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Sabine Mecking

Principal Oceanographer

Affiliate Assistant Professor, Oceanography

Email

smecking@apl.washington.edu

Phone

206-221-6570

Research Interests

Large-Scale Ocean Circulation, Climate Variability, Tracers, Biogeochemical Cycling

Biosketch

Dr. Mecking's research interests are in interdisciplinary oceanography involving large-scale ocean circulation, ocean mixing, tracer ages, biogeochemical cycling, and thermocline ventilation. One particular focus is how these processes are affected by decadal-scale climate variability and how they relate to the uptake and storage of carbon in the ocean. Her work involves participation in hydrographic cruises, data analysis, and combining data with general circulation models through collaboration with modelers. Dr. Mecking joined APL-UW in 2006.

Education

Vordiplom Oceanography, Universitat Hamburg, Germany, 1993

M.S. Oceanography, University of Washington, 1997

Ph.D. Oceanography, University of Washington, 2001

Projects

Modeling CFC and SF6 Mixed Layer Boundary Conditions

Chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF6) are tracers that enter the ocean surface mixed layer through air–sea gas exchange and are then transported into the ocean interior. Because of their long time-scale evolution, these tracers are used to estimate ocean interior ventilation time scales (ages) as well as anthropogenic carbon uptake by the ocean.

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28 Sep 2012

Chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF6) are man-made, transient tracers that enter the ocean surface mixed layer through air–sea gas exchange and that then are transported into the ocean interior as part of the general ocean circulation. Because of their conservative and time-evolving nature, these tracers are widely used to estimate ocean interior ventilation time scales (ages) as well as anthropogenic carbon uptake by the ocean.

Through a variety of model test cases, we quantify the roles of air–sea gas exchange, mixed layer warming/cooling, and entrainment in disrupting the air–sea equilibrium of the tracer concentrations. The model results aid the interpretation of data from global surveys (e.g., WOCE and CLIVAR/CO2 Repeat Hydrography) and observational programs.

Atlantic Ocean: Transport and Divergence of Carbon, Oxygen, and Nutrients

Estimates of the transport and divergence of carbon, oxygen, and nutrients in the Atlantic Ocean are based on two approaches: a multi-box inverse model based on WOCE/JGOFS data, and tracer data sets from the same period.

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29 Nov 2011

This project seeks to provide data-based estimates of the transport and divergence of carbon, oxygen, and nutrients in the Atlantic Ocean based on two approaches: 1) using a multi-box inverse model based on the long line data collected during the WOCE/JGOFS period, and 2) using tracer age data sets from the same time period. This first part is done in collaboration with Alison Macdonald at WHOI. The latter part includes a GCM-based analysis of possible tracer age biases due to mixing, which is performed in collaboration with LuAnne Thompson at UW. The goal of the project is to evaluate the location and magnitude of oceanic uptake/outgassing of CO2 as well as the size of the biological carbon pump (see poster at 2010 Ocean Sciences Meeting). Collaborators: Alison Macdonald (WHOI), LuAnne Thompson (UW). Funding: NSF

Mixed Layer Boundary Conditions of Chlorofluorocarbons in the North Pacific

A series of model experiments with the Hallberg Isopycnal Model (HIM) are used to investigate the mixed layer boundary conditions of CFCs in the North Pacific Ocean and the the implications of possible winter-time undersaturations on the interpretation of CFC-derived age distributions and anthropogenic carbon estimates in the ocean interior.

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28 Nov 2011

The purpose of this research is to perform a series of model experiments with the Hallberg Isopycnal Model (HIM) to investigate 1) mixed layer boundary conditions of CFCs in the North Pacific Ocean and 2) the implications of possible winter-time undersaturations on the interpretation of CFC-derived age distributions and anthropogenic carbon estimates in the ocean interior. The results from the modeling study will be used to aid the interpretation of the U.S. CLIVAR/CO2 Repeat Hydrography data in the North Pacific which consist of the meridional P16N line and zonal P2 line conducted along 152W in 2006 and along 30N in 2004, respectively. The project is performed in collaboration with LuAnne Thompson and Mark Warner at UW. Funding: NOAA

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Repeat Hydrography

The U.S. CLIVAR/CO2 Repeat Hydrography Program began in 2003 with the goal of repeating, on decadal time scales, several of the long line WOCE sections conducted in the 1990s. Data are used to investigate climate variability base don oxygen measurements and carbon distributions.

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27 Nov 2011

The U.S. CLIVAR/CO2 Repeat Hydrography Program began in 2003 with the goal of repeating, on decadal time scales, several of the long line WOCE sections conducted in the 1990s in order to determine (among other things) changes in the storage of anthropogenic carbon, heat and freshwater in the ocean, as well as changes in water mass transports and ventilation rates. After participation in some of the U.S. CLIVAR/CO2 Repeat Hydrography cruises (P16N and I9N as co-chief scientist), data from these sections have been used for investigation of climate variability in the North Pacific Ocean and elsewhere based on oxygen measurements and of decadal changes in Pacific carbon distributions (in collaboration with R. Feely and C. Sabine at NOAA/PMEL and C. Langdon at RSMAS/UM).

In a smaller effort, in collaboration with Rolf Sonnerup at JISAO/UW, funding was sought to collect sulfur hexafluoride (SF6) and CFC measurements on an UW student cruise that took place in September 2008. This cruise repeated part of the CLIVAR/CO2 and WOCE P16N cruise track along 152W which was also occupied during an earlier student cruise (1997). The SF6 data from this section provide the first high resolution SF6 section in the North Pacific Ocean and allow, combined with the CFCs, to better determine the mean ages and the anthropogenic CO2 in the thermocline as well as changes therein. In addition, distributions of SF6 in the North Pacific are being simulated with the off-line code of HIM. Funding: NSF, NOAA

Tracer Age-based Estimates of Carbon Export and Ventilation Variability in the Indian Ocean

This new project investigates the strength of the biological carbon pump in the Indian Ocean and changes in ventilation time scales at the southern entry point to the Indian Ocean

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26 Nov 2011

This is a new project that investigates the strength of the biological carbon pump in the Indian Ocean as well changes in ventilation time scales at the southern entry point to the Indian Ocean along 32S. Collaborators: LuAnne Thompson (UW), Alison Macdonald (WHOI). Funding: NSF

Publications

2000-present and while at APL-UW

Evaluation of oceanic transport parameters using transient tracers from observations and model output

Trossman, D.S., L. Thompson, S. Mecking, M.J. Warner, F.O. Bryan, and S. Peacock, "Evaluation of oceanic transport parameters using transient tracers from observations and model output," Ocean Model., 74, 1-21, doi:10.1016/j.ocemod.2013.11.001, 2014.

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1 Feb 2014

A method is presented to find the age distribution of ocean waters, the transit-time distribution (TTD), by combining an eddying global ocean model's estimate of the TTD with hydrographic observations of CFC-11, temperature, and salinity. The method uses a mixture model of an assumed form of the TTD, an inverse Gaussian (IG), and an established Bayesian statistical method. All known significant sources of uncertainty are propagated to arrive at estimates of two oceanic transport parameters associated with the IG TTD, the mean age and either the half-variance or the Peclet number. It is found that the uncertainties on mean age do not overlap zero in most locations using only CFC-11, temperature, and salinity. However, the uncertainty on the other IG parameter does not overlap zero in only a few locations. With the inclusion of another transient tracer (3He/3H), the uncertainty on this other IG parameter does not overlap zero in just a few additional locations in the deep North Atlantic Ocean. Neither a single- nor mixture-IG representation is adequate for representing the full TTD in the ocean, particularly in the Southern Ocean.

Differences between the IG parameters estimated using the model's tracers as data (BayesPOP) and those estimated using tracer observations as data (BayesObs) provide information about the sources of model biases, and give a more nuanced picture than can be found by comparing the simulated CFCs with observed CFCs. Using the differences between each of the oceanic transport parameters from BayesObs and those from BayesPOP with and without a constant Pe assumption along each of the hydrographic cross-sections considered here, it is found that the model's eddy mixing biases often lead to larger model errors than the model's mean advection time biases. It is also found that mean advection time biases in the model can be statistically significant at the 95% level where mode water is found in the Southern Ocean.

Mixed layer saturations of CFC-11, CFC-12, and SF6 in a global isopycnal model

Shao, A.E., S. Mecking, L. Thompson, and R.E. Sonnerup, "Mixed layer saturations of CFC-11, CFC-12, and SF6 in a global isopycnal model," J. Geophys. Res., 118, 4978-4988, doi:10.1002/jgrc.20370, 2013.

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4 Oct 2013

The use of CFC-11, CFC-12, and SF6 to quantify oceanic ventilation rates, interior water age, and formation rates requires knowledge of the saturation levels at the sea surface. While their atmospheric histories are relatively well known, physical processes in the mixed layer in conjunction with limited air-sea gas exchange can cause surface concentrations to be in disequilibrium with the atmosphere. We use an offline tracer advection-diffusion code that evolves tracers using along-isopycnal and cross-isopycnal mass fluxes from a global, climatological run of the Hallberg Isopycnal Model to reconstruct the saturation level of all three tracers over the entirety of their atmospheric histories. Disequilibria on a global scale occur in regions associated with deep winter mixed layers and are found throughout the time period of the release of these chemicals into the atmosphere. Sensitivity studies using targeted model simulations, focusing on the North Pacific, show that seasonal cycles in temperature and salinity that affect gas solubility as well as entrainment of water containing low concentration of tracers during mixed layer deepening are the dominant causes of undersaturation. When using the transit time distribution method, our results show that these undersaturations introduce a significant bias toward older ages for North Pacific Central Mode Water but do not significantly affect estimates of anthropogenic carbon inventory.

Transit time distributions and oxygen utilization rates in the Northeast Pacific Ocean from chlorofluorocarbons and sulfur hexafluoride

Sonnerup, R.E., S. Mecking, and J.L. Bullister, "Transit time distributions and oxygen utilization rates in the Northeast Pacific Ocean from chlorofluorocarbons and sulfur hexafluoride," Deep-Sea Res. I, 72, 61-71, doi:10.1016/j.dsr.2012.10.013, 2013.

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1 Feb 2013

Depth profiles of dissolved chlorofluorocarbon-11 (CFC-11) and sulfur hexafluoride (SF6) were measured during a September 2008 cruise in the Northeast Pacific Ocean. For each water sample, the two tracers were used in concert to estimate likely mean ages and widths of parameterized 1-D transit time distributions (TTDs). In shallow waters (<250 m), the TTDs' mean ages were relatively loosely constrained due to the slow decrease of atmospheric CFC-11 since 1994. In the main thermocline (25.0–26.6 σθ, ~300–550 m), the CFC-11/SF6 tracer pair constrained TTDs' mean ages to within ±10%. Deeper than 26.8 σθ (~600 m), SF6 levels in 2008 were too low for the CFC-11/SF6 tracer pair to constrain the TTDs' mean ages. Within the main thermocline of the subtropical North Pacific Ocean (20°–37°N along 152°W), the TTDs'9 mean ages were used to estimate Oxygen Utilization Rates (OURs) of ~11 μmol kg-1 yr-1 on 25.0–25.5 σθ (~160 m), attenuating to very low rates (0.12 μmol kg-1 yr-1) by 26.8–27.0 σθ (~600 m). Depth integration of the in-situ OURs implied an average carbon remineralization rate of 1.7±0.3 mol C m-2 yr-1 in this region and depth range, somewhat lower than other independent estimates. Along the 152°W section, depth integrating the apparent OURs implied carbon remineralization rates of 2.5–3.5 mol C m-2 yr-1 from 20°N to 30°N, 3.5–4.0 mol C m-2 yr-1 from 30°N to 40°N, and 2–2.7 mol C m-2 yr-1 north of 45°N.

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On the formation, ventilation, and erosion of mode waters in the North Atlantic and Southern oceans

Trossman, D.S., L. Thompson, S. Mecking, and M.J. Warner, "On the formation, ventilation, and erosion of mode waters in the North Atlantic and Southern oceans," J. Geophys. Res., 117, doi:10.1029/2012JC008090, 2012.

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21 Sep 2012

The mean residence times, subduction rates, and formation rates of Subtropical Mode Water (STMW) and Subpolar Mode Water (SPMW) in the North Atlantic and Subantarctic Mode Water (SAMW) in the Southern Ocean are estimated by combining a model and observations of chlorofluorocarbon-11 (CFC-11) via Bayesian Model Averaging (BMA), a statistical technique that weights model estimates according to how close they agree with observations. Subduction rates are estimated in two different ways to investigate the non-advective contribution to thermocline ventilation, which in turn are compared to formation rate estimates. One subduction rate estimate is based on entrainment/detrainment velocities and the other subduction rate estimate allows ventilation to be both an advective and diffusive process instead of a purely advective one by using transit-time distributions (TTDs). It is found that the subduction of all three mode waters is mostly an advective process, but up to about one-third of STMW subduction likely owes to non-advective processes. Also, while the formation of STMW is mostly due to subduction, the formation of SPMW is mostly due to other processes. About half of the formation of SAMW is due to subduction and half is due to other processes. A combination of air-sea flux, acting on relatively short timescales, and turbulent mixing, acting on a wide range of timescales, is likely the dominant SPMW erosion mechanism. Air-sea flux is likely responsible for most STMW erosion, and turbulent mixing is likely responsible for most SAMW erosion.

Direct observations of basin-wide acidification of the North Pacific Ocean

Byrne, R.H., S. Mecking, R.A. Feely, and X. Liu, "Direct observations of basin-wide acidification of the North Pacific Ocean," Geophys. Res. Lett., 37, doi:10.1029/2009GL040999, 2010.

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20 Jan 2010

Global ocean acidification is a prominent, inexorable change associated with rising levels of atmospheric CO2. Here we present the first basin-wide direct observations of recently declining pH, along with estimates of anthropogenic and non-anthropogenic contributions to that signal. Along 152 deg W in the North Pacific Ocean (22–56 deg N), pH changes between 1991 and 2006 were essentially zero below about 800 m depth. However, in the upper 500 m, significant pH changes, as large as –0.06, were observed. Anthropogenic and non-anthropogenic contributions over the upper 800 m are estimated to be of similar magnitude. In the surface mixed layer (depths to ~100 m), the extent of pH change is consistent with that expected under conditions of seawater/atmosphere equilibration, with an average rate of change of –0.0017/yr. Future mixed layer changes can be expected to closely mirror changes in atmospheric CO2, with surface seawater pH continuing to fall as atmospheric CO2 rises.

The WOCE-era 3-D Pacific Ocean circulation and heat budget

Macdonald, A.M., S. Mecking, P.E. Robbins, J.M. Toole, G.C. Johnson, L. Talley, M. Cook, and S.E. Wijffels, "The WOCE-era 3-D Pacific Ocean circulation and heat budget," Prog. Oceanogr., 281-325, doi:10.1016/j.pocean.2009.08.002, 2009.

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1 Sep 2009

To address questions concerning the intensity and spatial structure of the three-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.

Climate variability in the North Pacific thermocline diagnosed from oxygen measurements: An update based on the U.S. CLIVAR/CO2 Repeat Hydrography cruises

Mecking, S., C. Langdon, R.A. Feely, C.L. Sabine, C.A. Deutsch, and D. Min, "Climate variability in the North Pacific thermocline diagnosed from oxygen measurements: An update based on the U.S. CLIVAR/CO2 Repeat Hydrography cruises," Global Biogeochem. Cycles, 22, doi:10.1029/2007GB003101, 2008.

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13 Aug 2008

New observations of oxygen variability in the North Pacific Ocean are reported on the basis of comparison of the U.S. Climate Variability and Predictability and Carbon (CLIVAR/CO2) Repeat Hydrography sections conducted along 30°N (2004) and 152–W (2006) with the earlier World Ocean Circulation Experiment (WOCE) data and other cruises along these sections. The largest changes in apparent oxygen utilization (AOU) continue to occur, as found in earlier North Pacific repeat section analyses, within the thermocline on σΘ = 26.6 kg m-3, which is the densest isopycnal to outcrop in the open North Pacific in climatological data. In the northeastern North Pacific along 152°W, where a total of five cruises (1980, 1984, 1991, 1997, and 2006) spanning a period of 26 years are available, the AOU changes correspond to an overall increase in AOU on σΘ = 26.6 kg m-3 from the 1980s/early 1990s to 2006. However, from 1997 to 2006 a decrease in AOU is observed within the boundary region between the subtropical and subpolar gyres at 40–45°N. Along the center axis of the subtropical gyre at 30°N, where two cruises are available (1994 and 2004), AOU has also substantially increased on σΘ = 26.6 kg m-3 from 1994 to 2004 in the eastern part of the section. The repeat section data along 152°W and 30°N are consistent with a pattern of decadal-scale ventilation anomalies that originate in the northwestern Pacific, possibly through variability (including cessation) of the σΘ = 26.6 kg m-3 outcrop, travel eastward along the subtropical-subpolar gyre boundary, and enter the northern portion of the subtropical gyre along the way. For the 152°W AOU data within the gyre boundary region (40–45°N), good agreement exists with the close-by time series data from Ocean Station P (50°N, 145°W) where a bidecadal cycle in AOU has been observed. In contrast, a sensible correlation with the Pacific Decadal Oscillation could not be found.

Decadal changes in Pacific carbon

Sabine, C.L., R.A. Feely, F.J. Millero, A.G. Dickson, C. Langdon, S. Mecking, and D. Greeley, "Decadal changes in Pacific carbon," J. Geophys. Res., 113, doi:10.1029/2007JC004577, 2008.

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18 Jul 2008

This paper uses the extended multiple linear regression (eMLR) technique to investigate changes over the last decade in dissolved inorganic carbon (DIC) inventories on a meridional line (P16 along 152°W) up the central Pacific and on a zonal line (P02 along 30°N) across the North Pacific. Maximum changes in the total DIC concentrations along P02 are 15–20 µmol kg-1 over 10 years, somewhat higher than the ~1 µmol kg-1 a-1 increase in DIC expected based on the rate of atmospheric CO2 increase. The maximum changes of 15–20 µmol kg-1 along the P16 line over the 14/15-year time frame fit with the expected magnitude of the anthropogenic signal, but there is a deeper than expected penetration of the signal in the North Pacific compared to the South Pacific. The effect of varying circulation on the total DIC change, based on decadal alterations of the apparent oxygen utilization rate, is estimated to be greater than 10 µmol kg-1 in the North Pacific, accounting for as much as 80% of the total DIC change in that region. The average anthropogenic CO2 inventory increase along 30µN between 1994 and 2004 was 0.43 mol m-2 a-1, with much higher inventories in the western Pacific. Along P16, the average Northern Hemisphere increase was 0.25 mol m-2 a-1 between 1991/1992 and 2006 compared to an average Southern Hemisphere anthropogenic CO2 inventory increase between 1991 and 2005 of 0.41 mol m-2 a-1.

Recent bottom water warming in the Pacific Ocean

Johnson, G.C., S. Mecking, B.M. Sloyan, and S.E. Wijffels, "Recent bottom water warming in the Pacific Ocean," J. Clim., 20, 5365-5375, 2007.

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1 Nov 2007

Decadal changes of abyssal temperature in the Pacific Ocean are analyzed using high-quality, full-depth hydrographic sections, each occupied at least twice between 1984 and 2006. The deep warming found over this time period agrees with previous analyses. The analysis presented here suggests it may have occurred after 1991, at least in the North Pacific. Mean temperature changes for the three zonal and three meridional hydrographic sections analyzed here exhibit abyssal warming often significantly different from zero at 95% confidence limits for this time period. Warming rates are generally larger to the south, and smaller to the north. This pattern is consistent with changes being attenuated with distance from the source of bottom water for the Pacific Ocean, which enters the main deep basins of this ocean southeast of New Zealand. Rough estimates of the change in ocean heat content suggest that the abyssal warming may amount to a significant fraction of upper World Ocean heat gain over the past few decades.

Circulation rate changes in the eastern subtropical North Pacific based on chlorofluorocarbon ages

Sonnerup, R.E., J.L. Bullister, and S. Mecking, "Circulation rate changes in the eastern subtropical North Pacific based on chlorofluorocarbon ages," Geophys. Res. Lett., 34, doi:10.1029/2006GL028813, 2007.

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25 Apr 2007

A space-time regression analysis of chlorofluorocarbon (CFC) data from the eastern North Pacific Ocean's subtropical thermocline (25.6–26.6 ) is used to extract age and velocity changes from a collection of 1980s and 1990s hydrographic sections. Results indicate substantial increases of CFC ages, from 0.2 yr yr-1 on 25.8 σ θ increasing with depth up to 0.4 yr yr-1 on 26.6 σ θ, and increases of meridional age gradients, implying a circulation slowdown. Using the regression-derived spatial and temporal derivatives, an isopycnal balance of advection and diffusion, including the effects of mixing on CFC ages, was applied to estimate changes in flow. Southward velocities at 20°N, 145°W generally decreased by ~ 0.03 ± 0.02 cm s-1 yr-1 on isopycnals 25.6 to 26.4 σ θ during the 1980s and 1990s, consistent with overturning changes from historical hydrographic data and with concurrent increases in AOU. The deeper (26.6 σ θ) age increase was consistent with mixing effects.

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