...HYPOX kickoff: Site introduction. Introduction to the Baltic Sea and the Gotland Deep Gregor Rehder (IOW)

Transcription

1 ...HYPOX kickoff: Site introduction Introduction to the Baltic Sea and the Gotland Deep Gregor Rehder (IOW)

2 Introduction to the Baltic Sea and the Gotland Deep Stratification Eutrophication Warming Processes

3 Baltic Sea Area: km 2 Volume: km 3 Av. Depth 52 m Maxi. Depth: 460 m (Landsort Deep Riverine flux: 440 km 3 /year Precipitation excess: 40 km 3 /year Fig. from C. Bernes, Monitor 19, 2005 Fresh water balance: 480 km 3 /year Salt water inflow : ~ 500 km 3 /year Highly variable Low Salinity : 7-8 g/kg at the surface Brackish water system Drainage area km 2

4 Salinity and stratification Fig. from C. Bernes, Monitor 19, 2005

5 The Great Belt The Sound ~8m Darss Sill ~18m Gedser Rostock Map compiled by J. Schneider, IOW

6 Saltwater inflow

7 Saltwater inflow controlled by sills Map compiled by J. Schneider, IOW

8 General Hydrography From : Feistel, Nausch, Wasmund, Chapter 10

9 Permanent halocline Figs. from C, Bernes Monitor 19, 2005

10 Bottom hypoxia Fig. from C. Bernes, Monitor 19, 2005

11 Major Inflow Events Major Baltic inflows (MBIs) between 1880 and 2007 and their seasonal distribution (upper right) shown in terms of their relative and five year running means of river runoff to the Baltic Sea (inside the entrance sills) averaged from September to March (shaded). From: Feistel, Nausch, Wasmund; Chapter 10 by Matthäus et al.

12 Hypoxia in the GD over the last 50years Fig. from C, Bernes, Monitor 19, 2005 from Stig Fonselius with add. ICES data

13 Redox governance of the phosphate reflux Fig. from C, Bernes, Monitor 19, 2005

14 Connection of the intermediate and upper nutrient pools?? (Benthic Pelagic coupling) Tendency of reduced P-load in the Baltic Proper in winter surface waters in the years following major inflows (but not after the event) Consequence of changed hydrography rather then reduced bottom phosphate release From : Feistel, Nausch, Wasmund, Chapter 12 by Nausch et al.

15 Effects on the balance of PO 4 and N Bacterial bloom in summer N- fixation Figs. from C. Bernes, Monitor 19, 2005

16 In summa Tendency for hypoxic conditions due to restricted inflow of saltwater and excess freshwater supply into the surface waters, leading to a stable permananent halocline in part of the system high natural nutrient load, enhanced by eutrophication nutrient input has considerable N-excess, but N-loss (denitrification, anammox) is larger than P-loss; imbalance fostered by hypoxic conditions PP is not N-limited due to N-fixing by cyanobacteria (a nuisance, a hazard, and a problem for counter-measurements) SO IS IT NEW AND IS IT ANTHROPOGENIC???

17 O 2 supply to the deep Gotland-Basin Climate changes in the Northern Hemisphere After von Storch et al., 2004) Laminated black sediments (anoxic) modern warm period cold phase incl. Little Ice Age Light grey homogeneous Muddy silt (oxic) Laminated black sediments (anoxic) medieval warm period From Leipe et al., 2008, Oceanologia 50,

18 Not new, but enhanced. Proxies indicate - higher PP in anox. conditions - Cyanobacteria in the MWP - low salinity in the MWP From Leipe et al., 2008, Oceanologia 50, higher PP in recent than past warm period

19 In summa Tendency for hypoxic conditions due to restricted inflow of saltwater and excess freshwater supply into the surface waters, leading to a stable permananent halocline in part of the system high natural nutrient load, enhanced by eutrophication nutrient input has considerable N-excess, but N-loss (denitrification, anammox) is larger than P-loss; imbalance fostered by hypoxic conditions PP is not N-limited due to N-fixing by cyanobacteria (a nuisance, a hazard, and a problem for counter-measurements) HOW WILL THE SYSTEM CHANGE???

20 (Meter) 0...HYPOX kickoff: Introduction to the Baltic and the Gotland Deep A model estimate Climate scenario simulation Feasibility study - A1B scenario (CLM) Bott enwiek Helsinki Sankt-Peterburg Bottensee Tallinn Time series for salinity and oxygen Oslo Kat tegat Göt eborg Sto ckholm Öland Gotland Gotl andsee Rïga. Klaipeda København Bornholm Bornholmsee Gdansk Rügen Wassertiefe Kiel Lübeck Rostock F. Tauber, T. Seifert, B. Kayser, Institut für Ostseeforschung Warnemünde >80 Intermediate water temperature at 70m depth T. Neumann, IOW, unpublished

21 All that gathered knowledge how can we matter? TF0140 TF0142 TF0144 Latitude [ ] TF0361 TF0360 TF0102 TF0145 TF0104 TF0103 TF0069 TF0109 TF0113 TF0114 TF0111 TF0115 ABBoje TF0112 TF0030 TF0121 TF0002 TF0001 TF0152 TF0010 TF0150 TF0040 TF0046 TF0011 TF0012 TF TF0284 TF Longitude [ ] 58.0 TF0240 TF0286 Latitude [ ] TF0242 TF0245 TF0270 TF0271 TF0272 TF TF TF0250 TF TF0200 TF0212 TF0213 TF0222 TF0256 TF0221 TF0255 TF Longitude [ ]

22 The questions to tackle Reflux and change in benthic community functioning across the redox-gradient (in particular N and P) as a function of the frequency and amplitude of redox state change need of characterization of (at least) the particulate phosphate which can be mobilized under hypoxic conditions 10 m High resolution understanding of mixing across the redoxcline and the halocline Moorings 150 m Profiling station Process dependence on the stability of the redox gradient Profiling station

23 Improvement of redox-sensitive PO 4 -flux Simulated and observed dissolved inorganic phosphorus (DIP) in the central Eastern Gotland Sea. The solid line is a simulation with iron phosphate and bioturbation, the dashed line is from a simulation with a model without these extensions and the dotted line refers to observations. a) surface; b) near bottom (235 m). From Neumann & Schernewski, 2008

24 The 2003 major saltwater inflow Daily temperature recorded at three horizons within the near-bottom layer of the Gotland); water depth: 224 m. The recording gap during 1998 was fractionally filled with CTD data from the BMP station. From: Feistel, Nausch, Wasmund; Chapter 10 by Matthäus et al.

25 Impact on oxygen and phosphate Tendency of reduced P-load in the Baltic Proper in winter surface waters in the years following major inflows (but not after the 2003-event) Consequence of changed hydrography rather then reduced bottom phosphate release From : Feistel, Nausch, Wasmund, Chapter 12 by Nausch et al.

26 Transport through and stability of the redoxcline Situation: long stagnation period Situation: after inflow NH 4 +, NO 3 - [µm] NH 4 +, NO 3 - [µm] Tiefe [m] NO 3 - -H 2 S overlap O 2 NH 4 + Tiefe [m] H 2 S free zone H 2 S, O 2 [µm] NO 3 - H 2 S H 2 S, O 2 [µm] Hannig et al. (2007): Limnol.Oceanogr. 52 Hannig et al. (2006) FEMS ME 57

27 Transport through and stability of the redoxcline Tiefe [m] NH + - 4, NO 3 [µm] H 2 S, O 2 [µm] O 2 NH 4 + NO 3 - H 2 S Very high denitrification rates (2.7 µm N 2 d -1 ) in overlapping zone of nitrate and sulfide Autotrophic denitrification NO H 2 S SO N 2 Chemocline: no overlap of NO 3 - and H 2 S => High rates of Anammox (0.05 µm N 2 d -1 ) Tiefe [m] NH 4 +, NO 3 - [µm] H 2 S, O 2 [µm] NO NH 4 + 0, NH NO N 15 N 0,15 14 N 15 N N 2 [µm] N 15 N N 2 [µm] 0,10 0,05 15 N 15 N 0 0, time [h] time [h] Hannig et al. (2007): Limnol.Oceanogr. 52; Hannig et al. (2006):FEMS ME 57