Summertime Nutrient Supply to Near-Surface Waters of the Northeastern Gulf of Mexico: 1998, 1999, and 2000

In the summers of 1998, 1999, and 2000, deep water eddies induced strong anticyclonic currents along the upper slope and outer shelf from the Mississippi River delta to the west Florida shelf. Those currents transported Mississippi River discharge eastward along the outer shelf and slope, reversing the normal offshore increase in salinity, with the exception of a few regions very near the coast that were influenced by the discharges from other rivers or bays. The entrainment of low-salinity river water resulted in anomalously high chlorophyll a concentrations in the upper 15 m over the outer shelf and upper slope, in contrast to the concentrations that typically occur over deep water in the subtropics in summer. Nitrate concentrations in this surface water were quite low except near the mouths of rivers, which act as point sources for nutrients; presumably, this was because of the rapid utilization of nitrate by phytoplankton. A significant supply of nutrients to the euphotic zone at regions quite removed from these point sources resulted from eddies intruding onto or formed over the slope. These caused mid-depth water rich in nutrients to be uplifted to within the euphotic zone, the uplift depending on the location and intensity of the eddies. Based on measurements at approximately 100 stations on each cruise, estimates were made of the quantity of nitrate and silicate in the upper 15 m of the water column and in the depth interval from 15m to 60 m, the nominal depth of the euphotic zone. Study results suggest that the nitrate and silicate in the near-surface interval of 0-15 m largely resulted from riverine discharge and subsequent advection, while the nutrients between 15 and 60 m resulted from uplift of waters by circulation features. The euphotic zone occupied at least the upper 60 m of the water column, but standing stocks of nitrate and silicate in the 15- to 60-m layer were between two and six times those in the upper 15 m on all three cruises and appeared to depend on the strength and relative proximity to the shelf break of local anticyclonic features. The effects of these circulation features were potentially significant in supplying nutrients to the euphotic zone during these summers

Hydrographic Properties and Inferred Circulation Over the Northeastern Shelves of the Gulf of Mexico During Spring to Midsummer of 1998

A hydrographic cruise was conducted 5-16 May 1998 over the northeastern shelves of the Gulf of Mexico, Observed distributions of temperature, salinity, oxygen, and nutrients were consonant with prior occurrences of upwelling, particularly near the head of DeSoto Canyon. Shipboard, moored, and satellite observations indicated these upwelling events were related to the presence of an anticyclonic circulation feature over the canyon. In addition, several cool water events occurred during spring in the nearshore region west of Pensacola; these may be attributed to atmospheric effects. High river discharges from rivers west of the Apalachicola during winter and spring likely resulted in the extensive surface distributions of low-salinity water observed from Mississippi Sound to Cape San Bias during the cruise. The combination of cool bottom temperatures and relatively low surface salinities over the inshore shelf west of Cape San Bias, with the usual seasonal warming, resulted in enhanced vertical stability. This stability likely inhibited vertical mixing and contributed to the development of the relatively low concentrations of dissolved oxygen observed in the bottom waters

Monsoon-driven seasonal hypoxia along the northern coast of Oman

Dissolved oxygen and current observations from a cabled ocean observatory in the Sea of Oman show that the annual recurrence of coastal hypoxia, defined as dissolved oxygen concentrations ≤63 μM, is associated with the seasonal cycle of local monsoon winds. The observations represent the first long-term (5+ years) continuous moored observations off the northern Omani coast. During the summer/fall southwest (SW) monsoon season (Jun-Nov), winds in the Sea of Oman generate ocean currents that result in coastal upwelling of subsurface waters with low dissolved oxygen concentrations. The source of the poorly oxygenated water is the oxygen minimum zone (OMZ) in the Arabian Sea, a layer approximately 1000-m thick within the 100 to 1200 m depth range, where dissolved oxygen values approach anoxia. During the winter monsoon season (Dec-Feb), the Sea of Oman winds are from the northwest, forcing strong and persistent southeast currents. These winds generate oceanic downwelling conditions along the coastal ocean that ventilate waters at depth. Possible impacts of the monsoon-driven seasonal hypoxia on local fisheries and implications due to climate change are also discussed in this study

Sperm Whale Seismic Study in the Gulf Of Mexico; Annual Report: Year 2

This report is about the cooperative research on sperm whales and their response to seismic exploration in the Gulf of Mexico

Sperm Whale Seismic Study in the Gulf of Mexico Annual Report

The Sperm Whale Seismic Study, year one, is the first report of a three year research project in the Gulf of Mexico to tag sperm whales and gather a variety of information, including genetic analyses, habitat, seasonal distribution, diving behavior, acoustic noises associated with behaviors and locations, as well as other information and analyses

Sperm Whale Seismic Study in the Gulf of Mexico, Annual Report: Years 3 and 4

This report covers the research conducted by several organizations to understand sperm whales in the Gulf of Mexico. Their team utilizes satellite-tracked radio tags, photographs, and genetic tests to better understand the whales

Northeastern Gulf of Mexico Chemical Oceanography and Hydrography Study: Synthesis Report

The three objectives for this study were to develop an oceanographic experimental design of research cruises covering the Northeastern Gulf of Mexico Physical Oceanography Program (NEGOM) study area, to collect the data needed to analyze the chemical oceanographic and hydrographic measurements, and to analyze the data to describe the vertical and horizontal spatial distributions and temporal variability of water properties

Understanding the Processes that Maintain the Oxygen Levels in the Deep Gulf of Mexico: Synthesis Report

Technical report generated as a result of a grant with the goal of understanding oxygen levels in the Gulf of Mexico at depths greater than 400 meter

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