Paleoceanographic evolution of the Gulf of Tehuantepec (Mexican Pacific) during the last ~6 millennia

Abstract

Oceanographic dynamics in the Gulf of Tehuantepec (GT) are the direct consequence of climate variability, mainly influenced by the strong wind regime locally called “Tehuanos” and the interactions between the Intertropical Convergence Zone (ITCZ) and El Niño Southern Oscillation (ENSO). The area is characterized by intense upwelling driven by the Tehuanos within one of the largest Oxygen Minimum Zones (OMZ) in the world. Upwelling carries nutrient-rich subsurface waters to the surface and provides marine resources to the coasts conforming one of the main economic sectors in the region. In this study, sediment core MD02-2521 is used to perform the first high-resolution paleoceanographic reconstruction of the last 6 millennia in the GT. The main focus is put on the analysis of the benthic foraminifera (BF) assemblages inhabiting within the OMZ, which appear to respond to bottom oxygenation and climate variations of the last ~6000 years. The microfossil assemblages throughout the sediment core revealed, first, intervals where the lack of foraminifera provide evidence of episodes of strong deoxygenation that triggered the dissolution of calcareous foraminiferal tests, second, a long-term decline of bottom-water oxygenation in the last ~2500 years likely responding to the southward migration of the ITCZ. Last, variations in response to the transitions between cold and warm periods occurred during the last 2–2.5 millennia and cyclicities of 1470 years resembling Bond Cycles suggest a climatic connection between the Pacific and Atlantic Oceans during the late-Holocene.

Paleoceanography of the Gulf of Tehuantepec during the Medieval Warm Period

“…(2020) for more details on the age model. Despite the portion of core used in this study contains a single radiocarbon dating, the age model is reliable since the average sedimentation rate is 1 mm/year, which is kept almost constant during the Holocene according to core MD02-2521 and other cores in the GT (Pichevin et al, 2010;Arellano-Torres et al, 2013;García-Gallardo et al, 2020). Micropaleontological analysis.…”

“…The core was retrieved in the GT (15°40.25'N; 95°18'N) with a Calypso Square Corer at 718.7 m depth during the Margins of North America (MONA) Campaign (IMAGES VIII/MD126) in June 2002 aboard the Marion Dufresne (Beaufort, 2002). Detailed information on the sediments is described in García-Gallardo et al (2020). Age model…”

“…University of Mexico). The samples were weighed, dried, sieved through a 63 µm sieve using tap water, dried at room temperature in Whatman™ filter papers, and weighed again (García-Gallardo et al, 2020). At least 300 specimens were collected from each sample.…”

“…In addition, the MWP has been recognized by some authors to possess analog characteristics to current and future climate change. A recent study in the GT by García-Gallardo et al (2020) found bottom water oxygen conditions shifts that varied synchronously with the Roman Warm Period (RWP), Dark Ages (DA), MWP, and Little Ice Age (LIA) from BFl records of sediment core MD02-2521. The present study focuses on the medieval-aged sediments of core MD02-2521 by amplifying the resolution of analyzed samples in the MWP to find out a more detailed response of this climatic optimum in the oceanographic and climatic conditions of the GT.…”

“…In the Northern Hemisphere (NH), a southward reach of the average position of the ITCZ starting at ~2500 yrs BP seems to be primarily caused by a decreasing trend in summer insolation in the NH related to orbital forcing (Hodell et al, 1991;Haug et al, 2001). Locally, in the Gulf of Tehuantepec (GT), the ~6 Millennia record of benthic foraminifera (BF) by García-Gallardo et al (2020) showed a shift at ~2500 years towards gradual deoxygenated bottom conditions, evidenced by a gradual increase of the benthic foraminifer E. sandiegoensis. Moreover, Poore et al (2004) found century-scale fluctuations in the relative position of the ITCZ in the Gulf of Mexico related to solar activity.…”