Understanding Spatial and Temporal Variations of Arctic Circulation Using Oxygen Isotopes of Seawater

Abstract:

The isotopic ratio of ¹⁸O to ¹⁶O in seawater (2005ppm in ocean water is defined as 𝛿¹⁸O_seawater≡0 permil or 0‰) is a fundamental ocean tracer due to its distinct linear relationship with salinity(𝛿¹⁸O -S) from regional inland freshwater sources. As opposed to salinity alone, 𝛿¹⁸O distinguishes river runoff from sea-ice melt and traces ocean circulation pathways from coastal to open waters and surface to deep waters.

Observations from the past 60 years of 𝛿¹⁸O seawater were compiled into a database by Schimdt et al. (1999), and subsequently used to calculate a 3-dimensional 1°x1° 𝛿¹⁸O global gridded dataset by LeGrande and Schmidt (2006). Although the Schmidt et al. (1999) Global Seawater Oxygen-18 Database (𝛿¹⁸O_obs) contains 25,514 measurements used to calculate the global gridded dataset, LeGrande and Schmidt (2006) point out that, “data coverage varies greatly from region to region,” with seasonal variability creating biases in areas where sea ice is present.

Python Pandas is used to automate the addition of 2,942 records to the Schmidt et al. (1999) Global Seawater Oxygen-18 Database (𝛿¹⁸O_obs), and examine the spatial and temporal distributions of ¹⁸O in the Arctic Ocean. 10 initial water masses are defined using spatial and temporal trends, clusters of observations, and Arctic surface circulation. Jackknife slope analysis of water mass 𝛿¹⁸O -S is used to determine anomalous data points and regional hydrology, resulting in 4 distinct Arctic water masses. These techniques are used to improve the gridded 𝛿¹⁸O_seawater dataset by distinguishing unique water masses, and accounting for seasonal variability of complex high latitude areas.