A data base of 179 reference sites documents the relations between the assemblages of organic-walled dinoflagellate cysts and sea-surface temperature, salinity, and seasonality throughout the North Atlantic, adjacent subpolar basins (Labrador Sea, Baffin Bay, Irminger and Iceland basins) and epicontinental environments off eastern Canada (estuary and Gulf of St. Lawrence, Hudson Bay). Principal-component analyses show close relationships between dinoflagellate cyst data and sea-surface conditions: the first component (71.1% of the variance) correlates with the winter temperature, salinity, and seasonal duration of sea-ice cover, whereas the second component (11.3% of the variance) appears mainly related to summer temperature. Transfer functions using the best analogue method were tested by reconstructing modern sea-surface conditions on the basis of the reference dinoflagellate cyst assemblages. The correlation coefficient between instrumental averages and reconstructed values ranges from 0.87 (August temperature) to 0.97 (annual duration of sea-ice cover). These transfer functions appear most accurate for the reconstruction of sea-surface conditions in marginal marine environments of high-latitude basins. The only reservation concerns the validity of reconstruction in offshore regions characterized by low productivity where sparse cyst fluxes may result from long-distance transport through currents. The transfer functions that were applied in, as an example, a late Quaternary sequence of the Davis Strait in the northern Labrador Sea, notably suggest seasonal sea-ice cover extent of 6–10 months/year and August temperature and salinity of 1–4 °C and 31–33‰, respectively, during the last glacial optimum (isotopic stage 2).