Carole M. Sakamoto

Chemical variability in the black sea implications of continuous vertical profiles that penetrated the oxic anoxic interface

Abstract During the 1988 Black Sea Expedition, we employed a pumping system to generate continuous vertical profiles of nutrients, sulfide, temperature, salinity and light transmission to depths as great as 360 m and to collect oxygen samples from discrete depths. The results can be summarized as follows: (1) In contrast to most prior investigators, we did not find regions where both oxygen and sulfide occurred at concentrations >~1 μ m. (2) The profiles demonstrated the existence of a double phosphate maxima in the central Black Sea which disappears at the margins. (3) Our results in combination with historical data strongly suggest that maximum nitrate concentrations in the upper layers of the Black Sea have risen significantly in recent years. The maximum nitrate value of ~7.5 μ M was similar in all pump profiles and found at a similar σ t , even though regional variation in the depth of the maximum was ~100 m. Our data also suggest an increase in the nitrate inventory of the Black Sea. (4) We found undulating patterns of chemical variables (particularly sulfide and ammonium) in the vicinity of the Bosporus, arising from the high salinity inflow. The effect of this process was still evident in one profile located 100 km to the northeast of the Bosporus. (5) In general, ammonium, nitrate and nitrite disappeared within the suboxic region, suggesting that this zone was a sink for all three species. This implies that the deeper strata are not supplying combined nitrogen to the photic zone at least during the spring and summer. (6) Small-scale vertical variability in chemical distributions in and near the oxic/anoxic interface was usually correlated with temperature and salinity fine structure. (7) Our data support the view that the oxic/anoxic interface is rising.

Biogeochemistry of hydrothermal vent mussel communities: the deep-sea analogue to the intertidal zone

Continuous measurements of sulfide, silicate and temperature were made in situ from the submersible Alvin in the Rose Garden and New Vent hydrothermal fields of the Galapagos Spreading Center. Continuous measurements of temperature also were made for an 18 day period in the Rose Garden field. The results demonstrate several adaptations that appear to have contributed to the success of the vent mussel Bathymodiolus thermophilus in the Rose Garden. Dense clusters of B. thermophilus can disperse the hydrothermal fluids laterally for distances of several meters. This results in a large increase in the area of the redox transition zone, where both dissolved oxygen and hydrogen sulfide are available. As a result, the animal communities can grow to occupy areas that would not otherwise provide adequate reduced substrates. Measurements of the temperature demonstrate a distinct tidal periodicity. This periodicity will result in a large range of environmental conditions within the vent community. The mussel can tolerate these wide ranges in condition because of its ability to accept long periods of anoxia and to filter feed.

Nutrient cycling and primary production in the marine systems of the Arctic and Antarctic

Abstract Primary production events in both the Arctic and the Antarctic are highly localized. Carbon-14 incubations that did not account for this caused antarctic primary production estimates to be revised too far downwards from the historic view of high productivity. The primary production regime in the Arctic is even more heterogeneous than in the Antarctic. Arctic primary production rates are in the process of being revised upwards because of a better spatial and temporal distribution of incubation experiments and a re-awakening of interest in estimating new production from the distribution of chemical variables. Similarly, recent examination of temporal changes in nitrate concentrations and recognition of the importance of ice-edge blooms has caused antarctic primary productivity to be revised upwards. In both the Arctic and the Antarctic, the ratio of “new” to total primary production is high, and neglect of this fact can lead to an underestimation of the potential that these regions have for influencing global cycles of bioactive chemicals. Some recent data on temporal changes in nitrate from Fram Strait emphasize the poor state of our knowledge by suggesting an unexpectedly high “new” production rate of ∼1 g C m −2 d −1 for a 35 day experiment that encountered an early Phaeocystis bloom. Chemical distributions suggest that new production over the shelf seas that border the Polar Basin is about 50 g Cm −2 yr −1 . The shelves in the Arctic Oceans marginal and adjacent seas comprise ∼ 25% of the total global continental shelf. These extensive shallow regions have much higher rates of primary production than the Polar Basin and may be globally significant sites of denitrification. Globally significant silica deposition could occur on these shelves or on the adjacent slopes. Because of the differences in geomorphology and stratification, global warming is likely to increase primary production in the Arctic and will probably decrease antarctic primary production. In addition to sharing high ratios of “new” to total primary production, high ammonium concentrations occur in the Arctic and Antarctic. It is possible that these accumulations arise from a strong repression of nitrification at low temperatures.

Influence of Rossby waves on nutrient dynamics and the plankton community structure in the North Pacific subtropical gyre

Ocean Time-Series (HOT) Program’s Station ALOHA (22� 45 0 N; 158� W). Nitrate concentrations were determined with OsmoAnalyzers deployed at depths of 120 and 180 m. Deployments in 1997 and 1999 captured monthlong events that brought relatively cold high-nitrate seawater up into the euphotic zone. These events were correlated with negative sea surface height (SSH) anomalies measured by the TOPEX/Poseidon satellite altimeter. These nutrient injections at the Hawaii site were predominantly associated with first baroclinic mode Rossby waves. Elevated nitrate concentrations resulted in increased Chl a concentrations, increased primary productivity, and shifts in the phytoplankton community structure, as determined by HPLC analysis of pigment concentrations. The relative increase in pigments associated with phytoplankton that can grow rapidly and exploit nitrate (e.g., haptophytes and pelagophytes) coincided with the passage of Rossby waves in 1997–1999. A long-term combination of satellite remote sensing, moored instrumentation or remote vehicles and periodic ship-based sampling is needed to fully characterize the spatial and temporal variability due to the passage of Rossby waves and their associated biological responses. INDEX TERMS: 4556 Oceanography: Physical: Sea level variations; 4572 Oceanography: Physical: Upper ocean processes; 4845 Oceanography: Biological and Chemical: Nutrients and nutrient cycling; 4815 Oceanography: Biological and Chemical: Ecosystems, structure and dynamics; 4894 Oceanography: Biological and Chemical: Instruments and techniques; KEYWORDS: nitrate, mooring, Rossby waves, phytoplankton, nutrient

Long-Term Nitrate Measurements in the Ocean Using the in situ Ultraviolet Spectrophotometer: Sensor Integration into the APEX Profiling Float

AbstractReagent-free optical nitrate sensors [in situ ultraviolet spectrophotometer (ISUS)] can be used to detect nitrate throughout most of the ocean. Although the sensor is a relatively high-power device when operated continuously (7.5 W typical), the instrument can be operated in a low-power mode, where individual nitrate measurements require only a few seconds of instrument time and the system consumes only 45 J of energy per nitrate measurement. Operation in this mode has enabled the integration of ISUS sensors with Teledyne Webb Researchs Autonomous Profiling Explorer (APEX) profiling floats with a capability to operate to 2000 m. The energy consumed with each nitrate measurement is low enough to allow 60 nitrate observations on each vertical profile to 1000 m. Vertical resolution varies from 5 m near the surface to 50 m near 1000 m, and every 100 m below that. Primary lithium batteries allow more than 300 vertical profiles from a depth of 1000 m to be made, which corresponds to an endurance near f...

Determination of copper in sea water using a flow-injection method with chemiluminescence detection

Abstract Dissolved copper can he rapidly determined in sea water by using a modification of a chemiluminescence method. The determination is based on the formation of a complex between copper and 1,10-phenanthroline and the subsequent emission of light during the oxidation of the complex by hydrogen peroxide. A flow-injection manifold was constructed which provides for the separation of copper from the sea water matrix with a column of immobilized 8-hydroxyquinoline. The column eluant was injected into a carrier stream, mixed with the reagents and delivered to a flow cell where emitted light was detected and used to quantify the amount of copper in the sample. The technique is noteworthy for its low detection limit (s 0.4 nM), the rapidly of sample processing (approximately 8 min sample−1), the small sample volumes required (approximately 4 ml), and the minimal precautions necessary for the prevention of sample contamination during shipboard processing.

Biogeochemical sensor performance in the SOCCOM profiling float array

The Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) program has begun deploying a large array of biogeochemical sensors on profiling floats in the Southern Ocean. As of February 2016, 86 floats have been deployed. Here the focus is on 56 floats with quality controlled and adjusted data that have been in the water at least 6 months. The floats carry oxygen, nitrate, pH, chlorophyll fluorescence, and optical backscatter sensors. The raw data generated by these sensors can suffer from inaccurate initial calibrations and from sensor drift over time. Procedures to correct the data are defined. The initial accuracy of the adjusted concentrations is assessed by comparing the corrected data to laboratory measurements made on samples collected by a hydrographic cast with a rosette sampler at the float deployment station. The long-term accuracy of the corrected data is compared to the GLODAPv2 data set whenever a float made a profile within 20 km of a GLODAPv2 station. Based on these assessments, the fleet average oxygen data are accurate to 1±1%, nitrate to within 0.5±0.5 µmol kg−1, and pH to 0.005±0.01, where the error limit is 1 standard deviation of the fleet data. The bio-optical measurements of chlorophyll fluorescence and optical backscatter are used to estimate chlorophyll a and particulate organic carbon concentration. The particulate organic carbon concentrations inferred from optical backscatter appear accurate to with 35 mg C m−3 or 20%, whichever is larger. Factors affecting the accuracy of the estimated chlorophyll a concentrations are evaluated.

Diverse, uncultivated bacteria and archaea underlying the cycling of dissolved protein in the ocean

Dissolved organic nitrogen (DON) supports a significant amount of heterotrophic production in the ocean. Yet, to date, the identity and diversity of microbial groups that transform DON are not well understood. To better understand the organisms responsible for transforming high molecular weight (HMW)-DON in the upper ocean, isotopically labeled protein extract from Micromonas pusilla, a eukaryotic member of the resident phytoplankton community, was added as substrate to euphotic zone water from the central California Current system. Carbon and nitrogen remineralization rates from the added proteins ranged from 0.002 to 0.35 μmol C l−1 per day and 0.03 to 0.27 nmol N l−1 per day. DNA stable-isotope probing (DNA-SIP) coupled with high-throughput sequencing of 16S rRNA genes linked the activity of 77 uncultivated free-living and particle-associated bacterial and archaeal taxa to the utilization of Micromonas protein extract. The high-throughput DNA-SIP method was sensitive in detecting isotopic assimilation by individual operational taxonomic units (OTUs), as substrate assimilation was observed after only 24 h. Many uncultivated free-living microbial taxa are newly implicated in the cycling of dissolved proteins affiliated with the Verrucomicrobia, Planctomycetes, Actinobacteria and Marine Group II (MGII) Euryarchaeota. In addition, a particle-associated community actively cycling DON was discovered, dominated by uncultivated organisms affiliated with MGII, Flavobacteria, Planctomycetes, Verrucomicrobia and Bdellovibrionaceae. The number of taxa assimilating protein correlated with genomic representation of TonB-dependent receptor (TBDR)-encoding genes, suggesting a possible role of TBDR in utilization of dissolved proteins by marine microbes. Our results significantly expand the known microbial diversity mediating the cycling of dissolved proteins in the ocean.

Net community production at Ocean Station Papa observed with nitrate and oxygen sensors on profiling floats

Six profiling floats equipped with nitrate and oxygen sensors were deployed at Ocean Station P in the Gulf of Alaska. The resulting six calendar years and 10 float years of nitrate and oxygen data were used to determine an average annual cycle for net community production (NCP) in the top 35 m of the water column. NCP became positive in February as soon as the mixing activity in the surface layer began to weaken, but nearly 3 months before the traditionally defined mixed layer began to shoal from its winter time maximum. NCP displayed two maxima, one toward the end of May and another in August with a summertime minimum in June corresponding to the historical peak in mesozooplankton biomass. The average annual NCP was determined to be 1.5 ± 0.6 mol C m−2 yr−1 using nitrate and 1.5 ± 0.7 mol C m−2 yr−1 using oxygen. The results from oxygen data proved to be quite sensitive to the gas exchange model used as well as the accuracy of the oxygen measurement. Gas exchange models optimized for carbon dioxide flux generally ignore transport due to gas exchange through the injection of bubbles, and these models yield NCP values that are two to three time higher than the nitrate-based estimates. If nitrate and oxygen NCP rates are assumed to be related by the Redfield model, we show that the oxygen gas exchange model can be optimized by tuning the exchange terms to reproduce the nitrate NCP annual cycle.

Development of automated surface seawater nitrate mapping systems for use in open ocean and coastal waters

Uncertainty concerning the cycles and budgets of the major bioactive chemicals in the sea is partially a function of undersampling in relation to the actual spatial and temporal variability. However, technologies are becoming increasingly available for development of inexpensive devices for the continuous measurement of ocean properties. We have leveraged on these technologies and built two versions of a nitrate mapping system that is designed to operate with minimal operator intervention and provide near real-time surface seawater nitrate data. The analyzers are based on microprocessor-controlled Kloehn syringe pump modules operating in a batch mode. A rapid response nitrate analyzer uses two syringe pump modules and is capable of a 2-min sampling rate, allowing high temporal/spatial resolution. A simpler system which uses a single syringe pump and provides nitrate data every 20 min has also been built. Both systems can be integrated with other sensors (e.g. fluorometers) and navigation data to either display real-time maps or a scrolling display of multiple parameters. These systems have been deployed for extended periods on coastal and open ocean cruises.