the Major Baltic Inflow in December. Oxygen conditions in the deep water were also reflected in nutrient concentrations. The good oxygen supply in the deep water of the Bornholm Basin resulted in phosphate concentrations