The Geological Record of Ocean Acidification Hönisch, Bärbel; Ridgwell, Andy; Schmidt, Daniela N. ...
Science (American Association for the Advancement of Science),
03/2012, Letnik:
335, Številka:
6072
Journal Article
Recenzirano
Odprti dostop
Ocean acidification may have severe consequences for marine ecosystems; however, assessing its future impact is difficult because laboratory experiments and field observations are limited by their ...reduced ecologie complexity and sample period, respectively. In contrast, the geological record contains long-term evidence for a variety of global environmental perturbations, including ocean acidification plus their associated biotic responses. We review events exhibiting evidence for elevated atmospheric CO₂, global warming, and ocean acidification over the past ~300 million years of Earth's history, some with contemporaneous extinction or evolutionary turnover among marine calcifiers. Although similarities exist, no past event perfectly parallels future projections in terms of disrupting the balance of ocean carbonate chemistry—a consequence of the unprecedented rapidity of CO₂ release currently taking place.
Comparison of ice cores from Greenland and Antarctica shows an asynchronous two‐step warming at these high latitudes during the Last Termination. However, the question whether this asynchrony extends ...to lower latitudes is unclear mainly due to the scarcity of paleorecords from the Southern Hemisphere. New data from a marine core collected off South Australia (∼36°S) allows a detailed reconstruction of sea‐surface temperatures over the Last Termination. This confirms the existence of an Antarctic‐type deglacial pattern and shows no indication of cooling associated with the Northern Hemisphere YD event. The SST record also provides a new comparison with the more extensive paleoclimatic data available from continental Australia. This shows a strong climatic link between onshore and offshore records for Australia and to Southern Hemisphere paleorecords. We also show a progressive SST drop over the last ∼6.5 kyr not seen before for the Australian region.
Anthropogenic carbon emissions are causing changes in seawater carbonate chemistry including a decline in the pH of the oceans. While its aftermath for calcifying microbes has been widely studied, ...the effect of ocean acidification (OA) on marine viruses and their microbial hosts is controversial, and even more in combination with another anthropogenic stressor, i.e., human-induced nutrient loads. In this study, two mesocosm acidification experiments with Mediterranean waters from different seasons revealed distinct effects of OA on viruses and viral-mediated prokaryotic mortality depending on the trophic state and the successional stage of the plankton community. In the winter bloom situation, low fluorescence viruses, the most abundant virus-like particle (VLP) subpopulation comprising mostly bacteriophages, were negatively affected by lowered pH with nutrient addition, while the bacterial host abundance was stimulated. High fluorescence viruses, containing cyanophages, were stimulated by OA regardless of the nutrient conditions, while cyanobacteria of the genus
were negatively affected by OA. Moreover, the abundance of very high fluorescence viruses infecting small haptophytes tended to be lower under acidification while their putative hosts' abundance was enhanced, suggesting a direct and negative effect of OA on viral-host interactions. In the oligotrophic summer situation, we found a stimulating effect of OA on total viral abundance and the viral populations, suggesting a cascading effect of the elevated
CO
stimulating autotrophic and heterotrophic production. In winter, viral lysis accounted for 30 ± 16% of the loss of bacterial standing stock per day (VMM
) under increased
CO
compared to 53 ± 35% in the control treatments, without effects of nutrient additions while in summer, OA had no significant effects on VMM
(35 ± 20% and 38 ± 5% per day in the OA and control treatments, respectively). We found that phage production and resulting organic carbon release rates significantly reduced under OA in the nutrient replete winter situation, but it was also observed that high nutrient loads lowered the negative effect of OA on viral lysis, suggesting an antagonistic interplay between these two major global ocean stressors in the Anthropocene. In summer, however, viral-mediated carbon release rates were lower and not affected by lowered pH. Eutrophication consistently stimulated viral production regardless of the season or initial conditions. Given the relevant role of viruses for marine carbon cycling and the biological carbon pump, these two anthropogenic stressors may modulate carbon fluxes through their effect on viruses at the base of the pelagic food web in a future global change scenario.
It has been shown that the deep Eastern Equatorial Pacific (EEP) region was poorly ventilated during the Last Glacial Maximum (LGM) relative to Holocene values. This finding suggests a more efficient ...biological pump, which indirectly supports the idea of increased carbon storage in the deep ocean contributing to lower atmospheric CO2 during the last glacial. However, proxies related to respired carbon are needed in order to directly test this proposition. Here we present Cibicides wuellerstorfi B/Ca ratios from Ocean Drilling Program Site 1240 measured by laser ablation inductively coupled plasma mass spectrometry (LA‐ICPMS) as a proxy for deep water carbonate saturation state (ΔCO32−, and therefore CO32−), along with δ13C measurements. In addition, the U/Ca ratio in foraminiferal coatings has been analyzed as an indicator of oxygenation changes. Our results show lower CO32−, δ13C, and O2 values during the LGM, which would be consistent with higher respired carbon levels in the deep EEP driven, at least in part, by reduced deep water ventilation. However, the difference between LGM and Holocene CO32− observed at our site is relatively small, in accordance with other records from across the Pacific, suggesting that a “counteracting” mechanism, such as seafloor carbonate dissolution, also played a role. If so, this mechanism would have increased average ocean alkalinity, allowing even more atmospheric CO2 to be “sequestered” by the ocean. Therefore, the deep Pacific Ocean very likely stored a significant amount of atmospheric CO2 during the LGM, specifically due to a more efficient biological carbon pump and also an increase in average ocean alkalinity.
Key Points
Combined CO32−, δ13C, and U/CaC evidence indicates increased respired carbon storage in the Last Glacial Maximum Eastern Equatorial Pacific
Along with reduced deep water ventilation, this evidence points to enhanced soft‐tissue pump efficiency driven by ocean circulation changes
Modest CO32− change suggests calcite dissolution as a further contribution to atmospheric CO2 drawdown via increased ocean alkalinity
Molecular abundances of
n-nonacosane are reported for a suite of 44 surface sediments and four deep sea cores distributed throughout the South China Sea (SCS), covering the last 220 ky at different ...time resolutions. The patterns of glacial to interglacial variability of the concentrations of this terrigenous marker are parallel for all cores, taking values linearly inversely correlated to the U
37
K′ index sea surface temperatures (SST), with high concentrations during cold-glacial intervals and low concentrations during warm-interglacial periods. The oscillations of this terrigenous marker likely result from the emergence and flooding of the shelves caused by sea-level variations which, together with SCS SSTs, have a clear dependency on the Northern Hemisphere climate evolution. Calculation of accumulation rates for the northernmost core together with the modern distribution of
n-nonacosane concentrations in surface sediments evidences the complexity of sedimentation patterns in the northern SCS. In particular, and in agreement with recent studies, terrigenous materials deposited there might originate from areas different than the highly loaded Pearl River. For paleoceanographic purposes, the noticeable general pattern of the
n-alkane concentration down-core profiles for the four cores studied, a parameter apparently unaffected by changes in sedimentation rates, prompts its use as a tracer of variations in terrigenous input into this basin over glacial to interglacial times.
Understanding oceanic processes, both physical and biological, that control atmospheric CO₂ is vital for predicting their influence during the past and into the future. The Eastern Equatorial Pacific ...(EEP) is thought to have exerted a strong control over glacial/interglacial CO₂ variations through its link to circulation and nutrient-related changes in the Southern Ocean, the primary region of the world oceans where CO₂-enriched deep water is upwelled to the surface ocean and comes into contact with the atmosphere. Here we present a multiproxy record of surface ocean productivity, dust inputs, and thermocline conditions for the EEP over the last 40,000 y. This allows us to detect changes in phytoplankton productivity and composition associated with increases in equatorial upwelling intensity and influence of Si-rich waters of sub-Antarctic origin. Our evidence indicates that diatoms outcompeted coccolithophores at times when the influence of Si-rich Southern Ocean intermediate waters was greatest. This shift from calcareous to noncalcareous phytoplankton would cause a lowering in atmospheric CO₂ through a reduced carbonate pump, as hypothesized by the Silicic Acid Leakage Hypothesis. However, this change does not seem to have been crucial in controlling atmospheric CO₂, as it took place during the deglaciation, when atmospheric CO₂ concentrations had already started to rise. Instead, the concomitant intensification of Antarctic upwelling brought large quantities of deep CO₂-rich waters to the ocean surface. This process very likely dominated any biologically mediated CO₂ sequestration and probably accounts for most of the deglacial rise in atmospheric CO₂.
The oceans are becoming more acidic due to absorption of anthropogenic carbon dioxide from the atmosphere. The impact of ocean acidification on marine ecosystems is unclear, but it will likely depend ...on species adaptability and the rate of change of seawater pH relative to its natural variability. To constrain the natural variability in reef-water pH, we measured boron isotopic compositions in a approximately300-year-old massive Porites coral from the southwestern Pacific. Large variations in pH are found over approximately50-year cycles that covary with the Interdecadal Pacific Oscillation of ocean-atmosphere anomalies, suggesting that natural pH cycles can modulate the impact of ocean acidification on coral reef ecosystems.
Cold-Water Corals (CWCs), and most marine calcifiers, are especially threatened by ocean acidification (OA) and the decrease in the carbonate saturation state of seawater. The vulnerability of these ...organisms, however, also involves other global stressors like warming, deoxygenation or changes in sea surface productivity and, hence, food supply via the downward transport of organic matter to the deep ocean. This study examined the response of the CWC
to low pH under different feeding regimes through a long-term incubation experiment. For this experiment, 152 polyps were incubated at pH 8.1, 7.8, 7.5 and 7.2 and two feeding regimes for 14 months. Mean calcification rates over the entire duration of the experiment ranged between -0.3 and 0.3 mg CaCO
g
d
. Polyps incubated at pH 7.2 were the most affected and 30% mortality was observed in this treatment. In addition, many of the surviving polyps at pH 7.2 showed negative calcification rates indicating that, in the long term, CWCs may have difficulty thriving in such aragonite undersaturated waters. The feeding regime had a significant effect on skeletal growth of corals, with high feeding frequency resulting in more positive and variable calcification rates. This was especially evident in corals reared at pH 7.5 (Ω
= 0.8) compared to the low frequency feeding treatment. Early life-stages, which are essential for the recruitment and maintenance of coral communities and their associated biodiversity, were revealed to be at highest risk. Overall, this study demonstrates the vulnerability of
corals to low pH and low food availability. Future projected pH decreases and related changes in zooplankton communities may potentially compromise the viability of CWC populations.
In this work, we present, for the first time, the seawater carbonate system measurements of two coastal time-series in the NW Mediterranean Sea, L’Estartit Oceanographic Station (EOS; 42.05°N ...3.2542°E) and the Blanes Bay Microbial Observatory (BBMO; 41.665°N 2.805°E). At these two time-series, measurements of total alkalinity (TA), pH, and associated variables, such as dissolved inorganic nutrients, temperature, and salinity, have been performed monthly since 2010 in surface seawater. Seasonality and seasonal amplitude are analogous in both time-series, with seasonality in pH T in situ (pH at in situ seawater conditions on the total hydrogen ion scale) primarily determined by seasonality in sea surface temperature. The evaluated pH T in situ trends at BBMO (-0.0021 ± 0.0003 yr -1 ) and EOS (-0.0028 ± 0.0005 yr -1 ) agree with those reported for coastal and open ocean surface waters in the Mediterranean Sea and open ocean surface waters of the global ocean, therefore indicating that these time-series are representative of global ocean acidification signals despite being coastal. The decreases in pH T in situ can be attributed to increases in total dissolved inorganic carbon (DIC; 1.5 ± 0.4 µmol kg -1 yr -1 at BBMO and 1.6 ± 0.6 µmolESkg -1 yr -1 at EOS) and sea surface temperature (0.08 ± 0.02 °C yr -1 at BBMO and 0.08 ± 0.04 °C yr -1 at EOS). The increases in carbon dioxide fugacity ( f CO 2 ; 2.4 ± 0.3 µmol kg -1 yr -1 at BBMO and 2.9 ± 0.6 µmol kg -1 yr -1 at EOS) follow the atmospheric CO 2 forcing, thus indicating the observed DIC increase is related to anthropogenic CO 2 uptake. The increasing trends in TA (1.2 ± 0.3 µmol kg -1 yr -1 at BBMO and 1.0 ± 0.5 µmol kg -1 yr -1 at EOS) buffered the acidification rates, counteracting 60% and 72% of the pH T in situ decrease caused by increasing DIC at EOS and BBMO, respectively. Once accounted for the neutralizing effect of TA increase, the rapid sea surface warming plays a larger role in the observed pH decreases (43% at EOS and 62% at BBMO) than the DIC increase (36% at EOS and 33% at BBMO).
In recent years, some of the ramifications of the ocean acidification problematic derived from the anthropogenic rising of atmospheric CO2 have been widely studied. In particular, the potential ...effects of a lowering pH on tropical coral reefs have received special attention. However, only a few studies have focused on testing the effects of ocean acidification in corals from the Mediterranean Sea, despite the fact that this basin is especially sensitive to increasing atmospheric CO2. In this context, we investigated the response to ocean acidification of the two zooxanthellate coral species capable of constituting the main framework of the community, the endemic Cladocora caespitosa and the non-native Oculina patagonica. To this end, we examined the response of both species to pCO2 concentrations expected by the end of the century, 800ppm, vs the present levels. Calcification rate measurements after 92days of exposure to low pH conditions showed the same negative response in both species, a decrease of 32–35% compared to corals reared under control conditions. In addition, we detected in both species a correlation between the calcification rate of colonies in control conditions and the degree of impairment of the same colonies at low pH. Independent of species, faster growing colonies were more affected by decreased pH. After this period of decreased pH, we conducted a recovery experiment, in which corals reared in the acidic treatment were brought back to control conditions. In this case, normal calcification rates were reached in both species. Overall, our results suggest that O. patagonica and C. caespitosa will both be affected detrimentally by progressive ocean acidification in the near future. They do not display differences in response between native and non-native species but do manifest differential responses depending on calcification rate, pointing to a role of the coral genetics in determining the response of corals to ocean acidification.
► The response of two temperate Mediterranean corals to ocean acidification was tested. ► Endemic species showed similar decreases in calcification rates than alien species. ► Faster growing colonies were more affected by acidification than those that grew slow. ► Corals recovered calcification to normal values after rising the pH to normal levels. ► Both species seem equally adapted to current natural fluctuations of seawater pH.
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