Cruise report from R/V Aranda week 37, 2016

Type: Report
Author: Örjan Bäck


The temperature in the surface water was high for the season, at its lowest in the northern Baltic Proper at 16.5 °C up to almost 20 °C in the Hanö Bay. The salinity on the west coast was normal or slightly below, in the Baltic Proper it was normal except in the northeast where it was somewhat lower than the monthly mean. Stratifications in density occurred at most places but not as extensive as earlier during the summer, most evident was a halocline in the Kattegat at around 20 meters depth and a thermocline, also at around 20 meters, in the Baltic Proper. Nutrients in the term of phosphate and inorganic nitrogen (nitrate, nitrite and ammonia) were depleted in the surface waters in the entire survey area. Higher concentrations of nutrients were found first below the pycnoclines, especially the deeper ones around 60 meters. The concentrations of silicate in the surface waters were normal, in the northeastern parts of the Baltic Proper just above normal. Acute hypoxia (dissolved O2 < 2 ml/l) was found from around 60-70 meters end below in the entire Baltic Proper. Hydrogen sulfide was found from 70 meters in the Western Gotland Basin, in the Eastern Gotland Basin close to the bottom at BY15 and at 70 meters and below at BY20 with some small pockets of oxygen at the bottom and at around 125 meters.