Deep Sea Research Part II: Topical Studies in Oceanography
A 1998–1992 comparison of inorganic carbon and its transport across 24.5°N in the Atlantic
Introduction
Throughout the last decade approximately ( of carbon) have been released into the atmosphere through the burning of fossil fuels (IPCC, 2001; Battle et al., 2000). Meanwhile, the amount of carbon in the atmosphere has increased at a rate of only ). The increased partial pressure of atmospheric CO2 has caused, through air–sea exchange, the amount of carbon stored in the ocean to increase by about (IPCC, 2001; Battle et al., 2000; Schimel et al., 1996; Siegenthaler and Sarmiento, 1993). These estimates strongly suggest that the ocean and ocean circulation are significant players in the global carbon cycle and control, in part, the rate of the atmospheric increase in CO2.
Just where the oceanic uptake of anthropogenic CO2 is occurring and how circulation patterns affect the sources and sinks of carbon within the oceans are not well understood. Until recently direct oceanic observations have been sparse and numerical models, which have been extremely good at producing similar net ocean CO2 storage estimates, have failed to produce a quantitative consensus on where the uptake and storage of anthropogenic carbon are occurring (Wallace, 2001; Orr et al., 2001). This study seeks to understand better one piece of this puzzle, that is the uptake and transport of carbon within the North Atlantic. We focus on the carbon transport across 24.5°N.
Previous estimates of the carbon transport across this line of latitude have been made. The earliest, Brewer et al. (1989) was based on carbon measurements taken at just nine stations occupied in the late fall of 1988, combined with the transport results of the full hydrographic transect made in 1981 (Hall and Bryden, 1982). The increased effort to measure carbon dioxide concentrations in seawater during the World Ocean Circulation Experiment (WOCE), the Ocean–Atmosphere Carbon Exchange Studies (OACES) and the US Joint Global Ocean Flux Study (JGOFS) programs has now provided us with a far more detailed view of the ocean carbon field. Rosón et al. (2002) presented inorganic carbon and anthropogenic carbon transport estimates based on data from the summer 1992 occupation of the Atlantic 24.5°N transect. Their carbon transport estimates along with estimates from previous studies at other latitudes suggested that to the north of 24.5°N the subpolar ocean takes up carbon from the atmosphere, whereas to the south it is released to the atmosphere. We compare their data and results to those from the winter 1998 occupation of the 24.5°N transect, with particular emphasis on the carbon and anthropogenic carbon fields. Calculated meridional transport of inorganic and anthropogenic carbon allows us to provide an updated view of the uptake and storage within the Atlantic Basin.
Section snippets
The observations
In 1998, the R.V. Ronald Brown made a high density hydrographic transect across the North Atlantic at 24.5°N (Fig. 1 in black) sponsored by OACES. It was the second transect along this line of latitude to obtain measurements of carbon and carbon related species. The second leg of the cruise, which made these measurements left Las Palmas on January 23, 1998 and arrived in Charleston S.C. 1 month later on February 24. This leg included 130 CTD stations at which oxygen, nutrient and
Method
To obtain an estimate of the absolute meridional velocity field for each of the two 24.5°N transects a simple inverse box model has been used. It is based upon the same box inverse model method introduced to the physical oceanographic community by Wunsch (1978) and later described in much greater detail in Wunsch (1996). The inverse method as used here is simply a technique for estimating ocean circulation based on hydrographic observations and a set of simple physical constraints. The
Discussion
The net northward transport of C★ANTH is opposite the net flow of total carbon and suggests, as has been found by others (Holfort et al., 1998; Rosón et al., 2002; Wallace, 2001), that in spite of today's greater atmospheric carbon levels, the pre-industrial southward transport of carbon within the Atlantic was stronger than it is today.
Taking the average of the 1998 and 1992 estimates1 for the
Acknowledgements
This research was carried out in part under the auspices of the Cooperative Institute of Marine and Atmospheric Studies (CIMAS), a Joint Institute of the University of Miami and the National Oceanic and Atmospheric Administration, cooperative agreement #NA67RJ0149, and it is was funded by the Global Carbon Cycle Program of the National Oceanic and Atmospheric Administration Office of Global Programs and the Office of Oceanic and Atmospheric Research. We gratefully acknowledge the support of J.
References (51)
- et al.
Seasonal and interannual variability of oceanic carbon dioxide species at the U.S. JGOFS Bermuda Atlantic Time-series Study BATS site
Deep-Sea Research II
(1996) - et al.
A technique for objective analysis and design of oceanographic experiments applied to MODE-73
Deep-Sea Research
(1976) - et al.
A chlorofluorocarbon section in the eastern North Atlantic
Deep-Sea Research
(1992) - et al.
Direct estimates and mechanisms of ocean heat transport
Deep-Sea Research
(1982) - et al.
Mechanisms of heat, freshwater, oxygen and nutrient transports and budgets at 24.5°N in the subtropical North Atlantic
Deep-Sea Research I
(2003) The global ocean circulationa hydrographic estimate and regional analysis
Progress in Oceanography
(1998)- et al.
Improvements on the back-calculation technique for estimating anthropogenic CO2
Deep-Sea Research I
(2002) - et al.
Two transatlantic sectionsmeridional circulation and heat flux in the subtropical North Atlantic Ocean
Deep-Sea Research
(1985) - et al.
Global sea–air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects
Deep-Sea Research II
(2002) - et al.
Riverine-drive interhemispheric transport of carbon
Global Biogeochemical Cycles
(2001)
Global carbon sinks and their variability inferred from atmospheric O2 and δ 13C
Science
Temporal evolution of CFC 11 and CFC 12 concentrations in the ocean interior
Journal of Geophysical Research
Carbon dioxide transport by ocean currents at 25°N latitude in the Atlantic Ocean
Science
Gradual increase of oceanic CO2
Nature
Transports through the Bering Straitannual and interannual variability
Journal of Geophysical Research
Climatic variability in upper ocean ventilation rates diagnosed using chlorofluorocarbons
Geophysical Research Letters
Meridional heat transport variability at 26.5°N in the North Atlantic
Journal of Physical Oceanography
Efficient representation of the North Atlantic in the early 80's. An atlas
Progress in Oceanography
Large-Scale Ocean Heat and Freshwater Transports during the World Ocean Circulation Experiment
Journal of Climate
Anthropogenic CO2 in the Atlantic Ocean
Global Biogeochemical Cycles
An improved method for detecting anthropogenic CO2 in the oceans
Global Biogeochemical Cycles
Normal monthly wind stress over the World Ocean with error estimates
Journal of Physical Oceanography
The meridional transport of dissolved inorganic carbon in the South Atlantic Ocean
Global Biogeochemical Cycles
Cited by (39)
Inverse Problems, Inverse Methods, and Inverse Models
2019, Encyclopedia of Ocean Sciences, Third Edition: Volume 1-5Inverse problems, inverse methods, and inverse models
2019, Encyclopedia of Ocean SciencesCalcium distribution in the subtropical Atlantic Ocean: Implications for calcium excess and saturation horizons
2016, Journal of Marine SystemsTrends in anthropogenic CO<inf>2</inf> in water masses of the Subtropical North Atlantic Ocean
2015, Progress in OceanographyCitation Excerpt :This Cant entrance is sustained up to 65 ± 13% due to lateral transports that carry Cant-loaded subtropical waters to these northern latitudes through the upper limb of the Meridional Overturning Circulation (MOC) (Álvarez et al., 2003; Macdonald et al., 2003; Rosón et al., 2003; Pérez et al., 2013). At 24.5°N, the MOC is responsible for almost 90% of the meridional heat flux (Johns et al., 2011) and it also transports up to 0.17–0.20 PgC y−1 of Cant (Macdonald et al., 2003; Rosón et al., 2003). Due to the importance of the North Atlantic Subtropical Gyre (NASTG) in the uptake of Cant from the atmosphere, the WOCE A05 hydrographic line, situated at 24.5°N, is suitable for the evaluation and quantification of the North Atlantic Cant sink.
The marine carbon cycle and ocean carbon inventories
2013, International GeophysicsUncoupled transport of chlorofluorocarbons and anthropogenic carbon in the subpolar North Atlantic
2010, Deep-Sea Research Part I: Oceanographic Research PapersCitation Excerpt :However, the patterns of CANT and CFC accumulation differ regionally because of differences in their atmospheric histories, temperature dependence and air–sea gas exchange equilibration time (Körtzinger et al., 1999; McNeil et al., 2003; Tanhua et al., 2009). Previous studies in the North Atlantic dealt with the relation between CANT and CFC distributions and their temporal evolution (e.g., Körtzinger et al., 1999; Macdonald et al., 2003; Tanhua et al., 2006), CANT transport (e.g., Álvarez et al., 2003; Macdonald et al., 2003; Rosón et al., 2002) and CFC-derived formation rates (e.g., Smethie and Fine, 2001; Rhein et al., 2002), but none have jointly studied their transports and the controlling mechanisms. The present work revises the CANT transport across the World Ocean Circulation Experiment (WOCE) A25 line (Fig. 1) published in Álvarez et al. (2003), with the new circulation patterns proposed by Lherminier et al. (2007, Lh07 hereinafter), where the circulation initially proposed in Álvarez et al. (2002, A02 hereinafter) is further constrained with ADCP data.