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From temporal variability to integrated metabolic balance: interpreting total alkalinity and dissolved inorganic carbon relationships in dynamic coral reef ecosystems

Tyler Cyronak, Yuichiro Takeshita, Rebecca Albright, Ken Caldeira, Bradley Eyre, Alyssa Griffin, David A. Koweek, Jennifer Mallon, Manoela Romano de Orte, Kai G. Schulz, and Kennedy Wolfe · Limnology and Oceanography Letters 11, e70155 · 2026

Key finding. Using high-frequency carbonate chemistry from an Australian reef flat together with numerical models, the slope of total alkalinity against dissolved inorganic carbon is shown to reflect the temporal co-variability of calcification and production rather than their time-integrated ratio — so the standard inference of reef metabolic balance from that slope does not hold without offshore reference conditions to anchor it.

A scatter plot of total alkalinity, 2240 to 2340 micromoles per kilogram, against dissolved inorganic carbon, 1850 to 2200. Grey circles are daytime measurements and black circles night-time ones, joined by faint lines into individual day-night tracks. A solid regression line runs through the cloud, crossing two dashed reference lines at an open diamond marking the offshore reference condition. An inset histogram shows the probability distribution of start-to-end slopes, peaked near zero and spanning roughly minus 2 to plus 2.
Each faint line is one day-night track across the reef flat, and their individual slopes vary far more than a single metabolic ratio would allow. The open diamond is the offshore reference water — without it there is nothing to anchor these excursions to, which is the paper's point about what the regression slope can and cannot tell you. Figure 2 from Cyronak et al. (2026), Limnology and Oceanography Letters 11, e70155. Reproduced under CC BY 4.0. Extracted from the published PDF and resized for web display.

What question did this research address?

Whether a coral reef is building carbonate faster than it dissolves it is usually inferred from seawater chemistry rather than measured directly. Plotting total alkalinity against dissolved inorganic carbon and taking the slope is the standard method, and that slope is read as the ratio of net ecosystem calcification to net ecosystem production.

That reading assumes the slope carries time-integrated information about the ecosystem. But both processes swing strongly over the day-night cycle, and the chemistry of the water arriving on the reef is not fixed either. This paper asked whether the slope means what the literature takes it to mean.

What did we find?

The slope measures co-variability, not ratio. How calcification and production move together through time governs the slope, and two reefs with the same metabolic ratio can produce different slopes if their processes are phased differently over the day.

Recovering the time-integrated ratio is still possible, but it takes more than the reef measurements themselves: diel observations have to be coupled with offshore reference conditions, which anchor the changes in alkalinity and inorganic carbon to an actual calcification-to-production ratio.

Metabolic balance is not a fixed property of a reef. It shifts systematically across the diel cycle and depends on light, so a single number describing a reef's balance is a time-average of something that is continuously moving.

The starting chemistry of the water matters as much as what the reef does to it, which is why analyses that omit the offshore end-member can misattribute a change in source water to a change in reef function.

Why does it matter?

Reef carbonate production is being monitored as an indicator of reef health under warming and acidification, and this is the method most of that monitoring uses. If the slope is being interpreted as a metabolic ratio when it is really a measure of co-variability, then a body of published inferences rests on a step that does not follow.

The fix is procedural rather than technological — sample the offshore water as well as the reef — which makes it something existing programmes can adopt without new instruments.

The point generalises beyond reefs. Any dynamic aquatic system where two processes vary together on a fast cycle has the same problem, so distinguishing metabolic co-variability from metabolic ratio is a general caution about reading process ratios off chemistry slopes.

Citation

Tyler Cyronak, Yuichiro Takeshita, Rebecca Albright, Ken Caldeira, Bradley Eyre, Alyssa Griffin, David A. Koweek, Jennifer Mallon, Manoela Romano de Orte, Kai G. Schulz, and Kennedy Wolfe (2026). From temporal variability to integrated metabolic balance: interpreting total alkalinity and dissolved inorganic carbon relationships in dynamic coral reef ecosystems. Limnology and Oceanography Letters 11, e70155.

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