Determining coral reef calcification and primary production using automated alkalinity, pH and pCO2 measurements at high temporal resolution

We investigated coral reef carbonate chemistry dynamics and metabolic rates using an automated system that measured total alkalinity (TA, 30 min intervals), pH on the total scale (pHT, 10 min intervals) and the partial pressure of carbon dioxide (pCO2, 1 min intervals) over 2 weeks at Heron Island (Great Barrier Reef, Australia). The calculation of pHT (using the pCO2 and TA pair) and pCO2 (using the pH and TA pair) had similar values to the measured pHT and pCO2 values. In contrast, calculated TA from the pCO2-pH pair showed a large discrepancy with measured TA (average difference between measured and calculated TA = 52 μmol kg−1). High frequency sampling allowed for detailed analysis of the observations and an assessment of optimum sampling intervals required to characterise the net ecosystem calcification (NEC) and production (NEP) using a slack water approach. Depending on the sampling interval (30 min–2 h time steps) used for calculations, the estimated daily NEC and NEP could differ by 12% and 30%, respectively. Abrupt changes in both NEC and NEP were observed at dawn and dusk, with positive NEC during these periods despite negative NEP. Integrating NEC and NEP over a full diel cycle using 1 or 2 h integration time steps resulted in small differences of 2–7% for NEC and 1–3% for NEP. A diel hysteresis pattern rather than a simple linear relationship was observed between the aragonite saturation state (Ωar) and NEC. The observed hysteresis supports recent studies suggesting that short-term observations of seawater Ωar may not be a good predictor of long-term changes in NEC due to ocean acidification. The slope of the DIC to TA relationship was slightly higher (0.33) in 2014 than in an earlier study in 2012 (0.30). The automated, high frequency sampling approach employed here can deliver high precision data and can be used at other coral reef research stations to reveal long-term changes in NEC and NEP potentially driven by ocean acidification, eutrophication or other local changes.

McMahon A., Santos I. R., Schulz K. G., Cyronak T. & Maher D. T., in press. Determining coral reef calcification and primary production using automated alkalinity, pH and pCO2 measurements at high temporal resolution. Estuarine, Coastal and Shelf Science. Article (subscription required).

0 Responses to “Determining coral reef calcification and primary production using automated alkalinity, pH and pCO2 measurements at high temporal resolution”



  1. Leave a Comment

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s




Subscribe to the RSS feed

Powered by FeedBurner

Follow AnneMarin on Twitter

Blog Stats

  • 1,082,959 hits

OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book