Oceanic Origin Research Articles

Oceanic and terrestrial origin of precipitation over 50 major world river basins: Implications for the occurrence of drought

The terrestrial and oceanic origins of precipitation over 50 major river basins worldwide were investigated for the period 1980–2018. For this purpose, we used a Lagrangian approximation that calculates the humidity that results in precipitation from the entire ocean area (ocean component of the precipitation, PLO) and the entire land area (land component, PLT) as well as the sum of both components (Lagrangian precipitation, PL). PL and its components were highly correlated with precipitation over the basins, where PLT accounted for >50 % of the PL in most of them. This confirmed the importance assigned by previous studies to terrestrial recycling of precipitation and moisture transport within the continents. However, the amount of PLO in almost all North American river basins was highlighted. The assessment of drought conditions through the Standardized Precipitation Index (SPI) at a temporal scale of 1- and 3-months revealed the number of drought episodes that affected each river basin, especially the Amazon, Congo, and Nile, because of the lower number of episodes but higher average severity and duration. A direct relationship between the severity of drought episodes and the respective severity computed on the oceanic and terrestrial SPI series was also found for the majority of basins. This highlights the influence of the severity of the SPI of oceanic origin for most basins in North America. However, for certain basins, we found an inverse relationship between the severity of drought and the associated severity according to the SPI of oceanic or terrestrial origin, thus highlighting the principal drought attribution. Additionally, a copula analysis provided new information that illustrates the estimated conditional probability of drought for each river basin in relation to the occurrence of drought conditions of oceanic or terrestrial origin, which revealed the possible main driver of drought severity in each river basin.

Antimicrobial therapeutics isolated from algal source: retrospect and prospect.

In the last few decades, attention on new natural antimicrobial compounds has arisen due to a change in consumer preferences and the increase in the number of resistant microorganisms. Algae are defined as photosynthetic organisms that demonstrate a wide range of adaptability to adverse environmental conditions like temperature extremes, photo-oxidation, high or low salinity, and osmotic stress. Algae are primarily known to produce large amounts of secondary metabolite against various kinds of pathogenic microbes. Among these algae, micro and microalgae of river, lake, and algae of oceanic origin have been reported to have antimicrobial activity against the bacteria and fungi of pathogenic nature. Various polar and non- polar extracts of micro- and macro algae have been used for the suppression of these pathogenic fungi. Apart from these, certain algal derivatives have also been isolated from these having antibacterial and antifungal potential. Among the bioactive molecules of algae, polysaccharides, sulphated polysaccharides, phyco-cyanobilins polyphenols, lectins, proteins lutein, vitamin E, B12 and K1, peptides, polyunsaturated fatty acids and pigments can be highlighted. In the present review, we will discuss the biological activity of these derived compounds as antifungal/ antibacterial agents and their most promising applications. A brief outline is also given for the prospects of these isolated phytochemicals and using algae as therapeutic in the dietary form. We have also tried to answer whether alga-derived metabolites can serve as potential therapeutics for the treatment of SARS-CoV-2 like viral infections too.

Origin of Moisture for the Precipitation Produced by the Exceptional Winter Storm Formed over the Gulf of Mexico in March 1993

On 12–15 March 1993, a severe winter storm (SC93) formed over the Gulf of Mexico, affecting the Caribbean Islands and the eastern coast of the United States (US) and Canada with a notable amount of precipitation, snow and severe local storms. In this study, we investigate the origin of the precipitation generated by SC93 by applying a widely used Lagrangian moisture source diagnostic method. Our findings revealed that most of the moisture came from the western North Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico. Moreover, the eastern US and Mexico acted as notable terrestrial moisture sources. Overall, the moisture contribution from the oceanic origin was higher than the terrestrial counterpart, and the moisture sources progressively shifted northward as the storm moved. In addition, the moisture uptake mainly occurred in the cyclone–anticyclone interaction region.

Different levels of disturbance influence the distributional patterns of native but not exotic plant species on New Zealand small islands

Disturbances of oceanic origin can severely affect plant communities on islands, but it is unclear whether they promote or deter biological invasions. Here, I collected floristic data from 97 small islands subject to different levels of ocean-borne disturbances (i.e. inside and outside Wellington Harbour, New Zealand). First, I tested how relationships between the richness of native and exotic species and island characteristics (e.g. area, isolation, height, distance from nearest dwelling) changed depending on island location. Next, I assessed compositional differences on inner and outer islands for both native and exotic species, and how they vary with geographic distance between islands (i.e. distance-decay). Results show that the richness of both native and exotic plant species was similarly related to island characteristics regardless of island location. Both native and exotic species richness consistently increased with area and nearest dwelling. However, only exotics richness always declined with isolation, while natives richness alone consistently increased with height (elevation). Natives on outer, more exposed islands were floristically more homogenous, and compositional differences changed less strongly with the distance between islands than inside Wellington harbour. In contrast, exotics exhibited similar distributional patterns regardless of island location. Different levels of ocean-borne disturbances might explain distinct distributional patterns in native species. Conversely, results for exotic species might reflect a lack of coastal specialists in the species pool. Perhaps time-lags in the invasion process and non-equilibrium dynamics play a role as well. Conservation bodies should similarly manage islands sustaining different levels of ocean-borne disturbances.

Современные проблемы геологии и нефтегазоносности недр Прикаспийской впадины

The deep structure and formation of the North Caspian (Precaspian) depression have not been fully understood due to the scarcity of depth studies at 18–22 km. The existing concepts and hypotheses are clearly insufficient to interpret the unexplained facts. New approaches and research efforts are necessary to solve the old problems. The current state of the depression deep structure problems is reviewed, and the existing explanation flaws are demonstrated. The depression consolidated crust has oceanic and riftogenic origin as it has been suggested by the author before. This explanation is supported by the Astrakhan deposit D-2 deep well core data. The Astrakhan-Aktobe zone arched uplift genesis, formation and role in the carbonate platforms emergence are discussed. Deep geothermy and fluid dynamics problems, as well as recent geophysical data are considered in view of the North Caspian depression hydrocarbon prospects.

Nature of the crust beneath the islands of the Mozambique Channel: Constraints from receiver functions

Starting in May 2018, a volcano-tectonic crisis occurred in the vicinity of Mayotte, a volcanic island in the Comoros Archipelago in the Mozambique Channel. The origin of the volcanism but also the subsurface architecture and nature of the crust, remain unknown. Here, based on receiver function analyses that provide S-wave velocity profiles, we determine the depth of Mohorovičić discontinuity (Moho) and VP/VS ratios for volcanic islands in the Mozambique Channel. We propose that the crust beneath Mayotte and Juan de Nova islands is of continental nature, while it appears to be of oceanic origin beneath Europa and Grande Glorieuse islands. Our results suggest that Mayotte edifice grew on an isolated continental block abandoned during the Gondwana breakup and the opening of the Mozambique Channel. The continental crust is underlain by a thick (9–10 km) and fast layer, interpreted as magmatic underplating which may result from the 20-Myr-long duration of the volcanism. The new velocity model determined from the seismic station on Mayotte can be used to relocate the seismicity related to the ongoing volcano-tectonic crisis.

Modeling of Possible Plume Mechanisms on Europa

AbstractPlumes spewing water high above Europa's surface have been inferred from several observation campaigns in the past decade. Whereas the occasional existence of plumes on Europa has thus been confirmed, the origin of the plumes remains uncertain. Most notably, it is still unclear whether the inferred plumes are of oceanic origin, possibly containing information about the ocean's habitability, or if they are of surficial nature, offering information on the highly processed surface instead. In this study, we use a Monte‐Carlo model to analyze three different plume models, two of which are surficial (near‐surface liquid inclusion and diapir), and one of which originates in the sub‐surface ocean (oceanic plume). We analyze all relevant Lyman‐ and OI 1304 emission mechanisms to determine the three models' emission profiles. These profiles are then compared to the Hubble Space Telescope/Space Telescope Imaging Spectograph measurements presented by Roth, Saur, et al. (2014, https://doi.org/10.1126/science.1247051) with the goal of determining which ab initio model fits these measurements best. Our analyses show that all three models investigated produce similar Lyman‐ and OI 130.4 nm emission profiles, with differences being perceivable only on scales well below the HST resolution and sensitivity. Since none of the models contradict the Roth, Saur, et al. (2014, https://doi.org/10.1126/science.1247051) observations, none of them can be ruled out as being the acting force behind the observed plumes. The currently available optical measurements are thus not sufficient to determine the physical nature of Europa's plumes, identification of which can only be achieved through higher resolution images or in situ measurements.

Elastic anisotropies of rocks in a subduction and exhumation setting

Abstract. Subduction and exhumation are key processes in the formation of orogenic systems across the world, for example, in the European Alps. For geophysical investigations of these orogens, it is essential to understand the petrophysical properties of the rocks involved. These are the result of a complex interaction of mineral composition and rock fabric including mineral textures (i.e., crystallographic preferred orientations). In this study we present texture-derived elastic anisotropy data for a representative set of different lithologies involved in the Alpine orogeny. Rock samples were collected in the Lago di Cignana area in Valtournenche, in the Italian northwestern Alps. At this locality a wide range of units of continental and oceanic origin with varying paleogeographic affiliations and tectono-metamorphic histories are accessible. Their mineral textures were determined by time-of-flight neutron diffraction. From these data the elastic properties of the samples were calculated. The data set includes representative lithologies from a subduction-exhumation setting. In subducted lithologies originating from the oceanic crust, the P-wave anisotropies (AVPs [%]) range from 1.4 % to 3.7 % with average P-wave velocities of 7.20–8.24 km/s and VP / VS ratios of 1.70–1.75. In the metasediments of the former accretionary prism the AVPs range from 3.7 % to 7.1 %, average P-wave velocities are 6.66–7.23 km/s and VP / VS ratios are 1.61–1.76. Continental crust which is incorporated in the collisional orogen shows AVP ranging from 1.4 % to 2.1 % with average P-wave velocities of 6.52–6.62 km/s and VP / VS ratios of 1.56–1.60. Our results suggest that mafic and felsic rocks in subduction zones at depth may be discriminated by a combination of seismic signatures: lower anisotropy and higher VP / VS ratio for mafic rocks, and higher anisotropy and lower VP / VS ratio for felsic rocks and metasediments.

Oceanic versus terrestrial origin of El Niño Southern Oscillation-associated continental precipitation anomalies.

Precipitation is significantly influenced by the El Niño Southern Oscillation (ENSO), which is considered to be the most important factor that brings about climate variability. In this study, the asymmetry of the origin of continental precipitation anomalies during El Niño and La Niña events was investigated. An already validated Lagrangian approach was used to determine the proportion of the total Lagrangian precipitation that is of oceanic and terrestrial origin. Further, the role of these components of the Lagrangian precipitation in regions with significant precipitation anomalies during the ENSO was investigated. A two-phase asymmetric behavior of precipitation, particularly in tropical regions, was obtained. For some of these regions, precipitation anomalies based on other datasets were also calculated to confirm the observed changes, and for these regions, it was observed that in all cases, the calculated anomaly of Lagrangian precipitation agreed with the precipitation change. The percentage of precipitation of oceanic origin was higher in most of these regions. However, it was observed that an increase in the percentage of precipitation of oceanic origin did not bring about a general increase in precipitation for all the regions, revealing the importance of precipitation of terrestrial origin during both phases of the ENSO.

Novel phenolic compound from Southern Ocean microalgae Chlorella sp. PR-1 and its antibacterial activity

Marine microalgae has been attracting the researcher’s attention for centuries. Development on microalgal research is majorly favoured by its medicinal, pharmaceutical or cosmeceutical properties. The advancement in the investigation related to microalgal products have been concentrated in the coastal zones because of the greater supply of raw material. The Southern Ocean, highly productive and relatively poorly studied ecosystem, constitutes approximately 10% of the global volume of the oceans. In this study, marine microalgae Chlorella sp. PR-1 was isolated from the Southern Ocean (Indian Sector) for the identification of bioactive antibacterial compounds. The antimicrobial activity of this microalgal extracts was evaluated against three gram positive (Staphylococcus aureus, Bacillus licheniformis, and Bacillus subtilis) and three gram negative bacteria (Pseudomonas aeruginosa, Salmonella typhimurium, and Escherichia coli). The extract showing antibacterial activity was further purified by thin layer and column chromatography. The antimicrobial activity was again evaluated and confirmed with the purified fraction against the same bacteria. The identification of the functional groups in the purified fraction was performed by infrared spectroscopic analysis. Based on gas chromatographic and mass spectroscopic analysis, the principle bioactive compound was proved to be 2,4-bis (1,1-dimethylethyl)- phenol. Thus, the bioactive compound isolated from marine microalga of Southern Ocean origin may be a novel alternative source of antibacterials in the future.

Mantle-like Hf[sbnd]Nd isotope signatures in ~3.5 Ga greenstones: No evidence for Hadean crust beneath the East Pilbara Craton

The geological setting of extensive ~3.5 Ga greenstone sequences in the Pilbara Craton (Australia) has been controversial for many years. Models range from a purely oceanic origin to emplacement over a pre-existing, possibly Hadean, sialic basement. Here we present new isotopic (NdHf) and trace element data for a geographically extensive suite of komatiitic-tholeiitic metavolcanic rocks which comprise much of the Pilbara Supergroup. Most of the samples have flat to mildly enriched normalised trace element patterns, often associated with a slight NbTa depletion. A small subset of samples, represented throughout the stratigraphy, show strong LREE enrichment and pronounced HFSE anomalies (low Nb/Th, high La/Nb and Zr/Y) either requiring a different magma source or the addition of an enriched component (possibly pre-existing continental crust). Despite this compositional diversity, the SmNd and LuHf data for all samples define ~3.5 Ga isochrons and yield homogeneous initial ratios (εNd = 1.15 ± 0.19; εHf = 2.29 ± 0.65) suggesting a magma source — or sources — slightly more depleted than the putative primitive (chondritic) mantle but consistent with recent observations of other primordial, deep mantle reservoirs. Published SmNd data for the Dresser Formation obtained during the Pilbara Drilling Project appear to be affected by alteration processes and are considered unreliable for the estimation of an accurate initial isotopic composition.The data for the enriched samples are inconsistent with assimilation of known examples of locally exposed continental crust as a mechanism responsible for their trace element characteristics. If an alternate crustal contaminant is invoked it cannot be much older than the basaltic magmatism itself. As a consequence, we see no evidence for an extensive Hadean (>4.0 Ga) sialic basement in the region.

Expansion-Oriented View On Origin of Oceans

Both the concepts of plate tectonics and continental drift conceive that the planet earth’s dimension, associated with its oceans, has remained unchanged throughout the past geological periods. In contrast, Hilgenberg’s model of earth expansion endorses that initially the planet was considerably small and devoid of oceans [1]. Based on earth expansion theory the author has pointed out that since the primordial condensed or small earth was devoid of oceans, initially the ocean-forming water must have been associated with the mantle, thereby turning that geosphere considerably fluid and pre-eminently suitable for planetary expansion. Expansion of the planet appears to have been caused owing to swelling up of the semi-fluid mantle in response to an external gravitational pull caused by an extra-terrestrial planetary body, probably the Moon. The primordial earth was completely covered with a relatively thin granitic crust, which, due to swelling up of the mantle developed a number of long and sinuous expansion cracks. Through these expansion cracks widespread eruption of molten magma took place spreading on both sides of the cracks to form rudimentary oceans basins. With continued expansion, the dimension of the oceans was broadened while the expansion cracks turned in to mid-oceanic ridges. Associated with expulsion of molten lava, large quantum of volatiles, chiefly constituted of water was released from the mantle that formed the ocean water while due to desiccation of the mantle, the process of expansion was eventually stopped.

Quantifying atmosphere and ocean origins of North American precipitation variability

How atmospheric and oceanic processes control North American precipitation variability has been extensively investigated, and yet debates remain. Here we address this question in a 50 km-resolution flux-adjusted global climate model. The high spatial resolution and flux adjustment greatly improve the model’s ability to realistically simulate North American precipitation, the relevant tropical and midlatitude variability and their teleconnections. Comparing two millennium-long simulations with and without an interactive ocean, we find that the leading modes of North American precipitation variability on seasonal and longer timescales exhibit nearly identical spatial and spectral characteristics, explained fraction of total variance and associated atmospheric circulation. This finding suggests that these leading modes arise from internal atmospheric dynamics and atmosphere-land coupling. However, in the fully coupled simulation, North American precipitation variability still correlates significantly with tropical ocean variability, consistent with observations and prior literature. We find that tropical ocean variability does not create its own type of atmospheric variability but excites internal atmospheric modes of variability in midlatitudes. This oceanic impact on North American precipitation is secondary to atmospheric impacts based on correlation. However, relative to the simulation without an interactive ocean, the fully coupled simulation amplifies precipitation variance over southwest North America (SWNA) during late spring to summer by up to 90%. The amplification is caused by a stronger variability in atmospheric moisture content that is attributed to tropical Pacific sea surface temperature variability. Enhanced atmospheric moisture variations over the tropical Pacific are transported by seasonal mean southwesterly winds into SWNA, resulting in larger precipitation variance.

Antarctic icebergs reorganize ocean circulation during Pleistocene glacials.

The dominant feature of large-scale mass transfer in the modern ocean is the Atlantic meridional overturning circulation (AMOC). The geometry and vigour of this circulation influences global climate on various timescales. Palaeoceanographic evidence suggests that during glacial periods of the past 1.5 million years the AMOC had markedly different features from today1; in the Atlantic basin, deep waters of Southern Ocean origin increased in volume while above them the core of the North Atlantic Deep Water (NADW) shoaled2. An absence of evidence on the origin of this phenomenon means that the sequence of events leading to global glacial conditions remains unclear. Here we present multi-proxy evidence showing that northward shifts in Antarctic iceberg melt in the Indian-Atlantic Southern Ocean (0-50°E) systematically preceded deep-water mass reorganizations by one to twothousand years during Pleistocene-era glaciations. With the aid of iceberg-trajectory model experiments, we demonstrate that such a shift in iceberg trajectories during glacial periods can result in a considerable redistribution of freshwater in the Southern Ocean. We suggest that this, in concert with increased sea-ice cover, enabled positive buoyancy anomalies to 'escape' into the upper limb of the AMOC, providing a teleconnection between surface Southern Ocean conditions and the formation of NADW. The magnitude and pacing of this mechanism evolved substantially across the mid-Pleistocene transition, and the coeval increase in magnitude of the 'southern escape' and deep circulation perturbations implicate this mechanism as a key feedback in the transition to the '100-kyr world', in which glacial-interglacial cycles occur at roughly 100,000-year periods.

U–Pb geochronology and trace-element composition of zircons from the Jinchang Au–Ni deposit, SW China, and their implications for tectonics

AbstractSituated between the South China Block and the Simao Block, the Ailaoshan Belt is a significant component of the Jinshajiang–Ailaoshan tectonic-magmatic-metallogenic belt of southwestern China. The formation of the Ailaoshan Belt is closely related to the evolution of the Palaeo-Tethys Ocean. In this study, we constrain ages of sedimentation in the Jinchang Au–Ni deposit in the Ailaoshan Belt, using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb ages of the youngest populations of detrital zircons separated from a chert layer and two uncomfortably overlying meta-sandstones. The combined data of the meta-sandstone samples from the Yiwanshui Formation yielded a concordant age of 250.8 ± 0.6 Ma (mean square weighted deviation (MSWD), 2.8; n = 26). The chert sample from the Jinchangyan Formation yielded a concordant age of 347.0 ± 1.5 Ma (MSWD, 2.8; n = 16). Detrital zircons from the meta-sandstone are characterized by low rare earth element contents (∑REE) and low Y, and high U and U/Yb ratio, suggesting a continental crustal origin. Zircons in the meta-sandstones were derived mainly from pre-collision subduction zone magmatic rocks related to the closure of the Palaeo-Tethys Ocean. In contrast, detrital zircons from the chert contain relatively high ∑REE and Y, and low U and U/Yb ratio, suggesting an oceanic crust origin. Zircons in the chert bed were derived mainly from ophiolites related to seafloor spreading in a branch of the Palaeo-Tethys Ocean.

PERTURBAÇÕES NO CAMPO GEOMAGNÉTICO CAUSADAS PELO TERREMOTO E PELO TSUNAMI DE MAULE, CHILE (2010)

Este estudo foca na análise das perturbações do campo geomagnético que estão relacionadas com o terremoto, e consequente tsunami, que ocorreram em 27 de fevereiro de 2010 em Maule, no Chile. O objetivo deste artigo é contribuir para uma melhor compreensão dos processos físicos envolvidos nos acoplamentos Tsunami-Atmosfera-Ionosfera (TAI) e Litosfera-Atmosfera-Ionosfera (LAI). Para isto, foram utilizados registros de magnetômetros fluxgate medidos em superfície fornecidos pelo projeto LISN (do inglês Low Latitude Ionospheric Sensor Network). A metodologia de filtragem do sinal por remoção da tendência relacionada à influência solar (linha de base Sq, do inglês Solar quiet) considerando os cinco dias geomagneticamente mais calmos foi aplicada. Os resultados mostraram distúrbios geomagnéticos, em ambas componentes H e Z, nos dados filtrados que ocorreram quase instantaneamente ou com atraso de até 100 minutos após a chegada do tsunami. Estes distúrbios são atribuídos aos mecanismos oceânico e ionosférico. Estudos como esse são importantes para uma futura condição de previsão e alerta de desastres dessa natureza.

An assessment of the changes in the behavior of the groundwater resources in arid environment with global warming in Morocco

This study aims to assess the effect of climate change on water resources in semi-arid environments, taking the Essaouira region in Morocco as an example. Analysis of climate data shows a decrease in precipitation of 12–16% and an increase in air temperature of 2.3 °C over the past three decades. A continuous drop in the piezometric level of more than 12 m for the Cenomanian-Turonian aquifer, 17 m for the Plio-Quaternary aquifer, around 8 m for the Barremian-Aptian aquifer and 5 m for the Hauterivian. Hydrogeochemical analysis together show that (i) the groundwater mineralization is controlled by the dissolution of evaporitic and carbonates minerals, by the reverse ions exchange phenomenon, and by sea water intrusion, especially at Plio-Quaternary aquifer; and (ii) the groundwater quality in the study area deteriorates gradually over time and space. The isotopic data shows that (i) the groundwater recharge in the study area is ensured by precipitation of oceanic origin without significant evaporation and that (ii) climate change has no remarkable effect on the isotopic content of the groundwater of the study area. However, the results of this article reflect that the Essaouira basin is very vulnerable to climate change.

Predictable Mode of Tropical Intraseasonal Variability in Boreal Summer

AbstractThis work uses a 19-yr ensemble hindcast of the European Centre for Medium-Range Weather Forecasts (ECMWF) and the average predictable time (APT) method to detect the most predictable tropical intraseasonal variability (ISV) mode. The first and most predictable mode (APT1) of tropical ISV is similar to a joint merger of the two Madden–Julian oscillation (MJO) modes with more weight on the second mode and is characterized by a tripole pattern with two positive centers in the equatorial western Indian Ocean and central Pacific Ocean and a negative center over the Maritime Continent. The APT1 doubles the skillful prediction period made by the MJO defined by a correlation skill of 0.5 (approximately 25 days in the ECMWF model), demonstrating its potential to become a skillful prediction target and to offer powerful subseasonal prediction sources. The underlying physical process and predictability source of the APT1 are further analyzed. The APT1 is very similar to the pattern triggered by the most predictable tropical intraseasonal sea surface temperature (SST) anomalies mode, suggesting its oceanic origin. Tropical ocean–atmosphere interaction plays a critical role in the APT1 by enhancing the evolution of tropical convection cells under WES (wind–evaporation–SST) and Bjerknes feedbacks. The internal atmospheric processes also have an important impact on the formation and maintenance of the APT1.

Atmospheric Nitrogen When Life Evolved on Earth.

The amount of nitrogen (N2) present in the atmosphere when life evolved on our planet is central for understanding the production of prebiotic molecules and, hence, is a fundamental quantity to constrain. Estimates of atmospheric molecular nitrogen partial surface pressures during the Archean, however, widely vary in the literature. In this study, we apply a model that combines newly gained insights into atmospheric escape, magma ocean duration, and outgassing evolution. Results suggest <420 mbar surface molecular nitrogen at the time when life originated, which is much lower compared with estimates in previous works and hence could impact our understanding of the production rate of prebiotic molecules such as hydrogen cyanide. Our revised values provide new input for atmospheric chamber experiments that simulate prebiotic chemistry on the early Earth. Our results that assume negligible nitrogen escape rates are in agreement with research based on solidified gas bubbles and the oxidation of iron in micrometeorites at 2.7 Gyr ago, which suggest that the atmospheric pressure was probably less than half the present-day value. Our results contradict previous studies that assume N2 partial surface pressures during the Archean were higher than those observed today and suggest that, if the N2 partial pressure were low in the Archean, it would likely be low in the Hadean as well. Furthermore, our results imply a biogenic nitrogen fixation rate from 9 to 14 Teragram N2 per year (Tg N2/year), which is consistent with modern marine biofixation rates and, hence, indicate an oceanic origin of this fixation process.

Evidence of Southern Ocean influence into the far Northwest Pacific (Northern Emperor Rise) since the Bølling–Allerød warming

The role of the Southern Ocean in releasing CO 2 (sequestered in the global ocean during the Last Glacial Maximum) into the atmosphere during deglaciation is an important topic for investigation of Earth's climate. Changes in global deep water circulation associated with upwelling of Circumpolar Deep Water (CDW) around Antarctica may have played a part in the CO 2 release, but remain poorly studied. The potential response of the Pacific Ocean, including the North Pacific, to upwelling of CDW with its vast reservoir of CO 2 remains unresolved. Here we combine productivity proxies, oxygen and carbon isotope values in benthic and planktic foraminifera, data on the occurrence and abundance of ice-rafted debris, and benthic foraminiferal species composition in three sediment cores with published data for three cores from the Northern Emperor Rise for the Last Glacial Maximum, deglaciation and Holocene in order to elucidate the North Pacific role in CO 2 redistribution in the past. Age models of the cores are based on radiocarbon data calibrated by 14 C atmospheric plateau tuning. The calcium carbonate content in all cores increased abruptly around 14.5 ka, indicating an influx of relatively young water enriched in carbonate ion, oxygen and nutrients, and sourced in the Southern Oceans. A decrease in the extent of sea ice at the NER area during early deglaciation is reflected in sharp increases in the productivity of siliceous phytoplankton near the onset of Bølling/Allerød warming, possibly facilitated by the influx of Southern Ocean-sourced nutrient-rich waters. • Stable isotope, lithological and micropaleontological proxies of 6 cores from the Western Subarctic Gyre (WSG) were studied. • Age models of cores over the last 25kyr were modified by radiocarbon data calibrated by 14C atmospheric plateau tuning. • Multiple lines of evidences support abrupt flushing of Southern Ocean origin water into the deep WSG since 14.5 ± 0.2 ka.