Drivers of Carbon Isotopic Fractionation in a Coral Reef Lagoon: Predominance of Demand over Supply

Authors

Matheus C. Carvalho, Southern Cross University - Lismore, Australia
Isaac R. Santos, Southern Cross University - Lismore, Australia
Damien T. Maher, Southern Cross University - Lismore, Australia
Tyler Cyronak, Southern Cross University - Lismore, AustraliaFollow
Ashly McMahon, Southern Cross University - Lismore, Australia
Kai G. Schulz, Southern Cross University - Lismore, Australia
Bradley D. Eyre, Southern Cross University - Lismore, Australia

Document Type

Article

Publication Date

3-15-2015

Publication Title

Geochimica et Cosmochimica Acta

ISSN

0016-7037

Volume

153

First Page

105

Last Page

115

Abstract

The carbon isotopic signature (δ13C) of coral skeletons is influenced by isotopic fractionation (ε_org) during photosynthetic dissolved inorganic carbon (DIC) fixation, but only a few direct ε_org measurements are available in coral communities. In particular, observations of ε_org at the ecosystem scale are lacking. Here we present high frequency (hourly) measurements of DIC and its δ¹³C in the water column and benthic chambers in a highly productive coral reef lagoon (Heron Island, Great Barrier Reef, Australia) and apply simple molar balance calculations to infer community ε_org. Variation in εorg was between 3.7‰ and 25.2‰ in the open lagoon, with lower values during the mid-afternoon and higher values in early morning and evening. The ε_org range was broader (0.3–30.1‰) in enclosed benthic chambers with a similar diel pattern. There was a strong correlation between carbon uptake rates and εorg in closed incubations, suggesting that C demand largely controlled εorg. Benthic chamber incubations revealed increased ε_org as water circulation increased, implying that C supply to photosynthesizing algae on the sediment also influenced ε_org. Hysteresis in carbon uptake through the day complicated the expected straightforward influence of irradiance on C demand, and consequently on ε_org. These results highlight the need for more in depth understanding on carbon uptake rates to fully understand δ¹³C variation in coral paleo-records.

Comments

©2015 Elsevier Ltd. All rights reserved.

Additional Comments

ARC Discovery grant #: DP110103638; ARC Linkage Infrastructure, Equipment and Facilities grant #: LE0668495

NSUWorks Citation

Matheus C. Carvalho, Isaac R. Santos, Damien T. Maher, Tyler Cyronak, Ashly McMahon, Kai G. Schulz, and Bradley D. Eyre. 2015. Drivers of Carbon Isotopic Fractionation in a Coral Reef Lagoon: Predominance of Demand over Supply .Geochimica et Cosmochimica Acta : 105 -115. https://nsuworks.nova.edu/occ_facarticles/1022.

ORCID ID

0000-0003-3556-7616

DOI

10.1016/j.gca.2015.01.012