IO7N to provide novel dataset of DO14C in the Indian Ocean

Author: Christian Lewis

DO14C – What is it?

DO14C is an acronym for “Dissolved Organic Radiocarbon (14C).” The DO in DO14C refers to a complex cycling of dissolved organic matter throughout the oceans, which includes proteins, amino acids, and many other compounds that are primarily produced through plankton photosynthesis in the surface ocean. The 14C refers to radiocarbon. Radiocarbon is a radioactive isotope of carbon that decays through time with a known half-life. This known half-life (~6000 years) allows scientists to very accurately determine the age of something by measuring how much radiocarbon is left. Oceanographers and geochemists can use radiocarbon dating of seawater to understand the cycling of organic matter in the ocean.

What does it tell us?

DO14C measurements in the Atlantic and Pacific Oceans have shown that organic carbon in the deep ocean is 4000-6000 14C years old. This is much older than the ~1000 years it takes the ocean to overturn. Therefore, DO14C measurements have shown us that the ocean can store organic carbon for much longer than inorganic carbon. This information is crucial for our understanding of the ocean’s carbon cycle and how it influences our climate on Earth.

DO14C has been measured more frequently in the Pacific and Atlantic Oceans, but this cruise will provide one of the first datasets of DO14C in the Indian Ocean, which is a unique location oceanographically.

How do scientists measure it?

Seawater for DO14C measurements are collected from the Niskin bottles on the CTD rosette into 1L glass bottles that have been acidified and baked prior to the cruise. Acidifying and baking out glassware removes extraneous carbon that could influence our measurements. All of our samples are frozen upon collection and stowed in a chest freezer on board where they await further processing on land at the University of California, Irvine.

Back in the lab, the seawater is oxidized to CO2(g) using ultra-violet light, isolated, and reduced to graphite. The graphite is then measured for radiocarbon content in an accelerator mass spectrometer (AMS), which measures the ratio of 14C to 12C (the more common flavor of carbon). From there, a radiocarbon age can be calculated, and new discoveries can be made!

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