Franco S. Medioli

Morphological variations of benthic foraminiferal tests in response to changes in ecological parameters; a review

Some of the relatively recent literature correlating morphological variation in benthic foraminifera with environmental parameters such as temperature, salinity, carbonate solubility, depth, nutrition, substrate, dissolved oxygen, illumination, pollution, water motion, trace elements, and rapid environmental fluctuation is reviewed. It appears some variables (most notably depth) are recorded more frequently, which may affect some conclusions. Although each variable is treated separately, it appears that almost no variables act independently on test morphologies. In reviewing the literature, it becomes clear that there are many individual trends, especially with shell ornamentation, but few broad ones, and that it is almost impossible, with exception of some of the larger reef-dwelling, symbiont-bearing foraminifera, to predict how any species will react to various parameters. The broad trends concern thinning or thickening of carbonate tests with changing carbonate availability, temperature, and salinity. It appears that many observations of morphological changes within species may not be recorded in the literature, perhaps because authors did not recognize the importance of small details that would be of importance at a later time.

Foraminifera as sea-level indicators

There are over 1000 foraminiferal species presently living in marine environments, but relatively few of these can be used as direct indicators of sea level. We detail here certain assemblages occupying marsh environments that can be used for that purpose. Marsh foraminiferal assemblages have been shown to occur worldwide within narrowly defined vertical zones some of which extend less than 10 cm in total vertical range. These assemblage zones, once known, can be relocated in paleo-marsh deposits and accurately related to paleo-sea level. The key to success of these organisms as sea-level indicators is that their primary controlling factor appears to be elevation above mean sea level.

A Comparison of Postglacial Arcellacean (Thecamoebian) and Pollen Succession in Atlantic Canada, Illustrating the Potential of Arcellaceans for Paleoclimatic Reconstruction

Cores dating back to deglaciation were taken from three lakes in Atlantic Canada and analyzed for arcellaceans and pollen. Paleotemperatures and paleo-precipitation were calculated from the pollen data using transfer functions. A sudden warming is recorded by the pollen around 10,000 years B.P., followed by a general warming to the mid Holocene Hypsithermal, then by a decrease in temperature and increase in effective precipitation to the present. The three lakes, two in western Newfoundland and one in eastern Nova Scotia, contain similar late glacial (13-10 ka), early Holocene (10-8 ka), mid Holocene (8-4 ka), and late Holocene (4-0 ka) arcellacean assemblages. Immediately following retreat of the ice sheets, Centropyxis aculeata, Centropyxis constricta, Difflugia oblonga, Difflugia urceolata, and Difflugia corona were common. The latter part of the late glacial is characterized by sparse assemblages dominated by C. aculeata. The arcellacean record thus suggests a climatic reversal in Atlantic Canada between 11,500 and 10,000 years B.P., analogous to the Younger Dryas, although this is not recorded by the pollen. Species diversity increased sharply at the beginning of the Holocene, and D. oblonga is the dominant taxon in early Holocene sediments. Difflugia oblonga remained common through the mid Holocene, but percentages of C. aculeata were very low, and Pontigulasia compressa and Difflugia bacillifera peaked in abundance during the Hypsithermal. The late Holocene is characterized by a resurgence in C. aculeata at the expense of other taxa. The increase in Heleopera sphagni and Nebella collaris since 5,000 years B.P. at the two sites in southwestern Newfoundland reflects paludification in response to increased precipitation since the Hypsithermal. Because the changes in arcellacean assemblages are regionally synchronous in all three lakes and coincide with climatically driven vegetational successions indicated by the pollen record, arcellaceans appear to respond to climatic change, and thus may be useful paleoecological and paleolimnological indicators. With their quicker generation time, these protists may be better suited than pollen to recording short-lived phenomena, like the mid-Holocene Hypsithermal and the Younger Dryas reversal.

POLLUTION MONITORING IN TWO NORTH AMERICAN ESTUARIES: HISTORICAL RECONSTRUCTIONS USING BENTHIC FORAMINIFERA

Both surface and core studies from two highly impacted estuaries (New Bedford Harbor, Massachusetts, USA and Halifax Harbour, Nova Scotia, Canada) were carried out to determine if benthic foraminifera could be used to detect changes through time in these areas. New Bedford Harbor is in a highly industrialized area that has undergone severe environmental stresses from a variety of sources for almost 400 years, and has been declared an U.S. Environmental Protection Agency (EPA) Superfund site (i.e., a site so impacted that a special EPA fund is set up to clean it up in designated time frame). Halifax Harbour has been subjected mostly to domestic pollution (i.e., organic carbon produced by human wastes), rather than industrial (chemical) pollution since the founding of the city in 1749. Although many geochemical studies have been done in both estuaries, there are few baseline data on the biota. In this paper we use benthic foraminiferal assemblages retrieved from sediment cores to reconstruct biotic changes of the recent past. It is then possible to correlate faunal changes with already known geochemical parameters. The character of the pollution has changed in New Bedford Harbor as remediation efforts have taken hold. This change was detected with the foraminifera. One outcome is that deformities among one species, Haynesina orbiculare, appear to occur simultaneously with high polychlorinated biphenyls (PCB’s) in the sediments. In Halifax Harbour, where the largest impact is due to high organic input from domestic sources, species tolerant of low-oxygen conditions are most prominent at present. Core studies show that prior to the rapid growth of Halifax (in the 1960s) the organic input was much lower than at present. The higher input of organic carbon (OC) at present is indicated by foraminiferal species tolerant of high OC in cores since 1960, generally those with agglutinated as opposed to calcareous tests. We define industrial vs. OC pollution in sediments using foraminifera as proxies, and further, the environmental history is accurately depicted without original baseline data. Data from these two estuaries can be compared to other sites where degradation may be in different stages, which can be assessed by looking at foraminiferal faunas in those areas.

Lacustrine thecamoebians (mainly arcellaceans) as potential tools for palaeolimnological interpretations

Abstract A number of thecamoebian genera of potential or demonstrated importance for palaeolimnological research (mainly Arcellacea) are discussed. What is known about their biology, ecology, spatial distribution, mechanisms of dispersal and characteristic associations is briefly reviewed in the introductory part. After a short discussion on the concept of species and the somewhat peculiar way in which it applies to this group of organisms, a chapter on systematic taxonomy, including an illustrated guide to the identification of the genera, is presented. The scarce fossil record of the group is then briefly discussed. Practical instructions on collection, preparation and observation of thecamoebians for palaeolimnological research are supplied. The paper closes with the presentation of a few studies performed by the authors as examples of how Arcellacea can become tools for the solution of palaeolimnological problems.

Agglutinated foraminifera and thecamoebians from the Late Carboniferous Sydney coalfield, Nova Scotia: paleoecology, paleoenvironments and paleogeographical implications

Abstract Agglutinated foraminifera and arcellaceans (“thecamoebians”) were examined from Carboniferous (late Westphalian-Stephanian) cyclothems in the Sydney Basin of Nova Scotia. Four distinctive assemblages are documented from the coal-bearing strata, and indicate deposition took place on an extensive coastal platform. The eastern part of the basin is dominated by Ammobaculites-Ammotium assemblages that indicate estuarine-low marsh paleoenvironments. Relationships between test size, grain size within the test, and grain size of the substrate are used to differentiate between upper mudflat and lower mudflat sub-facies within estuarine facies. Mixed assemblages dominated by Trochammina, Ammotium and Ammobaculites indicate vegetated substrates, analogous to modern lower marsh environments, and flanked the estuarine system in the eastern and western areas of the basin. Rich Trochammina and thecamoebian assemblages are restricted to the western area of the basin, indicating deposition within the upper part of the tidal range. Trochammina assemblages, typically found underlying coal seams, may indicate vegetated substrates equivalent to modern high marsh facies. Thecamoebian assemblages, dominated by an agglutinated difflugid type, indicate freshwater paleoenvironments. Encystment of the thecamoebian populations suggests paleoenvironments were short lived.

Fossil Thecamoebians: Present Status and Prospects for the Future

Some basic facts concerning the biology, ecology and taxonomic problems of thecamoebians are reviewed and summarized on the assumption that this information is useful for the palaeontological applications of this group.

INFAUNAL BENTHIC FORAMINIFERA IN SOME NORTH AMERICAN MARSHES AND THEIR INFLUENCE ON FOSSIL ASSEMBLAGES

We have looked at a series of living and total assemblages of foraminifera in cores from two well-studied salt marshes (Chezzetcook Inlet, Canada, and North Inlet, South Carolina) and replotted data from a marsh in Nanaimo, British Columbia. The data from the three sites indicate that: 1) the infaunal living specimens appear to have little impact on the total assemblages at depth; 2) there is little evidence of test breakdown except for the well-known dissolution of calcareous tests that occurs in these acidic marsh sediments, although there is an inexplicable taphonomic breakdown of specimens in the southeastern USA; 3) the upper 1-cm slice of sediment provides a representative assemblage to use as a modern analogue for fossil benthic foraminiferal assemblages (as opposed to larger segments); and 4) foraminifera do not migrate vertically in the sediment to escape seasonal ice. We also include a taxonomic discussion of the most common Trochammina species, since some new names have been assigned to various formae of Trochammina macrescens.

Biogeographic Distribution of Modern Thecamoebians in a Transect Along the Eastern North American Coast

Thecamoebians in general, and the superfamily Arcellacea in particular, seem ideally suited as paleolimnological tools. The scarcity of baseline biogeographical studies, however, severely limits their value as modern analogs for paleoecological reconstructions. A comparison of the modern arcellacean fauna studied from four lakes from Baffin Island (63°N), Nova Scotia (45°N), Virginia (38°N) and southern Florida (27°N) with the information available in the literature shows how several trends in arcellacean distribution exist in eastern North America.

Micropaleontological Documentation for Early Holocene Fall of Relative Sea-Level on the Atlantic Coast of Nova-Scotia

The presence of a marsh sequence between two shallow-water marine deposits in an offshore core from Lunenburg, Nova Scotia, indicates fall of relative sea level followed by rise of relative sea level. The marsh sequence is now 27 m below datum level, with a C 14 date of 7,070 yr B.P. This sequence suggests that the glacial forebulge migrated through this area 7,000 yr ago, that 27 m of submergence has occurred since then, and that prior to 7,000 yr B.P. the site was characterized by low-amplitude emergence. This is at present the only sequence where the entire regression-transgression record is preserved along this coast; the accuracy required to demonstrate this can be obtained only by using established marsh foraminiferal zonations.