Ocean acidification in the Bering Sea: comparing and contrasting two recent studies
Two recent science publications have calculated acidification rates in the Bering Sea over the past several decades. The first study, led by scientists at the University of Rhode Island (URI), compiled a large dataset of ship-based observations and used a statistical technique to extrapolate that data to the entire region. The second study, led by scientists at the University of Washington (UW) and NOAA Pacific Marine Environmental Laboratory, used a computational ocean model to simulate the Bering Sea.
Both studies found that surface waters on the Bering Sea shelf have acidified over the past several decades due to carbon accumulation in the ocean (i.e. ocean acidification). Further, both found a comparable rate of pH decline that is also close to the rate of global ocean pH decline due to ocean acidification.
Bering Sea sunset. Image by Freepik
However, the URI study also found that the Bering Sea was acidifying less quickly than neighboring waters to both the south (North Pacific Ocean) and the north (Western Arctic Ocean). The study attributed this relatively lower acidification to increasing plankton productivity, which absorbs some of the accumulated carbon in surface waters. Meanwhile, the faster acidification rates in the Western Arctic Ocean were attributed to decreasing sea ice and increasing freshwater river runoff.
The URI study also noted a much lower rate of decrease in surface aragonite saturation state (Ωarag), compared to both the UW model study and the global rate of Ωarag decline. Aragonite is a soluble form of calcium carbonate which marine calcifying organisms such as pteropods use to build and maintain their shells. Alaskan waters are naturally low in Ωarag compared to other areas of the ocean, thus any further declines due to ocean acidification can tip the system towards aragonite dissolution (hard for shell-builders!). Thus, the different rates of Ωarag decline between the two studies can have large implications for when surface waters pass this tipping point and highlights the need for additional study.
While the URI study only tracked surface water conditions, the UW model study tracked the full water column. The UW study found that Bering Sea shelf bottom waters are acidifying at nearly 3 times the rate as surface waters. This is because bottom waters have a lower buffer capacity than surface waters, so the same amount of carbon added can yield a much greater change. Further, the increasing plankton productivity for the Bering Sea noted by both studies can also generate more acidic bottom waters when that biological material sinks to the bottom and is respired. Tracking bottom water acidification is especially important for red king crab since laboratory experiments have shown decreasing growth and survival under lower pH conditions.
Read the studies:
Title: Pacific-Arctic Ocean acidification: Decadal trends and drivers. (URI study)
Publication: Global Biogeochemical Cycles. April 2025
Authors: Thomas Caero, Hongie Wang, Annika Jersild
Title: Amplified bottom water acidification rates on the Bering Sea shelf from 1970-2022.(UW study)
Publication: Biogeosciences, July 2025
Authors: Darren Pilcher, Jessica Cross, Natalie Monacci, Linquan Mu, Kelly Kearney, Albert Herman, Wei Cheng
Fig 1: The map above shows the trend in surface water pH values modeled by Caero et al (URI study) for the time period 2003 – 2021. Areas of blue indicate a decrease in pH and areas of red show an increase in pH. Gray shows no statistically significant trend.
Fig. 2: The graph above shows the decreasing trend in the annual average pH of Bering Sea bottom water for the time period 1970-2022, modeled by Pilcher et al (UW study). The bottom pH values are approaching 7.8 which is a level demonstrated to negatively affect growth and survival of red king crab. Because these are averaged over the year, it is likely that pH is below 7.8 during portions of the year.
Fig 3: The maps show the trend of surface and bottom pH from 1970-2022 modeled by UW. Darker colors indicate a larger decrease in pH (increase in acidity). The study found that Bering Sea shelf bottom waters (right) are acidifying at nearly three times the rate as surface waters (left).