Anthropogenic CO2 in the Azores region

Abstract

The AZORES-I cruise was conducted in August 1998, spanning the length of three latitudinal large-scale sections at 22, 28 and 32ºW. The oceanic carbon system was oversampled by measuring total alkalinity, total inorganic carbon and pH. It is thus possible to estimate anthropogenic CO₂ (C_ANT) and to investigate its relationship with the main water masses that are present. C C_ANT is calculated using the latest back-calculation techniques: φC_Tº and TrOCA methods. Although the two approaches produce similar vertical distributions, the results of the TrOCA method show higher C_ANT variability and produce higher inventories than those of the φC_Tº method. The large proportion of Mediterranean Water found in the northern part of the study area is the main cause of the observed increase northwards of C C_ANT inventories. Changes in C C_ANT inventories between 1981 and 2004 are evaluated using data from the TTO-NAS, OACES-93 and METEOR-60/5 cruises. According to the φC_Tº and TrOCA approaches, the average long-term rates of C C_ANT inventory change are 1.32±0.11 mol C m^-2 y^-1 (P=0.008) and 1.18±0.16 mol C m^-2 y^-1 (P=0.018), respectively. During the 1993-1998 a significant increase in the C C_ANT storage rate was detected by the φC_Tº method. It is thought that this stems directly from the enhanced Labrador Seawater formation after the increased advection observed at the time.