FEHMARNBELT HYDROGRAPHY Final Report FEHMARNBELT FIXED LINK HYDROGRAPHIC SERVICES (FEHY) Marine Water - Baseline Hydrography, Water Quality and Plankton of the Baltic Sea E1TR0057 - Volume I Prepared for: Femern A/S By: DHI/IOW Consortium in association with LICengineering, Bolding & Burchard and Risø DTU FEHMARNBELT HYDROGRAPHY Responsible editor: FEHY consortium / co DHI Agern Allé 5 DK-2970 Hørsholm Denmark FEHY Project Director: Ian Sehested Hansen, DHI www.dhigroup.com Please cite as: FEHY (2013). Fehmarnbelt Fixed Link. Marine Water- Baseline. Hydrography, Water Quality and Plankton of the Baltic Sea. Report No. E1TR0057 - Volume I Report : 194 pages May 2013 ISBN 978-87-92416-27-8 Maps: Unless otherwise stated: DDO Orthofoto: DDO®, copyright COWI Geodatastyrelsen (formerly Kort- og Matrikelstyrelsen), Kort10 and 25 Matrikelkort GEUS (De Nationale Geologiske Undersøgelser for Danmark og Grønland) HELCOM (Helsinki Commission – Baltic Marine Environment Protection Commission) Landesamt für Vermessung und Geoinformation Schleswig-Holstein (formerly Landes- vermessungsamt Schleswig-Holstein) GeoBasis-DE/LVermGeo SH Model software geographic plots: Also data from Farvandsvæsenet and Bundesamt für Seeschifffahrt und Hydrographie Photos: Photos taken by consortium members unless otherwise stated © Femern A/S 2013 All rights reserved. The sole responsibility of this publication lies with the author. The European Union is not responsible for any use that may be made of the information contained therein. TABLE OF CONTENTS 1 EXTENDED SUMMARY ..................................................................................... 1 1.1 Hydrography of the Baltic Sea ......................................................................... 1 1.1.1 Driving forces ................................................................................................ 2 1.1.2 Estuarine Circulation and Water Masses ............................................................ 6 1.1.3 Regular inflow and major inflows ..................................................................... 8 1.1.4 Mixing processes .......................................................................................... 10 1.1.5 Resulting salinities, temperatures and water levels ........................................... 12 1.1.6 Marine optics, transparency ........................................................................... 18 1.2 Nutrients and oxygen in the Baltic Sea ............................................................ 20 1.2.1 Seasonal nutrient cycles ................................................................................ 21 1.2.2 Long-term trends .......................................................................................... 22 1.2.3 Inorganic nutrients in the depth ..................................................................... 22 1.2.4 Oxygen ....................................................................................................... 24 1.3 Cyanobacteria and phytoplankton in the Baltic Sea ........................................... 25 1.3.1 Spatial and seasonal distribution..................................................................... 25 1.3.2 Long-term trends in phytoplankton composition ............................................... 28 1.3.3 Long-term trends in total phytoplankton biomass and primary production ............ 28 1.4 Present pressures ......................................................................................... 28 1.4.1 Major constructions ....................................................................................... 28 1.4.2 Ship traffic ................................................................................................... 28 1.4.3 Eutrophication and hazardous substances ........................................................ 29 1.5 Consequences of climate change .................................................................... 31 2 THE AREA – NATURAL CONDITIONS AND EXTERNAL FORCING ........................... 33 2.1 Geographical setting ..................................................................................... 33 2.1.1 Bathymetric data and hypsography ................................................................. 34 2.1.2 Geographical structure of the Baltic Sea .......................................................... 41 2.1.3 Hydrographic implications .............................................................................. 47 2.2 River runoff to the Baltic Sea.......................................................................... 49 2.2.1 Discharge data and the HBV model ................................................................. 49 2.2.2 Regional inputs, seasonal and inter-annual variability ........................................ 53 2.3 Nutrient inputs ............................................................................................. 57 2.3.1 Riverine input ............................................................................................... 61 2.3.2 Atmospheric deposition of nutrients ................................................................ 64 2.4 Meteorological conditions in the Baltic Sea area ................................................ 66 2.4.1 Observational and model data ........................................................................ 67 2.4.2 Typical transient weather patterns .................................................................. 69 2.4.3 Seasonal meteorological conditions over the Baltic Sea ..................................... 71 2.4.4 Inter-annual variations .................................................................................. 76 3 HYDROGRAPHICAL STATE OF THE BALTIC SEA ................................................. 78 3.1 Sea Level ..................................................................................................... 78 3.1.1 Introduction ................................................................................................. 78 3.1.2 Tides ........................................................................................................... 78 3.1.3 River inflow .................................................................................................. 78 3.1.4 Density difference ......................................................................................... 78 3.1.5 Wind set-up ................................................................................................. 79 3.1.6 Seiching ...................................................................................................... 81 3.1.7 Climate change ............................................................................................ 82 3.1.8 Extreme water levels ..................................................................................... 82 3.2 Waves and tides in the Baltic Sea ................................................................... 84 3.2.1 Wind-induced waves ..................................................................................... 84 3.2.2 Tides ........................................................................................................... 88 E1TR0057 Volume I i FEHY 3.3 Baltic water masses — stratification and horizontal gradients ............................ 94 3.3.1 Regional distribution of salinity ...................................................................... 97 3.3.2 Temperature .............................................................................................. 105 3.3.3 Stratification .............................................................................................. 107 3.3.4 Optical water types ..................................................................................... 108 3.4 Estuarine Circulation ................................................................................... 110 3.4.1 Long-term exchange ................................................................................... 110 3.4.2 Major Baltic Inflows ..................................................................................... 112 3.5 Wind-Driven Currents .................................................................................. 115 3.5.1 Ekman current and transport ........................................................................ 115 3.5.2 Upwelling, coastal jets and Kelvin waves ........................................................ 116 3.5.3 Interaction of the coastal zone and the open sea ............................................ 118 3.6 Turbulence and mixing ................................................................................ 119 3.6.1 Bulk estimates for basin-scale mixing ............................................................ 120 3.6.2 Mixing processes ......................................................................................... 121 3.6.3 Entrainment in buoyancy-driven inflows ......................................................... 121 3.6.4 Internal wave mixing ................................................................................... 123 3.6.5 Upwelling and mixing .................................................................................. 124 3.6.6 Other mixing processes ............................................................................... 125 3.7 Sea ice ...................................................................................................... 127 3.7.1 Baltic Sea .................................................................................................