Miliammina Fusca Research Articles

Late 20th Century benthic foraminiferal distribution in Central San Francisco Bay, California: Influence of the Trochammina hadai invasion

The distribution of foraminifera in most of San Francisco Bay is well documented, but this is not the case for the subembayment known as Central Bay. To resolve this, 55 grab samples obtained in 199 were analyzed to characterize the foraminiferalfauna in the surface sediments of the area. Thirty-five species were identified, including the invasive Japanese species Trochammina hadai that was introduced into the bay in the early 1980s. A cluster analysis of the samples from Central Bay produced three groups (biofacies) and one outlier. The Shallow Subtidal Biofacies is characterized by a marsh to shallow-subtidal agglutinated fauna, dominated by T. hadai but also including T. inflata, T. macrescens, Haplophragmoides subinvolutum, and Miliammina fusca. The Intermediate Subtidal Biofacies, the Intermediate Subtidal Outlier, and the Deep Subtidal Biofacies are dominated by calcareous taxa, most notably Ammonia tepida, Elphidium excavatum, and Elphidiella hannai. Ammonia tepida is most abundant in the warmer, intermediate depths of eastern Central Bay, abundances of E. excavatum peak in the cooler estuarine water near Alcatraz Island, and E. hannai thrives in the cold water west of Angel Island in a transitional setting between the deep subtidal estuarine and the nearshore marine environments. The recovery of oceanic species as far east as Angel Island indicate that western Central Bay is the most marine-influenced region of San Francisco Bay. Samples collected from 1965 onward were also compared with those from 1998 to investigate how the distribution of benthic foraminifera in Central Bay has changed over the latter half of the 20th Century, particularly in response to the invasion by Trochammina hadai. In 1998, T. hadai was recovered at 46 of 55 sites in Central Bay, comprising from 0.3 to 97% (mean = 23%) of the foraminiferal fauna. With the species’ affiliation for shallow environments, it is not unexpected that it dominated the fauna of the Shallow Subtidal Biofacies (68-97%, mean = 77%) and was also a significant component of the Intermediate Subtidal Biofacies (7-51%, averaging 28%). In the deeper waters west of Alcatraz Island, the abundance of T. hadai was significantly less (mean = 8%), most likely reflecting allochthonous specimens that were the result of post-mortem transport. A cluster analysis clearly distinguishes pre- and post-invasion biofacies, illustrating how dominant T. hadai has become in Central Bay.

Reconstrução paleoambiental da Laguna de Maricá, RJ, com base em foraminíferos bentônicos

Com o objetivo de avaliar a evolução costeira baseada na distribuição dos foraminíferos bentônicos e nos aspectos sedimentológicos, duas testemunhagens foram realizadas na Laguna de Maricá, Rio de Janeiro. Duas biofácies foram reconhecidas: (i) biofácies Ap-At (Ammonia parkinsoniana - A. tepida) correspondendo à metade inferior de ambos os testemunhos, caracterizada pela abundância de foraminíferos calcário-hialinos, entre os quais destacam-se Ammonia parkinsoniana e A. tepida, associada à intercalação de lama siltosa e lama arenosa com conchas desgastadas e quebradas, sugerindo eventos de ondas de tempestades; e (ii) biofácies Ac-As (Ammotium cassis - A. salsum) compreendendo à metade superior dos testemunhos, caracterizada por espécies aglutinantes, como Ammotium cassis, A. salsum, Trochammina inflata, Miliammina fusca e Ammobaculites spp., associados à lama siltosa e à ocorrência de alguns micromoluscos, indicando uma fase de baixa energia hidrodinâmica. Este registro da distribuição de foraminíferos calcários e aglutinantes relaciona-se principalmente com a dinâmica de abertura e fechamento da barreira arenosa da Laguna de Maricá.

Intertidal foraminiferal fauna and the distribution of Elphidiidae at Chupa Inlet, western White Sea

The bright colouration of the cytoplasm in intertidal rotaliid foraminifera and their particle-gathering activity reliably reveals live specimens in fresh samples, without any fixatives or dyes applied. Using this approach, we demonstrate that live representatives of three rotaliid species, all belonging to the genus Elphidium, were common on intertidal mud and sand beaches. Two species, E. excavatum clavatum and E. albiumbilicatum, lived close to freshwater outflows, whereas E. williamsoni occupied beaches bathed by waters with normal salinity (surface 26–27‰ in the western White Sea). A least 13 species were found alive in the intertidal zone. Among non-calcareous foraminifera, Miliammina fusca, Ammotium cassis and Ovammina opaca were the most numerous.

Modern foraminifera, δ13C, and bulk geochemistry of central Oregon tidal marshes and their application in paleoseismology

We assessed the utility of δ13C and bulk geochemistry (total organic content and C:N) to reconstruct relative sea-level changes on the Cascadia subduction zone through comparison with an established sea-level indicator (benthic foraminifera). Four modern transects collected from three tidal environments at Siletz Bay, Oregon, USA, produced three elevation-dependent groups in both the foraminiferal and δ13C/bulk geochemistry datasets. Foraminiferal samples from the tidal flat and low marsh are identified by Miliammina fusca abundances of >45%, middle and high marsh by M. fusca abundances of <45% and the highest marsh by Trochamminita irregularis abundances >25%. The δ13C values from the groups defined with δ13C/bulk geochemistry analyses decrease with an increasing elevation; −24.1±1.7‰ in the tidal flat and low marsh; −27.3±1.4‰ in the middle and high marsh; and −29.6±0.8‰ in the highest marsh samples. We applied the modern foraminiferal and δ13C distributions to a core that contained a stratigraphic contact marking the great Cascadia earthquake of AD 1700. Both techniques gave similar values for coseismic subsidence across the contact (0.88±0.39m and 0.71±0.56m) suggesting that δ13C has potential for identifying amounts of relative sea-level change due to tectonics.

A multiproxy study between the Río de la Plata and the adjacent South-western Atlantic inner shelf to assess the sediment footprint of river vs. marineinfluence

Proxies of terrigenous versus marine input (Al and Ti, Fe/Ca and Ti/Ca ratios), origin of organic matter (δ13C, δ15N and C/N ratio), productivity (Corg; Nt; CaCO3, P, Ca, and Ba content; and Ba/Al and Ba/Ti ratios), hydrodynamics (grain size, mean diameter and sorting) and biological records of the main features of the environment (benthic foraminifera assemblage distribution) were used to assess the sediment footprint of river vs. marine influence along the salinity gradient between the Rio de la Plata (RdlP) estuary and the adjacent South Western Atlantic Shelf. These criteria permitted characterisation and interpretation of the sedimentary processes influencing transition between three known environments: tidal river, estuarine and marine zones. Increases in sand and clay content at the transition between tidal river and proper estuarine zones indicate resuspension/deposition processes associated with the maximum turbidity zone (MTZ). The MTZ was also characterised by an increase in mixed organic matter content indicated by stable carbon and nitrogen isotope values, an increment in productivity proxies (Corg, Nt and CaCO3) and the substitution of the Miliammina fusca assemblage (brackish environments) for the Ammonia tepida assemblage (estuarine environments). The transition between estuarine and marine environments was characterised by a sharp (up to 99%) increase in sand content, reflecting the progradation of modern RdlP sediments toward relict continental shelf sediment. C/N values typical of the marine environment, decreased trace element concentrations and the distribution of the Buliminella elegantissima assemblage (a more marine assemblage) also highlight the marine environment. This paper is particularly important as a tool both to better understand sedimentological dynamics in salinity fronts (along the shelf sediment of large estuaries) and to elaborate more precise palaeoenvironmental and palaeoceanographic reconstructions.

Modern Salt-Marsh and Tidal-Flat Foraminifera From Sitkinak and Simeonof Islands, Southwestern Alaska

We describe the modern distribution of salt-marsh and tidal-flat foraminifera from Sitkinak Island (Trinity Islands) and Simeonof Island (Shumagin Islands), Alaska, to begin development of a dataset for later use in reconstructing relative sea-level changes caused by great earthquakes along the Alaska-Aleutian subduction zone. Dead foraminifera were enumerated from a total of 58 surface-sediment samples collected along three intertidal transects around a coastal lagoon on Sitkinak Island and two intertidal transects on Simeonof Island. Two distinctive assemblages of salt-marsh foraminifera were recognized on Sitkinak Island. Miliammina fusca dominated low-marsh settings and Balticammina pseudomacrescens dominated the high marsh. These two species make up >98% of individuals. On Simeonof Island, 93% of individuals in high-marsh settings above mean high water were B. pseudomacrescens . The tidal flat on Simeonof Island was dominated by Cibicides lobatulus (60% of individuals), but the lower limit of this species is subtidal and was not sampled. These results indicate that uplift or subsidence caused by repeated earthquakes along the Alaska-Aleutian subduction zone could be reconstructed in coastal sediments using alternating assemblages of near monospecific B. pseudomacrescens and low-marsh or tidal-flat foraminifera.

Recent benthic foraminifers as indicators of the sedimentary dynamics of the Tina Mayor and Tina Menor estuaries (S Bay of Biscay, N Spain)

Recent benthic foraminifers from two estuaries in the North Spanish coastal region (Tina Mayor and Tina Menor) were analysed with the aim of characterising the ecology and dynamics of the different estuarine sub-environments. A total of 35 benthic foraminifer species were taxonomically determined in the Tina Mayor estuary, 22 of which contained living individuals during the sampling. For Tina Menor, there were 51 species, 30 of them biocenotic. The most abundant species in these estuaries were Ammonia tepida, Cribroelphidium williamsoni, Jadammina macrescens, Lobatula lobatula, Miliammina fusca, Rosalina globularis and Trochammina inflata. In Tina Menor, Haynesina germanica was also abundant. In the foraminifer assemblages, live (biocenotic) and dead (thanatocenotic) specimens were differentiated and processed statistically by a multivariate cluster-Q type analysis and detrended correspondence ordination analysis (DCA). Groupings of biocenotic assemblages were obtained for both estuaries indicating an ecologic separation of marine mouth, low and high marsh and zones with strong salinity oscillations in these estuaries. Thanatocenotic groupings, nevertheless, showed a different organisation of that of the ecologic groups, which were indicative of a transport of individuals from the mouth to the inner/mid estuary locations, along the main and/or secondary channels of these estuaries. Local differences between Tina Mayor and Tina Menor can be explained by the different physiographies of the estuary as a consequence of the different geological/sedimentological histories of both estuaries. Benthic foraminifer assemblages are distributed in the estuary following three zones: an outer estuary having marine characteristics with L. lobatula and R. globularis, a mid estuary, including a subtidal mudflat with variable salinity (A. tepida, C. williamsoni) and a marsh (J. macrescens, M. fusca and T. inflata), which is different in both estuaries.Tina Mayor is filled with more sediment, and it has a reduced mudflat and a large high marsh located above the MHW (Mean High Waters), where T. inflata is the species marker of the intervals between the MHW and MHWST (Mean High Waters Spring Tides) levels. In Tina Menor, estuary mudflats crossed with brackish secondary channels (with H. germanica) below MHWNT (Mean High Waters Neap Tides) are more developed, though the environments of low marsh with scarce vegetation (with M. fusca) are dominant in intervals between MHWNT and MHW. The relative abundance of M. fusca, particularly in the mid estuary, differentiates Tina Mayor and Tina Menor from other estuaries of Cantabria. Biocenotic and thanatocenotic assemblages show a general similarity in both estuaries (Sanders's index, >70%). Samples with low similarity are evidence of the effect of post-mortem transport mostly produced by suspension. The percentage of exotic specimens is always less than 35%, supporting the mesotidal characteristic of both estuaries. The present results confirm the value of benthic foraminifers as markers of estuarine sub-environments, supporting their value for detecting changes in past estuarine environments.

DISTRIBUTION OF FORAMINIFERA IN THE SETIU ESTUARY AND LAGOON, TERENGGANU, MALAYSIA

The Setiu wetland of peninsular Malaysia is threatened by expansion of aquaculture. Water quality of the estuary-lagoon complex is becoming affected by nutrients introduced into the system at floating fish cages and by the clear-cutting of large areas of fringing mangrove forest for the creation of land-based fish and shrimp pens. We report here on the distribution of benthic foraminifera in the estuary-lagoon and related environmental variables. These data will form the baseline against which future environmental monitoring will be compared. Four thanatofacies are recognized by cluster analysis of the dead foraminiferal abundance data; their distribution is closely related to variations in salinity and other parameters related to the hydrodynamics of the region. This relation is confirmed by DCA and DCCA analyses. A low salinity estuarine thanatofacies (D1) has a low diversity assemblage dominated by the agglutinated taxa Ammotium directum , Trochammina amnicola , Miliammina fusca and Ammobaculites exiguus. A medium salinity lagoon thanatofacies (D2) has low diversity and is strongly dominated by the agglutinated Ammobaculites exiguus. Ammobaculites exiguus and Ammonia aff. A. aoteana dominate a high diversity, high salinity thanatofacies (D3) in both the estuary and the lagoon. A normal marine salinity thanatofacies (D4), found at an inlet and in the immediately adjacent lagoon, has a high diversity assemblage dominated by the calcareous taxa Amphistegina lessonii and Ammonia aff. A. aoteana . Five biofacies recognized by cluster analysis of live foraminiferal data exhibit similar salinity-related distribution patterns as the thanatofacies.

A foraminiferal proxy record of 20th century sea-level rise in the Manukau Harbour, New Zealand

The present study aimed to extract a sea-level history from northern New Zealand salt-marsh sediments using a foraminiferal proxy, and to extend beyond the longest nearby tide-gauge record. Transects through high-tidal salt marsh at Puhinui, Manukau Harbour, Auckland, New Zealand, indicate a zonation of dominant foraminifera in the following order (with increasing elevation): Ammonia spp.–Elphidium excavatum, Ammotium fragile, Miliammina fusca, Haplophragmoides wilberti–Trochammina inflata, Trochamminita salsa–Miliammina obliqua. The transect sample faunas are used as a training set to generate a transfer function for estimating past tidal elevations in two short cores nearby. Heavy metal, 210Pb and 137Cs isotope analyses provide age models that indicate 35 cm of sediment accumulation since ~1890 AD. The first proxy-based 20th century rates of sea-level rise from New Zealand’s North Island at 0.28 ± 0.05 cm year–1 and 0.33 ± 0.07 cm year–1 are estimated. These are faster than the nearby Auckland tide gauge for the same interval (0.17 ± 0.1 cm year–1), but comparable to a similar proxy record from southern New Zealand (0.28 ± 0.05 cm year–1) and to satellite-based observations of global sea-level rise since 1993 (0.31 ± 0.07 cm year–1).

Quantitative vertical zonation of salt-marsh foraminifera for reconstructing former sea level; an example from New Jersey, USA.

We present a quantitative technique to reconstruct sea level from assemblages of salt-marsh foraminifera using partitioning around medoids (PAM) and linear discriminant functions (LDF). The modern distribution of foraminifera was described from 62 surface samples at three salt marshes in southern New Jersey. PAM objectively estimated the number and composition of assemblages present at each site and showed that foraminifera adhered to the concept of elevation-dependent ecological zones, making them appropriate sea-level indicators. Application of PAM to a combined dataset identified five distinctive biozones occupying defined elevation ranges, which were similar to those identified elsewhere on the U.S. mid-Atlantic coast. Biozone A had high abundances of Jadammina macrescens and Trochammina inflata; biozone B was dominated by Miliammina fusca; biozone C was associated with Arenoparrella mexicana; biozone D was dominated by Tiphotrocha comprimata and biozone E was dominated by Haplophragmoides manilaensis. Foraminiferal assemblages from transitional and high salt-marsh environments occupied the narrowest elevational range and are the most precise sea-level indicators. Recognition of biozones in sequences of salt-marsh sediment using LDFs provides a probabilistic means to reconstruct sea level. We collected a core to investigate the practical application of this approach. LDFs indicated the faunal origin of 38 core samples and in cross-validation tests were accurate in 54 of 56 cases. We compared reconstructions from LDFs and a transfer function. The transfer function provides smaller error terms and can reconstruct smaller RSL changes, but LDFs are well suited to RSL reconstructions focused on larger changes and using varied assemblages. Agreement between these techniques suggests that the approach we describe can be used as an independent means to reconstruct sea level or, importantly, to check the ecological plausibility of results from other techniques.

INFLUENCE OF PATCHINESS ON MODERN SALT-MARSH FORAMINIFERA USED IN SEA-LEVEL STUDIES (NORTH CAROLINA, USA)

We collected replicate samples at stations placed systematically along a transect at Oregon Inlet (North Carolina, USA) to investigate spatial homogeneity of dead assemblages of salt-marsh foraminifera. Analysis of variance (ANOVA) was used to investigate the differences in mean proportions for six species ( Miliammina fusca, Trochammina inflata, Arenoparrella mexicana, Tiphotrocha comprimata, Haplophragmoides wilberti and Jadammina macrescens ) selected because of their importance in distinguishing assemblages across salt marshes in the study region. As expected, ANOVA’s on all species indicated significant differences among low-, middle-, and high-marsh zones defined by their flora. No significant differences were found between stations in the low- and high-marsh indicating homogeneity in these zones. In contrast, for all six species in the middle-marsh zone, significant outcomes for ANOVA, cluster analysis and post-hoc comparisons suggested that the middle-marsh should be divided into two zones. In addition, two species exhibited a patchy (inhomogeneous) distribution among all stations in the middle marsh. If confirmed by additional studies, our results indicate that sampling of modern salt-marshes to document the distribution of foraminifera for use in sea-level reconstructions should recognize the spatial variability associated with the middle-marsh floral zone.

ECOLOGICAL DISTRIBUTION OF THE FORAMINIFERA IN A TIDAL LAGOON-BRACKISH LAKE, NEW ZEALAND, AND ITS HOLOCENE ORIGINS

The shallow subtidal to intertidal sandy mudflats of an unusual, 6 km 2 , alternating tidal lagoon–brackish lake (Lake Onoke, New Zealand) has a remarkably consistent foraminiferal fauna dominated (>80%) by Miliammina fusca . During intervals when the gravel barrier across its mouth is closed, the salinity in the lake declines and the level may rise to 1 m above the extreme astronomical tide level (EHWS) of the sea outside. A transect of samples through and above the salt marsh on the edge of Lake Onoke identifies three elevation-related foraminiferal zones: M. fusca (up to mid tide level, MSL); M. fusca-Trochamminita salsa (MSL to mean high water level, MHW); and T. salsa-Haplophragmoides wilberti (MHW to 1 m above EHWS). This is the first record of foraminiferal faunas living above EHWS in New Zealand. Foraminiferal faunas in Holocene sediment cores indicate that a much larger, ancestral Lake Onoke (~20 km 2 ) was created 4000–3000 cal yr BP, presumably by the growth of a gravel barrier across the previously open mouth to the sea. During the late Holocene, river sand prograded southwards into ancestral Lake Onoke creating swampy alluvial flats that separate modern Lake Onoke from its freshwater counterpart, Lake Wairarapa. Foraminiferal faunas indicate the early Holocene (6500-4000 cal yr BP) presence of an elongate (30 km-long), mostly intertidal embayment extending up the lower Wairarapa Valley beneath present-day Lakes Onoke and Wairarapa. Foraminifera-based elevation estimates suggest that during the early Holocene, this embayment subsided at a rate of about 1–2 mm per yr, sufficient to accommodate the accumulating mud and retain an extensive area (>20 km 2 ) of tidal flats. A slowing rate of subsidence accompanied by eustatic sea-level fall probably account for late Holocene aggradation.

Suitability of salt-marsh foraminifera as proxy indicators of sea level in Tasmania

Abstract This paper aims to establish whether contemporary salt-marsh foraminifera from eastern Tasmania are suitably related to elevation and can therefore be used to reconstruct past sea levels. A proxy reconstruction of recent sea-level change in Tasmania is potentially useful because in New Zealand a prominent early 20th century acceleration of sea-level rise has been documented which requires regional confirmation. Forty-three surface samples were collected from two salt marshes in the Little Swanport Estuary. Common species are: Trochammina inflata, Jadammina macrescens, Miliammina fusca, Trochamminita irregularis and Trochamminita salsa. The latter two species have been previously grouped together as T. salsa, but are distinguished here because they occupy distinct vertical niches. We performed regression analyses on the agglutinated foraminifera and their surface elevations using the software package C2 and tested the accuracy of various regression models by comparing predicted heights of the two transects with surveyed heights. We found that the surveyed heights are closely matched by elevations predicted by Weighted-Average Partial-Least-Squares (WA-PLS) models. These models predict sea level to within ± 0.10 m. PLS models showed favourable statistical parameters but were unreliable when used for predictions. Applications of PLS regression models in sea-level reconstructions therefore require caution. We compare our results with other studies from around the world and conclude that microtidal coastlines provide the most advantageous conditions for precise sea-level reconstructions.

The application of foraminifera to reconstruct the rate of 20th century sea level rise, Morbihan Golfe, Brittany, France

Foraminiferal assemblages preserved within salt-marsh sediment can provide an accurate and precise means to reconstruct relative sea level due to a strong relationship with elevation, which can be quantified using a transfer function. We collected a set of surface samples from two salt marshes in the Morbihan Golfe, France to determine foraminiferal distribution patterns. Dominant taxa included Jadammina macrescens, Trochammina inflata, Haplophragmoides spp. and Miliammina fusca. We developed a foraminifera-based transfer function using a modern training set of 36 samples and 23 species. The strong relationship between observed and predicted values (r 2 jack = 0.7) indicated that foraminiferal distribution is primarily controlled by elevation with respect to the tidal frame and precise reconstructions of former sea level are possible (RMSEP jack = 0.07 m). The application of the transfer function to a short salt-marsh core (0.32 m) allowed the reconstruction of former sea levels, which were placed in a chronological framework using short-lived radionuclides ( 210Pb and 137Cs). The agreement between the foraminifera-based sea level curve and the Brest tide-gauge record confirms the reliability of transfer function estimates and the validity of this methodology to extend sea level reconstructions back into the pre-instrumental period. Both instrumental and microfossil records suggest an acceleration of sea level rise during the 20th century.

Foraminíferos bentônicos em sedimentos de fundo da lagoa de Maricá, Estado do Rio de Janeiro

A study of benthic foraminifera was carried out on sediments from the bottom of Maricá lagoon located in the Região dos Lagos, state of Rio de Janeiro. This region is suffering with disordered human occupation and there has been an increase in the occupation rates and several projects for tourist resorts in the area. The response of the foraminifera to such activities was important for the ecological characterization. The laboratory treatment of the samples followed the specific methodology for foraminifera. The dominant species were Miliammina fusca and Miliammina spp., followed by Haplophragmoides spp., Trochammina inflata, Trochammina spp, Ammobaculites dilatatus and Arenoparrella mexicana. Those species have agglutinated tests that characterize paralic environments with low energy and salinity variations, in coastal regions. A comparative study with the Guanabara Bay showed distinct assemblages and distinct environments. In spite of the anthropogenic pollution influence in the lagoon, that pollution has not reached critical levels, and this response could suggest an efficient environment control by public policies to preserve the ecosystem.

The application of intertidal foraminifera to reconstruct coastal subsidence during the giant Cascadia earthquake of AD 1700 in Oregon, USA

Changes in species assemblages of intertidal foraminifera can be used to estimate the amount of earthquake-related subsidence during plate-boundary earthquakes at the Cascadia subduction zone. The accuracy and precision of foraminiferal methods in paleoenvironmental reconstruction is underpinned by the relations between contemporary taxa and their environment, which are used to calibrate fossil foraminiferal assemblages in sediment sequences. A contemporary training set of surface sediment samples from five intertidal marshes along the Oregon coast was used to determine foraminiferal distributions and prevailing environmental control(s) along elevational transects. Dominant taxa include Balticammina pseudomacrescens, Trochamminita irregularis, Haplophragmoides wilberti, Trochammina inflata, Jadammina macrescens and Miliammina fusca. Unconstrained cluster analysis and detrended correspondence analysis was used to identify two elevation-dependent faunal zones: Faunal Zone I (upland, high marsh, middle marsh) dominated by Balticammina pseudomacrescens, Haplophragmoides wilberti and Trochammina inflata, and Faunal Zone II (low marsh and tidal flat) dominated by Miliammina fusca. Site-specific differences in assemblages at three marshes enabled further subdivision of Faunal Zone I. Zone Ia is based on one or more of Balticammina pseudomacrescens, Trochammina inflata, Trochamminita irregularis and Haplophragmoides sp., and Zone Ib on Jadammina macrescens, Haplophragmoides sp., Trochammina inflata and Miliammina fusca. Canonical correspondence analysis (CCA) and partial CCA of the training set from the Nehalem River marsh transect was used to infer that the zonation of foraminifera is elevation-dependent (39% of explained variance). A transfer function was developed to reconstruct sudden changes in relative sea-level during plate-boundary earthquakes in Oregon. The results indicate a robust performance of the transfer function ( r jack 2 = 0.82) with the error estimate (RMSEP jack = 0.20 m) comparable to local and regional transfer functions from other temperate marshes. To illustrate the potential of the technique, the transfer function was applied to reconstruct subsidence during the AD 1700 earthquake using at Alsea Bay, Oregon. The reconstruction (0.18 ± 0.20 m) is less than half the subsidence estimate of Nelson et al. [2008. Great-earthquake palogeoesy and tsunamis of the past 2000 years at Alsea Bay, central Oregon coast, USA. Quaternary Science Reviews, 27, 747–768] using their foraminiferal transfer function, perhaps because of differences in taxonomy and the species relationship to elevation.

Taphonomic signatures and patterns of test degradation on tropical, intertidal benthic foraminifera

The preservational condition of benthic foraminifera from tropical intertidal sediments in Cleveland Bay, north Queensland, Australia was examined in order to provide systematic descriptions of taphonomic signatures and semi-quantitative estimates of test degradation. The primary aim was to improve understanding of the processes of test degradation experienced by intertidal foraminifera during early burial. Eight common tropical, intertidal foraminiferal species were examined: Arenoparrella mexicana, Miliammina fusca, Miliammina obliqua and Trochammina inflata from two upper mangrove stations, and Ammonia aoteana, Elphidium excavatum clavatum, Pararotalia venusta and Parrellina hispidula from two mudflat stations. Taphonomic alteration was broadly divided into surface/textural features and larger-scale, structural losses to tests. Surface alteration of calcareous tests was dominated by the etching and roughening associated with dissolution processes, with limited evidence for bioerosion and abrasion. Both surficial etching and larger-scale structural damage were closely related to test architecture, with degradation most intense on porous chamber walls, as opposed to non-porous-areas, interlocular walls and chamber tips. Furthermore, all calcareous species exhibited consistent pathways of degradation whereby the most recently formed chambers were the most vulnerable to degradation. The correspondence between larger-scale test loss and these patterns of surface textural alteration, suggests calcareous test degradation is primarily driven by dissolution. Degradation of agglutinated tests contrasts in a number of ways. Pristine tests of all four species examined exhibited a smooth, outer organic coating, which may be missing from other specimens. The extent to which this initial loss effects further test breakdown is uncertain, but appears to differ between species. M. obliqua and some specimens of A. mexicana exhibited structural damage which corresponded to clear cement losses and agglutinant disaggregation. More generally, agglutinated species displayed fracturing and test breakages which bore no conspicuous relation to cement loss. Furthermore, neither surface alteration nor structural loss affected any part of agglutinated tests preferentially, and therefore pathways of degradation were inconsistent across specimens. The fact that agglutinated tests degrade in a more arbitrary manner, compared with calcareous tests, is taken as evidence that their degradation is (1) not entirely controlled by test architecture, and (2) at least partially driven by physical/mechanical processes. We suggest that, if agglutinated tests are not already inherently weaker than their calcareous counterparts, the loss of organic cements may sufficiently weaken agglutinated tests so as to increase susceptibility to physical damage. Tests were also graded according to the extent to which they were structurally degraded. Average taphonomic grades and taphonomic variability (i.e. standard deviation) for all species at Cocoa Creek were statistically invariant with depth, contrary to expectations based on the concept of progressive burial through a taphonomically-active zone. This indicates that shallow sub-surface sediments are significantly homogenised, and that sediment mixing and infaunal test production imparts a considerable effect on the development of surface and sub-surface dead assemblages at the study site.

Distribution of modern salt-marsh foraminifera in the Albemarle–Pamlico estuarine system of North Carolina, USA: Implications for sea-level research

We described the distributions of foraminifera from ten physiographically distinct salt marshes in the Albemarle–Pamlico estuarine system, North Carolina using 193 surface samples. We defined elevation-dependent ecological zones at individual sites using cluster analysis and detrended correspondence analysis. Additionally, seven principal biozones of salt-marsh foraminifera were identified that have distinctive spatial distributions reflecting a pattern of salinity regimes caused by the current configuration of barrier-island inlets. High salinity sites along the southern Outer Banks are associated with sub-tidal calcareous assemblages, low marshes dominated by Miliammina fusca and high marsh environments defined by Haplophragmoides wilberti, Trochammina inflata and Arenoparrella mexicana. In contrast, lower salinity marshes have Ammobaculites spp. in sub-tidal settings, Miliammina fusca-dominated low marshes and high marsh settings characterized by Jadammina macrescens. Spatial variation of foraminiferal populations and the potential for biozones to migrate in response to changing inlet configuration and salinity, suggests that datasets of modern salt-marsh foraminifera from multiple environments would be appropriate for reconstructing Holocene relative sea level in North Carolina.

Environmental constraints of foraminiferal assemblages distribution across a brackish tidal marsh (Caminha, NW Portugal)

Foraminiferal living assemblages from a brackish tidal marsh were studied across three sampling transects, under Spring and Autumn conditions. Foraminiferal analysis was also extended to the dead assemblages of Spring samples. Altimetric control of each sampling point was acquired through the connection to the national datum by GPS differential positioning combined with a regional geoid model. The influence of the geochemical characteristics on the assemblages including chemical composition of the estuarine and marsh surface sediments, in addition to salinity, pH and calcite saturation of estuarine and marsh interstitial waters was evaluated. A high affinity was found between Spring and Autumn living assemblages, probably related to the low number of representative species. The affinity also found between living and dead assemblage was seen as a consequence of low pH and calcite undersaturation that prevent the accumulation effect of several generations of foraminifera. Salinity appears as a clear constraint to the foraminiferal assemblages composition that is enhanced by calcite undersaturation in brackish marshes interstitial waters and sediments. Generally abundant marsh species like Trochammina inflata, Jadammina macrescens and the calcareous foraminifera are limited to an episodic presence. Foraminiferal assemblages distribution across brackish tidal marsh can be assumed as an elevation proxy. The high marsh IB sub-zone is dominated by Haplophragmoides sp. and Haplophragmoides manilaensis. Low marsh zone II is characterised by the dominance of Miliammina fusca but can be subdivided in an IIA upper part, where is followed by Pseudothurammina limnetis, and in a IIB lower part defined by a subsidiary presence of Psammosphaera sp. Haplophragmoides manilaensis dominance between 1.55 m and 1.67 m, at living as well as dead assemblages, suggests this species as a potential sea-level indicator for the brackish tidal marshes.

Mineralogy of agglutinated benthic foraminifera; implications for paleo-environmental reconstructions

Abstract Benthic foraminifera of recent salt marsh environments are often dominated by species with an agglutinated test. The grains used for test construction by these foraminifera are collected from their surrounding environment. In this study we investigate the role of sediment grain size and mineralogical composition for richness, population density and taxonomic composition of agglutinating foraminifera. Foraminifera from 15 stations of the tidal marsh of the Canche estuary (Pas-de-Calais, France) were studied. The species richness depends on the grain size of the sediment, whereas the density is not related to sediment grain size. The distribution of foraminifera species throughout the tidal marsh may depend on many environmental parameters such as OM as well as tidal elevation, already largely discussed in literature. The mineralogical composition of the agglutinated grains in Trochammina inflata and Arenoparrella mexicana is very different from that of sediment; the composition of Jadammina macrescens is generally different from that of the sediment with some exceptions, and in Miliammina fusca, Paratrochammina haynesi and Remaneica plicata the mineralogical compositions are similar to those of the sediment. The studied species may be able to select their preferred grains based upon composition even if a particular mineral is scarce in the sediment.