Seawater carbonate chemistry and boron incorporation of planktic foraminifer Orbulina universa during experiments, 2011

Culture experiments with living planktic foraminifers reveal that the ratio of boron to calcium (B/Ca) in Orbulina universa increases from 56 to 92 µmol mol-1 when pH is raised from 7.61 +/- 0.02 to 8.67 +/- 0.03 (total scale). Across this pH range, the abundances of carbonate, bicarbonate, and borate ions also change (+ 530, - 500, and + 170 µmol kg-1, respectively). Thus specific carbonate system control(s) on B/Ca remain unclear, complicating interpretation of paleorecords. B/Ca in cultured O. universa also increases with salinity (55-72 µmol mol-1 from 29.9-35.4 per mil) and seawater boron concentration (62-899 µmol mol-1 from 4-40 ppm B), suggesting that these parameters may need to be taken into account for paleorecords spanning large salinity changes (~ 2 per mil) and for samples grown in seawater whose boron concentration ([B]SW) differs from modern by more than 0.25 ppm. While our results are consistent with the predominant incorporation of the charged borate species B(OH)4 into foraminiferal calcite, the behavior of the partition coefficient KD (defined as [B/Ca]calcite/B(OH)4/HCO3seawater) cannot be explained by borate incorporation alone, and suggests the involvement of other pH-sensitive ions such as CO3 For a given increase in seawater B(OH)4, the corresponding increase in B/Ca is stronger when B(OH)4 is raised by increasing [B]SW than when it is raised by increasing pH. These results suggest that B incorporation controls should be reconsidered. Additional insight is gained from laser-ablation ICP-MS profiles, which reveal variable B/Ca distributions within individual shells.

Seawater carbonate chemistry and processes during experiments with crabs Chionoecetes tanneri and Cancer magister, 2007

Rising levels of atmospheric carbon dioxide could be curbed by large-scale sequestration of CO2 in the deep sea. Such a solution requires prior assessment of the impact of hypercapnic, acidic seawater on deep-sea fauna. Laboratory studies were conducted to assess the short-term hypercapnic tolerance of the deep-sea Tanner crab Chionoecetes tanneri, collected from 1000 m depth in Monterey Canyon off the coast of central California, USA. Hemolymph acid- base parameters were monitored over 24 h of exposure to seawater equilibrated with ~1% CO2 (seawater PCO2 ~6 torr or 0.8 kPa, pH 7.1), and compared with those of the shallow-living Dungeness crab Cancer magister. Short-term hypercapnia-induced acidosis in the hemolymph of Chionoecetes tanneri was almost uncompensated, with a net 24 h pH reduction of 0.32 units and a net bicarbonate accumulation of only 3 mM. Under simultaneous hypercapnia and hypoxia, short-term extracellular acidosis in Chionoecetes tanneri was completely uncompensated. In contrast, Cancer magister fully recovered its hemolymph pH over 24 h of hypercapnic exposure by net accumulation of 12 mM bicarbonate from the surrounding medium. The data support the hypothesis that deep-sea animals, which are adapted to a stable environment and exhibit reduced metabolic rates, lack the short-term acid-base regulatory capacity to cope with the acute hypercapnic stress that would accompany large-scale CO2 sequestration. Additionally, the data indicate that sequestration in oxygen-poor areas of the ocean would be even more detrimental to deep-sea fauna.

Seawater carbonate chemistry, growth rate and morphology of Calcidiscus leptoporus (RCC1135) during experiments, 2011

The coccolithophore Calcidiscus leptoporus (strain RCC1135) was grown in dilute batch culture at CO2 levels ranging from ~200 to ~1600 µatm. Increasing CO2 concentration led to an increased percentage of malformed coccoliths and eventually (at ~1500 µatm CO2) to aggregation of cells. Carbonate chemistry of natural seawater was manipulated in three ways: first, addition of acid; second, addition of a HCO3/CO3 solution; and third, addition of both acid and HCO3/CO3 solution. The data set allowed the disentangling of putative effects of the different parameters of the carbonate system. It is concluded that CO2 is the parameter of the carbonate system which causes both aberrant coccolithogenesis and aggregation of cells.

Carbonate saturation in the water column of station M8_056 off Cap Sao Vincente, Portugal (Table 1)

Changes in the dissolved oxygen content, the alkalinity, and the pH in sea water near the ocean floor are interpreted in terms of chemical and biochemical processes at the sediment water interface. A simple model provides a plausible explanation of the observed phenomena. Special emphasis is given to the importance of borate corrections in the calculation of the solution effects of calcium carbonate.

Seawater carbonate chemistry, chlorophyll a and photosynthetic carbon fixation rate under different light and pCO2 conditions during experiments, 2010

We carried out short term pCO2/pH perturbation experiments in the coastal waters of the South China Sea to evaluate the combined effects of seawater acidification (low pH/high pCO2) and solar UV radiation (UVR, 280-400 nm) on photosynthetic carbon fixation of phytoplankton assemblages. Under photosynthetically active radiation (PAR) alone treatments, reduced pCO2 (190 ppmv) with increased pH resulted in a significant decrease in the photosynthetic carbon fixation rate (about 23%), while enriched pCO2 (700 ppmv) with lowered pH had no significant effect on the photosynthetic performance compared to the ambient level. The apparent photosynthetic efficiency decreased under the reduced pCO2 level, probably due to C-limitation as well as energy being diverged for up-regulation of carbon concentrating mechanisms (CCMs). In the presence of UVR, both UV-A and UV-B caused photosynthetic inhibition, though UV-A appeared to enhance the photosynthetic efficiency under lower PAR levels. UV-B caused less inhibition of photosynthesis under the reduced pCO2 level, probably because of its contribution to the inorganic carbon (Ci)-acquisition processes. Under the seawater acidification conditions (enriched pCO2), both UV-A and UV-B reduced the photosynthetic carbon fixation to higher extents compared to the ambient pCO2 conditions. We conclude that solar UV and seawater acidification could synergistically inhibit photosynthesis.

Seawater carbonate chemistry near the Island of Ischia, Italy, 2008

We present the first study of the effects of ocean acidification on settlement of benthic invertebrates and microfauna. Artificial collectors were placed for 1 month along pH gradients at CO2 vents off Ischia (Tyrrhenian Sea, Italy). Seventy-nine taxa were identified from six main taxonomic groups (foraminiferans, nematodes, polychaetes, molluscs, crustaceans and chaetognaths). Calcareous foraminiferans, serpulid polychaetes, gastropods and bivalves showed highly significant reductions in recruitment to the collectors as pCO2 rose from normal (336-341 ppm, pH 8.09-8.15) to high levels (886-5,148 ppm) causing acidified conditions near the vents (pH 7.08-7.79). Only the syllid polychaete Syllis prolifera had higher abundances at the most acidified station, although a wide range of polychaetes and small crustaceans was able to settle and survive under these conditions. A few taxa (Amphiglena mediterranea, Leptochelia dubia, Caprella acanthifera) were particularly abundant at stations acidified by intermediate amounts of CO2 (pH 7.41-7.99). These results show that increased levels of CO2 can profoundly affect the settlement of a wide range of benthic organisms.

Seawater carbonate chemistry, primary production, biomass and calcification of plankton and bacteria, 2009

Production (abundance and biomass) and net calcification rates of the coccolithophorid Pleurochrysis carterae under different partial pressures of CO2 (pCO2) were examined using short (15, 24 and 39 h), long (7 d) and dark (7 d) incubation experiments. Short incubations were conducted at ambient, 500 and 820 ppm pCO2 levels in natural seawater that was enriched with nutrients and inoculated with P. carterae. Long incubations were conducted at ambient and 1200 ppm pCO2 levels in natural seawater (0.2 µm filtered as well as unfiltered) that was enriched with nutrients and inoculated with P. carterae. Dark incubations were conducted at ambient and 1200 ppm pCO2 in unfiltered seawater that was inoculated with P. carterae. The abundance and biomass of coccolithophorids increased with pCO2 and time. The abundance and biomass of most noncalcifying phytoplankton also increased, and were hardly affected by CO2 inputs. Net calcification rates were negative in short incubations during the pre-bloom phase regardless of pCO2 levels, indicating dissolution of calcium carbonate. Further, the negative values of net calcification in short incubations became less negative with time. Net calcification rates were positive in long incubations during blooms regardless of pCO2 level, and the rate of calcification increased with pCO2. Our results show that P. carterae may adapt to increased (~1200 ppm) pCO2 level with time, and such increase has little effect on the ecology of noncalcifying groups and hence in ecosystem dynamics. In dark incubations, net calcification rates were negative, with the magnitude being dependent on pCO2 levels.

Seawater carbonate chemistry and calcification rate in flume experiment

Ocean acidification (OA) poses a severe threat to tropical coral reefs, yet much of what is know about these effects comes from individual corals and algae incubated in isolation under high pCO2. Studies of similar effects on coral reef communities are scarce. To investigate the response of coral reef communities to OA, we used large outdoor flumes in which communities composed of calcified algae, corals, and sediment were combined to match the percentage cover of benthic communities in the shallow back reef of Moorea, French Polynesia. Reef communities in the flumes were exposed to ambient (400 ?atm) and high pCO2 (1300 ?atm) for 8 weeks, and calcification rates measured for the constructed communities including the sediments. Community calcification was reduced by 59% under high pCO2, with sediment dissolution explaining ~ 50% of this decrease; net calcification of corals and calcified algae remained positive but was reduced by 29% under elevated pCO2. These results show that, despite the capacity of coral reef calcifiers to maintain positive net accretion of calcium carbonate under OA conditions, reef communities might transition to net dissolution as pCO2 increases, particularly at night, due to enhanced sediment dissolution.

Seawater carbonate chemistry, calcification and respiration duirng experiments with a pteropod Creseis acicula, 2010

Among marine calcifiers, shelled pteropods are expected to be particularly sensitive to ocean acidification, generated by the uptake of anthropogenic CO2 by the ocean, and the associated decrease of the seawater saturation state with respect to aragonite (omega aragonite). The few available studies have mostly focused on polar species although pteropods are also important components of temperate and tropical ecosystems. It is also unknown which parameter of the carbonate system controls calcification. Specimens of the temperate Mediterranean species Creseis acicula were maintained under seven different conditions of the carbonate chemistry, obtained by manipulating pH and total alkalinity, with the goal to disentangle the effects of pH and omega aragonite. Respiration, excretion as well as rates of net and gross calcification were not directly affected by a decrease in pH but decreased significantly with a decrease of omega aragonite. The decrease of gross calcification rates is consistent with that reported for polar species. Although the organisms were apparently able to maintain gross calcification rates under slightly undersaturated aragonite conditions, the clear net dissolution signal observed below saturation suggests that they are not able to build a shell in seawater corrosive to aragonite. The decrease in respiration and excretion, and the low O:N molar ratio, could be due to the short time that the organisms were allowed to acclimatize to their new environment.

Chemical composition of interstitial solutions from sediments of DSDP Legs 6-8, 11, 12, 14, 15, and 22

Through the Deep Sea Drilling Project samples of interstitial solutions of deeply buried marine sediments throughout the World Ocean have been obtained and analyzed. The studies have shown that in all but the most slowly deposited sediments pore fluids exhibit changes in composition upon burial. These changes can be grouped into a few consistent patterns that facilitate identification of the diagenetic reactions occurring in the sediments. Pelagic clays and slowly deposited (<1 cm/1000 yr) biogenic sediments are the only types that exhibit little evidence of reaction in the pore waters. In most biogenic sediments sea water undergoes considerable alteration. In sediments deposited at rates up to a few cm/1000 yr the changes chiefly involve gains of Ca(2+) and Sr(2+) and losses of Mg(2+) which balance the Ca(2+) enrichment. The Ca-Mg substitution may often reach 30 mM/kg while Sr(2+) may be enriched 15-fold over sea water. These changes reflect recrystallization of biogenic calcite and the substitution of Mg(2+) for Ca(2+) during this reaction. The Ca-Mg-carbonate formed is most likely a dolomitic phase. A related but more complex pattern is found in carbonate sediments deposited at somewhat greater rates. Ca(2+) and Sr(2+) enrichment is again characteristic, but Mg(2+) losses exceed Ca(2+) gains with the excess being balanced by SO4(post staggered 2-) losses. The data indicate that the reactions are similar to those noted above, except that the Ca(2+) released is not kept in solution but is precipitated by the HCO3(post staggered -) produced in SO4(post staggered 2-) reduction. In both these types of pore waters Na(+) is usually conservative, but K(+) depletions are frequent. In several partly consolidated sediment sections approaching igneous basement contact, very marked interstitial calcium enrichment has been found (to 5.5 g/kg). These phenomena are marked by pronounced depletion in Na(+), Si and CO2, and slight enhancement in Cl(-). The changes are attributed to exchange of Na(+) for Ca(2+) in silicate minerals forming from submarine weathering of igneous rocks such as basalts. Water is also consumed in these reactions, accounting for minor increases in total interstitial salinity. Terrigenous, organic-rich sediments deposited rapidly along continental margins also exhibit significant evidences of alteration. Microbial reactions involving organic matter lead to complete removal of SO4(post staggered 2-), strong HCO3(post staggered -) enrichment, formation of NH4(post staggered +), and methane synthesis from H2 and CO2 once SO4(post staggered 2-) is eliminated. K+ and often Na+ (slightly) are depleted in the interstitial waters. Ca(2+) depletion may occur owing to precipitation of CaCO3. In most cases interstitial Cl- remains relatively constant, but increases are noted over evaporitic strata, and decreases in interstitial Cl- are observed in some sediments adjacent to continents.