Open Marine Waters Research Articles

Return to the Ross Ice Shelf Project (RISP), Site J-9 (1977–1979): perspectives of West Antarctic Ice Sheet history from Miocene and Holocene benthic foraminifera

Abstract. In 1977–1978 and 1978–1979, the Ross Ice Shelf Project (RISP) recovered sediments from beneath the largest ice shelf in Antarctica at Site J-9 (∼82° S, 168° W), ∼450 km from open marine waters at the calving front of the Ross Ice Shelf and 890 km from the South Pole, one of the southernmost sites for marine sediment recovery in Antarctica. One important finding was the discovery of an active macrofauna, including crustaceans and fish, sustained below the ice shelf far from open waters. The sediment has a thin, unconsolidated upper unit (up to 20 cm thick) and a texturally similar but compacted lower unit (>1 m thick) containing reworked early, middle, and late Miocene diatom and calcareous benthic foraminiferal assemblages. A probable post-Last Glacial Maximum (LGM) disconformity separates the upper unit containing a dominantly agglutinated foraminiferal assemblage, from the lower unit consisting mostly of reworked Miocene calcareous benthic species, including Trifarina fluens, Elphidium magellanicum, Globocassidulina subglobosa, Gyroidina sp., and Nonionella spp. The presence of the polar planktic foraminiferal species Neogloboquadrina pachyderma and the endemic Antarcticella antarctica supports the late Miocene diatom age for the matrix of the lower unit. The microfossil assemblages indicate periods of ice sheet collapse and open-water conditions south of Site J-9 during warm intervals of the early, middle, and late Miocene, including the Miocene Climatic Optimum (∼17–14.7 Ma), demonstrating the dynamic nature of the West Antarctic Ice Sheet (WAIS) and Ross Ice Shelf during the Neogene. The foraminiferal assemblage of the upper unit is unique to the Ross Sea and suggests the influence of a sub-ice-shelf water mass proximal to the retreating post-LGM grounding zone. This unique assemblage is strongly dominated by the bathyal, cold-water agglutinated genus Cyclammina.

Prvi opis proizvodnje piva pomoću morskih kvasaca

Most of the yeast species we encounter daily are terrestrial, but they are also found in the marine environment. Marine yeasts occur in estuaries, coastal and open marine waters, sediments, and as epi- and endobionts of various marine organisms. This study focuses on the fermentation capabilities of marine yeasts isolated from the central Adriatic Sea for use in the brewing process. Sampling was performed at a sea temperature of 12°C to avoid collecting yeasts introduced into the marine environment by human activities. Four nutrient media designed for yeast isolation and growth were used to isolate yeasts from the marine samples: Yeast Malt Agar (YM), Yeast Malt Agar with antibiotics, acidified Yeast Malt Agar, and Sabouraud Dextrose Agar. Sixteen yeast colonies were successfully isolated, and only three were positive in the fermentationtest and were further determined to species level. Of the three species identified as capable of fermentation, Candida famata completely fermented the wort and produced a beer. Candida pelliculosa fermented slowly over an extended period and did not produce a usable beer, while Candida sake did not ferment the wort at all. To our knowledge, this is the first time that marine yeast isolates have been used experimentally for beer fermentation, indicating potential for use as nonconventionalyeasts in brewing and beer production. Further investigations should include professional standard fermentation, aroma and genetic studies.

A fjord with a land-terminating glacier: Meltwater, bio-optics, particulate matter, nutrients, phytoplankton species, and primary production in west Greenland

Land-terminating glaciers and submarine melting of marine-terminating glaciers are significant features in Arctic regions and are foreseen to become more frequent as marine-terminating glaciers ultimately develop into a land-terminated state. A transition driven by the continuous rise in Arctic air temperatures, and emphasizes the importance of studies of land-terminating glaciers their bio-optical properties and biogeochemistry. Kangerlussuaq in west Greenland with a land-terminating glaciers and was selected for this study. During a research cruise we measured spectral and PAR attenuation, particulate matter concentrations, salinity, nutrient concentrations, Chla, and phytoplankton species composition, along a transect from river outlet to open marine waters. Results showed that surface waters in Kangerlussuaq were strongly influenced by meltwater with low salinities, high particulate matter concentrations, high PAR and spectral light attenuation coefficients, and low nutrient concentrations. Spectral composition was also affected by the particulate matter. PAR photic depths varied between 4 and 9 m dependent on particulate matter concentrations. There was a decrease with distance from outlet in silicate concentrations, and opposite for phosphate, which increased significantly from river outlet to the marine. Phytoplankton species number (42) and diversity were high at the marine station but low (3) in turbid waters dominated by the diatom Skeletonema costatum in high numbers. A meltwater plume covered about 50 % of the Kangerlussuaq at average discharges in early August. Primary production was quantified with a simple model based on light attenuation coefficients, and showed a near exponential decrease in production with increase in attenuation.

The Mixoplankton Database (MDB): Diversity of photo-phago-trophic plankton in form, function, and distribution across the global ocean.

Protist plankton are major members of open-water marine food webs. Traditionally divided between phototrophic phytoplankton and phagotrophic zooplankton, recent research shows many actually combine phototrophy and phagotrophy in the one cell; these protists are the "mixoplankton." Under the mixoplankton paradigm, "phytoplankton" are incapable of phagotrophy (diatoms being exemplars), while "zooplankton" are incapable of phototrophy. This revision restructures marine food webs, from regional to global levels. Here, we present the first comprehensive database of marine mixoplankton, bringing together extant knowledge of the identity, allometry, physiology, and trophic interactivity of these organisms. This mixoplankton database (MDB) will aid researchers that confront difficulties in characterizing life traits of protist plankton, and it will benefit modelers needing to better appreciate ecology of these organisms with their complex functional and allometric predator-prey interactions. The MDB also identifies knowledge gaps, including the need to better understand, for different mixoplankton functional types, sources of nutrition (use of nitrate, prey types, and nutritional states), and to obtain vital rates (e.g. growth, photosynthesis, ingestion, factors affecting photo' vs. phago' -trophy). It is now possible to revisit and re-classify protistan "phytoplankton" and "zooplankton" in extant databases of plankton life forms so as to clarify their roles in marine ecosystems.

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Commercial fish catch in the Iraqi marine waters from December 2018 to December 2019 was investigated. The study is based on three stations: the first station is located at the Shatt Al-Arab estuary, the second represents the area between the Shatt Al-Arab Estuary and open marine waters, and the third is associated with the Iraqi territorial marine waters. The total weight of the catch was 1881 kg, represented by 500, 654, and 727 kg in the first, second and third stations respectively. The third station was the highest with a majority of the family Sciaenidae by 464 kg, while the lowest was the family Scombridae by 0.5 kg. The total number of species included 37 species, belonging to 27 genera, 19 families, and 6 orders, the largest order represented by a high number of species was the Perciformes and the lowest versatile orders were Oreclotiformes, Nemipterideaformes and Scombridaeformes; while the order Scorpaeniformes was found by only one species.

Low-latitude ?upper Barremian–lower Aptian palynoflora and paleovegetation of the Biyadh Formation (Arabian Plate, eastern margin of northern Gondwana): evidence for a possible cold snap

A palynological analysis of core and cuttings samples from successions assigned to the Biyadh Formation of Saudi Arabia in the Arabian Gulf (eastern margin of northern Gondwana) revealed diverse and well-preserved palynological assemblages including bryophyte and fern spores, gymnosperm and flowering plant pollen, dinocysts, and acritarchs. Palynological data corroborates earlier geological and stratigraphic models, indicating a ?late Barremianearly Aptian age. The fluctuations of dinocyst abundance and diversity proved extremely useful to detect fine-scale sea-level changes in carbonate platforms with episodic terrigenous inputs. In agreement with current understanding of dinocyst paleoenvironmental distribution trends, Cribroperidinium and Aptea? vannophora are restricted to inner neritic/?fluvial-influenced settings, while Spiniferites and Trichodinium have been confirmed as more open marine water (middle/outer neritic) indicators. The composition of the terrestrial assemblages is dominated by fluvially-transported spores, mainly released by ferns and probable tree ferns. The overall floral composition is considered to reflect a seasonal, humid, climate punctuated by episodic droughts. Recurrent increases in abundance of wind-pollinated cheirolepid and Araucariaceae pollen, observed in assemblages otherwise characterized by low dinocyst content, are interpreted to represent sea-level falls and basinward expansion/migration of conifer-dominated coastal vegetation. The abundance of the dinocysts Cepadinium variabilis and Pseudoceratium nohrhansenii sp. nov., previously recorded at higher latitudes, is interpreted to reflect the invasion of cooler/colder water masses, confirming a significant ?latest Barremian/early Aptian global cold episode, possibly related to the OAE1a event. The following new dinocyst taxa are described: Pseudoceratium nohrhansenii sp. nov. and Protobatioladium alhajrii sp. nov.

Comment on Strauss et al., 2020: Subsidence analysis of salt tectonics‐driven minibasins (Northern Calcareous Alps, Austria)

Comment on Strauss et al., 2020: Subsidence analysis of salt tectonics‐driven minibasins (Northern Calcareous Alps, Austria)

Mineralogy and geochemistry of the Late Triassic Baluti Formation, Northern Iraq

The petrography and geochemistry of clastic rocks collected from two sections from the Baluti Formation northern Iraq, have been investigated to infer the depositional environment of the Late Triassic Baluti Formation. Petrographic study of the carbonate unit shows that they consist mainly of heterogeneous poorly sorted grainstones and packstones, ooids, intraclasts, peloids, bioclasts and green algae (Halimeda). The abundant and heterogeneous size of these constituents suggests a subtidal lagoon/oolitic shoal depositional environment with an open marine water circulation. Trace element concentrations of the shales and marlstones reveal a wide difference in the depositional environment. The paleoclimate proxies (C-value, Sr/Cu, Rb/Sr, Ga/Rb, and Sr/Ba ratios) and presence of illite suggest a hot and arid to semiarid climates during the deposition of the Buluti sediments, which coincide with the Late Triassic global warming. The combined use of the Cd/Mo and Co*Mn proxies indicate the deposition mainly in open marine settings on the continental margin associated with upwelling and subordinate restricted marine settings. Trace element redox proxies (V/(V + Ni), Th/U, V/Cr, Ni/Co, and V/Ni ratios indicates anoxic to dysoxic to marginally oxic marine conditions. This difference in paleoredox conditions is likely to arise from the variation in the hydrographic conditions of the depositional basin including water depth, upwelling oxidation degree in the water column and salinity.

Biostratigraphy and paleoenvironment of Maastrichtian foraminiferal assemblages from a succession located NW of Tuxtla Gutiérrez, Chiapas (SE Mexico)

During the Maastrichtian, two lithostratigraphic units were deposited in the central Chiapas region; the Ocozocoautla and Angostura formations. The first unit crops out northwest of the city of Tuxtla Gutiérrez in central Chiapas. It is a complex lithological unit mainly composed of siliciclastic rocks interbedded with limestone. Overlying it, the Angostura limestone is recognized. This study focuses on a taxonomic study of the larger benthic and planktic foraminifera from both formations in order to assign age and to infer the paleoenviroment.
 The Ocozocoautla Formation includes an association of benthic as well as significant planktic foraminifera. Based on the microfossils stratigraphic distribution, two biozones were defined: the Pseudorbitoides rutteni–Ayalaina rutteni Assemblage Zone of earliest Maastrichtian and the upper part of the Gansserina gansseri Interval Zone of early Maastrichtian.
 The Angostura Formation contains dasycladacean algae and larger foraminifera considered as important age markers in shallow-water environments. Two foraminiferal interval zones were defined, Praechubbina breviclaustra Interval Zone of early late Maastrichtian and Chubbina jamaicensis Total Range Zone of late to latest Maastrichian age.
 The microfacies (grainstone, wackestone–packstone, wackestone) as well as the foraminiferal assemblage enable the paleoenvironment to be reconstructed, suggesting a deposit that developed in an open-water marine setting with moderate to high energy, characterized by benthic and planktic foraminifera in the Ocozocoautla Formation, while in the Angostura Formation a shallow-water marine protected environment is inferred.
 The paleobiogeographical distribution of the assemblage from both the Ocozocoautla and Angostura formations mostly contains endemic benthic foraminifera of the Caribbean Province and other few Tethysian forms of the Angostura Formation.

Two versions of short-term phytoplankton ecophysiology and taxonomic assemblages in the Arctic Ocean’s North Water (Canada, Greenland)

Abstract Photosynthetic performance in open marine waters is determined by how well phytoplankton species are adapted to their immediate environment and available light. Although there is light for 24 h a day during the Arctic summer, little is known about short-term (h) temporal variability of phytoplankton photosynthetic performance in Arctic waters. To address this, we sampled the North Water (76.5°N) every 4 h over 24 h at two stations on the East and West sides that are influenced by different water masses and current conditions. We specifically investigated phytoplankton pigments, the xanthophyll cycle (XC), which is an indication of photoprotective capacity, and photosynthesis–irradiance (PE) response curves, at the surface and 20 m depth. The photophysiological parameters on the two sides differed along with the taxonomic signal derived from accessory pigments. On both sides, surface XC pigments showed high photoprotection capacity with the dinodinoxanthin–diatoxanthin (DD) and the violaxanthin, antheraxanthin and zeaxanthin cycles correlated with incoming radiation. The PE results showed that communities dominated by small flagellates on the western side performed better compared to diatom dominated communities on the eastern side. We conclude that phytoplankton and photosynthetic capacity differed consistent with known hydrography, with implications for a changing Arctic.

The sedimentology and sequence stratigraphy of contourites and associated rocks at the northeastern passive margin of Gondwana during the Early Triassic (Induan - Mirga Mir Formation), Iraqi Kurdistan

Contourite deposits are recognized for the first time from the Lower Triassic Mirga Mir Formation in the Kurdistan region, Northern Iraq. The formation represents deposition on the southern passive margin of the Neo-Tethys during its early opening stages. The contourites are characterized by lenticular and sorted siltstones to fine-grained sandstones with current ripples, cross beddings and scour surfaces. These current structures are associated with thin-bedded (5–20 cm) limestones and shales. Petrographic investigations of the associated carbonate successions show both skeletal and non-skeletal grains such as peloids, ooids, intraclasts and extraclasts. Deposition occurred in a ramp setting at the southern passive margin of the Neo-Tethys and the skeletal grains reveal deep open marine and shallow warm water. Four different facies associations are recognized: Offshoal/basinal, foreshoal/slope, shoal and back shoal/lagoon. Field observations and thin section analysis revealed four main contourite facies in the studied outcrops, namely muddy contourites, silty contourites, sandy contourites and calcareous sandy contourites. The contourites are integrated with the basinal, offshoal, foreshoal and slope deposits. Stable isotope data from the carbonates of Mirga Mir Formation show that the δ18O (‰) values are negatives but the δ13C data shows negative and positive values. They show that had underwent meteoric diagenesis and that the δ13C values still preserving their primary depositional signal. The carbon isotopes data conforms to available data from the surrounding countries and by comparison with Early Triassic δ13C stratigraphic trends, it had captured at least two of the well-known positive spikes and at least one of the negative dips. Sequence stratigraphic analysis and stacking patterns revealed that the Mirga Mir Formation can be divided into two third-order depositional sequences. Each sequence is characterized by TST deposits followed by HST deposits and without LST.

Insights on aquatic microbiome of the Indian Sundarbans mangrove areas.

Anthropogenic perturbations have strong impact on water quality and ecological health of mangrove areas of Indian Sundarbans. Diversity in microbial community composition is important causes for maintaining the health of the mangrove ecosystem. However, microbial communities of estuarine water in Indian Sundarbans mangrove areas and environmental determinants that contribute to those communities were seldom studied. Nevertheless, this study attempted first to report bacterial and archaeal communities simultaneously in the water from Matla River and Thakuran River of Maipith coastal areas more accurately using 16S rRNA gene-based amplicon approaches. Attempt also been made to assess the capability of the environmental parameters for explaining the variation in microbial community composition. Our investigation indicates the dominancy of halophilic marine bacteria from families Flavobacteriaceae and OM1 clade in the water with lower nutrient load collected from costal regions of a small Island of Sundarban Mangroves (ISM). At higher eutrophic conditions, changes in bacterial communities in Open Marine Water (OMW) were detected, where some of the marine hydrocarbons degrading bacteria under families Oceanospirillaceae and Spongiibacteraceae were dominated. While most abundant bacterial family Rhodobacteracea almost equally (18% of the total community) dominated in both sites. Minor variation in the composition of archaeal community was also observed between OMW and ISM. Redundancy analysis indicates a combination of total nitrogen and dissolved inorganic nutrients for OMW and for ISM, salinity and total nitrogen was responsible for explaining the changes in their respective microbial community composition. Our study contributes the first conclusive overview on how do multiple environmental/anthropogenic stressors (salinity, pollution, eutrophication, land-use) affect the Sundarban estuary water and consequently the microbial communities in concert. However, systematic approaches with more samples for evaluating the effect of environmental pollutions on mangrove microbial communities are recommended.

Surface vector fields estimation using soft computing and remote sensing data at an open water marine renewable test site

Galway Bay has one of the world’s few open water marine renewable test sites and so is of national and international interest. A high frequency radar system has been deployed in Galway Bay area to monitor near real time surface currents and waves since July 2011. In this research, a soft computing approach was applied to estimate surface vector fields using the observed radar data. Results indicate that soft computing is a novel and promising method to estimate surface vector fields. It provides a potential way to obtain useful information of coastal water body for marine renewable energy development and assessment.

Organic iron complexes enhance iron transport capacity along estuarine salinity gradients of Baltic estuaries

Abstract. Rivers discharge a notable amount of dissolved Fe (1.5×109 mol yr−1) to coastal waters but are still not considered important sources of bioavailable Fe to open marine waters. The reason is that the vast majority of particular and dissolved riverine Fe is considered to be lost to the sediment due to aggregation during estuarine mixing. Recently, however, several studies demonstrated relatively high stability of riverine Fe to salinity-induced aggregation, and it has been proposed that organically complexed Fe (Fe-OM) can “survive” the salinity gradient, while Fe (oxy)hydroxides are more prone to aggregation and selectively removed. In this study, we directly identified, by X-ray absorption spectroscopy, the occurrence of these two Fe phases across eight boreal rivers draining into the Baltic Sea and confirmed a significant but variable contribution of Fe-OM in relation to Fe (oxy)hydroxides among river mouths. We further found that Fe-OM was more prevalent at high flow conditions in spring than at low flow conditions during autumn and that Fe-OM was more dominant upstream in a catchment than at the river mouth. The stability of Fe to increasing salinity, as assessed by artificial mixing experiments, correlated well to the relative contribution of Fe-OM, confirming that organic complexes promote Fe transport capacity. This study suggests that boreal rivers may provide significant amounts of potentially bioavailable Fe beyond the estuary, due to organic matter complexes.

Llandovery (lower Silurian) nodular barite from the northern margin of Yangtze Block, South China, and its paleoceanographic implications

The Llandovery epoch (Early Silurian) was marked by the interruption of widespread oceanic anoxia and associated oxygenation of seawater. The first oxygenation event appears to occur near the Rhuddanian–Aeronian stages boundary. However, ventilation of the marine environments is a dynamic process, differing in timing and magnitude from place to place, basic variations in the nature of marine circulation; e.g., open shelf versus restricted shelf. The correlation of oxygenation events from open to restricted shelf environments is of significance to enhancing our understanding of marine ventilation processes. Here, we describle nodular barite that accumulated in the open marine environment near the boundary at the northern margin of the Yangtze Block, South China, emphasizing its origin and environmental implications. Petrographic evidence suggests that the nodular barite is early diagenetic. Barium was likely derived from the dissolution of biogenic barite as suggested by the 87Sr/86Sr values of the diagenetic barite. The REE + Y pattern, low Y/Ho and high Ce*/Ce values of the barite nodules demonstrate that microbial degradation of organic matter in association with Ce oxidation controlled REE composition of the nodules. PAAS-normalized positive Eu anomalies of the studied barite, however, suggest an anoxic porewater environment perhaps related to bacterial sulfate reduction or the anaerobic oxidation of methane focused within the sulfate-methane transition zone (SMTZ) as also indicated by the minor contribution of radiogenic terrigenous Sr isotopes. We infer that high marine productivity and the associated transport of biogenic barite to the sea floor was critical to the formation of the studied barite nodules. Diagenetic barite formation and preservation in Aeronian stage deposits may indicate that circulation of open marine water masses had been much ameliorated. Our results are consistent with earlier suggestions that the restricted shelf experienced a transition from anoxic or even euxinic conditions to a more oxygenated (probably suboxic) condition during the early Aeronian. The approximately contemporaneous nature of this transition and global cooling associated with the glacial pulses indicate the critical role that global climate change near the Rhuddanian–Aeronian (R-A) boundary played in the redox evolution of the Yangtze Block, South China.

The smallest recorded specimen of Xiphactinus audax from the Niobrara Chalk of Kansas and its implications for juvenile ichthyodectid ecology

ABSTRACT Juvenile specimens of Xiphactinus audax are rarely preserved in the fossil record and are typically represented by disarticulated cranial elements. Here we report the smallest specimen of Xiphactinus to date, consisting of the left and right dentaries and the right preoperculum. Based on the size of the new specimen and the rarity of small ichthyodectids in the Niobrara Chalk, it is interpreted as a juvenile. We suggest that the early life of Xiphactinus was spent in shallow margins of seaways for protection and to utilize rich food resources, and they were rare in open marine water. Today, juvenile predatory large-bodied fish are rare in open-water sediments, but shallow, nearshore deposits are lacking from the Western Interior Seaway, providing a complicating bias. The teeth of this juvenile X. audax specimen indicate that the diet did not notably change during growth and that even the small specimens would have been piscivorous predators. This is typical of large-bodied predatory fish such as tarpon that utilize estuaries and other shallow environs to mitigate juvenile mortality and do not change their diets much throughout ontogeny. This use of nearshore environments could explain why our Xiphactinus is so small and why such small specimens are rare.

Non-reversible and Reversible Heat Tolerance Plasticity in Tropical Intertidal Animals: Responding to Habitat Temperature Heterogeneity.

The theory for thermal plasticity of tropical ectotherms has centered on terrestrial and open-water marine animals which experience reduced variation in diurnal and seasonal temperatures, conditions constraining plasticity selection. Tropical marine intertidal animals, however, experience complex habitat thermal heterogeneity, circumstances encouraging thermal plasticity selection. Using the tropical rocky-intertidal gastropod, Echinolittorina malaccana, we investigated heat tolerance plasticity in terms of laboratory acclimation and natural acclimatization of populations from thermally-dissimilar nearby shorelines. Laboratory treatments yielded similar capacities of snails from either population to acclimate their lethal thermal limit (LT50 variation was ∼2°C). However, the populations differed in the temperature range over which acclimatory adjustments could be made; LT50 plasticity occurred over a higher temperature range in the warm-shore snails compared to the cool-shore snails, giving an overall acclimation capacity for the populations combined of 2.9°C. In addition to confirming significant heat tolerance plasticity in tropical intertidal animals, these findings reveal two plasticity forms, reversible (laboratory acclimation) and non-reversible (population or shoreline specific) plasticity. The plasticity forms should account for different spatiotemporal scales of the environmental temperature variation; reversible plasticity for daily and tidal variations in microhabitat temperature and non-reversible plasticity for lifelong, shoreline temperature conditions. Non-reversible heat tolerance plasticity, likely established after larvae settle on the shore, should be energetically beneficial in preventing heat shock protein overexpression, but also should facilitate widespread colonization of coasts that support thermally-diverse shorelines. This first demonstration of different plasticity forms in benthic intertidal animals supports the hypothesis that habitat heterogeneity (irrespective of latitude) drives thermal plasticity selection. It further suggests that studies not making reference to different spatial scales of thermal heterogeneity, nor seeking how these may drive different thermal plasticity forms, risk misinterpreting ectothermic responses to environmental warming.

Precession and atmospheric CO2 modulated variability of sea ice in the central Okhotsk Sea since 130,000 years ago

Recent reduction in high-latitude sea ice extent demonstrates that sea ice is highly sensitive to external and internal radiative forcings. In order to better understand sea ice system responses to external orbital forcing and internal oscillations on orbital timescales, here we reconstruct changes in sea ice extent and summer sea surface temperature (SSST) over the past 130,000 yrs in the central Okhotsk Sea. We applied novel organic geochemical proxies of sea ice (IP25), SSST (TEXL86) and open water marine productivity (a tri-unsaturated highly branched isoprenoid and biogenic opal) to marine sediment core MD01-2414 (53°11.77′N, 149°34.80′E, water depth 1123 m). To complement the proxy data, we also carried out transient Earth system model simulations and sensitivity tests to identify contributions of different climatic forcing factors. Our results show that the central Okhotsk Sea was ice-free during Marine Isotope Stage (MIS) 5e and the early-mid Holocene, but experienced variable sea ice cover during MIS 2–4, consistent with intervals of relatively high and low SSST, respectively. Our data also show that the sea ice extent was governed by precession-dominated insolation changes during intervals of atmospheric CO2 concentrations ranging from 190 to 260 ppm. However, the proxy record and the model simulation data show that the central Okhotsk Sea was near ice-free regardless of insolation forcing throughout the penultimate interglacial, and during the Holocene, when atmospheric CO2 was above ∼260 ppm. Past sea ice conditions in the central Okhotsk Sea were therefore strongly modulated by both orbital-driven insolation and CO2-induced radiative forcing during the past glacial/interglacial cycle.

Marine oxygen production and open water supported an active nitrogen cycle during the Marinoan Snowball Earth

The Neoproterozoic Earth was punctuated by two low-latitude Snowball Earth glaciations. Models permit oceans with either total ice cover or substantial areas of open water. Total ice cover would make an anoxic ocean likely, and would be a formidable barrier to biologic survival. However, there are no direct data constraining either the redox state of the ocean or marine biological productivity during the glacials. Here we present iron-speciation, redox-sensitive trace element, and nitrogen isotope data from a Neoproterozoic (Marinoan) glacial episode. Iron-speciation indicates deeper waters were anoxic and Fe-rich, while trace element concentrations indicate surface waters were in contact with an oxygenated atmosphere. Furthermore, synglacial sedimentary nitrogen is isotopically heavier than the modern atmosphere, requiring a biologic cycle with nitrogen fixation, nitrification and denitrification. Our results indicate significant regions of open marine water and active biologic productivity throughout one of the harshest glaciations in Earth history.

Transfer of lipid molecules and polycyclic aromatic hydrocarbons to open marine waters by dense water cascading events

Settling particles were collected by a set of moored sediment traps deployed during one year in the western Gulf of Lion along Cap de Creus and Lacaze-Duthiers submarine canyons and on the adjacent southern open slope. These traps collected particles during periods of pelagic settling and also during events of deep water flushing by dense shelf water cascading (DSWC). Analyses of lipid biomarkers (n-alkanes, n-alkan-1-ols, sterols and C37-C38 alkenones) and polycyclic aromatic hydrocarbons (PAHs) showed much higher transfer of terrestrial lipids and PAHs to open deep waters during DSWC than in the absence of cascading. The area of highest lateral fluxes was mostly located at 1000m depth but also at 1500m depth and extended along the canyons and to the adjacent slope. Higher fluxes were observed near the bottom (30m above bottom; mab) than at intermediate waters (500 mab) which is consistent with the formation and sinking of dense water over the continental shelf, and its transport through the canyons towards the continental slope and deep basin. DSWC involved the highest settling fluxes of terrestrial lipids and PAHs ever described in marine continental slopes and the pelagic domain, as illustrated by peak values of C23-C33 odd carbon numbered alkanes (405ngm−2d−1), C22-C32 even carbon numbered alkan-1-ols (850ngm−2d−1), β-sitosterol+sitostanol (4800ngm−2d−1) and PAHs (55µgm−2d−1). The algal lipids also showed higher transfer to deep waters during DSWC but to a lower extent than the terrigenous compounds. However, the C37-C38 alkenones constituted an exception and their settling fluxes were not influenced by DSWC. The lack of influence of the DSWC on the C37-C38 alkenone settling is consistent with absence of haptophyte algal inputs from the continental shelf and reinforces the reliability of these molecules for palaeothermometry and palaeoproductivity measurements in pelagic systems.