Variation of upwelling/oceanic conditions during the latest Pleistocene through Holocene off the central Peruvian coast: A diatom record

Diatoms are well preserved in partly laminated Holocene and late Pleistocene sediments on the upper continental slope of central Peru. Accumulation rates of diatom species previously recognized as tropical (oceanic, warm water) and subtropical (neritic, cooler water, upwelling) changed markedly downcore in Kasten cores obtained at 11°15′S, 12°58′S, and 13°37′S latitude. Subtropical species (e.g., Thalassiosira eccentrica “group”, Thalassiothrix frauenfeldii, Chaetoceros spp. resting spores, Delphineis spp.) predominated in late Pleistocene sediments of the two southern cores. A mix of tropical and subtropical diatom assemblages occurred in latest Pleistocene sediments, while tropical species (e.g., Coscinodiscus nodulifer/radiatus, Pseudoeunotia doliolus, Thalassionema nitzschioides var. parva) predominated in the late Holocene sediments. In the northern core latest Pleistocene sediments also contained a mix of tropical and subtropical species. Similarly, late Holocene sediments contained predominately tropical species of diatoms. Neoglacial periods (200–400 yr B.P., 2000–2700 yr B.P.), however, were sometimes characterized by a greater abundance of subtropical species and punctuated periodically with blooms of Skeletonema costatum and Rhizosolenia shrubsolei. It is proposed that during times of Southern Hemisphere cooling, Peruvian coastal waters north of 12°S were subjected to episodic mixing with warmer water masses before being overwhelmed by tropical waters that may have either passed southward across a weakened Equatorial Front or arose from intensified offshore countercurrents. Coastal waters south of 12°S latitude were probably unaffected by the tropical influence. Rather, these waters may have undergone intensified upwelling during the last Glacial epoch.     

Catching of Greenland halibut <Emphasis Type="Italic">Reinhardtius hippoglossoides</Emphasis> (Pleuronectidae) on the shelf edge of the Laptev and East Siberian Seas

The first capture of the Greenland (or Black) halibut Reinhardtius hippoglossoides in the Arctic Ocean on the border with the East Siberian Sea (79°03′–79°08′ N 139°59′–141°16′ E, 259–277 m) and the repeated findings of the species in the Laptev Sea (78°03′–78°04′ N 132°56′–133°04′ E, 307 m; 78°33′–78°35′ N 138°44′–138°48′ E, 125 m) are reported. Fish (79 specimens with the length of 15.0–44.5 cm) were caught during four bottom trawlings on the edge of the continental shelf of the two seas in the transformed waters of Atlantic origin, as evidenced by the discovery of the indicator species of these waters—the Glacier lanternfish Benthosema glaciale (Myctophidae)—in one of the stomachs of halibut. The other captures of Greenland halibut in the Arctic were also reviewed.     

Diatom taphocoenoses in the coastal upwelling area off South West Africa

The diatom floral composition of 124 sediment samples from the South East Atlantic records the influence of coastal upwelling on sediment composition off South West Africa. Inner shelf samples between 19° and 24°S are rich in diatom valves and the patterns of diatom species distribution in these samples are related to the coastal upwelling process. Comparison with recent phytoplankton data shows that the sediment assemblages preserve many of the important species of the diatom biocoenoses, including Chaetoceros (resting spores), Delphineis karstenii, Thalassiosira eccentrica, and Thalassionema nitzschioides. Delphineis karstenii, a pioneer species in enriched coastal water, occurs nearshore and Chaetoreros resting spores are widespread, with highest relative abundance values in some more offshore samples. The abundance of the Thalassiosira eccentrica group and of Thalassionema nitzschioides in sediment samples in and near Walvis Bay reflects the recurrence of intense upwelling off this part of the coast. An abundance of large centric species has been reported in hydrological conditions characteristic of newly upwelled waters and, correspondingly, Actinocyclus octonarius and some large Coscinodiscus species occur in the sediments in nearshore patches or belts.     

Distribution patterns of diatom surface sediment assemblages in the Laptev Sea (Arctic Ocean)

The modern diatom distribution in the Laptev Sea, Arctic Ocean, was investigated in 89 surface sediment samples. Diatom concentrations are relatively low showing values between 0.01×10⁶ and 6.7×10⁶ valves per gram dry sediment. Based on a factor analysis using seventeen taxa or taxa groups five diatom surface sediment assemblages can be defined: the ice diatom assemblage of the central region of the Laptev Sea, the Chaetoceros assemblage of the eastern and southeastern shelf, the Thalassiosira antarctica assemblage of the continental slope and deep sea, the freshwater diatom assemblage in the vicinity of river mouths and deltas, and the Thalassiosira nordenskioeldii assemblage which shows a patchy occurrence on the central Laptev Sea shelf. The distribution pattern of diatom assemblages in surface sediment is significantly related to oceanographic conditions of surface water masses. The main factors controlling the distribution of diatoms in the Laptev Sea are the riverine freshwater input during the summer which strongly affects the salinity conditions, and the sea-ice extent. Furthermore, the composition of the Thalassiosira antarctica assemblage of the continental slope is largely influenced by dissolution and lateral transport processes.     

Spring phytoplankton assemblages in the Southern Ocean between Australia and Antarctica

Variations of phytoplankton assemblages were studied in November–December 2001, in surface waters of the Southern Ocean along a transect between the Sub-Antarctic Zone (SAZ) and the Seasonal Ice Zone (SIZ; 46.9°–64.9°S; 142°–143°E; CLIVAR-SR3 cruise). Two regions had characteristic but different phytoplankton assemblages. Nanoflagellates(<20 μm) and pico-plankton (∼2 μm) occurred in similar concentrations along the transect, but were dominant in the SAZ, Sub-Antarctic Front (SAF), Polar Front Zone (PFZ) and the Inter-Polar Front Zone (IPFZ), (46.9°–56.9°S). Along the entire transect their average cell numbers in the upper 70 m of water column, varied from 3 × 10⁵ to 1.1 × 10⁶ cells l⁻¹. Larger cells (>20 μm), diatoms and dinoflagellates, were more abundant in the Antarctic Zone-South (AZ-S) and the SIZ, (60.9°–64.9°S). In AZ-S and SIZ diatoms ranged between 2.7 × 10⁵ and 1.2 × 10⁶ cells l⁻¹, dinoflagellates from 3.1 × 10⁴ to 1.02 × 10⁵ cells l⁻¹. A diatom bloom was in progress in the AZ-S showing a peak of 1.8 × 10⁶ cells l⁻¹. Diatoms were dominated by Pseudo-nitzschia spp., Fragilariopsis spp., and Chaetoceros spp. Pseudo-nitzschia spp. outnumbered other diatoms in the AZ-S. Fragilaropsis spp. were most numerous in the SIZ. Dinoflagellates contained autotrophs (e.g. Prorocentrum) and heterotrophs (Gyrodinium/Gymnodinium, Protoperidinium). Diatoms and dinoflagellates contributed most to the cellular carbon: 11–25 and 17–124 μg C l⁻¹, respectively. Small cells dominated in the northern region characterized by the lowest N-uptake and new production of the transect. Larger diatom cells were prevalent in the southern area with higher values of N-uptake and new production. Diatom and nanoflagellate cellular carbon contents were highly correlated with one another, with primary production, and productivity related parameters. They contributed up to 75% to the total autotrophic C biomass. Diatom carbon content was significantly correlated to nitrate uptake and particle export, but not to ammonium uptake, while flagellate carbon was well correlated to ammonium uptake, but not to export. Diatoms have contributed highly to particle export along the latitudinal transect, while flagellates played a minor role in the export.     

Diversity and Distribution of Marine Microbial Eukaryotes in the Arctic Ocean and Adjacent Seas

We analyzed microbial eukaryote diversity in perennially cold arctic marine waters by using 18S rRNA gene clone libraries. Samples were collected during concurrent oceanographic missions to opposite sides of the Arctic Ocean Basin and encompassed five distinct water masses. Two deep water Arctic Ocean sites and the convergence of the Greenland, Norwegian, and Barents Seas were sampled from 28 August to 2 September 2002. An additional sample was obtained from the Beaufort Sea (Canada) in early October 2002. The ribotypes were diverse, with different communities among sites and between the upper mixed layer and just below the halocline. Eukaryotes from the remote Canada Basin contained new phylotypes belonging to the radiolarian orders Acantharea, Polycystinea, and Taxopodida. A novel group within the photosynthetic stramenopiles was also identified. One sample closest to the interior of the Canada Basin yielded only four major taxa, and all but two of the sequences recovered belonged to the polar diatom Fragilariopsis and a radiolarian. Overall, 42% of the sequences were <98% similar to any sequences in GenBank. Moreover, 15% of these were <95% similar to previously recovered sequences, which is indicative of endemic or undersampled taxa in the North Polar environment. The cold, stable Arctic Ocean is a threatened environment, and climate change could result in significant loss of global microbial biodiversity.     

At the rainbow’s end: high productivity fueled by winter upwelling along an Arctic shelf

Herein we document findings from a unique scientific expedition north of Svalbard in the middle of the polar night in January 2012, where we observed an ice edge north of 82°N coupled with pronounced upwelling. The area north of Svalbard has probably been ice-covered during winter in the period from approximately 1790 until the 1980s, a period during which heavy ice conditions have prevailed in the Barents Sea and Svalbard waters. However, recent winters have been characterized by midwinter open water conditions on the shelf, concomitant with northeasterly along-shelf winds in January 2012. The resulting northward Ekman transport resulted in a strong upwelling of Atlantic Water along the shelf. We suggest that a reduction in sea ice and the upwelling of nutrient-rich waters seen in the winter of 2012 created conditions similar to those that occurred during the peak of the European whaling period (1690–1790) and that this combination of physical features was in fact the driving force behind the high primary and secondary production of diatoms and Calanus spp., which sustained the large historical stocks of bowhead whales (Balaena mysticetus) in Arctic waters near Spitsbergen.     

Development and evaluation of a diatom-conductivity model from lakes in West Greenland

1. The area around Kangerlussuaq (Søndre Strømfjord; West Greenland, 67°N 51°W) contains thousands of lakes ranging from coastal, dilute (conductivity < 30 μS cm^–1) oligotrophic systems to subsaline (～4000 μS cm^–1), closed basin lakes close to the ice sheet margin. In closed basins, salinity (or conductivity) is often a proxy for effective moisture, and thus palaeorecords of lake conductivity can provide valuable palaeoclimatic data. Little or nothing is known about the recent history of these lakes and hence it is difficult to evaluate how they will respond to effects of future changes. 2. Over 100 lakes have been sampled (1996–2000) between the ice sheet and the outer coast for a variety of water chemical and limnological variables. Surface sediments were taken from a subset of 40 lakes and analysed for diatoms. Diatom responses to 28 environmental variables were analysed by multivariate ordination techniques and indicate that the main gradient is highly correlated to conductivity (explaining ～12% of species variance). Despite the relatively short gradient (24–4072 μS cm^–1), diatom assemblages exhibit a clear response to conductivity. The most saline lakes do not contain a true saline flora. 3. We developed a range of weighted averaging (WA) and weighted‐averaging partial least squares (WA‐PLS) models from this training data set and found two component WA‐PLS models performed best. The effects of data transformation and omission of dissolution susceptible species (Diatoma spp.) on model performance were also examined. The error statistics for the preferred WA‐PLS (2) model (r²_jack=0.88, root mean square error of prediction (RMSEP)=0.217 log μS cm^–1) compare well with other published models. 4. A ²¹⁰Pb‐dated short core from a meromictic, subsaline lake (Braya Sø; location 67°N, 51°W, max. depth 23 m; conductivity 2600 μS cm^–1) was analysed for diatoms. Diatom preservation is poor and some taxa (e.g. Diatoma spp.) are badly corroded. Lake water conductivity was reconstructed using WA‐PLS models. Diatom‐inferred conductivity ranges from 1800 to 4400 μS cm^–1 over the last 600 years (extrapolated ²¹⁰Pb chronology). 5. The Kangerlussuaq area of West Greenland is an important area for palaeoclimatic research, located as it is between the Greenland ice sheet (ice core records) and the Davis Straits to the west. The development of a statistically robust transfer function for diatoms and conductivity will enable the reconstruction of conductivity from the many subsaline lakes around the head of the fjord and, hence, regional estimates of changing palaeoprecipitation.     

Seasonal sea ice cover as principal driver of spatial and temporal variation in depth extension and annual production of kelp in Greenland

We studied the depth distribution and production of kelp along the Greenland coast spanning Arctic to sub‐Arctic conditions from 78 ºN to 64 ºN. This covers a wide range of sea ice conditions and water temperatures, with those presently realized in the south likely to move northwards in a warmer future. Kelp forests occurred along the entire latitudinal range, and their depth extension and production increased southwards presumably in response to longer annual ice‐free periods and higher water temperature. The depth limit of 10% kelp cover was 9–14 m at the northernmost sites (77–78 ºN) with only 94–133 ice‐free days per year, but extended to depths of 21–33 m further south (73 ºN–64 ºN) where >160 days per year were ice‐free, and annual production of Saccharina longicruris and S. latissima, measured as the size of the annual blade, ranged up to sevenfold among sites. The duration of the open‐water period, which integrates light and temperature conditions on an annual basis, was the best predictor (relative to summer water temperature) of kelp production along the latitude gradient, explaining up to 92% of the variation in depth extension and 80% of the variation in kelp production. In a decadal time series from a high Arctic site (74 ºN), inter‐annual variation in sea ice cover also explained a major part (up to 47%) of the variation in kelp production. Both spatial and temporal data sets thereby support the prediction that northern kelps will play a larger role in the coastal marine ecosystem in a warmer future as the length of the open‐water period increases. As kelps increase carbon‐flow and habitat diversity, an expansion of kelp forests may exert cascading effects on the coastal Arctic ecosystem.     

Opal phytoplankton assemblages of the Late Quaternary sapropel layers S5 and S7 from the southeastern Mediterranean Sea (“Meteor”-Cruise 40/4, Site 67)

Well-preserved opal planktic assemblages containing diatom and silicoflagellate species were discovered in the finely laminated sapropels S5 and S7 from Site 67, core GeoTüKL51 during “RV Meteor”-Cruise 40, Leg 4 (34° 48 N; 27° 17 E). The siliceous microflora, composed quasi-exclusively of warm water species, is here studied for taxonomy, stratigraphy and ecology, as well as for quantitative distribution. The diatom assemblage is very diverse and dominated by rhizosolenids, which are generally characteristic of stratified, oligotrophic waters. A significant shift to higher abundances of Pseudosoleniacalcar-avis is observed in the upper part of Sapropel S5, with a simultaneous decrease in the abundances of Thalassionema bacillaris/frauenfeldii,T.nitzschioides,T. oestrupii and Chaetoceros sp., which is probably due to nutrient - poor conditions in the surface waters.     

Heterotrophic activity of bacterioplankton along the gradients of the chlorophyll <Emphasis Type="Italic">a</Emphasis> concentration and water temperature in marine and limnetic ecosystems

The dependence of the heterotrophic activity of bacterioplankton (V, μg C L^–1 h^–1) on the concentration of chlorophyll a (Chl, μg L^–1) and the water temperature (T) was examined for lakes (37°29′–80°36′ N) and marine polar waters (69°16′–80°36′ N). It was shown that ~76% of the V variations was related to changes in Chl and T.     

Pelagic primary production during summer along 65 to 72°N off West Greenland

The distribution of phytoplankton biomass and primary production were studied during summer 1993 at 16 stations from 65 to 72°N off West Greenland, ranging more than 900 km. Hydrography, nutrients and chlorophyll a profiles revealed a significant change in structure from south to north. Nitrate was depleted in the euphotic zone at most stations except close to the ice edge (West Ice) or close to outflow from large glaciers. The vertical distribution of phosphate followed that of nitrate, but was never depleted. Despite two stations with relatively high surface concentrations, silica showed the same distribution as the other two nutrients. In the south, chlorophyll a concentration and primary production were lower than north of Disko Bay (69°N), associated with a well-mixed versus a salinity-generated stratification, respectively. In Vaigat, a high-production station was identified, (st. 910, 69°52′69N–51°30′61W) with a chlorophyll a concentration in the euphotic zone of >13 μg l⁻¹ and an area primary production of 3.2 g C m⁻² day⁻¹. This is seldom encountered in arctic waters and was presumably due to nutrient-rich melt-water originating from the Iluliíssat Glacier. The overall primary production for the studied area was 67–3207 mg C m⁻² day⁻¹ (mean ± SD=341± 743 mg C m⁻² day⁻¹), which is within the range of the few results published for West Greenland and eastern Canadian Arctic waters. Accepted: 24 October 1998     

Evidence for a pan-Arctic sea-ice diatom diet in Strongylocentrotus spp

The Arctic marine food web is based on organic matter produced by both phytoplankton and sea-ice algae. With the decline of Arctic sea ice, the sustained availability of organic carbon of sea-ice origin is unclear. Recently, the detection of the sea-ice diatom biomarker IP₂₅ in a range of Arctic benthic macrofauna indicated that this is a highly suitable biomarker for the identification of organic carbon derived from sea-ice primary production in Arctic food webs. However, the data presented previously were restricted to a single geographical region in the Canadian Arctic. Here, we show that IP₂₅ is present in sea urchins of the genus Strongylocentrotus collected from ten locations with seasonal sea-ice cover from the Canadian Archipelago, Greenland and Spitsbergen. In contrast, IP₂₅ was not found in specimens of Echinus esculentus collected from the southwest UK, where sea ice is absent. Our findings provide evidence that the presence of IP₂₅ in macrobenthic organisms can be used across different Arctic regions as a versatile indicator of a diet containing carbon of sea-ice origin.     

Verbreitung von Makrozooplankton in der Grönlandsee im Spätherbst 1988 (Crustacea: Ostracoda, Hyperiidea [Amphipoda], Euphausiacea)

The horizontal and vertical distribution and the abundance of ostracods, hyperiids (amphipods) and euphausiids in the Greenland Sea along a transect parallel 74°45′N (from 15°45′E to 08°30′W) are described. The samples were taken by RV “Meteor” in late autumn of 1988. 8 species of the above named groups have been recorded in two different water masses which were touched by the transect. 5 stations were situated in the realm of the Atlantic waters of the Spitsbergen Current. HereDiscoconchoecia elegans, Meganyctiphanes norvegica, andThemisto compressa are indicators for the southern Atlantic water. 6 stations belong to the Arctic area dominated by Arctic Surface Water, whereBoroecia borealis, Themisto abyssorum, Thysanoessa longicaudata, andThysanoessa inermis are quite abundant as borealsubarctic species, whereasThemisto libellula is a true species of pure Arctic water.

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Mitarbeiterin der Taxonomischen Arbeitsgruppe an der Biologischen Anstalt Helgoland     

Microplankton response to environmental conditions in the Alboran Sea (Western Mediterranean): One year sediment trap record

The present work analyses the seasonal evolution of planktonic assemblages and particle fluxes through the water column in the Eastern Alboran Sea (Western Mediterranean) at 35º55.47'N/01º30.77'W. A Sediment trap was deployed below the influence of the Almeria-Oran Front (AOF), a semi-permanent geostrophic front, during July 1997 to June 1998. Overall, the temporal variability of coccolithophore, planktonic foraminifer, diatom, benthic and wind-carried biogenic particle fluxes is linked to the seasonal evolution of sea surface hydrological structures. Maximum planktonic fluxes were found during high-productivity periods and wind-induced upwelling, following a trimodal pattern, with maximum fluxes in July 1997, November–December 1997, and April–May 1998. These periods were characterized by vertical mixing and the full development of anticyclonic gyres in the Alboran Sea. The annual flux of coccolithophores was dominated by the “small Gephyrocapsa Group” and Emiliania huxleyi, whereas Turborotalita quinqueloba and Globigerina bulloides dominated the foraminiferal fluxes, and Chaetoceros Resting Spores (RS) were predominant in the diatom assemblage. Benthic specimens were also collected with the sediment trap, suggesting a variable influence of bottom water activity. Wind-driven particles (phytoliths and fresh-water diatoms) were collected along the year, but their fluxes followed the local wind regime.The high Sea Surface Temperature (SST) during fall due to weaker than usual westerly winds, and the pressure anomaly prevailing in the Alboran Sea during early winter, were reflected in the planktonic assemblages by the proliferation of warm, lower photic layer inhabitants and/or oligotrophic taxa of coccolithophores (Florisphaera profunda), planktonic foraminifers (Globigerinoides ruber and Globorotalia inflata) and diatoms (Leptocylindrus danicus). These unusual climatic conditions in the eastern Alboran Sea must have been caused by the 1997–1998 ENSO event.     

Distinct patterns of Arctic cod (<Emphasis Type="Italic">Boreogadus saida</Emphasis>) presence and absence in a shallow high Arctic embayment,revealed across open-water and ice-covered periods through acoustic telemetry

With climate change resulting in unpredictable sea ice conditions between years, it is crucial to gain a more comprehensive understanding of the subsequent effects on Arctic marine ecosystems. Arctic cod (Boreogadus saida) play a key role in the Arctic marine food web, serving as a food source that is estimated to contribute up to 75 % of energy transfer to higher trophic levels. To investigate Arctic cod residency and distribution in Resolute Bay (74°44′N, 095°04′W), 85 individuals from four locations in the bay were captured, measured, weighed, implanted with acoustic tags and subsequently tracked on an acoustic array of 49 receivers. Two main periods of residence in the bay were identified, the first in open water and the second under ice cover, and both concluded with a collective mass departure of fish. A generalised linear mixed model was used to investigate the influence of variables on Arctic cod presence/absence in the bay, indicating that ingress and egress were influenced by environmental changes, particularly those associated with the transition from open-water to the ice-covered period. Timing and distribution, during the study period, appeared to be influenced by a combination of physiological acclimation, and a balance between resource availability and refuge from predators. Receiver site Residence Index (RI) analysis revealed strong site fidelity of fish towards the northern areas of the bay, and this behaviour was consistent between tagging groups and individuals, indicating that the majority of tagged cod were representative of a single school. This study represents the first employment of acoustic telemetry to monitor the movements of individual Arctic cod over 9 months, incorporating both open-water and ice-covered periods.     

Deglacial ocean and climate seasonality in laminated diatom sediments, Mac.Robertson Shelf, Antarctica

The palaeoceanography and climate history of the East Antarctic Margin (EAM) are less well understood than those of West Antarctica. Yet, the EAM plays an important role in deep ocean circulation and the global ocean system and has likely done so in the past. Deglacial-age marine sediments from the EAM provide clues about its past role during this critical period of rapid climate change. Several deep basins across the EAM such as Iceberg Alley (∼67°S, 63°E) on the Mac.Robertson Shelf (MRS) accommodate thick marine sequences that archive the deglaciation in the form of diatom-rich, continuously laminated (varved) sediments. These laminated sediments are pristinely preserved and contain seasonal and long-term information on the cryospheric and palaeoceanographic changes associated with the rapid retreat of the glacial ice sheet across the MRS. We present results of microfabric analysis of the lower ∼2 m of deglacial varves from jumbo piston core JPC43B (Iceberg Alley). Backscattered electron imagery (BSEI) of polished thin sections and scanning electron microscope secondary electron imagery (SEI) of lamina-parallel fracture surfaces are used to analyze the varves. One hundred and ninety-two laminations are investigated and their nature and temporal significance are discussed in terms of seasonal deposition and cyclicity of diatom species. Our high-resolution palaeodata record exceptionally high diatom production and silica flux associated with the retreat of the East Antarctic Ice Sheet, and seasonal sea-ice changes along the EAM. This information is invaluable for assessing cryospheric-oceanographic variation and, therefore, the local and regional response to this period of rapid climate change. Varves are made up of lamina couplets comprising (i) thickly laminated to thinly bedded orange/orange-brown very pure diatom ooze dominated by Hyalochaete Chaetoceros spp. vegetative cells and resting spores, and (ii) brown/blue-grey terrigenous angular quartz sand, silt and clay with an abundant mixed diatom flora. The colour variation between these two types of lamination is striking. Using floristic and textural information we interpret the diatom oozes as spring flux and the terrigenous laminae as summer flux. Each couplet pair represents one annual cycle and reflects seasonal changes in nutrient availability and stratification associated with the cyclical advance and retreat of seasonal sea-ice. The diatom oozes can reach up to ∼7.5 cm in thickness indicating enormous silica flux to the sea floor associated with ice sheet retreat.     

Swamps,springs and diatoms: wetlands of the semi-arid Bogoria-Baringo Rift,Kenya

Lakes Bogoria and Baringo lie in a semi-arid part of the Kenya Rift Valley between 0° 15′–0° 30'N and 36° 02′–36° 05′E. Nevertheless, the area around these lakes contains numerous wetland systems that have been formed: along lake shorelines; along faults where hot, warm and cold springs have developed; and along river systems that cross the rift floor. Six major types of wetland are recognized: Proximal Hot Springs; Hot Spring Marshes; Blister Wetlands; Typha and Cyperus papyrus Swamps; Floodplain Marshes; Hypersaline Lake Littoral Wetlands; and Freshwater Lake Littoral Wetlands. These show significant variability in terms of geomorphic setting, water chemistry, temperature, plant communities and diatom floras. They are variously dominated by macrophytes, such as Cyperus laevigatus, Typha domingensis and Cyperus papyrus. In some cases macrophytes are absent. In hot spring settings and in hypersaline lake littoral zones bacterial mats are common. Although absent in some samples, diatoms occur in at least parts of all of the wetlands, varying in diversity, abundance and species composition. Canonical correspondence analysis indicates that diatom floras show a close relationship with pH, temperature, and specific conductivity, with other environmental variables such as Si and nitrate being of secondary importance. Common diatoms include: Anomoeoneis sphaerophora var. guntheri, Navicula tenella, N. cuspidata, and Nitzschia invisitata in hot springs, where diversity is generally low and abundance is variable. Other wetland types contain distinctive diatom floras that variously include: Fragilaria brevistriata, Gomphonema parvulum, Navicula tenelloides, Nitzschia communis, N. latens, N. sigma, Rhopalodia gibberula, and Stauroneis anceps.