Daily patterns of fluorescence in vivo in the central equatorial Pacific

A daily cycle of fluorescence in vivo was strikingly apparent in surface waters of the central equatorial Pacific between latitudes 4N and 10S, but not in waters to the north or south of this zone. These changes in fluorescence did not represent changes in chlorophyll-a concentration, but rather a photoinhibition of fluorescence by ambient light. Higher nutrient and chlorophyll-a concentrations were found in the region where cycling occurred...

A Comparison of Methods for Determining Significant Wave Heights-Applied to a 3-m Discus Buoy during Hurricane Katrina

In August 2005, the eye of Hurricane Katrina passed 90 km to the west of a 3-m discus buoy deployed in the Mississippi Sound and operated by the Central Gulf of Mexico Ocean Observing System (CenGOOS). The buoy motions were measured with a strapped-down, 6 degrees of freedom accelerometer, a three-axis magnetometer, and from the displacement of a GPS antenna measured by postprocessed-kinematic GPS. Recognizing that an accelerometer experiences a large offset due to gravity, the authors investigated four different means of computing wave heights. In the most widely used method for a buoy with a strapped-down, 1D accelerometer, wave heights are overestimated by 26% on average and up to 56% during the peak of the hurricane. In the second method, the component of gravity is removed from the deck relative z-axis accelerations, requiring pitch and roll information. This is most similar to the motion of the GPS antenna and reduces the overestimation to only 5% on average. In the third method, the orientation data are used to obtain a very accurate estimate of the vertical acceleration, reducing the overestimation of wave heights to 1%. The fourth method computes an estimate of the true earth-referenced vertical accelerations using the accelerations from all three axes but not the pitch and roll information. It underestimates the wave heights by 2.5%. The fifth method uses the acceleration from all three axes and the pitch and roll information to obtain the earth-referenced vertical acceleration of the buoy, the most accurate measure of the true wave vertical acceleration. The primary conclusion of this work is that the measured deck relative accelerations from a strapped- down, 1D accelerometer must be tilt corrected in environments of high wave heights

Wave Heights during Hurricane Katrina: An Evaluation of PPP and PPK Measurements of the Vertical Displacement of the GPS Antenna

In August 2005 the eye of Hurricane Katrina passed 49 n mi to the west of a 3-m discus buoy operated by the Central Gulf of Mexico Ocean Observing System (CenGOOS). Buoy motions were measured with a strapped-down 6 degrees of freedom accelerometer, a three-axis magnetometer, and a survey-grade GPS receiver. The significant wave heights were computed from the buoy\u27s accelerometer record and from the dual-frequency GPS measurements that were processed in two different ways. The first method was postprocessed kinematic (PPK) GPS, which requires another GPS receiver at a fixed known location, and the other was precise point positioning (PPP) GPS, which is another postprocessed positioning technique that yields absolute rather than differential positions. Unlike inertial measurement units, either GPS technique can be used to obtain both waves and water levels. The purpose of this note is to demonstrate the excellent reliability and accuracy of both methods for determining wave heights and periods from a GPS record. When the motion of the GPS antenna is properly understood as the motion of the buoy deck and not the true vertical motion of the sea surface, the GPS wave heights are as reliable as a strapped-down 1D accelerometer

Hurricane Katrina Winds Measured By a Buoy-Mounted Sonic Anemometer

The eye of Hurricane Katrina passed within 49 n mi of an oceanographic observing system buoy in the Mississippi Bight that is part of the Central Gulf of Mexico Ocean Observing System. Although a mechanical anemometer failed on the buoy during the hurricane, a two-axis sonic anemometer survived and provided a complete record of the hurricane\u27s passage. This is the first reported case of a sonic anemometer surviving a hurricane and reporting validated data, and it demonstrates that this type of anemometer is a viable alternative to the mechanical anemometers traditionally used in marine applications. The buoy pitch and roll record during the storm show the importance of compensating the anemometer records for winds oblique to the horizontal plane of the anemometers. This is made apparent in the comparison between the two wind records from the anemometers during the hurricane

Development, Operation, and Results From the Texas Automated Buoy System

The Texas Automated Buoy System (TABS) is a coastal network of moored buoys that report near-real-time observations about currents and winds along the Texas coast. Established in 1995, the primary mission of TABS is ocean observations in the service of oil spill preparedness and response. The state of Texas funded the system with the intent of improving the data available to oil spill trajectory modelers. In its 12 years of operation, TABS has proven its usefulness during realistic oil spill drills and actual spills. The original capabilities of TABS, i.e., measurement of surface currents and temperatures, have been extended to the marine surface layer, the entire water column, and the sea floor. In addition to observations, a modeling component has been integrated into the TABS program. The goal is to form the core of a complete ocean observing system for Texas waters. As the nation embarks on the development of an integrated ocean observing system, TABS will continue to be an active participant of the Gulf of Mexico Coastal Ocean Observing System (GCOOS) regional association and the primary source of near-surface current measurements in the northwestern Gulf of Mexico. This article describes the origin of TABS, the philosophy behind the operation and development of the system, the resulting modifications to improve the system, the expansion of the system to include new sensors, the development of TABS forecasting models and real-time analysis tools, and how TABS has met many of the societal goals envisioned for GCOOS

Characterization of Subsurface Polycyclic Aromatic Hydrocarbons at the Deepwater Horizon Site

Here, we report the initial observations of distributions of polycyclic aromatic hydrocarbons (PAH) in subsurface waters near the Deepwater Horizon oil well site (also referred to as the Macondo, Mississippi Canyon Block 252 or MC252 well). Profiles of in situ fluorescence and beam attenuation conducted during 9-16 May 2010 were characterized by distinct peaks at depths greater than 1000 m, with highest intensities close to the wellhead and decreasing intensities with increasing distance from the wellhead. Gas chromatography/mass spectrometry (GC/MS) analyses of water samples coinciding with the deep fluorescence and beam attenuation anomalies confirmed the presence of polycyclic aromatic hydrocarbons (PAH) at concentrations reaching 189 mu g L(-1) (ppb). Subsurface exposure to PAH at levels considered to be toxic to marine organisms would have occurred in discrete depth layers between 1000 and 1400 m in the region southwest of the wellhead site and extending at least as far as 13 km. Citation: Diercks, A.-R., et al. (2010), Characterization of subsurface polycyclic aromatic hydrocarbons at the Deepwater Horizon site, Geophys. Res. Lett., 37, L20602, doi: 10.1029/2010GL045046

Analyses of Water Samples From the Deepwater Horizon Oil Spill: Documentation of the Subsurface Plume

Surface and subsurface water samples were collected in the vicinity of the Deepwater Horizon (DWH) wellhead in the Gulf of Mexico. Samples were extracted with dichloromethane and analyzed for a toxic component, polycyclic aromatic hydrocarbons (PAHs), using total scanning fluorescence (TSF) and by gas chromatography/mass spectrometry (GC/MS). An aliquot of fresh, floating oil from a surface sample was used as a DWH oil reference standard. Twelve of 19 samples collected from 24 May 2010 to 6 June 2010 on the R/V Walton Smith cruise contained TSF maximum intensities above background (0.7 µg L À1 based on 1 L sample size). These 12 samples had total petroleum hydrocarbon (TPH) concentrations as measured by quantitative gas chromatography flame ionization detector (FID) ranging from 2 to 442 µg L À1 . Quantitative GC/MS analysis of these 12 samples resulted in total PAH concentrations ranging from 0.01 to 59 µg L À1 . Low molecular weight, more water-soluble naphthalene and alkylated naphthalene dominated the PAH composition patterns for 11 of the 12 water samples. Sample 12 exhibited substantially reduced concentrations of naphthalenes relative to other PAH compounds. The total PAH concentrations were positively correlated (R 2 = 0.80) with the TSF maximum intensity (MI). TSF is a simple, rapid technique providing an accurate prediction of the amount of PAH present in a sample. TSFderived estimates of the relative contribution of PAH present in the oil provided evidence that PAH represented~10% of the higher molecular weight TPH. The subsurface oil plume was confirmed by the analyses of discrete water samples for TSF, TPH, and PAH

Characterization of Subsurface Polycyclic Aromatic Hydrocarbons at the Deepwater Horizon Site

Here, we report the initial observations of distributions of polycyclic aromatic hydrocarbons (PAH) in subsurface waters near the Deepwater Horizon oil well site (also referred to as the Macondo, Mississippi Canyon Block 252 or MC252 well). Profiles of in situ fluorescence and beam attenuation conducted during 9-16 May 2010 were characterized by distinct peaks at depths greater than 1000 m, with highest intensities close to the wellhead and decreasing intensities with increasing distance from the wellhead. Gas chromatography/mass spectrometry (GC/MS) analyses of water samples coinciding with the deep fluorescence and beam attenuation anomalies confirmed the presence of polycyclic aromatic hydrocarbons (PAH) at concentrations reaching 189 μg L−1 (ppb). Subsurface exposure to PAH at levels considered to be toxic to marine organisms would have occurred in discrete depth layers between 1000 and 1400 m in the region southwest of the wellhead site and extending at least as far as 13 km

Effect of mixing in continuous ocean sampling systems

Typescript (photocopy).Small-scale variability of many properties in the ocean can best be studied by pumping water through a hose to analytical systems on board a ship. Sampling, however, tends to obliterate small-scale features of the resulting data. The effect of this process can be assessed using the theory of systems analysis. This treats the sampling system as a linear filter acting on the inlet concentration stream to produce a filtered output. The sampling system consists of a centrifugal pump coupled to a long hose. Impulse response functions are derived for the pump and for the hose. Frequency response functions are then derived for the pump and for the hose. The frequency response of the sampling system is the product of the frequency response functions of the individual components. The system gain function is transposed to a environmental scale by dividing frequency into the velocity of the pump inlet through the water. For sampling from a ship while underway, the spatial resolution at the analyzer is decreased in direct proportion to the ship's speed and the length of the hose. Resolution is increased in proportion to the square root of the pressure generated by the pump. Pump internal volumes substantially reduce resolution when they approach 2% of the volume of the hose