Ann E. Jochens

Red tides in the Gulf of Mexico: Where, when, and why?

[1] Independent data from the Gulf of Mexico are used to develop and test the hypothesis that the same sequence of physical and ecological events each year allows the toxic dinoflagellate Karenia brevis to become dominant. A phosphorus-rich nutrient supply initiates phytoplankton succession, once deposition events of Saharan iron-rich dust allow Trichodesmium blooms to utilize ubiquitous dissolved nitrogen gas within otherwise nitrogen-poor sea water. They and the co-occurring K. brevis are positioned within the bottom Ekman layers, as a consequence of their similar diel vertical migration patterns on the middle shelf. Upon onshore upwelling of these near-bottom seed populations to CDOM-rich surface waters of coastal regions, light-inhibition of the small red tide of ~1 ug chl l(-1) of ichthytoxic K. brevis is alleviated. Thence, dead fish serve as a supplementary nutrient source, yielding large, self-shaded red tides of ~10 ug chl l(-1). The source of phosphorus is mainly of fossil origin off west Florida, where past nutrient additions from the eutrophied Lake Okeechobee had minimal impact. In contrast, the P-sources are of mainly anthropogenic origin off Texas, since both the nutrient loadings of Mississippi River and the spatial extent of the downstream red tides have increased over the last 100 years. During the past century and particularly within the last decade, previously cryptic Karenia spp. have caused toxic red tides in similar coastal habitats of other western boundary currents off Japan, China, New Zealand, Australia, and South Africa, downstream of the Gobi, Simpson, Great Western, and Kalahari Deserts, in a global response to both desertification and eutrophication.

Near-Resonant Ocean Response to Sea Breeze on a Stratified Continental Shelf

Abstract The spatial structure and temporal characteristics of sea breeze and the associated coastal ocean response in the northwest Gulf of Mexico are investigated using moored instruments, hydrographic stations, and wind measurements. Near the study area of 30°N, motions in the diurnal–inertial band (DIB) may be significantly enhanced by a near-resonant condition between local inertial and diurnal forcing frequencies. Wavelet analysis is used to quantify the results. Results indicate that diurnal sea-breeze variability peaks in summer and extends at least 300 km offshore with continuous seaward phase propagation. The maximum DIB oceanic response occurs in June when there is a shallow mixed layer, strong stratification, and an approximately 10-day period of continuous sea-breeze forcing. DIB current variance decreases in July and August as the consequence of the deepening of the mixed layer and a more variable phase relationship between the wind and current. River discharge varies interannually and can s...

Low‐Frequency Circulation Over the Texas‐Louisiana Continental Shelf

Low-frequency circulation over the Texas-Louisiana continental shelf is examined. Currents over the inner shelf are upcoast (Rio Grande to Mississippi River) in summer and downcoast in nonsummer and are driven by an annual cycle of winds. This results in an annual signal for salinity, with lowest salinity waters occurring (a) in late spring along the inner portion of the western shelf when downcoast flows carry the high discharges from the Mississippi-Atchafalya and other rivers to the Mexican border, and (b) in summer over the inner and outer eastern shelf when the upcoast flow causes a pooling of the discharges from the Mississippi-Atchafalya rivers over that shelf. Upcoast winds during summer also result in high salinities over the western shelf due to advection from off Mexico and upwelling. Currents over the outer shelf are variable, but predominantly upcoast throughout the year, probably a result of the integrated effects of anticy-clonic eddies impinging on the shelf edge. Comparison of currents in the weather band (2-10 d) with the mesoscale band (10-100 d) suggests the shelf is divided at approximately the 50-m isobath. The weather band predominates over the inner shelf, reflecting frequent passage of fronts over the region. The mesoscale band predominates over the outer shelf, indicating the presence of offshelf eddies that frequent this region.

Hydrographic and acoustic evidence for enhanced plankton stocks in a small cyclone in the northeastern Gulf of Mexico

Mesoscale eddies (diameters of hundreds of km) have been shown to influence plankton production as well as the distribution of seabirds and marine mammals in the Gulf of Mexico. Smaller circulation features (eddies with diameters of tens of km) may have similar effects. We show that a small, sub-mesoscale cyclone located on the continental shelf and slope in the northeastern Gulf of Mexico during November 1997 was an area of enhanced nutrients, chlorophyll, and acoustic volume backscattering strength ðSvÞ: Nitrate concentrations at mid-depth in the euphotic zone were as high as 2mM, surface chlorophyll exceeded 1m gl � 1 , and Sv was as much as 15 dB referenced to 1 m � 1 4p � 1 greater within this feature than in surrounding waters. Since Sv at 153 kHz is a proxy for the abundance of sound-scattering mesozooplankton and micronekton, we infer that this cyclone was locally enriched in biomass of these organisms. As with mesoscale eddies, smaller cyclones could also function as patches of favorable habitat for higher-trophic-level organisms and their prey. r 2003 Elsevier Science Ltd. All rights reserved.

Bay of campeche circulation : An update

We address four independent sources of observational evidence pertaining to circulation in the Bay of Campeche (BOC), located south of 23°N in the western Gulf of Mexico, with the objective of characterizing its mean circulation, its variability, and the probable forcing thereof. The observational information includes historic hydrographic and dissolved oxygen data, Lagrangian current data, satellite-derived sea surface height anomaly (SSHA), and special observations of marine winds in the BOC. The hydrographic data reveals that the mean surface circulation relative to 425 db and to 800 db includes a weak cyclone with cyclic transport of about 4x10 6 m 3 .s -1 . Ten years of near-surface drifter observations shows a statistically meaningful mean cyclonic pattern of current with westward intensification that is consistent with the mean surface dynamic topography relative to 800 db. Observations of mean currents in the BOC at 900 m based on deep floats by G. L. Weatherly and others allows estimation of the current shear from the Lagrangian data and this is geostrophically consistent with that from the dynamic topography relative to 800 m. The mean cyclonic wind stress curl field deduced from two sources of marine wind data indicate a forced Sverdrup transport consistent with that observed. Moreover a seasonal cycle is suggested in the near surface drifter data that is coherent with the seasonal signal in the wind stress curl. Finally, the historic SSHA for a period of over 8 years in the 1990s allows a characterization of the dominant empirical spatial patterns and their temporal variability.

Eddy Forced Variations in On‐ and off‐Margin Summertime Circulation Along the 1000‐m Isobath of the Northern Gulf of Mexico, 2000–2003, and Links with Sperm Whale Distributions Along the Middle Slope

In summers 2000-2003, NOAA Ship Gordon Gunter and TAMU R/V Gyre dropped XBTs and logged ADCP data while carrying out visual and passive-acoustic surveys for sperm whales along the 1000-m isobath of the northern Gulf of Mexico. The ships also made CTD casts, particularly when/where the XBT and ADCP data indicated the ships were passing into or out of anticyclonic and/or cyclonic slope eddies. The fine-scale resolution of the ship surveys, when combined with the meso-scale resolution of remote sensing surveys of sea surface height and ocean color, document the summer-to-summer variability in the intensity and geographic location of Loop Current eddies, warm slope eddies, and areas of cyclonic circulation over this middle slope region of the northern Gulf of Mexico. These variations forced striking year-to-year differences in the locations along the 1000-m isobath where there was on-margin and off-margin flow, and in locations where sperm whales were encountered along the 1000-m isobath. For example, when there was on-margin flow into the Mississippi Canyon region in early summer 2003, sperm whales were very rarely seen or heard there. In contrast, later that summer and during other summers when flow was along-margin or off-margin there, sperm whales were locally abundant. In this report we describe how eddy-forced variations in on-margin and off-margin flow changed the meso-scale circulation along the 1000-m isobath, and we show that most sperm whales were encountered in regions of negative SSH and/or higher-than-average surface chlorophyll.

Development of a Coastal Ocean Observing System for the Gulf of Mexico

A regional coastal ocean observing system being developed under the U.S. Integrated Ocean Observing System, a Global Ocean Observing System contribution, is the Gulf of Mexico Coastal Ocean Observing System (GCOOS). A wide range of users will be provided with estuarine and marine system products, information, and data by GCOOS, which will be a sustained ocean observing system. GCOOS is being developed through the GCOOS Regional Association. GCOOS building activities include real-time physical data connection via the Internet from extant observing systems to the National Data Buoy Center, extant observing systems inventory development, and mechanism establishment and implementation for ongoing identification of regional need priority pilot projects, and stakeholder priorities and requirements. Identification of products and measurements emergency responders and managers need for better southeastern United States and Gulf of Mexico inundation and storm surge prediction and mitigation is being provided through an inundation and storm surge workshop. GCOOS enhancement funding from private and governmental sources is being sought. The authors argue that new federal resources for regional coastal ocean observing systems must be committed for GCOOS to evolve to its full potential.

Cabled ocean observatories in Sea of Oman and Arabian Sea

An ocean observatory—consisting of a real-time, cabled array in the Sea of Oman and an internally recording, autonomous mooring array recently upgraded to a cabled array in the northern Arabian Sea—celebrated more than 2500 days of continuous operation in July 2012. The observatory, which measures a range of properties, such as water current velocities, temperature, salinity, pressure, dissolved oxygen, and turbidity, is part of the Lighthouse Ocean Research Initiative (LORI) project [du Vall et al., 2011], which was designed as a pilot project and installed in 2005 in the region off Abu Bakara (Figures 1a and 1b). The initial goal of the project was to prove that an in situ, cabled ocean observatory can return high-quality scientific data on a real-time basis over longer time periods than conventional moored systems. That same year, an autonomous array was deployed off Ras al Hadd and on Murray Ridge in the Arabian Sea (Figure 1a).

One System, Many Societal Benefits: Building an Efficient, Cost-Effective Ocean Observing System for the Gulf of Mexico

Abstract During a decade of building the Gulf of Mexico Coastal Ocean Observing System (GCOOS), there has been convincing evidence that an integrated “system of systems” is an effective, efficient system that provides many societal benefits, including economic development opportunities. The Gulf community has come a long way toward establishing a regional ocean observing system, and with input from more than 700 stakeholders, the GCOOS Regional Association has developed a comprehensive blueprint for monitoring in the Gulf. This blueprint, the GCOOS Build-out Plan, can and should serve as a guide for future investments, including those intended to generate meaningful ecosystem indicators that inform the restoration process and ascertain the success of restoration efforts. With an unprecedented opportunity via The Clean Water Act penalty monies, the region is poised to build on extensive multi-institutional, interdisciplinary relationships to expand existing infrastructure into a comprehensive system that can address the myriad issues facing the Gulf.

Integrating Observing Systems to benefit stakeholders: A case study in the Gulf of Mexico

The U.S. Integrated Ocean Observing System is being designed to be an end-to Dend, integrated, sustained, operational System of Systems that provides data, information and products to benefit a broad range of stakeholders in their decision-making. These design concepts form the basis of pilot projects being undertaken by the Gulf of Mexico Coastal Ocean Observing System Regional Association (GCOOS-RA). This paper presents a case study of the GCOOS-RA Harmful Algal Bloom Integrated Observing System (HABIOS) Project. A set of research activities related to harmful algal blooms is examined for eventual transition from pilot project to an integrated operational system. The end-to-end nature of the system is explored from the perspectives of design and operation, data management and communication, modeling and analysis, decision-support tools and outreach, and benefits to stakeholders at national, regional, state, and local levels. The case study of the HABs pilot projects will demonstrate that HAB-related observations need to be both sustained and operational, and that progress is being may through the integration of the efforts of many entities concerned with detecting and monitoring HAB events and mitigating HAB impacts.