Canadian Basin freshwater sources and changes: Results from the 2005 Arctic Ocean Section

We present measurements of oxygen isotope ratios and nutrient concentrations along the 2005 Arctic Ocean Section aboard the icebreaker Oden. The data are used to estimate freshwater contributions from meteoric water (mainly river runoff), sea‐ice meltwater, and Chukchi Sea shelf water, itself a combination of Pacific and indigenous Arctic water types. Nutrients ratios are combined to form quasi‐conservative water‐mass tracers (phosphate‐star, N‐star, and the empirical Arctic N‐P relationship) and used along with salinity and δ18O, which are conservative in the ocean interior. Disagreements between two different freshwater analyses in the Western Arctic are largely resolved using a salinity‐dependent Redfield ratio, a new estimate of the Pacific end‐member, and an analysis of the Bering Strait inflow contribution to detraining shelf waters. Freshwater components from 2005 are placed into the context of the overlapping 1994 Arctic Ocean Section (aboard the Louis St. Laurent) and a time series of hydrographic/tracer casts between 1987 and 1992 in the Canada Basin. Compared to 1987–1994; the 2005 transect exhibits increased meteoric water concentrations in the northern part of the Canadian Basin and a decrease in the southern part. This pattern is related to changes in the distribution of wind‐stress curl during the several years prior to each sampling campaign. In addition, a previously observed correlation between sea‐ice formation and river runoff disappears over the Central Arctic in 2005, a change that we attribute to a northward shift of sea‐ice formation. Resampling approximately every 3 years should resolve the dynamics driving changes in freshwater and nutrient distributions. Key Points Oxygen isotope and nutrient data from the 2005 Arctic Ocean Section are presentedWater‐mass and freshwater sources are examined over the Canadian BasinThe history of freshwater sources to the Canada Basin from 1987 through 2005 is discussed