Josephine Y. Aller

The effect of biogenic irrigation intensity and solute exchange on diagenetic reaction rates in marine sediments

The activities of infaunal macrobenthos strongly influence the pathways, rates, and extent of organic matter remineralization and associated reactions in marine sediments. Solute transport during irrigation is a particularly important process that stimulates microbial activity and net remineralization, both within and adjacent to the bioturbated zone. Part of the stimulation proximal to the bioturbated zone is due to redox oscillation and oxidant supply during transport, but part of both the near and far-field effects are a result of other factors. Experiments designed to simulate different degrees of diffusive exchange, and thus infaunal abundances or activity, demonstrate a regular and strong dependence of anaerobic remineralization on diffusive transport. For example, net production of NH 4 + , HPO 4 = , I - , and Mn ++ increases as the effective distance between burrows becomes ≤2 cm (burrow abundance ≥800 m -2 ) in otherwise identical anoxic sediment. Corresponding changes in sedimentary bacterial numbers, exoenzyme activity, per cell growth rate (RNA), and solid phase properties (N, C/N, P) indicate that the increases in net rates are due in part to an absolute increase in total production. Transport-reaction models and experimental results demonstrate that relative decreases in the uptake of solutes into biomass, abiogenic precipitation reactions, and increased removal of inhibiting metabolites all occur simultaneously, enhancing both total and net remineralization. The phenonomenological first-order rate constant for organic matter decomposition is therefore a function not only of the reductant and oxidant pool properties, but also the environmental transport regime. Solid phase reaction products can differ substantially as a function of diffusive openness. For example, both organic P and the organic Plinorganic P ratio increase in more diffusively-open (irrigated) compared to diffusively-closed, anoxic sediment. The sensitivity of solute concentrations, microbial activity and diagenetic reaction balances to diffusive transport regime, indicates that macrofauna can functionally manipulate these properties through relatively small changes in burrow spacing patterns and individual burrow geometries.

Evidence for localized enhancement of biological associated with tube and burrow structures in deep-sea sediments at the HEEBLE site, western North Atlantic

Relict burrows on the Nova Scotian Rise act as traps for highly reactive, relatively fresh organic matter from recent diatom blooms in surface waters. As such, the burrows are sites of enhanced biological activity and intensive decomposition in otherwise organic-poor sediment. These infilled burrows, as well as normally inhabited structures significantly influence sediment chemistry and the three-dimensional distributions and abundances of sediment microorganisms, meio- and macroinfauna. A tube dwelling of Amphicteis sp. (an ampharetid polychaete) and 5 burrows of various configurations were examined from box cores from a depth of ∼4820 m at the HEEBLE site. Bacterial abundances were significantly greater (P < 0.05) in sediment immediately surrounding the burrows than in ambient sediment (12 vs 7 × 109g1). Organic carbon and nitrogen concentrations were also slightly higher near burrows. Meiofauna, particularly nematodes and foraminifera, double or even triple their densities around burrows compared with ambient sediment possibly responding to enhanced microorganism standing stocks. Total sediment ATP concentrations mirror the patterns of bacterial and meiofaunal abundances and show highest concentrations in the innermost radial zone around burrows. Sedimentary Mn and Fe distributions imply more reducing conditions and metabolically reactive organic matter near burrows. The existence of detectable, solid-phase Mn and Fe gradients associated with burrows indicate that these structures had been stable for periods of at least several weeks. At the HEBBLE site, 30–120 burrows of diameter 0.2–5 cm were visible per m2 of seafloor, with substantially greater numbers of smaller-diameter burrows evident from X-radiographs. Although only ∼1% of the total exposed bottom surface is covered by the large-diameter burrows, each burrow can influence a surrounding radius of ∼3 cm, and thus affect sedimentary characteristics of 10–34% of the bottom (at steady state). Despite periodic erosion of the seafloor by strong near-bottom currents, filled and unfilled burrow structures are sufficiently long lived and the response of the associated organisms sufficiently rapid that distinct biogeochemical properties develop around them.

A marine biogenic source of atmospheric ice-nucleating particles

The amount of ice present in clouds can affect cloud lifetime, precipitation and radiative properties. The formation of ice in clouds is facilitated by the presence of airborne ice-nucleating particles. Sea spray is one of the major global sources of atmospheric particles, but it is unclear to what extent these particles are capable of nucleating ice. Sea-spray aerosol contains large amounts of organic material that is ejected into the atmosphere during bubble bursting at the organically enriched sea–air interface or sea surface microlayer. Here we show that organic material in the sea surface microlayer nucleates ice under conditions relevant for mixed-phase cloud and high-altitude ice cloud formation. The ice-nucleating material is probably biogenic and less than approximately 0.2 micrometres in size. We find that exudates separated from cells of the marine diatom Thalassiosira pseudonana nucleate ice, and propose that organic material associated with phytoplankton cell exudates is a likely candidate for the observed ice-nucleating ability of the microlayer samples. Global model simulations of marine organic aerosol, in combination with our measurements, suggest that marine organic material may be an important source of ice-nucleating particles in remote marine environments such as the Southern Ocean, North Pacific Ocean and North Atlantic Ocean.

Quantifying sediment disturbance by bottom currents and its effect on benthic communities in a deep-sea western boundary zone

Abstract Erosion, transport and redeposition of sediment by near-bottom currents are major sources of disturbance for soft-sediment habitats and associated benthic communities. This phenomenon takes place in western boundary slope regions of the deep sea such as the HEBBLE area on the Nova Scotian Rise, western North Atlantic. Bottom disturbance in this western boundary region can be characterized and quantified, first in terms of the driving force—the current and directly related bed shear stress; and second, by the expression of the current effect as observed in sedimentary fabric, %CaCO 3 , and granulometry. These physical characteristics can be correlated with biologic features, including abundances and activities of sediment microorganisms, and apparently, in abundances and distributions of meio- and macrofauna. Currents measured at heights of 1–59 m above the seabed at the HEBBLE site (4815–4830 m) from February 1982 to 15 September 1986 show evidence of “benthic storms” with current speeds of 15–23 cm s −1 for ⩾2 days. These “storms” occur with a frequency of about 21 days and have mean durations of 7 ± 5.8 days. Storms with mean velocities over 23 cm s −1 occur every 10 months and last 12 ± 11 days. X-radiographs of vertical slabs of sediment taken from box cores at the HEBBLE site show stratification features related to current speeds and bed shear stress, immediately preceeding the time of core collection. These relationships are corroborated by radiochemical distributions of 234 Th. Both erosional and depositional processes affect physical and chemical properties of the sediment and have positive and negative effects on the benthic community. Erosional periods result in sediment transport and sweeping of surficial organic matter, micro-organisms, larvae and juveniles from the area. During transitional periods of intermediate current velocities there is deposition of fresh organic matter, removal of metabolites, and mechanical stimulation of sediment micro-organisms. Periods of decelerating current speeds result in rapid deposition of several cm of sediment on to the seabed, burying organisms and filling-in burrows. Benthic macro- and meiofaunal abundances are maximum during these depositional periods. Periods of low current speed are not necessarily periods of low physical disturbance.

Fluidized muds: a novel setting for the generation of biosphere diversity through geologic time.

Reworked and fluidized fine-grained deposits in energetic settings are a major modern-day feature of river deltas and estuaries. Similar environments were probably settings for microbial evolution on the early Earth. These sedimentary systems act as efficient biogeochemical reactors with high bacterial phylogenetic diversity and functional redundancy. They are temporally rather than spatially structured, with repeated cycling of redox conditions and successive stages of microbial metabolic processes. Intense reworking of the fluidized bed entrains bacteria from varied habitats providing new, diverse genetic materials to contribute to horizontal gene transfer events and the creation of new bacterial ecotypes. These vast mud environments may act as exporters and promoters of biosphere diversity and novel adaptations, potentially on a globally important scale.

Molluscan death assemblages on the Amazon Shelf: implication for physical and biological controls on benthic populations

The Amazon Continental Shelf is an example of an environment impacted by frequent and intense physical disturbance with regions of high sedimentation rates. Cycles of extensive sediment erosion and deposition result in periods of sediment remobilization and instability in the seabed, and cause marked seasonal and spatial variations in the transport of water column organisms and benthic infauna. In this study, the molluscan death assemblages on the Amazon shelf are examined in an effort to understand how this physical regime is reflected in death assemblages as well as to provide insight into biological controls on mortality. Inner Shelf regions of <20 m water depth, comprise ∼50% of the total shelf area that extends to 100 m and have no relict shell beds or randomly dispersed shells, although a few living shell-bearing species are occasionally present. Extensive death assemblages are found deeper than 40 m. Bivalves were most numerous on the shelf, although gastropods dominate at the stations with the most extensive shell assemblages. The incidence of boring varied between 3 general groups of stations from 5, 12, and 30%, and tended to be similar for gastropods and bivalves. Evidence for significant exposure time on the sediment surface alternating with periods of burial was found. Fewer than one third of all specimens reached adult size suggesting settlement in a marginal habitat. In general the most abundant taxa in the living community were also dominant in death assemblages. The most abundant relict bivalve, Crassinella lunulata however, which reached densities of 5578 m−2, were never found alive on the shelf. This species along with old reworked fragments of coral and bryozoans, indicate onshore transport from south of the shelf or from the outer shelf, where relict coraline deposits are exposed, followed by deposition and downward mixing of shells into the deposit. In spite of the overwhelming influence of the physical regime, the incidence of boring is comparable to other environments suggesting significant biological control of benthic populations.

Experimental evaluation of the influences of biogenic reworking on carbonate preservation in nearshore sediments

Abstract Laboratory experiments using two different species of marine infaunal deposit feeders have shown directly that macrofaunal activities influence sedimentary carbonate preservation. Feeding, burrowing and irrigation increase solute transport and solid phase reaction rates simultaneously, leading to more rapid carbonate dissolution than in sediments without fauna. These findings help to explain previously reported regular temporal fluctuations of foraminifera assemblages and spatial patterns of carbonate dissolution in nearshore deposits and represent one more example of how bioturbation accelerates elemental cycles in marine sediments.

Fisheries and Water Level Fluctuations in the World's Largest Desert Lake

Hydrological regimes are significant drivers of fisheries production in many African Lakes due to their influence on fish habitat and food availability, breeding success, and catchability. Lake Turkana, Kenya will undergo substantial changes in hydrology due to water regulation and extraction along the Omo River in neighboring Ethiopia, which provides over 90% of its water. The objective of this study was to predict how the lakes fisheries, which provide an important livelihood and protein source in the region, will respond to hydrological change. While variations in fishing effort are poor predictors of fisheries catch in the lake, water levels and their fluctuations strongly influence fisheries production. Seasonal oscillations play a particularly important role and with complete loss of these oscillations the lakes predicted fisheries yield will decrease by over two thirds. The fishery is predicted to collapse at a lake level decline of 25 m, regardless of seasonal amplitude magnitude. The lakes total littoral habitat, where fisheries are currently concentrated, will increase in surface area with lake level declines of <25 m. However, the extent of productive, dynamic littoral habitat will decrease with dampening of the lakes seasonal oscillations. The most severe habitat loss will occur in the lakes Turkwel Sector, which hosts the regions highest human population densities, and North Sector, where inter-tribal conflict over resources is common and likely to be exacerbated by lake level decline. The continued ecological functioning of Lake Turkana necessitates immediate efforts to develop and apply a water resource management plan rooted in science.

Development of a Capillary Waveguide Biosensor Analytical Module for Use with the MBARI Environmental Sample Processor

The Monterey Bay Aquarium Research Institute’s Environmental Sample Processor (ESP) is well established as an innovative sampling and instrument platform for sensors designed for in situ monitoring of microorganisms in the ocean. The platform can be deployed for periods up to 3 months and real-time data can be remotely downloaded at any time. A daughter platform, the micro fl uidic block (MFB), is used as an interface between the ESP and analytical modules to permit rapid deployment of new sensor technologies. We have developed a capillary waveguide biosensor (CWB) which employs nucleic acid hybridization for detection and quanti fi cation of speci fi c microorganisms, and have integrated it with the MFB for use with the ESP. An important aspect of the CWB is the use of a combined capillary waveguide/hybridization surface that can be regenerated for repeated use. This chapter describes design issues related to the integration of the CWB and MFB and the development of coating protocols to maximize the operational life of the capillary.