R. Kipp Shearman

Long-Term Sea Surface Temperature Variability along the U.S. East Coast

Sea surface temperature variations along the entire U.S. East Coast from 1875 to 2007 are characterized using a collection of historical observations from lighthouses and lightships combined with recent buoy and shore-based measurements. Long-term coastal temperature trends are warming in the Gulf of Maine [1.0 86 0.38C (100 yr) 21 ] and Middle Atlantic Bight [0.7 86 0.38C (100 yr) 21 ], whereas trends are weakly cooling or not significant in the South Atlantic Bight [20.1 86 0.38C (100 yr) 21 ] and off Florida [20.3 86 0.28C (100 yr) 21 ]. Over the last century, temperatures along the northeastern U.S. coast have warmed at a rate 1.8‐ 2.5 times the regional atmospheric temperature trend but are comparable to warming rates for the Arctic and Labrador, the source of coastal ocean waters north of Cape Hatteras (368N). South of Cape Hatteras, coastal ocean temperature trends match the regional atmospheric temperature trend. The observations and a simple model show that along-shelf transport, associated with the mean coastal current system running from Labrador to Cape Hatteras, is the mechanism controlling long-term temperature changes for this region and not the local air‐sea exchange of heat.

Declining Oxygen in the Northeast Pacific

AbstractClimate models predict a decrease in oceanic dissolved oxygen and a thickening of the oxygen minimum zone, associated with global warming. Comprehensive observational analyses of oxygen decline are challenging, given generally sparse historical data. The Newport hydrographic (NH) line off central Oregon is one of the few locations in the northeast Pacific with long oxygen records. Good quality data are available here primarily in two time blocks: 1960–71 and 1998–present. Standard sampling extends from midshelf (bottom depth of 58 m) to 157 km offshore (bottom depth of 2880 m). Shipboard measurements have been supplemented in recent years (2006–present) with data from autonomous underwater gliders. Oxygen declines significantly over this 50-yr period across the entire NH line. In addition to decrease in the vicinity of the oxygen minimum depth (~800 m), oxygen decreases across a range of density surfaces σθ = 26–27 within the thermocline, in the depth range 100–550 m. A core of decreasing oxygen (...

Diagnosis of the Three-Dimensional Circulation Associated with Mesoscale Motion in the California Current

A high-resolution upper-ocean survey of a cyclonic jet meander and an adjacent cyclonic eddy in the California Current region near 388N, 1268W was conducted as part of the summer of 1993 Eastern Boundary Currents program. Temperature and salinity were measured from a SeaSoar vehicle, and velocity was measured by shipboard acoustic Doppler current profiler (ADCP). SeaSoar data show a density front at a depth of 70‐100 m with strong cyclonic curvature. The geostrophic velocity fields, referenced to the ADCP data at 200 m, show a strong surface-intensified jet (maximum speed of 0.9 m s 21) that follows the density front along a cyclonic meander. Relative vorticities within the jet are large, ranging from 20.8 f to 11.2 f, where f is the local Coriolis parameter. The SeaSoar density and ADCP velocity data are used to diagnose the vertical velocity via the Q-vector form of the quasigeostrophic omega equation. The diagnosed vertical velocity field shows a maximum speed of 40‐45 m d21. The lateral distribution of vertical velocity is characterized by two length scales: a large (;75 km) pattern where there is downwelling upstream and upwelling downstream of the cyclonic bend, and smaller patches arrayed along the jet core with diameters of 20‐30 km. Geostrophic streamline analysis of vertical velocity indicates that water parcels make net vertical excursions of 20‐30 m over 2‐3 days, resulting in net vertical velocities of 7‐15 m d21. Water parcels moving along geostrophic streamlines experience maximum vertical velocities in the regions of maximum alongstream change in relative vorticity, an indication of potential vorticity conservation.

The latmix summer campaign: Submesoscale stirring in the upper ocean

AbstractLateral stirring is a basic oceanographic phenomenon affecting the distribution of physical, chemical, and biological fields. Eddy stirring at scales on the order of 100 km (the mesoscale) is fairly well understood and explicitly represented in modern eddy-resolving numerical models of global ocean circulation. The same cannot be said for smaller-scale stirring processes. Here, the authors describe a major oceanographic field experiment aimed at observing and understanding the processes responsible for stirring at scales of 0.1–10 km. Stirring processes of varying intensity were studied in the Sargasso Sea eddy field approximately 250 km southeast of Cape Hatteras. Lateral variability of water-mass properties, the distribution of microscale turbulence, and the evolution of several patches of inert dye were studied with an array of shipboard, autonomous, and airborne instruments. Observations were made at two sites, characterized by weak and moderate background mesoscale straining, to contrast diff...

Buoyancy-Driven Coastal Currents off Oregon during Fall and Winter

During fall/winter off the Oregon coast, oceanographic surveys are relatively scarce because of rough weatherconditions.Thischallengehasbeenovercomebytheuseofautonomousunderwaterglidersdeployed along the Newport hydrographic line (NH-Line) nearly continuously since 2006. The discharge from the coastal rivers between northern California and the NH-Line reach several thousands of cubic meters per second, and the peaks are comparable to the discharge from the Columbia River. This freshwater input creates cross-shelf density gradients that together with the wind forcing and the large-scale Davidson Current results in strong northward velocities over the shelf. A persistent coastal current during fall/winter, which the authorscalltheOregonCoastalCurrent(OCC),hasbeenrevealed bythegliderdataset.Basedon atwo-layer model, the dominant forcing mechanismof the OCC is buoyancy,followed by the Davidson Current and then the wind stress, accounting for 61% (622.6%), 26% (618.6%), and 13% (611.7%) of the alongshore transports, respectively. The OCC average velocities vary from 0.1 to over 0.5ms 21 , and transports are on average 0.08 (60.07) Sverdrups (Sv; 1 Sv [ 10 6 m 3 s 21 ), with the maximum observed value of 0.49 Sv, comparable to the summertime upwelling jet off the Oregon coast. The OCC is a surface-trapped coastal current, and its geometryis highly affectedby the wind stress, consistentwith Ekmandynamics.The windstress has an overallsmall direct contribution to the alongshoretransport;however,it plays a primaryrole in modifyingthe OCC structure. The OCC is a persistent, key component of the fall/winter shelf dynamics and influences the ocean biogeochemistry off the Oregon coast.

Diagnosis of the Three-Dimensional Circulation in Mesoscale Features with Large Rossby Number

Several diagnoses of three-dimensional circulation, using density and velocity data from a high-resolution, upper-ocean SeaSoar and acoustic Doppler current profiler (ADCP) survey of a cyclonic jet meander and adjacent cyclonic eddy containing high Rossby number flow, are compared. The Q-vector form of the quasigeostrophic omega equation, two omega equations derived from iterated geostrophic intermediate models, an omega equation derived from the balance equations, and a vertical velocity diagnostic using a primitive equation model in conjunction with digital filtering are used to diagnose vertical and horizontal velocity fields. The results demonstrate the importance of the gradient wind balance in flow with strong curvature (high Rossby number). Horizontal velocities diagnosed from the intermediate models (the iterated geostrophic models and the balance equations), which include dynamics between those of quasigeostrophy and the primitive equations, are significantly reduced (enhanced) in comparison with the geostrophic velocities in regions of strong cyclonic (anticyclonic) curvature, consistent with gradient wind balance. The intermediate model relative vorticity fields are functionally related to the geostrophic relative vorticity field; anticyclonic vorticity is enhanced and cyclonic vorticity is reduced. The iterated geostrophic, balance equation and quasigeostrophic vertical velocity fields are similar in spatial pattern and scale, but the iterated geostrophic (and, to a lesser degree, the balance equation) vertical velocity is reduced in amplitude compared with the quasigeostrophic vertical velocity. This reduction is consistent with gradient wind balance, and is due to a reduction in the forcing of the omega equation through the geostrophic advection of ageostrophic relative vorticity. The vertical velocity diagnosed using a primitive equation model and a digital filtering technique also exhibits reduced magnitude in comparison with the quasigeostrophic field. A method to diagnose the gradient wind from a given dynamic height field has been developed. This technique is useful for the analysis of horizontal velocity in the presence of strong flow curvature. Observations of the nondivergent ageostrophic velocity field measured by the ADCP compare closely with the diagnosed gradient wind ageostrophic velocity.

Failure to bloom: Intense upwelling results in negligible phytoplankton response and prolonged CO2 outgassing over the Oregon shelf

During summer, upwelled water with elevated CO2 partial pressure (pCO2) and nutrients outcrops over the Oregon (OR) inner shelf. As this water transits across the shelf, high rates of primary production fueled by the upwelled nutrients results in net atmospheric CO2 drawdown. Upwelled source-waters typically have pCO2 approaching 1000 µatm that is then reduced to ∼200 µatm. For almost the entire month of July 2008, strong and persistent upwelling brought cold (∼8°C), saline (∼33.5), high-pCO2 (>600 µatm) water to our midshelf buoy site, and high-pCO2 water was broadly distributed over the shelf. Chlorophyll levels, as a proxy for phytoplankton biomass, were low (< 2 mg m−3) on the shelf during the period of most intense upwelling, and satellite data showed no evidence of a downstream phytoplankton bloom. A small chlorophyll increase to ∼4 mg m−3 was observed at our buoy site following a decrease in the strength of southward wind stress 10 days after upwelling initiated. Chlorophyll levels further increased to ∼10 mg m−3 only after a cease in upwelling. These higher levels were coincident with the appearance of water masses having temperature and salinity properties distinct from recently upwelled water. We suggest that rapid offshore transport and subsequent subduction before phytoplankton populations could respond is the most likely explanation for the persistent low chlorophyll and elevated surface-water pCO2 throughout the July upwelling event. This mechanism likely dominates under conditions of strong and persistent upwelling-favorable winds that coincide with close proximity of low-density offshore waters, which may have implications for the biogeochemical functioning of this system under future climate scenarios.

Evaporative dense water formation and cross‐shelf exchange over the northwest Australian inner shelf

and dense waters onshore, with a strong front near the 25 m isobath. The front is evident in satellite sea surface temperature (SST) imagery along the majority of the northwest Australianshelf,exhibitingacomplexfilamentaryandeddystructure.Cross‐shelfbuoyancy fluxes estimated from the mean, two‐dimensional heat and salt budgets are comparable to parameterizations of cross‐shelf eddy driven fluxes; however, the same fluxes can be achieved by cross‐shelf transports in the bottom boundary layer of about 0.5 m 2 s −1 (and an overlying return flow).

Anomalous Near-Surface Low-Salinity Pulses off the Central Oregon Coast

From mid-May to August 2011, extreme runoff in the Columbia River ranged from 14,000 to over 17,000 m3/s, more than two standard deviations above the mean for this period. The extreme runoff was the direct result of both melting of anomalously high snowpack and rainfall associated with the 2010–2011 La Niña. The effects of this increased freshwater discharge were observed off Newport, Oregon, 180 km south of the Columbia River mouth. Salinity values as low as 22, nine standard deviations below the climatological value for this period, were registered at the mid-shelf. Using a network of ocean observing sensors and platforms, it was possible to capture the onshore advection of the Columbia River plume from the mid-shelf, 20 km offshore, to the coast and eventually into Yaquina Bay (Newport) during a sustained wind reversal event. Increased freshwater delivery can influence coastal ocean ecosystems and delivery of offshore, river-influenced water may influence estuarine biogeochemistry.

CASPER: Coupled Air-Sea Processes and Electromagnetic (EM) ducting Research

CapsuleCASPER objective is to improve our capability to characterize the propagation of radio frequency (RF) signals through the marine atmosphere with coordinated efforts in data collection, data analyses, and modeling of the air-sea interaction processes, refractive environment, and RF propagation.