Novel insights into deep ventilation of the Gulf of Mexico and its linkage to the Labrador Sea

Deep water (>2000m) ventilation in the Gulf of Mexico and its susceptibility to changes of the Atlantic Meridional Overturning Circulation (AMOC) are poorly understood. Existing residence times estimates range from 250 to 500 years and temporal variability is unknown. As part of the CIGOM project, we collected radiocarbon profiles throughout the southern Gulf of Mexico and the northwestern Caribbean. These results are compared with existing data from the region. The radiocarbon and DIC distributions in the deep Gulf and Caribbean are consistent with dissolved oxygen patterns. This suggests an increase of the apparent radiocarbon age over the last few decades. Caribbean deep-water radiocarbon values show a clear difference between the northern Yucatan Basin and the Venezuelan Basin with higher values in the former. The Δ¹⁴C offset between the deep Yucatan Basin (~80‰) and the deep Gulf of Mexico (~94‰) translates to an apparent radiocarbon age difference of ~110 years. This indicates much shorter residence times for the deep GOM than previously suggested. The deep GOM remains free of bomb ¹⁴C and anthropogenic CO₂.

The radiocarbon-based residence times are in good agreement with residence times derived from multiyear volume transport measurements in Yucatan Stait (≤100 years) and a ventilation scheme based on extensive entrainment and diapycnal mixing within the GOM. The new residence times of GOM deep water are considered relative to the observed variability of Labrador Sea deep-water formation and proposed AMOC changes over similar time scales (decades to centuries).