Alleviated photoinhibition on nitrification in the Indian Sector of the Southern Ocean

Nitrification,a central process in the marine nitrogen cycle,produces regenerated nitrate in the euphotic zone and emits N_(2)O,a potent greenhouse gas as a by-product.The regulatory mechanisms of nitrification in the Southern Ocean,which is a critical region for CO_(2)sequestration and radiative benefits,remain poorly understood.Here,we investigated the in situ and dark nitrification rates in the upper 500 m and conducted substrate kinetics experiments across the Indian Sector in the Cosmonaut and Cooperation seas in the late austral summer.Our findings indicate that light inhibition of nitrification decreases exponentially with depth,exhibiting a light threshold of 0.53%photosynthetically active radiation.A positive relationship between dark nitrification and apparent oxygen utilization suggests a dependence on substrate availability from primary production.Importantly,an increased NH_(4)^(+) supply can act as a buffer against photo-inhibitory damage.Globally,substrate affinity(α)increases with depth and transitions from light to dark,decreases with increasing ambient NH_(4)^(+)and exhibits a latitudinal distribution,reflecting substrate utilization strategies.We also reveal that upwelling in Circumpolar Deep Water(CDW)stimulates nitrification through the introduction of potentially higher iron and deep diverse nitrifying microorganisms with higherα.We conclude that although light is the primary limiting factor for nitrification in summer,coupling between substrate availability and CDW upwelling can overcome this limitation,thereby alleviating photoinhibition by up to 45%±5.3%.

Size fractionated biomass and productivity of phytoplankton and new production in the Prydz Bay and the adjacent Indian sector of the Southern Ocean during the austral summer 1998/1999

The paper deals with the studies on the cell abundance, the composition of dominant species, size fractionated biomass and productivity of phytoplankton, new production, the environmentally restricted mechanism in the Prydz Bay and the adjacent Indian sector of the Southern Ocean during the austral summer 1998/1999. The results showed that there was marked feature of spatial zonation in the sea areas investigated. In the Prydz Bay and its adjacent continental shelf, the biomass and productivity of phytoplankton were high; those of continental slope and open ocean area were obviously low. The nutrient concentration had opposite distribution trend, due to the consumption of phytoplankton. It mainly affected by the vertical stability of water column, grazing pressure of zooplankton, temperature and light etc. The results of size-fractionation showed that the average contribution of netplankton to total chlorophyll a in studied sea areas was 52.2 %, those of nano- and picoplankton were 29.4 % and 18.4 %, respectively. The average contribution of netplankton to total primary production was 52.4 %, those of nano- and picoplankton were 28.7 % and 18.9 %, separately. It is same as previous conclusion that the contribution of picoplankton to productivity is slightly larger than that to biomass of phytoplankton communities. The average new production and f-ratio were 230.6 mg/ (m(2.)d) and 0.43, respectively.

Compensating Errors in Cloud Radiative and Physical Properties over the Southern Ocean in the CMIP6 Climate Models

The Southern Ocean is covered by a large amount of clouds with high cloud albedo.However,as reported by previous climate model intercomparison projects,underestimated cloudiness and overestimated absorption of solar radiation(ASR)over the Southern Ocean lead to substantial biases in climate sensitivity.The present study revisits this long-standing issue and explores the uncertainty sources in the latest CMIP6 models.We employ 10-year satellite observations to evaluate cloud radiative effect(CRE)and cloud physical properties in five CMIP6 models that provide comprehensive output of cloud,radiation,and aerosol.The simulated longwave,shortwave,and net CRE at the top of atmosphere in CMIP6 are comparable with the CERES satellite observations.Total cloud fraction(CF)is also reasonably simulated in CMIP6,but the comparison of liquid cloud fraction(LCF)reveals marked biases in spatial pattern and seasonal variations.The discrepancies between the CMIP6 models and the MODIS satellite observations become even larger in other cloud macroand micro-physical properties,including liquid water path(LWP),cloud optical depth(COD),and cloud effective radius,as well as aerosol optical depth(AOD).However,the large underestimation of both LWP and cloud effective radius(regional means~20%and 11%,respectively)results in relatively smaller bias in COD,and the impacts of the biases in COD and LCF also cancel out with each other,leaving CRE and ASR reasonably predicted in CMIP6.An error estimation framework is employed,and the different signs of the sensitivity errors and biases from CF and LWP corroborate the notions that there are compensating errors in the modeled shortwave CRE.Further correlation analyses of the geospatial patterns reveal that CF is the most relevant factor in determining CRE in observations,while the modeled CRE is too sensitive to LWP and COD.The relationships between cloud effective radius,LWP,and COD are also analyzed to explore the possible uncertainty sources in different models.Our study calls for more rigorous calibration of detailed cloud physical properties for future climate model development and climate projection.

Bathymetrical influences on spatial and temporal characteristics of chlorophyll-a concentrations in the Southern Ocean from 2002 to 2012(October to March)using MODIS

Phytoplankton blooms,particularly in the Southern Ocean,can have significant impact on global biogeochemistry cycling.To investigate the accuracy of chlorophyll-a distribution,and to better understand the spatial and temporal dynamics of phytoplankton biomass,we examine chlorophyll-a estimates(October-March from 2002 to 2012)derived from Moderate Resolution Imaging Spectrometer(MODIS)data following the ocean chlorophyll-a 3 model(OC3M)algorithm.Noticeable seasonality occurs in the temporal distribution of chlorophyll-a concentrations,which shows the highest value in December and January and an increasing tendency during the 2002-2012 period.The spatial distribution of chlorophyll-a varies greatly with latitude,as higher latitudes experience more phytoplankton blooms(chlorophyll-a concentration larger than 1 mg/m3)and marginal seas(Ross Sea and Amundsen Sea)show different bloom anomalies caused by two dominant algae species.Areas at higher latitudes and shallow water(<500 m)experience the shorter icefree periods with greater seasonality.A noticeable bathymetry gradient exists at 2500-m isobaths,while water at the 500-2500-m depth experiences quite long ice-free periods with a stable water environment.Blooms generally occur near topographic features where currents have strong interactions when the water depth is more than 2500 m.Based on these findings,we can classify the Southern Ocean into two bloom subregions,0-500 m as an enhanced bloom zone(EBZ),and 500-2500 m as a moderate bloom zone(MBZ).The EBZ has a quite high-bloom probability of about 30%,while the MBZ has only 10%.

Heat oscillation in the upper ocean of the southern South China Sea

Data used in this study are temperature/depth profiles taken over the upper 400 m of the ocean in the southern South China Sea (4°-14° N, 106°-120° E) for the period 1961-1973. The data are analyzed on the grid 2 (latitude) by 2 (longitude) in space and bimonthly in time. The vertically averaged temperature (TAV) over the upper 100 m of the ocean is calculated as the estimate of the heat content in the upper ocean.The TAV is cooler in the northwest region of the study area and warmer in the southeast in the annual and seasonal mean figures. The first EOF (Empirical Orthogonal Function) of anomalous TAV accounts for 41 % of the total variance for the period 1961-1973. The time function associated with it displays a significant interannual changes in the heat content, with 2-4 a oscillation period and associated with the ENSO events. During ENSO event TAV increases with the tendency of increasing towards equator along the basin. This anomalous states also exist in the water layers below 100 m depth. The isotherm is usually deepened during ENSO period. The deepened amplitude of the isotherm decreases with depth, and varies with ENSO events, seasons and regions. The reason for that is related to weak monsoon in El Nino year and associated eddy activity. Besides this, there is a gain in heat in the upper ocean because of the strong subtropical high during ENSO period.

Permo–Triassic and Liassic Tethyan Oceanic Tracts within the Pontide Belt Along the Southern Margin of Eurasia, Northern Anatolia

The Pontide belt in northern Turkey includes three major tectonic terranes,the Strandja Massif（Sj M）,and the Istanbul（ISZ）and Sakarya Zones（SZ）(Fig.1).We present new age and geochemical data from ophiolites and ophiolitic mélanges within the Sakarya Zone and show that these mafic–ultramafic rocks are the remnants of Tethyan oceanic lithosphere formed in different tectonic settings.The main ophiolite occurrences investigated in this study along the Karakaya Suture（KS）are associated with the latest Triassic Cimmeride orogeny,and in the Küre–Yusufeli ophiolite belt are part of the Alpide orogeny.The Karakaya Suture Zone ophiolites in northern west Turkey are comprised mainly of the Denizgoren（?anakkale）ophiolite,Bo?azk?y（Bursa）,Geyve（Sakarya）,Almac?k（Düzce）and?ele（Bolu）metaophiolites.The Denizg?ren ophiolite largely contains upper mantle peridotites,which are equivalents of the Permo–Triassic Lesvos peridotites and mélange units farther SW in the northern Aegean Sea.The Bo?azk?y ophiolite includes serpentinite and metagabbro,and the Almac?k and Geyve ophiolites display an almost complete Penrose–type sequence consisting of serpentinizeduppermantleperidotites,cumulate ultramafic–mafic rocks,isotropic gabbros,dolerite and plagiogranite dikes,and extrusive rocks.U–Pb zircon dating of plagiogranite dikes from?ele has revealed an igneous age of 260 Ma,and 255,235,227 Ma from Almac?k（Bozkurt et al.,2012a,b）.Consistent with the previouslypublished Permo–Triassic age,we obtained a 268.4±6.3 Ma U–Pb zircon age from a plagiogranite dike within the Almacik ophiolite to the west.This KS ophiolite belt containing the?ele,Almac?k,Geyve ophiolites within the SZ extends westward into the Armutlu Peninsula and then into the Biga Peninsula（i.e.Denizg?ren ophiolite）and most likely connects with the remnants of the Triassic Meliata–Meliac ocean basin（Stampfli and Borel,2002）in the Balkan Peninsula.The KS ophiolites also continue eastward within the Pontide Belt into the Elekda?ophiolite（eastern Kastamonu）and then to the Refahiye ophiolite in NE Anatolia.Triassic granites in the SZ represent a magmatic arc that formed as a result of the northward subduction of the Izmir–Ankara–Erzincan oceanic lithosphere existing during the late Paleozoic through Cretaceous（Sarifakioglu et al.,2014）beneath the Pontides.We obtained a U–Pb zircon age of 231±2 Ma from a metagranitic intrusion into the Variscan basement of the SZ in the Kastamonu region of the central Pontides.This metagranite is enriched in LILE（Rb:63 ppm;Ba:65 ppm;Sr:200 ppm）and depleted in HFSE（Y:12.58 ppm;Yb:1.26 ppm;Ti O2:0.2 wt.%;Nb:7.6 ppm;Hf:3.9 ppm）,characterizing it as subduction–related calc-alkaline pluton.Lead（3.9 ppm）,U（1.6 ppm）and Ce（59 ppm）contents are interpreted as evidence for contamination by continental crust.The Küre basin to the north opened during the late Triassic to Liassic,following a backarc rifting episode in the central Pontides.Metabasic dike intrusions in the Devrekani metamorphic massif represent the first magmatic stage of this backarc rifting event.Whole-rock 40Ar-39Ar dating ofthe metabasic dikes has yielded cooling ages of 160.5±1.2 Ma. We infer that this age was reset due to thermal heating during the emplacement of the Middle Jurassic granitoids as the Küre oceanic basin was closing. The Küre ophiolite contains upper mantle peridotites and oceanic crustal rocks composed mainly of pillow–massive–breccia basalts, dacitic and rhyolitic lavas–tuffs, diabase dyke swarms, massive gabbros and a limited extent mafic cumulates. We obtained 182.6±1.9 Ma as a whole-rock 40Ar-39 Ar age from a pillow basalt and a U–Pb zircon age of 171±1 Ma from the granitic intrusion cross-cutting the peridotites. The easternmost representatives of the Küre ophiolite occur in the Yusufeli（Artvin） area in the eastern part of the Pontide belt. Here, oceanic crustal rocks are tectonically related to metamorphic rocks of the Variscan basement of the SZ. The ophiolitic crustal rocks contain isotropic gabbro and mafic and felsic dikes. Serpentinized upper mantle peridotites are scarce. Pillow lava basalts are overlain by a thick metasandstone–metashale association with locally foliated meta–lava and some manganiferous chert and mudstone interlayers. We obtained a U–Pb zircon age of 172.5±1.4 Ma from the granitic intrusion cross-cutting the Yusufeli ophiolite and of 181.9±0.9 Ma from a felsic dike（plagiogranite） in the Yusufeli ophiolite. The Middle Jurassic granites are related to the closure of the Küre-Yusufeli marginal ocean basin. The Küre and Yusufeli ophiolites have been previously interpreted as the remnants of the Paleotethys or the Intra-Pontide Ocean. However, we posit that these ophiolites represent amarginal, short-lived（;0 Ma） ocean basin, which opened during the late Triassic through Liassic, and then closed in Dogger. This oceanic lithosphere is similar to the Evros ophiolite in the northeastern Greece in terms of its ages and geochemical characteristics.

Circulation and its seasonal variability in region around the Kerguelen Plateau

A coupled ice-ocean isopycnal numerical model of the Southern Ocean is established tostudy the circulation and its seasonal variability in the region around the Kerguelen Plateau. An analysis of the simulated results shows significant stripe-like structure and non-zonal feature of the Antarctic Cir-cumpolar Current (ACC) in this region. ACC begins to bifurcate and to turn its direction before meeting the plateau. The southernmost branch of ACC is near to the Antarctic coast and displays its strong interaction with the westward Antarctic Slope Current. The northern branch of ACC has a tendency of annual variations while the southern one varies in a semiannual cycle. The variation phases of both branches are coincident with that of the wind stress in this region.

Reproductive characteristics of Antarctic Krill，Euphausia superba Dana，in the Prydz Bay region

Experiments and observations on reproduction of Antarctic krill Euphausia superba Dana,were conducted on board ship of R/V 'JIDI' during the austral summer of 1993 in the Prydz Bay region. The development of ovaria oocytes in gravid females,spawning epicces, and brood size were studied. The sexual maturity process and spawning season were discussed Fifty-three live gravid females captured at two stations in January, 1993 were cultured in a cool-room on board. They spawned within 1 to 16 days after capture. Most of them spawned only once except two, that spawned secondly on the 5th and 7th day after first spawning. The brood size of first spawning ranged from 225 to 5919 eggs with the average of 2132 eggs. The second brood was rather small,about 500 eggs. There were 0～213 (mean 32) mature oocytes remained in the post-spawn ovaries, and revitellogenesis was not observed. Brood size increased with the increasing of they length, but the correlation was not good. The number of ovarian oocytes in gravid female ranged from 2188 to 9263 with a mean of 5283. The composition of oocytes of different type varied in different samples. That all oocytes become completely matured seems to be an indication of pre-spawning. Spawning could take place through the summer with the peakspawning occurring from late January to late February. Interannual variation in peak spawning season might be significant.