Ocean acidification (OA) is expected to reduce the calcification rates of marine organisms, yet we have little understanding of how OA will manifest within dynamic, real-world systems. Natural CO(2), ...alkalinity, and salinity gradients can significantly alter local carbonate chemistry, and thereby create a range of susceptibility for different ecosystems to OA. As such, there is a need to characterize this natural variability of seawater carbonate chemistry, especially within coastal ecosystems. Since 2009, carbonate chemistry data have been collected on the Florida Reef Tract (FRT). During periods of heightened productivity, there is a net uptake of total CO(2) (TCO(2)) which increases aragonite saturation state (Ω(arag)) values on inshore patch reefs of the upper FRT. These waters can exhibit greater Ω(arag) than what has been modeled for the tropical surface ocean during preindustrial times, with mean (± std. error) Ω(arag)-values in spring = 4.69 (±0.101). Conversely, Ω(arag)-values on offshore reefs generally represent oceanic carbonate chemistries consistent with present day tropical surface ocean conditions. This gradient is opposite from what has been reported for other reef environments. We hypothesize this pattern is caused by the photosynthetic uptake of TCO(2) mainly by seagrasses and, to a lesser extent, macroalgae in the inshore waters of the FRT. These inshore reef habitats are therefore potential acidification refugia that are defined not only in a spatial sense, but also in time; coinciding with seasonal productivity dynamics. Coral reefs located within or immediately downstream of seagrass beds may find refuge from OA.
Aragonite saturation state (Ωarag) in surface and subsurface waters of the global oceans was calculated from up‐to‐date (through the year of 2012) ocean station dissolved inorganic carbon (DIC) and ...total alkalinity (TA) data. Surface Ωarag in the open ocean was always supersaturated (Ω > 1), ranging between 1.1 and 4.2. It was above 2.0 (2.0–4.2) between 40°N and 40°S but decreased toward higher latitude to below 1.5 in polar areas. The influences of water temperature on the TA/DIC ratio, combined with the temperature effects on inorganic carbon equilibrium and apparent solubility product (K′sp), explain the latitudinal differences in surface Ωarag. Vertically, Ωarag was highest in the surface mixed layer. Higher hydrostatic pressure, lower water temperature, and more CO2 buildup from biological activity in the absence of air‐sea gas exchange helped maintain lower Ωarag in the deep ocean. Below the thermocline, aerobic decomposition of organic matter along the pathway of global thermohaline circulation played an important role in controlling Ωarag distributions. Seasonally, surface Ωarag above 30° latitudes was about 0.06 to 0.55 higher during warmer months than during colder months in the open‐ocean waters of both hemispheres. Decadal changes of Ωarag in the Atlantic and Pacific Oceans showed that Ωarag in waters shallower than 100 m depth decreased by 0.10 ± 0.09 (−0.40 ± 0.37% yr−1) on average from the decade spanning 1989–1998 to the decade spanning 1998–2010.
Key Points
Climatological aragonite saturation in surface and subsurface global oceans are presented
Mechanisms controlling aragonite saturation state distributions are discussed
Subannual and decadal changes of aragonite saturation state are presented
Syntheses of carbonate chemistry spatial patterns are important for predicting ocean acidification impacts, but are lacking in coastal oceans. Here, we show that along the North American Atlantic and ...Gulf coasts the meridional distributions of dissolved inorganic carbon (DIC) and carbonate mineral saturation state (Ω) are controlled by partial equilibrium with the atmosphere resulting in relatively low DIC and high Ω in warm southern waters and the opposite in cold northern waters. However, pH and the partial pressure of CO
(pCO
) do not exhibit a simple spatial pattern and are controlled by local physical and net biological processes which impede equilibrium with the atmosphere. Along the Pacific coast, upwelling brings subsurface waters with low Ω and pH to the surface where net biological production works to raise their values. Different temperature sensitivities of carbonate properties and different timescales of influencing processes lead to contrasting property distributions within and among margins.
The global oceans serve as the largest sustained natural sink for increasing atmospheric carbon dioxide (CO2) concentrations. As this CO2 is absorbed by seawater, it not only reacts causing a ...reduction in seawater pH (or acidification) but also decreases the carbonate mineral saturation state (Ω), which plays an important role in calcification for many marine organisms. Ocean acidification could affect some of the most fundamental biological and geochemical processes of the sea in coming decades. Observations obtained in situ from Volunteer Observing Ships and multiple geochemical surveys have been extended using satellite remote sensing and modeled environmental parameters to derive estimates of sea‐surface alkalinity (AT) and carbon dioxide partial pressure (pCO2,sw). Pairing estimates of AT and pCO2,sw have permitted characterization of the changes in sea‐surface Ω, which have transpired over the past decade throughout the Greater Caribbean Region as a consequence of ocean acidification. The results reveal considerable spatial and temporal variability throughout the region. Despite this variability, we observed a strong secular decrease in aragonite saturation state (Ωarg) at a rate of approximately −0.012 ± 0.001 Ωarg yr−1 (r2 = 0.97, P < 0.001).
New England coastal and adjacent Nova Scotia shelf waters have a reduced buffering capacity because of significant freshwater input, making the region's waters potentially more vulnerable to coastal ...acidification. Nutrient loading and heavy precipitation events further acidify the region's poorly buffered coastal waters. Despite the apparent vulnerability of these waters, and fisheries' and mariculture's significant dependence on calcifying species, the community lacks the ability to confidently predict how the region's ecosystems will respond to continued ocean and coastal acidification. Here, we discuss ocean and coastal acidification processes specific to New England coastal and Nova Scotia shelf waters and review current understanding of the biological consequences most relevant to the region. We also identify key research and monitoring needs to be addressed and highlight existing capacities that should be leveraged to advance a regional understanding of ocean and coastal acidification.
Time of Emergence (ToE) is the time when a signal emerges from the noise of natural variability. Commonly used in climate science for the detection of anthropogenic forcing, this concept has recently ...been applied to geochemical variables to assess the emerging times of anthropogenic ocean acidification (OA) mostly in the open ocean using global climate and Earth System Models. Yet studies of OA variables are scarce within costal margins, due to limited multidecadal time-series observations of carbon parameters. ToE provides important information for decision making regarding strategic configuration of observing assets to ensure they are optimally positioned either for signal detection and/or process elicitation and to identify the most suitable variables in discerning OA-related changes. Herein, we present a short overview of ToE estimates on an OA variable, CO2 fugacity ƒ(CO2,sw), in the North American ocean margins using coastal data from Surface Ocean CO2 Atlas (SOCAT) V5. ToE suggests an average theoretical timeframe for an OA signal to emerge of 23(±13) years, but with considerable spatial variability. Most coastal areas are experiencing additional secular and/or multi-decadal forcing(s) that modifies the OA signal, and such forcing may not be sufficiently resolved by current observations. We provide recommendations that will help scientists and decision makers design and implement OA monitoring systems in the next decade addressing the objectives of OceanObs19 in support of the United Nations Decade of Ocean Science for Sustainable Development (2021-2030) and the Sustainable Development Goal (SDG) 14.3 Target to “Minimize and address the impacts of OA ”.
Sedimentary basins can contain close to 20% by volume of pore fluids commonly classified as brines. These fluids can become undersaturated with respect to calcite as a result of migration, dispersive ...mixing, or anthropogenic injection of CO
2. This study measured calcite dissolution rates in geologically relevant Na–Ca–Mg–Cl synthetic brines (50–200
g
L
−1 TDS). The dissolution rate dependency on brine composition, pCO
2 (0.1–1
bar), and temperature (25.0–82.5
°C) was modeled using the empirical rate equation
R
=
k
(
1
-
Ω
)
n
where
R is the rate,
k and
n are empirical fitting terms and 1
−
Ω the degree of disequilibrium with respect to calcite. When
Ω is defined relative to an apparent steady-state solubility,
n can be assumed first-order over the range of
Ω investigated (
Ω
=
0.2–1.0). Rates increased with increasing pCO
2 as did its sensitivity to increased brine total dissolved salt (TDS) concentration. At 0.1
bar, rates were nearly independent of the TDS (
k
=
13.0
±
2.0
×
10
−3
mol
m
−1
h
−1). However, at higher CO
2 partial pressures, rates became composition dependent and the rate constant,
k, was shown to be a function of temperature, pCO
2, ionic strength and calcium and magnesium activity. The rate constant (
k) can be estimated from a multiple regression (MR) model of the form
k
=
β
0
+
β
1
(
t
)
+
β
2
(
pCO
2
)
+
β
3
(
I
)
+
β
4
a
Ca
2
+
+
β
5
a
Mg
2
+
.
A relatively high activation energy (
E
a
=
20
kJ
mol
−1) was measured, along with a stirring rate independence suggesting that the dissolution is dominated by surface-controlled processes at
Ω
>
0.2 in these calcium-rich brines. The addition of 1
g
L
−1
SO
4
2
-
resulted in a rate inhibition that was highly sensitive to increasing concentrations of calcium and magnesium. Consequently, even though sulfate concentrations in subsurface formation waters are generally less than that in seawater, at TDS concentrations greater than 200
g
L
−1, its effect on the rate may be of similar magnitude. These findings provide an opportunity to improve reaction-transport models in carbonate-bearing saline reservoirs, where pCO
2 is >0.1
atm (pH
<
∼6.5), by adding considerably more realistic reaction kinetics. This will be of considerable importance in modeling of CO
2 sequestration in carbonate-hosted reservoirs.
Ocean acidification causes declines in calcification rates of corals because of decreasing aragonite saturation states (Ω(arag)). Recent evidence also indicates that increasing sea surface ...temperatures may have already reduced growth and calcification rates because of the stenothermic threshold of localized coral populations. Density banding in coral skeletons provides a record of growth over the coral's lifespan. Here we present coral extension, bulk density and calcification master chronologies from seven subtropical corals (Montastraea faveolata) located in the Florida Keys, USA with a 60-year common period, 1937-1996. Linear trends indicate that extension increased, density decreased and calcification remained stable while the most recent decade was not significantly different than decadal averages over the preceding 50 years for extension and calcification. The results suggest that growth rates in this species of subtropical coral have been tolerant to recent climatic changes up to the time of collection (1996).
A successful integrated ocean acidification (OA) observing network must include 1) scientists and technicians from a range of disciplines (from physics to chemistry to biology to technology ...development) and across the globe; 2) government, private, and intergovernmental support; 3) regional cohorts working together on regionally specific issues; 4) publicly accessible data from the open ocean to coastal to estuarine systems; 5) close integration with other networks focusing on related measurements or issues including the social and economic consequences of OA; and 6) observation-based informational products useful for decision making such as management of fisheries and aquaculture. The Global Ocean Acidification Observing Network (GOA-ON), a key player in this vision, seeks to expand and enhance geographic extent and availability of coastal and open ocean observing data to ultimately inform adaptive measures and policy action, especially in support of the United Nations 2030 Agenda for Sustainable Development. GOA-ON works to empower and support regional collaborative networks such as the Latin American Ocean Acidification Network, supports new scientists entering the field with training, mentorship, and equipment, refines approaches for tracking biological impacts, and stimulates development of lower-cost methodology and technologies allowing for wider participation of scientists. GOA-ON seeks to collaborate with and complement work done by other observing networks such as those focused on carbon flux into the ocean, tracking of carbon and oxygen in the ocean, observing biological diversity, and determining short- and long-term variability in these and other ocean parameters through space and time.
To assess the impact of ocean acidification on the carbonate chemistry of the shelf waters off the southeastern United States (South Atlantic Bight SAB), we measured carbonate mineral saturation ...states from January 2005 to May 2006. The findings reveal that aragonite (Ωarag: 2.6-4.0) and calcite (Ωcal: 4.1-6.0) saturation states were considerably higher than those recently reported along the West Coast of North America. Different water mass age between the Atlantic and Pacific Oceans during global ocean circulation is the primary reason for the higher carbonate mineral saturation states in the SAB than along the West Coast. The contrasting water temperatures in the two coasts contribute to such differences. Both upwelling and freshwater discharge also play important roles in controlling saturation state. Carbonate mineral saturation in the surface water of the West Coast is strongly controlled by the upwelling of high-salinity, low-temperature, low-oxygen, and low-pH deep water. In comparison, saturation states in the surface water of the SAB coast are rarely affected by upwelling. Instead, they are strongly influenced by the input of low-saturation-state water from rivers. Continued increases of atmospheric CO₂ under the Intergovernmental Panel on Climate Change Bl emission scenario will decrease the carbonate mineral saturation states by up to 40% by the end of this century, and aragonite will approach undersaturation near the coast.
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