Do coastal fronts influence bioerosion patterns along Patagonia? Late Quaternary ichnological tools from Golfo San Jorge

Abstract

Late Quaternary marine molluscan skeletal concentrations from Argentina constitute a remarkable record of variations in palaeoceanographical conditions during interglacial times (mainly ca. 125 ka to present). Particularly, the Golfo San Jorge coastal area represents an extraordinary geographical zone to target from different points of view, mainly due to its linkage between northern and southern Patagonia, characterized by particular and contrasting physico-chemical conditions with direct consequences for littoral marine communities, determining their composition and structure. Among varied biological activities controlled by different environmental factors (i.e., substrate nature, sedimentation rates, water depth, sea surface temperature, salinity, nutrients-productivity), bioerosion traces can provide palaeoenvironmental evidence with important implications for palaeoclimate interpretations. In addition, the application of bioerosion patterns regionally and through time is a recent valuable worthy palaeoenvironmental tool not as yet developed for Patagonia. We attempted to characterize, qualitatively/semiquantitatively, the ichnotaxonomic composition of the coastal area of northern Golfo San Jorge since the Late Pleistocene; to compare results with those obtained for other geographical areas along Patagonia and the Bonaerensian coastal sectors; lastly, to evaluate its palaeoenvironmental/palaeoclimatic significance in a clue area in terms of circulation patterns near the Southern Ocean climatic pump. At Bustamante (Northern Patagonia Frontal System) Domichnia traces were dominant during the Late Pleistocene while Praedichnia in the mid-Holocene. Bustamante exhibits the highest ichnodiversity for the whole Argentinean coastal area. Ichnodiversity is not strongly different between Late Pleistocene and mid-Holocene interglacials and compared to present; however, the relative abundance of some ichnotaxa (e.g., Oichnus, Iramena, Pennatichnus, at Camarones; Oichnus, Iramena, Pinaceocladichnus, at Bustamante) differs across time. These variations, particularly the highest abundance in the Late Pleistocene (mainly Last Interglacial) of traces made by bryozoans-associated at present with modern enhanced productivity levels and coastal fronts in the Argentine continental shelf-point to higher productivity and more intensified northern Patagonia Front, as a result of a different palaeocirculation pattern, reinforcing previous independent sources of evidence based on molluscan palaeobiogeographical analyses.

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

“…The trends observed are in agreement with our previous interpretations (e. g., Aguirre et al, 2011Aguirre et al, , 2013Richiano et al, 2017). In general terms, our results agree with climatic interpretations so far proposed for the last two interglacials worldwide: MIS 5e warmer than the MIS 1 Hypsithermal and today.…”

“…In addition, the absence of T. atra (Fig. 10) and different mid-Holocene bioerosion patterns corroborate warmer SST in comparison with both the present and the Late to Middle Pleistocene (Aguirre et al, 2013;Richiano et al, 2015Richiano et al, , 2017 (Fig. 11).…”

“…3. Physical features of the Patagonian nearshore and Mar Argentino (sector shown with an inserted rectangle in A) (modified from Aguirre et al, 2013;Richiano et al, 2017. (A): substrates (modified from Parker et al, 1997).…”

“…1B-F), and of the coeval Pleistocene Tegula atra (Lesson) (Gastropoda) ( Fig. 1G-I), in combination with palaeobiodiversity, palaeobiogeographical and bioerosion trends (Aguirre et al, 2011(Aguirre et al, , 2013(Aguirre et al, , 2017Richiano et al, 2013Richiano et al, , 2015Richiano et al, , 2017, we aim to investigate how SST and productivity levels in the Pleistocene (especially MIS 5e) and mid-Holocene (MIS 1) compare to today along the Patagonia coast and whether general patterns can be linked to climate changes and coastal fronts. Particular questions to be addressed are: 1) Were Late to Middle Pleistocene interglacial surface oceanic waters in Patagonia colder or warmer than during the mid-Holocene and today?…”

Bioerosion ichnodiversity in barnacles from the Ross Sea, Antarctica

“…Few studies were conducted in the cold-temperate region Patagonia (e.g. Ituarte et al 2005;Malumián et al 2006;Richiano et al 2017;Aguirre et al 2019) and in the polar region Antarctica. Bioeroded traces were observed on Seymour Island, Antarctica (Casadío et al 2001(Casadío et al , 2007, and bioerosive activities were recorded in the Ross Sea in scallops and molluscs (Alexander and DeLaca 1987;Cerrano et al 2001;Hancock et al 2015), and sub-fossil skeletal material (Frank et al 2014(Frank et al , 2020.…”