Mecking
Sabine
Mecking
Sabine
No Thumbnail Available
Search Results
Now showing
1 - 5 of 5
-
PreprintThe WOCE–era 3–D Pacific Ocean circulation and heat budget( 2009-08-17) Macdonald, Alison M. ; Mecking, Sabine ; Toole, John M. ; Robbins, Paul E. ; Johnson, Gregory C. ; Wijffels, Susan E. ; Talley, Lynne D. ; Cook, Margaret F.To address questions concerning the intensity and spatial structure of the 3–dimensional circulation within the Pacific Ocean and the associated advective and diffusive property flux divergences, data from approximately 3000 high–quality hydrographic stations collected on 40 zonal and meridional cruises have been merged into a physically consistent model. The majority of the stations were occupied as part of the World Ocean Circulation Experiment (WOCE), which took place in the 1990s. These data are supplemented by a few pre–WOCE surveys of similar quality, and time–averaged direct–velocity and historical hydrographic measurements about the equator. An inverse box model formalism is employed to estimate the absolute along–isopycnal velocity field, the magnitude and spatial distribution of the associated diapycnal flow and the corresponding diapycnal advective and diffusive property flux divergences. The resulting large–scale WOCE Pacific circulation can be described as two shallow overturning cells at mid– to low latitudes, one in each hemisphere, and a single deep cell which brings abyssal waters from the Southern Ocean into the Pacific where they upwell across isopycnals and are returned south as deep waters. Upwelling is seen to occur throughout most of the basin with generally larger dianeutral transport and greater mixing occurring at depth. The derived pattern of ocean heat transport divergence is compared to published results based on air–sea flux estimates. The synthesis suggests a strongly east/west oriented pattern of air–sea heat flux with heat loss to the atmosphere throughout most of the western basins, and a gain of heat throughout the tropics extending poleward through the eastern basins. The calculated meridional heat transport agrees well with previous hydrographic estimates. Consistent with many of the climatologies at a variety of latitudes as well, our meridional heat transport estimates tend toward lower values in both hemispheres.
-
PreprintChanges in ocean heat, carbon content, and ventilation : a review of the first decade of GO-SHIP Global Repeat Hydrography( 2015-05-30) Talley, Lynne D. ; Feely, Richard A. ; Sloyan, Bernadette M. ; Wanninkhof, Rik ; Baringer, Molly O. ; Bullister, John L. ; Carlson, Craig A. ; Doney, Scott C. ; Fine, Rana A. ; Firing, Eric ; Gruber, Nicolas ; Hansell, Dennis A. ; Ishii, Masayoshi ; Johnson, Gregory ; Katsumata, K. ; Key, Robert M. ; Kramp, Martin ; Langdon, Chris ; Macdonald, Alison M. ; Mathis, Jeremy T. ; McDonagh, Elaine L. ; Mecking, Sabine ; Millero, Frank J. ; Mordy, Calvin W. ; Nakano, T. ; Sabine, Chris L. ; Smethie, William M. ; Swift, James H. ; Tanhua, Toste ; Thurnherr, Andreas M. ; Warner, Mark J. ; Zhang, Jia-ZhongThe ocean, a central component of Earth’s climate system, is changing. Given the global scope of these changes, highly accurate measurements of physical and biogeochemical properties need to be conducted over the full water column, spanning the ocean basins from coast to coast, and repeated every decade at a minimum, with a ship-based observing system. Since the late 1970s, when the Geochemical Ocean Sections Study (GEOSECS) conducted the first global survey of this kind, the World Ocean Circulation Experiment (WOCE) and Joint Global Ocean Flux Study (JGOFS), and now the Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP) have collected these “reference standard” data that allow quantification of ocean heat and carbon uptake, and variations in salinity, oxygen, nutrients, and acidity on basin scales. The evolving GO-SHIP measurement suite also provides new global information about dissolved organic carbon, a large bioactive reservoir of carbon.
-
ArticlePacific anthropogenic carbon between 1991 and 2017(American Geophysical Union, 2019-04-29) Carter, Brendan ; Feely, Richard A. ; Wanninkhof, Rik ; Kouketsu, Shinya ; Sonnerup, Rolf E. ; Pardo, Paula Conde ; Sabine, Christopher L. ; Johnson, Gregory C. ; Sloyan, Bernadette M. ; Murata, Akihiko ; Mecking, Sabine ; Tilbrook, Bronte ; Speer, Kevin G. ; Talley, Lynne D. ; Millero, Frank J. ; Wijffels, Susan E. ; Macdonald, Alison M. ; Gruber, Nicolas ; Bullister, John L.We estimate anthropogenic carbon (Canth) accumulation rates in the Pacific Ocean between 1991 and 2017 from 14 hydrographic sections that have been occupied two to four times over the past few decades, with most sections having been recently measured as part of the Global Ocean Ship‐based Hydrographic Investigations Program. The rate of change of Canth is estimated using a new method that combines the extended multiple linear regression method with improvements to address the challenges of analyzing multiple occupations of sections spaced irregularly in time. The Canth accumulation rate over the top 1,500 m of the Pacific increased from 8.8 (±1.1, 1σ) Pg of carbon per decade between 1995 and 2005 to 11.7 (±1.1) PgC per decade between 2005 and 2015. For the entire Pacific, about half of this decadal increase in the accumulation rate is attributable to the increase in atmospheric CO2, while in the South Pacific subtropical gyre this fraction is closer to one fifth. This suggests a substantial enhancement of the accumulation of Canth in the South Pacific by circulation variability and implies that a meaningful portion of the reinvigoration of the global CO2 sink that occurred between ~2000 and ~2010 could be driven by enhanced ocean Canth uptake and advection into this gyre. Our assessment suggests that the accuracy of Canth accumulation rate reconstructions along survey lines is limited by the accuracy of the full suite of hydrographic data and that a continuation of repeated surveys is a critical component of future carbon cycle monitoring.
-
ArticleInfluence of mixing on CFC uptake and CFC ages in the North Pacific thermocline(American Geophysical Union, 2004-07-17) Mecking, Sabine ; Warner, Mark J. ; Greene, Catherine E. ; Hautala, Susan L. ; Sonnerup, Rolf E.A diagnostic, isopycnal advection-diffusion model based on a climatological, geostrophic flow field is used to study the uptake of chlorofluorocarbons (CFCs) into the portion of the thermocline that outcrops in the open North Pacific (σ θ ≤ 26.6 kg m−3). In addition to advection, isopycnal diffusion is required to match the CFC data collected during the World Ocean Circulation Experiment (WOCE) in the early 1990s. Using reduced outcrop saturations of 80–95% for isopycnals outcropping in the northwestern North Pacific (σ θ ≥ 25.4 kg m−3), together with an isopcynal interior diffusivity of 2000 m2 s−1 and enhanced diffusion (5000 m2 s−1) in the Kuroshio Extension region, further improves the model-data agreement. Along-isopycnal diffusion is particularly important for isopycnals with shadow zones/pool regions in the western subtropical North Pacific that are isolated from direct advective ventilation. The isopycnal mixing causes an estimated increase in CFC-12 inventories on these isopycnals, compared to advection only, ranging from 10–20% (σ θ = 25.6 kg m−3) to 50–130% (σ θ = 26.6 kg m−3) over the subtropics in 1993. This contribution has important consequences for subduction rate estimates derived from CFC inventories and for the location of the subsurface CFC maxima. When tracer ages are derived from the modeled CFC distributions, time-evolving mixing biases become apparent that reflect the nonlinearities in the atmospheric CFC time histories. Comparison with model-calculated ideal ages suggests that during the time of WOCE (∼1993), ventilation ages based on CFC-12 were biased young by as much as 16–24 years for pCFC-12 ages of 25 years, underestimating ideal ages by as much as 40–50%.
-
ArticleUnabated bottom water warming and freshening in the south Pacific Ocean.(American Geophysical Union, 2019-02-20) Purkey, Sarah G. ; Johnson, Gregory C. ; Talley, Lynne D. ; Sloyan, Bernadette M. ; Wijffels, Susan E. ; Smethie, William M. ; Mecking, Sabine ; Katsumata, KatsuroAbyssal ocean warming contributed substantially to anthropogenic ocean heat uptake and global sea level rise between 1990 and 2010. In the 2010s, several hydrographic sections crossing the South Pacific Ocean were occupied for a third or fourth time since the 1990s, allowing for an assessment of the decadal variability in the local abyssal ocean properties among the 1990s, 2000s, and 2010s. These observations from three decades reveal steady to accelerated bottom water warming since the 1990s. Strong abyssal (z > 4,000 m) warming of 3.5 (±1.4) m°C/year (m°C = 10−3 °C) is observed in the Ross Sea, directly downstream from bottom water formation sites, with warming rates of 2.5 (±0.4) m°C/year to the east in the Amundsen‐Bellingshausen Basin and 1.3 (±0.2) m°C/year to the north in the Southwest Pacific Basin, all associated with a bottom‐intensified descent of the deepest isotherms. Warming is consistently found across all sections and their occupations within each basin, demonstrating that the abyssal warming is monotonic, basin‐wide, and multidecadal. In addition, bottom water freshening was strongest in the Ross Sea, with smaller amplitude in the Amundsen‐Bellingshausen Basin in the 2000s, but is discernible in portions of the Southwest Pacific Basin by the 2010s. These results indicate that bottom water freshening, stemming from strong freshening of Ross Shelf Waters, is being advected along deep isopycnals and mixed into deep basins, albeit on longer timescales than the dynamically driven, wave‐propagated warming signal. We quantify the contribution of the warming to local sea level and heat budgets.