FY 2009
Estimating the storage of anthropogenic carbon in the subtropical Indian Ocean: A comparison of five different approaches
Álvarez, M., C. Lo Monaco, T. Tanhua, A. Yool, A. Oschlies, J.L. Bullister, C. Goyet, N. Metzl, F. Touratier, E. McDonagh, and H.L. Bryden
Bioscience, 6(4), 681–703 (2009) |
The subtropical Indian Ocean along 32°S was for
the first time simultaneously sampled in 2002 for inorganic
carbon and transient tracers. The vertical distribution and
inventory of anthropogenic carbon (CANT) from five different
methods: four data-base methods (1C*, TrOCA, TTD
and IPSL) and a simulation from the OCCAM model are
compared and discussed along with the observed CFC-12
and CCl4 distributions. In the surface layer, where carbonbased
methods are uncertain, TTD and OCCAM yield the
same result (7±0.2 molCm−2), helping to specify the surface
CANT inventory. Below the mixed-layer, the comparison
suggests that CANT penetrates deeper and more uniformly
into the Antarctic Intermediate Water layer limit than
estimated from the much utilized 1C* method. Significant
CFC-12 and CCl4 values are detected in bottom waters,
associated with Antarctic Bottom Water. In this layer,
except for 1C* and OCCAM, the other methods detect
significant CANT values. Consequently, the lowest inventory
is calculated using the 1C* method (24±2 molCm−2)
or OCCAM (24.4±2.8 molCm−2) while TrOCA, TTD, and
IPSL lead to higher inventories (28.1±2.2, 28.9±2.3 and
30.8±2.5 molCm−2 respectively). Overall and despite the
uncertainties each method is evaluated using its relationship
with tracers and the knowledge about water masses in the
subtropical Indian Ocean. Along 32°S our best estimate for
the mean CANT specific inventory is 28±2 molCm−2. Comparison
exercises for data-based CANT methods along with time-series or repeat sections analysis should help to identify
strengths and caveats in the CANT methods and to better constrain
model simulations. |