Upper-water Column Research Articles

Comparative genomics of two ecotypes of the marine planktonic copiotroph Alteromonas macleodii suggests alternative lifestyles associated with different kinds of particulate organic matter

Alteromonas macleodii is a common marine heterotrophic gamma-proteobacterium. Isolates from this microbe cluster by molecular analysis into two major genotypic groups or ecotypes, one found in temperate latitudes in the upper water column and another that is for the most part found in the deep water column of the Mediterranean. Here, we describe the genome of one strain of the 'deep ecotype' (AltDE) isolated from 1000 m in the Eastern Mediterranean and compare this genome with that of the type strain ATCC 27126, a representative of the global 'surface' ecotype. The genomes are substantially different with DNA sequence similarity values that are borderline for microbes belonging to the same species, and a large differential gene content, mainly found in islands larger than 20 kbp, that also recruit poorly to the Global Ocean Sampling project (GOS). These genomic differences indicate that AltDE is probably better suited to microaerophilic conditions and for the degradation of recalcitrant compounds such as urea. These, together with other features, and the distribution of this genotypic group, indicate that this microbe colonizes relatively large particles that sink rapidly to meso and bathypelagic depths. The genome of ATCC 27126 on the other hand has more potential for regulation (two component systems) and degrades more sugars and amino acids, which is consistent with a more transient particle attachment, as would be expected for lineages specialized in colonizing smaller particulate organic matter with much slower sinking rates. The genomic data are also consistent with a picture of incipient speciation driven by niche specialization.

Evolution of the Irminger and East Icelandic Current systems through the Holocene, revealed by diatom-based sea surface temperature reconstructions

Sediment core MD99-2269, from the northern shelf of Iceland, has been studied to assess the stability of the East Icelandic–Irminger Current system during the Holocene. The 25.4 m long Holocene section was studied with a 40 years average resolution. The chronology is based on the combination of 24 14C AMS dates and two tephra layers. Diatoms are utilized to quantify the development and variability of the August sea surface temperature (SST) for the last 11.5 cal kyr BP. Three different transfer function methods have been used to reconstruct August SST at the site: weighted average-partial least squares (WA-PLS), maximum likelihood (ML) and Imbrie and Kipp (I&K). The combined use of the three methods allows the August SST reconstruction with a higher confidence level than with using only one statistical technique. These three reconstructions generate very similar August SST trends through the Holocene. The onset of the Holocene climate optimum is characterized at the site by a rapid August SST increase at 10.4 cal kyr BP of almost 4 °C. The Holocene climate optimum is recorded between 10.4 and 4.7 cal kyr BP. The August SSTs were around 2 °C warmer during the major part of the Holocene compared with the August SSTs for the later half of the Holocene. Combining the diatom record with the benthic foraminifera records from the same core enables us to reconstruct the evolution of both surface and bottom water masses during the Holocene. This reconstruction shows dominance of the Arctic waters throughout the water column at the onset of the Holocene, and subsequent increase of the influence of the Atlantic water, especially during the Holocene climate optimum. This strong dominance of Atlantic water tends to decrease between 4.7 and 2.2 cal kyr BP, especially in the upper part of the water column. Since 2.2 cal kyr BP the trend is reversed, suggesting an increased influence of Atlantic water at least in the upper water column.

Particle export from the euphotic zone: Estimates using a novel drifting sediment trap, 234Th and new production

We describe the first results obtained using a novel free-drifting neutrally buoyant sediment trap called PELAGRA (Particle Export measurement using a LAGRAngian trap). The trap uses an APEX float (Autonomous Profiling EXplorer) to maintain its location at a predetermined depth or density horizon and is designed to be deployed in the depth range 100–600 m for periods of up to a week. PELAGRA was deployed into a well characterised region of the Northeast (NE) Atlantic over the Porcupine Abyssal Plain (PAP) during the summers of 2003, 2004, 2005 and 2006 in post-bloom conditions. In parallel, measurements were made of total and new primary production and estimates of particle export based on 234Th deficits in the upper water column. Samples of sinking material from PELAGRA were recovered almost uncontaminated by “swimmers”. The material collected differed from that obtained using water bottles and an in situ filtration system and this indicated selective export of centric diatoms. Fluxes of 234Th into the traps were less than that calculated from the deficit of this isotope in the upper water column. It is concluded that this reflects export events that had occurred prior to these deployments. Fluxes of organic carbon into the PELAGRA traps were similar to those expected from measurements of new production in the upper mixed layer. During 2006, simultaneous PELAGRA deployments at depths of 150 and 250 m provided a direct measurement of the decrease in flux with depth. This decrease was substantially more than that predicted by the often-used “Martin equation” and yielded a “ b value” of 1.7. Using this value in the NE Atlantic about 14% of the total production reaches a depth of 150 m during the post-bloom period under nutrient limitation.

Responses of piscivorous seabirds at the Pribilof Islands to ocean climate

Climate variability and change are expected to influence the seasonal cycle in North Pacific sub-arctic marine ecosystems. The hypothesis that timing of nesting and productivity of piscivorous seabirds [kittiwakes (Rissa tridactyla and Rissa brevirostris) and murres (Uria aalge and Uria lomvia)] at the Pribilof Islands are related to variation in ocean climate as indexed by changes in sea-ice concentrations (SICs) and sea-surface temperatures (SSTs) was tested. To test this hypothesis, timing and productivity of the seabirds were correlated with the winter sea-ice extent, defined as area-averaged SICs, and with winter, spring, and summer SST near the Pribilofs over a 32-yr period, 1975–2006. Timing and productivity for the two species of kittiwake were strongly correlated with each other and between the two breeding locations, St. George and St. Paul islands. Similar results were found for the two species of murres, although kittiwakes and murres were not strongly correlated with each other. Kittiwakes bred progressively earlier, advancing their hatching dates by 0.58 to 0.88 d/yr over the study period. In contrast, there were no overall trends for murres, with the exception of thick-billed murres at St. Paul that nested progressively later, delaying breeding by 0.47 d/yr. Because of these trends, residuals from quadratic regressions were used to ‘‘detrend’’ the data (including cases where no significant trend was observed) for interannual comparisons with climate variables. Detrended kittiwake timing was inversely correlated with maximum SIC and positively correlated with winter SST. We found no strong relationships between the timing of murre nesting and SIC or SST with either raw or detrended data. Both raw and detrended data revealed a positive relationship between kittiwake productivity and SIC, and an inverse relationship with winter and spring SST. Murre productivity was correlated negatively with summer SST, but unrelated to SST in other seasons and to SIC. Timing and productivity were correlated inversely for murres and kittiwakes at both sites, but were significant only for raw (i.e. nondetrended) murre data and for detrended kittiwake data. Detrending emphasizes high-frequency (interannual) variability by suppressing low-frequency (interdecadal) variability, indicating that lowfrequency change in murre timing has an effect on productivity, whereas interannual variation is responsible for the timing–productivity relationship for kittiwakes. These contrasting responses of surface-foraging kittiwakes and deep-diving murres provide insight into how the eastern Bering Sea ecosystem is responding to climate variability and change, and suggest that the food web has changed more substantially in the upper water column than at depth. Published by Elsevier Ltd.

Interranual variability in horizontal patterns of larval fish assemblages in the northeastern Aegean Sea (eastern Mediterranean) during early summer

Larval fish community structure was studied in the northeastern Aegean Sea (NEA) over an area influenced by the advection of Black Sea water (BSW). Sampling was carried out in early summer during a period of 4 years (2003–2006). Taxonomic composition and abundance presented high variability in space that remained relatively constant among years. Tow depth and indicators of trophic conditions in the upper water column (i.e., zooplankton displacement volume, fluorescence) explained significantly the structure of larval assemblages during all surveys. The northern continental shelf (Thracian and Strymonikos shelf), where a large amount of enriched, low salinity BSW is retained, was dominated by larvae of epipelagic species, mainly anchovy ( Engraulis encrasicolus). Interannual changes in horizontal extension of the BSW seemed to match closely observed changes in the distribution of anchovy larvae. Mesopelagic fish larvae were particularly abundant beyond the continental shelf (over the North Aegean Trough) where a strong frontal structure is created between the low salinity waters of BSW origin and the high salinity waters of the Aegean Sea. Larvae of certain mesopelagic species (e.g., Ceratoscopelus maderensis) may occasionally be transported inshore when the prevailing current meanders towards the coast or feeds anticyclonic gyres over the continental shelf.

Redox sensitivity of P cycling during marine black shale formation: Dynamics of sulfidic and anoxic, non-sulfidic bottom waters

A high-resolution geochemical record of a 120 cm black shale interval deposited during the Coniacian–Santonian Oceanic Anoxic Event 3 (ODP Leg 207, Site 1261, Demerara Rise) has been constructed to provide detailed insight into rapid changes in deep ocean and sediment paleo-redox conditions. High contents of organic matter, sulfur and redox-sensitive trace metals (Cd, Mo, V, Zn), as well as continuous lamination, point to deposition under consistently oxygen-free and largely sulfidic bottom water conditions. However, rapid and cyclic changes in deep ocean redox are documented by short-term (∼15–20 ka) intervals with decreased total organic carbon (TOC), S and redox-sensitive trace metal contents, and in particular pronounced phosphorus peaks (up to 2.5 wt% P) associated with elevated Fe oxide contents. Sequential iron and phosphate extractions confirm that P is dominantly bound to iron oxides and incorporated into authigenic apatite. Preservation of this Fe–P coupling in an otherwise sulfidic depositional environment (as indicated by Fe speciation and high amounts of sulfurized organic matter) may be unexpected, and provides evidence for temporarily non-sulfidic bottom waters. However, there is no evidence for deposition under oxic conditions. Instead, sulfidic conditions were punctuated by periods of anoxic, non-sulfidic bottom waters. During these periods, phosphate was effectively scavenged during precipitation of iron (oxyhydr)oxides in the upper water column, and was subsequently deposited and largely preserved at the sea floor. After ∼15–25 ka, sulfidic bottom water conditions were re-established, leading to the initial precipitation of CdS, ZnS and pyrite. Subsequently, increasing concentrations of H 2S in the water column led to extensive formation of sulfurized organic matter, which effectively scavenged particle-reactive Mo complexes (thiomolybdates). At Site 1261, sulfidic bottom waters lasted for ∼90–100 ka, followed by another period of anoxic, non-sulfidic conditions lasting for ∼15–20 ka. The observed cyclicity at the lower end of the redox scale may have been triggered by repeated incursions of more oxygenated surface- to mid-waters from the South Atlantic resulting in a lowering of the oxic–anoxic chemocline in the water column. Alternatively, sea water sulfate might have been stripped by long-lasting high rates of sulfate reduction, removing the ultimate source for HS − production.

Dynamics of turbid buoyant plumes and the feedbacks on near‐shore biogeochemistry and physics

The near‐shore waters of the New York/New Jersey Bight in April 2005 exhibited distinct regions of turbid water with clearly differing optical properties associated with the Hudson River plume. We examined the effect of variable light attenuation on the hydrodynamics and ecological response of the Hudson River plume and its environs using field observations and a 3‐dimensional bio‐physical model. Important feedback mechanisms between the attenuation of light and the resulting impact on the mixed layer depth were revealed from the modeling results. High concentrations of chlorophyll, detritus and colored dissolved organic matter in the upper water column as a result of enhanced stratification increase the attenuation of light and modify the buoyancy driven circulation. This further impacts the growth of phytoplankton in the model and subsequently modifies the vertical profile of the attenuation coefficient, which in turn feeds back into the overall heat budget.

Ecosystem responses to short-term climate variability in the Gulf of the Farallones, California

We conducted an integrated study from physics to upper trophic-level predators in the Gulf of the Farallones, California. We hypothesized that decreased zooplankton abundance for upper trophic-level predators in the Gulf of the Farallones during 2004 and 2005 was a response to reduced upwelling-favorable winds and primary production. Based on their trophic ecology, we hypothesized that planktivorous auklets and omnivorous murres will show differential responses to upwelling variability. We examined these hypotheses by analyzing time series on oceanographic variables associated to upwelling and the biological responses at low, mid and high trophic-levels. We found that reduced upwelling-favorable wind was correlated with anomalously high SST and low chlorophyll a concentration from July 2004 to August 2005. During 2005, low chlorophyll concentrations were related to reduced krill abundance in the upper water column and decreased seabird abundance in the vicinity of the breeding colony in the study area. Decreased krill abundance was associated with late timing of nesting and reduced breeding success, with auklets showing a more pronounced response. This study shows how short-term climate variability can affect primary through tertiary productivity, and supports an interpretation of “bottom-up” control of ecosystem dynamics.

Dissolved iron distribution in the tropical and sub tropical South Eastern Pacific

Abstract. Dissolved iron (DFe) distributions (<0.2 μm) were determined in the upper water column (0–400 m) of the south eastern tropical and subtropical Pacific, in October–November 2004. Data were collected along a transect extending from the Marquesas Islands to the Chilean coast with most of the stations located in the south Pacific gyre. The concentrations of DFe presented large variability with highest values observed at both extremities of the transect. In the Chilean upwelling, DFe concentrations ranged between 1.2–3.9 nM. These high values result from inputs from the continental margin and are likely maintained by anoxic conditions in the water corresponding to the Oxygen Minimum Zone (OMZ). In subsurface waters near the Marquesas, that were also associated with the extension of the OMZ, DFe concentrations varied between 0.15–0.41 nM. Vertical transport of this water by mesoscale activity eastward of the archipelago may explain the dissymmetric east-west distribution of chlorophyll-a evidenced by satellite images. Using the new tracer Fe*=DFe−rFe:P (PO43−) we show that DFe was in deficit compared to PO43− resulting from the remineralisation of organic matter. This suggests that the Marquesas islands and the surrounding plateau are not a significant source of DFe. In the gyre, DFe concentrations in the upper 350 m water column were around 0.1 nM and the ferricline was located well below the nitracline. These low concentrations reflect the low input of DFe from the atmosphere, from the ventilation of the upper thermocline with water containing low DFe, and from the low biological activity within this ultra oligotrophic gyre.

Molecular and biogeochemical evidence for ammonia oxidation by marine Crenarchaeota in the Gulf of California

Nitrification plays an important role in marine biogeochemistry, yet efforts to link this process to the microorganisms that mediate it are surprisingly limited. In particular, ammonia oxidation is the first and rate-limiting step of nitrification, yet ammonia oxidation rates and the abundance of ammonia-oxidizing bacteria (AOB) have rarely been measured in tandem. Ammonia oxidation rates have not been directly quantified in conjunction with ammonia-oxidizing archaea (AOA), although mounting evidence indicates that marine Crenarchaeota are capable of ammonia oxidation, and they are among the most abundant microbial groups in the ocean. Here, we have directly quantified ammonia oxidation rates by 15N labeling, and AOA and AOB abundances by quantitative PCR analysis of ammonia monooxygenase subunit A (amoA) genes, in the Gulf of California. Based on markedly different archaeal amoA sequence types in the upper water column (60 m) and oxygen minimum zone (OMZ; 450 m), novel amoA PCR primers were designed to specifically target and quantify 'shallow' (group A) and 'deep' (group B) clades. These primers recovered extensive variability with depth. Within the OMZ, AOA were most abundant where nitrification may be coupled to denitrification. In the upper water column, group A tracked variations in nitrogen biogeochemistry with depth and between basins, whereas AOB were present in relatively low numbers or undetectable. Overall, 15NH4+ oxidation rates were remarkably well correlated with AOA group A amoA gene copies (r2=0.90, P<0.001), and with 16S rRNA gene copies from marine Crenarchaeota (r2=0.85, P<0.005). These findings represent compelling evidence for an archaeal role in oceanic nitrification.

Temporal and Spatial Variations in Water Quality on New York South Shore Estuary Tributaries: Carmans, Patchogue, and Swan Rivers

The chemical and biological impacts of anthropogenic physical modifications (i.e., channelization, dredging, bulkhead, and jetty construction) to tributaries were assessed on New York’s Long Island South Shore Estuary. Water-quality data collected on Carmans, Patchogue, and Swan Rivers from 1997 to 2005 indicate no significant differences in nutrient levels, temperature, or pH among the rivers, but significant differences in light transmittance, dissolved oxygen (DO), salinity, and sediments were observed. Patchogue River (PR) and Swan River (SR) were significantly more saline than Carmans River (CR), PR and SR had less light transmittance than CR, and both exhibited severe warm season hypoxia. CR was rarely hypoxic and only at the lower layer of the deepest station in warm seasons. Deep stations on PR had hypoxic readings year round, but the shallower SR was well-oxygenated at all stations after the fall turnover. There were wide diel and seasonal variations in chlorophyll a on each river, and measurements were significantly higher at poorly flushed stations. In warm seasons, this often resulted in hyperventilation with supersaturated DO in the upper water column on sunny days, and suboxic conditions at nights and/or in deeper layers. PR sediments were anoxic, SR sediments ranged from normal to anoxic, and CR sediments were normal at all stations. Polyaromatic hydrocarbon concentrations in PR sediments were over three orders of magnitude higher than SR and CR sediments. Benthic invertebrate assessment of species richness, biotic index, and Ephemeroptera, Plecoptera and Trichoptera richness indicated that PR was severely impacted, SR ranged from slightly to severely impacted, and CR ranged from non-impacted to slightly impacted. Diversity and abundance of plankton were comparable on SR and CR, and were significantly higher than on PR. The data indicate that nutrients do not play a major role in hypoxia in these estuarine tributaries but that physical forces dominate. The narrow inlets, channelization, and abrupt changes in depth near the inlets of PR and SR foster hypoxic conditions by inducing salinity stratification that limits vertical mixing and by restricting horizontal water mass exchange with the bay. The study suggests that other tributaries with such physical modifications should be examined to assess the temporal and spatial extent of hypoxia.

Zinc‐cobalt colimitation of Phaeocystis antarctica

We present evidence demonstrating the capability of Phaeocystis antarctica colonies to substitute cobalt (Co) and zinc (Zn) as micronutrients, in which Co limitation is alleviated by additions of Zn and vice versa. Maximal growth rates and biomass were determined by fluorescence and the values obtained under replete Zn and no added Co conditions were significantly higher than under replete Co and no added Zn conditions, suggesting a preference for Zn over Co. The observation of Zn‐Co substitution in this high‐latitude member of the Prymnesiophyceae class, coupled with similar previous observations in the coccolithophore Emiliana huxleyi and several centric diatoms, suggests that Zn‐Co substitution could be a widespread global phenomenon in eukaryotic phytoplankton. The Zn‐Co biochemical substitution seen in Phaeocystis might be the result of evolutionary pressure for maintaining growth rates in high export environments in which rapid depletion of Zn, Co, and carbon occur simultaneously in the upper water column.

Advances in upward looking sonar technology for studying the processes of change in Arctic Ocean ice climate

A major impetus for scientific studies of climate change in the Arctic Ocean has beenthe reduction in the areal extent and thickness of its sea ice cover. An extendedmeasurement record of the horizontal dimensions of this ice cover is available for thefull Arctic Ocean Basin based upon a record compiled from more than 30 years ofrelatively continuous satellite based measurements. Unfortunately, data accumulationsfor the ice cover’s vertical dimension, ie, sea ice thickness, tend to be limited to data setswith durations no longer than 15 years, reflecting underlying greater measurementdifficulties. Moreover, the longest duration ice thickness data collection efforts have beenconfined only to two specific portions of the Basin, namely, Fram Strait and the Canadiansector of the Beaufort Sea. Elsewhere, the available data sets are either of notablyshorter duration or non-existent.Upward-looking sonar (ULS) has been and continues to be the primary source ofdata with volumes and accuracy sufficient for meaningfully monitoring ice thickness.Originally deployed from polar-traversing submarines during the Cold War, the limitedamounts and accessibility of the collected data stimulated development of purpose-builtsea-floor moored ULS instrumentation which, beginning in the late 1980s, began tosupply the bulk of newly acquired ice draft and ice under-surface topography data.Technological advances have subsequently led to new generations of ULS instrumentsincluding ice-profiling sonar (IPS), incorporating much expanded on-board data storagecapacities (69 Mbytes to 8 Gbytes) and powerful real-time firmware which now allowunprecedented temporal (ping rates of up to 1Hz) and horizontal resolution of icetopography. These instruments operate autonomously during one year or longer deployments,returning draft data on time and spatial scales of 1s and 1m or better, respectively,which are essential to understandings of mechanical and thermodynamical aspectsof sea ice processes. Such processes govern ocean-atmosphere exchanges in polarwaters, thereby determining ice extent and thickness parameters. The larger data storage capacities of the newest instruments also allow collection of additional informationassociated with acoustic returns from different levels in the upper water column and thelower ice cover. Such data have potential for improving understandings of ice processesoccurring during the initial freeze-up and early consolidation phases of sea ice growth onthe basis of acoustic backscatter from frazil, grease, shuga and nilas ice forms. WithInternational Polar Year programmes now well underway, ice profiling instruments,sharing a common technology, are and/or will be deployed in unprecedented numbersfrom both fixed subsurface moorings and drifting buoys. This deployment commitmentholds great promise for delivery of data with both temporal and spatial detail and arealcoverage sufficient to strongly upgrade present capabilities for monitoring and modellingice cover change.

Influence of the heavy fuel spill from the Prestige tanker wreckage in the overlying seawater column levels of copper, nickel and vanadium (NE Atlantic ocean)

The water column above the Prestige wreckage was sampled during two consecutive campaigns: Prestinaut (December 2002) two weeks after the tanker sunk and HidroPrestige0303 (March 2003) one month after the sealing of the main fuel leaks. Samples of the original cargo fuel and the emulsified fuel in the surface of the ocean were also collected. Analysis of the fuel indicated the release of 135 kg of Cu, 1700 kg of Ni and 5300 kg of V from the original fuel to the water column, remaining 35 kg of Cu, 3100 kg of Ni and 13,800 kg of V in the emulsified fuel. The metal partitioning between the water column and the emulsioned floating fuel, Cu > Ni ~ V, are in accordance with the stability index for the metal–nitrogen bond in metalloporphyrins. This release had an impact on dissolved trace metal concentrations in the water column. An increase on dissolved copper (2.8–4.7 nM) and nickel (2.2–8.0 nM) with respect to natural values (1–3 nM for Cu and 1.6–5 nM for Ni) was observed. Values for vanadium (28–35 nM) were in the range of pristine North Atlantic waters (30–36 nM). This contamination was especially observed in the upper water column (0–50 m), associated with the mixing of seawater with the fuel moving upwards, and in deep waters, where the residence time of fuel is higher. Future research in this field should focus on the environmental variables and the processes that control the release of contaminants from fuels for a better assessment of the contamination in oil-spill events.

Spatial and temporal patterns of transparency and light attenuation in the Salton Sea, California, 1997–1999

Transparency, as measured by Secchi disk depth (SD), and light attenuation (Kd(PAR)) were measured in the Salton Sea in 1997–1999. Linear regression models were used to evaluate the relative importance of phytoplankton and non-phytoplankton substances in determining SD and Kd(PAR). Paired measurements of SD and Kd(PAR) made in 1999 were used to track relative changes in the importance of light absorption and scattering processes. Phytoplankton biomass was a poor predictor of both SD and Kd(PAR) at mid-lake stations, and this is most likely due to high concentrations of non-phytoplankton substances such as inorganic particulate matter in the Salton Sea. During strong windstorms in the warmer part of the year, the upper water column mixes with hydrogen sulfide-laden bottom waters, causing large crashes in plankton populations. This previously reported phenomenon also strongly affects the light regime through the production of gypsum crystals, which scatter large portions of penetrating light. Since a large amount of variation in both SD and Kd(PAR) is not explained by phytoplankton biomass, any use of this relationship to forecast future changes in water clarity through nutrient reductions must be done with caution.

Iron study during a time series in the western Weddell pack ice

Samples of sea ice, snow, brine and underlying seawater were collected in the western Weddell pack ice at the ISPOL drifting station (Ice Station POLarstern, 68°S/55°W) in spring–summer period (November 2004–January 2005). Total-dissolvable, dissolved and particulate Fe concentrations in the sea ice environment were determined every 5 days during the time series, together with relevant physical, chemical and biological parameters. From 29 November to 30 December, a decrease in all forms of Fe measured was observed, likely to be the result of enhanced ice permeability as summer proceeds. At the beginning of the time series, melting of the upper ice layer took place together with brine drainage process. This would enable the seeding of Fe from the ice matrix towards the upper water column below. 70% of this Fe was supplied during the first 10 days of the survey, while the ice cover is still present. Flux estimates from the sampled area furthermore highlight the relevant role of the pack ice in the biogeochemical cycle of Fe in the western Weddell Sea.

Light‐stimulated production of dissolved DMSO by a particle‐associated process in the Ross Sea, Antarctica

Dimethylsulfoxide (DMSO) is an abundant form of methylated sulfur in marine systems and it is known to be produced from dimethylsulfide (DMS). Using radiolabeled 35S‐DMS and gas chromatography techniques, we quantified the dissolved DMSO (DMSOd) produced from photo‐ and biological oxidation of dissolved DMS and compared the DMSOd production from these pathways with the net change in DMSOd concentrations in unfiltered seawater samples. The net change in DMSOd in light‐exposed treatments exceeded DMSOd production from photo‐ plus biological oxidation of dissolved DMS. This indicated that DMSOd was produced by one or more light‐driven processes likely associated with particulate material. Results from in situ incubation arrays showed that the relative importance of DMSOd production processes was dependent on irradiation depth, with the unidentified particle‐associated process and dissolved DMS photooxidation the main DMSOd sources close to the surface (0–10 m) and biological oxidation of dissolved DMS the main process at depths at which the light level was low (&gt;10 m). Deckboard and in situ incubations revealed that DMSOd production from the particle‐associated process was stimulated by ultraviolet radiation. Higher particle‐associated production of DMSOd in samples more prone to suffer light‐induced stress supports the hypothesis that this process was related to phytoplanktonic biosynthesis and release of DMSO because of oxidative stress. Our results suggest that particle‐associated DMSOd production is an important source of DMSOd in surface waters of the Ross Sea and also help to explain why DMSOd is periodically the main organosulfur compound detected in the upper water column.

Iron isotopes constrain biologic and abiologic processes in banded iron formation genesis

The voluminous 2.5 Ga banded iron formations (BIFs) from the Hamersley Basin (Australia) and Transvaal Craton (South Africa) record an extensive period of Fe redox cycling. The major Fe-bearing minerals in the Hamersley–Transvaal BIFs, magnetite and siderite, did not form in Fe isotope equilibrium, but instead reflect distinct formation pathways. The near-zero average δ 56Fe values for magnetite record a strong inheritance from Fe 3+ oxide/hydroxide precursors that formed in the upper water column through complete or near-complete oxidation. Transformation of the Fe 3+ oxide/hydroxide precursors to magnetite occurred through several diagenetic processes that produced a range of δ 56Fe values: (1) addition of marine hydrothermal Fe 2 + aq , (2) complete reduction by bacterial dissimilatory iron reduction (DIR), and (3) interaction with excess Fe 2 + aq that had low δ 56Fe values and was produced by DIR. Most siderite has slightly negative δ 56Fe values of ∼ −0.5‰ that indicate equilibrium with Late Archean seawater, although some very negative δ 56Fe values may record DIR. Support for an important role of DIR in siderite formation in BIFs comes from previously published C isotope data on siderite, which may be explained as a mixture of C from bacterial and seawater sources. Several factors likely contributed to the important role that DIR played in BIF formation, including high rates of ferric oxide/hydroxide formation in the upper water column, delivery of organic carbon produced by photosynthesis, and low clastic input. We infer that DIR-driven Fe redox cycling was much more important at this time than in modern marine systems. The low pyrite contents of magnetite- and siderite-facies BIFs suggests that bacterial sulfate reduction was minor, at least in the environments of BIF formation, and the absence of sulfide was important in preserving magnetite and siderite in the BIFs, minerals that are poorly preserved in the modern marine record. The paucity of negative δ 56Fe values in older (Early Archean) and younger (Early Proterozoic) BIFs suggests that the extensive 2.5 Ga Hamersley–Transvaal BIFs may record a period of maximum expansion of DIR in Earth’s history.

생태계모델을 이용한 황해투기해역에서의 춘계 식물플랑크톤 대증식 연구

To explore limiting factors of spring bloom caused by waste disposal after dumping activity commenced in the Yellow Sea, we used a 1-dimensional temperature-ecological coupled model. The vertical structure of temperature and vertical diffusivity (Kh) are calculated by the temperature model with sea surface temperature using the 2.5 layers turbulence closure scheme. The ecological model applied results at the temperature model consisted of five state variables (DIN, DIP, phytoplankton, zooplankton, and detritus) forced by photosynthetically available radiation. We simulate year-to-year variations of plankton and nutrients using the coupled model from 1998 to 2000 and compare results of the model with observed data. It turned out that temperature is the growth factor of spring bloom in dumping area. During the winter the weak stratification made sufficient supply of the accumulated nutrients from the sea bed into the upper water column and led to the bloom in the coming spring. Radiation also turned out to be another important factor of spring bloom in the study area. Insufficient radiation of March 1999 showed low chlorophyll-a concentration despite sufficient nutrients in the surface.

Mixed-Layer Deepening During Heinrich Events: A Multi-Planktonic Foraminiferal δ 18 O Approach

Proxies from Greenland ice cores and North Atlantic marine sediment cores document repeated extreme climate swings of a few decades to millennia during the last glacial cycle, including periods of intense ice rafting called Heinrich events (HEs). We have found similar oxygen isotope variations recorded in mixed-layer-and thermocline-dwelling planktonic foraminifera during HEs 0, 1, and 4, suggesting that three foraminiferal taxa calcified their shells at similar temperatures in a homogenized upperwater column. This implies that the surface mixed layer was deeper during HEs. Similar deepening occurred on the northern margin of the ice-rafted-debris belt, implying that these deep mixed layers during HEs were widespread in the region. We suggest that an increase in storminess during HEs intensified the vertical mixing of meltwater from ice rafting in the upper ocean.