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[1] Palynological, geochemical, and physical records were used to document Holocene paleoceanographic changes in marine sediment core from Dease Strait in the western part of the main axis of the Northwest Passage (core 2005-804-006 PC latitude 68°59.552′N, longitude 106°34.413′W). Quantitative estimates of past sea surface conditions were inferred from the modern analog technique applied to dinoflagellate cyst assemblages. The chronology of core 2005-804-006 PC is based on a combined use of the paleomagnetic secular variation records and the CALS7K.2 time-varying spherical harmonic model of the geomagnetic field. The age-depth model indicates that the core spans the last ∼7700 cal years B.P., with a sedimentation rate of 61 cm ka −1 . The reconstructed sea surface parameters were compared with those from Barrow Strait and Lancaster Sound (cores 2005-804-004 PC and 2004-804-009 PC, respectively), which allowed us to draw a millennial-scale Holocene sea ice history along the main axis of the Northwest Passage (MANWP). Overall, our data are in good agreement with previous studies based on bowhead whale remains. However, dinoflagellate sea surface based reconstructions suggest several new features. The presence of dinoflagellate cysts in the three cores for most of the Holocene indicates that the MANWP was partially ice-free over the last 10,000 years. This suggests that the recent warming observed in the MANWP could be part of the natural climate variability at the millennial time scale, whereas anthropogenic forcing could have accelerated the warming over the past decades. We associate Holocene climate variability in the MANWP with a largescale atmospheric pattern, such as the Arctic Oscillation, which may have operated since the early Holocene. In addition to a large-scale pattern, more local conditions such as coastal current, tidal effects, or ice cap proximity may have played a role on the regional sea ice cover. These findings highlight the need to further develop regional investigations in the Arctic to provide realistic boundary conditions for climatic simulations.

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Dinocyst assemblages and the physical properties of two sediment cores collected in the easternmost part of the main axis of the Northwest Passage, Canadian Arctic Ocean (cores 2004-804-009 BC and 2004-804-009 PC, 74°11.2′N, 81°11.7′W) were used to reconstruct changes in sea-surface conditions and to characterize changes in the depositional environment. Core 2004-804-009 PC spans the last 12 180 calibrated (cal) years BP, with sedimentation rates ranging from 45 to 122 cm/ka. Quantitative estimates of sea-surface parameters reveal relatively large hydrographic variability at millennial time scale. Before 11 000 cal years BP, our records suggest terrigenous inputs related to the last deglaciation. Between 11 000 and 9600 cal years BP, harsh conditions prevailed with August sea-surface temperatures <2 °C and the dominance of heterotrophic taxa. This episode was followed by a gradual increase in the relative abundance of phototrophic taxa and the establishment of milder condition with sea-surface temperature (SST) reaching ∼2 °C ∼8300 cal years BP, possibly related to increased exchange between the Arctic Ocean and the North Atlantic Ocean. From 6000 cal years BP to the late Holocene, climate variability could be the results of changes in the synoptic-scale atmospheric pattern such as the Arctic oscillation.