Hans W. Jannasch

Moorings and Drifters for Real-Time Interdisciplinary Oceanography

Abstract A telemetering electronics/control unit (OASIS) has been developed for use on moorings and free-floating drifters. The OASIS controllers are part of a long-term “coastal ocean observatory,” consisting of an infrastructure of ships, submersibles, an array of remote sensing platforms (moorings, drifters), communication links between sensors and laboratory, and data management facilities. The OASIS controller coordinates retrieval of data from a varying array of up to 28 oceanographic sensors, which may output digital, analog, or frequency data. The controller provides scheduling, sensor control software, data logging, preliminary data processing, and two-way telemetry between remote platform and ship or shore station. Telemetry allows real-time access to data and permits users to alter control parameters as necessary. Two OASIS moorings have been successfully deployed off the central California coast since 1992. Real-time access and two-way telemetry has allowed the moorings to become testbeds for ...

Continuous sampling of hydrothermal fluids from Loihi Seamount after the 1996 event

For at least 9 years prior to July 1996, hydrothermal fluids flowed from Peles Vents on Loihi Seamount, Hawaii. In July–August 1996 a tectonic-volcanic event occurred that destroyed Peles Vents, creating a pit crater (Peles Pit) and several sites with hydrothermal venting. In October 1996 we deployed two new continuous water samplers (OsmoSamplers) at two of these hydrothermal sites and collected fluids using traditional sampling techniques to monitor the evolution of crustal and hydrothermal conditions after the event. The samplers were recovered in September 1997, and additional discrete vent fluid samples were collected. The OsmoSampler located along the south rift at Naha Vents captured a change in composition from a low-chlorinity, high-K fluid (relative to bottom seawater) to a high-chlorinity, low-K fluid. These changes are consistent with the fluid cooling during ascent and being derived from several different sources, which include high- (>330°C) and low- ( 330°C) into which magmatic volatiles were added. During the deployment, thermal and fluid fluxes decreased. At Naha the transport of heat and chemicals was decoupled. The chemical and thermal evolution of hydrothermal fluids after the event on Loihi is consistent with previous models based on events that have occurred along mid-ocean ridges. The event at Loihi clearly had an effect on the local hydrography; however, the integrated effect of chemical fluxes to global budgets from similar events is uncertain. Chemical fluxes from similar events may have a global impact, if ratios of chemical (e.g., CO2, Fe/Mn, Mg, sulfate, and K) to thermal anomalies greatly exceed, or are in the opposite direction to, fluxes from mid-ocean ridge hydrothermal systems.

Seawater transport and reaction in upper oceanic basaltic basement: chemical data from continuous monitoring of sealed boreholes in a ridge flank environment

Osmotically pumped fluid samplers were deployed in four deep-sea boreholes that were drilled during Ocean Drilling Program (ODP) Leg 168 on the eastern flank of the Juan de Fuca Ridge. Samplers were recovered from ODP Sites 1024 and 1027 and aliquots were analyzed for a variety of dissolved ions. Results from both of the samplers show a drastic change in the major ion composition within the first 20–40 days after the borehole was sealed at the seafloor followed by a more gradual change in composition. This gradual change ceased after 820 days at Site 1024 but continued throughout the 3-year deployment at Site 1027. We modeled this change in composition to estimate the flux of formation fluid through the open borehole. The rapid early change requires a flow of ∼1500 kg of formation fluid per day. The more gradual later change requires flow rates of 38 kg/day at Site 1024 and 17.5 kg/day at Site 1027. The latter fluxes require a minimum average specific discharge of meters to hundreds of meters per year through the surrounding basaltic matrix. Trace element data show surprisingly little contamination given the presence of steel casing, Li-organic-rich grease at each joint, cement, and drilling muds. Observed changes in trace element concentrations relative to those of bottom seawater provide a measure for the global significance of cool (23°C; ODP Site 1024) ridge flank hydrothermal systems relative to warm (64°C; Baby Bare and ODP Site 1027) hydrothermal systems and illustrate the importance of these cooler systems to global geochemical budgets.

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...

Nitrate Sources and Sinks in Elkhorn Slough, California: Results from Long-term Continuous in situ Nitrate Analyzers

Nitrate and water quality parameters (temperature, salinity, dissolved oxygen, turbidity, and depth) were measured continuously with in situ NO3 analyzers and water quality sondes at two sites in Elkhorn Slough in Central California. The Main Channel site near the mouth of Elkhorn Slough was sampled from February to September 2001. Azevedo Pond, a shallow tidal pond bordering agricultural fields further inland, was sampled from December 1999 to July 2001. Nitrate concentrations were recorded hourly while salinity, temperature, depth, oxygen, and turbidity were recorded every 30 min. Nitrate concentrations at the Main Channel site ranged from 5 to 65 μM. The propagation of an internal wave carrying water from ≈100 m depth up the Monterey Submarine Canyon and into the lower section of Elkhorn Slough on every rising tide was a major source of nitrate, accounting for 80–90% of the nitrogen load during the dry summer period. Nitrate concentrations in Azevedo Pond ranged from 0–20 μM during the dry summer months. Nitrate in Azevedo Pond increased to over 450 μM during a heavy winter precipitation event, and interannual variability driven by differences in precipitation was observed. At both sites, tidal cycling was the dominant forcing, often changing nitrate concentrations by 5-fold or more within a few hours. Water volume flux estimates were combined with observed nitrate concentrations to obtain nitrate fluxes. Nitrate flux calculations indicated a loss of 4 mmol NO3 m−2 d−1 for the entire Elkhorn Slough and 1 mmol NO3 m−2 d−1 at Azevedo Pond. These results suggested that the waters of Elkhorn Slough were not a major source of nitrate to Monterey Bay but actually a nitrate sink during the dry season. The limited winter data at the Main Channel site suggest that nitrate was exported from Elkhorn Slough during the wet season. Export of ammonium or dissolved organic nitrogen, which we did not monitor, may balance some or all of the NO3 flux.

Deep-Sea DuraFET: A Pressure Tolerant pH Sensor Designed for Global Sensor Networks

Increasing atmospheric carbon dioxide is driving a long-term decrease in ocean pH which is superimposed on daily to seasonal variability. These changes impact ecosystem processes, and they serve as a record of ecosystem metabolism. However, the temporal variability in pH is observed at only a few locations in the ocean because a ship is required to support pH observations of sufficient precision and accuracy. This paper describes a pressure tolerant Ion Sensitive Field Effect Transistor pH sensor that is based on the Honeywell Durafet ISFET die. When combined with a AgCl pseudoreference sensor that is immersed directly in seawater, the system is capable of operating for years at a time on platforms that cycle from depths of several km to the surface. The paper also describes the calibration scheme developed to allow calibrated pH measurements to be derived from the activity of HCl reported by the sensor system over the range of ocean pressure and temperature. Deployments on vertical profiling platforms enable self-calibration in deep waters where pH values are stable. Measurements with the sensor indicate that it is capable of reporting pH with an accuracy of 0.01 or better on the total proton scale and a precision over multiyear periods of 0.005. This system enables a global ocean observing system for ocean pH.

In situ enrichment of ocean crust microbes on igneous minerals and glasses using an osmotic flow-through device

The Integrated Ocean Drilling Program (IODP) Hole 1301A on the eastern flank of Juan de Fuca Ridge was used in the first long-term deployment of microbial enrichment flow cells using osmotically driven pumps in a subseafloor borehole. Three novel osmotically driven colonization systems with unidirectional flow were deployed in the borehole and incubated for 4 years to determine the microbial colonization preferences for 12 minerals and glasses present in igneous rocks. Following recovery of the colonization systems, we measured cell density on the minerals and glasses by fluorescent staining and direct counting and found some significant differences between mineral samples. We also determined the abundance of mesophilic and thermophilic culturable organotrophs grown on marine R2A medium and identified isolates by partial 16S or 18S rDNA sequencing. We found that nine distinct phylotypes of culturable mesophilic oligotrophs were present on the minerals and glasses and that eight of the nine can reduce nitrate and oxidize iron. Fe(II)-rich olivine minerals had the highest density of total countable cells and culturable organotrophic mesophiles, as well as the only culturable organotrophic thermophiles. These results suggest that olivine (a common igneous mineral) in seawater-recharged ocean crust is capable of supporting microbial communities, that iron oxidation and nitrate reduction may be important physiological characteristics of ocean crust microbes, and that heterogeneously distributed minerals in marine igneous rocks likely influence the distribution of microbial communities in the ocean crust.

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.

Implications of carbon flux from the Cascadia accretionary prism: results from long-term, in situ measurements at ODP Site 892B

A 403-day in situ field experiment at Ocean Drilling Program Site 892B sought to quantify the flux of methane along a fluid-active fault and to experimentally determine rates of methane hydrate and authigenic carbonate deposition associated with fluid expulsion from the borehole. An instrument package was deployed that osmotically sampled fluid, measured borehole pressure and flow rates, and contained reaction chambers in which deposition of gas hydrates and carbonates was anticipated, and from which microbial communities might be extracted. Flow is highly variable in the three-phase water–methane system that exists at Site 892B. Flow rates fluctuate over two orders of magnitude in response to tidally induced pressure variations and gas hydrate formation and dissociation. Hydrate formation began 45 days into the experiment and reduced the initial flow (∼2 l/day) to 20 ml/day. Unexpectedly, the hydrate destabilized after about 125 days. Tidally induced flow reversals are common (∼25% of time) in this setting characterized by ‘overpressured’ pore waters. These reversals pump sulfate-rich bottom water into near-surface sediments where Archaea anaerobically oxidize CH4 and induce carbonate precipitation. At the sediment–water interface, authigenic carbonates are undergoing dissolution. Methanotrophs dominated the microbial community where fluid is discharged to ambient seawater. All expelled methane is apparently oxidized in the water column.