The connection of phytoplankton biomass in the Marguerite Bay polynya of the western Antarctic Peninsula to the Southern Annular Mode

Antarctic coastal polynyas are biological hotspots in the Southern Ocean that support the abundance of hightrophic-level predators and are important for carbon cycling in the high-latitude oceans.In this study,we examined the interannual variation of summertime phytoplankton biomass in the Marguerite Bay polynya(MBP)in the western Antarctic Peninsula area,and linked such variability to the Southern Annular Mode(SAM)that dominated the southern hemisphere extratropical climate variability.Combining satellite data,atmosphere reanalysis products and numerical simulations,we found that the interannual variation of summer chlorophyll-a(Chl-a)concentration in the MBP is significantly and negatively correlated with the spring SAM index,and weakly correlated with the summer SAM index.The negative relation between summer Chl-a and spring SAM is due to weaker spring vertical mixing under a more positive SAM condition,which would inhibit the supply of iron from deep layers into the surface euphotic layer.The negative relation between spring mixing and spring SAM results from greater precipitation rate over the MBP region in positive SAM phase,which leads to lower salinity in the ocean surface layer.The coupled physical-biological mechanisms between SAM and phytoplankton biomass revealed in this study is important for us to predict the future variations of phytoplankton biomasses in Antarctic polynyas under climate change.

Observed features of stable surface seawater isotopes across the Pacific, Indian and Southern oceans

The marine hydrological process is still unclear due to scarce observations.Based on stable water isotopes in surface seawater along the 33rd Chinese National Antarctic Science Expedition from November 2016 to April 2017,this study explored the hydrological processes in the Pacific,Indian and Southern oceans.The results show that the Northwest Pacific(0°–26°N)is a region with strong evaporation(theδ18O-δD slope is 6.58),while the southern Indian Ocean is a region with strong precipitation(theδ18O-δD slope is 9.57).The influence of continental runoff and water mass mixing reduces the correlation betweenδ18O and salinity in the eastern Indian Ocean.The characteristics of the isotopes and hydrological parameters indicate that the Agulhas Front and sub-Tropical Convergence do not merge in the Antarctic–Indian Ocean region.The freezing of sea ice near the Antarctic continent decreases theδ18O andδD by 0.40‰and 7.0‰,respectively,compared with those near 67°S.This study is helpful for understanding marine hydrological processes and promoting the understanding and research of the nature of ocean responses in the context of climate change.

Geochemical characteristics of Sr isotopes in the LS33 drill core from the Qiongdongnan Basin, South China Sea, and their response to the uplift of the Tibetan Plateau

Making full use of modern analytical and testing techniques to explore and establish new indexes or methods for extracting paleoseawater geochemical information from sediments will help to reconstruct the sedimentary paleoenvironment in different research areas.The connection between the subsidence of the South China Sea basin and the uplift of the Tibetan Plateau has been a scientific concern in recent decades.To explore the information on the sedimentary paleoenvironment,provenance changes and uplift of Tibetan Plateau contained in core sediments(debris),we selected core samples from Well LS33 in the Qiongdongnan Basin,South China Sea,and analyzed the contents of typical elements(Al,Th,and rare earth elements)that can indicate changes in provenance and the Sr isotopic compositions,which can reveal the geochemical characteristics of the paleoseawater depending on the type of material(authigenic carbonate and terrigenous detritus).The results show the following:(1)during the late Miocene,the Red River transported a large amount of detrital sediments from the ancient continental block(South China)to the Qiongdongnan Basin.(2)The authigenic carbonates accurately record changes in the 87Sr/86Sr ratios in the South China Sea since the Oligocene.These ratios reflect the semi-closed marginal sea environment of the South China Sea(relative to the ocean)and the sedimentary paleoenvironment evolution process of the deep-water area of the Qiongdongnan Basin from continental to transitional and then to bathyal.(3)Since the Neogene,the variations in the 87Sr/86Sr ratio in the authigenic carbonates have been consistent with the variations in the uplift rate of the Tibetan Plateau and the sediment accumulation rate in the Qiongdongnan Basin.These consistent changes indicate the complex geological process of the change in the rock weathering intensity and terrigenous Sr flux caused by changes in the uplift rate of the Tibetan Plateau,which influence the Sr isotope composition of seawater.

Export of Greenland Sea water across the Mohn Ridge induced by summer storms

The Mohn Ridge separates the Greenland Sea and the Lofoten Basin.Previous studies identified the export across the Mohn Ridge(EMR)from the Greenland Basin into the Lofoten Basin using water mass analysis and the tracer diffusion method,but there is still lack of direct current measurements.A surface mooring with four current meters was deployed on the Mohn Ridge from June 5 to June 18 in 2015,when three cyclones passed in the adjacent area.In the absence of cyclones,the flow on the Mohn Ridge was northeastward,parallel to the ridge.When cyclones appeared,the EMR occurred to transport Greenland Sea water into the Lofoten Basin.The probable mechanism is the sea level height variation caused by the perturbation of the low pressure of cyclones,which yields an outward pressure gradient force to drive the outflow.Our results suggest that the outflow is intermittent and only happens during cyclone activities.The annual mean volume flux of EMR was roughly estimated by the limited data,which is about 3.8×10^(6)m^(3)/s,a little bit smaller than the estimation based on volume conservation.The results indicate that the contribution of the cyclonic storms to EMR is a greatly important mechanism that potentially influences the global thermohaline circulation through the Greenland-Scotland Ridge overflow.

An efficient algorithm for generating a spherical multiple-cell grid

This paper presents an efficient algorithm for generating a spherical multiple-cell(SMC)grid.The algorithm adopts a recursive loop structure and provides two refinement methods:(1)an arbitrary area refinement method and(2)a nearshore refinement method.Numerical experiments are carried out,and the results show that compared with the existing grid generation algorithm,this algorithm is more flexible and operable.

Top-down control on major groups of global marine diazotrophs

Dinitrogen(N_(2))fixed by a group of prokaryotes(diazotrophs)is the dominant process adding bioavailable nitrogen into the ocean.Although it has been intensively studied how N_(2) fixation is controlled by resources(bottom-up factors),it is unclear whether the grazing(top-down control)effectively impacts growth and distribution of different diazotroph groups.In this study,we evaluate this question by conducting log-log regression of diazotroph biomass onto corresponding N_(2) fixation rates in the global ocean.The slope of the regression for Trichodesmium is~0.8,indicating that a small portion of the increase in N_(2) fixation does not accumulate as its biomass.This leads to a conclusion that Trichodesmium is under a substantial top-down control,although bottom-up control still dominates.We also analyze the residuals of the regression in the North Atlantic,concluding that free trichomes of Trichodesmium are subject to stronger top-down control than its colonies.The weak correlation between the biomass and N_(2) fixation of unicellular cyanobacterial diazotrophs indicates that the degree of top-down control on this type of diazotrophs varies greatly.The analyses obtain unrealistic results for diatom-diazotroph assemblages due to complicated nitrogen sources of these symbioses.Our study reveals the variability of top-down control among different diazotroph groups across time and space,suggesting its importance in improving our understandings of ecology of diazotrophs and predictions of N_(2) fixation in biogeochemical models.Measurements of size-specific N_(2) fixation rates and growth rates of different diazotroph groups can be useful to more reliably analyze the top-down control on these key organisms in the global ocean.

Spatial patterns and environmental associations of deep scattering layers in the northwestern subtropical Pacific Ocean

The mesopelagic communities are important for food web and carbon pump in ocean,but the large-scale studies of them are still limited until now because of the difficulties on sampling and analyzing of mesopelagic organisms.Mesopelagic organisms,especially micronekton,can form acoustic deep scattering layers(DSLs)and DSLs are widely observed.To explore the spatial patterns of DSLs and their possible influencing factors,the DSLs during daytime(10:00–14:00)were investigated in the subtropical northwestern Pacific Ocean(13°–23.5°N,153°–163°E)using a shipboard acoustic Doppler current profiler at 38 kHz.The study area was divided into three parts using k-means cluster analysis:the northern part(NP,22°–24°N),the central part(CP,17°–22°N),and the southern part(SP,12°–17°N).The characteristics of DSLs varied widely with latitudinal gradient.Deepest core DSLs(523.5 m±17.4 m),largest nautical area scattering coefficient(NASC)(130.8 m^(2)/n mile^(2)±41.0 m^(2)/n mile^(2)),and most concentrated DSLs(mesopelagic organisms gathering level,6.7%±0.7%)were observed in NP.The proportion of migration was also stronger in NP(39.7%)than those in other parts(18.6%in CP and 21.5%in SP)for mesopelagic organisms.The latitudinal variation of DSLs was probably caused by changes in oxygen concentration and light intensity of mesopelagic zones.A positive relationship between NASC and primary productivity was identified.A four-months lag was seemed to exist.This study provides the first basin-scale baselines information of mesopelagic communities in the northwest Pacific with acoustic approach.Further researches are suggested to gain understandings of seasonal and annual variations of DSLs in the region.

Genetic variation of the small yellow croaker(Larimichthys polyactis)inferred from mitochondrial DNA provides novel insight into the fluctuation of resources

The small yellow croaker(Larimichthys polyactis)belongs to the family Sciaenidae,which is an offshore warm fish species and widely distributed in the western Pacific.In this study,the variation of genetic diversity and genetic differentiation among L.polyactis populations was analyzed by mitochondrial DNA control region.A total of 110 polymorphic sites were checked,which defined 134 haplotypes.High level of haplotype diversity(h=0.993±0.002)was detected in the examined range.Population genetic structure analyse(analysis of molecular variance,Fst)showed there were high gene flow among L.polyactis populations.The result showed that there were relatively high genetic diversity and low genetic differentiation among the Yellow Sea and the East China Sea populations,which can be attributed to diverse habitats,wide distribution range and high mutation rate of control region.Using phylogenetic methods,coalescent analyses(neutrality tests,mismatch distribution analysis,Bayesian skyline analyses)and molecular dating interpreted in conjunction with paleoclimatic and physiographic evidence,we inferred that the genetic make-up of extant populations of L.polyactis was shaped by Pleistocene environmental impacts on the historical demography of this species.Besides,relatively constant genetic diversity and larger effective population size were detected in recent L.polyactis population.The result showed that the fishing policy certainly,such as the summer closed fishing,played a role in protecting resources of L.polyactis.This study can offer a wealth of biological novelties which indicates genetic structure of L.polyactis population and provides the foundation for resources protection and policy setting.

Identifying the sensitive areas in targeted observation for predicting the Kuroshio large meander path in a regional ocean model

With the Regional Ocean Modeling System(ROMS),this paper investigates the sensitive areas in targeted observation for predicting the Kuroshio large meander(LM)path using the conditional nonlinear optimal perturbation approach.To identify the sensitive areas,the optimal initial errors(OIEs)featuring the largest nonlinear evolution in the LM prediction are first calculated;the resulting OIEs are localized mainly in the upper 2500 m over the LM upstream region,and their spatial structure has certain similarities with that of the optimal triggering perturbation.Based on this spatial structure,the sensitive areas are successfully identified,located southeast of Kyushu in the region(29°–32°N,131°–134°E).A series of sensitivity experiments indicate that both the positions and the spatial structure of initial errors have important effects on the LM prediction,verifying the validity of the sensitive areas.Then,the effect of targeted observation in the sensitive areas is evaluated through observing system simulation experiments.When targeted observation is implemented in the identified sensitive areas,the prediction errors are effectively reduced,and the prediction skill of the LM event is improved significantly.This provides scientific guidance for ocean observations related to enhancing the prediction skill of the LM event.

The mitochondrial genome of Chaeturichthys stigmatias provides novel insight into the interspecific difference with Amblychaeturichthys hexanema

Chaeturichthys stigmatias and Amblychaeturichthys hexanema belong to the family Gobiidae,which are offshore warm fish species and widely distribute in the western Pacific Ocean.In this study,the mitochondrial cytochrome c oxidase subunit I(COI)sequences and 12 S ribosomal RNA(12 S rRNA)sequences were used to analyze the interspecific differences between the two species.The phylogenetic analysis showed that the interspecific distance was significantly higher than the intraspecific genetic distance.The Neighbor-Joining tree showed two separate clusters,without sharing haplotype.The mitochondrial genome sequence of C.stigmatias was also reported.This genome was 17134 bp in size,with a high A+T content of 55.9%.The phylogenetic analysis based on the tandem 13 coding protein genes nucleotide sequences indicated that C.stigmatias showed a close relationship with A.hexanema.This study can provide the basic genetic data for two species and will help for constructing the phylogeny of the Gobiiade.

The construction of high precision geostrophic currents based on new gravity models of GOCE and satellite altimetry data

The new gravity field models of gravity field and steady-state ocean circulation explorer(GOCE),TIM_R6 and DIR_R6,were released by the European Space Agency(ESA)in June 2019.The sixth generation of gravity models have the highest possible signal and lowest error levels compared with other GOCE-only gravity models,and the accuracy is significantly improved.This is an opportunity to build high precision geostrophic currents.The mean dynamic topography and geostrophic currents have been calculated by the 5th(TIM_R5 and DIR_R5),6th(TIM_R6 and DIR_R6)release of GOCE gravity field models and ITSG-Grace2018 of GRACE gravity field model in this study.By comparison with the drifter results,the optimal filtering lengths of them have been obtained(for DIR_R5,DIR_R6,TIM_R5 and TIM_R6 models are 1°and for ITSG-Grace2018 model is 1.1°).The filtered results show that the geostrophic currents obtained by the GOCE gravity field models can better reflect detailed characteristics of ocean currents.The total geostrophic speed based on the TIM_R6 model is similar to the result of the DIR_R6 model with standard deviation(STD)of 0.320 m/s and 0.321 m/s,respectively.The STD of the total velocities are 0.333 m/s and 0.325 m/s for DIR_R5 and TIM_R5.When compared with ITSG-Grace2018 results,the STD(0.344 m/s)of total geostrophic speeds is larger than GOCE results,and the accuracy of geostrophic currents obtained by ITSG-Grace2018 is lower.And the absolute errors are mainly distributed in the areas with faster speeds,such as the Antarctic circumpolar circulation,equatorial region,Kuroshio and Gulf Stream areas.After the remove-restore technique was applied to TIM_R6 MDT,the STD of total geostrophic speeds dropped to 0.162 m/s.

INFORMATION FOR AUTHORS

Acta Oceanologica Sinica(AOS)is a comprehensive academic journal edited by the Editorial Committee of Acta Oceanologica Sinica and is designed to provide a forum for important research papers of the marine scientific community which reflect the information on a worldwide basis.

Advances in interscale and interdisciplinary approaches to the South China Sea

The South China Sea(SCS)connects the Pacific Ocean and the Indian Ocean,and acts as an important part in regional and global climate systems(e.g.,Qu et al.,2009;Wang et al.,2009).Multi-scale dynamic and biogeochemical processes in the SCS,comprising a hot spot in marginal sea studies,have attracted great attentions from researchers(e.g.,Chen et al.,2020;Hu et al.,2020).The South China Sea Annual Meeting(SCSAM)2021,recently held on October 22–24 in Zhanjiang,China,focused on academic exchanges of the newly research results and progresses in the interdisciplinary multi-scale processes in the SCS.The SCSAM 2021 is the eighth international workshop of the series,which started in April 2013(Zhu,2013)and renamed as SCSAM in 2018.There were 90 oral presentations and 57 posters in the meeting this year,which attracted attentions of more than 2000 audiences both on line and on site.This short article summaries the cutting-edge advances in interscale and interdisciplinary approaches to the SCS from the meeting presentations and the associated research.

Submesoscale eddies in the East China Sea detected from SAR images

Seven-year(2005-2011)Synthetic Aperture Radar(SAR)images are applied to study oceanic eddies in the East China Sea.It is found that most of these eddies detected from the SAR images are less than 10 km,which are submesoscale eddies.Seasonal differences are evident in the distribution of eddies,with the highest and the lowest number of eddies noted in summer and winter,respectively.Since slick streaks in SAR images look dark,an eddy identified due to the slicks is referred to as“black eddy”.As a result of wave-current interactions in the zones of current shear,it can be seen that an eddy exhibits a bright curve,the eddy is called“white eddy”.During the seven years,95 black eddies and 50 white eddies are identified in the study area.Black eddies are found in the whole study area while white eddies are mainly distributed in the vicinity of the Kuroshio Current.This study suggests that the distribution of the white eddy is denser around the Kuroshio because of the strong shear in the Kuroshio region.In terms of the eddy sizes,white eddies are generally smaller than black eddies.

Dietary separation between co-occurring copepods in a food-limited tropical coral reef of the Sanya Bay

Food differentiation among coexistent species in the field is important strategy for copepods to acquire materials and maintain population stabilization.In situ diet analysis of co-occurring six copepod species in coral waters of the Sanya Bay was conducted using a PCR protocol based on 18 S ribosomal gene.Various prey organisms were uncovered,including dinoflagellate,diatom,green algae and plant,protozoa and metazoan.All these spatially coexisting six species showed different dietary diversity,with the food niche breadth(B)ranging from 1.00(Temora turbinate in morning)to 10.68(Calanopia elliptica in night).While food overlap between all these copepods were low,with the average value of the diet niche overlap index being approximately 0.09.Even temporally co-existing species sampled from the same time point fed on different groups of prey items with the food overlap index of 0.04 to 0.07 in midday and night but 0 in morning.As the most important dominant copepod in the Sanya Bay,Subeucalanus subcrassus seems to be capable to regulate its feeding,by exhibiting a rhythm of herbivorous feeding in midday and carnivorous feeding in morning and night,to better coordinate with other competitors for utilization of food resources.For most copepods,none of the prey items belonged to the dominant phytoplankton in the ambient water,indicating that copepod can better their survival by widening the choice of potential food resources in food limited environment.The dietary separation observed here might be important strategy for copepod to maintain population stabilization and thriving in the Sanya coastal waters.

A newly developed ocean significant wave height retrieval method from Envisat ASAR wave mode imagery

The main objective of this paper is to propose a newly developed ocean Significant Wave Height (SWH) retrieval method from Envisat Advanced Synthetic Aperture Radar (ASAR) imagery. A series of wave mode imagery from January, April and May of 2011 are collocated with ERA-Interim reanalysis SWH data. Based on the matched datasets, a simplified empirical relationship between 22 types of SAR imagery parameters and SWH products is developed with the Genetic Algorithms Partial Least-Squares (GA-PLS) model. Two major features of the backscattering coefficient σ0 and the frequency parameter S10 are chosen as the optimal training feature subset of SWH retrieval by using cross validation. In addition, we also present a comparison of the retrieval results of the simplified empirical relationship with the collocated ERA-Interim data. The results show that the assessment index of the correlation coefficient, the bias, the root-mean-square error of cross validation (RMSECV) and the scattering index (SI) are 0.78, 0.07 m, 0.76 m and 0.5, respectively. In addition, the comparison of the retrieved SWH data between our simplifying model and the Jason-2 radar altimeter data is proposed in our study. Moreover, we also make a comparison of the retrieval of SWH data between our developed model and the well- known CWAVE_ENV model. The results show that satisfying retrieval results are acquired in the low-moderate sea state, but major bias appears in the high sea state, especially for SWH>5 m.

Rare earth elements and yttrium in ferromanganese deposits from the South China Sea:distribution,composition and resource considerations

Ferromanganese nodules and crusts contain relatively high concentration of rare earth elements（REE） and yttrium（REY）,with a growing interest in exploitation as an alternative to land-based REY resources.On the basis of comprehensive geochemical approach,the abundance and distribution of REY in the ferromanganese nodules from the South China Sea are analyzed.The results indicate that the REY contents in ferromanganese deposits show a clear geographic regularity.Total REY contents range from 69.1×10^-6 to 2 919.4×10^-6,with an average value of 1 459.5×10^-6.Especially,the enrichment rate of Ce content is high,accounting for almost 60% of the total REY.This REE enrichment is controlled mainly by the sorption of ferromanganese oxides and clay minerals in the nodules and crusts.Moreover,the total REY are higher in ferromanganese deposits of hydrogenous origin than of diagenetic origin.Finally,Light REE（LREE） and heavy REE（HREE） oxides of the ferromanganese deposits in the study area can be classified into four grades： non-enriched type,weakly enriched type,enriched type,and extremely enriched type.According to the classification criteria of rare earth resources,the Xisha and Zhongsha platform-central deep basin areas show a great potential for these rare earth metals.

Methane seepage intensities traced by sulfur isotopes of pyrite and gypsum in sediment from the Shenhu area,South China Sea

The northern slope of the South China Sea is a gas-hydrate-bearing region related to a high deposition rate of organic-rich sediments co-occurring with intense methanogenesis in subseafloor environments.Anaerobic oxidation of methane（AOM） coupled with bacterial sulfate reduction results in the precipitation of solid phase minerals in seepage sediment,including pyrite and gypsum.Abundant aggregates of pyrites and gypsums are observed between the depth of 667 and 850 cm below the seafloor（cmbsf） in the entire core sediment of HS328 from the northern South China Sea.Most pyrites are tubes consisting of framboidal cores and outer crusts.Gypsum aggregates occur as rosettes and spheroids consisting of plates.Some of them grow over pyrite,indicating that gypsum precipitation postdates pyrite formation.The sulfur isotopic values（δ^34 S） of pyrite vary greatly（from –46.6‰ to –12.3‰ V-CDT） and increase with depth.Thus,the pyrite in the shallow sediments resulted from organoclastic sulfate reduction（OSR） and is influenced by AOM with depth.The relative high abundance and δ^34 S values of pyrite in sediments at depths from 580 to 810 cmbsf indicate that this interval is the location of a paleo-sulfate methane transition zone（SMTZ）.The sulfur isotopic composition of gypsum（from–25‰ to –20.7‰） is much lower than that of the seawater sulfate,indicating the existence of a 34 S-depletion source of sulfur species that most likely are products of the oxidation of pyrites formed in OSR.Pyrite oxidation is controlled by ambient electron acceptors such as MnO2,iron（Ⅲ） and oxygen driven by the SMTZ location shift to great depths.The δ^34 S values of gypsum at greater depth are lower than those of the associated pyrite,revealing downward diffusion of 34 S-depleted sulfate from the mixture of oxidation of pyrite derived by OSR and the seawater sulfate.These sulfates also lead to an increase of calcium ions from the dissolution of calcium carbonate mineral,which will be favor to the formation of gypsum.Overall,the mineralogy and sulfur isotopic composition of the pyrite and gypsum suggest variable redox conditions caused by reduced seepage intensities,and the pyrite and gypsum can be a recorder of the intensity evolution of methane seepage.

Towards a semi-empirical model of the sea ice thickness based on hyperspectral remote sensing in the Bohai Sea

Sea ice thickness is one of the most important input parameters for the prevention and mitigation of sea ice disasters and the prediction of local sea environments and climates. Estimating the sea ice thickness is currently the most important issue in the study of sea ice remote sensing. With the Bohai Sea as the study area, a semiempirical model of the sea ice thickness（SEMSIT） that can be used to estimate the thickness of first-year ice based on existing water depth estimation models and hyperspectral remote sensing data according to an optical radiative transfer process in sea ice is proposed. In the model, the absorption and scattering properties of sea ice in different bands（spectral dimension information） are utilized. An integrated attenuation coefficient at the pixel level is estimated using the height of the reflectance peak at 1 088 nm. In addition, the surface reflectance of sea ice at the pixel level is estimated using the 1 550–1 750 nm band reflectance. The model is used to estimate the sea ice thickness with Hyperion images. The first validation results suggest that the proposed model and parameterization scheme can effectively reduce the estimation error associated with the sea ice thickness that is caused by temporal and spatial heterogeneities in the integrated attenuation coefficient and sea ice surface. A practical semi-empirical model and parameterization scheme that may be feasible for the sea ice thickness estimation using hyperspectral remote sensing data are potentially provided.

Factors dominating bacterioplankton abundance and production in the Nordic seas and the Chukchi Sea in summer 2012

Abundance and production of bacterioplankton were measured in the Nordic seas and Chukchi Sea during the 5th Chinese Arctic Research Expedition in summer 2012. The results showed that average bacterial abundances ranged from 3.31×10^11 cells/m^3 to 2.25× 10^11 cells/m^3, and average bacterial productions （calculated by carbon） were 0.46 mg/（m^3·d） and 0.54 mg/（m^3·d） in the Nordic seas and Chukchi Sea, respectively. T-test result showed that bacterial abundances were significantly different between the Nordic seas and Chukchi Sea, however, no significant difference was observed regarding bacterial productions. Based on the slope of lg bacterial biomass versus lg bacterial production, bacterial communities in the Nordic seas and Chukchi Sea were moderately dominated by bottom-up control. Both Pearson correlation analysis and multivariable linear regression indicated that temperature had significant positive correlation with bacterial abundance in the Chukchi Sea, while no correlations with productions in both areas. Meanwhile, Chl a had positive correlations with both bacterial abundance and production in these two regions. As the temperature and Chl a keep changing in the future, we suggest that both bacterial abundance and production been hanced in the Chukchi Sea but weaken in the Nordic seas, though the enhancement will not be dramatic as a result of higher pressure of predation and viral lysis.