We present new flow‐weighted data for δ18OH2O, dissolved organic carbon (DOC), dissolved barium and total alkalinity from the six largest Arctic rivers: the Ob', Yenisey, Lena, Kolyma, Yukon and Mackenzie. These data, which can be used to trace runoff, are based upon coordinated collections between 2003 and 2006 that were temporally distributed to capture linked seasonal dynamics of river flow and tracer values. Individual samples indicate significant variation in the contributions each river makes to the Arctic Ocean. Use of these new flow‐weighted estimates should reduce uncertainties in the analysis of freshwater transport and fate in the upper Arctic Ocean, including the links to North Atlantic thermohaline circulation, as well as regional water mass analysis. Additional improvements should also be possible for assessing the mineralization rate of the globally significant flux of terrigenous DOC contributed to the Arctic Ocean by these major rivers.

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The utility of dissolved barium (Ba) as a quasi‐conservative tracer of Arctic water masses has been demonstrated previously. Here we report distributions of salinity, temperature, and Ba in the upper 200 m of the Canada Basin and adjacent areas observed during cruises conducted in 2003–2004 as part of the Joint Western Arctic Climate Study and Beaufort Gyre Exploration Project. A salinity–oxygen isotope mass balance is used to calculate the relative contributions from sea ice melt, meteoric, and saline end‐members, and Ba measurements are incorporated to resolve the meteoric fraction into separate contributions from North American and Eurasian sources of runoff. Large fractions of Eurasian runoff (as high as 15.5%) were observed in the surface layer throughout the Canada Basin, but significant amounts of North American runoff in the surface layer were only observed at the southernmost station occupied in the Canada Basin in 2004, nearest to the mouth of the Mackenzie River. Smaller contributions from both Eurasian and North American runoff were evident in the summer and winter Pacific‐derived water masses that comprise the underlying upper halocline layer in the Canada Basin. Significant amounts of Eurasian and North American runoff were observed throughout the water column at a station occupied in Amundsen Gulf in 2004. This suggests the export of runoff from both sources through the passages of the Canadian Arctic Archipelago.