High-Frequency Dynamics of Ocean pH: A Multi-Ecosystem Comparison

TLDR

Ocean acidification effects on marine life are poorly predictable because chronic, species‑specific pH data are lacking. The study compiles continuous, high‑resolution upper‑ocean pH time series from diverse ecosystems to enable hypothesis testing and guide management of acidification refugia. Autonomous sensors collected these time series, providing spatial and temporal pH variation that informs the design of OA experiments by setting tolerance guardrails based on natural exposure ranges. The data reveal month‑long pH variability with SDs of 0.004–0.277, ranges of 0.024–1.430 units, site‑dependent diel and stochastic patterns, and show that many organisms already experience pH regimes beyond 2100 projections, linking exposure history to resilience.

Abstract

The effect of Ocean Acidification (OA) on marine biota is quasi-predictable at best. While perturbation studies, in the form of incubations under elevated pCO2, reveal sensitivities and responses of individual species, one missing link in the OA story results from a chronic lack of pH data specific to a given species' natural habitat. Here, we present a compilation of continuous, high-resolution time series of upper ocean pH, collected using autonomous sensors, over a variety of ecosystems ranging from polar to tropical, open-ocean to coastal, kelp forest to coral reef. These observations reveal a continuum of month-long pH variability with standard deviations from 0.004 to 0.277 and ranges spanning 0.024 to 1.430 pH units. The nature of the observed variability was also highly site-dependent, with characteristic diel, semi-diurnal, and stochastic patterns of varying amplitudes. These biome-specific pH signatures disclose current levels of exposure to both high and low dissolved CO2, often demonstrating that resident organisms are already experiencing pH regimes that are not predicted until 2100. Our data provide a first step toward crystallizing the biophysical link between environmental history of pH exposure and physiological resilience of marine organisms to fluctuations in seawater CO2. Knowledge of this spatial and temporal variation in seawater chemistry allows us to improve the design of OA experiments: we can test organisms with a priori expectations of their tolerance guardrails, based on their natural range of exposure. Such hypothesis-testing will provide a deeper understanding of the effects of OA. Both intuitively simple to understand and powerfully informative, these and similar comparative time series can help guide management efforts to identify areas of marine habitat that can serve as refugia to acidification as well as areas that are particularly vulnerable to future ocean change.