Along-stream changes and seasonality in Denmark Strait Overflow Water properties: Insights from novel oxygen observations in the Irminger Sea

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Abstract
Denmark Strait Overflow Water (DSOW) is formed in the Nordic Seas and is a key water mass transported by the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). DSOW facilitates the transmission of climate signals into the deep ocean, both directly from the Nordic Seas and indirectly from the Irminger Sea via entrainment. Here, we use new hydrographic and oxygen observations from BGC-Argo profiling floats and moored instruments along with a simple streamtube model to investigate along-stream changes and seasonality in DSOW properties. We suggest that the along-stream changes in DSOW oxygen are consistent with mixing with entrained ambient waters. Novel year-round moored oxygen measurements offshore of Cape Farewell, Greenland reveal seasonality in DSOW oxygen properties that is similar to the seasonality in DSOW salinity. Model results suggest that this observed seasonality reflects seasonality in the source waters, rather than seasonality in the properties of the entrained waters or the strength of entrainment. We suggest that future changes in dense water properties in the Nordic Seas could substantially influence overflow properties. This finding may have consequences for future projections of AMOC strength and the ventilation of the deep North Atlantic.