- Earthworms produce granules of calcium carbonate that form from an amorphous calcium carbonate suspension.
- The microspherulites of amorphous calcium carbonate coalesce and recrystallize.
- Fractionation of C isotopes occurs as the ACC recrystallizes with εcalcite-ACC = −1.20 ± 0.52%.
- This is consistent with a dissolution-reprecipitation pathway rather than solid state rearrangement.
- This may be important for the interpretation of CaCO3-based C isotope environmental proxies.
In this study we investigate carbon isotope fractionation during the crystallization of biogenic calcium carbonate. Several species of earthworm including Lumbricus terrestrissecrete CaCO3. Initially a milky fluid comprising micro-spherules of amorphous CaCO3(ACC) is secreted into pouches of the earthworm calciferous gland. The micro-spherules coalesce and crystalize to form millimetre scale granules, largely comprising calcite. These are secreted into the earthworm intestine and from there into the soil. L. terrestriswere cultured for 28 days in two different soils, moistened with three different mineral waters at 10, 16 and 20 °C. The milky fluid in the calciferous glands, granules in the pouches of the calciferous glands and granules excreted into the soil were collected and analysed by FTIR spectroscopy to determine the form of CaCO3 present and by IRMS to determine δ13C values. The milky fluid was ACC. Granules removed from the pouches and soil were largely calcite; the granules removed from the pouches contained more residual ACC than those recovered from the soil. The δ13C values of milky fluid and pouch granules became significantly more negative with increasing temperature (p ≤ 0.001). For samples from each temperature treatment, δ13C values became significantly (p ≤ 0.001) more negative from the milky fluid to the pouch granules to the soil granules (−13.77, −14.69 and −15.00 respectively at 10 °C; −14.37, −15.07 and −15.18 respectively at 16 °C and −14.89, −15.41 and −15.65 respectively at 20 °C). Fractionation of C isotopes occurred as the ACC recrystallized to form calcite with the fractionation factor εcalcite-ACC = −1.20 ± 0.52‰. This is consistent with the crystallization involving dissolution and reprecipitation rather than a solid state rearrangement. Although C isotopic fractionation has previously been described between different species of dissolved inorganic carbon and various CaCO3 polymorphs, this is the first documented evidence for C isotope fractionation between ACC and the calcite it recrystallizes to. This phenomenon may prove important for the interpretation of CaCO3-based C isotope environmental proxies.
Typical FTIR spectra for milky fluid, a granule recovered from one of the pouches (pouch granule), and a granule recovered from the soil (soil granule); all spectra relate to samples from the same earthworm. Reference spectra for synthetic calcite and ACC are also shown. Spectra are vertically offset on the absorbance axis for clarity. The major calcium carbonate peaks (υ1 to υ4) are labelled. Calcite shows peaks at ∼714 cm−1 (υ4), ∼866 cm−1 (υ2), ∼1090 cm−1 (υ1) and 1420–1470 cm−1 (υ3); amorphous calcium carbonate lacks the ∼714 cm−1 peak.
Many biominerals form from amorphous calcium carbonate (ACC), but this phase is highly unstable when synthesised in its pure form inorganically. Several species of earthworm secrete calcium carbonate granules which contain highly stable ACC. We analysed the milky fluid from which granules form and solid granules for amino acid (by liquid chromatography) and functional group (by Fourier transform infrared (FTIR) spectroscopy) compositions. Granule elemental composition was determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and electron microprobe analysis (EMPA). Mass of ACC present in solid granules was quantified using FTIR and compared to granule elemental and amino acid compositions. Bulk analysis of granules was of powdered bulk material. Spatially resolved analysis was of thin sections of granules using synchrotron-based μ-FTIR and EMPA electron microprobe analysis. Results The milky fluid from which granules form is amino acid-rich; the CaCO3 phase present is ACC. Even four years after production, granules contain ACC. No correlation exists between mass of ACC present and granule elemental composition. Granule amino acid concentrations correlate well with ACC content, consistent with a role for amino acids (or the proteins they make up) in ACC stabilisation. Intra-granule variation in ACC and amino acid concentration was high for granules produced by the same earthworm. Maps of ACC distribution produced using synchrotron-based μ-FTIR mapping of granule thin sections and the relative intensity of the ν2: ν4 peak ratio, cluster analysis and component regression using ACC and calcite standards showed similar spatial distributions of likely ACC-rich and calcite-rich areas. We could not identify organic peaks in the μ-FTIR spectra and thus could not determine whether ACC-rich domains also had relatively high amino acid concentrations. No correlation exists between ACC distribution and elemental concentrations determined by EMPA. Conclusions ACC present in earthworm CaCO3 granules is highly stable. Our results suggest a role for amino acids (or proteins) in this stability. We see no evidence for stabilisation of ACC by incorporation of inorganic components. Graphical abstract Synchrotron-based μ-FTIR mapping was used to determine the spatial distribution of amorphous calcium carbonate in earthworm-produced CaCO3 granules.
At one of the world’s deepest undersea hydrothermal vents, tiny shrimp are piled on top of each other, layer upon layer, crawling on rock chimneys that spew hot water. Bacteria, inside the shrimps’ mouths and in specially evolved gill covers, produce organic matter that feed the crustaceans.
Scientists at NASA’s Jet Propulsion Laboratory in Pasadena, California, are studying this mysterious ecosystem in the Caribbean to get clues about what life could be like on other planetary bodies, such as Jupiter’s icy moon Europa, which has a subsurface ocean.
“For two-thirds of the Earth’s history, life has existed only as microbial life,” said Max Coleman, senior research scientist at JPL. “On Europa, the best chance for life would be microbial.”
The particular bacteria in the vents are able to survive in extreme environments because of chemosynthesis, a process that works in the absence of sunlight and involves organisms getting energy from chemical reactions. In this case, the bacteria use hydrogen sulfide, a chemical abundant at the vents, to make organic matter. The temperatures at the vents can climb up to a scorching 750 degrees Fahrenheit (400 degrees Celsius), but waters just an inch away are cool enough to support the shrimp. The shrimp are blind, but have thermal receptors in the backs of their heads.
“The overall objective of our research is to see how much life or biomass can be supported by the chemical energy of the hot submarine springs,” Coleman said.
Hydrogen sulfide is toxic to organisms in high concentrations, but the bacteria feeding the shrimp need a certain amount of this chemical to survive. Nature has worked out a solution: The shrimp position themselves on the very border between normal, oxygenated ocean water and sulfide-rich water so that they and the bacteria can coexist in harmony.
“It’s a remarkable symbiotic system,” Coleman said.
Coleman was part of a team led by Chris German at the Woods Hole Oceanographic Institution, in Woods Hole, Massachusetts, that discovered these vents in 2009, off the west coast of Cuba. This research, funded under NASA’s Astrobiology Science and Technology for Exploring Planets program, detected the vents by picking up the chemical signals of their plumes of water in the ocean.
The researchers returned in 2012 on the RV Atlantis with a robotic vehicle called Jason, supported by the National Science Foundation. Scientists collected extensive specimens from two hydrothermal vent fields: The Von Damm field at 7,500 feet (2,300 meters) and Piccard at more than 16,000 feet (4,900 meters), which is the world’s deepest.
Coleman and collaborator Cindy Van Dover, marine biologist at Duke University, Durham, North Carolina, examined the shrimp for the first time when the same team returned in 2013 on the RV Falkor, provided by the Schmidt Ocean Institute in Palo Alto, California. Van Dover returned soon after using the robotic vehicle Hercules aboard the Exploration Vessel Nautilus, and did more collections and studies.
A bonus finding from studying this extreme oasis of life is that some of the shrimp, called Rimicaris hybisae, appear to be cannibalistic. The researchers discovered that when the shrimp arrange themselves in dense groups, bacteria seem to be the main food supplier, as the shrimp likely absorb the carbohydrates that the bacteria produce. But in areas where the shrimp are distributed more sparsely, the shrimp are more likely to turn carnivorous, eating snails, other crustaceans, and even each other.
Although the researchers did not directly observe Rimicaris hybisae practicing cannibalism, scientists did find bits of crustaceans in the shrimps’ guts. And Rimicaris hybisae is the most abundant crustacean species in the area by far.
“Whether an animal like this could exist on Europa heavily depends on the actual amount of energy that’s released there, through hydrothermal vents,” said Emma Versteegh, a postdoctoral fellow at JPL.
The group received funding for shrimp-collecting expeditions from NASA’s Astrobiology Science and Technology for Exploring Planets (ASTEP) program, through a project called “Oases for Life.” That name is especially appropriate for this investigation, Coleman said.
“You go along the ocean bottom and there’s nothing, effectively,” Coleman said. “And then suddenly we get these hydrothermal vents and a massive ecosystem. It’s just literally teeming with life.”
This research was conducted in collaboration with the Woods Hole Oceanographic Institution and Duke University. The Schmidt Ocean Institute provided technical and financial support for marine and underwater robotic operations during the 2013 RV Falkor cruise. The California Institute of Technology in Pasadena manages JPL for NASA.
Jet Propulsion Laboratory, Pasadena, Calif.
My presentation at Goldschmidt 2014.
The Mineralogical Society enabled me to attend this year’s European Geosciences Union General Assembly by means of a Senior Bursary. My postdoctoral project at NASA-JPL has yielded interesting data on speciation of carbon in basalts, and carbon in the food chain around the world’s deepest hydrothermal vents (Mid-Cayman Rise). I have been keen to present and discuss my findings at an international meeting and an excellent opportunity to do so arose with the session “Hydrothermal energy transfer and its relation to ocean carbon cycling: from mechanisms and rates to services for marine ecosystems” at EGU2014.
As I am relatively new to the field of hydrothermal vent research, it was exciting to meet people, whom I only knew by name. The session started off with several excellent oral presentations, of which I learned a lot. Did you know, for example, that Hydrothermal particulate organic carbon could be the dominant source of carbon to the seafloor? And that iron in the ocean probably mostly derives from hydrothermal sources? In the afternoon I presented my poster entitled: “Previously unsuspected dietary habits of hydrothermal vent fauna: The bactivorous shrimp Rimicaris hybisae can be carnivorous”. There was considerable interest for my poster and I had some lively discussions with colleagues in the field. Also, I received some good suggestions on the interpretation of my data.
It had been five years since I had been to an EGU General Assembly, and I almost forgot how nice it is to also stay in touch with the wider field of earth sciences, and some “old” interests. It was great to learn about new developments in for example stable-isotope biogeochemistry and palaeoclimatology. After having worked in several positions in different countries, a meeting like EGU also provides the opportunity to catch up with many former colleagues. Many stories were told, but more importantly, many plans were made for research collaborations and future grant proposals. All in all, a very productive meeting. Thank you, Mineralogical Society, for enabling me to attend it!