Journal article
Detangling stable carbon isotopes in giant clam shells; discrepancies between shell layers and the Suess effect
Abstracts with programs - Geological Society of America, Vol.51(5)
Geological Society of America, 2019 annual meeting & exposition (2019)
Sep 2019
Abstract
Giant clams, Tridacna, are sentient bivalves that live in symbiosis with algae in shallow, tropical coral reefs in the Pacific and Indo-Pacific Oceans. Their aragonitic shells mineralize at a fast rate, producing robust seasonal records of their ambient environment. Stable isotope ratios are often measured from the carbonate of these shells as oxygen is known to be in isotopic equilibrium with seawater, thus useful for reconstructing sea surface temperatures. During the collection of delta (super 18) O values, delta (super 13) C is also obtained, yet often not discussed or interpreted. Giant clams are composed of two distinct shell layers, inner and outer, from which delta (super 13) C values are not equivalent. Here, we present a comparison of delta (super 13) C and delta (super 18) O values from both shell layers of T. derasa and T. squamosa collected from Palau in 2017 and T. maxima collected from American Samoa in 1982. Values of delta (super 18) O are used to calibrate growth rate between layers and show that growth is not always proportional. Profiles of delta (super 13) C from the inner shell layer of T. derasa are typically 0.5 ppm greater than the outer shell layer while the difference is about 1.0 ppm for T maxima. Values of delta (super 13) C from T. squamosa are nearly equal between the shell layers, although there is a trend towards lower values in the outer layer with age. On the other hand, previous studies of T. gigas show that the outer layer is more enriched in (super 13) C than the inner layer. Values of delta (super 13) C from the inner layer of contemporaneous specimens are not statistically different across species. These discrepancies suggest there are species specific fractionations occurring in the outer shell layer, implying that it is important to note which layer is analyzed, especially for climatological assessments. Additional biochemical studies are required to determine the cause of fractionation in the outer shell layer or any effects from symbiotic algae. A temporal comparison of these and all published inner layer delta (super 13) C profiles shows depletion at the same rate as the depletion of atmospheric CO (sub 2) due to the Suess Effect. Under the assumptions that 1) mineralization of the inner shell layer is similar among species, 2) there are no overriding environmental effects and 3) the atmosphere is well mixed, we find that the inner shell layer of the giant clam is an adequate record of the Suess Effect.
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Details
- Title
- Detangling stable carbon isotopes in giant clam shells; discrepancies between shell layers and the Suess effect
- Creators
- Michelle Gannon - Drexel UniversityDavid VelinskyChristopher S. RomanekAnonymous
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.51(5)
- Conference
- Geological Society of America, 2019 annual meeting & exposition (2019)
- Publisher
- Geological Society of America (GSA)
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Environmental Biogeochemistry; Biodiversity, Earth, and Environmental Science (BEES)
- Identifiers
- 991020836499704721