Late Quaternary nearshore molluscan patterns from Patagonia: Windows to southern southwestern Atlantic-Southern Ocean palaeoclimate and biodiversity changes?

AGUIRRE, M.L.; RICHIANO, S.; VOELKER, A.H.L.; DETTMAN, D.L.; SCHÖNE, B.R.; PANARELLO, H.O.; DONATO, M.; PERAL, L. GÓMEZ; CASTRO, L.E.; MEDINA, R.

GLOBAL AND PLANETARY CHANGE

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2019

0921-8181

Variedapproaches (palaeobiodiversity, palaeobiogeography, bioerosion, geochemistry)to unique Patagonian late Quaternary molluscan assemblages in the southwesternAtlantic, with ages especially from interglacial Marine Isotope Stage (MIS) 5eand MIS 1, provide large-scale and long-temporal palaeoenvironmental data forthe southern SWA. Together with new patterns of δ18O and δ13C variations in modern, mid-Holocene, and Lateto Middle Pleistocene shells of Protothaca antiqua(Bivalvia) and the coeval Pleistocene Tegula atra(Gastropoda), the overall sources of evidence illustrate possible responses torecent palaeoclimate and sea-ice changes around the southernmost SWA-westernAntarctica, leading to modern conditions. For the mid-Holocene, the influenceof the Hypsithermal is confirmed. In the northern Golfo San Matías, the highestδ18O and δ13C values support higher salinity and seasurface temperatures (SST), and a Golfo San Matías Front stronger than today.Lower δ18O values in the northern Golfo SanJorge (GSJ) compared to the Late to Middle Pleistocene suggest warmermid-Holocene waters, independently supported by thermally anomalous molluscantaxa, geographical shifts of areas of endemism and absence of T. atra (cold water proxy); overallhigher δ13C values compared to present suggesthigher productivity. For the Late to Middle Pleistocene (particularly MIS 5e),highest δ13C values (relative to modern andmid-Holocene trends) match with the location of tidal fronts and areas ofmaximum chlorophyll-a concentrations today. Accordingly, these fronts may havebeen already active and significantly intensified due to the prevailing climateconditions that included colder waters and stronger upwelling from the southernGSJ southwards. This is independently supported by palaeobiogeographical andbioerosion trends and the dominance of the cold water species T. atra during the Pleistocene,which is dispersed from the SE Pacific into the SWA by rafting on kelps and whoseoccurrence is controlled by SST, light, winds, and nutrientconcentration/productivity. Repeated, abrupt climate oscillations during thelast glacial cycle with significant impact on SST, ice melting andsurface-ocean stratification in the western Antarctica-Weddell Sea-AntarcticCircumpolar Current realm are so far the only available plausible explanationsto account for the different mid-Holocene and modern patterns, and for theregional disappearance of T. atra after MIS5e. Further palaeoceanographic research in this key area is needed tounderstand how all these mechanisms operated in the past, potentiallyinfluencing the Patagonian shelf waters and coastal fronts.