The distribution of tritium and CFCs in the Weddell Sea during the mid-1980s

Transient tracer data (tritium, CFC11 and CFC12) from the southern, central and northwestern Weddell Sea collected during Polarstern cruises ANT III-3, ANT V-2/3/4 and during Andenes cruise NARE 85 are presented and discussed in the context of hydrographic observations. A kinematic, time-dependent, multi-box model is used to estimate mean residence times and formation rates of several water masses observed in the Weddell Sea.Ice Shelf Water is marked by higher tritium and lower CFC concentrations compared to surface waters. The tracer signature of Ice Shelf Water can only be explained by assuming that its source water mass, Western Shelf Water, has characteristics different from those of surface waters. Using the transient nature of tritium and the CFCs, the mean residence time of Western Shelf Water on the shelf is estimated to be approximately 5 years. Ice Shelf Water is renewed on a time scale of about 14 years from Western Shelf Water by interaction of this water mass with glacial ice underneath the Filchner-Ronne Ice shelf. The Ice Shelf Water signature can be traced across the sill of the Filchner Depression and down the continental slope of the southern Weddell Sea. On the continental slope, new Weddell Sea Bottom Water is formed by entrainment of Weddell Deep Water and Weddell Sea Deep Water into the Ice Shelf Water plume. In the northwestern Weddell Sea, new Weddell Sea Bottom Water is observed in two narrow, deep boundary currents flowing along the base of the continental slope. Classically defined Weddell Sea Bottom Water (θ ≤ −0.7°C) and Weddell Sea Deep Water (−0.7°C ≤ θ ≤ 0°C) are ventilated from the deeper of these boundary currents by lateral spreading and mixing. Model-based estimates yield a total formation rate of 3.5Sv for new Weddell Sea Bottom Water (θ = −1.0°C) and a formation rate of at least 11Sv for Antarctic Bottom Water (θ = −0.5°C).     

Variation of roughness length of a mobile sand bed in a tidal flow

Velocity profiles, suspended sand concentration, and ripple shapes were measured over the tidal cycle on a mobile bed. Variations in ripple shape or dimensions, and the effects of mobile sediment could not account for the variations in bed roughness length, which increased systematically during the tide from 0.5 to 1.3 cm. The effects of acceleration could be the cause as they would lead to the same pattern of variation, but existing theory does not give the correct magnitude.     

Simultaneous exposure of English sole (Parophrys vetulus) to sediment-associated xenobiotics: Part 1—uptake and disposition of 14C-polychlorinated biphenyls and 3H-benzo[a]pyrene

English sole (Parophrys vetulus) were exposed to environmentally realistic levels of sediment-associated ³H-benzo[a]pyrene (3 μg BaP/g sediment, dry weight) and ¹⁴C-Aroclor 1254 (1 μg PCBs/g), separately and together, for up to 10 days. BaP and its metabolites in tissues reached steady-state concentrations by the first day of the exposure, whereas PCBs did not approach steady-state concentrations until the tenth day of exposure. Simultaneous exposure of sole to BaP and PCBs, relative to separate exposure to the xenobiotics, significantly increased the concentrations of BaP-derived radioactivity and decreased the concentrations of PCB-derived radioactivity in some tissues and bile. Accumulation of PCB-derived radioactivity, estimated as the burden in tissues, was significantly greater (4- to 13-fold) than that of BaP-derived radioactivity throughout the experiments and regardless of the type of exposure. The rank of the concentrations of PCB-derived radioactivity in tissues and bile was: bile ～ liver > brain > kidney ～ gill > skin ～ blood ～ muscle and for BaP-derived radioactivity the order was: bile > liver > gill > kidney > skin ～ blood > muscle > brain. BaP-derived radioactivity in liver and bile was present primary (85–99%) as metabolites, whereas PCB-derived radioactivity was present equally as parent compounds and metabolites in bile and primarily (98 %) as parent compounds in liver. Hydrolysis of bile from PCB/BaP-exposed sole with β-glucuronidase/arylsulfatase released 35 % of the BaP-derived radioactivity and 32 % of the PCB-derived radioactivity as primary metabolites. A much higher proportion of the BaP-derived radioactivity (64 %) than the PCB-derived radioactivity (13 %) in bile was unaffected by the enzyme treatment, indicating differences in the conjugation of the primary metabolites of PCBs and BaP. The results suggest that in contaminated environments the tissue to sediment concentration ratios for PCBs would exceed that for BaP and its metabolites; however, BaP would be continually absorbed and metabolized by sole to potentially carcinogenic and mutagenic compounds. In addition, the tissue levels of these toxic compounds may be increased by simultaneous exposure to PCBs.     

A fish hepatocyte model for the investigation of the effects of environmental contaminants

An isolated fish hepatocyte culture system was developed as a models ystem to investigate the mechanisms of action of environmental contaminants. Hepatocytes were isolated from striped bass (Morone saxatilis) by an adaptation of the two stage perfusion technique of Seglen.¹ The system was used to evaluate metal binding protein (MBP) induction in response to cadmium, a primary inducer of metallothionein (MT) in rat hepatocytes. Striped bass hepatocytes appeared to be refractory to the induction of MBP by cadmium, since there was no significant increase in the synthesis of MBP for any of the doses at any of the time points investigated. However, when a similar experiment was performed using rat hepatocytes there was induction of MBP that was related to both dose and time. These comparative experiments indicate that although there are similarities between the hepatocytes of the two species in regard to ³⁵S incorporation into low molecular weight metal-binding proteins, there appear to be significant quantitative differences as well in regard to MBP kinetics. This in vitro model system could potentially be utilized to investigate the toxicological properties of other environmental contaminants.     

Ensuring confidence in radionuclide-based sediment chronologies and bioturbation rates

Sedimentary records of naturally occurring and fallout-derived radionuclides are widely used as tools for estimating both the ages of recent sediments and rates of sedimentation and bioturbation. Developing these records to the point of data interpretation requires careful sample collection, processing, analysis and data modeling. In this work, we document a number of potential pitfalls that can impact sediment core records and their interpretation. This paper is not intended as an exhaustive treatment of these potential problems. Rather, the emphasis is on potential problems that are not well documented in the literature, as follows: (1) the mere sampling of sediment cores at a resolution that is too coarse can result in an apparent diffusive mixing of the sedimentary record at rates comparable to diffusive bioturbation rates observed in many locations; (2) ²¹⁰Pb profiles in slowly accumulating sediments can easily be misinterpreted to be driven by sedimentation, when in fact bioturbation is the dominant control. Multiple isotopes of different half lives and/or origin may help to distinguish between these two possible interpretations; (3) apparent mixing can occur due simply to numerical artifacts inherent in the finite difference approximations of the advection diffusion equation used to model sedimentation and bioturbation. Model users need to be aware of this potential problem. Solutions to each of these potential pitfalls are offered to ensure the best possible sediment age estimates and/or sedimentation and bioturbation rates can be obtained.     

On the relevance of iron adsorption to container materials in small-volume experiments on iron marine chemistry: Fe-aided assessment of capacity, affinity and kinetics

Iron chemistry in seawater has been extensively studied in the laboratory, mostly in small-volume sample bottles. However, little has been reported about iron wall sorption in these bottles. In this paper, radio-iron ⁵⁵Fe was used to assess iron wall adsorption, both in terms of capacity, affinity and kinetics. Various bottle materials were tested. Iron sorption increased from polyethylene/polycarbonate to polymethylmetacrylate (PMMA)/high-density polyethylene/polytetrafluoroethylene to glass/quartz, reaching equilibrium in a 25–70 h period. PMMA was studied in more detail: ferric iron (Fe(III)) adsorbed on the walls of the bottles, whereas ferrous iron (Fe(II)) did not. Considering that in seawater the inorganic iron pool mostly consists of ferric iron, the wall will be a factor that needs to be considered in bottle experiments.The present data indicate that for PMMA with specific surface (S)-to-volume (V) ratio S/V, both iron capacity (42 ± 16 × 10^− 9 mol/m² or 1.7 × 10^− 9 mol/L recalculated for the S/V-specific PMMA bottles used) and affinity (log K_Fe'W = 11.0 ± 0.3 m²/mol or 12.4 ± 0.3 L/mol, recalculated for the S/V-specific PMMA bottles used) are of similar magnitude as the iron capacity and -affinity of the natural ligands in the presently used seawater and thus cannot be ignored.Calculation of rate constants for association and dissociation of both Fe'L (iron bound to natural occurring organic ligands) and Fe'W (iron adsorbed on the wall of vessels) suggests that the two iron complexes are also of rather similar kinetics, with rate constants for dissociation in the order of 10 ⁻⁴–10^− 5 L/s and rate constants for association in the order of 10⁸ L/(mol s). This makes that iron wall sorption should be seriously considered in small-volume experiments, both in assessments of shorter-term dynamics and in end-point observations in equilibrium conditions. Therefore, the present data strongly advocate making use of iron mass balances throughout in experiments in smaller volume set-ups on marine iron (bio) chemistry.     

Robust Range-Only Beacon Localization

In this paper, we present a system capable of simultaneously estimating the position of an autonomous underwater vehicle (AUV) and the positions of stationary range-only beacons. Notably, our system does not require beacon positions a priori, and our system performs well even when range measurements are severely degraded by noise and outliers. We present a powerful outlier rejection method that can identify groups of range measurements that are consistent with each other, and a method for initializing beacon positions in an extended Kalman filter (EKF). We have successfully applied our algorithms to real-world data and have demonstrated a simultaneous localization and mapping (SLAM) system whose navigation performance is comparable to that of systems that assume known beacon locations     

High-resolution sediment echosounding off Peru: Late Quaternary depositional sequences and sedimentary structures of a current-dominated shelf

About 6000 km of both bathymetric and high-resolution acoustic profiles were acquired on the shelf and upper slope offshore Peru between 9° S and 14° S. Two new sediment echosounder systems – SEL-96 and SES-2000DS – provided details of the sedimentary structures of the Quaternary sequences within the Sechura-Salaverry, Huacho and Pisco Basins. To a great extent, the poleward undercurrent determines the distribution of sediments. The undercurrent has generated numerous erosional unconformities, it has winnowed hardgrounds and has created mudwaves common between 250 m and 400 m water depth. Distinct subbottom reflectors within sedimentary units represent hiatuses due to periods of intensified winnowing or non-deposition. Erosional unconformities usually marked by pronounced reflectors suggest shifts of the undercurrent system related to climatic changes and eustatic variations of sea level. On a larger scale, the stacked prograding depositional sequences reflect the sea-level cycles of the Middle Pleistocene to the Holocene. Based on the stratigraphy of our piston cores and that of Ocean Drilling Program (ODP) Site 680, the depositional sequences limited by extended unconformities were assigned to oxygen isotope stages 1 to 7. Other sedimentary structures are small straight channels that were conduits for downslope sediment transport. Deformed sediments associated with synsedimentary normal faults result from creep movements indicating beginning slope failure.     

Environmental overview of Eckernförde Bay,northern Germany

This environmental overview of Eckernförde Bay (northern Germany) summarizes the results of previous studies relevant to the Office of Naval Research's Coastal Benthic Boundary Layer (CBBL) Baltic field exercise conducted during 1993–1994. Significant environmental characteristics include the following: (1) surface sediment distribution is related to water depth, dictated primarily by hydrodynamic reworking of older glacial deposits; (2) the origin and characteristics of small-scale sedimentary structures depend on storm-generated waves and currents; (3) the proximity of the sea surface and sediment —water interface results in a pelagic—benthic coupling that drives biogeochemical processes and produces organicrich, acoustically turbid sediments; and (4) the bay floor is complicated topographically by pockmarks and manmade sedimentary structures.     

Estrogenic responses to xenobiotics in channel catfish (Ictalwus punctatus)

Several environmentally relevant contaminants are characterized as xenoestrogens by virtue of their ability to induce responses similar to 17β-estradiol (E2). There is concern that exposure to these xenoestrogens may result in endocrine and, thus, reproductive disruption. The objective of the present research was to determine whether xenobiotics known to elicit estrogenic responses in mammals were estrogenic in channel catfish, and if these compounds were capable of altering normal physiological response to E2. Sexually immature catfish were exposed by intraperitoneal injection to E2, suspected xenoestrogens or combination doses of E2 and xenoestrogen. Appearance of vitellogenin (Vg) in serum was used as the bioindicator of estrogenicity; Vg was measured by ELISA 7 days after injection. The ED₅₀ of E2 for the appearance of Vg in blood, 0.6 mg/kg, was used as the positive control. Synthetic estrogens, ethinylestradiol, mestranol and DES were effective in inducing Vg; the antiestrogen tamoxifen inhibited response to E2 when given in a combination dose. Treatment by both methoxychlor and p-nonylphenol resulted in Vg appearance in serum; the doses required were 300 times that of E2, and the vitellogenic response was less when compared to the E2-induced response. In addition, a combination dose of methoxychlor with E2 decreased the magnitude of the response to E2. Other mammalian xenoestrogens, o,p′-DDT, chlordecone, lindane and β-HCH, were not able to produce a vitellogenic response in this study.