Transient biouptake flux and accumulation by microorganisms: The case of two types of sites with Langmuir adsorption

The uptake of a chemical species by an aquatic microorganism is modelled considering two kinds of sites where Langmuirian adsorption is followed by first order internalisation kinetics. Simpler models, such as only one internalisation route (while most of the adsorption takes place on non-internalising sites) or a linear isotherm for adsorption on one or both sites, become limiting cases of this double-Langmuirian model. The model considers the sites located on the spherical (or semi-spherical) surface of the organism, and takes diffusion from the medium into explicit account. The numerical solution for the internalisation flux shows a maximum. We provide an estimate for the time needed to reach a certain proximity to steady state. The transient solution confirms that the analytical expressions for the steady-state flux are usually valid and that the accumulated amounts reflect the impact of the short-time uptake. The Instantaneous Steady-State Approximation (ISSA), where an intercept of the linear regression of accumulated amount as a function of time is interpreted as an adsorbed amount, can be critically assessed with the transient numerical code for two cases: (i) when the total burden of metal on the cell is the input data and (ii) when an extraction procedure provides further information on the adsorbed and internalised amount.     

A climatology of mesoscale model simulated low-level wind jets over Cook Inlet and Shelikof Strait, Alaska

Weather in the North Gulf of Alaska is characterized by a high frequency of deep synoptic-scale low-pressure systems, especially during the cold season. The strong pressure gradients of these storms interact with the extremely rugged terrain of the coastal mountains to produce a variety of channeled flows. These surface wind regimes are not well documented in the scientific community, due to the paucity of observations. Modeling of these phenomena in regions of complex terrain is of great interest to those working with hydrodynamic, wave, and pollutant transport models in coastal and shelf areas. Such models, when coupled with ocean and coastal-ecology counterparts, give a broad view of the role surface winds play in shaping local coastal marine ecosystem in this region. This paper presents a climatology of simulated low-level wind jets over the domain of Cook Inlet and Shelikof Strait along Alaska's south-central coast. Daily simulations using the RAMS model were conducted in a 36-h forecast mode for the cold-season period 10/1/03 to 3/31/04. Systematic analysis of the resulting simulated low-level wind field makes it possible to characterize these jets and gap flows in spatial and temporal detail. The comparison between the RAMS winds and the Synthetic Aperture Radar (SAR)-derived winds when available verifies the existence of these wind jets and the capability of the model to simulate these cases. Clearly, the results of a study in this region depend on the fidelity of the model at these scales (O[5 km]). The SAR comparisons attempt to help establish this. From the 6 months of simulations over Cook Inlet and Shelikof Strait, the low-level wind jets are classified into 10 different regimes by location and orientation. These regimes are categorized into four more general groups: cross-channel westerly, easterly, and up and down Inlet flows. The nature of a particular regime is largely a function of pressure gradient orientation and local topography. Jets in the same group have a similar occurrence distribution with time. Some form of jet occurred in the study region almost daily each month of the period, with December 2003 having the highest frequency of wind jets.     

A community-wide intercomparison exercise for the determination of dissolved iron in seawater

The first large-scale international intercomparison of analytical methods for the determination of dissolved iron in seawater was carried out between October 2000 and December 2002. The exercise was conducted as a rigorously “blind” comparison of 7 analytical techniques by 24 international laboratories. The comparison was based on a large volume (700 L), filtered surface seawater sample collected from the South Atlantic Ocean (the “IRONAGES” sample), which was acidified, mixed and bottled at sea. Two 1-L sample bottles were sent to each participant. Integrity and blindness were achieved by having the experiment designed and carried out by a small team, and overseen by an independent data manager. Storage, homogeneity and time-series stability experiments conducted over 2.5 years showed that inter-bottle variability of the IRONAGES sample was good (< 7%), although there was a decrease in iron concentration in the bottles over time (0.8–0.5 nM) before a stable value was observed. This raises questions over the suitability of sample acidification and storage.     

Dynamic evolution of the 1997–1999 El Niño–La Niña cycle in the southern California Current System

The development of the strongest El Niño event on record in the equatorial Pacific in 1997–1998 and the rapid transition to strong La Niña conditions in 1998–1999 had a large impact on the physical and biological environment of the West Coast. We investigate the evolution of the physical structure and circulation dynamics of the southern California Current System (CCS) during this period based on hydrographic data collected on 25 cruises over a 45-month period (February 1996–October 1999). The El Niño period was characterized by a significant increase in dynamic height, extreme water mass characteristics, a strengthening and broadening of the poleward nearshore flow, and a temporary reversal of net alongshore transport. By early 1999, conditions in the CCS had reversed. The data suggest that remotely driven forcing (propagating oceanic waves) contributed to the anomalies observed during the El Niño period, while the cool-water conditions of 1999 were most likely a result of anomalous local atmospheric forcing.     

Nutrient variability during El Niño 1997–98 in the California current system off central California

Nutrient conditions off central California during the 1997–98 El Niño are described. Data were collected on 11 cruises from March 1997 to January 1999 along a hydrographic section off central California, as well as every two weeks at a coastal station in Monterey Bay. Perturbations associated with El Niño are shown as anomalies of thermohaline and nutrient distributions along this section. The anomalies were obtained by subtracting seasonal averages for the period from April 1988 to April 1991 from the 1997–98 observations. The first indications of El Niño conditions (high sea levels) were observed at Monterey between late May and early June 1997, but the coastal nutricline did not begin to deepen until August 1997. It reached maximum depth of 130 dbar in January 1998 at the time that maximum sea level anomalies were observed. During this period: (1) the highest subsurface temperature anomalies coincided with subsurface nutrient anomaly minima at the depth of the pycnocline; (2) southern saline and nutrient-poor waters occupied the upper 80 dbar of the water column along the entire section; and (3) nitrate levels were close to zero in the euphotic zone, collapsing the potential new primary production in the coastal domain. At the end of February 1998, the nutricline shoaled to 40 dbar at the coast although it remained anomalously deep offshore. Higher temperatures and lower nutrient levels were observed for the entire section through August 1998 although in contrast with the previous winter, there was a strong freshening mainly due to an onshore movement of subarctic waters.     

Fractal Dimension and Fractals in Ocean Engineering

- This paper discusses the application of fractal dimension and fractals in ocean engineering. To handle some ocean environment problems, the existing fractal method, in which the fractal dimension is a constant, can be used. For some complicated problems in ocean engineering, this paper presents the concept of the variable dimension fractals (D = f(r)), i. e., the fractal dimension D is the function of characteristic scale r instead of a constant. By using variable dimension fractals, several deformation and stress states of offshore structures are described.     

Controls on organic carbon distribution in sediments from the eastern Arabian Sea Margin

 Sediment cores from the upper continental slope of the eastern Arabian Sea have high organic carbon (OC), CaCO₃, and sand content at the top. The values decrease with increasing depth in the Holocene and Upper Pleistocene. Topographic highs show highest OC and lower CaCO₃ in the Holocene clayey sediments and vice versa in the Pleistocene sandy sediments. The OC is immature and marine or a mixture of both marine and terrestrial in the Holocene sediments and is mostly terrestrial and/or reworked marine in the Pleistocene sediments. Productivity is the main controlling factor for the organic carbon enrichment. Texture and reworking also influence the organic carbon variations. Received: 29 May 1996/Revision received: 10 January 1997     

A residual analysis method for quantitative comparison of spatial data from the Iceland-Faeroes Front

A spatial statistical method has been developed from the well-known Kriging technique in geostatistics, as a way of providing quantitative comparison between a pair of spatial data sets, and a measure for such a comparison. This residual analysis method is applied to oceanographic data in order to compare Iceland-Faeroes Front (IFF) model predictions against appropriate field observations, with an aim to assess the IFF model performance and its prediction accuracy. The method is also used to evaluate the model-generated dynamical variability within the model predictions, as well as the natural variability within the frontal observations. From the results, it has been found that the IFF model is highly robust, and gives better predictions at depth 150–350 m than elsewhere. Within such a depth (i.e. 250–350 m), there is also evidence to suggest that the main frontal region is most active above the IF Ridge. The natural variability obtained from the observations appears to be comparable to the model-generated dynamical variability after 20 days of integration, indicating a certain degree of accuracy in the model predictions. The method reported in this paper could also be extended for further use in model data assimilation. Thus, the work not only demonstrates how spatial statistics can be applied to oceanographic data, but also opens up new statistical tools for data handling in ocean modelling.