Remineralization ratios of carbon, nutrients, and oxygen in the North Atlantic Ocean: A field databased assessment

Abstract

Remineralization ratios of carbon, nutrients, and oxygen have been assessed in the North Atlantic Ocean along the WOCE 1A/E section. The study is based on an extensive field data set comprising dissolved inorganic carbon (DIC), nitrate and nitrite (NO3/2), phosphate (PO4), and oxygen (O2) data as well as hydrographic data. A procedure has been introduced which normalizes DIC data to constant salinity and temperature and corrects for the contamination from anthropogenic CO2. The remaining variability on the normalized DIC values (DICbio) can be attributed to the remineralization of organic matter. DICbio can thus be seen as carbon‐analogy to the apparent oxygen utilization (AOU). The consecutive evaluation of the remineralization ratios obtains two different regimes separated at the density level ρ = 1027.7 kg m−3. In the shallower level the ratios (C/N = 4.5; C/P = 67, AOU/C = 2.0; N:P = 15; AOU:P = 134; AOU/N = 9.0) are shifted toward relatively higher nutrient release and higher oxygen consumption with respect to the Redfield ratios of particulate organic matter (POM). In contrast, in the deeper levels the ratios are shifted toward relatively higher carbon release and lower oxygen demand (C/N = 11; C/P = 152, AOU/C = 0.86; N:P = 13.9; AOU:P = 130; AOU/N = 9.4). The depth integrated inventories of the remineralization products (DIC, NO3/2, PO4, and AOU) provide water column averaged ratios for the investigation area (C/N = 8.8; C/P = 124, AOU/C = 1.1; N:P = 14.2; AOU:P = 131; AOU/N = 9.3) which imply a higher efficiency of the biological carbon pump in the North Atlantic Ocean than predicted with respect to the elemental composition of POM.