Millennial-scale marine productivity changes and the persistence of Antarctic intermediate water off Baja California, Mexico, during the last 6-60 kyr

A high-resolution record of 818O and 813C of Uvigerina peregrina (hereinafter: 818OU and 813CU) and biogenic opal was used to reconstruct water column conditions in the SW margin of the Baja California peninsula for the last 6-60 kyr. The core was collected from a depth of 700 m in the oxygen deficient zone of the Magdalena margin. Although the 818OU values showed a large change associated with the passage from glacial conditions to the Holocene, the MIS-3 and MIS-2 were characterized by a low variability. Our results indicated a rapid cooling and/or increase in salinity immediately after H5 that persisted until H1. However, the 813CU values showed significant variability associated to the incursions of the Antarctic Intermediate Water (AAIW) in the Magdalena margin during the MIS-3 and MIS-2. This agrees with the 813C composition of water mass end-members at intermediate depths in the Pacific Ocean. Enhanced ventilation during MIS-3 was inferred from the 813CU values, which were very similar to the 813C values of the AAIW end-members evidencing the persistence of the AAIW in the region. This conclusion is also supported by the trend of sedimentary 815N and other dissolved oxygen proxies in the area. A depletion of the 813CU at a millennial scale suggests intermittent pulses of a water mass richer in nutrients, which generated an increase in exported productivity, and thus, concomitantly depleted the dissolved oxygen levels at intermediate depths. Moreover, exported productivity showed a decreasing long-term trend during the second half of MIS-3, briefly punctuated by millennial-scale increases in exported productivity sustained by nutrient export from the Southern Ocean via the AAIW. (c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

A high-resolution record of 818O and 813C was used to reconstruct water column conditions in the SW margin of the Baja California peninsula, showing significant variability during different periods and indicating rapid cooling and/or increase in salinity associated with certain events.