This cruise was a part of the “Verbundprojekt BIOACID” (Biological Impacts of Ocean ACIDification) Phase II (consortium 4 of 5), funded by the German Ministry for Education and Research (BMBF). It was also connected to the Norwegian-German collaborative project Tibia (“Trophic interactions in the Barents Sea - steps towards an Integrated Ecosystem Assessment (TIBIA)”, see www.caff.is/marine/marine-expert-networks/benthos) between AWI and the IMR in Tromsø. 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 Tromsø in the morning of September 11th, heading North towards Svalbard. In the morning of September 13th, we reached the first scientific station in Hornsund, where a CTD was deployed. 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 EK60 profiles). In Hornsund, bottom waters were around 0°C cold and contained polar cod (Boreogadus saida). After fishing, we deployed several box grabs for sampling the first 30cm of sediment. This daily sampling protocol was repeated at all other stations unless stated otherwise. After a day of cruising, we reached North East Svalbard and sampled two stations at the center and opening of Rijpfjorden on September 15th and 16th, the protocol here was substantiated by several bottom trawls that yielded surprisingly little material. Afterwards, we moved into Hinlopen Strait, sampling waters of Atlantic and Barents Sea origin in a northwest-southeast transect during September 17th and 18th. The following day found us back in biologically diverse Atlantic waters at the Northwestern tip of Svalbard around Moffen Island, yielding schools of larval/juvenile herring, capelin, redfish and polar cod (and a few 0-class Antlantic cod) in the surface waters as well as a bottom trawl of mostly adult Atlantic cod (Gadus morhua) and several haddock (Melanogrammus aeglefinus). On our way to the AWI Hausgarten, we stopped over on the Yermak plateau on September 20th, where we found similar diversity as the day before. On September 21st, we sampled AWI Hausgarten with CTD, box grabs and several shallow juvenile fish trawls under deteriorating weather conditions. We therefore had to abandon our sampling schedule and the following days found us moving back and forth between shelter in Kongsfjord, Forlandsundet and Krossfjorden and the open water towards the Hausgarten, trying to complete the transect Kongsfjord-Hausgarten. This transect showed a succession of juvenile/larval fish species dominated by redfish (Sebastes sp.) in the open ocean towards Polar cod (B. saida) close to the shore (further abundant species included herring and capelin). Sampling in Forlandsundet revealed a rich and diverse ecosystem with polychaetes, annelids, holothurians, echinoderms and crustaceans (mainly Hyas araneus), again dominated by Atlantic cod (G. morhua). The last stations of the cruise were carried out in Billefjord on September 27th and 28th, here, the very cold bottom waters (-1,7°C) were populated by Polar cod as the only fish species plus several spider crabs (H. araneus). On September 29th, we handed over RV Heincke in Longyearbyen to the chief scientist of HE 451.2, Dr. Katrin Latarius. Thus ended a successful cruise, in which we were able to carry out about 90% of the planned station work, took a great amount of sediment and biological samples and brought around 150 juvenile Polar cod and about 60 juvenile Atlantic cod back to the home institute in Bremerhaven alive.