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  • Eddies
  • In situ oceanic observations
  • Ocean
  • Ocean circulation
  • American Geophysical Union  (19)
  • MDPI  (2)
  • MDPI Publishing
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  • 1
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    Spatial variability of movement, structure, and formation of Warm Core Rings in the Northwest Atlantic Slope Sea (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-25
    Description: Author Posting. © American Geophysical Union, 2022. 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 127(8),(2022): e2022JC018737, https://doi.org/10.1029/2022jc018737.
    Description: Gulf Stream Warm Core Rings (WCRs) have important influences on the New England Shelf and marine ecosystems. A 10-year (2011–2020) WCR dataset that tracks weekly WCR locations and surface areas is used here to identify the rings' path and characterize their movement between 55 and 75°W. The WCR dataset reveals a very narrow band between 66 and 71°W along which rings travel almost due west along ∼39°N across isobaths – the “Ring Corridor.” Then, west of the corridor, the mean path turns southwestward, paralleling the shelfbreak. The average ring translation speed along the mean path is 5.9 cm s−1. Long-lived rings (lifespan 〉150 days) tend to occupy the region west of the New England Seamount Chain (NESC) whereas short-lived rings (lifespan 〈150 days) tend to be more broadly distributed. WCR vertical structures, analyzed using available Argo float profiles indicate that rings that are formed to the west of the NESC have shallower thermoclines than those formed to the east. This tendency may be due to different WCR formation processes that are observed to occur along different sections of the Gulf Stream. WCRs formed to the east of the NESC tend to form from a pinch-off mechanism incorporating cores of Sargasso Sea water and a perimeter of Gulf Stream water. WCRs that form to the west of the NESC, form from a process called an aneurysm. WCRs formed through aneurysms comprise water mostly from the northern half of the Gulf Stream and are smaller than the classic pinch-off rings.
    Description: AS and AG are grateful for financial support from NOAA (NA11NOS0120038), NSF (OCE-1851242 and OCE-2123283), SMAST, and UMass Dartmouth. GG was supported by NSF under grant OCE-1657853. MA was supported by NSF under grant OCE-2122726 and by ONR under grant N00014-22-1-2112.
    Keywords: Gulf Stream ; Warm core rings ; Trajectories ; Eddies ; Aneurysm ; Ring formation
    Repository Name: Woods Hole Open Access Server
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  • 2
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    Iron depletion in the deep chlorophyll maximum: mesoscale eddies as natural iron fertilization experiments (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hawco, N. J., Barone, B., Church, M. J., Babcock-Adams, L., Repeta, D. J., Wear, E. K., Foreman, R. K., Bjorkman, K. M., Bent, S., Van Mooy, B. A. S., Sheyn, U., DeLong, E. F., Acker, M., Kelly, R. L., Nelson, A., Ranieri, J., Clemente, T. M., Karl, D. M., & John, S. G. Iron depletion in the deep chlorophyll maximum: mesoscale eddies as natural iron fertilization experiments. Global Biogeochemical Cycles, 35(12), (2021): e2021GB007112, https://doi.org/10.1029/2021GB007112.
    Description: In stratified oligotrophic waters, phytoplankton communities forming the deep chlorophyll maximum (DCM) are isolated from atmospheric iron sources above and remineralized iron sources below. Reduced supply leads to a minimum in dissolved iron (dFe) near 100 m, but it is unclear if iron limits growth at the DCM. Here, we propose that natural iron addition events occur regularly with the passage of mesoscale eddies, which alter the supply of dFe and other nutrients relative to the availability of light, and can be used to test for iron limitation at the DCM. This framework is applied to two eddies sampled in the North Pacific Subtropical Gyre. Observations in an anticyclonic eddy center indicated downwelling of iron-rich surface waters, leading to increased dFe at the DCM but no increase in productivity. In contrast, uplift of isopycnals within a cyclonic eddy center increased supply of both nitrate and dFe to the DCM, and led to dominance of picoeukaryotic phytoplankton. Iron addition experiments did not increase productivity in either eddy, but significant enhancement of leucine incorporation in the light was observed in the cyclonic eddy, a potential indicator of iron stress among Prochlorococcus. Rapid cycling of siderophores and low dFe:nitrate uptake ratios also indicate that a portion of the microbial community was stressed by low iron. However, near-complete nitrate drawdown in this eddy, which represents an extreme case in nutrient supply compared to nearby Hawaii Ocean Time-series observations, suggests that recycling of dFe in oligotrophic ecosystems is sufficient to avoid iron limitation in the DCM under typical conditions.
    Description: The expedition and analyses were supported by the Simons Foundation SCOPE Grant 329108 to S. G. John, M. J. Church, D. J. Repeta, B. Van Mooy, E. F. DeLong, and D. M. Karl. N. J. Hawco was supported by a Simons Foundation Marine Microbial Ecology and Evolution postdoctoral fellowship (602538) and Simons Foundation grant 823167.
    Keywords: Chlorophyll ; Photosynthesis ; Iron limitation ; Oligotrophic ; Prochlorococcus ; Eddies
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  • 3
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    Revisiting the seasonal cycle of the Timor throughflow: impacts of winds, waves and eddies (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Peña‐Molino, B., Sloyan, B., Nikurashin, M., Richet, O., & Wijffels, S. Revisiting the seasonal cycle of the Timor throughflow: impacts of winds, waves and eddies. Journal of Geophysical Research: Oceans, 127, (2022): e2021JC018133, https://doi.org/10.1029/2021jc018133.
    Description: The tropical Pacific and Indian Oceans are connected via a complex system of currents known as the Indonesian Throughflow (ITF). More than 30% of the variability in the ITF is linked to the seasonal cycle, influenced by the Monsoon winds. Despite previous efforts, a detailed knowledge of the ITF response to the components of the seasonal forcing is still lacking. Here, we describe the seasonal cycle of the ITF based on new observations of velocity and properties in Timor Passage, satellite altimetry and a high-resolution regional model. These new observations reveal a complex mean and seasonally varying flow field. The amplitude of the seasonal cycle in volume transport is approximately 6 Sv. The timing of the seasonal cycle, with semi-annual maxima (minima) in May and December (February and September), is controlled by the flow below 600 m associated with semi-annual Kelvin waves. The transport of thermocline waters (〈300 m) is less variable than the deep flow but larger in magnitude. This top layer is modulated remotely by cycles of divergence in the Banda Sea, and locally through Ekman transport, coastal upwelling, and non-linearities of the flow. The latter manifests through the formation of eddies that reduce the throughflow during the Southeast Monsoon, when is expected to be maximum. While the reduction in transport associated with the eddies is small, its impact on heat transport is large. These non-linear dynamics develop over small scales (〈10 km), and without high enough resolution, both observations and models will fail to capture them adequately.
    Description: B. Peña-Molino, B. M. Sloyan, M. Nikurashin, and O. Richet were supported by the Centre for Southern Hemisphere Oceans Research (CSHOR). CSHOR is a joint research Centre for Southern Hemisphere Ocean Research between QNLM and CSIRO. S. E. Wijffels was supported by the US National Science Foundation Grant No. OCE-1851333.
    Keywords: Indonesian Throughflow ; Timor Passage ; Seasonal cycle ; Moorings ; Transport ; Eddies
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  • 4
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    Little change in ice age water mass structure from Cape Basin benthic neodymium and carbon isotopes (2022)
    American Geophysical Union
    Details
    Publication Date: 2022-05-27
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hines, S. K. V., Bolge, L., Goldstein, S. L., Charles, C. D., Hall, I. R., & Hemming, S. R. Little change in ice age water mass structure from Cape Basin benthic neodymium and carbon isotopes. Paleoceanography and Paleoclimatology, 36(11), (2021): e2021PA004281, https://doi.org/10.1029/2021PA004281.
    Description: A common conception of the deep ocean during ice age episodes is that the upper circulation cell in the Atlantic was shoaled at the Last Glacial Maximum compared to today, and that this configuration facilitated enhanced carbon storage in the deep ocean, contributing to glacial CO2 draw-down. Here, we test this notion in the far South Atlantic, investigating changes in glacial circulation structure using paired neodymium and benthic carbon isotope measurements from International Ocean Discovery Program Site U1479, at 2,615 m water depth in the Cape Basin. We infer changes in circulation structure across the last glacial cycle by aligning our site with other existing carbon and neodymium isotope records from the Cape Basin, examining vertical isotope gradients, while determining the relative timing of inferred circulation changes at different depths. We find that Site U1479 had the most negative neodymium isotopic composition across the last glacial cycle among the analyzed sites, indicating that this depth was most strongly influenced by North Atlantic Deep Water (NADW) in both interglacial and glacial intervals. This observation precludes a hypothesized dramatic shoaling of NADW above ∼2,000 m. Our evidence, however, indicates greater stratification between mid-depth and abyssal sites throughout the last glacial cycle, conditions that developed in Marine Isotope Stage 5. These conditions still may have contributed to glacial carbon storage in the deep ocean, despite little change in the mid-depth ocean structure.
    Description: This work was supported by NSF grant OCE-1831415 (S. K. V. Hines, S. L. Goldstein., S. R. Hemming.).
    Description: 2022-04-25
    Keywords: Ocean circulation ; Neodymium isotopes ; Carbon isotopes
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  • 5
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    Field-portable microplastic sensing in aqueous environments: a perspective on emerging techniques (2021)
    MDPI
    Details
    Publication Date: 2022-10-20
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Blevins, M. G., Allen, H. L., Colson, B. C., Cook, A.-M., Greenbaum, A. Z., Hemami, S. S., Hollmann, J., Kim, E., LaRocca, A. A., Markoski, K. A., Miraglia, P., Mott, V. L., Robberson, W. M., Santos, J. A., Sprachman, M. M., Swierk, P., Tate, S., Witinski, M. F., Kratchman, L. B., & Michel, A. P. M. Field-portable microplastic sensing in aqueous environments: a perspective on emerging techniques. Sensors, 21(10), (2021): 3532, https://doi.org/10.3390/s21103532.
    Description: Microplastics (MPs) have been found in aqueous environments ranging from rural ponds and lakes to the deep ocean. Despite the ubiquity of MPs, our ability to characterize MPs in the environment is limited by the lack of technologies for rapidly and accurately identifying and quantifying MPs. Although standards exist for MP sample collection and preparation, methods of MP analysis vary considerably and produce data with a broad range of data content and quality. The need for extensive analysis-specific sample preparation in current technology approaches has hindered the emergence of a single technique which can operate on aqueous samples in the field, rather than on dried laboratory preparations. In this perspective, we consider MP measurement technologies with a focus on both their eventual field-deployability and their respective data products (e.g., MP particle count, size, and/or polymer type). We present preliminary demonstrations of several prospective MP measurement techniques, with an eye towards developing a solution or solutions that can transition from the laboratory to the field. Specifically, experimental results are presented from multiple prototype systems that measure various physical properties of MPs: pyrolysis-differential mobility spectroscopy, short-wave infrared imaging, aqueous Nile Red labeling and counting, acoustophoresis, ultrasound, impedance spectroscopy, and dielectrophoresis.
    Description: We greatly thank our funding agencies: Gerstner Philanthropies (to A.P.M.M.), the Richard Saltonstall Charitable Foundation (to A.P.M.M.), and the Wallace Research Foundation (to A.P.M.M. and S.S.H.). Funding for M.G.B. was provided by a Draper Fellowship and to B.C.C. by an MIT Martin Fellowship. Draper thanks EPA region 9 for their partnership and support through a Cooperative Research and Development Agreement, an industry/government agreement regarding funding and personnel contributions of time and expertise.
    Keywords: Microplastics ; Plastic pollution ; Sensors ; Analytical chemistry ; Environment ; Water ; Ocean ; Marine pollution ; Polymers ; Freshwater ; Aqueous solutions
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  • 6
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    Modeled three-dimensional currents and eddies on an alongshore-variable barred beach (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-10-20
    Description: 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(7), (2021): e2020JC016899, https://doi.org/10.1029/2020JC016899.
    Description: Circulation in the nearshore region, which is critical for material transport along the coast and between the surf zone and the inner shelf, includes strong vortical motions. The horizontal length scales and vertical structure associated with vortical motions are not well documented on alongshore-variable beaches. Here, a three-dimensional phase-resolving numerical model, Simulating WAves till SHore (SWASH), is compared with surfzone waves and flows on a barred beach, and is used to investigate surfzone eddies. Model simulations with measured bathymetry reproduce trends in the mean surfzone circulation patterns, including alongshore currents and rip current circulation cells observed for offshore wave heights from 0.5 to 2.0 m and incident wave directions from 0 to 15° relative to shore normal. The length scales of simulated eddies, quantified using the alongshore wavenumber spectra of vertical vorticity, suggest that increasing wave directional spread intensifies small-scale eddies ( (10) m). Simulations with bathymetric variability ranging from alongshore uniform to highly alongshore variable indicate that large-scale eddies ( (100) m) may be enhanced by surfzone bathymetric variability, whereas small-scale eddies ( (10) m) are less dependent on bathymetric variability. The simulated vertical dependence of the magnitude and mean length scale (centroid) of the alongshore wavenumber spectra of vertical vorticity and very low-frequency (f ≈ 0.005 Hz) currents is weak in the outer surf zone, and decreases toward the shoreline. The vertical dependence in the simulations may be affected by the vertical structure of turbulence, mean shear, and bottom boundary layer dynamics.
    Description: Support was provided by the University of Washington Royalty Research Fund, the National Science Foundation, the Office of Naval Research, a National Defense Science and Engineering Graduate Fellowship, a Vannevar Bush Faculty Fellowship, the United States Army Corps of Engineers, the United States Coastal Research Program, Sea Grant, and the WHOI Investment in Science Program.
    Description: 2021-12-26
    Keywords: Surf zone ; Eddies ; Circulation ; Vorticity ; Wave breaking ; Modeling
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  • 7
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    The dynamical structure of a warm core ring as I\inferred from glider observations and along-track altimetry (2021)
    MDPI
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Meunier, T., Pallas Sanz, E., de Marez, C., Perez, J., Tenreiro, M., Ruiz Angulo, A., & Bower, A. The dynamical structure of a warm core ring as I\inferred from glider observations and along-track altimetry. Remote Sensing, 13(13), (2021): 2456, https://doi.org/10.3390/rs13132456.
    Description: This study investigates the vertical structure of the dynamical properties of a warm-core ring in the Gulf of Mexico (Loop Current ring) using glider observations. We introduce a new method to correct the glider’s along-track coordinate, which is, in general, biased by the unsteady relative movements of the glider and the eddy, yielding large errors on horizontal derivatives. Here, we take advantage of the synopticity of satellite along-track altimetry to apply corrections on the glider’s position by matching in situ steric height with satellite-measured sea surface height. This relocation method allows recovering the eddy’s azimuthal symmetry, precisely estimating the rotation axis position, and computing reliable horizontal derivatives. It is shown to be particularly appropriate to compute the eddy’s cyclo-geostrophic velocity, relative vorticity, and shear strain, which are otherwise out of reach when using the glider’s raw traveled distance as a horizontal coordinate. The Ertel potential vorticity (PV) structure of the warm core ring is studied in details, and we show that the PV anomaly is entirely controlled by vortex stretching. Sign reversal of the PV gradient across the water column suggests that the ring might be baroclinically unstable. The PV gradient is also largely controlled by gradients of the vortex stretching term. We also show that the ring’s total energy partition is strongly skewed, with available potential energy being 3 times larger than kinetic energy. The possible impact of this energy partition on the Loop Current rings longevity is also discussed.
    Description: This research was funded by a grant of the National Council of Science and Technology of Mexico—Secretariat of Energy Hydrocarbons Trust, project 201441. This is a contribution of the Gulf of Mexico Research Consortium (CIGoM).
    Keywords: Gliders ; Altimetry ; Mesoscale ; Eddies ; Warm-core rings ; Potential vorticity ; Gulf of Mexico
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  • 8
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    FRIS revisited in 2018: on the circulation and water masses at the Filchner and Ronne Ice Shelves in the Southern Weddell Sea (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Janout, M. A., Hellmer, H. H., Hattermann, T., Huhn, O., Sueltenfuss, J., Osterhus, S., Stulic, L., Ryan, S., Schroeder, M., & Kanzow, T. FRIS revisited in 2018: on the circulation and water masses at the Filchner and Ronne Ice Shelves in the Southern Weddell Sea. Journal of Geophysical Research: Oceans, 126(6), (2021): e2021JC017269, https://doi.org/10.1029/2021JC017269.
    Description: The Filchner-Ronne Ice Shelf (FRIS) is characterized by moderate basal melt rates due to the near-freezing waters that dominate the wide southern Weddell Sea continental shelf. We revisited the region in austral summer 2018 with detailed hydrographic and noble gas surveys along FRIS. The FRIS front was characterized by High Salinity Shelf Water (HSSW) in Ronne Depression, Ice Shelf Water (ISW) on its eastern flank, and an inflow of modified Warm Deep Water (mWDW) entering through Central Trough. Filchner Trough was dominated by Ronne HSSW-sourced ISW, likely forced by a recently intensified circulation beneath FRIS due to enhanced sea ice production in the Ronne polynya since 2015. Glacial meltwater fractions and tracer-based water mass dating indicate two separate ISW outflow cores, one hugging the Berkner slope after a two-year travel time, and the other located in the central Filchner Trough following a ∼six year-long transit through the FRIS cavity. Historical measurements indicate the presence of two distinct modes, in which water masses in Filchner Trough were dominated by either Ronne HSSW-derived ISW (Ronne-mode) or more locally derived Berkner-HSSW (Berkner-mode). While the dominance of these modes has alternated on interannual time scales, ocean densities in Filchner Trough have remained remarkably stable since the first surveys in 1980. Indeed, geostrophic velocities indicated outflowing ISW-cores along the trough's western flank and onto Berkner Bank, which suggests that Ronne-ISW preconditions Berkner-HSSW production. The negligible density difference between Berkner- and Ronne-mode waters indicates that each contributes cold dense shelf waters to protect FRIS against inflowing mWDW.
    Description: This study used samples and data provided by the Alfred Wegener Institute Helmholtz-Center for Polar- and Marine Research in Bremerhaven (Grant No. AWI-PS111_01). The authors thank Captain Schwarze and the crew of RV Polarstern for a very successful expedition. We acknowledge support from the EU Horizon 2020 grants 820575 (HHH, SØ) and 821001 (TK, SØ).
    Keywords: Ocean circulation ; Ocean-ice shelf interaction ; Water masses ; Weddell Sea ; Filcher and Ronne shelves
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  • 9
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    Surface methane concentrations along the mid-Atlantic bight driven by aerobic subsurface production rather than seafloor gas seeps. (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-27
    Description: 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): e2019JC015989, doi:10.1029/2019JC015989.
    Description: Relatively minor amounts of methane, a potent greenhouse gas, are currently emitted from the oceans to the atmosphere, but such methane emissions have been hypothesized to increase as oceans warm. Here, we investigate the source, distribution, and fate of methane released from the upper continental slope of the U.S. Mid‐Atlantic Bight, where hundreds of gas seeps have been discovered between the shelf break and ~1,600 m water depth. Using physical, chemical, and isotopic analyses, we identify two main sources of methane in the water column: seafloor gas seeps and in situ aerobic methanogenesis which primarily occurs at 100–200 m depth in the water column. Stable isotopic analyses reveal that water samples collected at all depths were significantly impacted by aerobic methane oxidation, the dominant methane sink in this region, with the average fraction of methane oxidized being 50%. Due to methane oxidation in the deeper water column, below 200 m depth, surface concentrations of methane are influenced more by methane sources found near the surface (0–10 m depth) and in the subsurface (10–200 m depth), rather than seafloor emissions at greater depths.
    Description: This research was supported by DOE Grant (DE‐FE0028980) to J. K. and by DOE‐USGS Interagency Agreement DE‐FE0026195.
    Description: 2020-10-04
    Keywords: Methane ; Ocean ; Isotopes ; Gas seeps ; Mid Atlantic bight ; Oxidation
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  • 10
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    Exceptional 20th century ocean circulation in the Northeast Atlantic (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Spooner, P. T., Thornalley, D. J. R., Oppo, D. W., Fox, A. D., Radionovskaya, S., Rose, N. L., Mallett, R., Cooper, E., & Roberts, J. M. Exceptional 20th century ocean circulation in the Northeast Atlantic. Geophysical Research Letters, 47(10), (2020): e2020GL087577, doi:10.1029/2020GL087577.
    Description: The North Atlantic subpolar gyre (SPG) connects tropical and high‐latitude waters, playing a leading role in deep‐water formation, propagation of Atlantic water into the Arctic, and as habitat for many ecosystems. Instrumental records spanning recent decades document significant decadal variability in SPG circulation, with associated hydrographic and ecological changes. Emerging longer‐term records provide circumstantial evidence that the North Atlantic also experienced centennial trends during the 20th century. Here, we use marine sediment records to show that there has been a long‐term change in SPG circulation during the industrial era, largely during the 20th century. Moreover, we show that the shift and late 20th century SPG configuration were unprecedented in the last 10,000 years. Recent SPG dynamics resulted in an expansion of subtropical ecosystems into new habitats and likely also altered the transport of heat to high latitudes.
    Description: We thank Janet Hope and UCL laboratory staff, colleagues who sailed on EN539, Kathryn Pietro‐Rose, Sean O'Keefe and Henry Abrams, Sara Chipperton, Tanya Monica, Laura Thrower and Kitty Green for sediment processing, Miles Irving for artwork assistance, James Rolfe for nitrogen isotope measurement, Maryline Vautravers and Michael Kucera for guidance, Arne Biastoch and Christian Mohn for discussion of VIKING20, and Chris Brierley, Meric Srokosz, and Jon Robson for comments. Funding was provided by National Science Foundation (NSF) grant OCE‐1304291 to D.W.O. and D.J.R.T., the Leverhulme Trust, National Environment Research Council (NERC) grant NE/S009736/1, and the ATLAS project to D.J.R.T. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement 678760 (ATLAS). This paper reflects only the authors views and the European Union cannot be held responsible for any use that may be made of the information contained herein.
    Keywords: Foraminifera ; Subpolar gyre ; North Atlantic ; Ocean circulation ; Industrial era
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  • 11
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    A preindustrial sea-level rise hotspot along the Atlantic Coast of North America (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Gehrels, W. R., Dangendorf, S., Barlow, N. L. M., Saher, M. H., Long, A. J., Woodworth, P. L., Piecuch, C. G., & Berk, K. A preindustrial sea-level rise hotspot along the Atlantic Coast of North America. Geophysical Research Letters, 47(4), (2020): e2019GL085814, doi:10.1029/2019GL085814.
    Description: The Atlantic coast of North America north of Cape Hatteras has been proposed as a “hotspot” of late 20th century sea‐level rise. Here we test, using salt‐marsh proxy sea‐level records, if this coast experienced enhanced sea‐level rise over earlier multidecadal‐centennial periods. While we find in agreement with previous studies that 20th century rates of sea‐level change were higher compared to rates during preceding centuries, rates of 18th century sea‐level rise were only slightly lower, suggesting that the “hotspot” is a reoccurring feature for at least three centuries. Proxy sea‐level records from North America (Iceland) are negatively (positively) correlated with centennial changes in the North Atlantic Oscillation. They are consistent with sea‐level “fingerprints” of Arctic ice melt, and we therefore hypothesize that sea‐level fluctuations are related to changes in Arctic land‐ice mass. Predictions of future sea‐level rise should take into account these long‐term fluctuating rates of natural sea‐level change.
    Description: This work is funded by the Natural Environment Research Council (grant NE/G003440/1). All radiocarbon dating was supported by the Natural Environment Research Council Radiocarbon Facility (allocations 1490.0810, 1566.0511, 1604.0112). Mark Wood assisted with fieldwork. Rob Scaife analyzed pollen data for core SN‐3.3. Sönke Dangendorf and Kevin Berk acknowledge the University of Siegen for their support within the PEPSEA project. Christopher Piecuch was supported by National Science Foundation awards OCE‐1558966 and OCE‐1834739. We thank project members Miguel Ángel Morales Maqueda, Chris Hughes, Vassil Roussenov and Ric Williams for valuable discussions. We are grateful to the International Space Science Institute (ISSI; Bern, Switzerland) for support of the International Team “Towards a unified Sea Level Record”. Data used in this paper are freely available online (https://www.doi.org/10/dgvq).
    Keywords: Sea level ; Late Holocene ; Common Era ; Climate ; Ocean
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  • 12
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    Improving near-surface retrievals of surface humidity over the global open oceans from passive microwave observations (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: 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 Earth and Space Science, 6(7), (2019): 1220-1233, doi:10.1029/2018EA000436.
    Description: Ocean evaporative fluxes are a critical component of the Earth's energy and water cycle, but their estimation remains uncertain. Near‐surface humidity is a required input to bulk flux algorithms that relate mean surface values to the turbulent fluxes. Several satellite‐derived turbulent flux products have been developed over the last decade that utilize passive microwave imager observations to estimate the surface humidity. It is known, however, that these estimates tend to diverge from one another and from in situ observations. Analysis of current state‐of‐the‐art satellite estimates provided herein reveals that regional‐scale biases in these products remain significant. Investigations reveal a link between the spatial coherency of the observed biases to atmospheric dynamical controls of water vapor vertical stratification, cloud liquid water, and sea surface temperature. This information is used to develop a simple state‐dependent bias correction that results in more consistent ocean surface humidity estimates. A principal conclusion is that further improvements to ocean near‐surface humidity estimation using microwave radiometers requires incorporation of prior information on water vapor stratification and sea surface temperature.
    Description: Data products used in this study are made publicly available via multiple repositories hosted by individual data product producers. JOFUROv2 and JOFUROv3 data are available online (https://j‐ofuro.scc.u‐tokai.ac.jp/en/). IFREMERv4 and NOCS surface data are available through the OceanHeatFlux project (https://www.ifremer.fr/oceanheatflux/Data). GSSTFv3 (doi:10.5067/MEASURES/GSSTF/DATA301) and MERRA‐2 data are obtained from the Goddard Earth Sciences Data and Information Services Center. HOAPSv3.2 data are available from Satellite Application Facility on Climate Monitoring (https://doi.org/10.5676/EUM_SAF_CM/HOAPS/V001). SEAFLUXv2 data are accessed through the National Centers for Environmental Information (http://doi.org/10.7289/V59K4885). Daily surface observations were provided by David Berry and Elizabeth Kent. This work is supported under the NASA Physical Oceanography Program Grant NNX14AK48A.
    Keywords: Humidity ; Passive microwave ; Ocean ; Turbulent fluxes ; Evaporation ; Remote sensing
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  • 13
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    Intraseasonal variability of surface salinity in the eastern tropical pacific associated with mesoscale eddies. (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: 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(4), (2019):2861-2875, doi: 10.1029/2018JC014175.
    Description: Strong variability in sea surface salinity (SSS) in the Eastern Tropical Pacific (ETPac) on intraseasonal to interannual timescales was studied using data from the Soil Moisture and Ocean Salinity, Soil Moisture Active Passive, and Aquarius satellite missions. A zonal wave number‐frequency spectral analysis of SSS reveals a dominant timescale of 50–180 days and spatial scale of 8°–20° of longitude with a distinct seasonal cycle and interannual variability. This intraseasonal SSS signal is detailed in the study of 19 individual ETPac eddies over 2010–2016 identified by their sea level anomalies, propagating westward at a speed of about 17 cm/s. ETPac eddies trap and advect water in their core westward up to 40° of longitude away from the coast. The SSS signatures of these eddies, with an average anomaly of 0.5‐pss magnitude difference from ambient values, enable the study of their dynamics and the mixing of their core waters with the surroundings. Three categories of eddies were identified according to the location where they were first tracked: (1) in the Gulf of Tehuantepec, (2) in the Gulf of Papagayo, and (3) in the open ocean near 100°W–12°N. They all traveled westward near 10°N latitude. Category 3 is of particular interest, as eddies seeded in the Gulf of Tehuantepec grew substantially in the vicinity of the Clipperton Fracture Zone rise and in a region where the mean zonal currents have anticyclonic shear. The evolution of the SSS signature associated with the eddies indicates the importance of mixing to their dissipation.
    Description: This research was carried out in part at the Jet Propulsion Laboratory (JPL), California Institute of Technology, under a contract with NASA and part at LOCEAN (Sorbonne Université, CNRS, IRD, MNHN) under a CNES Postdoctoral fellowship. This work is supported by NASA Grants NNX11AE83G and NNX14AH38G and is a contribution to the TOSCA/SMOS‐Ocean proposal supported by CNES. We thank the reviewers for their thoughtfully comments that lead to a much‐improved manuscript. We benefited from numerous data sets made freely available and are listed here: The SMOS debias_v2 SSS have been produced by LOCEAN laboratory and ACRI‐st company that participate to the Ocean Salinity Expertise Center (CEC‐OS) of Centre Aval de Traitement des Donnees SMOS (CATDS). of CATDS at IFREMER, Plouzane, France (http://www.catds.fr/Products, see documentation: http://www.catds.fr/Products/Available‐products‐from‐CEC‐OS/L3‐Debiased‐Locean‐v2); the Aquarius/SAC‐D and SMAP data was produced by Remote Sensing Systems and distributed by PODAAC (https://podaac.jpl.nasa.gov/dataset/AQUARIUS_L3_SSS_SMI_7DAY_V4; https://podaac.jpl.nasa.gov/dataset/SMAP_RSS_L3_SSS_SMI_8DAY‐RUNNINGMEAN_V2); the SLA product is processed and distributed by CMEMS (http://marine.copernicus.eu); the global atlas of eddies is produced by AVISO (https://www.aviso.altimetry.fr/en/data/products/value‐added‐products/global‐mesoscale‐eddy‐trajectory‐product.html); the GPCP precipitation data set (http://eagle1.umd.edu/GPCP_CDR/Monthly_Data) is described in the project technical report (http://eagle1.umd.edu/GPCP_ICDR/GPCPmonthlyV2.3.pdf); Woods Hole Oceanographic Institution OAFlux evaporation data set (ftp://ftp.whoi.edu/pub/science/oaflux/data_v3); UCAR high‐resolution terrain data set (High res terrain data set https://rda.ucar.edu/datasets/ds759.2/#!description); Chelton et al. (1998) Global Atlas of the First‐Baroclinic Rossby Radius of Deformation and Gravity‐Wave Phase Speed (http://www‐po.coas.oregonstate.edu/research/po/research/rossby_radius/).
    Description: 2019-09-28
    Keywords: Eddies ; Mesoscale ; Salinity ; Pacific
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  • 14
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    Impact of circulation on export production, dissolved organic matter, and dissolved oxygen in the ocean : results from Phase II of the Ocean Carbon-cycle Model Intercomparison Project (OCMIP-2) (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 21 (2007): GB3007, doi:10.1029/2006GB002857.
    Description: Results are presented of export production, dissolved organic matter (DOM) and dissolved oxygen simulated by 12 global ocean models participating in the second phase of the Ocean Carbon-cycle Model Intercomparison Project. A common, simple biogeochemical model is utilized in different coarse-resolution ocean circulation models. The model mean (±1σ) downward flux of organic matter across 75 m depth is 17 ± 6 Pg C yr−1. Model means of globally averaged particle export, the fraction of total export in dissolved form, surface semilabile dissolved organic carbon (DOC), and seasonal net outgassing (SNO) of oxygen are in good agreement with observation-based estimates, but particle export and surface DOC are too high in the tropics. There is a high sensitivity of the results to circulation, as evidenced by (1) the correlation of surface DOC and export with circulation metrics, including chlorofluorocarbon inventory and deep-ocean radiocarbon, (2) very large intermodel differences in Southern Ocean export, and (3) greater export production, fraction of export as DOM, and SNO in models with explicit mixed layer physics. However, deep-ocean oxygen, which varies widely among the models, is poorly correlated with other model indices. Cross-model means of several biogeochemical metrics show better agreement with observation-based estimates when restricted to those models that best simulate deep-ocean radiocarbon. Overall, the results emphasize the importance of physical processes in marine biogeochemical modeling and suggest that the development of circulation models can be accelerated by evaluating them with marine biogeochemical metrics.
    Description: R. G. N. and J. L. S. acknowledge the support of NASA grants NAG5-6451 and NAG5-6591, respectively, as part of the JGOFS Synthesis and Modeling Program. G. K. P. and F. J. acknowledge support by the Swiss National Science Foundation. European contributions were supported by the EU GOSAC Project (ENV4-CT97- 0495).
    Keywords: Export production ; Numerical modeling ; Ocean circulation
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  • 15
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    Deposition and recirculation of tritium in the North Pacific Ocean (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. 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 109 (2004): C06009, doi:10.1029/2003JC002150.
    Description: Tritium data, primarily from the GEOSECS and WOCE cruises of the 1970s and 1990s, are used to estimate the time-evolving 3H inventory of the North Pacific basin. In the years between the two surveys, there have been changes both laterally and vertically in the distribution of 3H in the North Pacific that reflect the mean circulation and exchanges of the basin. We develop a simple multibox model of the shallow circulation of the North Pacific to explore the long-term redistribution and changes in 3H inventories within the basin. To do this, we derived a new estimate of the delivery of bomb 3H to the North Pacific by precipitation for the period 1960–1997 and include other minor sources such as rivers. Vapor deposition dominates over direct precipitation of tritium to the basin, while inputs from continental runoff and the inflow from the south contribute over an order of magnitude less. The model predicted tritium budget of 25.1 ± 3.3 kg compares well with the estimated WOCE inventory of 23.4 ± 2.0 kg. We explore in detail the sensitivity of the budget calculations to model circulation and assumptions, as well as uncertainties in observations. We find that the ratio of tritium in vapor to that in precipitation is the most sensitive variable in the model budget, and the basin tritium inventory is consistent with a vapor-to-precipitation ratio of 0.67 (range 0.60–0.74), predictably somewhat less than the isotopic equilibrium value of 0.89. An inverse calculation shows that despite uncertainties in the tritium source function, the data also help constrain aspects of the basin circulation, including the Indonesian Throughflow.
    Description: Support for this work was provided by UK Natural Environment Research Council grant GR3/12800, and by the U.S. National Science Foundation grant OCE26080500.
    Keywords: Transient tracer ; Ocean circulation ; Ventilation
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  • 16
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    Glacial water mass geometry and the distribution of δ13C of ΣCO2 in the western Atlantic Ocean (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 20 (2005): PA1017, doi:10.1029/2004PA001021.
    Description: Oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa Cibicidoides and Planulina from 25 new piston cores, gravity cores, and multicores from the Brazil margin. The cores span water depths from about 400 to 3000 m and intersect the major water masses in this region. These new data fill a critical gap in the South Atlantic Ocean and provide the motivation for updating the classic glacial western Atlantic δ13C transect of Duplessy et al. (1988). The distribution of δ13C of ΣCO2 requires the presence of three distinct water masses in the glacial Atlantic Ocean: a shallow (∼1000 m), southern source water mass with an end-member δ13C value of about 0.3–0.5‰ VPDB, a middepth (∼1500 m), northern source water mass with an end-member value of about 1.5‰, and a deep (〉2000 m), southern source water with an end-member value of less than −0.2‰, and perhaps as low as the −0.9‰ values observed in the South Atlantic sector of the Southern Ocean (Ninnemann and Charles, 2002). The origins of the water masses are supported by the meridional gradients in benthic foraminiferal δ18O. A revised glacial section of deep water δ13C documents the positions and gradients among these end-member intermediate and deep water masses. The large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation.
    Description: This research was supported by the National Science Foundation by grants OCE-9986748 and OCE-9905605.
    Keywords: Ice age ; Ocean circulation ; Ocean chemistry
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  • 17
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    Circulation of the North Atlantic Ocean from altimetry and the Gravity Recovery and Climate Experiment geoid (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 111 (2006): C03005, doi:10.1029/2005JC003128.
    Description: We discuss the ocean circulation derived from the temporally averaged sea surface height, which is referenced to the recently released geoid from the Gravity Recovery and Climate Experiment (GRACE) mission (GRACE Gravity Model 02 (GGM02)). The creation of a precise, independent geoid allows for the calculation of the reference gravitational potential undulation surface, which is associated with the resting ocean surface height. This reference height is then removed from the temporally averaged sea surface height, leaving the dynamic ocean topography. At its most basic level the dynamic ocean topography can be related to the ocean's surface circulation through geostrophy. This has previously been impracticable because of large uncertainties in previous estimates of the Earth's geoid. Prior geoids included the temporally averaged sea surface from altimeters as a proxy for the geoid and therefore were unsuitable for calculations of the ocean's circulation. Geoid undulations are calculated from the GRACE geoid and compared to those from the NASA Goddard Space Flight Center and National Imagery and Mapping Agency Joint Earth Geopotential Model (EGM96) geoid. Error estimates are made to assess the accuracy of the new geoid. The deep ocean pressure field is also estimated by combining the calculated dynamic ocean topography with hydrography. Finally, the derived circulation is compared to independent observations of the circulation from sea surface drifters and subsurface floats. It is shown that the GGM02 geoid is significantly more accurate for use in estimating the ocean's circulation.
    Description: This work was supported by grants NNG04GE95G from the National Aeronautics and Space Administration and OCE 01-37122 from the National Science Foundation and the Young Investigator Program award N00014-03-1-0545 from the Office of Naval Research.
    Keywords: Ocean circulation ; Geoid ; Altimetry index
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  • 18
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    Correction to “Decadal analysis of hydrography and in situ nutrient budgets in the western and eastern North Atlantic subtropical gyre” (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. 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 113 (2008): C03005, doi:10.1029/2008JC004762.
    Keywords: Nutrient transport ; Eddies ; Altimetry
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  • 19
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    Physical mechanisms for the offshore detachment of the Changjiang Diluted Water in the East China Sea (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2008. 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 113 (2008): C02002, doi:10.1029/2006JC003994.
    Description: Physical mechanisms for the summertime offshore detachment of the Changjiang Diluted Water (CDW) into the East China Sea are examined using the high-resolution, unstructured-grid, Finite-Volume Coastal Ocean Model (FVCOM). The model results suggest that isolated low salinity water lens detected west of Cheju Island can be formed by (1) a large-scale adjustment of the flow field to the Changjiang discharge and (2) the detachment of anticyclonic eddies as a result of baroclinic instability of the CDW front. Adding the Changjiang discharge intensifies the clockwise vorticity of the subsurface current (originating from the Taiwan Warm Current) flowing along the 50-m isobath and thus drives the low-salinity water in the northern coastal area of the Changjiang mouth offshore over a submerged plateau that extends toward Cheju Island. Given a model horizontal resolution of less than 1.0 km, the CDW front becomes baroclinically unstable and forms a chain of anticyclonic and cyclonic eddies. The offshore detachment of anticyclonic eddies can carry the CDW offshore. This process is enhanced under northward winds as a result of the spatially nonuniform interaction of wind-induced Ekman flow and eddy-generated frontal density currents. Characteristics of the model-predicted eddy field are consistent with previous theoretical studies of baroclinic instability of buoyancy-driven coastal density currents and existing satellite imagery. The plume stability is controlled by the horizontal Ekman number. In the Changjiang, this number is much smaller than the criterion suggested by a theoretical analysis.
    Description: The development of FVCOM is supported by the Massachusetts Fisheries Institute through NOAA grants DOC/ NOAA/NA04NMF4720332 and DOC/NOAA/NA05NMF4721131 and also the U.S. GLOBEC Northwest Atlantic/Georges Bank program through NSF grants OCE-0234545 and OCE-0227679, NOAA grant NA160P2323 and ONR subcontract grant from Woods Hole Oceanographic Institution. P. Ding is supported by the Chinese National Key Basic Research Project grant 2002CB412403. X. Mao is supported by the National Natural Science Foundation of China (NSFC) grant 40576079.
    Keywords: Unstructured grid model ; Eddies ; River plume baroclinic instability
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  • 20
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    Modeling transport and fate of riverine dissolved organic carbon in the Arctic Ocean (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 23 (2009): GB4006, doi:10.1029/2008GB003396.
    Description: The spatial distribution and fate of riverine dissolved organic carbon (DOC) in the Arctic may be significant for the regional carbon cycle but are difficult to fully characterize using the sparse observations alone. Numerical models of the circulation and biogeochemical cycles of the region can help to interpret and extrapolate the data and may ultimately be applied in global change sensitivity studies. Here we develop and explore a regional, three-dimensional model of the Arctic Ocean in which, for the first time, we explicitly represent the sources of riverine DOC with seasonal discharge based on climatological field estimates. Through a suite of numerical experiments, we explore the distribution of DOC-like tracers with realistic riverine sources and a simple linear decay to represent remineralization through microbial degradation. The model reproduces the slope of the DOC-salinity relationship observed in the eastern and western Arctic basins when the DOC tracer lifetime is about 10 years, consistent with published inferences from field data. The new empirical parameterization of riverine DOC and the regional circulation and biogeochemical model provide new tools for application in both regional and global change studies.
    Description: I.M.M. and M.J.F. are grateful to National Science Foundation for financial support.
    Keywords: Arctic Ocean ; Ocean circulation ; Biogeochemical processes
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  • 21
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    Decadal analysis of hydrography and in situ nutrient budgets in the western and eastern North Atlantic subtropical gyre (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2007. 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 112 (2007): C07025, doi:10.1029/2006JC003788.
    Description: The current debate about the mechanisms and magnitude of new nutrient input to the euphotic zone in subtropical gyres calls for studies which consider large and mesoscale perspectives by combining in situ time series and remote observations. We carried out a first of its kind comparative analysis of hydrography and sea level anomaly (SLA) at the oligotrophic time series stations BATS (Bermuda Atlantic Time Series Study) and ESTOC (European Station for Time Series, Canary Islands) using concomitant 10-yr in situ and satellite altimetry data. The stations are located at about the same latitude in the western and eastern boundaries of the subtropical North Atlantic gyre, respectively, and provide the opportunity to study differences that may exist between both regions. Observed SLA was 0.25 m at BATS, compared with 0.12 m at ESTOC, a consequence of the higher eddy kinetic energy in the western compared with the eastern subtropical gyre. We quantified a detailed in situ nutrient budget for both time series stations; ESTOC received about 75% of the nutrients available for new production at BATS (in average 0.28 mol N m−2 yr−1 compared with 0.38 mol N m−2 yr−1, respectively), but the difference was not significant. However, significant differences in input mechanisms existed between both stations; eddy pumping constituted the main new nutrient source BATS, whereas wintertime convection was the main nutrient supply mechanism at ESTOC. In addition, the nutricline was significantly shallower at ESTOC compared with BATS, partly compensating for shallower mixed-layer depths and SLA variability at the western station. We found considerable interannual variability in both eddy pumping and wintertime convection which may be related to NAO-induced changes in the pattern of the subtropical gyre.
    Description: This work was supported by a NASA-EOS grant to Susanne Neuer.
    Keywords: Nutrient transport ; Eddies ; Altimetry
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