95 research outputs found
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 1990â97. This time period was chosen because it corresponded to intense wintertime convectionâthe deepest and densest in the historical recordâsuggesting 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 sâ1), 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)
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 sâ1) and an eastward transport of 0.42 Sv (1 Sv ⥠106 m3 sâ1). 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
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): 1910â1914, 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, 1644â166
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 midâIceland 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 NIJâdominant scenario was present during different times of the year for the two successive mooring deploymentsâappearing 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 highâfrequency variability is driven by meanâtoâeddy 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 twoâmonth 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 SĂŠmundsson for the deployment and recovery of the moorings. D. Torres and F. Bahr processed the second year of mooring data. We thank K. VĂ„ge, 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 OCEâ1558742 (J. H., R. P., P. L., and M. S.) and OCEâ1534618 (M. S.). The mooring data are available at http://kogur.whoi.edu/php/index.php.2019-12-0
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 highâresolution 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 Î(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
AMOD: a morpholino oligonucleotide selection tool
AMOD is a web-based program that aids in the functional evaluation of nucleotide sequences through sequence characterization and antisense morpholino oligonucleotide (target site) selection. Submitted sequences are analyzed by translation initiation site prediction algorithms and sequence-to-sequence comparisons; results are used to characterize sequence features required for morpholino design. Within a defined subsequence, base composition and homodimerization values are computed for all putative morpholino oligonucleotides. Using these properties, morpholino candidates are selected and compared with genomic and transcriptome databases with the goal to identify target-specific enriched morpholinos. AMOD has been used at the University of Minnesota to design âŒ200 morpholinos for a functional genomics screen in zebrafish. The AMOD web server and a tutorial are freely available to both academic and commercial users at
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 nutrientârich 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 radiumâ228, which is a soluble radionuclide produced in sediments, and a numerical model of an inert, generic sedimentâderived 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 sedimentâsourced materials in the spring and summer due to continued sedimentâwater 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 OCEâ1458305 to M. Charette, OCEâ1458424 to W. Moore, OCEâ1434085 to D. Kadko, PLRâ1504333 to R. Pickart, and OPPâ1822334 to M. Spall. Funding was also provided by National Oceanic and Atmospheric Administration Grant NA14âOAR4320158 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
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
Dynamics of downwelling in an eddy-resolving convective basin
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): 2341â2347, doi:10.1175/2010JPO4465.1.The mean downwelling in an eddy-resolving model of a convective basin is concentrated near the boundary where eddies are shed from the cyclonic boundary current into the interior. It is suggested that the buoyancy-forced downwelling in the Labrador Sea and the Lofoten Basin is similarly concentrated in analogous eddy formation regions along their eastern boundaries. Use of a transformed Eulerian mean depiction of the density transport reveals the central role eddy fluxes play in maintaining the adiabatic nature of the flow in a nonperiodic region where heat is lost from the boundary current. The vorticity balance in the downwelling region is primarily between stretching of planetary vorticity and eddy flux divergence of relative vorticity, although a narrow viscous boundary layer is ultimately important in closing the regional vorticity budget. This overall balance is similar in some ways to the diffusiveâviscous balance represented in previous boundary layer theories, and suggests that the downwelling in convective basins may be properly represented in low-resolution climate models if eddy flux parameterizations are adiabatic, identify localized regions of eddy formations, and allow density to be transported far from the region of eddy formations.This study was supported by the
National Science Foundation under Grants OCE-0726339
and OCE-0850416
Physical controls on the macrofaunal benthic biomass in Barrow Canyon, Chukchi Sea
Author Posting. © American Geophysical Union, 2021. 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 126(5), (2021): e2020JC017091, https://doi.org/10.1029/2020JC017091.A region of exceptionally high macrofaunal benthic biomass exists in Barrow Canyon, implying a carbon export process that is locally concentrated. Here we offer an explanation for this benthic âhotspotâ using shipboard data together with a set of dynamical equations. Repeat occupations of the Distributed Biological Observatory transect in Barrow Canyon reveal that when the northward flow is strong and the density front in the canyon is sharp, plumes of fluorescence and oxygen extend from the pycnocline to the seafloor in the vicinity of the hotspot. By solving the quasi-geostrophic omega equation with an analytical flow field fashioned after the observations, we diagnose the vertical velocity in the canyon. This reveals that, as the along stream flow converges into the canyon, it drives a secondary circulation cell with strong downwelling on the cyclonic side of the northward flow. The downwelling quickly advects material from the pycnocline to the seafloor in a vertical plume analogous to those seen in the observations. The plume occurs only when the phytoplankton reside in the pycnocline, since the near-surface vertical velocity is weak, also consistent with the observations. Using a wind-based proxy to represent the strength of the northward flow and hence the pumping, in conjunction with a satellite-derived phytoplankton source function, we construct a time series of carbon supply to the bottom of Barrow Canyon.This work was funded by National Science Foundation grants PLR-1504333 and OPP-1733564 (Robert S. Pickart, Frank Bahr), OPP-1822334 (Michael A. Spall), PLR-1304563 (Kevin R. Arrigo), OPP-1204082 and OPP-1702456 (Jacqueline M. Grebmeier); National Oceanic and Atmospheric Administration grants NA14OAR4320158 and NA19OAR4320074 (Robert S. Pickart, Peigen Lin, Leah T. McRaven), CINAR-22309.02 (Jacqueline M. Grebmeier)
- âŠ