A multiparametric linear regression technique was used for waters in the Southern Ocean to estima... more A multiparametric linear regression technique was used for waters in the Southern Ocean to estimate the change in both delta13CDIC (Deltadelta13CDIC) and dissolved inorganic carbon (DIC) (DeltaDIC) between 1978 and 1998, due to the accumulation of anthropogenic CO2. The observed decrease in Delta13CDIC at the surface, the Suess effect, was -0.015 ± 0.0030/00 yr-1 in the Sub-Antarctic Zone and -0.005 ± 0.0030/00 yr-1 in the Antarctic Zone, similar to values reported for the southern Indian Ocean [Gruber et al; 1999; Sonnerup et al., 2000]. To compare the Deltadelta13CDIC with DeltaDIC, we used the ratio of these two anomalies (DeltaRC=-Deltadelta13CDIC/DeltaDIC0/00 (mumol; kg-1)-1). Along the section, DeltaRC ranged from 0.015 ± 0.005 at 42°S to 0.007 ± 0.0050/00 (mumol; kg-1)-1 at 54°S. The spatial variability in DeltaRC in the Southern Ocean reflects different timescales for processes controlling the uptake of 13C from those controlling the uptake of 12C and indicates that Deltadelta13CDIC decouples from DeltaDIC poleward of the Sub-Antarctic Zone. The variations of DeltaRC along the section suggest that the delta13CDIC anomaly is not a good predictor of the anthropogenic CO2 inventory in the Southern Ocean. Some methods for determining anthropogenic CO2 uptake both on the global and regional scale assume the penetration depths of Deltadelta13CDIC to be the same as DeltaDIC, which implies a constant value for DeltaRC in the ocean at ˜0.0160/00 (mumol; kg-1)-1 [Heimann and Maier-Reimer, 1996; Ortiz et al., 2000; Bauch et al., 2000]. The use of a constant DeltaRC and the observed Deltadelta13CDIC to estimate anthropogenic CO2 could lead to an underestimate in the inventory of anthropogenic CO2 for the Southern Ocean by ˜50%.
ABSTRACT Ocean acidification leads to changes in marine carbonate chemistry that are predicted to... more ABSTRACT Ocean acidification leads to changes in marine carbonate chemistry that are predicted to cause a decline in future coral reef calcification. Several laboratory and mesocosm experiments have described calcification responses of species and communities to increasing CO2. The few in situ studies on natural coral reefs that have been carried out to date have shown a direct relationship between aragonite saturation state (Ωarag) and net community calcification (Gnet). However, these studies have been performed over a limited range of Ωarag values, where extrapolation outside the observational range is required to predict future changes in coral reef calcification. We measured extreme diurnal variability in carbonate chemistry within a reef flat in the southern Great Barrier Reef, Australia. Ωarag varied between 1.1 and 6.5, thus exceeding the magnitude of change expected this century in open ocean subtropical/tropical waters. The observed variability comes about through biological activity on the reef, where changes to the carbonate chemistry are enhanced at low tide when reef flat waters are isolated from open ocean water. We define a relationship between net community calcification and Ωarag, using our in situ measurements. We find net community calcification to be linearly related to Ωarag, while temperature and nutrients had no significant effect on Gnet. Using our relationship between Gnet and Ωarag, we predict that net community calcification will decline by 55% of its preindustrial value by the end of the century. It is not known at this stage whether exposure to large variability in carbonate chemistry will make reef flat organisms more or less vulnerable to the non-calcifying physiological effects of increasing ocean CO2 and future laboratory studies will need to incorporate this natural variability to address this question.
Ocean acidification, via an anthropogenic increase in seawater carbon dioxide (CO2 ), is potentia... more Ocean acidification, via an anthropogenic increase in seawater carbon dioxide (CO2 ), is potentially a major threat to coral reefs and other marine ecosystems. However, our understanding of how natural short-term diurnal CO2 variability in coral reefs influences longer term anthropogenic ocean acidification remains unclear. Here, we combine observed natural carbonate chemistry variability with future carbonate chemistry predictions for a coral reef flat in the Great Barrier Reef based on the RCP8.5 CO2 emissions scenario. Rather than observing a linear increase in reef flat partial pressure of CO2 (pCO2 ) in concert with rising atmospheric concentrations, the inclusion of in situ diurnal variability results in a highly nonlinear threefold amplification of the pCO2 signal by the end of the century. This significant nonlinear amplification of diurnal pCO2 variability occurs as a result of combining natural diurnal biological CO2 metabolism with long-term decreases in seawater buffer capacity, which occurs via increasing anthropogenic CO2 absorption by the ocean. Under the same benthic community composition, the amplification in the variability in pCO2 is likely to lead to exposure to mean maximum daily pCO2 levels of ca. 2100 μatm, with corrosive conditions with respect to aragonite by end-century at our study site. Minimum pCO2 levels will become lower relative to the mean offshore value (ca. threefold increase in the difference between offshore and minimum reef flat pCO2 ) by end-century, leading to a further increase in the pCO2 range that organisms are exposed to. The biological consequences of short-term exposure to these extreme CO2 conditions, coupled with elevated long-term mean CO2 conditions are currently unknown and future laboratory experiments will need to incorporate natural variability to test this. The amplification of pCO2 that we describe here is not unique to our study location, but will occur in all shallow coastal environments where high biological productivity drives large natural variability in carbonate chemistry.
... a life‐cycle of 12 years with important veliger larval development during winter/spring mont... more ... a life‐cycle of 12 years with important veliger larval development during winter/spring months [Gannefors et al., 2005; Seibel and Dierssen ... The three‐dimensional Coupled Ice, Atmosphere, and Ocean (CIAO) model used here [Arrigo et al., 2003; Tagliabue and Arrigo, 2005 ...
A multiparametric linear regression technique was used for waters in the Southern Ocean to estima... more A multiparametric linear regression technique was used for waters in the Southern Ocean to estimate the change in both delta13CDIC (Deltadelta13CDIC) and dissolved inorganic carbon (DIC) (DeltaDIC) between 1978 and 1998, due to the accumulation of anthropogenic CO2. The observed decrease in Delta13CDIC at the surface, the Suess effect, was -0.015 ± 0.0030/00 yr-1 in the Sub-Antarctic Zone and -0.005 ± 0.0030/00 yr-1 in the Antarctic Zone, similar to values reported for the southern Indian Ocean [Gruber et al; 1999; Sonnerup et al., 2000]. To compare the Deltadelta13CDIC with DeltaDIC, we used the ratio of these two anomalies (DeltaRC=-Deltadelta13CDIC/DeltaDIC0/00 (mumol; kg-1)-1). Along the section, DeltaRC ranged from 0.015 ± 0.005 at 42°S to 0.007 ± 0.0050/00 (mumol; kg-1)-1 at 54°S. The spatial variability in DeltaRC in the Southern Ocean reflects different timescales for processes controlling the uptake of 13C from those controlling the uptake of 12C and indicates that Deltadelta13CDIC decouples from DeltaDIC poleward of the Sub-Antarctic Zone. The variations of DeltaRC along the section suggest that the delta13CDIC anomaly is not a good predictor of the anthropogenic CO2 inventory in the Southern Ocean. Some methods for determining anthropogenic CO2 uptake both on the global and regional scale assume the penetration depths of Deltadelta13CDIC to be the same as DeltaDIC, which implies a constant value for DeltaRC in the ocean at ˜0.0160/00 (mumol; kg-1)-1 [Heimann and Maier-Reimer, 1996; Ortiz et al., 2000; Bauch et al., 2000]. The use of a constant DeltaRC and the observed Deltadelta13CDIC to estimate anthropogenic CO2 could lead to an underestimate in the inventory of anthropogenic CO2 for the Southern Ocean by ˜50%.
ABSTRACT Ocean acidification leads to changes in marine carbonate chemistry that are predicted to... more ABSTRACT Ocean acidification leads to changes in marine carbonate chemistry that are predicted to cause a decline in future coral reef calcification. Several laboratory and mesocosm experiments have described calcification responses of species and communities to increasing CO2. The few in situ studies on natural coral reefs that have been carried out to date have shown a direct relationship between aragonite saturation state (Ωarag) and net community calcification (Gnet). However, these studies have been performed over a limited range of Ωarag values, where extrapolation outside the observational range is required to predict future changes in coral reef calcification. We measured extreme diurnal variability in carbonate chemistry within a reef flat in the southern Great Barrier Reef, Australia. Ωarag varied between 1.1 and 6.5, thus exceeding the magnitude of change expected this century in open ocean subtropical/tropical waters. The observed variability comes about through biological activity on the reef, where changes to the carbonate chemistry are enhanced at low tide when reef flat waters are isolated from open ocean water. We define a relationship between net community calcification and Ωarag, using our in situ measurements. We find net community calcification to be linearly related to Ωarag, while temperature and nutrients had no significant effect on Gnet. Using our relationship between Gnet and Ωarag, we predict that net community calcification will decline by 55% of its preindustrial value by the end of the century. It is not known at this stage whether exposure to large variability in carbonate chemistry will make reef flat organisms more or less vulnerable to the non-calcifying physiological effects of increasing ocean CO2 and future laboratory studies will need to incorporate this natural variability to address this question.
Ocean acidification, via an anthropogenic increase in seawater carbon dioxide (CO2 ), is potentia... more Ocean acidification, via an anthropogenic increase in seawater carbon dioxide (CO2 ), is potentially a major threat to coral reefs and other marine ecosystems. However, our understanding of how natural short-term diurnal CO2 variability in coral reefs influences longer term anthropogenic ocean acidification remains unclear. Here, we combine observed natural carbonate chemistry variability with future carbonate chemistry predictions for a coral reef flat in the Great Barrier Reef based on the RCP8.5 CO2 emissions scenario. Rather than observing a linear increase in reef flat partial pressure of CO2 (pCO2 ) in concert with rising atmospheric concentrations, the inclusion of in situ diurnal variability results in a highly nonlinear threefold amplification of the pCO2 signal by the end of the century. This significant nonlinear amplification of diurnal pCO2 variability occurs as a result of combining natural diurnal biological CO2 metabolism with long-term decreases in seawater buffer capacity, which occurs via increasing anthropogenic CO2 absorption by the ocean. Under the same benthic community composition, the amplification in the variability in pCO2 is likely to lead to exposure to mean maximum daily pCO2 levels of ca. 2100 μatm, with corrosive conditions with respect to aragonite by end-century at our study site. Minimum pCO2 levels will become lower relative to the mean offshore value (ca. threefold increase in the difference between offshore and minimum reef flat pCO2 ) by end-century, leading to a further increase in the pCO2 range that organisms are exposed to. The biological consequences of short-term exposure to these extreme CO2 conditions, coupled with elevated long-term mean CO2 conditions are currently unknown and future laboratory experiments will need to incorporate natural variability to test this. The amplification of pCO2 that we describe here is not unique to our study location, but will occur in all shallow coastal environments where high biological productivity drives large natural variability in carbonate chemistry.
... a life‐cycle of 12 years with important veliger larval development during winter/spring mont... more ... a life‐cycle of 12 years with important veliger larval development during winter/spring months [Gannefors et al., 2005; Seibel and Dierssen ... The three‐dimensional Coupled Ice, Atmosphere, and Ocean (CIAO) model used here [Arrigo et al., 2003; Tagliabue and Arrigo, 2005 ...
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