Thorium Isotopes as Tracers of Scavenging and Particle Dynamics in the Arctic Ocean

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Thorium Isotopes as Tracers of Scavenging and

Particle Dynamics in the Arctic Ocean

S. Bradley Moran, Katherine M. Ellis,

Richard W. Nelson and John N. Smith

The role of the Arctic Ocean in the global carbon cycle remains a key ques-

tion in studies of global climate change. The Arctic Ocean and its adjacent

seas are characterized by spatial and temporal extremes in the rate of biological

sequestration of atmospheric CO2, ranging from oligotrophic conditions in

the central Arctic to production rates in the Bering and Chukchi Seas that are

among the highest reported for any ocean. An important objective of Arctic

research is to quantify the fraction of total primary production exported from

Arctic surface waters to the ocean bottom in the form of sinking particulate

organic carbon and associated biogenic debris. In addition, the Arctic has the

largest ratio of shelf to deep waters of any oceanic region, making it a particu-

larly good place to study the importance of shelfbasin interactions on parti-

cle dynamics and chemical transport.

As part of AOS-94, field sampling was conducted with the primary goals

of:

Using 234Th as a tracer to quantify scavenging and the export flux of

organic carbon by particle sinking from the upper waters and the coup-

ling of chemical transport between the shelves and the interior Arctic

Ocean; and

Using 230Th and 232Th to quantify rates of particle cycling in the inter-

mediate and deep Arctic waters.

Collection of these data within the framework of other AOS-94 field pro-

grams will contribute to the international effort to better understand the role

of the Arctic Ocean in the global carbon cycle and climate change. Summar-

ized here are preliminary 234Th results of this research. Samples were also

collected for determination of full-depth vertical profiles of long-lived 230Th

(half-life = 7.5 104 years) and 232Th (half-life = 1.4 1010 years) at several

locations along the cruise track. These samples are being analyzed using highly

sensitive thermal ionization mass spectrometry.

S. Bradley Moran is from the Graduate School of Oceanography at the University of Rhode Island in Narragan-

sett, Rhode Island, U.S.A. Katherine Ellis, Richard Nelson and John Smith are from the Bedford Institute of

Oceanography in Dartmouth, Nova Scotia, Canada.