Analysis of Primary Productivity Variability in the Transitional Zone of the Mexican Pacific during the Late and Middle Holocene

The transitional zone of the Mexican Pacific is a complex region in terms of its oceanographic conditions. This leads to changes in primary and exported productivity over various time scales. This study employs geochemical tracers—organic carbon (CO), biogenic opal, and calcium carbonate—to assess sedimentary records' primary and exported productivity. Analyzing responses to past warm periods is crucial for understanding marine productivity in future climate change scenarios. The objective of the present study was to quantify organic carbon content and to infer changes in primary and exported productivity in the transitional zone of the Mexican Pacific for the late Holocene and the final part of the middle Holocene. The sediment core, collected at a depth of 680 meters on the southwestern margin of Baja California Sur. It has a length of 137 cm and was sectioned at intervals of 1 cm, representing 137 samples. The estimated age from ¹⁴C was 5466 years. Each one-centimeter interval denotes 33 years. CO analysis used a COSTECH 4010 elemental analyzer with 0.2% analytical accuracy, employing BBOT and Urea certified standards. Biogenic opal determination follows the molybdenum blue spectrophotometric method by Mortlock and Froelich (1989). CO content ranged from 8% and 14%, showing periodic changes at ~300, ~170, and ~100 years. Biogenic opal ranged from 0.2 to 19.3%, with abrupt changes at ~310, ~270, and ~70 years. Organic carbon and biogenic opal exhibited a positive correlation, indicating increased productivity during warm periods like the Roman Warm Period (1800 to 2200 years ago) and the Medieval Warming Period (700 to 1100 years ago). This suggests responsiveness to oceanographic conditions across various time scales.