Impact of Labrador Sea convection on the North Atlantic meridional overturning circulation

Author Posting. © American Meteorological Society, 2007. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 37 (2007): 2207-2227, doi:10.1175/jpo3178.1.The overturning and horizontal circulations of the Labrador Sea are deduced from a composite vertical section across the basin. The data come from the late-spring/early-summer occupations of the World Ocean Circulation Experiment (WOCE) AR7W line, during the years 1990–97. This time period was chosen because it corresponded to intense wintertime convection—the deepest and densest in the historical record—suggesting that the North Atlantic meridional overturning circulation (MOC) would be maximally impacted. The composite geostrophic velocity section was referenced using a mean lateral velocity profile from float data and then subsequently adjusted to balance mass. The analysis was done in depth space to determine the net sinking that results from convection and in density space to determine the diapycnal mass flux (i.e., the transformation of light water to Labrador Sea Water). The mean overturning cell is calculated to be 1 Sv (1 Sv ≡ 106 m3 s−1), as compared with a horizontal gyre of 18 Sv. The total water mass transformation is 2 Sv. These values are consistent with recent modeling results. The diagnosed heat flux of 37.6 TW is found to result predominantly from the horizontal circulation, both in depth space and density space. These results suggest that the North Atlantic MOC is not largely impacted by deep convection in the Labrador Sea.This work was funded by the National Science Foundation through Grants OCE-0450658 (RP) and OCE-024978 (MS)

Response to a steady poleward outflow. Part I : the linear, quasigeostrophic problem

Author Posting. © American Meteorological Society, 2009. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 39 (2009): 1541-1550, doi:10.1175/2008JPO3999.1.The response of a zonal channel to a uniform, switched-on but subsequently steady poleward outflow is presented. An eastward coastal current with a Kelvin wave’s cross-shore structure is found to be generated instantly upon initiation of the outflow. The current is essentially in geostrophic balance everywhere except for the vicinity of the outflow channel mouth, where the streamlines must cross planetary vorticity contours to feed the current. The adjustment of this region generates a plume that propagates westward at Rossby wave speeds. The cross-shore structure of the plume varies with longitude, and at any given longitude it evolves with time. The authors show that the plume evolution can be understood both conceptually and quantitatively as the westward propagation of the Kelvin current’s meridional spectrum, with each spectral element propagating at its own Rossby wave group velocity.This work was completed at Woods Hole Oceanographic Institution while T.S. Durland was supported by the Ocean and Climate Change Institute. M.A. Spall was supported by NSF Grant OCE-0423975, and J. Pedlosky by NSF Grant OCE-0451086. T.S. Durland acknowledges additional report preparation support from NASA Grant NNG05GN98G

Corrigendum

Author Posting. © American Meteorological Society, 2010. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 40 (2010): 1910–1914, doi:10.1175/2010JPO4483.1.Corrigendum: Spall, M. A., R. S. Pickart, P. S. Fratantoni, and A. J. Plueddemann, 2008: Western Arctic shelfbreak eddies: Formation and transport. J. Phys. Oceanogr., 38, 1644–166

Western Arctic shelfbreak eddies : formation and transport

Author Posting. © American Meteorological Society, 2008. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 38 (2008): 1644-1668, doi:10.1175/2007JPO3829.1.The mean structure and time-dependent behavior of the shelfbreak jet along the southern Beaufort Sea, and its ability to transport properties into the basin interior via eddies are explored using high-resolution mooring data and an idealized numerical model. The analysis focuses on springtime, when weakly stratified winter-transformed Pacific water is being advected out of the Chukchi Sea. When winds are weak, the observed jet is bottom trapped with a low potential vorticity core and has maximum mean velocities of O(25 cm s−1) and an eastward transport of 0.42 Sv (1 Sv ≡ 106 m3 s−1). Despite the absence of winds, the current is highly time dependent, with relative vorticity and twisting vorticity often important components of the Ertel potential vorticity. An idealized primitive equation model forced by dense, weakly stratified waters flowing off a shelf produces a mean middepth boundary current similar in structure to that observed at the mooring site. The model boundary current is also highly variable, and produces numerous strong, small anticyclonic eddies that transport the shelf water into the basin interior. Analysis of the energy conversion terms in both the mooring data and the numerical model indicates that the eddies are formed via baroclinic instability of the boundary current. The structure of the eddies in the basin interior compares well with observations from drifting ice platforms. The results suggest that eddies shed from the shelfbreak jet contribute significantly to the offshore flux of heat, salt, and other properties, and are likely important for the ventilation of the halocline in the western Arctic Ocean. Interaction with an anticyclonic basin-scale circulation, meant to represent the Beaufort gyre, enhances the offshore transport of shelf water and results in a loss of mass transport from the shelfbreak jet.This study was supported by the National Science Foundation Office of Polar Programs under Grants 0421904 and 035268 (MS), and by the Office of Naval Research Grant N00014-02-1-0317 (RP and PF). Analysis by AJP was supported by the Office of Naval Research under Grant N00014-97-1-0135 and by the National Science Foundation under Grant OPP-9815303

Structure and variability of the North Icelandic Jet from two years of mooring data

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(6), (2019): 3987-4002, doi:10.1029/2019JC015134.Mooring data from September 2011 to July 2013 on the Iceland slope north of Denmark Strait are analyzed to better understand the structure and variability of the North Icelandic Jet (NIJ). Three basic configurations of the flow were identified: (1) a strong separated East Greenland Current (EGC) on the mid‐Iceland slope coincident with a weak NIJ on the upper slope, (2) a merged separated EGC and NIJ, and (3) a strong NIJ located at its climatological mean position, coincident with a weak signature of the separated EGC at the base of the Iceland slope. Our study reveals that the NIJ‐dominant scenario was present during different times of the year for the two successive mooring deployments—appearing mainly from September to February the first year and from January to July the second year. Furthermore, when this scenario was active it varied on short timescales. An energetics analysis demonstrates that the high‐frequency variability is driven by mean‐to‐eddy baroclinic conversion at the shoreward edge of the NIJ, consistent with previous modeling work. The seasonal timing of the NIJ dominant scenario is investigated in relation to the atmospheric forcing upstream of Denmark Strait. The resulting lagged correlations imply that strong turbulent heat fluxes in a localized region on the continental slope of Iceland, south of the Spar Fracture zone, lead to a stronger NIJ dominant state with a two‐month lag. This can be explained dynamically in terms of previous modeling work addressing the circulation response to dense water formation near an island.The authors thank the crew members of the R/V Knorr, RRS James Clark Ross, and R/V Bjarni Sæmundsson for the deployment and recovery of the moorings. D. Torres and F. Bahr processed the second year of mooring data. We thank K. Våge, B. Harden, Z. Song, J. Li, and M. Li for helpful discussions regarding the work. Funding was provided by the National Science Foundation under grants OCE‐1558742 (J. H., R. P., P. L., and M. S.) and OCE‐1534618 (M. S.). The mooring data are available at http://kogur.whoi.edu/php/index.php.2019-12-0

Observational and modeling evidence of seasonal trends in sediment-derived material inputs to the Chukchi Sea

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 125(5), (2020): e2019JC016007, doi:10.1029/2019JC016007.Benthic inputs of nutrients help support primary production in the Chukchi Sea and produce nutrient‐rich water masses that ventilate the halocline of the western Arctic Ocean. However, the complex biological and redox cycling of nutrients and trace metals make it difficult to directly monitor their benthic fluxes. In this study, we use radium‐228, which is a soluble radionuclide produced in sediments, and a numerical model of an inert, generic sediment‐derived tracer to study variability in sediment inputs to the Chukchi Sea. The 228Ra observations and modeling results are in general agreement and provide evidence of strong benthic inputs to the southern Chukchi Sea during the winter, while the northern shelf receives higher concentrations of sediment‐sourced materials in the spring and summer due to continued sediment‐water exchange as the water mass traverses the shelf. The highest tracer concentrations are observed near the shelfbreak and southeast of Hanna Shoal, a region known for high biological productivity and enhanced benthic biomass.This study presents data from multiple Arctic expeditions over the past two decades, and we are indebted to the captains, crews, and scientific parties that made this data collection possible. This work was funded by NSF awards OCE‐1458305 to M. Charette, OCE‐1458424 to W. Moore, OCE‐1434085 to D. Kadko, PLR‐1504333 to R. Pickart, and OPP‐1822334 to M. Spall. Funding was also provided by National Oceanic and Atmospheric Administration Grant NA14‐OAR4320158 to R. Pickart. L. Kipp was supported by an Ocean Frontier Institute Postdoctoral Fellowship. Radium data used in this manuscript are available in Table S1.2020-10-2

Transport of Pacific water into the Canada Basin and the formation of the Chukchi Slope Current

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 123 (2018): 7453-7471, doi:10.1029/2018JC013825.A high‐resolution regional ocean model together with moored hydrographic and velocity measurements is used to identify the pathways and mechanisms by which Pacific water, modified over the Chukchi shelf, crosses the shelf break into the Canada Basin. Most of the Pacific water flowing into the Arctic Ocean through Bering Strait enters the Canada Basin through Barrow Canyon. Strong advection allows the water to cross the shelf break and exit the shelf. Wind forcing plays little role in this process. Some of the outflowing water from Barrow Canyon flows to the east into the Beaufort Sea; however, approximately 0.4 to 0.5 Sv turns to the west forming the newly identified Chukchi Slope Current. This transport occurs at all times of year, channeling both summer and winter waters from the shelf to the Canada Basin. The model indicates that approximately 75% of this water was exposed to the mixed layer within the Chukchi Sea, while the remaining 25% was able to cross the shelf during the stratified summer before convection commences in late fall. We view the Ό(0.5) Sv of the Chukchi Slope Current as replacing Beaufort Gyre water that would have come from the east in the absence of the cross-topography flow in Barrow Canyon. The weak eastward flow on the Beaufort slope is also consistent with the local disruption of the Beaufort Gyre by the Barrow Canyon outflow.Bureau of Ocean and Energy Management Grant Number: M12AC00008; DOC | National Oceanic and Atmospheric Administration (NOAA) Grant Number: NA16OAR4310248; National Science Foundation (NSF) Grant Numbers: PLR-1415489, OCE-15331702019-04-2

Temporal Trends and Clinical Trial Characteristics Associated with the Inclusion of Women in Heart Failure Trial Steering Committees:A Systematic Review

Background: Trial steering committees (TSCs) steer the conduct of randomized controlled trials (RCTs). We examined the gender composition of TSCs in impactful heart failure RCTs and explored whether trial leadership by a woman was independently associated with the inclusion of women in TSCs. Methods: We systematically searched MEDLINE, EMBASE, and CINAHL for heart failure RCTs published in journals with impact factor ≥10 between January 2000 and May 2019. We used the Jonckheere-Terpstra test to assess temporal trends and multivariable logistic regression to explore trial characteristics associated with TSC inclusion of women. Results: Of 403 RCTs that met inclusion criteria, 127 (31.5%) reported having a TSC but 20 of these (15.7%) did not identify members. Among 107 TSCs that listed members, 56 (52.3%) included women and 6 of these (10.7%) restricted women members to the RCT leaders. Of 1213 TSC members, 11.1% (95% CI, 9.4%-13.0%) were women, with no change in temporal trends (P=0.55). Women had greater odds of TSC inclusion in RCTs led by women (adjusted odds ratio, 2.48 [95% CI, 1.05-8.72], P=0.042); this association was nonsignificant when analysis excluded TSCs that restricted women to the RCT leaders (adjusted odds ratio 1.46 [95% CI, 0.43-4.91], P=0.36). Conclusions: Women were included in 52.3% of TSCs and represented 11.1% of TSC members in 107 heart failure RCTs, with no change in trends since 2000. RCTs led by women had higher adjusted odds of including women in TSCs, partly due to the self-inclusion of RCT leaders in TSCs

Role of shelfbreak upwelling in the formation of a massive under-ice bloom in the Chukchi Sea

Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 105 (2014): 17-29, doi:10.1016/j.dsr2.2014.03.017.In the summer of 2011, an oceanographic survey carried out by the Impacts of Climate on EcoSystems and Chemistry of the Arctic Pacific Environment (ICESCAPE) program revealed the presence of a massive phytoplankton bloom under the ice near the shelfbreak in the central Chukchi Sea. For most of the month preceding the measurements there were relatively strong easterly winds, providing upwelling favorable conditions along the shelfbreak. Analysis of similar hydrographic data from summer 2002, in which there were no persistent easterly winds, found no evidence of upwelling near the shelfbreak. A two-dimensional ocean circulation model is used to show that sufficiently strong winds can result not only in upwelling of high nutrient water from offshore onto the shelf, but it can also transport the water out of the bottom boundary layer into the surface Ekman layer at the shelf edge. The extent of upwelling is determined by the degree of overlap between the surface Ekman layer and the bottom boundary layer on the outer shelf. Once in the Ekman layer, this high nutrient water is further transported to the surface through mechanical mixing driven by the surface stress. Two model tracers, a nutrient tracer and a chlorophyll tracer, reveal distributions very similar to that observed in the data. These results suggest that the biomass maximum near the shelfbreak during the massive bloom in summer 2011 resulted from an enhanced supply of nutrients upwelled from the halocline seaward of the shelf. The decade long trend in summertime surface winds suggest that easterly winds in this region are increasing in strength and that such bloom events will become more common.This study was supported by the National Science Foundation under Grant OCE-0959381 (MAS), and by the Ocean Biology and Biogeochemistry Program and the Cryosphere Science Program of the National Aeronautic and Space Administration under Award NNX10AF42G (RSP;KRA). GWKM was supported by the Natural Sciences and Engineering Research Council of Canada. ETB was supported by the U. S. Navy