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In cold polar waters, temperatures sometimes drop below the freezing point, a process referred to as supercooling. However, observational challenges in polar regions limit our understanding of the spatial and temporal extent of this phenomenon. We here provide observational evidence that supercooled waters are much more widespread in the seasonally ice-covered Southern Ocean than previously reported. In 5.8% of all analyzed hydrographic profiles south of 55° S, we find temperatures below the surface freezing point (‘potential’ supercooling), and half of these have temperatures below the local freezing point (‘in-situ’ supercooling). Their occurrence doubles when neglecting measurement uncertainties. We attribute deep coastal-ocean supercooling to melting of Antarctic ice shelves, and surface-induced supercooling in the seasonal sea-ice region to winter-time sea-ice formation. The latter supercooling type can extend down to the permanent pycnocline due to convective sinking plumes—an important mechanism for vertical tracer transport and water-mass structure in the polar ocean.

Biogeochemical Argo floats, profiling to 2,000‐m depth, are being deployed throughout the Southern Ocean by the Southern Ocean Carbon and Climate Observations and Modeling program (SOCCOM). The goal is 200 floats by 2020, to provide the first full set of annual cycles of carbon, oxygen, nitrate, and optical properties across multiple oceanographic regimes. Building from no prior coverage to a sparse array, deployments are based on prior knowledge of water mass properties, mean frontal locations, mean circulation and eddy variability, winds, air‐sea heat/freshwater/carbon exchange, prior Argo trajectories, and float simulations in the Southern Ocean State Estimate and Hybrid Coordinate Ocean Model (HYCOM). Twelve floats deployed from the 2014–2015 Polarstern cruise from South Africa to Antarctica are used as a test case to evaluate the deployment strategy adopted for SOCCOM's 20 deployment cruises and 126 floats to date. After several years, these floats continue to represent the deployment zones targeted in advance: (1) Weddell Gyre sea ice zone, observing the Antarctic Slope Front, and a decadally‐rare polynya over Maud Rise; (2) Antarctic Circumpolar Current (ACC) including the topographically steered Southern Zone chimney where upwelling carbon/nutrient‐rich deep waters produce surprisingly large carbon dioxide outgassing; (3) Subantarctic and Subtropical zones between the ACC and Africa; and (4) Cape Basin. Argo floats and eddy‐resolving HYCOM simulations were the best predictors of individual SOCCOM float pathways, with uncertainty after 2 years of order 1,000 km in the sea ice zone and more than double that in and north of the ACC., Key Points SOCCOM float deployment strategy is based on prior water mass, frontal zone, forcing, and circulation information from data and modelsThese floats were deployed in the sea ice zone, Weddell and Ross Seas, Antarctic Circumpolar Current, and Subantarctic and Subtropical ZonesFloats have already provided information on carbon outgassing, mixing during Maud Rise polynya, oxygen utilization, and net community production

International audience; Ecosystem-based management (EBM) is the dominant paradigm, at least in theory, for coastal resource management. However, there are still relatively few case studies illustrating thorough application of principles of EBM by stakeholders and decision-makers. At Elkhorn Slough, a California estuary, we launched an EBM initiative in 2004. Stakeholders collaboratively developed and evaluated large-scale restoration alternatives designed to decrease two types of rapid habitat change occurring in the estuary, erosion of channels and dieback of salt marsh. In the end, decision-makers rejected large-scale alternatives altering the mouth of the estuary, and instead opted for small- to medium-scale restoration projects and recommended an added emphasis on reduction of nutrient-loading. We describe seven challenges encountered during the application of EBM principles: (1) interdisciplinary collaboration is difficult due to differences in professional culture and values, (2) roles and responsibilities of different participants are often not sufficiently clear, (3) implementing EBM is very costly in time and human resources, (4) an ecosystem services framework may not resonate with stakeholders already committed to biodiversity conservation, (5) conflicts arise from differences in desired restoration targets, (6) multiple geographic and jurisdictional scales cannot be simultaneously addressed, and (7) understanding of ecosystem drivers and processes may change rapidly. We recommend approaches to overcoming each of these challenges so that our experiences implementing EBM at one estuary can inform collaborative decision-making initiatives elsewhere. © 2015 The Authors.

The Southern Ocean is of outsized significance to the global oxygen and carbon cycles with relatively poor measurement coverage due to harsh winters and seasonal ice cover. In this study, we use recent advances in the parameterization of air-sea oxygen fluxes to analyze 9 years of oxygen data from a recalibrated Argo oxygen data set and from air-calibrated oxygen floats deployed as part of the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project. From this combined data set of 150 floats, we find a total Southern Ocean oxygen sink of -18380 Tmol yr(-1) (positive to the atmosphere), greater than prior estimates. The uptake occurs primarily in the Polar-Frontal Antarctic Zone (PAZ, -9430 Tmol O-2 yr(-1)) and Seasonal Ice Zone (SIZ, -1119.3 Tmol O-2 yr(-1)). This flux is driven by wintertime ventilation, with a large portion of the flux in the SIZ passing through regions with fractional sea ice. The Subtropical Zone (STZ) is seasonally driven by thermal fluxes and exhibits a net outgassing of 4729 Tmol O-2 yr(-1) that is likely driven by biological production. The Subantarctic Zone (SAZ) uptake is -25 +/- 12 Tmol O-2 yr(-1). Total oxygen fluxes were separated into a thermal and nonthermal component. The nonthermal flux is correlated with net primary production and mixed layer depth in the STZ, SAZ, and PAZ, but not in the SIZ where seasonal sea ice slows the air-sea gas flux response to the entrainment of deep, low-oxygen waters.

Optical in situ chemical sensors enable sampling intervals and durations that rival acoustic techniques used for measuring currents. Coupling these high-frequency biogeochemical and physical measurements in estuaries to address ecosystem-scale questions, however, is still comparatively novel. This study investigated how tides affect ecosystem metabolism in a mesotidal estuary in central California (Elkhorn Slough). Dissolved oxygen measurements were used to estimate the terms in a control volume budget for a tidal creek/marsh complex at tidal timescales over several weeks. Respiration rates were 1.6 to 7.3 g O2 m−2 day−1; net community production approached 20 g O2 m−2 day−1. We found that aquatic NCP integrated throughout the creek complex varied significantly over the spring-neap cycle. The intertidal contribution to aquatic metabolism was net heterotrophic during spring tides and generally in balance during neap tides because spring-tide marsh inundation was limited to nighttime, and therefore the marsh could not contribute any primary production to the water column. At the estuary scale, the fortnightly export of oxygen from the main channel to the intertidal was largely balanced by an advective flux up-estuary.

Vertical profiles of nitrate down to 1000 m depth were obtained about every 5 days and over several years by four profiling floats deployed near Station ALOHA in the North Pacific subtropical gyre. As a first step, we study the episodic and rapid (10–30 days) changes in the depth of constant-nitrate surfaces observed in the float records. These changes are in general correlated with similar changes in the depth of isopycnal surfaces and have a small horizontal scale (horizontal wavelength less than 2°). They are furthermore observed over the whole water column sampled by the floats and throughout the year, with no apparent seasonal cycle. Using these characteristics as well as a 7-year high-resolution time series of potential density at Station ALOHA and a high-resolution numerical simulation of the circulation around the station, we conclude that these episodic changes correspond to the depth anomalies associated with the rapid changes and/or small-scale features of the eddy field. Large vertical velocities associated with submesoscale frontal processes are confined to the surface mixed layer (SML) and play no role in the episodic nitrate events except, perhaps, in late winter to early spring when the SML reaches the top of the nutricline. As a second step, we study the variations of nitrate concentration along isopycnal surfaces, which enables us to isolate the effects of biological processes. In the lower euphotic zone (125–200 m), the nitrate variations reflect the response of the ecosystem to the eddy variability: the shallower the isopycnal surface, the lower the nitrate concentration, and conversely, with nitrate varying in Redfield stoichiometric proportions with oxygen anomaly (defined here as dissolved oxygen minus oxygen saturation). In the upper euphotic zone (0–125 m), in contrast, eddy-induced variations in along-isopycnal oxygen anomaly do not conform with current knowledge about supply and variability of nitrate, ammonium and dissolved organic matter; some other nitrogen source that remains to be identified is required for mass balance.

Chemical fluxes into and out of permeable seafloor sediments, such as those found on much of the continental shelf, are difficult to measure using conventional techniques. To overcome this difficulty, the eddy correlation method was adapted by oceanographers to determine oxygen flux across the sediment-water interface. In this article, we demonstrate that the eddy correlation method can also be used to measure nitrate flux across the sediment-water interface. A modified ISUS (In Situ Ultraviolet Spectrophotometer) optical nitrate sensor was used to measure dissolved nitrate at a frequency of 1.8 Hz. These observations were combined with vertical velocity measurements to calculate nitrate fluxes. Oxygen fluxes were also determined using a fast oxygen electrode system. The results for nitrate and oxygen flux compare well with simultaneous benthic flux chamber measurements made at a muddy sediment site at 95 m depth in Monterey Bay on the central California coast. The nitrate fluxes determined by the eddy correlation technique were considerably higher than benthic flux chamber values at sandy sediment sites at similar depths to the north and south of Monterey Bay. This difference is expected in permeable sediments where lateral flow through sediments will ventilate chamber water.

The NH4-Digiscan is an in situ analyzer designed for measuring ammonium in estuarine, coastal, and shelf waters at depths of less than 3 m. This wet chemical analyzer uses micro-solenoid pumps to propel sample and reagents, a gas diffusion cell to isolate the analyte from the matrix, and a conductivity detector for analyte detection. Instrument measurements are stable for deployments of at least 30 d. In estuarine and coastal waters, the analyzer is capable of sampling hourly and has a detection limit of 0.2 µM. In shelf waters, the NH4-Digiscan can be configured to have a detection limit of 0.014 µM. The simple chemistry, in situ capability, and high resolution sampling minimizes the use of toxic reagents, minimizes many of the problems plaguing ammonium analyses, and adequately captures the high temporal variability of coastal waters, which is often undersampled. The analyzer has been successfully deployed on coastal moorings, benthic flux chambers, and on a drifter 500 km west of Monterey Bay, California. The system can also be easily configured for laboratory bench top analysis of discrete samples.

An ocean observatory that consists of an array of moored sensor platforms, telemetry, and data collection and dissemination software was designed for monitoring the biogeochemistry and physical dynamics of coastal and estuarine ecosystems. The Land-Ocean Biogeochemical Observatory (LOBO) consists of robust moorings that can withstand tidal currents and weather. The moorings are highly configurable, can be deployed in waters as shallow as 0.5 m, are relatively easy to maintain, and accommodate a complete array of standard and novel sensors. The sensors communicate with an on-board controller which relays data to shore in near-real time. Up to five LOBO moorings have been simultaneously deployed and maintained in Elkhorn Slough, California, since November 2003. Continuous hourly data of biological, chemical, and physical properties are relayed to shore, processed, and disseminated to users through a web interface in near-real time. This article describes the design, implementation, and functionality of the LOBO monitoring system.

Gypsum is a highly soluble rock and is dissolved readily to form caves, sinkholes, disappearing streams, and other karst features that typically are also present in limestones and dolomites. Gypsum karst is widespread in the USA and has caused problems at several sites where dams were built, or where dam construction was considered. Gypsum karst is present (at least locally) in most areas where gypsum crops out, or is less than 30–60 m below the land surface. These karst features can compromise on the ability of a dam to hold water in a reservoir, and can even cause collapse of a dam. Gypsum karst in the abutments or foundation of a dam can allow water to pass through, around, or under a dam, and solution channels can enlarge quickly, once water starts flowing through such a karst system. The common procedure for controlling gypsum karst beneath the dam is a deep cut-off trench, backfilled with impermeable material, or a close-spaced grout curtain that hopefully will fill all cavities. In Oklahoma, the proposed Upper Mangum Dam was abandoned before construction, because of extensive gypsum karst in the abutments and impoundment area. Catastrophic failure of the Quail Creek Dike in southwest Utah in 1989 was due to flow of water through an undetected karstified gypsum unit beneath the earth-fill embankment. The dike was rebuilt, at a cost of US $12 million, with construction of a cut-off trench 600 m long and 25 m deep. Other dams in the USA with severe gypsum-karst leakage problems in recent years are Horsetooth and Carter Lake Dams, in Colorado, and Anchor Dam, in Wyoming.

Evaporites, including rock salt (halite) and gypsum (or anhydrite), are the most soluble among common rocks; they dissolve readily to form the same types of karst features that commonly are found in limestones and dolomites. Evaporites are present in 32 of the 48 contiguous states in USA, and they underlie about 40% of the land area. Typical evaporite-karst features observed in outcrops include sinkholes, caves, disappearing streams, and springs, whereas other evidence of active evaporite karst includes surface-collapse structures and saline springs or saline plumes that result from salt dissolution. Many evaporites also contain evidence of paleokarst, such as dissolution breccias, breccia pipes, slumped beds, and collapse structures. All these natural karst phenomena can be sources of engineering or environmental problems. Dangerous sinkholes and caves can form rapidly in evaporite rocks, or pre-existing karst features can be reactivated and open up (collapse) under certain hydrologic conditions or when the land is put to new uses. Many karst features also propagate upward through overlying surficial deposits. Human activities also have caused development of evaporite karst, primarily in salt deposits. Boreholes (petroleum tests or solution-mining operations) or underground mines may enable unsaturated water to flow through or against salt deposits, either intentionally or accidentally, thus allowing development of small to large dissolution cavities. If the dissolution cavity is large enough and shallow enough, successive roof failures can cause land subsidence and/or catastrophic collapse. Evaporite karst, natural and human-induced, is far more prevalent than is commonly believed.

Evaporites, including gypsum (or anhydrite) and salt, are the most soluble of common rocks; they are dissolved readily to form the same type of karst features that typically are found in limestones and dolomites, and their dissolution can locally result in major subsidence structures. The four basic requirements for evaporite dissolution to occur are: (1) a deposit of gypsum or salt; (2) water, unsaturated with CaSO4 or NaCl; (3) an outlet for escape of dissolving water; and (4) energy to cause water to flow through the system. Evaporites are present in 32 of the 48 contiguous states of the United States, and they underlie about 35–40% of the land area. Karst is known at least locally (and sometimes quite extensively) in almost all areas underlain by evaporites, and some of these karst features involve significant subsidence. The most widespread and pronounced examples of both gypsum and salt karst and subsidence are in the Permian basin of the southwestern United States, but many other areas also are significant. Human activities have caused some evaporite–subsidence development, primarily in salt deposits. Boreholes may enable (either intentionally or inadvertently) unsaturated water to flow through or against salt deposits, thus allowing development of small to large dissolution cavities. If the dissolution cavity is large enough and shallow enough, successive roof failures above the cavity can cause land subsidence or catastrophic collapse.

The McCauley Sinks, in the Holbrook basin of northeastern Arizona, are comprised of some 50 individual sinkholes within a 3-km-wide depression. The sinks are grouped in a semi-concentric pattern of three nested rings. The outerring is an apparent tension zone containing ring fractures. The two innerrings are semi-circular chains of large sinkholes, ranging up to 100m across and 50m deep. Severalsub-basins within the larger depression show local downwarping and possible incipent sinkholes.

Evaporites are the most soluble of common rocks; they are dissolved readily to form the same range of karst features that typically are found in limestones and dolomites. Evaporites, including gypsum (or anhydrite) and salt, are present in 32 of the 48 contiguous United States, and they underlie about 35–40% of the land area. Evaporite outcrops typically contain sinkholes, caves, disappearing streams, and springs. Other evidence of active karst in evaporites includes surface-collapse features and saline springs or saline plumes that result from dissolution of salt. Many evaporites, including some in the deeper subsurface, also contain evidence of paleokarst that is no longer active; this evidence includes dissolution breccias, breccia pipes, slumped beds, and collapse structures. Evaporites occur in 24 separate structural basins or geographic districts in the United States, and either local or extensive evaporite karst is known in almost all of these basins or districts. Human activities also have caused development of evaporite karst, primarily in salt deposits. Boreholes or underground mines may enable (either intentionally or inadvertently) unsaturated water to flow through or against salt deposits, thus allowing development of small to large dissolution cavities. If the dissolution cavity is large enough and shallow enough, successive roof failures can cause land subsidence or catastrophic collapse. Evaporite karst, both natural and human-induced, is far more prevalent than commonly believed.

Iron has been measured for 16 months with ∼21 day resolution at three stations in the upwelling ecosystem of central California, providing the first detailed assessment of the annual iron cycle in the coastal zone. A large pulse of iron occurs during the first spring upwelling event of the year. Iron concentrations then decay up to 100-fold over several months, although upwelling continues. Excess surface nitrate and low iron are the result during the summer and fall at the two stations furthest offshore (20 and 45 km), while nitrate is depleted and iron high nearshore (5 km). Phytoplankton biomass, primary production and community structure appear to be controlled by iron concentrations in offshore waters during this period.

Dissolved and particulate trace metal concentrations (dissolved Fe, Zn, Cd, Co, Cu and Ni; particulate Fe, Mn and Al) were measured along two transects in the Ross Sea during austral summer of 1990. Total Fe concentrations in southern Ross Sea and inshore waters were elevated >3.5 times that of northern waters. Dissolved Zn, Cd and Co concentrations were lower by factors of 4.5, 3.5 and 1.6 in southern surface waters relative to northern waters. Dissolved Cu and Ni concentrations were similar in both areas. Elevated Fe concentrations coincided with areas of increased productivity, phytoplankton biomass and nutrient drawdown, indicating that Fe is an important factor controlling the location of phytoplankton blooms in the Ross Sea. Particulate concentrations of Fe, Mn and Al indicate two possible sources of iron to the Ross Sea, resuspension of continental shelf sediments and iron incorporated in annual sea ice and released with meltwaters.

The availability of iron, an essential nutrient, controls rates of phytoplankton primary productivity in the open-ocean, upwelling ecosystems of the equatorial Pacific1,2. Upwelling injects large amounts of macronutrients into the euphotic zone of eastern boundary currents, such as the California Current System (CCS), where iron can become the limiting factor on productivity3,4. Iron addition to samples from some areas of the CCS has been shown to increase rates of biomass production5,6, but the processes that control iron availability in these systems remain poorly understood. Here we report measurements of dissolvable iron (that is, dissolved plus leachable iron at pH 3) in transects across the CCS in March of 1997 and 1998. We foundhigh concentrations of iron in 1997 during strong upwelling conditions. During the 1998 El Nino, the concentration of dissolvable iron in surface waters was low, even though that yearwas marked by high river flow and low offshore salinity. These results indicate that the primary source of iron in the CCS isresuspension of particles in the benthic boundary layer, followed by upwelling of this iron-rich water, rather than direct riverine input. This source of iron must be an essential but variable component of the high productivity found in upwelling ecosystems.

The question of whether the plankton communities in low-nutrient regions of the ocean, comprising 80% of the global ocean surface area, are net producers or consumers of oxygen and fixed carbon is a key uncertainty in the global carbon cycle. Direct measurements in bottle experiments indicate net oxygen consumption in the sunlit zone, whereas geochemical evidence suggests that the upper ocean is a net source of oxygen. One possible resolution to this conflict is that primary production in the gyres is episodic and thus difficult to observe: in this model, oligotrophic regions would be net consumers of oxygen during most of the year, but strong, brief events with high primary production rates might produce enough fixed carbon and dissolved oxygen to yield net production as an average over the annual cycle. Here we examine the balance of oxygen production over three years at sites in the North and South Pacific subtropical gyres using the new technique of oxygen sensors deployed on profiling floats. We find that mixing events during early winter homogenize the upper water column and cause low oxygen concentrations. Oxygen then increases below the mixed layer at a nearly constant rate that is similar to independent measures of net community production. This continuous oxygen increase is consistent with an ecosystem that is a net producer of fixed carbon (net autotrophic) throughout the year, with episodic events not required to sustain positive oxygen production.

Evaporites, including gypsum (or anhydrite) and salt, are the most soluble of common rocks; they are dissolved readily to form caves, sinkholes, disappearing streams, and other karst features that typically are found in limestones and dolomites. The four basic requirements for evaporite karst to develop are: (1) a deposit of gypsum or salt; (2) water, unsaturated with CaSO4 or NaCl; (3) an outlet for escape of dissolving water; and (4) energy to cause water to flow through the system. Evaporites are present in 32 of the 48 contiguous states, and they underlie about 35–40% of the land area; they are reported in rocks of every geologic system from the Precambrian through the Quaternary. Evaporite karst is known at least locally (and sometimes quite extensively) in almost all areas underlain by evaporites. The most widespread and pronounced examples of both gypsum and salt karst are in the Permian basin of the southwestern United States, but many other areas are also significant. Human activities have caused some evaporite-karst development, primarily in salt deposits. Boreholes may enable (either intentionally or inadvertently) unsaturated water to flow through or against salt deposits, thus allowing development of small to large dissolution cavities. If the dissolution cavity is large enough and shallow enough, successive roof failures above the cavity can cause land subsidence or catastrophic collapse.

This talk will focus on the development and operation of a global scale, chemical sensor network that is distributed throughout the world's ocean. The daily, seasonal and interannual changes in the concentrations of inorganic carbon, pH, dissolved oxygen and nitrate that are driven by photosynthesis and respiration are basic tracers of ocean metabolism. This metabolism has a fundamental control on the earth's climate, as production of organic matter in the surface ocean acts to lower atmospheric carbon dioxide by about 200 ppm. It is possible that these rates of elemental cycling will change in the future as the surface ocean warms [1]. However, there are no existing observing systems that allow ocean metabolism to be observed directly at a global scale. In particular, sampling chemistry from ships does not work because of the expense and remoteness of most of the ocean. At the global scale, ocean productivity can only be sensed indirectly from satellite ocean color observations. Global scale sensor networks using robotic platforms equipped with chemical sensors are required to directly observe ocean metabolism [2]. The Argo network (http://www.argo.ucsd.edu), which is used to monitor the heat content of the ocean, is a model for such a system. There are >3000 Argo profiling floats throughout the ocean. They rise from 2000 m depth at 5 to 10 day intervals measuring temperature and salinity during the ascent and then transmit the data to low earth orbit communications networks. This cycle is repeated for the 5 year life of each float. The BioArgo system is now working to build a complementary network equipped with pH, oxygen, nitrate and biooptical sensors [3]. More than 200 profiling floats with oxygen and >40 floats with nitrate are now operating from the Arctic to the Antarctic in all of the major ocean basins (http://argo.jcommops.org/maps.html, scroll right to the Bio map). These sensors have demonstrated exceptional stability and precision over time periods now reaching four years [4-7]. Experimental pH sensors are now operating on profiling floats with a precision and stability near 0.001 pH over an annual cycle. These results demonstrate the feasibility of establishing a global chemical sensor network. This talk will review the methods used to develop chemical sensors with multi-year stability and the development of a global observing system.

Introduction The current study summarizes years of investigations of salt karst and resultant collapse features in and around the Anadarko Basin of western Oklahoma and the Texas Panhandle. These investigations have involved integrated studies of: 1) the subsurface distribution and thickness of Permian salt beds; and 2) field studies to identify areas where outcropping strata are disrupted and disturbed.

The discussion of karst risk should be ongoing and investigations may proceed on a step-by-step basis as new information is gathered. It’s important to determine whether to investigate all sites underlain by a potentially karstic unit or try to rank the sites based on risk before focusing the investigation on those with potentially higher risk. Perturbine karst investigation costs can easily reach $20,000 and more, so investigating each site in a 100-turbine development can be a significant commitment. When possible, start karst evaluation early, manage available cash with a stepwise approach, and communicate.

133 Introduction This study examines aspects of the subsurface geology of an area along the Clear Fork of Brazos River (Clear Fork) in parts of Throckmorton, Haskell, Shackelford, and Jones Counties, Texas (Figure 1). The study area extends from the town of Lueders in the southwest to Paint Creek in the northeast. It includes the originally proposed Cedar Ridge Reservoir damsite (CR) and the newly proposed damsite (site A), located about 8 km farther upstream (to the southwest). The study focuses on the distribution, thickness, and structure of a series of gypsum beds present in the Permian-age Jagger Bend/Valera Formation, which dips gently to the west at a rate of about 7 m/km. Abstract Cedar Ridge Dam and Reservoir will be built to supply water for the city of Abilene, Texas. The original damsite (CR) was to be located on Clear Fork of Brazos River in Throckmorton County, but initial coring of the damsite encountered unsuspected gypsum beds in the Permianage Jagger Bend/Valera Formation. Gypsum is a highly soluble rock that typically contains karst features, and its presence in a dam foundation or impoundment area could allow water to escape from the reservoir. A decision was made to look at potential sites farther upstream (to the southwest), where west-dipping gypsum beds would be deeper underground and karst problems would be minimized or eliminated.

In situ measurements of dissolved manganese and total dissolved iron were conducted in hydrothermal plumes over the Juan de Fuca Ridge using a submersible chemical analyzer (Scanner). The Scanner was deployed as part of a CTD/transmissometer/rosette instrument package on both tow-yos and vertical casts during the VENTS Leg I cruise in 1989. Dissolved manganese and total dissolved iron concentrations, along with temperature and light attenuation anomalies, were determined over the ridge crest every 5 s. Discrete samples for laboratory analyses of dissolved iron II, total dissolved iron II+III and manganese were also collected. Metal to heat ratios (Me:Q) measured in situ were extremely variable in one steady state plume, while an event plume had constant Me:Q. Uniform values of Mn:Q in the event plume demonstrate that Mn behaves conservatively in the near-field plume. Variability in the Mn: Q ratios in a steady state plume indicated the presence of at least two hydrothermal sources with distinct Me:Q values. A simple mixing model shows that the contribution of Mn from high Me:Q sources, with a composition characteristic of black smoker vents, varies between 1% and 99% within the core of the steady state plume with an average value of 55%. On average, over 50% of the excess heat within the plume originates from low Me:Q ratio sources, with a composition characteristic of low-temperature, diffuse flow vent fluids. Less than 4% of the volume of hydrothermal fluids in the plume originates from black smokers. The Fe II concentrations were used to provide an estimate of plume age on a transect across the ridge axis. Plume ages were about 2.5 days on axis and >12 days off axis. These plume ages were modeled to provide estimates of plume transport and horizontal diffusion and show excellent agreement with ages determined using 222Rn.

Seasonal (spring and summer) depletion of dissolved inorganic carbon occurs in the surface mixed layers of most of the unproductive or oligotrophic regions of the world's oceans. The missing dissolved inorganic carbon is thought to be converted to particulate carbon by photosynthesis, yet there are seemingly insufficient dissolved nutrients present to support the required amount of plant growth. A possible nutrient supply mechanism has now been identified in a study in the North Pacific. Short-lived transport events — lasting less than 10 days — connect the nutrient-poor surface waters with deep-water stocks of dissolved nitrates. When the water column from the surface to a depth of 250 metres is considered as a whole, there is near equivalence in nutrient supply and demand. Concentrations of dissolved inorganic carbon (DIC) decrease in the surface mixed layers during spring and summer in most of the oligotrophic ocean. The missing DIC is thought to be converted to particulate carbon by photosynthesis, but known mechanisms do not seem to supply enough nutrients for the photosynthesis. Here it is shown that short-lived transport events connect deep-water nitrate stocks with nutrient-poor surface waters. Concentrations of dissolved inorganic carbon (DIC) decrease in the surface mixed layers during spring and summer in most of the oligotrophic ocean. Mass balance calculations require that the missing DIC is converted into particulate carbon by photosynthesis1,2,3. This DIC uptake represents one of the largest components of net community production in the world ocean2,4. However, mixed-layer waters in these regions of the ocean typically contain negligible concentrations of plant nutrients such as nitrate and phosphate3,5. Combined nutrient supply mechanisms including nitrogen fixation, diffusive transport and vertical entrainment are believed to be insufficient to supply the required nutrients for photosynthesis6,7. The basin-scale potential for episodic nutrient transport by eddy events is unresolved8,9. As a result, it is not understood how biologically mediated DIC uptake can be supported in the absence of nutrients. Here we report on high-resolution measurements of nitrate (NO3−) and oxygen (O2) concentration made over 21 months using a profiling float deployed near the Hawaii Ocean Time-series station in the North Pacific subtropical gyre. Our measurements demonstrate that as O2 was produced and DIC was consumed over two annual cycles, a corresponding seasonal deficit in dissolved NO3− appeared in water at depths from 100 to 250 m. The deep-water deficit in NO3− was in near-stoichiometric balance with the fixed nitrogen exported to depth. Thus, when the water column from the surface to 250 m is considered as a whole, there is near equivalence between nutrient supply and demand. Short-lived transport events (

HYDROTHERMAL vents along mid-ocean ridges are an important source of elements such as lithium, silicon, manganese and iron to the world's oceans1. The venting produces both episodic and steady-state hydrothermal plumes with unique thermochemical signatures in the mid-water column. The particulate phases in these plumes (predominantly iron oxides and hydroxides) also scavenge phosphorus, vanadium, arsenic, lead, polonium and several rare-earth elements from sea water2–5. Thus, on a global scale, hydrothermal plumes are both a source for some elements and a sink for others. Ultimately, the particulate metals precipitated from plumes form extensive regions of metalliferous sediments over the crests and flanks of mid-ocean ridges6, 7. Although the metalliferous sediment coverage is vast and well documented, only a tiny fraction of the vents responsible for these sediments have been located (Fig. la). To date, both the number and location of hydrothermal vents and the detailed distribution of chemical constituents within the resultant plumes are poorly understood because of under-sampling of the mid-ocean ridges and the overlying waters. Here we present the results of high-resolution mapping of the chemical and thermal characteristics of hydrothermal plumes in near real time using a novel submersible chemical analyser (Scanner)8, 9 and a conductivity/temperature/depth/trans-missometer instrument package (CTDT)10. We show that the kinetics of iron oxidation in the plume can be used to constrain estimates of the plume's age, and that variation in the ratio of manganese content to excess heat can be explained by the mixing of several different vent fluids.

The Oklahoma Geological Survey has developed several maps and reports for preliminary screening of the state of Oklahoma to identify areas that are generally acceptable or unacceptable for disposal of a wide variety of waste materials. These maps and reports focus on the geologic and hydrogeologic parameters that must be evaluated in the screening process. One map (and report) shows the outcrop distribution of 35 thick shale or clay units that are generally suitable for use as host rocks for surface disposal of wastes. A second map shows the distribution of unconsolidated alluvial and terrace-deposit aquifers, and a third map shows the distribution and hydrologic character of bedrock aquifers and their recharge areas. These latter two maps show the areas in the state where special attention must be exercised in permitting storage or disposal of waste materials that could degrade the quality of groundwater. State regulatory agencies and industry are using these maps and reports in preliminary screening of the state to identify potential disposal sites. These maps in no way replace the need for site-specific investigations to prove (or disprove) the adequacy of a site to safely contain waste materials.

Sinkholes usually have a higher probability of occurrence and a greater genetic diversity in evaporite terrains than in carbonate karst areas. This is because evaporites have a higher solubility, and commonly a lower mechanical strength. Subsidence damage resulting from evaporite dissolution generates substantial losses throughout the world, but the causes are only well-understood in a few areas. To deal with these hazards, a phased approach is needed for sinkhole identification, investigation, prediction, and mitigation. Identification techniques include field surveys, and geomorphological mapping combined with accounts from local people and historical sources. Detailed sinkhole maps can be constructed from sequential historical maps, recent topographical maps and digital elevation models (DEMs) complemented with building-damage surveying, remote sensing, and high-resolution geodetic surveys. On a more detailed level, information from exposed paleosubsidence features (paleokarst), speleological explorations, geophysical investigations, trenching, dating techniques, and boreholes, may help to recognize dissolution and subsidence features. Information on the hydrogeological pathways including caves, springs and swallow holes, are particularly important especially when corroborated by tracer tests. These diverse data sources make a valuable database - the karst inventory. From this dataset, sinkhole susceptibility zonations (relative probability) may be produced based on the spatial and temporal distribution of the features and good knowledge of the local geology. Sinkhole distribution can be investigated by spatial distribution analysis techniques including studies of preferential elongation, alignment and nearest neighbor analysis. More objective susceptibility models may be obtained by analyzing the statistical relationships between the known sinkholes and the conditioning factors, such as weather conditions. Chronological information on sinkhole formation is required to estimate the probability of occurrence of sinkholes (number of sinkholes/km² year). Such spatial and temporal predictions, derived from limited records and based on the assumption that past sinkhole activity may be extrapolated to the future, are non-corroborated hypotheses. Validation methods allow us to assess the predictive capability of the susceptibility maps and to transform them into probability maps. Avoiding the most hazardous areas by preventive planning is the safest strategy for development in sinkhole-prone areas. Corrective measures could be to reduce the dissolution activity and subsidence processes, but these are difficult. A more practical solution for safe development is to reduce the vulnerability of the structures by using subsidence-proof designs.

Evaporite karst is widespread, but relatively unknown when compared with carbonate karst; this special issue addresses that lack of familiarity. Evaporite rocks have much higher solubilities and faster dissolution rates than carbonate rocks and they also commonly have lower mechanical strengths and more ductile reheologies. Many of these factors are dependent on the local hydrogeology, and when combined they can result in areas where karst features evolve on a human time scale, rather than a geological timescale. Karst collapse and subsidence are common in such areas, making them problematical for the local population. The evaporite-karst environment is very sensitive to changes in the local hydrology and hydrogeology, so that human factors such as groundwater extraction, drainage, and irrigation can act as triggering events for karst collapses. Some evaporite-karst features such as caves and saline springs have been beneficially exploited, but most of them, including sinkholes, subsidence, and groundwater degradation, pose a threat to the local environment and a hazard to development. The papers in this special issue of Environmental Geology arose from a successful session on Evaporite Karst convened by us at the Sixth International Conference on Geomorphology. This was held in Zaragoza, Spain, in September 2005 and was organised by Zaragoza University and the International Association of Geomorphologists (IAG; http://www.geomorph.org/). Authors of the twenty-eight presented abstracts were invited to submit full papers to this special issue. Nineteen papers were proposed and sixteen papers have been accepted and are published here.

The Land/Ocean Biogeochemical Observatory (LOBO) system was initially developed by MBARI under the NSF Biocomplexity program to monitor the land/ocean interface for coastal zone management. The system utilizes highly robust and accurate sensors to provide sustained monitoring of critical watershed habitats in challenging environmental conditions in real time. With the incorporation of novel anti-fouling technology developed by WET Labs, the system has an unprecedented six week maintenance cycle, greatly reducing operational costs while providing high quality data sets. LOBO measurements include nitrate, dissolved oxygen, conductivity, temperature, chlorophyll fluorescence, turbidity and CDOM. A LOBO was deployed in the Northwest Arm of Halifax Harbour in January of 2007 and has been monitoring the biogeochemical parameters continuously since (see http://lobo.satlantic.com ). Despite heavy icing at -20degC, heavy winds, and sea ice the system reported data every hour where the detailed nature of the annual spring phytoplankton bloom was recorded at high resolution. The coincident and continuous record of nutrients, phytoplankton and other physical and chemical parameters is unique, and provides a robust means to base predictive coastal ecosystem models in sensitive marine areas.

[1] The flux of dissolved iron from sediments to the water column was measured with flux chambers along the California coast over a five-year period. High fluxes were observed from sediments on the continental shelf. The measured fluxes were an average of 75 times larger than flux values derived from pore-water iron gradients. The iron flux was significantly correlated with the oxidation of organic matter, which allows an extrapolation to the global shelf. The input from shelf sediments is at least as significant as the global input of dissolved iron from aerosols, which has been presumed to be the dominant external iron source. Evidence of this input is seen 100's of kilometers offshore where it can enable the high productivity of broad coastal regions seen in satellite images.

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

[1] Here we report measurements of iron and aluminum in surface and subsurface waters during late March and late May of 2001 on transects between central California and Hawaii. A large cloud of Asian dust was detected during April 2001, and there was a clear signal in surface water iron due to aerosol deposition on the May transect. Iron and aluminum concentrations increased synchronously by 0.5 and 2 nM along the southern portion of the transect, which includes the Hawaii Ocean Time series (HOT) station, from background values in March (0.1 to 0.2 nM Fe). These changes occurred in a ratio that is close to the crustal abundance ratio of the metals, which indicates a soil aerosol source. A vertical profile of dissolved iron was also measured at the HOT station in late April and this profile also shows a large increase near the surface. Direct observations of aerosol iron concentration at Mauna Loa Observatory on Hawaii indicate that aerosol concentrations were significantly lower than climatological values during this period. Soil aerosol concentrations along the transect were estimated using the real-time Navy Aerosol Analysis and Prediction System (NAAPS). The NAAPS results show a large meridional gradient with maximum concentrations in the boundary layer north of 30°N. However, the deposition of iron and aluminum to surface waters was highest south of 25°N, near Hawaii. There were only weak signals in the ecosystem response to the aerosol deposition.

The flux of manganese from continental margin sediments to the ocean was measured with a free-vehicle, benthic flux chamber in a transect across the continental shelf and upper slope of the California margin. The highest fluxes were observed on the shallow continental shelf. Manganese flux decreased linearly with bottom water oxygen concentration, and the lowest fluxes occurred in the oxygen minimum zone (at a depth of 600 to 1000 meters). Although the flux of manganese from continental shelf sediments can account for the elevated concentrations observed in shallow, coastal waters, the flux from sediments that intersect the oxygen minimum cannot produce the subsurface concentration maximum of dissolved manganese that is observed in the Pacific Ocean.

Four periods of extreme turbidity were measured in Monterey Submarine Canyon over the past 12 yr. These turbid events occurred simultaneously with the four largest flood events of the nearby Salinas River. They filled the canyon with fresher, warmer, and, apparently, buoyant water that extended to depths below 1 km. The low-salinity signature must reflect underflow of the Salinas River plume that was driven to depth by negative buoyancy contributed from the suspended sediment. A flux estimate for the 1995 event suggests that one-half, or more, of the river's suspended sediment load was carried down the canyon in the underflow. Underflows may contribute significantly to the carbon budget of the continental slope.

Hawaiian volcanoes are exceptional examples of intraplate hotspot volcanism. Hotspot volcanoes, which frequently host large eruptions and related earthquakes, flank-failure landslides, and associated tsunamis, can present severe hazards to populated regions. Many studies have focused on subaerial parts of Hawaiian volcanoes, but the deep-water flanks of the edifices, which can reach 5700 m below sea level, remain poorly understood because they are so inaccessible. In 1998 a collaborative program between Japan and the United States was initiated to explore the evolution of Hawaiian volcanoes, including their growth and degradation.

Evaporites, mainly gypsum (oranhydrite) andsalt,arethemostsoluble of common rocks. Theserocksaredissolved readily toform caves, sinkholes, disappearing streams, andotherkarstfeatures commonly associated withlimestone and dolomite. The principal difference between evaporite and carbonate karst is thatevaporite-karst features can form rapidly, inamatterofdays, weeks, oryears, whereas carbonate-karst features typically takeyears, decades, orcenturies to form, Evaporites underlie 35-40%ofthecontiguous UnitedStates, andprobablyunderlie alesser, yetstillsignificant, percentage of all the World's landarea Evaporite karst is known to be present at leastlocally(andsometimes quite extensively) inalmostall areas underlain byevaporites.

In May 1986, we investigated processes contributing to the unique characteristics of oceanic fronts in the western Mediterranean Sea. Simulated in situ measurements of 14C-based primary production were made in conjunction with precise chemical, physical and optical analyses coordinated with remote sensing. Eight transects consisting of 4–7 vertical stations were made across density fronts associated with the Almeria Gyre and the Algerian Current. A model was developed to describe the relationship between chlorophyll-specific primary production (mg C mg Chl−1h−1) and depth in the water column. Model regressions for Modified Atlantic Water (MAW, salinity = 36.5–36.8), Mediterranean water (37.6–38.0), and intermediate frontal water were not significantly different, and a single equation based on the pooled data was used to estimate regional production. East of 0° longitude, primary production integrated over the upper 100 m (ΣP) in Mediterranean water was 0.47 g C m−2 d−1 (range0.33–0.60) and 0.88 g C m−2 d−1 (range 0.50–1.30) in MAW and frontal regions. higher ΣP in MAW and frontal regions could be attributed partially to higher integrated chlorophyll, although locationof the chlorophyll maximum higher in the water column was also an important contributing factor. The chlorophyll maximum was shallower in MAW than in Mediterranean-type water. The depth of chlorophyll maxima generally coincided with the nitracline rahter than isopycnal surfaces, supporting the view that chlorophyll distributions and primary production were primarily influenced by nutrient supply.

The Wink Sink, in Winkler County, Texas, is a collapse feature that formed in June 1980 when an underground dissolution cavity migrated upward by successive roof failures until it breached the land surface. The original cavity developed in the Permian Salado Formation salt beds more than 400 m (1,300 ft) below ground level. Natural dissolution of salt occurred in the vicinity of the Wink Sink in several episodes that began as early as Salado time and recurred in later Permian, Triassic, and Cenozoic times. Although natural dissolution occurred in the past below the Wink Sink, it appears likely that the dissolution cavity and resultant collapse described in this report were influenced by petroleum-production activity in the immediate area. Drilling, completion, and plugging procedures used on an abandoned oil well at the site of the sink appear to have created a conduit that enabled water to circulate down the borehole and dissolve the salt. When the dissolution cavity became large enough, the roof failed and the overlying rocks collapsed into the cavity. Similar collapse features exist where underground salt beds have been intentionally dissolved during solution mining or accidentally dissolved as a result of petroleum-production activity.