Kathy Córdova Rodríguez

Los tardígrados marinos constituyen un componente importante de la meiofauna en ecosistemas bentónicos; sin embargo, su diversidad en el Perú permanece escasamente documentada. El objetivo del presente estudio fue registrar y describir morfológicamente un tardígrado marino juvenil bídáctilo recolectado en sedimentos intermareales de la costa sur del Perú. Las muestras de sedimento fueron obtenidas durante la marea baja en la playa La Francesa, distrito de Quilca, provincia de Camaná, Arequipa, y procesadas mediante técnicas de separación de meiofauna. Los organismos recuperados fueron observados bajo microscopía óptica y documentados fotográficamente para su análisis morfológico. El ejemplar identificado presenta dos garras por extremidad, característica diagnóstica de algunos representantes de la familia Halechiniscidae. Este hallazgo constituye el primer registro en el Perú de un tardígrado marino juvenil bídáctilo y aporta nueva información sobre la diversidad de tardígrados marinos en la costa del Pacífico sudoriental, resaltando la necesidad de realizar estudios adicionales sobre la meiofauna en ambientes intermareales del país.

Palaeoceanographic proxies are essential in reconstructing past climate change and accurate estimates of past conditions require reliable calibrations. The chemical signature of benthic foraminiferal calcite reflects bottom water conditions, but the effects of their microhabitat, biomineralization, metabolism, ontogeny can challenge a straightforward interpretation of past seawater conditions. In this study we compared stable isotopes of oxygen (δ18OBF) and carbon (δ13CBF) values of age-constrained benthic foraminifera from surface sediments of the Southeast Pacific (SEP) with contemporary in-situ water column values for δ18O equilibrium calcite (δ18Oeqcal) and δ13C of dissolved inorganic carbon (δ13CDIC). The ages of benthic foraminifera, based on radiocarbon and oxygen isotope stratigraphy, show a cluster of older surface sediments sites at intermediate water depths off north Chile, likely associated with sediment erosion. Epifaunal benthic foraminifera δ18OBF values reveal a 1:1 relationship with δ18Oeqcal of ambient bottom waters across the region, while infaunal foraminifera show positive δ18OBF-δ18Oeqcal offsets. Epifaunal benthic foraminifera δ13CBF values closely match ambient bottom waters δ13CDIC in most cases. In contrast, infaunal benthic foraminifera show negative δ13CBF-δ13CDIC offset. At sites shallower than 1000 m, both epifaunal and infaunal benthic foraminifera display significant positive δ13CBF-δ13CDIC offsets. This offset is likely attributed to a combination of microbiological processes occurring within the bottom and pore waters under low to intermediate oxygen conditions, influencing the carbonate pool and the inorganic carbon speciation in the SEP. This is not likely a regionally restricted phenomenon and may have broader implications for improving the reliability of δ13C- and δ18O-based proxies in palaeoceanographic studies.

Planktic and benthic foraminiferal iodine (I) to calcium (Ca) molar ratios have been proposed as an exciting new proxy to assess subsurface and bottom water oxygenation in the past. Compared to trace metals, the analysis of iodine in foraminiferal calcite is more challenging, as iodine is volatile in acid solution. Here, we compare previous analyses that use tertiary amine with alternative analyses using tetramethylammonium hydroxide (TMAH) and ammonium hydroxide (NH₄OH) to stabilize iodine in solution. In addition, we assess the effect of sample size and cleaning on planktic and benthic foraminiferal I/Ca. Our stabilization experiments with TMAH and NH₄OH show similar trends as those using tertiary amine, giving relatively low I/Ca ratios for planktic and benthic foraminifera samples from poorly oxygenated waters, and high ratios for well‐oxygenated waters. This suggests that both alternative methods are suitable to stabilize iodine initially dissolved in acid. Samples that contain 5–10 specimens show a wide spread in I/Ca. Samples containing 20 specimens or more show more centered I/Ca values, indicating that a larger sample size is more representative of the average planktic foraminifera community. The impact of cleaning on planktic and benthic foraminifera I/Ca ratios is very similar to Mg/Ca, with the largest effect occurring during the clay removal step. The largest iodine contaminations were recorded at locations characterized by moderate to high organic carbon contents. In those circumstances, we recommend doubling the oxidative cleaning steps (4 instead of 2 repetitions) to ensure that all organic material is removed.