Interannual variability (2014-2019) of hydrography, fluorescence and nutrient distribution in Vestfjorden, Lofoten

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.