ALBERT

Description: The Ocean Reference Station at 20°S, 85°W under the stratus clouds west of northern Chile is being maintained to provide ongoing climate-quality records of surface meteorology; air-sea fluxes of heat, freshwater, and momentum; and of upper ocean temperature, salinity, and velocity variability. The Stratus Ocean Reference Station (ORS Stratus) is supported by the National Oceanic and Atmospheric Administration’s (NOAA) Climate Observation Program. It is recovered and redeployed annually, with cruises that have come between October and December. During the 2008 cruise on the NOAA ship Ronald H. Brown to the ORS Stratus site, the primary activities were recovery of the Stratus 8 WHOI surface mooring that had been deployed in October 2007, deployment of a new (Stratus 9) WHOI surface mooring at that site; in-situ calibration of the buoy meteorological sensors by comparison with instrumentation put on board by staff of the NOAA Earth System Research Laboratory (ESRL); and observations of the stratus clouds and lower atmosphere by NOAA ESRL. A buoy for the Pacific tsunami warning system was also serviced in collaboration with the Hydrographic and Oceanographic Service of the Chilean Navy (SHOA). The DART (Deep-Ocean Assessment and Reporting of Tsunami) carries IMET sensors and subsurface oceanographic instruments. A DART II buoy was deployed north of the STRATUS buoy, by personnel from the National Data Buoy Center (NDBC) Argo floats and drifters were launched, and CTD casts carried out during the cruise. The ORS Stratus buoys are equipped with two Improved Meteorological (IMET) systems, which provide surface wind speed and direction, air temperature, relative humidity, barometric pressure, incoming shortwave radiation, incoming longwave radiation, precipitation rate, and sea surface temperature. Additionally, the Stratus 8 buoy received a partial CO2 detector from the Pacific Marine Environmental Laboratory (PMEL). IMET data are made available in near real time using satellite telemetry. The mooring line carries instruments to measure ocean salinity, temperature, and currents. The ESRL instrumentation used during the 2008 cruise included cloud radar, radiosonde balloons, and sensors for mean and turbulent surface meteorology. Finally, the cruise hosted a teacher participating in NOAA’s Teacher at Sea Program.

Description: Funding was provided by the National Oceanic and Atmospheric Administration under Grant No. NA17RJ1223 for the Cooperative Institute for Climate and Ocean Research (CICOR).

Description: Author Posting. © Sears Foundation for Marine Research, 2009. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 67 (2009): 273-303, doi:10.1357/002224009789954757.

Description: An idealized model for a convective basin is used to investigate the mechanisms of variability of the formation and export of dense water. In this model, which consists of two isopycnic layers, dense water formation is induced by surface buoyancy loss in the interior, which is at rest. Newly formed dense water is transmitted to the surrounding boundary current through parameterized eddy fluxes. Variability in the formation and export of dense water is due to changes in the two main drivers: variations in the surface buoyancy fluxes and variations in the large-scale wind via a barotropic boundary current. Numerical integrations of the nonlinear model, with parameters and forcings corresponding to the Labrador Sea, show that the rate of dense water formation in the interior of the basin is strongly affected by changes in the buoyancy forcing, but not significantly affected by seasonal to interannual changes in the wind-driven barotropic boundary current. The basin tends to integrate the buoyancy forcing variability with a memory time scale set by eddies, which is decadal for the Labrador Sea. Variability in dense water export, on the contrary, is strongly affected by changes in the wind-driven barotropic boundary current but hardly affected by changes in buoyancy forcing. Indeed changes in the transport of dense water at the basin outflow are dominated by those at the basin inflow, which, in this model, are directly related to fluctuations in the wind-driven barotropic boundary current. These results, which are consistent with analytical solutions of the linear model, suggest that fluctuations in the surface buoyancy fluxes in the interior Labrador Sea have little impact on the interannual variability of the dense water transport by the Deep Western Boundary Current at the outflow of the Labrador Sea, which is dominated by fluctuations in the wind-driven North Atlantic subpolar gyre, but influence the formation and export of recently ventilated waters.

Description: Support for JD from the NOAA Office of Hydrologic Development through a scientific appointment administered by UCAR is gratefully acknowledged. Support for FS was provided by NSF grant OCE−0525929. Support for MAS was provided by NSF grant OCE−0423975.

Description: Author Posting. © Sears Foundation for Marine Research, 2009. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 67 (2009): 361-384, doi:10.1357/002224009789954739.

Description: A significant fraction of the lateral heat transport into the Labrador Sea's interior, needed to balance the net heat loss to the atmosphere, is attributed to the Irminger Current Anticyclones. These mesoscale eddies advect warm, salty boundary current water, of subtropical origin, from the boundary current to the interior— but when or how they release their anomalous heat content has not been previously investigated. In this study, we discuss the seasonal and interannual evolution of these anticyclones as inferred from the analysis of hydrographic data from the Labrador Sea from 1990 to 2004. The 29 identified anticyclones fall into two categories, which we refer to as unconvected and convected. Unconvected anticyclones have properties that are close to those of the boundary current, including a fresh surface layer, and they are found near the boundaries and never observed in winter. Convected anticyclones, on the other hand, contain a mixed layer, lack a freshwater cap and are observed throughout the year. Using a one-dimensional mixing model, it is shown that the convected eddies are those Irminger Current Anticyclones that have been modified by the large winter buoyancy loss of the region. This provides evidence that such eddies can survive the strong winter buoyancy loss in the Labrador Sea and that their anomalous heat and salt content is not trivially mixed into the Sea's interior. Finally, we observe a clear trend in the eddies' properties toward warmer and saltier conditions after 1997 reflecting changes in the source waters and the reduced atmospheric forcing over the Labrador Sea.

Description: The work was funded by National Science Foundation grant number OCE-0525929.

Description: Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 55 (2008): 926-946, doi:10.1016/j.dsr.2008.03.012.

Description: Hudson Strait delivers a large amount of fresh water to the subpolar North Atlantic due to a large riverine input into the upstream Hudson Bay System and to the rerouting of Arctic Ocean waters. The fresh waters flowing out of Hudson Strait feed the Labrador Current, a current that has a significant impact on the climate and ecosystem of the entire northeastern seaboard. The lack of measurements from the strait have, until recently, made it difficult to determine the relative contribution of Hudson Strait to the properties and variability of the Labrador Current compared to other sources. This study describes the first year round observations of the outflow as obtained from a moored array deployed midstrait from August 2004 to 2005, and from a highresolution hydrographic section conducted in September of 2005. The outflow from Hudson Strait has the structure of a buoyant boundary current spread across the sloping topography of its southern edge. The variability in the flow is dominated by the extreme semidiurnal tides and by vigorous, mostly barotropic, fluctuations over several days. The fresh water export is seasonally concentrated between June and March with a peak in NovemberDecember, consistent with the seasonal riverine input and seaice melt. It is highly variable on weekly timescales due to synchronous salinity and velocity variations. The estimated volume and liquid fresh water transports during 20042005 are respectively of 11.2 Sv and 7888 (2829) mSv relative to a salinity of 34.8 (33). This implies that the Hudson Strait outflow accounts for approximately 15% of the volume and 50% of the fresh water transports of the Labrador Current. This larger than previously estimated contribution is partially due to the recycling, within the Hudson Bay System, of relatively fresh waters that flow into Hudson Strait, along its northern edge. It is speculated that the source of this inflow is the outflow from Davis Strait.

Description: Straneo acknowledges support from the Woods Hole Oceanographic Institution's Ocean and Climate Change Institute and the Comer Foundation, in particular, as well as support for NSF OCE0629411. Support to FJS from NSERC Research Grant and the Canadian Program on Energy Research and Development.

Description: Author Posting. © Sears Foundation for Marine Research, 2008. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 66 (2008): 325-345, doi:10.1357/002224008786176016.

Description: The properties of water mass transformation in a semi-enclosed basin, separated from the open ocean by a sill and subject to surface cooling, are analyzed both theoretically and numerically using an ocean general circulation model. This study extends previous studies of convection in a marginal sea to the case with a sill. The sill has a strong impact on both the properties of the dense water formed in the interior and on those of the waters flowing out the marginal sea. It results in a colder interior and colder outflow compared to the case with no sill. Dynamically, this is explained by considering that the sill limits the geostrophic contours over which the open ocean/marginal sea exchange can occur. The impact of the sill, however, is not simply limited to a topographic constriction; instead the sill also decreases the stability of the boundary current, which, in turn, results in relatively large heat flux into the interior and colder outflow. The theories that relate the properties of the dense waters formed in the interior, and those of the outflow, are modified to include the impact of the sill. These are found to compare well with the numerical simulations and provide a useful tool for the interpretation of these results. These idealized simulations capture the basic features of the water mass transformation processes in the Nordic Seas and, in particular, provide a dynamical explanation for the difference between the dense waters formed and the source of the overflows water.

Description: DI was supported by the Polar Ocean Climate Processes (ProClim) project funded by the Norwegian Research Council. FS was supported by a visiting scientist fellowship from the Bjerknes Centre for Climate Research (Bergen, Norway) and by NSF Ocean Sciences Grant 0525929. Support for MAS was provided by NSF Office of Polar Programs Grant 0421904 and NSF Ocean Sciences Grant 0423975.