Opal Phytoliths Research Articles

Intraspecific morphological variation with biometry of Distephanus speculum (Silicoflagellata)

Living specimens of Distephanus speculum (Silicoflagellata) were collected in waters of <150 m depth in the Pacific Sector of the Southern Ocean (57°31.6′S, 150°02.9′E), South of Tasman Island, and a biometric study has been conducted. The skeleton of D . speculum has a simple morphology, which can be readily expressed quantitatively. Using a new methodology, repeated measurements were obtained and converted to numerical indices. The circumference of the basal rings was the most useful character for subdivision into groups, and using this parameter we recognized two populations in the 620 studied specimens: (1) 500 individuals were placed in Group A, with a basal ring circumference of 53 to 67 µm, and a difference in length of spine axes from 2 to 6 μm; and (2) 120 individuals were placed in Group B (basal ring circumference 80 to 105 µm, difference in length of spine axes 3 to 6 µm). The circumference of the basal ring in Group B is approximately 10 µm smaller than in Distephanus speculum giganteus [Bukry, D., 1979. Comments on opal phytoliths and stratigraphy of Neogene Silicoflagellates and Coccoliths at Deep Sea Drilling Project Site 397 off Northwest Africa. Initial report of the DSDP, Washington, 49:977–1009.], and Distephanus boliviensis [Bukry, D., 1976a. Silicoflagellate and coccolith stratigraphy, Norwegian–Greenland Sea. Initial Report of DSDP LEG 38. Initial report of the DSDP, Washington, 38:843–855.; Bukry, D., 1976b. Silicoflagellate and coccolith stratigraphy, southeastern Pacific Ocean, Deep Sea Drilling Project Leg 34. Initial report of the DSDP, Washington, 34:715–735].

Distinct silicon and germanium pathways in the soil‐plant system: Evidence from banana and horsetail

Plants strongly impact the continental silicon cycle by taking up Si and precipitating opal phytoliths which are recycled into the soil. Studying Ge incorporation, a chemical analog of Si, relative to Si may provide a useful tracer of Si pathways. However, Ge uptake and transport through plants and the impact on Ge/Si of phytoliths remain poorly understood. Here, we report Ge uptake and accumulation and Ge/Si fractionation in all plant parts and solutions from: (1) hydroponic banana, (2) in situ sampled banana, and (3) horsetails. We further combine these data with δ29Si from banana plants. Our data reconcile opposite conclusions drawn from previous studies on Ge uptake and pathways. No discrimination of Ge occurred at the root‐solution interface. Banana and horsetails were shown to accumulate Ge in roots: a previous study provided evidence of low Ge/Si ratios in root phytoliths which contrasts with high bulk Ge/Si ratios in roots we report here. This suggests that Ge is organically trapped in roots. Consequently, shoots display lower Ge/Si ratios, without fractionation between shoot parts since Ge would follow transpiration stream as silicon, and is not discriminated between shoot parts. This contrasts with the two‐step discrimination against heavy Si isotopes, at the root‐solution interface, and then within the shoots. The soil composition (clays versus Fe oxides) has a leading role on the Ge/Si signatures of plants which may in turn impact on the Si and Ge fluxes to the global ocean.

Biogenic silica: a neglected component of the coupled global continental biogeochemical cycles of carbon and silicon

AbstractOn geological time‐scales (≥106 years), the global geochemical cycles of carbon and silicon are coupled by the drawdown of atmospheric CO2 through chemical weathering of Ca‐ and Mg‐silicate minerals in continental rocks. Rivers transport the soluble products of weathering (cations, alkalinity and silicic acid) to the oceans, where they are utilized by marine ecosystems. On decadal to glacial–interglacial time‐scales, however, large biotic fluxes and storages of Si within terrestrial and freshwater ecosystems need to be taken into account. Recent studies have emphasized the importance of Si‐accumulating plants, which deposit significant amounts of amorphous hydrated silica in their tissues as opal phytoliths. These include grasses, sedges, palms, some temperate deciduous trees and conifers, and many tropical hardwoods. Landscapes dominated by accumulator plants, such as tropical rainforests, grasslands, herbaceous wetlands and bamboo forests, act as ‘silica factories’. Important ‘silica bioengineers’ in freshwater ecosystems comprise diatoms, sponges and chrysophytes. This paper reviews the biological role of Si in higher plants, the impact of vegetation on rates of chemical weathering, the fluxes of Si through catchment ecosystems, lakes and rivers, and the potential contribution of new geochemical and isotopic tracers to Si biogeochemistry. Multiproxy investigations of lake sediments will provide novel insights into past variations in Si biocycling from terrestrial to aquatic realms on 10–106 year time‐scales. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Towards an understanding of late Quaternary variations in the continental biogeochemical cycle of silicon: multi‐isotope and sediment‐flux data for Lake Rutundu, Mt Kenya, East Africa, since 38 ka BP

AbstractSilicon is an essential nutrient for marine diatoms, which dominate the export of organic carbon to the deep ocean. Despite the dominance of the oceanic Si budget by fluvial inputs and the role of the land biosphere in controlling Si losses from rocks and soils to rivers, few studies have considered how continental biogeochemical Si fluxes varied on an orbital timescale. We reconstruct changes in Si cycling by the catchment‐lake ecosystem of Lake Rutundu, Mt Kenya (3078 m a.s.l.), over the last ca. 38 ka, using a novel combination of lake‐sediment fluxes and stable‐isotope (δ13C, δ15N, δ18O, δ30Si) data. Under glacial conditions (38.3–14.3 ka BP), high diatom productivity was maintained by substantial losses of dissolved SiO2 and soil nutrients from a sparse, leaky, terrestrial ecosystem. During the following period of enhanced monsoon rainfall and seasonality (14.3–9.5 ka BP), rapid Si cycling by fire‐prone, mesic grassland was associated with substantial aeolian transport of opal phytoliths by smoke plumes, but greatly reduced nutrient losses in runoff. Invasion of tall, subalpine shrubs after 9.5 ka BP further enhanced landscape stability, leading to very low sediment fluxes of both phytoliths and diatoms. This case study offers new insights into processes that may have operated at biome to continental scales during the late Quaternary. © Natural Environment Research Council (NERC) copyright 2008. Reproduced with the permission of NERC. Published by John Wiley &amp; Sons, Ltd.

Extending the Phytolith Evidence for Early Maize (Zea mays ssp. mays) and Squash (Cucurbita sp.) in Central New York

The timing of the adoptions of maize and squash across eastern North America has been a topic of long-standing interest among archaeologists and paleoethnobotanists. The use of flotation for macrobotanical remains beginning in the 1960s and 1970s coupled with the application of accelerator mass spectrometry dating beginning in the 1980s has led to substantial revisions of knowledge about the history of these crops in the region. A complementary source of evidence for the crops' histories in the eastern North America comes from opal phytoliths. Analysis of phytolith assemblages recovered from charred food residues has shown that maize and squash were being used in central New York well before the macrobotanical record indicates. In combination with previously analyzed samples, 16 additional residue assemblages help to clarify the history of maize and squash in central New York. The results indicate that maize and squash were being used in New York by 2270 B.P. and 2945 B.P., respectively.

Paleolimnological evidence of Holocene climatic changes in Lake Blanca, southern Uruguay

Paleolimnological data are presented on Holocene climatic changes in Lake Blanca, a small (0.6 km2), coastal fresh waterbody in southern Uruguay. Using a sediment core that extended to 7,300 year BP, analyses of pooid, panicoid and chloridoid phytoliths (Poaceae) allowed us to identify 16 Opal Phytoliths Association Zones (OPAZ). Both temperature and humidity indices were calculated from relative percentages of opal phytoliths and the climatic trends were inferred. During the early Holocene, prior to the first Holocene marine transgression (∼ ∼8,000–7,000 yr BP), cool-arid climatic conditions were inferred. After the first Holocene transgression, predominance of cool-humid conditions was registered until about 4,000 yr BP. A transition from cool-semiarid/arid to alternate warm-temperate and humid-very-humid conditions was detected for ∼∼4,000–1,000 yr BP. Increases in trophic state were observed because of such a climatic amelioration. After ∼ ∼1,000 yr BP, a shift from warm to temperate and cool temperatures was inferred. Such a cooling episode was assigned to a “LIA” which took place by the end of the 18th century and the beginning of the 19th century. A decrease in trophic state was observed during this climatic deterioration. After such a little ice age, present temperate humid conditions were established. The humidity indices calculated from relative percentages of opal phytoliths for the last ∼ ∼70 years were compared to annual rainfall data. Such a comparison showed that opal phytoliths are reliable indicators of humidity.

Distribution of opal phytoliths in a tropical rain forest at Lambir Hills National park, northern Borneo

Distribution of opal phytoliths in a tropical rain forest at Lambir Hills National park, northern Borneo

Relationships between Trophic State, Paleosalinity and Climatic Changes during the First Holocene Marine Transgression in Rocha Lagoon, Southern Uruguay

Paleolimnological data are presented on trophic development, climatic change and sea level variations in Rocha Lagoon, a 72 km2 coastal lagoon in southern Uruguay. Using a sediment core that extended from 7000 to about 3700 yr BP, analyses of organic matter, carbonate, diatoms and chrysophyte cysts were used to track the early Holocene paleolimnological conditions of Rocha Lagoon. Opal phytoliths were also counted and identified, both temperature and humidity indices were calculated, and Opal Phytolith Association Zones (OPAZ) were identified by performing Principal Coordinates Analysis (PCO). Diatom Association Zones (DAZ) corresponding to marine/brackish and brackish/freshwater episodes were closely related to changes in trophic state. Those DAZ representing marine/brackish stages exhibited a lower trophic state than those DAZ dominated by brackish and freshwater diatoms. This highlights that during the first Holocene marine transgression, Rocha Lagoon did not continuously exhibit marine/brackish conditions as reported in previous papers. Instead, three brackish/freshwater episodes related to sea level variation and changes in humidity were identified. The first episode, by ~6000 yr BP, was related to sea level change as no significant changes in either temperature or humidity indices were observed. The second episode, between 5000 and 4400 yr BP, was related to both a sea level decrease and an increase in humidity, as a transition from humid to very humid climate was inferred. Concomitant decreases in salinity and increases in trophic state were also observed. The third episode, after ~4000 yr BP, was related to the end of the first Holocene regressive phase when sea level was slightly below present levels. Further decreases in salinity and increases in trophic state were detected. The paleoclimatic trends inferred in this study were in close agreement with other regional studies on climatic change, as cool temperatures were inferred. However, major changes in humidity were also detected. A humid to very humid climate was inferred for ~7000–4500 yr BP, but the occurrence of a semiarid/arid climate was inferred for ~4500–3700 yr BP. Our data suggest that during transgressive and regressive events there might be higher frequency and lower amplitude sea level oscillations that might lead to changes in salinity and trophic state of coastal aquatic systems. Such oscillations could only be tracked by high resolution analyses of sedimentary records and could be best interpreted with complementary data on paleoclimate. In addition, microfossils such as diatoms and opal phytoliths were shown to be very sensitive to such paleoenvironmental changes.

Grass Phytolith Analysis

The vegetative history of eastern North Da kota is broadly known from pollen and multi-proxy investigations of lake basins from across the re gion (Clark et al. 2001; Dean and Schwalb 2000; Wright et al. 2004). These records suggest that parkland or savanna rapidly developed following glacial retreat and subsequent drainage of glacial Lake Agassiz to the south (10,800 to 9400 14C year B.P.) with true grasslands (or prairie) emerging by 9000 14C year B.P. Changes in grassland com position of the region is poorly documented in the fossil record throughout the Holocene. While stable carbon isotopes offer some insight (Clark et al. 2001), this proxy is limited in that it cannot dis tinguish between changes in forest cover from C3 grasslands. Fossil phytolith assemblages are used to infer changes in Holocene grassland vegetation and cli mate at the Rustad site. The evidence presented comes from two stratigraphic columns allowing evaluation of local variability in phytolith assem blages and validation of results. The soils and sedi ments sampled in this study span much of the last 9,000 years. Several major environmental changes are hypothesized to have occurred during this time and should be detectable with opal phytolith analy sis. First, the early Holocene (12,000 to 8000 years B.P.) was a period of major climatic warming. Grassland response to this warming should show up in the phytolith record as a shift from a C3 grass dominated cover to a mixed grass prairie including both tall (mesic adapted) and short (xe ric adapted) C4 grasses along with diverse C3 grass taxa. Second, sometime during the mid-Holocene (8000 to 5000 years B.P.) many, but not all, re gional paleoenvironmental records suggest one or more periods of higher temperatures and greater aridity, broadly labeled the Altithermal. This mid Holocene aridity should be detectable in the phytolith record as a relative increase in phytolith morphotypes from the xeric-adapted, C4 short grasses such as blue grama, side oats grama, and buffalo grass. The goal of this chapter is to report the find ings of phytolith analysis and offer some prelimi nary interpretations. The analysis focuses on the grass phytolith portion of the assemblages, al though there is great potential for additional in formation from the arboreal phytolith component and from other proxy data, including carbon iso topes, terrestrial snails, and vertebrate fauna. METHODS

A Keith Phase Burial on the High Plains of Kansas

A flexed adult male burial was excavated from the cut bank of a dry tributary of Museum Creek, Sheridan County, Kansas. Associated artifacts include a well-worn grinding stone and a bone tool of indeterminate function. Analysis of sediment from the grinding stone led to the identification of diagnostic opal phytoliths from hackberry fruits. The geographic location of the burial and a radiocarbon age determination of 1370 ± 70 RCYBP are sufficient to place the burial site in the Keith phase taxon. A summary of Keith phase burials shows a great degree of variation in burial practices. The location of the solitary 14SD351 burial suggests that it is far from a settlement.

Relationships between Holocene sea-level variations, trophic development, and climatic change in Negra Lagoon, Southern Uruguay

Paleolimnological data are presented on trophic development, climatic change and sea level variations in Negra Lagoon, a 142 km2 coastal lagoon in southern Uruguay. Using a sediment core that extended to the early Holocene, analyses of organic matter, carbonate, diatoms and opal phytoliths allowed us to track changes in trophic state and paleosalinity levels, which were closely related to Holocene sea level variation, temperature and humidity. Diatom Association Zones (DAZ) corresponding to transgressive events were dominated by marine/brackish taxa and relatively low organic matter values, while those DAZ corresponding to regressive events showed increases in brackish/freshwater diatoms and organic matter. Opal Phytoliths Association Zones (OPAZ) also were identified, temperature and humidity indices were calculated, and climatic trends were inferred. During the middle Holocene (i.e., ~5000–4000 yr BP), cool–dry climatic conditions were established. After ~4000 yr BP, a transition from cool to warm–humid conditions was observed, but fully warm humid conditions established only after ~1700 yr BP. Such climatic amelioration led to increases in trophic state.

Phytoliths as paleoenvironmental indicators in a dune field on the northern Great Plains

Recent applications of grass phytolith analysis on the northern Great Plains emphasize the use of this proxy as an indicator of regional paleoenvironmental change. In contrast, opal phytolith assemblages from a late Holocene (<4100 14C yrs BP) parabolic dune correlate more strongly with localized changes in topography and moisture during episodes of soil formation. This is because soils on eolian landforms are often short-lived, produce low phytolith inheritance, and are less likely to form and preserve during less humid intervals. Phytolith assemblages preserved in these contexts therefore lack the temporal and spatial integration necessary to be clear indicators of regional vegetative succession and climate change.

Mid–late Holocene cultural and environmental dynamics in Eastern Uruguay

This paper reviews the relationship between prehistoric mounds (5000 years BP to 17th century) with main landscape features, particularly wetlands, in the east of Uruguay. Former archeological researchers did recognize this relationship, but it was interpreted by extrapolating current environments to 5000 years of cultural behavior. In an effort to better understand how environmental dynamics were linked to the cultural record, a set of proxy records (diatoms, opal phytoliths, gastropods, shells) were introduced to take into account local environmental evolution data according to global and regional environmental evolution models. The main environmental events during the mid and late Holocene show a high correspondence with mound builders’ spatial arrangements.

Glacial anticyclone recorded in Palouse loess of northwestern United States

Climate simulations for the Last Glacial Maximum using general circulation models typically show a glacial anticyclone that produced an easterly wind anomaly south of the North American ice sheets. Evidence of this phenomenon has not been found in eolian sedimentary deposits that record surface wind patterns. Luminescence ages of loess and accompanying paleoecologic records from opal phytoliths and paleosol units across the Columbia Plateau, Washington State, United States, document a decrease, up to fivefold, in regional dust production and accumulation from 35 ka to 15 ka. This interval corresponds to simulations indicating that a glacial anticyclone weakened prevailing south-southwesterly winds that have shaped the eolian landscape of the Columbia Plateau since at least 75 ka. At the same time that the glacial anticyclone suppressed dust production and accumulation, enhanced cold and dry conditions resulted in soil formation dominated by intense bioturbation in periglacial steppe accompanied by shallow calcium carbonate precipitation. This is the first evidence from eolian deposits in North America verifying that the glacial anticyclone altered surface wind patterns and affected eolian systems during the Last Glacial Maximum.

Changes in Opal Phytolith Concentrations of Bambusoideae Morphotypes in Holocene Peat Soils from the Pseudo-Alpine Zone on Mount Tairappyo, Central Japan

Like many other nival mountains in Japan, Mount Tairappyo in the Mikuni Mountains (36°48′N, 138°49′E, 1, 984m a. s. l.) lacks the subalpine conifer forest zone. Instead of conifers, grasses cover large areas of slopes above the upper limit of montane broadleaf forest (1, 600-1, 700m a. s. l.). An examination of phytoliths from peat soils focused on understanding the Holocene landscape evolution, particularly for changes in Bambusoideae (mostly Sasa) grasses occupying the present-day subalpine zone. Bambusoideae grasses, which densely covered slopes in the early Holocene, would have begun to decline between 5, 600 and 4, 940 cal yrs BP. This situation seemed to have persisted until 1, 300 to 680 cal yrs BP, when Bambusoideae grasses began to recover. This change in grassland vegetation from the middle to late Holocene epoch was probably induced by variance of snowmelt timimg related to climatic variabilities.

Dental microwear in grazing and browsing Gotland sheep ( Ovis aries) and its implications for dietary reconstruction

Microwear patterns and formation processes are examined in modern browsing and grazing Gotland sheep from Denmark. Clear differences in microwear patterning are identified between Gotland sheep, which included a high proportion of leaves, bark and twigs of deciduous trees and shrubs in their diet, and those which primarily had access to graze species, with the browsing group exhibiting enamel surfaces dominated by pitted microwear features, the grazers a predominance of striations. Analysis of abrasives in dung suggests that these trends can be attributed to higher levels of soil ingestion in the grazing population and are a consequence both of grassland management practices and height of feeding within the vegetation canopy. These findings question previous interpretations of microwear patterning in browsing and grazing ungulates, which have equated striated enamel features with the ingestion of high levels of opal phytoliths, and thus have significant implications for palaeodietary reconstruction in such species, both within archaeological and palaeontological contexts. To address further the implications of these results, comparison is made between the Gotland sheep and modern grazing and fodder-fed sheep and goats from elsewhere in Europe. It is concluded that dental microwear analysis has the potential to address questions relating to grassland management practices and the use of certain fodders, such as leafy-hay, but that it may ultimately prove more difficult to distinguish ‘fresh’ browsing sheep from some grazing populations, specifically those in which levels of soil ingestion are reduced.

A 340,000 year continental climate record from tropical Africa – news from opal phytoliths from the equatorial Atlantic

Information on the tropical African continental climate and vegetation during the last 340 kyr is derived from a detailed study of opal phytoliths at the eastern equatorial Atlantic site M16772 (1°21′S, 11°58′W). Total phytoliths as well as C 3 and C 4 grass phytoliths are compared to the distribution pattern of other continental climate proxies (freshwater and limnobiontic diatoms). Total phytolith accumulation rate is dominated by C 4 grasses and their variability confirms the cold stages and interstadials as times of arid conditions in the southern Sahara and Sahel regions, and indicates an increase in aridness from Termination II to Termination I. The good agreement between the total phytoliths and freshwater diatom records observed for most of the 340 kyr is interpreted as indicative of atmospheric dust as the main source of both sediment constituents to this core site. Exceptionally higher land rainfall and river input to the eastern equatorial Atlantic are suggested by the excess of freshwater diatoms over total phytoliths and the limnobiontic diatoms observed during ice growth phases of oxygen isotopic interglacial stages 9, 7 and the 5/4 transition. Major alterations in continental aridity and/or wind strength conditions over north Africa, as reflected by the total and arid phytolith frequency spectrum, appear clearly determined by global ice volume and the 100 kyr cycle characteristic for high-latitude climate change. Limnobiontic diatoms, which reflect lake desiccation, respond also to the 41 kyr obliquity cycle. Freshwater diatoms, on the other hand, contain significant variance at 23 kyr periodicities, reflecting the precessional forcing of the African monsoons which determine the precipitation level over the south Saharan and Sahelian source regions. Rapid hydrological fluctuations, as depicted by the changes in the relative contribution of C 3 and C 4 grasses to the total phytoliths, appear to respond to higher than 19 kyr frequencies, which are observable in all but the aridity index spectra.

An Examination of the Palaeobotanical and Chronological Evidence for an Early Introduction of Maize (Zea mays L.) into South America: A Response to Pearsall

In a recent article, Pearsall (2002) essentially agreed with the methodology for tracing the use of maize using opal phytolith assemblages from food residues in utilized ceramics employed at the Valdivia ceremonial centre of La Emerenciana. However, in contrast to our multiple lines of evidence suggesting a late 2200–1900cal bc introduction and largely ceremonial use of maize, Pearsall maintains an earlier (8 to 7000bp ) arrival and intensive economic use of maize solely on the basis of opal phytoliths from archaeological soils in Valdivia I–III contexts at Real Alto. An examination of the typological, methodological, chronological, morphological, genetic, and archaeological data from various regions of the Americas suggests that an early introduction into South America is inconsistent with our multiple lines of evidence. Analysis of Pearsall’s cross-shaped typology and methodology for the identification of maize phytoliths indicates it is both typologically inconsistent and methodologically unreliable to assessing the presence and/or significance of the plant in Valdivia. Our multidisciplinary evidence indicate maize entered coastal Ecuador more recently than had been previously assumed, and maintained a ceremonial, rather than solely an economic role for most of Andean prehistory.

Characteristics of the opal phytoliths derived from Piaceae leaves

Characteristics of the opal phytoliths derived from Piaceae leaves

Opal phytoliths detected in aeolian dust, so-called &quot;Kosa&quot;, in March and April, 2002(Photo)

Opal phytoliths detected in aeolian dust, so-called &quot;Kosa&quot;, in March and April, 2002(Photo)