C. Marcela Borel

Radiocarbon Reservoir Ages and Hardwater Effect for the Northeastern Coastal Waters of Argentina

Accelerator mass spectrometry (AMS) radiocarbon dates were obtained for 18 mollusk shells collected alive along the Buenos Aires province coast, Argentina, over the period AD 1914-1935. Reservoir ages were estimated for all samples on the basis of the tree-ring calibration curve for the Southern Hemisphere (SHCal04, McCormac et al. 2004) and the marine Δ R values calculated as the difference between the conventional 14C age and the age deduced from the marine, mixed-layer model calculation (Marine04, Hughen et al. 2004). For most coastal locations, a great Δ R scatter was observed, ranging from 191 to 2482 yr, which is explained by the input of varying content of dissolved carbonate by rivers and groundwater (hardwater effect) and indicates a serious limitation for shell-based 14C chronologies. Within the interior of Baha Blanca estuary, Δ R values ranged from 40 to 50 46 as a consequence of the local geological particularities of the environment. This suggests that, with some restrictions, the marine calibration curve with standard parameters ( Δ R = 0) could be used at this location.

Azadinium poporum from the Argentine Continental Shelf, Southwestern Atlantic, produces azaspiracid-2 and azaspiracid-2 phosphate

The marine dinophycean genus Azadinium has been identified as the primary source of azaspiracids (AZA), a group of lipophilic phycotoxins known to accumulate in shellfish. Blooms of Azadinium in the southern Atlantic off Argentina have been described from the 1990s, but due to a lack of cultures, the diversity of South-Atlantic Azadinium has not yet been fully explored and their toxin production potential is completely unknown. During a spring 2010 research cruise covering the El Rincón (ER) estuarine system (North Patagonian coast, Argentina, Southwestern Atlantic) a search was conducted for the presence of Azadinium. Although neither Azadinium cells nor AZA in field plankton samples were detected, 10 clonal strains of Azadinium poporum were successfuly established by incubation of sediment samples. Argentinean A. poporum were more variable in size and shape than the type description but conformed to it by the presence of multiple pyrenoids with starch sheath, in plate pattern and arrangement, and in the position of the ventral pore located on the left side of the pore plate. In contrast to all previous description of A. poporum, isolates of the Argentinean A. poporum possessed a distinct field of pores on the second antapical plate. Conspecificity of the Argentinean isolates with A. poporum was confirmed by molecular phylogeny of concatenated ITS and LSU rDNA sequences, where all Argentinean isolates together with some Chinese A. poporum strains formed a well-supported ribotype clade within A. poporum. All isolates produced AZA with the same profile, consisting of AZA-2 as the major compound and, to a lesser extent, its phosphated form. This is the first report of a phosphated marine algal toxin. This first confirmation of the presence of AZA producing Azadinium in the Argentinean coastal area underlines the risk of AZA shellfish contamination episodes in the Southwestern Atlantic region.

Holocene changes in trophic states of shallow lakes from the Pampa plain of Argentina

Changes in trophic status of shallow lakes from the southeastern Pampa plain of Argentina are evaluated based on the relative presence of submerged macrophytes and phytoplankton. The evolution of lake Lonkoy is reconstructed for the last 5000 years, using pollen, non-pollen palynomorphs (NPPs) and macrofossil remain analyses, revealing three main lake stages. A macrophyte-dominated clear lake prevailed until 670 cal yr BP. Afterwards, the lake changed to a turbid phytoplankton-dominated state. Recently, the lake has turned to a turbid phase, caused by resuspended sediment. These results are compared with two other paleolimnological records from the region, lakes Hinojales and Nahuel Rucá, revealing a similar late-Holocene evolution, with a shift from a macrophyte- to phytoplankton-dominated lake, occurring at broadly the same time. The shift of states may be attributed to a shift in climate after 1000 cal. yr BP towards wetter conditions during the Medieval Climate Anomaly.

THE PROBLEMATIC AQUATIC PALYNOMORPH GENUS COBRICOSPHAERIDIUM HARLAND AND SARJEANT, 1970 EMEND., WITH NEW RECORDS FROM THE HOLOCENE OF ARGENTINA

Abstract The aquatic palynomorph genus Cobricosphaeridium Harland and Sarjeant, 1970 was described from Holocene deposits of Australia. Restudy of the type material shows that these palynomorphs may represent the eggs of crustaceans, and that earlier attributions to the division Dinoflagellata are unsustainable. The genus Aquadulcum Harland and Sarjeant, 1970, also first described as a dinoflagellate from the Holocene of Australia, is treated as a synonym of Cobricosphaeridium, and the following new combinations are proposed: C. awendae, C. myalupense, C. pikeae, C. serpens, C. yanchepense, C.? ovatum, and C.? vermiculatum. Previous records of the genus are restricted to the Holocene and indicate a freshwater affinity. Cobricosphaeridium has now been found in Holocene subsurface brackish deposits of Laguna Hinojales in eastern Argentina. This is the first record of this genus from South America and unequivocally extends its ecological range into a brackish environment. Several species are represented, including Cobricosphaeridium hinojalensis new species; and their potential as paleoenvironmental indicators is evaluated.

BRACKISH TO FRESHWATER DINOFLAGELLATE CYST ASSEMBLAGES FROM THE LA COLONIA FORMATION (PALEOCENE?), NORTHEASTERN PATAGONIA, ARGENTINA

Abstract. A palynological analysis of the section of La Colonia Formation exposed at Estancia San Miguel yielded conspicuous assemblages of organic-walled dinoflagellate cysts (dinocysts) and green algae. The monotypic palaeoperidinioid dinocyst assemblage of ?Ginginodinium sp. in the basal beds of this section indicates low-salinity water conditions in a restricted shallow marine paleoenvironment. The green-algaedominated assemblages together with specimens of ?Morkallacysta spp., Dinocysts type P and ?Vesperopsis sp. recorded in the middle and upper part of the San Miguel section indicate brackish to freshwater and freshwater depositional conditions, respectively. The changes in the composition of the palynological assemblages, in agreement with the analysis of the sedimentary facies, reflect a salinity-drop in the water bodies and a progressive upward-shallowing trend. The occurrence of specimens of the neritic open marine Cribroperidinium spp., Apteodinium sp., Circulodinium sp. and Areoligera sp. cf. A. circumsenonensis Fensome et al. is here considered as reflecting contemporaneous transported material from the adjacent shelf. The marine part of the La Colonia Formation is associated to Late Cretaceous and Paleocene ages. Nevertheless, palynomorphs together with a stratigraphical criterion suggest an age non older than Paleocene for the deposits of the unit at the San Miguel section.

ANCIENT COASTAL ENVIRONMENTS IN A MAASTRICHTIAN - ?PALEOCENE ATLANTIC SHORELINE: A PHYTOPLANKTON APPROACH

Abstract. In this contribution we describe planktonic assemblages, comprising their taxonomic composition and palaeoecological attributes, from the La Colonia Formation, Patagonia, Argentina. The palynological samples are from the section exposed at Estancia San Miguel, in the Telsen area, Chubut province. Diverse organic-walled remains of Chlorophyta and Charophyta taxa are documented. These include coenobia of two species of Pseudopediastrum , colonies of Botryococcus and zygospores of the form-genus Ovoidites (resembling extant genera of Zygnemataceae). The green algae together with dinoflagellate cysts (analyzed in a previous detailed study) indicate brackish to freshwater and freshwater depositional conditions for the middle and upper part of the Estancia San Miguel section, respectively. These water bodies developed along a coastal plain in the northern Patagonia probably during the Paleocene, in a phase of the extensive first transgressive event of the South Atlantic. The earliest record of Pseudopediastrum brevicorne for Patagonia is presented. KEYWORDS. Organic-walled algae. Palaeoecology. Fresh/brackish water. Maastrichtian–?Paleocene. Patagonia Resumen. ANTIGUOS AMBIENTES COSTEROS EN UNA LINEA DE COSTA ATLANTICA DEL MAASTRICHTIANO– ?PALEOCENO: UN ENFOQUE DESDE EL FITOPLANCTON. En esta contribucion se presentan asociaciones planctonicas, incluyendo sus aspectos taxonomicos y atributos paleoecologicos, de la Formacion La Colonia, Patagonia, Argentina. Las muestras palinologicas estudiadas provienen de la seccion expuesta en Estancia San Miguel, area de Telsen, provincia de Chubut. Se documentan diversos elementos de pared organica de taxones de Chlorophyta y Charophyta. Estos incluyen cenobios de dos especies de Pseudopediastrum , colonias de Botryococcus y cigosporas del morfogenero Ovoidites (similares a cigosporas de generos actuales de Zygnemataceae). Las algas verdes junto a los quistes de dinoflagelados (presentados en un detallado estudio previo) indican condiciones depositacionales de agua salobre a dulce para la parte media y de agua dulce para la parte superior de la seccion Estancia San Miguel. Estos cuerpos de agua se desarrollaron a lo largo de una planicie costera en el norte de Patagonia, posiblemente durante el Paleoceno, en una fase del extensivo primer evento transgresivo del Atlantico Sud. Se presenta el registro mas temprano de Pseudopediastrum brevicorne para Patagonia. PALABRAS CLAVE. Algas de pared organica. Paleoecologia. Agua dulce/salobre. Maastrichtiano–?Paleoceno. Patagonia