Radiolarian abundance of sediment core Y8

A high-resolution record of radiolarian faunal changes from Site Y8 south of the Subtropical Front (STF), offshore eastern New Zealand, provides insight into the paleoceanographic history of the last 265 kyrs. Quantitative analysis of radiolarian paleotemperature indicators and radiolarian-based sea surface temperature (SST) estimates reveal distinct shifts during glacial-interglacial (G-I) climate cycles encompassing marine isotope stages (MIS) 8-1. Faunas at Site Y8 are abundant and diverse and consist of a mixture of species typical of the subantarctic, transitional and subtropical zones which is characteristic of subantarctic waters just south of the STF. During interglacials, diverse radiolarian faunas have increased numbers of warm-water taxa (not, vert, similar 15%) while cool-water taxa decrease to not, vert, similar 11% of the assemblage. Warmest climate conditions occurred during MIS 5.5 and the early Holocene Climatic Optimum (HCO) at the onset of MIS 1 where SSTs reach maxima of 12.8 and 12.9 °C, respectively. This suggests that temperatures during the HCO were comparable to the Eemian, one of the warmest interglacial intervals of the Late Quaternary. Glacials are characterized by less diverse radiolarian faunas with cool-water taxa increasing to 49% of the assemblage. Coolest climate conditions occurred in MIS 4 and 2 where SSTs are reduced to 5.4 °C and 4.3 °C, respectively. Radiolarian faunal changes and SST estimates clearly identify major water masses and oceanic fronts in the offshore eastern New Zealand area. During warmest MIS 5.5 and early MIS 1 substantial influence of northern-sourced Subtropical Surface Water (STW) is evident at Site Y8. This implies southward incursions of STW around the eastern crest of Chatham Rise with the STF displaced towards higher latitudes and spinning off eddies as far south as Campbell Plateau. Additionally, increased flow of the Southland Current (SC) might have enhanced the local occurrence of warm-water radiolarians derived from the subtropical Tasman Sea. Coolest glacials are marked by a strong inflow of cool, southern-sourced waters at Site Y8 indicating a more vigorous flow along the Subantarctic Front (SAF).

Distribution of diatom species as abundance estimates from vertical multinet hauls from 150 m water depth in the Indian Ocean

During the Indian Ocean Expedition of R/V METEOR phytoplankton samples were taken with a multiple closing net (Multinet) at 103 stations. In this material the diatoms were investigated. In all 247 taxa could be identified which belong to 242 species and 5 varieties of formae of 80 genera. Of these 1 variety, 15 pecies, and 3 genera are newly described. New combinations were made for 18 species, and a number of old combinations was reinstated.

The seasonal sea-ice zone in the glacial Southern Ocean as a carbon sink, supplementary datasets

Reduced surface-deep ocean exchange and enhanced nutrient consumption by phytoplankton in the Southern Ocean have been linked to lower glacial atmospheric CO2. However, identification of the biological and physical conditions involved and the related processes remains incomplete. Here we specify Southern Ocean surface-subsurface contrasts using a new tool, the combined oxygen and silicon isotope measurement of diatom and radiolarian opal, in combination with numerical simulations. Our data do not indicate a permanent glacial halocline related to melt water from icebergs. Corroborated by numerical simulations, we find that glacial surface stratification was variable and linked to seasonal sea-ice changes. During glacial spring-summer, the mixed layer was relatively shallow, while deeper mixing occurred during fall-winter, allowing for surface-ocean refueling with nutrients from the deep reservoir, which was potentially richer in nutrients than today. This generated specific carbon and opal export regimes turning the glacial seasonal sea-ice zone into a carbon sink.

(Appendix A) Radiolarian abundance in ODP Hole 202-1241A

A quantitative radiolarian study at Ocean Drilling Program Site 1241 in the eastern tropical Pacific enables us to reconstruct paleoceanographic changes that occurred since the latest middle Miocene. Today, this site is located just under the Eastern Pacific Warm Pool (EPWP). Based on the abundance variations of radiolarian characteristic species which are indicators of upwelling and thermocline changes, it is suggested that three notable changes occurred at 10.6, 9.8, and 4.2 Ma in the region. Four distinct periods of oceanographic conditions bounded by these notable changes were characterized on the basis of the following: (1) stratified seawater (12.0 to 10.6 Ma); (2) a shallowing of the thermocline and an increasing of upwelling (10.6 to 9.8 Ma); (3) significant inflow of warm water to the eastern tropical Pacific caused by an intensified Northern Equatorial Countercurrent (NECC), resulting in the formation of EPWP (9.8 to 4.2 Ma); and (4) the reduction of the EPWP and the NECC, and an increase in upwelling (4.2 to 0 Ma). The timing of these paleoceanographic events indicated the strong relations with the opening and closing of the Indonesian and Central American (Panama) Seaways. The reduction of the EPWP (this study) and the deepening of the thermocline in western Pacific at about 4.2 Ma (Cannariato and Ravelo, 1997; Chaisson and Ravelo, 2000) indicated a change from a state resembling El Niño in the late Miocene and the early Pliocene time to a state resembling La Niña by the late Pliocene

Under-ice fauna, sea-ice concentration, sea-ice thickness and under-ice water parameters from the Eurasian central Arctic Ocean during POLARSTERN cruise ARK-XXVII/3 (PS80) in August-September 2012

Arctic sea-ice decline is expected to have a significant impact on Arctic marine ecosystems. Ice-associated fauna play a key role in this context because they constitute a unique part of Arctic biodiversity and transmit carbon from sea-ice algae into pelagic and benthic food webs. Our study presents the first regional-scale record of under-ice faunal distribution and the environmental characteristics of under-ice habitats throughout the Eurasian Basin. Sampling was conducted with a Surface and Under-Ice Trawl, equipped with a sensor array recording ice thickness and other physical parameters during trawling. We identified 2 environmental regimes, broadly coherent with the Nansen and Amundsen Basins. The Nansen Basin regime was distinguished from the Amundsen Basin regime by heavier sea-ice conditions, higher surface salinities and higher nitrate + nitrite concentrations. We found a diverse (28 species) under-ice community throughout the Eurasian Basin. Change in community structure reflected differences in the relative contribution of abundant species. Copepods (Calanus hyperboreus and C. glacialis) dominated in the Nansen Basin regime. In the Amundsen Basin regime, amphipods (Apherusa glacialis, Themisto libellula) dominated. Polar cod Boreogadus saida was present throughout the sampling area. Abrupt changes from a dominance of ice-associated amphipods at ice-covered stations to a dominance of pelagic amphipods (T. libellula) at nearby ice-free stations emphasised the decisive influence of sea ice on small-scale patterns in the surface-layer community. The observed response in community composition to different environmental regimes indicates potential long-term alterations in Arctic marine ecosystems as the Arctic Ocean continues to change.

(Table T3) Distribution of radiolarian taxa in sediments of ODP Leg 180 sites

Cores from the 11 sites drilled during Leg 180 showed radiolarian assemblages that appear only in the Quaternary sediments. The most diverse and well-preserved assemblages were found in hemipelagic sediments from Holes 1108A, 1110A, and 1115B.

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.

(Table T1) Abundance of radiolarian skeletons in scrape samples of ODP Hole 178-1098B

Palmer Deep is a series of three glacially overdeepened basins on the Antarctic Peninsula shelf, ~20 km southwest of Anvers Island. Site 1098 (64°51.72'S, 64°12.48'W) was drilled in the shallowest basin, Basin I, at 1012 m water depth. The sediment recovered was primarily laminated, siliceous, biogenic, pelagic muds alternating with siliciclastic hemipelagic sediments (Barker, Camerlenghi, Acton, et al., 1999). Sedimentation rates of 0.1725 cm/yr in the upper 25 m and 0.7-0.80 cm/yr in the lower 25 m of the core have been estimated from 14C (Domack et al., 2001). The oldest datable sediments have an age of ~13 ka and were underlain by diamicton sediments of the last glacial maximum (Domack et al., 2001). The large-scale water-mass distribution and circulation in the vicinity of Palmer Deep is dominated by Circumpolar Deep Water (CDW) below 200 m (Hofmann et al., 1996). Palmer Deep is too far from the coast to be influenced by glacial meltwater and cold-tongue generation associated with it (Domack and Williams, 1990; Dixon and Domack, 1991). Circulation patterns in the Palmer Deep area are not well understood, but evidence suggests southward flow across Palmer Deep from Anvers Island to Renaud Island (Kock and Stein, 1978). The water south of Anvers Island is nearly open with loose pack ice from February through May. The area is covered with sea ice beginning in June (Gloersen et al., 1992; Leventer et al., 1996). Micropaleontologic data from the work of Leventer et al. (1996) on a 9-m piston core has revealed circulation and climate patterns for the past 3700 yr in the Palmer Deep. The benthic foraminifer assemblage is dominated by two taxa, Bulimina aculeata and Bolivina pseudopunctata, which are inversely related. High relative abundances of B. aculeata occur cyclically over a period of ~230 yr. The assemblage associated with high abundance of B. aculeata in Palmer Deep resembles that from the Bellingshausen shelf, which is associated with CDW. In addition to the faunal evidence, hydrographic data indicate incursions of CDW into Palmer Deep (Leventer et al., 1996). A distinctive diatom assemblage dominated by a single genus was associated with peaks in B. aculeata, whereas a few different assemblages were associated with lows in B. aculeata. Leventer et al. (1996) interpreted the variability in diatom assemblages as an indication of changes in productivity associated with changes in water column stability. Abelmann and Gowing (1997) studied the horizontal and vertical distributions of radiolarians in the Atlantic sector of the Southern Ocean. They show that the spatial distribution of radiolarian assemblages reflects hydrographic boundaries. In a transect from the subtropical Atlantic to polar Antarctic zones, radiolarians in the upper 1000 m of the water column occurred in distinct surface and deep-living assemblages related to water depth, temperature, salinity, and nutrient content. Living assemblages resembled those preserved in underlying surface sediments (Abelmann and Gowing, 1997). Circumantarctic coastal sediments from neritic environments contained a distinctive assemblage dominated by the Phormacantha hystrix/Plectacantha oikiskos group and Rhizoplegma boreale (Nishimura et al., 1997). Low diversity and species compositions distinguished the coastal sediments from the typical pelagic Antarctic assemblages. Factors that controlled the assemblages were water depth, proximity to the coast, occurrence of sea ice, and steepness of topography, rather than temperature and salinity. Nishimura et al. (1997) found a gradient of sorts from deep-water sites containing diverse assemblages typical of pelagic environments to coastal sites with low diversity assemblages dominated by P. hystrix/P. oikiskos group and R. boreale. In general, sites between these two extremes had increased proportions of the coastal assemblage with decreasing water depth (Nishimura et al., 1997). At a site near Hole 1098 (GC905), they showed that the relative abundance of the coastal assemblage increased downcore (Nishimura et al., 1997). The purpose of the research presented here was to make a cursory investigation into the radiolarian assemblages as possible paleoenvironmental indicators.