Figure 2. Pore-water concentration profiles for sulfate (SO₄^2-) and methane (CH₄); total dissolved carbon dioxide (CO₂) and alkalinity (Alk.); and isotopic composition profiles of ¹³CCO₂ and ¹⁴SSO₄ for (A) Site 994, (B) Site 995, and (C) piston core (PC) 11-8. Concentration is expressed in millimolar (mM) units for sulfate, CO₂, and alkalinity; methane concentration is expressed in micromolar (µM) units. Measurement uncertainties are shown with error bars, but are generally smaller than symbol size. Carbon isotopic composition is relative to the Peedee belemnite (PDB) standard; sulfur isotopic compositions are relative to Canyon Diablo Troilite (CDT). Representative seawater values for concentration and isotopic composition are shown with solid arrows pointing to the x-axes. The sulfate-methane interface (SMI) is shown by the horizontal dashed lines. Sulfate gradients are linear (note correlation coefficients, r², from least-square regression) within >95% probability (r test; Young, 1962).