Relative abundance of diatom species in surface samples from the Southern Ocean, Sea ice species

Diatoms from 228 Southern Ocean core-top sediment samples were examined to determine the geographic distributions of 32 major diatom species/taxa preserved in the sediments of three zonally-distinct regions; Sea Ice, Open Ocean and the Tropical/Subtropical. In the first of three papers, 14 species/taxa occurring in the region where sea ice covers the ocean surface on an annual basis are geographically documented. Comparisons are drawn between the diatom abundances on the sea floor, sea ice parameters (annual duration and concentration in February and September) and February sea-surface temperature. Such parameters are commonly used in reconstructing past oceanographic conditions in the Sea Ice and Open Ocean zones. Analysis of the geographic patterns and sea-surface parameter correlations reveals species-specific distributions regulated primarily by sea ice coverage and sea-surface temperature, which support the use of diatom remains for the estimation of these past sea-surface environmental parameters. Comparison with reliable accounts of the 14 species from the sediments or plankton also provides the first glimpses into species-specific ecology and habitat linkages.

Biogenic opal and diatoms in surface sediments of the South Western Atlantic

Based on 66 surface sediment samples collected in the SW Atlantic Ocean between 27 and 50°S, this study presents an overview of the spatial distribution of biogenic opal and diatom concentrations, and diatom assemblages. Biogenic opal has highest values in the deepest, pelagic stations and decreases toward the slope. Diatoms closely follow the spatial trend of opal. Diatom assemblages reflect the present-day dominant hydrographical features. Antarctic diatoms are the main contributors to the preserved diatom community in core top sediments, with coastal planktonic and tropical/subtropical diatoms as secondary components. Dominance of Antarctic diatoms between 35 and 50°S in the pelagic realm mirrors the northward displacement of Antarctic-source water masses, characterized by high nutrient content and low salinity. Northward of ca. 35°S, the highest contribution of tropical/subtropical, pelagic diatoms, typical for nutrient-poor and high salinity waters, matches the main southward path of the Brazil Current. Mixing of Antarctic and tropical waters down up to 45°S is clearly illustrated by the diatom assemblage. Concentrations of biogenic opal and diatoms rather reflect the path of predominant water masses, but are less correlated with surface water productivity in the SW Atlantic.

Flux data of NU2_trap (Table A1)

Flux of bulk components, carbonate- and silicate-bearing skeleton organisms, and the d15N-isotopic signal were investigated on a 1-year time-series sediment trap deployed at the pelagic NU mooring site (Namibia Upwelling, ca. 29°S, 13°E) in the central Benguela System. The flux of bulk components mostly shows bimodal seasonality with major peaks in austral summer and winter, and moderate to low export in austral fall and spring. The calcium carbonate fraction dominates the export of particulates throughout the year, followed by lithogenic and biogenic opal. Planktonic foraminifera and coccolithophorids are major components of the carbonate fraction, while diatoms clearly dominate the biogenic opal fraction. Bulk d15N isotopic composition of particulate matter is positively correlated with the total mass flux during summer and fall, while negatively correlated during winter and spring. Seasonal changes in the intensity of the main oceanographic processes affecting the NU site are inferred from variations in bulk component flux, and in the flux and diversity patterns of individual species or group of species. Influence from the Namaqua (Hondeklip) upwelling cell through offshore migration of chlorophyll filaments is stronger in summer, while the winter flux maximum seems to reflect mainly in situ production, with less influence from the coastal and shelf upwelling areas. On a yearly basis, dominant microorganisms correspond well with the flora and fauna of tropical/subtropical waters, with minor contribution of near-shore organisms. The simultaneous occurrence of species with different ecological affinities mirrors the fact that the mooring site was located in a transitional region with large hydrographic variability over short-time intervals.

Late Holocene diatom abundaces in sediment core HC-11

The study of diatoms in core HC11 collected from the southwestern part of Chukchi Sea, allowed to distinguish 3 diatoms ecological zones, reflecting paleoenvironmental changes during the last 2300 years. The sediment age was based on the sedimentation rates, determined by 210Pb and radiocarbon dating of mollusk shells. The environmental changes of Chukchi Sea revealed by examination of diatoms correlates with global climate changes - the warming of the early and middle Subatlantic and cooling of the late Subatlantic (Little Ice Age). Warming early and middle Subatlantic in the Chukchi Sea was probably stronger than the warming of the late 20th century and was not accompanied by significant changes in sea level.