Ocean Acidification Background Context

This short post is drawn from the introductory section of essay Shell Games in my ebook Blowing Smoke, foreword from Prof. Judith Curry of Georgia Tech. The thrust of that essay was scientific misconduct by Fabricius concerning Milne Bay coral reefs and by PMEL concerning the Netarts Bay oyster hatchery. Both were hyped by a deeply misleading ‘fake news’ climate alarm series in the Seattle Times. This redrafted and reillustrated essay introduction section concerns neither of those misconduct examples. As discussed with Charles the Moderator, it hopefully accomplishes two things I have not seen at WUWT despite being a regular contributor and reader since 2011. First, it provides seawater chemistry basics with ‘deep dive’ links. Second, it sets that basic understanding against published pH measurements and background ocean biology, something even Jim Steele’s excellent coral posts did not fully provide.

Obiter dictum. We acknowledge that seawater is basic and cannot truly acidify (pH<7). But that is a losing semantic quibble, not a winning skeptical argument. The generally accepted linguistic convention—for better or worse–is that lowering seawater pH means ‘acidification’. There is no doubt that adding dissolved CO2 does lower pH. The relevant questions are how much and whether that amount matters. This post answers both questions (a little, not much) without the two specific false alarms that motivated the ebook version.

There are certainly some ocean related AGW consequences beyond any scientific doubt. Henry’s Law requires that the partial pressures of atmospheric and dissolved ocean CO2 equilibrate. Rising atmospheric CO2 must increase dissolved seawater CO2. That is long established simple physical chemistry.

This lowers pH by increasing carbonic acid. NOAA PMEL has documented this in the central Pacific at Station Aloha off Mauna Loa where sea surface pH has declined from 8.11 to 8.07 since 1991, as dissolved pCO2 increased from ≈325 to ≈360μatm while atmospheric CO2 increased from about 355 to 395 ppm. That is Δ0.04 pH in 24 years.


But for two reasons, Station Aloha cannot be linearly extrapolated into the future as IPCC AR4 erroneously did. First and foremost, ocean pH is not a linear chemical system driven only by Henry’s law; it is a system highly buffered by dissolved minerals and seafloor carbonates. Taking seawater chemical buffering into account, IPCC AR5 3.8.2 suggested that doubled atmospheric CO2 might cause surface pH to decline by Δ0.15-0.2, less than half of AR4. This is well within the normal diurnal and seasonal biological seawater pH variation for almost all ocean waters. It is no cause for the alarms sounded by the Seattle Times series Sea Change.

Ocean surface pH is not uniform. It varies diurnally, seasonally, by ecosystem, and by underlying ocean depth. At the deep ocean and biologically barren PMEL Station Aloha site north of tropical Hawaii, seasonal surface variation is only Δ0.1 pH. Moderately fertile Southern Ocean surface seasonality is Δ0.5 pH. Seasonal surface variation is as high as biologically fertile Δ1.43 pH depending on which of and where the Pacific’s 8 biological marine ecosystems are evaluated.[i]


How marine creatures do under experimental aquarium conditions of roughly doubled CO2 (with food, light, and temperature held constant) depends on species. [ii] Crustaceans, temperate urchins, calcifying (coralline) algae, limpets, and mussels do well. Oysters, conch, bay scallops, and some tropical corals don’t. But aquariums do not reflect the important interplay of many other ecosystem factors also affecting these creatures.

For a specific example, Florida Bay conchs thrive amidst complex interactions between seasonal pH and salinity that drive extreme pH swings, even though Woods Hole aquarium studies suggest they should not. The Everglades mangrove fringe in Florida Bay has a low salinity winter pH 5.8 yet serves as a crucial ‘predator safe’ nursery ecosystem for many Florida Bay marine species. Yet toward Key West (the ‘Conch Republic’) pH peaks as high as 9.8 during sunny summer days with elevated (from evaporation) salinity.[iii] The maximum geographic separation is just 90 miles, the average only 25 miles. Such extreme pH changes come from Thallassia sea grass photosynthesis consuming dissolved CO2, plus evaporative high salinity (>50ppt) driving calcium carbonate precipitation. Florida Bay demonstrates the enormous variability and resilience of actual marine ecosystem biodiversity.


Florida Bay. Photo courtesy South Florida Water Management District


[i] Hofmann et. al., High-frequency dynamics of ocean pH: a multi ecosystem comparison, PLoS One 6: e28983 (2011)

[ii] Oceanus 48 (2010), the Woods Hole Oceanographic Institution publication.

[iii] NOAA/National Park Service Joint Report: NOAA Technical Memorandum NOS NCCOS CCMA154, same as NPS Special Report 01-02. Page 64.

via Watts Up With That?


December 23, 2018 at 04:09PM

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