Shifts in the oligotrophic warm conditions of the Gulf of Mexico over
MIS-6 to MIS-1 based on planktonic foraminifera assemblages and Mg/Ca
ratios
Abstract
Collected from the southwestern Gulf of Mexico (GoM), the marine piston
Core RC10-265 was used to reconstruct surface water masses, circulation
and paleotemperature shifts at orbital scales, over the last
~180 ka. The chronology was constructed based on
radiocarbon ages, planktonic foraminifera biostratigraphy and stable
oxygen isotopes (δ18O). The ocean surface conditions were reconstructed
based on planktonic foraminifera assemblages and the sea surface
temperatures (SST) based on Mg/Ca ratios, analysed through LA-ICP-MS.
Applying a Q-mode Factor Analysis, two scenarios were characterised
through seven species. (1) The subtropical assemblage (Globigerinoides
ruber - Globoconella inflata (positive scores) and the Globorotalia
menardii group - Pulleniatina obliquiloculata (negative scores))
suggests that during the end of MIS-6, and MIS-4 to MIS-2, the surface
waters were colder (~22-25 °C), with less oligotrophic and
a more profound mixed layer depth (MLD) relative to interglacials. (2)
The tropical assemblage (Globigerinoides ruber - Neogloboquadrina
dutertrei - Globorotalia truncatulinoides (positive scores) and
Globoconella inflata - Globigerina falconensis (negative scores))
suggests that during the early MIS-6, MIS-5e to 5b and MIS-1, the
surface waters were warm (~28-32 °C), oligotrophic, with a
shallow MLD like average modern conditions. Despite evidence of early
diagenesis by clay coatings, the reconstructed paleotemperatures are
consistent with palaeothermometry studied in the Caribbean and northern
Gulf. The studied information shows the relevance of the Loop Current
(extended vs. contracted mode) and the associated variability in
mesoscale eddies as a key control of the GoM paleoecology and
paleotemperatures at orbital scales.