Long-term evolutionary and ecological responses of calcifying phytoplankton to changes in atmospheric CO 2 (original) (raw)
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Algal constraints on the cenozoic history of atmospheric CO2
Geochimica et Cosmochimica Acta, 2006
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 an upper constraint on pCO 2 5 over the Cenozoic based on the living geological record. Specifically, our premise is that the contrasting calcification tolerance of various extant species of coccolithophore to raised pCO 2 reflects an "evolutionary memory" of past atmospheric composition. The different times of first emergence of each morphospecies allows an upper constraint of past pCO 2 to be placed on Cenozoic timeslices. Further, our hypothesis has 10 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.
Species-specific growth response of coccolithophores to Palaeocene–Eocene environmental change
Nature Geoscience, 2013
Coccolithophores-single-celled calcifying phytoplankton -represent an essential footing to marine ecosystems, yet their sensitivity to environmental change, and in particular increases in atmospheric CO 2 , is poorly understood 1 . During the Palaeocene-Eocene Thermal Maximum (PETM), about 56 million years ago, atmospheric CO 2 concentrations rose rapidly and the oceans acidified 2,3 , making this an ideal time interval to examine coccolithophore responses to environmental change.
Coccolithophore cell size and the Paleogene decline in atmospheric CO2
Earth and Planetary Science Letters, 2008
Alkenone-based Cenozoic records of the partial pressure of atmospheric carbon dioxide (pCO 2 ) are founded on the carbon isotope fractionation that occurred during marine photosynthesis (ε p37:2 ). However, the magnitude of ε p37:2 is also influenced by phytoplankton cell sizea consideration lacking in previous alkenone-based CO 2 estimates. In this study, we reconstruct cell size trends in ancient alkenone-producing coccolithophores (the reticulofenestrids) to test the influence that cell size variability played in determining ε p37:2 trends and pCO 2 estimates during the middle Eocene to early Miocene. At the investigated deep-sea sites, the reticulofenestrids experienced high diversity and largest mean cell sizes during the late Eocene, followed by a long-term decrease in maximum cell size since the earliest Oligocene. Decreasing haptophyte cell sizes do not account for the long-term increase in the stable carbon isotopic composition of alkenones and associated decrease in ε p37:2 values during the Paleogene, supporting the conclusion that the secular pattern of ε p37:2 values is primarily controlled by decreasing CO 2 concentration since the earliest Oligocene. Further, given the physiology of modern alkenone producers, and considering the timings of coccolithophorid cell size change, extinctions, and changes in reconstructed pCO 2 and temperature, we speculate that the selection of smaller reticulofenestrid cells during the Oligocene primarily reflects an adaptive response to increased [CO 2(aq) ] limitation.
Decrease in coccolithophore calcification and CO2 since the middle Miocene
Nature Communications, 2016
Marine algae are instrumental in carbon cycling and atmospheric carbon dioxide (CO 2) regulation. One group, coccolithophores, uses carbon to photosynthesize and to calcify, covering their cells with chalk platelets (coccoliths). How ocean acidification influences coccolithophore calcification is strongly debated, and the effects of carbonate chemistry changes in the geological past are poorly understood. This paper relates degree of coccolith calcification to cellular calcification, and presents the first records of size-normalized coccolith thickness spanning the last 14 Myr from tropical oceans. Degree of calcification was highest in the low-pH, high-CO 2 Miocene ocean, but decreased significantly between 6 and 4 Myr ago. Based on this and concurrent trends in a new alkenone e p record, we propose that decreasing CO 2 partly drove the observed trend via reduced cellular bicarbonate allocation to calcification. This trend reversed in the late Pleistocene despite low CO 2 , suggesting an additional regulator of calcification such as alkalinity.
A coccolithophore concept for constraining the Cenozoic carbon cycle
Biogeosciences, 2007
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.
Coccolithophore productivity response to greenhouse event of the Paleocene–Eocene Thermal Maximum
Earth and Planetary Science Letters - EARTH PLANET SCI LETT, 2007
During the Paleocene-Eocene Thermal Maximum (PETM), rapid release of isotopically light C to the ocean-atmosphere system elevated the greenhouse effect and warmed temperatures by 5-7°C for 10 5 yr. The response of the planktic ecosystems and productivity to the dramatic climate changes of the PETM may represent a significant feedback to the carbon cycle changes, but has been difficult to document. We examine Sr/Ca ratios in calcareous nannofossils in sediments spanning the PETM in three open ocean sites as a new approach to examine productivity and ecological shifts in calcifying plankton. The large heterogeneity in Sr/Ca among different nannofossil genera indicates that nannofossil Sr/Ca reflects primary productivity-driven geochemical signals and not diagenetic overprinting. Elevated Sr/Ca ratios in several genera and constant ratios in other genera suggest increased overall productivity in the Atlantic sector of the Southern Ocean during the PETM. Dominant nannofossil genera in tropical Atlantic and Pacific sites show Sr/Ca variations during the PETM which are comparable to background variability prior to the PETM. Despite acidification of the ocean there was not a productivity crisis among calcifying phytoplankton. We use the Pandora ocean box model to explore possible mechanisms for PETM productivity change. If independent proxy evidence for more stratified conditions in the Southern Ocean during the PETM is robust, then maintenance of stable or increased productivity there likely reflects increased nutrient inventories of the ocean. Increased nutrient inventories could have resulted from climatically enhanced weathering and would have important implications for burial rates of organic carbon and stabilization of climate and the carbon cycle.
Sensitivity of coccolithophores to carbonate chemistry and ocean acidification
Nature, 2011
About one-third of the carbon dioxide (CO 2 ) released into the atmosphere as a result of human activity has been absorbed by the oceans 1 , where it partitions into the constituent ions of carbonic acid. This leads to ocean acidification, one of the major threats to marine ecosystems 2 and particularly to calcifying organisms such as corals 3,4 , foraminifera 5-7 and coccolithophores 8 . Coccolithophores are abundant phytoplankton that are responsible for a large part of modern oceanic carbonate production. Culture experiments investigating the physiological response of coccolithophore calcification to increased CO 2 have yielded contradictory results between and even within species . Here we quantified the calcite mass of dominant coccolithophores in the present ocean and over the past forty thousand years, and found a marked pattern of decreasing calcification with increasing partial pressure of CO 2 and concomitant decreasing concentrations of CO 3 22 . Our analyses revealed that differentially calcified species and morphotypes are distributed in the ocean according to carbonate chemistry. A substantial impact on the marine carbon cycle might be expected upon extrapolation of this correlation to predicted ocean acidification in the future. However, our discovery of a heavily calcified Emiliania huxleyi morphotype in modern waters with low pH highlights the complexity of assemblage-level responses to environmental forcing factors.
Calcification response of a key phytoplankton family to millennial-scale environmental change
Scientific Reports, 2016
Coccolithophores are single-celled photosynthesizing marine algae, responsible for half of the calcification in the surface ocean, and exert a strong influence on the distribution of carbon among global reservoirs, and thus Earth’s climate. Calcification in the surface ocean decreases the buffering capacity of seawater for CO2, whilst photosynthetic carbon fixation has the opposite effect. Experiments in culture have suggested that coccolithophore calcification decreases under high CO2 concentrations ([CO2(aq)]) constituting a negative feedback. However, the extent to which these results are representative of natural populations, and of the response over more than a few hundred generations is unclear. Here we describe and apply a novel rationale for size-normalizing the mass of the calcite plates produced by the most abundant family of coccolithophores, the Noëlaerhabdaceae. On average, ancient populations subjected to coupled gradual increases in [CO2(aq)] and temperature over a fe...
The Biological bulletin, 2014
A natural pH gradient caused by marine CO2 seeps off Vulcano Island (Italy) was used to assess the effects of ocean acidification on coccolithophores, which are abundant planktonic unicellular calcifiers. Such seeps are used as natural laboratories to study the effects of ocean acidification on marine ecosystems, since they cause long-term changes in seawater carbonate chemistry and pH, exposing the organisms to elevated CO2 concentrations and therefore mimicking future scenarios. Previous work at CO2 seeps has focused exclusively on benthic organisms. Here we show progressive depletion of 27 coccolithophore species, in terms of cell concentrations and diversity, along a calcite saturation gradient from Ωcalcite 6.4 to <1. Water collected close to the main CO2 seeps had the highest concentrations of malformed Emiliania huxleyi. These observations add to a growing body of evidence that ocean acidification may benefit some algae but will likely cause marine biodiversity loss, espec...