Spatial variation of total CO<SUB>2</SUB> and total alkalinity in the northern Indian Ocean: A novel approach for the quantification of anthropogenic CO<SUB>2</SUB> in seawater

Abstract

As part of a cooperative effort of the Joint Global Ocean Flux Study (JGOFS) and of the World Ocean Circulation Experiment (WOCE) program, we have measured total CO 2 (TCO 2) and total alkalinity (TA) along three sections in the northern Indian Ocean. One section through the Gulf of Aden to the Arabian Sea is parallel to the coast of Yemen. One section is across the Arabian Sea along the nominal 9N latitude and the other section is across the Bay of Bengal along the nominal 10N latitude. The measurements were performed on board R/V Knorr in September-October 1995. The primary purpose of this work is to understand the penetration of anthropogenic CO 2 along these ocean sections. Here, we present a novel approach to the calculation of anthropogenic CO 2 in the ocean based upon the fundamentals of water-sources mixing. Consequently, we rst describe the observations and mixing of water-sources before we describe the quanti cation of anthropogenic CO 2 concentrationsin these waters. The data show large spatial variations in surface seawater of both total CO 2 (up to 50 µmol kg 2 1) and total alkalinity (up to 40 µmol kg 2 1). The variations are mainly associated with physical processes characterized by water masses of different temperature and salinity. For example, at depths we observed low TCO 2 concentration at longitude 54E 6 2E associated with the low-salinity water mass owing northward. The contrasts between the sections across the Arabian Sea and the Bay of Bengal emphasize the large property differences between the two ocean basins. Multiparametric analyses on the data clearly show the relative contributions of different water-sources in each of the ocean sections. The mixing coefficients calculated from the multiparametric analyses are further used to quantify anthropogenic CO 2 concentrations in each water-source. The results indicate that the surface water-sources contain 47.8, 42.1 and 50.4 µmol kg 2 1 in the Gulf of Aden, the Arabian Sea and the Bay of Bengal, respectively. In the surface waters there is slightly more anthropogenic CO 2 across the Bay of Bengal than across the Arabian Sea. In contrast, anthropogenic CO 2 has penetrated signi cantly deeper in the Gulf of Aden than in the Arabian Sea and in the Bay of Bengal.

Trends in anthropogenic CO2 in water masses of the Subtropical North Atlantic Ocean

“…For modern measurements the C ant ΔC * error would thus be lower (Gruber, 1998) A T , and was derived from Δ 14 C and CFC-11 tracer data in the global ocean, to establish which water parcels can be assumed to be free of C ant . The method assumes that A T is not affected by the increase of atmospheric CO 2 (Goyet et al, 1999) and uses a constant oxygen to carbon Redfield ratio (Rc) value of 1.35 (after ) to calculate the biological contribution to C T , while both φC T 0 and ΔC* methods use the l4 Rc ratio of 1.45 proposed by Anderson and Sarmiento (1994). Despite being a simple universal equation , it provides comparable C ant inventories to those obtained by other approaches in the Atlantic (Vázquez-Rodríguez et al, 2009b Given the availability of CFC measurements on four cruises (1992, 1998, 2004 and 2010), C (Touratier et al, 2007).…”

Anthropogenic carbon distribution in the eastern South Pacific Ocean

“…C * approach of Gruber et al, 1996;Pérez et al, 2002; LM approach of Lo Monaco et al, 2005a;Vázquez-Rodríguez et al, 2009). Others are based upon completely new concepts such as water-mass mixing (Goyet et al 1999); or similarity with CFCs or SF 6 penetration (e.g. Goyet and Brewer, 1993; TTD approach of Waugh et al, 2004;Waugh et al, 2006;Tanhua et al, 2008); or a new water-mass tracer "TrOCA" (Touratier and Goyet, 2004a, b;Touratier et al, 2007).…”

Multiple constraints on regional CO2 flux variations over land and oceans

“…The MIT model has a surface to depth gradient of DIC that is underestimated by $25% compared to the observations of Goyet et al [1999], which may reduce variability, while the OPA model captures this gradient quite well. The OPA model shows variations in surface chlorophyll that are overestimated by 1.5 compared to satellite observations, while the simplified export parameterization of the MIT model tends to damp export flux variability.…”