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- Henderiks, Jorijntje, et al.
(författare)
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A coccolithophore concept for constraining the Cenozoic carbon cycle
- 2007
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 4, s. 323-329
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Tidskriftsartikel (refereegranskat)abstract
- An urgent question for future climate, in light of increased burning of fossil fuels, is the temperature sensitivity of the climate system to atmospheric carbon dioxide (pCO(2)). To date, no direct proxy for past levels of pCO(2) exists beyond the reach of the polar ice core records. We propose a new methodology for placing a constraint on pCO(2) over the Cenozoic based on the physiological plasticity of extant coccolithophores. Specifically, our premise is that the contrasting calcification tolerance(1) of various extant species of coccolithophore to raised pCO(2) reflects an "evolutionary memory" of past atmospheric composition. The different times of evolution of certain morphospecies allows an upper constraint of past pCO(2) to be placed on Cenozoic timeslices. Further, our hypothesis has implications for the response of marine calcifiers to ocean acidification. Geologically "ancient" species, which have survived large changes in ocean chemistry, are likely more resilient to predicted acidification.
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| 3. |
- Henderiks, Jorijntje, et al.
(författare)
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Algal constraints on the Cenozoic history of atmospheric CO2?
- 2006
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Future acidification of the oceans due to raised carbon dioxide levels will cause a drastic change in ocean chemistry that has not been experienced for at least the last 650,000 years, and will likely reduce marine calcification.Coccolithophores, calcareous haptophyte algae, constitute a key biological group subjected to this global process. The rate at which the natural populations can acclimatise or adapt to changes in ocean chemistry is an essential factor in how their natural feedback mechanisms will operate in future.Novel experiments testing the environmental tolerance of different extant coccolithophore species to various conditions of seawater carbonate chemistry reveal the need to consider species-specific effects when evaluating whole ecosystem responses to elevated pCO2 (Langer, 2006). Specifically, PIC/POC ratios in Coccolithus pelagicus appeared unaffected by the range in CO2 tested (Langer, 2006), which to date remains unexplained.We argue that the evolutionary history of the Coccolithus genus, which originated in the early Paleocene, holds not only invaluable information on how species evolve within ‘planktic super-species’ (de Vargas, 2004) whilst keeping rather conservative coccolith morphologies, as will be demonstrated. It potentially is also a crucial factor in constraining maximum levels of atmospheric CO2 experienced in the geological past.
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| 5. |
- Henderiks, Jorijntje, et al.
(författare)
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Coccolithophore growth, chemistry and calcification under decoupled ocean carbonate chemistry
- 2008
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Konferensbidrag (populärvet., debatt m.m.)abstract
- Excess anthropogenic atmospheric CO2 is absorbed largely by the oceans, causing acidification of the biologically productive surface waters with potential detrimental effects on marine biocalcification (The Royal Society, 2005). Despite the intracellular nature of coccolithophore calcification, previous experimental work confirmed that some (but not all) modern coccolithophores decrease calcification as pCO2 increases. However, from these culture experiments, it has been impossible to determine which carbonate system parameter is fundamental to coccolithogenesis across different species of coccolithophore because the DIC is fixed and the carbonate saturation state and pH are inversely proportional to pCO2. Additionally, these culture scenarios do not accurately capture the chemistry of the modern evolving ocean where increasing pCO2 drives a decrease in ocean pH but also an increase in dissolved inorganic carbon (DIC). Our aim was to decouple the pH from the DIC in culture experiments of three species: Emiliania huxleyi, Gephyrocapsa oceanica and Coccolithus braarudii (pelagicus), representative of two distinct phylogenetic orders and major families of coccolithophore, in order to disentangle which carbonate system parameter is crucial for calcification and develop a mechanistic view of coccolithophore response to elevated pCO2.Cultures were grown in North Sea water, under a constant pH of 8.13 ± 0.02, but with manipulated dissolved inorganic carbon (DIC) concentrations to represent surface water conditions ranging from the last glacial maximum to ~5 times pre-industrial pCO2. Our results confirm that there are strong species-specific responses and potentially fundamental differences in physiology between E. huxleyi and G. oceanica on the one, and C. braarudii on the other hand. At pH 8, algal growth rates, cell size and calcite production by E. huxleyi and G. oceanica remained unaffected by large increases in carbonate ion and DIC. By contrast, C. braarudii showed drastically lowered growth rates, significantly smaller cell and coccosphere diameters as well as coccolith malformation, under highly elevated carbonate ion and DIC. Due to the distinct isotopic composition of bicarbonate and carbonate ions, the isotopic composition of coccolithophore calcite could provide additional information on the physiological pathway of calcification. Both δ13C and δ18O of G. oceanica remained constant across all culture treatments. But the isotopic composition of C. braarudii was significantly depleted under low carbonate ion and DIC conditions, most likely as a result of kinetic controls at the higher growth rates under these conditions. G. oceanica therefore appears to respond primarily to pH, and C. braarudii to carbonate ion. This contrasting behaviour likely reveals fundamentally different physiological pathways of carbon metabolism and calcification between these two species, which could be reminiscent of adaptation to ambient conditions at the time of evolution of each lineage (Henderiks and Rickaby, 2007).ReferencesHenderiks, J. and Rickaby, R. E. M.: A coccolithophore concept for constraining the Cenozoic carbon cycle, Biogeosciences, 4, 323-329, 2007.The Royal Society: Ocean acidification due to increasing atmospheric carbon dioxide, Policy Document 12/05, 60 pp., 2005.
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| 6. |
- Henderiks, Jorijntje, et al.
(författare)
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Evolution of coccolithophores: Tiny algae tell big tales
- 2008
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Ingår i: 33rd International Geological Congress, Oslo.
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Konferensbidrag (populärvet., debatt m.m.)abstract
- The study of calcareous marine biota provides important insight into the climate past, present and future. Biocalcification by marine biota has evolved across many major phyla (e.g. bacteria, eukaryotic algae, protozoans and metazoans) and is a dynamic interface between the biosphere, geosphere and atmosphere. Biocalcification is controlled by both physical and (paleo-)biological processes, which vary considerably on both spatial and temporal scales. A better understanding of these variations and how processes of different scales interact within the global system is critical for more reliable prediction of climate change and its impacts in the future.Coccolithophores, a group of calcifying unicellular algae, constitute a major fraction of oceanic primary productivity, and generate a continuous rain of calcium carbonate (in the form of coccoliths) to the seafloor. Hence, they play an important role in the global carbon cycle, representing natural feedbacks in the climate system. Coccolithophores are a crucial biological group subjected to present-day climate change and ocean acidification due to oceanic uptake of excess atmospheric CO2. It is not known to what extent the natural populations can acclimatize or adapt to these changes, nor how their natural feedback mechanisms will operate in future. However, we can learn valuable lessons from their past and present-day behavior: Coccolithophore evolutionary rates are fast, with a fossil record dating back to 220 million years. Their global and abundant fossil occurrences in deep-sea sediments provide detailed records of plankton evolution that can be readily compared to proxy records of past ocean environmental parameters. In addition, cultivation of extant species of coccolithophore can inform us how modern calcifiers respond to different experimental physico-chemical conditions, and what factors are pivotal to sustain algal growth and biocalcification. Intriguingly, distinct responses between different modern species could relate to variable evolutionary adaptation strategies of their Cenozoic ancestors.
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| 7. |
- Henderiks, Jorijntje, et al.
(författare)
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Phytoplankton size : Climatic adaptation and long-term evolution
- 2010
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Marine phytoplankton, such as diatoms and coccolithophores, constitute the base of the marine food chain and are a fundamental component in biogeochemical cycles. The overall ecological success of marine phytoplankton, but also its taxonomic diversity and size distribution, determines the efficiency by which fixed carbon is transferred to higher trophic levels and into the deep ocean- and sedimentary carbon reservoirs. Therefore, we need a better understanding of the mechanisms and rates of adaptation within phytoplankton to evaluate marine ecosystems under present-day and future climate scenarios of rapidly rising ocean temperatures and lowering of ocean pH (‘ocean acidification’). The likely response of coccolithophores, the most prominent group of calcifying algae, in particular has provoked controversy.We have hypothesized that species-specific responses to climatic perturbations within extant members of this group are due to differences in the mechanism and rate of climatic adaptation inherent to their respective evolutionary lineages (Henderiks, J. and Rickaby, R.E.M., A coccolithophore concept for constraining the Cenozoic carbon cycle, Biogeosciences 4: 323-329, 2007). The Cenozoic ancestors of all extant coccolithophores have experienced much higher levels of CO2 and lower ocean pH than today, according to proxy reconstructions over the past 60 million years. However, we show that different lineages display different levels of variation in coccolith shape and cell size, and that this could indicate that some species are more adaptable to climatic change than others. The observed geological trends in algal cell size also have implications for long-term feedbacks in the Cenozoic carbon cycle.
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| 10. |
- Rickaby, Rosalind E. M., et al.
(författare)
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Perturbing phytoplankton : response and isotopic fractionation with changing carbonate chemistry in two coccolithophore species
- 2010
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Ingår i: Climate of the Past. - : Copernicus Publications on behalf of the European Geosciences Union. - 1814-9324 .- 1814-9332. ; 6, s. 771-785
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Tidskriftsartikel (refereegranskat)abstract
- All species of coccolithophore appear to respond to perturbations of carbonate chemistry in a different way. Here, we show that the degree of malformation, growthrate and stable isotopic composition of organic matter and carbonate produced by two contrasting species of coccolithophore (Gephyrocapsa oceanica and Coccolithus pelagicusssp. braarudii) are indicative of differences between their photosynthetic and calcification response to changing DIC levels (ranging from 1100 to 7800 μmol kg−1) at constant pH (8.13±0.02). Gephyrocapsa oceanica thrived under all conditions of DIC, showing evidence of increased growth rates at higher DIC, but C. braarudii was detrimentally affected at high DIC showing signs of malformation, and decreased growth rates. The carbon isotopic fractionation into organic matter and the coccoliths suggests that C. braarudii utilises a common internal pool of carbon for calcification and photosynthesis but G. oceanica relies on independent supplies for each process. All coccolithophores appear to utilize bicarbonate as their ultimate source of carbon for calcification resulting in the release of a proton. But, we suggest that this proton can be harnessed to enhance the supply of CO2(aq) for photosynthesis either from a large internal HCO−3 pool which acts as a pH buffer (C. braarudii), or pumped externally to aid the diffusive supply of CO2 across the membrane from the abundant HCO−3 (G. oceanica), likely mediated by an internal and external carbonic anhydrase respectively. Our simplified hypothetical spectrum of physiologies may provide a context to understand different species response to changing pH and DIC, the species specific Ep and calcite “vital effects”, as well as accounting for geological trends in coccolithophore cell size.
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