Moyer RP (2008) Carbon Isotopes (δ13C & Δ14C) and Trace Elements (Ba, Mn, Y) in Small Mountainous Rivers and Coastal Coral Skeletons in Puerto Rico. Ph.D. Dissertation, The Ohio State University, School of Earth Sciences, Columbus, OH. 260pp.
Abstract:
Tropical small mountainous rivers (SMRs) may transport up to 33% of the total
carbon (C) delivered to the oceans. However, these fluxes are poorly quantified and
historical records of land-ocean carbon delivery are rare. Corals have the potential to
provide such records in the tropics because they are long-lived, draw on dissolved
inorganic carbon (DIC) for calcification, and isotopic variations within their skeletons are
useful proxies of palaeoceanographic variability. The ability to quantify riverine C inputs
to the coastal ocean and understand how they have changed through time is critical to
understanding global carbon budgets in the context of modern climate change. A seasonal
dual isotope (13C & 14C) characterization of the three major C pools in two SMRs and
their adjacent coastal waters within Puerto Rico was conducted in order to understand the
isotope signature of DIC being delivered to the coastal oceans. Additionally a 56-year
record of paired coral skeletal C isotopes (δ13C & Δ14C) and trace elements (Ba/Ca,
Mn/Ca, Y/Ca) is presented from a coral growing ~1 km from the mouth of an SMR. Four
major findings were observed: 1) Riverine DIC was more depleted in δ13C and Δ14C than
seawater DIC, 2) the correlation of δ13C and Δ14C was the same in both coral skeleton
and the DIC of the river and coastal waters, 3) Coral δ13C and Ba/Ca were annually
coherent with river discharge, and 4) increases in coral Ba/Ca were synchronous with the
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timing of depletions of both δ13C and Δ14C in the coral skeleton and increases in river
discharge. This study represents a first-order comprehensive C isotope analysis of major
C pools being transported to the coastal ocean via tropical SMRs. The strong coherence
between river discharge and coral δ13C and Ba/Ca, and the concurrent timing of increases
in Ba/Ca with decreases in δ13C and Δ14C suggest that river discharge is simultaneously
recorded by multiple geochemical records. Based on these findings, the development of
coral-based proxies for the history of land-ocean carbon flux would be invaluable to
understanding the role of tropical land-ocean carbon fluxes in the context of global
climate change.