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The continental shelf ocean circulation is driven by a combination of local and deep ocean forcing, where the local forcing is by surface momentum and buoyancy (heat and fresh water) fluxes and by land-derived fresh water fluxes, and the deep ocean forcing is by momentum and buoyancy fluxes transmitted across the shelf break. While all continental shelves share the same response physics, their geom etries, river distributions, and boundary currents make their individual behaviors unique. Here we consider the responses of the West Florida Continental Shelf (WFS) to external forcing on time scales ranging from the passage of synoptic scale weather systems to interannual anomalies. Our approach is to combine measure ments made over several years with applied numerical model experiments, and we describe several features of the time and space varying circulation that may have relevance to the ecological workings of the WFS. These include the role of the bot tom Ekman layer in transporting cold, nutrient-rich waters of deep-ocean origin to the nearshore; seasonal reversals of the inner shelf currents; seasonal reversals of the outer-shelf currents that can occur independent of the Gulf of Mexico Loop Current to provide a WFS pathway for Mississippi River water in spring and sum mer; the formation of a spring cold tongue and the associated "Green River" phe nomenon; and ventilations by deep-ocean water that may occur interannually.

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The annual cycle of sea surface temperature and ocean-atmosphere fluxes on the west Florida shelf is described using in situ measurements and climatology. Seasonal reversals in water temperature tendency occur when the net surface heat flux changes sign in boreal spring and fall. Synoptic-scale variability is also important. Momentum and heat flux variations result in successive water column stratification and destratification events, particularly at shallower depths during spring. Fall is characterized by destratification of the water column and a series of steplike decreases in the temperature. These are in response to both tropical storms and extratropical fronts. Tropical storms are responsible for the largest momentum fluxes, but not necessarily for the largest surface heat fluxes. A one-dimensional analysis of the temperature equation suggests that surface heat flux is primarily responsible for the spring and fall seasonal ocean temperature changes, but that synoptic-scale variability is also controlled by the ocean circulation dynamics. During summer, the situation is reversed and the major influence on water temperature is ocean dynamics, with the heat flux contributing to the synoptic-scale variability. There is also evidence of interannual variability: the wintertime temperatures get increasingly colder from 1998 to 2000, and the greatest stratification and coldest subsurface temperatures occur in 1998. NCEP-NCAR reanalysis fields do not reproduce the high spatial flux variability observed in situ or with satellite measurements. Reconciling these differences and their impacts on the climate variability of this region provides challenges to coupled oceanatmosphere models and their supporting observing systems.

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The annual anthropogenic ocean carbon uptake of 2.6 6 0.5 Gt C is changing ocean composition (e.g., pH) at unprecedented rates, but our ability to track this trend effectively across various ocean ecosystems is limited by the availability of low-cost, high-quality autonomous pH sensors. The Wendy Schmidt Ocean Health XPRIZE was a year-long competition to address this scientific need by awarding $2 million to developers who could improve the performance and reduce the cost of pH sensors. Contestants' sensors were deployed in a series of trials designed to test their accuracy, repeatability, and stability in laboratory, coastal, and open-ocean settings. This report details the validation efforts behind the competition, which included designing the sensor evaluation trials, providing the conventional true pH values against which sensors were judged, and quantifying measurement uncertainty. Expanded uncertainty (coverage factor k 5 2, corresponding to 95% confidence) of validation measurements throughout the competition was approximately 0.01 pH units. A custom tank was designed for the coastal trials to expose the sensors to natural conditions, including temporal variability and biofouling, in a spatially homogenous environment. The competition prioritized the performance metrics of accuracy, repeatability, and stability over specific applications such as high-frequency measurements. Although the XPRIZE competition focused on pH sensors, it highlights considerations for testing other marine sensors and measuring seawater carbonate chemistry.

Current observations are compared from upward-and downward-looking acoustic Doppler current profilers (ADCPs) deployed on the West Florida Shelf (WFS). Despite regional differences, statistical analyses show good agreement between all sets of observations throughout the water column except in the upper few meters where all downward-looking ADCPs exhibit small, but significant, reduction in rms speed values. Evidence suggests that this reduction is mooring related. It is possible that the presence of near-surface bubbles caused by wave activity could bias the near-surface observations. Otherwise, either the upward-or downward-looking mooring systems produce equivalent observations with differences due to spatial variations.

Observed relative humidity variations on the coastal ocean of the West Florida Continental Shelf (WFS) are examined over the 5-yr period 1998-2003. Despite considerable daily variability within seasons, the monthly mean values are nearly constant at about 75%. Summertime specific humidity is twice that during winter, so high air temperatures are responsible for the low summer monthly mean relative humidities. Winter has the greatest relative humidity variability; values range from less than 50% to over 100% as extratropical fronts move over the WFS. Saturation (and fog) occurs as warm moist air passes over colder water. Two different sensors, mounted on multiple moorings, were used to make these observations. Monthly mean values from the Rotronics MP-100F are higher than the Hygrometrix 1020SHT. In addition to sensor differences, a contributing cause to this offset appears to be the locations chosen for sensor deployment. NCEP reanalysis climatology over the WFS and land-based coastal data both show an annual cycle in monthly mean relative humidity, with higher values in summer, suggesting that the reanalysis field is influenced by land. Air-sea fluxes over the WFS are sensitive to small spatial variability in the coastal ocean and atmosphere. The large grid spacing of the NCEP reanalysis does not capture this variability. The lack of coastal ocean data for assimilation biases the NCEP reanalysis fields toward land-based measurements. Increased spatial coverage via evolving Coastal Ocean Observing Systems should remedy this problem by providing required information for describing and understanding the complicated ocean-atmosphere interactions that occur on continental shelves.