Upper-water Column Research Articles

Estimating iron and aluminum removal rates in the eastern equatorial Pacific Ocean using a box model approach

Iron limitation plays an important role in maintaining the high-nitrate low-chlorophyll (HNLC) condition in the equatorial upwelling zone. The rate and depth of upwelling control Fe supply to the euphotic zone. This study constrains the transport fluxes and budget of two trace metals, Fe and Al, in the upper ocean. They are co-delivered to the eastern equatorial Pacific surface waters via the Equatorial Undercurrent and upwelling but show distinct biogeochemical cycling processes. We combine the results of the in situ measurements of dissolved Fe and Al (dFe and dAl) with the modeled velocity fields to calculate the physical fluxes. The model calculations are evaluated with the conservation of heat, volume transport, NO 3 and Si(OH) 4 budgets for the equatorial Pacific. The vertical flux due to upwelling provides averaged dFe and dAl supply rates of 1.45 μmol m −2 d −1 and 11.51 μmol m −2 d −1, respectively. The sum of the net physical fluxes in the eastern equatorial Pacific for dFe and dAl are 0.41 μmol m −2 d −1 and 2.77 μmol m −2 d −1, respectively. These estimates are equal to the net biological and chemical removal rates of dFe and dAl. The calculated dFe:C net removal ratio is in the range of 3-9 μmol:mol, which agrees with most other estimates. This suggests that the majority of net dFe removal is due to biological uptake in the upper water column. The results of this box model approach illustrate the usefulness of combining the modeled outputs and in situ measurements, which provide additional constraints on Fe transport and cycling in the equatorial Pacific and possibly other HNLC regions.

Interannual and seasonal variation of the population structure, abundance, and biomass of the arctic copepod Calanus glacialis in the White Sea

The results of multiyear observations of the seasonal and inter-annual variability of the population structure, abundance, and biomass of the arctic calanoids copepod Calanus glacialis in the White Sea are presented. The spring season represents the most crucial period for the population’s seasonal dynamics. During the spring, the maximal abundance, biomass, and contribution of C. glacialis to the total zooplankton biomass is observed. The interannual variability of the abundance is closely related to the timing of the spring warming of the upper water column and the respective shifts of the onset of reproduction and the offspring development. The development of a new generation to the overwintering copepodite stage IV is usually completed three to four weeks later in the cold years compared to the warm ones. Our multiyear observations suggest that C. glacialis could be more tolerant of Arctic warming than it is usually believed. The high abundance of the C. glacialis population in the White Sea indicates that this arctic species is able to cope with the seasonal surface warming and should continue to do so, being provided with the cold water “refuge” in the deep sea.

Contrasting local retention and cross-shore transports of the East Australian Current and the Leeuwin Current and their relative influences on the life histories of small pelagic fishes

Transport between shelf and offshore environments supports a significant proportion of ocean primary productivity and is critical to the life cycle of many marine species. While fundamental differences in the underlying dynamics of eastern and western boundary currents have been recognized and studied for more than half a century, the implications for physical dispersal rates have received much less attention. In this study we explore how Australia’s two major boundary current systems, the East Australian Current and the Leeuwin Current, differ in their local retention and cross-shore transports in the upper water column and how these differences favor contrasting life histories of small pelagic fishes. The results suggest that the East Australian Current forms a partial barrier to onshore transport, but is effective in entraining shelf waters and transporting them offshore, particularly in the region where the current separates from the coast. Blue mackerel ( Scomber australasicus) spawn on the outer-shelf in this separation region and may thereby maximize the dispersion of eggs and larvae in the mainly oligotrophic waters of the southern Coral Sea. In contrast, the Leeuwin Current system promotes onshore transport through the combined effects of mean onshore flow and eddy-induced mixing. In the Great Australian Bight, sardine ( Sardinops sagax) and anchovy ( Engraulis australis) may exploit the high coastal retention of the Leeuwin Current system by spawning on the inner-shelf during summer when the current is weakest and winds assist retention and enhance production through local upwelling.

Activity, abundance and diversity of nitrifying archaea and bacteria in the central California Current

A combination of stable isotope and molecular biological approaches was used to determine the activity, abundance and diversity of nitrifying organisms in the central California Current. Using (15)NH(4)(+) incubations, nitrification was detectable in the upper water column down to 500 m; maximal rates were observed just below the euphotic zone. Crenarchaeal and betaproteobacterial ammonia monooxygenase subunit A genes (amoA), and 16S ribosomal RNA (rRNA) genes of Marine Group I Crenarchaeota and a putative nitrite-oxidizing genus, Nitrospina, were quantified using quantitative PCR. Crenarchaeal amoA abundance ranged from three to six genes ml(-1) in oligotrophic surface waters to > 8.7 x 10(4) genes ml(-1) just below the core of the California Current at 200 m depth. Bacterial amoA abundance was lower than archaeal amoA and ranged from below detection levels to 400 genes ml(-1). Nitrification rates were not directly correlated to bacterial or archaeal amoA abundance. Archaeal amoA and Marine Group I crenarchaeal 16S rRNA gene abundances were correlated with Nitrospina 16S rRNA gene abundance at all stations, indicating that similar factors may control the distribution of these two groups. Putatively shallow water-associated archaeal amoA types ('Cluster A') decreased in relative abundance with depth, while a deep water-associated amoA type ('Cluster B') increased with depth. Although some Cluster B amoA sequences were found in surface waters, expressed amoA gene sequences were predominantly from Cluster A. Cluster B amoA transcripts were detected between 100 and 500 m depths, suggesting an active role in ammonia oxidation in the mesopelagic. Expression of marine Nitrosospira-like bacterial amoA genes was detected throughout the euphotic zone down to 200 m. Natural abundance stable isotope ratios (delta(15)N and delta(18)O) in nitrate (NO(3)(-)) and nitrous oxide (N(2)O) were used to evaluate the importance of nitrification over longer time scales. Using an isotope mass balance model, we calculate that nitrification could produce between 0.45 and 2.93 micromol m(-2) day(-1) N(2)O in the central California Current, or approximately 1.5-4 times the local N(2)O flux from deep water.

Dinoflagellate cyst distribution in surface sediments along the south-western Mexican coast (14.76° N to 24.75°N)

Abstract In this study, we explore the relationship between the modern assemblages of organic-walled dinoflagellate cysts and sea-surface conditions (temperature, salinity, primary productivity) and water depth and distance to the coast. Statistical treatments were performed on 95 surface sediment samples from sites located along the south-western Mexican coast (14.76° N to 24.75°N). Redundancy analysis (RDA) illustrates that the principal parameters correlated with the regional cyst distribution are the distance to the coast and the productivity in the upper water column, which is closely related to upwelling intensity. Empirical observations coupled with RDA provide insight into the spatial coverage of some cyst taxa produced by dinoflagellate species potentially responsible for harmful algal blooms along the coast. They also allow the recognition of four zones of assemblages, which are linked to the upwelling intensity and the productivity and characterize La Paz Bay, the south-western Mexican margin (from 15.95° N to 23.11° N), the northern part of the Gulf of Tehuantepec and the southern part of the Gulf of Tehuantepec.

Distribution and seasonal dynamics of arsenic in a shallow lake in northwestern New Jersey, USA

Elevated concentrations of arsenic (As) occurred during warm months in water from the outlet of Lake Mohawk in northwestern New Jersey. The shallow manmade lake is surrounded by residential development and used for recreation. Eutrophic conditions are addressed by alum and copper sulfate applications and aerators operating in the summer. In September 2005, arsenite was dominant in hypoxic to anoxic bottom water. Filterable As concentrations were about 1.6-2 times higher than those in the upper water column (23-25μg/L, mostly arsenate). Hypoxic/anoxic and near-neutral bottom conditions formed during the summer, but became more oxic and alkaline as winter approached. Acid-leachable As concentrations in lake-bed sediments ranged up to 694mg/kg in highly organic material from the tops of sediment cores but were <15mg/kg in geologic substrate. During warm months, reduced As from the sediment diffuses into the water column and is oxidized; mixing by aerators, wind, and boat traffic spreads arsenate and metals, some in particulate form, throughout the water column. Similar levels of As in sediments of lakes treated with arsenic pesticides indicate that most of the As in Lake Mohawk probably derives from past use of arsenical pesticides, although records of applications are lacking. The annual loss of As at the lake outlet is only about 0.01% of the As calculated to be in the sediments, indicating that elevated levels of As in the lake will persist for decades.

Distribution of size fractionated dissolved iron in the Canary Basin

The distribution of size fractionated dissolved iron (DFe, <0.2 μm) species was determined in the upper water column (0–150 m) of the Canary Basin (25–32°N and 18–24°W) on a research cruise in October 2002. A DFe concentration gradient resulting from a decrease in both soluble iron (SFe, <0.02 μm) and colloidal iron (CFe, 0.02–0.2 μm) was shown to extend from the coast of North West Africa into the oligotrophic gyre (varying from ∼1 nM in the shelf region to 0.15 nM in the most off shore waters). At the time of this study, the dominant dissolved Fe input to the region was deduced to be the advection of shelf and upwelled waters rather than Saharan dust deposition. SFe and CFe fractions had mean concentrations (± one standard deviation) of 0.25 ± 0.11 and 0.21 ± 0.16 nM, respectively ( n = 58). Colloidal iron formed a highly variable fraction of DFe (ca. 0–80%, mean of 42%) in the region but was less variable in the low iron, oligotrophic intermediate waters (0.18 ± 0.06 nM, 31.7°N, 22.0°W, 0–1300 m depth). The high variability found at the most productive near-shelf stations was driven by biological processing and mixing of different water masses. In contrast, less variability between SFe and CFe at the remote off shore stations suggested that vertical variations in the water column were controlled more by chemical partitioning and vertical particle fluxes with evidence of preferential biological uptake and/or removal of SFe in the most remote surface waters.

INFLUENCE OF DICHLORVOS IN ROOM ON BEHAVIORS OF JAPANESE MEDAKA

In order to develop an early-warning biosensor system based on Japanese medaka (oryzias latipes) for predicting the impact on health of long-term and low-level exposure to indoor chemical compounds, we investigated the effect on behavioral changes of medaka exposed to Dichlorvos (2,2-dichlorovinyl dimethyl phosphate, DDVP), which is a kind of agricultural compounds having a potential to flows into indoors and be inhaled by resident and may affect residents' health badly and fatally in agricultural districts, as well as Formaldehyde and Toluene which are representative indoor chemicals. We used a laboratory water-quality measuring instrument to observe behavioral changes of fish. During the experiments, the three-dimensional coordinates of the fish are recorded by two CCD cameras every three seconds. P value of <0.05 was considered to indicate significance. When exposed to these chemicals in water, the fish showed the altered behaviors compared to one under a control treatment, e.g. body movement distance and duration time near the lower water column by the fish significantly decreased, while body angle near the upper water column and duration time near the upper water column by the fish increased compared to the normal state.

On the Upper Ocean Thermal Structure in a Western North Pacific Ocean Model: Model Evaluation and Sensitivity Study

Seasonal variations in the upper water column of the western North Pacific are simulated with the Regional Ocean Model System (ROMS). The model is driven by surface fluxes of heat, momentum and freshwater without prescribing sea surface temperature or salinity. A series of numerical experiments are conducted to explore the sensitivity of the upper ocean thermal structure to the parameterized solar penetration scheme and two common practices to control model climate through a flux correction term and a nudging term. The absorption of solar radiation by the water column beneath the sea surface destabilizes the upper layers to cause a stronger mixing and deeper mixed layer in the warm season (from April to September). Therefore, removing solar penetration from the model results in an exceptionally stable surface layer, and tends to produce an overly shallow mixed layer in the warm season. The experiment with a prescribed net surface heat flux shows that the model is unable to maintain a heat balance in the upper water column, producing a cooling trend. Experiments with a flux correction term are able to keep the simulated sea surface temperature (SST) from a long term drift by adjusting the amount of the net surface heat flux. However, unrealistic net surface heat flux is produced in the experiment, when the model assumes no solar penetration. The implementation of a weak temperature nudging (1/50 days) toward a long term mean climatology prevents the model from simulating a cold bias during long term integration. The experiment with solar penetration and a weak nudging produces reasonable interannual variability during the period of 1995 - 2006 without flux corrections. The nudging terms steer advective heat fluxes towards the climatological mean state so as to avoid long-term drift in upper water column heat content. A detailed understanding of the function of nudging terms in controlling the hydrodynamics of the water column remains to be investigated.

Origin and tentative identification of tri to pentaunsaturated ketones in sediments from Lake Fryxell, East Antarctica

Chromatographic and mass spectrometric analysis of surface sediments from perennially ice-covered Lake Fryxell (McMurdo Dry Valleys, East Antarctica) enabled tentative identification from mass spectral data of previously unreported pentaunsaturated ketones, octatriacontapentaen-2-one (C 38:5Me), nonatriacontapentaen-3-one (C 39:5Et) and tetradecapentaen-2-one (C 40:5Me). In addition, the C 37, C 38 and C 40 alkenones occur as di, tri and tetraunsaturated compounds, whereas the C 39 alkenones only include the tetraunsaturated components. Analysis of environmental DNA extracted from the water column of Lake Fryxell produced two 18S rDNA sequences closely related to Isochrysis spp., Chrysotila lamellosa and haptophyte sequences previously recognized in sediment samples collected from a Greenland lake and from Ace Lake, Antarctica. Based on the alkenone distribution, coupled with phylogenetic data, we propose that haptophytes related to Isochrysis and/or C. lamellosa are the source organisms of alkenones in Lake Fryxell. The occurrence of pentaunsatured alkenones may represent a response to the year-round cold water temperature (ca. 1 °C average), likely combined with oxygen supersaturation and growth under light- and nutrient-limited conditions in the upper water column.

Phytoplankton community structure and stocks in the Southern Ocean (30–80°E) determined by CHEMTAX analysis of HPLC pigment signatures

Abstract The geographic distribution, stocks and vertical profiles of phytoplankton of the seasonal ice zone off east Antarctica were determined during the 2005–2006 austral summer during the Baseline Research on Oceanography, Krill and the Environment-West (BROKE-West) survey. CHEMTAX analysis of HPLC pigment samples, coupled with microscopy, permitted a detailed survey along seven transects covering an extensive area between 30°E and 80°E, from 62°S to the coast. Significant differences were found in the composition and stocks of populations separated by the Southern Boundary of the Antarctic Circumpolar Current (SB), as well as a small influence of the Weddell Gyre in the western sector of the ‘zone south of the Antarctic Circumpolar Current’ (SACCZ). Within the SACCZ, we identified a primary bloom under the ice, a secondary bloom near the ice edge, and an open-ocean deep population. The similarity of distribution patterns across all transects allowed us to generalise a hypothesized sequence for the season. The primary phytoplankton bloom, with stocks of Chl a up to 239 mg m−2, occurred about 35 days before complete disappearance of the sea ice, and contained both cells from the water column and those released from melting ice. These blooms were composed of haptophytes (in particular, colonies and gametes of Phaeocystis antarctica), diatoms and cryptophytes (or the cryptophyte symbiont-containing ciliate Myrionecta rubrum). Aggregates released by melting ice quickly sank from the upper water column and Chl a stocks declined to 56–92 mg m−2, but the bloom of diatoms and, to a lesser extent, cryptophytes continued until about 20 days after ice melt. The disappearance of sea ice coincided with a sharp increase in P. antarctica and grazing, as indicated by increasing phaeophytin a and phaeophorbide a. Chlorophyllide content suggests that the diatom bloom then senesced, probably due to iron exhaustion. Stocks rapidly declined, apparently due to grazing krill that moved southward following the retreating sea ice. We suggest that grazing of the bloom and export of faecal pellets stripped the upper water column of iron (as suggested by low Fv/Fm ratios and CHEMTAX pigment ratios in Haptophytes – iron was not measured). Thus, export of iron by grazing, and possibly sedimentation, created a southward migrating iron gradient, limiting growth in the upper water column. North of the postulated iron gradient, a nanoflagellate community developed at depth, with Chl a stocks from 36–49 mg m−2. This community was probably based on regenerated production, sustained by residual and/or upwelling iron, as indicated by a close correspondence between distributions of Chl a and profiles of Fv/Fm. The community consisted of haptophytes (chiefly Phaeocystis gametes), dinoflagellates, prasinophytes, cryptophytes, and some small diatoms. Selective grazing by krill may have fashioned and maintained the community. North of the SB, Chl a ranged from 40–67 mg m−2 and was found predominantly in the mixed layer, but Fv/Fm ratios remained low, suggesting the community of P. antarctica and diatoms was iron-limited. These interpretations provide a cogent explanation for the composition and structure of late summer microbial populations in the marginal ice zone.

Deciphering the depositional environment of the laminated Crato fossil beds (Early Cretaceous, Araripe Basin, North-eastern Brazil)

The laminated limestones of the Early Cretaceous Crato Formation of the Araripe Basin (North-eastern Brazil) are world-famous for their exceptionally well-preserved and taxonomically diverse fossil fauna and flora. Whereas the fossil biota has received considerable attention, only a few studies have focused on the sedimentary characteristics and palaeoenvironmental conditions which prevailed during formation of the Crato Fossil Lagerstatte. The Nova Olinda Member represents the lowermost and thickest unit (up to 10 m) of the Crato Formation and is characterized by a pronounced rhythmically bedded, pale to dark lamination. To obtain information on palaeoenvironmental conditions, sample slabs derived from three local stratigraphic sections within the Araripe Basin were studied using high-resolution multiproxy techniques including detailed logging, petrography, μ-XRF scanning and stable isotope geochemistry. Integration of lithological and petrographic evidence indicates that the bulk of the Nova Olinda limestone formed via authigenic precipitation of calcite from within the upper water column, most probably induced and/or mediated by phytoplankton and picoplankton activity. A significant contribution from a benthonic, carbonate-secreting microbial mat community is not supported by these results. Deposition took place under anoxic and, at least during certain episodes, hypersaline bottom water conditions, as evidenced by the virtually undisturbed lamination pattern, the absence of a benthonic fauna and by the occurrence of halite pseudomorphs. Input of allochthonous, catchment-derived siliciclastics to the basin during times of laminite formation was strongly reduced. The δ18O values of authigenic carbonate precipitates (between −7·1 and −5·1‰) point to a 18O-poor meteoric water source and support a continental freshwater setting for the Nova Olinda Member. The δ13C values, which are comparatively rich in 13C (between −0·1 and +1·9‰), are interpreted to reflect reduced throughflow of water in a restricted basin, promoting equilibration with atmospheric CO2, probably in concert with stagnant conditions and low input of soil-derived carbon. Integration of lithological and isotopic evidence indicates a shift from closed to semi-closed conditions towards a more open lake system during the onset of laminite deposition in the Crato Formation.

Vertical structure of tidal current in a typically coastal raft-culture area

In this paper vertical structure of tidal current in a typically coastal raft-culture area is discussed by field measurement and a numerical model. The observations show that the vertical structure changed dramatically. A tidal surface boundary layer (SBL) is well formed due to the frictional effects induced by extensive, high-density suspended culture as surface obstruction. Both the aquaculture drag and the bottom friction are much higher than those in non-raft-culture areas, and show an obvious variation with tidal flow. The significant earlier ebbing and earlier flooding appear in the upper water column instead of the seabed. And the maximal phase lag is about 1 h within one tide cycle. A 1D hydrodynamic model was modified to include the SBL and parameterized with the field data. It replicated the observed velocity profile and was then used to investigate the impacts of varying culture density and bottom friction on the vertical tidal-current structure. Modeling results indicate that the surface current velocity was largely damped because culture activities enhanced the frictional effects on flow intensively. The magnitude and vertical structure of tidal current are determined together with aquaculture drag and bottom friction. In addition, the vertical velocity structure has a nonlinear trend along with culture density and bottom friction. This study is a theoretical foundation for optimizing aquaculture configuration through regulating culture density and species distribution.

Acoustic scattering in the coastal ocean at Monterey Bay, CA, USA: Fine-scale vertical structures

Fine-structure (centimeters to meters) in vertical profiles of acoustic volume scattering strength is a common and ecologically significant characteristic of the coastal marine water column. The processes that create these structures modify the availability of food and exposure to predation for secondary producers at and below spatial and temporal scales that characterize their daily ambits. Thin acoustic scattering layers may persist for weeks at a particular coastal location, but they may also appear and disappear in only a few hours. These layers are usually evidence of mesozooplankton and micronekton having aggregated at peaks, gradients, or boundaries in the vertical distribution of various water column properties that characterize a marine ecosystem. The behaviors of both predators and prey are implicated in the generation of complex, time-dependent patterns of fine-structure. Specifically, diel vertical migration to layers of prey, isolumes, isotherms, isopycnals, or chemoclines can be responsible for the nighttime formation of thin acoustic layers. Physical processes such as horizontal shear, internal waves, water mass intrusions, tidal forcing, wind mixing of the upper water column, and horizontal advection modify acoustic scattering patterns by changing the vertical distributions of organisms that scatter sound.

Transparent exopolymer particles (TEP) link phytoplankton and bacterial production in the Gulf of Aqaba

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 56:217-225 (2009) - DOI: https://doi.org/10.3354/ame01322 AME Special: 'Progress and perspectives in aquatic primary productivity: highlights of the GAP VIII workshop, Eilat, Israel, 2008' Transparent exopolymer particles (TEP) link phytoplankton and bacterial production in the Gulf of Aqaba Edo Bar-Zeev1,*, Ilana Berman-Frank1, Noga Stambler1,2, Evaristo Vázquez Domínguez3, Tamar Zohary4, Elisa Capuzzo5, Efrat Meeder6,7, David J. Suggett8, David Iluz1,2, Gal Dishon1, Tom Berman4 1The Mina & Everard Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan 52900, Israel 2Department of Geography and Environment, Bar-Ilan University, Ramat-Gan 52900, Israel 3CSIC, Institut de Ciències del Mar, Passeig Marítim de la Barceloneta, 39-43, 08003 Barcelona, Spain 4Israel Oceanographic and Limnological Research, The Yigal Allon Kinneret Limnological Laboratory, Tiberias 14102, Israel 5School of Life Sciences, Napier University, Edinburgh EH10 5DT, UK 6The Interuniversity Institute for Marine Sciences Coral Beach, POB 469, 88103 Eilat, Israel 7Institute of Earth Sciences, The Hebrew University Edmond J. Safra Campus, Jerusalem 91904, Israel 8Department of Biological Sciences, University of Essex, Colchester CO4 3SQ, UK *Email: liquidoni@gmail.com ABSTRACT: Variations in transparent exopolymer particles (TEP), bacterial biomass production (BP) and primary productivity (PP) were followed over 52 h at a deep water station in the Gulf of Aqaba (Eilat, Israel) during the spring, in April 2008. About 20 h after the start of the study, there was a short (~15 h) but intense storm event that probably caused a nutrient pulse and, subsequently, a brief outgrowth of diatoms in the euphotic layer. Concentrations of TEP and BP ranged from 23 to 228 µg gum xanthan equivalents l–1 and from 0.2 to 0.6 µg C l–1 h–1, respectively. Concentrations of TEP and BP were measured in unfiltered and in GF/C (1.2 µm)-prefiltered samples. Most of the TEP (59 ± 21% of total TEP, mean ± SD) were in the smaller (GF/C-filtered) size fraction (0.4–1.2 µm); however, after the crash of the diatom bloom, the majority of TEP were in the >1.2 µm size fraction. In the GF/C-filtered fraction, BP averaged 59 ± 12% and 93 ± 5% of total BP in the upper water column and from 300 m, respectively. Significant correlations were observed between TEP and BP, suggesting that active heterotrophic bacteria may have been associated with these particles. During the 3 d of our study, PP and BP in the euphotic zone averaged 480 and 225 mg C m–2 d–1, respectively, suggesting that about half or more of the primary produced carbon was metabolized by heterotrophic bacteria in the upper water column. Coincident with strong mixing caused by the storm, TEP concentrations decreased in the surface water and increased at depth. We suggest that TEP acted to link carbon flux between the primary producers and heterotrophic bacteria, and that the downward movement of TEP from the upper water layers may be an important process in transferring organic carbon to deeper waters of the Gulf of Aquaba. Sinking TEP could provide not only organic carbon substrates for associated bacteria but also form ‘hot spots’ of elevated microbial metabolism and nutrient cycling throughout the water column. KEY WORDS: Transparent exopolymer particles · TEP · Bacterial productivity · Primary productivity · Carbon cycling · Size fractionation · Gulf of Aqaba Full text in pdf format PreviousNextCite this article as: Bar-Zeev E, Berman-Frank I, Stambler N, Vázquez Domínguez E and others (2009) Transparent exopolymer particles (TEP) link phytoplankton and bacterial production in the Gulf of Aqaba. Aquat Microb Ecol 56:217-225. https://doi.org/10.3354/ame01322Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 56, No. 2-3. Online publication date: September 03, 2009 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2009 Inter-Research.

Nd/Ca ratios in plankton‐towed and core top foraminifera: Confirmation of the water column acquisition of Nd

Planktic foraminifera have been used as recorders of the neodymium (Nd) isotopic composition of seawater, although there is still controversy over the precise provenance of the Nd signal. We present an extensive, multispecific plankton tow Nd/Ca data set from several geographic locations (SE Atlantic, NE Atlantic, Norwegian Sea, and western Mediterranean), together with core top samples from the Mediterranean region. The range of Nd/Ca ratios in plankton‐towed foraminifera, cleaned only of organic material, from all regions (0.01–0.7 μmol/mol), is similar to previously published analyses of sedimentary foraminifera cleaned using both oxidative and reductive steps, with distribution coefficients (Kd) ranging between 4 and 302. For the Mediterranean, where core top and plankton tow data are both available, the range for plankton tows (0.05–0.7 μmol/mol) is essentially identical to that for the core tops (0.1–0.5 μmol/mol). Readsorption of Nd during cleaning is ruled out by the fact that the plankton tow samples underwent only an oxidative cleaning process. We find a relationship between manganese (Mn) and Nd in plankton tow samples that is mirrored by a similar correlation in core top samples. This relationship suggests that Fe‐Mn coatings are of negligible importance to the Nd budgets of foraminifera as the Nd/Mn ratio it implies is over an order of magnitude greater than that seen in other Fe‐Mn oxide phases. Rather, since both plankton tows and core tops present a similar behavior, the Nd/Mn relationship must originate in the upper water column. The data are consistent with the acquisition of Nd and Mn from the water column by binding to organic material and the fact that intratest organic material is shielded from both aggressive cleaning and diagenetic processes. Collectively, the results help to explain two abiding puzzles about Nd in sedimentary planktic foraminifera: their high REE contents and the fact that they record a surface water Nd isotopic signal, regardless of the cleaning procedure used.

Behavior of particulate materials during iron fertilization experiments in the Western Subarctic Pacific (SEEDS and SEEDS II)

Abstract During two mesoscale iron-enrichment studies in the northwestern subarctic Pacific (SEEDS in 2001 summer and SEEDS II in 2004 summer), particulate materials from the iron-induced phytoplankton bloom in the upper water column were monitored to analyze the export processes beneath the upper mixed layer, mainly with drifting sediment traps. We could not observe the total downward export process of the high accumulation of particulate organic carbon from the mixed layer induced by the large diatom bloom of SEEDS [e.g., Tsuda, A., Takeda, S., Saito, H., Nishioka, J., Nojiri, Y., Kudo, I., Kiyosawa, H., Shiomoto, A., Imai, K., Ono, T., Shimamoto, A., Tsumune, D., Yoshimura, T., Aono, T., Hinuma, A., Kinugasa, M., Suzuki, K., Sohrin, Y., Noiri, Y., Tani, H., Deguchi, Y., Tsurushima, N., Ogawa, H., Fukami, K., Kuma, K., Saino, T., 2003. A mesoscale iron enrichment in the western subarctic Pacific induces large centric diatom bloom. Science 300, 958–961] because the 2-week observation period was too short to examine the decline phase of the bloom. In contrast, in SEEDS II, the particulate organic carbon and particulate organic nitrogen were accumulated 123 and 23 mmol m −2 , respectively, in the mixed layer until day-15 (days from iron-enrichment), and then ca. 90% were removed from the mixed layer by day-25. The sediment traps at 40 m depth between day-15 and day-25 accounted for at least more than 35% of these particles. There was no large variation in chemical composition in settling particles above 100 m depth throughout the experimental periods both in SEEDS and SEEDS II. The content of biogenic opal remained more than 50% of all settling particles during SEEDS, while the content of biogenic calcium carbonate was relatively high, with a low biogenic opal content of consistently less than 30% during SEEDS II. These results suggest that high standing stock of seed population of diatoms before the iron fertilization, indicated by low C/Si ratio of particulate matter, is an important factor to induce the large diatom bloom in SEEDS.

The life history characteristics of the wood-boring bivalve Teredo bartschi are suited to the elevated salinity, oligotrophic circulation in the Gulf of Aqaba, Red Sea

In the Gulf of Aqaba, the slow, unidirectional surface inflow of oligotrophic waters from the Red Sea may limit the dispersal of planktotrophic larvae, thus favouring brooded over planktonic development. A site at the northern end of the Gulf was used to examine recruitment by wood borers of the family Teredinidae (Bivalvia) with brooded or planktotrophic larvae. Wood panels exposed for 4 months at depths from 6 m to 36 m became colonised by the brooding Teredo bartschi and a few individuals of the planktotrophic Bankia carinata. Driftwood at the site contained T. bartschi and the brooding isopod wood-borer Limnoria tripunctata. No significant variation in intensity of recruitment with depth was detected. The size distributions of shells within the panels were unimodal, suggesting a single period of recruitment, but shell size was negatively correlated with the degree of crowding. For T. bartschi, the length and width of pallets proved to be good predictors of shell diameter. Pallet width also defines the diameter of the siphonal opening. Across the range of animal sizes sampled, this opening tended to be larger in T. bartschi than that calculated from reported widths of Teredo navalis, a species which grows in more plankton-rich waters. Groups of larval shells, which averaged 66 μm in width, were found on the inner surface of about 7% of all adult shells investigated. They had the characteristic D outline and pitted surface of a prodissoconch I shell with or without a small amount of prodissoconch II growth. These would have resulted from a single spawning event at about the time of year that nutrient-rich waters mix into the upper water column. At Aqaba, a sink population of T. bartschi is likely to be maintained by adults rafting from the Red Sea. These observations build a picture of the life history strategy of T. bartschi: brooding with maternal rather than egg-derived nutrition; release of a non-feeding pediveliger; limited larval dispersal; rapid development of a synchronous brooding capability; dispersal by rafting as adults.

228Ra/ 226Ra and 226Ra/Ba ratios in the Western Mediterranean Sea: Barite formation and transport in the water column

226Ra, 228Ra and Ba distributions as well as 228Ra/ 226Ra and 226Ra/Ba ratios were measured in seawater, suspended and sinking particles at the DYFAMED station in the Western Mediterranean Sea at different seasons of year 2003 in order to track the build-up and fate of barite through time. The study of the 228Ra ex/ 226Ra ex ratios (Ra ex = Ra activities corrected for the lithogenic Ra) of suspended particles suggests that Ba ex (Ba ex = Ba concentrations corrected for the lithogenic Ba, mostly barite) formation takes place not only in the upper 500 m of the water column but also deeper (i.e. throughout the mesopelagic layer). Temporal changes in the 228Ra ex/ 226Ra ex ratios of sinking particles collected at 1000 m depth likely reflect changes in the relative proportion of barite originating from the upper water column (with a high 228Ra/ 226Ra ratio) and formed in the mesopelagic layer (with a low 228Ra/ 226Ra ratio). 228Ra ex/ 226Ra ex ratios measured in sinking particles collected in the 1000 m-trap in April and May suggest that barite predominantly formed in the upper water column during that period, while barite found outside the phytoplankton bloom period (February and June) appears to form deeper in the water column. Combining ratios of both the suspended and sinking particles provides information on aggregation/disaggregation processes. High 226Ra ex/Ba ex ratios were also found in suspended particles collected in the upper 500 m of the water column. Because celestite is expected to be enriched in Ra [Bernstein R. E., Byrne R. H. and Schijf J. (1998) Acantharians: a missing link in the oceanic biogeochemistry of barium. Deep-Sea Res. II 45, 491–505], acantharian skeletons may contribute to these high ratios in shallow waters. The formation of both acantharian skeletons and barite enriched in 226Ra may thus contribute to the decrease in the dissolved 226Ra activity and 226Ra/Ba ratios of surface waters observed between February and June 2003 at the DYFAMED station.

Eddy overturning across a shelf edge front: Kongsfjorden, west Spitsbergen

Eddy overturning across a shelf edge front has been investigated in a simplified model setup comprising an along‐slope uniform shelf and slope with a slope current. Results from three model runs are presented, each initiated with and nudged toward a sharp shelf edge front in temperature, salinity, density, and velocity. Data collected off Kongsfjorden at Spitsbergen were used for initiating the model runs. Three distinctly different density fronts were used to initialize the model runs, one with a negative cross‐frontal density gradient toward the shelf, one with a positive density gradient, and one with a combination of negative density gradient in the upper water column and a positive in the lower water column. The model results indicate that the initial cross‐frontal density gradients determine the eddy overturning direction, acting toward flattened or terrain‐following isopycnals. The steady state modeled fronts resemble quite well the observed front structures, as well as temperature and salinity fields. This indicates that eddy overturning plays an important role in cross‐frontal exchange of water masses along the shelf edge front off west Spitsbergen. The Eulerian mean cross‐slope flow is close to zero, and the corresponding fluxes do not describe the correct vertical distribution.