Recurrent Red-tides in the Southampton Water Estuary Caused by the Phototrophic CiliateMesodinium rubrum

In the Southampton Water estuary (southern England, U.K.), red-tides caused by the planktonic, phototrophic ciliateMesodinium rubrum(=Myrionecta rubra) occur during most summers and sometimes in autumn. These events were investigated in detail between 1985 and 1987 and were characterized by levels of chlorophylla(chl a) of over 100 μg l⁻¹, cell numbers ofM. rubrumof over 1×10³ ml⁻¹, oxygen saturations of around 150%, and depleted numbers of macrozooplankton. Initiation of red-water did not appear to be triggered by irradiance or nutrients, but coincided with an increase in temperature and water column stability. This enhanced stability was promoted by increased surface to bottom gradients of both temperature and salinity, and by reduced mixing during neap tides. Development of red-water was accompanied by removal of most of the dissolved NH⁺₄from the water column, whereas some NO⁻₃persisted, presumably maintained by freshwater input. NO⁻₃and NH⁺₄gradually returned to pre-bloom concentrations as the red-water declined in late summer. Maximal biomass ofM. rubrumappeared to be limited by irradiance, and self-shading probably imposed an upper limit of around 300 mg chl a m⁻²within the water column. At the observed levels of chl a, irradiance values within the population maximum between 1 and 3 m depth were only just of the order (≈15 μmol photons m⁻² s⁻¹) required to balance estimated respiratory demands. Oxygen concentration became undersaturated during the late bloom phase, with minimal values of 20–30% saturation recorded in deeper waters; however, despite this and reduced numbers of macrozooplankton, direct deleterious effects on other organisms were not observed.     

A note on turbulent perturbations of salinity in a partially mixed estuary

Measurements of salinity perturbations in a partially mixed estuary have been used to evaluate the usefulness of an inductive salinometer and to determine some of the characteristics of the salinity perturbations. The salinometer performed satisfactorily under most conditions. Although internal wave like effects were present, the turbulence fluctuations were dominant. The salinity fluctuations and the turbulent fluxes $\text{sw}$ and $\text{su}$ were found to behave in a manner similar to the density fluctuations in a thermally stratified atmospheric boundary layer and a laboratory open channel flow. A quadrant analysis suggested that the contribution of each quadrant to the turbulent flux changed with Ri. The turbulence parameters ν and c_γ were found to decrease and increase respectively as Ri increases.     

Patterns of pH change inferred from chrysophyte microfossils in Adirondack and northern New England lakes

The silica-scaled chrysophytes are being used increasingly in paleolimnological studies of lake acidification. This study compares the distribution of scaled chrysophytes in the surface sediment of a calibration set of lakes from the Adirondack Park and from northern New England. With the exception of two taxa, species distributions with respect to pH are similar in the two regions. The stratigraphic distribution of chrysophytes is then compared in five Adirondack and three New England lakes. All the presently acid lakes indicate recent lake acidification, with more acid tolerant chrysophytes increasing in relative frequency in the recent sediments. Because the timing of these species changes is unrelated to any watershed disturbances that may have occurred in the lakes' catchments, atmospheric deposition of acids is believed responsible for these recent pH changes.This is the seventh of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D. F. Charles and D. R. Whitehead are guest editors for this series.     

STUDY ON GIS FOR YIELD ESTIMATION BY REMOTE SENSING IN JILIN MAIZE BELT

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A dated cave sediment record of Pleistocene transgressions on Berry Head,Southwest England

Berry Head, a limestone headland in Torbay, southwest England, exhibits a series of subaerial marine erosion platforms and raised beaches spanning an altitude range of 97 m. Solution caves on the headland show preferred horizontal development at elevations that are correlated with the marine erosion platforms, and developed in a marine/freshwater mixing zone whose position was controlled by high sea-level still-stands. Corbridge Cave in Berry Head Quarry lies below the raised beaches in Torbay, and contains evidence of three marine transgressions in the form of fine-grained marine ponding deposits with a marine microfauna. Uranium-series dating of intercalated speleothems indicates that a transgression during oxygen isotope stage 5e reached an elevation of 5.8 m OD, while an earlier transgression (probably during stage 7) reached at least 7.2 m OD. These findings are used to constrain possible interpretations of the aminostratigraphy of raised beaches in Southwest Britain, and a correlation of the Unnamed Stage of Bowen, Sykes, Reeves, Miller, Andrews, Brew and Hare with oxygen isotope stage 5e is proposed.     

Biostratigraphic and aminostratigraphic constraints on the age of the Middle Pleistocene glacial succession in north Norfolk,UK

Considerable debate surrounds the age of the Middle Pleistocene glacial succession in East Anglia following some recent stratigraphical reinterpretations. Resolution of the stratigraphy here is important since it not only concerns the glacial history of the region but also has a bearing on our understanding of the earliest human occupation of north‐western Europe. The orthodox consensus that all the tills were emplaced during the Anglian (Marine Isotope Stage (MIS) 12) has recently been challenged by a view assigning each major till to a different glacial stage, before, during and after MIS 12. Between Trimingham and Sidestrand on the north Norfolk coast, datable organic sediments occur immediately below and above the glacial succession. The oldest glacial deposit (Happisburgh Till) directly overlies the ‘Sidestrand Unio‐bed’, here defined as the Sidestrand Hall Member of the Cromer Forest‐bed Formation. Dating of these sediments therefore has a bearing on the maximum age of the glacial sequence. This paper reviews the palaeobotany and describes the faunal assemblages recovered from the Sidestrand Unio‐bed, which accumulated in a fluvial environment in a fully temperate climate with regional deciduous woodland. There are indications from the ostracods for weakly brackish conditions. Significant differences are apparent between the Sidestrand assemblages and those from West Runton, the type site of the Cromerian Stage. These differences do not result from contrasting facies or taphonomy but reflect warmer palaeotemperatures at Sidestrand and a much younger age. This conclusion is suggested by the higher proportion of thermophiles at Sidestrand and the occurrence of a water vole with unrooted molars (Arvicola) rather than its ancestor Mimomys savini with rooted molars. Amino acid racemisation data also indicate that Sidestrand is significantly younger than West Runton. These data further highlight the stratigraphical complexity of the ‘Cromerian Complex’ and support the conventional view that the Happisburgh Till was emplaced during the Anglian rather than the recently advanced view that it dates from MIS 16. Moreover, new evidence from the Trimingham lake bed (Sidestrand Cliff Formation) above the youngest glacial outwash sediments (Briton's Lane Formation) indicates that they also accumulated during a Middle Pleistocene interglacial – probably MIS 11. All of this evidence is consistent with a short chronology placing the glacial deposits within MIS 12, rather than invoking multiple episodes of glaciation envisaged in the ‘new glacial stratigraphy’ during MIS 16, 12, 10 and 6. Copyright © 2009 John Wiley & Sons, Ltd.     

Time scale of an early to mid-Paleozoic orogenic cycle of the long-lived Central Asian Orogenic Belt, Inner Mongolia of China: Implications for continental growth

We present a detailed, new time scale for an orogenic cycle (oceanic accretion–subduction–collision) that provides significant insights into Paleozoic continental growth processes in the southeastern segment of the long-lived Central Asian Orogenic Belt (CAOB). The most prominent tectonic feature in Inner Mongolia is the association of paired orogens. A southern orogen forms a typical arc-trench complex, in which a supra-subduction zone ophiolite records successive phases during its life cycle: birth (ca. 497–477 Ma), when the ocean floor of the ophiolite was formed; (2) youth (ca. 473–470 Ma), characterized by mantle wedge magmatism; (3) shortly after maturity (ca. 461–450 Ma), high-Mg adakite and adakite were produced by slab melting and subsequent interaction of the melt with the mantle wedge; (4) death, caused by subduction of a ridge crest (ca. 451–434 Ma) and by ridge collision with the ophiolite (ca. 428–423 Ma). The evolution of the magmatic arc exhibits three major coherent phases: arc volcanism (ca. 488–444 Ma); adakite plutonism (ca. 448–438 Ma) and collision (ca. 419–415 Ma) of the arc with a passive continental margin. The northern orogen, a product of ridge-trench interaction, evolved progressively from coeval generation of near-trench plutons (ca. 498–461 Ma) and juvenile arc crust (ca. 484–469 Ma), to ridge subduction (ca. 440–434 Ma), microcontinent accretion (ca. 430–420 Ma), and finally to forearc formation. The paired orogens followed a consistent progression from ocean floor subduction/arc formation (ca. 500–438 Ma), ridge subduction (ca. 451–434 Ma) to microcontinent accretion/collision (ca. 430–415 Ma); ridge subduction records the turning point that transformed oceanic lithosphere into continental crust. The recognition of this orogenic cycle followed by Permian–early Triassic terminal collision of the CAOB provides compelling evidence for episodic continental growth.     

Development of the mixed conifer forest in northern New Mexico and its relationship to Holocene environmental change

Chihuahueños Bog (2925 m) in the Jemez Mountains of northern New Mexico contains one of the few records of late-glacial and postglacial development of the mixed conifer forest in southwestern North America. The Chihuahueños Bog record extends to over 15,000 cal yr BP. An Artemisia steppe, then an open Picea woodland grew around a small pond until ca. 11,700 cal yr BP when Pinus ponderosa became established. C/N ratios, δ¹³C and δ¹⁵N values indicate both terrestrial and aquatic organic matter was incorporated into the sediment. Higher percentages of aquatic algae and elevated C/N ratios indicate higher lake levels at the opening of the Holocene, but a wetland developed subsequently as climate warmed. From ca. 8500 to 6400 cal yr BP the pond desiccated in what must have been the driest period of the Holocene there. C/N ratios declined to their lowest Holocene levels, indicating intense decomposition in the sediment. Wetter conditions returned after 6400 cal yr BP, with conversion of the site to a sedge bog as groundwater levels rose. Higher charcoal influx rates after 6400 cal yr BP probably result from greater biomass production rates. Only minor shifts in the overstory species occurred during the Holocene, suggesting that mixed conifer forest dominated throughout the record.