Marine & Environmental Sciences Faculty Proceedings, Presentations, Speeches, Lectures

Drivers of pCO2 Variability in Two Contrasting Coral Reef Lagoons: The Influence of Submarine Groundwater Discharge

Event Name/Location

Australian Marine Sciences Association Golden Jubilee Conference, Gold Coast, Australia, July 7-11, 2013

Presentation Date

7-2013

Document Type

Conference Proceeding

ORCID ID

0000-0003-3556-7616

Description

The drivers behind pCO2 variability in coral reefs need to be elucidated in order to properly assess the impacts of ocean acidification. We show that commonly occurring submarine groundwater discharge (SGD) processes can be a significant source of CO2 to two contrasting coral reef ecosystems. In Rarotonga (Cook Islands), SGD was dominated by a steep hydraulic gradient and fresh groundwater inputs high in pCO2 (5,501 matm). In Heron Island (Great Barrier Reef), SGD was driven by the tidal pumping of seawater into the permeable island and saline groundwater recirculation with a lower pCO2 (1,397 matm). Both lagoons were net sources of CO2 to the atmosphere (3.00 and 9.67 mmol CO2 m-2 d-1). SGD derived CO2 fluxes were at least 3-fold higher than the atmospheric fluxes, and enough to lower the average pH to 7.96 in Rarotonga and 8.04 in Heron Island. The relationships between water column pH and aragonite saturation state (WAr) and radon (222Rn) concentrations indicate that SGD may enhance the local acidification of some coral reef lagoons. Studies measuring the carbon chemistry of coral reefs (e.g. community metabolism, calcification rates) may need to consider SGD-derived CO2.

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