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Abstract: Recent coccoliths from 74 surface sediment samples recovered from the southeastern Pacific off Chile were examined quantitatively to investigate modern regional gradients of sea surface productivity and temperature. All findings are based on coccolith accumulation rates. Therefore an approach was designed to estimate recent sedimentation rates based on 210Pb and bulk chemistry analyses of the same set of surface samples. Highest total coccolith accumulation rates were found off north-central Chile, where seasonal upwelling takes place. Based on a multiple linear regression between calculated coccolith accumulation rates and World Ocean Atlas derived sea surface temperatures, a calibration model to reconstruct annual average temperatures of the uppermost 75m of the water column is provided. The model was cross-validated and the SST estimates were compared with SST observed and SST estimates based on diatoms and planktonic foraminifera, showing a good correlation. [Copyright &y& Elsevier]

The scanning Electron Microscope (SEM) and the Petrographic Microscope (Light Microscope, LM) are devices which both are used in routine analysis of coccolithophore assemblages, but comparisons and/or combinations of quantitative data from both sources are difficult. In this paper a comparison is made between the results obtained with the Flores and Sierro settling technique (1997) for LM and the Andruleit filtration technique (1996) for SEM, considering their advantages and drawbacks. Twenty-six surface sediment samples from the South Atlantic and Southeast Pacific were studied. All the taxa distinguished were reduced to fourteen groups accounting for 100%. The biogeographical patterns of coccolithophorid species and species groups determined using both techniques are highly comparable, although the trends in relative and absolute numbers are not always identical. In particular, the numbers of coccoliths per gram of sediment are higher in the case of the filtration technique/SEM-technique than for the settling technique/LM technique and an approach is introduced to estimate LM values using SEM counts with a linear regression equation. The results obtained allow different methodologies to be compared for the study of current coccolithophore biogeography. [ABSTRACT FROM AUTHOR]

Abstract Ocean net primary productivity (Npp) is a key component of the marine carbon cycle. Multi-model Npp projections based on a few decades of satellite data show large uncertainties, in particular at low latitudes (30°N−30°S). Calibration of sedimentary proxies with satellite-based Npp estimates allows for the quantitative reconstruction of this variable at longer time-scales. Relative abundance of deep-photic zone coccolithophore species Florisphaera profunda in the fossil record can potentially be used as a quantitative proxy for Npp. However, the robustness of this proxy calibration has been tested in very specific oceanographic settings using surface sediment samples. Here, we use a global dataset of surface sediment (n = 1258) and sediment trap (n = 26) samples with relative abundance data of F. profunda (%) to test the robustness of this proxy as a quantitative indicator of Npp. We study the modern and paleo-ecology of this species and the main factors affecting its latitudinal distribution. Results show that F. profunda % is a strong indicator of Npp at latitudes between 30°N and 30°S, while at higher latitudes temperature-related variables are more important. We develop a global calibration model between satellite Npp estimates and F. profunda for the latitudinal range between 30°N and 30°S, and we apply it to several low-latitude sediment cores with available F. profunda counts covering the Late Glacial Maximum (LGM; 24–19 ka) and the Mid-to-Late Holocene period (MLH; <6 ka). Reconstructed Npp during the LGM is 15% higher than during the MLHdue to the intensification of trade winds that enhanced oceanic upwelling at low latitudes. Highlights • An extensive new modern and fossil global dataset of Florisphaera profunda relative abundances. • F. profunda % show strong correlation to net primary productivity (Npp) only at low latitudes. • Temperature control of F. profunda at high latitudes does not warrant its use as Npp indicator. • F. profunda -Npp calibration allows quantitative reconstruction of past ocean productivity. • Reconstructed Npp at low latitudes is 15% higher during the LGM than the MLH. [ABSTRACT FROM AUTHOR]

The high-latitude Northern Hemisphere is a key region in the global climate balance. Variations in sea-ice extent affect biological productivity, CO 2 exchange and carbon drawdown. Marine proxies indicative of proximity of the ice-marginal zone are therefore essential to understand these processes. Amphimelissa setosa is nowadays a dominant radiolarian species in the Arctic basin and very abundant in the high-latitude North Atlantic. This species, now absent from the North Pacific, has been widely used as a qualitative proxy of modern and past environmental conditions in the high-latitude Northern Hemisphere. Using our new and published data on the distribution of A. setosa in plankton, sediment trap, surface sediment and downcore samples, we provide a quantitative ecological context for the occurrence of this species. We find that the optimal depth and season of A. setosa in the modern North Atlantic and the Chukchi Sea are 160 m and the late boreal summer/early fall (August–October), respectively. A regression model combining environmental variables (temperature, salinity, silicate and chlorophyll- a concentrations, apparent oxygen utilization, sea-ice) at that season and depth, are able to explain 43% of the distribution of this species in surface sediments. Based on these new findings, we conclude that the presence of A. setosa in surface sediments is closely related to high primary production in the proximity of the sea-ice and areas of ice rafting. The onset of this species started at ca. 1.5 Ma in the North Pacific, linked to a gradual cooling, increased silica availability and southward advance of the ice-margins since the Early Pleistocene. Amphimelissa setosa 's decline in this region was likely caused by the development of a quasi-permanent halocline, perennial sea-ice and depletion of silica during marine isotope stage 4. In the high-latitude North Atlantic, the relative abundance of A. setosa appears to be related to cooling and supply of dissolved silica from the continent during ice-rafting events. The comprehensive approach taken in this study suggest that A. setosa is a useful proxy to explore past variations in the ice-cover in the high-latitude Northern Hemisphere. • We discuss modern and fossil significance of the radiolarian Amphimelissa setosa. • A. setosa is a new proxy for near ice-edge conditions. • Onset of A. setosa in the N Pacific (1.5 Ma) linked to sea-ice southward expansion. • Disappearance in the N Pacific (MIS 4) driven by Si deprivation and halocline changes. [ABSTRACT FROM AUTHOR]