Search

Isotopes of Sr, O, and C were studied from a 227-cm long sediment core in order to develop a high-resolution paleosalinity record to investigate the paleohydrology of Laguna de la Leche, north coastal Cuba, during the Middle to Late Holocene. Palynological, plant macrofossil, foraminiferal, ostracode, gastropod, and charophyte data from predominantly euryhaline taxa, coupled with a radiocarbon-based chronology, indicate that the wetland evolved through four phases: (1) an oligohaline (0.5–5‰) lake existed from ∼ 6200 to ∼ 4800 cal yr B.P.; (2) water level in the lake increased and the system freshened from ∼ 4800 to ∼ 4200 cal yr B.P.; (3) a mesohaline (5–18‰) lagoon replaced the lake ∼ 4200 cal yr B.P.; and (4) mangroves enclosed the lagoon beginning ∼ 1700 cal yr B.P., forming a mesohaline lake. Isotopic ratios were measured on specimens of the euryhaline foraminifer Ammonia beccarii, although several measurements were also made on other calcareous microfossils in order to identify potential taphonomic and/or vital effects. The 87Sr/86Sr results show that the average salinity of Laguna de la Leche was ∼ 1.7‰ during the early lake phase and ∼ 8‰ during the lagoon phase — a change driven by relative sea level rise. The δ18O results do not record the salinity increase seen in the 87Sr/86Sr data, but instead indicate high evaporation from the lake surface; this in turn suggests that the value of ∼ 1.7‰ may slightly underestimate the average salinity of the wetland, at least for the period prior to ∼ 4800 cal yr B.P. Variability in δ13C was controlled by plant productivity, episodic marine incursions, and vegetation community change. There is some evidence for seasonal effect and the lateral transport of microfossils prior to burial. The isotopic data independently confirm the hydrological interpretations made using the euryhaline indicators and have permitted the reconstruction of a significantly higher resolution paleosalinity record than would be possible using the paleoecological data. However, our results show that Sr isotopes, while often cited as a powerful paleosalinity tool, must be used in conjunction with other indicators when investigating paleosalinity trends; relying solely on any single isotopic or ecological indicator can lead to inaccurate results, especially in semi-enclosed and closed hydrological systems.

Laguna de la Leche, north coastal Cuba, is a shallow (≤ 3 m), oligohaline (∼ 2.0–4.5‰) coastal lake surrounded by mangroves and cattail stands. A 227-cm core was studied using loss-on-ignition, pollen, calcareous microfossils, and plant macrofossils. From ∼6200 to ∼ 4800 cal yr BP, the area was an oligohaline lake. The period from ∼ 4800 to ∼ 4200 cal yr BP saw higher water levels and a freshened system; these changes are indicated by an increase in the regional pollen rain, as well as by the presence of charophyte oogonia and an increase in freshwater gastropods (Hydrobiidae). By ∼ 4000 cal yr BP, an open mesohaline lagoon had formed; an increase in salt-tolerant foraminifers suggests that water level increase was driven by relative sea level rise. The initiation of Laguna de la Leche correlates with a shift to wetter conditions as indicated in pollen records from the southeastern United States (e.g., Lake Tulane). This synchronicity suggests that sea level rise caused middle Holocene environmental change region-wide. Two other cores sampled from mangrove swamps in the vicinity of Laguna de la Leche indicate that a major expansion of mangroves was underway by ∼ 1700 cal yr BP.

The authors present stratigraphic data from Los Buchillones, a now submerged Taino village on the north coast. of central Cuba that was occupied from some time prior to A-D. 1220 until 1640 or later. Los Buchillones is one of the best-preserved sites in the Caribbean, with material culture remains that include palm thatch and wooden structural elements from some of the more than 40 collapsed structures. The purpose of this study was to investigate the environinent and site-formation processes of the Taino settlement. Sediment cores were sampled from the site and its vicinity to permit integration of the geological and archaeological stratigraphics. The cores were analyzed for color, texture, mollusk content, elemental geochemistry, and mineralogy. The results of the stratigraphic work are consistent with regional sea-level data that shows relative sea level has risen gradually during the late Holocene, but has remained relatively stable since the time the Taino first occupied Los Buchillones. Of the two structures partially cleared, at least one appears to have been built over the water, supported on pilings. Site selection is likely to have resulted from a consideration of environmental factors, such as access to marine, terrestrial, and lagoonal resources, and proximity to freshwater springs. (c) 2006 Wiley Periodicals, Inc.

Pollen and diatom assemblages, and peat stratigraphies, from a coastal wetland on the northern shore of Lake Erie were used to analyze water level and climatic changes since the middle Holocene and their effects on wetland plant communities. Peat deposition began 4700 cal yr B.P. during the Nipissing II transgression, which was driven by isostatic rebound. At that time, a diatom-rich wild rice marsh existed at the site. Water level dropped at the end of the Nipissing rise at least 2 m within 200 yr, leading to the development of shallower-water plant communities and an environment too dry for most diatoms to persist. The sharp decline in water level was probably driven primarily by outlet incision, but climate likely played some role. The paleoecological records provide evidence for post-Nipissing century-scale transgressions occurring around 2300, 1160, 700 and 450 cal yr B.P. The chronology for these transgressions correlates with other studies from the region and implies climatic forcing. Peat inception in shallow sloughs across part of the study area around 700 cal yr B.P. coincides with the Little Ice Age. These records, considered alongside others from the region, suggest that the Little Ice Age may have resulted in a wetter climate across the eastern Great Lakes region.

We present an analysis of modern pollen and diatom assemblages in surficial sediments in a coastal marsh at Rondeau Provincial Park, on the northern shore of Lake Erie in southwestern Ontario, Canada. The objectives of the study were (1) to determine how pollen and diatom assemblages in surface sediments vary as a function of the dominant vegetation community and moisture availability at the sampling site and (2) to analyze pollen-vegetation relationships of four dominant wetland plants: Cephalanthus occidentalis, Phragmites australis, Typha spp., and Zizania aquatica, in order to improve interpretations of fossil sequences. Canonical variate analysis (CVA) was used to compare pollen and diatom spectra from sampling sites in three marsh zones delineated on the basis of moisture availability. Using the pollen or the diatom datasets, the resulting discriminant functions correctly classified 86% of the wettest sites, 72% of those with intermediate moisture availability, and only 25% of the sites in the driest parts of the wetland. Since 35% of the sampling sites were misclassified by the CVA on the basis of pollen assemblages, a representation factor approach is needed to complement the comparative approach when analyzing pollen datasets from wetland contexts. Percent cover vegetation data at sediment sampling sites are used to illustrate pollen-vegetation relationships for the ecologically important wetland plants at the site. Phragmites australis and Typha spp. produce small amounts of pollen relative to their abundance, while Cephalanthus occidentalis and Zizania aquatica produce abundant pollen, which is deposited highly locally in the case of Cephalanthus. These data will enable improved interpretations of fossil pollen and diatom sequences from wetland contexts.

Multiple proxy indicators are regularly used to present robust arguments for paleoenvironmental change. We use fossil pollen and diatoms from a 495-cm core taken from Cootes Paradise, a coastal wetland in the western end of Lake Ontario, to investigate ecological changes in the late Holocene. We use consensus analysis to demonstrate that pollen diagrams are best zoned after the data have been split into source area, in this case upland and wetland taxa, because each group responds differently to environmental change. We also use consensus analysis to demonstrate the sensitivity of clustering to the distance measure used. The record begins at 2400 14C years BP, when the wetland was dominated by shallow water emergents and epiphytic diatoms. At 2100 14C years BP, a decline in the epiphytic diatoms Epithemia spp., a rise in Poaceae (cf. Zizania aquatica) pollen and a coincident increase in pollen concentration suggest a water level rise at this time. At about 800 14C years BP, the diatom record shows a pulse in small benthic Fragilaria species; shortly after, a shift occurs in the upland tree pollen spectra involving an increase in Pinus and a decline in Fagus. This shift in upland forest trees has been associated elsewhere with the Little Ice Age and the diatom data present some evidence for impacts of this climatic event on aquatic systems. The diatom and pollen records both indicate large changes associated with the effects of European settlement, including rises in Ambrosia as well as Typha angustifolia pollen. Planktonic diatoms dominate post-settlement assemblages indicating large-scale hydrological and ecological changes, probably associated with the introduction of carp and alterations to the Iroquois bar which separates the wetland from Lake Ontario. Our work at Cootes Paradise is important for multi-proxy coastal wetland studies in general, in addition to the late Holocene environmental history and prehistory of the Great Lakes region.

Although prehistoric native peoples probably used wild rice for food and ceremony, evidence is sparse. Macrofossil remains of wild rice are uncommon on archaeological sites even where the plant is still common nearby. The association between documented human habitation and wild rice is explored with pollen records from associated wild rice wetlands. For this, reliable identification of wild rice pollen is essential. Three approaches are examined: (1) the pollen spectral signature (percentage and density of grass pollen), (2) coeval community pollen types, and (3) the pollen morphology (size and sculpturing) of wild rice versus other stand-forming wetland grasses. We report pollen spectra from a contemporary wild rice marsh and compare it with fossil pollen from Cootes Paradise, a wetland at the western end of Lake Ontario. The pollen signature from the modern wild rice wetlands was similar to that of the fossil site, but this correspondence does not confirm that the fossil grass pollen is wild rice. Wild rice pollen is separable by size from that of all the stand-forming wetland grasses examined, but the fossil pollen from Bull's Point is not the same size as that of modern wild rice. Scanning electron microscopy (SEM), however, indicates that wild rice pollen is identifiable by its sculpturing and that the fossil pollen has an identical micromorphology.

The prairie–deciduous forest ecotone changes from a distinct boundary in northern Minnesota to a fragmented mosaic type in Wisconsin, Iowa, and Illinois. The differences largely can be attributed to topography and fire, but edaphic factors, the survival of disjunct relicts, and the differential migration rates of some taxa are contributory. Fossil pollen spectra from the Driftless Area attest to the persistence of the mosaic character throughout the Holocene. Modern surface spectra illustrate the difficulties of recognizing vegetation changes along and across the ecotone.

Archaeological evidence from the marine terrace and fen at the site indicates brief episodic occupation for over 5000 years. Five cultural episodes have been identified, although the site is renowned for its Norse settlement. A fen on the site has provided both artifacts and fossil pollen. Although the pollen spectra are dominated by disturbance taxa, they indicate little or no human impact. Both the archaeological data and the pollen spectra are consistent with brief episodes of occupancy. Relationships between regional environmental changes and the human response are indistinct, although a cool interval after 2500 B.P. coincides with a 1000 year hiatus in occupation. For the Norse period, the pollen record is compatible with the view that L'Anse aux Meadows was a small, short-lived way station.

The pollen record from the upper fill in Tamarack Creek, Wisconsin, documents succession in a nonacid wetland environment subject to a high frequency of fire. Interpretation of changes in local and extralocal communities is aided by reconstruction of the fire history at the site. Variations in the regional vegetation are difficult to determine. The mosaic character of the prairie-deciduous forest ecotone in this area appears to have remained largely unchanged throughout the record.