Holger Cremer

The postglacial environmental development of Raffles Sø, East Greenland: Inferences from a 10,000 year diatom record

A 341 cm long sediment sequence was recovered from the unofficially named Raffles Sø on Raffles Ø, outer Scoresby Sund region, East Greenland. The sediment sequence consists in the upper part (0–230 cm) of a stratified gyttja enriched in organic carbon and biogenic silica whereas the lower core part (235–341 cm) is composed of terrigenous, consolidated glacio-limnic sediments. 14C-AMS measurements indicate that the sediment sequence represents the entire Holocene lake history from 10,030 calibrated radiocarbon years.The geochemical parameters (opal, total organic carbon (TOC), total nitrogen (TN)) and the total diatom concentration show similar developments during the Holocene, and reflect changes in biological production and nutrient input into the lake. These records clearly reveal a broad Holocene TOC-opal-maximum interval between 5200 and 1800 cal. yrs BP.The diatom flora consisted of 66 taxa representing 20 genera but only seven taxa were abundant and, sometimes, these were monospecifically dominant during the Holocene. In the sediment core from Raffles Sø four successive stratigraphical zones can be distinguished. Accumulation of diatom valves began at 9900 cal. yrs BP with a Stephanodiscus minutulus (Kütz.) Cleve and Möller dominated assemblage (stratigraphic zone 1) followed by a diatom flora dominated by Cyclotella pseudostelligera Hustedt and, less frequently, by Diatoma tenuis Agardh (9400 until 5900 cal. yrs BP, zone 2). Cyclotella sp. A, a taxon which belongs to the Cyclotella rossii-comensis-tripartita-complex, was the dominant floral element between 5200 and 1800 cal. yrs BP (zone 3). From 1800 cal. yrs BP, the periphytic taxa Fragilaria capucina var. gracilis (Østr.) Hustedt and F. capucina var. rumpens (Kütz.) Lange-Bertalot attained highest relative abundances, also almost monospecifically (zone 4).The distribution and composition of the diatom assemblages in the sediment record from Raffles Sø probably reflect past variations in the extent of the lake-ice cover during the growing season. More or less ice-free conditions during summer may have prevailed during the early Holocene until ca. 1800 cal. yrs BP, which allowed growth of planktonic diatoms (Cyclotella taxa) in the pelagic lake region. From 1800 cal. yrs BP, colder conditions lead to a perennial lake-ice cover with a small ice-free moat in summer which favored the growth of periphytic, littoral species (Fragilaria capucina varieties).

The Holocene Diatom Flora of Marine Bays in the Windmill Islands, East Antarctica

Abstract The Holocene diatom flora identified in three sediment cores from marine bays in the Windmill Islands (East Antarctica) is described and depicted for the first time. One hundred and twenty-four diatom taxa could be identified of which eighty-one taxa have a circum-Antarctic distribution. All taxa are listed in a table together with appropriate references and remarks on ecology and biogeography. The most diverse genera are Fragilariopsis, Navicula and Thalassiosira. Some taxa (e.g., Chaetoceros spp., Fragilariopsis curta, F. cylindrus, Navicula glaciei and Synedropsis spp.) have the potential to be used as indicator taxa for the reconstruction of palaeoceanographic conditions in the Windmill Islands.

Palaeoclimatic significance of late Quaternary diatom assemblages from southern Windmill Islands, East Antarctica

Abstract The late Quaternary palaeoenvironmental history of the southern Windmill Islands, East Antarctica, has been reconstructed using diatom assemblages from two long, well-dated sediment cores taken in two marine bays. The diatom assemblage of the lowest sediment layers suggests a warm climate with mostly open water conditions during the late Pleistocene. During the following glacial, the Windmill Islands were covered by grounded ice preventing any in situ bioproductivity. Following deglaciation, a sapropel with a well-preserved diatom assemblage was deposited from ∼10 500 cal yr BP. Between ∼10 500 and ∼4000 cal yr BP, total organic carbon (Corg) and total diatom valve concentrations as well as the diatom species composition suggest relatively cool summer temperatures. Hydrological conditions in coastal bays were characterised by combined winter sea-ice and open water conditions. This extensive period of glacial retreat was followed by the Holocene optimum (∼4000 to ∼1000 cal yr BP), which occurred later in the southern Windmill Islands than in most other Antarctic coastal regions. Diatom assemblages in this period suggest ice-free conditions and meltwater-stratified waters in the marine bays during summer, which is also reflected in high proportions of freshwater diatoms in the sediments. The diatom assemblage in the upper sediments of both cores indicates Neoglacial cooling from ∼1000 cal yr BP, which again led to seasonally persistent sea-ice on the bays. The Holocene optimum and cooling trends in the Windmill Islands did not occur contemporaneously with other Antarctic coastal regions, showing that the here presented record reflects partly local environmental conditions rather than global climatic trends.

Colonization, succession, and extinction of marine floras during a glacial cycle: A case study from the Windmill Islands (east Antarctica) using biomarkers

With the exception of the diatoms, little is known of the extinction, colonization, and succession of marine floras during glacial cycles. Here we study both morphological and biochemical fossils in two sediment cores from the Antarctic to unravel the sequence of events over a single glacial cycle. The cores, from the nearshore continental shelf off the Windmill Islands (66°S, 110°E), east Antarctica, span the period from Marine Isotope Stage 3 or earlier to the present. New high-performance liquid chromatography and mass spectrometry methods were used to study fossil pigments with additional data from siliceous microfossils, lithological analyses, and radiocarbon dates. Results show two response processes. First, there is the large-scale impact of the expanding ice sheet in removing the flora from the inner shelf, primarily through the denial of light, destabilization of the substratum, and elimination of habitats. Second, there are a number of glacial climate interactions that have a surprisingly strong influence on recolonization and succession. These include sea ice extent and the proximity of the ice edge, the annual duration of open water, the stabilization of the substratum first by benthic diatoms and later by macrophyte algae, and relative sea level. A period of warmer climate in the mid-Holocene had a considerable influence on the composition and species diversity of the marine flora. These are the first data on the timing of colonization and succession of marine floras over a glacial cycle based on both morphological and biochemical fossils.

A microscopical study of diatom phytoplankton in deep crater Lake El'gygytgyn, Northeast Siberia

Abstract : A survey of the planktonic diatom community was carried out during summer2003 in Lake El’gygytgyn, a deep, cold, low conductive and oligotrophic crater lake inthe Northeast Siberian Arctic. Five planktonic diatom species were identified: Cy-clostephanos dubius , Cyclotella ocellata , Cyclotella tripartita , Pliocaenicus costatus ,and Stephanocostis chantaicus . The morphological details of the five taxa are docu-mented by light and partly also scanning electron micrographs. Additionally, ecologicaland biogeographic data are provided. This is the first evidence of S. chantaicus in a north-east Siberian lake and one of the first findings of P. costatus outside the Baikal Lake re-gion. The diatom community in summer 2003 was almost monospecificly dominated by Cyclotella ocellata (>96%), a species that displays a tremendous morphological variabil-ity. High concentrations and accumulation rates of diatom frustules during the ice-cov-ered period (May–June 2003) indicated considerable under-ice phytoplankton growth.

Diatoms (Bacillariophyceae) and Dinoflagellate Cysts (Dinophyceae) from Rookery Bay, Florida, U.S.A.

Abstract. This paper is a report on the diatoms and dinoflagellate cysts identified in a sediment core and a water sample recovered from Rookery Bay, a subtropical estuarine system located on the west coast of Florida. Eighty-eight diatom taxa representing 48 genera, many of which have been rarely observed, and 14 dinoflagellate cyst genera with 20 taxa were identified in Rookery Bay. All taxa are briefly annotated and documented by light micrographs. The most common diatom taxa in the surface sediment sample are Amphicocconeis disculoides, Chaetoceros resting spores, Cyclotella litoralis, Cymatosira belgica, Neodelphineis pelagica, Paralia sulcata, and Pleurosigma rhombeum. The most abundant dinoflagellate cyst taxa in the surface sample include Brigantedinium spp., Lingulodinium machaerophorum, Polyspheridium zoharyi, Spiniferites bentorii, and Spiniferites ramosus.

An analysis of the limnology and sedimentary diatom flora of fourteen lakes and ponds from the Windmill Islands, East Antarctica

The limnology and sedimentary diatom flora of fourteen lakes and ponds from the Windmill Islands, East Antarctica, is presented. Saline lakes, saline ponds and freshwater ponds are represented in this dataset. The Windmill Island lake diatom flora represents an intermediate floral assemblage between that of the freshwater lakes of the Larsemann Hills and the saline lakes of Vestfold Hills, East Antarctica. Variations within this assemblage are related to water chemistry variables in the Windmill Island lakes. In particular, a lakewater salinity/phosphate gradient can explain the variation observed in the sedimentary diatom flora of the lakes and ponds included in this study.

Siberian shelf sediments contain clues to paleoclimate forcing

The Earths heat budget is the result of a complex interaction that depends on the atmosphere, the oceans, and how this heat is exchanged geographically. Most people today are somewhat aware of a number of problems that may arise from global warming. However, to what extent these changes will occur remains a major issue in climate prediction. Obviously, one of the imminent features of the global climate system is the natural, steep temperature gradient that exists between the cold polar regions—where the Earth is most easily able to release heat—and the much warmer, lower latitudes. If one follows the more recent literature, there seems to be little doubt that future temperature increase will first be detected in the Arctic [Dickson, 1999], due to the various temperature-related processes that occur there [Johannessen et al., 1995; Grotefendt et al., 1998].

Three‐hundred‐year hydrological changes in a subtropical estuary, Rookery Bay (Florida): Human impact versus natural variability

The coastal wetland ecosystems in Florida are highly sensitive to changes in freshwater budget, which is driven by regional sea surface temperature, tropical storm activity, and the El Nino-Southern Oscillation (ENSO). Although studying Florida wetlands is pivotal to the understanding of these interacting climate systems, wetland dynamics have been severely altered by recent land use and drainage activities. To gather insights into the natural variability of the coastal ecosystems in Florida versus the effects of anthropogenic impact in the area, we present a 300-year record of changes in the hydrological cycle from a shallow subtropical estuary (Rookery Bay) on the western shelf of Florida, Gulf of Mexico. Palynological (pollen and organic-walled dinoflagellate cysts), diatom, and sedimentological analyses of a sediment core reveal significant changes in past runoff and wetland development. The onset and development of human impact in Florida are evident from high influx of Ambrosia pollen at about A.D. 1900, indicative of land clearance and disturbed conditions. To date, this is the southernmost record of Ambrosia increase related to human impact in the United States. Wetland drainage and deforestation since A.D. 1900 are evident from the reduced freshwater wetland and pine vegetation, and lower abundances of phytoplankton species indicative of lagoonal and brackish conditions. High runoff after A.D. 1900 relates to increased erosionand may correspondingly reflect higher impact from hurricane landfalls in SW Florida. Several phases with high siliciclastic input and greater wetland pollen abundance occur that predate the human impact period. These phases are interpreted as periods with higher runoff and are likely related to regional longer-term climate variability. Copyright 2008 by the American Geophysical Union.

Paleolimnological Reconstructions of Holocene Environments and Climate from Lake Lyadhej-To, Ural Mountains, Northern Russia

Abstract A sediment core recovered in Lake Lyadhej-To at the northwestern edge of the Ural Mountains reflects the complete Holocene environmental history from ∼11,000 cal. yr B.P. Five limnological episodes are identified in the diatom and geochemical records. The initial lake stage, Episode I (∼11,000–10,850 cal. yr B.P.) is characterized by the absence of biogenic production and a high influx of clastic sediments. Episode II (∼10,850–8650 cal. yr B.P.) is characterized by ice-free conditions during summer, highest bioproductivity, strong growth of planktic diatoms and anoxic bottom waters. This period represents the Holocene climatic optimum. Deterioration of climatic conditions commenced in Episode III (∼8650–7000 cal. yr B.P.) as indicated by distinctly lower bioproductivity and longer persistence of winter ice on the lake. During Episode IV (∼7000–2500 cal. yr B.P.), the diatom and pollen records indicate that temperatures were cool and the growing season was short. Finally, in Episode V (∼2500 cal. yr B.P. to present), limnological conditions, indicated by increased organic carbon and diatom deposition, initially suggest improved conditions followed by a return to modern conditions beginning ∼500 cal. yr B.P. The pollen stratigraphy from Lake Lyadhej-To is consistent with other paleoclimatic records from northern Eurasia, confirming rapid postglacial warming, the presence of dense tree forests during the climatic optimum, and finally a gradual southward retreat of the treeline towards its modern location.