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Peter Huybers
,
Geoffrey Gebbie
, and
Olivier Marchal

temperature gradients and thus constrain density gradients. Here, δ 13 C was considered as a conservative tracer—omitting the effect of organic matter remineralization on δ 13 C (oxidation of organic matter, which has a relatively low 13 C/ 12 C ratio, tends to reduce the δ 13 C of ambient dissolved inorganic carbon). The study of LW95 comprised two separate components. First, they combined their model with temperature, salinity, and dissolved phosphorous data to produce a modern reference

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Burkard Baschek
and
David M. Farmer

1. Introduction Air bubbles are injected into the surface layer of the ocean by breaking waves. Vertical currents associated with wave motion or Langmuir cells can carry the bubbles to depths of more than twice the wave height, or 10–15 m ( Thorpe and Stubbs 1979 ; Thorpe 1982 ; Farmer and Li 1995 ). A similar, but more extreme, phenomenon has been observed in tidal fronts, where gas bubbles can reach 160-m depth ( Farmer et al. 2002 ; Baschek et al. 2006 ). Gas bubbles are active tracers

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James Kent
,
Christiane Jablonowski
,
Jared P. Whitehead
, and
Richard B. Rood

1. Introduction Accurate representation of tracer transport is important to weather and climate models. In climate simulations with the Met Office’s Unified Model there are typically 25 individual tracers ( Collins et al. 2008 ), whereas in the chemistry version of the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM), over 100 tracers are transported ( Lamarque et al. 2008 ). The tracer transport scheme is considered part of the dynamical core—the fluid dynamics

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R. M. Holmes
,
Casimir de Lavergne
, and
Trevor J. McDougall

1. Introduction The transport of tracers within the ocean plays an important role not only in ocean dynamics, thermodynamics, and biogeochemistry, but also as a method with which to observe the ocean and infer circulation properties. Because, by its nature, tracer transport integrates over both spatial and temporal scales, it allows us to measure the large-scale, integral impact of a range of smaller-scale processes that are difficult to observe directly. However, in order to correctly

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Fong Ngan
and
Ariel F. Stein

1. Introduction NOAA’s Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model is one of the most commonly used tools to simulate the transport and dispersion of pollutants for a variety of atmospheric applications. An objective performance evaluation against independent measurement datasets, such as tracer experiments, is fundamental to assess the model reliability to simulate transport and dispersion features under different meteorological conditions. For this reason, NOAA

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Josef I. Bisits
,
Geoffrey J. Stanley
, and
Jan D. Zika

1. Introduction The ocean’s transport and uptake of tracers, such as heat and carbon, is strongly dependent on mixing processes ( Groeskamp et al. 2017 ) and strongly constrained by the structure of isopycnal surfaces (surfaces of constant density), which descend from their outcrop at the sea surface down into the ocean interior. Isopycnal mixing has been shown to influence the stability of the climate in the long term ( Sijp et al. 2006 ) and is linked to large-scale climate variability

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Philippe Lucas-Picher
,
Daniel Caya
,
Sébastien Biner
, and
René Laprise

reported in a more or less qualitative way so far: the limited-area domain is “small” or “large,” the atmospheric circulation is “stronger” in winter than in summer, midlatitude domains show “less” IV than circumpolar ones, etc. The present work introduces, for the first time, a method to quantify the flushing regime as an indicator of the forcing of the LBC on the RCM for a given configuration. This method uses aging tracers, which measure the time that air parcels spend within the limited-area domain

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Xiaozhou Ruan
and
Raffaele Ferrari

location in the ocean, while tracer release experiments (TREs) best quantify the net mixing experienced by the tracer cloud over a large patch of ocean. Diapycnal mixing rates are often reported as a diapycnal diffusivity κ , which quantifies the local rate at which turbulence spreads a tracer across density surfaces. Microstructure profilers record in situ high-frequency temperature and velocity variance which are then converted into a diapycnal diffusivity under various assumptions about the

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Henri F. Drake
,
Xiaozhou Ruan
, and
Raffaele Ferrari

1. Introduction The lower limb of the ocean’s meridional overturning circulation traces the diabatic life cycle of abyssal bottom waters ( Talley 2013 ), which store vast quantities of climatically active tracers like heat and carbon. Bottom waters are formed at the surface of the Southern Ocean by atmospheric cooling and brine rejection and are consumed in the abyssal ocean by buoyancy-flux convergence due to small-scale mixing and geothermal heating ( Abernathey et al. 2016 ; de

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Marta Abalos
,
William J. Randel
,
Douglas E. Kinnison
, and
Rolando R. Garcia

1. Introduction The distribution and variability of chemical compounds in the upper troposphere and lower stratosphere (UTLS) play a particularly important radiative role in the climate system (e.g., Forster and Shine 1997 ; Forster and Shine 2002 ). Because of the very different chemical composition of the troposphere and the stratosphere and the resulting strong tracer gradients in this transition region, transport processes are major drivers of variability in the UTLS composition ( Holton

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