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1.
This paper investigates a time interval within the Late Ludfordian (Late Silurian), involving changes in faunal composition
(the Lau Event), a major positive carbon isotope excursion (CIE), and contemporaneous sea-level changes in remote palaeo-basins.
Based on the Silurian strata of Gotland (Sweden), we integrate sequence stratigraphy, carbon isotope stratigraphy, and platform-scale
palaeoecological changes associated with this turbulent time period in Earth history. Three depositional sequences (sequences
Nos. 1–3), including two separate periods of forced regression (falling stage systems tracts, FSSTs) are identified from outcrop
and drillcore studies. The sequence stratigraphical framework is interpreted to reflect glacio-eustatic sea-level changes.
The CIE starts at the onset of the initial FSST (sequence No. 1), just below the last appearance datum of the conodont Polygnathoides siluricus. The values increase through the ensuing lowstand and transgressive systems tracts (LST and TST) of sequence No. 2 and peak
in the following highstand systems tract (HST). A second forced regression (FSST of sequence No. 2) took place in the lower Ozarkodina snajdri Zone. δ13C data are scarce from these siliciclastic strata, but inferably remain high. The δ13C values increase within the LST and earliest TST of sequence No. 3, before a decreasing trend starts within the early TST.
δ13C values return to pre-excursion levels within the ensuing HST. The CIE is closely associated with an increase in stromatolites
(mats and oncoids) across a wide range of depths and sedimentary environments, and correlations to other basins indicate a
global increase in cyanobacterial activity. A drastic decline in level-bottom benthic faunas during the FSST of sequence No.
2 is, however, interpreted as a local response to the progradation of a delta complex (the Burgsvik Sandstone). Biological
carbonate production replenishes rapidly within the TST of sequence No. 3, succeeding a thin LST dominated by reworked siliciclastics
and chemically precipitated carbonates (ooids). The detailed relationship between the CIE and sea-level change presented herein
is not fully consistent with previous reports on the CIEs associated with the lower Silurian Ireviken and Mulde events, respectively.
Based on our facies analysis and sequence stratigraphical interpretation, two main mechanisms are suggested as responsible
for the Late Ludfordian CIE: (1) a change in the riverine C-weathering flux towards the 13C end member following glacio-eustatically induced subaerial exposure of carbonate platforms throughout the tropics, and,
(2) increased photosynthetic activity by benthic cyanobacteria exaggerating the δ13C values of precipitated carbonates. 相似文献
2.
The Ludlow deposits of the Winnica Formation in the Rzepin section (Holy Cross Mountains, Poland) have been studied with respect
to their facies evolution and stable carbon isotope ratios from whole-rock samples. The C-isotope curve of the Rzepin section
records a distinct positive excursion with maximal values of +8.9‰. A Late Ludlow positive isotope excursion is known from
different paleocontinents and thus is regarded as a global isotope event. The presence of the event allows for a chemostratigraphic
correlation of the Rzepin profile with the classical, biostratigraphically well-dated Gotland section. The Ludlow deposits
of the Holy Cross Mountains are interpreted in terms of sea-level changes during the isotope excursion. Because the Rzepin
and Gotland sections are positioned on the opposite sides of the same foreland basin, a comparison of their sequence stratigraphy
allows to test the regularities of the sea-level changes on the shelf of Baltica. In the present paper, a modified view of
the recently published sequence stratigraphy of the Gotland succession is presented. Our results indicate that the positive
Ludlow δ13C excursion is connected with prolonged low-stand conditions with small, internal transgressive pulses. 相似文献
3.
This study explored the potential for otolith geochemistry in snapper (Family: Lutjanidae) to identify residency in juvenile
nursery habitats with distinctive carbon isotope values. Conventional bulk otolith and muscle stable isotope analyses (SIA)
and essential amino acid (AA) SIA were conducted on snapper collected from seagrass beds, mangroves, and coral reefs in the
Red Sea, Caribbean Sea, and Pacific coast of Panama. While bulk stable isotope values in otoliths showed regional differences,
they failed to distinguish nursery residence on local scales. Essential AA δ13C values in otoliths, on the other hand, varied as a function of habitat type and provided a better tracer of residence in
different juvenile nursery habitats than conventional bulk otolith SIA alone. A strong linear relationship was found between
paired otolith and muscle essential AA δ13C values regardless of species, geographic region, or habitat type, indicating that otolith AAs recorded the same dietary
information as muscle AAs. Juvenile snapper in the Red Sea sheltered in mangroves but fed in seagrass beds, while snapper
from the Caribbean Sea and Pacific coast of Panama showed greater reliance on mangrove-derived carbon. Furthermore, compound-specific
SIA revealed that microbially recycled detrital carbon, not water-column-based new phytoplankton carbon, was the primary carbon
source supporting snapper production on coastal reefs of the Red Sea. This study presented robust tracers of juvenile nursery
residence that will be crucial for reconstructing ontogenetic migration patterns of fishes among coastal wetlands and coral
reefs. This information is key to determining the importance of nursery habitats to coral reef fish populations and will provide
valuable scientific support for the design of networked marine-protected areas. 相似文献
4.
The δ15N and δ13C values of particulate organic material (POM) were analyzed from 35 sites in the Florida Keys over the time interval 2000
to 2002. The sites within the study area were delineated into nine transects stretching from Key West to Key Largo. Each transect
consisted of three to five sites extending from close to the Keys to the edge of the reef tract. The POM had mean δ15N and δ13C values of +3.6‰ (σ = ±3.2‰) and −19.9‰ (σ = ±0.6‰) respectively. Over the study period there were no statistically significant
changes in δ15N, δ13C, or C:N. For the majority of the sampling dates, the δ13C values showed a distinct inshore (δ13C = −18.3‰, σ = ±1.0‰) to offshore gradient (δ13C = −21.4, σ = ±0.9‰). In contrast, the δ15N values showed no consistent patterns related to the distance from land. The more positive δ13C values of the nearshore samples suggest that the source of the carbon and the nitrogen in the POM in the nearshore was mainly
derived from the degradation of seagrass detritus and not from the input of anthropogenically derived material from the Florida
Keys. In contrast, the POM on the outer reef was dominated by marine plankton. As mineralization and nitrification of the
organic nitrogen pool are major contributors to the dissolved inorganic nitrogen in the water column, it is unlikely that
variations in the δ15N of the algae and other benthic organisms reported in the Florida Keys are related to the input of sewage. 相似文献
5.
Coral reefs form the most diverse of all marine ecosystems on the Earth. Corals are among their main components and owe their bioconstructing abilities to a symbiosis with algae (Symbiodinium). The coral–algae symbiosis had been traced back to the Triassic (ca 240 Ma). Modern reef-building corals (Scleractinia) appeared after the Permian–Triassic crisis; in the Palaeozoic, some of the main reef constructors were extinct tabulate corals. The calcium carbonate secreted by extant photosymbiotic corals bears characteristic isotope (C and O) signatures. The analysis of tabulate corals belonging to four orders (Favositida, Heliolitida, Syringoporida and Auloporida) from Silurian to Permian strata of Europe and Africa shows these characteristic carbon and oxygen stable isotope signatures. The δ18O to δ13C ratios in recent photosymbiotic scleractinians are very similar to those of Palaeozoic tabulates, thus providing strong evidence of such symbioses as early as the Middle Silurian (ca 430 Ma). Corals in Palaeozoic reefs used the same cellular mechanisms for carbonate secretion as recent reefs, and thus contributed to reef formation. 相似文献
6.
Dorothée Kopp Yolande Bouchon-Navaro Sébastien Cordonnier Alexandre Haouisée Max Louis Claude Bouchon 《Helgoland Marine Research》2010,64(3):181-190
The role of herbivorous fishes in maintaining low macroalgal cover was evaluated on coral reefs on several reef sites from
Guadeloupe, either protected or not. Grazing by herbivorous fishes was assessed on different algal facies using fish-bite
counts. Algal consumption by fish was estimated as well as algal production. Bite counts revealed that herbivorous fishes
feed preferentially on algal turf and avoid brown macroalgae. The algal consumption varied between 0.4 and 2.8 g m−2 days−1 and was higher inside marine protected areas than outside. Comparison with algal production revealed that herbivorous fishes
did not succeed in regulating algal growth. The insufficient number of grazers may lead to the dominance of stable assemblages
of macroalgae on coral reefs, preventing the recovery of reef into previous coral-dominated ecosystems. 相似文献
7.
Oyster reefs are among the most threatened coastal habitat types, but still provide critical habitat and food resources for
many estuarine species. The structure of oyster reef food webs is an important framework from which to examine the role of
these reefs in supporting high densities of associated fishes. We identified major trophic pathways to two abundant consumers,
gray snapper (Lutjanus griseus) and crested goby (Lophogobius cyprinoides), from a subtropical oyster reef using stomach content and stable isotope analysis. The diet of gray snapper was dominated
by crabs, with shrimp and fishes also important. Juvenile gray snapper fed almost entirely on oyster reef-associated prey
items, while subadults fed on both oyster reef- and mangrove-associated prey. Based on trophic guilds of the gray snapper
prey, as well as relative δ13C values, microphytobenthos is the most likely basal resource pool supporting gray snapper production on oyster reefs. Crested
goby had omnivorous diets dominated by bivalves, small crabs, detritus, and algae, and thus were able to take advantage of
prey relying on production from sestonic, as well as microphytobenthos, source pools. In this way, crested goby represent
a critical link of sestonic production to higher trophic levels. These results highlight major trophic pathways supporting
secondary production in oyster reef habitat, thereby elucidating the feeding relationships that render oyster reef critical
habitat for many ecologically and economically important fish species. 相似文献
8.
Palaeozoic cold seep carbonates from Europe and North Africa—an integrated isotopic and geochemical approach 总被引:1,自引:0,他引:1
In this paper, we report the highest and lowest carbon isotope values known from Palaeozoic carbonate rocks. These unusual δ13C values (−50 to +23.5‰) are due to microbial methanogenesis and methanotrophy in Silurian to Carboniferous carbonates. Trace elements were used to decipher the primary mineralogy of the carbonate cements. Very high Sr values and low amounts of Mg, Fe and Mn point toward aragonite precursors, whereas high Fe and Mn values are indicative of primary calcites and allow reconstruction of the redox conditions. Four carbonate deposits are described from the Meseta and the Antiatlas of Morocco, the Pyrenees (France) and the Harz mountains (Germany). The highest δ13C values in concretion below the uppermost Silurian Spinatrypa Mound (Moroccan Meseta) give evidence, that CO2 was produced during methanogenesis. δ13C values between −10 and −32‰indicate that the formation of microbial carbonates and cements in the Middle Devonian Hollard Mound (Antiatlas) and in the Lower Carboniferous sediments of the Iberg (Harz) formed at thermogenetic methane or petroleum seeps. The Late Bashkirian carbonate mound of the High Pyrenees (Tantes Mound) is the first Palaeozoic carbonate with seepage fluids being dominated by biogenic methane. Matrix carbonates exhibit δ13C values as low as −34‰. In some parts, voids make up more than 50 vol% of the mound. They are filled with several generations of cement. The earliest void filling is isopachous fibrous cement, which represents former aragonite. Most negative δ13C values of −50‰were measured in these isopachous fibrous cements. The difference of 55‰in δ13C values between normal sediments and early aragonite cements can only be explained by the contribution of CO2 from anaerobic oxidation of biogenic methane in a cold seep setting. 相似文献
9.
S. Jupiter G. Marion M. Henderson V. Schrameyer M. McCulloch O. Hoegh-Guldberg 《Coral reefs (Online)》2008,27(4):887-903
Coral core records, combined with measurements of coral community structure, were used to assess the long-term impact of multiple
environmental stressors on reef assemblages along an environmental gradient. Multiple proxies (luminescent lines, Ba/Ca, δ15N) that reflect different environmental conditions (freshwater discharge, sediment delivery to the nearshore, nutrient availability
and transformations) were measured in Porites coral cores collected from nearshore reefs at increasing distance from the intensively agricultural region of Mackay (Queensland,
Australia). The corals provide a record (1968–2002) of the frequency and intensity of exposure to terrestrial runoff and fertilizer-derived
nitrogen and were used to assess how the present-day coral community composition may have been influenced by flood-related
disturbance. Reefs closest to the mainland (5–32 km offshore) were characterized by low hard coral cover (≤10%), with no significant
differences among locations. Distinct annual luminescent lines and elevated Ba/Ca values (4.98 ± 0.63 μmol mol−1; mean ± SD) in the most inshore corals (Round Top Island; 5 km offshore) indicated chronic, sub-annual exposure to freshwater
and resuspended terrestrial sediment that may have historically prevented reef formation. By contrast, corals from Keswick
Island (32 km offshore) indicated episodic, high-magnitude exposure to Pioneer River discharge during extreme flood events
(e.g., 1974, 1991), with strongly luminescent lines and substantially enriched coral skeletal δ15N (12–14‰). The reef assemblages at Keswick and St. Bees islands were categorically different from all other locations, with
high fleshy macroalgal cover (80.1 ± 7.2% and 62.7 ± 7.1%, respective mean ± SE) overgrowing dead reef matrix. Coral records
from Scawfell Island (51 km offshore) indicated little exposure to Pioneer catchment influence: all locations from Scawfell
and further offshore had total hard and soft coral cover comparable to largely undisturbed nearshore to middle shelf reefs
of the southern Great Barrier Reef. 相似文献
10.
Jari Syv?ranta Aurélia Martino Dorothée Kopp Régis Céréghino Frédéric Santoul 《Hydrobiologia》2011,658(1):383-388
We tested the impacts of most common sample preservation methods used for aquatic sample materials on the stable isotope ratios
of carbon and nitrogen in clams, a typical baseline indicator organism for many aquatic food web studies utilising stable
isotope analysis (SIA). In addition to common chemical preservatives ethanol and formalin, we also assessed the potential
impacts of freezing on δ13C and δ15N values and compared the preserved samples against freshly dried and analysed samples. All preservation methods, including
freezing, had significant impacts on δ13C and δ15N values and the effects in general were greater on the carbon isotope values (1.3–2.2‰ difference) than on the nitrogen isotope
values (0.9–1.0‰ difference). However, the impacts produced by the preservation were rather consistent within each method
during the whole 1 year experiment allowing these to be accounted for, if clams are intended for use in retrospective stable
isotope studies. 相似文献
11.
Eberhard Gischler 《Facies》2006,52(3):341-360
A first systematic study of composition, texture, and distribution of modern sediments in two Maldivian atolls reveals the predominance of skeletal carbonates. Fragments of corals, calcareous algae, mollusks, benthic foraminifera, and echinoderms are identified in the grain-size fraction >125 μm. Non-skeletal grains such as cemented fecal pellets and aggregate grains only occur in small percentages. Fragments of skeletal grains, aragonite needles, and nanograins (<1 μm) are found in the grain-size fraction <125 μm. Needles and nanograins are interpreted to be largely of skeletal origin. Five sedimentary facies are distinguished (1–5), for which the Dunham-classification is applied. Fore reef, reef, back reef, as well as lagoonal patch reef and faro areas in both atolls are characterized by the occurrence of coral grainstones (1), which also contain fragments of red coralline algae, the codiacean alga Halimeda, and mollusks. On reef islands, coral-rich sediment is cemented to form intertidal beachrock and supratidal cayrock. Skeletal grains in atoll-interior lagoons are mainly mollusks and foraminifera. The lagoon of Rasdhoo Atoll is covered in the west by mudstones (2), in the center by mollusk packstones (3) and mollusk wackestones (4), and by hard bottoms with corals in the east adjacent to channels through the atoll reef margin. The interior lagoon of Ari Atoll contains mollusk wackestones (4) in the center and mollusk-foraminifer packstones (5). Marginal lagoon areas are characterized by hard bottoms with corals. Facies distribution appears to be an expression of depositional energy, which decreases from the atoll margin towards the center in Ari Atoll, and towards the west in Rasdhoo Atoll. Predominant sediment mineralogies include aragonite and high-magnesium calcite. Mean aragonite content decreases from 90% in coral grainstone to 70–80% in mollusk packstone, mollusk wackestone, and mudstone, and to 50% in mollusk-foraminifer packstone. Stable isotopes of oxygen and carbon in bulk samples range from −3 to −1.5 (δ18O) and from +0.4 to +3.2 (δ13C). It is not possible to delineate facies based on O- and C-isotopes. 相似文献
12.
K. M. Gorbatenko S. I. Kiyashko A. Ye. Lazhentsev V. A. Nadtochii A. B. Savin 《Russian Journal of Marine Biology》2008,34(7):497-506
The composition, abundance, diet and trophic status of zooplankton, bottom invertebrates, fish and nekton were analyzed based
on the data collected by the staff of the TINRO-Center during complex bottom trawl catches on the Bering Sea shelf in the
fall of 2004. The stomach contents of mass fish species were analyzed and the nitrogen and carbon isotopic composition of
36 mass species of plankton, benthos, nekton and nektobenthos, which together make up the basis of pelagic and bottom communities,
was determined. It was found that zooplankton noticeably differ from benthic invertebrates in carbon isotopic composition:
δ13C values in zooplankton varied from −20.3‰ to −17.9‰; in benthos—from −17.5‰to −13.0‰; and in fish—from −19.2‰ (juvenile walleye
pollock) to −15.3‰ (saffron cod). The levels of 13C isotope in the tissues of fish depended mostly on the share of pelagic or benthic animals in their diet. δ15N values in the studied species ranged from 8.6‰ (in sea urchins) to 17.2‰ (in large Pacific cods), which corresponds to a
trophic level of 2.8. Obviously the δ15N values reflect the degree of predation and generally show the ratio of primary, secondary and tertiary consumers in a fish’s
diet. Trophic interactions manifest a high degree of interdependence between benthic and pelagic communities (even without
taking into account such lower components of the food web as phytoplankton, bacteria, and protozoa) occurring in most nektonic
species that depend on both bottom and pelagic food. 相似文献
13.
Dr. Georg A. Heiss 《Facies》1995,33(1):19-34
Summary In a fringing reef at Aqaba at the northern end of the Gulf of Aqaba (29°26′N) growth rates, density, and the calcification
rate ofPorites were investigated in order to establish calculations of gross carbonate production for the reefs in this area. Colony accretion
ofPorites decreases with depth as a function of decreasing growth rates. The calcification rate ofPorites is highest in shallow water (0–5 m depth) with 0.9 g·cm−2·yr−1 and falls down to 0.5 g·cm−2·yr−1 below 30 m. Scleractinian coral gross production is calculated from potential productivity and coral coverage. It is mainly
dependent on living coral cover and to a lesser extent on potential productivity. Total carbonate production on the reef ranged
from 0 to 2.7 kg/m2 per year, with a reef-wide average of 1.6 kg/m2 perycar. Maximum gross carbonate production by corals at Aqaba occurs at the reef crest and in the middle fore-reef from
10 to 15 m water depth. Production is low in sandy reef parts. Below 30 m depth values still reach ca. 50% of shallow water
values. Mean potential production of colonies and gross carbonate production of the whole reef community at Aqaba is lower
than in tropical reefs. However, carbonate production is higher than in reef areas at the same latitude in the Pacific, indicating
a northward shift of reef production in the Red Sea. 相似文献
14.
The isotopic composition of tree ring cellulose was obtained over a 2-year period from small-diameter riparian-zone trees
at field sites that differed in source water isotopic composition and humidity. The sites were located in Utah (cool and low
humidity), Oregon (cool and high humidity), and Arizona (warm and low humidity) with source water isotope ratio values of
–125/–15‰ (δD/δ18O), –48/–6‰, and –67/–7‰, respectively. Monthly environmental measurements included temperature and humidity along with measurements
of the isotope ratios in atmospheric water vapor, stream, stem, and leaf water. Small riparian trees used only stream water
(both δD and δ18O of stem and stream water did not differ), but δ values of both atmospheric water vapor and leaf water varied substantially
between months. Differences in ambient temperature and humidity conditions between sites contributed to substantial differences
in leaf water evaporative enrichment. These leaf water differences resulted in differences in the δD and δ18O values of tree ring cellulose, indicating that humidity information was recorded in the annual rings of trees. These environmental
and isotopic measurements were used to test a mechanistic model of the factors contributing to δD and δ18O values in tree ring cellulose. The model was tested in two parts: (a) a leaf water model using environmental information
to predict leaf water evaporative enrichment and (b) a model describing biochemical fractionation events and isotopic exchange
with medium water. The models adequately accounted for field observations of both leaf water and tree ring cellulose, indicating
that the model parameterization from controlled experiments was robust even under uncontrolled and variable field conditions.
Received: 7 April 1999 / Accepted: 8 December 1999 相似文献
15.
We evaluated the potential utility of stable isotope analysis of tissues commonly archived by aquatic biologists. Previous
studies with chemically preserved samples have shown contradictory results, which present an obstacle for the use of archived
sample materials. We tested the effects of ethanol and formalin preservation on zooplankton and of ethanol on benthic macroinvertebrate
δ13C and δ15N values. We found that neither formalin nor ethanol had a significant effect on δ13C and δ15N values of preserved zooplankton. Nor did ethanol significantly affect δ13C or δ15N values of macroinvertebrates. However, ethanol preservation slightly, but significantly decreased C:N ratios of both zooplankton
and macroinvertebrates, probably reflecting some extraction of lipids. Overall, the effects of preservatives on δ13C and δ15N values that we observed were minor. We also compared δ13C and δ15N values analysed from roach scales and perch operculum bones with those analysed from muscle tissue. Decalcification of scales
and operculum bones only slightly improved our comparison to muscle tissue δ13C and δ15N values. Decalcified scales had slightly higher δ13C and lower δ15N values. Similarly, decalcified operculum bones showed slightly increased δ13C and decreased δ15N values to those for fish muscle. Our results confirm that scales and operculum bones can provide a suitable proxy for fish
muscle in isotope studies with minor correction. We conclude that various archived sample materials can indeed be used with
confidence for historical reconstructions of freshwater food webs by stable isotope analysis.
Handling editor: K. Martens 相似文献
16.
Summary “Travertines” (tufa pinnacles) of the Miocene Riescrater basin have been investigated to test whether carbon, oxygen and strontium
isotopes can be used for the recognition of fossil subaquatic spring deposits in high-alkalinity settings. The Ries basin
“travertines” have so far been interpreted as a product of subaerial to sublacustrine artesian springs discharging calcareous
groundwater into a freshwater or slightly saline lake. However, recent studies on microfacies and fabric development propose
a formation at Ca2+-supplying sublacustrine springs of a soda lake. Geochemical analysis of “travertines” of the castle rock Wallerstein, including
“sickle-cell” limestones, thrombolites, non-skeletal stromatolites, and speleothems, now support the latter interpretation.
High Sr contents surpassing that of the contemporaneously formed dolomitic algal biocherms of the lake shore point to an aragonitic
composition of primary precipitates. the δ13C values of diagenetically moderately to weakly altered “travertine” facies types are in the same range of the impact-brecciated
Upper Jurassic limestones, thus, are inconsistent with a mixture of soil-derived CO2 and CO3
2− from the Jurassic limestones. In addition, the δ18O values are too high to support a significant contribution of CO3
2− by meteoric waters seeping through marine Jurassic limestones. Instead the δ13C and δ18O values indicate an origin of the CO3
2− from a lake water body characterized by evaporation. This is consistent with a sodium-rich lake water as indicated by high
sodium contents of aragonitic algal bioherms of the lake shore. The87Sr/86Sr isotope ratio of the “travertine” mound carbonates are consistent with calculated mixing of spring waters discharging from
the crystalline basement and lake water high in dissolved inorganic carbon. This points to an origin of the divalent cations
from sublacustrine spring waters. In turn,87Sr/86Sr isotope ratios of green algal reef carbonates of the lake shore are closer to that of the Upper Jurassic carbonates, due
to surface run-off from surrounding limestone uplands. 相似文献
17.
Summary Givetian to early Carboniferous sediments of South China are characterized by carbonates. Middle and Late Devonian strata
are best developed in the Guilin area. Reefs and organic shoals are recorded by various lithofacies types indicating the existence
of an extended carbonate platform and a change of the composition of reef communities in time. Starting in the late Devonian,
stromatoporoids and corals were replaced by algae that subsequently played an important role together with stromatoporoids,
receptaculitids and fasciculate rugose corals in reef communities. In Houshan, 5 km west of Guilin, a coral-bafflestone reef
occurs in the Frasnian strata, situated near an offshore algal-stromatoporoid reef. The coral reef was formed in a back-reef
area adjacent to the inner platform margin. The coral-bafflestone reef is unique among the late Devonian reefs of South China
with regard to the biotic composition. The reef is composed of fasciculate colonies ofSmithiphyllum guilinense n. sp. embedded within in packstones and wackestones. The height of colonies reaches 1 m. The community is low-diverse. The
species ofSmithiphyllum occurring in the Frasnian reef complexes of Guilin exhibit a distinct facies control:Smithiphyllum guilinense occurs in or near to margin facies and formed bafflestone, constituting a coral reef whereasSmithiphyllum occidentale
Sorauf, 1972 andSmithiphyllum sp.—characterized by small colonies with thin corallites—are restricted to the back-reef and marginal slope facies. The bush-like
coral colonies baffled sediments. Algae and stromatoporoids (mainlyStachyodes) are other reef biota. Reef-dwelling organisms are dominated by brachiopods.
The reefs are composed from base to top of five lithofacies types: 1) cryptalgal micrite, 2) peloidal packstone, 3) stromatactis
limestone, 4) coral-bafflestone, and 5) pseudopeloidal packstone. The reef complex can be subdivided into back-reef subfacies,
reef flat and marginal subfacies, and marginal fore-slope subfacies. The Houshan coral-bafflestone reef is not a barrier reef
but a coral patch reef located near the inner margin of a carbonate platform. 相似文献
18.
Eduard A. Titlyanov Serguei I. Kiyashko Tamara V. Titlyanova John A. Raven 《Aquatic Ecology》2010,44(1):13-21
Studies were performed of the carbon and nitrogen stable isotope (δ13C and δ15N) composition (δ13C and δ15N) of the corals Porites cylindrica and P. lutea (5 years after damaging the colonies by the bleaching events) and of epilithic algae settled onto damaged areas of coral
colonies. Coral polyps and three epilithic algal communities (‘red algal turf, green algal turf and red calcified crusts’)
were sampled along the boundary between communities of coral polyps and algal colonizers from differently illuminated habitats
from 2 to 90% of incident surface photosynthetically active radiation (PAR0). It was found that communities with a predominance of red algae significantly differed from communities with a predominance
of green algae in δ13C but not in δ15N values. An influence of habitat irradiance was found only for communities of coral polyps for δ13C and δ15N values: under bright light (70–90% PAR0) polyp tissues of both coral species were significantly enriched in heavy carbon isotopes and insignificantly in nitrogen
isotopes (δ13C values difference ~4‰) relative to tissues of corals under lower light 15–50% PAR0. On the basis of these results we assumed that differences in light intensities in the habitat ranging from 15 to 90% PAR0 do not influence on accessibility of the main carbon and nitrogen sources for corals and algae, and exchange by these elements
between organisms. We also assumed that the relative enrichment in the heavy carbon isotopes of coral tissues in high light
is a result of decreased isotope fractionation (or the absence of fractionation in photosynthesis of their zooxanthellae). 相似文献
19.
Ann M. A. Harding Keith A. Hobson Wojciech Walkusz Kasia Dmoch Nina J. Karnovsky Thomas I. Van Pelt Jan T. Lifjeld 《Polar Biology》2008,31(6):725-733
The little auk (Alle alle), a small and abundant planktivorous seabird that breeds in the high Arctic, has the potential to be used as a monitor of
the composition and abundance of lower trophic-level zooplankton. We investigated age- and sex-related sources of variation
in diet and stable isotope (δ13C and δ15N) values of little auks breeding in Spitsbergen during the summer of 2002 to evaluate this possibility. Stable isotope profiles
of both adult and chick blood changed over the breeding season, with blood δ15N values increasing and δ13C values decreasing. This could represent a switch to higher trophic-level prey derived from more pelagic sources. However,
while chick blood δ13C values followed those values in their meals, this was not the case for blood δ15N values, suggesting additional physiological mechanisms influencing blood δ15N values in growing chicks. Chicks had consistently lower δ15N values than their parents, which may indicate they were being fed on lower trophic-level prey items or may alternatively
reflect complexities in chick blood δ15N values through the growth period. These results have several important implications for use of stable isotope analysis as
a tool to detect changes in seabird diet and availability of lower trophic-level prey in high-Arctic marine environments.
Until physiological aspects of stable isotope discrimination are well understood, we caution against using chicks of this
seabird as any form of isotopic monitor. 相似文献
20.
This study explores the giant oyster Hyotissa hyotis as a novel environmental archive in tropical reef environments of the Indo-Pacific. The species is a typical accessory component
in coral reefs, can reach sizes of tens of centimetres, and dates back to the Late Pleistocene. Here, a 70.2-mm-long oxygen
and carbon isotope transect through the shell of a specimen collected at Safaga Bay, northern Red Sea, in May 1996, is presented.
The transect runs perpendicularly to the foliate and vesicular layers of the inner ostracum near the ligament area of the
oyster. The measured δ18O and δ13C records show sinusoidal fluctuations, which are independent of shell microstructure. The δ13C fluctuations exhibit the same wavelength as the δ18O fluctuations but are phase shifted. The δ18O record reflects the sea surface temperature variations from 1957 until 1996, possibly additionally influenced by the local
evaporation. Due to locally enhanced evaporation in the semi-enclosed Safaga Bay, the δ18Oseawater value is estimated at 2.17‰, i.e., 0.3–0.8‰ higher than published open surface water δ18O values (1.36–1.85‰) from the region. The mean water temperature deviates by only 0.4°C from the expected value, and the
minimum and maximum values are 0.5°C lower and 2.9°C higher, respectively. When comparing the mean monthly values, however,
the sea surface temperature discrepancy between reconstructed and global grid datasets is always <1.0°C. The δ13C signal is weakly negatively correlated with regional chlorophyll a concentration and with the sunshine duration, which may
reflect changes in the bivalve’s respiration. The study emphasises the palaeogeographic context in isotope studies based on
fossils, because coastal embayments might not reflect open-water oceanographic conditions. 相似文献