Report from the SMHI monitoring cruise with R/V Aranda

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Örjan Bäck Sveriges Meteorologiska och Hydrologiska Institut Oceanografiska Laboratoriet 17--1 Dnr: S/Gbg-17-9 Report from the SMHI monitoring cruise with R/V Aranda Survey period: 17--1-17--3

1 Örjan Bäck Sveriges Meteorologiska och Hydrologiska Institut Oceanografiska Laboratoriet Dnr: S/Gbg-17-9 Report from the SMHI monitoring cruise with R/V Aranda Survey period: Principal: The Swedish Meteorological and Hydrological Institute and the Swedish Agency for Marine and Water Management. SUMMARY The May cruise, which is part of the Swedish national marine monitoring programme, covered the Skagerrak, the Kattegat, the Sound and the Baltic Proper. Oxygen concentrations close to zero were found in many parts of the Baltic Proper. Anoxic conditions, when hydrogen sulfide forms, were measured in the Western Gotland Basin from about metres depth and in the Eastern Gotland Basin but only at BY1 Gotland Deep close to the bottom. Areas with acute hypoxia (dissolved < ) were found from the Bornholm Basin to the Eastern Gotland Basin starting at around 7- metres and below, in the Western Gotland Basin already at metres. Silicate concentrations were higher or much higher than the season mean in all areas. Dissolved inorganic nitrogen was more or less consumed in the upper water layers in the entire survey area, which is normal for the season. Concentrations of phosphate were also at normal levels; very low concentrations in the Kattegat and Skagerrak at around.1 µ or below, a bit higher in the Baltic Proper,.1-. µ, where the highest values were found in the Western Gotland Basin. Surface water temperatures were normal in the entire survey area and varied between 1 to 11 C on the west coast and between and 9 C in the Baltic Proper. Surface salinity levels were slightly above normal in the Skagerrak and the Western Gotland Basin, normal levels were measured the remaining areas. A strong surface current was observed on the west coast at Å1 and at the stations to the east, also at the station Släggö, inside the archipelago, there was a strong surface current. Next regular cruise is scheduled to start the 1 th of June. Adress: Sven Källfelts Gata 1 71 Västra Frölunda Telefon: 11-9 E-post: orjan.back@smhi.se WWW:

2 RESULTS The expedition was conducted aboard the Finnish research vessel Aranda. It started in Helsinki on the 1 th of May and ended in Helsinki on the 3 rd, with a short stop in Lysekil on the th. At the beginning of the expedition the winds were moderate from the south, when reaching the west coast the wind speed decreased and turned north. The expedition ended with westerly winds up to 1m/s in the southern Baltic Proper with decreasing wind speeds as we moved towards Helsinki. The weather was sunny during major parts of the expedition with portions of fog and mist. Extra personnel from SMHI were on board to perform maintenance on the Huvudskär ocean buoy. The upper part of the buoy was lifted to inspect and address any possible damage, wear or fouling. This report is based on data that have passed a first quality control. When data are published at the nation oceanographic data centre some values might have changed after further quality controls have been performed. Data from this cruise will be published as soon as possible on the data center s webpage, normally within a week after the cruise. Download data here: The Skagerrak The surface temperature in the Skagerrak was normal for the season and varied between 1 and 11 C. The salinity in the surface was slightly above normal and varied from 1 psu in the southern and eastern parts to 3 psu in the outer parts. Thermocline and halocline coincided at around -1 metres depth. A strong surface current was observed at Å1 and at the stations to the east, also at the station Släggö, inside the archipelago, there was a strong surface current. Nutrients dissolved organic nitrogen, DIN (the sum of nitraite, nitrite and ammonia), and dissolved organic phosphorus, DIP (only available as phosphate) were generally depleted in the upper layers with low concentrations which is normal during this time of the year. However higher concentrations of both phosphate, up to. µ, and inorganic nitrogen, up to µ, were found at Å1 at the surface down to metres. Silicate levels in the upper layers were higher than normal for the season at all stations except Släggö, with concentrations up to 3. µ. The chlorophyll fluorescence was highest in the surface and indicated that phytoplankton still was blooming in the Skagerrak. Some peaks deeper down around 1-1 metres, below the pycnocline, at Å1 and Å1 could be older blooms currently sinking towards the bottom. The water column was well oxygenated at all sampled stations in the Skagerrak. The Kattegat and the Sound The surface temperatures were normal in the entire area; 11 C down to the thermocline at 7- metres, at N1 Falkenberg down to 1 metres, below that the temperature sank quickly down to -7 C. At the second stop at Anholt E the surface temperature had risen to 1 C. The salinity was normal for the season and varied in the surface waters in Kattegatt between 1 and 1 psu, in the Sound somewhat lower, around 9 psu. The halocline and thermocline coincided at all stations, where also fluorescence maxima were observed which indicate phytoplankton blooms in the pycnocline where there are some nutrients available. Alternatively these fluorescence maxima

3 comes from older blooms that have sunk down to the pycnocline, further analysis of the phytoplankton samples will give more information. Concentrations of DIN and DIP in the Kattegatt showed normal levels for the season while silicate concentrations were just above normal, mainly at W Landskrona and in the surface at Fladen. DIN and DIP were generally consumed above the pycnocline, except in the Sound where.3 µ of phosphate was found. Below the pycnocline concentrations of DIN and DIP increased, highest values were found in the Sound. The bottom water in the area was well oxygenated with concentrations of. in the Kattegat and. in the Sound. The Baltic Proper The temperature in the surface water was normal for the season and varied between and 9 C, lowest in the Western Gotland Basin. The salinity was somewhat higher than normal in the Eastern Gotland Basin both above and below the halocline, while it was normal in the rest of the sampled area. A weak thermocline had started to form at around 1- metres. The halocline was found at -7 metres depth, except in the Arkona Basin where it was a bit shallower. Nutrients in the form of dissolved inorganic nitrogen were fully consumed in the water column down to the halocline, in the Eastern Gotland Basin even down to metres. Below the halocline higher nutrient concentrations were found, somewhat varying but within range for what s considered normal for the season. The phosphate concentrations in the upper water mass were normal for the season with values around.3 µ in the south western Baltic Proper and.1 µ in the eastern Gotland Basin. In the Western Gotland Basin slightly above normal with values around. µ. Higher concentrations were found in the lower water mass at around normal levels for the season, except in the Eastern Gotland Basin where concentrations were lower than normal, probably due to the oxygenation that has happened after large inflows of dense oxygen rich water. Silicate concentrations above the halocline in the entire Baltic Proper have been higher than normal during a longer period, also during the May cruise. Values varied between 13-1 µ in the Baltic Proper except at the coastal station Ref M1V1, where values at and metres where on normal levels at around 9 µ. Oxygen concentrations close to zero were found in many parts of the Baltic Proper. Anoxic conditions, when hydrogen sulfide forms, were measured in the Western Gotland Basin from about metres depth and in the Eastern Gotland Basin but only at BY1 Gotland Deep close to the bottom. Areas with acute hypoxia (dissolved < ) were found from the Bornholm Basin to the Eastern Gotland Basin starting at around 7- metres and below, in the Western Gotland Basin already at metres. In the Arkona Basin the whole water column was well oxygenated. At both BY1 and at the station to the south, -CTRY-BP, oxygen concentrations increased up to -3 at 9 metres and below; evidence that dense oxygen rich water from an earlier inflow has traveled to the southern parts of the Eastern Gotland Basin and can possibly continue further north. A hint of a signal from this could be seen at around 1 metres in the oxygen profiles from the stations to the north. Fluorescence measurements from the CTD showed some phytoplankton activity in the surface in the Bornholm Basin and in the Eastern Gotland Basin, with a peak around the surface at BY1.

4 Figur 1. Transect showing oxygen and salinity through the Baltic Proper, from the Sound to the Eastern Gotland Basin.

DELTAGARE Namn Från Örjan Bäck Chief Scientist SMHI Carl Johan Andersson SMHI Johan Håkansson SMHI Sari Sipilä SMHI Karin Wesslander SMHI Erik Udehn Helsinki Lysekil SMHI BILAGOR - Track chart -

5 DELTAGARE Namn Från Örjan Bäck Chief Scientist SMHI Carl Johan Andersson SMHI Johan Håkansson SMHI Sari Sipilä SMHI Karin Wesslander SMHI Erik Udehn Helsinki Lysekil SMHI BILAGOR - Track chart - Table over stations, sampled parameters and number of sampling depths - Map showing bottom oxygen concentrations - Vertical profiles for regular monitoring stations - Monthly average surface water plots for regular monitoring stations

6 SMHis hydrografiska stationer Basstation X HELCOM-station Karteringsstation O Karteringsområde SYKEs hydrografiska stationer Basstation ~Y9 ~~ :._BY31 t> 9 BY3 BY :.:.SY1 e BY1 e BCS

7 Date: 17-- Time: 1: Ship: AR Year: Ser Cru Stat Proj Stat Lat Lon Start Start Bottom Secchi Wind Air Air WCWI CZPP No No T T S S P D D H P P N N N A N A S H C C no no code name date time depth depth dir vel temp pres elac hohp de btl e e a a h o o h t t t t m t l i u o o yyyymmdd hhmm m m C hpa aove loy m m l l x x s o o r r r o o k o m m m tueo apt p p t t y y s t i a z n t y 3 u n n hdsb o - s t t p b c b c b c s t t t t t t i v s l d l d l d i a s m i p t 39 7 BPNX EXT HUVUDSKÄR x x x - x - x x x BPWX3 BAS BY3 NORRKÖPINGSDJ x x x - x - x x x x x x x x x x - x - - x 7 BPWX BAS BY3 KARLSÖDJ x-x- 1 1 x x x x - x x x x x x x x x x - x x - x 1 7 BPWK1 BAS REF M1V xxxx x x x x x x x - x x x x x x x x x BPSH BAS HANÖBUKTEN x x x x x - x x - x x x x x x x - x - - x 3 7 BPSA3 BAS BY ARKONA xxx- x x x x - x x - x x x x x x x - x x BPSA BAS BY x--- x x x x - x x - x x x x x x x - x SOCX39 BAS W LANDSKRONA x x x x x - x x - x x x x x x x - x - - x 7 KAEX9 BAS ANHOLT E xxxx 1 1 x x x x x x x - x x x x x x x x x x x x 7 7 KANX BAS N1 FALKENBERG xxxx 7 7 x x x x x x x - x x x x x x x x x KANX BAS FLADEN x x x x x - x x - x x x x x x x - x SKEX3 BAS P x x x x x - x x - x x x x x x x - x - - x 1 7 SKEX1 BAS Å xxx- 1 1 x x - x x x x - x x x x x x x x x - - x 11 7 SKEX17 BAS Å x - x - - x SKEX1 BAS Å x x x x x - x x - x x x x x x x - x - x x 13 7 SKEX1 BAS Å x - x - - x x SKEX1 BAS Å x x x x x - x x - x x x x x x x - x - x FIBG7 BAS SLÄGGÖ xxx- 9 9 x x x x - x x - x x x x x x x - x - x KAEX9 BAS ANHOLT E xxxx 1 1 x x x x x x x - x x x x x x x x x x BPSB BAS BY CHRISTIANSÖ x x x x x - x x - x x x x x x x - x BPSB7 BAS BY BORNHOLMSDJ xxxx 1 1 x x x x x x x - x x x x x x x x x x BPSE1 BAS -CTRY-BP x-x- 1 1 x x x x - x x - x x x x x x x - x x - x 7 BPEX13 BAS BY x x x x x - x x - x x x x x x x - x BPEX1 BAS BY1 GOTLANDSDJ xxxx x x - x x x x x x x x x x x x x x x - x 7 BPEX1 EXT BY1 GOTLANDSDJ x x - x - x x x x x x x x x x - x - - x 3 7 BPEX BAS BY FÅRÖDJ x x x - x - x x x x x x x x x x - x - - x

8 Bottom water oxygen concentration () Ship: Aranda Date: Series: N N 7 N N N N H S.3 H H S S E 11 E 13 E 1 E 17 E 19 E 1 E 3 E E 7 E

9 STATION BY3 NORRKÖPINGSDJ SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO DIN saturation % OXYGEN IN BOTTOM WATER (depth >= 17 m) Month Year

10 Vertical profiles BY3 NORRKÖPINGSDJ May Mean 1-1 St.Dev Oxygen PO DIN

11 STATION BY3 KARLSÖDJ SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO DIN saturation % OXYGEN IN BOTTOM WATER (depth >= 1 m) Month Year

12 Vertical profiles BY3 KARLSÖDJ May Mean 1-1 St.Dev Oxygen PO DIN

13 STATION REF M1V1 SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO 3 DIN saturation % OXYGEN IN BOTTOM WATER (depth >= 17 m) Month Year

14 Vertical profiles REF M1V1 May Mean 1-1 St.Dev Oxygen PO DIN

15 STATION HANÖBUKTEN SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO DIN saturation % OXYGEN IN BOTTOM WATER (depth >= 7 m) Month Year

16 Vertical profiles HANÖBUKTEN May Mean 1-1 St.Dev Oxygen PO DIN

17 STATION BY ARKONA SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO DIN saturation % OXYGEN IN BOTTOM WATER (depth >= m) Month Year

18 Vertical profiles BY ARKONA May Mean 1-1 St.Dev Oxygen PO DIN

19 STATION BY1 SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO DIN saturation % OXYGEN IN BOTTOM WATER (depth >= m) Month Year

20 Vertical profiles BY1 May Mean 1-1 St.Dev Oxygen PO DIN

21 STATION W LANDSKRONA SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO DIN saturation % OXYGEN IN BOTTOM WATER (depth >= m) Month Year

22 Vertical profiles W LANDSKRONA May Mean 1-1 St.Dev Oxygen PO DIN

23 STATION ANHOLT E SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO DIN saturation % OXYGEN IN BOTTOM WATER (depth >= m) Month Year

24 Vertical profiles ANHOLT E May Mean 1-1 St.Dev Oxygen PO DIN

25 STATION N1 FALKENBERG SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO 3 DIN saturation % OXYGEN IN BOTTOM WATER (depth >= m) Month Year

26 Vertical profiles N1 FALKENBERG May Mean 1-1 St.Dev Oxygen PO DIN

27 STATION FLADEN SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO 3 DIN saturation % OXYGEN IN BOTTOM WATER (depth >= 7 m) Month Year

28 Vertical profiles FLADEN May Mean 1-1 St.Dev Oxygen PO DIN

29 STATION P SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO 3 DIN saturation % OXYGEN IN BOTTOM WATER (depth >= 7 m) Month Year

30 Vertical profiles P May Mean 1-1 St.Dev Oxygen PO DIN

31 STATION Å17 SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO DIN saturation % OXYGEN IN BOTTOM WATER (depth >= 3 m) Month Year

32 Vertical profiles Å17 May Mean 1-1 St.Dev Oxygen PO DIN

33 STATION Å1 SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO DIN saturation % OXYGEN IN BOTTOM WATER (depth >= 1 m) Month Year

34 Vertical profiles Å1 May Mean 1-1 St.Dev Oxygen PO DIN

35 STATION Å13 SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO DIN saturation % OXYGEN IN BOTTOM WATER (depth >= m) Month Year

36 Vertical profiles Å13 May Mean 1-1 St.Dev Oxygen PO DIN

37 STATION SLÄGGÖ SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO 3 DIN saturation % OXYGEN IN BOTTOM WATER (depth >= m) Month Year

38 Vertical profiles SLÄGGÖ May Mean 1-1 St.Dev Oxygen PO DIN

39 STATION ANHOLT E SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO DIN saturation % OXYGEN IN BOTTOM WATER (depth >= m) Month Year

40 Vertical profiles ANHOLT E May Mean 1-1 St.Dev Oxygen PO DIN

41 STATION BY CHRISTIANSÖ SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO DIN saturation % OXYGEN IN BOTTOM WATER (depth >= m) Month Year

42 Vertical profiles BY CHRISTIANSÖ May Mean 1-1 St.Dev Oxygen PO DIN 1 1

43 STATION BY BORNHOLMSDJ SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO DIN saturation % OXYGEN IN BOTTOM WATER (depth >= m) Month Year

44 Vertical profiles BY BORNHOLMSDJ May Mean 1-1 St.Dev Oxygen PO DIN

45 STATION BY1 SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO DIN saturation % OXYGEN IN BOTTOM WATER (depth >= 1 m) Month Year

46 Vertical profiles BY1 May Mean 1-1 St.Dev Oxygen PO DIN

47 STATION BY1 GOTLANDSDJ SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO DIN saturation % OXYGEN IN BOTTOM WATER (depth >= m) Month Year

48 Vertical profiles BY1 GOTLANDSDJ May Mean 1-1 St.Dev Oxygen PO DIN

49 STATION BY FÅRÖDJ SURFACE WATER (-1 m) 1 1 Annual Cycles Mean 1-1 St.Dev PO DIN saturation % OXYGEN IN BOTTOM WATER (depth >= 17 m) Month Year

50 Vertical profiles BY FÅRÖDJ May Mean 1-1 St.Dev Oxygen PO DIN

Report from the SMHI monitoring cruise with R/V Aranda

Martin Hansson Swedish Meteorological and Hydrological Institute Oceanographic Laboratory 17-3-17 Dnr: S/Gbg-17- Report from the SMHI monitoring cruise with R/V Aranda Survey period: 17-3-9 to 17-3-1 Principal: