Deep water of the Gdansk Deep (Baltic Sea): development over the last 20 years

Abstract. This study examines the development of the deep layer of the Gdansk Deep in the Baltic Sea over the past 20 years (2003–2023), with a focus on changes in dissolved oxygen levels and hydrological parameters following major Baltic inflows (MBIs) in 2003 and 2014 The Gdansk Deep has experienced significant changes within deep layer in 2003–2023, with increasing temperature, stable salinity, and decreasing dissolved oxygen content. The temperature increases in the deep layer of the Gdansk Deep may be attributed to increased number of warm summer inflows and global ocean temperature rise. Data from environmental monitoring and various sources was used to describe seasonal and interannual variations in dissolved oxygen concentration and suggests potential additional sources of oxygen apart from MBIs, including deep convection and intra-pycnocline intrusions.