1994 Arctic Ocean Section
Total Carbonate and Total Alkalinity:
Tracers of Shelf Waters in the Arctic Ocean
E. Peter Jones
Modern oceanographic measurements include a suite of many tracers, each
of which often has a significance in determining the origin of a particular
water mass and tracing its circulation. In the Arctic Ocean, total carbonate and
total alkalinity have been shown to be effective tracers of waters that have
flowed into central regions from the continental shelves. In addition, these
measurements are an integral part of an assessment of carbon fluxes into and
within the Arctic Ocean.
Total alkalinity and total carbonate in seawater are closely related to salin-
ity, with small deviations from a linear relationship resulting primarily from
the dissolution or precipitation of calcium carbonate. In near-surface water,
carbon from biological decay can also be a significant contributor to changes
in total carbonate. Biological productivity can be assessed with the aid of total
alkalinity and nutrient measurements, and the total carbonate and total alkalin-
ity data will contribute to an assessment of the carbon budget of the Arctic
Ocean.
Total alkalinity and total carbonate analyses are best carried out on "fresh"
samples: the analyses were done onboard ship within about 20 hours after
they were collected, using standard techniques (potentiometric titration and
coulometry). Samples were collected at almost all oceanographic stations at
almost all sampling depths, typically 36 from the surface to the bottom, using
the rosette sampler. The time between stations did not allow water from every
sampling depth to be analyzed, though more than 90% of them were. The
quality of the data is high, reflected in replicate analyses with an average dif-
ference of just over 1 part per thousand for total alkalinity and 0.9 parts per
thousand for total carbonate.
Higher total alkalinity values observed in the near-surface water at many
stations during AOS-94 are attributed to dissolved calcium carbonate brought
into the Arctic Ocean by runoff. This signal helps to determine the sources of
fresh water by separating river runoff from sea ice meltwater, and it helps in
tracing the circulation pattern of river runoff. Near-surface "excess" alkalinity,
indicating the presence of river runoff, was found at all stations in the Canada
E. Peter Jones is from the Bedford Institute of Oceanography in Dartmouth, Nova Scotia, Canada.
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