Faculty of Biosciences, Fisheries and Economics, Department of Arctic and Marine Biology Interannual variability (2014-2019) of hydrography, fluorescence and nutrient distribution in Vestfjorden, Lofoten. Daniel Fernández Román BIO-3950 Master’s thesis in Marine Ecology (May 2020) Acknowledgements: First of all, I would like to thank to my two amazing supervisors Angelika and Ingrid. I was really lucky to be able to work with you two, both in the cruise and during your supervision over the development of this exciting study to me. It was a very fun and enriching process. Thanks for all the patience, hard work and the skype meetings during the Corona times. Working on my master thesis helped me to grow as a researcher but also as a person, and that is thanks to you two. I would like to thank also to Svein Kristiansen and Hans Christian Eilertsen for providing me with the nutrient data from (2015-2018) and to Jofrid Skarðhamar for sharing with me the freshwater runoff data from Vestfjorden. Thanks to the crew of R/V Helmer Hansen and to all the professors and students involved in the courses BIO-2010 Marine Ecology and BIO-2516 Ocean Climate from 2014-2019. And of course I cannot forget about my family and friends who helped and supported me during my two years of master. Thanks to my dad, Alejandro for inspiring me and give me his scientific curiosity and to my mum, Susana, for teaching me to never surrender. Thanks to my friends that made these two years in Tromsø truly unforgettable. Thanks to the Svalbard crew for an amazing month up north, to Theo for your great friendship and the endless ski-trips / photo tours/ hiking / camping / sailing / fishing. To Alex for all the talks and ski trips we shared and for being the first person I met here in Tromsø when I came in firstly in 2017. Og takk til Siva, for alle opplevelsene sammen og at du va en skikkelig pro nosk lærer til mæ. I cannot mention all of you but this applies to everyone, it has been great to share these two years with all of you guys! And of course also my friends back home, thanks to the Cinderelic Olympic Team (Miguel, Marto and Pelos) for more than twenty years of friendship, to Olatz for your endless counselling and to everyone there that supported me in the last two years. To all of you, THANK YOU! Daniel Fernández Román, Tromsø, June 2020. Abstract Vestfjorden is an area of great ecological relevance since it is one of the main spawning areas of North East Atlantic cod. The survival rate of the cod larvae depends greatly on the abundance of zooplankton, which in turn depends on phytoplankton. Due to the extreme seasonality of high latitude fjords with a short productive season, understanding the phytoplankton distribution in spring is crucial. Phytoplankton is greatly affected by hydrography and nutrient distribution. This study aims to identify a common pattern in hydrography, nutrient concentration and phytoplankton distribution in Vestfjorden and the impact of hydrography on phytoplankton distribution. To do that, hydrographic variables (T, S, ρ), nutrient concentration and fluorescence were sampled in different surveys in spring from 2014 to 2019. The results showed that Vestfjorden was stratified throughout spring in all years. In Spring, the surface layer was colder (3.0 – 4.0 ºC) and fresher (32.6 – 33.9 g/kg), than the bottom layer (7.0 – 7.5 ºC) and (> 34.9 g/kg). The formation of hydrographic features such as fronts or eddies were observed in the middle of the fjord. The phytoplankton distribution was linked to hydrography, especially to the presence of hydrographic features. The spring bloom may be triggered in the middle of the fjord, linked to the front/eddy, due to the suppression of vertical mixing. If not such structure is developed, the onset of the bloom may be delayed. Keywords: Spring bloom, phytoplankton, eddy, front, stratification, Vestfjorden, hydrographic feature Table of Contents 1 Introduction: ....................................................................................................................... 5 2 Theoretical background ...................................................................................................... 7 2.1 Physical processes in a fjord ........................................................................................ 7 2.2 The physical environment of Vestfjorden ................................................................. 11 2.3 Role of nutrients in the ocean. Northern Norway nutrient distribution. .................... 13 2.4 Interaction between hydrographic features and phytoplankton growth .................... 15 2.5 The spring bloom. ...................................................................................................... 16 3 Data and methods: ............................................................................................................ 20 3.1 Data available: ........................................................................................................... 20 3.2 Hydrographic data: .................................................................................................... 21 3.3 Water Sampling: ........................................................................................................ 24 3.4 Nutrient data analysis: ............................................................................................... 24 3.5 Chlorophyll a filtration and analysis: ........................................................................ 24 3.6 Meteorological data ................................................................................................... 25 4 Results .............................................................................................................................. 26 4.1 Meteorology and freshwater runoff ........................................................................... 26 4.2 Hydrography .............................................................................................................. 28 4.2.1 Temperature ....................................................................................................... 28 4.2.2 Salinity ............................................................................................................... 30 4.2.3 Density: .............................................................................................................. 30 4.3 Biological parameters ................................................................................................ 35 4.3.1 Fluorescence and chlorophyll a (Chl a) .............................................................. 35 4.3.2 Nutrient concentration ........................................................................................ 36 5 Discussion ........................................................................................................................ 42 5.1 Hydrography .............................................................................................................. 42 5.1.1 Common hydrographic patterns in Vestfjorden ................................................. 42 Page 1 of 57 5.1.2 Eddies and fronts in Vestfjorden ........................................................................ 46 5.2 Phytoplankton distribution and its relations with hydrography................................. 47 5.2.1 Common phytoplankton distribution in Vestfjorden during spring ................... 47 5.2.2 Influence of hydrography and hydrographic features on the phytoplankton distribution ....................................................................................................................... 48 6 Conclusion ........................................................................................................................ 51 7 References ........................................................................................................................ 52 List of Tables Table I All the transects taken during all the teaching cruises. The “x” means there is no data for that station. CTD means there are hydrography data (T, S, Density, Fluorescence) and nutrients that there are nutrient data (NO3 + NO2 , SiOH4 , PO4)............................................. 21 Table II Air temperature in Bodø from March and April 2014-2019. The range in the temperature average is the standard deviation. The maximum and minimum temperatures are for the entire March-April period. ............................................................................................ 26 Table III Horizontal temperature difference (2014-2019) from inner (station 1) fjord to outer fjord (station 6). ........................................................................................................................ 29 Table IV Mixed layer depth (m) for each station and year. When more than one depth is given, a second ML was detected. In that case, the first value indicates the depth of the shallow ML and the start of the first pycnocline. The depth range after represents the start of the second ML, and the start of the second pycnocline. When < 10 m is shown, the ML was shallower than 10 m. Mixed is used when the water column is mixed ................................................................. 31 List of Figures Figure 1 Upper water column currents along the Norwegian coast. Vestfjorden is located in the grey box. Figure adapted from figure 2 in Sætre, (1999). (Original from Sætre, 1983). ......... 12 Page 2 of 57 Figure 2 Map of the stations of the cruises. Stn 1, 2, 3,