Physical controls and interannual variability of the Labrador Sea spring phytoplankton bloom in distinct regions

We investigated the variability of the spring phytoplankton bloom in the Labrador Sea, dividing into distinct biogeographical zones, then analyzing the relationship between the bloom and physical forcings. The spring phytoplankton bloom in the north Labrador Sea varied in intensity by a factor of 4 and in timing of onset by 3 weeks over the 11-year record from SeaWiFS satellite ocean chlorophyll, 1998–2008. This north bloom (north of 60 °N and west of the Labrador shelves) is earliest and most intense, owing in part to the offshore-directed freshwater stratification from the West Greenland Current. On interannual timescales, significant correlations were found between the north bloom intensity and ocean processes, namely offshore advection, eddy activity and runoff from Greenland. In contrast, the central Labrador Sea is later and weaker, and only a correlation between the bloom timing and irradiance was found. As the subpolar gyre shifts in strength and shape, freshwater outflow from the Arctic and Greenland changes, we may expect further changes in the biological response as indicated by these relationships.     

Deglacial seasonal and sub‐seasonal diatom record from Palmer Deep,Antarctica

The Antarctic Peninsula is one of the most sensitive regions of Antarctica to climate change. Here, ecological and cryospheric systems respond rapidly to climate fluctuations. A 4.4 m thick laminated diatom ooze deposited during the last deglaciation is examined from a marine sediment core (ODP Site 1098) recovered from Basin I, Palmer Deep, western Antarctic Peninsula. This deglacial laminated interval was deposited directly over a glaciomarine diamict, hence during a globally recognised period of rapid climate change. The ultra‐high‐resolution deglacial record is analysed using SEM backscattered electron imagery and secondary electron imagery. Laminated to thinly bedded orange‐brown diatom ooze (near monogeneric Hyalochaete Chaetoceros spp. resting spores) alternates with blue‐grey terrigenous sediments (open water diatom species). These discrete laminae are interpreted as austral spring and summer signals respectively, with negligible winter deposition. Sub‐seasonal sub‐laminae are observed repeatedly through the summer laminae, suggesting variations in shelf waters throughout the summer. Tidal cycles, high storm intensities and/or intrusion of Circumpolar Deep Water onto the continental shelf introduced conditions which enhanced specific species productivity through the season. Copyright © 2005 John Wiley & Sons, Ltd.     

Physical controls and mesoscale variability in the Labrador Sea spring phytoplankton bloom observed by Seaglider

We investigated the 2005 spring phytoplankton bloom in the Labrador Sea using Seaglider, an autonomous underwater vehicle equipped with hydrographic, bio-optical and oxygen sensors. The Labrador Sea blooms in distinct phases, two of which were observed by Seaglider: the north bloom and the central Labrador Sea bloom. The dominant north bloom and subsequent zooplankton growth are enabled by the advection of low-salinity water from West Greenland in the strong and eddy-rich separation of the boundary current. The glider observed high fluorescence and oxygen supersaturation within haline-stratified eddy-like features; higher fluorescence was observed at the edges than centers of the eddies. In the central Labrador Sea, the bloom occurred in thermally stratified water. Two regions with elevated subsurface chlorophyll were also observed: a 5 m thin-layer in the southwest Labrador Current, and in the Labrador shelf-break front. The thin layer observations were consistent with vertical shearing of an initially thicker chlorophyll patch. Observations at the front showed high fluorescence down to 100 m depth and aligned with the isopycnals defining the front. The high-resolution Seaglider sampling across the entire Labrador Sea provides first estimates of the scale dependence of coincident biological and physical variables.     

Impact melt rocks from New Quebec Crater,Quebec, Canada

Abstract— Approximately 1500 g of float samples of impact melt rocks have been recovered from gravel deposits ～4 km north and northeast of the rim of the 3.4 km diameter New Quebec Crater (61°17′N; 73°40′W) in northern Quebec, Canada. Previously, only two small samples of impact melt rocks were known. The newly recovered samples have cryptocrystalline to microcrystalline matrices with microlites of andesine and pigeonite. Mineral clasts of quartz and feldspar occur and, in some cases, show shock metamorphic features. The melt rocks have a normative mineralogy corresponding to ～70% quartz, orthoclase and albite and are compositionally similar. Their major element composition can be modeled as a mix of granitic gneisses that make up the target rocks. The melt rocks show enrichments, however, in Cr (21 ppm), Co (9 ppm), Ni (12 ppm) and Ir (1.5 ppb) over the target rocks. Interelement ratios suggest a chondritic impacting body, although they do not define a specific type. Assuming a C-1 chondrite, the impact melt rocks average ～2% meteoritic contamination. Stepwise ⁴⁰Ar-³⁹Ar dating using a laser on three chips from three samples give integrated ages of 0.6–2.5 Ma. From the best plateau ages, the age of the New Quebec impact is taken to be 1.4 ± 0.1 Ma, which places it before the first major northern hemisphere continental glaciation of the Pleistocene. A number of considerations suggest that the impact melt rocks were originally deposited in fractures in the crater wall and later transported to their discovery site by glacial ice and melt water.     

Equi-density surfaces in synchronously rotating close binaries built on polytropic model ν=3

A direct numerical method, involving no perturbational procedures, is described and used for the computation of the surfaces of constant potential, pressure and density in synchronously rotating close binaries with both components built on polytropic model =3.Originally presented at the IAU Colloquium No. 16 held at the University of Pennsylvania, Philadelphia, U.S.A., September 8–11, 1971.Part of this work was done while in residence as a member of the Institute for Advanced Study, Princeton, N.J.     

Identifying “free” and “bound” lipid fractions in stalagmite samples: An example from Heshang Cave,Southern China

Stalagmites are good archives for paleoecological change, as they are easy to date, and contain multiple environmental proxy records, including climatic records from oxygen isotopes. Lipid biomarkers preserved within stalagmites have recently been used to investigate changes in the overlying soil and vegetation. However, the understanding of lipid records from stalagmites is still at an early stage, and is hindered by the low abundances of lipids preserved and the complexity of the organic matter signal. Here the first results of a sequential extraction procedure are presented, that enables examination of the distribution patterns of “free” (solvent extraction) and “bound” (including physically bound within the calcite matrix and chemically bound to macromolecules) lipids in a stalagmite from southern China. In both groups the dominant compounds are saturated fatty acids, which are an order of magnitude more abundant in the “bound” phase. n-alkanes and n-alcohols chiefly appear in the “free” lipids. In contrast, 3-hydroxy acids are predominantly released under strong acid reflux conditions, suggesting a principal input from bacterial membrane compounds. A direct comparison between the present results and the published data from an Ethiopian stalagmite shows significant differences in the lipid signals from separate sites, with a stronger microbial signal in the Chinese sample. This preliminary investigation of lipid distributions in different modes highlights the importance of microbial geochemical processes in karst systems and supports the use of stalagmites in paleoecological reconstruction.     

The feeling of participation: Everyday spaces and urban change

Initiatives around ‘public participation’ and ‘community involvement’ have become increasingly central to UK government policy programmes, particularly within interventions aimed at disadvantaged neighbourhoods. These initiatives have been the subject of extensive critical comment, essentially focusing on the ways in which power is often maintained by state agencies, whatever the surrounding rhetoric. This article attempts to consider what more productive forms of participation might feel like, through drawing on fieldwork with two small community groups on housing estates in Stoke-on-Trent, UK, to look at how and why they were able to generate successful participation in their activities. The importance of the small-scale interactions and feelings that made up their spaces of participation is explored. These can be characterised through ideas such as ‘feeling comfortable’, ‘feeling at home’, ‘helping out’ and ‘keeping going’, and involve everyday sociability and informal forms of volunteering. If government is serious about supporting political participation in such contexts it needs to consider how official projects might learn from these kinds of spaces.     

Reflections on Progression in Learning about Place

This commentary is a response to Larsen and Harrington's article titled "Developing a Learning Progression for Place" (2018). Within the author focuses learning progressions, subject structure, and the challenge of place complexity.     

Shock metamorphism in sillimanite from the Haughton impact structure,Devon Island,Canada

Clasts of shocked garnet-sillimanite gneisses comprise a minor fraction of the allochthonous breccia at the Haughton impact structure. Refractive indices of the diaplectic and fused components of the gneisses, and reduced specific gravity indicate shock pressures from 35 to 55±5 GPa and effective post-shock temperatures from 500° to 1,000° C in a suite of selected samples.Sillimanites remain birefringent but display several effects of shock metamorphism. Shock-produced planar features and planar fractures are highly developed; optic axial angle (2V _y ) increases from near normal (26°) to over 80° within a sample; there is a reduction in optical relief and a development of a pale brown colouring which generally deepens in shade as shock level increases. There is no unambiguous evidence, optically or from X-ray investigation, of a high-pressure Al₂SiO₅ polymorph or breakdown to mullite and silica. The highly shocked sillimanites have anomalous K₂O contents from 0.11% to 0.92%. Potassium appears to substitute for aluminum and, to a lesser degree, for iron while retaining sillimanite stoichiometry, and the amount of substitution generally reflects increased shock level. The source of the contributed potassium is the coexisting shock-fused feldspar glass. The glass of each sample is derived primarily from melted alkali feldspar with a minor and varied admixture from the breakdown of mafic minerals. The glasses are depleted in K₂O, although Na₂O is unaffected, and the extent of depletion can be correlated with the increased K₂O content of the associated sillimanite. The incorporation of potassium in shocked sillimanites is a function of both degree of shock deformation and availability of potassium from other coexisting shocked phases. It is speculated that the brown colouration is a function of ferrous iron content and may reflect post-crater thermal history rather than shock level.Contribution from the Earth Physics Branch No. 951