Imagine you have a cup of soda containing Coca-Cola, Pepsi, Dr. Pepper, and Mug Root Beer. Can you tell how much of each brand was added to your cup by taste? Probably not.
Like the mix of different sodas, Arctic seawater can contain Pacific water, Atlantic water, Siberian rivers, North American rivers, and sea-ice melt. We call these water types.
Also like the soda, Arctic water types have different “flavors”. Instead of tasting them, we use chemistry to tell the water types apart. By measuring many types of “flavors” (different minerals dissolved in the water) we can identify each water type.
We will use salinity, stable isotopes of oxygen (d18O), total alkalinity, barium, and nutrients (e.g., nitrate, phosphate, silicate) to distinguish the different water types. Individually, these chemical tracers cannot be used to tell all the different water types apart. But together they form a type of chemical fingerprint specific to each water type. For example, both Siberian and North American rivers are characterized by very similar salinities and d18O but they have different total alkalinities and barium concentrations (see Figure 3). So, while salinity or d18O can be used to identify these river waters as freshwater sources, total alkalinity and barium are needed if the specific source (North America or Siberia) is to be identified.