The main objectives of this cruise were to elucidate whether climate change (mainly ocean acidification and warming, OAW) affects interacting species differently due to divergent physiological optima and ranges, expressed in thermal tolerance windows and associated performance capacities and phenologies of specific life stages. To determine the degree of the ongoing ‘Atlantification’ of the waters around (Western) Svalbard, we took sediment samples to analyse the benthic epi- and meiofauna. Further, we intended to obtain specimens of both Polar cod (B. saida) and Atlantic cod (G. morhua) in the Atlantic and polar waters around Svalbard, which were used in experiments on board and back at the Alfred Wegener Institute. We left port in Trondheim in the morning of September 21st, heading North towards Svalbard. Due to severe storms in the Norwegian Sea, we had to travel close to the Norwegian shoreline and eventually seek shelter inside Vestfjorden/Lofoten Islands until September 25th. A second attempt to reach Bjørnøya (Bear Island) on September 26th failed again due to weather, this time weathering off in Fugløysund/Troms (see figure 1 for cruise track). Around noon of September 28th, we finally reached the first scientific station at Bjørnøya (HE519_1), where we deployed a CTD and two short bottom trawls (mainly Atlantic cod, Gadus morhua, and haddock, Melanogrammus aeglefinus) and continued to the Southern tip of Svalbard to reach Hornsund in the morning of September 29th. The first station at Svalbard was carried out in Hornsund (HE519_2), where a CTD and a multicorer was deployed, to sample the water column and first 30cm of sediment. Following this, we ran several juvenile fish trawls with fish lift at different depths from surface waters to close to the bottom, specifically aiming for flocks of juvenile fish under the surface, at the thermocline and above ground (water layers of interest derived from CTD and EK80 profiles). This daily sampling protocol was repeated at all other stations unless stated otherwise. In Hornsund, the whole water body including bottom waters were around 3°C and well mixed by the rough weather. The dominant fish species throughout the water column was Atlantic cod (Gadus morhua) and bottom waters only contained few polar cod (Boreogadus saida). During the following night, we steamed to North West Svalbard to sample a station north of Moffen Island (HE519_3) on September 30th. Due to deteriorating weather conditions, the fisheries protocol had to be reduced to angling of 50 Atlantic cod for population genetic studies. The overall weather situation forbade to go further east and the stations planned for Rijpfjorden and Hinlopenstreet had to be cancelled. The day after, we sampled Raudfjorden (HE519_4, 5, 6), which was under Atlantic influence at this time of the year (juv. Atlantic cod, haddock and herring, Clupea harengus, only few remaining polar cod). On October 2nd, we had to seek shelter in the Krossfjorden/Kongsfjorden system, the stations envisaged for Yermak plateau and the Hausgarten-transect had to be cancelled. Krossfjorden (HE519_7) did not show any specific stratification of its water column, yet at its northern tip the deep bottom waters were still relatively cold (0.8°C) and we found several Polar cod there. Due to its western exposure, Kongsfjorden (HE_519_8, 9, 10) was very well mixed with bottom temperatures >2°C and was clearly dominated by Atlantic cod over the whole of its west-east trajectory. In the afternoon of October 4th, we called at Ny Ålesund to load frozen samples and expedition material of the AWIPEV summer campaign and transport them to AWI in Bremerhaven. The next morning saw us stopping over shortly at Longyearbyen for a medical appointment of a crew member, followed by a short multicorer station in Isfjorden (HE519_11) on the way to Billefjorden the same day. The last stations of the cruise were carried out in Billefjorden (HE519_12, 13) on October 5th and 6th. Due to its geographical position and relative shallow sill (30-40m), the water body was clearly structured into warmer surface waters (3-5°C) and the very cold bottom waters (-1,4°C), which were populated by Polar cod as the only fish species on the bottom. The surface waters contained flocks of young Atlantic cod and swarms of herring. In the evening of October 6th, the scientific program of cruise HE519 ended and we sailed back to Longyearbyen to bid three members of the scientific crew farewell on the morning of October 7th. The weather forecast once more did not look promising so we left Svalbard three days earlier than planned to sail home as close to shore as possible. After several delays due to seeking shelter under land along the Norwegian coast, we arrived in Bremerhaven 10 days later in the early morning of October 16th. Thus ended a challenging research cruise, with relatively meagre results due to the extremely bad weather. Nonetheless, we were able to carry out about 50% of the planned station work, took a great amount of sediment cores and biological samples. In only nine days of station work, 2 bottom trawls, 9 multicorer placements, 11 CTD profiles and 16 pelagic fish trawls with fish lift could be realised. We brought more than 250 juvenile Polar cod back to the home institute in Bremerhaven alive.