Christina L. De La Rocha's research while affiliated with French National Centre for Scientific Research and other places

Publications (79)

Article
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The Paleocene‐Eocene Thermal Maximum (PETM, ca. 56 Ma) is marked by a negative carbon isotope excursion (CIE) and increased global temperatures. The CIE is thought to result from the release of ¹³C‐depleted carbon, although the source(s) of carbon and triggers for its release, its rate of release, and the mechanisms by which the Earth system recove...
Article
Numerical simulations of ocean biogeochemical cycles need to adequately represent particle sinking velocities (SV). For decades, Stokes' Law estimating particle SV from density and size has been widely used. But while Stokes' Law holds for small, smooth, and rigid spheres settling at low Reynolds number, it fails when applied to marine aggregates c...
Article
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The stable isotope composition of dissolved silicon in seawater (δ30SiDSi) was examined at 10 stations along the GEOVIDE section (GEOTRACES GA-01), spanning the North Atlantic Ocean (40–60° N) and Labrador Sea. Variations in δ30SiDSi below 500 m were closely tied to the distribution of water masses. Higher δ30SiDSi values are associated with interm...
Article
Full-text available
The stable isotope composition of dissolved silicon in seawater (δ³⁰SiDSi) was examined at 10 stations along the GEOVIDE section, spanning the North Atlantic Ocean (40° N–60° N) and Labrador Sea. Near-surface water δ³⁰SiDSi could not be evaluated due to the very low dissolved silicon (DSi) concentrations (30SiDSi below 500 m were closely tied to th...
Article
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The fraction of net primary production that is exported from the euphotic zone as sinking particulate organic carbon (POC) varies notably through time and from region to region. Phytoplankton containing biominerals, such as silicified diatoms have long been associated with high export fluxes. However, recent reviews point out that the magnitude of...
Article
Transport of sediment across riverine flood plains contributes a significant but poorly constrained fraction of the total chemical weathering fluxes from rapidly eroding mountain belts which has important implications for chemical fluxes to the oceans and the impact of orogens on long term climate. We report water and bedload chemical analyses from...
Article
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Biosilicification has driven variation in the global Si cycle over geologic time. The evolution of different eukaryotic lineages that convert dissolved Si (DSi) into mineralized structures (higher plants, siliceous sponges, radiolarians, and diatoms) has driven a secular decrease in DSi in the global ocean leading to the low DSi concentrations seen...
Article
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Silicon isotope ratios (expressed as δ30Si) in marine microfossils can provide insights into silica cycling over geologic time. Here, we used δ30Si of sponge spicules and radiolarian tests from the Paleogene Equatorial Transect (ODP Leg 199) spanning the Eocene and Oligocene (~50-23 Ma) to reconstruct dissolved silica (DSi) concentrations in deep w...
Data
The effect of food concentration on pellet production rates. Pellet production (pellets ind.-1 d-1) of Centropages sp., Temora longicornis and Acartia sp. as a function of Chl-a concentration (μg l-1) in mesocosms media in a) aggregated and b) dispersed treatments (mean ± SD). (Closed circles) Centropages sp., (open circles) T. longicornis, (grey c...
Article
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Zooplankton feeding activity is hypothesized to attenuate the downward flux of elements in the ocean. We investigated whether the zooplankton community composition could influence the flux attenuation, due to the differences of feeding modes (feeding on dispersed vs. aggregated particles) and of metabolic rates. We fed 5 copepod species—three calan...
Chapter
Wouldn’t it be cool to live in a world that was full of microscopic houses made of glass? Not just plain glass houses either, but ones with nanoscale details, the minuscule evocations of windows and doors, flagpoles, antennas, and weathervanes. What about living in a world that also boasted bazillions of organisms roaming around with glass skeleton...
Chapter
People split into two different camps—those who believe that crystals have special powers and those who roll their eyes. We (the authors) have long been eye rollers. We are scientists, after all. Acquaintances professing spiritual exuberance for quartz or steeping Himalayan rocks to make crystal energy tea send us into stammers of embarrassment. Cr...
Chapter
Any undertaking on silica requires first setting a few terms straight, namely silicon, silica, silicic acid, silicate, and silicone. Even scientists get these words confused. So here it is stripped down to bare bone: Silicon is the element. Silica refers to a tetrahedron formed by one silicon atom bound to four oxygen atoms or to material consistin...
Chapter
Not that you’d necessarily think so if you read the Interwebs or watch a modern Hollywood movie, but human beings are smart. Say what you want about the typical intellect of internet comment makers, but even the greatest of the other living great apes couldn’t even dream of being one, much less of being a coder, and what whale or dolphin knows to h...
Chapter
If pressed to sum up this book with two phrases, we’d pick Silica is your friend and We owe just about everything to silicate weathering. Not only does silicate weathering liberate silica from silicate minerals so it can participate in the silica cycle and all the biomineralization, diatom blooming, and collagen production that goes along with that...
Chapter
Beginning at the beginning sounds like a good call. Or, if not at the beginning, at least at a big beginning. Will the origin of life on Earth do? Silica was more than there. Together silicate minerals, seawater, and hydrothermal heat set in motion a surprisingly simple sequence of chemical reactions that resulted in Earth’s first metabolism, the f...
Chapter
For as long as it has had both water and rock, the Earth has had a silica cycle. This cycle begins with the creation of the silicate rock of new mountains, mountain belts, and ocean floor. Weathering wears these materials down, transferring their silica slowly to the sea. Thanks to plate tectonics, solid silica that ends up at the bottom of the oce...
Chapter
Wouldn’t you like to have beautiful nails and hair and strong bones? Walk down the supplements aisle of your local drugstore and you might get the idea this takes silica. Buy these capsules, please! Colloidal silica gel, horsetail silica, food grade diatomaceous earth, choline-stabilized orthosilicic acid, monomethyl trisilanol. The variety of supp...
Chapter
It took us about 180,000 years but finally we did it. We hit Earth’s carrying capacity for hunters and gatherers. That happened more or less 10,000 years ago and in order to keep going forth and multiplying, humanity had to learn how to farm. Talk about a multidisciplinary endeavor. There were plants and animals to be bred, tools to be designed, ma...
Chapter
We hate to be the ones to break it to you, but if lawns can hate, yours hates you. You mow it, probably once a week during the growing season, and then tidy up, conscientiously clearing away the clippings, bagging them up for the garbage truck. Do you know what it is you are doing? Blades of grass are stocked full of silica in the form of phytolith...
Book
Do you know silica, the tetrahedra of silicon and oxygen constituting the crystals of New Agers and the desiccant in a box of new shoes? It’s no mere mundane mineral. As chemically reacting silicate rocks, silica set off the chain of events known as the origin of life. As biomineralized opal, it is the cell wall, skeleton, spicules, and scales of o...
Article
Full-text available
Despite being one of Earth's major geochemical cycles, the evolution of the silicon cycle has received little attention and changes in oceanic dissolved silica (DSi) concentration through geologic time remain poorly constrained. Silicon isotope ratios (expressed as δ³⁰Si) in marine microfossils are becoming increasingly recognised for their ability...
Article
The silicon isotope composition (δ³⁰Si) of dissolved silicon (DSi) and biogenic silica (BSi) provides information about the silicon cycle and its role in oceanic carbon uptake in the modern ocean and in the past. However, there are still questions outstanding regarding the impact of processes such as oceanic mixing, export and dissolution on the is...
Article
Full-text available
The silicon isotope composition of biogenic silica (δ30SiBSi) in the ocean is a function of the δ30Si of the available dissolved Si (DSi; H2SiO4), the degree of utilisation of the available DSi, and, for some organisms, the concentration of DSi. This makes δ30SiBSi in sediment archives a promising proxy for past DSi concentrations and utilisation....
Article
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The Ganges is one of the world's largest rivers and lies at the heart of a body of literature that investigates the interaction between mountain orogeny, weathering and global climate change. Three regions can be recognised in the Ganges basin, with the Himalayan orogeny to the north and the plateaus of peninsular India to the south together delimi...
Article
Land ocean silica fluxes pass estuaries. Recent data suggest that the isotopic composition of dissolved silica (DSi) is not altered during this transition. This could have major implication for the oceanic isotopic silicon cycle. To improve our knowledge about isotopic Si cycling in estuaries we investigate the silicon isotopic composition (δ30Si)...
Article
The biological pump is the set of processes by which inorganic carbon (e.g., carbon dioxide) is fixed into organic matter via photosynthesis and then sequestered away from the atmosphere generally by transport into the deep ocean. This may be accomplished by the passive sinking of particulate organic matter, through the vertical migration of zoopla...
Conference Paper
This study reports the silicon isotopic composition (δ30Si) of dissolved silicon (DSi) from surface water at the RaTS site in coastal region of the West Antarctic Peninsula (WAP), within Ryder Bay in the Bellingshausen Sea in the Pacific sector. Samples are from the beginning of December 2004 to the middle of February 2005, and from the end of Dece...
Article
Chemical weathering of silicate minerals releases elements into solution whereas the neoformation of secondary minerals works in the opposite direction, potentially confounding estimates of silicate weathering rates. Silicon isotopes (δ30Si) may be a useful tool to investigate these processes. Here, we present 82 δ30Si measurements from surface wat...
Article
Mediated principally by the sinking of organic rich particles from the upper ocean, the biological carbon pump (BCP) is a significant component of the global carbon cycle. It transfers roughly 11 GT C yr-1 into the ocean’s interior and maintains atmospheric carbon dioxide at significantly lower levels than would be the case if it did not exist. Mor...
Article
Full-text available
This study presents six new water column profiles of the silicon isotopic composition (�30Si) of dissolved silicon (DSi) from the Atlantic and Indian sectors of the Southern Ocean and a variable depth box model of silica cycling in the mixed layer that was constructed to illuminate the evolution of surface ocean �30Si over the full course of a year...
Article
A laboratory experiment was designed to investigate the effects of ocean acidification (three levels) in the presence or absence of the clay mineral illite (five concentrations) on the coagulation of organic particles. The formation of aggregates > 1 mm from marine detritus and phytoplankton, and their characteristics and sinking velocity, were mon...
Article
Correlation between particulate organic carbon (POC) and calcium carbonate sinking through the deep ocean has led to the idea that ballast provided by calcium car-bonate is important for the export of POC from the surface ocean. While this idea is certainly to some extent true, it is worth considering in more nuance, for example, examining the diff...
Article
Full-text available
Correlation between particulate organic carbon (POC) and calcium carbonate sinking through the deep ocean has led to the idea that ballast provided by calcium carbonate is important for the export of POC from the surface ocean. While this idea is certainly to some extent true, it is worth considering in more nuance, for example, examining the diffe...
Article
Full-text available
The silicon isotopic composition (δSi30) of the headwaters of the Ganges River, in the Himalaya, ranged from +0.49±0.01‰ to +2.17±0.04‰ at dissolved silicon (DSi) concentrations of 38 to 239 μM. Both the concentration and isotopic composition of DSi in the tributaries increased between the highest elevations to where the Ganges leaves the Himalayas...
Article
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To examine the potentially competing influences of microzooplankton and calcite mineral ballast on organic matter remineralization, we incubated diatoms in darkness in rolling tanks with and without added calcite minerals (coccoliths) and microzooplankton (rotifers). Concentrations of particulate organic matter (POM), suspended or in aggregates, of...
Article
Full-text available
Correlation between particulate organic carbon (POC) and calcium carbonate sinking through the deep ocean has led to the idea that ballast provided by calcium carbonate is important for the export of POC from the surface ocean. While this idea is certainly to some extent true, it is worth considering in more nuance, for example, examining the diffe...
Article
Full-text available
To examine the potentially competing influences of microzooplankton and calcite mineral ballast on organic matter remineralization, we incubated diatoms in darkness in rolling tanks with and without added calcite minerals (coccoliths) and microzooplankton (rotifers). Concentrations of particulate organic matter (POM in suspension or in aggregates),...
Article
Full-text available
This study presents 6 new water column profiles of the silicon isotopic composition (δ30Si) of dissolved silicon (DSi) from the Atlantic and the Indian sectors of the Southern Ocean and a variable depth box model of silica cycling in the mixed layer constructed to illuminate the evolution of surface ocean δ30Si over the full course of a year. In ke...
Article
[1] Chemical weathering is an integral part of both the rock and carbon cycles and is being affected by changes in land use, particularly as a result of agricultural practices such as tilling, mineral fertilization, or liming to adjust soil pH. These human activities have already altered the terrestrial chemical cycles and land-ocean flux of major...
Article
Full-text available
To examine the potentially competing influences of microzooplankton and calcite mineral ballast on organic matter remineralization, we incubated diatoms in darkness in rolling tanks with and without added calcite minerals (coccoliths) and microzooplankton (rotifers). Concentrations of particulate organic matter (POM), suspended or in aggregates, of...
Article
Full-text available
Over the past few decades, we have realized that the silica cycle is strongly intertwined with other major biogeochemical cycles, like those of carbon and nitrogen, and as such is intimately related to marine primary production, the efficiency of carbon export to the deep sea, and the inventory of carbon dioxide in the atmosphere. For nearly 20 yea...
Article
Iron solubility (cFeS) ranged from 0.4 to 1.5 nmol L-1, decreasing from south to north in three different Southern Ocean zones (the Coastal Zone, the Antarctic Zone, and the Polar Frontal Zone plus the Subantarctic Zone). This decrease was at times correlated with an increase in temperature. Organic Fe solubility (cFe(S, org)), which was obtained b...
Article
Full-text available
Dissolved silicon (DSi) in rivers currently represents ~85% of DSi input to the ocean, giving it a significant influence over the average stable isotopic composition (δ30Si) of seawater. In the modern ocean, both the average δ30Si of silica exported to the sediments and of deep water DSi should therefore be very close to the average value of the ri...
Article
There is a strong correlation between sinking fluxes of CaCO3 biominerals and particulate organic carbon (POC), leading to suggestions that sinking fluxes of CaCO3 might control the amount of POC reaching the deep sea. Research has shown that CaCO3 (which is considerably denser than both seawater and particulate organic matter), in the form of cocc...
Article
Seawater samples from two separate cruises in the Southern Ocean (ANTXXI/3 (EIFeX) and ANTXXIII/9) were collected for measurements of iron solubility by 55Fe addition. For both sets of samples, a significant loss of the dissolved portion of the added Fe was observed during the 72hour duration of each Fe solubility measurement incubation. The decrea...
Article
We report here the silicon isotopic composition (δ30Si) of dissolved silicon (DSi) from 42 surface water samples from the Drake Passage, the Weddell Gyre, other areas south of the Southern Boundary of the Antarctic Circumpolar Current (ACC), and the ACC near the Kerguelen Plateau, taken between the beginning of February and the end of March 2007. F...
Chapter
Full-text available
Introduction Accumulation rates of biogenic silica (BSi) have long been used to infer past levels of primary production (e.g. Charles et al., 1991; Mortlock et al., 1991; Kumar et al., 1995; Schelske 1999; Frank et al., 2000; Anderson et al., 2002; Chase et al., 2003). In some respects, BSi measurements are more useful than organic carbon accumulat...
Article
Understanding the response of diatoms to nutrient stress is important, both on its own terms and for the accurate portrayal of this key group of organisms in ecological and biogeochemical models. We therefore examined the growth and elemental composition of Thalassiosira weissflogii grown to nutrient depletion and then its recovery after nutrient r...
Article
Measurements of δ13C, δ15N, and C/N on diatom-bound organic matter were made over the Holocene and Last Glacial Maximum (LGM) from three sediment cores in the Southern Ocean, one each from the Atlantic, Indian, and Pacific sectors. The site in the Scotia Sea (Atlantic sector) differed considerably from the other two sites by having markedly lower δ...
Article
Full-text available
Correlations of particulate organic carbon (POC) and mineral fluxes into sediment traps in the deep sea have previously suggested that interactions between organic matter and minerals play a key role in organic matter flux to the deep. Here experiments were carried out in rolling tanks to observe the incorporation of suspended biogenic minerals ( c...
Article
Full-text available
Inorganic carbon concentrating mechanisms (CCMs) catalyse the accumulation of CO(2) around rubisco in all cyanobacteria, most algae and aquatic plants and in C(4) and crassulacean acid metabolism (CAM) vascular plants. CCMs are polyphyletic (more than one evolutionary origin) and involve active transport of HCO(3)(-), CO(2) and/or H(+), or an energ...
Article
Full-text available
The effect of phytoplankton on the other compartments of a simple microbial loop consisting of dissolved matter, bacteria and nanoflagellates was investigated in three 1000 1 mesocosms. These mesocosms were inoculated with a natural bacterial community and (1) no other additions (No Addition tank), (2) Phaeocystis globosa (Phaeocystis tank), or (3)...
Article
An 18 million year record of the Ca isotopic composition (δ44/42Ca) of planktonic foraminiferans from ODP site 925, in the Atlantic, on the Ceara Rise, provides the opportunity for critical analysis of Ca isotope-based reconstructions of the Ca cycle. δ44/42Ca in this record averages +0.37 ± 0.05 (1σ SD) and ranges from +0.21‰ to +0.52‰. The record...
Article
By altering the number, size, and density of particles in the ocean, the activities of different phytoplankton, zooplankton, and microbial species control the formation, degradation, fragmentation, and repackaging of rapidly sinking aggregates of particulate organic carbon (POC) and are responsible for much of the variation in the efficiency of the...
Data
An 18 million year record of the Ca isotopic composition (d44/42Ca) of planktonic foraminiferans from ODP site 925, in the Atlantic, on the Ceara Rise, provides the opportunity for critical analysis of Ca isotope-based reconstructions of the Ca cycle. ?44/42Ca in this record averages +0.37+/-0.05 (1 sigma SD) and ranges from +0.21? to +0.52?. The r...
Article
The delta Si-30 and delta N-15(diatom) of diatom opal provide a view of nutrient utilization in past oceans and are used to formulate and test hypotheses concerning Southern Ocean productivity and fluctuations in atmospheric CO2 over glacial cycles. Water column profiles of the Si and N isotopic composition of nutrients and the delta N-15(diatom) o...
Article
Full-text available
It has been proposed that the calcium isotopic composition (delta^{44/42}Ca) of marine biogenic carbonates can be used to reconstruct past changes in the Ca2+ content of the ocean, lending insight into in weathering fluxes of Ca to the oceans and atmospheric concentrations of CO2. Here we present a 20 million year record of the delta^{44/42}Ca of p...
Article
There has long been scepticism about the geochemical evidence that the ancient ocean was markedly warm. A fresh approach bolsters the case for an ocean that, in the distant past, was indeed quite hot.
Article
Full-text available
To address whether the incorporation of suspended minerals drives the sedimentation of particulate organic carbon in the ocean or vice versa, incubations of phytoplankton-detritus aggregates were set up in rolling tanks containing seawater and suspended clay ( illite) or calcium carbonate at concentrations ranging between 10 and 50,000 mu g L-1. Th...
Article
Here we present the first known record of the germanium isotopic composition of sedimentary diatom opal and the results of diatom culturing experiments. Analyses were performed using a hydride generation system coupled to a MC-ICP-MS and variations in the 74Ge/70Ge ratio are reported as delta74Ge. Diatom cultures grown in the laboratory showed no n...
Article
A 2-box model has been used to assess the impact of both long- and short-term budgetary imbalance in the silica cycle on the average silicon isotopic composition (δ30Si) of the ocean and marine sediments. Over a 100-ky time span, such as a Quaternary glacial cycle, a sustained change in the riverine flux of silicon to the oceans could alter the ave...
Article
The influence of temperature on calcium (Ca) isotope fractionation during biomineralization was investigated through the paired analyses of δ44/42Ca (via MC-ICP-MS) and δ18O on the calcite tests of 12 species of planktonic foraminifera from core-top sediments. Samples were collected from a suite of box-cores from sites between 60°N and 30°S in the...
Article
The ecological success of marine diatoms comes despite their unusual additional requirement for silicon, a nutrient that often limits their growth in the ocean. There may be, however, some physiological and ecological advantages to silicon limitation. A model of nitrogen and silicon metabolism in diatoms (Flynn et al. 1997; Flynn and Martin- Jezequ...
Article
Previous work has demonstrated the variable temperature dependence of calcium isotope fractionation (delta 44Ca) in planktonic foraminifera up to 0.240/00 ° C-1. While the majority of this work has focused on cultured samples and plankton tows, there have been no detailed studies of core-top sediments. Here we present the results of delta 44Ca (44C...
Article
Marine diatoms take up silicic acid for the buildup of their opaline shells and discriminate against the heavier silicon isotope. For the first time, the overall oceanic distribution of silicon isotopes has been estimated by integration of the Hamburg Model of the Ocean Carbon Cycle, version 4 (HAMOCC4). It is shown that the relationship between th...
Article
The silicon isotope composition (δ30Si) of biogenic opal provides a view of the silica cycle at times in the past. Reconstructions require the knowledge of silicon isotope fractionation during opal biomineralization. The δ30Si of specimens of hexactinellid sponges and demosponges growing in the modern ocean ranged from -1.2‰ to -3.7‰ (n = 6), corre...
Data
The silicon isotope composition (d30Si) of biogenic opal provides a view of the silica cycle at times in the past. Reconstructions require the knowledge of silicon isotope fractionation during opal biomineralization. The d30Si of specimens of hexactinellid sponges and demosponges growing in the modern ocean ranged from -1.2 per mil to -3.7 per mil...
Article
Widespread utilization of silicon isotope ratio variations (δ29Si and δ30Si) as a geochemical and paleoceanographic tracer has been hampered by the hazardous nature of the analysis, which requires the use of a fluorinating gas. Multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) provides a safer means of silicon isotope analysis...
Article
Significant variations in the isotopic composition of marine calcium have occurred over the last 80 million years. These variations reflect deviations in the balance between inputs of calcium to the ocean from weathering and outputs due to carbonate sedimentation, processes that are important in controlling the concentration of carbon dioxide in th...
Article
The first data on the distribution of the stable isotopes of silicon in marine and freshwater systems are reported. Both marine and riverine δ30Si are more positive than δ30Si of igneous rocks, suggesting isotopic fractionation during weathering and clay formation and/or biomineralization. The δ30Si value for dissolved silicic acid from several oce...