The 8.2 ka event, a significant cooling period approximately 8200 years ago, is partially reconstructed from sediment cores in the Norwegian and North Seas. These reconstructions are crucial for understanding past climate variability and informing future climate change predictions. However, the accuracy of these reconstructions can be compromised by various geological processes, including tsunamis. Tsunamis are capable of disturbing the seabed and reworking offshore sediments, potentially mixing layers of different ages and altering the sediment composition, leading to inaccurate climate interpretations. The Storegga Slide, a massive submarine landslide off the coast of Norway, triggered a giant tsunami that has been extensively documented onshore. This study aims to determine whether the Storegga tsunami, which is dated to the coldest decades of the 8.2 ka event, contaminated or altered the sediment records used to reconstruct the 8.2 ka cooling event. The study's importance lies in its potential to improve the accuracy of past climate reconstructions and refine our understanding of the 8.2 ka event's magnitude and impact.

Previous research has demonstrated the impact of tsunamis on sediment redistribution. The 2011 Tohoku tsunami in Japan, for instance, resulted in the redeposition of mud and sand layers on the Sendai shelf. Studies of the Storegga tsunami deposits onshore in Scotland, Norway, Shetland, and the Faroe Islands have provided insights into the tsunami's impact. The existing literature indicates a potential for significant sediment reworking by the Storegga tsunami, but the extent of this reworking and its impact on climate records has not been fully investigated. The 8.2 ka cold event has been studied extensively, with various proxies, including foraminifera and oxygen isotopes, used to reconstruct the magnitude and duration of the cooling. However, the potential influence of the Storegga tsunami on these proxies has not been systematically assessed. This gap in the literature motivates the current research.

The study employs a two-pronged approach. First, computer simulations, using a linear shallow water model, were used to model the Storegga Slide and the resulting tsunami. These simulations provided estimates of the maximum flow velocity of the tsunami in the Norwegian and North Seas. The model parameters were chosen to best match observed landslide runout and tsunami run-up heights. The simulations considered the landslide rheology (cohesive clay-rich debris flow) and generated flow velocity maps representing the maximum flow velocity of the water column. Second, a detailed re-investigation of sediment core MD95-2011, retrieved from the Vøring plateau, was conducted. This core is known to contain a distinct 8.2 ka cold event layer. The analysis involved examination of grain size, foraminifera abundance and species composition, and oxygen isotope values. Radiocarbon dating of planktonic foraminifera (*Neogloboquadrina pachyderma* and *Neogloboquadrina incompta*) within the 8.2 ka layer was undertaken to determine the age of the sediments. Furthermore, the study assessed critical velocities for erosion at three sediment core sites (LINK14, 28-03, and MD95-2011) by considering the boundary layer thickness influenced by bottom friction and using both the Sundborg diagram and equations from Miller et al. to estimate erodible grain sizes for each current velocity. The age-depth models were also evaluated to account for potential hiatuses.

The computer simulations showed that maximum flow velocities during the Storegga tsunami exceeded 1 m/s at depths shallower than 250 m on the Norwegian shelf and in the North Sea. Velocities of 2-5 m/s were calculated for shallower regions around Shetland, the Faroe Islands, and western Norway. Even at depths of up to 1000 m, velocities above 1 m/s were simulated, particularly near the Storegga Slide. The re-investigation of sediment core MD95-2011 revealed a 2 cm thick 8.2 ka layer with a distinct change in grain size, foraminifera abundance and species, and oxygen isotope values. The mixture of foraminifera species indicated re-sedimentation. Importantly, radiocarbon dating of *N. pachyderma* within this layer yielded ages ranging from 10,690-11,170 cal yr BP, significantly older than the 8200 yr BP expected for the 8.2 ka event. Similarly, *N. incompta* dates fell between 8680-9190 cal yr BP, older than the surrounding layers. The analysis further suggested a 400-year hiatus at the lower boundary of the 8.2 ka layer, indicative of erosion. The upward fining of grains and presence of benthic foraminifera characteristic of shallower waters supported the interpretation of the 8.2 ka layer as a turbidite deposited from the shelf break. Similar findings suggesting contamination from tsunami currents were also observed in cores LINK14 and 28-03, although with varying intensity. The simulations suggest that strong currents capable of moving grains up to 1 mm were likely experienced over large areas down to 1000 m water depth. Moreover, the release of turbidity currents from the shelf breaks contributed to the deposition of turbidites, as demonstrated for core MD95-2011.

The findings strongly suggest that the Storegga tsunami significantly impacted the sediment layers in the Norwegian and North Seas, particularly those previously interpreted as representing the 8.2 ka cold event. The significantly older radiocarbon dates for foraminifera in the 8.2 ka layer in MD95-2011 directly contradict the previously held interpretation of an abrupt and dramatic cooling event at that time. The redeposition of older sediments, as indicated by the mixed foraminifera assemblage and the presence of shallow-water benthic species at depth, points towards the substantial impact of tsunami currents on the sedimentary record. This demonstrates that the previously reported significant cooling at this location must be reassessed, and its interpretation as a solely climatic event is now challenged. This research highlights the critical importance of considering geological disturbances, such as tsunamis, when interpreting paleoclimate records. The study's implications extend beyond the 8.2 ka event, cautioning against accepting sediment records at face value and emphasizing the need for careful consideration of geological processes that might have influenced sediment distribution and composition.

This study demonstrates that the Storegga tsunami significantly reworked sediments in the Nordic Seas, contaminating previous 8.2 ka cold event records. The radiocarbon dating and sedimentological analysis clearly show that the '8.2 ka layer' in several cores is a redeposited turbidite, not representing in-situ climate conditions. Previous interpretations of a large, abrupt cooling event should be reevaluated. Future research should focus on identifying and mitigating the impacts of such geological events on other paleoclimate records to improve the accuracy of climate reconstructions.

The study primarily focuses on a limited number of sediment cores. While the findings are compelling, further analysis of additional cores from the region is needed to strengthen the conclusions. The accuracy of the tsunami simulations relies on the chosen model parameters and input data, introducing uncertainties into the flow velocity estimates. Furthermore, the interpretation of the sediment record depends on the assumptions made in age-depth modelling, particularly concerning hiatuses.