Distinct Water Masses Research Articles

The landscape genetics of yellow perch (Perca flavescens) in a large fluvial ecosystem

Landscape genetics is being increasingly applied to elucidate the role of environmental features on the population structure of terrestrial organisms. However, the potential of this framework has been little explored in aquatic ecosystems such as large rivers. Here, we used a landscape genetics approach in order to (i) document the population structure of the yellow perch (Perca flavescens) by means of genetic variation at microsatellite markers, (ii) assess to what extent the structure was explained by landscape heterogeneity, and (iii) interpret the relevance of interactions between genetics and landscape for management and conservation. Analysis of the genetic variation among 1715 individuals from 16 localities and distributed over 310 km in the freshwater section of the Saint Lawrence River (Québec, Canada) revealed a relatively modest level of genetic structuring (F(ST) = 0.039). Application of the Monmonier's algorithm combining geographical and genetic information identified three zones of restricted gene flow defining four distinct populations. Physical barriers played a more important role on gene flow and genetic structure than waterway geographical distance. We found correlations between genetic differentiation and presence of distinct water masses in the sector of Lake Saint-Louis (r = 0.7177, P = 0.0340) and with fragmentation of spawning habitats in the sector of Lake Saint-Pierre (r = 0.8578, P = 0.0095). Our results support the treatment of four distinct biological units, which is in contrast with the current basis for yellow perch management. Finally, this study showed that landscape genetics is a powerful means to identify environmental barriers to gene flow causing genetic discontinuities in apparently highly connected aquatic landscapes.

Spatial and seasonal patterns in water quality in an embayment-mainstem reach of the tidal freshwater Potomac River, USA: a multiyear study

Spatial and temporal patterns in water quality were studied for seven years within an embayment-river mainstem area of the tidal freshwater Potomac River. The purpose of this paper is to determine the important components of spatial and temporal variation in water quality in this study area to facilitate an understanding of management impacts and allow the most effective use of future monitoring resources. The study area received treated sewage effluent and freshwater inflow from direct tributary inputs into the shallow embayment as well as upriver sources in the mainstem. Depth variations were determined to be detectable, but minimal due mainly to the influence of tidal mixing. Results of principal component analysis of two independent water quality datasets revealed clear spatial and seasonal patterns. Interannual variation was generally minimal despite substantial variations in tributary and mainstem discharge among years. Since both spatial and seasonal components were important, data were segmented by season to best determine the spatial pattern. A clear difference was found between a set of stations located within one embayment (Gunston Cove) and a second set in the nearby Potomac mainstem. Parameters most highly correlated with differences were those typically associated with higher densities of phytoplankton: chlorophyll a, photosynthetic rate, pH, dissolved oxygen, BOD, total phosphorus and Secchi depth. These differences and their consistency indicated two distinct water masses: one in the cove harboring higher algal density and activity and a second in the river with lower phytoplankton activity. A second embayment not receiving sewage effluent generally had an intermediate position. While this was the most consistent spatial pattern, there were two others of a secondary nature. Stations closer to the effluent inputs in the embayment sometimes grouped separately due to elevated ammonia and chloride. Stations closer to tributary inflows into the embayment sometimes grouped separately due to dilution with freshwater runoff. Segmenting the datasets by spatial region resulted in a clarification of seasonal patterns with similar factors relating to algal activity being the major correlates of the seasonal pattern. A basic seasonal pattern of lower scores in the spring increasing steadily to a peak in July and August followed by a steady decline through the fall was observed in the cove. In the river, the pattern of increases tended to be delayed slightly in the spring. Results indicate that the study area can be effectively monitored with fewer study sites provided that at least one is located in each of the spatial regions.

Summer phytoplankton pigments and community composition related to water mass properties in the Gulf of Gabes

Variations in phytoplankton pigments and community composition were examined in the Gulf of Gabes in relationship to water mass properties, characterised by the influence of the Modified Atlantic Water and by the thermal stratification. Data were collected on board the R/V Hannibal during July 2005. Distinct water masses were identified using cluster analysis of temperature–salinity ( T– S) characteristics. Three major clusters appeared based on the combined effects of temperature and salinity. The first cluster was identified as the cool and less salty bottom Modified Atlantic Water (MAW). The warmer and saltier Mediterranean Mixed Water (MMW) represented the second cluster. The third cluster was the Transition Water (TW) separating the two previous clusters. The pigment and taxonomic composition of these water masses were examined. Chlorophyll a was rather low (<200 ng l −1). Chlorophyll b was generally the most abundant accessory pigment and fucoxanthin dominated the accessory pigments in the MAW. Proportions of chlorophyll a associated with different phytoplankton classes were estimated using CHEMTAX software, and did not present significant variations among water groups. The results pointed out variations in the relative contribution of each phytoplankton taxa in each station group. Chlorophytes and prasinophytes accounted for 65% of chlorophyll a in the MMW. Diatoms and chlorophytes were relatively abundant in the MAW contributing to almost 63% of chlorophyll a. An unstructured community, slightly dominated by prasinophytes, chlorophytes and cryptophytes, characterised the TW. Different trophic statuses were observed in these water masses, the MMW and the MAW being characterised by mesotrophy, while an oligotrophy was observed in the TW. Nutrient availability, particularly the P-limitation supported by the summer stratification, as revealed by the high N:P ratio (greater than 20), seems to enhance the development of small-sized phytoplankton, thereby supporting the regenerated production.

Invertebrate communities and epiphytic biomass associated with metaphyton and emergent and submerged macrophytes in a large river

The contribution of metaphyton and submerged and emergent macrophytes as support to phytophilous organisms was compared from the standpoint of epiphytic chlorophyll and of invertebrate biomass, taxonomic composition and size distribution. This study was carried out in a fluvial lake of the St. Lawrence River (Lac Saint-Pierre, Quebec) at 5 sites with chemically and physically distinct water masses. Invertebrate and epiphyton biomass were consistently higher in complex filamentous mats (overall mean: 61 ± 5 [SE] mg and 124 ± 18 μg Chl a /g vegetation dry mass, respectively) and submerged plants (overall mean: 48 ± 7 mg and 195 ± 56 μg Chl a /g vegetation d.m.) than in the simple emergent stems (overall mean: 4 ± 1 mg and 45 ± 15 μg Chl a /g vegetation d.m.). Taxonomic composition of the invertebrate communities varied largely among types of vegetation and sites. Sampling site (and hence water physical and chemical characteristics) explained a larger fraction of the variation in invertebrate composition (28%) than vegetation type (9%). Overall, metaphyton hosted an invertebrate fauna more abundant and more diverse, with larger organisms and more semi-aquatic taxa, than that of nearby vascular macrophytes. However, at the scale of this river segment (~ 300 km2), metaphyton contributed < 1% to total phytophilous invertebrate biomass compared to 96% and 4% for submerged and emergent plants, respectively. In the river trophic network, vascular plants thus appear to support the bulk of the food supply, which is periodically enriched and diversified by the appearance of metaphyton blooms.

Stable isotopes document seasonal changes in trophic niches and winter foraging individual specialization in diving predators from the Southern Ocean

1. Climatic variation outside the breeding season affects fluctuations in population numbers of seabirds and marine mammals. A challenge in identifying the underlying biological mechanisms is the lack of information on their foraging strategies during winter, when individuals migrate far from their breeding grounds. 2. We investigated the temporal variability in resource partitioning within the guild of five sympatric Subantarctic penguins and fur seals from Crozet Islands. The stable isotopic ratios of carbon (delta(13)C) and nitrogen (delta(15)N) for whole blood were measured for penguins and fur seals, as were the isotopic ratios for penguin nails and food. Animals were sampled at two periods, during breeding in summer and at their arrival in the colonies in spring (hereafter winter, since the temporal integration of blood amounting to several months). 3. In summer, delta(13)C and delta(15)N for blood samples defined three foraging areas and two trophic levels, respectively, characterizing four nonoverlapping trophic niches. King penguins and female Antarctic and Subantarctic fur seals are myctophid eaters foraging in distinct water masses, while both macaroni and rockhopper penguins had identical isotopic signatures indicating feeding on crustaceans near the archipelago. 4. Isotopic ratios were almost identical in summer and winter suggesting no major changes in the species niches, and hence, in the trophic structure of the guild during the nonbreeding period. A seasonal difference, however, was the larger variances in delta(13)C (and also to a lesser extent in delta(15)N) values in winter, thus verifying our hypothesis that trophic niches widen when individuals are no longer central place foragers. 5. Winter isotopic ratios of macaroni penguins and male Antarctic fur seals had large variances, indicating individual foraging specializations. The range of delta(13)C and delta(15)N values of male fur seals showed, respectively, that they dispersed over a wide latitudinal gradient (from Antarctica to north of the archipelago) and fed on different prey (crustaceans and fish). 6. By comparing summer and winter isotopic ratios and examining the summer diet, we highlight the feeding habits of marine predators that were not previously addressed. The findings have a number of implications for understanding the functioning of the pelagic ecosystem and on the demography of these species.

Is Interleaving in the Agulhas Current Driven by Near-Inertial Velocity Perturbations?

Abstract Recent observations taken at a number of latitudes in the Agulhas Current reveal that the water mass structure on either side of its dynamical core is distinctly different. Moreover, interleaving of these distinct water masses is observed at over 80% of the stations occupied in the current, particularly within the subsurface density layer between tropical surface water and subtropical surface water masses, and within the intermediate layer between the Antarctic Intermediate Water and Red Sea water masses. Direct velocity measurements allow for a comparison between the characteristic vertical length scales of the Agulhas intrusions and those of velocity perturbations found throughout the current. It is found that the interleaving scales match those of the velocity perturbations, which are manifest as high-wavenumber vertical shear layers and are identified as near-inertial oscillations. Furthermore, the properties of the intrusions indicate that double diffusion is not an important process in their development: they are generally not associated with a density anomaly, their slope and thickness fall outside the predicted maxima for instability, and a strong horizontal shear field acts to separate water parcels more quickly than intrusions would be able to grow by double-diffusive processes. Instead, the position, thickness, and slope of Agulhas intrusions relative to the background salinity and density field suggest that they are forced by rotating inertial velocities, with subsequent growth possibly driven by small-scale baroclinic instabilities. However, not all the evidence points conclusively toward advectively driven intrusions. For instance, there is a discrepancy between the observed salinity anomaly amplitude and the predicted inertial displacement given the background salinity gradient, which deserves further examination. Hence, there is a future need for more pointed observations and perhaps the development of an analytical or numerical model to understand the exact nature of Agulhas intrusions.

Sponge-specific Bacterial Associations of the Mediterranean Sponge Chondrilla nucula (Demospongiae, Tetractinomorpha)

A stable and specific bacterial community was shown to be associated with the Mediterranean sponge Chondrilla nucula. The associated bacterial communities were demonstrated to be highly similar for all studied specimens regardless of sampling time and geographical region. In addition, analysis of 16S rDNA clone libraries revealed three constantly C. nucula-associated bacterial phylotypes belonging to the Acidobacteria, the Gamma- and Deltaproteobacteria present in sponge specimens from two Mediterranean regions with distinct water masses (Ligurian Sea and Adriatic Sea). For the first time, candidate division TM7 bacteria were found in marine sponges. A major part (79%) of the C. nucula-derived 16S rDNA sequences were closely related to other sponge-associated bacteria. Phylogenetic analysis identified 14 16S rRNA gene sequence clusters, seven of which consisted of exclusively sponge-derived sequences, whereas the other seven clusters contained additional environmental sequences. This study adds to a growing database on the stability and variability of microbial consortia associated with marine sponges.

Global gridded data set of the oxygen isotopic composition in seawater

We present a new 3‐dimensional 1° × 1° gridded data set for the annual mean seawater oxygen isotope ratio (δ18O) to use in oceanographic and paleoceanographic applications. It is constructed from a large set of observations made over the last 50 years combined with estimates from regional δ18O to salinity relationships in areas of sparse data. We use ocean fronts and water mass tracer concentrations to help define distinct water masses over which consistent local relationships are valid. The resulting data set compares well to the GEOSECS data (where available); however, in certain regions, particularly where sea ice is present, significant seasonality may bias the results. As an example application of this data set, we use the resulting surface δ18O as a boundary condition for isotope‐enabled GISS ModelE to yield a more realistic comparison to the isotopic composition of precipitation data, thus quantifying the ‘source effect’ of δ18O on the isotopic composition of precipitation.

The chemostratigraphy of a Paleoproterozoic MnF- BIF succession -the Voelwater Subgroup of the Transvaal Supergroup in Griqualand West, South Africa

The Paleoproterozoic Voelwater Subgroup in Griqualand West, South Africa, is an exceptionally well preserved succession of banded iron formation, braunite lutite and shallow marine limestone/dolostone. A detailed chemostratigraphic study was carried out on this succession, resulting in a comprehensive set of whole rock geochemical data, including stable isotope (δ13Ccarb, δ13Corg, δ18Ocarb) and 87Sr/86Sr isotope data. The results are in excellent agreement with previous investigations and reveal trends that correspond closely to mineralogical variations and reflect systematic changes in the depositional environment. Total inorganic carbonate contents (TIC) and δ13Ccarb values increase systematically from manganiferous iron formation at the base of the succession to dolostones that mark the top of the Voelwater Subgroup. These first order trends transgress across all lithologies and mirror the interplay of synsedimentary carbonate formation (utilizing dissolved marine bicarbonate), and Fe-Mn-rich carbonate formation during suboxic early diagenesis. First order trends are modulated by second order variations associated with lithological changes in the lower portion of the Voelwater Subgroup, constituted by three symmetrical cycles of iron formation and braunite lutite deposition. These second order trends, delineated by TIC and δ13Ccarb, as well as δ18Ocarb and major element concentrations (Mn, Fe, SiO2) can be attributed to repeated physicochemical changes in the MnF-BIF depositional environment. Variations in 87Sr/86Sr isotope composition do not relate to lithological changes. Instead, carbonate-rich and/or Sr-rich samples of MnF and BIF with well-preserved early diagenetic carbonate textures define a tight cluster with 87Sr/86Sr signatures of ~0.703 to ~0.706, in good agreement with Paleoproterozoic oceanic crust. Carbonate- and Sr-poor BIF samples with markedly more radiogenic 87Sr/86Sr signatures (~0.711 to ~0.722), in contrast, show evidence of extensive post-depositional recrystallization, apparent effects of dia- or epigenetic fluid flow. Chemostratigraphy and lithostratigraphy of the Voelwater Subgroup are in good agreement with models that predict a layered Paleoproterozoic ocean, with a hydrothermally-dominated Fe-Mn-rich deep water mass, overlain by a mass of oxygenated shallow marine water. A facies distribution model for the Voelwater Subgroup is proposed, taking into consideration not only the presence of these two isotopically distinct water masses, but also abundance and transport of organic carbon and shallow marine carbonate muds, as well as the transformation of primary iron- and manganese oxihydroxide precipitates into carbonate minerals during early suboxic diagenesis.

Diversity and Distribution of Marine Microbial Eukaryotes in the Arctic Ocean and Adjacent Seas

We analyzed microbial eukaryote diversity in perennially cold arctic marine waters by using 18S rRNA gene clone libraries. Samples were collected during concurrent oceanographic missions to opposite sides of the Arctic Ocean Basin and encompassed five distinct water masses. Two deep water Arctic Ocean sites and the convergence of the Greenland, Norwegian, and Barents Seas were sampled from 28 August to 2 September 2002. An additional sample was obtained from the Beaufort Sea (Canada) in early October 2002. The ribotypes were diverse, with different communities among sites and between the upper mixed layer and just below the halocline. Eukaryotes from the remote Canada Basin contained new phylotypes belonging to the radiolarian orders Acantharea, Polycystinea, and Taxopodida. A novel group within the photosynthetic stramenopiles was also identified. One sample closest to the interior of the Canada Basin yielded only four major taxa, and all but two of the sequences recovered belonged to the polar diatom Fragilariopsis and a radiolarian. Overall, 42% of the sequences were <98% similar to any sequences in GenBank. Moreover, 15% of these were <95% similar to previously recovered sequences, which is indicative of endemic or undersampled taxa in the North Polar environment. The cold, stable Arctic Ocean is a threatened environment, and climate change could result in significant loss of global microbial biodiversity.

Oceanographic influences on seabirds and cetaceans of the eastern tropical Pacific: A review

This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific, the oceanic region centered on the eastern Pacific warm pool, but also including the equatorial cold tongue and equatorial current system, and summarizes what is known about oceanographic influences on seabirds and cetaceans there. The eastern tropical Pacific supports on the order of 50 species of seabirds and 30 species of cetaceans as regular residents; these include four endemic species, the world’s largest populations for several others, three endemic sub-species, and a multi-species community that is relatively unique to this ecosystem. Three of the meso-scale physical features of the region are particularly significant to seabirds and cetaceans: the Costa Rica Dome for blue whales and short-beaked common dolphins, the Equatorial Front for planktivorous seabirds, and the countercurrent thermocline ridge for flocking seabirds that associate with mixed-species schools of spotted and spinner dolphins and yellowfin tuna. A few qualitative studies of meso- to macro-scale distribution patterns have indicated that some seabirds and cetaceans have species-specific preferences for surface currents. More common are associations with distinct water masses; these relationships have been quantified for a number of species using several different analytical methods. The mechanisms underlying tropical species–habitat relationships are not well understood, in contrast to a number of higher-latitude systems. This may be due to the fact that physical variables have been used as proxies for prey abundance and distribution in species–habitat research in the eastern tropical Pacific. Though seasonal and interannual patterns tend to be complex, species–habitat relationships appear to remain relatively stable over time, and distribution patterns co-vary with patterns of preferred habitat for a number of species. The interactions between seasonal and interannual variation in oceanographic conditions with seasonal patterns in the biology of seabirds and cetaceans may account for some of the complexity in species–habitat relationship patterns. Little work has been done to investigate effects of El Niño-Southern Oscillation cycles on cetaceans, and results of the few studies focusing on oceanic seabirds are complex and not easy to interpret. Although much has been made of the detrimental effects of El Niño events on apex predators, more research is needed to understand the magnitude, and even direction, of these effects on seabirds and cetaceans in space and time.

Remarkable heterogeneity in meso- and bathypelagic bacterioplankton assemblage composition

We investigated meso- to bathypelagic (500-3,000 m) bacterioplankton assemblage composition at 19 locations in the North Atlantic Ocean beneath the offshore Amazon River plume, in the North Pacific Ocean near the Hawaiian archipelago, at the San Pedro Ocean Time Series (SPOTS) station off southern California, and in the Coral Sea off eastern Australia with a sensitive high-throughput fingerprinting approach, automated rRNA intergenic spacer analysis (ARISA), to examine variation between bacterial assemblages at different stations. Temperature and salinity were used to identify distinct water masses within gyres. ARISA fingerprints each contained 15-117 operational taxonomic units (OTUs) per assemblage; however, the OTU composition of fingerprints varied among stations, even within the same water mass. Fingerprints from 500 m at the SPOTS station over 4 yr shared on average a Sorensen Index (proportional representation similarity) of 0.68 ± 0.01, whereas at more oceanic stations at 500 m, fingerprints shared a Sorensen Index of 0.48 ± 0.01 and a Whittaker Index of 0.38 ± 0.01. At deeper depths (1,000 and 2,000 m), fingerprints were equally variable, sharing Sorensen Indices of 0.42 ± 0.02 and 0.50 ± 0.02 and Whittaker indices of 0.33 ± 0.01 and 0.34 ± 0.03, at 1,000 m and 3,000 m, respectively. Mesopelagic, moderately productive waters were more stable than those at less productive, open-ocean gyre stations, suggesting that variability in bacterioplankton communities at depth is influenced by organic matter supply and patchiness.

The salinity front in the North Equatorial Current: A landmark for the spawning migration of the Japanese eel (Anguilla japonica) related to the stock recruitment

The North Equatorial Current (NEC) region is the only spawning area of the Japanese eel. The 2002 expedition of the R.V. Hakuho Maru indicated that the larval distribution of this species is likely related to a salinity front generated by two distinct water masses in the NEC. The cruise occurred during an El Nino event and the salinity front had moved southward by about 4° of latitude. Smaller larvae (<10 mm TL) were collected just south of the salinity front where these young larvae have never been collected in usual years. Drifters released at stations around the salinity front showed that most of them were transported into the Mindanao Current region. The southward shift of the spawning area associated with a southward movement of the salinity front may have been caused by the 2002 El Nino and would increase larval transport into the Mindanao Current region. Analyses of stable isotope ratios suggested that younger leptocephali have been living in the westward flows south of the salinity front and that their diet may change with development. These findings indicate that differences of the water masses separated by the salinity front probably help to determine the spawning location and the salinity front functions as a landmark for the spawning migration of the Japanese eel.

Microbial community composition and growth rates in the NW Pacific during spring 2002

The IOC North Pacific expedition in spring (May 2002) sailed from Osaka, Japan, to Honolulu, Hawaii, and surveyed the region from roughly 22 to 50°N and 147°E to 158°W. Nine stations were chosen to characterize three distinct water masses, as well as their boundary regions: the Kuroshio Current, the North Pacific subarctic gyre, and the North Pacific subtropical gyre. Grazing largely balanced growth at all stations, with an average net growth rate of 0.11 ± 0.16 d−1 (cell‐based) and 0.06 ± 0.15 d−1 (chlorophyll‐based). The stations could be distinguished, however, by phytoplankton community composition and growth response to nutrient additions (ammonium, phosphate, manganese, and iron). Nutrients were undetectable in surface waters of the Kuroshio Current, where a centric diatom‐dominated bloom showed a significant growth response to added nutrients. Iron limitation was observed for the cyanobacteria Synechococcus at the two subarctic gyre stations; however, the photosynthetic eukaryotes, which dominated the photosynthetic biomass at these stations, were not nutrient‐limited. Four oligotrophic subtropical gyre stations were dominated by photosynthetic bacteria (Prochlorococcus and Synechococcus) and small (&lt;5 μm) eukaryotic autotrophs, which exhibited a dramatic increase in growth rate with macronutrient additions but displayed little or no increased growth with iron additions alone. Overall, the ratio of heterotroph consumer biomass to autotroph biomass was higher in the Prochlorococcus‐dominated subtropical gyre sites (0.5) than the subarctic or Kuroshio Current sites (0.2–0.3).

Acquisition of the neodymium isotopic composition of the North Atlantic Deep Water

The North Atlantic Deep Water (NADW) neodymium isotopic composition (Nd IC) is increasingly used in oceanography and paleoceanography to trace large‐scale circulation and weathering processes, notably to investigate past variations of the global thermohaline circulation. Although the present‐day NADW Nd IC is well characterized at ɛNd = −13.5, the acquisition of this isotopic signature (in other words, the causes of this value) has so far been very sparsely documented. Such an understanding is, however, fundamental to the interpretation of paleo records. Nd IC and rare earth element concentrations were measured at 9 stations within the North Atlantic Subpolar Gyre (SIGNATURE cruise, summer 1999). The comparison of this data set with our understanding of water mass circulation provides a description of how the three layers constituting the NADW, the Labrador Sea Water (LSW, ɛNd = −13.9 ± 0.4), North East Atlantic Deep Water (NEADW, ɛNd −13.2 ± 0.4), and North West Atlantic Bottom Water (NWABW, ɛNd −14.5 ± 0.4), acquire their Nd IC through distinct water mass mixings and lithogenic inputs. These different mechanisms, acting upon water masses from very diverse sources, seem to bring the Nd IC of the three NADW layers to values close together and similar to that of the NADW. It is suggested that sediment/seawater interactions significantly lower the NEADW and NWABW Nd IC along the South East Greenland margin. Since these interactions do not significantly modify the Nd content of these water masses, sediment remobilizations leading to the Nd IC variations are probably associated with Nd removal fluxes from the water mass toward the sediment, a process called boundary exchange. On the other hand, LSW seems to acquire its Nd IC from the Subpolar Mode Waters from which it is formed by deep convection, and no other mechanism needs to be invoked. Its unradiogenic signature could ultimately be linked to fresh water runoff from the Canadian Shield. These conclusions should allow more precise interpretations of paleoceanographic Nd IC records, taking into account the distinct histories of the three NADW layers, including distinct water mass mixings and distinct lithogenic inputs.

Analysis of Recharge‐Induced Geochemical Change in a Contaminated Aquifer

Recharge events that deliver electron acceptors such as O2, NO3, SO4, and Fe3+ to anaerobic, contaminated aquifers are likely important for natural attenuation processes. However, the specific influence of recharge on (bio)geochemical processes in ground water systems is not well understood. The impact of a moderate-sized recharge event on ground water chemistry was evaluated at a shallow, sandy aquifer contaminated with waste fuels and chlorinated solvents. Multivariate statistical analyses coupled with three-dimensional visualization were used to analyze ground water chemistry data (including redox indicators, major ions, and physical parameters) to reveal associations between chemical parameters and to infer processes within the ground water plume. Factor analysis indicated that dominant chemical associations and their interpreted processes (anaerobic and aerobic microbial processes, mineral precipitation/dissolution, and temperature effects) did not change significantly after the spring recharge event of 2000. However, the relative importance of each of these processes within the plume changed. After the recharge event, the overall importance of aerobic processes increased from the fourth to the second most important factor, representing the variability within the data set. The anaerobic signatures became more complex, suggesting that zones with multiple terminal electron-accepting processes (TEAPs) likely occur in the same water mass. Three-dimensional visualization of well clusters showed that water samples with similar chemical associations occurred in distinct water masses within the aquifer. Water mass distinctions were not based on dominant TEAPs, suggesting that the recharge effects on TEAPs occurred primarily at the interface between infiltrating recharge water and the aquifer.

Upper Ordovician (Mohawkian) carbon isotope (δ 13C) stratigraphy in eastern and central North America: Regional expression of a perturbation of the global carbon cycle

The Guttenberg carbon isotope excursion (GICE) documented from eastern North America demonstrates the effects that regional, geochemically distinct water masses, upwelling, and ocean circulation have on the carbon isotope record from carbonate platforms. Late Turinian–Chatfieldian carbonates from Oklahoma, Kentucky, Virginia, and West Virginia record a positive carbon isotope excursion (≥ + 3.0‰), the GICE excursion. The GICE excursion has relations to established biostratigraphy (beginning in the North American Midcontinent Phragmodus undatus Conodont Zone and continuing through the Plectodina tenuis Zone), sequence, and event stratigraphy. Previously established models for positive carbon isotope shifts on carbonate platforms have been tested during the GICE excursion, where geochemically distinct water masses are defined for the Upper Ordovician. A major eustatic sea-level rise before the GICE promoted a greater exchange of open ocean waters onto the carbonate platform of Laurentia; however, restricted or sluggish circulation and exchange between water masses within the epeiric seas and the adjacent Iapetus Ocean were still apparent. Local variations documented in the GICE excursion are directly related to upwelling of nutrient rich isotopically light waters, increased primary productivity, and the subsequent organic carbon production and burial.

Coccolithophore assemblages and morphotypes of Emiliania huxleyi in the boundary zone between the cold Oyashio and warm Kuroshio currents off the coast of Japan

Living coccolithophore assemblages were studied off the Japanese coast in the boundary zone between the cold Oyashio and the warm Kuroshio Currents as well as in adjacent water masses. A total of 64 coccolithophore taxa were identified. Ten taxa that comprised more than 10% of at least one sample were designated major taxa. Morphological observations and morphometric measurements enabled us to sub-divide the Emiliania huxleyi into four morphotypes: Type A, Type B, Type B/C, and Type B/C-2. Based on the composition of major taxa and morphotypes of Emiliania huxleyi, four coccolithophore assemblages were recognized, corresponding to distinct water masses: Oyashio Current, Tsugaru Warm Current, Kuroshio Current, and Western North Pacific Central Water (WNPCW). In the Oyashio Current regime, the standing crop of coccolithophores was high, although diversity was low. The floral assemblage was dominated by E. huxleyi Type B and consistently contained Coccolithus pelagicus ssp. pelagicus HOL, Calciopappus caudatus, and Syracosphaera orbiculus. In the Tsugaru Warm Current regime, the flora was characterized by abundant E. huxleyi Type B/C-2 and Gephyrocapsa oceanica as well as by relatively common Braarudosphaera bigelowii. In the Kuroshio Current regime, E. huxleyi Type A, Gephyrocapsa ericsonii, or G. oceanica were abundant. The coccolithophore flora in the WNPCW was characterized by abundant E. huxleyi Type A, Discosphaera tubifera, and Umbellosphaera tenuis Type IV. Large Emiliania huxleyi specimens (≥4.2 μm in length) only occurred north of the Oyashio Front, while to the south, E. huxleyi were consistently ≤4.1 μm long, regardless of the morphotype. Large E. huxleyi can be a useful paleoenvironmental indicator for reconstructing past migrations of the Kuroshio and Oyashio Currents in the North Pacific Ocean.

Glacial water mass geometry and the distribution of δ13C of ΣCO2 in the western Atlantic Ocean

Oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa Cibicidoides and Planulina from 25 new piston cores, gravity cores, and multicores from the Brazil margin. The cores span water depths from about 400 to 3000 m and intersect the major water masses in this region. These new data fill a critical gap in the South Atlantic Ocean and provide the motivation for updating the classic glacial western Atlantic δ13C transect of Duplessy et al. (1988). The distribution of δ13C of ΣCO2 requires the presence of three distinct water masses in the glacial Atlantic Ocean: a shallow (∼1000 m), southern source water mass with an end‐member δ13C value of about 0.3–0.5‰ VPDB, a middepth (∼1500 m), northern source water mass with an end‐member value of about 1.5‰, and a deep (&gt;2000 m), southern source water with an end‐member value of less than −0.2‰, and perhaps as low as the −0.9‰ values observed in the South Atlantic sector of the Southern Ocean (Ninnemann and Charles, 2002). The origins of the water masses are supported by the meridional gradients in benthic foraminiferal δ18O. A revised glacial section of deep water δ13C documents the positions and gradients among these end‐member intermediate and deep water masses. The large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation.

The partitioning of zinc, manganese, cadmium and selenium within copepods in oceanic waters east of New Zealand

The partitioning of Zn, Mn, Cd and Se within mesozooplankton, mainly calanoid copepods, is reported for two geographically close but biogeochemically distinct water masses (subtropical (ST) and subantarctic (SA) waters) during a transect east of New Zealand in austral spring 1997. Particular attention was paid to avoiding sample contamination during collection, handling and chemical analysis by using trace metal clean techniques. Mesozooplankton underwent a sequential chemical leaching scheme to determine the degree and type of elemental associations within labile and refractory tissues. All four elements showed a positive correlation with the phosphorus content of each fraction indicating a consistent relationship to the amount of tissue dissolved in each fraction. Ratios of Cd : P and Zn : P in samples from SA waters were over twice those in ST waters. However, no significant differences were found between Mn : P and Se : P ratios for samples from the two water masses.