GGR Critical Review of Analytical Developments in 2003

The articles that comprise this critical review serve to draw attention to research papers published in specific fields of interest during 2003, provide critical comment on the relevance and importance of individual publications in these fields, and offer an overview of the comparative importance of advances in particular areas. In this way, these articles aim to assist experts in the field by keeping them informed of relevant recent publications, as well as providing an important resource for students or early career researchers who are embarking on studies in an area new to them. This year, five papers provide summaries of developments in bulk sample determinations employing (1) ICP-AES and ICP-MS (trace elements), (2) XRF and atomic absorption spectrometry and INAA, (3) isotope ratio measurements (TIMS, MC-ICP-MS, ICP-MS, ToF), as well as in situ measurements conducted using (4) secondary ion mass spectrometry and (5) laser ablation ICP-MS (trace element and isotope ratio determinations).     

Reaction pathways for quartz dissolution determined by statistical and graphical analysis of macroscopic experimental data

In light of recent work on the reactivity of specific sites on large (hydr)oxo-molecules and the evolution of surface topography during dissolution, we examined the ability to extract molecular-scale reaction pathways from macroscopic dissolution and surface charge measurements of powdered minerals using an approach that involved regression of multiple datasets and statistical graphical analysis of model fits. The test case (far-from-equilibrium quartz dissolution from 25 to 300 °C, pH 1-12, in solutions with [Na⁺] ? 0.5 M) avoids the objections to this goal raised in these recent studies. The strategy was used to assess several mechanistic rate laws, and was more powerful in distinguishing between models than the statistical approaches employed previously. The best-fit model included three mechanisms—two involving hydrolysis of Si centers by H₂O next to neutral (>Si-OH⁰) and deprotonated (>Si-O⁻) silanol groups, and one involving hydrolysis of Si centers by OH⁻. The model rate law is

     

Subglacial comminution in the deforming bed: Inferences from SEM analysis

This study investigates the variations in erosional processes beneath Briksdalsbreen; a Norwegian valley glacier, with a thin coarse grained deforming bed. The subglacial zone was investigated in situ, close to the central glacial flow line (Site A) and close to the valley wall (Site B), via boreholes. The till was collected using two different sediment samplers and the bed was examined using a borehole video camera. In order to evaluate how representative borehole sampling was of the subglacial environment, the results from in situ subglacial samples were compared with random samples taken from an exposed subglacial surface in the glacier foreland, as well as a sample taken from the site after glacier retreat. The results indicated that the texture of the exposed subglacial surface was similar to in situ samples from subglacial Site B (close to the valley wall), and that the samples collected with the ‘small’ sediment sampler had the closest fit. SEM analysis revealed eroded quartz grains at both sites as a result of rotation (abrasion) and fracture. The samples from close to the valley wall were very poorly sorted, with evidence for rounding and preservation of pre-weathered surfaces, which suggest that a relatively simple pattern of erosion from crushing to rotation dominated. However, the till from the centre of the glacier was better sorted, more angular, and with few pre-weathered surfaces. We suggest that this results from a more complex glacial erosional history associated with greater strain and longer residence time within the deforming layer. When compared with other deformation tills, it was confirmed that there is a relationship between grain size and erosional style. Clay-rich tills show little comminution, fine sand-rich tills generate a significant silt component, whilst the coarse sand-rich tills at Briksdalsbreen showed complex deformational styles but no significant silt component.     

Pesticides associated with suspended sediemnts entering San Francisco Bay following the first major storm of water year 1996

Estuaries receive large quantities of suspended sediments following the first major storm of the water year. The first-flush events transport the majority of suspended sediments in any given year, and because of their relative freshness in the hydrologic system, these sediments may carry a significant amount of the sediment-associated pesticide load transported into estuaries. To characterize sediment-associated pesticides during a first-flush event, water and suspended sediment samples were collected at the head of the San Francisco Bay during the peak in suspended sediment concentration that followed the first major storm of the 1996 hydrologic year. Samples were analyzed for a variety of parameters as well as 19 pesticides and degradation products that span a wide range of hydrophobicity. Tidal mixing at the head of the estuary mixed relatively fresh suspended sediment transported down the rivers with suspended sediments in estuary waters. Segregation of the samples into groups with similar degrees of mixing between river and estuary water revealed that transport of suspended sediments from the Sacramento-San Joaquin drainage basin strongly influenced the concentration and distribution of sediment-associated pesticides entering the San Francisco Bay. The less-mixed suspended sediment contained a different distribution of pesticides than the sediments exposed to greater mixing. Temporal trends were evident in pesticide content after samples were segregated according to mixing history. These results indicate sampling strategies that collect at a low frequency or do not compare samples with similar mixing histories will not elucidate basin processes. Despite the considerable influence of mixing, a large number of pesticides were found associated with the suspended sediments. Few pesticides were found in the concurrent water samples and in concentrations much lower than predicted from equilibrium partitioning between the aqueous and sedimentary phases. The observed sediment-associated pesticide concentrations may reflect disequilibria between sedimentary and aqueous phases resulting from long equilibration times at locations where pesticides were applied, and relatively short transit times over which re-equilibration may occur.     

Physical processes in Jupiter's ring: Clues to its origin by Jove!

The particles making up the Jovian ring may be debris which has been excavated by micrometeoroids from the surfaces of many unseen (R ? 1 km) parent bodies (or “mooms” as we will occasionally call them) residing in the ring. A distribution of particle sizes exists: large objects are sources for the small visible ring particles and also account for the absorption of charged particles noted by Pioneer; the small grains are generated by micrometeoroid impacts, by jostling collisions among different-sized particles, and by self-fracturing due to electrostatic stresses. The latter are most effective in removing surface asperities to thereby produce smooth and crudely equidimensional grains. The presence of intermediate-sized (radius of several to several hundred microns) objects is also expected; these particles will have a total area comparable to the area of the visible ring particles. The nominal size (?2 μm) of the visible particles derived from their forward-scattering characteristics is caused, at least in part, by a selection effect but may also reflect a fundamental grain size or the preferential generation of certain sizes along with the destruction of others. The tiny ring particles have short lifetimes (?10²?10³ years) limited by erosion due to sputtering and meteoroid impacts. Plasma drag significantly modifies orbits in ～10² years but Poynting-Robertson drag is not effective (T_PR ～ 10⁵ years) in removing debris. The ring width is influenced by the distribution of source satellites, by the initial ejection velocity off them, by electromagnetic scattering, and by solar radiation forces. In the absence of electromagnetic forces, debris will reimpact a mother satellite or collide with another particle in about 10 years. A relative drift between different-sized particles, caused by a lessened effective gravity due to the Lorentz force, will substantially shorten these times to less than a month. The ring thickness is determined by a balance between initial conditions (abetted perhaps by electromagnetic scattering) and collisional damping; existence of the “halo” over the diffuse disk compared to its relative absence over the bright ring indicates the presence of mooms in the bright ring but not in the faint disk. Small satellites (R ? 1 km) will not reaccumulate colliding dust grains whereas satellites having the size of J14 or J16 may be able to do so, depending upon their precise shape, size, density, and location. Visible ring structure could indicate separate source satellites. The particles in the faint inner disk are delivered from the bright ring by orbital evolution principally under plasma drag. The halo is comprised of small particles (～0.1 μm) partially drawn out of the faint disk by interactions with the tilted Jovian magnetic field.     

How long does oyster shell last on an oyster reef?

A reduction in population abundance, brought on by an unprecedented 6 years of low recruitment, has reduced shell input through natural mortality on Delaware Bay oyster beds. Quantitative stock surveys provide an estimate of surficial shell over the same time period, permitting the reconstruction of the time history of shell since 1998 and estimation of the rates of shell addition and loss. Shell loss rates were unexpectedly high. In most cases, half of the shell added to an oyster bed in Delaware Bay in a given year is lost over a subsequent period of 2–10 years. Unexpectedly, the shortest half-lives, typically two to three years, are at intermediate salinities. Half-lives increase upbay into lower salinity and downbay into higher salinity to about 10 years. Minimal shell doubling times were calculated under the assumption of no shell loss, a maximum accretion rate. Minimal doubling times vary from somewhat less than a decade to more than a score of years. Doubling times of decadal scale emphasize that shell has the potential to accumulate rapidly on human time scales. The rarity of definitive documentation of shell accumulation, in terms of reef vertical accretion or lateral expansion, can only be explained if most shell produced yearly does not long remain recognizably intact. Doubling times are not rapid on the scale of oyster generation time, however. Management of essential fish habitat in the estuarine realm must include management of the shell budget and management of commercial shell-producing species must include the provision of animals as carbonate producers for habitat maintenance. Shell, at least in estuarine habitats, may have low preservational potential, even in areas that, when preserved, will appear to be shellbeds. The biases in the fossil record may not be minimized in shell-rich environments of preservation because shelliness does not imply good preservability.     

Lipid biomarkers of deep-sea hydrothermal vent polychaetes—Alvinella pompejana, A. caudata, Paralvinella grasslei and Hesiolyra bergii

The lipid composition was determined for 5 species of polychaete annelids collected by the Deep Submergence Vehicle ALVIN from high temperature chimneys at the 2500 m depth hydrothermal vent field of the East Pacific Rise. These are the first lipid biomarker analyses reported for these hydrothermal vent polychaetes. Lipid content was low in all samples (1.6–35.9 mg g^–1 wet mass) and was dominated by polar lipid (78–90% of total lipid) with 8–19% sterol (ST), and very low storage lipid (triacylglycerol and wax ester). Total polyunsaturated fatty acids (PUFA) were moderately high (22–31% of total fatty acids (FA)) with extremely low or no docosahexaenoic acid (DHA, 22:6(n-3)). Eicosapentaenoic acid (EPA, 20:5(n-3)) levels were 5–6% in Alvinella pompejana and A. caudata and 10.3–13.7% in an errantiate polychaete (likely Hesionidae) and Hesiolyra bergii. There were greater PUFA and a greater EPA/AA (AA is arachidonic acid, 20:4(n-6)) ratio in the anterior versus the posterior half of A. pompejana, which may correlate to the strong temperature gradient reported in its tube. Total nonmethylene interrupted diunsaturated fatty acids (NMID) were 4–9% of total FA for most polychaete species and included several 20:2 and 22:2 components. The principal monounsaturated fatty acids (MUFA) included 18:1(n-7)c (14–19%), 16:1(n-7)c (2.6–10%) and 20:1(n-11)c (3–7% of total FA). These polychaete species may desaturate and elongate the bacterial-derived 18:1(n-7)c to obtain the essential FA EPA and AA. The major ST in the polychaetes is cholesterol (89–98% of total ST) with less cholesterol in the gut contents of A. pompejana. Other ST included 24-ethylcholesterol (1.5–5% of total ST) with lesser amounts of 24-methylenecholesterol, desmosterol, lathosterol, 24-methylcholesterol, 24-ethylcholesterol, and the stanols dehydrocholestanol and cholestanol. The high ST levels could play a role in thermal adaptation of membranes at the hydrothermal vent environment. Differences in the FA profiles separated the closely related species A. pompejana and A. caudata from Paralvinella grasslei, H. bergii, and the errantiate polychaete (likely Hesionidae).     

Distribution and transport patterns of northern rock sole, Lepidopsetta polyxystra, larvae in the southeastern Bering Sea

We report the size, abundance, and distribution (horizontal, vertical) of northern rock sole, Lepidopsetta polyxystra, larvae collected from ichthyoplankton surveys on the southeastern Bering Sea shelf near Unimak Island, in Unimak Pass, and in the Gulf of Alaska south of Unimak Island. The greatest abundances of larvae occurred within Unimak Pass and in the Bering Sea northeast of Unimak Island. Larvae were smaller and more abundant in 2002 than in 2003. Larval abundance and size varied with depth. Highest abundances were at depths of 10-30 m during the day, and larger fish appeared to migrate from below 20 m to 0-10 m at night. There was evidence of multiple spawning locales and larval dispersal pathways that were depth- and area-specific. Northern rock sole larvae spawned west of Unimak Pass along the Aleutian Islands may be transported northward by the Bering Slope Current. Larvae spawned in the Gulf of Alaska and advected through Unimak Pass are differentially dispersed, primarily to the middle and outer shelves along the 100 m and 200 m isobaths, or along the Alaska Peninsula. Larvae spawned along the Alaska Peninsula east of Unimak Island appear to have the greatest chance of being transported to nursery areas in the coastal domain. Dispersal of near-surface northern rock sole larvae in any of these locations is likely influenced by wind-driven advection, but below-surface (>10 m) northern rock sole larval transport is probably more affected by factors that modulate geostrophic flow rather than wind-driven surface currents.