The absorption of atmospheric carbon dioxide (CO₂) into the ocean lowers the pH of the waters. This so-called ocean acidification could have important consequences for marine ecosystems. To better ...understand the extent of this ocean acidification in coastal waters, we conducted hydrographic surveys along the continental shelf of western North America from central Canada to northern Mexico. We observed seawater that is undersaturated with respect to aragonite upwelling onto large portions of the continental shelf, reaching depths of ∼40 to 120 meters along most transect lines and all the way to the surface on one transect off northern California. Although seasonal upwelling of the undersaturated waters onto the shelf is a natural phenomenon in this region, the ocean uptake of anthropogenic CO₂ has increased the areal extent of the affected area
Puget Sound is a large estuary complex in the U.S. Pacific Northwest that is home to a diverse and economically important ecosystem threatened by anthropogenic impacts associated with climate change, ...urbanization, and ocean acidification. While ocean acidification has been studied in oceanic waters, little is known regarding its status in estuaries. Anthropogenically acidified coastal waters upwelling along the western North American continental margin can enter Puget Sound through the Strait of Juan de Fuca. In order to study the combined effects of ocean acidification and other natural and anthropogenic processes on Puget Sound waters, we made the first inorganic carbon measurements in this estuary on two survey cruises in February and August of 2008. Observed pH and aragonite saturation state values in surface and subsurface waters were substantially lower in parts of Puget Sound than would be expected from anthropogenic carbon dioxide (CO
2) uptake alone. We estimate that ocean acidification can account for 24–49% of the pH decrease in the deep waters of the Hood Canal sub-basin of Puget Sound relative to estimated pre-industrial values. The remaining change in pH between when seawater enters the sound and when it reaches this deep basin results from remineralization of organic matter due to natural or anthropogenically stimulated respiration processes within Puget Sound. Over time, however, the relative impact of ocean acidification could increase significantly, accounting for 49–82% of the pH decrease in subsurface waters for a doubling of atmospheric CO
2. These changes may have profound impacts on the Puget Sound ecosystem over the next several decades. These estimates suggest that the role ocean acidification will play in estuaries may be different from the open ocean.
Surface ocean carbon chemistry is changing rapidly. Partial pressures of carbon dioxide gas (pCO2) are rising, pH levels are declining, and the ocean's buffer capacity is eroding. Regional ...differences in short‐term pH trends primarily have been attributed to physical and biological processes; however, heterogeneous seawater carbonate chemistry may also be playing an important role. Here we use Surface Ocean CO2 Atlas Version 4 data to develop 12 month gridded climatologies of carbonate system variables and explore the coherent spatial patterns of ocean acidification and attenuation in the ocean carbon sink caused by rising atmospheric pCO2. High‐latitude regions exhibit the highest pH and buffer capacity sensitivities to pCO2 increases, while the equatorial Pacific is uniquely insensitive due to a newly defined aqueous CO2 concentration effect. Importantly, dissimilar regional pH trends do not necessarily equate to dissimilar acidity (H+) trends, indicating that H+ is a more useful metric of acidification.
Key Points
Chemical thermodynamics imparts a coherent spatial pattern of carbonate chemistry responses to anthropogenic carbon accumulation
Nonuniform ocean acidification is anticipated with rising sea surface pCO2
The use of H+ trends rather than pH trends is necessary to accurately decipher regional differences in ocean acidity change
It has become clear that anthropogenic carbon invasion into the surface ocean drives changes in the seasonal cycles of carbon dioxide partial pressure (pCO2) and pH. However, it is not yet known ...whether the resulting sea‐air CO2 fluxes are symmetric in their seasonal expression. Here we consider a novel application of observational constraints and modeling inferences to test the hypothesis that changes in the ocean's Revelle factor facilitate a seasonally asymmetric response in pCO2 and the sea‐air CO2 flux. We use an analytical framework that builds on observed sea surface pCO2 variability for the modern era and incorporates transient dissolved inorganic carbon concentrations from an Earth system model. Our findings reveal asymmetric amplification of pCO2 and pH seasonal cycles by a factor of two (or more) above preindustrial levels under Representative Concentration Pathway 8.5. These changes are significantly larger than observed modes of interannual variability and are relevant to climate feedbacks associated with Revelle factor perturbations. Notably, this response occurs in the absence of changes to the seasonal cycle amplitudes of dissolved inorganic carbon, total alkalinity, salinity, and temperature, indicating that significant alteration of surface pCO2 can occur without modifying the physical or biological ocean state. This result challenges the historical paradigm that if the same amount of carbon and nutrients is entrained and subsequently exported, there is no impact on anthropogenic carbon uptake. Anticipation of seasonal asymmetries in the sea surface pCO2 and CO2 flux response to ocean carbon uptake over the 21st century may have important implications for carbon cycle feedbacks.
Plain Language Summary
The ocean uptake of human released carbon dioxide (CO2) is causing the natural seasonal swings in seawater CO2 to grow over time. Using observations and numerical models, we conduct a theoretical experiment to see how the surface ocean may respond to continued carbon additions under “business‐as‐usual” future atmospheric CO2 concentrations. We find that between 1861 and 2100, the chemical properties of CO2 in seawater cause the seasonal CO2 maximum to grow by more than the seasonal CO2 minimum. As a result, the rate of summer surface ocean CO2 growth is different than winter, requiring year‐round observations to accurately measure the overall annual ocean carbon absorption. Additionally, these seasonal CO2 changes affect how much carbon is lost from the ocean during high‐CO2 periods relative to how much carbon is gained from the atmosphere during low‐CO2 periods, creating a trend in the average ocean carbon absorption over years to decades that must be considered in the interpretation of marine carbon cycle observations and numerical models. These findings are important as they have implications for future rates of climate change and ocean acidification.
Key Points
Asymmetric amplification of surface ocean pCO2 and pH seasonal cycles is anticipated over the 21st century under RCP8.5
Expected seasonal asymmetries highlight ongoing challenges with using a summer‐biased observing network to estimate anthropogenic trends
Projecting onto Revelle factor perturbations, the pCO2 seasonal cycle response may have important implications for carbon cycle feedbacks
The oceanic sink for anthropogenic CO 2 from 1994 to 2007 Gruber, Nicolas; Clement, Dominic; Carter, Brendan R ...
Science (American Association for the Advancement of Science),
03/2019, Letnik:
363, Številka:
6432
Journal Article
Recenzirano
Odprti dostop
We quantify the oceanic sink for anthropogenic carbon dioxide (CO
) over the period 1994 to 2007 by using observations from the global repeat hydrography program and contrasting them to observations ...from the 1990s. Using a linear regression-based method, we find a global increase in the anthropogenic CO
inventory of 34 ± 4 petagrams of carbon (Pg C) between 1994 and 2007. This is equivalent to an average uptake rate of 2.6 ± 0.3 Pg C year
and represents 31 ± 4% of the global anthropogenic CO
emissions over this period. Although this global ocean sink estimate is consistent with the expectation of the ocean uptake having increased in proportion to the rise in atmospheric CO
, substantial regional differences in storage rate are found, likely owing to climate variability-driven changes in ocean circulation.
For over two decades, NOAA’s Pacific Marine Environmental Laboratory (PMEL) has been developing and deploying autonomous ocean carbon measurement technologies. PMEL currently maintains a network of ...air-sea CO₂ and ocean acidification time-series measurements on 33 surface buoys, including the world’s longest record of air-sea CO₂ measured from a buoy. These sites are located in every ocean basin and in a variety of ecosystems, from coastal to open ocean and subpolar to tropical. The network provides more than half of today’s ocean carbonate chemistry timeseries records that qualify as long-term, publicly available, and collected at subseasonal timescales. Here, we briefly review the motivation for establishing the network, the research and applications made possible from the observations, and how sustained autonomous time series generate unique information about a changing ocean needed to inform mitigation and adaptation approaches in a changing world.
A significant impetus for recent ocean biogeochemical research has been to better understand the ocean's role as a sink for anthropogenic CO2. In the 1990s the global carbon survey of the World Ocean ...Circulation Experiment (WOCE) and the Joint Global Ocean Flux Study (JGOFS) inspired the development of several approaches for estimating anthropogenic carbon inventories in the ocean interior. Most approaches agree that the total global ocean inventory of Cant was around 120 Pg C in the mid-1990s. Today, the ocean carbon uptake rate estimates suggest that the ocean is not keeping pace with the CO2 emissions growth rate. Repeat occupations of the WOCE/JGOFS survey lines consistently show increases in carbon inventories over the last decade, but have not yet been synthesized enough to verify a slowdown in the carbon storage rate. There are many uncertainties in the future ocean carbon storage. Continued observations are necessary to monitor changes and understand mechanisms controlling ocean carbon uptake and storage in the future.
Good news and bad news of blue carbon Sabine, Christopher L.
Proceedings of the National Academy of Sciences - PNAS,
04/2018, Letnik:
115, Številka:
15
Journal Article
Recenzirano
Odprti dostop
Traditionally, ocean acidification researchers have focused on how secular changes in carbon dioxide or pH will impact organisms. Global mean pH is estimated to have decreased by 0.1 pH units ...(representing a 28% increase in acidity) since the preindustrial age and may drop another 0.3 pH units by the end of this century. Several recent papers, however, have highlighted the importance of understanding changes in the short-term variability in carbon parameters in addition to the secular trends. An article in PNAS by Pacella et al. examines how net community metabolism (NCM) in a coastal seagrass bed can help slow the long-term secular change in ocean acidification but exacerbates the short-term variations in carbon system parameters. These short-term variations can drive the pH or the saturation state of the waters with respect to aragonite below a threshold for certain organisms that may prevent them from ever benefitting from the long-term relief.
The continental shelf region off the west coast of North America is seasonally exposed to water with a low aragonite saturation state by coastal upwelling of CO2-rich waters. To date, the spatial and ...temporal distribution of anthropogenic CO2 (Canth) within the CO2-rich waters is largely unknown. Here we adapt the multiple linear regression approach to utilize the GO-SHIP Repeat Hydrography data from the northeast Pacific to establish an annually updated relationship between Canth and potential density. This relationship was then used with the NOAA Ocean Acidification Program West Coast Ocean Acidification (WCOA) cruise data sets from 2007, 2011, 2012, and 2013 to determine the spatial variations of Canth in the upwelled water. Our results show large spatial differences in Canth in surface waters along the coast, with the lowest values (37–55 μmol kg−1) in strong upwelling regions off southern Oregon and northern California and higher values (51–63 μmol kg−1) to the north and south of this region. Coastal dissolved inorganic carbon concentrations are also elevated due to a natural remineralized component (Cbio), which represents carbon accumulated through net respiration in the seawater that has not yet degassed to the atmosphere. Average surface Canth is almost twice the surface remineralized component. In contrast, Canth is only about one third and one fifth of the remineralized component at 50 m and 100 m depth, respectively. Uptake of Canth has caused the aragonite saturation horizon to shoal by approximately 30–50 m since the preindustrial period so that undersaturated waters are well within the regions of the continental shelf that affect the shell dissolution of living pteropods. Our data show that the most severe biological impacts occur in the nearshore waters, where corrosive waters are closest to the surface. Since the pre-industrial times, pteropod shell dissolution has, on average, increased approximately 19–26% in both nearshore and offshore waters.
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•The coastal waters off the US west coast are seasonally exposed to waters with low aragonite saturation.•Large spatial differences in Canth occur in surface waters along the coast.•Average surface Canth is almost twice the surface remineralized component (Cbio).•Uptake of Canth has caused the aragonite saturation horizon to shoal by approximately 30–50 m.•Pteropod shell dissolution has increased approximately 19–26% since the pre-industrial era.
The oceanic sink for anthropogenic CO2 from 1994 to 2007 Gruber, Nicolas; Clement, Dominic; Carter, Brendan R ...
Science (American Association for the Advancement of Science),
03/2019, Letnik:
363, Številka:
6432
Journal Article
Recenzirano
Odprti dostop
The state of ocean CO2 uptakeThe ocean is an important sink for anthropogenic CO2 and has absorbed roughly 30% of our emissions between the beginning of the industrial revolution and the mid-1990s. ...This effect is an important moderator of climate change, but can we count on it to remain as strong in the future? Gruber et al. calculated the ocean uptake of anthropogenic CO2 for the interval from 1994 to 2007, which continued as expected. They also observed clear regional deviations from this pattern, suggesting that there is no guarantee that uptake will remain as robust with time.Science, this issue p. 1193We quantify the oceanic sink for anthropogenic carbon dioxide (CO2) over the period 1994 to 2007 by using observations from the global repeat hydrography program and contrasting them to observations from the 1990s. Using a linear regression–based method, we find a global increase in the anthropogenic CO2 inventory of 34 ± 4 petagrams of carbon (Pg C) between 1994 and 2007. This is equivalent to an average uptake rate of 2.6 ± 0.3 Pg C year−1 and represents 31 ± 4% of the global anthropogenic CO2 emissions over this period. Although this global ocean sink estimate is consistent with the expectation of the ocean uptake having increased in proportion to the rise in atmospheric CO2, substantial regional differences in storage rate are found, likely owing to climate variability–driven changes in ocean circulation.
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